12 ms·

Why nothing can go faster than the speed of light

• chime 16y ago
  For those not familiar with RobotRollCall (the author of the linked comment) check out his profile and other answers. He is one of the best contributors to AskScience and can explain almost any theoretical physics topic in understandable terms. People joke that he is actually Neil deGrasse Tyson and that he should really get this own column / talk show.
  • jimmyjim 16y ago
    She is one of the best contributors to AskScience
    • robertk 16y ago
      Who is she?
      • JacobAldridge 16y ago
        As far as I could tell from that conversation, she is anonymous and wants to stay that way. So RRC could be somebody massively well-known in the science world using this as a non-tenure approved outlet, or is masquerading as knowledgeable but is a patent clerk with no scientific credibility.
        • kenjackson 16y ago
          or is masquerading as knowledgeable but is a patent clerk with no scientific credibility. It appears that these patent clerks with no scientific credibility are some of the few great things the patent office has bestowed upon us.
          • deleted 16y ago
            [deleted]
        • deleted 16y ago
          [deleted]
        • syllogism 16y ago
          I don't think anyone could claim she's "masquerading" as knowledgeable, regardless of what (if any) formal education she's had.
          • neutronicus 16y ago
            It's a joke. Einstein was a patent clerk.
      • tastybites 16y ago
        http://www.charlierose.com/view/interview/10943 http://www.charlierose.com/view/interview/10943 This is the person who jumped to mind first.
      • mazsa 16y ago
        He is Brian Greene http://www.amazon.com/Fabric-Cosmos-Space-Texture-Reality/dp/0375727205 http://www.amazon.com/Fabric-Cosmos-Space-Texture-Reality/dp... (Cf. Index: 'speed of light', p.564), at least in this context:)
        • mistermann 16y ago
          How do you know?
          • mazsa 16y ago
            I mean, maybe it is a dog http://en.wikipedia.org/wiki/On_the_Internet,_nobody_knows_youre_a_dog http://en.wikipedia.org/wiki/On_the_Internet,_nobody_knows_y... who is paraphrasing Greene:) But who cares? It is Greene "at least in this context".
    • nandemo 16y ago
      Meta-comment: I often see the above pattern on HN. Someone writes a very informative comment with a minor inaccuracy. Someone replies to it only to correct that inaccuracy. The reply then gets way more upvotes than the original comment. I don't particularly care about "karma", so what bothers me is not that the original commenter didn't get enough points, but rather what people in the community think it's important in a conversation.
      • ryanjmo 16y ago
        I think the point that it was a she and not he is particularly important. I also think the point that the original commenter missed this point is particularly important. Knowing the HN community, that is the reason why the comment got voted up.
        • langarto 16y ago
          I think the point that it was a she and not he is particularly important Why? I don't see why it should be relevant at all!
          • petsos 16y ago
            It may not be important by itself, but it is important to be right. Her nationality may also not be relevant but if someone writes that she is Chinese and she is actually Russian (example), it is important that it gets corrected.
            • fedd 16y ago
              is she Russian? :)
            • tesseract 16y ago
              Fortunately this is not a common scenario, because the nature of the English language doesn't make it easy to inadvertently imply that someone is Chinese, Russian, or indeed any nationality at all. (I am aware that singular 'they' is grammatical. Doesn't stop it from sounding really awkward when the referent is a specific individual.)
    • kayoone 16y ago
      Why ? Someone states its Brian Greene in the comments => http://www.amazon.com/Fabric-Cosmos-Space-Texture-Reality/dp/0375727205 http://www.amazon.com/Fabric-Cosmos-Space-Texture-Reality/dp... because that passage is actually in there somewhere.
    • giardini 16y ago
      How do we know whether RobotRollCall is a woman or a man?
  • wnoise 16y ago
    Very understandable explanations -- unfortunately sometimes misleading explanations.
    • ars 16y ago
      Sometimes? Judging by the number of bewildered comments here I would say everytime!
  • cuchoperl 16y ago
    I would really like to see RobotRollCall in the Khan Academy.
  • tptacek 16y ago
    This is also a great one: http://www.reddit.com/r/askscience/comments/flzut/i_have_some_questions_about_the_big_bang/c1ho3ao?context=3 http://www.reddit.com/r/askscience/comments/flzut/i_have_som... More of her best-of comments would be most welcome. And, MORE THREADS LIKE THIS PLEASE.
• sabat 16y ago
  Good explanation of space/time -- in short, you're always moving in space and time, and the more you move in space, the less you move in time. Vice-versa. Brian Greene does a pretty good job of explaining all this in the Elegant Universe. If you're into this kind of thing, check it out.
  • ars 16y ago
    But there is no such thing as moving in space. You can only move relative to another object. You may even move fast relative to one object and slow relative to another, meaning your clock ticks at a different rate relative to each of those objects. There is no absolute clock - you can only compare your clock with someone else's clock.
    • sabat 16y ago
      There is no absolute clock - you can only compare your clock with someone else's clock. Look, I'm only a layman, but from what I understand, the speed of light is the absolute clock.
      • ars 16y ago
        But the speed of light can only be measured relative to YOU. So what looks like 90% of the speed of light to you, can look like 10% of the speed of light to someone else.
        • deleted 16y ago
          [deleted]
        • sabat 16y ago
          Actually that's just flat-out wrong. Light has an absolute speed. It's the only absolute thing in the universe. It's not relative. And -- this comes directly from Brian Greene -- the speed of light always looks like the speed of light, no matter how fast you're travelling. The speed of light never looks like 10% of the speed of light. It's always the same -- a constant.
• rdtsc 16y ago
  What helped me with a better understanding of time dilation is short paragraph from RobotRollCall: """ If you're moving through space, then you're not moving through time as fast as you would be if you were sitting still. Your clock will tick slower than the clock of a person who isn't moving. """
  • ars 16y ago
    Maybe it helped you, but it's utterly inaccurate and incorrect. There is no such thing as "moving through space". There is only moving relative to another object. And BOTH of your clocks tick slower! Relative to each other.
    • oewolf 16y ago
      If you're moving with a speed near the speed of light, time-passing for you will be slowed down compared to a person that is standing still. And if you would stay, say for a minute in that speed and go check on the standing person, you will perceive that she is aging very fast.
      • ars 16y ago
        No, you would see her aging very slow. Since you are standing still, and it's she who is moving near the speed of light. And if she checked you YOU would be the one aging very slow, since she is standing still and you are moving fast. You are still thinking in terms of absolute motion "you're moving". You are not moving, you can only compare your speed with someone else's.
        • oewolf 16y ago
          Hmm so if someone moves near the speed of light, time basically stops for everyone?
          • ars 16y ago
            Remember - he isn't moving near the speed of light THEY are. He is standing still. But if he accelerates then things are quite different, and much more complicated.
• thret 16y ago
  I found her lengthy explanation patronising and unhelpful. "you change your direction of motion through spacetime, but not your speed of motion through spacetime." This is article a long-winded way of restating the question, and leaves the reader thinking they know the answer when they simply have a different understanding of the same problem.
  • tel 16y ago
    Yeah, but a misunderstanding that's somewhat closer to the truth than before. Unless you want to explain Minkowskian spacetime, hyperbolic rotation, and its connection to Maxwell's equations... I think that coupling "motion through time" and "motion through space" like she explains is a good step forward from "cosmic speed limit".
  • akozak 16y ago
    Some might call that science. It's worth thinking a bit about what a satisfying answer might be like for you. Maybe there just isn't a way to understand or think about the question that's satisfying.
• ck2 16y ago
  Once you understand that, then read about (what I think is super-cool) : frame dragging. http://en.wikipedia.org/wiki/Frame-dragging http://en.wikipedia.org/wiki/Frame-dragging It causes satellites around earth to move a few feet each year.
  • lurker19 16y ago
    As I read the Wikipedia article, the frame dragging effect is hypothesized and has not yet been observed, though experiments have been designed and some are in progress.
    • ck2 16y ago
      They put two dummy satellites in orbit and measured the effect. Tried to find a better source but this will do for now: http://articles.cnn.com/2004-10-20/tech/warped.space_1_black-hole-lageos-frame http://articles.cnn.com/2004-10-20/tech/warped.space_1_black...
• joelmichael 16y ago
  If you were moving in a "completely horizontal" direction, wouldn't you not be moving through time at all, but only through space? That means you could move infinitely fast, not with a strict limit.
  • ars 16y ago
    No, you would not be moving at all. Compared to yourself you are always standing still, and your clock always ticks at what you think is a normal rate. Other things may be moving relative to you though and THEIR clock might be slow. (Unless you accelerate, in which case things get more complicated.)
  • uvdiv 16y ago
    Yes, but that kind of motion (tachyonic) is unphysical. It violates causality: you can imagine that by "rotating" the "horizontal" motion very slightly "downwards", in a different reference frame it is backwards time travel. The salient thing is that there are three disconnected classes of 4-vectors: timelike (massive particles), spacelike (tachyons), and lightlike (massless particles). Lorentz coordinate transforms can only take you between 4-vectors of a particular type: e.g. there's no inertial reference frame where timelike motion looks like tachyonic motion.
• jerf 16y ago
  Another way to look at it that is arguably simpler (and with greater loss, of course): Imagine the XY plane with every point described by integers in both X and Y marked. That is, (0, 0), (1, 4), (-2, -5), etc. Connect each of them to their four neighbors with a line segment. Now suppose you are at (3, 4) and you want to move to (4, 5), and you may only use the lines given to you. You move to the right, you move up, you're there. And you can move the other way, too, all the line segments are bi-directional. That works in space; that does not work in time. You can't stop moving or change direction in time. You can put X and Y on that grid and have something meaningful, but you can't say it's X and T; that would imply the ability to freely move back in time or forward at your discretion, which is not true. A simplified explanation of space and time's actual shape is that when you are at (3, 4) and you are moving through time (in the first coordinate, let's say), you've got lines that lead to (4, 4.1) and (4, 3.9) and so on, but the lines only go to a certain angle, which for simplicity's sake I'll say is the obvious 45 degree angle, which means you've got lines that go to (4, 3) and (4, 5), but nothing else below 3 or above 5. You can only move along those lines, and as there is no line to (4, -2) from your start position, there is no way to get there. The bound of those lines is the speed of light. The pictures of the "light cone" you may have seen are in some sense not merely a helpful picture but actually a true picture of the universe. You can not move faster than the speed of light because you can only move between connected points in the universe, and to move faster than the speed of light is to bypass that restriction. The universe is literally not shaped that way. The shape of the universe forbids faster-than-light. You don't have any choices other than those lines and none of the lines go faster than light. This is a grotesque simplification, but I think the core point is accurate. Exceeding the speed of light is impossible for reasons above and beyond the mere "exceeding the speed of sound" or other things were. To travel faster than the speed of light requires changing the shape of the universe. (And to the extent that certain theories permit it under some circumstances, such as the Alcubierre drive theory[1], I suspect that we'd find that even if we could implement one of these things the universe would still find a way not covered in those theories to shut it down, cosmic-censorship-style[2], or like [3]. I would also note that all "practical" FTL drives proposed to date have inevitably required the existence of at least one impossibility, such as stable negative mass, and it means little to prove that if I have one impossibility like stable negative mass I can have another like FTL.) Also, because this is a grotesque simplification, please note that picking apart holes in my picture is not even remotely the same as picking apart holes in the theory of relativity, let alone picking apart holes in the Universe. In particular don't get caught up with things that may appear to be going backward; that's an illusion of this attempt to embed an explanation into Euclidean space, not a real problem with the physics. [1]: http://en.wikipedia.org/wiki/Alcubierre_drive http://en.wikipedia.org/wiki/Alcubierre_drive [2]: http://en.wikipedia.org/wiki/Cosmic_censorship http://en.wikipedia.org/wiki/Cosmic_censorship [3]: http://books.google.com/books?id=_mo4AAAAIAAJ&pg=PA132&lpg=PA133&ots=MPipJx9GjV&dq=hawking+wormhole+time+machine+vacuum+explosion http://books.google.com/books?id=_mo4AAAAIAAJ&pg=PA132&#... (reading pages 132 and 133)
• jazzychad 16y ago
  I found that the author gave a great setup for an explanation, and then balked at giving the actual answer. > For right now, if you just believe that four-velocities can never stretch or shrink because that's just the way it is In other words, nothing can go faster than the speed of light because that's the way it is? The author needs to explain why the magnitude of this four-velocity vector is the speed of light! I was hooked after the first few paragraphs, but then felt like it dead-ended in a circular argument.
  • kalvin 16y ago
    She wrote several followup answers in the comments thread, one of which addresses your question (though it might not be satisfying!): http://www.reddit.com/r/askscience/comments/fjwkh/why_exactly_can_nothing_go_faster_than_the_speed/c1gi47a http://www.reddit.com/r/askscience/comments/fjwkh/why_exactl... Someone else wrote my favorite answer: "Basically, the way to think of it is not that light is the fastest thing, but rather that there is a speed, c, which the geometry of space and time demands is the fastest possible speed. One can also work out that anything without mass must travel at this fastest possible speed c. Light is one of those things, therefore light travels at c. It's only an accident of history that we call c "the speed of light": that's the context we discovered c's existence in. As for why it's the speed it is, well, it's the speed in our universe. It's actually much more natural to say c=1 and all speeds are then unitless numbers between 0 and 1. From this point of view c is 300 Mm/s because of how we chose to define the meter and the second." http://www.reddit.com/r/askscience/comments/fjwkh/why_exactly_can_nothing_go_faster_than_the_speed/c1gi276 http://www.reddit.com/r/askscience/comments/fjwkh/why_exactl...
    • scorpion032 16y ago
      As of today, meter is defined in terms of the speed of light. We have come a full circle! > The meter is the length of the path travelled by light in vacuum during a time interval of 1/299 792 458 of a second. via: http://physics.nist.gov/cuu/Units/meter.html http://physics.nist.gov/cuu/Units/meter.html
      • 16y ago
• ScottBurson 16y ago
  I would just explain that a photon has zero mass, but nonzero energy and momentum and finite velocity. Intuitively (meaning: in a Newtonian universe), one would think that a particle with zero mass would have to have infinite velocity to have nonzero energy and momentum, right? And yet, its velocity is finite. That demonstrates that the universe is not Newtonian. It also sets up an intuitive connection (which is what we're looking for here, right?) between the speed of light and one's intuitive sense of an infinite velocity. Again, of course, this brings us to the question of why the universe is this way: why it is Einsteinian rather than Newtonian. But that question really belongs to the realm of metaphysics, not that of physics.
  • ars 16y ago
    Actually that question is easy to answer. The universe is Einsteinian because otherwise e could not equal mc2. And if that were the case then stars could not shine, and a TON of other things would not work. Atoms could not exist either. The reason is that as you go faster you have more energy (obviously) and since you have more energy your mass increases. Since your mass increases you need even more energy to increase your speed (since now you weigh more). Take that to the limit and you find that as you reach the speed of light your mass goes to infinity. So it's necessary that it's impossible to exceed the speed of light - for example if you had two objects each traveling at 51% of the speed of light (relative to third placed in between them). Then relative to each other they are going faster than light - which means they have more than infinite energy. Can't do that. So relativity is necessary if you want mass to be interchangeable with energy.
    • diziet 16y ago
      You mean to say they will be approaching each other at 81%~ speed of light. http://en.wikipedia.org/wiki/Velocity-addition_formula http://en.wikipedia.org/wiki/Velocity-addition_formula Surely you must read up on modern physics a little bit, sir!
      • ars 16y ago
        That's the point - because relativity exists, the measured speed is not simply the addition of the two. I was explaining why that is necessary if you want e=mc2
• sliverstorm 16y ago
  eh, it's more fun to imagine we will one day surpass the speed of light. It hasn't been disproved so conclusively that I know about said proof, so as of yet I can continue imagining the barrier will be broken.
  • 83457 16y ago
    I like the way the Asimov talks about hyperspace, a currently unknown dimension that allows for "jumping" through/over huge segments of space without technically traveling faster than light, completely circumventing the issue of faster than light travel and extreme time dilation.
• tastybites 16y ago
  Does it work in the other direction, or can you only take away time velocity to give to space velocity? i.e., can you make your time slow down by coming to a full and complete "stop" in space, since I assume nothing in the universe is truly at rest?
  • burgerbrain 16y ago
    "So is there any such a thing as a complete and full "stop" in space" No, and that is why in a nutshell why this explanation is actually doing a disservice.
    • stcredzero 16y ago
      No analogy is perfect, in particular many analogies are trying to link our everyday experience with things that extend outside of it. If we take this and your statement further, we could just declare that all analogies are doing a disservice, and all pop science writers should be flogged.
  • augustl 16y ago
    Afaik you can. Relative to an observer looking at a black hole, time is at a complete standstill on the surface of the black hole, thanks to the extremely strong gravity. This time stop is (again afaik) why black holes stop shrinking.
• olalonde 16y ago
  This explains why there's a limit to speed but not why this limit is light's speed.
  • augustl 16y ago
    Afaik the answer is that the limit is the limit, and the speed of light is unlimited - but there is a limit, so the speed of light is the same as the fastest speed possible. So the limit is not the light's speed, they just happen to be the same.
  • ars 16y ago
    Are you asking why light travels at this speed? It's because otherwise light could not exist. If you are asking why the limit is this specific number then no one knows. But then again we don't know the reason for any of the constants.
• rbanffy 16y ago
  It's a good explanation, really, but do we need to have only one? Can't we keep Reddit things in Reddit and HN things in HN? If I am in a Reddit mood, I will go to Reddit. If I'm more in a HN mood, I will come here.
  • biot 16y ago
    Following your argument to its logical conclusion, HN should stop linking to external sites because if people are in a site X mood, they will go to site X, for any value X. For myself, I don't visit Reddit unless there's something interesting linked to from elsewhere, such as HN. Thus, I appreciate this being posted to HN.
    • rbanffy 16y ago
      > HN should stop linking to external sites because if people are in a site X mood, they will go to site X, for any value X Your reasoning is flawed. The value of HN is its community and the discussions it's capable of spawninf. There are sites for discussing an ampler spectrum of subjects (like, for instance, the nature of the universe and laws of physics) and sites for discussing news that interest specifically to hackers (according to the definition implied in the "Hackers and Painters" book).
      • SoftwareMaven 16y ago
        And that argument is exactly why the comment should be linked here. If the Reddit comment had been a blog post, everything would have been fine, right? I want to see the comment and get to stay here for the conversation.
  • AndrewS 16y ago
    I enjoyed reading the article, and I wouldn't have found it if it wasn't here on HN. If it shouldn't be here (according to the HN community) it wouldn't be sitting at the top of the news page.
    • rbanffy 16y ago
• retube 16y ago
  What I want to know is what happens if the arrow is rotated more than 90 degrees?
• csomar 16y ago
  The motion I'm referring to is motion in the futureward direction. May be you should consider the fact, that while you are not moving- let's assume that your are in space and way far from earth or any other thing-, your brain, heart and blood do. If they don't, you wouldn't exist. It's in my believe that we are living in a single dimension world, and it's not quite different than a dream; actually it's the same thing. Just think about it ;)
• sambeau 16y ago
  Stephen Hawking predicted that things can travel faster than the speed of light through quantum uncertainty. This is how information can escape from a black hole. http://en.wikipedia.org/wiki/Hawking_radiation http://en.wikipedia.org/wiki/Hawking_radiation Put simply it works like this: light travels at a constant speed, but due to quantum uncertainty nothing is in one exact place, it 'teleports' around an average point. Thus, if it 'teleports' in the direction that the light was travelling it has moved faster than the speed of light.
  • rbanffy 16y ago
    > if it 'teleports' in the direction that the light was travelling Yes, but those fluctuations average out very quickly.
  • aerique 16y ago
    So this would mean that on average nothing can travel faster than the speed of light?
    • ars 16y ago
      No, it means that the quantum world is very very weird. It's a strict limit, not an average. It's just that the quantum world has strange definitions of location.
• cgart 16y ago
  Oh, finally we got here cool discussion. Here is how I explain that one "could" travel faster then the speed of light! HOWEVER, and this is VERY IMPORTANT, this depends on your definition of the speed. So imagine following experiment: There are two space ships which are built like these russian matroshkas. One smaller space ship is in the hangar of a bigger one. The bigger one starts from the earth and accelerates to the speed of light (or just until 0.999c). Now, the smaller ship starts and can again accelerate from the bigger ship point of view until 0.999c. So, if there is just a simple velocity measure instrument, which is measuring acceleration by F = m*a, and we know the relative space ship mass "m" as it was relative to the earth, then knowing how much force our engine produces we can compute the acceleration. And hence our velocity measurement device will add small "a" to the current velocity by every thrust of the engine. So given that type of measurement, our smaller space ship can accelerate to the speed of 2c relative to the earth. HOWEVER, due to the relativistic effects the people living on the earth would never ever realize that this ship was moving with 2c, since they are measuring speed by looking how far the ship went in the certain amount of time. And due to the time dilation they will never realize that this ship was actually much farther away then it looks like. So, regarding to this experiment, we can travel faster then the light. However, this is only due to the definition of the speed. A counter argument would be that the mass "m" is also changing. However, one could argue that the mass is represented by the amount of particles per volume unit and hence remain constant if volume remain constant. Ok, another guy could argue again that the size of the volume shrinks, but I could then argue that if size of the volume shrinks, then the density of the particles per volume unit from the earth point of view would increase and could end up in a singularity or just black hole, so big bang ?:confused: This kind of experiment fits well into my experience of the world, where I just cannot accept some of the constraints we get from the nature :) Yes, you cannot travel faster then the speed of light, BUT this is only because I stay at the earth and measure your speed by looking how fast you come back. But this pure guy who is traveling could measure the speed as I've proposed and would then realize that, in deed he was faster then the "earth's speed of light" :)
  • CJefferson 16y ago
    Unfortunately, you are trying to impose a traditional world, where speeds are additive, onto relativity. It just doesn't work that way. A light beam fired from Earth would overtake the smaller ship, so in Earth's frame it is going slower than the speed of light.
• zrgiu 16y ago
  what I don't understand is why the light is the point of reference. Just because it's the fastest "thing" we know ? Or is there some other reason ?
  • jarin 16y ago
    Photons and gluons are the only two particles that we know to be massless and therefore capable of moving at the speed c (some neutrinos might be massless, but we know at least 2 of them are not). Since gluons are never observed as free particles and we're all familiar with photons, we call it the speed of light.
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• deleted 16y ago
  [deleted]
• adobriyan 16y ago
  My gut feeling is that article is dragged :-) into somewhat irrelevant things like Poincare group et al. Why maximum limit exist at all? How Universe without this limit will look like? How Universe with limit which is not equal to speed of light will look like? Antropic principle inevitably pops up.
  • ars 16y ago
    See my answer here: http://news.ycombinator.com/item?id=2244559 http://news.ycombinator.com/item?id=2244559 In order for e=mc2 you are required to have relativity. And a world without that could not exist.
• Stormbringer 16y ago
  People keep asking this, and similar things like "if you were travelling in a vehicle at the speed of light and you turned on the headlights, what would happen?" For me the easiest answer is to understand that from the point of view of the person travelling near the speed of light the beam of light moves away from them at the speed of light. So after ~1 second they are 300,000Km apart. On the other hand, from the point of view of a 'stationary' observer, the light and the spaceship emitting it are moving at almost exactly the same speed. So after ~1 second they are maybe 1 meter apart. How can this be? Our minds naturally want to reject this as nonsense. But the thing the gripping hand is holding that makes this true is that to the stationary observer and the person travelling near the speed of light time is moving at different rates. The person who is moving ~1m slower than the speed of light is experiencing time enormously much slower than the person 'standing still'. The time difference is 300,000,000 times (sic). Our brains reject this, because we think of time as an absolute rock solid constant, when in fact even with our primitive understanding and slow speeds we can demonstrate experimentally that time is in fact flexible, and it does slow down the faster you get.
  • Kilimanjaro 16y ago
    Say you just flick the lights on and off quickly just to let one photon escape. Where will that photon be in reality in one second? 300kkm apart from the rocket? one meter apart?
    • tel 16y ago
      The part that makes this so hard to grasp is that this question is ill-posed. The "in reality" part is nonsensical. A primary insight to general relativity is that it makes no sense to define location (or motion) except relative to an observer. This means there's no "true" position or motion, simply an infinite set of equivalently meaningful but disagreeing ways to observe them. (For interest's sake, acceleration is the lowest order local phenomenon. An object does not need an external observer to measure it's own acceleration due to the appearance of locally measurable "forces".) So the answer is to excise "in reality" and then state that both answers are equally meaningful and correct.
• vlisivka 16y ago
  Wave cannot travel faster than speed of wave in medium. Matter is form of electromagnetic wave, thus matter cannot travel faster that speed of electromagnetic wave in medium ("vacuum"). Everything that is not a form of electromagnetic wave, OR disconnected from electromagnetic medium, will be not bound to speed of light. Imagine water and water waves. Water waves will never travel faster than speed of wave in water. BUT, you can freeze water and push it faster than water wave just because it is not a part of water anymore. I hope, super-cold vacuum (below 0K) or matter in cocoon of super-cold vacuum will be able to travel faster than speed of light. PS. Of course, I cannot even imagine, how we can freeze vacuum, because we cannot even interact with it.
  • 83457 16y ago
    It is easier to just think of it as freezing ether.
  • ars 16y ago
    The entire point of relativity is that there is no medium. There are plenty of particles that do not interact electromagnetically - the neutrino for example. The speed of light has to do with the nature of reality, not the method of transportation.
    • vlisivka 16y ago
      Relativity is theory. We are talking about real world. We already know, that vacuum can generate particles, thus it is not completely empty: http://scienceblog.com/40901/theoretical-breakthrough-generating-matter-and-antimatter-from-the-vacuum/ http://scienceblog.com/40901/theoretical-breakthrough-genera... You can find much more information about faster than speed traveling here: http://en.wikipedia.org/wiki/Faster_than_light_travel http://en.wikipedia.org/wiki/Faster_than_light_travel .
      • ars 16y ago
        Relativity describes the real world. You seem to want to talk about theoretical ideas that have no evidence. You quite misunderstood that article, it's not the vacuum that produces the particles, it is the massive energy they are beaming that produces them. The stuff in the wikipedia article is just ideas that may work mathematically but have little bearing on the real world. At least for now. Maybe someday we'll figure them out, but for now it's just ideas.
• coderdude 16y ago
  It's a shame that about 30% of the comments in this thread are about how the author of the Reddit comment is female. I have a feeling the discussion on Reddit actually trumps the discussion on HN for this one. What's worse is that you have to wade through this irrelevance to get to the "good" comments on here.
• nazgulnarsil 16y ago
  Awesome explanation. But what I've never understood is what the universe looks like to photons. What does it mean for a photon to travel between two points from the frame of reference of the photon?
  • ars 16y ago
    Time does not exist for the photon, so from the photons point of view it is at both locations simultaneously.
    • nazgulnarsil 16y ago
      erm, i looked up the answer. frames are inertial, thus photons don't have a frame of reference.
      • ars 16y ago
        How so? Photons are inertial - meaning non-accelerating.
• Jun8 16y ago
  No answer can be given to this question, it is one of the axioms of relativity theory. The explanation is trying to explain the axiom in terms of the theory built on it. I found these answers to be more informative: http://physics.stackexchange.com/questions/2230/why-and-how-is-the-speed-of-light-constant http://physics.stackexchange.com/questions/2230/why-and-how-...
• Steuard 16y ago
  Two comments. First, as she alludes to in her edit, the "rotated arrow" picture that RobotRollCall uses here is subtly backward. It does suggest the right things and I used to think of it that way, but it eventually gets you in trouble. (In actuality, as you start to move through space, your motion through time speeds up... but this still leaves your arrow the same length because the geometry of space-time is hyperbolic: the Pythagorean theorem reads "x^2 - t^2 = c^2" instead of "x^2 + t^2 = c^2". This ends up avoiding LOTS of issues, some of which were stumbling blocks for people in the comments to her post. But it's certainly harder to visualize!) Second, several people have complained that RRC avoided the underlying question by saying "the arrow is always the same length". I think they may not be giving that answer the credit it deserves. Her claim isn't that the speed of light is the longest possible arrow (which I agree wouldn't help at all), but rather that every object's arrow has exactly this same length. That shifts the speed of light from being an arbitrary constraint to being simply a label for this universal fact. The question "Why is every arrow the same length?" is still valid, but there's much less reason to worry about it: no known process can change that length, just as no known process can change the rest mass of an electron.
  • Steuard 16y ago
    It doesn't stand on its own terribly well without some substantial discussion in class to back it up, but here's a handout that I've given to classes to try and discuss this stuff a little: http://othello.alma.edu/~jensens/teaching/classes/spacetime.pdf http://othello.alma.edu/~jensens/teaching/classes/spacetime....
• aufreak3 16y ago
  Here is what seems like a reasonable "explanation" to me - -- We figured out a few things about electric and magnetic fields. In particular, a changing electric field creates a magnetic field and a changing magnetic field creates an electric field. So if you setup a changing electric field in a specific way, you can setup a cycle between the two field types. Now, these fields hold energy and by virtue of this cycle, become capable of carrying away this energy - what we call "light" - just as waves on water carry energy away from the starting point at a certain speed. The strange thing about E and B though is that this "speed" is a constant that is independent of the reference frame you choose to monitor it. In other words, this wave would move at the same speed relative to you no matter how you happened to be moving and you can therefore never "catch up" with it. Therefore no "thing" (matter) can move faster than light. -- In physics, recursive "why"s always lead to "that's the way it is" tautologies. For instance, if atoms are mostly empty space, why don't we fall through the floor? Pauli figured out that no two fermions with same spin state can occupy the same space. Why can't fermions do that? They are spin-1/2 particles and their wave function amplitudes cancel out if you account for the fact that fundamental particles of the same type are indistinguishable. Why does the combined wave function cancel out? .. 'cos that's what seems to agree with experiment - i.e. because you don't see people falling through floors. Progress seems to be about trying to extend this "explanation chain" by one step more. So string theory can step in and add "because vibrating strings, which is what we're made of, behave like this" .. and then it stops at some point again.
• statictype 16y ago
  She's got a lot of good stuff in her comment history. I really wish Instapaper worked with reddit comments. Lots of good reading there.
• hammock 16y ago
  The top answer on Reddit was not helpful to me, and seemed tautological even in the face of its length. WHY can't the arrow stretch? That is the crucial question; that is the original question. The original question was not "is there/why is there a tradeoff between space and time." The question was "Why can't the arrow stretch, why can't we go faster than light allows?"
• boh 16y ago
  I remember reading an article a while back: "Scientists Make Radio Waves Travel Faster Than Light" article: http://www.universetoday.com/33752/device-makes-radio-waves-travel-faster-than-light/ http://www.universetoday.com/33752/device-makes-radio-waves-... the paper it's based on: http://arxiv.org/abs/physics/0405062 http://arxiv.org/abs/physics/0405062 Anyone with a Physics background care to comment on the validity of this study?