I really think calling it "the speed of light" encourages misunderstanding. As this video notes, it's not a fundamental property of light, but rather a fundamental property of the universe. "The speed of light" makes it sound like it's a property of light, and its function as a speed limit seems arbitrary and even nonsensical. And it's often explained as "light goes this speed, and nothing can faster." Explaining it first and foremost as a property of the universe, that it's the limit on how fast information can travel, and that light simply goes as fast as possible (which is slower in a medium) is, I think, a much better way to communicate these concepts. I like PBS SpaceTime's idea of it being "the speed of causality", as that's both a more accurate conception and it just happens to fit the term "c". (this also eliminates the need for the implied "in a vacuum" which also may confuse people) It's the speed of causality, and when light is otherwise uninhibited, it goes at that speed.
@Anonymous Really? I have had the impression that light does slow down. That's why it bends. c is always c, but when light passes through a medium, it's going less than c. The speed of causality is always the same, but light can vary depending upon the medium. That's a big reason why I dislike calling c "the speed of light". Light can go slower, but "the speed of light" doesn't change, and that is confusing. At least, that's how I read it. Light, when unencumbered, goes at c, but in a medium it slows a little bit below c.
But that is an interesting way to put it. On further thought, I don't think that explaination is any different than why anything else slows down when entering a "heavier" (or however you'd put it) medium. Like when you are in water. You move more slowly because of all of the water molecules you bounce off of.
This is the same feeling you get from those exams where there’s only one problem and every answer is based on the previous one, till you realize you made a mistake on the first one 🙃
in all my years of life i have never heard an explanation that the speed of light is actually the speed of causality. this is revolutionary. thank you so much. you make the nature of our universe so clear
It really isn't taught well enough, it took me way too long also, and now I know this a lot of theories started to make sense too. Like why having FTL communication actually breaks causality. I've heard so many explanations about it, but I never understood why light speed mattered, it's because It doesn't matter. Casualty speed does, "C". in schools they should explain light speed as causality speed, and then mention as a foot note that light travels at this speed because it doesn't have mass.
You wouldn't survive to feel anything unfortunately. The energy from the light coming from everywhere in the universe simultaneously will instantly vaporize you, along with the earth.
@@jeremias-serus None of that is actually true though. An infinite sum doesn't have to have an infinite value. Assuming a fairly uniform distribution of matter in an infinite universe there would be a hard limit on the total amount of light hitting the Earth just as there is now in our universe. The sky would not be lit up. It would most likely look about the same with the exception that we would not see the past but the present.
@@Ryrzard No one's saying it would have infinite outputs, that's because there aren't infinite stars. Only that the amount of outputs visible from Earth would be obscenely large. Easily so to the point that the entire sky should blinding.
exactly....I believe it's because space itself is actually not a very compressible medium (Or rather, very resistant to expanding or contracting....but since it's a vacuum is a constant and therefore puts a limit on a photons speed)
How do you know it's slow? For all we know, in certain directions light might travel almost instantly, but slow to a crawl in the opposite way. The speed of light has not been proven to be a constant, because it has not been able to be accurately measured for one directional speed There is much evidence to support light travels faster going from the center of the galaxy to the edge, than it does going from the edge to the center Due to light being a particle, this is likely since the cosmic background radiation, or cmb, acts similar to air drag on light, since cmb radiates from the center of the galaxy to the outer edge of the galaxy, that means there's cosmic wind, it is something we'd almost never be able to observe without a reference point outside our galaxy, since we're already affected by the cosmic wind. However this drag causes light to have a maximum speed since it has mass, literally the exact same concept as terminal velocity, however it would be different speeds based on what direction in comparison to the cosmic wind, and this speed difference would cause what we consider time dilation, since time for us is a measurement based on the speed of light and particles Also photons and gluons, as well as all particles have mass, they're just to small to measure, calculations have been done with the assumption that they have mass, that work mathematically and are often more accurate than those that don't, it's not something that matters outside quantum mechanics however
@@thezyreick4289 We know that no mass can travel at the speed of Light or its mass would become infinite. Do you agree with this fundamental? Therefore....light is not a particle Secondly....did you know that as light propogates...it red shifts....or its frequency slows down.....case in point CMB So....try again from there knowing these two things.
@@drd1924 no, I don't agree with your statement that no mass can travel at the speed of light, or it's mass would become infinite. Because the photons that make up the energy source called light, have mass, energy has mass. That's not a random statement, einstein stated and proved mathematically energy has mass, and we use that in modern physics as a fundamental law. Light redshifts? No fucking shit, all particles decay, what's the surprise? If the particles grouped together to form light decay, it too decays if it cannot find suitable particles to replace the lost particles that caused the decay. Why do you think stable particles are stable? Its because they don't have any problem replacing lost parts to keep themselves balanced and stable, that goes for every stage of particle from celestial bodies like black holes, all the way down to gluons and all the infinitely small particles that make them up. Or what, you one of those loons that claim a gluon wills itself into existence for the fucking hell of it? No, they form from energy, guess what energy has? Mass, guess what mass is? A physical manifestation in reality, so no shit energy is just particles, and when they come together right they form gluons and every other form of matter we know to exist. Think before you speak, and you should check your own crap you're saying isn't contradicting itself before speaking Trying to say a mass of energy doesn't have mass because it'd be infinite if it did, the hells wrong with you? If it don't have mass it can't exist, it can't interact with anything How the fuck you think they discovered the higgs boson? They collided photons together dumbass, how can you collide 2 things together if neither have any mass?????
@@drd1924 also, if my belief is so fundamentally wrong, then prove the theory I believe in is wrong. Go on, here is a link en.m.wikipedia.org/wiki/Scalar%E2%80%93tensor%E2%80%93vector_gravity Feel free, put it through the wringer, test it on the bullet cluster, I don't care, it works for the bullet cluster and explains it perfectly fine without breaking, test it on black holes, does that too, fuck take it to the quantum realm, I'm still testing it there, I'm not the one who made it, but no matter how much I test it, I cant break it, so please, try to help me break this theory because that's how I choose my theory, I don't assume shit's right, I do my absolute best to break it, and when I can't break it, then I know it's right, never need to assume
Problem is our linear thinking. There’s even universe possible where time runs backwards and yet it doesn’t break the casuality. In an universe where light has no speed limit, sure the physics might be different but that is not even slightly to say that there will be casuality problem, and also who is to say that they need to have casuality, we don’t know anything unlike us.
The fact that light starts behaving differently when observed reminds me of how in video games certain things don't render unless you are close enough and look at it, like, instead of rendering countless photon particles it simplifies it to a wave
"Observed" doesn't mean viewed. Us looking at it is not what matters. In fact, we can't "look" at it at all unless it enters our retinas. Instead, we can observe the after-effects of it interacting with something else. What "observed" actually means is interacting with light, which experimentally usually involves efforts to measure it. The word "observed" should never have been used by scientists. It's similar to terms like "god particle" and "big bang" -- the terms carry a lot of connotative baggage and are entirely misleading. Light's behavior has nothing to do with conscience observers. The Higgs Boson has nothing to do with "god," and isn't any more important than any other quantum particle. And the beginning of the universe was (most likely) not a massive explosion from a single point in space.
Definitely a very underrated channel that more people need to see. You should have your own Netflix special hosting along side NdGT! Thanks for making very difficult subject matter easy to understand and accessible.
@Asymmetrical Horse particles don’t “behave differently” you are interpreting wave/particle duality to mean that (for example) an electron is sometimes a wave and sometimes a particle, depending on how/if it is observed, but it’s not one or the other, the electron has *both* wave properties and particle properties at all times, and depending on the experimental setup one characteristic or the other will be observed, but both properties are always there. The so-called “quantum eraser” illustrates this nicely, see en.m.wikipedia.org/wiki/Quantum_eraser_experiment
Wave function, the total possible probability of finding a particle in any given location within the function as it is defined. This is like an upper and lower bound for the location as we understand particle interactions. Before we measure it, how do we know? We don't... That is why we measure... The function is either correct or not, measuring allows us to update the function. You cannot throw energy or another particle at a particle and expect it to continue doing what it was doing before. Meaning, once you measure it, you no longer know where it is because it was deflected by the measurement. But you can infer how fast it was going based on the particle that you measured with.
I have never heard a presentation that talked about a universe without a speed limit. And I thought I’d listened to every lecture, and concept of the universe ever presented. This was a fantastic presentation
Fun fact: if c was infinite, that might also cause capacitors to hold no charge because at least one of the permeability or permittivity would have to be 0
I would say it is more a question of would these constants work in the same manner? If we are making such a fundamental change as changing the speed of light, it is reasonable to assume lots of other things will change as well.
Wow, Arvin!!! I have never heard a talk like this that connects so many complex phenomena together in such a comprehensive manner...great production and graphics too!!! 👏👏👏
i think you have it wrong: on cosmic scales, the universe is BIG. it takes years to reach the next start because distance is vast, not because light is slow
@@scruffytube5169 And that is because the space itself could travel/expand at a much faster rate than the speed of light. We have no appreciation as to how large this value could be, perhaps the speed of light really is insignificant compared to the rate at which the space expands beyond the observable universe.
Causality might have something to say about that. That was his point about non-locality. However, think about the desktop toy, Newton's cradle, causation is happening everywhere at local scales. So yeah, it may seem like photons are "slow" as they traverse their lone paths, even if they feel no time. But literally everything is happening around it along the way. Measuring one photon is great for physics but it doesn't do us any good to try and observer the universe from that point of view...
10:08 - So the speed of light is really the speed of causality. Light just happens to be one of multiple things that's capable of traveling at the speed of causality. We call it the "speed of light" because light was the first thing we observed traveling at this speed.
Excellent as always Arvin. I cant believe Ive never thought about what the night sky would look like if the speed of light was instantaneous...... thats such a simple concept that has never crossed my mind before today. Thank you for bringing it to my attention, now I have more to ponder about.
@@Tailspin80 but then we would be able to see beyond the cosmological constant, which depending on if the universe is infinitely big or not, then there wouldn’t anywhere you couldn’t see light from a far away galaxy/star anything with The homogeneous matter dispersal in the universe. No loss of illumination from redshifted light, every wavelength visible at all times.
@@brianpj5860 Not sure, but wouldn’t the received light intensity be dominated by local sources? You would be able to see light from the observable universe but the distant sources would be very faint.
@@Tailspin80 I'm with you. When he said that, I was like, "not so fast, sir!" Even local sources of light become diffuse over space alone. Time diffusion seems unnecessary in order to have a universe of infinite light speed. Light traveling from an infinite number of light sources in the universe would have an infinite number of celestial bodies blocking them from our view. Come on!
Great video, some food for thought! I wonder: if the speed of light was infinite, would it mean that magnetic and electric resistance of space would be zero? Would it make electricity and magnetism behave oddly as well, like easy superconductivity or something?
Yes, excellent point! Many things would be affected including EM forces, as well as gravity. You can't really change the speed of light without affecting a bunch of other things.
Thank you so much! This is the first video ever that made me understand, why there has to be a speed limit for causality und why the speed of electromagnetic waves equals that speed.
That phrase makes no sense what so ever. If all observers can be aware of an event at the same time, there being no difference in the time taken for light to reach observers at different distances, then there would be uniform agreement on causality of events rather than the current relative effect that makes all observers disagree (and then need understand Special Relativilty to piece back what the sequence must have been). True that is not the universe we are in where one can use time delays beween receivers to calculate distance from a source (eg position with GPS), but I don't see that breaking causality. Indeed one could still be aware of one's position, if one used the reduced signal intensity through inverse-square law to calculate distance. Inverse square law still holding would party break earlier argument Ash raises 4:00 that one would be obliterated by the radiation from a million hypernova in space reaching us at once. This is I think invoking Olbers' Paradox of why is the night sky not white from the light from stars if we lived in an infinite static universe (anwser being that light is finite, universe is finite in size, universe is finite in age, universe is expanding and red shift). With infinite speed light from beyond just the limits of the Observeable universe bubble (now 46 billion light year radius and light having travelled 13billion years) would reach us. However the intensity of that far-distance light would still be reduced by the inverse square law. Absorption of light by interstellar dust further reduces the intensity of received light. While given infinite time that dust then would heat up and start emitting light of its own as black-body radiation, that this does not occur is partly explained by the universe having existed for only a finite period of time and the universe is not static, but is expanding, so light from far off universe would still be increasingly diminished by inverse-square law. The final component to the solution to Olbers' Paradox in our universe is that the expanding universe also causes light to progressively red-shift for farther objects, which I don't think would still occur if light had infinite speed.
You are a lot closer to the truth than you realize. Mutual agreement = democracy. If all observers agree you have objective or 100% absolute democracy. The laws of physics conform to a principle of objective democracy. The velocity of light is the same & equal for all observers, it is independent of the observer's perspective, it conforms to a principle of objective democracy therefore. Democracy is the correct word to use here. Objective democracy is a target or goal -- teleology. Teleological physics (syntropy) is dual to non-teleological physics (entropy). Syntropy (prediction) is dual to increasing entropy -- the 4th law of thermodynamics!
@@bi1iruben I wanted to post this same question myself. In a universe with an infinite speed of light, we are guaranteed to see events in the exact order in which they happen. How can that break causality?
As a chemistry instructor teaching conversion factors and dimensional analysis - the realization that the speed of causality is a conversion factor between space and time BLEW MY MIND.
Hi again Arvin. You are becoming endearing! That was not there when I met you. Now it is. It is present in the expressions of your face as you speak. Very nice. Felicitaciones mi amigo!
Hey, this was very cool. I’m just impressed at the clarity of your delivery, the depth of your explanation and your visualisations. I’m glad I found your channel!
5:00 Can someone expand on this? How / Why an infinite C breaks causality? how would different observers not agree that A caused B? Wouldn't both observers just see A and then B, but both would observe it at the same time?
The illustration of the flashlight on the train was superb. Perfectly visualized maximum speed even if you could measure it on the train from the standing reference. Beautiful. Thank you.
I watched this after watching a video that stated that we cannot prove the speed of light is constant depending on the direction. The example in that video mentioned a person on Mars could have received the signal in like 19 minutes and sending back the signal took only like a minute.
It takes a lot for me to downvote a video, but this sentence achieved that for me. The Michaelson-Morely experiment in 1997 killed the Ether, not relativity.
Haven't watched it, but to answer the question directly(as I think it is), if light's speed could be infinite, then a blackhole wouldn't be able to keep it from escaping its gravitational pull.
I follow a lot of Scientific TH-cam channels, but You, sir have answered all questions my head asks at 2am. I will now like, suscribe and sleep soundly..
This was one of the best videos I ever watched: You really nailed explaining thing fundamental principle simply! AWESOME!!!! WELL DONE!!!! I literally (Not making it up) got goosebumps
@@b4ph0m3tdk9 Yes. These are called permeability & permittivity. But why is light slowed down by these? Arvin Ash doesn't say why. He just says they give some resistance. The click bait-ness of this video becomes more obvious the more you delve into & think about permittivity & permeability. ok sorry but wall of text because it's complicated: Boze Science explains permeability nicely using simple diagrams. Space does not bend magnetic field lines because it has low permeability. Iron does because it has high permeability. Permittivity is found in 2 basic equations: force between 2 charges = QQ / 4pi times permittivity times r squared & capacitance = permittivity times area / the distance between the capacitor plates The reason why permittivity increases capacitor is explained by DrPhysicsA & Eugene animation guy whathsiname & there's a video by...can't remember non-Ivy league US university videos with few views can be very good sometimes. Materials with high permittivity are insulators eg plastic. The atoms in the plastic become polarised when the plastic is placed in the middle of a capacitor. The electron clouds get pulled towards the positive capacitor plate. This strips the plastic atoms of their electrons clouds & effectively causes a mass of positive charge to appear near the negative plate. Electrons love this & try to cram onto the negative capacitor plate to get near to the positive charge in the plastic. Thus you end up cramming more electrons on there. Thus the capacitance has increased. This process probably happens in a vacuum as well but on a smaller scale. Veritasium's video 'Empty space is not empty' shows that it isn't empty. & physicists seem to talk about vacuum polarization & maybe electron-pair shielding around an atom or something with Feynman diagrams. I dunno about this stuff yet. But this polarisation process can explain why force between 2 charges is inversely proportional to permittivity because when something becomes polarised the positive & negative parts are separated & there is an electric field between them which acts in the opposite direction to the electric field which caused the polarisation in the 1st place. Effectively the atom (or smaller thing) is acting like a spring. It takes energy to move the electron cloud away from the protons in the nucleus. NB Like a spring. The way in which permeability slows down light is a hard nice puzzle. At least this video has made me think about it. What i have now is that the magnetic part of light is basically a form of momentum. (See G Chang's vid = hydraulic analogy of LC circuit). & a big object with momentum takes time to slow down. Time. It takes time to slow down. What slows it down? I think the spring of polarisation that occurs in dielectrics & in vacuum. Plastic has high permittivity because you can spend a good 15 minutes pulling & stretching those electron clouds. Ok not 15 minutes but a long arse time. They like being stretched. Stretching things can take a while sometimes. It takes time. Don't ask me why there's a square root in there c = 1/square root of permittivity times permeability. i do not know why! (Yet) i think DrPhysicsA is really going to help me today with his video on reactance. So the video title effectively asks why are permeability & permittivity not zero? Also it asks why do these 2 values slow light down? If they were 0 then c would not get slowed down. It would be infinite. Since Ash does not answer these questions other than a very brief "it causes resistance" the title is click bait. It's a shame as his videos are pretty good IMO & I do learn things from them.
@@alwaysdisputin9930 Fabric of space it self sets a limit for how fast information can travel, but the resistance mentioned does NOT slow light down, as you say, it takes energy out of light.
@@b4ph0m3tdk9I agree it takes energy out of light but see the equation at 1:20 v = 1 over √ɛ₀ μ₀ See also Arvin Ash's video 'Why is the speed of light what it is? Maxwell equations visualized' th-cam.com/video/FSEJ4YLXtt8/w-d-xo.html v = 1 over something means 'inversely proportional' So as ɛ₀ μ₀ go up, then v goes down For example, glass has a higher ɛ than space therefore light travels slower in glass, this causes refraction Another way of saying it is c² = 1 / ɛ₀ μ₀ which is interesting because E = mc² & nukes release a lot of energy because E = mc² & c² is huge which means nukes are powerful because ɛ₀ μ₀ are near to zero i.e. nukes are powerful because space doesn't slow light down very much Edit: This comment initially started with 'No v = 1 over √ɛ₀ μ₀ which was a bit harsh & unskilful of me because i was focusing on the thing i disagree with whereas I agree that: the resistance in space takes energy out of light. I think this is true because empty space is not empty & vacuum polarisation occurs & that is like compressing a spring which takes energy
Several months ago, I read someone's comment proposing that if we live in a simulated reality, then the speed of light/travel in space has to be limited as the "Matrix" needs time to load the remote scenes when one travels in simulated space.
Marvellous explanation of the matter! Most importantly that it's not the speed of light but on the most general scale the speed of causality which defines the universe!!!
Light's intensity would still drop with the square of the distance. You still wouldn't have a fully bright sky and the super novas would still not kill us. Also causality would still be conserved, because you would get Galilean transformations and they are consistent too. But the one comment down there is right, e0 or m0 would need to be zero and that would be bad news for electronics.
@@ArvinAsh Great explanation for permittivity and permeability. And if we can understand these terms then relativity is much easier! But now question arises to my mind, how can we calculate that property of space that affects speed of electric and magnetic field.? I mean it seems like a simple constant in an equation just as G constant in newtonian gravity equation. If this works there then it should work there too(am I wrong again). BUT the MOST Major of my all questions comes now. Hw did scientists actually found that electric has finite speed(means it is travelling out of charge)? And also how did they found its velocity then after confirming that it has finite velocity? Make a video on that 🥰please.
You touched on refraction. The eye can only form an image when the curvature of the eye (and lens) refracts light onto the retina. We could not ‘see’ as we do now. Could seeing even be a thing? My expensive DSLR would be useless? Could I get my money back?
DSLR work on different properties, but the lense is not part of that. You can change the lense. In your eye the lense changes, no need for extra parts. If you tried taking pictures without a lense... Would they still give your money back?
There was a brilliant communication moment on the train. The light moving from the stationary observer and the light moving from the train passenger move at the same objective speed. The train passenger perceives the time component of "m/s" differently, which is why the "photon speed + train speed" paradox doesn't apply. Thanks for sharing. This was interesting.
why the need of slowing time? since light is massless, it doesn´t gain any „push“ from train, it simply starts to propage itself through space at it´s speed, no matter if source of light is moving, or not, right?
@@7JeTeL7 _"why the need of slowing time?"_ - watch the video at 7:30 again. From the outside observer's point of the view, the relative speed between the guy on the train and the light is less than c (it's c-v, where v is the speed of the train wrt. the outside observer). If the observer on the train would use the same length and time measurements as the outside observer, he would necessarily measure that slower relative speed of the light. In reality, he measures speed c.
@@renedekker9806 i don´t think so; guy in the train would measure distance for which light travelled from point (that point is obviously not in the train; it would be something outside the train, like telegraph pole or something) where he turned flashlight on...this would not aplly for, let´s say, gun; i am moving in train with 0.5 bullet speed and i shoot from the gun same time like someone outside, while passing him; my bullet would be 1.5 bullet speed(since it´s carring momentum of the train) while bullet shot from outsiders gun would travell it´s regular speed; both would see, that train bullet is faster, while in experiment with light speeed would be same(since it doesn´t carry momentum)
@@7JeTeL7 _"guy in the train would measure distance for which light travelled from point (that point is obviously not in the train"_ - the guy on the train obviously measures the points on the train. When we are talking about the speed of light, then it is measured wrt yourself. When you are on the train, then obviously, that is on the train. _"while in experiment with light speeed would be same"_ - Exactly, the light from the flashlight on the train measures as speed c for both of you. The light from the flashlight outside the train ALSO measures as speed c for both of you.
@@renedekker9806 i am sorry, but guy in train must always count from starting point/or, if he chooses train itself as reference point, he must add distance which he travelled from that point during measurment; both approaches give same speed...massless property of light is, that it doesn´t matter how fast its source moves; source of light doesn´t give momentum to light, so it´s speed is constatnt, no matter where it came from...why slowing time to solve this?
But from the point of view of light itself, a photon doesn't experience time and so wouldn't that mean that it leaves and reaches its destination instantly ? It depends on the point of view that you are looking at it from, relativity!
C is not a fundamental property of universe. It is only a fine tune convention to obtain more precise data, necessary on then new quantum mechanics. Nobody knows if light in other zones of Universe is lower or higher, presuming the vacuum is equal everywhere, which is an epic presumption...
I think a better question to ask would be: what would happen if "c" approached infinity? This would get rid of the causality problem to some degree and mostly give us Newton's mechanics.
@Zhang ShiYing can you provide an example of a setup in which some measurement doesn't approach a limit as "c" approaches infinity? It might exist, but I can't think of one, so my question stands. And the Universe definitely won't happen all at once cause speeds below "c" exist. I mean, most computer physics engines work as if "c" is infinite.
@Zhang ShiYing ...and that's relevant how? "c" is a parameter, we can take a limit of any measurement as "c" approaches infinity while other parameters remain the same to get a model of the world where "c" is infinite.
crazy how ive been discussing my interest in quantum mechanics to my coworkers in fast food and they ask me pretty simple questions in response about this exact topic! very serendipitous.
this is a 5-star science video Arvin that should be shown in every school science class. thank you thank you for living proof that the internet can increase the spread of human understanding
FINALLY!!! Clarity on the space/time/causality/locality/speed of light relationship!!! Best one I've ever come across!! Profoundly appreciative for the Enlightening presentation (pun intended)!!!
There are old vids of him that have already discussed the topic. Namely the black hole and parallel universe ones. He've got an interesting diagram concerning that. Plus, it is location inside the event horizon where time and space switches role, not only the singularity. (according to his vids, if I didn't misunderstand)
Time and space switch roles at horizons. Singularities don’t physically exist. They are mathematical issues that arise with coordinate systems applied to highly curved spacetime.
What a video! He's underrated! I hope I can give a suggestion. Changing the channel logo may bring more viewers, that is why I saved this vid for the last and it was the best on this topic! It brings the feeling of an Indian youtuber who uses Xenogenesis as his intro song. Just trying to help. Again, fantastic video!
You must have lived a long time to remember that experiment! I had no clue the average Joe of the 1880's was even aware that such an experiment was taking place by the elitists philosophers of the time
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That's the render speed of the computer that runs this simulation. They needed to set a limit so the game engine is able to keep up with players moving.
Interesting thought. I don't know if you're serious or not.
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@@johnmckown1267 Some experts think we might live in a simulation so if that's the case than the game/rendering engine must have limits. For example our primitive engines have LoD and Draw Distance to keep things smooth and manageable. The universe engine might have the Speed of Light limit for the same purpose.
I know some scientists have invoked the simulation hypothesis based on presumed probabilities. I even made a video about it. But realistically, I don't think we live in a simulation. There is no evidence that we do. All the hype is based on statistics, which are based on presumed assumptions about the future, and not on any known probabilities.
@@ArvinAsh I like what Sabine Hossenfelder more or less said. If you can't measure it / observe it / test it, it's not science, it's religion/belief/philosophy.
@ There is something about the results of quantum mechanics that really feel uncomfortably like looking at the edge cases of an optimization from the inside. Like maybe entanglement and late resolution of variables leads to easier calculations or a huge reduction in storage requirements. A good analogy might be floating point math. It lets you work with really big numbers and is largely correct for a pretty nice savings in storage. However, its not too hard to get some shocking results with it if you didn't realize how it worked to begin with.
The little curvy e symbol (Greek letter epsilon) is the permittivity of space. It is the capability of a vacuum to permit electric fields. Or to put in his terms, the permittivity is the resistance the electric fields experience. The little u shaped symbol (Greek letter mu) is the permeability. It is the capability of space to allow the formation of magnetic lines of force or magnetic fields. Again, using his terms, the permeability is the resistance the magnetic fields experience. Since we are dealing with electromagnetic waves which are nothing more that alternating electric and magnetic fields, it makes perfect sense that the speed of the waves would be affected by both factors.
if we disregard the extreme cases of 0 and infinite value, it is interesting to ask how would the universe be if the speed of light was 1/100 or 1/10 the current measured value. Both general relativity and quantum physics does not depend on any explicit value for c just it is finite. Is the universe invariant to all finite values of c.
Different finite values would mess with some of the other constants of physics, possibly preventing the formation of atoms, etc. I’m sure some minor variation would still work.
There was once a science fiction story where the speed of light was imagined to be 20 MPH. I don’t recall the author or title. It may have been George Gamow.
@@laurelcreek7 Yes I read it years ago. It was George Gamow, Mr Tompkins in Wonderland, first published in 1939, it’s a short story. Here’s a snippet… When he opened his eyes again, he found himself sitting not on a lecture room bench but on one of the benches installed by the city for the convenience of passengers waiting for a bus. It was a beautiful old city with medieval college buildings lining the street. He suspected that he must be dreaming but to his surprise there was nothing unusual happening around him; even a policeman standing on the opposite corner looked as policemen usually do. The hands of the big clock on the tower down the street were pointing to five o’clock and the streets were nearly empty. A single cyclist was coming slowly down the street and, as he approached, Mr Tompkins’s eyes opened wide with astonishment. For the bicycle and the young man on it were unbelievably shortened in the direction of the motion, as if seen through a cylindrical lens. The clock on the tower struck five, and the cyclist, evidently in a hurry, stepped harder on the pedals. Mr Tompkins did not notice that he gained much in speed, but, as the result of his effort, he shortened still more and went down the street looking exactly like a picture cut out of cardboard. archive.org/stream/MrTompkinsInWonderlandMrTompkinsExploresTheAtom/tompkins_djvu.txt
@@cloudpoint0 I think the author does not take into effect of relativistic effect as in special theory of relativity into account assuming it is valid in such a universe. The cyclist and all others would still be moving at a very very small fraction of 20mph exactly like we do now with respect to 300000 km per sec. But thanks for the link. It will be an interesting read.
I find it interesting that the speed of light is "algebraically infinite" in the sense that the group of real numbers under normal addition is isomorphic to the group (-c,c) under velocity composition in SR. In other words, if one was to "squish" the group of real numbers under addition to fit in an interval, the binary operation to equip on the interval is precisely velocity composition in SR.
*Arvin*, I have a question I've never seen answered (or asked for that matter!) concerning the speed of light being the limit at which information can be transmitted. It's a though experiment, but please bear with me. ❓ Imagine I have an extremely long, thin cylinder of a solid material. For this example, say this object is just over 11,000,000 miles long (i.e. a light-minute) and an inch in diameter. I am at one end of the 'rod' and have a person/receiver set up at the other end. If I instantaneously push the rod say a fraction of an inch toward the receiver and send him a pulse of light, will the person at the receiving end detect that I have pushed the rod instantaneously - i.e. a full minute before the light pulse arrives? If so, I can use this mechanical set-up to transfer information much faster than sending him a pulse of light. If this is fallacious, what explanation limits the transfer of information using my 'rod' to the speed of light or less?
The person would not feel your push on the rod instantly, In fact the wave or your push would travel much slower than the speed of light, because each electron in each atom would have to bump into the next atom, which would have to bump in the the next atom, and so on for 11,0000,000 miles. This propagation is normally so fast a ordinary lengths that you think it is instantaneous, but over long distances, it would propagate quite slow compare to speed of light.
@@ArvinAsh I studied mechanical engineering in college, but I learnt both special relativity and quantum mechanics in a course on modern physics. One of the consequences of special relativity-as you just explained to Steve-is that no object can be perfectly rigid. Otherwise sound waves within that object would travel at infinite speed. That was okay for another course, _Strength of Materials,_ where they taught us to calculate stresses and strains-deformation under different types of forces. All using tensors, because we were big kids now. On the other hand, there was yet another course on rotations of solid objects-you know, angular velocity, moment of inertia tensor and all that. The professor always started off assuming a perfectly rigid object: One that does not get deformed as it rotates or when forces and torques are applied to it. Taken together, it was all very weird: Solids cannot be perfectly rigid, but they have to be in order to rotate. I mean, if you want to pass one course, you have to believe certain things. To pass another course, you have to believe the exact opposite. And you have to pass all the courses to get your degree. I can imagine how hard it must have been for Lewis Carroll's Alice when asked to believe in impossible things! And so today I'm completely disillusioned with the way students are taught science. I'm not surprised that so many people drop out, don't trust science, are superstitious, believe in the supernatural and weird conspiracies, endanger everyone through rash acts, and end up voting for unsuitable candidates.
@@nHans I'm only a sofware engineer, with a BSc., and I'm not the best in physics, but as I can see it, one of the worst thing in modern physics (education) is that we still talk about "objects" (made of some kind of (solid, rigid) matter) even at a university level. I mean, it's pretty good model for Newtonian physics, but seems very poor model when talking about particles or huge objects of the universe. (But maybe, it would be the best to not talk about (solid) objects when even when discussing "normal" things. It always annoys me, that if we analyze for instance the forces and movements of a bus and inside of it... then we would consider the seats as part of the bus (same object), because it moves relatively together with the whole bus. Then we would say that the people standing inside the bus are not part if it. But if they sit down, and hold themselves tightly, then they behave like they would be almost the part of the bus... just because of the frictions. Whereas in the reality, nothing there is really 1 object. There are many-many particles interecting with each other.)
Great video again, Arvin. One question though: on the part where we see both the stationary observer and the moving train observer flashing their lights in the same direction as the moving train, the stationary observer would see the train observer's flashlight's light with increased frequency, while the train observer would see the stationary observer's flashlight's light with decreased frequency, right?
@@s_i_am-R Energy is a conserved quantity that arises in a time symmetric system according to Noether's theorem which shows that for every symmetry in nature there is an associated conserved property/quantity. In relativity the rate of time is not the same between observers thus the energy will not be the same between different frames of reference. Energy still holds within a specific frame or reference and because there is a conversion factor between the rate of time in two reference frames you can still define an energy transformation between reference frames allowing the property to continue to be valid but the energy between two different frames of reference will always be different.
@@s_i_am-R To wrap my head around that, I like to think of frequency for light as a sort of placeholder for mass in the sense that a more massive object (or in the case of light, a higher frequency) would have more energy than a less massive object (or in the case of light, a lower frequency) moving at the same speed.
@@s_i_am-R I guess the moving source has to give some change in the property of lights. So here energy may be increasing in effect with increase in frequency.
Suppose we could not see light, and used sound waves to navigate about in our lives, how could we measure the speed of causality? Furthermore, suppose the speed of causality was actually a little higher than the measured speed of light in the vacuum, how could we detect this?
Very interesting video but one question I have is unanswered: what would happen if the speed of light slows over time? For example, what if it was (near) infinite at the Big Bang and then gradually slowed to its present day speed? Is that possible and, if so, how would it affect our universe?
@@djayjp , true, whatever stars are currently beyond our view would come into view (we have no way of knowing how many that would be), but we would also lose some light, because already dead stars wouldn't be showing in our sky like they do now.
Pretty sure its locality Quantum mechanics doesn't care about locality as the quantum wavefunction of everything extends over all space but causality still matters as in information still takes time to propagate even through quantum interactions that are nonlocal i.e. quantum entanglement. It seems a natural consequence then to suspect that space is emergent representing the universes resistance to information propagation per time interval or the amount of bits of information that can react at any timestep or fundamental (plank?) time unit. Regardless like you said the delayed choice quantum eraser and bells inequality either space or time in an emergent property rather than a fundamental element of reality. Beyond the plank limit at least one but possibly both cease to have any meaning and are derived of some deeper fundamental principal or quantity. Throwing away space just seems the easier path to reconciling relativity with quantum mechanics. Regardless it tells us that stuff at or beyond the fundamental limit is really alien
But the quantum eraser experiment does not break causality. It just demonstrates a paradox. And all paradoxes are, by definition, based on flawed logic or bad science. A paradox cannot exist. QED
Thank you, Arvin, for such a great video. I have one question: We know that the Universe is expanding in an accelerated manner. The expansion means stretching of space-time which also includes vacuum I believe. I was wondering why it doesn't affect the speed of light? At the end of the day, even if we don't have the so-called aether, photons still glide on the fabric of space-time. Am I missing something very fundamental? Is it because their wavelength and their frequency change and adjust themselves to maintain the speed? I was trying to relate the fabric of space-time with stretched vibrating strings in which the velocity of the waves depends on the material density of the string. The permittivity and permeability should change as space expands if we consider how a normal fabric acts when stretched.
_"In 1784, John Michell proposed, in the context of Newton's corpuscular theory of light, that if the escape velocity from a mass exceeded the speed of light, then the mass would be invisible. In his picture, light emitted from the object would go up, curve around, and come back down.Michell's picture is enticing, but it is different from what general relativity predicts. General relativity predicts that any light emitted within the horizon is dragged inward, even if the light is pointed directly outward. The picture at left, which shows light going up, turning around, and falling back down, is misleading.Imagine light rays, photons, as fishes swimming fiercely in the current. Outside the horizon, space is falling into the black hole at less than the speed of light (or the speed of fishes), and photon-fishes swimming upstream can make way against the flow. At the horizon, space is falling into the black hole at the speed of light. At the horizon a photon-fish swimming directly upstream will just stay there, swimming like crazy, but not going anywhere, the inward flow of space exactly canceling the fish's motion. Inside the horizon, the space waterfall falls faster than the speed of light, carrying everything with it. However hard it tries to swim upstream, the photon-fish inside the horizon is carried by the flow of space inevitably inward to its ultimate fate. _ _In the image at right, the (happy) fish upstream can make way against the current, but the (sad) fish downstream is swept to the bottom of the waterfall. This picture was drawn by my daughter Wild, and provided the cover image for the June 2008 issue of the American Journal of Physics^4. _ _Doesn't relativity say that nothing can go faster than light? It is true that nothing can travel through space faster than light. However, in general relativity, space itself can do whatever it likes. _ _The idea of space moving is one that you may have met before in cosmology (the study of the Universe at large), in the notion that the Universe expands." _ jila.colorado.edu/~ajsh/insidebh/waterfall.html#schw (TY YT for completely not italicising) I really liked Action Labs video about white holes. If we pee into our kitchen sinks then the pee creates a circle. Or alternatively turn on the tap & it creates a circle. I prefer the pee method however. Action Labs says this is called a 'hydraulic jump'. Action Labs shows the hydraulic jump is like the event horizon of a white hole because waves can only travel 1 way. (& IMO a white hole is a time-reversed black hole) Practical Engineering's video 'What is a Hydraulic Jump' is illuminating for showing this: th-cam.com/video/7tjf8HWiR3Y/w-d-xo.html The pee hits the sink & travels towards the sink walls. A wave is created which is reflected & travels towards the sink hole. Then the wave gets stuck. Why? Because it's speed matches the speed of the pee underneath it. The stuck wave IS the hydraulic jump. It is like a wave on a treadmill. It seems therefore that the answer to your question is that the wave doesn't care about the universe being stretched underneath it. It travels on top.
@@TheOnlineBlackboard Thank you for replying. If I am not wrong, the color is characterized by frequency. Wavelength changes I agree due to expansion. Then to preserve the speed of light, the frequency changes as well and that's why the color. So the universe tries to preserve the speed of light. This isn't how normal fabrics work. The velocity changes with the stretch as the density and hence resistance changes. But here the resistance (those two constants) stays the same no matter how much it is stretched.
If I was traveling at the speed of light, and I looked at some light, would I measure it to still be traveling at the speed of light, or would it seem to be still, relative to me?
You would measure it to be traveling at C. The speed is the same no matter how fast you are traveling. Time would also seem to tick normally for you. Only when you stopped and compared the time on your watch to someone standing still would you see a difference.
In addition to what Arvin said, note also that you cannot travel at light speed because you have mass :) As your speed approaches c, the energy required to accelerate would approach infinity.
@@aclearlight I can't say what would happen exactly at C, since nothing with mass can travel at that. But no matter how close you got to C, 99.99(infinite 9) - from your perspective, nothing would be different.
@@aclearlight If you travel at c, your trip would take 0 seconds from your frame of reference, no matter what distance you are going. In turn, for a resting observer, you would appear to be frozen in time for the duration of the trip, but your trip still takes time.
One thing tripping me up a bit is that around the 3 minute mark Arvin explains since space exhibits a resistance to the propagation of electromagnetic waves, this sets up a finite limit to the speed of light. Explaining this as resistance implies to me that this would cause photons to decelerate and eventually come to a stop. Obviously this is not what happens, and before this I was fine with an arbitrary upper limit on the speed of causality, but now he has me wondering about the "resistance" property of space. 🤔
The funny thing is, for a photon, light does travel at infinite speed. When it leaves its origin, it will arrive at its destination instantly from the photon's perspective.
The more I watch universe videos the more I become afraid that we are just someone's pc simulation. Speed is light is literally a set constant by the developers to ensure things work...
@@ghotifish1838 because it would mean everything is worthless, and nothing you've ever done has mattered. Sure, being afraid versus not caring doesnt make any difference if that's what you're saying, but the fear of the possibility of this being true isnt really something many can control.
@@MrJohansen ye but since u can't control it why worry about it? It's like death, there's no point worrying your whole life about dying. Likewise there's no point in worrying about if we are in a simulation or not
it wouldn't stop causality from working entirely. You could still agree on the order of events at the same location. You just get the bonus of being able to agree on the order of events at all locations
At least it appears to be, given we have pretty much no idea what „space fabric“ is, beyond an abstract concept. What‘s it made of, how can it expand and be curved by gravity etc.
This comment provides a fascinating overview of the history of our understanding of light, from classical physics to quantum mechanics, and explores the consequences of a universe with an infinite speed of light. It's amazing to think that the properties of empty space can have such a profound impact on the fundamental laws of the universe, and this comment does an excellent job of explaining why the speed of light is so crucial to the structure of space and time. Additionally, the mention of Magellan TV is a great reminder that there is always more to learn about the wonders of the universe, and I'm sure many viewers will be inspired to check out the service after watching this video.
.. And so is an all pervasive, inertial (as in momentum-conserving), quantised matter-energy field, I'd argue... I'd go as far as to say its as essential as the fundamental speed of the electrostatic force that carries light... This field is what the matter we detect is made of, as well as being the medium for the electrostatic force. The MM experiment and later experiments only disproved a type of aether (field) that by classical necessity must not interact with matter.. A single subspace field (or binary, 2 particle field) with ONE FORCE providing a mechanism for mass, that is able to emerge the Standard Model (minus its hypothetical, made up fudges) is far from ruled out...
But if the universe just came to life randomly on its own, it can only exist if speed limit exists. In any universe where there is no such limit, you are by definition, not there to observe.
To observe implies intelligent life. For life to evolve there must be a cosmic speed limit, otherwise emerging life would immediately propagate to the entire universe and destroy it, or itself. Ergo, we must live in a version of the universe where c is finite.
@@Tailspin80 It is more like the other way around. Intelligent life implies observation. Universe does not require intelligent life, to exist. Infinite number of universes can exist without intelligent life. Amongst those, infinite number of universes can exist where laws of physics doesn’t allow even to structure emerge, and therefore life is impossible. For example there might be an universe where speed of light is infinite, time doesn’t exist, and the universe ends in an instant. Obviously there is no intelligent life there. The fact that we are here thinking about it, observing our universe, implies that we are in an universe which ALLOWS structure and intelligent life to emerge. If there is infinite number of universes, and amongst those there is just 1 which allows intelligent life, we are necessarily in that 1 universe.
the universe as the speed of light approaches infinity remains consistent so i don't see how causality is suddenly erased or how relative reference frames go away either - the speed of light, if infinite, means all people always measure it to be the same regardless. in fact, time dilation naturally goes away as the value of c approaches infinity.
Thanks for the video, even as someone who has dealt with the subject, I really enjoyed this amazing explanation - that's an immediate subscription for me.
This makes great sense to me after this. Thank you. You can’t break the speed of light because that would break the causality chain. Light is the mediator of causality. Maybe as we approach the speed of light, the photons we are emitting start to build up against the photons in front of them, like you see sound waves do in front of an airplane that is about to break the sound barrier. This causes resistance to movement maybe. Maybe the Big Bang was caused by something that somehow broke the speed of light, which would mean that the object has broken the “causality barrier.” Sonic boom... Big Bang? I’m literally just talking out of my ass.
The answer is way more simple than that. Basically whenever an object accelerates it takes exponentially more energy to move. This amount of energy is an asymptote with a limit at the speed of light. Any object with mass would require infinite energy to get to the speed of light. Technically if an object were to go the speed of light its mass would become infinite and that doesn't make much sense. Thats why only things with zero mass go the speed of light.
@@Rangvald8909 @joule400 That’s called *Cherenkov radiation,* which occurs when electrons move at speeds close to 𝑐 through a medium other than a vacuum, for instance water, which has its speed of light at approximately ⅔𝑐.
I really think calling it "the speed of light" encourages misunderstanding. As this video notes, it's not a fundamental property of light, but rather a fundamental property of the universe. "The speed of light" makes it sound like it's a property of light, and its function as a speed limit seems arbitrary and even nonsensical. And it's often explained as "light goes this speed, and nothing can faster."
Explaining it first and foremost as a property of the universe, that it's the limit on how fast information can travel, and that light simply goes as fast as possible (which is slower in a medium) is, I think, a much better way to communicate these concepts. I like PBS SpaceTime's idea of it being "the speed of causality", as that's both a more accurate conception and it just happens to fit the term "c". (this also eliminates the need for the implied "in a vacuum" which also may confuse people)
It's the speed of causality, and when light is otherwise uninhibited, it goes at that speed.
@Anonymous Really? I have had the impression that light does slow down. That's why it bends. c is always c, but when light passes through a medium, it's going less than c. The speed of causality is always the same, but light can vary depending upon the medium. That's a big reason why I dislike calling c "the speed of light". Light can go slower, but "the speed of light" doesn't change, and that is confusing.
At least, that's how I read it. Light, when unencumbered, goes at c, but in a medium it slows a little bit below c.
But that is an interesting way to put it. On further thought, I don't think that explaination is any different than why anything else slows down when entering a "heavier" (or however you'd put it) medium. Like when you are in water. You move more slowly because of all of the water molecules you bounce off of.
Thanks, that definitely shed light on the topic.
You seriously just helped me understand it a little
Oh dude, so it's like the universe's bandwidth?
This is the same feeling you get from those exams where there’s only one problem and every answer is based on the previous one, till you realize you made a mistake on the first one 🙃
All of our test is almost exactly like this everytime, the only difference is ours is way more vauge and loosely said
in all my years of life i have never heard an explanation that the speed of light is actually the speed of causality. this is revolutionary. thank you so much. you make the nature of our universe so clear
I recommend PBS spacetime. It is a very good physics channel - and the one that first taught me light speed isn't about light.
See here: th-cam.com/video/msVuCEs8Ydo/w-d-xo.html
It really isn't taught well enough, it took me way too long also, and now I know this a lot of theories started to make sense too.
Like why having FTL communication actually breaks causality. I've heard so many explanations about it, but I never understood why light speed mattered, it's because It doesn't matter. Casualty speed does, "C". in schools they should explain light speed as causality speed, and then mention as a foot note that light travels at this speed because it doesn't have mass.
Seeing the night sky with the speed of light being infinite would be either magnificent or terrifying, either way I’d like to see.
You wouldn't survive to feel anything unfortunately. The energy from the light coming from everywhere in the universe simultaneously will instantly vaporize you, along with the earth.
It would be blinding at the very least. Instantly destructive at the worst :P
I mean it would just be pure white. In fact you'd probably not be able to see at all.
@@jeremias-serus None of that is actually true though. An infinite sum doesn't have to have an infinite value. Assuming a fairly uniform distribution of matter in an infinite universe there would be a hard limit on the total amount of light hitting the Earth just as there is now in our universe. The sky would not be lit up. It would most likely look about the same with the exception that we would not see the past but the present.
@@Ryrzard No one's saying it would have infinite outputs, that's because there aren't infinite stars. Only that the amount of outputs visible from Earth would be obscenely large. Easily so to the point that the entire sky should blinding.
This is one of the best videos on physics that I've ever seen (and I've seen many). It pulls together and explains so many fundamental concepts.
What I found really interesting is, how slow C is on a cosmic scale...it's like internet from the 90's
Great video! :)
exactly....I believe it's because space itself is actually not a very compressible medium
(Or rather, very resistant to expanding or contracting....but since it's a vacuum is a constant and therefore puts a limit on a photons speed)
How do you know it's slow? For all we know, in certain directions light might travel almost instantly, but slow to a crawl in the opposite way. The speed of light has not been proven to be a constant, because it has not been able to be accurately measured for one directional speed
There is much evidence to support light travels faster going from the center of the galaxy to the edge, than it does going from the edge to the center
Due to light being a particle, this is likely since the cosmic background radiation, or cmb, acts similar to air drag on light, since cmb radiates from the center of the galaxy to the outer edge of the galaxy, that means there's cosmic wind, it is something we'd almost never be able to observe without a reference point outside our galaxy, since we're already affected by the cosmic wind. However this drag causes light to have a maximum speed since it has mass, literally the exact same concept as terminal velocity, however it would be different speeds based on what direction in comparison to the cosmic wind, and this speed difference would cause what we consider time dilation, since time for us is a measurement based on the speed of light and particles
Also photons and gluons, as well as all particles have mass, they're just to small to measure, calculations have been done with the assumption that they have mass, that work mathematically and are often more accurate than those that don't, it's not something that matters outside quantum mechanics however
@@thezyreick4289 We know that no mass can travel at the speed of Light or its mass would become infinite.
Do you agree with this fundamental?
Therefore....light is not a particle
Secondly....did you know that as light propogates...it red shifts....or its frequency slows down.....case in point CMB
So....try again from there knowing these two things.
@@drd1924 no, I don't agree with your statement that no mass can travel at the speed of light, or it's mass would become infinite.
Because the photons that make up the energy source called light, have mass, energy has mass. That's not a random statement, einstein stated and proved mathematically energy has mass, and we use that in modern physics as a fundamental law.
Light redshifts? No fucking shit, all particles decay, what's the surprise?
If the particles grouped together to form light decay, it too decays if it cannot find suitable particles to replace the lost particles that caused the decay.
Why do you think stable particles are stable? Its because they don't have any problem replacing lost parts to keep themselves balanced and stable, that goes for every stage of particle from celestial bodies like black holes, all the way down to gluons and all the infinitely small particles that make them up.
Or what, you one of those loons that claim a gluon wills itself into existence for the fucking hell of it? No, they form from energy, guess what energy has? Mass, guess what mass is? A physical manifestation in reality, so no shit energy is just particles, and when they come together right they form gluons and every other form of matter we know to exist.
Think before you speak, and you should check your own crap you're saying isn't contradicting itself before speaking
Trying to say a mass of energy doesn't have mass because it'd be infinite if it did, the hells wrong with you? If it don't have mass it can't exist, it can't interact with anything
How the fuck you think they discovered the higgs boson? They collided photons together dumbass, how can you collide 2 things together if neither have any mass?????
@@drd1924 also, if my belief is so fundamentally wrong, then prove the theory I believe in is wrong. Go on, here is a link
en.m.wikipedia.org/wiki/Scalar%E2%80%93tensor%E2%80%93vector_gravity
Feel free, put it through the wringer, test it on the bullet cluster, I don't care, it works for the bullet cluster and explains it perfectly fine without breaking, test it on black holes, does that too, fuck take it to the quantum realm, I'm still testing it there, I'm not the one who made it, but no matter how much I test it, I cant break it, so please, try to help me break this theory because that's how I choose my theory, I don't assume shit's right, I do my absolute best to break it, and when I can't break it, then I know it's right, never need to assume
Somewhere in a distant parallel universe, “Why doesn’t the speed of light has a limit? What if it was finite?”
Problem is without causality how would one be able to think? ;)
Causality defines the distinction between events, so without it there wouldn’t be any asymmetry or nuance whatsoever.
Problem is our linear thinking. There’s even universe possible where time runs backwards and yet it doesn’t break the casuality. In an universe where light has no speed limit, sure the physics might be different but that is not even slightly to say that there will be casuality problem, and also who is to say that they need to have casuality, we don’t know anything unlike us.
So many arguments against FTL come down to "you can't break the rules, if you follow the rules."
@@henrytjernlund what do you mean exactly, can you give an example?
Finally youtubes algorithm has shown me something I'm actually interested in
Welcome
Just saw your comment right after I finished writing basically the same thing!
Same
Magnetic moment M= IA mia
Lucky you. I had to go looking for videos like this because the algorithm kept recommending videos of sebaceous cysts and pimples being drained. 🤢
The fact that light starts behaving differently when observed reminds me of how in video games certain things don't render unless you are close enough and look at it, like, instead of rendering countless photon particles it simplifies it to a wave
damnnn thats such an intuitive thought! wow man
A highly suggestive thought indeed!
Omg, we are in a video game , confirmed
"Observed" doesn't mean viewed. Us looking at it is not what matters. In fact, we can't "look" at it at all unless it enters our retinas. Instead, we can observe the after-effects of it interacting with something else. What "observed" actually means is interacting with light, which experimentally usually involves efforts to measure it.
The word "observed" should never have been used by scientists. It's similar to terms like "god particle" and "big bang" -- the terms carry a lot of connotative baggage and are entirely misleading. Light's behavior has nothing to do with conscience observers. The Higgs Boson has nothing to do with "god," and isn't any more important than any other quantum particle. And the beginning of the universe was (most likely) not a massive explosion from a single point in space.
@@ecMathGeek this doesn't contradict my point
Definitely a very underrated channel that more people need to see. You should have your own Netflix special hosting along side NdGT! Thanks for making very difficult subject matter easy to understand and accessible.
"This would lead to a bizarre universe". As opposed to our completely non bizarre one? Lol. I find the universe pretty bizarre as it is.
Well perhaps, but it is comprehensible, not chaotic.
@Asymmetrical Horse light is diaper than wave and practical
@Asymmetrical Horse particles don’t “behave differently” you are interpreting wave/particle duality to mean that (for example) an electron is sometimes a wave and sometimes a particle, depending on how/if it is observed, but it’s not one or the other, the electron has *both* wave properties and particle properties at all times, and depending on the experimental setup one characteristic or the other will be observed, but both properties are always there. The so-called “quantum eraser” illustrates this nicely, see en.m.wikipedia.org/wiki/Quantum_eraser_experiment
Wave function, the total possible probability of finding a particle in any given location within the function as it is defined. This is like an upper and lower bound for the location as we understand particle interactions. Before we measure it, how do we know? We don't... That is why we measure... The function is either correct or not, measuring allows us to update the function. You cannot throw energy or another particle at a particle and expect it to continue doing what it was doing before. Meaning, once you measure it, you no longer know where it is because it was deflected by the measurement. But you can infer how fast it was going based on the particle that you measured with.
Multiverse confirmed
This is the best explanation about this topic I’ve ever had so far.
Hello
7:10 is what finally made me understand why the speed of light is constant for observers traveling at different speeds.
I love your enthusiasm, your presentations are inspiring and very appreciated. Thank you Arvin.
“Honey, I never drive faster than I can see. Besides that, it's all in the reflexes.”
Did you just quote Jack Burton in response to a physics video? Well played sir!
@@sonofawil who?
yes sir the check is in the mail
@@elck3 Jack Burton… ME!
🤣
I have never heard a presentation that talked about a universe without a speed limit. And I thought I’d listened to every lecture, and concept of the universe ever presented. This was a fantastic presentation
I normally don't comment on videos but this was something really interesting, thank you!
Fun fact: if c was infinite, that might also cause capacitors to hold no charge because at least one of the permeability or permittivity would have to be 0
True. I remember the capacity formula when he mentioned permeability.
This is true, but, there would be no matter, so, no capacitors either
I would say it is more a question of would these constants work in the same manner?
If we are making such a fundamental change as changing the speed of light, it is reasonable to assume lots of other things will change as well.
Wow, Arvin!!! I have never heard a talk like this that connects so many complex phenomena together in such a comprehensive manner...great production and graphics too!!! 👏👏👏
In Cosmic Scales, Light is Super Slow. It takes years to reach the next star, Lol. Once again, Great video with great insights !!
i think you have it wrong:
on cosmic scales, the universe is BIG. it takes years to reach the next start because distance is vast, not because light is slow
@@scruffytube5169 same thing, different wordings
@@scruffytube5169 And that is because the space itself could travel/expand at a much faster rate than the speed of light. We have no appreciation as to how large this value could be, perhaps the speed of light really is insignificant compared to the rate at which the space expands beyond the observable universe.
Causality might have something to say about that. That was his point about non-locality. However, think about the desktop toy, Newton's cradle, causation is happening everywhere at local scales. So yeah, it may seem like photons are "slow" as they traverse their lone paths, even if they feel no time. But literally everything is happening around it along the way. Measuring one photon is great for physics but it doesn't do us any good to try and observer the universe from that point of view...
If we are travelling at light speed, wouldn't we not age..and hence instant in out perceptive.. 🤔
Ah yes, one of the precious times the TH-cam algorithm recommends a new-to-me channel I truly love. I smashed subscribe instantly.
Are you also a PBS SpaceTime fan? Or MinutePhysics? Or SFIA? Or Physics Girl?
@@coopergates9680 PBS SpaceTime yes; gonna check the others out now, thanks for the tip!
@@ofconsciousness Primarily astrophysics? Or a few other topics also?
@@coopergates9680 yeah I follow a lot of channels. Two Minute Papers, Anton Petrov, Dr Becky, Jabrils, Short and Sweet AI, etc
@@ofconsciousness Computerphile and numberphile? Oh... and this one lol
th-cam.com/video/rYLzxcU6ROM/w-d-xo.html
10:08 - So the speed of light is really the speed of causality. Light just happens to be one of multiple things that's capable of traveling at the speed of causality. We call it the "speed of light" because light was the first thing we observed traveling at this speed.
Yes. That is a good way of putting it.
That was probably one of the best explanations I've seen. Really good visuals too. A must see.
Excellent as always Arvin. I cant believe Ive never thought about what the night sky would look like if the speed of light was instantaneous...... thats such a simple concept that has never crossed my mind before today. Thank you for bringing it to my attention, now I have more to ponder about.
I don’t think it would look any different if we assume that light attenuates by the inverse square law.
@@Tailspin80 but then we would be able to see beyond the cosmological constant, which depending on if the universe is infinitely big or not, then there wouldn’t anywhere you couldn’t see light from a far away galaxy/star anything with The homogeneous matter dispersal in the universe.
No loss of illumination from redshifted light, every wavelength visible at all times.
@@brianpj5860 Not sure, but wouldn’t the received light intensity be dominated by local sources? You would be able to see light from the observable universe but the distant sources would be very faint.
it crossed my mind just about 2 weeks ago. i think i am entangled with arvins brain
@@Tailspin80 I'm with you. When he said that, I was like, "not so fast, sir!" Even local sources of light become diffuse over space alone. Time diffusion seems unnecessary in order to have a universe of infinite light speed. Light traveling from an infinite number of light sources in the universe would have an infinite number of celestial bodies blocking them from our view. Come on!
Very well done! Really nice breakdown, and I truly appreciate your calm and sagely voice, which does wonders to relay the complex information.
Great video, some food for thought!
I wonder: if the speed of light was infinite, would it mean that magnetic and electric resistance of space would be zero? Would it make electricity and magnetism behave oddly as well, like easy superconductivity or something?
Yes, excellent point! Many things would be affected including EM forces, as well as gravity. You can't really change the speed of light without affecting a bunch of other things.
Thank you so much!
This is the first video ever that made me understand, why there has to be a speed limit for causality und why the speed of electromagnetic waves equals that speed.
This was fascinating. Thank you. I want more theoretical video like this, I’ll run through your channel now!
Light: *Goes as fast as the universe can allow*
Humans: Why don't you go faster?
Light: *Sad light noises*
that makes me think how would happy light noises sound lol
From lights perspective it gets anywhere instantly tho.
@@kaydens6964 ?
@@deltamico the faster you go the shorter the distance, once you reach light speed there’s no concept of distance
....and the light noises would be travelling almost 900,000 times slower than the light itself, so we wouldn't even know what made the noise
“There would be no agreement on causality”.... sounds like politics! Lol Great vid as usual- thanks!
That phrase makes no sense what so ever. If all observers can be aware of an event at the same time, there being no difference in the time taken for light to reach observers at different distances, then there would be uniform agreement on causality of events rather than the current relative effect that makes all observers disagree (and then need understand Special Relativilty to piece back what the sequence must have been). True that is not the universe we are in where one can use time delays beween receivers to calculate distance from a source (eg position with GPS), but I don't see that breaking causality. Indeed one could still be aware of one's position, if one used the reduced signal intensity through inverse-square law to calculate distance.
Inverse square law still holding would party break earlier argument Ash raises 4:00 that one would be obliterated by the radiation from a million hypernova in space reaching us at once. This is I think invoking Olbers' Paradox of why is the night sky not white from the light from stars if we lived in an infinite static universe (anwser being that light is finite, universe is finite in size, universe is finite in age, universe is expanding and red shift). With infinite speed light from beyond just the limits of the Observeable universe bubble (now 46 billion light year radius and light having travelled 13billion years) would reach us. However the intensity of that far-distance light would still be reduced by the inverse square law. Absorption of light by interstellar dust further reduces the intensity of received light. While given infinite time that dust then would heat up and start emitting light of its own as black-body radiation, that this does not occur is partly explained by the universe having existed for only a finite period of time and the universe is not static, but is expanding, so light from far off universe would still be increasingly diminished by inverse-square law. The final component to the solution to Olbers' Paradox in our universe is that the expanding universe also causes light to progressively red-shift for farther objects, which I don't think would still occur if light had infinite speed.
You are a lot closer to the truth than you realize. Mutual agreement = democracy.
If all observers agree you have objective or 100% absolute democracy.
The laws of physics conform to a principle of objective democracy.
The velocity of light is the same & equal for all observers, it is independent of the observer's perspective, it conforms to a principle of objective democracy therefore.
Democracy is the correct word to use here.
Objective democracy is a target or goal -- teleology.
Teleological physics (syntropy) is dual to non-teleological physics (entropy).
Syntropy (prediction) is dual to increasing entropy -- the 4th law of thermodynamics!
@@bi1iruben Imagine writing a large paragraph in a youtube comment section over a joke.
@@bi1iruben I wanted to post this same question myself. In a universe with an infinite speed of light, we are guaranteed to see events in the exact order in which they happen. How can that break causality?
@@31ll087 imagine complaining about someone writing a large paragraph in a TH-cam comment over a joke.
As a chemistry instructor teaching conversion factors and dimensional analysis - the realization that the speed of causality is a conversion factor between space and time BLEW MY MIND.
So if we are not moving in space, we are moving at C in time scale.
Hi again Arvin. You are becoming endearing! That was not there when I met you. Now it is. It is present in the expressions of your face as you speak. Very nice. Felicitaciones mi amigo!
Hey, this was very cool. I’m just impressed at the clarity of your delivery, the depth of your explanation and your visualisations. I’m glad I found your channel!
5:00 Can someone expand on this?
How / Why an infinite C breaks causality? how would different observers not agree that A caused B? Wouldn't both observers just see A and then B, but both would observe it at the same time?
Listening second time now. Maybe 🤔 after 10 times I’ll begin to understand.
@Nobita Plotiwst: He is Jeff Bezozs
The illustration of the flashlight on the train was superb. Perfectly visualized maximum speed even if you could measure it on the train from the standing reference. Beautiful. Thank you.
I watched this after watching a video that stated that we cannot prove the speed of light is constant depending on the direction. The example in that video mentioned a person on Mars could have received the signal in like 19 minutes and sending back the signal took only like a minute.
"In 1905...Albert Einstein killed the idea of the ether."
Michelson & Morely: "Are we a joke to you?"
I caught that too.
The ether is literally a placeholder for unknown functions
It takes a lot for me to downvote a video, but this sentence achieved that for me. The Michaelson-Morely experiment in 1997 killed the Ether, not relativity.
@@NeilFein you got a typo, it's 1887 - but you're right
Wouldn’t be the first time he stole credit for something.
Haven't watched it, but to answer the question directly(as I think it is), if light's speed could be infinite, then a blackhole wouldn't be able to keep it from escaping its gravitational pull.
I follow a lot of Scientific TH-cam channels, but You, sir have answered all questions my head asks at 2am. I will now like, suscribe and sleep soundly..
This was one of the best videos I ever watched: You really nailed explaining thing fundamental principle simply! AWESOME!!!! WELL DONE!!!! I literally (Not making it up) got goosebumps
You actually got something from this video? Oh. Well you must be able to say why the speed of light is not infinite then?
He said it the video. Space fabric puts up a certain resistance which limits how fast light can travel through space.
@@b4ph0m3tdk9 Yes. These are called permeability & permittivity. But why is light slowed down by these? Arvin Ash doesn't say why. He just says they give some resistance. The click bait-ness of this video becomes more obvious the more you delve into & think about permittivity & permeability. ok sorry but wall of text because it's complicated:
Boze Science explains permeability nicely using simple diagrams. Space does not bend magnetic field lines because it has low permeability. Iron does because it has high permeability.
Permittivity is found in 2 basic equations: force between 2 charges = QQ / 4pi times permittivity times r squared
& capacitance = permittivity times area / the distance between the capacitor plates
The reason why permittivity increases capacitor is explained by DrPhysicsA & Eugene animation guy whathsiname & there's a video by...can't remember non-Ivy league US university videos with few views can be very good sometimes.
Materials with high permittivity are insulators eg plastic. The atoms in the plastic become polarised when the plastic is placed in the middle of a capacitor. The electron clouds get pulled towards the positive capacitor plate. This strips the plastic atoms of their electrons clouds & effectively causes a mass of positive charge to appear near the negative plate. Electrons love this & try to cram onto the negative capacitor plate to get near to the positive charge in the plastic. Thus you end up cramming more electrons on there. Thus the capacitance has increased.
This process probably happens in a vacuum as well but on a smaller scale. Veritasium's video 'Empty space is not empty' shows that it isn't empty. & physicists seem to talk about vacuum polarization & maybe electron-pair shielding around an atom or something with Feynman diagrams. I dunno about this stuff yet.
But this polarisation process can explain why force between 2 charges is inversely proportional to permittivity because when something becomes polarised the positive & negative parts are separated & there is an electric field between them which acts in the opposite direction to the electric field which caused the polarisation in the 1st place. Effectively the atom (or smaller thing) is acting like a spring. It takes energy to move the electron cloud away from the protons in the nucleus. NB Like a spring.
The way in which permeability slows down light is a hard nice puzzle. At least this video has made me think about it. What i have now is that the magnetic part of light is basically a form of momentum. (See G Chang's vid = hydraulic analogy of LC circuit). & a big object with momentum takes time to slow down. Time. It takes time to slow down.
What slows it down? I think the spring of polarisation that occurs in dielectrics & in vacuum. Plastic has high permittivity because you can spend a good 15 minutes pulling & stretching those electron clouds. Ok not 15 minutes but a long arse time. They like being stretched. Stretching things can take a while sometimes. It takes time.
Don't ask me why there's a square root in there c = 1/square root of permittivity times permeability. i do not know why!
(Yet)
i think DrPhysicsA is really going to help me today with his video on reactance.
So the video title effectively asks why are permeability & permittivity not zero? Also it asks why do these 2 values slow light down? If they were 0 then c would not get slowed down. It would be infinite. Since Ash does not answer these questions other than a very brief "it causes resistance" the title is click bait. It's a shame as his videos are pretty good IMO & I do learn things from them.
@@alwaysdisputin9930 Fabric of space it self sets a limit for how fast information can travel, but the resistance mentioned does NOT slow light down, as you say, it takes energy out of light.
@@b4ph0m3tdk9I agree it takes energy out of light but see the equation at 1:20
v = 1 over √ɛ₀ μ₀
See also Arvin Ash's video 'Why is the speed of light what it is? Maxwell equations visualized'
th-cam.com/video/FSEJ4YLXtt8/w-d-xo.html
v = 1 over something means 'inversely proportional'
So as ɛ₀ μ₀ go up, then v goes down
For example, glass has a higher ɛ than space therefore light travels slower in glass, this causes refraction
Another way of saying it is c² = 1 / ɛ₀ μ₀
which is interesting because E = mc²
& nukes release a lot of energy because E = mc² & c² is huge
which means nukes are powerful because ɛ₀ μ₀ are near to zero
i.e. nukes are powerful because space doesn't slow light down very much
Edit: This comment initially started with 'No v = 1 over √ɛ₀ μ₀
which was a bit harsh & unskilful of me because i was focusing on the thing i disagree with whereas I agree that: the resistance in space takes energy out of light. I think this is true because empty space is not empty & vacuum polarisation occurs & that is like compressing a spring which takes energy
To photons, everything happens instantaneously.
So nothing happens?
Turtles perceive everything the same way.
@@moistmike4150 what?
@@tuneboyz5634 Turtles perceive everything the same way as photons. Google it.
You an Ubuntu fan?
I love this channel because it give best explanation on TH-cam
I loved this video! TH-cam subtitled it for me. I'm of Spanish talk. Great job!!!!!
Several months ago, I read someone's comment proposing that if we live in a simulated reality, then the speed of light/travel in space has to be limited as the "Matrix" needs time to load the remote scenes when one travels in simulated space.
Marvellous explanation of the matter! Most importantly that it's not the speed of light but on the most general scale the speed of causality which defines the universe!!!
Light's intensity would still drop with the square of the distance. You still wouldn't have a fully bright sky and the super novas would still not kill us. Also causality would still be conserved, because you would get Galilean transformations and they are consistent too. But the one comment down there is right, e0 or m0 would need to be zero and that would be bad news for electronics.
May you please elaborate on why it would be bad for electronics🥺.
This is a good one Arvin. I like how you give a new look to physics.
You are such a great explainer. Magnificent!
Thank you so much for your videos... they’re incredibly interesting and inspiring, and so well put together... Bravo my friend!
Thank you. Much appreciated.
@@ArvinAsh Great explanation for permittivity and permeability. And if we can understand these terms then relativity is much easier! But now question arises to my mind, how can we calculate that property of space that affects speed of electric and magnetic field.? I mean it seems like a simple constant in an equation just as G constant in newtonian gravity equation. If this works there then it should work there too(am I wrong again).
BUT the MOST Major of my all questions comes now.
Hw did scientists actually found that electric has finite speed(means it is travelling out of charge)? And also how did they found its velocity then after confirming that it has finite velocity? Make a video on that 🥰please.
You touched on refraction. The eye can only form an image when the curvature of the eye (and lens) refracts light onto the retina. We could not ‘see’ as we do now. Could seeing even be a thing? My expensive DSLR would be useless? Could I get my money back?
Your eye will be useless ask god to return you money
DSLR work on different properties, but the lense is not part of that. You can change the lense. In your eye the lense changes, no need for extra parts. If you tried taking pictures without a lense... Would they still give your money back?
@@Robert_McGarry_Poems 14 days time over....so now its late to claim for ur money
You shouldn't have bought into the hype and been content with your phone camera
Everything that you “see” is resolved by a “graphics program” running in your Visual Cortex, which is your brains “graphics card”.
Still the most informative YT channel. Please keep educating Arvin!!
this channel = physics + philosophy. the only channel on youtube that I have found to have this quality.
This is a very good channel, but there are some others that address philosophy of science. "Up and Atom" is one.
Veritasium, Vsauce, Carl Sagan's lectures
There was a brilliant communication moment on the train. The light moving from the stationary observer and the light moving from the train passenger move at the same objective speed. The train passenger perceives the time component of "m/s" differently, which is why the "photon speed + train speed" paradox doesn't apply. Thanks for sharing. This was interesting.
why the need of slowing time? since light is massless, it doesn´t gain any „push“ from train, it simply starts to propage itself through space at it´s speed, no matter if source of light is moving, or not, right?
@@7JeTeL7 _"why the need of slowing time?"_ - watch the video at 7:30 again. From the outside observer's point of the view, the relative speed between the guy on the train and the light is less than c (it's c-v, where v is the speed of the train wrt. the outside observer). If the observer on the train would use the same length and time measurements as the outside observer, he would necessarily measure that slower relative speed of the light.
In reality, he measures speed c.
@@renedekker9806 i don´t think so; guy in the train would measure distance for which light travelled from point (that point is obviously not in the train; it would be something outside the train, like telegraph pole or something) where he turned flashlight on...this would not aplly for, let´s say, gun; i am moving in train with 0.5 bullet speed and i shoot from the gun same time like someone outside, while passing him; my bullet would be 1.5 bullet speed(since it´s carring momentum of the train) while bullet shot from outsiders gun would travell it´s regular speed; both would see, that train bullet is faster, while in experiment with light speeed would be same(since it doesn´t carry momentum)
@@7JeTeL7 _"guy in the train would measure distance for which light travelled from point (that point is obviously not in the train"_ - the guy on the train obviously measures the points on the train. When we are talking about the speed of light, then it is measured wrt yourself. When you are on the train, then obviously, that is on the train.
_"while in experiment with light speeed would be same"_ - Exactly, the light from the flashlight on the train measures as speed c for both of you. The light from the flashlight outside the train ALSO measures as speed c for both of you.
@@renedekker9806 i am sorry, but guy in train must always count from starting point/or, if he chooses train itself as reference point, he must add distance which he travelled from that point during measurment; both approaches give same speed...massless property of light is, that it doesn´t matter how fast its source moves; source of light doesn´t give momentum to light, so it´s speed is constatnt, no matter where it came from...why slowing time to solve this?
But from the point of view of light itself, a photon doesn't experience time and so wouldn't that mean that it leaves and reaches its destination instantly ?
It depends on the point of view that you are looking at it from, relativity!
C is not a fundamental property of universe. It is only a fine tune convention to obtain more precise data, necessary on then new quantum mechanics.
Nobody knows if light in other zones of Universe is lower or higher, presuming the vacuum is equal everywhere, which is an epic presumption...
@@rubenangelvarisco9719 That's true and I didn't think about that if I'm honest.
Thanks for the reminder.
I think a better question to ask would be: what would happen if "c" approached infinity?
This would get rid of the causality problem to some degree and mostly give us Newton's mechanics.
@Zhang ShiYing can you provide an example of a setup in which some measurement doesn't approach a limit as "c" approaches infinity?
It might exist, but I can't think of one, so my question stands.
And the Universe definitely won't happen all at once cause speeds below "c" exist. I mean, most computer physics engines work as if "c" is infinite.
@Zhang ShiYing ...and that's relevant how?
"c" is a parameter, we can take a limit of any measurement as "c" approaches infinity while other parameters remain the same to get a model of the world where "c" is infinite.
crazy how ive been discussing my interest in quantum mechanics to my coworkers in fast food and they ask me pretty simple questions in response about this exact topic! very serendipitous.
this is a 5-star science video Arvin that should be shown in every school science class. thank you thank you for living proof that the internet can increase the spread of human understanding
FINALLY!!! Clarity on the space/time/causality/locality/speed of light relationship!!! Best one I've ever come across!! Profoundly appreciative for the Enlightening presentation (pun intended)!!!
Ask the thing called “Singularity” where time and space switch roles.
source?
There are old vids of him that have already discussed the topic. Namely the black hole and parallel universe ones. He've got an interesting diagram concerning that.
Plus, it is location inside the event horizon where time and space switches role, not only the singularity.
(according to his vids, if I didn't misunderstand)
Time and space switch roles at horizons. Singularities don’t physically exist. They are mathematical issues that arise with coordinate systems applied to highly curved spacetime.
Time is just a description of change... don’t know what all the fuss is about.
@@davidkincade7161 Are you sure? Things also change over space
What a video! He's underrated!
I hope I can give a suggestion. Changing the channel logo may bring more viewers, that is why I saved this vid for the last and it was the best on this topic! It brings the feeling of an Indian youtuber who uses Xenogenesis as his intro song. Just trying to help. Again, fantastic video!
The theory of ether was killed way before einstein, as far as I remember by the michelson Morley experiment in the 1880s.
You must have lived a long time to remember that experiment! I had no clue the average Joe of the 1880's was even aware that such an experiment was taking place by the elitists philosophers of the time
That's the render speed of the computer that runs this simulation. They needed to set a limit so the game engine is able to keep up with players moving.
Interesting thought. I don't know if you're serious or not.
@@johnmckown1267 Some experts think we might live in a simulation so if that's the case than the game/rendering engine must have limits. For example our primitive engines have LoD and Draw Distance to keep things smooth and manageable. The universe engine might have the Speed of Light limit for the same purpose.
I know some scientists have invoked the simulation hypothesis based on presumed probabilities. I even made a video about it. But realistically, I don't think we live in a simulation. There is no evidence that we do. All the hype is based on statistics, which are based on presumed assumptions about the future, and not on any known probabilities.
@@ArvinAsh I like what Sabine Hossenfelder more or less said. If you can't measure it / observe it / test it, it's not science, it's religion/belief/philosophy.
@ There is something about the results of quantum mechanics that really feel uncomfortably like looking at the edge cases of an optimization from the inside. Like maybe entanglement and late resolution of variables leads to easier calculations or a huge reduction in storage requirements. A good analogy might be floating point math. It lets you work with really big numbers and is largely correct for a pretty nice savings in storage. However, its not too hard to get some shocking results with it if you didn't realize how it worked to begin with.
The little curvy e symbol (Greek letter epsilon) is the permittivity of space. It is the capability of a vacuum to permit electric fields. Or to put in his terms, the permittivity is the resistance the electric fields experience.
The little u shaped symbol (Greek letter mu) is the permeability. It is the capability of space to allow the formation of magnetic lines of force or magnetic fields. Again, using his terms, the permeability is the resistance the magnetic fields experience.
Since we are dealing with electromagnetic waves which are nothing more that alternating electric and magnetic fields, it makes perfect sense that the speed of the waves would be affected by both factors.
Most underrated channel on TH-cam
Probably one of ur best episodes Ever Arvin. 🙌
Absolutely brilliant, my favorite video so far! I understand so many things now that I was never really able to reconcile during physics class.
if we disregard the extreme cases of 0 and infinite value, it is interesting to ask how would the universe be if the speed of light was 1/100 or 1/10 the current measured value. Both general relativity and quantum physics does not depend on any explicit value for c just it is finite. Is the universe invariant to all finite values of c.
Different finite values would mess with some of the other constants of physics, possibly preventing the formation of atoms, etc. I’m sure some minor variation would still work.
There was once a science fiction story where the speed of light was imagined to be 20 MPH. I don’t recall the author or title. It may have been George Gamow.
@@laurelcreek7
Yes I read it years ago. It was George Gamow, Mr Tompkins in Wonderland, first published in 1939, it’s a short story.
Here’s a snippet…
When he opened his eyes again, he found himself sitting not on a lecture room bench but on one of the benches installed by the city for the convenience of passengers waiting for a bus. It was a beautiful old city with medieval college buildings lining the street. He suspected that he must be dreaming but to his surprise there was nothing unusual happening around him; even a policeman standing on the opposite corner looked as policemen usually do. The hands of the big clock on the tower down the street were pointing to five o’clock and the streets were nearly empty. A single cyclist was coming slowly down the street and, as he approached, Mr Tompkins’s eyes opened wide with astonishment. For the bicycle and the young man on it were unbelievably shortened in the direction of the motion, as if seen through a cylindrical lens. The clock on the tower struck five, and the cyclist, evidently in a hurry, stepped harder on the pedals. Mr Tompkins did not notice that he gained much in speed, but, as the result of his effort, he shortened still more and went down the street looking exactly like a picture cut out of cardboard.
archive.org/stream/MrTompkinsInWonderlandMrTompkinsExploresTheAtom/tompkins_djvu.txt
@@cloudpoint0 That's it! Thanks very much.
@@cloudpoint0 I think the author does not take into effect of relativistic effect as in special theory of relativity into account assuming it is valid in such a universe. The cyclist and all others would still be moving at a very very small fraction of 20mph exactly like we do now with respect to 300000 km per sec. But thanks for the link. It will be an interesting read.
I find it interesting that the speed of light is "algebraically infinite" in the sense that the group of real numbers under normal addition is isomorphic to the group (-c,c) under velocity composition in SR. In other words, if one was to "squish" the group of real numbers under addition to fit in an interval, the binary operation to equip on the interval is precisely velocity composition in SR.
Oaaw woh what did I read!!
I understood most of the words.
Another great video. Thank you for explaining it in such an understandable way.
*Arvin*, I have a question I've never seen answered (or asked for that matter!) concerning the speed of light being the limit at which information can be transmitted. It's a though experiment, but please bear with me.
❓ Imagine I have an extremely long, thin cylinder of a solid material. For this example, say this object is just over 11,000,000 miles long (i.e. a light-minute) and an inch in diameter. I am at one end of the 'rod' and have a person/receiver set up at the other end. If I instantaneously push the rod say a fraction of an inch toward the receiver and send him a pulse of light, will the person at the receiving end detect that I have pushed the rod instantaneously - i.e. a full minute before the light pulse arrives?
If so, I can use this mechanical set-up to transfer information much faster than sending him a pulse of light.
If this is fallacious, what explanation limits the transfer of information using my 'rod' to the speed of light or less?
The person would not feel your push on the rod instantly, In fact the wave or your push would travel much slower than the speed of light, because each electron in each atom would have to bump into the next atom, which would have to bump in the the next atom, and so on for 11,0000,000 miles. This propagation is normally so fast a ordinary lengths that you think it is instantaneous, but over long distances, it would propagate quite slow compare to speed of light.
@@ArvinAsh I studied mechanical engineering in college, but I learnt both special relativity and quantum mechanics in a course on modern physics. One of the consequences of special relativity-as you just explained to Steve-is that no object can be perfectly rigid. Otherwise sound waves within that object would travel at infinite speed.
That was okay for another course, _Strength of Materials,_ where they taught us to calculate stresses and strains-deformation under different types of forces. All using tensors, because we were big kids now.
On the other hand, there was yet another course on rotations of solid objects-you know, angular velocity, moment of inertia tensor and all that. The professor always started off assuming a perfectly rigid object: One that does not get deformed as it rotates or when forces and torques are applied to it.
Taken together, it was all very weird: Solids cannot be perfectly rigid, but they have to be in order to rotate. I mean, if you want to pass one course, you have to believe certain things. To pass another course, you have to believe the exact opposite. And you have to pass all the courses to get your degree. I can imagine how hard it must have been for Lewis Carroll's Alice when asked to believe in impossible things!
And so today I'm completely disillusioned with the way students are taught science. I'm not surprised that so many people drop out, don't trust science, are superstitious, believe in the supernatural and weird conspiracies, endanger everyone through rash acts, and end up voting for unsuitable candidates.
@@ArvinAsh What if the density of the rod is very high, or the distance between atoms is very low?
@@shahkarimi3587 then wouldn't atoms/electrons have to travel more to bump each other?
@@nHans I'm only a sofware engineer, with a BSc., and I'm not the best in physics, but as I can see it, one of the worst thing in modern physics (education) is that we still talk about "objects" (made of some kind of (solid, rigid) matter) even at a university level. I mean, it's pretty good model for Newtonian physics, but seems very poor model when talking about particles or huge objects of the universe. (But maybe, it would be the best to not talk about (solid) objects when even when discussing "normal" things. It always annoys me, that if we analyze for instance the forces and movements of a bus and inside of it... then we would consider the seats as part of the bus (same object), because it moves relatively together with the whole bus. Then we would say that the people standing inside the bus are not part if it. But if they sit down, and hold themselves tightly, then they behave like they would be almost the part of the bus... just because of the frictions. Whereas in the reality, nothing there is really 1 object. There are many-many particles interecting with each other.)
Great video again, Arvin. One question though: on the part where we see both the stationary observer and the moving train observer flashing their lights in the same direction as the moving train, the stationary observer would see the train observer's flashlight's light with increased frequency, while the train observer would see the stationary observer's flashlight's light with decreased frequency, right?
Yes, frequencies would be different. Speed would be the same.
@@ArvinAsh how is it possible when energy is same
I guess length of wave differs right
@@s_i_am-R Energy is a conserved quantity that arises in a time symmetric system according to Noether's theorem which shows that for every symmetry in nature there is an associated conserved property/quantity.
In relativity the rate of time is not the same between observers thus the energy will not be the same between different frames of reference. Energy still holds within a specific frame or reference and because there is a conversion factor between the rate of time in two reference frames you can still define an energy transformation between reference frames allowing the property to continue to be valid but the energy between two different frames of reference will always be different.
@@s_i_am-R To wrap my head around that, I like to think of frequency for light as a sort of placeholder for mass in the sense that a more massive object (or in the case of light, a higher frequency) would have more energy than a less massive object (or in the case of light, a lower frequency) moving at the same speed.
@@s_i_am-R I guess the moving source has to give some change in the property of lights. So here energy may be increasing in effect with increase in frequency.
Suppose we could not see light, and used sound waves to navigate about in our lives, how could we measure the speed of causality? Furthermore, suppose the speed of causality was actually a little higher than the measured speed of light in the vacuum, how could we detect this?
I often wondered in what sense space and time 'switch'; and now you've highlighted the connection between the two. Great stuff.
Very interesting video but one question I have is unanswered: what would happen if the speed of light slows over time? For example, what if it was (near) infinite at the Big Bang and then gradually slowed to its present day speed? Is that possible and, if so, how would it affect our universe?
Perhaps it is slowing, and we perceive that as an expanding universe...
@@eclectichoosier5474 wow... have we just solved one of the biggest questions in physics?
@@markrobinsontraining I'm guessing..... no.
Now you gave us a full range of information. "All in one" ! Genial!
4:00 uh no. Quadratic fall off for light propagation would still be real.
I was thinking this too!! Especially the bit about the night sky being totally lit up
@@skyscall I think there would be a little more light because light from all the stars beyond our observable universe would still reach us.
@@djayjp , true, whatever stars are currently beyond our view would come into view (we have no way of knowing how many that would be), but we would also lose some light, because already dead stars wouldn't be showing in our sky like they do now.
@@SgtSupaman Ah very true forgot about that. Cheers
Meanwhile in the same universe, the delayed choice quantum eraser experiment breaks locality or causality or both.
Pretty sure its locality Quantum mechanics doesn't care about locality as the quantum wavefunction of everything extends over all space but causality still matters as in information still takes time to propagate even through quantum interactions that are nonlocal i.e. quantum entanglement. It seems a natural consequence then to suspect that space is emergent representing the universes resistance to information propagation per time interval or the amount of bits of information that can react at any timestep or fundamental (plank?) time unit.
Regardless like you said the delayed choice quantum eraser and bells inequality either space or time in an emergent property rather than a fundamental element of reality. Beyond the plank limit at least one but possibly both cease to have any meaning and are derived of some deeper fundamental principal or quantity. Throwing away space just seems the easier path to reconciling relativity with quantum mechanics. Regardless it tells us that stuff at or beyond the fundamental limit is really alien
But the quantum eraser experiment does not break causality. It just demonstrates a paradox. And all paradoxes are, by definition, based on flawed logic or bad science. A paradox cannot exist. QED
@@BritishBeachcomber But it doe break both locality or causality or both. Check what scientists in physics says about it.
@@BritishBeachcomber The flawed logic is to assume causality and locality. The experiment don't tell us what, tho
Great video, clear explanation, nicely put.
Thank you, Arvin, for such a great video. I have one question: We know that the Universe is expanding in an accelerated manner. The expansion means stretching of space-time which also includes vacuum I believe. I was wondering why it doesn't affect the speed of light? At the end of the day, even if we don't have the so-called aether, photons still glide on the fabric of space-time. Am I missing something very fundamental? Is it because their wavelength and their frequency change and adjust themselves to maintain the speed? I was trying to relate the fabric of space-time with stretched vibrating strings in which the velocity of the waves depends on the material density of the string. The permittivity and permeability should change as space expands if we consider how a normal fabric acts when stretched.
Yes the wavelength of the photon stretch, that is why far away objects are redshifted. The expansion causes the light to "stretch" :)
_"In 1784, John Michell proposed, in the context of Newton's corpuscular theory of light, that if the escape velocity from a mass exceeded the speed of light, then the mass would be invisible. In his picture, light emitted from the object would go up, curve around, and come back down.Michell's picture is enticing, but it is different from what general relativity predicts. General relativity predicts that any light emitted within the horizon is dragged inward, even if the light is pointed directly outward. The picture at left, which shows light going up, turning around, and falling back down, is misleading.Imagine light rays, photons, as fishes swimming fiercely in the current. Outside the horizon, space is falling into the black hole at less than the speed of light (or the speed of fishes), and photon-fishes swimming upstream can make way against the flow. At the horizon, space is falling into the black hole at the speed of light. At the horizon a photon-fish swimming directly upstream will just stay there, swimming like crazy, but not going anywhere, the inward flow of space exactly canceling the fish's motion. Inside the horizon, the space waterfall falls faster than the speed of light, carrying everything with it. However hard it tries to swim upstream, the photon-fish inside the horizon is carried by the flow of space inevitably inward to its ultimate fate.
_
_In the image at right, the (happy) fish upstream can make way against the current, but the (sad) fish downstream is swept to the bottom of the waterfall. This picture was drawn by my daughter Wild, and provided the cover image for the June 2008 issue of the American Journal of Physics^4.
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_Doesn't relativity say that nothing can go faster than light? It is true that nothing can travel through space faster than light. However, in general relativity, space itself can do whatever it likes.
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_The idea of space moving is one that you may have met before in cosmology (the study of the Universe at large), in the notion that the Universe expands."
_
jila.colorado.edu/~ajsh/insidebh/waterfall.html#schw
(TY YT for completely not italicising)
I really liked Action Labs video about white holes. If we pee into our kitchen sinks then the pee creates a circle. Or alternatively turn on the tap & it creates a circle. I prefer the pee method however. Action Labs says this is called a 'hydraulic jump'.
Action Labs shows the hydraulic jump is like the event horizon of a white hole because waves can only travel 1 way.
(& IMO a white hole is a time-reversed black hole)
Practical Engineering's video 'What is a Hydraulic Jump' is illuminating for showing this: th-cam.com/video/7tjf8HWiR3Y/w-d-xo.html
The pee hits the sink & travels towards the sink walls. A wave is created which is reflected & travels towards the sink hole. Then the wave gets stuck. Why? Because it's speed matches the speed of the pee underneath it. The stuck wave IS the hydraulic jump. It is like a wave on a treadmill.
It seems therefore that the answer to your question is that the wave doesn't care about the universe being stretched underneath it. It travels on top.
@@TheOnlineBlackboard Thank you for replying. If I am not wrong, the color is characterized by frequency. Wavelength changes I agree due to expansion. Then to preserve the speed of light, the frequency changes as well and that's why the color. So the universe tries to preserve the speed of light. This isn't how normal fabrics work. The velocity changes with the stretch as the density and hence resistance changes. But here the resistance (those two constants) stays the same no matter how much it is stretched.
If I was traveling at the speed of light, and I looked at some light, would I measure it to still be traveling at the speed of light, or would it seem to be still, relative to me?
You would measure it to be traveling at C. The speed is the same no matter how fast you are traveling. Time would also seem to tick normally for you. Only when you stopped and compared the time on your watch to someone standing still would you see a difference.
In addition to what Arvin said, note also that you cannot travel at light speed because you have mass :) As your speed approaches c, the energy required to accelerate would approach infinity.
@@ArvinAsh So time wouldn't be "stopped" for an observer traveling at c?
@@aclearlight I can't say what would happen exactly at C, since nothing with mass can travel at that. But no matter how close you got to C, 99.99(infinite 9) - from your perspective, nothing would be different.
@@aclearlight
If you travel at c, your trip would take 0 seconds from your frame of reference, no matter what distance you are going. In turn, for a resting observer, you would appear to be frozen in time for the duration of the trip, but your trip still takes time.
One thing tripping me up a bit is that around the 3 minute mark Arvin explains since space exhibits a resistance to the propagation of electromagnetic waves, this sets up a finite limit to the speed of light. Explaining this as resistance implies to me that this would cause photons to decelerate and eventually come to a stop. Obviously this is not what happens, and before this I was fine with an arbitrary upper limit on the speed of causality, but now he has me wondering about the "resistance" property of space. 🤔
in the first 10 seconds of the video and already in a sense of awe! This is art
The funny thing is, for a photon, light does travel at infinite speed. When it leaves its origin, it will arrive at its destination instantly from the photon's perspective.
Hello, your comment doesn’t have sense, the speed of light has a value, hence the proton travel at such value.
@@10418 look up special relativity and time dilation
th-cam.com/video/ZGoDK18b3LE/w-d-xo.html
Very informative, thank you
The more I watch universe videos the more I become afraid that we are just someone's pc simulation. Speed is light is literally a set constant by the developers to ensure things work...
Bruh if we're in a PC simulation our developers are really shit at making good games. All the time they put into lore and the gameplay is trash.
This is more or less the conclusion I also came to a few years back.
What's the point of being afraid
@@ghotifish1838 because it would mean everything is worthless, and nothing you've ever done has mattered. Sure, being afraid versus not caring doesnt make any difference if that's what you're saying, but the fear of the possibility of this being true isnt really something many can control.
@@MrJohansen ye but since u can't control it why worry about it? It's like death, there's no point worrying your whole life about dying. Likewise there's no point in worrying about if we are in a simulation or not
PhysicsEminem has entered the room
it wouldn't stop causality from working entirely. You could still agree on the order of events at the same location. You just get the bonus of being able to agree on the order of events at all locations
Ohh that explanation of space/time continuum clicked with me. The constant of lights speed is a property of space fabric it self. Thanks
At least it appears to be, given we have pretty much no idea what „space fabric“ is, beyond an abstract concept. What‘s it made of, how can it expand and be curved by gravity etc.
I was literally imagining this question 4 days ago.
Same!
You were spied
This comment provides a fascinating overview of the history of our understanding of light, from classical physics to quantum mechanics, and explores the consequences of a universe with an infinite speed of light. It's amazing to think that the properties of empty space can have such a profound impact on the fundamental laws of the universe, and this comment does an excellent job of explaining why the speed of light is so crucial to the structure of space and time. Additionally, the mention of Magellan TV is a great reminder that there is always more to learn about the wonders of the universe, and I'm sure many viewers will be inspired to check out the service after watching this video.
If you were to design a workable universe, a speed limit is fundamentally necessary from a creative point of view.
.. And so is an all pervasive, inertial (as in momentum-conserving), quantised matter-energy field, I'd argue... I'd go as far as to say its as essential as the fundamental speed of the electrostatic force that carries light... This field is what the matter we detect is made of, as well as being the medium for the electrostatic force. The MM experiment and later experiments only disproved a type of aether (field) that by classical necessity must not interact with matter.. A single subspace field (or binary, 2 particle field) with ONE FORCE providing a mechanism for mass, that is able to emerge the Standard Model (minus its hypothetical, made up fudges) is far from ruled out...
But if the universe just came to life randomly on its own, it can only exist if speed limit exists. In any universe where there is no such limit, you are by definition, not there to observe.
To observe implies intelligent life. For life to evolve there must be a cosmic speed limit, otherwise emerging life would immediately propagate to the entire universe and destroy it, or itself. Ergo, we must live in a version of the universe where c is finite.
@@Tailspin80 It is more like the other way around. Intelligent life implies observation.
Universe does not require intelligent life, to exist. Infinite number of universes can exist without intelligent life. Amongst those, infinite number of universes can exist where laws of physics doesn’t allow even to structure emerge, and therefore life is impossible. For example there might be an universe where speed of light is infinite, time doesn’t exist, and the universe ends in an instant. Obviously there is no intelligent life there.
The fact that we are here thinking about it, observing our universe, implies that we are in an universe which ALLOWS structure and intelligent life to emerge. If there is infinite number of universes, and amongst those there is just 1 which allows intelligent life, we are necessarily in that 1 universe.
Shulk:"I'm feeling it"
Einstein:"you're already dead!"
Niche reference to awesome JRPG. I like it.
On man, that was such a clear explanation, thank you for answering this...
That's coming up right now!
the universe as the speed of light approaches infinity remains consistent so i don't see how causality is suddenly erased or how relative reference frames go away either - the speed of light, if infinite, means all people always measure it to be the same regardless. in fact, time dilation naturally goes away as the value of c approaches infinity.
Yea.....
Arvin. Your channel is amazing!
If speed of light was infinite we would see black holes.
Even if the speed of light was infinite, we wouldn't be able to see black holes as they wouldn't exist.
They wouldn’t be black then, must regular celestial bodies...
The universe doesn’t care about anything, whats there is just there..
Yeah, until we talk about quantum mechanics. Those little finicky things just "know" when being observed and act the certain way.
Thanks for the video, even as someone who has dealt with the subject, I really enjoyed this amazing explanation - that's an immediate subscription for me.
This makes great sense to me after this. Thank you. You can’t break the speed of light because that would break the causality chain. Light is the mediator of causality. Maybe as we approach the speed of light, the photons we are emitting start to build up against the photons in front of them, like you see sound waves do in front of an airplane that is about to break the sound barrier. This causes resistance to movement maybe. Maybe the Big Bang was caused by something that somehow broke the speed of light, which would mean that the object has broken the “causality barrier.” Sonic boom... Big Bang?
I’m literally just talking out of my ass.
The answer is way more simple than that. Basically whenever an object accelerates it takes exponentially more energy to move. This amount of energy is an asymptote with a limit at the speed of light. Any object with mass would require infinite energy to get to the speed of light. Technically if an object were to go the speed of light its mass would become infinite and that doesn't make much sense. Thats why only things with zero mass go the speed of light.
There actually is a photonic boom effect and recently scientist captured it on film no less
@@joule400 do you have a name of the paper? That is super interesting
@@Rangvald8909 @joule400
That’s called *Cherenkov radiation,* which occurs when electrons move at speeds close to 𝑐 through a medium other than a vacuum, for instance water, which has its speed of light at approximately ⅔𝑐.