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What evidence supports the big bang theory?

  1. Jun 19, 2013 #1
    off the top of my head:

    - isotropic microwave radiation corresponding to 3.73K blackbody curve
    - hubble's law
    - red shift of galaxies
    - 3:1 ratio between hydrogen and helium, and the relative abundance of them

    is there any more?

    and also, can someone explain the hydrogen-helium ratio thing, I've read about it and I still don't get why exactly it supports the big bang theory
  2. jcsd
  3. Jun 19, 2013 #2

    Simon Bridge

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  4. Jun 20, 2013 #3
    I was going to add a few things till I took a look at the link. Thats a good site Simon pretty much says it all.
  5. Jun 29, 2013 #4
    I assume the website posted talks about Big Bang nucleosynthesis but I might as well post a brief summary:

    Near the beginning, the Universe was hot enough that nuclear fusion could take place. The only thing available was Hydrogen nuclei (i.e. protons). The process turned this Hydrogen into Helium. The study of such reactions tells us how quickly a quantity of Hydrogen will turn into Helium. The model of the Big Bang indicates the universe would have cooled sufficiently to prevent fusion after a certain amount of time. If we examine how much Hydrogen would have turned into Helium in this amount of time, it exactly matches what we observe. Thus the model (the theory) seems to fit precisely with observed reality and can be termed an "evidence" if one desires to do so.
  6. Jun 29, 2013 #5


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    The other 3 pillars of the big bang are:
    The large scale structure of the universe;
    cosmic microwave background [CMB];
    expansion of the universe [redshift]
  7. Jun 30, 2013 #6
    a more accurate description of the primordial elements...and discrepancies from model.... is here:


    and let's not get carried away too far about the big bang....

    is outside the applicable realm of our major theories [GR and QM reflect divergences]
    says nothing about time zero itself,not how things started,
    ...so why we don't see new universes spawned is not apparent.
    Misses dark matter, dark energy...95% of all matter energy in the universe,
    says nothing about the type of expansion,
    nothing about baryogenesis...matter over antimatter,
    inflation is a manual add on to big bang theory..and it didn't work so well,
    .....so slow roll inflation was manually added by Guth/Linde.....
    .....then people had to figure out how to stop it once started [I forget how that was solved]...
    cyclic models, while not as well developed and not as widely accepted, offer some fascinating ......alternative possibilities....
    does not explain why initial space was flat and final space[black hole] is so curved...nor any connection between them [But GR offers 'wormhole' type' insights]

    Interesting footnote. FROM THE ROAD TO REALITY:

    Roger Penrose seems to think such an arbitrary introduction of an inflationary field to 'fix' problems of the 'old model'.....
    but he acknowledges 'inflationary cosmology, as described, has become a major part of the body of modern cosmological thinking'..

    edit: I just noticed Hubble's law....things like that and large scale structure are within the boundaries of the solutions from GR...but those kind of things fit so nicely because we adjusted the model parameters {wisely} to fit observations..that is, all the observables applicable to the Lambda CDM versions of the general FLRW cosmological model.

    Yet unquestionably a monumental achievement overall to have such a good perspective from about Planck time after the big bang out as far to the future as we have.
    Last edited: Jun 30, 2013
  8. Jul 1, 2013 #7
    Most of the problems Naty1 mentioned are resolved by inflation. (e.g. "time zero")
  9. Jul 1, 2013 #8
    Inflation does NOT start at time zero.
    And the problems are NOT resolved by inflation.

    Inflation is a 'manual override' which works really well....and Penrose captures the sense that
    this is 'artificial'.....
    Last edited: Jul 1, 2013
  10. Jul 1, 2013 #9


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    Aren't all successful theories "manual overrides that work pretty well"?
  11. Jul 1, 2013 #10
    I didn't say inflation starts at time zero; I said inflation solves the "time zero" problem.
  12. Jul 5, 2013 #11
    What is the difference?? We must be talking about two different things.
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