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Direct Experimental Evidence of Lorentz Transformations

  1. Jan 3, 2015 #1
    Direct experimental evidence of time slowing down for moving clocks is well-known. With the advent of atomic clocks, round trip journeys taken by these clocks on slow moving(compared to light speed) jets show time differences with clocks that have not taken the journey.

    But is there experimental evidence of length contraction. I am thinking of something like sending a large molecule through a narrow stationary slit. At room temperature(slow speeds) the molecule would not make it through the slit, but if they can be accelerated to ~10% of the speed of light, more of the molecules will go through the slit.

    In this example I use a molecule since it might be easy to accelerate, but any projectile would do.
     
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  3. Jan 3, 2015 #2

    ghwellsjr

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    Length Contraction was provided by Lorentz as the explanation for the null result of the Michelson Morley Experiment. Isn't that good enough?
     
  4. Jan 3, 2015 #3

    mathman

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    Length contraction would not help it going through the slit. You would need width contraction, which doesn't happen.
     
  5. Jan 3, 2015 #4

    russ_watters

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  6. Jan 4, 2015 #5

    bcrowell

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    Magnetism is a purely relativistic effect, and there are simple, ordinary examples of magnetic phenomena that have extremely direct interpretations in terms of length contraction. There is a nice presentation of this in the classic textbook Electricity and Magnetism, by Purcell. A similar and somewhat simpler presentation is given in sec. 23.2 of my book Light and Matter: http://www.lightandmatter.com/lm/
     
  7. Jan 4, 2015 #6

    Meir Achuz

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    "Length Contraction was provided by Lorentz as the explanation for the null result of the Michelson Morley Experiment."
    But Lorentz was wrong. There is no direct experimental evidence of length contraction, but there is inferred corroboration.
    For instance, as Russ suggests, the extended decay length of muons can be interpreted as the distance getting smaller in the muon's rest frame.
     
  8. Jan 4, 2015 #7

    Dale

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    Lorentz was wrong about the aether, not about length contraction.
     
  9. Jan 4, 2015 #8

    bcrowell

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    I suppose this depends on what you consider to be "direct." I would claim that the evidence I gave in #5 is extremely direct.
     
  10. Jan 5, 2015 #9

    Dale

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    That is a good point. In some sense, the requirement for "direct" evidence simply means that the requestor is aware that there is experimental evidence but remains unconvinced by it for whatever reason.
     
  11. Jan 6, 2015 #10

    Meir Achuz

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    "Length Contraction was provided by Lorentz as the explanation for "Length Contraction was provided by Lorentz as the explanation for the null result of the Michelson Morley Experiment."
    Do you think that Lorentz gave the correct explanation of the null result of the Michelson Morley Experiment?
     
  12. Jan 6, 2015 #11

    ghwellsjr

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    What does correct mean? If it explains all the experimental results then you cannot say it is incorrect. The difference between Lorentz's explanation and Einstein's explanation is a matter of assumptions or postulates. Both correctly explain the experimental results. We cannot chose between them by any experiment. The choice is philosophical and we generally choose Einstein's because it is simpler, not because we can claim it is correct and Lorentz's is incorrect.
     
  13. Jan 6, 2015 #12
    With the advent of of atomic clocks in the last century we could measure small changes in elapsed time to better than1 part per billion enabling slowly moving clocks to show different times. I am convinced of Lorentz contraction, but I was hoping for some way to measure changes in the length of slowly moving rods to 1 part per billion.
     
  14. Jan 6, 2015 #13

    Vanadium 50

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    No way. Forget moving rods - start with the simpler case of a stationary rod. A part per billion means if you have it a few inches long you need the faces to be flat to within a single atom. It means you need to control the temperature of the rod to within one ten-thousandth of a degree.
     
  15. Jan 6, 2015 #14

    bcrowell

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    That's exactly what happens in the example I described in #5. The drift velocity of the charge carriers is ~1 cm/s. They length-contract, and the result is a measurable force.
     
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