216 thoughts on “Relatively Speaking

  1. Thanks for this, it makes some extremely counterintuitive propositions considerably easier to grok. Students confused by Lorentzian transformations def can benefit from sims.

  2. The video makes a claim that in order to explain the train paradox (Einstein’s Theory of Relativity), one must think of the train not as a rigid object but rather, to be thought of as many rectangles connected though the many flexible connections…

    Isn’t the train a rigid object? If yes, is the theory of relativity wrong? If not, how could the train NOT be a solid, rigid object?

  3. I find the video entirely uneducative. It gets close to the theory of relativity only if every claim is a metaphor. The claims apply close to the speed of light, but the tunnel, the train, Sarah and Adam are not objects that would get anywhere close to the speed of light.

    It would be more educational this way: Close to the speed of light, there are no rigid objects. Think of everything as wavy flow.

  4. Erik: I find the video entirely uneducative.

    I wouldn’t use that phrase. However, it does seem very misleading. We see a train travelling at what appears to be normal speeds, but we are supposed to imagine that it is travelling near the speed of light (and without derailing).

  5. Neil Rickert: We see a train travelling at what appears to be normal speeds, but we are supposed to imagine that it is travelling near the speed of light (and without derailing).

    We see a train travelling superslow, and at that speed somehow we are supposed to make sense of ridiculous length differences from the different perspectives, so that from one perspective the train fits into the tunnel and from the other it doesn’t. Obvious question: How come the tunnel is the same length from every perspective?

    Then the monorail. From Sarah’s perspective, the train is allegedly shorter than the hole in the monorail, and therefore (???) would fall into the hole. Obvious objection: No it wouldn’t; it depends on the speed. Close to the speed of light, why would it?

    The correct educational exposition: There are no trains etc. close to the speed of light. Any “object” has a fluid/airy nature at that speed.

  6. Erik, I think you need to think a bit more about what ‘close to the speed of light’ means–and relative to what/whom.

  7. walto:
    Erik, I think you need to think a bit more about what ‘close to the speed of light’ means–and relative to what/whom.

    Do I? That’s why you are cautiously silent about it, so that your own ignorance would not show? 🙂

    Go ahead, spell it out: What does speed of light mean and relative to what/whom?

  8. walto:
    Erik, you are a very dependable dipshit . Think instead of insult for once in your life.

    Ha ha, so you say I was insulting?

    Next time when you try to give a teaching moment, remember to formulate a full thought complete with the teaching. And collect some strength of character so that you won’t guano all over yourself before you manage to teach anyone. Otherwise it will always be me teaching you, like just now yet again.

  9. walto:
    Thanks for this, it makes some extremely counterintuitive propositions considerably easier to grok.Students confused by Lorentzian transformations def can benefit from sims.

    Yes, I think saying they are counter-intuitive is putting it mildly.

    Like for instance, the way to solve the paradox of Sarah seeing both doors closing from her perspective, is for Adams train to compress itself so it fits inside the tunnel also. It seems we have just discarded the meaning of length, is compressing something is different than it being shorter.

    I think the producer of the video also does a poor job of explaining why they always choose Sarah’s perspective as the default, and then twisting Adam’s to match.

  10. I didn’t understand anything. Irritating music.
    I have seen better things then this on this subject which i never had interest in before.
    I bumped into the stupid ideas of quantum mechanics/cats and suspect its very wrong after Einstens suff or something.
    i wonder if einstein and the rest realkly got it right.
    just like in origin subjects, biology, geology, etc, there is crazy dumb wrong ideas.

    Physics is less complicated then biology but still it must be complicated.
    however once again its seriously studied by few people and possibly thats the problem about figuring it out.

  11. J-Mac:
    Isn’t the train a rigid object? If yes, is the theory of relativity wrong? If not, how could the train NOT be a solid, rigid object?

    There’s no such thing as a completely rigid object. If you squashed the train (say, between a couple of bulldozers), it’d get a little shorter. Maybe not much, but at least some.

    The video’s treatment as a bunch of rectangles is closer to reality, but still not entirely accurate. The train is actually made of atoms, connected by electromagnetic forces. You can think of the interatomic forces as little springs connecting the atoms. They may be stiffer (highly rigid material) or softer (more flexible material), but they always have some degree of flexibility.

    If you push on the atoms at one point (e.g. the front of the train), they move, which compresses the springs connecting them to the atoms a little further away, which move, which compresses the springs connecting them to the atoms a little further… And you wind up with a wave of motion and compression traveling through the material. This is a sound wave, and it propagates at … wait for it … the speed of sound in that material. Which is always less than the speed of light in vacuum. Just as relativity requires.

  12. Gordon Davisson,

    But what is causing the compression, suddenly stopping?

    I don’t think that is a fair rationalization, because the question regarding the tunnel, and the length of the train has nothing to do with suddenly stopping, it has to do with the length of the train the moment two ends are closed. Its certainly possible to imagine both doors are connected from the top, so that they can only close simultaneously. In that case, Sarah would see the train fully inside the tunnel, whilst Adam would have to experience the door hitting some part of the train. There is no rationalization in that scenario for a sudden compression of the train, other than just trying to force the theory to make sense, when it doesn’t.

  13. Gordon Davisson: The train is actually made of atoms, connected by electromagnetic forces.

    Are atoms themselves anything other than nodes of electromagnetic forces? Are they like tiny little hard billiard balls, according to you?

  14. phoodoo,

    Listen to the part on simultaneity again. Yes, it’s wildly counterintuitive, but people have been coming to grips with it for over a hundred years now. That you and Erik have trouble grokking it is actually not an example of thinking your way to a refutation of Special Relativity.

    I’m really hoping you aren’t going to claim you’ve got hold of the raw Michelson-Morley data, and have discovered that the whole thing was faked. (Or that you and WMJ have experienced aether during a psi event.). Isn’t it ever possible for you guys to conceive that you may just have trouble understanding some things? It’s kind of the human condition.

  15. Personally I find Quantum Mechanics more accessible than Relativity. It is nicely seen in the quantum changes between elements of the periodic table. It is not well-known, but Einstein got his Nobel Prize for contributions to quantum mechanics (the photelectric effect), not specifically relativity!

    The periodic table of elements illustrate something proceeding directly from quantum mechanics:

  16. phoodoo:
    walto,

    Was this suppose to be a retort to my objection?

    Yes. Your example assumed simultaneity when you wrote this:

    Its certainly possible to imagine both doors are connected from the top, so that they can only close simultaneously.

  17. phoodoo,

    I was about to point out the same thing, but walto beat me to it. By the way, Wikipedia has a helpful article on the paradox discussed in the video:

    Ladder paradox

    Enjoy!

  18. walto: Yes. Your example assumed simultaneity when you wrote this:

    Its certainly possible to imagine both doors are connected from the top, so that they can only close simultaneously.

    Right, its one door with two ends to it. From whose perspective is it no longer one door, and how?

    That is what you failed to address.

  19. Gordon Davisson:
    The video’s treatment as a bunch of rectangles is closer to reality, but still not entirely accurate.

    One would hope…because I would have a hard time imagining the train being squashed to a 1/3 of its length packed with people… 😉

  20. phoodoo: Right, its one door with two ends to it. From whose perspective is it no longer one door, and how?

    That is what you failed to address.

    You can either have one space-time event or more than one. Where there’s any difference in space-time, there’s more than one–‘information’ has to move. So, no simultaneity.

    Anyhow, I’m no more an expert in this stuff than you are. And it’s been difficult for laypeople to grasp relativity even after reading popularizations by such mavens as Russell and Jastrow. Instead of always thinking all the scientists must be wrong when you can’t get how something is possible, you are going to have to learn the humility to accept that non-experts–since about the middle of the 19th Century–have had to come to understand that it’s much more likely that they are the confused ones when this happens.

    If it’s any consolation, even Einstein thought that quantum indeterminacy was nothing but “spooky action at a distance” and couldn’t accept THAT. (I’m totally with him on this, but, again, WTHDIK?)

  21. There are TWO theories of relativity, the Special Theory and then the General Theory.

    The Special Theory is a special case within the General Theory. The Special Theory deals with the effects of VELOCITY whereas the General Theory mostly with ACCELERATION where acceleration and gravity are related as equivalent under Einstein’s equivalence principle.

    The relativistic train issue is a case of special relativity.

    Evidence of special relativity is combination of special relativity and quantum mechanics appears again in the Periodic Table of elements! The actinide and lanthanide series of heavy elements like Uranium.

    https://en.wikipedia.org/wiki/Relativistic_quantum_chemistry

    Relativistic quantum chemistry combines relativistic mechanics with quantum chemistry to explain elemental properties and structure, especially for the heavier elements of the periodic table. A prominent example of such an explanation is the color of gold; due to relativistic effects, it is not silvery like most other metals.

    The term “relativistic effects” was developed in light of the history of quantum mechanics. Initially quantum mechanics was developed without considering the theory of relativity.[1] By convention, “relativistic effects” are those discrepancies between values calculated by models considering and not considering relativity.[2] Relativistic effects are important for the heavier elements with high atomic numbers. In the most common layout of the periodic table, these elements are shown in the lower area. Examples are the lanthanides and actinides.[3]

    https://en.wikipedia.org/wiki/Relativistic_quantum_chemistry

  22. @6:00 it’s being claimed that if the train was a solid rectangle and a force were applied at one end of the train, then it would have to be felt instantaneously at the other end of the train, which would violate Einstein’s principle that no information can travel faster than the speed of light…

    Obviously Einstein’s principle seems to be false as the “information” between entangled particles travels instantaneously and faster than the speed of light, over long distances, which was proven by many experiments…

    There are some who insist on denying this very fact but what’s new?

  23. J-Mac: There are some who insist on denying this very fact but what’s new?

    What fact is that?

    If the train was infinitely long, how much faster would the “information” between the entangled particles then have to travel over the speed of light? ;P

  24. OMagain: What fact is that?

    If the train was infinitely long, how much faster would the “information” between the entangled particles then have to travel over the speed of light? ;P

    If the universe is infinitely long, quantum entanglement should work instantaneously across the universe between 2 or more entangled particles…

  25. There is an alternative at least to a part of this whole story but I don’t think anybody here is ready to accept that…
    “Time is an illusion…however a persistent one”…

  26. phoodoo:
    Gordon Davisson,

    But what is causing the compression, suddenly stopping?

    A sudden stop that begins at the front of the train. And note that the train gets shorter from both Adam’s and Sarah’s perspective (although they’d describe the amount of compression differently).

    Think about it for a moment: a train that hits a brick wall at high speed is going to get shorter as a result. There are things about relativity that’re counterintuitive and hard to understand, but this isn’t one of them. Similarly, a stationary train that gets whacked in the face by an oncoming brick wall at high speed will also get shorter as a result. Short enough that it fits entirely inside the tunnel.

    If the train’s stoppage started at the back — say, if it had a really strong hook at the back that caught on the entrance to the tunnel — the train is going to get stretched out as a result. Stretched enough that its front end will be sticking out the far end of the tunnel before it stops (or even before the front begins to slow down).

    I don’t think that is a fair rationalization, because the question regarding the tunnel, and the length of the train has nothing to do with suddenly stopping, it has to do with the length of the train the moment two ends are closed.Its certainly possible to imagine both doors are connected from the top, so that they can only close simultaneously.In that case, Sarah would see the train fully inside the tunnel, whilst Adam would have to experience the door hitting some part of the train.There is no rationalization in that scenario for a sudden compression of the train, other than just trying to force the theory to make sense, when it doesn’t.

    It’s not a rationalization, it’s an explanation of how relativity works. You’ve just not understood it.

    Let me give you a bit of my perspective, since I studied physics in college. While studying physics, I ran into a number of things that just didn’t make sense. But what I found that as I looked into the problem further the problem was with my understanding, not with the physics. Either I just wasn’t thinking about things correctly, or the physics was conflicting with some intuition of mine, and my intuition was wrong.

    Once I’d looked into it — and thought about it — enough, it turned out that the experts had been right and I’d been wrong. Every time.

    In the specific case of the train paradox, I’ve already gone through understanding it and why there’s no actual problem, and I can state with confidence that the problem is entirely in your understanding. Specifically, you’re thinking of simultaneity as absolute, but according to relativity it isn’t. This is a conflict between relativity and how you intuitively think of as how time works.

    Now, it’s possible that your intuition is right and relativity is wrong, but that’s not sufficient to make a case that there’s something wrong with relativity itself. And since the evidence supports relativity, I’m pretty sure the problem is with your intuition.

    Another thing you should realize is that all these “rationalizations” may look like a bunch of unrelated ad-hoc attempts to patch over problems, but that’s just because you’re looking at the theory on a very superficial level. At a deeper level, special relativity is based on Minkowski geometry, and once you understand that (which takes work), all these weird and apparently ad-hoc things fall out as automatic consequences of that deeper theory.

    I had roughly the same problem understanding quantum mechanics when I was an undergrad — it looked like a bunch of ad-hoc pieces that didn’t really fit together. But then I took a proper QM class that started from a more formal mathematical approach (linear algebra!), and all those ad-hoc oddities fell out automatically as consequences of the math.

  27. Mung:
    Persistence assumes time. It was a joke.

    Really? It all depends on what persistence is and where it is located…

  28. J-Mac: Obviously Einstein’s principle seems to be false as the “information” between entangled particles travels instantaneously and faster than the speed of light, over long distances, which was proven by many experiments…

    Entangled particles do not transmit information.

  29. Steve Schaffner: Entangled particles do not transmit information.

    What do they transmit to change their “quantum states” then when one entangled particle is say… measured…? The act of the measurement of one instantaneously affects the other…What’s being transmitted then if it is not information about their quantum states?

  30. J-Mac: What do they transmit to change their “quantum states” then when one entangled particle is say… measured…? The act of the measurement of one instantaneously affects the other…What’s being transmitted then if it is not information about their quantum states?

    That is one explanation, there are others.

  31. Gordon Davisson,

    Gordon Davisson: But what is causing the compression, suddenly stopping?

    You didn’t seem to get the point Gordon. I said forget the stopping part.

    I am asking about the moment before the trains begins to stop. If two doors, which are attached come closing down at both sides of the tunnel together, will it hit the train before it has begun to stop? If Sarah sees the doors as not hitting the train, what changes in Adams perspective to make the same result?

    I don’t think you can claim the doors close at different times, because there is no rational reason why the doors suddenly became detached. You can’t say they become detached just to satisfy Adams perspective, you need to give a cause.

  32. newton: That is one explanation, there are others.

    Why would I care about other explanations? Einstein was wrong about the spooky action at the distance”– the entanglement communication between particles…
    The alternative would be that entanglement is instantaneous because the entangled particles are part of the same thing, i.e. spacetime being a part of something else…dark energy for example…

  33. phoodoo:
    Gordon Davisson,

    You didn’t seem to get the point Gordon.I said forget the stopping part.

    I am asking about the moment before the trains begins to stop.If two doors, which are attached come closing down at both sides of the tunnel together, will it hit the train before it has begun to stop?If Sarah sees the doors as not hitting the train, what changes in Adams perspective to make the same result?

    I don’t think you can claim the doors close at different times, because there is no rational reason why the doors suddenly became detached.You can’t say they become detached just to satisfy Adams perspective, you need to give a cause.

    You’re still thinking of simultaneity as absolute. Whether the doors close at the same time or different times depends on what reference frame you’re using. If the two doors close simultaneously in Sarah’s reference frame, then in Adam’s reference frame the door at the end of the tunnel closes first (and then the train crashes into it, gets squashed, and then after the back of the train has entered the tunnel the back door closes after it.

    Saying the doors are “attached” doesn’t change this at all. The front and back of the train are attached to each other two, but that doesn’t mean they stop/slow/whatever “at the same time” in any reference frame. The same is true of doors.

    Ok, let me get more specific, to illustrate the point. Rather than doors, let’s just put lights at the ends of the tunnel, and wire them to a switch in the middle of the tunnel. When Sarah flips the switch, electrical pulses travel out the wires and light the two lights. Electrical signals in wire generally propagate at roughly half of lightspeed, but that doesn’t matter here; as long as it propagates at the same speed and through the same length to get to each of the two lights, it’ll reach them simultaneously and the two lights will light up together. According to Sarah, that’s exactly what happens here, and (if she times it right) the light at the right of the tunnel will light before the front of the train gets there, and the light at the left will light after the back of the train has passed.

    But look at it from Adam’s point of view. In his reference frame, the two electrical signals are traveling through moving wire, so their speed (relative to the wire) will depend on how the wire’s moving. Essentially, the signal going to the left has to fight its way upstream against the wire’s motion, and so it takes longer. The signal going right is going “downstream”, so it’s faster and gets there first. So according to Adam the light at the right lights up first (before the front of the train gets there) and the light at the left lights up later (after the back of the train passes).

    BTW, we could also attach a system like this to the train, with lights at the front and back of the train. But if the timing mechanism (wires, whatever) is attached to the train and set up to light the lights simultaneously in Adam’s reference frame, then Sarah will see the light at the back of the train lighting up first.

  34. J-Mac: What do they transmit to change their “quantum states” then when one entangled particle is say… measured…? The act of the measurement of one instantaneously affects the other…What’s being transmitted then if it is not information about their quantum states?

    We don’t know how the math of QM connects up to reality; there are a number of very different proposals for what the connection might be (the various “interpretations” of QM), but we don’t know which one is right (or if it’s actually something we haven’t thought of).

    Some interpretations involve faster-than-light causal influences, which is what you’re talking about (the technical term is “nonlocality”). Some don’t. But even in the nonlocal interpretations, these nonlocal effects cannot be used to send information.

    In a Bell’s-theorem-type experiment, you have two spatially separated experiments running, and when you compare the results of the experiments you find correlations that cannot be explained by classical effects. But you can detect these correlations only after the fact, when you have both sets of results together. There’s no way for one of the experimenters to detect what the other’s doing at the time.

    And as I said, there are local interpretations of QM that’re consistent with all of our experimental results. So the faster-than-light causal influences might not even exist.

  35. J-Mac: Why would I care about other explanations?

    You wouldn’t unless you wanted to examine all possibilities.

    Einstein was wrong about the spooky action at the distance”– the entanglement communication between particles…
    The alternative would be that entanglement is instantaneous because the entangled particles are part of the same thing, i.e. spacetimebeing a part of something else…dark energy for example…

    That would be an alternate explanation

  36. phoodoo,

    No no, Forget that they are doors for a second, assume that instead it is a giant dome like a waiter uses to bring food to a table. If the dome comes down right when the train is in the tunnel, and Sarah sees it not hit the train because the train was funny inside the tunnel, than Adams train which is never fully inside the tunnel would get hit by the dome.

    You can claim that things don’t happen at the same time, but to claim that physical reality is also a complete illusion, and it changes to suit whatever situation you need is not justified by relativity. Suddenly things just come apart, and come back together, or become something else just to suit the theory, now we are in a completely different realm, now we are just saying that nothing exists, but is all just atoms that can become waves and go anywhere at any time.

  37. newton: You wouldn’t unless you wanted to examine all possibilities.

    That would be an alternate explanation

    Why do you think I had not considered ALL the possibilities?

  38. phoodoo,

    Now, of course you the make the claim that physical reality is indeed an illusion, and things can change their shape and form at anytime, at will, but I am pretty sure the theory of relativity doesn’t say anything about how atoms rearrange themselves to suit any shape it needs to to please Adam and Sarah’s visions.

  39. phoodoo:
    phoodoo,

    No no, Forget that they are doors for a second, assume that instead it is a giant dome like a waiter uses to bring food to a table.If the dome comes down right when the train is in the tunnel, and Sarah sees it not hit the train because the train was funny inside the tunnel, than Adams train which is never fully inside the tunnel would get hit by the dome.

    You are still assuming absolute simultaneity. It doesn’t matter if you’re talking about doors closing at the same time, or a dome coming down flat so that the right edge hits the ground at the same time as the left. If two spatially separated events happen at the same time in one reference frame, then there’ll be other frames where one happens before the other (and still other frames where the other happens before the one). It’s not that there are practical difficulties arranging simultaneous events, it’s that it’s just not defined in any absolute sense.

    For your dome example, if Sarah sees the left and right sides of the dome as landing simultaneously (in her reference frame), then Adam’ll see the right side as landing first (in his reference frame), before the front of the train gets there, and the left side landing later, after the end of the train has passed under it.

    You can claim that things don’t happen at the same time, but to claim that physical reality is also a complete illusion, and it changes to suit whatever situation you need is not justified by relativity.Suddenly things just come apart, and come back together, or become something else just to suit the theory, now we are in a completely different realm, now we are just saying that nothing exists, but is all just atoms that can become waves and go anywhere at any time.

    No, no, no, no! This is not what relativity says at all! The objects and events are described differently in different reference frames (e.g. Sarah vs. Adam), but they are just different ways of describing the same actual things. Essentially, they’re using different coordinate systems to describe the location of events in spacetime, and it’s entirely normal for the same thing to be assigned different coordinates in different coordinate systems.

    Too abstract? Ok, take a simple example: Bob, Claire, and Doug are describing the location of two rocks, on big and one small. Bob says that the big rock is four feet past the small one, and three feet to the right. Claire agrees that the big rock is for feet further ahead, but says that the small one is three feet to the left. Doug, on the other hand, says that the big rock is five feet straight ahead from the small one. Do they disagree? No, they’re just looking at the rocks from three different angles, and therefore are using different definitions of “ahead”, “left”, and “right” to describe their locations. They are using different coordinate systems to describe the rocks, and if you take into consideration the difference in their coordinate systems their descriptions are all perfectly consistent.

    The same is true for Adam and Sarah; they’re describing the same events, just using different definitions of “before”, “after”, “moving left”, “moving right”, standing still”, etc. And again, if you take into consideration the difference in their coordinate systems their descriptions are all perfectly consistent.

    But in order to do this, you need to understand the Lorentz transformation, which is what describes how coordinates shift between different reference frames. If you can’t get your head around the Lorentz transformation (including non-absolute simultaneity), this will never make sense to you.

    But that’s a problem with your understanding, not with relativity.

  40. J-Mac:
    Gordon Davisson,

    Are you serious?Have you read my previous posts? I doubt that…

    Which ones? I’ve read everything you’ve said in this thread, anyway. I disagree with a lot of it, but I’ve read it…

  41. Gordon!

    So nice to see you. You’re probably the smartest guy I’ve encountered on the internet. It’s an honor to know someone from your family of illustrious Nobel prize winning scientists — Clinton Davisson and Owen Richardson!

    I learned special relativity through independent routes, but the most compelling was taking Maxwell’s equations of electro dynamics and then showing the Lorentz transformation as a consequence. I’ve since forgotten how I did the derivation, but it was the my very first homework assignment in physics grad school! This looks similar to what I had to do:

    http://www.gsjournal.net/old/physics/hamdan1.pdf

    So if one accepts the accepted principles of Electromagnetism, relativity is a consequence.

    That said, there have been two rival relativistic theories. One by Einstein and the other by Lorentz. I’ve been following experiments by Cahill trying to defend the Lorentzian version of relativity, which allows for an ether. I tried unsuccessfully to duplicate Cahill’s experiments, but I couldn’t get my laser interferometer to stabilize. Cahill suggested other experiments, but then I ran out of time and money (since I was financing the experiments on my own).

    I’m sorry to admit, so much of what I learned in General Relativity is forgotten. I can hardly read the tensor notations anymore! Cahill seemed quite comfortable with such math, and it looked good as far as I could tell.

    But in any case, here is some of Cahill’s interesting work on revisiting the Michelson-Morely experiment.

    https://arxiv.org/pdf/physics/0610076.pdf

    I wrote to Cahill and he suggested an alternate experiment. The interferometer I tried unsuccessfully to build was this one:

    https://arxiv.org/pdf/0707.1172v2.pdf

    The interferometer seemed to be a good measurement of stress and temperature on the optical fiber! I wasn’t able to measure the Ether as the oscilloscope readouts were way to noisy.

    Hope you are well. Happy Thanksgiving.

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