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Proof of the Big Bang and the Age of The Universe?

  1. Jan 9, 2009 #1
    What real proof is there of the Big Bang? I have never heard anything that is convincing. And how do scientists determine the age of the universe, is it really calculated or is it just estimated?
     
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  3. Jan 9, 2009 #2

    berkeman

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    What reading have you been doing to learn about it? It would be best if you had specific questions about information from reputable sources. Maybe if you posted some links to the information that has confused you?

    Have you read information sites like this? http://www.big-bang-theory.com/
     
  4. Jan 9, 2009 #3

    berkeman

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    BTW, you can also do a forum search, or you can look at the bottom of this page for related threads. It would be good for you to read those as well, as you formulate specific questions.
     
  5. Jan 9, 2009 #4

    Nereid

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    Welcome to PF, RiseAgainst! :smile:

    I do not know how much formal training you have had, in science, nor to what level, so the following may be far to simplistic (please let me know if it is).

    First, in modern science, we don't talk about "real proof" - that's something only possible in mathematics - rather we use 'consistency'.

    For example, we can say that all experiments conducted, and observations made, here on Earth, and in our solar system, are consistent with (Einstein's) General theory of Relativity (GR). We can also say that GR has no internal inconsistencies - its logic is sound and the mathematics it is built with well-established (and, in this case, proven).

    Second, the term 'the Big Bang' is not used by the scientists who study this branch of astrophysics (cosmologists); rather there are a number of models whose scopes (or domains of applicability) are clearly stated and limited. Perhaps the most widely studied model* is the LCDM one, which is based on GR and the Standard Model (of particle physics) plus "Lambda" and "Cold Dark Matter".

    There are 'three pillars' to support the LCDM model; that is three sets of independent observations (or phenomena) which can be fully explained by the model (or, saying this another way, the LCDM model is consistent with all relevant observations in these there sets): the Hubble relationship, the primordial abundance of light nuclides, and the Cosmic Microwave Background (CMB).

    Each of these sets of observations is quite extensive, comprising millions, or billions, of individual datapoints, and each has been reported in (collectively) thousands of papers published in scientific journals. The science behind the observations, and their analyses, has been intensely scrutinised, challenged, argued over, and generally put through the wringer ... over the past many decades, so each observational pillar is extremely solid.

    It is very important to keep in mind that LCDM models say nothing whatsoever about the origin of the universe; in fact, their domains of applicability go only to when the universe was extremely hot and dense - as hot and dense as the collisions in the most energetic of particle physicists' colliders - and no further (though there are other cosmological models whose domains of applicability do go beyond this).

    If you don't find this convincing - and I expect that you may not - please ask more questions!

    I'll leave the question of the estimated age of the universe to a later post.

    * it's actually a class of models
     
  6. Jan 9, 2009 #5

    atyy

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    Is LCDM consistent with GR? If GR predicts a singularity, but LCDM is not applicable beyond a certain density, then isn't LCDM inconsistent with GR? Or does GR not predict a singularity, or does it predict that it becomes inconsistent when LCDM also becomes inapplicable?
     
  7. Jan 9, 2009 #6

    Nereid

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    Good questions all, atty! :smile:

    At the level of my reply to RA, we could say that the domain of applicability of a model such as LCDM cannot be more extensive than that of the theories of physics upon which it is based (or from which it is derived)*.

    As LCDM relies upon two such theories of physics - the second is the Standard Model of particle physics - its domain of applicability cannot extend into the Planck regime (at its most extreme) or beyond the energy regimes probed by SLAC, Fermilab etc (at the other).

    * and any such model may have an even narrower domain, of course.
     
  8. Jan 10, 2009 #7

    Chalnoth

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    This is a good essay on the subject:
    http://www.toarchive.org/faqs/astronomy/bigbang.html

    The short answer is a wide variety of independent, mutually-corroborating data.

    As for the age, it's basically estimated based upon the observed expansion rate and contents of the universe combined with gravity to extrapolate the age.
     
  9. Jan 10, 2009 #8

    Chronos

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    RiseAgainst, can you recite the 'four pillars' mantra of modern cosmology? Try starting there and reading a bit before leaping to conclusions.
     
  10. Jan 11, 2009 #9
    Thanks, it helped me make more sense of the concept. I've taken a lot of classes about science and physics but never really touched on this subject. So this was a good explanation to start me off.
     
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