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Infinite and Eternal Universe

  1. May 30, 2013 #1
    I have been thinking about the idea that the universe is infinite in size and have wondered if it is not also possible that the universe is infinite in time as well - that is to say, the universe has always been here and always will be here, that it doesn't have a beginning or an end. This idea is not consistent with the Big Bang which many people accept as true, but it seems to me that if the universe is infinite in size then it would take an infinite amount of time to decay, therefore it seems fair enough to say that the universe will always exist, so it seems only the next step to suggest that it has always existed. Is this idea possible?
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  3. May 30, 2013 #2
    the size of the universe can be finite or infinite. Time however is another matter. Some theories hold that time started when the universe did essentially, however multi-verse theories argue that if a multi-verse does exist time must also exist.

    Setting aside multiverse, if you extrapolate expansion, and inflation back in time the universe described by the big bang has a beginning. or rather a start point described as a hot dense state.
    the singularity of that beginning is where the mathematics no longer makes sense, as opposed to a blackhole singularity.

    One key rule to remember a finite value can never become infinite.

    So in the BB paradigm with a singularity beginning time is not infinite even if the universe lasts forever.

    by the way welcome to the forum
  4. May 30, 2013 #3


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    Just as a suggestion: when you come up with a question in cosmology (ALL science for that matter, but I'm using cosmology as an example) the first thing that you might find useful to do is ask yourself "Hm ... I wonder if any of the 10's of thousands of scientists that have been thinking about this stuff for 100 years or more have already thought of this question?"

    When you look at it that way, you might end up phrasing your question as "OK, apparently my idea is wrong, but I want to find out WHY it's wrong" rather than "I have this neat new idea that I'd like to ask about" which implies that you think none of the 10's of thousands of scientists who have been thinking about this stuff for 100 years HAVE thought of it.
  5. May 30, 2013 #4
    Possibly, maybe, terribly unlikely.....I can't think of anything at the moment less likely....

    There seem to be two possibilities..the universe has a beginning and an end [or sorts]...or it goes on forever as you suggest.

    no mainstream scientists believe what you posit is correct.

    what do you know about current theory?? Anything observational to support your idea??
    For example, the uniform expansion of the universe has STRONG implications.

    Here is a place to get some more concrete understanding:

  6. May 30, 2013 #5
    Kinda related: If spacetime is infinite, does this imply the mass of the universe is also infinite?

    I can sort of accept an infinite spacetime, but can't seem to get my mind around infinite mass...
  7. May 30, 2013 #6


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  8. May 31, 2013 #7
    It depends on what you mean when you use the word "Universe", if you mean our observable patch , it had a beginning of sorts in the big bang. But that only tells us the universe was in a hot desnse state 13.8 bio year ago. It doesnt tell us there was no time before the big bang. That may or may not be true, there are many theories that posit the unvierse existed befoe the big bang and may have existed foreover. Google these phrases:
    "Loop quanutm cosmology" "Baum Frmapton model" Caroll Chen Model" "Confomral Cyclic Cosmology" "eternal inflation" for a few suggestions. At the moment its an open question.
  9. May 31, 2013 #8


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    If you are doing cosmology it is perfectly legitimate to assume that the universe has no end or beginning in time.

    The standard model has no end---it continues expanding into the indefinite future.

    Keep in mind that the standard cosmic model (so-called "LCDM" that pretty much every specialist in observational cosmology uses) might be WRONG. Scientists don't fully believe their models. They continue to challenge and test them to see if they need improvement. The currently accepted LCDM gives an amazingly good fit to the mountains of data that have accumulated from astronomical observation, but it is still merely the best we have so far. Merely the most reliable accurate fit.

    The fact that the standard model has a beginning--a point in time where it blows up and stops giving reasonable numbers--is widely considered to be a symptom that it is incomplete and needs fixing. It is apparently not applicable at extreme energy density, so it is not trusted. A considerable number of researchers have gotten interested in modifications of the standard cosmic model that include quantum effects on geometry at extreme density around start of expansion, and the modified models do not fail. No odd or "singular" behavior--no "blow-up" at the start of expansion. So in these models time just continues on back, not uncommonly into a contracting phase. Quantum effects at high density cause the contraction to rebound.

    It's certainly legitimate to assume that the universe goes back indefinitely in time, just as (according to standard LCDM) it goes forward indefinitely into the future. There are models that are time-infinite in both past and future, and which are just as good a fit to the data collected so far---recover the good fit of the LCDM.

    But it is also legitimate to assume that it does NOT go back indefinitely. Cosmologists have a choice of models to work with (and presumably if they are wise they never fully commit to one or the other :biggrin: )

    I'm not talking about "multiverse" stuff. Ordinary cosmology just deals with the universe we experience and with models we can hope to test by comparison with observation. There was a bubble of "multi" speculation in the mid 2000s---peaked sometime around 2003-2008. Since 2008 I've been seeing less and less mention at the professional level (i.e. conference talks and journal articles).
  10. May 31, 2013 #9
    I suspect there will be more to the answer than meets the eye. Solutions of the EFE often take the form of approximations to ideal systems and form part of the idealized FLRW cosmological model. Further some 96% of the mass/energy in the universe is dark....and we know little about it. It is strongly suspect neither GR nor QM are exact theories since they have some divergence issues [like the Big Bang and black holes]. Finally, our existing theories can't even identify if spacetime is infinite or finite, bounded or unbounded.

    I don't know all the math details to know what all this means for sure but I would not be surprised if the answer surprises.

    Since when has the cosmos not surprised us? 1930's: OMG, the universe is expanding! It wasn't until the 1970's that 'mainstream' astronomers acknowledged Vera Rubin's 'galaxy rotation problem' findings were real and that the vast bulk of the mass in the universe "is invisible and unknown in origin and character."..... Ooops, everybody had missed dark matter and dark energy...no biggie, tho, just 96% of all the mass/energy!!!
    Last edited: May 31, 2013
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