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Evidence that time and space began at the instant of the big

  1. Jun 13, 2015 #1
    What evidence is there that time and space began at the instant of the big bang rather than, on the other hand, that space and time existed before the big bang and that the universe simply popped into existence into preexisting space because of Murphy's law; or has this been dis-proven somehow?

    Isn't it theoretically possible for a universe to pop into preexisting space if it is large enough and there is enough time? I accept the current scientific consensus that space and time began at the big bang but i am just curious about the evidence confirming this so please don't think I am trying to put forward my own theory. I just don't understand how you prove one of these hypotheses over the other so I would appreciate being enlightened.
  2. jcsd
  3. Jun 13, 2015 #2


    Staff: Mentor

    The big bang is not an instant, and the big bang theory does not say that space and time began at an instant. The term "big bang", properly speaking, refers to the hot, dense state that the universe was in about 13.7 billion years ago, and that's all.

    As for what came before that hot, dense state, the best current hypothesis is inflation; but there are various versions of inflation, and they say different things about how, if at all, the spacetime of our observable universe fits into a larger picture. So the best we can say about your question right now is that we don't really know.
  4. Jun 13, 2015 #3
    Ok fair enough, thanks for your response, it just seems like a lot of physicists have been saying that space and time probably began at the first instant of the big bang.

    Also do you think that if space is infinite then logically speaking space would have to have existed before the big bang?
  5. Jun 13, 2015 #4


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    Yeah, but that's a simplification because we just don't know and there's not a lot of point in getting wrapped up in what, if anything, came before one Plank Time since at present there is no known way to "see"/"detect"/whatever anything that early in the universe so it is a convenient simplification, particularly in pop-science to just say that everything started at the singularity.

    No. Why would it?

    Just FYI, you really need to get clear on your terminology. "The Big Bang" has two significantly different meanings and you are treating it as though it has only one.

    1) "The Big Bang Singularity" --- "singularity" just means "the place where our math models give unphysical results and we don't know WHAT was going on.

    2) "The Big Bang Theory" --- the description of how the universe evolved starting at about one Plank Time after the singularity.

    It's very common for the phrase "the big bang" to be used to mean the big bang theory, which is fine if everyone knows what's being talked about, but when it is used in pop-science it causes confusion. The singularity is not understood at all and the big bang theory is quite well understood.
  6. Jun 13, 2015 #5


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    Staff: Mentor

    While the first part was addressed, the second part wasn't: no, what happened in the Big Bang explicitly excludes the idea of a pre-existing space for the universe to expand into.
  7. Jun 13, 2015 #6
    Its mainly just scientific curiosity like the multiverse which we couldn't possibly hope to verify empirically.

    And to answer your question, if space expanded out at some particular rate when the big bang singularity erupted then it would be finite regardless of the rate of change. The only other possibility is that the rate of expansion would have to be infinite when the singularity erupted for space to become infinite, right? This seems unlikely since astronomers can calculate the rate of expansion and it is finite. So therefore, if space is infinite then the only other possibility would be that space has always been infinite before the big bang singularity because it couldnt have been infinite otherwise; maybe with certain areas of space that have different rates of expansion--kind of like the anthropic principle with anything that can happen will happen.

    Anyways thanks for your response and ill try to make my terminology more clear in the future.
  8. Jun 13, 2015 #7
    Ok thanks, can I ask what specifically excludes it? Is there some aspect about inflation that prohibits pre existing space?
  9. Jun 13, 2015 #8


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    Or it came into existence infinite in extent. Either one is pretty mind-blowing but we just cannot tell and may never be able to tell.
  10. Jun 13, 2015 #9


    Staff: Mentor

    There was no such thing as an actual "big bang singularity". The big bang theory does not say there was one. As phinds said, that is a pop science misstatement. So there's no point in asking what happened when the singularity erupted, since our current theory does not say such an event ever actually happened.
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