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List of things nearing the speed of light

  1. May 7, 2012 #1

    I would be interrested in building a list of things moving close to the speed of light.
    This list would contain these information:

    name of the experiment/observation
    nature of the object nearing the speed of light
    method used to create the fast object
    method used to measure the speed
    measured speed
    precision of the measurement
    bibliographic references

    I would be curious to see how long this list could be, and if it grows faster with time.
    Maybe such observations are not really recorded any more since they are maybe ubiquitous.

  2. jcsd
  3. May 7, 2012 #2


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    Do you want to include particles and ions or only macroscopic bodies? How do you want to define near the speed of light (e.g. > .9 c)?
  4. May 7, 2012 #3


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    Documenting all ~10^85 or so Neutrinos in the observable universe might be...difficult.
  5. May 7, 2012 #4


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    Everything is moving close to the speed of light in some frame.
  6. May 7, 2012 #5


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    Good one! "The earth was seen moving .9999+c by a trillion protons in Switzerland this morning."
  7. May 7, 2012 #6
    labatros..interesting question:

    First thing I thought of...Dalespam, was that you who posted this in another thread???? Whoever it was, I saved that observation for my notes as a reminder....gotta love it....a one sentence synopsis of relativity....

    Assuming we are not alone in the universe, there are likely billions upon billions of observations of US moving at the speed or beyond the speed of light....and I'm guessing the vast majority of observers are receding so rapidly they can't even see us now and may never be able to see us.

    So I'm going to guess the vast majority of 'activities' are moving beyond the speed of light ...beyond our horiozn...and what can observe might well be utterly insignificant by comparison....as is a grain of sand to the universe....

    Anyway, to help out a bit more,: locally, from our insignificant frame here on earth: how about considering every light bulb and auto headlamp that is switched on here on earth....lots of photons there!! and sunlight....and star light....CMBR....from 46bly distant....radio and tv transmissions over air.....such electromagnetyic waves all travel really fast....as do fiber optic signals in lightguide the world ....many laser pulses....and maybe electric signals in wires [not drift velocity, however]....and graviational waves from just about every pair of rotating masses in the universe....and electromagnetic pulses from every lightning strike.......and all the light reflections from steller gas....how fast are the ejections from all the pulsars in the universe....those are radiation, right.....and gravitons moving between all electrons and nuclei....and all the photons carrying electromagnetic forces..[what particles mediates strong, weak, radioactive decay forces..].....all cosmological horizons....from every observer here on.... earth...all information signals of any kind....fluctuations in the gravitational field of earth....electrical brain signals in albatros??.....I'm pooped!!!
    Last edited: May 7, 2012
  8. May 7, 2012 #7
    I am fairly sure lalbatros meant to say "I would be interrested in building a list of things moving close to (but less than) the speed of light (from the Earth rest frame).
  9. May 7, 2012 #8


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    How about all the galaxies at the edge of the observable universe?
  10. May 7, 2012 #9


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    That's a tricky one. They have recession velocities much greater than c. However that just means there is a standard way of dividing spacetime into spacelike hypersufaces in which the growth of proper distances between them by time is greater than c. That is not a relative velocity in the normal sense - it is equivalent to the statement that from earth, if rocket A is going east at .9c, and rocket B is going west at .9c, then in earth's spacetime foliation, the proper distance between A and B is growing at 1.8c.

    To get a relative velocity (in GR) you really need proximity. You can parallel transport the 4 velocity of one galaxy to near the the world line of another, but there are countless paths on which you could do this, getting different results (all less than c; some fairly close to c for very distant galaxies for some reasonable paths).

    In any case, the accepted answer is that recession velocity is well defined but is not a relative velocity; and that relative velocity between distant galaxies is undefined.
    Last edited: May 7, 2012
  11. May 7, 2012 #10


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    I assumed it was clear the OP meant 'relative to earth', and seriously await clarification of the questions I asked in #2. For particles and ions, the answer is obvious, and voluminous. For something at least as big as a particle of dust, I don't actually have any idea whether anything close to c has been produced or observed. There is no evidence of meteorites ever striking earth at more than a small fraction of c.
  12. May 8, 2012 #11
    Of course I was thinking to objects moving relative to humans frame of reference.
    Yet, I am not sure this is absolutely necessary, but it may help a discussion.
    I also implied inertial frames of reference, which is maybe really necessary.

    I was asking this question because I could not find so many examples.
    "What is the experimental basis of Special Relativity?" doesn't give so many.
    I reproduce them below.
    The OPERA results are interresting in this respect.
    They remind us that electromagnetic waves, neutrinos and other things share the same limit speed.
    I did not see measurements of fast neutrons, maybe they are not fast enough in our labs.
    I did not see astronomical objects.

    Naïvely speaking, a huge database of observed speeds (relative to us) would be an overwhelming proof of SR, I believe.
    Specially if objects like neutrinos are involved, which are supposedly not related to the electromagnetic interactions.

    Of course any sort of object, including planets, screws of plasma jets could be useful.
    It is difficult to decide what "close to c" may exactly mean.
    However, in the end the data should illustrate that c is indeed the limit.
    Massless particles are of course the most convincing.
    However, speeds of protons measured as function as their energy could also be convincing: would you know about such measurements? What about data from cyclotrons, are the energies large enough? What about CERN data?

    I have no doubt that such speed data are common.
    But it would be interresting to have them compiled, somehow.

    Experiments that Show the Limiting Velocity c

    Alspector et al., Phys. Rev. Lett. 36, pg 837 (1976).
    A comparison of neutrino and muon velocities, at Fermilab.

    Kalbfleisch et al., Physics Review Letters 43, pg 1361 (1979).
    A comparison of muon, neutrino, and antineutrino velocities over a range of energies, at Fermilab.

    Guiragosian et al., Phys. Rev. Lett. 34 no. 6 (1975), pg 335.
    Relative velocity measurements of 15 GeV electrons and gammas. No significant difference was observed within ~2 parts in 107. See also Brown et al.

    G.L. Greene et al.,“Test of special relativity by a determination of the Lorentz limiting velocity: Does E=mc2?” Physical Review D 44 (1991) R2216.
    An analysis combining the results of several experiments gives the result that the Lorentz limiting velocity must be equal to the speed of light to within 12 parts per million.

    Stodolsky, “The Speed of Light and the Speed of Neutrinos”, Phys. Lett. B201 no. 3 (1988), pg 353.
    A comparison of neutrino and photon speeds from supernova SN1987A puts a limit of about 1 part in 108 on their speed difference.
    Last edited: May 8, 2012
  13. May 8, 2012 #12
    Thanks a lot for feeding somewhat the first column of the list, although many are more guesses than records.
    Have gravitons really been measured within the nucleus?
    Last edited: May 8, 2012
  14. May 8, 2012 #13


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    Every accelerator is such a measurement because the timing circuitry is designed to work based on the limiting speed being c and would need to be different if the limiting speed were not c. This means every particle or ion accelerated to high energy verifies the limiting speed of c. Generally, no one bothers to write a paper formally analyzing this for every accelerator - it is considered obvious for a long time.

    I am glad you clarified because I guessed the above was self evident and you were asking instead asking about macroscopic bodies (and not asking about limiting velocity at all; your OP didn't mention it) - for which I don't know. Quite generally, I don't know if there has been any observation considered evidence for two macroscopic bodies with relative velocity near c (barring the ambiguous concept of relative velocity at cosmological distances).
  15. May 8, 2012 #14


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    Gravitons have never been measured, and there are fairly strong theoretical arguments that no direct measurement (similar to the photoelectric effect) will ever be possible. Measurement of the speed of gravitational waves should be possible, but no such measurements have yet been made.
  16. May 8, 2012 #15
    Thanks for this remark.
    I like the idea of using (accelerators) engineering as more experimental support for SR.
    It could be interresting to check how precise the timing requirements are and the resulting precision on evaluating the particle velocity.
    Would you know some paper on that?
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