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Big Bang : 'Proofs' and observations

  1. Mar 21, 2006 #1
    As I discussed with a friend's cousin, who is completing a Ph.D. in Astrophysics, he said that the ONLY evidence for the Big Bang was the seen redshift from the other galaxies around.

    Is he right, or is he wrong?

    If he is right, how can we base cosmology over a single, 'weak' proof like that?

    And if wrong... what can be said in favor of the big bang theory?
  2. jcsd
  3. Mar 21, 2006 #2


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    He's wrong. Besides the fact that galaxies aren't the only thing we see redshifted (the cosmic microwave background), the distribution of galaxies (and the cmb) also supports the BBT. In addition, it was a mathematical prediction of GR (meaning evidence for GR is indirect evidence for the BBT). I suspect the age of objects we see is also evidence of a finite age for the universe. I'm sure there's more, but this isn't quite my area...

    Besides, it is a little unfair to call redshift a single piece of evidence, since it has been observed in tens of thousands of separate galaxies and other objects.

    Also, when the question is simple, evidence and answers are simple: how many pieces of information would you require to conclude a car coming toward you will hit you if it doesn't stop? Just one: velocity.
    Last edited: Mar 21, 2006
  4. Mar 21, 2006 #3


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    He's wrong. Have a look here:

  5. Mar 21, 2006 #4


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    That's very disturbing...you probably shouldn't tell us which program he's going through.
  6. Mar 21, 2006 #5
    maybe he meant...

    one line of reasoning that follows directly from the redshift data is that everything is moving away from us at a speed proportional to its distance. If you run time backwards things necessarily had to be closer together. As you bring them closer together they heat up. maybe your friend meant that the redshifts alone show that the universe evolved from a hotter denser state which is the common thread that all versions of the big bang theory contain. as the other posters have pointed out there are many other pieces of evidence in support of the big bang theory which have led to more specefic predictions...

  7. Mar 21, 2006 #6
    Or maybe after you were listening to him, you did not transcribe or remember what he said exactly (maybe one of the words was muttered or something else) ;)
  8. Mar 21, 2006 #7
    Don't worry. I *did* argue with the man. Cosmic microwave background wasn't, or so he said, a viable evidence or proof whatsoever of the big bang theory.

    I'm quite literate in astrophysics, but i can't compete with an Univ. guy :P

    And.... the Big Bang predicted by GR? how is that?
  9. Mar 21, 2006 #8


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    GR predicts (or maybe "explains" is a better word) the large-scale shape and behavior of the universe.

    http://www.astronomycafe.net/anthol/bang.html [Broken]

    Last edited by a moderator: May 2, 2017
  10. Mar 22, 2006 #9


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    I would agree that redshift [the Hubble thing] was the foundation for BBT, but, many other corroborating observations have since emerged. The 'three pillars' explanation is a good place to start. I disagree with the characterization that the CMB is not a viable test. It is the most convincing proof of all. But, astrophysics is a very diverse field of study. Your friend's cousin could well be an expert in a particular area of knowledge and only have cursory knowledge of BBT.
  11. Mar 24, 2006 #10
    What possible "observations"? I promise next time I'll be short
    A) A large-scale uniform universe (and groupings in " small scale " thanks to the gravitational attraction)
    B) A light which stretches with the distance because its wavelength lengthens with the space (red-shift)
    C) all the stars have a limited age (meaning the universe has a time origin and an initial radius close to zero)
    D) the sky is not covered with an infinity of stars and the possibility of a black night (The cosmic horizon: an observation of a space limited by the time of creation and the time of distribution of the light from the source to the observer)
    E) the relative density of light atoms (helium, deuterium, lithium) which implies an universe initially hot like the stars core.
    F) A plasma which cooling emits an isotropic light during the recombination nucleus - electrons forming atoms ( cosmic microwave background radiation)
    G) An evolution of the galactic structures since the origin
    And other observations deducted of previous ones and more subtle
    H) An increase of the C.M.B. temperature radiation "reheating" distant galaxies
    I) The phenomenon of recombination engendered by the first generations of stars which ionize the atoms of their environment
    J) An estimation of the number of families of elementary particles on which depends the density of the universe and thus the proportion of light elements constituted by fusion during the nucleosynthesis. The proportion of the types of the first atoms (for instance He4) has to correspond to the numbers of families of particles observed in the big accelerators.
    K) Fluctuations in density of the cosmic microwave background radiation at the origin of the big scale structures (but not quite enough)
    L) the observation of a mass of baryonic "classical" matter of the production of the first atoms by the nucleosynthesis
    M) A production of space rays bound to an age of first forming of the couples of stars with neutrons
    N) An asymmetry of the behavior of particles and their antiparticles which may (partly) justify different production rates between particule and anti-particule pairs (roughly said) and the little advantage of the classical matter (the stars, the dust,ourselves) after annihilation of the quasi-totality of the formed pairs
    O) Observation in the accelerators of convergence between fundamental nuclear and electromagnetics forces (unification theory) in (relative) agreement with the models of creation of particles in the primordial universe.
  12. Sep 1, 2006 #11
    Can I just point out that "proofs" is a bad word to use in the title?
    The Big Bang is just a theory and never will be anything more: it's passed every test it's come up against (albeit passing through a few modificatons like inflation) but hasn't been proven and never will be.
    On the other hand it could easily be disproved like the Steady State theory was; in science you can keep accumulating evidence for a theory for as long as you like and you'll never prove it - but one piece of evidence can disprove.
  13. Sep 1, 2006 #12
    I think that a big bang of some type would be self-evident. The only thing that galaxies tend to do is run into each other and make a larger galaxy. This action would tend to sweep the cosmos somewhat clean over a great span of time.

    Since there are galaxies there to see, it seems self-evident that a big bang of some type would have to occur to re-distribute the matter back into galaxies over a wide area.

    The more interesting point to pursue would be to try and determine if there were any big bangs before the last one.

  14. Sep 2, 2006 #13
    It is an elaborate and very persuasive working hypothesis used by almost all professional cosmologists in their attempts to understand the history of the universe. But despite the successes of their ratiocination, the universe remains rather like the wind that John Masefield described a long time ago:

    "A very queer thing is the wind
    I don't know how it beginn'd
    And nobody knows where it goes,
    It is wind, it beginn'd, and it blows."
  15. Sep 4, 2006 #14
    isn't cosmic microwave background was one of the strongest pieces of evidence we have of a big bang?
  16. Sep 5, 2006 #15


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    CMB is indeed considered by many to be the "best" evidence in support of BBT. However, I think the person qouted in the OP might have been emphasizing the seminal role that redshift had in first generating that model.

    That is to say; if the CMB had been discovered first, it is somewhat unlikely that anyone would have looked at it and said, "Hey look, a nearly-uniform emission of radiation in the microwave frequencies is emminating from all directions in space at once. Why, that must mean the Universe began in a collosal explosion!". It just isn't a natural conclusion to draw from that piece of evidence.

    So in a way, CMB only becomes a support of BBT after BBT has been accepted, or at least partially accepted. And the same is true for all the other supporting observations. So if the Hubble Redshift ahd not been dicovered first, the CMB would not have been seen as evidence of the Big Bang (or at least, probably not), and in fact that model might not even exist.

    If that was what the gentleman was saying, then I can see where he might be right, although it is very hard to say. Who knows what the human mind would have perceived, if history had gone some way other than the way it went, and the evidence we now have were replaced with other observations?
    Last edited: Sep 5, 2006
  17. Sep 5, 2006 #16


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    Yes, and there are many other lines of evidence as well. The person the OP is referring to was either very wrong or chose their words poorly. Either way, I don't think this issue warrants further discussion, especially since the person in question isn't posting here.

    If you would like to continue asking about the Big Bang theory in general, feel free to start another thread about it, but I'm closing this one.
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