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Happy Birthday, Special Relativity

  1. Jun 30, 2005 #1

    robphy

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  3. Jun 30, 2005 #2

    George Jones

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    100 years young, still compellingly beautiful, and a long life ahead of her!
     
  4. Jun 30, 2005 #3
    Special Relativity is amazing and although it is its' 100th Birthday today, I predict that General Relativity will not live to its centennial, and will be revised sometime before 2016.
     
  5. Jun 30, 2005 #4

    Pengwuino

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    Lets all give SR a present, whos with me
     
  6. Jun 30, 2005 #5

    selfAdjoint

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    How about a moratorium on amateur attempts to falsify it? No more trains, twins, spaceships,...
     
  7. Jun 30, 2005 #6

    selfAdjoint

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    How about a moratorium on amateur attempts to falsify it? No more trains, twins, spaceships,...

    STO LAT!
     
  8. Jun 30, 2005 #7

    robphy

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    Trains, spaceships, etc... help us understand the consequences.

    Here are some ideas for a "birthday present for SR":

    1) draw more spacetime diagrams and appeal to geometry,
    2) adopt consistent and unambiguous terminology [definitions!], and
    3) eliminate poor phrases and poor analogies.

    I think (1) helps make the algebraic calculations more concrete.
    I think (2) gives us a common language.
    I think (3) removes "myths" and other "folklore".
    Otherwise, folks are arguing over semantics, often misusing or misinterpreting mathematical symbols.

    (When we analyze forces on an object, we draw [or should be drawing] Free Body Diagrams before plopping down equations. We should do the same for analyzing situations in relativity.)

    4) drop the word "Theory" when discussing Special Relativity.
    [tex]\mbox{Theory of\hspace{-9ex}{\color{red}-------------} Special Relativity}[/tex]
    [tex]\mbox{Special Theory of\hspace{-9ex}{\color{red}-------------} Relativity}[/tex]
    [tex]\mbox{Special Relativity Theory\hspace{-7ex}{\color{red}-----------}}[/tex]
     
  9. Jun 30, 2005 #8

    Aer

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    All of you seem to have some background in relativity, hopefully one or more of you will be able to clarify something for me. My question is posted here - post #26. Although it would be helpful if you read the details of the problem as posted in the thread starter.
     
  10. Jun 30, 2005 #9

    Pengwuino

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    Never! Ether ether ether!!!

    On a more serious note, people should be allowed to try to falsify things. If they figure something out that we all missed, more power to them! Didn't Einstein say one of the reasons he was able to come up with SR was that he thought like a child and went against conventional wisdom?

    And by the way, when i ask this question to myself, i feel like im asking a stupid question but i wanted to ask other people anyways incase its not actually stupid. Can you derive SR from classical physics?
     
    Last edited: Jun 30, 2005
  11. Jun 30, 2005 #10
    geeze, we're such geeks.
     
  12. Jun 30, 2005 #11
    Yeah, why not? It's essentially a consequence of Maxwell's equations, which are purely classical. (Assuming of course that Maxwell's equations are written the same in all reference frames.) So yes.
     
  13. Jun 30, 2005 #12

    Integral

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    All you NEED to derive SR is Einstein's 2 postulates. Of course all he had to base it on was Classical Physics. So I would guess if you wanted a derivation based on Classical Physics you need only read Einstein.
     
  14. Jun 30, 2005 #13

    Aer

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    So what exactly is your reason for dropping the word "theory"

    Theory: a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena; "theories can incorporate facts and laws and tested hypotheses"; "true in fact and theory"

    Are you implying Special Relativity is not any of the above? :confused:
     
  15. Jun 30, 2005 #14
    I'm not wearing socks tomorrow! :biggrin:
     
  16. Jun 30, 2005 #15
    Maybe we should make it the Special Law of Relativity! Of course, that can cause problems when it needs revision, but Einstein deserves it. When did Newton's theories start getting called laws?
     
  17. Jul 1, 2005 #16
    The answer to your question is yes. Using basic classical physics and an ether frame you can derive equations that match the predictions of special relativity to almost 100%.
     
  18. Jul 1, 2005 #17

    arildno

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    Sir Joseph Larmorr (Lormar?) developed an ether theory superficially consistent with classical physics, and thus, in the first decade of the 20th century, Cambridge theoretical physicists dismissed Einsein's approach as both unnecessary and overly philosophical.

    However, when GR came along, Larmor's theory was shown to fail miserably when trying to accomodate effects of gravitation. That is why his project was abandoned.
     
  19. Jul 1, 2005 #18

    pervect

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    Using basic classical physics and an ether frame, one can predict that the Michelson-Morley expeirment should not have a null result. Unfortunately, experimentally, it does have a null result. This should be enough to show that the "ether" idea is not compatible with basic classical physics. Only a wild "ether enthusiast" could make the claims that wisp is making above.

    At this point in time, one has to add in additional forces and/or "scalar fields" to have any sort of preferred frame or "ether". There is currently no direct experimental evidence that such forces or scalar fields exist. The assumption that such forces or scalar fields may exist is not "basic" classical physics, but a highly speculative extension to classical physics.
     
  20. Jul 1, 2005 #19

    selfAdjoint

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    That was Larmor. And don't forget Voigt, who had an ether theory where the speed of light was independent of source speed, and actually derived some genuine relativistic results.
     
  21. Jul 2, 2005 #20
    Scientists agree that the "null result" of the MMx does not rule out the existence of ether. And Dayton Miller's work did detect an ether flow effect when he repeated the MMX at altitude.
    I believe there is a simple explanation for the null result on the earth's surface on what effectively is a two-way light speed measurement.
    I'm not a wild ether enthusiast, just someone open-minded enough to challenge views that do not comply with commonsense principles.
     
  22. Jul 2, 2005 #21

    selfAdjoint

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    Fair enough but we have had many theads on ether alternatives to GR. The devil is in the details and I refer you to them. Look up ether, and also aether, in this subforum.
     
    Last edited: Jul 2, 2005
  23. Jul 2, 2005 #22

    pervect

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    There are a lot of tests of special relativity nowadays, other than the MMX experiment. The MMX is just one experiment of a long line of experiments. Relativity has passed them all. Including a large number of tests of the "one-way" isotropy of the speed of light.

    http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#one-way tests

    MMX is important because it is the first (and as far as I know the only) prediction that "ether theories" nave ever made. Ether theories failed this experimental test (their very first test). Any "ether theory" that we have now that is compatible with MMX is the result of a "fix-up" of a failed theory.

    There are a very few varieties ether theories out there that actually are indistinguishable from special relativity. In these cases, the "ether" is not so much disproven as shown to be irrelevant. In these cases, you can use the ether if you want, but since the special relativistic expalantion is much more elegant, and more importantly much more widely understood, there is no compelling reason to use ether theories that are equivalent to SR.

    Many more ether theorists than the few varieties that are compatible with SR _claim_ to have theories that are compatible with SR (read: indistinguishable from SR). These claims are often incorrect. This is unfortunate, because a few people seem to have mental blocks due to their personal philosophies which seem to prevent them from understanding or accepting special relativity. "Ether theories" could serve a potentially useful purpose in providing a philosophical interpretation of relativity that they might be able to accept philosphically.

    My expeirence has been that it is only people who are attracted to ether theories are one who have a strict and rigid personal philosphy of how the universe "should be", one that they have made up in advance, and one that conflicts with relativity. In general, such people ignore the experimental results and go with their preconceived notions. Occasionally they can find a way to justify their pursuit of their preconceived ideas in as being "open minded", which is really rather ironic.

    My experience has also been that people who urge others to be "open minded" really want other people to believe the exact same thing that they do :-).

    In any event, being "open minded" isn't particularly compelling to me. Being correctly able to predict the results of experiments (i.e., being not "open minded", but being *right*) is the real goal, IMO.
     
  24. Jul 5, 2005 #23
    I've spent a lot of time looking at the one-way tests and have not been convinced by the link suggested, which I believe was compiled by Tom Roberts and others. (PS: The link has gone off line)
    I found his write up on ether classes missed out completely an important third class, which is the real answer. I posted a longer explanation on this or a similar forum a year back, explaining the errors in his work.

    I'm not convinced that GPS tests are valid one-way tests, because all calculations are based on the assumption that the speed of light is constant. And the amazing accuracy that results has a lot of help from correction tables/factors added in.

    With the recent progress made by researchers at the U.S. National Institute of Standards and Technology, soon we will have atomic clocks that are 1,000 times more accurate than current ones.
    I hope soon that someone will have the sense to carry out a basic one-way speed of light test using two of these clocks and a laser. That will be the real test for SR.

    The advantage of a good ether theory is that it will explain the physical cause of relativistic effects, something that relativity cannot do. The equations may not look as simple as the SR ones, but the important thing is to understand the truth so that real progress can be made.
     
  25. Jul 5, 2005 #24

    pervect

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    There is a class of ether theories that one-way tests cannot falsify - thoes are the ether theories that actually are equivalent to SR.

    Relativity, however, makes a beautiflly simple prediction that is in accordance with all experiments to date:

    This prediction is that the clock synchorinzation method that makes momentum an isotropic function of the measured velocity is the same clock synchroization method in which the speed of light is isotropic.

    Thus when coordinates are used that make matter behave isotropically, light also is isotropic, and vice-versa - when coordiantes are used that make light behave isotropically, matter is also isotropic.
     
  26. Jul 5, 2005 #25
    Pervect

    This was the basis for Tom Roberts' work on ether class types - if they are equivalent to SR then no experiment can divide the two. So why bother with the ether?

    However, the important third class that he missed out can be shown to be only approximate to SR, and not 100% equivalent. New advances in clock technology should show up this difference, if people are prepared to look for it.
     
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