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When did the big bang end?

  1. Aug 22, 2008 #1
    Your indulge is greatly appreciated. I am a not a scientist. I am a historian who is fascinated by science. My questions are:

    How long did the Big Bang last? When did the Big Bang end? Alternate questions are: Did the Big Bang “happen” 14.7 billions years ago? Or did the Big Bang “begin” 14.7 billion years ago?

    In trying to understand inflation, the relative weakness of gravity, dark energy, an infinitely expanding universe vs. the Big Crunch, etc., etc., I have often wondered if I am seeing – as the ancients did – the sun and the night sky revolving around the Earth.

    I understand that the following point is not analogous to the singularity, the resultant Big Bang, etc., so again, I ask your indulgence. In any case, an insect lands on a firework that has been loaded into a canister for firing. Twenty seconds later, the “unconscious” insect is falling to the ground along with the spent residue of the firework. However, the insect survives to document “each conscious second” of its amazing journey.

    How would the insect describe its Big Bang event? It absolutely depends on when it lost consciousness – after one second – after ten seconds – after fifteen seconds. As for our Big Bang event, we know when the detonation took place – but do we know if we have even cleared the canister yet?
  2. jcsd
  3. Aug 22, 2008 #2


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    Big Bang is not a good term. It just caught on in the press and popular media. It is used imprecisely to mean either the standard expansion cosmology model as a whole, or else to mean the moment in time when the observed expansion started.

    Because it is not a precise scientific term, it is not used consistently and it can mean different things.

    A good article to read is one by Lineweaver in Scientific American. I have a link to it in my signature. It is very accessible with lots of pictures. Even though easy reading it is also assigned reading in college courses! It is called "Misconceptions about the Big Bang".

    You may have misconceptions, so you should read this article. Look in my sig under Lineweaver. The version I link to is at a Princeton astronomy department server.

    We have no scientific evidence that there was a singularity at the start of expansion. There could just as well have been a bounce (contraction to high density followed by re-expansion) with never any infinite density or pointsize universe. Just very high density. so it is probably a good idea not to speak of "the singularity" as if it existed.

    (leave that to popularizers writing mass market books, they love to talk about "the singularity" because the word fascinates the public :smile:)

    The Big Bang should not be pictured as an explosion. Lineweaver's SciAm article will explain more about this. Big Bang is a really misleading term. First introduced by Fred Hoyle who was attacking the expansion cosmology model---he used the term as a way to mock and discredit expansion---make it sound preposterous. But the term caught on with journalists, so we are stuck with it. I prefer to say expansion cosmology model---the version that has become standard.
    Last edited: Aug 22, 2008
  4. Aug 23, 2008 #3
    I agree with Marcus, the whole big bang term really is just an catch phrase that everyone likes to use because its what they've been taught. The new more refined theory uses the term "Inflationary Expansion" which I believe is worlds better than the big bang.

    This new term explains to us that there was no real bang per say but rather a massive expansion on the order of 10^30 magnitude at a point in time. When was this point in time you may ask? We've got it to be around that 13.7 billion years but then again even this is up for discussion since we may simply be looking at one of many points in our universe that experienced inflation so many billions years in the past. The whole question of when did it end, well thats interesting since it really denotes and beginning and an end which is something I've never really been comfortable with. When did the inflation really begin? Will this inflation ever really stop? Technically the inflation is still going on, see Edwin Hubble's redshift observations of stars and galaxies. They are all moving away from a point which denotes a inflation as non are blue shifting or moving inwards. The amount of energy released during that initial point was so massive that its been powering this inflation for an amazing amount of time and we theorize it may stop one day in whats known as the big freeze when all energy is used up but even this is some trillion years away. So I would say the big bang or more correctly inflationary expansion never stopped and won't for a good long time.
  5. Aug 24, 2008 #4
    G'day from the land of ozzzzzzz

    This is quite interesting even though I do not agree with the Big Bang Theory.

    Foundations of Big Bang Cosmology
    WMAP's Universe NASA

    As for the age of the universe being 13.7 Gyrs.

    One needs to understand the complexity and the extraordinary mega mega size of galaxies and cluster of galaxies. When we look into deep field images 13.2 Gyrs we see ready form galaxies and cluster of galaxies that according to the BBT were created in just 500 million years. If you know anything about the evolution on planet Earth 3 billion years for life and 5 Gyrs for the Earth to evolve. It becomes a big big question as to the formation of over 100 billion galaxies to just form in just 500 million years.
  6. Aug 24, 2008 #5


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    The bib bang is technically a work in progress. After the four fundamental forces split and inflation, the observable properties of the universe were fixed, and after recombination, the results were observable.
  7. Aug 25, 2008 #6
    G'day from the land of ozzzzzzzz

    Chronos said

    What observable properties?

    What results?
  8. Aug 25, 2008 #7


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    CMB, large scale structure, elemental abundances, etc.
  9. Aug 27, 2008 #8
    I am the author of the original question: when did the big bang end? Thank you for the information and insights. I now understand that the “big bang” is today basically a euphemism (and a misnomer) for the “expansion cosmology model” or “inflationary expansion." I also now understand that I did not ask the right question – or ask my question right. As a result, my question may have been answered, but I am still confused as to whether “we know if we have even cleared the canister yet?” If you will again indulge me, I will try again.

    Since the demise of the steady state model, one constant in cosmology models is that the universe was once younger – and that the universe is getting older. We estimate that the age of the universe is 13.7 billion (or so) years old. And we do so based primarily on our present-day technology that allows us to “see” the universe as it existed 13-plus billion years ago – at which point we see “events” that we perceive as “unique” – that is, these events occurred and, as they say, the rest is history. (Even so, there is the caveat that the laws of physics, as we understand (have defined) them, may not have applied at the time – for example, inflation – the expanding of the universe faster than the speed of light.)

    Here is my question. Ten billion years ago, there was a planet with intelligent life orbiting a star. On this planet, the intelligence and the technology of the inhabitants were exactly identical to that of Earth today. Given that they can (as we can) “see” 13 billion years “back” and that they know what we know, what would (might) they be able to see? Might they be “only” able to see what we can see? And if the same scenario existed 10 billion years from now, might looking back 13-plus billion years result in the same view as we have today?

    In Sundance’s reply, it was noted that the big bang “is better thought of as the simultaneous appearance of space everywhere in the universe. That region of space that is within our present horizon was indeed no bigger than a point in the past. Nevertheless, if all of space both inside and outside our horizon is infinite now, it was born infinite. If it is closed and finite, then it was born with zero volume and grew from that.”

    Perhaps (I wish I could be sure), my question is – is there some “inflation(?)” component in regard to not only “space” – but also to “time?” How does the relativity of time factor into any or all of this?
  10. Aug 27, 2008 #9


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    Hi Chas,
    the main message in my response to you (post #2) was to urge you to read Lineweaver's SciAm article


    I keep the URL in my sig because it is so generally helpful, especially to newcomers. I'm curious. Have you read it yet?

    I would guess not because your last point indicates you think that inflation is defined as a period when the universe expands faster than light. But we are talking about mainstream cosmology here. You are asking about the normal model universe, that the majority of experts use. You can't define inflation that way because space is expanding at the present time FTL. Expanding FTL is typical at all times, not just during a brief inflation era.

    Lineweaver explains this. There is no substitute for reading an article that will help you get out of probably a half-dozen misconceptions that people ordinarily have.

    If you don't start off with a clear idea of the mainstream model you will be more vulnerable to fringe notions and crackpot models. There are plenty of people pushing that stuff---anti-mainstreamers. So I urge you to get straight on the mainstream model. Then once you understand that you can explore fringe ideas if you choose to. (but you wont start out so confused)
    since expansion is about 13.7 billion years old, people back 10 billion years ago would see expansion as 3.7 billion years old-----according to the standard mainstream model.

    They would be a lot closer to the time when the first stars formed and the first stars collected into galaxies. So it would be easier for them, than it is for us, to study these early processes in detail.

    It would be hard for a planet similar to Earth to form back then because heavy elements were not as abundant. And on Earth intelligent life has taken some 4.5 billion years to evolve and that planet would still be comparatively young. But assuming for the sake of discussion that there were a planet like Earth back then, they would see the early universe processes clearly that we see only dimly. Qualitatively the same world-view, just sharper detail.

    You also asked about a planet existing when the universe has been expanding for 23.7 billion years (10 billion years in future).
    Not an attractive thought. Universe thinned out some. Fewer galaxies visible. Some light redshifted so much it becomes hard to detect. The Cosmic Microwave Background, from which we learn so much, redshifted and dim. Bad news.
    Larry Krauss has written an article about this. Be glad we live now and not in the universe's old age.
    Here's Krauss' article:

    Not a radical difference, but as things get harder to see you need better instruments.
    Last edited: Aug 27, 2008
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