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A Layman's Question of the Big Bang

  1. Jun 23, 2008 #1
    Most of the discussions at this forum are way beyond my level of understanding, but I thought this might be a good place to start. My background is just a college level knowledge of physics, and a hobbyist's interest in astronomy.

    My question involves the mass of the universe, and a description of a singularity. It is my understanding that the visible universe consists of approximately 125 billion galaxies, averaging approximately 100 billion stars each. It's also my understanding that this amount of matter comprises at most, 10% of the total mass of the universe.

    What totally amazes and bewilders me, is how a mass of this enormity can have been so infinitely compressed into a point singularity that was then the object of the Big Bang explosion. How did all this matter exist in the same place at the same time? Is space and time no longer relevant here?

    Any help in understanding this (in layman's language please :-) would be greatly appreciated.

    p.s. please excuse or correct any misstatements I may have made, but I think the gist of the question is clear.
  2. jcsd
  3. Jun 23, 2008 #2


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    There was no matter in the beginning of the universe; it was far too hot. Matter didn't condense out of the expanding universe until quite some time later*, when the universe had cooled enough for the first protons and electrons to form.

    *According to this Wiki article:
    that was between 3 and 17 minutes into the universe's life (which is a huge, huge length of time in cosmology).
  4. Jun 23, 2008 #3
    Thank you for your reply to my query. Your reply made me think of a couple of follow-on questions.

    1) If it was not the mass of the universe that was converted to energy in the big bang explosion, where did that energy come from to generate such an explosion?


    2) If the universe eventually stops expanding and begins contracting back to the original big bang source point, what is the current thinking as to what will happen to all that matter when it arrives back at that single point?

    Thanks again for any help.
  5. Jun 23, 2008 #4


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    We have no idea. Science has nothing to say about what preceded the BB. Maybe another universe, maybe the BB simply erupted out of a quantum fluctuation.

    Presumably, the reverse: the matter will be super-heated until it reverts to energy (a la E=mc^2).
  6. Jun 23, 2008 #5


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    You appear to be holding the misconception that the big bang was an explosion: it was not, and nowhere in the standard model of cosmology do scientists say that there was an explosion. All the standard model says is that there was once a time at which the universe was a lot smaller, and a lot denser than it is today.
  7. Jun 23, 2008 #6


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    There is a lot of current research on what could have preceded the big bang. The first comprehensive scholarly book on the subject is scheduled to come out late this year. The editor, R. Vaas, has collected chapters by a range of experts covering the various theoretical models and schools of thought on pre-big-bang. Here's the Amazon.com page on the book.

    The general field of research pertaining to this is Quantum Cosmology. There are a lot of scholarly papers on it, but it's new enough that there are no books as yet. Here is a keyword search that gets the research journal articles:


    These are recent (2006 or later) and listed in order of how much the paper has been cited (referenced) in other research---so generally speaking you get the most important or widely referred-to papers first.

    The top 10 or 20 are nearly all studying the case where the big bang is preceded by a contracting phase----with gravity becoming repellent at high density so that there is, in effect, a bounce.

    Current thinking is that the universe will NOT stop expanding and contract back down to a high-density state.
    But if it WERE to contract, then at least one group of theorists already have modeled that case quite a bit. Both with extensive computer modeling and with analytical equation-models. It would exactly fit the pre-big-bang conditions of a contracting phase which you get in many of the research papers listed in that link.

    The bottom line, I guess, is that science has a lot to SAY about pre-big-bang, but it is not conclusive. It is an active research area, evolving rapidly, where much of what they are working on has not yet been tested. The work needs to be checked against observations, and eventually it will be.

    So there is nothing here that one should recommend that anybody believe. Just watch the field develop, learn about the leading approaches, keep an eye out for proposals to check theory against detailed observation of the microwave background, gammaray bursts and soforth.
    A good SciAm article on big bang and expansion cosmology in general
    Princeton undergrads get to read this in beginning atro/cosmo. It is excellent. Clears up misconceptions about "explosion" etc.
    Last edited by a moderator: May 3, 2017
  8. Jun 24, 2008 #7


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    One Quantum Cosmology model I have found particularly interesting is a result of M-theory. In this theory, it turns out that there is a certain point in very small scales at which one can no longer make a distinction between contraction and expansion. This was considered a possible explanation for the transition between the Big Crunch and the following BIg Bang.

    However, it looks like all observation is pointing to an ever-expanding universe, so oscilating-universe models are not looking too good right now.
  9. Jun 26, 2008 #8
    Making a loaf of raisin bread provides a better analogy to the big bang and the expansion of the universe than an explosion.

    The Universe is expanding, and not only that, but the rate of expansion is increasing. The Universe is moving like a runaway train. One day it may end in a Big Rip, when all the matter is torn apart as it expands, even overtaking gravity that holds objects together and annihilating galaxies, stars, and planets.

    One thing I don't get tho, is what started the expansion in the first place, gravity is always attractive, what is expanding space right now, and why is it accelerating? A quantum fluctuation wouldn't provide that kind of impetus surely :)
  10. Jul 4, 2008 #9
    As others have said what happened before the Big Bang is still a mystery, also there are many common misunderstandings about the Big Bang, like a) it was a "Bang" or expolsion b) that there was a small greatly condensed piece of matter, etc... But there are some contradictions with the laws of theormdyanmics... because energyshouldn't ever be able to be greater at any one time, than another....
  11. Jul 5, 2008 #10
    You might wanna read about Cosmological Inflation and Ekpyrotic Universe for some more info on this.
    You can find for example in the Wiki.
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