BangCrunch cosmology

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Dinosaur, Aug 26, 2017.

  1. Dinosaur Rational Skeptic Valued Senior Member

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    Circa 1950-1960 There were three competing cosmologies.

    Big Bang

    Alternating Bangs & Crunches

    Steady State aka Continuous Creation.​

    Steady State was given up when Quasars were discovered. They indicated that the universe was different in the distant past. It was my favorite, but I gave it up sooner than its main advocate: Fred Hoyle. The originator of a theory is often the last to give it up.
    Does anyone know/remember why BangCrunch was given up?
     
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  3. timojin Valued Senior Member

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    You must be pretty old boy
     
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  5. Dr_Toad It's green! Valued Senior Member

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    I think it still has some adherents.. I'll look up some things, because now I'm curios as well.
     
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  7. Michael 345 Valued Senior Member

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    Not sure if the following is the ( a ) reason Big Crunch has been given up but here goes

    The most distant galaxies have been observed accelerating
    I also seem to have heard the gravity constant is decreasing
    It is decreasing because the average density of the Universe decreasing

    My view on the acceleration is due to expansion having NO resistance outside of the Universe the Big Bang is still in operation

    As gravity constant decreases (somewhat like a bungie cord loosing threads as they snap) not enough gravity will remain to slow and then reverse expansion and start Big Crunch

    Eventually, in some of the article I have read, the density of the Universe will be so low components of atoms will dissipate because the energy binding them will not be strong enough to hold them together

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  8. Dinosaur Rational Skeptic Valued Senior Member

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    From Timojin Post 2
    I am 87

    I intend to live forever: So far, so good.
     
  9. Michael 345 Valued Senior Member

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    Let me know when you get there I'm a few years behind if you check your review mirror occasionally

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  10. Boris2 Valued Senior Member

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    Correct
    Unlikely because it has nowt to do with the Universe as such but just between two bodies.
    See above
    No, there is no "outside".
    No, see above.
    Haven't heard that.
     
  11. James R Just this guy, you know? Staff Member

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    In theory, the universe could end in a big crunch if the average density of matter in the universe was high enough. If it's too low, the universe will expand forever. In between these two cases, there's a critical density, which would cause the universe to expand forever, but at an ever-slowing rate.

    The above might well have been the state of play in 1950-60. In fact, all options were viable up until about the 1990s, IIRC. The problem was that the measured density of the universe is very very close to that critical value; it might be a bit greater, or a bit less, or right on critical.

    However, some crucial observations (including of Type I supernovas) led to the discovery that the universe is actually accelerating in its expansion, despite the observed density near the critical value. And so cosmologists started to take the idea of a cosmological constant (a.k.a. "dark energy") seriously.

    The observational evidence as it is today suggests that the density of the universe is pretty much right on the critical value, but there will be no big crunch because dark energy is driving further expansion.
     
  12. Boris2 Valued Senior Member

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  13. DaveC426913 Valued Senior Member

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    Yeah. What JamesR said.
    It was a few decades ago that they refined the curvature of the universe. It had had a range from < 1 to >1, but has since been calculated much closer to 1.0. That means there is essentially insufficient gravitational attrction to cause it to stop its expansion and begin contracting.
     

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