Comments by "Dr Gamma D" (@DrDeuteron) on "Einstein's twin paradox explained - Amber Stuver" video.

  1.  @emmaarip3946  no, stella experiences less time between when she leaves terra and when she sees her again than the time terra experiences, which is why we say Stella is younger than terra.
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  2. the body doesn't slow down. If your resting (at rest) heart rate is 100 BPM, it's still 100 BPM, it's just that your "M" (minute), differs from your tubby sister's back on Mother Earth.
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  3. ChatGPT can't do physics. And you have failed to abstract. Biology is not part of the problem.
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  4. there are 3 inertial frames: Terra on Earth, Stella outbound, Stella inbound. Stella occupies two of them.
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  5. it's 45 deg in Stella's frame of reference.
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  6. I think you're being hyperbolic.
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  7.  @stewiesaidthat  🤦‍♀️
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  8. People who take the inertial path between 2 events always age the most, no matter what the competing path is.
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  9. A major conclusion of SR is that you cannot move relative to light. You certainly can't go faster, nor equal, but in reality: you can't go half speed, or 1 millionth the speed of light. No matter what your state of motion, if you flash your flashbulb, the light will move away from you in all directions at "c", and any other observer, who can move at speed v in +/-(c-epsilon), with epsilon arbitrarily small, will see that exact same light move outward in a prefect spherical shell expanding at "c".
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  10. don't get hung up on semantics: time is not a universal parameter that tics the same everywhere; instead, it is a local piece of spacetime that tics at different rates for different people, depending on their velocity.
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  11.  @SlayerWSS  1) you can't go light speed, but you can go c(1-e) with e-->0. 2) you then age 10*sqrt(2e) years, which also approaches zero. So, your age would still be 20y.
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  12. then each sees the other aging slower than themselves. That's why it is a paradox.
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  13. Perception plays no role. By Terra's clock, Stella's clock is running slow, and by Stella's clock, Terra's clock is running slow. And by "clock running slow", I mean "time progresses more slowly."
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  14. so what?
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  15. What does the background universe have to do with anything? The paradox is the same if the background universe is at rest with respect to either of Stella’s frames, or none of the 3 frames.
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  16.  @DrZaheerAbbas08  that's a failure to abstract, which is a crucial part of thought experiments. OK, so now we place Stella and Terra in Teslas in deep space, long after all other galaxies have expanded past the cosmic horizon. now what?
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  17.  @DrZaheerAbbas08  again, a failure to abstract. Forget the universe, forget gravity, forget the earths the sun, and the galaxy. Twins paradox is about the geometry of Minkowski space, M4, which has neither. Moreover, the so-called fixed stars, now superseded by the CMB’s so called rest frame, implies an absolute frame of rest. That sort of thinking will spoil one’s understanding of M4, which is a space in which you are always at rest in your frame, no matter how much you moved to get there.
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  18.  @DrZaheerAbbas08  the paradox is resolved when you accept that the outgoing twin and the ingoing twin at the same time have completely different defintions of now back on earth. Which is in itself another paradox called the andromeda paradox. As David mermin said, the most important lesson from relativity is the time between distant events is meaningless. But, if you startin Minkowski space and just look at the proper time on world line, there is nothing to solve, since all frames agree the inertial path has the longest proper time. I studied this stuff under Kip Thorne, have a phd, and have used it at work for decades, so there is no word salad. And many PhDs in physics can do calculations but don’t really understand it….
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  19. this video correctly explains what each twin observes regarding signals from the other twin, but it does little to explain the resolution of the paradox.
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  20. We need a moratorium on one-way speed of light comments.
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  21. but she only travels 5.2 light years.
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  22. no, stella's still young and...err beautiful...there is literally less time on her path from launch to reunion than on tara's path. If she cranked her speed up towards the speed-of-light, the time on her path would approach zero. She could exist and age for a few seconds, while tara ages 23 years.
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  23. !ts a thought exper!ment
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  24. that's why it's a paradox. It just went missing when Stella turned back to Earth.
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  25.  @skywalker4886  that's b/c this video only explains what they see looking out the window. It is not helpful. Basically, T sees S age at 1/2 speed, and S sees T age at 1/2 speed. The paradox happens when S turns around, the time on Earth just gets a new value...not dilation or anything, it's just that S's definition of "the present" jumps forward...hence a huge chunk of missing time. See "The Andromeda Paradox"...it's weird, and it is a paradox, but not a contradiction. Relativity is self-consistent.
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  26. dude. no. not even close.
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  27. length contraction is hard to imagine. Part of it is deciding where the ends of a ruler are at the same time, when time difference depends on velocity times distance
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  28. So when doin SR thought experiment, one imagine all observers have a lattice of clocks and rulers telling them where and when events occur, even outside their light cone. The light delay is not really considered, except in the simultaneous ⚡️ strikes on a 🚂, which is used to set up the relativity of simultaneity
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  29. if the CMB defines the absolute rest frame, then why are distant at-rest galaxies receding from us at high speed?
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  30.  @richardepp8698  your talking about the surface of last scattering. not the radiation. Doppler shift does not change speed, as light moves at c, always. My point was that there is no absolute rest frame, because in the frame with CMB dipole at the origin, there is a CMB dipole everywhere that is not the origin, so any translated frame is now not at rest. Which makes it not a rest frame
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  31.  @zakelwe she didn’t travel at all. First the star came to her, and then the earth came back.
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  32.  @DaSoggyTurd  your body reacts to time by aging.
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  33. locally. which is globally, in special relativity.
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  34. Stella's not length contract because Stellas not moving in Stella's frame. Terra's the one who sees her squished, while she's moving, wrt to Terra.
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  35.  @rogerg4916  Stella is compressed in Terra's frame. It's not a matter of appearance. Just like you're compressed right now in the frame of some cosmic ray muon.
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  36. ​ @whatthe4423  Killing Vectors
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  37. there are no reference frames at the speed of light. What is it that you think 100+ years of science doesn't understand?
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  38. they'll have to wait for a General Relativity video....
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  39. The video doesn't explain the paradox; rather, it explains what the twins see looking out the window. It does that clearly and correctly; however, that doesn't explain how Terra out aged Stella.
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  40.  @shubhamss3328  no, the delay only confuses thing (unless you're using the Bondi k-calculus).
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  41. it's not a theory, it's an experimental fact.
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  42. it's all relative
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  43. Just because this video doesn't explain what is going on, doesn't mean they're the same age. d(proper time)/d(clock time) = sqrt(1- (v(t)/c)**2) where v(t) is tangent to the path taken. In any reference frame defining the clock and path, Stella's is less than Terra's.
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  44. it's a good explanation of how they send signals to each other.
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  45. it's not "wrong", it just doesn't explain much. It shows what they see looking out the window and sending signals. It doesn't address the root of the paradox, which is that when Stella is at the distant star, the time on earth is not unique. It really is a paradox.
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  46. that's why it's a paradox
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  47.  @AMC2283  There is no paradox in Minkowski space, since relativity is self-consistent. The paradox appears in our reference frames.
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  48.  @rogerg4916  The paradox is this: T takes 23 years to go from start to finish. T sees S's clock run at 1/2 speed the whole time, which is does. S takes 11.5 years from start to fin...but, motion is relative, so S sees T's clock run at 1/2 speed for both legs of the trip, ticking of 2.875y on each leg (lame of TEDx to chose non-integer numbers) for a total of 5.75y. So there is 17.25 y of time passage that just goes missing. That is a paradox.
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  49. but that is a position dependent frame.
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  50.  @iyziejane  Right, that is the preferred frame at Earth. Since the Hubble constant is about 1 yard per hour per light year, the 'at rest' frame in the Andromeda Galaxy is moving away from us at 35 miles per second....which is about Earth orbital speed, btw.
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  51. 1) on each leg of the journey, Stella sees terra age 2 7/8 years for a total clock ticking of 5 3/4 years, yet Terra has aged 23y during Stella's 11 1/2 year trip. Where's the missing 17 1/4 yr?
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  52. let's push this into the number 2 spot: https://www.youtube.com/watch?v=AvgOYmKCm2c
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  53. not exactly. There's a paradox b/c, on each leg of the trip, Stella ages 5-3/4 years, but sees Terra's clock dilated to tic off a mere 2-7/8. For the whole trip Stella see's Terra's clock running slower, yet Terra is older.
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  54.  @AtomicPunk23  no, I never discuss light images. That's for real experiments. In thought experiments, one is permitted to rely on an imaginary lattice of clocks and rulers to measure everything, now, everywhere. The key to this paradox is that Stella has to get a new lattice of observers when she turns around, and that lattice is 11.5 years later on Earth than the original one, even thought they coincide at her turn around point.
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  55. but that Doppler effect included time-dilation, which is why it was symmetric between Stella and Terra. It had no aether in it.
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  56. the video assumes you already know about time-dilation.
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  57.  @ctvxl  How is Stella moving at a high percentage of the speed of light? On her space ship: light moves at c in all directions. How fast is she going, and which way does she go to get closer to c?
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  58. Both see the other's clock ticking slower, so each see each other as younger (further back in time), A similar thing happens on the highway: two cars passing each other in opposite directions both see each other further to the left (in most countries).
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  59.  @ctvxl  you can't move through space. If you could then you could stop in space, and that would be an absolute rest frame. There is no absolute rest frame.
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  60.  @avneeshsharma9335  yes Stella’s worldline is inertial, and inertial world lines maximize proper time. In sr and gr.
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  61. Cesium came before NIST.
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  62. Terra Firma and Stellar Stella.
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  63. in who's reference does she teleport instantly? If time difference between disappearing and reappearing is zero, then in is either positive or negative in other frames.
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  64. OK: Imagine it doesn't orbit the sun.
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  65.  @shrodingerscat8940  that, too. It's a failure to abstract. separates physicists from engineers.
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  66. That is correct, during each leg of the trip, Earth tubby and Space tubby see the other's clock running slower, but on return: Space is younger than Earth. That's why its a paradox.
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  67. He also proved atoms exist and that light is quantized, in THE SAME YEAR as SR. (1905).
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  68. No, not at all.
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  69. But that a fault of the video. You don’t need the rest of the universe, that just confuses things.
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  70.  @hareecionelson5875  Sit on it.
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  71. GPS navigation, anything that uses an electron beam over 50kV, atomic clocks, Universal Coordinated Time aka "what time is it?", ring-laser gyros, proton beam cancer therapy, proper use of star-trackers for interplanetary navigation, neutrino astronomy, ...just off the top of my head.
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  72.  @chickenduckquack  "concentrate on what is being said"? bru. you're spitting nonsense.
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  73.  @chickenduckquack  but we can count Cs atoms’ cycles and see they are asynchronous , which rules out ur theory
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  74.  @chickenduckquack  if you don’t understand it, you have no business talking about time. Moreover, I am referencing observation, so calling it rando is not supported. But why the goofy theory? We have working theories of time, and implementations to use it here on earth and in deep space navigation, and it all would not work with your theory
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  75.  @chickenduckquack  "you might just as well have said that 'chocolate is nice'." == rando. this is a semi-physics video, why are you here with the strange thesis "time is invented and thus cannot be dilated"...what's the point?
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  76.  @chickenduckquack  read some stuff by David W Allan (inventor of Allan variance), you'll learn something about the practicalities of time measurement. His stuff is on-line. But this video is about relativity, which is a totally different thing.
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  77.  @chickenduckquack  this video isn't about time-dilation, its it is assumed. It's about the twin paradox and proper time on two world lines with the same endpoints being different, which is an experimentally observed fact, but looks paradoxical in 3 + 1. The arrow of time stuff is about entropy (thermodynamics or statistical physics), and it also comes up in cosmology (i.e. FLRW metric) , and "believe" isn't a thing here. This is basic 100+ year old physics.
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  78.  @chickenduckquack  make one coherent point and I will be happy to set you straight. Just one. Right here, right now: _____
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  79. Yes, it is.
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  80.  @yannick7049  Veritasium created so many c-deniers.
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  81. you know it's a thought experiment, right?
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  82. no, you can't travel at c, but you can get arbitrarily close, and then the property time approaches 0. Note: you are moving arbitrarily close to c right now in some reference frame.
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  83. but Stella already sees the Earth clock running at 1/2 speed.
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  84. Nothing in this video is wrong, it just doesn't explain anything relevant. How the twins receive each others' light signals is an interesting afterthought.
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  85.  @dougsteel7414  correction: it makes to mistakes. 1) The narrator compares two observers to each other, when she should compare them with each other. Strunk and White do not approve. Then, she correctly calls it an "apparent contradiction", which is one of the 3 definitions "a paradox", but then immediately claims it "isn't paradox". The twin paradox is absolutely paradoxical, as are many things in relativity when analyzed in different inertial frames. Of course, when one works in Minkowski space and looks at proper time along a world line, which is a Lorentz invariant, there are neither contradiction nor paradoxes.
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  86. 👍
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  87. Stella is 10 ly from Earth, but Earth isn't 10 ly from Stella.
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  88. you're correct: it's weird. Different frames don't agree on the time between 2 events, nor the distance (which is not weird). What they do agree on is [(c*time difference squared) minus (spatial separation squared)]. All of SR can be derived from that.
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  89. earth doesn't move in thought experiments.
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  90.  @oloanbataragurusamosir2770  just imagine terra is in a space station at the Lagrange point. If you want to learn physics, you're gonna have to focus on the problem at hand. Of course, when Hafele and Keating did the experiment, they worried about this that and the other thing.
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  91.  @oloanbataragurusamosir2770  ok. well the fact is: in this thought experiment is that you don't care about the earth moving.
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  92. at any point, there is a frame that is at rest with respect to the rest of universe (e.g: no doppler shift in the CMB), but it's different at any other point in the universe....but that's cosmology, not special relativity.
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  93. Terra is length contracted in Stella's frame. Stella sees her move 5 ly away, and then 5 ly coming back. Since terra is doing that at 0.866c, each leg takes 5-3/4 year; however, Stella sees Terra's clocks dilated, so she only ticks 2-7/8y on each leg, or 5-3/4 total, while Stella ticks 11-1/2 on her own. Yet Terra is 11.5 y older then Stella when the reunite: Definitely a paradox.
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  94. well Morgan Freeman had a conflict.
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  95. you cannot be serious.
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  96. well it's worse than that, since one can define 'at rest wrt to the universe' by zero-ing your motion wrt to the CMB. The problem is, that only holds at a point. Once you move somewhere else, the new 'at rest frame' is moving relative to the old one. Or: comoving cosmological coordinates are expanding.
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  97.  @renedekker9806  Exactly. It's best for ppl learning SR to not consider cosmological things (except Mach's Principle). Learn it, and then unlearn it in GR. It's what Einstein did. BTW: There's no absolute not-rotating frame either. If you're near a Kerr blackhole: you need to rotate wrt to the fixed stars to feel like you are not rotating.
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  98.  @renedekker9806  right, and near a spinning blackhole, you have to rotate relative to an asymptotic non-rotating frame to be in your non-rotating frame. See: "Tendex and Vortex lines".
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  99. your second is wrong. The Earth spins once in approximately: 86400 x [1 - 1/(365 + 1/4 - 1/100 + 1/400)]
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  100.  @stewiesaidthat  A solar day (86,400s) is not the rotation period, a sidereal day is. Also: "irregardless" is not a word.
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  101. Stella is going sqrt(3)/2, so half of that is sqrt(3)/4. Media sees Terra moving away at sqrt(3)/4, but Stella is moving away at 2*sqrt(3)/11. Media needs to go sqrt(3)/3 to be half way between 0 and sqrt(3)/2.
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  102. By using a turbo encabulator. They were made by Rockwell Aerospace.
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  103. Are you trying to solve the paradox, or the problem? The problem is solved by integrating proper time over the world line, and the inertial world line between two events maximizes proper time. That is basic Lagrangian formulation of SR. The paradox arises when you work in space + time with different frames. Both sisters see each other's clock running slower, all the time. Stella has two frames, while Terra has 1: that can never be consider "symmetric". When Stella switches frames, the clock bias back on Earth moves forward in time: paradox resolved.
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  104.  @AMC2283  there is a paradox. That is why it's called "The Twin Paradox". There is no contradiction, though.
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  105.  @stewiesaidthat  You are suffering from a failure to abstract. Gravity is not part of the problem. If "g" bothers you, put terra in a space station in deep space. It doesn't matter what Terra and Stella are. You can replace them with clocks, or 2 lumps of radioactive material--whatever can be used to measure the passage of time.
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  106.  @stewiesaidthat  you were talking about gravity on Earth, which is irrelevant. What's not understood about the twin paradox? It arises because when Stella is at the turn around point, the time on Earth depends on her direction of travel. It has nothing to do with time dilation.
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  107.  @stewiesaidthat  yeah, that is totally wrong and focusing on things that are just not part of the thought experiment. In Minkowski space, the total elapsed proper time along a worldline is the integral of dt/gamma(t) where t is the coordinate time and gamma is the Lorentz factor. In any inertial frame, this will show that Terra experience the most proper time from start to finish compared with any path that accelerates. That is all there is to it.
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  108.  @AMC2283  thanks scotty.
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  109. Actually Stella sees it move 1/2 speed on Earth, so Terra sees Stella seeing Terra's clock run at 1/4 speed.
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  110. we have observed stuff approaching, e.g. relativistic beaming of jets. Really any relativistic doppler shift is sufficient proof using "Bondy's k-calculus"
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  111. so how does that explain the paradox, because Stella see's Terra's light clock running slow on both legs of her trip.
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  112. What does a planet have to do with anything here?
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  113.  @stewiesaidthat  that explanation was truly hilarious 😂
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  114.  @stewiesaidthat  the earth has nothing to do with time. time is defined by an atomic transition's inverse frequency.
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  115. The real time video chat you describe allows you to talk to the future, and the past....so yeah, it creates unresolvable paradoxes.
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  116. Stella measures that tara's clock ticks off 2.875 years for each of Stella 5.75 year legs, leaving 17.5 years unaccounted for.
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  117.  @TenebrisOfChaos  but it doesn't. The view of terra's signals is doppler shifted, but not her understanding of terra's clock.
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  118. yup. it's just that Stella's path had less of it.
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  119.  @grahamgillard3722  why would a clock perform differently at different altitudes?
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  120.  @grahamgillard3722  that’s why relativity was revolutionary. NIST can measure time running slower on the floor of the lab vs on a table in the same room.
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  121.  @grahamgillard3722  time runs slower. Time is measured by an atomic transition, where the period is determined by fundamental constants. Said transition on the table will oscillate 1,000,000,000,000,000 times, while the one on the floor does 999,999,999,999,999. Note that the atoms are identical and can even be in an entangled quantum state, so that the 2 atoms a both on the floor and table at the same time, with time flowing differently for each state. Time is relative, and physics with time as a universal parameter would be a mathematical mess.
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  122. pretty sure grandmothers are required for birth. we need to change the name of the paradox.
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  123. how did it go?
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  124. "its name"... seriously?
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  125. What universe? There’s no universe in this thought experiment.
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  126. lol
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  127. Terra is heavy, but Stella is weightless.
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  128. no
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  129. thought experiments don't care about that. Imagine Terra is in a stationary space station.
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  130. That’s why its a paradox.
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  131.  @cptnoremac  yes, that’s why it’s a paradox. A paradox does not need to be a contradiction
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  132.  @cptnoremac  well, define see. In this video it means observe light from. Ofc, that is not abstract enough for thought experiments, where everyone is equipped with an infinite lattice grad students with rulers and clocks, reporting o the coordinates of events. Ppl who cannot abstract to this point, and are fixated on delayed light signals, will probably never really understand relativity.
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  133. that's why it is a paradox! Stella sees Tara age only 2.875 years per leg of the trip, but when Stella turns around, Tara doesn't age, rather the time on Earth just jumps forward 17.25 years. It's not time dilation, but a change in clock bias. It is not a contradiction, but it is a paradox for mere humans.
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  134. Terra = terra firma = 🌏 Stella = stellar = stars ✨ = 👩‍🚀
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  135. It doesn't.
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  136. It’s a paradox.
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  137.  @joepierson3859  the angle btw Stella's two worldline segments can never be 90 degrees, as it's 2*arctan(v/c). For her, that is 82 degrees.
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  138. What do you mean "it did not REALLY move closer"? Go study Bell's Spaceship Paradox: if the planets and stars all accelerate uniformly and simultaneously in Stella's reference frame, then they must spread apart in their reference frame. Since they don't spread apart in their reference frame (what do they know about Stella?), then they really do move closer together in her frame.
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  139. close! t2 - x2 = s2
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  140.  @Everan226  ...or, I've being doing it for 35 years.
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  141.  @Everan226  If you draw a line between 2 points on a sheet that are "c" apart, and then project that onto two orthogonal axis (with projection a and b), then a2+b2=c2 is true for any and all choice of axes. This is Euclidean geometry: In spacetime, if you have two events separated in space by "x" and in time by "t", then the so-called invariant interval "s" satisfies t2-x2=s2 (in units with speed-of-light=1). People moving at different velocities will have different values of "x" (obviously) which means (surprisingly) they measure different values of t....but they all agree on s. All of special relativity is derivable from the invariant interval, and it's called "Minkowskian Geometry". So every observer picks out their own slice of spacetime that they call "The Present", or "Everywhere, Now". The twin paradox arises because "now" on Earth changes when Stella turns around (see: The Andromeda Paradox...and it is a paradox).
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  142. 10 ly is one way, 20 ly is round trip. Still, the choice of speed and distance has a bunch of irrational number rounded to prime numbers,...simply terrible for thought experiments.
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  143. would you prefer "Earth" and "Star"?
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  144. Lorentz factor relates time/space between 2 inertial frames. There are no inertial frames at the speed-of-light.
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  145.  @stewiesaidthat  then build your own non-relativistic GPS receiver and enjoy being lost,
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  146.  @stewiesaidthat  time doesn't stop at the speed of light b/c there are no reference frames at c.
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  147. Each sees the other age more slowly on both legs of the trip, but when they return, they are the same age. That's why it's a paradox, in spite of this video saying it isn't.
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  148. that would be stellar, because you need to keep yourself planted on terra firma.
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  149. there is no Earth. It's an abstraction. If you don't like it: feel free to start on a deep space station.
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  150. that's not right. Stella doesn't age at all during the infinite acceleration. Terra doesn't either: they both measure that the turn around takes 0 time. The weird thing is, right before the turn around, Stella measures Terra to be younger, but right after Terra is much older. She didn't age[1], it's just that Stella's definition of "now" back on Earth jumps into the former future (on Earth). [1] if Stella then turns back away from earth, Terra is younger again....it's not time dilation, (you can't age backwards), but the definition of "simultaneity at distant locations" that changes Terra's clock bias in Stella's frame.
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  151. why would you say that? Particles in accelerators follow relativistic kinematics. Seems to be working in the lab.
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  152. CD will calculate that AB has aged 8.5y, but only "see" the 1st 4.25 years thanks to delayed light propagation. Simultaneous in the Earth's frame, AB will be +8.5y and see that CD has only aged 0.30 y, b/c time dilation. Objects 1 & 2 are superfluous and add confusion, as does starting in the moving frame. It is tradition to start labels (A) on earth, and put (A') in motion. You want to keep the labels as clear a possible, and in line with tradition. Also, having 2 ppl in each frame just adds confusion. Keep. It. Simple.
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  153. Time is a universal parameter in quantum mechanics. It’s a nonrelativistic theory. In quantum field theory, it’s relativistic, so there not gonna be a save for your hypothesis
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  154. they did do a bad choice of numbers. I don't know why...you get to make the problem up so pick better numbers! amirite?
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  155. yup, you can travel to the future, but you cannot come back.
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  156. But she took a non inertial path from start to finish.
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  157. really, the Twin Paradox is about local flat spacetime. "The rest of the universe" gets into Mach's Principle and the global structure of general relativity.
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  158.  @StRanGerManY  Not just linear momentum, but angular momentum, too. You would think we can at least define a global state of "not-rotating", since you can 'feel' (measure) rotation (with gyros). However, in the Kerr Metric, near a rotating blackhole, you must spin with respect to distant observes in order to be not spinning locally.
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  159. terra = Earth stella = Stars still confused?
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  160. the whole video is about the observed light signals....did you watch it?
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  161. no.
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  162.  @loc4725  Lorentz transform says: t' = gamma * (t - vx/c^2) which disagrees with your post.
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  163. wrong video!
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  164. this video didn't address the resolution of the paradox (which isn't asymmetry), all it did is describe light signals that the twins see.
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  165. have you heard about "Thought Experiments"?
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  166. It's accurate, it just doesn't explain the paradox.
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  167. What you have committed is a failure to abstract. So let’s put them on a space station in deep intergalactic space: now what?
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  168. t = gamma(t' + vx'/c^2) so when -v changes to +v, t back on Earth jumps forward and makes up for all the "missing" time caused by gamma in both frames. So it's not time dilation that's weird, it's that "now" far away depends on your velocity.
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