I've been trying to understand special relativity all my life (I'm 65). Now, in just a dozen videos, Dr. Don has finally gotten it through my thick head. Thank you! TRIPLE the Fermilab budget, please.
I don't know, he's maybe wasting our time a little bit when he explains how to measure a stick a good two or three times before getting to the relativistic version.
He's not wasting our time, but some of this presentation is _false_ . 8:56 What you would actually _see_ of the basketball is a spherical ball, albeit with the seams strangely reconfigured. This is Penrose-Terrell rotation, and he almost certainly would know of it, relativistic colliding nuclear particles notwithstanding. math.ucr.edu/home/baez/physics/Relativity/SR/penrose.html
@@cosmoscoaching I think maybe he means that he does not know where the equations are coming from. Solving these two equations is easy... but the problem is.... they are hard to imagine.
@@dreamdiction TIME DILATION IS FULLY EXPLAINED, AS THE ULTIMATE MATHEMATICAL UNIFICATION OF PHYSICS/PHYSICAL EXPERIENCE IS CLEARLY PROVEN: A PHOTON may be placed at the center of what is THE SUN (as A POINT, of course), AS the reduction of SPACE is offset by (or BALANCED with) the speed of light; AS ELECTROMAGNETISM/ENERGY IS GRAVITY; AS E=MC2 IS F=MA. Gravity IS ELECTROMAGNETISM/energy. (The stars AND PLANETS are POINTS in the night sky.) Time DILATION ULTIMATELY proves ON BALANCE that electromagnetism/ENERGY IS GRAVITY, as C4 is a POINT that is ELECTROMAGNETIC/GRAVITATIONAL (ON BALANCE) as SPACE; AS E=mc2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Time DILATION proves that electromagnetism/ENERGY IS GRAVITY, AS E=mc2 is DIRECTLY and fundamentally derived from F=ma. E=mc2 IS F=ma. A planet AND a star thus constitute what is A POINT in the night sky. It ALL CLEARLY makes perfect sense. Gravity IS ELECTROMAGNETISM/ENERGY. ACCORDINGLY, I have ALSO fully explained the MATHEMATICAL UNIFICATION of Einstein's equations and Maxwell's equations (GIVEN THE ADDITION OF A FOURTH SPATIAL DIMENSION); AS E=mc2 IS F=ma. The Sun AND the Earth are F=ma AND E=mc2. Great. SO, ultimately and truly, TIME is NECESSARILY possible/potential AND actual IN BALANCE; AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. AGAIN, time DILATION ULTIMATELY proves ON BALANCE that E=MC2 is F=ma; AS ELECTROMAGNETISM/energy is gravity. Great. Indeed, this NECESSARILY represents, INVOLVES, AND DESCRIBES what is possible/potential AND actual IN BALANCE. (E=mc2 IS F=ma.) Therefore, INSTANTANEITY is thus FUNDAMENTAL to what is the FULL and proper UNDERSTANDING of physics/physical experience; AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. SO, GRAVITATIONAL force/ENERGY IS proportional to (or BALANCED with/as) inertia/INERTIAL RESISTANCE; AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. Accordingly, the rotation of WHAT IS THE MOON matches it's revolution. MOREOVER, a given PLANET (including WHAT IS THE EARTH) sweeps out equal areas in equal times consistent WITH/AS E=MC2, F=MA, AND what is perpetual motion; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. "Mass"/ENERGY IS GRAVITY. ELECTROMAGNETISM/ENERGY IS GRAVITY. Gravity AND ELECTROMAGNETISM/energy are linked AND BALANCED opposites, AS E=MC2 IS F=MA; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. GREAT !!! It ALL CLEARLY makes perfect sense. BALANCE and completeness go hand in hand. Very importantly, outer "space" involves full inertia; AND it is fully invisible AND black. E=mc2 IS F=ma. "Mass"/ENERGY involves BALANCED inertia/INERTIAL RESISTANCE consistent with/as what is BALANCED ELECTROMAGNETIC/gravitational force/ENERGY, AS E=mc2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. (Energy has/involves GRAVITY, AND ENERGY has/involves inertia/INERTIAL RESISTANCE.) E=MC2 IS F=ma. Objects fall at the SAME RATE (neglecting air resistance, of course), AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Gravity IS ELECTROMAGNETISM/energy. E=MC2 IS F=ma. It ALL CLEARLY makes perfect sense. Magnificent !!! By Frank DiMeglio
Omfg I understood everything and I'm an idiot! Dropped out of high school and lost memory of most my childhood and schooling This guy is a science/maths god! I whole heartedly believe in the adage "The only good is knowledge and the only evil is ignorance" -Socrates. You sir are a champion of good! Thank you so much! Thanks to you I actually think I could do physics! Me of all people! Your so great at teaching! ❤
I misunderstood length contraction until your caveat about the time of measurement in the primed frame. That, and the fact that if you take away the stick, you still have coordinates doing their thing, was super illuminating. Thank you for such a crispy clear explanation! I’m learning how current densities transform from one inertial frame to another and this was the missing piece. Many thanks! 😁☺️🙌🏽🎊
hey i am also confused about that , can you help me ? As of now I am confused why current densities remain constant in primed frame but not in the moving elctron's frame , since in the rest/prime frame the current densities should also be changed
@@zhinkunakur4751 In understanding SPACE, what is gravity, TIME, AND time dilation (ON BALANCE), it is important is it to understand what is a BALANCED displacement of what is SPACE. ELECTROMAGNETISM/energy is gravity ON/IN BALANCE. Consider what is E=MC2. TIME is NECESSARILY possible/potential AND actual ON/IN BALANCE. Consider TIME AND time dilation ON BALANCE. (c squared CLEARLY represents a dimension of SPACE ON BALANCE.) Indeed, the stars are POINTS in the night sky ON BALANCE. The rotation of WHAT IS THE MOON matches the revolution. Consider what is THE EYE, AND notice what is the TRANSLUCENT AND BLUE sky ON BALANCE. NOW, consider what is the BALANCED MIDDLE DISTANCE in/of SPACE. CLEARLY, BALANCED inertia/INERTIAL RESISTANCE is fundamental (ON BALANCE). “Mass"/ENERGY IS GRAVITY. ON BALANCE, consider what is the orange (AND setting) Sun. “Mass"/ENERGY involves BALANCED inertia/INERTIAL RESISTANCE consistent WITH/as what is BALANCED electromagnetic/gravitational force/ENERGY, AS ELECTROMAGNETISM/energy is CLEARLY AND NECESSARILY proven to be gravity (ON/IN BALANCE); AS gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE (ON BALANCE) consistent WITH E=MC2, F=ma, TIME, AND time dilation ON BALANCE. This CLEARLY AND NECESSARILY represents, DESCRIBES, AND INVOLVES what is possible/potential AND actual ON/IN BALANCE, AS ELECTROMAGNETISM/energy is CLEARLY (AND NECESSARILY) proven to be gravity (ON/IN BALANCE). Notice what is the fully illuminated (AND setting/WHITE) MOON ON BALANCE. Great. TIME is NECESSARILY possible/potential AND actual ON/IN BALANCE. Indeed, inertia/INERTIAL RESISTANCE is proportional to (or BALANCED with/AS) GRAVITATIONAL force/ENERGY; AS ELECTROMAGNETISM/energy is CLEARLY AND NECESSARILY proven to be gravity (ON/IN BALANCE). This CLEARLY explains what is E=MC2 AND F=ma ON BALANCE, AS TIME is NECESSARILY possible/potential AND actual ON/IN BALANCE !! (Consider TIME AND time dilation ON BALANCE.) Great. Indeed, consider WHAT IS THE EARTH/ground ON BALANCE. I have mathematically proven why the rotation of WHAT IS THE MOON matches the revolution, AS ELECTROMAGNETISM/energy is CLEARLY (AND NECESSARILY) proven to be gravity (ON/IN BALANCE). Consider TIME AND time dilation ON BALANCE, AS the stars AND PLANETS are POINTS in the night sky ON BALANCE; AS c squared CLEARLY represents a dimension of SPACE ON BALANCE. (Consider what is THE EYE ON BALANCE.) I have mathematically proven what is the fourth dimension, AS ELECTROMAGNETISM/energy is CLEARLY AND NECESSARILY proven to be gravity (ON/IN BALANCE) !!! I have explained why what are OBJECTS may fall at the SAME RATE. By Frank Martin DiMeglio
I think you are not considering the observer who Co-moves with the electron can't perceive that. The phenomenon in particle lab and acceleration of electrons is.. 🤔 Well. You get wavefronts, and the measurements at the first one, has more electric charge density, similar to the ambulance which has Doppler effect. Now, this is an effect that happens for real. It's odd of course. And the reference frames do work. I repeat. These phenomena occur, weird but real
What would happen if you put a length contracted stick into a barn, closed the doors, then it hits the door and decelerates (assume very strong door) The stick is longer than the barn, yet it is inside the barn and no longer subject to length contraction?
The observer who sees the stick moving but the barn stationary, sees that the stick has shrunk and can fit in the barn. Then, the stick hits the right door. Assuming the observer could see inside the barn, of course (maybe there is a window or a larger door facing the observer that is open), then they would be amazed as they watched the stick suddenly grow rapidly and kick the other door back open. That's the primed observer. The unprimed observer would see that the barn is shrunk initially and moving, but that the stick was stationary and longer. But remember, events that are simultaneous for one observer are not simultaneous for another. So the unprimed observer would see the stick enter the barn, and then hit the right door. Immediately the unprimed observer would see that the stick is starting to shrink because it is now moving relative to the unprimed observer, since it is being accelerated to the left (hits the door and decelerates). The unprimed observer would then see the back door try to close but it would hit the stick and be pushed back. So both observers would agree that the back (left) door tried to close but hit the trailing end of the stick before it could close all the way, resulting in it being kicked back open.
Well, a stick hitting a barn door at 85% of the speed of light would be pretty spectacular as teh energy released would vaporise everything in a considerable radius.
You like a real serious professor one would expect in a university talking about dry topics, but your t-shirts and the prefessional nature of your presentation reveal someone with a superior sense of humor who mastered the true art of subtly delivering the punchlines. Keep those videos comming!
This sounds like the basis of most arguments, one person sees/perceives one thing that the other doesn't, all the while the truth is actually perpendicular to them. Lol. Thank you, Dr. Lincoln, for your insight as always, these are a pleasure to watch.
I like that Lincoln often sticks to the appropriate equation in his explanations, which is helpful in the education sector. But, for seasoned pros, we know that length is actually defined by the distance a beam of light travels. So, you have had enough of education already, you don't even need the equations any more. You know when someone is moving, the time he/she spent on moving while measuring the stick needs to be added to the equation of calculating the stick's length. Then, of course, the length of the stick will vary depending on the speed he/she travels.
Great explanation! The basic math really helps a lot in understanding the relations there. Just please keep up making those awesome physics videos, I really love those.
Hamani Maka because universal constants don t change no matter what happens, the object’s length contracts, but it will never be shorter than Planck length.
I really don't know but I would think it would have to otherwise you would start changing the physics observed between different inertial frames of reference. I think that Planck length is inextricably tie two things like electromagnetic force and gravitational force
@@hotelmike7722 Yes. You'd basically have "different" plank lengths for each observer. But it doesn't change physics, objects themselves are different when they're moving, and that cancels the change.
I'm so glad I found out about this channel. One should never judge a channel by its number of subscribers, or should do it the opposite way : the more subscribers, the more likely the content is for everyday people 😂
so whats the physics of length contraction? proving it mathematically isn't saying why space time contracts. I get it mathematically ,but I still fail to see how space time contracts when a mass is moving at high speeds. how does space time contract? is it because the mass going at such speeds warps space time? if so does that mean it has a greater gravitational pull as there is more energy from the object.
Spacetime doesn't contract at all in these examples. It's just that different observers might have different perspectives on spacetime based on their relative speeds. In fact, near the end of the video, it's mentioned that you don't need a stick to derive the same effect, so mass is completely not involved. Remember: special relativity shares a lot in common with the idea that the world looks upside down if you stand on your head; it's just that instead of normal rotation, you need the math for hyperbolic rotations, which is pretty unintuitive. As for the why question, rephrased to "why do observer's perspectives on spacetime change with speed": well, that's just the way it looks if you look closely enough. I suppose it's a fruitful philosophical or religious question, but not a particularly scientific one.
I believe that all this is intimately connected with the relativity of simultaneity. I think that having a firm grasp of that helps to understand spacetime.
The stick is made of particles. When a force acts on one end of the stick to begin moving it, the force can only be transmitted through each particle, at most, at the speed of light. If the stick is moving near the speed of light, the particles can still only interact with each other at the speed of light. This means it still takes time for one end to affect the other. Since the stick is going nearly the same speed as the particles can transmit the force, this means the particles will need more time to "catch up" with the particles ahead of them. Due to the fact they're moving, this also means the transmission of the force will need to happen over a greater distance in space, compared to the stationary stick. This is why time slows down as you move faster through space. It's also why you appear to turn into spaghetti to people who aren't moving; the particles literally need to cover more space to transmit the fact you're moving so fast. You can really think of time as being how fast your particles can interact with each other. That's why time isn't the same for everyone.
Professor Don I like your every videos it helps me a lot to understand physics again in an interesting manner. Thank you Sir. Sir kindly make a video on why scientists are facing difficulties in achieving superconductivity at room temperature.
for me it is the best of Dr Lincoln so far (and I've seen them all) but what strikes me is the supreme role of algebra in reaching the conclusion and how Dr Lincoln surrendered his problem to it. you might think this is obvious and simple but i still see algebra as being on top of even Relativity. sheer magic.
So wierd, it says 100+ comments but I can only see about 10 and no replies to comments. My internet speed must be approaching the speed of light and I am experiencing information contraction...
As they say, everything is relative from the perspective of the observer. A perfect example is when you're standing on Earth you feel no motion at all while an observer from the space station can actually see the movement. Then of course things start getting weird at near the speed of light which is what this video is trying to tackle (among other things).
Dr Lincoln, you have a geology based doppelganger in Nick Zentner. You make incredibly complex subjects very accessible to laymen. AND, you have a way of communicating that is very enjoyable to watch and hear. You and Mr Zenter should be required subjects for people studying to become teachers.
A muon approching earth at almost speed of light, sees a flat earth. So , is earth flat ? According to the muon it is. Is length contraction a real effect, or a perspective effect? If 2 persons move away from each other, they see the other getting smaller and smaller. Nobody is getting realy smaller.
Yves Bulté Yes, someone IS really getting contracted. Who is getting contracted is relative. Each observer is correct in his own inertial frame of reference.
High-speed particles with short half-lives travel farther than they would be able to in their short lifetimes without relativistic effects. From an outside perspective, time is running slow for the particle. From the particle's perspective, the universe is "flattened", so the travel distance is shorter.
8:15 ... and what we find is that the length of the stick in the primed frame is the length in the umprimed frame, divided by gamma. 8:38 And, using the fact that both observers can claim that they are stationary, this means that a moving stick is shorter than an stationary one. Now, there's one important thing to remember and that is that the shrinking only occurs in the direction of motion. There is no shrinking side to side. 8:52 This means if you start with a basketball and accelerate i to high speeds, it will look like a pancake- still round in the direction perpendicular to the motion, but flat parallel to the direction of motion. 9:05
This was the best explanation of this I have seen using pre high school math! I wish there was something similar available way back when I was at University. When we got in to tensor algebra of relativity we had probably still a rather foggy picture of what was going on as explained here. Which is evidently still true since people still promote non existent paradoxes. Many courses on advanced subjects would benefit from starting with a simple explanation like this. Quite the opposite I remember the professor talk about achieving mathematical maturity first and then getting into applications later. I think this is the wrong approach, at least for applied math and physics. In my view math is a simplified language to describe reality, so it helps to have an idea of the what You try to describe in the physical world.It is like skimming a book helps to get an overview before getting into the details.
I simply used the thought experiment from your Lorentz factor derivation. The equations in my derivation were: L₀=c•∆t L=∆t•√(c²-v²) So: ∆t=L₀/c And now if we do some simple algebra, we get: L=L₀•√[1-(v/c)²] L=L₀/γ
It appears to me that the primed measurment is shorter because they are arriving earlier at each measument point due to the time dilation they are experiencing. Since they are in a separate reference frame while at relativistic velocities, it wouldn't make a difference to say they are physically shorter, or temporally faster. That is why only the length shortens, and not the width. It is only a difference in observation between the primed and unprimed points of view. It doen't matter if it is "real" or not, the measurment will always be shorter. Is this an accurate observation?
As always, Doc, spot on! I am re-teaching myself relativity from my university physics days, and your videos are always a great addition to my studies!
The math is easy enough that any high schooler who does their homework could keep up with this video. Please keep doing videos with math in it like this. People need to understand that math allows us to understand things even if we can't directly observe them.
For the lazy~ Link: en.wikipedia.org/wiki/Terrell_rotation Relevant quote: "A previously popular description of special relativity's predictions, in which an observer sees a passing object to be contracted (for instance, from a sphere to a flattened ellipsoid), was wrong."
The Terrel Penrose effect was revisited by Robert J. Deissler in the 2005 paper "The appearance, apparent speed, and removal of optical effects for relativistically moving objects"
Boaz Augusto Matos The solution to the Teleportation noncloning theorem ,which for now, has been hidden from human knowledge by our Creator, thats truly brilliant thinking !
we have known for quite some time, that perspective makes objects appear smaller and smaller as distance increases... this has no influence on the optically slower or faster objects velocity, as time is not a cause anyway. How do equations, deal with optically observed, variable velocity and compressed distances, through perspective?
The whole moving vs. stationary thing (or here primed/unprimed) has always confused me, since it's contrary to what I would usually call them. In a previous video I learned the stationary time is the time of the observer that SEES the clock NOT moving (so IS moving alongside the clock) while the moving time is the time of the observer that SEES the clock moving (so is not moving alongside the clock). Now this part at 1:30 hopelessly confuses me. Based on the whole stationary/moving thing I just mentioned, the person SEEING the situation NOT moving should be the moving person, no? But now apparently it isn't? I just don't get it. Well, it's not like I expect an answer on a six year old video 😆
Yeah i asked my Prof. the same question that i have now. Considering you want to close the doors of the barn in the moment something is moving with 86% the speed of light through the barn the doors had to move even faster than that while being static in at least one position the door hinge. What changes their position in spacetime relative to the barn and to the stick going through it. What would actually happen? I only wish there was someone who claims he can communicate complex topics very well to give a good or at least a correct answer to this question ;-)
I always think of it this way. Distance per unit time = speed. If we both agree that light travels at the same speed, then we must disagree on how long something took or how much distance was covered in order to get the same answer for the speed of light. The very definition of speed connects time and space and Relativity show us how.
8:55 this is wrong. The basketball will **not** appear/look flat. In fact it will pretty much stay somewhat round but with some additional weird effects. Google Penrose-Terrell effect. This is the problem when we speak of "what an observer sees" because "seeing" in SRT does not translate well into what we mean with this word in everyday life (camera/eye).
the step from 4:45 to the end when it will be the opposite, geting shorter instead of longer, is a tricky interpretation. Why should one not stay with the first result and search a way to the second?
Hi Dr. Lincoln-- I know this video is from some time ago, but I just watched it hoping for a bit more insight about relativity. Good explanation of how we can use math to anticipate what we'll experience, and I followed all the math - much like the equation juggling in college physics, math, and chemistry, but at the same time I was hoping in the end for an explanation of what one might actually experience. If you could wrap up such math derivations/explanations with what it would mean to a human observer, that would be great.
There's a powerful analogy here between Lorentz transformations ("boosts"), and rotations in space. The latter use circular trig functions, the former use hyperbolic trig fns. And the angle, θ (for rotations), is analogous to a boost parameter, α. Both these parameters are unlimited; the limitation to below-light-speed comes in because the speed (β = v/c) is tanh(α), and because -1 < tanh < 1. The speed then, is analogous to slope (= tan θ) in the rotation case. And just as slopes don't add when two rotations are combined, so speeds don't add when two boosts are combined. Instead, it is θ and α that add. Furthermore, the length of a moving stick is analogous to a single spatial component of a rotated object. When you rotate a cube, you don't expect the "sideways" view of one edge to remain the same length; rather, that apparent length, x, of the edge, "mixes" with another, perpendicular component, y, in such a way that √(x² + y²), the true length of the edge, remains constant. In the boost case, you can't expect the length component, x, to stay the same; rather, √(x² - c²t²), the true length of the stick, remains constant. For a rotation, the invariant length follows from the identity, cos² + sin² = 1. For a boost, the invariant 'interval' follows from the identity, cosh² - sinh² = 1. Thus we get the metric for spacetime. The above analogy, and the mathematics that flows from it, are, AFAIK, due to the late John Archibald Wheeler. I post them here for those who want to delve a little more into said mathematics. Thanks for a careful, detailed, easy-to-understand look at how this works! Fred
I think it's β = i*v/c. And those hyperbolic trig functions are from cos(arctan(i*y/x))+sin(arctan(i*y/x)). If you get a sum or a difference in there it's because you did cos(arctan(i*y/x))+i*sin(arctan(i*y/x)). Which probably means you gotta tan(pi/4-arctan(y/x)/2). Since c is m/s, I suppose it can also be m/(i*s). Which might imply a real time in velocity and an imaginary time in the speed of light.
@@thomasolson7447 No, it actually *is* β = v/c. There's no physical meaning to "imaginary" time or space; rather, the difference between Lorentz transformations in spacetime and orthogonal transformations in Euclidean n-space, is fundamentally that the former relies on hyperbolic trig functions, while the latter relies on circular trig functions. Those two classes of trig function are mathematically related in complex analysis, but that fact tells us nothing about the underlying physics.
@@ffggddss I haven't really thought it out completely. My thoughts are that if you freeze a reference frame (with respect to time), the gamma part is the real part. The 'v' part runs perpendicular to the plane of the frozen reference frame. It also comes with its own quadratic polynomial built in. If you take a moment and go through the hyperbolic identities with 'e' expansion, you'll see that they are almost the same thing. The imaginary value is also consistent with vector addition. It is just tangent addition with an 'i.' (i*v/c-i*m/n)/(1+i^2*(v/c)*(m/n)) No calculus needed. (v/(i*c)-m/(i*n))/(1+(v/c)*(m/n)/i^2), also works if i is a factor of imaginary time.
What happens to length if the difference in velocity between two observers is greater than light speed? What I mean is, if you have three observers, one is stationary, the second is moving at 86% the speed of light, and the third is moving at 86% the speed of light in the opposite direction, how will the two moving observers see each other. Also, how would this affect the scenario of a stick traveling through the barn?
very well explained... the example with the barn is really weird. not so the fact that the 40 m stick fits in a 20 m barn but that the space seen from a moving observer is shrinked regarding to the stick but not regarding to the barn. as they have the same location (stick inside barn) it means that the space is shrinked and not shrinked at the same time/space?!
Great explanation. I have a slight issue with saying this is what you would "see" rather than this is what you would "measure". In fact a moving sphere does not look flattened. When we talk about seeing we are talking about the light rays entering the eye. Roger Penrose showed in the1950s that a sphere does not look contracted (See the wikipedia page for the Terrel rotation - also from the 1950s). What happens is that the celestial sphere centred at the observer is transformed by a Möbius map (when considered as the Riemann sphere using stereographic projection) (Note that the proper orthochronous Lorentz transformations are isomorphic to the Möbius group). Möbius maps preserve circles-and-straight-lines and stereographic projection also preserves circles, so the sphere does not seem distorted.
You are right, I called it Lorentz rotation, and it is obvious. As the ball passes, you still see a round ball, but it is rotated so you see its backside. consider th e light entering your eyes as forming what you see, not what is.
I watched this video last night and I'm reviewing it again this morning. I've been slowly trying to wrap my head around these concepts for a while now and truthfully many explanations, such as the rubber sheet explaining gravity, don't really help much because they oversimplify. I especially like Dr. Lincoln's explanations because they are easy to follow yet don't approach things at the "rubber sheet" level. Pondering length contraction and some other aspects of GR and other such subjects has raised questions in my mind about what is the underlying physical reality. The video begins with Dr. Lincoln saying that we "see" a length contraction. That's the observation. Understood. But supposing that there were a way to physically measure another object as I pass it at relativistic speeds would that observation be the same as the observation from photons. Is space actually contracting or does it just appear that way?
Does this explain why the length of white highway markers (separating the two lanes of traffic) appear shorter as you drive .. than their length measured at a stand still. That is they appear shorter than the car while driving .. than they do with the car parked along side the line.
At 6:52, i am not getting the point and stuck, as both primed and unprimed will see the length as the same time so if one equates both time in prime frame to be same, then at 6:52, why is unprimed time too also equal to zero. Anyone please clarify me as i am stuck like for a week now at this point. Many text books tend to derive this derivation where in prime frame the stick is placed and is moving wrt primed frame and one derives very easily the formula. But what if the measurement is done where the rod is now in un prime frame and the prime frame is moving.
I couldn't see this question in the comments, apologies f it's been asked already: at 7:21 you divide the left hand side of the equation (zero) by gamma, but only the first term on the right hand side. This seems wrong to me, as both terms on the right should be divided by gamma. As the left term is gamma *(t2-t1), the unprimed times (for the observer that sees the stationary stick), I'm wondering if gamma for t2 and t1 =1, which would allow it to be removed from that term.... or have I missed something?
All nice and good so far. But what if the length L = 1 lp (Planck length) ? From the primed observer's perspective I get it, nothing changes. But from the unprimed observer's perspective does the object simply cease to exist ? Does it cross into another dimension ? Does it become a photon or some sort of similar and yet to be discovered contraption ? Or maybe the Planck length "constant" is actually much more relative than we are told ?
You sir, you are that such a person! We study time dilation and length contraction in my modern physics course. I find this concept fascinating. You have explained it very well! Thank you.
I still got the principles while I completely didn’t understand the equation. Thanks, that’s very friendly for someone like me who doesn’t quite into Math😊
Great video professor Don. I had to rewind it like 10 times but it was worth the effort. I still need to watch it a couple times. But now I understand for the first time the math it's all about.
Great video Dr Don. What about simple distance compression (i.e. perspective length compression ?) Does the perspective ratio change for off Earth satellite observations ?? Uncompressed for the immediate environment of the observer , observationally proportionately compressed for anything at a distance (i.e. unique to the observer) Time/Velocity moves slower observationally for the Observed yet both observed and observer are experiencing time at the same rate ? So no velocity required for x,y,z length compression only distance ? *;-))
So would you say it 'is' shorter when moving near light speeds? Maybe the Lorentz transformation is more like from fitting the observations, and what is a side observation is the effect of velocity on matter.
Could you explain to me why a wire with current on it is still neutral charged for a not moving charge next to it even though that charge sees the electrons including the gabs between them moving and this contracting?
How are you supposed to use those equations? I can't enter them into a calculator or a spreadsheet, as an apostrophe doesn't appear on the calculator keypad, and the ' symbol means something else in a spreadsheet.
If stick was moving from left to the right and its speed dropped inside the center of the barn to 0m/s, which door will be crashed first? Edit: Or which door remains open? Edit 2: I'm assuming that both doors will become open for not moving observer because the stick will grow. But then, you need to observe only one door to know at which state the second door is (for not moving you) and no matter how long the barn is... So, you may knew that the other door was closed, but you don't know at which state the other door when stick is inside (if it wan't to stop by some reason), but if yours is opened suddenly, you will know, because your measurement stick was long enough to reach the second door too. Edit 3: By closing the door I'm measuring not the state of the other door but the "luck" of the stick (if it stopped or not inside). The info about the second door is just result of the long stick.
What if there were two sticks one after another? Would they behave like one stick or would there appear gap between them? For long enough stick wouldn't one end go backward or faster than light to achieve desired length?
They would behave as one stick. The touching ends are at the same position and move together. There wouldn’t be a separation between them. All observers would measure the same distance between them as 0. If there was a gap between them, the gap would shrink by the same factor as the lengths of the sticks.
Jamal Wills but the ‘end’ of a stick is arbitrary. It could be seen as trillions of tiny sticks end on end. If two sticks with one ‘gap’ stay close together then the first must be falling back slightly and the second moving slightly forward in the frame of reference of the stationary observer with no plausible explanation. If there were three sticks how would the middle one know to ‘stay still’ and let the other two shuffle up? It doesn’t because no contraction takes place. It is only observed length that changes in a different frame of reference because what appears simultaneous to one observer does not appear so to another.
Thank you for such a nice explanation.I always had a nagging feeling about "bookish" explanation of length contraction and knew that, there is a better explanation.Thanks for making it clear.
Great explanation, Thanks! Imagine the accretion disk of a black hole. Incoming matter moving faster and faster, getting flatter and flatter, packing immeasurable density into the disk.
My question regards the path of travel from the frame of reference of the moving object, or one of a comoving observer. Does the observer see the path ahead contract? If so is it an illusory effect caused by time dialation, and even if so, wouldnt this still mean that assuming it's possible, a traveler could reach almost anywhere in the observable universe in a couple of years from their perspective with a 1g constant acceleration capable ship?
Would a length contracted rigid stick be able to cross a gap that contracts to a length small enough for it to cross but be too large for a primed observer?
Very interesting video. I have one question: suppose that I move towards Alpha Centauri at such a high speed that the distance dilates to 7 light minutes. Then I (as the primed observer) will see that star at a distance of 8 light minutes. Does that mean that I will also feel its heat? After all, our Sun is at that distance from Earth and we can feel its heat.
the thing with the barn and the stick works because according to one observer the stick was short enough to fit in the barn and according to the other because the doors close at different times. but what if you took the experiment further and made a circuit whereby both doors being shut simultaneously completes the circuit and lights a single lamp which both observers can see. does the lamp light or not? and if one observer sees the lamp lit but the other does not, how can that work? does the lamp only emit photons in one direction (clearly not possible)? what if the circuit completing and electricity flowing caused some permanent change of state in something which both observers could meet up and examine together later on? like, what if it electrocuted one of them? for a thought experiment intended to illustrate the principle, that only raised a bunch of confusing questions for me
Can you use a candle to mark the passage of time? And can you send another lit candle on a trip around the moon? Is there a way to make a length comparison to show time dilation?
since you get both time and length in motion by dividing by gamma, wouldn't that mean that the prime observer still would observe traveling the same amount of distance in the same amount of time as the unprimed observer?
A lot of math for something very simple. The moving stick shrinks in all respects due to the pressure of the aether, the quantum fields, through which it moves. The aether presses on matter and the matter shortens. The observer inside the space craft also becomes shorter, everything does, proportional to the speed and the pressure the aether exerts. The inside observer still sees the yard stick as being one 6:37 yard long. The outside observer sees the space ship go by and observes that the yard stick is marked off in 36 inches but all dimensions are shorter.
In the experiment of the 2 atomic cloks, one of them travels on a speed aircraft, the other one stays on the ground. When the traveller clock comes back and you compare both cloks, you can see that the one which travelled is some nano-seconds late. That means that it keeps a permanent trace of time dilatation. Is it possible to arrange a similar experiment where a device may keep permanent trace of length shrinking ?
I watched the video at home sitting at my computer desk and it was 11:22 long. I watched it again on a fast moving train and it was a different length. What is going on here?
I get it that the stick contracts along the direction of travel-left to right for instance. But what will happen if the stick is rotated 90° so it is perpendicular to the direction of travel? Will the stick suddenly lengthens and will the observer notice the change?
I was wondering what happens in the apparent ladder paradox should you keep nearly invincible barn doors shut around a nearly invincible ladder, what that would presumably do to the trapped object, and what exactly is happening with the energy involved. Im guessing it converts the energy its carrying in its relativistic motion in to potential energy like a coiled up spring, but I might need to think about it some more.
A bit too lazy to do the math/think about it - but what would happen with the stick/barn example if you shut both doors permanently? What would be the sequence of events from the perspective of an observer stationary relative to the barn?
One of the most gifted physics educators of our time!! Keep up the outstanding work Dr. Lincoln!
I've been trying to understand special relativity all my life (I'm 65). Now, in just a dozen videos, Dr. Don has finally gotten it through my thick head. Thank you! TRIPLE the Fermilab budget, please.
I finally understood the barn paradox. Math and animations were easy to understand. Thanks for another great video
I love this guy, because he is not afraid to give the derivations and you know you can trust every word he says.
So..... the earth could be flat at high speed..... mmmhhhhhmmmmmmmmm.........
Oh - Don't you start with that. (-:
(But it does kind of make sense though)
Gaspar Albertengo Not for the people ON the earth, for the observer. It's like saying a siren sounds distorted for the people in the car.
@@satunnainenkatselija4478 r u indian or Russia
We are not outside that frame of reference though.
@@DoctorRocker66 the Reptilians from Nibiru think the Earth is flat... :)
Answer: This happens when a man enters into a cold pool of water.
Question: What is Length Contraction?
I understood that reference!
🤣🤣🤣🤣🤣🤣🤣🤣
Primed and unprimed both in the cold pool have length contraction
@@kseriousr I understood that reference
typical comment coming from the back rank of basically any classes all around the world!😅
Way cool, and the math isn't that tough. And you're definitely NOT wasting our time!
it was a rhetorical question buddy
I don't know, he's maybe wasting our time a little bit when he explains how to measure a stick a good two or three times before getting to the relativistic version.
He's not wasting our time, but some of this presentation is _false_ .
8:56 What you would actually _see_ of the basketball is a spherical ball, albeit with the seams strangely reconfigured.
This is Penrose-Terrell rotation, and he almost certainly would know of it, relativistic colliding nuclear particles notwithstanding.
math.ucr.edu/home/baez/physics/Relativity/SR/penrose.html
@Kisa Vorobianinov if this was just optical effect you wouldn't be fittinv 20 meter stick in 10 metre.
This channel has a strong PBS Space Time vibe and I love it, great video.
I like how you put the equations in there while you're talking about it even if I don't understand the math I still get the principal excellent videos
All the math in this video is high school level, is just algebra.
hahahaha he's a con man and he got you.
Mate, why are you studying special relativity if you don't know high school Math?
@@cosmoscoaching I think maybe he means that he does not know where the equations are coming from. Solving these two equations is easy... but the problem is.... they are hard to imagine.
@@dreamdiction TIME DILATION IS FULLY EXPLAINED, AS THE ULTIMATE MATHEMATICAL UNIFICATION OF PHYSICS/PHYSICAL EXPERIENCE IS CLEARLY PROVEN:
A PHOTON may be placed at the center of what is THE SUN (as A POINT, of course), AS the reduction of SPACE is offset by (or BALANCED with) the speed of light; AS ELECTROMAGNETISM/ENERGY IS GRAVITY; AS E=MC2 IS F=MA. Gravity IS ELECTROMAGNETISM/energy. (The stars AND PLANETS are POINTS in the night sky.) Time DILATION ULTIMATELY proves ON BALANCE that electromagnetism/ENERGY IS GRAVITY, as C4 is a POINT that is ELECTROMAGNETIC/GRAVITATIONAL (ON BALANCE) as SPACE; AS E=mc2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Time DILATION proves that electromagnetism/ENERGY IS GRAVITY, AS E=mc2 is DIRECTLY and fundamentally derived from F=ma. E=mc2 IS F=ma. A planet AND a star thus constitute what is A POINT in the night sky. It ALL CLEARLY makes perfect sense. Gravity IS ELECTROMAGNETISM/ENERGY. ACCORDINGLY, I have ALSO fully explained the MATHEMATICAL UNIFICATION of Einstein's equations and Maxwell's equations (GIVEN THE ADDITION OF A FOURTH SPATIAL DIMENSION); AS E=mc2 IS F=ma. The Sun AND the Earth are F=ma AND E=mc2. Great. SO, ultimately and truly, TIME is NECESSARILY possible/potential AND actual IN BALANCE; AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. AGAIN, time DILATION ULTIMATELY proves ON BALANCE that E=MC2 is F=ma; AS ELECTROMAGNETISM/energy is gravity. Great. Indeed, this NECESSARILY represents, INVOLVES, AND DESCRIBES what is possible/potential AND actual IN BALANCE. (E=mc2 IS F=ma.) Therefore, INSTANTANEITY is thus FUNDAMENTAL to what is the FULL and proper UNDERSTANDING of physics/physical experience; AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. SO, GRAVITATIONAL force/ENERGY IS proportional to (or BALANCED with/as) inertia/INERTIAL RESISTANCE; AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. Accordingly, the rotation of WHAT IS THE MOON matches it's revolution. MOREOVER, a given PLANET (including WHAT IS THE EARTH) sweeps out equal areas in equal times consistent WITH/AS E=MC2, F=MA, AND what is perpetual motion; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. "Mass"/ENERGY IS GRAVITY. ELECTROMAGNETISM/ENERGY IS GRAVITY. Gravity AND ELECTROMAGNETISM/energy are linked AND BALANCED opposites, AS E=MC2 IS F=MA; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. GREAT !!! It ALL CLEARLY makes perfect sense. BALANCE and completeness go hand in hand. Very importantly, outer "space" involves full inertia; AND it is fully invisible AND black. E=mc2 IS F=ma. "Mass"/ENERGY involves BALANCED inertia/INERTIAL RESISTANCE consistent with/as what is BALANCED ELECTROMAGNETIC/gravitational force/ENERGY, AS E=mc2 IS F=ma; AS ELECTROMAGNETISM/ENERGY IS GRAVITY. (Energy has/involves GRAVITY, AND ENERGY has/involves inertia/INERTIAL RESISTANCE.) E=MC2 IS F=ma. Objects fall at the SAME RATE (neglecting air resistance, of course), AS ELECTROMAGNETISM/ENERGY IS GRAVITY. Gravity IS ELECTROMAGNETISM/energy. E=MC2 IS F=ma. It ALL CLEARLY makes perfect sense. Magnificent !!!
By Frank DiMeglio
Mr Lincoln, please keep these videos coming!!!!!!!!
constellationpegasus Dr. 😉👍
Please, Doctor Lincoln! (He deserves it.)
ScienceNinjaDude Then Zoltan it is.
Omfg I understood everything and I'm an idiot! Dropped out of high school and lost memory of most my childhood and schooling This guy is a science/maths god! I whole heartedly believe in the adage "The only good is knowledge and the only evil is ignorance" -Socrates. You sir are a champion of good! Thank you so much! Thanks to you I actually think I could do physics! Me of all people! Your so great at teaching! ❤
💟
2:18 Actually, I tried to do that a few hours ago.....
But somewhat, my derivation was:
d’=t’•√(c²-v²)
Your derivation is correct!
I misunderstood length contraction until your caveat about the time of measurement in the primed frame. That, and the fact that if you take away the stick, you still have coordinates doing their thing, was super illuminating. Thank you for such a crispy clear explanation! I’m learning how current densities transform from one inertial frame to another and this was the missing piece. Many thanks! 😁☺️🙌🏽🎊
hey i am also confused about that , can you help me ? As of now I am confused why current densities
remain constant in primed frame but not in the moving elctron's frame , since in the rest/prime frame the current densities should also be changed
@@zhinkunakur4751 In understanding SPACE, what is gravity, TIME, AND time dilation (ON BALANCE), it is important is it to understand what is a BALANCED displacement of what is SPACE. ELECTROMAGNETISM/energy is gravity ON/IN BALANCE.
Consider what is E=MC2. TIME is NECESSARILY possible/potential AND actual ON/IN BALANCE. Consider TIME AND time dilation ON BALANCE. (c squared CLEARLY represents a dimension of SPACE ON BALANCE.) Indeed, the stars are POINTS in the night sky ON BALANCE. The rotation of WHAT IS THE MOON matches the revolution. Consider what is THE EYE, AND notice what is the TRANSLUCENT AND BLUE sky ON BALANCE. NOW, consider what is the BALANCED MIDDLE DISTANCE in/of SPACE. CLEARLY, BALANCED inertia/INERTIAL RESISTANCE is fundamental (ON BALANCE). “Mass"/ENERGY IS GRAVITY. ON BALANCE, consider what is the orange (AND setting) Sun. “Mass"/ENERGY involves BALANCED inertia/INERTIAL RESISTANCE consistent WITH/as what is BALANCED electromagnetic/gravitational force/ENERGY, AS ELECTROMAGNETISM/energy is CLEARLY AND NECESSARILY proven to be gravity (ON/IN BALANCE); AS gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE (ON BALANCE) consistent WITH E=MC2, F=ma, TIME, AND time dilation ON BALANCE. This CLEARLY AND NECESSARILY represents, DESCRIBES, AND INVOLVES what is possible/potential AND actual ON/IN BALANCE, AS ELECTROMAGNETISM/energy is CLEARLY (AND NECESSARILY) proven to be gravity (ON/IN BALANCE). Notice what is the fully illuminated (AND setting/WHITE) MOON ON BALANCE. Great. TIME is NECESSARILY possible/potential AND actual ON/IN BALANCE. Indeed, inertia/INERTIAL RESISTANCE is proportional to (or BALANCED with/AS) GRAVITATIONAL force/ENERGY; AS ELECTROMAGNETISM/energy is CLEARLY AND NECESSARILY proven to be gravity (ON/IN BALANCE). This CLEARLY explains what is E=MC2 AND F=ma ON BALANCE, AS TIME is NECESSARILY possible/potential AND actual ON/IN BALANCE !! (Consider TIME AND time dilation ON BALANCE.) Great. Indeed, consider WHAT IS THE EARTH/ground ON BALANCE. I have mathematically proven why the rotation of WHAT IS THE MOON matches the revolution, AS ELECTROMAGNETISM/energy is CLEARLY (AND NECESSARILY) proven to be gravity (ON/IN BALANCE). Consider TIME AND time dilation ON BALANCE, AS the stars AND PLANETS are POINTS in the night sky ON BALANCE; AS c squared CLEARLY represents a dimension of SPACE ON BALANCE. (Consider what is THE EYE ON BALANCE.) I have mathematically proven what is the fourth dimension, AS ELECTROMAGNETISM/energy is CLEARLY AND NECESSARILY proven to be gravity (ON/IN BALANCE) !!! I have explained why what are OBJECTS may fall at the SAME RATE.
By Frank Martin DiMeglio
I think you are not considering the observer who Co-moves with the electron can't perceive that.
The phenomenon in particle lab and acceleration of electrons is.. 🤔 Well. You get wavefronts, and the measurements at the first one, has more electric charge density, similar to the ambulance which has Doppler effect.
Now, this is an effect that happens for real. It's odd of course. And the reference frames do work. I repeat. These phenomena occur, weird but real
Mind blown yet again. Thank you Dr. Lincoln for another great video explanation!!!!
What would happen if you put a length contracted stick into a barn, closed the doors, then it hits the door and decelerates (assume very strong door)
The stick is longer than the barn, yet it is inside the barn and no longer subject to length contraction?
The observer who sees the stick moving but the barn stationary, sees that the stick has shrunk and can fit in the barn. Then, the stick hits the right door.
Assuming the observer could see inside the barn, of course (maybe there is a window or a larger door facing the observer that is open), then they would be amazed as they watched the stick suddenly grow rapidly and kick the other door back open. That's the primed observer.
The unprimed observer would see that the barn is shrunk initially and moving, but that the stick was stationary and longer. But remember, events that are simultaneous for one observer are not simultaneous for another.
So the unprimed observer would see the stick enter the barn, and then hit the right door. Immediately the unprimed observer would see that the stick is starting to shrink because it is now moving relative to the unprimed observer, since it is being accelerated to the left (hits the door and decelerates). The unprimed observer would then see the back door try to close but it would hit the stick and be pushed back.
So both observers would agree that the back (left) door tried to close but hit the trailing end of the stick before it could close all the way, resulting in it being kicked back open.
Well, a stick hitting a barn door at 85% of the speed of light would be pretty spectacular as teh energy released would vaporise everything in a considerable radius.
You like a real serious professor one would expect in a university talking about dry topics, but your t-shirts and the prefessional nature of your presentation reveal someone with a superior sense of humor who mastered the true art of subtly delivering the punchlines. Keep those videos comming!
It was an amazing,I hope it gets more views,it made it really clear
This sounds like the basis of most arguments, one person sees/perceives one thing that the other doesn't, all the while the truth is actually perpendicular to them. Lol. Thank you, Dr. Lincoln, for your insight as always, these are a pleasure to watch.
i bet no other video on youtube descibes relativity like this series here.congradulations.
I like that Lincoln often sticks to the appropriate equation in his explanations, which is helpful in the education sector. But, for seasoned pros, we know that length is actually defined by the distance a beam of light travels. So, you have had enough of education already, you don't even need the equations any more. You know when someone is moving, the time he/she spent on moving while measuring the stick needs to be added to the equation of calculating the stick's length. Then, of course, the length of the stick will vary depending on the speed he/she travels.
Great explanation! The basic math really helps a lot in understanding the relations there. Just please keep up making those awesome physics videos, I really love those.
One of the oldest but underrated channel , tho it has quality content 😟
When an object travels at a high speed,does the plank length contract ?
Hamani Maka no
@@fool5541 why?
Hamani Maka because universal constants don t change no matter what happens, the object’s length contracts, but it will never be shorter than Planck length.
I really don't know but I would think it would have to otherwise you would start changing the physics observed between different inertial frames of reference. I think that Planck length is inextricably tie two things like electromagnetic force and gravitational force
@@hotelmike7722 Yes. You'd basically have "different" plank lengths for each observer. But it doesn't change physics, objects themselves are different when they're moving, and that cancels the change.
I'm so glad I found out about this channel. One should never judge a channel by its number of subscribers, or should do it the opposite way : the more subscribers, the more likely the content is for everyday people 😂
so whats the physics of length contraction? proving it mathematically isn't saying why space time contracts. I get it mathematically ,but I still fail to see how space time contracts when a mass is moving at high speeds. how does space time contract? is it because the mass going at such speeds warps space time? if so does that mean it has a greater gravitational pull as there is more energy from the object.
Spacetime doesn't contract at all in these examples. It's just that different observers might have different perspectives on spacetime based on their relative speeds. In fact, near the end of the video, it's mentioned that you don't need a stick to derive the same effect, so mass is completely not involved. Remember: special relativity shares a lot in common with the idea that the world looks upside down if you stand on your head; it's just that instead of normal rotation, you need the math for hyperbolic rotations, which is pretty unintuitive.
As for the why question, rephrased to "why do observer's perspectives on spacetime change with speed": well, that's just the way it looks if you look closely enough. I suppose it's a fruitful philosophical or religious question, but not a particularly scientific one.
I believe that all this is intimately connected with the relativity of simultaneity. I think that having a firm grasp of that helps to understand spacetime.
The stick is made of particles. When a force acts on one end of the stick to begin moving it, the force can only be transmitted through each particle, at most, at the speed of light.
If the stick is moving near the speed of light, the particles can still only interact with each other at the speed of light. This means it still takes time for one end to affect the other.
Since the stick is going nearly the same speed as the particles can transmit the force, this means the particles will need more time to "catch up" with the particles ahead of them. Due to the fact they're moving, this also means the transmission of the force will need to happen over a greater distance in space, compared to the stationary stick.
This is why time slows down as you move faster through space. It's also why you appear to turn into spaghetti to people who aren't moving; the particles literally need to cover more space to transmit the fact you're moving so fast.
You can really think of time as being how fast your particles can interact with each other. That's why time isn't the same for everyone.
It all boils down to the fact that since photons cannot slow down, the universe must compensate for that.
I can't even see the replies
I have to give to you. If I don't fully get the explanation of a physical phenomenon, I always turn to Fermilab to clear it out. Many thanks!
Professor Don I like your every videos it helps me a lot to understand physics again in an interesting manner. Thank you Sir. Sir kindly make a video on why scientists are facing difficulties in achieving superconductivity at room temperature.
for me it is the best of Dr Lincoln so far (and I've seen them all) but what strikes me is the supreme role of algebra in reaching the conclusion and how Dr Lincoln surrendered his problem to it. you might think this is obvious and simple but i still see algebra as being on top of even Relativity. sheer magic.
So wierd, it says 100+ comments but I can only see about 10 and no replies to comments. My internet speed must be approaching the speed of light and I am experiencing information contraction...
I can give you a heads up, if you’re lost.
Basically, I own the Universe, now.
9:01 actually your eye won’t just see contraction along x direction , you’ll also see a rotation effect. See Terrell effect
Yes, follow the light rays.
Now when I see pancake I always ask myself - is it really flat or it is just moving on speed of light relative to me?
As they say, everything is relative from the perspective of the observer. A perfect example is when you're standing on Earth you feel no motion at all while an observer from the space station can actually see the movement. Then of course things start getting weird at near the speed of light which is what this video is trying to tackle (among other things).
Dr Lincoln, you have a geology based doppelganger in Nick Zentner. You make incredibly complex subjects very accessible to laymen. AND, you have a way of communicating that is very enjoyable to watch and hear. You and Mr Zenter should be required subjects for people studying to become teachers.
A muon approching earth at almost speed of light, sees a flat earth. So , is earth flat ? According to the muon it is. Is length contraction a real effect, or a perspective effect? If 2 persons move away from each other, they see the other getting smaller and smaller. Nobody is getting realy smaller.
Yves Bulté a muon would decay faster than light is able to travel from the Earth to it's positon if It wants to see the whole Earth
Yves Bulté a muon can't even travel at the speed of light because it has masa
Yves Bulté Yes, someone IS really getting contracted. Who is getting contracted is relative. Each observer is correct in his own inertial frame of reference.
High-speed particles with short half-lives travel farther than they would be able to in their short lifetimes without relativistic effects. From an outside perspective, time is running slow for the particle. From the particle's perspective, the universe is "flattened", so the travel distance is shorter.
"From a certain point of view" yes, the Earth is flat. :) Vsauce has a video about it.
8:15 ... and what we find is that the length of the stick in the primed frame is the length in the umprimed frame, divided by gamma. 8:38 And, using the fact that both observers can claim that they are stationary, this means that a moving stick is shorter than an stationary one. Now, there's one important thing to remember and that is that the shrinking only occurs in the direction of motion. There is no shrinking side to side. 8:52 This means if you start with a basketball and accelerate i to high speeds, it will look like a pancake- still round in the direction perpendicular to the motion, but flat parallel to the direction of motion. 9:05
This was the best explanation of this I have seen using pre high school math!
I wish there was something similar available way back when I was at University. When we got in to tensor algebra of relativity we had probably still a rather foggy picture of what was going on as explained here. Which is evidently still true since people still promote non existent paradoxes. Many courses on advanced subjects would benefit from starting with a simple explanation like this. Quite the opposite I remember the professor talk about achieving mathematical maturity first and then getting into applications later. I think this is the wrong approach, at least for applied math and physics. In my view math is a simplified language to describe reality, so it helps to have an idea of the what You try to describe in the physical world.It is like skimming a book helps to get an overview before getting into the details.
I simply used the thought experiment from your Lorentz factor derivation.
The equations in my derivation were:
L₀=c•∆t
L=∆t•√(c²-v²)
So:
∆t=L₀/c
And now if we do some simple algebra, we get:
L=L₀•√[1-(v/c)²]
L=L₀/γ
This might explain something I have observed on Grindr...
It appears to me that the primed measurment is shorter because they are arriving earlier at each measument point due to the time dilation they are experiencing. Since they are in a separate reference frame while at relativistic velocities, it wouldn't make a difference to say they are physically shorter, or temporally faster. That is why only the length shortens, and not the width. It is only a difference in observation between the primed and unprimed points of view. It doen't matter if it is "real" or not, the measurment will always be shorter. Is this an accurate observation?
01:19 I'm a musician, Don... I have to trust you! 🤯
The way you shown things makes the math raiser. You get it to say what is needed for your explanation.
As always, Doc, spot on! I am re-teaching myself relativity from my university physics days, and your videos are always a great addition to my studies!
This is the third video I see about this topic and this one is the most comprehensive! Thank you!
I hope you take care of your gym time.
the term "simultaneous" should not be used to explain relativity
Isn't it that every observer can define and use the concept of simultaneously for events, but it may not be simultaneously for another observer?
Why? It's a relative notion.
The math is easy enough that any high schooler who does their homework could keep up with this video. Please keep doing videos with math in it like this. People need to understand that math allows us to understand things even if we can't directly observe them.
A sphere will never flattened to an ellipsoid.... Terrell Penrose effect... the misconception of length contraction must be removed from the vido.
For the lazy~
Link: en.wikipedia.org/wiki/Terrell_rotation
Relevant quote: "A previously popular description of special relativity's predictions, in which an observer sees a passing object to be contracted (for instance, from a sphere to a flattened ellipsoid), was wrong."
The Terrel Penrose effect was revisited by Robert J. Deissler in the 2005 paper "The appearance, apparent speed, and removal of optical effects for relativistically moving objects"
Everything just clicked in the last minute of this video. What an amazing explanation!
Great video, great explanation. Relativity is the second most weird thing in the universe. Guess what is the first.
Boaz Augusto Matos The solution to the Teleportation noncloning theorem ,which for now, has been hidden from human knowledge by our Creator, thats truly brilliant thinking !
ScienceNinjaDude it was meant to be Quantum Mechanics.... but I forgot women...
English food ...
Belly button fluff?
My mother
Love the barn example. Also, saying that these effects are measured during {X} experiment is really helpful. These series of videos are great!
And this person is Matt from PBS Space Time :D
we have known for quite some time, that perspective makes objects appear smaller and smaller as distance increases... this has no influence on the optically slower or faster objects velocity, as time is not a cause anyway. How do equations, deal with optically observed, variable velocity and compressed distances, through perspective?
I wish too there would be such a person. But not found yet... jk
The whole moving vs. stationary thing (or here primed/unprimed) has always confused me, since it's contrary to what I would usually call them. In a previous video I learned the stationary time is the time of the observer that SEES the clock NOT moving (so IS moving alongside the clock) while the moving time is the time of the observer that SEES the clock moving (so is not moving alongside the clock).
Now this part at 1:30 hopelessly confuses me. Based on the whole stationary/moving thing I just mentioned, the person SEEING the situation NOT moving should be the moving person, no? But now apparently it isn't? I just don't get it.
Well, it's not like I expect an answer on a six year old video 😆
Next weak: "Length contraction: the imaginary explanation"
Yeah i asked my Prof. the same question that i have now. Considering you want to close the doors of the barn in the moment something is moving with 86% the speed of light through the barn the doors had to move even faster than that while being static in at least one position the door hinge. What changes their position in spacetime relative to the barn and to the stick going through it. What would actually happen? I only wish there was someone who claims he can communicate complex topics very well to give a good or at least a correct answer to this question ;-)
I always think of it this way. Distance per unit time = speed. If we both agree that light travels at the same speed, then we must disagree on how long something took or how much distance was covered in order to get the same answer for the speed of light. The very definition of speed connects time and space and Relativity show us how.
8:55 this is wrong. The basketball will **not** appear/look flat. In fact it will pretty much stay somewhat round but with some additional weird effects. Google Penrose-Terrell effect.
This is the problem when we speak of "what an observer sees" because "seeing" in SRT does not translate well into what we mean with this word in everyday life (camera/eye).
the step from 4:45 to the end when it will be the opposite, geting shorter instead of longer, is a tricky interpretation. Why should one not stay with the first result and search a way to the second?
At a fraction of the speed of light, objects should look contracted until we get past them. After we get past them, shouldn't they look dilated?
Hi Dr. Lincoln-- I know this video is from some time ago, but I just watched it hoping for a bit more insight about relativity. Good explanation of how we can use math to anticipate what we'll experience, and I followed all the math - much like the equation juggling in college physics, math, and chemistry, but at the same time I was hoping in the end for an explanation of what one might actually experience. If you could wrap up such math derivations/explanations with what it would mean to a human observer, that would be great.
There's a powerful analogy here between Lorentz transformations ("boosts"), and rotations in space. The latter use circular trig functions, the former use hyperbolic trig fns.
And the angle, θ (for rotations), is analogous to a boost parameter, α.
Both these parameters are unlimited; the limitation to below-light-speed comes in because the speed (β = v/c) is tanh(α), and because -1 < tanh < 1.
The speed then, is analogous to slope (= tan θ) in the rotation case. And just as slopes don't add when two rotations are combined, so speeds don't add when two boosts are combined. Instead, it is θ and α that add.
Furthermore, the length of a moving stick is analogous to a single spatial component of a rotated object.
When you rotate a cube, you don't expect the "sideways" view of one edge to remain the same length; rather, that apparent length, x, of the edge, "mixes" with another, perpendicular component, y, in such a way that √(x² + y²), the true length of the edge, remains constant.
In the boost case, you can't expect the length component, x, to stay the same; rather, √(x² - c²t²), the true length of the stick, remains constant.
For a rotation, the invariant length follows from the identity, cos² + sin² = 1.
For a boost, the invariant 'interval' follows from the identity, cosh² - sinh² = 1.
Thus we get the metric for spacetime.
The above analogy, and the mathematics that flows from it, are, AFAIK, due to the late John Archibald Wheeler.
I post them here for those who want to delve a little more into said mathematics.
Thanks for a careful, detailed, easy-to-understand look at how this works!
Fred
I think it's β = i*v/c. And those hyperbolic trig functions are from cos(arctan(i*y/x))+sin(arctan(i*y/x)). If you get a sum or a difference in there it's because you did cos(arctan(i*y/x))+i*sin(arctan(i*y/x)). Which probably means you gotta tan(pi/4-arctan(y/x)/2). Since c is m/s, I suppose it can also be m/(i*s). Which might imply a real time in velocity and an imaginary time in the speed of light.
@@thomasolson7447 No, it actually *is* β = v/c.
There's no physical meaning to "imaginary" time or space; rather, the difference between Lorentz transformations in spacetime and orthogonal transformations in Euclidean n-space, is fundamentally that the former relies on hyperbolic trig functions, while the latter relies on circular trig functions. Those two classes of trig function are mathematically related in complex analysis, but that fact tells us nothing about the underlying physics.
@@ffggddss I haven't really thought it out completely. My thoughts are that if you freeze a reference frame (with respect to time), the gamma part is the real part. The 'v' part runs perpendicular to the plane of the frozen reference frame. It also comes with its own quadratic polynomial built in. If you take a moment and go through the hyperbolic identities with 'e' expansion, you'll see that they are almost the same thing. The imaginary value is also consistent with vector addition. It is just tangent addition with an 'i.'
(i*v/c-i*m/n)/(1+i^2*(v/c)*(m/n))
No calculus needed.
(v/(i*c)-m/(i*n))/(1+(v/c)*(m/n)/i^2), also works if i is a factor of imaginary time.
Your explanation is so cool! Thanks! Many textbooks contain mistakes and confusion! Thanks for this wonderful video!
What happens to length if the difference in velocity between two observers is greater than light speed? What I mean is, if you have three observers, one is stationary, the second is moving at 86% the speed of light, and the third is moving at 86% the speed of light in the opposite direction, how will the two moving observers see each other. Also, how would this affect the scenario of a stick traveling through the barn?
Thank you, Dr. Don Fermi of Lincoln Labs!
Well done. A good follow-on would be exploring how this is related to what happens to coordinate and proper distance in Schwarzschild geometry.
very well explained... the example with the barn is really weird. not so the fact that the 40 m stick fits in a 20 m barn but that the space seen from a moving observer is shrinked regarding to the stick but not regarding to the barn. as they have the same location (stick inside barn) it means that the space is shrinked and not shrinked at the same time/space?!
Great explanation. I have a slight issue with saying this is what you would "see" rather than this is what you would "measure". In fact a moving sphere does not look flattened. When we talk about seeing we are talking about the light rays entering the eye. Roger Penrose showed in the1950s that a sphere does not look contracted (See the wikipedia page for the Terrel rotation - also from the 1950s). What happens is that the celestial sphere centred at the observer is transformed by a Möbius map (when considered as the Riemann sphere using stereographic projection) (Note that the proper orthochronous Lorentz transformations are isomorphic to the Möbius group). Möbius maps preserve circles-and-straight-lines and stereographic projection also preserves circles, so the sphere does not seem distorted.
You are right, I called it Lorentz rotation, and it is obvious. As the ball passes, you still see a round ball, but it is rotated so you see its backside. consider th e light entering your eyes as forming what you see, not what is.
i thought this guy was bs, but now, he has cleared my misconceptions. this guy is better than pbs.
I watched this video last night and I'm reviewing it again this morning. I've been slowly trying to wrap my head around these concepts for a while now and truthfully many explanations, such as the rubber sheet explaining gravity, don't really help much because they oversimplify. I especially like Dr. Lincoln's explanations because they are easy to follow yet don't approach things at the "rubber sheet" level.
Pondering length contraction and some other aspects of GR and other such subjects has raised questions in my mind about what is the underlying physical reality. The video begins with Dr. Lincoln saying that we "see" a length contraction. That's the observation. Understood. But supposing that there were a way to physically measure another object as I pass it at relativistic speeds would that observation be the same as the observation from photons. Is space actually contracting or does it just appear that way?
Does this explain why the length of white highway markers (separating the two lanes of traffic) appear shorter as you drive .. than their length measured at a stand still. That is they appear shorter than the car while driving .. than they do with the car parked along side the line.
At 6:52, i am not getting the point and stuck, as both primed and unprimed will see the length as the same time so if one equates both time in prime frame to be same, then at 6:52, why is unprimed time too also equal to zero.
Anyone please clarify me as i am stuck like for a week now at this point. Many text books tend to derive this derivation where in prime frame the stick is placed and is moving wrt primed frame and one derives very easily the formula. But what if the measurement is done where the rod is now in un prime frame and the prime frame is moving.
I couldn't see this question in the comments, apologies f it's been asked already: at 7:21 you divide the left hand side of the equation (zero) by gamma, but only the first term on the right hand side. This seems wrong to me, as both terms on the right should be divided by gamma. As the left term is gamma *(t2-t1), the unprimed times (for the observer that sees the stationary stick), I'm wondering if gamma for t2 and t1 =1, which would allow it to be removed from that term.... or have I missed something?
All nice and good so far. But what if the length L = 1 lp (Planck length) ? From the primed observer's perspective I get it, nothing changes. But from the unprimed observer's perspective does the object simply cease to exist ? Does it cross into another dimension ? Does it become a photon or some sort of similar and yet to be discovered contraption ? Or maybe the Planck length "constant" is actually much more relative than we are told ?
You sir, you are that such a person! We study time dilation and length contraction in my modern physics course. I find this concept fascinating. You have explained it very well! Thank you.
Sir, I really love your videos. Thank you so much for sharing and please continue.
There are two triggers in front of each barn yard door, that will go off when the one of the door closes. Which trigger goes off first?
I still got the principles while I completely didn’t understand the equation. Thanks, that’s very friendly for someone like me who doesn’t quite into Math😊
Great video professor Don. I had to rewind it like 10 times but it was worth the effort. I still need to watch it a couple times. But now I understand for the first time the math it's all about.
Great video Dr Don.
What about simple distance compression (i.e. perspective length compression ?)
Does the perspective ratio change for off Earth satellite observations ??
Uncompressed for the immediate environment of the observer , observationally proportionately compressed for anything at a distance (i.e. unique to the observer)
Time/Velocity moves slower observationally for the Observed yet both observed and observer are experiencing time at the same rate ?
So no velocity required for x,y,z length compression only distance ?
*;-))
So would you say it 'is' shorter when moving near light speeds? Maybe the Lorentz transformation is more like from fitting the observations, and what is a side observation is the effect of velocity on matter.
Could you explain to me why a wire with current on it is still neutral charged for a not moving charge next to it even though that charge sees the electrons including the gabs between them moving and this contracting?
How are you supposed to use those equations? I can't enter them into a calculator or a spreadsheet, as an apostrophe doesn't appear on the calculator keypad, and the ' symbol means something else in a spreadsheet.
If stick was moving from left to the right and its speed dropped inside the center of the barn to 0m/s, which door will be crashed first?
Edit: Or which door remains open?
Edit 2: I'm assuming that both doors will become open for not moving observer because the stick will grow. But then, you need to observe only one door to know at which state the second door is (for not moving you) and no matter how long the barn is... So, you may knew that the other door was closed, but you don't know at which state the other door when stick is inside (if it wan't to stop by some reason), but if yours is opened suddenly, you will know, because your measurement stick was long enough to reach the second door too.
Edit 3: By closing the door I'm measuring not the state of the other door but the "luck" of the stick (if it stopped or not inside). The info about the second door is just result of the long stick.
What if there were two sticks one after another? Would they behave like one stick or would there appear gap between them? For long enough stick wouldn't one end go backward or faster than light to achieve desired length?
They would behave as one stick. The touching ends are at the same position and move together. There wouldn’t be a separation between them. All observers would measure the same distance between them as 0.
If there was a gap between them, the gap would shrink by the same factor as the lengths of the sticks.
Jamal Wills but the ‘end’ of a stick is arbitrary. It could be seen as trillions of tiny sticks end on end. If two sticks with one ‘gap’ stay close together then the first must be falling back slightly and the second moving slightly forward in the frame of reference of the stationary observer with no plausible explanation. If there were three sticks how would the middle one know to ‘stay still’ and let the other two shuffle up? It doesn’t because no contraction takes place. It is only observed length that changes in a different frame of reference because what appears simultaneous to one observer does not appear so to another.
Lord ... It's Space itself that shrinks. See @ 10:12 ...
Thank u Dr Don I certainly enjoy your demonstration ofknowledge
Thank you for such a nice explanation.I always had a nagging feeling about "bookish" explanation of length contraction and knew that, there is a better explanation.Thanks for making it clear.
So the ∆x in the Lorentz transformation for an object (not 2 events) is the length measured by Unprimed when t1=t2, and vice versa?
Great explanation, Thanks! Imagine the accretion disk of a black hole. Incoming matter moving faster and faster, getting flatter and flatter, packing immeasurable density into the disk.
My question regards the path of travel from the frame of reference of the moving object, or one of a comoving observer. Does the observer see the path ahead contract? If so is it an illusory effect caused by time dialation, and even if so, wouldnt this still mean that assuming it's possible, a traveler could reach almost anywhere in the observable universe in a couple of years from their perspective with a 1g constant acceleration capable ship?
Would a length contracted rigid stick be able to cross a gap that contracts to a length small enough for it to cross but be too large for a primed observer?
Very interesting video. I have one question: suppose that I move towards Alpha Centauri at such a high speed that the distance dilates to 7 light minutes. Then I (as the primed observer) will see that star at a distance of 8 light minutes. Does that mean that I will also feel its heat? After all, our Sun is at that distance from Earth and we can feel its heat.
the thing with the barn and the stick works because according to one observer the stick was short enough to fit in the barn and according to the other because the doors close at different times. but what if you took the experiment further and made a circuit whereby both doors being shut simultaneously completes the circuit and lights a single lamp which both observers can see. does the lamp light or not? and if one observer sees the lamp lit but the other does not, how can that work? does the lamp only emit photons in one direction (clearly not possible)? what if the circuit completing and electricity flowing caused some permanent change of state in something which both observers could meet up and examine together later on? like, what if it electrocuted one of them? for a thought experiment intended to illustrate the principle, that only raised a bunch of confusing questions for me
Can you use a candle to mark the passage of time? And can you send another lit candle on a trip around the moon? Is there a way to make a length comparison to show time dilation?
since you get both time and length in motion by dividing by gamma, wouldn't that mean that the prime observer still would observe traveling the same amount of distance in the same amount of time as the unprimed observer?
A lot of math for something very simple. The moving stick shrinks in all respects due to the pressure of the aether, the quantum fields, through which it moves. The aether presses on matter and the matter shortens. The observer inside the space craft also becomes shorter, everything does, proportional to the speed and the pressure the aether exerts. The inside observer still sees the yard stick as being one 6:37 yard long. The outside observer sees the space ship go by and observes that the yard stick is marked off in 36 inches but all dimensions are shorter.
In the experiment of the 2 atomic cloks, one of them travels on a speed aircraft, the other one stays on the ground. When the traveller clock comes back and you compare both cloks, you can see that the one which travelled is some nano-seconds late. That means that it keeps a permanent trace of time dilatation. Is it possible to arrange a similar experiment where a device may keep permanent trace of length shrinking ?
Could there be an objective understanding of this with space and time being emergent properties relative to the energy and momentum of our actions?
I watched the video at home sitting at my computer desk and it was 11:22 long. I watched it again on a fast moving train and it was a different length. What is going on here?
I get it that the stick contracts along the direction of travel-left to right for instance. But what will happen if the stick is rotated 90° so it is perpendicular to the direction of travel? Will the stick suddenly lengthens and will the observer notice the change?
I was wondering what happens in the apparent ladder paradox should you keep nearly invincible barn doors shut around a nearly invincible ladder, what that would presumably do to the trapped object, and what exactly is happening with the energy involved.
Im guessing it converts the energy its carrying in its relativistic motion in to potential energy like a coiled up spring, but I might need to think about it some more.
A bit too lazy to do the math/think about it - but what would happen with the stick/barn example if you shut both doors permanently? What would be the sequence of events from the perspective of an observer stationary relative to the barn?