Comments by "Lepi Doptera" (@lepidoptera9337) on "Time Stops at the Speed of Light. What Does that Mean?" video.

  1.  @post_metro  And that is, indeed, the billion dollar question. "Time" only exists if there is an energy flow mechanism that allows us to "keep time" and to synchronize clocks. In other words, "time" is only a good order parameter in a relativistic universe in which there is no "absolute" matter background that blocks the flow of energy. Thankfully at the surface of last scattering the universe would have been transparent for both neutrinos and gravitational waves, already, so the universe could actually "keep time". Now, if we go back a little further the universe becomes opaque for neutrinos, but it's still transparent for gravitational waves. But what happens if we go back even further than that? Is there ever a state for which even gravitational waves can't travel freely? If there is, then the conventional definition of time breaks down and then, I believe, we need a new mental model for what spacetime means.
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  2. Yes, it is. It's also 100% false.
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  3. No, it doesn't mean that. ;-)
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  4. Suppose you do something that can't be done, have you really done it? ;-)
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  5.  @ondrejs2  Suppose you do something that can't be done in your mind, did you really do it in your mind? :-)
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  6.  @ondrejs2  Neither did I, but here we both are. :-)
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  7. Because we generally don't consider bullshit. ;-)
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  8. Light's "proper time" is a distance. It's easily measured in wavelengths. The only mystery here is why people don't know high school physics.
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  9. Have you ever seen anything that you didn't observe? That's a tautology. :-)
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  10. The "length" of a trip isn't zero. It's would just take zero Eigentime. The two are not the same. Even light "knows" that by counting wavelengths. Since the number of wavelengths between two points is a scalar, it's the same for all observers. So while light doesn't have time, it has length.
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  11. The speed of light doesn't have anything to do with light.
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  12. Photons don't move. You simply misunderstand the meaning of the word "photon". One can form coordinate systems from light just fine. You are using them all the time. It's called "the GPS system". Your cell phone receives four or more electromagnetic waves and based on their relative phases can tell where you are and what time it is.
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  13.  @IncoSoft2  Why are you telling me with so many words that you don't understand physics, though? I don't care. ;-)
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  14.  @IncoSoft2  Why are you telling me all the things I have known for like half a century, if not longer? That's a waste of time. ;-)
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  15. The correct formula doesn't break anywhere. You just don't know the correct formula.
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  16.  @AORD72  The point is that there is nothing "special" about the case of vanishing rest mass. Energy and momentum are perfectly well defined. All this worry about "what happens to photons" is unnecessary. Nothing special happens. There is simply no rest system without rest mass. That's all. One can still define coordinate systems and time perfectly fine with three and four independent plane waves. That's what GPS does.
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  17.  @AORD72  Awh, you are so cute when you are feeling sorry for yourself. :-)
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  18.  @AORD72  Let me know when you are ready to talk about physics rather than yourself. ;-)
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  19. Hey! There is the kid who wasn't paying attention when they explained the clock to him! ;-)
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  20. A paradox would means shoddy thinking. Yes, we do have that, albeit without much of a paradox. ;-)
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  21.  @DB-thats-me  Paradoxes are deliberate teaching tools that show a particular pattern of thinking that leads to the wrong results and that should be avoided. The misunderstanding of the nature of the photon is not such a deliberate teaching tool. It's just a very widespread mistake. So is the lack of understanding of the material nature of rest systems and clocks.
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  22. Time is always passing at the same rate. What changes is the flow of energy between two points. In other words: it's always Doppler effect.
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  23. Photons don't have a path. There are simply way too many people in the world who don't understand what the word "photon" means. :-)
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  24.  @waynemorellini2110  I don't imagine anything. I have measured trillions of quanta of energy. Not one had a path. A quantum of energy is simply the energy that a free quantum field deposits in an external system that we call "detector". Unless that irreversible energy flow takes place, that quantum of energy does not even exist.
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  25.  @waynemorellini2110  A photon is a small amount of energy. That's all it ever was and will be. We told you that in high school, by the way, but you weren't listening. ;-)
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  26.  @waynemorellini2110  You mean like the trillions of quanta that high energy physics detector hardware that was designed by me has measured? That way? Tell me, how many quantum measurements have you done personally? ;-)
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  27. Such a universe can't exist. It's not logically self-consistent. That follows directly from gauge-field theory and gauge-field theory follows directly from relativity... which is another word to say that the universe is completely empty. :-)
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  28.  @dr_shrinker  Science is the description of what has been observed. A universe without matter has not been observed. Are you trying to start a new religion here? All of your questions are about things that don't exist. ;-)
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  29.  @dr_shrinker  You comment reeks of intellectual laziness. ;-)
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  30.  @dr_shrinker  I didn't see a question. I keep seeing ever larger heaps of bullshit, though. :-)
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  31.  @dr_shrinker  Ah, so now you are pretending to be from the English department. :-)
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  32. No. Both concepts are complete bullshit. ;-)
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  33. It doesn't take zero seconds because one can't accelerate a clock to the speed of light. That light does not measure distance is complete bogus, by the way. It counts its own wavelengths just fine. This is just another case of bullshit from Sabine.
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  34. Awh, you are so cute when you are announcing that you weren't paying attention in school. ;-)
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  35. Yes, that was a dumb question. Do it again! ;-)
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  36. You can travel with light? What else can you do? Leap giant buildings like Superman? ;-)
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  37. We don't need observers in physics. We only need irreversible energy flow. ;-)
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  38. One can't make a clock that moves at the speed of light.
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  39.  @bogdang66  Because a clock has to have an energy source and an energy source is massive. Nothing with rest mass can move at the speed of light.
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  40.  @bogdang66  The mirrors that are defining the rest system of the clock have rest mass and so does the trapped electromagnetic field. One can't make a light clock without those conditions. A freely propagating electromagnetic wave does not serve that purpose.
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  41.  @bogdang66  Yes, measuring time requires energy flow. A clock is not a thermodynamic system, so I am not sure why everybody is trying to drag entropy into it. One can, of course, make a crappy clock out of a cooling piece of hot matter, but why would one?
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  42. There are no particles. There are only massive and massless fields and both are just two sides of the same coin, so you can't actually separate them. What happened at the surface of last scattering is that the universe became transparent because the ionization of the hydrogen and helium gas mixture stopped. It really just went from hot gas to cold gas and then back to hot gas when the first stars formed.
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  43. Who tested what? That we can't accelerate a clock to the speed of light? Every accelerator facility can test that for you.
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  44. That's also not true. It's a feature of the naively interpreted theory, not a feature of nature. One can make clocks from anti-matter just fine and they only run forwards, not backwards.
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  45.  @ggtt2547  What weirdness is that? There is nothing weird about quantum mechanics, you just don't know enough about it.
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  46.  @ggtt2547  Sabine doesn't understand quantum mechanics. She talks nonsense about it both on YouTube and in her publications.
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  47. Only causality does. Every THING is slower.
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  48. It's just a coordinate transformation. Objects don't change their lengths. They don't even appear to be shorter. In reality they would appear slightly rotated and distorted.
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  49.  @johnnyragadoo2414  The problem with the Lorentz transformation is that it is only valid in one point. This means that naively applying it to two different locations is already stretching the limits of its meaning. Any two different points in spacetime are always separated by a length AND a time difference. We can, of course, use the clock synchronization scheme suggested by Einstein to "distribute" a global time value across an extended coordinate system and it is that procedure that makes things appear longer or shorter. I question the physicality of that procedure somewhat, even though it leads to "fun" numerical effects like the barn example etc.. In reality, though, if you look at something moving at relativistic speeds, there won't be any shortening effect. The time it takes for the light from that object to reach us negates the Lorentz contraction.
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  50. The simplest interpretations are known to be always wrong. They are based on intellectual laziness. ;-)
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  51. You are really crap at guessing. ;-)
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  52. It's only a problem if you weren't paying attention in special relativity class.
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  53. Time is that which the clocks show. Since one can't accelerate a clock to the speed of light (because it is massive), the entire question is nonsensical. That light can "measure" spacetime just fine without a time measurement should be obvious. That is what the GPS system does by combining four or more distance measurements. If you want the precise mathematical explanation, you can find it in Misner, Thorne, Wheeler "Gravitation". It's a very good introductory textbook that discusses general relativity from a geometric perspective.
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  54. And there is the kid who wasn't paying attention in physics. ;-)
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  55. How do we implement fiction? We write it on paper. ;-)
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  56. Wow, you had a really dishonest ex-girlfriend. ;-)
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  57.  @krensak  Einstein didn't need that mental model. That the Maxwell equations were Lorentz invariant rather than Galileo invariant was well known. The only "problem" that Einstein had to solve is what to do about classical mechanics.
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  58. Yes, it does make sense. The real reason is much more simple, though. A clock is always a massive system. Such systems can not be accelerated to the speed of light.
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  59. No, it doesn't. What it means is that you weren't paying enough attention in your special relativity and quantum mechanics classes. ;-)
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  60. We are teaching to the little kids that time is that which the clocks show. It is amazing how few kids listen. Of course time is an emergent phenomenon. Nobody of importance ever said otherwise. ;-)
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  61.  @kylelochlann5053  Did I ever build a clock? Yes. As an experimentalist I actually did. Plenty of them. Have you ever seen a clock that didn't have an energy reservoir like a spring or a battery? I haven't. An energy reservoir necessarily means a massive system. All of these systems are emergent.
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  62. Everybody looks at you like you are crazy? I can't imagine why... snicker. ;-)
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  63.  @ollieb2520  Can you point me to where Feynman is supposed to have said that in a physics paper? ;-) I don't know what "taking the perspective" of a physical property means. How do I "take the perspective" of "red" in the phrase "red car"? Quanta are small amounts of energy. Energy is a system property. "Energy" is in the same category as "red". What's the perspective of properties? I was never taught that. Neither were you. You just don't know that you are making a severe category error.
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  64.  @ollieb2520  That's Nahim talking. I was asking for a citation of Feynman. The QED path integrals don't have these potentials. Absolutely nothing goes backwards in time.
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