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Star orbits and the Big Bang

  1. May 18, 2014 #1
    Hey PF! Have two questions here for everyone. Recently had a professor define the The Big Bang as "the expansion and cooling of the universe from an originally hot and dense state", but is this correct? To me it sounded more like the description of cosmic inflation...thoughts?

    Additionally, was recently reading about galaxy types and star orbits. Which types of galaxies do you think astronomers would find stars that orbit in flat, coplanar orbits? My thought is solely spiral galaxies, but is that right? Do irregular or elliptical contain stars that orbit in such a manor? I didn't think irregular because i thought orbits would be all over place since irregular galaxies are created through collisions or galaxy's interacting and the resulting gravitation interaction would skew star orbits.

    Thanks PF
  2. jcsd
  3. May 18, 2014 #2


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    That is an excellent description of the big bang, which is indeed a theory that describes the evolution of the universe as an expansion from a hot dense state. Why do you think it is not?
  4. May 19, 2014 #3
    Because i have read that the (rapid) expansion of the universe is a descriptive for inflation and i have also seen the big bang theory defined simply as the instantaneous expansion of space and time...
  5. May 19, 2014 #4


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    Any description that says it was an instantaneous expansion is utterly wrong

    Inflation is a hypothesized PART of the expansion from a hot dense state. It occurred (IF it occurred) in a very tiny fraction of a second, a tiny fraction of a second after the singularity, and caused an unbelievably massive expansion of the universe. By human standards this would have been for all practical purposes "instantaneous" however, as a scientific description of what happened, "instantaneous" is nonsense.

    Inflation is not proven but it explains more than any other theory about the characteristics of the very early part of the expansion.
  6. May 22, 2014 #5
    Phinds thank you for your help that makes much more sense now!
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