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Before Bigbang

by pixel01
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pixel01
#1
Mar30-07, 01:34 AM
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Can anyone tell me what the universe was before Bigbang?

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Chronos
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Mar30-07, 02:50 AM
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Not by physics as currently known. We hit the wall at one planck tick after the putative big bang - i.e., current theories cease to have any predictive value before that point. On the brighter side, our theories are astonishingly predictive thereafter. The reason for this has much to do with our inability [to date] to derive a workable quantum theory of gravity. While such a theory may not necessarily unlock the gate to what lays beyond the planck wall, it should at least illuminate the keyhole. In some branches of theory, the big bang is not a 'true' beginning, but rather a single 'bounce' in an indeterminite [infinite?] series of bounces. Some find that comforting, as it avoids the creationist overtones lurking behind the 'universe from nothing' proposition. But no variant of the 'bounce' proposition [at least AFAIK] grants us access to prior bounces. The information contained in previous cycles is utterly annihilated in the process. To me, that seems like an overly complicated way of arriving at the same conclusion - what came before the big bang has no observational consequences in our universe - which is the same as saying it is not testable, hence unfalsifiable, hence of little, if any, scientific value.
pixel01
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Mar30-07, 04:12 AM
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christianjb
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Mar30-07, 04:15 AM
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Before Bigbang

Quote Quote by pixel01 View Post
Can anyone tell me what the universe was before Bigbang?

Thanks
Stephen Hawking had a pithy answer to that one.

Asking what came before the big-bang is like asking what the Earth is like south of the south pole.

Still- it goes against intuition, because it's hard not to think of the big-bang having a cause.
EL
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Mar30-07, 04:43 AM
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Quote Quote by pixel01 View Post
Can anyone tell me what the universe was before Bigbang?

Thanks

Assuming an inflationary scenario (http://en.wikipedia.org/wiki/Cosmic_inflation ), I'm of the opinion that what should be called the "Big Bang" is what happens at the end of the inflation when all matter is created in the reheating process.
So one possible answer to your question is: inflation.
mjsd
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Mar30-07, 06:00 AM
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Quote Quote by pixel01 View Post
Can anyone tell me what the universe was before Bigbang?

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Interesting... if spacetime itself is created at the big bang, then it is meaningless to talk about "before" because time did not exist before the big bang
Just Passin By
#7
Mar30-07, 09:30 AM
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But does Time really exsist anyway? teh Aztecs were off only either 4 hours or 4 days. But still time was never recorded until humanoid life forms realized the coming and going of the sun and moon.
russ_watters
#8
Mar30-07, 09:57 AM
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There was a lot that wasn't recorded before humans recorded it.....Since humans are the first on earth (as far as we know ), that would be, uh, everything.

Yah, time exists.

And don't tell birds and other animals that they don't notice the coming and going of the sun (or the seasons, for that matter) - they might be insulted.
Just Passin By
#9
Mar30-07, 10:18 AM
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I get what your saying, but if "time" was thought of as something to guide us from day to day, isn't "time" also just a standard, or better yet, a belief that we humans have come to accept as something that really exists but in a way dosen't?
russ_watters
#10
Mar30-07, 12:49 PM
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No. You are confusing time with the units of time. A "day" is a human construct just like a "meter" is, but that doesn't mean that time and length do not exist.
BillJx
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Mar31-07, 01:06 AM
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Quote Quote by russ_watters View Post
No. You are confusing time with the units of time. A "day" is a human construct just like a "meter" is, but that doesn't mean that time and length do not exist.
The answer I like is that time is a concept that we use to understand relationships between events, and space is a concept we use to understand relationships between objects. I forget whose definitions those are.

Events define change (or vice versa) so I guess you could say that time is a way of organizing a world of continual change. Keeping in mind that I haven't gone past first year physics, I like to think of time as a large scale effect of the uncertainty principle.
hellfire
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Mar31-07, 06:40 AM
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Quote Quote by mjsd View Post
Interesting... if spacetime itself is created at the big bang, then it is meaningless to talk about "before" because time did not exist before the big bang
You may be interested in this point of view beyond general relativity:

The Issue of the Beginning in Quantum Gravity. A. Ashtekar
http://arxiv.org/physics/0605078

In semipopular articles and radio shows, relativists now like to emphasize that the question “what was there before?” is rendered meaningless because the notions of ‘before’ and ‘after’ refer to a space-time geometry. We now have a new paradigm, a new dogma: In the Beginning there was the big bang.

But general relativity is incomplete. For, it ignores quantum effects entirely. Over the last century, we have learned that these effects become important in the physics of the small and should in fact dominate in parts of the universe where matter densities become enormous. So, there is no reason to trust the predictions of general relativity near spacetime singularities. The classical physics of general relativity does come to a halt at the big-bang. But applying general relativity near a singularities is an extrapolation which has no justification whatsoever. We need a theory that incorporates not only the dynamical nature of geometry but also the ramifications of quantum physics. Does the ‘correct’ or ‘true’ physics stop at the big-bang also in quantum gravity? Or, is there yet another paradigm shift waiting in the wings?
mjsd
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Mar31-07, 08:30 PM
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Quote Quote by hellfire View Post
You may be interested in this point of view beyond general relativity:

The Issue of the Beginning in Quantum Gravity. A. Ashtekar
http://arxiv.org/physics/0605078
mm.... this is the point of view of the gr-qc clan, I wonder what the hep-th and the string gang got to say about this?

In any case, all we can say is "we don't know yet...."
marcus
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Apr3-07, 11:22 AM
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Quote Quote by mjsd View Post
mm.... this is the point of view of the gr-qc clan, I wonder what the hep-th and the string gang got to say about this?
...
Prominent members of string community would like to see the Loop result duplicated----that is, removal of the BB singularity in a string context as well. They showed this by putting money where mouth and setting up a KITP workshop.

Resolving classical singularities has been a quantum gravity goal for a long time (long before the appearance of Loop Quantum Cosmology in 2001, or of string for that matter.) Singularities are not supposed to occur in nature, but are places where the theory breaks down---In this case where classic Gen Rel breaks and evolution backwards in time stops.

So leading string people, at the Santa Barbara Kavli Institute that David Gross directs, invited LQC people to a three-week workshop (Jan-Feb 2007) called
"The Quantum Nature of Spacetime Singularities"
http://online.kitp.ucsb.edu/online/singular_m07/

If you know the string scene at all you would probably recognize some of the names Steve Shenker, Gary Horowitz, Robert Brandenberger, Steve Giddings ... (David Gross sat in some of the time, not sure how much though.)

Horowitz gave the keynote and started off with questions like what does it mean to remove spacetime singularities, what came before the big bang...etc.

you can watch most of the talks on video, they are online at Kavli ITP.

Leading Loop people there included Ashtekar (you were commenting on his article The Issue of the Beginning), and Bojowald, and Thiemann.

The Loop talks discussed LQC achievement of a correct classical limit and of deterministic timeevolution back past where the BB singularity occurs in classical GR. The talks caused a lot of excitement and provoked much questioning. Thiemann was given an extra hour---the only one of more than a dozen speakers to get that. Afterwards Bojowald appears to have been offered some kind of position at KITP.

It's clear that KITP string thinkers are maintaining a proper posture of reserve and skepticism on the one hand, but that on the other hand they are extremely interested in LQC results.

BTW LQC has undergone a radical change since 2004 having to do with what Ashtekar calls improved or new dynamics. So they were talking about that too, as well as removing singularities.

and they talked about current work on BH singularities too.
marcus
#15
Apr3-07, 12:04 PM
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Quote Quote by pixel01 View Post
Can anyone tell me what the universe was before Bigbang?
The latest major paper to come out on this is available for download here
http://arxiv.org/gr-qc/0703144

The main point at present can be briefly summed up by saying there is no scientific justification for asserting that time stops at some point in the past some 14 billion years ago.

There are two equally good models: classical GR-based cosmology and LQC.

LQC duplicates all the good stuff that the classical model does---it converges to the classical picture just moments (a few planck time units) after the start of expansion, but the difference is that it does not break down at the start of expansion.

So we have two models which fit the data gathered so far equally well. One breaks down at start of expansion and one keeps on working back in time past that point.

You dont have to believe one over the other, and you dont have to believe either. IF we were only working with classic 1915 Gen Rel and classic cosmology, then we would have a reason to say time stop there, looking backward. Because the only model we know broke down there. But as of 2001 and especially since the improvement of 2005 we dont have just one model. We have TWO: one that experiences a failure or "singularity" and one that does not, but continues to compute back into the past. (there are others as well but not so prominent or being worked on so much.)

So at present we have no scientific reason to prefer one over the other (later there will be testing to decide, one can see what they see about stuff we can observe in present and decide which is better, but so far no tests have distinguished). So we cannot justifiably say time stops when you look back 14 billion years.
======
That would be the main message.

Some further detail in case you or anyone is interested:
The LQC folks at Penn State are currently running computer models of case after case with different data and probing back before the start of expansion in these different cases. sometimes they find a contracting phase of the universe---something that looks roughly analogous to our space soon after the start of exansion but it is contracting instead---sometimes the model does NOT give a classical region of spacetime before the bounce. I don't think anyone can answer your question in the sense of saying with any confidence what the universe was like before the bounce or before the start of expansion. One can say that this is being probed both analytically and with computer modeling, primarily at Ashtekar's institute at Penn State.
hayzie
#16
Apr4-07, 11:45 AM
P: 5
I still cant see how there was nothing before the big bang. i cant get my mind around the concept of time and distance not existing.

Its probably the concept of reality that i cant get past. I only believe in things i can touch, smell, see and hear but that doesnt mean they dont exist.

e.g. The after life, God, Heaven. stuff like that i cant see physically possible.

After you die is like before you where born. star dust
marcus
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Apr4-07, 02:13 PM
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Quote Quote by hayzie View Post
I still cant see how there was nothing before the big bang. i cant get my mind around the concept of time and distance not existing.
...
Why should you WANT to get your mind around that idea?

Please read the preceding posts #14 and #15. There is no scientific grounds for believing that time and space did not exist before the start of expansion.

At the present stage a lot of us need to get over the idea that was peddled in earlier decades (by prominent scientists!) that somehow Science tells us that there was nothing before the start of expansion.

Equally good models give different answers about that. Some cruise along smoothly back in time to before expansion started, and some break down.
There WILL be tests to try to exclude one or the other, based on what the predict about what we can observe at the present time.
But so far there is no empirical reason to prefer one or the other.

So there is no scientific grounds for saying that before a certain event there was nothing. It depends on which model.

So I'd say you need to clean your head out of the idea that anyone expects you to believe there was nothing before big bang. If they come at you with that tell them Science doesn't say that there was nothing.

that was a misconception that somehow became popular (may have had something to do with the attention-loving celebrity in the wheelchair )
FeynmanMH42
#18
Apr4-07, 08:15 PM
P: 68
Quote Quote by marcus View Post
Why should you WANT to get your mind around that idea?

Please read the preceding posts #14 and #15. There is no scientific grounds for believing that time and space did not exist before the start of expansion.

At the present stage a lot of us need to get over the idea that was peddled in earlier decades (by prominent scientists!) that somehow Science tells us that there was nothing before the start of expansion.

Equally good models give different answers about that. Some cruise along smoothly back in time to before expansion started, and some break down.
There WILL be tests to try to exclude one or the other, based on what the predict about what we can observe at the present time.
But so far there is no empirical reason to prefer one or the other.

So there is no scientific grounds for saying that before a certain event there was nothing. It depends on which model.

So I'd say you need to clean your head out of the idea that anyone expects you to believe there was nothing before big bang. If they come at you with that tell them Science doesn't say that there was nothing.

that was a misconception that somehow became popular (may have had something to do with the attention-loving celebrity in the wheelchair )
I thought said celebrity had mathematically proven for his PhD thesis that an expanding universe would have had its beginnings in a Big Bang singularity thus giving space and time a beginning with no "before"?


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