I don't claim i fully grasped all the details, but this is the best description i heard of curved space time and how it genrrates gravity. Much, much better than the massive ball placed on thin fabric animation.
Idiots only explain gravity with a stretched fabric and a ball. There is no fabric in space. The perception of top and bottom is only for us. There is no top or bottom for space. There is no direction for space, so there is no possibility of a fabric in one space plane. Also, this idiot should explain where the curvature first come to be in the first place. It is a circular stupid explanation, curvature comes from gravity and gravity came from curvature. Fact is, all physicists are lying to us about the Space.
It doesn't describe how it generates gravity. In fact, Gravity remains one of the most perplexing phenomena in physics. It explains how space-time, under the _influence_ of a gravitational field causes the attributes of falling objects. It is also defective, as are most such popular expositions, in explaining why _not-falling_ objects-such as the apocryphal apple hanging over Newton's head-seem to be under some mysterious influence. Eg., the mysterious apple(s) seem always to bend their branches _down._ That question always elicits a separate video, such as the ingenious/notorious dialekt's river-model of the matter. Yet others present the baffling accelerating-surface claim about GR: the apple is exerting no force on the branch, the branch is continually accelerating... _upwards_ . Entailed by that interpretation is the understanding that apple trees in southern New Zealand have their branches' acceleration in another direction. If all that is too hard for the average person to grasp, even with the help of some dodgy videos to help you over their spongy arguments, they may eventually resort to the claim that in HS physics the teachers lied to us about the meaning of... _direction._ I think that's easier than redefining the meanings of vectors, momenta, and acceleration.
I'm not against the use of SI, but I am against the notion of one person or a group of people telling others what convention they can or cannot use. I use both conventions, and I also use proper conversions when necessary. It all depends on the context of the problem that I'm working with. I do not buy fuel by the liter. I buy it by the gallon, and I measure my vehicles economic efficiency based on miles per gallon. When I buy milk, I buy it by the gallon or 1/2 gallon, not by the liter. Again, it all depends on the domain and context of the workspace. Now, if I was working in a lab and doing some chemistry and or physics, perhaps I would use the SI units, but again that still depends on the domain, context and workspace of the current problem. Only someone who is either ignorant or arrogant wouldn't understand this. I have the understanding and intelligence to use multiple formats and conventions, and I'm sure there are many others that do too. There is nothing wrong with someone else using miles as opposed to kilometers. Also, when I step on a scale to measure my weight, I'm measuring weight in lbs., I'm not measuring my mass in kilograms. The comment alone "stop using miles..." is condescending.
Excellent explanation. After watching other videos on this topic, your video using the cone and illustrating how objects move around the cone -- really helps clarify the topic. Thank you. New subscriber.
Sometimes (rarely) I'm in a mindset to understand videos like this. This one hit me in the right way at the right time. Very well done. I learned a lot. Thanks.
I'd be curious to know how to calculate how long it would take for two masses to get to the speed of light by mutual gravity and how far apart they would have to start. I'd like to know if that's really possible with anything that doesn't include a black hole as one of the objects.
Its never possible to reach the speed of light ...ever. ...unless it involves event horizon of black hole. Here spacetime is falling into (or rather warped) at light speed but only at point of event horizon. And once at that that horizon you are never coming back to report. A neutron star is closest next thing and you could crash into one of these at 99%+ light speed.. but never at 100%. You can have 2 neutron stars at 2 solar masses each crash together. They would crash together at 100% light speed but the boundary of where that happened would be exact the formation of a new event horizon of a new black hole which (as we know from theory and now from gravity wave evidence) always forms from merging of neutron stars.
Damn, you guys are good. I am kinda keeping up (when somebody offers amazingly structured explanation mostly) and i always feel like i would need a little bit more IQ or computing/projecting brainpower to join the top thinkers. Maybe a lot of power lol looking at some of the complex math implications some ppl can do. Hopefuly big part is knowledge and training and im not actually too far apart to justify using the word "im actually stupid conpared" 😅
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance. The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain. And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
i thought the same. If the object is standing still and only moves through time it should just follow the time path. So why it starts shifting towards the space part of the diagram i can understand either and the video doesn't explain this
Because of the warping of spacetime. The object was moving in a straight line through spacetime, along the time axis. Now the presence of the massive object has caused the underlying 'grid' of spacetime to warp in such as way that the line of movement through spacetime (ie geodesic) is no longer parallel with the time axis but pointing into the space axis as well. So some of the movement through time is diverted into movement through space in the direction of the massive object. No external forces are acting on the object - the shift of movement into space is caused by the change in spacetime geometry itself. Pretty mind bending.
The shortest distance between two points is a straight line. All celestial bodies warp the "fabric" of space, and create gravity wells. When a smaller object comes close to the rim of a larger object's gravity well, it gets caught in that object's orbit through mass bending space-time. It's similar to how water circles a drain, but it's an all directions. Everything in space is falling.
@@jonathanspruance4502 I am sitting here glued by gravity to my seat (and by my interest in the topic). But since I am absolutely certain that 'time' is a concept only, I'm in need of a different explanation. What is it in actuality that the temporal concept is actually 'about'?
@@jonathanspruance4502 Why does the object have to move in a straight line? Of course if it moves in a straight line it will move towards the space axis and thus the “falling” of the Apple. But why does the path have to be a straight line? Why doesn’t it just move along the curved time path since it’s standing still?
1:45 - if space is contracted around a mass, then time doesn't actually need to run slower because the photon is still moving over the same amount of space. If you stretched a 10 x 10 grid and watched a ball cross that grid, it would still cross 10 grid lines.
The use of gravity to illustrate "space-time" which in turn causes gravity is not an explanation. Also, Einstein's failed General Theory implies that gravity is not a force also implies that light and massive objects should follow the same path through space and that light is not affected by gravity, because of the claim that light is massless, yet His General Theory implies that gravity can suck light into a hypothetical singularity. The entire General Theory of Einstein is built on impossible conundrums. Light bending in an atmosphere was always considered to be why light bends in the Sun's atmosphere. Others had predicted this refractive index accurately prior to Einstein, such as Soldner. Einstein simply did not understand this concept of refractive index in optical lensing. Gravity is caused by the implied flux density gradient of Gauss's Law for Gravity, which acts as an energy gradient, confirmed by GPS and atomic clocks.
@@JoeDeglman Where is the evidence that General Relativity has failed? Where? Proof by assumption statement like this is typical of someone with a pet belief and no education. General Relativity states gravity is a force. Someone has not read the General Theory of Relativity. Light being affected by gravity is what General Relativity is all about. Where did you get this stuff? Are you familiar with the experiments? "His General Theory implies that gravity can suck light into a hypothetical singularity." - No. Have you ever taken a course in physics?
@@geoffwales8646 the JWST also shows that these galactic halos also have a substantial dust atmosphere that acts as an optical lense to do the bending as a refractive index. Just like the Sun, bending of light only occurs through an atmosphere as a refractive index as an optical lensing function. No bending of light has ever been observed through the vacuum of space around a massive object, in contradiction of the GRT, where there is no atmosphere. The previous images of galaxies from Hubble were in the optical range and the dust atmosphere wasn't observed previously because the atmosphere of galactic halos emits in the infrared not in the visible. .
@@MrMoose1347 but it would average the two? As you move away from one time is speeding up but as you move closer to the other it’s slowing down, so there has to be a point in the middle that matches the surface time right?
@@nunya3399 ah I see what you are getting at. We do account for travel gravitationally and by acceleration. Gravity is general relativity and acceleration is special relativity. When gps orbit earth it accounts for both. So not were they meet in the middle just where we account for both
2 questions that the video made me confused about. 1. The initial flashlight beam of light had to have been significant in width for the difference in distances traveled between top and bottom "light fibers" to be different. Was the initial experiment based on two stars spaced far apart from one another? In that case, how did we determine that the light arrived to us from each star at the same time, since light has always been streaming from them to us, and we don't know precisely when a given photon was emitted? 2. When you roll up the spacetime diagram and say that "light only travels through space," I understand this is correct from the photon's perspective, but you appear to be rolling up the stationary apple's spacetime diagram. Wouldn't that diagram also have light spiraling along a helix, since from the apple's perspective light travels through the apple's time at a 45 degree angle to apple's space? It seems like you are mixing/combining the apple's perspective into the photon's perspective into one unified spacetime manifold, on which I just don't understand how you can be certain about the geometry of circular, helical, and straight line paths coursed out by different material objects. Maybe we can call this some higher dimensional "God's" spacetime manifold who sees the absolute truth in terms of distance and time?
@@HowDoYouKnowThough so we don’t spiral along. We move in a straight path along curved spacetime. This was found out by how light acted. We took measurements of this and found out the limit to motion of mass & energy as the equivalence principle was found. Taking this into account we know have lights constant speed over distance and distance. Hell that means to get time (the rest of the equation) we just plug and play. Let me know if ya have any questions
@@MrMoose1347there's no such thing as a straight path of you want to really get into it. Space is not straight, there are no fixed points anywhere in all of existence and everything is moving at a relative speed and rate of time to everything else.
@@MrMoose1347 the point you were making was a bit pedantic, I went a bit further. Everything is relative, everything interacts with everything, there's literally no such thing as a straight line.
The thing that throws people off is this name, “curved spacetime.” Sure, when you look at a rolled up piece of paper, or a digital graphic, we see the curve. But in reality there is no curve. Space is devoid of geometry. There is nothing surrounding the earth. Its literally enpty space. Wheres the curve? You have to remember that einsteins theory is just that, a theory. Yes it happens to align with how we perceive things to work, but it doesnt provide all the answers. Its just the best explanation we currently have. We dont understand the nature of space. Thats the issue here. When you consider this example, a rolled up piece of paper, that is one way to describe gravity. But the age old question remains unanswered, WHY does gravity exist? I believe thats something we can never know. Einstein explained the how. The why he had absolutely no idea. No one does, and no one ever will. Thats why after watching all these gravity videos, everyone has the same response, “eh, i guess it makes sense.” It can never make total sense until we understand the fundamental nature of the universe. Unknowable unfortunately. Why are things attracted to each other? Who knows, the just are 😁
There are a few mistakes because of over simplification in this video. For example the ball falling from an infinite high tower would not reach ligthspeed. The potential energy in a gravitational field is finite! So an object with mass cannot reach the speed of light.
Agreed, of course. I wrote the followingI comment ... f the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance. The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain. And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
Why does light moves only through time in the flat spacetime diagram wrapped in a cilinder at 3:25? Light does not travel through space only, it also travel through time, its speed is not infinite.
There is no "time" to move through, unless you mean the along the direction of some observer world-line, but you still have to choose such a world-line. That said, yes, light will move equally through the spatial and temporal coordinates of the observer, Δx=Δt.
You’re confusing the speed of time with the device that’s measuring time . Time is not speeding up or slowing down , it’s the device that you’re using to measure time that is measuring it faster or slower . Time is a constant and doesn’t speed up or slow down , however the device measuring it does .
Yes … the device you are using to measure “time” is affected by its place in a gravitational field, and the various accelerations it undergoes… once you account for those variables, any differences in two time measuring devices will be factored out …
“Time isn’t speeding up or slowing down it’s the device you are using” um….its measured motion so both time and the clock are being talked about when dilating.
I would also put some explanation to cover the difference between those two persons curved path (since they are forced by the contact with the ground) vs straight path of falling object (since there is no contact with the ground during the path).
Question? since even deep space contains micro-gravity, what is creating the micro-gravity? The Gravity Probe B experiment detected something called "Frame Grabbing", where the Earth is grabbing space/time as it turns on its axis. Wonder if this had been further examined as to impacts to time?
7:09 - I am not a physicist, but I think that is the definition of terminal velocity. "The velocity a free-falling object would reach by the time it struck the surface". It's the same velocity as would take to achieve escape (velocity). On the Earth, that is around 11.186 km/s., not C. Now, from the event horizon of a Black Hole, it would be C.
My comment was: If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance. The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain. And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
7:03 The iron ball would reach the speed of light? Relative to what? How could the height of the tower be infinite? How long would reaching the speed of light take? How would the speed of the ball be measured?
You would need infinite energy to move a massed object at the speed of light! My comment was: If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance. The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain. And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
speed of lite is the same relative to everyting, if you don't know that what are you doing here, watch some basic videos or you'll just get more confused
Can you expand just a little more and in the extreme case of going trough an event horizon where the time and space axis switch? How would you represent that in a video graphic? And by the way....excelent video!
For a particular choice of coordinates, the Schwarzschild-Droste coordinates, the temporal and radial components of the metric tensor switch algebraic sign.
Understanding the "switch" is easier than many think. It sounds brain-bending that time and space switch places, but it's really just the fact that the singularity is the ONLY future of your light cone. Because anywhere you would like to maneuver when "falling" into a black hole, you will ALWAYS (100% of cases) meet the singularity (it's just in your light cone across all possibilities). The Penrose diagram has this brain twist in it, but from a simpler point of view, it's just that. Like when it's Friday night and you are out with friends, the beer is your 100% future :D (if you drink). I like to hypothesize that all singularities are the same (like in the SAME spot), because when you have a spherical universe (like an expanding balloon and space-time is its surface), when you do this 90-degree warp (like black holes do) from the surface, eventually this warp ends in the middle of the sphere. So all black holes point to the same "space/spot/something/singularity" :) . Just food for thought.
The time and space axes never switch. That is nonsense. Time is time and space is space. Minkowski was wrong with his quote ("Henceforth, space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality")!
Can anyone help confirm this for me? I've always found the twin paradox a bit confusing because, as I see it, the twins can never meet in a way that would cause one to be older than the other. Here's why: as the twins travel towards each other, their clocks would start to synchronize. By the time they are close enough to "meet," their clocks would essentially align, placing them on the same "time" line and making them the same age again. From my understanding, the only way the paradox could play out is if one twin traveled near the speed of light towards the other and could observe the other's clock. However, the idea that their clocks tick at different rates is something that seems to only hold from the perspective of an external observer outside both reference frames. So, what I'm asserting is that it's not accurate to say the twins could meet and be different ages because they could never technically meet under these conditions. The differences in their clocks are only apparent to an outside observer. Is my reasoning correct?
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance. The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain. And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
If you take the derivative of the space time curve at any point along the curve, will you obtain the acceleration due to gravity at that point as determined by the inverse square law?
at 4:27 what if you turned the funnel around so it was smaller the closer to earth and you swapped the time and space axis? would that work? or does that not make sense?
“Object mass" refers to the inherent amount of matter in an object, which is a constant value and does not change with its speed, while "speed mass" is not a standard term, but could be interpreted as the apparent increase in mass an object experiences when moving at very high speeds near the speed of light, according to the theory of relativity; essentially, the faster an object moves, the slightly greater its "relativistic mass" appears to be, although this effect is only noticeable at extreme speeds.
Not only do objects moving at light speed experience time as zero, the space between their origin and where they land is compressed down to zero distance as well.
Gosh I hate it when people put trash on TH-cam. Space and time are both metrics and don't create anything. That is the same as saying the measurement of one meter can create life. I hate ignorant people that can not learn basic stuff.
The gravitational field is not necessarily stronger at the bottom of the ocean trench, as it is highest at the Earth's surface and then gets weaker as one approaches the center of the Earth (where there is no gravitational field at all). So while clocks do go faster higher in the atmosphere, they will also go faster at the center of the Earth.
A clock at the surface of the Earth runs faster than a clock at the center. Not by much, the time dilation is 1.0000000003 between the core and surface.
That's the backing paper from book covering film... wow, it's all so simple.. but where did the book covering go?where did it come from and if we join the two sides together will it create a worm hole between Rymans and Smith's?
I think you are mixing up gravitational time dilation (GTD) with spacetime curvature. GTD arises when you think you are stationary and yet you are actually in an accelerated frame of reference, as indeed we are standing on the surface of the Earth. GTD is observer dependent, meaning it is possible to find observers that do not see it (a free falling observer won’t experience GTD for example). Where there is GTD, there is apparent (or fake) gravity. Once we accept the Earth is accelerating upwards, it is actually unsurprising that objects appear to fall and that all objects regardless of their mass ‘fall’ at the same rate, because the Earth is actually accelerating upwards at the same rate. Most of what we see as gravity on Earth is because of its acceleration upwards. What is holding the Earth in, keeping it the same size? Spacetime curvature. Spacetime curvature is caused by mass and energy. It is observer independent; all observers will agree on the curvature. Spacetime curvature is what gives rise to real gravity, and what attracts objects together in space. It emerges in the form of what we call tidal forces. The rolled up diagram you used is flat spacetime but rolled into a cone to illustrate the time dilation. That time dilation is GTD. GTD arises from an accelerating reference frame. When it is flattened out the time axis is curved, while the free falling world line (of a falling object) is not. This is a specific version of a spacetime diagram describing flat spacetime (not curved) and actually drawn from the perspective of a free falling body. The time dilation on the curved diagram is a result of a mapping between the object’s inertial frame of reference and our (standing on Earth) accelerating reference frame and is not the same thing as spacetime curvature. The free falling body has no acceleration itself and sees us and all the Earth accelerating towards it.
4:19 a cylinder is flat. but also a cone is flat. this is not spacetime curvature, this is the local equivalence principle: gravity due to acceleration in flat minkowski spacetime. notice that you do not need curvature to experience gravity it's a nice visual, but it's very inaccurate because gravity is not caused by curvature, it's cause by being in accelerated reference frame. Geometry, curved or otherwise, dictates what counts as a force free path.
Eddington’s „observation“ was technically a joke. He had not even the needed instruments, or the needed accuracy to perform such observation. He just wanted „to confirm“ Einsteins prediction…no matter what.
@@PADARM Oh yes, Einstein’s prediction had to be proved at any rate. Eddington was cheating and all others later ones too. They sold to you simple refraction for bending of space time and you did buy it.
The speed of light is not a constant as once thought, and this has now been proved by Electrodynamic theory and by Experiments done by many independent researchers. The results clearly show that light propagates instantaneously when it is created by a source, and reduces to approximately the speed of light in the farfield, about one wavelength from the source, and never becomes equal to exactly c. This corresponds the phase speed, group speed, and information speed. Any theory assuming the speed of light is a constant, such as Special Relativity and General Relativity are wrong, and it has implications to Quantum theories as well. So this fact about the speed of light affects all of Modern Physics. Often it is stated that Relativity has been verified by so many experiments, how can it be wrong. Well no experiment can prove a theory, and can only provide evidence that a theory is correct. But one experiment can absolutely disprove a theory, and the new speed of light experiments proving the speed of light is not a constant is such a proof. So what does it mean? Well a derivation of Relativity using instantaneous nearfield light yields Galilean Relativity. This can easily seen by inserting c=infinity into the Lorentz Transform, yielding the GalileanTransform, where time is the same in all inertial frames. So a moving object observed with instantaneous nearfield light will yield no Relativistic effects, whereas by changing the frequency of the light such that farfield light is used will observe Relativistic effects. But since time and space are real and independent of the frequency of light used to measure its effects, then one must conclude the effects of Relativity are just an optical illusion. Since General Relativity is based on Special Relativity, then it has the same problem. A better theory of Gravity is Gravitoelectromagnetism which assumes gravity can be mathematically described by 4 Maxwell equations, similar to to those of electromagnetic theory. It is well known that General Relativity reduces to Gravitoelectromagnetism for weak fields, which is all that we observe. Using this theory, analysis of an oscillating mass yields a wave equation set equal to a source term. Analysis of this equation shows that the phase speed, group speed, and information speed are instantaneous in the nearfield and reduce to the speed of light in the farfield. This theory then accounts for all the observed gravitational effects including instantaneous nearfield and the speed of light farfield. The main difference is that this theory is a field theory, and not a geometrical theory like General Relativity. Because it is a field theory, Gravity can be then be quantized as the Graviton. Lastly it should be mentioned that this research shows that the Pilot Wave interpretation of Quantum Mechanics can no longer be criticized for requiring instantaneous interaction of the pilot wave, thereby violating Relativity. It should also be noted that nearfield electromagnetic fields can be explained by quantum mechanics using the Pilot Wave interpretation of quantum mechanics and the Heisenberg uncertainty principle (HUP), where Δx and Δp are interpreted as averages, and not the uncertainty in the values as in other interpretations of quantum mechanics. So in HUP: Δx Δp = h, where Δp=mΔv, and m is an effective mass due to momentum, thus HUP becomes: Δx Δv = h/m. In the nearfield where the field is created, Δx=0, therefore Δv=infinity. In the farfield, HUP: Δx Δp = h, where p = h/λ. HUP then becomes: Δx h/λ = h, or Δx=λ. Also in the farfield HUP becomes: λmΔv=h, thus Δv=h/(mλ). Since p=h/λ, then Δv=p/m. Also since p=mc, then Δv=c. So in summary, in the nearfield Δv=infinity, and in the farfield Δv=c, where Δv is the average velocity of the photon according to Pilot Wave theory. Consequently the Pilot wave interpretation should become the preferred interpretation of Quantum Mechanics. It should also be noted that this argument can be applied to all fields, including the graviton. Hence all fields should exhibit instantaneous nearfield and speed c farfield behavior, and this can explain the non-local effects observed in quantum entangled particles. *TH-cam presentation of above arguments: th-cam.com/video/sePdJ7vSQvQ/w-d-xo.html *More extensive paper for the above arguments: William D. Walker and Dag Stranneby, A New Interpretation of Relativity, 2023: vixra.org/abs/2309.0145 *Electromagnetic pulse experiment paper: www.techrxiv.org/doi/full/10.36227/techrxiv.170862178.82175798/v1 Dr. William Walker - PhD in physics from ETH Zurich, 1997
If the speed of light is not a constant then Relativity can not be correct, any theory based on it is also wrong. General Relativity is not compatible with Quantum mechanics. So either one or both of the theories is wrong. The evidence I present says Relativity is the problem. Science will not advance , if the foundations of physics is not challenged.
@@MrMoose1347If the speed of light is not a constant then Relativity can not be correct, any theory based on it is also wrong. General Relativity is not compatible with Quantum mechanics. So either one or both of the theories is wrong. The evidence I present says Relativity is the problem. Science will not advance , if the foundations of physics is not challenged.
If the Eiffel-Tower were of infinite hight there would be no gravity at all. This is a classical solution which is duplicated by GR in the Newtonian limit of „weak gravity (earth) and slow speeds (v
@@atticuswalker Not equivalent , with the earth scenario its a single mass and photons are taking a similar path , with a supernova the light take wildly different paths
Does light really bend? When looking at a fish in water, why is the fish ahead when looking through water? Could the same happen in space near a planet or star?
How skillful are scientists in explaining problems they cannot understand with fabricated solutions? They create a paradox with nonsense questions, and then they think they have solved that paradox with another nonsense. The speed of light is constant only if they are in the same plane. When the plane is different, the speed is different. For example, the near beam should reach the large mass earlier because it travels less distance than the far beam logic. It's not like that, though. The ray that stays away from the larger mass appears to arrive at the same time because it moves faster than the one that is closer. When you incorrectly construct the universe, light and movement, such absurd questions and solutions are called science. This is not science. He's deceiving people
Another thing that seems quirky and weird to me is how can light speed up and slow down, or slow down and speed back up depending on the medium that it's going through... And they call this a 'constant"⁉️😂
@@drakeeblis1788 No. It's specifically the speed of light in a vacuum. And it's not primarily about light. Light is a massless particle hence travels at C in a vacuum. But can be slowed by shining through non-vacuum.
@@drakeeblis1788 Let me explain please. First of all, it is necessary to know what light is and how its movement occurs. As you know, the space that is thought to be empty is actually full. It only has a much sparser texture compared to mass. I think that at this point, weak force or weaker forces are involved. (weaker force has not yet been fully defined) weaker force is the subatomic particles that I call formation points, which are too weak to be mass. They move just like a Newton pendulum. But they are connected to each other in every direction. The reason for quantum fluctuations is their movement. The most important task of these structures is the communication network with the ebb. In other words, light seems to move through these structures. Just like the balls from a Newton pendulum do not go anywhere but transmit the movement. Think of it in the same way but in 3 dimensions. The distance between the balls increases or decreases the speed of light. If the distance is greater, therefore it means it is farther from the mass, then light moves faster. Because there is no time between two formation points. It is the collisions of two or more formation points that express time. I hope this was a sufficient explanation for you to understand. In fact, the topic is so broad that it is harder to write. Thank you for bearing with me.
The cone can work well if a gravity is the only force. I wonder how should air resistance force be put on the cone? Maybe as a force opposite to gravity increasing speed in time direction or maybe air resistance modifies somehow the cone?
Nope... you got it wong. Acceleration along space axis . . what we call gravity. . . is direct result of warping of space-time... more specifically differential time. Not the other way round.
@@pretzelogic2689 Space-time (4 dimensions) is what warps - not just space. It is a fundamental fabric of the universe. It does so in the presence of any energy-momentum. Since mass (matter) has an equivalent energy (E=mc2) then it also warps in the presence of mass (any mass size but more noticeable for us with planet size masses like Earth) . That warp gives rise to differences - a gradient - in the flow of time which gives rise to space (which rememeber is connected to time as 4D fabric) flowing in towards the direction of the warp (towards the mass) - which we experience as an acceleration and historically have labelled it as a force of gravity. So it is warped space-time gives rise to what we call gravity. Not the other way round. To go into greater depth involves EInsteinian tensor mathematics. A bit too much for youtube comments section.
@@jayceasar2661 Prove what exactly? that time flows at different rates depending on how close to the energy-momentum (mass) centre you are? Without accepting that the algorthim in your GPS makes allowance for this - then it would not work and you couldn't use google maps to go anywhere. 'Proof' enough for you?
@@bbbf09 You said it yourself: "...it also warps in the presence of mass..." Your "also" refers to energy. Energy mass, fungible. Thanks for repeating what I said.
Wait.. at 7:04 you're saying that an iron ball falling infinitely from the Eiffel Tower into a gravitational field would eventually accelerate to the speed of light? Well, problem is, only massless things like photons can travel at light speed, and any object with mass would require energy equivalent to the mass of the entire universe to accelerate to the speed of light, which would also include the mass of the infinitely long Eiffel Tower that the iron ball would be falling next to. So the iron ball would never reach light speed, because if it did it wouldn't be an iron ball anymore, but a stream of photons that used to be the iron ball, the Eiffel Tower, and the rest of the mass of the universe.
Correct. My comment was: If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance. The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain. And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
@@DABmongerthere's more wrong with the example than that but you're missing the point. Dropping any mass onto a black hole would be a better example. By the way if the tower is infinitely tall the ball wouldn't fall at all because it would be too far from the source. Assuming the tower itself doesn't have mass. On another note if there was no ground and the ball was somehow affected by gravity, any air around it would also be in freefall. Terminal velocity only exists if there is a ground for the air to push against, otherwise there isn't any friction of falling.
@Richinnameonly Me thinks you're overanalysing, and a lot. The creator will giving a simple example, and there is a terminal velocity constraint on Earth, plus nothing with mass can travel at light speed You're adding elements to a simple example, none of which was the creator's intention.
I knew it, I knew that it would come the day when Millennials would start thinking they can think like geniuses too and would start spurting out all kinds of nonsensical krap calling them scientific theories. Time, or time dilation, creates gravity as much as chronometers create speed, duh...
@@somerandomboi8239 You are right, Einstein said many things but the things on which he was right he was able to prove them mathematically, with equations. There is np mathematical proof for this assumption, it is pure speculation.
@@rubenoteiza9261 I may have been wrong to react this way, as I am not yet at this chapter but am just watching stuff in order to gain some basic intuition for when I do get into it seriously. I just do find these playing-arounds with ideas and imagery useful for visualizing concepts, and couldn't comprehend what you meant by dunking on it, esp. with your end sentence about time and gravity. What does cause it then? Because we all agree that it is not a classical force. Then of course, maybe you see something profoundly wrong in the video that I couldn't catch?
So that means in a wormhole where the space could be infinite the time slows down almost to a stop and the speed grows as much as it almost gets to the speed of light ?
i think the video explaining that object will drop accelerately as it reach toward the earth. But I didn't catch why the object move towards earth as well as why the moon doesn't drop to the earth. Or I miss some concept in the video?
Question. In this model of spacetime it flares wider as it approaches the center of mass of the earth. But, in another model, spacetime funnels into a point towards the center of mass of something like a black hole.
No. In this model the larger diameter denotes longer time taken to cover the same unit of space. The closer to massive object the slower the time gets. Your second sentence is about spacetime, and is correct.
It's just an inverted visualization, since space and time are represented by perpendicular axes. When discussing the differences of motion through space and/or time, it is helpful to invert the cones in order to show the consistency of the distances travelled.
In 7:24 minute you show curved space and the apple that falls. Please can you show all unit measures of curved space time when the apple falls with 9,81m/s^2 acceleration?
Cann you tell me when you folded then what will be in background of that in which folding occur because space you folded then what will left in background
Wow. It looks like you could work out the geometry that gravity bends spacetime into by using the acceleration of gravity and that last diagram (6:00).
if light propagates in all directions then why and how do we see/locate the object emitting light? wouldn’t we see the light from the object everywhere?
I am not a physicist but have a question on this. Light travels in different velocities in different optical mediums. Are we sure there is nothing in the space? Maybe something near the earth has different density that cause light travel slower.
No,they are not sure. And not only that, they don’t even know if Space is isotropic. Or even worse, they can’t even test it. They only talk and, if you believe it, they don’t need more than that.
@@O-Kyklop Yes, on large scales, space is considered isotropic, meaning it looks the same in all directions. This assumption is a key part of the cosmological principle, which suggests that the universe is homogeneous and isotropic when viewed on a sufficiently large scale. This is supported by observations, such as the uniformity of the cosmic microwave background radiation . However, on smaller scales, the distribution of matter (like galaxies and stars) is not perfectly uniform.
@@MrMoose1347 Ok. It means you can’t make a prediction for a certain location you can’t check up directly.,……which is most of the Universe. Not a very solid theoretical background, isn’t it?
I watched 2 videos and i still can't understand it ig. Correct me if i am wrong. So if if throw and object from an height, Its always in rest during mid air. and when i collides with ground it comes in motion, coz ground is in motion too
Is that true that you eventually reach speed of light if falling down infinitely? If you're jumping off a plane, your falling speed increases but only to a certain speed and then, unless you're not already on the ground (ouch), your falling speed will remain constant (the exact number would be devided from your weight) and yet far from speed of light. that is if the gravity is constant.
@@rodolfosantana9015 well if you imagine a flat earth (no, not like that) and fire a laser beam horizontally, after 186,232 miles it will fall for one second with acceleration "g", so like 16 feet, and that is following curved space time, and (switching to metric) 300 Mm long parabola curved by 5m has a radius of curvature of c^2/g = 10 Pm. (peta meters)..so about 60,000 AU...space is pretty flat around Earth, yet you can't fall 20 feet without getting hurt.
...and a few years before that, somebody noticed fruit falling... one gets the feeling that our host believes gravity has an independent metaphysical existence, and it is just "out there."
@@NondescriptMammal ?? How in the world is it not clear? How could anyone possibly think it's a literal representation of spacetime? If you think that, then you shouldn't be bothering to ponder this stuff, you should be watching Bob the Builder or something...
@@xtraspecialj I assume that the maker of this video means for the cylinder to be taken seriously. It isn't just presented as a momentary visual aid to help understand... Everything that follows in this video to reach its conclusions, is derived from the geometry of that cylinder. All the example cases and intermediary conclusions presented afterward, rely directly on the construction of that cylinder. The cylinder is indispensable to this video's attempt to validate the assertion that "the curvature of spacetime causes gravity".
Imagine traveling a road that takes 5 minutes to reach your destination. If a sinkhole or crash blocks the path (representing mass in space), you can't continue straight. The obstruction diverts traffic, and you must take a longer route. This detour increases your travel time to 8 minutes. This time dilation reflects changes in spacetime; with increased distance, time dilates. Acceleration also affects spacetime but in a different way. Changing your speed alters the perceived contraction of space and consequently affects the duration of time. Relativity encompasses more than just relationships between measurements. It involves how units of measure change relatively due to different conditions experienced while traveling through spacetime.
Matter tells space-time how to curve, and space-time tells matter how to move. This is because space and time are not flat, but can be warped, stretched, and pulled by matter. Time is relative and not constant. The rate at which time passes depends on your frame of reference. You just need to look at the constant adjustments that have to be made for time dilation to GPS satellites due to Special Relativity (velocity - clocks run slower) and General Relativity (weaker gravitational field - clocks run faster). Overall effect for both GPS satellites and travelling in an aircraft ... clocks tick faster. However, moving at sea level -> clocks run slower, so you age slightly less.
I would like to see an explanation of how "space time" curvature causes the tides. I assume that space time is curved between the moon and the earth ( or between the sun and the earth) and that curvature of space time causes the tides, but I'm having difficulty visualizing how that works.
What causes space-time to be curved? The presence of matter-mass. Why-how does the presence of matter-mass cause space-time to be curved? Isn't general relativity just some Riemann mathematical geometry applied to describe a force, which doesn't "explain" anything? Why can't other forces-at-a-distance be described in the same way?
@@MrMoose1347 I think it would be better for us to follow Nietzsche's thinking and say that there is no empty space but rather there's nothing but fields of force. Force, not space, is primary. Time? Well, that's just the counting of processes that run because of forces.
What force, (force = mass x acceleration) causes the acceleration. The 'rubber sheet' model assumes the object is already moving with respect to the major mass's centre of mass. A static model requires a force to begin acceleration. And more - where does the energy come from to accelerate the object. If an object falls inside a total vacuum calorimeter, it would register heat when the object hits the end of its travel. Where did the energy come from?
From it's initial creation. Everything in space is falling. An object will stay in motion until acted upon by an opposing force. If an object finds itself roaming space alone, then it will speed up because it's falling.
Great video. It shows that gravity is not a force but geometry. The curvature of spacetime create gravity However, I still do not understand how big masses -like the sun - can curve spacetime. Why don't they just " hang" there in space and leave space unaffected.?
I think if we divide it to the atomic level then it is better to understand. I believe anything that has mass fundamentally cures space-time, which means an atom curves space-time, but it's just negligible. But when they form massive objects, the curvature is visible, like in case of sun (Einstein's Demonstration of this with mercury's position), or the extreme curvature of black hole curving the light's path into the black hole itself. Correct me if I'm wrong.
Could it be that "energy of the vacuum", virtual particles popping in and out of existence, etc., are simply the outer limits of the invisible aspect of mass so that all the matter in the universe actually extends into all the spaces that look empty to us? If so then every photon zipping through a galaxy takes a route no part of which is straight... meaning images we make of the very distant stars can only be approximations (to say nothing of the movement of those stars during the centuries of photon flight).
saying 'the flow of time' is a contradiction as it implies distance traveled of an arbitrary quantity 'q' moving from point 'a' to point 'b'. So how can anyone invoke a term witch itself is defined in terms of time to describe time?
Why do goose down and a metal ball fall at the same speed in a vacuum? How does gravity determine how much force to apply to objects of different masses so that they fall at the same speed?
Maybe centripetal force and gravity are the same thing. Since space-time is bent, a centripetal force occurs in the opposite direction. In centrifugal force, centripetal force occurs because we bend the movement of the object in flat space. Where the two are balanced, a stable orbit is formed. As a result, spacecraft in Earth's orbit balance gravity with centrifugal force, that is, centripetal acceleration. In this way, he avoids falling.
No. If anything you could expect a shorter span as it would be harder to sustain a longer second Though a ‘’low’’ orbit term may be misleading as it depends on whether the observer is in a higher orbit or the surface of the earth
@@skalderman let me be clear because your answer is weird. Do humans born on earths surface experience longer attention spans when they leave earths primary atmosphere and exist in a place of considerably less gravity? The reason why i am wondering is because when i practice becoming aware of my attention span and experience "the moment i can feel it come and go into memory. But does it change in space? Does the moment feel longer?
@@ninjxxitty Interesting question. The term low confused me. In theory as you go higher in the orbit time intervals should shorten and thus you might be able to maintain a longer attention span per second. However frankly I dont think thats practically sensible because there are whole a lot of factors like your energy levels, information entropy, wear and tear of radiation etc. I would say our consciousness would not care about the relative length of a time interval save the energy issue
@@skalderman you gave me an idea. Imagine a spacetime grid. Then pinch it where matter would be. You understand how the lines skew as they intersect? What if you thought of each skewed square as a moment of time. The closer to the center the faster the intervals of time feel. The farther out the slower time feels. Sort of like the shore of an ocean. Big waves take longer and arrive less frequently meanwhile the tiny waves are frequent and everywhere. Thoughts? Its just an idea. What i care most about is how consciousness feels in the moment versus transitioning to memory.
Space-time is NOT nothing, it's something that gets curved when influenced by mass... but curved is not the best word to describe what's really happening. The best word is COMPRESSED. And to be exact, only space it's getting compressed, like a sponge. While you're moving with the same speed through compressed space, you are obviously expiercing less time. The interesting thing is to realize the nature of the different quantum fields, their interactions and how they create the gravity (the curvature/compression) in macro space-time, while there is no such phenomena in micro scales.
I understand what you're saying about compressed. If it was compressed, explain the speed of light in compressed spacetime. Try this: The space goes somewhere. It goes into time. Time dilation. Can we balance the books using time?
“Today’s scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality. ” ― Nikola Tesla
...little confused here. I heard dropping a steel ball from a height & a feather, they'll fall at the same speed ( in a vaccum - no air resisrance ) , and they'll reach a certain speed but won't keep accellerating infinatly towards light speed. I know I must have missed something in your example though.
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance. The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain. And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
Simply removing mass from directly interacting with other masses, by projecting its effect onto "the fabric of spacetime", does not explain the deflection of a massless photon in a curved spacetime. It just leaves that interaction undefined.
Your explanation is excellent, although you need to be mindful of where the observer is at all times and all events need to be described in relation to a perspective from a certain point within the diagram itself at every stage, one cannot observe the effects as if we can safely refer to any absolute time, every time reference must be relative to another somewhere else, so time doesn't slow down for something falling into a gravity well unless you assume we are observing from outside the well, it's a small, but important distinction that permeates every sentence. On a side note, I believe I have worked out why gravity, not just that gravity is the effect of the curvature, I worked out why the curvature is the shape it is based upon the conservation of angular momentum within Einstein's field equation, if you're interested, I can relate it to you, it provides a reason for the shape of the tensor based up on the careful application of conservation laws and some base postulates from both Newton and Einstein together, I consider it to be the cherry on top of Einstein's field equation, because it explains why an effect like gravity must exist just given the postulates alone, and gravity the same shape does exist according to Einstein and observations.
The following doesn't make sense to me: How can two people in different timeframes interact? Surely, everything that currently exists, does so in the present moment. If the implication is that the present moment, the now, doesn't exist and everybody is on their own timeline then, wouldn't that render the past and future meaningless? I'm confused.
The same way you can talk to someone of the phone who is at the opposite side of the Earth - there is a delay, because the speed of light (or the maximum speed at which the information can travel) is not infinite, but each one of you remains in your own timeframe. And YES, you are correct - time is relative! That's the whole point of relativity! You're not confused - you've just graduated yourself to a new understanding. CONGRATULATIONS! 😄 🎆
And someone could talk to another person who is higher or lower than them, or is moving faster or slower (perhaps in circles, say). These two people would have different reference frames, but could stay in contact even without a telephone.
Light passes from C to D ( a smaller distance ) with the same amount of time that Light passes from A to B ( a bigger distance ) ??? This is only possible if the time for the Light ( C to D ) passes slower Time curvature, And at 6:00 the draw are not on scale ‘cause 90 degrees = Light speed into the space, The apple goes at the speed of light in time when he is at rest ( in space ) So if we do the drawing at scale… the curve of the border is almost impossible to see ( 9.8 m/s < 300 000 km/s ) and the fact that ( at rest in space ) the apple going forward in time on the Drawing goes towards the border ( where the ticks are separated by larger time ) means that the apple goes naturally where the time passes slowly and slowly, so … right to the center of mass, but we can’t because we have the surface of the planet that stop us to go further towards the center of mass. And if we want to do a accurate drawing for example for a black hole, the more you get into the black hole the more the angles become wide because for each meter ( at a certain point ) times passes a lot slower, so the draw at the borders become like a trumpet until we hit the distance from the center of mass when it forms a perfect quart of a circle and that in consequence the time axis of the space-time is perpendicular compared to the path of the apple in time ( so when he is at rest on space ). And that means that the apple goes at the speed of light into the center of the black hole and time don’t passes anymore
The curvature of space-time is a mathematical abstraction. It's a mathematical description of the effects of gravity. Not an explanation for the cause. Space-time is a mathematical construct, and has no material properties. Space-time is a metric; in physics, a metric is a numerical value derived from measurements, a number, a quantity, to be used in math equations to make accurate predictions. Space-time is a number, a quantity used in the field equations of general relativity, not a material which can bend, curve or warp. Those are figures of speech that refer to the illustrations mapping the gravitational field and its effect on how objects move in that field. No one thinks that the curved lines of isobars drawn on a weather map, or the longitudes and latitudes drawn on a globe map represent anything that is physically real, but when it comes to the space-time metric, the concept has been so thoroughly reified in our imaginations that it almost feels like an attack on our reality narrative to be reminded that it’s only a metric. We even have that absurd phrase, the “fabric of space-time” only because those illustrations are drawn with grid lines that resemble an open weave fabric.
According to Kaluza Klein Theory, charge is momentum in an extra dimension, and the EM field is really distortions in the spacetime fabric which redirect some of that motion into the large macro dimensions
no, curved spacetime is NOT the fundamental cause of gravity. it is a model that is able to represent the logic of gravity. but we don't know if spacetime is a real thing. is it useful when we model reality? yes. does it mean it exists? no. exactly relativity proved this when it turned out that gravity is NOT a force. however, in classical (Newtonian) mechanics the concept of force for gravity was extremely useful. so this should be a lesson for us to stay critical and self-reflexive, i.e. to differentiate abstract models from reality. as regards gravity, of course it can be considered as the curvature of spacetime, but this is a too geometrical interpretation which assumes the existence of spacetime which is far from evident. in my opinion, a better definition for gravity can be derived from the generalisations of the concepts of inertia and straight line using non-Euclidian geometry (which are also geometrical concepts, of course, but the existence of inertia is more trivial than the existence of spacetime). thus gravity is nothing but the manifestation of constraint in relation to space and time, which is basically revealed in the rotation of the light cone and thus in the gradual inversion of the roles of space and time.
The expanding cone coordinates are more intuitive than other curved spacetime videos by far 🙏
that's not saying much. and changes the meaning of intuitive. to sort of understand.
the concensus can't be explained intuitively.
This video is more intuitive
th-cam.com/video/6H5vYP6ssUY/w-d-xo.htmlsi=mkPaqWe0o2mSLpeQ
I don't claim i fully grasped all the details, but this is the best description i heard of curved space time and how it genrrates gravity. Much, much better than the massive ball placed on thin fabric animation.
That ball on stretchy fabric analogy, along with the order analogy for entropy, need to go the way of the dodo.
Agree with you. The massive ball placed on a fabric is a nonsense!
It is funny that to demonstrate gravity using stretched material, you need gravity.
Idiots only explain gravity with a stretched fabric and a ball. There is no fabric in space. The perception of top and bottom is only for us. There is no top or bottom for space. There is no direction for space, so there is no possibility of a fabric in one space plane. Also, this idiot should explain where the curvature first come to be in the first place. It is a circular stupid explanation, curvature comes from gravity and gravity came from curvature. Fact is, all physicists are lying to us about the Space.
It doesn't describe how it generates gravity. In fact, Gravity remains one of the most perplexing phenomena in physics. It explains how space-time, under the _influence_ of a gravitational field causes the attributes of falling objects.
It is also defective, as are most such popular expositions, in explaining why _not-falling_ objects-such as the apocryphal apple hanging over Newton's head-seem to be under some mysterious influence. Eg., the mysterious apple(s) seem always to bend their branches _down._
That question always elicits a separate video, such as the ingenious/notorious dialekt's river-model of the matter. Yet others present the baffling accelerating-surface claim about GR: the apple is exerting no force on the branch, the branch is continually accelerating... _upwards_ . Entailed by that interpretation is the understanding that apple trees in southern New Zealand have their branches' acceleration in another direction.
If all that is too hard for the average person to grasp, even with the help of some dodgy videos to help you over their spongy arguments, they may eventually resort to the claim that in HS physics the teachers lied to us about the meaning of... _direction._ I think that's easier than redefining the meanings of vectors, momenta, and acceleration.
Stop using miles....
Yep, science is international, maybe use the SI?
If you're so informed, why are you here?
I'm not against the use of SI, but I am against the notion of one person or a group of people telling others what convention they can or cannot use. I use both conventions, and I also use proper conversions when necessary. It all depends on the context of the problem that I'm working with. I do not buy fuel by the liter. I buy it by the gallon, and I measure my vehicles economic efficiency based on miles per gallon. When I buy milk, I buy it by the gallon or 1/2 gallon, not by the liter. Again, it all depends on the domain and context of the workspace. Now, if I was working in a lab and doing some chemistry and or physics, perhaps I would use the SI units, but again that still depends on the domain, context and workspace of the current problem. Only someone who is either ignorant or arrogant wouldn't understand this. I have the understanding and intelligence to use multiple formats and conventions, and I'm sure there are many others that do too. There is nothing wrong with someone else using miles as opposed to kilometers. Also, when I step on a scale to measure my weight, I'm measuring weight in lbs., I'm not measuring my mass in kilograms. The comment alone "stop using miles..." is condescending.
No
@skilz8098 Yeah whatever, the entire world uses kilometers.
Excellent explanation. After watching other videos on this topic, your video using the cone and illustrating how objects move around the cone -- really helps clarify the topic. Thank you. New subscriber.
Sometimes (rarely) I'm in a mindset to understand videos like this. This one hit me in the right way at the right time. Very well done. I learned a lot. Thanks.
if you believe it. and ignore the contradictions.
@@atticuswalkercontradictions?
@@kwisclubta7175 so, in other words you are mesmerized by the bullshit...
@@drakeeblis1788 That's not very nice.
You explain my first semester of Calculus perfectly. 😀
By far the best explanation I’ve seen! Thank you
I'd be curious to know how to calculate how long it would take for two masses to get to the speed of light by mutual gravity and how far apart they would have to start. I'd like to know if that's really possible with anything that doesn't include a black hole as one of the objects.
Its never possible to reach the speed of light ...ever. ...unless it involves event horizon of black hole. Here spacetime is falling into (or rather warped) at light speed but only at point of event horizon. And once at that that horizon you are never coming back to report.
A neutron star is closest next thing and you could crash into one of these at 99%+ light speed.. but never at 100%. You can have 2 neutron stars at 2 solar masses each crash together. They would crash together at 100% light speed but the boundary of where that happened would be exact the formation of a new event horizon of a new black hole which (as we know from theory and now from gravity wave evidence) always forms from merging of neutron stars.
Damn, you guys are good. I am kinda keeping up (when somebody offers amazingly structured explanation mostly) and i always feel like i would need a little bit more IQ or computing/projecting brainpower to join the top thinkers. Maybe a lot of power lol looking at some of the complex math implications some ppl can do. Hopefuly big part is knowledge and training and im not actually too far apart to justify using the word "im actually stupid conpared" 😅
I don't get how the iron ball would reach the speed of light? That's not possible as it has mass.
It would have to travel an infinite distance
That's why iron will be burnt down at some point due to heat and pressure in my point of view. The faster it goes the more mass it gains.
@canadians4trump2024Or lack of knowledge and understanding.
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance.
The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain.
And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
Infinity is your friend.
6:00 why though? Why is the object moving towards a space where time passes slower?
i thought the same. If the object is standing still and only moves through time it should just follow the time path. So why it starts shifting towards the space part of the diagram i can understand either and the video doesn't explain this
Because of the warping of spacetime. The object was moving in a straight line through spacetime, along the time axis. Now the presence of the massive object has caused the underlying 'grid' of spacetime to warp in such as way that the line of movement through spacetime (ie geodesic) is no longer parallel with the time axis but pointing into the space axis as well. So some of the movement through time is diverted into movement through space in the direction of the massive object. No external forces are acting on the object - the shift of movement into space is caused by the change in spacetime geometry itself. Pretty mind bending.
The shortest distance between two points is a straight line. All celestial bodies warp the "fabric" of space, and create gravity wells. When a smaller object comes close to the rim of a larger object's gravity well, it gets caught in that object's orbit through mass bending space-time. It's similar to how water circles a drain, but it's an all directions. Everything in space is falling.
@@jonathanspruance4502 I am sitting here glued by gravity to my seat
(and by my interest in the topic).
But since I am absolutely certain that 'time' is a concept only,
I'm in need of a different explanation.
What is it in actuality that the temporal concept is actually 'about'?
@@jonathanspruance4502 Why does the object have to move in a straight line? Of course if it moves in a straight line it will move towards the space axis and thus the “falling” of the Apple. But why does the path have to be a straight line? Why doesn’t it just move along the curved time path since it’s standing still?
Professor Francis Yu - th-cam.com/video/6S8YxnbBe-Q/w-d-xo.html
Plus th-cam.com/video/CnvOybT2WwU/w-d-xo.html
The correct question is: why does mass curve spacetime?
The correct question is, why and how does the Higgs field give objects mass?
If someone knew that, they’d already have multiple Nobel prizes.
Spacetime is just math. It does nothing.
Because mass is a degree of freedom that deflects momentum.
@@geoffwales8646Higgs field contributes 1-2 % of mass to protons and neutrons. The rest of the mass comes from the binding energy of the strong force
1:45 - if space is contracted around a mass, then time doesn't actually need to run slower because the photon is still moving over the same amount of space. If you stretched a 10 x 10 grid and watched a ball cross that grid, it would still cross 10 grid lines.
Space in contracted in the direction of travel.
This explanation of gravity as an effect of curved-space-time is mind blowing.
It’s old. However it’s rarely explained properly
The use of gravity to illustrate "space-time" which in turn causes gravity is not an explanation.
Also, Einstein's failed General Theory implies that gravity is not a force also implies that light and massive objects should follow the same path through space and that light is not affected by gravity, because of the claim that light is massless, yet His General Theory implies that gravity can suck light into a hypothetical singularity.
The entire General Theory of Einstein is built on impossible conundrums.
Light bending in an atmosphere was always considered to be why light bends in the Sun's atmosphere. Others had predicted this refractive index accurately prior to Einstein, such as Soldner. Einstein simply did not understand this concept of refractive index in optical lensing.
Gravity is caused by the implied flux density gradient of Gauss's Law for Gravity, which acts as an energy gradient, confirmed by GPS and atomic clocks.
@@JoeDeglman Where is the evidence that General Relativity has failed? Where?
Proof by assumption statement like this is typical of someone with a pet belief and no education.
General Relativity states gravity is a force. Someone has not read the General Theory of Relativity.
Light being affected by gravity is what General Relativity is all about. Where did you get this stuff?
Are you familiar with the experiments?
"His General Theory implies that gravity can suck light into a hypothetical singularity." - No.
Have you ever taken a course in physics?
@@JoeDeglman Light bends around large masses as can be seen in galactic halos.
@@geoffwales8646 the JWST also shows that these galactic halos also have a substantial dust atmosphere that acts as an optical lense to do the bending as a refractive index. Just like the Sun, bending of light only occurs through an atmosphere as a refractive index as an optical lensing function.
No bending of light has ever been observed through the vacuum of space around a massive object, in contradiction of the GRT, where there is no atmosphere.
The previous images of galaxies from Hubble were in the optical range and the dust atmosphere wasn't observed previously because the atmosphere of galactic halos emits in the infrared not in the visible.
.
If you’re directly between two massive objects of the same mass, does time pass as if you were on the surface of either one?
No. Outside objects and surface of object will yield 2 different times
@@MrMoose1347 but it would average the two? As you move away from one time is speeding up but as you move closer to the other it’s slowing down, so there has to be a point in the middle that matches the surface time right?
@@nunya3399 ah I see what you are getting at. We do account for travel gravitationally and by acceleration. Gravity is general relativity and acceleration is special relativity. When gps orbit earth it accounts for both. So not were they meet in the middle just where we account for both
2 questions that the video made me confused about.
1. The initial flashlight beam of light had to have been significant in width for the difference in distances traveled between top and bottom "light fibers" to be different. Was the initial experiment based on two stars spaced far apart from one another? In that case, how did we determine that the light arrived to us from each star at the same time, since light has always been streaming from them to us, and we don't know precisely when a given photon was emitted?
2. When you roll up the spacetime diagram and say that "light only travels through space," I understand this is correct from the photon's perspective, but you appear to be rolling up the stationary apple's spacetime diagram. Wouldn't that diagram also have light spiraling along a helix, since from the apple's perspective light travels through the apple's time at a 45 degree angle to apple's space? It seems like you are mixing/combining the apple's perspective into the photon's perspective into one unified spacetime manifold, on which I just don't understand how you can be certain about the geometry of circular, helical, and straight line paths coursed out by different material objects. Maybe we can call this some higher dimensional "God's" spacetime manifold who sees the absolute truth in terms of distance and time?
Two very excellent questions.
@@HowDoYouKnowThough so we don’t spiral along. We move in a straight path along curved spacetime. This was found out by how light acted. We took measurements of this and found out the limit to motion of mass & energy as the equivalence principle was found. Taking this into account we know have lights constant speed over distance and distance. Hell that means to get time (the rest of the equation) we just plug and play. Let me know if ya have any questions
@@MrMoose1347there's no such thing as a straight path of you want to really get into it. Space is not straight, there are no fixed points anywhere in all of existence and everything is moving at a relative speed and rate of time to everything else.
@@glenwaldrop8166 bro just read that again. I didn’t say otherwise
@@MrMoose1347 the point you were making was a bit pedantic, I went a bit further.
Everything is relative, everything interacts with everything, there's literally no such thing as a straight line.
One of the best explanations I have seen. Thanks
Best explanation yet
This is easily one of the better explanations of gravity. Kudos to you.
man been trying to wrap my head around this, but after watching this, i get it a little...
Me, too. Emphasis on LITTLE.
The thing that throws people off is this name, “curved spacetime.” Sure, when you look at a rolled up piece of paper, or a digital graphic, we see the curve. But in reality there is no curve. Space is devoid of geometry. There is nothing surrounding the earth. Its literally enpty space. Wheres the curve?
You have to remember that einsteins theory is just that, a theory. Yes it happens to align with how we perceive things to work, but it doesnt provide all the answers. Its just the best explanation we currently have. We dont understand the nature of space. Thats the issue here. When you consider this example, a rolled up piece of paper, that is one way to describe gravity. But the age old question remains unanswered, WHY does gravity exist? I believe thats something we can never know.
Einstein explained the how. The why he had absolutely no idea. No one does, and no one ever will. Thats why after watching all these gravity videos, everyone has the same response, “eh, i guess it makes sense.” It can never make total sense until we understand the fundamental nature of the universe. Unknowable unfortunately. Why are things attracted to each other? Who knows, the just are 😁
@@trenken
I read your post... Earth is surrounded by space. Einstein said there is no space or time... it's space time. You changed it to JUST space.
@@francus7227it's just space because you don't know nothing about time...
@@trenkenmaybe that’s the life cycle of matter? Create black holes basically.
Nice way to illustrate! :)
There are a few mistakes because of over simplification in this video. For example the ball falling from an infinite high tower would not reach ligthspeed. The potential energy in a gravitational field is finite! So an object with mass cannot reach the speed of light.
Agreed, of course. I wrote the followingI comment ...
f the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance.
The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain.
And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
It sure would; given the infinite amount of time.
@@ktl4539 Nope, even in infinite time the ball still deals with a finite amount of energy.
Why does light moves only through time in the flat spacetime diagram wrapped in a cilinder at 3:25? Light does not travel through space only, it also travel through time, its speed is not infinite.
There is no "time" to move through, unless you mean the along the direction of some observer world-line, but you still have to choose such a world-line. That said, yes, light will move equally through the spatial and temporal coordinates of the observer, Δx=Δt.
You’re confusing the speed of time with the device that’s measuring time . Time is not speeding up or slowing down , it’s the device that you’re using to measure time that is measuring it faster or slower . Time is a constant and doesn’t speed up or slow down , however the device measuring it does .
Yes. Time is a constant. The device measuring time changes
Yes … the device you are using to measure “time” is affected by its place in a gravitational field, and the various accelerations it undergoes… once you account for those variables, any differences in two time measuring devices will be factored out …
Does it apply for digital clocks too?
@@kpbalaji
Yes
“Time isn’t speeding up or slowing down it’s the device you are using” um….its measured motion so both time and the clock are being talked about when dilating.
I would also put some explanation to cover the difference between those two persons curved path (since they are forced by the contact with the ground) vs straight path of falling object (since there is no contact with the ground during the path).
I thought time is an illusion
Why?
Question? since even deep space contains micro-gravity, what is creating the micro-gravity?
The Gravity Probe B experiment detected something called "Frame Grabbing", where the Earth is grabbing space/time as it turns on its axis. Wonder if this had been further examined as to impacts to time?
7:09 - I am not a physicist, but I think that is the definition of terminal velocity. "The velocity a free-falling object would reach by the time it struck the surface". It's the same velocity as would take to achieve escape (velocity). On the Earth, that is around 11.186 km/s., not C. Now, from the event horizon of a Black Hole, it would be C.
My comment was:
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance.
The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain.
And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
7:03 The iron ball would reach the speed of light?
Relative to what?
How could the height of the tower be infinite?
How long would reaching the speed of light take?
How would the speed of the ball be measured?
You would need infinite energy to move a massed object at the speed of light!
My comment was:
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance.
The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain.
And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
speed of lite is the same relative to everyting, if you don't know that what are you doing here, watch some basic videos or you'll just get more confused
Can you expand just a little more and in the extreme case of going trough an event horizon where the time and space axis switch? How would you represent that in a video graphic? And by the way....excelent video!
For a particular choice of coordinates, the Schwarzschild-Droste coordinates, the temporal and radial components of the metric tensor switch algebraic sign.
Understanding the "switch" is easier than many think. It sounds brain-bending that time and space switch places, but it's really just the fact that the singularity is the ONLY future of your light cone. Because anywhere you would like to maneuver when "falling" into a black hole, you will ALWAYS (100% of cases) meet the singularity (it's just in your light cone across all possibilities). The Penrose diagram has this brain twist in it, but from a simpler point of view, it's just that. Like when it's Friday night and you are out with friends, the beer is your 100% future :D (if you drink). I like to hypothesize that all singularities are the same (like in the SAME spot), because when you have a spherical universe (like an expanding balloon and space-time is its surface), when you do this 90-degree warp (like black holes do) from the surface, eventually this warp ends in the middle of the sphere. So all black holes point to the same "space/spot/something/singularity" :) . Just food for thought.
@@fjbayt much like going over a waterfall
The time and space axes never switch. That is nonsense. Time is time and space is space. Minkowski was wrong with his quote ("Henceforth, space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality")!
@@romanjanek5283 FYI: singularities don't exist and time and space don't switch.
Can anyone help confirm this for me? I've always found the twin paradox a bit confusing because, as I see it, the twins can never meet in a way that would cause one to be older than the other. Here's why: as the twins travel towards each other, their clocks would start to synchronize. By the time they are close enough to "meet," their clocks would essentially align, placing them on the same "time" line and making them the same age again.
From my understanding, the only way the paradox could play out is if one twin traveled near the speed of light towards the other and could observe the other's clock. However, the idea that their clocks tick at different rates is something that seems to only hold from the perspective of an external observer outside both reference frames.
So, what I'm asserting is that it's not accurate to say the twins could meet and be different ages because they could never technically meet under these conditions. The differences in their clocks are only apparent to an outside observer. Is my reasoning correct?
That’s why it’s a paradox. Neither can be older than the other
really..."the iron ball would reach the speed of light". as far as physics goes, objects with mass can't ever get to the speed of light.
Inside a blackhole? Speed of communication.
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance.
The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain.
And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
If you take the derivative of the space time curve at any point along the curve, will you obtain the acceleration due to gravity at that point as determined by the inverse square law?
Great video
at 4:27 what if you turned the funnel around so it was smaller the closer to earth and you swapped the time and space axis? would that work? or does that not make sense?
beautiful explanation and illustration.
“Object mass" refers to the inherent amount of matter in an object, which is a constant value and does not change with its speed, while "speed mass" is not a standard term, but could be interpreted as the apparent increase in mass an object experiences when moving at very high speeds near the speed of light, according to the theory of relativity; essentially, the faster an object moves, the slightly greater its "relativistic mass" appears to be, although this effect is only noticeable at extreme speeds.
"Light beams which only move through space..." I cannot get my head around this. So light doesn't move through time?
@@grahamthomas7821 technically they do but it’s the shortest time. All massless objects not just light
Not only do objects moving at light speed experience time as zero, the space between their origin and where they land is compressed down to zero distance as well.
@@reidflemingworldstoughestm1394 that’s perspective.
@@MrMoose1347 That's physics. Perspective is drawing.
@@reidflemingworldstoughestm1394 perspective can be drawn but isn’t strictly drawing.
It is described as curvature but is something else. In Einstein’s theory, it is more of a functional analogy
Gosh I hate it when people put trash on TH-cam. Space and time are both metrics and don't create anything. That is the same as saying the measurement of one meter can create life. I hate ignorant people that can not learn basic stuff.
This is good work Sir…
This is all taken from another channel @scienceclic
The gravitational field is not necessarily stronger at the bottom of the ocean trench, as it is highest at the Earth's surface and then gets weaker as one approaches the center of the Earth (where there is no gravitational field at all). So while clocks do go faster higher in the atmosphere, they will also go faster at the center of the Earth.
Excellent point
A clock at the surface of the Earth runs faster than a clock at the center. Not by much, the time dilation is 1.0000000003 between the core and surface.
@@fjbayt NO - the time dilation runs proportional to the Newtonian potential, which is lowest at the center of the Earth.
@@KaiVieira-jj7di You are right, my mistake, i got confused, i ll erase the comment
Interesting. I've just been taking a look at 'How Does Gravity Work Underground? (An In-Depth Explanation)'
That's the backing paper from book covering film... wow, it's all so simple.. but where did the book covering go?where did it come from and if we join the two sides together will it create a worm hole between Rymans and Smith's?
I think you are mixing up gravitational time dilation (GTD) with spacetime curvature. GTD arises when you think you are stationary and yet you are actually in an accelerated frame of reference, as indeed we are standing on the surface of the Earth. GTD is observer dependent, meaning it is possible to find observers that do not see it (a free falling observer won’t experience GTD for example). Where there is GTD, there is apparent (or fake) gravity. Once we accept the Earth is accelerating upwards, it is actually unsurprising that objects appear to fall and that all objects regardless of their mass ‘fall’ at the same rate, because the Earth is actually accelerating upwards at the same rate. Most of what we see as gravity on Earth is because of its acceleration upwards. What is holding the Earth in, keeping it the same size? Spacetime curvature.
Spacetime curvature is caused by mass and energy. It is observer independent; all observers will agree on the curvature. Spacetime curvature is what gives rise to real gravity, and what attracts objects together in space. It emerges in the form of what we call tidal forces.
The rolled up diagram you used is flat spacetime but rolled into a cone to illustrate the time dilation. That time dilation is GTD. GTD arises from an accelerating reference frame. When it is flattened out the time axis is curved, while the free falling world line (of a falling object) is not. This is a specific version of a spacetime diagram describing flat spacetime (not curved) and actually drawn from the perspective of a free falling body. The time dilation on the curved diagram is a result of a mapping between the object’s inertial frame of reference and our (standing on Earth) accelerating reference frame and is not the same thing as spacetime curvature. The free falling body has no acceleration itself and sees us and all the Earth accelerating towards it.
4:19 a cylinder is flat. but also a cone is flat.
this is not spacetime curvature, this is the local equivalence principle: gravity due to acceleration in flat minkowski spacetime. notice that you do not need curvature to experience gravity
it's a nice visual, but it's very inaccurate because gravity is not caused by curvature, it's cause by being in accelerated reference frame. Geometry, curved or otherwise, dictates what counts as a force free path.
Eddington’s „observation“ was technically a joke. He had not even the needed instruments, or the needed accuracy to perform such observation. He just wanted „to confirm“ Einsteins prediction…no matter what.
It's incredible how the press just picked up on Einstein after that.
@@greggstrasser5791
At first sight, yes.
@@O-Kyklop It was later demonstrated countless times with modern technology.
@@PADARM
Oh yes, Einstein’s prediction had to be proved at any rate.
Eddington was cheating and all others later ones too. They sold to you simple refraction for bending of space time and you did buy it.
Why is light beam travelling horizontal in the unrolled up diagram ? It should be 45 degrees, right ?
The speed of light is not a constant as once thought, and this has now been proved by Electrodynamic theory and by Experiments done by many independent researchers. The results clearly show that light propagates instantaneously when it is created by a source, and reduces to approximately the speed of light in the farfield, about one wavelength from the source, and never becomes equal to exactly c. This corresponds the phase speed, group speed, and information speed. Any theory assuming the speed of light is a constant, such as Special Relativity and General Relativity are wrong, and it has implications to Quantum theories as well. So this fact about the speed of light affects all of Modern Physics. Often it is stated that Relativity has been verified by so many experiments, how can it be wrong. Well no experiment can prove a theory, and can only provide evidence that a theory is correct. But one experiment can absolutely disprove a theory, and the new speed of light experiments proving the speed of light is not a constant is such a proof. So what does it mean? Well a derivation of Relativity using instantaneous nearfield light yields Galilean Relativity. This can easily seen by inserting c=infinity into the Lorentz Transform, yielding the GalileanTransform, where time is the same in all inertial frames. So a moving object observed with instantaneous nearfield light will yield no Relativistic effects, whereas by changing the frequency of the light such that farfield light is used will observe Relativistic effects. But since time and space are real and independent of the frequency of light used to measure its effects, then one must conclude the effects of Relativity are just an optical illusion.
Since General Relativity is based on Special Relativity, then it has the same problem. A better theory of Gravity is Gravitoelectromagnetism which assumes gravity can be mathematically described by 4 Maxwell equations, similar to to those of electromagnetic theory. It is well known that General Relativity reduces to Gravitoelectromagnetism for weak fields, which is all that we observe. Using this theory, analysis of an oscillating mass yields a wave equation set equal to a source term. Analysis of this equation shows that the phase speed, group speed, and information speed are instantaneous in the nearfield and reduce to the speed of light in the farfield. This theory then accounts for all the observed gravitational effects including instantaneous nearfield and the speed of light farfield. The main difference is that this theory is a field theory, and not a geometrical theory like General Relativity. Because it is a field theory, Gravity can be then be quantized as the Graviton.
Lastly it should be mentioned that this research shows that the Pilot Wave interpretation of Quantum Mechanics can no longer be criticized for requiring instantaneous interaction of the pilot wave, thereby violating Relativity. It should also be noted that nearfield electromagnetic fields can be explained by quantum mechanics using the Pilot Wave interpretation of quantum mechanics and the Heisenberg uncertainty principle (HUP), where Δx and Δp are interpreted as averages, and not the uncertainty in the values as in other interpretations of quantum mechanics. So in HUP: Δx Δp = h, where Δp=mΔv, and m is an effective mass due to momentum, thus HUP becomes: Δx Δv = h/m. In the nearfield where the field is created, Δx=0, therefore Δv=infinity. In the farfield, HUP: Δx Δp = h, where p = h/λ. HUP then becomes: Δx h/λ = h, or Δx=λ. Also in the farfield HUP becomes: λmΔv=h, thus Δv=h/(mλ). Since p=h/λ, then Δv=p/m. Also since p=mc, then Δv=c. So in summary, in the nearfield Δv=infinity, and in the farfield Δv=c, where Δv is the average velocity of the photon according to Pilot Wave theory. Consequently the Pilot wave interpretation should become the preferred interpretation of Quantum Mechanics. It should also be noted that this argument can be applied to all fields, including the graviton. Hence all fields should exhibit instantaneous nearfield and speed c farfield behavior, and this can explain the non-local effects observed in quantum entangled particles.
*TH-cam presentation of above arguments: th-cam.com/video/sePdJ7vSQvQ/w-d-xo.html
*More extensive paper for the above arguments: William D. Walker and Dag Stranneby, A New Interpretation of Relativity, 2023: vixra.org/abs/2309.0145
*Electromagnetic pulse experiment paper: www.techrxiv.org/doi/full/10.36227/techrxiv.170862178.82175798/v1
Dr. William Walker - PhD in physics from ETH Zurich, 1997
Interesting, but it is a book rather than a comment.
@@walidkhier5640See my short TH-cam presentation.
Well it’s been proven and you can say otherwise but your comment and sources don’t disprove relativity. It all works very well.
If the speed of light is not a constant then Relativity can not be correct, any theory based on it is also wrong. General Relativity is not compatible with Quantum mechanics. So either one or both of the theories is wrong. The evidence I present says Relativity is the problem. Science will not advance , if the foundations of physics is not challenged.
@@MrMoose1347If the speed of light is not a constant then Relativity can not be correct, any theory based on it is also wrong. General Relativity is not compatible with Quantum mechanics. So either one or both of the theories is wrong. The evidence I present says Relativity is the problem. Science will not advance , if the foundations of physics is not challenged.
If the Eiffel-Tower were of infinite hight there would be no gravity at all. This is a classical solution which is duplicated by GR in the Newtonian limit of „weak gravity (earth) and slow speeds (v
The assumption that all photons from A/B should reach C/D at same time needs a proof. It may not.
they don't. we saw the same light from a supernova . arrive 3 different times.
@@atticuswalker Not equivalent , with the earth scenario its a single mass and photons are taking a similar path , with a supernova the light take wildly different paths
@@stoppernz229 Because spacetime curved. Floathead says the same thing as this guy.
@@atticuswalker did you?
@@wiktorchm what. see the light myself. nope. but I haven't seen the cmb either. don't doubt it's real.
Does light really bend? When looking at a fish in water, why is the fish ahead when looking through water? Could the same happen in space near a planet or star?
I see it backwards. Gravity (mass) creates time and space.
Gravity doesn’t create time. Motion is time. That’s why gravity (distances) warp time. And speed affects velocity. Mass warps spacetime.
No, a photon is the most extreme form of motion, yet time = zero.
No, at the time of inflation, there was time AND space, but no mass at all.
@ that energy still has motion
@@JockularK yes because it’s a force carrier. Showing the limit to information travel.
Why are you using miles / second to express the speed of light. Ughh.
How skillful are scientists in explaining problems they cannot understand with fabricated solutions? They create a paradox with nonsense questions, and then they think they have solved that paradox with another nonsense. The speed of light is constant only if they are in the same plane. When the plane is different, the speed is different. For example, the near beam should reach the large mass earlier because it travels less distance than the far beam logic. It's not like that, though. The ray that stays away from the larger mass appears to arrive at the same time because it moves faster than the one that is closer. When you incorrectly construct the universe, light and movement, such absurd questions and solutions are called science. This is not science. He's deceiving people
Your comment may be deceitful even to yourself,
there is a big difference between hypothesis and fact.
Seems wild to claim scientists are just full of nonsense and 'construct the universe' incorrectly, hinting you have all the answers.
Another thing that seems quirky and weird to me is how can light speed up and slow down, or slow down and speed back up depending on the medium that it's going through... And they call this a 'constant"⁉️😂
@@drakeeblis1788 No. It's specifically the speed of light in a vacuum.
And it's not primarily about light. Light is a massless particle hence travels at C in a vacuum. But can be slowed by shining through non-vacuum.
@@drakeeblis1788 Let me explain please. First of all, it is necessary to know what light is and how its movement occurs. As you know, the space that is thought to be empty is actually full. It only has a much sparser texture compared to mass. I think that at this point, weak force or weaker forces are involved. (weaker force has not yet been fully defined) weaker force is the subatomic particles that I call formation points, which are too weak to be mass. They move just like a Newton pendulum. But they are connected to each other in every direction. The reason for quantum fluctuations is their movement. The most important task of these structures is the communication network with the ebb. In other words, light seems to move through these structures. Just like the balls from a Newton pendulum do not go anywhere but transmit the movement. Think of it in the same way but in 3 dimensions. The distance between the balls increases or decreases the speed of light. If the distance is greater, therefore it means it is farther from the mass, then light moves faster. Because there is no time between two formation points. It is the collisions of two or more formation points that express time. I hope this was a sufficient explanation for you to understand. In fact, the topic is so broad that it is harder to write. Thank you for bearing with me.
The cone can work well if a gravity is the only force. I wonder how should air resistance force be put on the cone? Maybe as a force opposite to gravity increasing speed in time direction or maybe air resistance modifies somehow the cone?
You got it wrong. The curvature of space time is a symptom of gravity.
Nope... you got it wong. Acceleration along space axis . . what we call gravity. . . is direct result of warping of space-time... more specifically differential time. Not the other way round.
@@bbbf09
Why does space warp?
@@pretzelogic2689 Space-time (4 dimensions) is what warps - not just space. It is a fundamental fabric of the universe.
It does so in the presence of any energy-momentum. Since mass (matter) has an equivalent energy (E=mc2) then it also warps in the presence of mass (any mass size but more noticeable for us with planet size masses like Earth) . That warp gives rise to differences - a gradient - in the flow of time which gives rise to space (which rememeber is connected to time as 4D fabric) flowing in towards the direction of the warp (towards the mass) - which we experience as an acceleration and historically have labelled it as a force of gravity. So it is warped space-time gives rise to what we call gravity. Not the other way round. To go into greater depth involves EInsteinian tensor mathematics. A bit too much for youtube comments section.
@@jayceasar2661 Prove what exactly? that time flows at different rates depending on how close to the energy-momentum (mass) centre you are? Without accepting that the algorthim in your GPS makes allowance for this - then it would not work and you couldn't use google maps to go anywhere. 'Proof' enough for you?
@@bbbf09
You said it yourself: "...it also warps in the presence of mass..." Your "also" refers to energy. Energy mass, fungible. Thanks for repeating what I said.
Wait.. at 7:04 you're saying that an iron ball falling infinitely from the Eiffel Tower into a gravitational field would eventually accelerate to the speed of light? Well, problem is, only massless things like photons can travel at light speed, and any object with mass would require energy equivalent to the mass of the entire universe to accelerate to the speed of light, which would also include the mass of the infinitely long Eiffel Tower that the iron ball would be falling next to. So the iron ball would never reach light speed, because if it did it wouldn't be an iron ball anymore, but a stream of photons that used to be the iron ball, the Eiffel Tower, and the rest of the mass of the universe.
Correct.
My comment was:
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance.
The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain.
And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
@@DABmongerthere's more wrong with the example than that but you're missing the point. Dropping any mass onto a black hole would be a better example. By the way if the tower is infinitely tall the ball wouldn't fall at all because it would be too far from the source. Assuming the tower itself doesn't have mass. On another note if there was no ground and the ball was somehow affected by gravity, any air around it would also be in freefall. Terminal velocity only exists if there is a ground for the air to push against, otherwise there isn't any friction of falling.
@Richinnameonly Me thinks you're overanalysing, and a lot. The creator will giving a simple example, and there is a terminal velocity constraint on Earth, plus nothing with mass can travel at light speed
You're adding elements to a simple example, none of which was the creator's intention.
I knew it, I knew that it would come the day when Millennials would start thinking they can think like geniuses too and would start spurting out all kinds of nonsensical krap calling them scientific theories. Time, or time dilation, creates gravity as much as chronometers create speed, duh...
Can't wait until you get the Nobel for refuting Einstein.
@@somerandomboi8239 Einstein never came up with that krap. He new better.
@@rubenoteiza9261 ok
@@somerandomboi8239 You are right, Einstein said many things but the things on which he was right he was able to prove them mathematically, with equations. There is np mathematical proof for this assumption, it is pure speculation.
@@rubenoteiza9261 I may have been wrong to react this way, as I am not yet at this chapter but am just watching stuff in order to gain some basic intuition for when I do get into it seriously. I just do find these playing-arounds with ideas and imagery useful for visualizing concepts, and couldn't comprehend what you meant by dunking on it, esp. with your end sentence about time and gravity. What does cause it then? Because we all agree that it is not a classical force.
Then of course, maybe you see something profoundly wrong in the video that I couldn't catch?
So that means in a wormhole where the space could be infinite the time slows down almost to a stop and the speed grows as much as it almost gets to the speed of light ?
Watching different videos is making my understanding better and better. An excellent presentation in a different way on time dilation.thanks a lot
Take a look at the comments, and you'll see that there's major errors in this video.
Why does the universe choose to have mass and light move on geodesic paths? Does it have anything to do with the law of least action?
i think the video explaining that object will drop accelerately as it reach toward the earth. But I didn't catch why the object move towards earth as well as why the moon doesn't drop to the earth. Or I miss some concept in the video?
if you want more explanation : th-cam.com/video/6H5vYP6ssUY/w-d-xo.htmlsi=tpzlCClld2pBPfU5
Question. In this model of spacetime it flares wider as it approaches the center of mass of the earth. But, in another model, spacetime funnels into a point towards the center of mass of something like a black hole.
No. In this model the larger diameter denotes longer time taken to cover the same unit of space. The closer to massive object the slower the time gets. Your second sentence is about spacetime, and is correct.
It's just an inverted visualization, since space and time are represented by perpendicular axes. When discussing the differences of motion through space and/or time, it is helpful to invert the cones in order to show the consistency of the distances travelled.
In 7:24 minute you show curved space and the apple that falls. Please can you show all unit measures of curved space time when the apple falls with 9,81m/s^2 acceleration?
The cone analogy, this is the best illustration I've ever seen!
Cann you tell me when you folded then what will be in background of that in which folding occur because space you folded then what will left in background
Wow. It looks like you could work out the geometry that gravity bends spacetime into by using the acceleration of gravity and that last diagram (6:00).
if light propagates in all directions then why and how do we see/locate the object emitting light? wouldn’t we see the light from the object everywhere?
I am not a physicist but have a question on this. Light travels in different velocities in different optical mediums. Are we sure there is nothing in the space? Maybe something near the earth has different density that cause light travel slower.
@@phillee8666 yes we are sure
No,they are not sure. And not only that, they don’t even know if Space is isotropic. Or even worse, they can’t even test it. They only talk and, if you believe it, they don’t need more than that.
@@O-Kyklop Yes, on large scales, space is considered isotropic, meaning it looks the same in all directions. This assumption is a key part of the cosmological principle, which suggests that the universe is homogeneous and isotropic when viewed on a sufficiently large scale. This is supported by observations, such as the uniformity of the cosmic microwave background radiation . However, on smaller scales, the distribution of matter (like galaxies and stars) is not perfectly uniform.
@@MrMoose1347 Ok. It means you can’t make a prediction for a certain location you can’t check up directly.,……which is most of the Universe.
Not a very solid theoretical background, isn’t it?
@@O-Kyklop but we can though
I watched 2 videos and i still can't understand it ig. Correct me if i am wrong.
So if if throw and object from an height, Its always in rest during mid air. and when i collides with ground it comes in motion, coz ground is in motion too
Things are only at rest in their frame
Is that true that you eventually reach speed of light if falling down infinitely? If you're jumping off a plane, your falling speed increases but only to a certain speed and then, unless you're not already on the ground (ouch), your falling speed will remain constant (the exact number would be devided from your weight) and yet far from speed of light. that is if the gravity is constant.
How much gravitational field/gravitational constant to make light bend?
The radius of curvature is c^2/g
You lost me at ^@@DrDeuteron
@@rodolfosantana9015 well if you imagine a flat earth (no, not like that) and fire a laser beam horizontally, after 186,232 miles it will fall for one second with acceleration "g", so like 16 feet, and that is following curved space time, and (switching to metric) 300 Mm long parabola curved by 5m has a radius of curvature of c^2/g = 10 Pm. (peta meters)..so about 60,000 AU...space is pretty flat around Earth, yet you can't fall 20 feet without getting hurt.
@@DrDeuteron
Why do Laser beams, in fact, bend upwards when fired parallel to the ground?
Indeed fleeing Earth mass.
@@O-Kyklop omg. please learn to abstract. We're doing a flat earth model.
...and a few years before that, somebody noticed fruit falling... one gets the feeling that our host believes gravity has an independent metaphysical existence, and it is just "out there."
But why do you wrap space-time in a cylindrical shape? What physical phenomenon explains this? Some kind of periodicity?
I believe it's just a way to visualize it to help understand. It's not a literal interpretation.
@@xtraspecialj Then that should be made clear when presented that way, or it just helps misunderstand
@@NondescriptMammal ?? How in the world is it not clear? How could anyone possibly think it's a literal representation of spacetime? If you think that, then you shouldn't be bothering to ponder this stuff, you should be watching Bob the Builder or something...
@@xtraspecialj I assume that the maker of this video means for the cylinder to be taken seriously. It isn't just presented as a momentary visual aid to help understand... Everything that follows in this video to reach its conclusions, is derived from the geometry of that cylinder. All the example cases and intermediary conclusions presented afterward, rely directly on the construction of that cylinder. The cylinder is indispensable to this video's attempt to validate the assertion that "the curvature of spacetime causes gravity".
@NondescriptMammal ... Yes, but it doesn't mean to be taken literally. It's simply an aid to help in understanding...
So you're saying the difference in the flow of time between 2 locations is the gradient that drives the apparent force of gravity?
Imagine traveling a road that takes 5 minutes to reach your destination. If a sinkhole or crash blocks the path (representing mass in space), you can't continue straight. The obstruction diverts traffic, and you must take a longer route. This detour increases your travel time to 8 minutes. This time dilation reflects changes in spacetime; with increased distance, time dilates.
Acceleration also affects spacetime but in a different way. Changing your speed alters the perceived contraction of space and consequently affects the duration of time.
Relativity encompasses more than just relationships between measurements. It involves how units of measure change relatively due to different conditions experienced while traveling through spacetime.
Matter tells space-time how to curve, and space-time tells matter how to move. This is because space and time are not flat, but can be warped, stretched, and pulled by matter.
Time is relative and not constant. The rate at which time passes depends on your frame of reference.
You just need to look at the constant adjustments that have to be made for time dilation to GPS satellites due to Special Relativity (velocity - clocks run slower) and General Relativity (weaker gravitational field - clocks run faster).
Overall effect for both GPS satellites and travelling in an aircraft ... clocks tick faster.
However, moving at sea level -> clocks run slower, so you age slightly less.
I would like to see an explanation of how "space time" curvature causes the tides. I assume that space time is curved between the moon and the earth ( or between the sun and the earth) and that curvature of space time causes the tides, but I'm having difficulty visualizing how that works.
The cone visualization was the core point making this video great. Thanks a lot, perfect explanation.
Wonderful explanation thank you 🙏
What causes space-time to be curved? The presence of matter-mass. Why-how does the presence of matter-mass cause space-time to be curved? Isn't general relativity just some Riemann mathematical geometry applied to describe a force, which doesn't "explain" anything? Why can't other forces-at-a-distance be described in the same way?
It exists in space so it has to adjust to the mass. So yes in a way it’s just some way to measure things
@@MrMoose1347 I think it would be better for us to follow Nietzsche's thinking and say that there is no empty space but rather there's nothing but fields of force. Force, not space, is primary. Time? Well, that's just the counting of processes that run because of forces.
@ when you say force I think energy and it is energy so you aren’t far off.
@@MrMoose1347 Just remember that energy is what you get when a force is applied-exerted, or when forces act against each other. Force is primary.
@ nope. You need energy to have force.
What force, (force = mass x acceleration) causes the acceleration. The 'rubber sheet' model assumes the object is already moving with respect to the major mass's centre of mass. A static model requires a force to begin acceleration. And more - where does the energy come from to accelerate the object. If an object falls inside a total vacuum calorimeter, it would register heat when the object hits the end of its travel. Where did the energy come from?
From it's initial creation. Everything in space is falling. An object will stay in motion until acted upon by an opposing force. If an object finds itself roaming space alone, then it will speed up because it's falling.
Great video. It shows that gravity is not a force but geometry. The curvature of spacetime create gravity
However, I still do not understand how big masses -like the sun - can curve spacetime. Why don't they just " hang" there in space and leave space unaffected.?
I’d argue it’s both. A force caused geometry. Mass existing in space literally forces space to play along.
I think if we divide it to the atomic level then it is better to understand. I believe anything that has mass fundamentally cures space-time, which means an atom curves space-time, but it's just negligible. But when they form massive objects, the curvature is visible, like in case of sun (Einstein's Demonstration of this with mercury's position), or the extreme curvature of black hole curving the light's path into the black hole itself.
Correct me if I'm wrong.
@@anulearntech Yes , and atoms are build of subatomic particles, who also have mass. Ok, I get it now. It all comes down to particles... :)
Could it be that "energy of the vacuum",
virtual particles popping in and out of existence, etc.,
are simply the outer limits of the invisible aspect of mass so that
all the matter in the universe actually extends into all the spaces that
look empty to us?
If so then every photon zipping through a galaxy takes a route
no part of which is straight... meaning images we make of the very distant stars
can only be approximations (to say nothing of the movement of those stars
during the centuries of photon flight).
@@REDPUMPERNICKEL and?
saying 'the flow of time' is a contradiction as it implies distance traveled of an arbitrary quantity 'q' moving from point 'a' to point 'b'. So how can anyone invoke a term witch itself is defined in terms of time to describe time?
I tell you, Millennials have already gone to college, graduated, and think they can also revolucionize Physics.
Energy is always in motion. Motion is time. So yes by the existence of energy distance has be traveled
Why do goose down and a metal ball fall at the same speed in a vacuum? How does gravity determine how much force to apply to objects of different masses so that they fall at the same speed?
Gravity is a constant and without air resistance they don’t flutter or slow either
Maybe centripetal force and gravity are the same thing. Since space-time is bent, a centripetal force occurs in the opposite direction. In centrifugal force, centripetal force occurs because we bend the movement of the object in flat space. Where the two are balanced, a stable orbit is formed. As a result, spacecraft in Earth's orbit balance gravity with centrifugal force, that is, centripetal acceleration. In this way, he avoids falling.
If gravity is caused by bending space-time, how about centrifugal force?
Mass existing causes space to curve around it.
Acceleration is just like gravity.
@@party4keeps28 not quite “just like it” more like related.
@@MrMoose1347
*"Mass existing causes space to curve around it.“*
It means Space must have a mass too.
Do people in low earth orbit have longer attention spans?
No. If anything you could expect a shorter span as it would be harder to sustain a longer second
Though a ‘’low’’ orbit term may be misleading as it depends on whether the observer is in a higher orbit or the surface of the earth
@@skalderman let me be clear because your answer is weird.
Do humans born on earths surface experience longer attention spans when they leave earths primary atmosphere and exist in a place of considerably less gravity?
The reason why i am wondering is because when i practice becoming aware of my attention span and experience "the moment i can feel it come and go into memory. But does it change in space? Does the moment feel longer?
@@ninjxxitty Interesting question. The term low confused me. In theory as you go higher in the orbit time intervals should shorten and thus you might be able to maintain a longer attention span per second. However frankly I dont think thats practically sensible because there are whole a lot of factors like your energy levels, information entropy, wear and tear of radiation etc. I would say our consciousness would not care about the relative length of a time interval save the energy issue
@@skalderman you gave me an idea.
Imagine a spacetime grid. Then pinch it where matter would be. You understand how the lines skew as they intersect? What if you thought of each skewed square as a moment of time. The closer to the center the faster the intervals of time feel. The farther out the slower time feels.
Sort of like the shore of an ocean. Big waves take longer and arrive less frequently meanwhile the tiny waves are frequent and everywhere.
Thoughts? Its just an idea. What i care most about is how consciousness feels in the moment versus transitioning to memory.
Space-time is NOT nothing, it's something that gets curved when influenced by mass... but curved is not the best word to describe what's really happening. The best word is COMPRESSED. And to be exact, only space it's getting compressed, like a sponge. While you're moving with the same speed through compressed space, you are obviously expiercing less time.
The interesting thing is to realize the nature of the different quantum fields, their interactions and how they create the gravity (the curvature/compression) in macro space-time, while there is no such phenomena in micro scales.
I understand what you're saying about compressed. If it was compressed, explain the speed of light in compressed spacetime. Try this: The space goes somewhere. It goes into time. Time dilation. Can we balance the books using time?
@@ragnaarminnesota6703You can't bend or dialate a concept. Space and time are concepts. Bending a concept is a reification fallacy.
@@slow-mo_moonbuggy Don't say fallacy. Explain. Compress explains. Fallacy does not.
@@ragnaarminnesota6703 Compress a concept? Can I compress other concepts like love and freedom?
“Today’s scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality. ”
― Nikola Tesla
GPS has to consider the dilation of space time to work. That is reality. And Tesla was only an engineer.
Wow great explanation
Well explained.
...little confused here. I heard dropping a steel ball from a height & a feather, they'll fall at the same speed ( in a vaccum - no air resisrance ) , and they'll reach a certain speed but won't keep accellerating infinatly towards light speed. I know I must have missed something in your example though.
@@paulfogarty7724 they will drop at the same rate and will never reach the speed of light if given the opportunity.
@@paulfogarty7724 this is because gravity is constant here but factors act against it like air resistance.
If the height of the Eiffel Tower was somehow infinite, the iron ball would reach its terminal velocity, when the force of gravity is perfectly matched by the forces of friction and air resistance.
The Eiffel Tower and iron ball would have to be in a vacuum, as well as having an infinite height, for the acceleration to remain.
And what's more, an iron ball has mass, and only massless particles can travel at the speed of light.
Simply removing mass from directly interacting with other masses, by projecting its effect onto "the fabric of spacetime", does not explain the deflection of a massless photon in a curved spacetime.
It just leaves that interaction undefined.
Excelent quality of graphics and animations, ideas most probably from the book Visualizing Relativity
Your explanation is excellent, although you need to be mindful of where the observer is at all times and all events need to be described in relation to a perspective from a certain point within the diagram itself at every stage, one cannot observe the effects as if we can safely refer to any absolute time, every time reference must be relative to another somewhere else, so time doesn't slow down for something falling into a gravity well unless you assume we are observing from outside the well, it's a small, but important distinction that permeates every sentence.
On a side note, I believe I have worked out why gravity, not just that gravity is the effect of the curvature, I worked out why the curvature is the shape it is based upon the conservation of angular momentum within Einstein's field equation, if you're interested, I can relate it to you, it provides a reason for the shape of the tensor based up on the careful application of conservation laws and some base postulates from both Newton and Einstein together, I consider it to be the cherry on top of Einstein's field equation, because it explains why an effect like gravity must exist just given the postulates alone, and gravity the same shape does exist according to Einstein and observations.
The following doesn't make sense to me: How can two people in different timeframes interact? Surely, everything that currently exists, does so in the present moment. If the implication is that the present moment, the now, doesn't exist and everybody is on their own timeline then, wouldn't that render the past and future meaningless? I'm confused.
The same way you can talk to someone of the phone who is at the opposite side of the Earth - there is a delay, because the speed of light (or the maximum speed at which the information can travel) is not infinite, but each one of you remains in your own timeframe.
And YES, you are correct - time is relative! That's the whole point of relativity! You're not confused - you've just graduated yourself to a new understanding. CONGRATULATIONS! 😄 🎆
And someone could talk to another person who is higher or lower than them, or is moving faster or slower (perhaps in circles, say).
These two people would have different reference frames, but could stay in contact even without a telephone.
May I have another? please?
Definitely a good video.
Light passes from C to D ( a smaller distance ) with the same amount of time that Light passes from A to B ( a bigger distance ) ???
This is only possible if the time for the Light ( C to D ) passes slower
Time curvature,
And at 6:00 the draw are not on scale ‘cause 90 degrees = Light speed into the space,
The apple goes at the speed of light in time when he is at rest ( in space )
So if we do the drawing at scale… the curve of the border is almost impossible to see ( 9.8 m/s < 300 000 km/s )
and the fact that ( at rest in space ) the apple going forward in time on the Drawing goes towards the border ( where the ticks are separated by larger time ) means that the apple goes naturally where the time passes slowly and slowly, so … right to the center of mass, but we can’t because we have the surface of the planet that stop us to go further towards the center of mass.
And if we want to do a accurate drawing for example for a black hole, the more you get into the black hole the more the angles become wide because for each meter ( at a certain point ) times passes a lot slower, so the draw at the borders become like a trumpet until we hit the distance from the center of mass when it forms a perfect quart of a circle and that in consequence the time axis of the space-time is perpendicular compared to the path of the apple in time ( so when he is at rest on space ).
And that means that the apple goes at the speed of light into the center of the black hole and time don’t passes anymore
The curvature of space-time is a mathematical abstraction. It's a mathematical description of the effects of gravity. Not an explanation for the cause.
Space-time is a mathematical construct, and has no material properties. Space-time is a metric; in physics, a metric is a numerical value derived from measurements, a number, a quantity, to be used in math equations to make accurate predictions. Space-time is a number, a quantity used in the field equations of general relativity, not a material which can bend, curve or warp. Those are figures of speech that refer to the illustrations mapping the gravitational field and its effect on how objects move in that field. No one thinks that the curved lines of isobars drawn on a weather map, or the longitudes and latitudes drawn on a globe map represent anything that is physically real, but when it comes to the space-time metric, the concept has been so thoroughly reified in our imaginations that it almost feels like an attack on our reality narrative to be reminded that it’s only a metric. We even have that absurd phrase, the “fabric of space-time” only because those illustrations are drawn with grid lines that resemble an open weave fabric.
Nice video 🧐✌️🥳.
Gravity can generate a fabric of spacetime with a large macro dimension (radial direction) paired with a small micro dimension (time direction)
According to Kaluza Klein Theory, charge is momentum in an extra dimension, and the EM field is really distortions in the spacetime fabric which redirect some of that motion into the large macro dimensions
according to this video you are right : th-cam.com/video/6H5vYP6ssUY/w-d-xo.htmlsi=tpzlCClld2pBPfU5
no, curved spacetime is NOT the fundamental cause of gravity. it is a model that is able to represent the logic of gravity. but we don't know if spacetime is a real thing. is it useful when we model reality? yes. does it mean it exists? no. exactly relativity proved this when it turned out that gravity is NOT a force. however, in classical (Newtonian) mechanics the concept of force for gravity was extremely useful. so this should be a lesson for us to stay critical and self-reflexive, i.e. to differentiate abstract models from reality.
as regards gravity, of course it can be considered as the curvature of spacetime, but this is a too geometrical interpretation which assumes the existence of spacetime which is far from evident. in my opinion, a better definition for gravity can be derived from the generalisations of the concepts of inertia and straight line using non-Euclidian geometry (which are also geometrical concepts, of course, but the existence of inertia is more trivial than the existence of spacetime). thus gravity is nothing but the manifestation of constraint in relation to space and time, which is basically revealed in the rotation of the light cone and thus in the gradual inversion of the roles of space and time.