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Absence of Massive Bodies Traveling at Relativistic Speeds

  1. May 29, 2012 #1
    I'm sure that this is not a new question, but it is one that has been puzzling me for a long time. In our universe, the large massive bodies are all moving relative to one another at low velocities relative to the speed of light (aside from the ultra large-scale systematic motion associated with the expansion of the universe). Why is there a paucity of random large bodies moving with velocities comparable to the speed of light?
  2. jcsd
  3. May 29, 2012 #2


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    Why would one expect to see that? It seems to me that in a universe where everything expanded from a Big Bang, objects near each other should be moving slowly relative to each other.
  4. May 30, 2012 #3
    Neutron stars would have equatorial rotational speeds getting right up there. 2 such stars in decaying orbits around their common center of mass would be moving at a fair pace too.

    Objects accelerated to relativistic velocities (by whatever hypothetical cause) in our galaxy will be traveling far in excess of galactic escape velocity and won't remain near us for very long.
  5. May 31, 2012 #4


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  6. May 31, 2012 #5
    Thanks very much guys. Your replies have been very helpful and interesting.

  7. May 31, 2012 #6
    Not according to the original models of the big bang. One of the original puzzles related to the big bang with standard cosmological models was why there is so much uniformity, i.e., why does it appear that the constituients of the visible universe were in some kind of thermal equilibrium, as seems to be evident from the fact that the CMBR is quite uniform and (as the OP noted) the major masses are all moving relatively slowly relative to the isotropic frame of the CMBR. This is NOT what one would expect under the simplest cosmological models, because of the horizon problem, i.e., the various parts of the universe were not causally connected, so they can't possibly have been in equilibrium, so we ought to see much less uniformity than we do.

    The resolution that is fairly well accepted today is "inflation", first proposed by Alan Guth in 1980. According to this theory, the universe underwent a period of fantastically rapid inflationary expansion (vastly more rapid than in the basic cosmological models like Friedman models). This is taken to explain why a tiny causally related region of the early universe (originally in thermal equilibrium) has expanded to cover the entire observable universe today, thereby accounting for the uniformity that we observe - although according to this explanation the uniformity wouldn't exist over the entire universe, just over the observable universe.
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