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Special Relativity Between Reality and Illusion

  1. Aug 14, 2006 #1
    Hi,
    Q1: Do the effects of time dilation and length contration really happen, or they seem to happen to us being in different inertial frame, because our means of observation ( say, by looking by means of coming relativistic beams of light) draw this illusion on us and show us something different from the reality.

    Q2: Do the 2 effects kind of cancel each other (contraction/dilation) so as to make the light speed constant?

    Q3: In Twin paradox, the difference in ageing should be just a relativistic concept (or at least, that's what I think). How could the physiological and chemical processes inside the bodies be affected. Is It possible that the chemical reaction used to proceed in 1 sec and now in 2 sec just because you travel so fast?!!

    thanks
     
  2. jcsd
  3. Aug 14, 2006 #2

    jtbell

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  4. Aug 14, 2006 #3

    DaveC426913

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    Q1: A reality does not exist over and above what we measure. So yes, it really happens.

    Q2: You've got the cart before the horse. Because space and time are limited by light speed, so it is that contraction and dilation are what happens.

    (Think of a seesaw. Spacetime and lightspeed are the axle, the 2 seats are measurable effects. You're saying "the seats go up and down, thus ensuring any movement of axle cancels out and it remains motionless". I'm saying "no - the axle remains motionless, period. It is the seats that are free to move, subject to the axle's domination".)

    Q3: "...a relativistic concept..." Relativity is the reality of our universe. What is illusory is our misguided perception that time runs at the same speed everywhere in it.


    This is very important to accept or you will always struggle with these issues. Our universe is not built the way Netwon thought. Time is not constant and unchanging, mass is not constant and unchanging. These things are resultant properties of the controlling principle of the universe which is relativity.
     
    Last edited: Aug 14, 2006
  5. Aug 14, 2006 #4

    pervect

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    A question about reality is ultimately a philosophical question. What is "real" - and how do you know when something is "real"?

    Because philosophical views vary so widely, we would need to know more about your personal philosphical views to give an intelligible answer.

    I personally tend to regard things which are observer-independent as "real". This philosophical viewpoint works well in most disciplines (but perhaps not in quantum mechanics). From my philosophical viewpoint, time and distance are not "real", or perhaps not "as real" as the Lorentz interval, because time and distance depend on the observer, while the Lorentz interval is observer-independent.

    This may or may not be useful to you, depending on your personal philosophy as to what constitutes "real".
     
  6. Aug 14, 2006 #5

    CarlB

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    There are several different points of view that these questions can be approached from. I will give here an approach that gives the same computations as the more common interpretation, but is less common. Essentially, it was this interpretation that was eliminated by Einstein's 1905 paper on special relativity. This is the "Lorentz-Poincare ether theory". You can learn more about it by searching on the web. For example:
    http://www.google.com/search?hl=en&lr=&q=lorentz+poincare+ether+site:arxiv.org

    A1: Reality does exist over and above what we measure, so no the effect does not "really" happen, at least in my opinion. You can choose either way of thinking about it, in that you will get the same result no matter which way you think about it. It's just a matter of interpretation. However, do note that if you get asked questions on an exam, your professor may insist that you accept one particular interpretation over another. In this case, simply parrot back what you've been told.

    A2: Yes, the speed of light is in units of length over time, so length and time both have to be affected together if the speed of light is to be unchanged by change of inertial reference frame.

    A3: Yes, if you wish you can think of the aging of a twin as being slowed down because the chemical reaction rates are slowed down. All these effects boil down to the same thing, that electricity and magnetism (and other forces) are effected by changes in reference frame. Since chemical processes are made out of electricity and magnetism, they too are slowed down.

    Maybe a parable would help here. When God designed the universe, he wanted complicated creatures to be able to exist on it. Complicated creatures need complicated chemistry and chemistry depends (almost) exactly on the laws of physics. In order to allow His creatures to thrive, He therefore designed the universe so that the laws of physics would be nearly identical for every inertial frame. That way, if a planet moved from one part of the galaxy to another, it wouldn't have all its creature's DNA suddenly quit working, for example.

    As a result of His design, it is very difficult for physicists to discern the difference between one inertial frame and another. This fact gives a tool for determining what physical laws matter must follow. The rule is that the results of your calculation cannot depend (much) on the choice you make for the frame of reference.

    Regarding the "almost" and "much" included in parentheses in the above. Compared to God (and mathematics), humans are very ineffective things. Humans are very weak and short lived. The equipment that they build is very clumsy and produces very inaccurate measurements. If humans were strong they would be able to accelerate electrons to the Plank mass with their bare hands. If humans were long lived they would be as old as the stars. If our equipment were not clumsy it could probe space down 10^500 factors below the size of quarks. If our measurements were accurate, we would know the mass of the electron to a trillion decimal places instead of twelve.

    Because of the ineffectiveness of humans, it is not possible for us to (yet) discern the difference between two inertial rest frames. Now there is a true reference frame and if we knew what it was, we could figure out how fast the twins were really aging, and we would know which was getting older faster. But God created the universe so that our chemistry would not depend on the inertial frame and in doing this, as an accidental side effect, He made it very nearly impossible for us to distinguish between inertial frames.

    Therefore, so long as the twins never meet again, we cannot tell which one is really aging faster. God knows, but we do not. Maybe someday we will figure out how to find the true reference frame, the one that gives real times. However, if the twins do eventually meet up again, then we can cancel out the effects of our not knowing what the true reference frame is, and then we can deduce which twin has aged more.

    Carl
     
    Last edited: Aug 14, 2006
  7. Aug 15, 2006 #6
    Hi,
    thanks to all of you.
    Wow..I didn't know my question is a topic of such controvestial arguments..I felt a bit that my question is somewhat philosophical.

    What I meant by "real" is that it is a physical phenomenon that is , as pervect said, observer-independent.
    I thought maybe these effects should not happen but because of our ineffective means of observation, they appear to be like so, which is against DaveC426913 veiw:)
    Like because the light (means of perception) travels from different positions or emitted at different times ,or because our motion makes us moving closer to a source of light farther than the other while they were simulatanious.
     
  8. Aug 15, 2006 #7

    russ_watters

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    Just for a little simple (too simple, but it is something that may not have been clear from the more in depth posts above), we do observe relativistic effects to occur. While determining exactly what happened depends on the observer, both observers will agree that relativity is the cause of any disagreement.

    To give an example, GPS satellites have their clock rates adjusted prior to launch so that they will stay in sync with earthbound clocks once launched in orbit.

    Regarding Q3, the twins paradox is a thought experiment and AFAIK, we have not yet been able to witness relativistic phenomena in biologic processes. But time dilation has shown up in enough differing physical processes that it is reasonable to conclude that it is not just individual physical processes that happen to be affected by speed in exactly the same way, but it is time itself that is observer dependent.
     
    Last edited: Aug 15, 2006
  9. Aug 15, 2006 #8

    George Jones

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    I agree with pervect about philosophy and personal philosophy.

    Personally, I (like, I think, Russ) vote real.

    After all, the universe isn't Strawberry Fields! :biggrin:
     
  10. Aug 15, 2006 #9
    A1: The data on the ISS satellite shows a slower clock while
    the GPS satellite shows a faster clock (compared with a ground
    clock). Since elevation makes all clocks faster (gravitational
    red shift), the slower clock can be argued to be real velocity time dilation,
    if mechanical effects are all accounted for.

    A2: This is the problem with Special Relativity. If length is contracted
    and time is dilated as well, neither length contraction nor time dilation
    are real but mere math manipulations.

    A3: It's possible that one moves through time at different "rates"
    according to their initial accelartions.
     
  11. Aug 16, 2006 #10
    Pervect gave the enlightening answer to all the questions - it is the Lorentz interval that is real - it is the same for all observers. Space measurments and time measurments individually are observer dependent - and therefore one needs a precise definition of what "real" means

    Example - in a GPS satellite - the satellite clock appears to run slower than the earth based clock (if we ignor altitude) - but the satellite clock has both a temporal component and a spatial component when measured from the earth clock - so the satellite clock accumulates less time during a one orbit journey - but according to SR it cannot be said that it runs slower - it just accumulates less time during the spacetime interval. In contrast, in Lorentz ether theory, the satellite clock is claimed to actually run slower.
     
    Last edited: Aug 16, 2006
  12. Aug 16, 2006 #11
    Quite correct, that is the difference between the two theories!

    While the theory of special relativity postulates a length contraction as a contraction of space and a time dilation as a contraction of time the Lorentz ether theory maintains the notion of absolute time and space and postulates that clock rates slow down due to mass increase and lengths get contracted due to traveling in the ether.

    So far both theories show the same results.
    Personally the Lorentz ether theory makes makes a lot more sense. :smile:
     
    Last edited: Aug 16, 2006
  13. Aug 16, 2006 #12
    Aren't you forgetting that Lorentz theory needed (and still needs) to have additional ad-hoc assumptions tailored specifically for each experiment? I.e. the LET principles are not sufficienr, one needs those ad-hoc additions in order to justify the results of the many experiments that are explianable by SR from first principles, no ad-hoc additions.
    So, SR and LET are NOT equivalent.
     
    Last edited: Aug 16, 2006
  14. Aug 16, 2006 #13

    CarlB

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    I've never heard of any such assumptions. To get the Lorentz theory from Einstein's special relativity, all one need do is assume that one of the inertial frames is the ether.

    The physical issues are well described in Physics Letters A 333 (2004) 355:
    http://www.citebase.org/abstract?id=oai:arXiv.org:physics/0410245 or
    http://arxiv.org/abs/physics/0410245

    Carl
     
  15. Aug 16, 2006 #14
    The Consoli paper is well known as an example of what happens when someone writes papers about hypothetical experiments in ignorance of previously executed experiments. Consoli/Constanzo seem ignorant of the fact that the MMX experiment in refractive media had already been run. Twice: once by Shamir and the second time by Trimmer, both times with null results. See references here:

    Trimmer et al., Phys. Rev. D8, p3321 (1973); Phys. Rev. D9 p2489 (1974).
    A triangle interferometer with one leg in glass. They set an upper limit on the anisotropy of 0.025 m/s. This is about one-millionth of the earth's orbital velocity and about 1/10,000 of its rotational velocity.

    Shamir and Fox, N. Cim. 62B no. 2 (1969), p258.
    A repetition of the MMX with the optical paths in perspex (n = 1.49), and a laser-based optics sensitive to ~0.00003 fringe. They report a null result with an upper limit on Vaether of 6.64 km/s.

    As to the support of my
    post, it comes from a well known CMWill paper on the subject:

    http://prola.aps.org/abstract/PRD/v45/i2/p403_1

    It is not sufficient to assume the presence of the one priviledged frame, one must also assume that light speed is isotropic in tha frame (but not in the other frames). One must also ad ad-hoc assumptions for each particular experiment (see the CMWill paper) or see the well known Mansouri-Sexl papers from 1977.
     
    Last edited: Aug 16, 2006
  16. Aug 16, 2006 #15

    CarlB

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    I don't mean to quote Consoli on the experiments, but instead simply to point out that Lorentzian relativity is equivalent to Einstein's special relativity. By "Lorentzian relativity" I do not mean to describe the 1904 theory of Lorentz (which if I recall, had moving objects contracted but did not deal with the rate of time experienced by moving objects and so was just wrong), but instead simply Einstein's relativity with the additional supernumerary postulate that one of the inertial reference frames is preferred (but undetectable). This, of course, is equivalent to Einstein's relativity.

    The phrase from logic that comes to mind is "absence of evidence is not evidence of absence".

    I don't have access to that at home, maybe you can quote from it. The abstract certainly doesn't read on Lorentzian relativity. I'm going to guess that the author showed that some theory that is not equivalent to Einstein's relativity was eliminated by experimental data.

    Carl
     
    Last edited: Aug 16, 2006
  17. Aug 16, 2006 #16
    "That" is the Mansouri-Sexl theory. And it requires additional ad-hoc hypothesises for each experiment. I have a scan of the Mansouri-Sexl papers, I'll try to append them on my next post.




    I have a scan of this paper someplace as well. CMWill is talking about the "official" LET, which is the Mansouri-Sexl test theory. He quotes exactly the ad-hoc "additions" for a series of experiments. That would complete the proof, correct?
     
  18. Aug 17, 2006 #17

    samalkhaiat

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  19. Aug 17, 2006 #18

    samalkhaiat

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  20. Aug 20, 2006 #19

    CarlB

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    Accidental means that it is a low energy symmetry, one that disappears at higher energies. Since the standard model is only an effective theory, any of its symmetries could be accidental.

    No, a lot of things are very very difficult. For example, if it were just a little bit easier to build nuclear weapons, a good bit of the world would have become radioactive wastelands back in the 1940s.

    Getting back to physics, if the elementary particles are composites made up of preons, we really cannot be certain what the maximum speed of those preons are. It's easy to suppose that they are just like everything else we see and limited to speed c, but then again, we can't get at them so we can't measure their speeds. It's a region where we have no measurements.

    Carl
     
    Last edited: Aug 20, 2006
  21. Aug 21, 2006 #20

    samalkhaiat

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