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Post by peanutfan on Apr 30, 2009 18:15:15 GMT -5
There's something that's itched at my brain for a while and I wanted to see if anyone could answer for me.
According to quantum physics, space and time are intertwined irrevocably; you cannot have one without the other.
According to Big Bang cosmology, the universe came into being approx. 14 billion years ago (rough guess...I haven't kept up on the latest research, so that might have changed since my last reading). All of space and time emerged from the singularity.
But if there was no space or time before the Big Bang, doesn't that render any calculation about the universe's age meaningless? If time began when the universe began, isn't it accurate to say the universe has been around "forever"?
Just thought I'd ask. Thanks for any help you all can give.
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Post by szaleniec on Apr 30, 2009 23:34:27 GMT -5
It's an interesting philosophical point. The way I see it is that in Big Bang cosmology there is indeed no contradiction between saying that the universe is 14 billion years old and that it's been around forever, simply because time itself doesn't extend back infinitely. Forever means for all time, and if time is bounded this means not for infinite time. In a closed universe, time doesn't extend infinitely ahead either; it does in a flat or open universe.
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karl
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Post by karl on May 1, 2009 12:23:58 GMT -5
not really no because the age of the universe is sort of guesstimated by looking at the distribution of stars and gallaxies and saying OK if we know where they are(very roughly) how fast they are moving (roughly) and they all started at the same point then you can work out when they were all at the same place, which works out at about 13.7 billion years ago.
It gets interesting later on because if there is enough matter in the universe then due to gravitation the expansion slows down and will eventualy stop in another 100 billion years or so and reverse and everything ends up at the same point again in the big crunch.Thermodynamics kind of says that when the universe starts to contract again then time will reverse as well because if it didnt then the contraction would violate the second law of thermodynamics.There is some debate as to wether this will actualy happen or not.There is also some debate as to wether this cycle of big bang/big crunch has been happening for an infinite amount of time in the past each time creating a new universe. Its an open question as to wether there is enough matter in the universe to stop and reverse the expansion, but its looking increasingly like there is.Nobody has the slightest idea what being in a contracting universe with reversed time would look like, or if life would be possible in such circumstances.
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karl
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Post by karl on May 1, 2009 18:23:52 GMT -5
if you take a party balloon and paint dots on it to represent matter, blow it up and youve got a good model of the universe (space) expanding and matter moving away in all directions.Only the real thing is in 4( or 10 or 18 depending on what day it is) dimensions
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Post by Shano on May 4, 2009 20:55:22 GMT -5
Um...
The increasingly more evidence is for open parabolical universe. The part of it that we observe is expanding faster and faster.
The prevalent opinion is that there was a Big Bang; yet there are severe unresolved problems and suggested solutions have been multiple universes, buble universe etc...
The current estimate is Omega_tot = 1.02 /pm 0.02 which is an open universe with parabolical case included. Yet where 76% of the energy density comes from (the so called dark energy) is currently completely unclear.
So back to the philosophical question about time. If there has been Big Bang than I would agree that the universe lasted forever and forever is about 14Gy. In the other cases things go back to their usual understanding.
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Post by Captain Obvious on May 7, 2009 22:14:31 GMT -5
Big Bang doesn't claim that the universe was created or came into existence 14 billion years ago, only that it expanded 14 billion years ago and that everything gets a little fuzzy when you squish stuff in that small.
It's entirely possible that another universe collapsed into a singularity and that singularity expanded into us and we will eventually collapse into a singularity which will expand into another universe which will.... on and on and on we go.
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Post by perv on May 9, 2009 0:25:43 GMT -5
Strictly from a non-scientific standpoint, I don't see the problem. Even if there was no time before the universe (no such this as before, either), as long as there was time during the life of the universe, it still has an age.
Interesting question about "forever". I guess you could say "forever" (past tense) is synonymous "since the beginning of time". By that definition the universe has indeed existed forever. But by the same token, you could say the universe will exist forever, regardless of whether or not it ends at some point. And that doesn't sound right. So an alternate definition of "forever" would be "an infinite amount of time". In which case, there hasn't been a forever, and I don't think anybody knows if there will be one in the future.
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