Special Relativity

This video reviews Special Relativity from the bottom-up viewpoint, in the spirit of John Bell.

  • We start with the three phenomena – length contraction, time dilation, clock desynchronization – and then derive that c is measured to be constant, and that you cannot tell which frame is at absolute rest.
  • We look at a breather (non-linear, localized wave) as a particle model.
  • Finally, we study a spinning ring.

After this, any confusion around paradoxes should melt away.



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13 Responses to Special Relativity

  1. P Vilas Tulachan says:

    Eexcellent explanation on Special Relativity! The animation is awesome. What tools didn’t use to create the animation?

  2. mark says:

    ok, your still stuffing this up. You are actually saying at 11:05 that special relativity is only an apparent difference, but Einstein said that there is a real length contraction, not just what he thinks he measured.

    You are claiming that the rulers have shrunk, that time has slowed, so the net effect is that the observer thinks the other observer has shrunk, and vice versa. and they are both right. But if both observer A and observer B both get the same result, because some trick of shrinking rulers, then the problem remains, one is claiming that the other has shrunk, compared to him, but they both cant be correct. If these claims are equally applicable to either ship, because we cant tell who is moving, then there can not be any difference measurable by anyone can there?

    • bernander says:

      Pretend that the guy at rest is “really” at rest, with no contraction or time dilation. Then the moving guy “really” does shrink and time dilate.
      So we can pretend there’s an external reality where things are not symmetric, but when the two guys measure each other it looks symmetric.

    • Michael McGinnis says:

      One way to look at the length contraction is to remember that when you measure the length of a moving object you are measuring the location of the back of the object compared to the location of the front at the same time. That is, you are noting their locations in space at a given instant in time, for you.

      But, what is simultaneous for you is not necessarily simultaneous for an observer in motion relative to you. In this way, the instantaneous measurement of the locations of the front and back of the object are actually different points in spacetime, depending on the motion of the observer.

  3. mark says:

    and your stupid method to synchronize clocks end up with them NOT synchronized!
    Who cares how fast light is? if 2 events happen at the same time, then of course someone further away than another observer, will “get the message”, or see the effect, later than the other guy, BUT he will make the adjustment in time because he knows that the message or light took a certain amount of time to reach him.
    So although it SEEMS to his senses that the two events were NOT synchronized, a bit of math will give him the assurance that in fact, the two events occurred at precisely the same instant, in ABSOLUTE time, not rubbery time or jello distances away.

    • bernander says:

      The person moving believes the clocks to be synchronized, trusting the synchronization procedure, but the person at rest clearly sees that they are not. Yes, that is the point.

      • mark says:

        Bernander, Please prove the rationale behind the claims presented here. So far you are just making stuff up and claim things will be a certain way, when logic and reason say they will not.
        You have not explained how what one observer “believes” he is seeing, can be some factor that actually changes the measurements of physics.

        • bernander says:

          I’m happy to discuss, but please keep the tone civil, and avoid words like “stupid” and “making stuff up.”

          All A and B can do is measure. (I avoid the words “see” and “observe” and “determine what is.”) In order to measure, they need rods and clocks and they need to synchronize clocks at different locations. That’s it. If A and his clocks all slow down, A has no way to tell. If A and his rods contract, A has no way to tell. If A’s two different methods for synchronizing clocks actually don’t work (even though the two methods yield the same wrong result), A has no way to tell.

          A trusts the clocks, A trusts the rods, A trusts the method(s) of synchronizing clocks. Same for B. Or instead of “trusts” use the word “believes that they can be used for measurements.”

          When A and B then measure the other’s clocks and rods, the results are symmetric, even though only one of them “really” is moving and suffer the three effects.

          Of course, if A and B somehow knew that one of them is “really” at absolute rest, they’d let that observer call the shots and decide what true length and clock rates are, but they don’t know that. That’s the whole point.

          • mark says:

            ok, ill promise to be civil. My beef is not with you, its with the Relativists that preach this stuff as if its gospel and true.
            You have just been taken on a ride, without knowing it. Thats my opinion.
            Now, A and B both have equal equipment, synchronized clocks and identical rods. B goes for a trip, he still measures the inside of his ship the same as it was before, and A watching B also is going to measure the ship as being the same as before it departed. Time will remain the same for both. Motion can not effect time or distance for either of them. How can you get from that logical expectation to Einsteins shrinking time and distance, but only for one of them? I am well aware of the theory, but I want to step through it one piece at a time, to show that it can’t be correct in any sense.

  4. Michael McGinnis says:

    Is the clock desynchronization for the moving clocks caused during acceleration, when the clock at the front is at higher potential energy (like gravitational potential energy) than the clock at the back?

    • bernander says:

      Yes and no. Yes: if B starts at rest with synchronized clocks, then accelerates, the front clock will then be ahead of his rear clock (according both to himself and to A who remained at rest). As you say, you can conclude this from the Equivalence Principle. Alternatively, you can conclude this from a situation similar to that of Bell’s paradox (in the video): cut the ship in half, accelerate both pieces to a velocity v, where both are length contracted, then slightly slow down the front half so that it again makes contact with the rear half; during this slowdown, its clock runs slightly faster than the rear half. B would also notice that his clocks are out of synch and would need to resynch them.
      No: the desynchronization of B’s clocks witnessed by A is different. Before B measures something, like c or A’s length of A’s clocks, he needs to first synchronize his own clocks. This he can do in various ways. Two ways are shown in the video. Both ways result in exactly the same desynchronization from A’s point of view (and perfect synchronization from B’s point of view).

  5. Anwar Shiekh says:

    The Lorentz contraction is real as it can be turned into a true compression

    Can. J. Phys., 70, 458, 1992

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