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What evidences of relativity do you find the most compelling

  1. Sep 2, 2005 #1
    Just like to get an idea what most other people find to be the most important evidences. GPS, MMX, Stillwell-Ives, Pound-Rebka, Perihelion of Mercury?

    Go ahead and list a few of your favorites but rank them from most to least important in your mind. SR GR... You can separate them if you want but I was thinking in broad terms...
     
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  3. Sep 2, 2005 #2
  4. Sep 2, 2005 #3

    LeonhardEuler

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    Well, I really don't know much about GR, but as for SR, here is what convinces me:
    1. The inconsistancy of Maxwell's equations without relativity
    2. The Michelson-Morely experiment
    3. The various technologies that depend on calculations from SR to work and do
    4. Hafele and Keating's experiments with muons.
    Those things pretty much clear any feeling of doubt in SR I had before studying it. I never actually believed that SR was wrong, but I could never really convince myself that all its wierd predictions were true before I learned about those things.
     
  5. Sep 2, 2005 #4

    Nereid

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    SR: QED (the most accurate theory we have, as in - the most detailed observations match theory ... to x decimal places, where x >12).

    GR: orbits of neutron star binaries (loss due to gravitational radiation ... detected from objects that are so impossibly far away, as measured by any distance scale that any human can reasonably claim to grasp, intuitively).
     
  6. Sep 3, 2005 #5

    jtbell

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    The fact that many many many experiments involving high-speed particles have been done at places like Fermilab, CERN, and SLAC, all using relativistic equations for mass, energy, and momentum, and producing consistent results for properties of electrons, protons, muons, etc. I would be astonished if all these experiments could be analyzed consistently using non-relativistic equations.
     
  7. Sep 3, 2005 #6

    Chronos

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    Pound-Rebka, hands down. GR is the only viable explanation. Nereid's example is also compelling. Only GR offers a good explanation for the decay of binary neutron star's orbits. PR is superior, IMO, because it rules out any weird cosmological effects. jt has the best example in favor of SR. Particle accelerators reconfirm SR daily. They do not, however, confirm GR as firmly as PR or binary neutron stars. Bear in mind SR is a special case of GR.
     
    Last edited: Sep 3, 2005
  8. Sep 3, 2005 #7

    quasar987

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    Could you please briefly describe what Pound-Rebka is? Thx.
     
  9. Sep 3, 2005 #8

    selfAdjoint

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    From Putting Relativity to the Test :

    Earthbound Redshift
    In 1960, Robert V. Pound and Glen A. Rebka demonstrated that a beam of very high energy gamma rays was ever so slightly redshifted as it climbed out of Earth's gravity and up an elevator shaft in the Jefferson Tower physics building at Harvard University. The redshift predicted by Einstein's Field Equations for the 74 ft. tall tower was but two parts in a thousand trillion. The gravitational redshift detected came within ten percent of the computed value. Quite a feat!

    Solar Redshift
    In the 1960s, a team at Princeton University measured the redshift of sunlight. Though small, given the Sun's mass and density, the redshift matched Einstein's prediction very closely.
     
  10. Sep 3, 2005 #9

    Garth

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    All the Pound-Rebka experiment has measured is that there is a red shift and this red shift is equal to the change in Newtonian gravitational potential. This is consistent with GR but it may be consistent with other explanations too, such as photons losing PE in a pseudo-Newtonian theory.

    Gravitational red shift in GR is a time-dilation effect caused by the curvature of space-time. This time dilation affects photons but the question remains as to what effect it might have on atoms as well.

    In GR, which treats fundamental particles as having constant proper mass, time dilation has no effect on atoms, therefore the red shift is a confirmation of the existence and amount of time-dilation as predicted by GR.

    However if time-dilation does have an effect on fundamental particles as well then this effect will be cancelled out when a time-dilated atom measures the energy of a time-dilated photon. In that case there must be another expanation for the red shift such as the atomic particles also gaining mass through gravitational potential energy. Not a red shift by the photon but a 'blue shift' by the atom. Of course this is not standard theory as that would violate the equivalence principle and a consistent theory to handle this would be required. The published and testable Self Creation Cosmology does just this.

    Garth
     
  11. Sep 3, 2005 #10

    quasar987

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    Hasn't there been an experiment where they mount a clock on a plane, make it fly, and after it lands back, compare the time on plane w/ time on earth, and the separation matches special relativity's prediction very well?
     
  12. Sep 3, 2005 #11

    Nereid

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    Would you like to contribute your favourite answer(s) to the OP's question Garth?
     
  13. Sep 3, 2005 #12

    Garth

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    Yes indeed!

    Of course we cannot prove relativity but rather perform experiments that are consistent with its predictions, the more hoops it 'jumps through' the more compelling the 'evidence' establishing it as the accepted model. A good scientific theory is one that not only has great explanatory power but one that can be falsified, both SR and GR can be falsified.

    I will not go into the no-aether/aether debates on these Forums about SR, which I take as well tested and of profound and robust foundations within its sphere of validity.

    My interest lies in GR, which also has passed through many 'hoops', not only at the time of its conception; the precession of the perihelion of Mercury and the deflection of light at the total eclipse of 1919 but of many others since, tested to a high precision, some by space technology that didn't exist in the first half of the last century.

    However most of these tests predict an effect that can be broken into a space-curvature component and a time-dilation component; which in GR are equal, each contributing half of the total effect. The deflection of starlight/radio waves passing close to the Sun is a prime example. However, it is possible that another theory may exist in which the space-curvature and time-dilation components contribute different proportions of the same overall prediction as GR.

    As a number of these tests have the same combination of equal space-curvature and time-dilation components it is not surprising that a theory that passes one test passes the others as well.

    The interesting thing about the geodetic precession of the Gravity Probe B gyros is that in that precession the space-curvature component contributes 2/3 and the time-dilation component only 1/3 of the total. Thus an alternative theory that passes the first set of tests would not also pass this one.

    Therefore I will find the Gravity Probe B geodetic precession measurement the most compelling evidence supporting the General Theory of Relativity.

    I cannot finish before adding that in Self Creation Cosmology in these tests the space-curvature effect is ½ that of GR while the time-dilation effect is 3/2 that of GR. Thus in the first set of tests (all those to date) the total prediction is [(½ x ½ + 3/2 x ½)GR] equal to GR whereas in the GPB geodetic measurement it is [(½ x 2/3 + 3/2 x 1/3)GR] = 5/6GR. i.e. 5.5120 arcsec/yr rather than the GR value of 6.6144 arcsec/yr. We wait and see!

    Garth
     
  14. Sep 3, 2005 #13

    Aether

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    Special relativity is empirically equivalent to an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity.

    So, aren't all of these "evidences of relativity" really evidences of something slightly more general than relativity per se?
     
  15. Sep 3, 2005 #14

    Nereid

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    Surely this begs the question, 'whence the time dilation and length contraction'?
    How could you tell?
     
  16. Sep 3, 2005 #15

    Aether

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    Yes it does.

    By the empirical equivalence of SR with an ether theory taking into account time dilation and length contraction but maintaining absolute simultaneity.

    I do not doubt any of the above mentioned evidence, not at all...except, wrt neutron star binaries isn't there an unresolved issue of a possible unseen third object? But since these two theories are emprically equivalent, how can any of the evidence mentioned possibly weigh in favor of relativity per se?
     
    Last edited: Sep 3, 2005
  17. Sep 3, 2005 #16

    Nereid

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    I think I missed it, first reading; you're talking about SR Aether, not GR?

    Unless I've completely missed the boat, this is not unlike Garth's idea - there are lots of theories that give 'SR' in its domain of applicability, the 'real' question is: "which of the generalisations best matches the full set of good observational and experimental results?"

    In this regard, I like the clarity of SCC - GPB will tell (unless the error bars are far, far larger than expected). (BTW, this 'tweak GR to test GR' has a long, and IMHO honourable, tradition).

    However, AFAIK, there isn't any 'ether-based' alternative to GR (except, possibly, as GR formulated in a way so as to include an 'ether', but - in terms of anything determinable experimentally or observationally - no different, even in principle).
     
  18. Sep 3, 2005 #17

    Aether

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    Yes, for now.

    Perhaps "which of the generalisations can definitely be ruled out"?

    Let the chips fall where they may...happy hunting Garth!

    Good point.
     
  19. Sep 3, 2005 #18
    I think this has been done quite a few times. In one instance a US Navy aircraft flew slowly in a 20-mile loop around Chesapeake Bay for fifteen hours. This was for GR, though.
     
  20. Sep 6, 2005 #19
    Yeah, the aether theory that is like GR is one in which aether has varying density. Light curvature is a refraction mechanism. It's an aether absorbton theory or some such where particles all absorb aether at some rate and cause a localized rarefaction of the medium and therefore gravity becomes equivelent to bouyancy.

    So yeah, in effect it's aether tailored to fit GR.


    Hafele-Keating
    That experiment is somewhat deprecated. GPS is better.
     
    Last edited: Sep 6, 2005
  21. Sep 6, 2005 #20

    Nereid

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    With anything observable - even in principle - to distinguish it/them from GR?
     
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