Tom Sawyer

What are the present theories of what caused the Big Bang? I realize that no one really has a good answer for that yet, but what is being looked into?

Basically, what I know about it is that about 13 billion years ago, something happened that caused the universe to start expanding.

I've heard that general relativity comes apart at Planck Time and that quantum gravity may be able to explain what happened before that, but I don't know what quantum gravity is.

Some people say this is part of a cycle of expansions and contractions and some say this was the first event, due to some kind of fluctuation in the "void". What are these ideas based on?

I've heard it said that it's meaningless to discuss what happened before the Big Bang or describe what is outside the universe since time and space are properties of the universe, rather than pre-existing conditions that the Big Bang occured within. That's a big one than I'm not able to wrap my mind around. What is this based on and is there evidence to support it, because this doesn't make a whole lot of sense to me.

I'd appreciate anyone giving me some explanations of these or pointing me to some good links that describe these things.

ekorczynski

As I previously posted to the somewhat rambling link titled "before nothing":

IMHO, there are severe semantic issues involved in any such attempt at a discussion, such that the only way to even begin an attempt is to start with clear and self-consistent definitions of terms.

Whether one is a theist, atheist, or agnostic/skeptic, if we try to talk about this using the English language, then we must agree upon definitions of at least the following terms: "God", "universe", "time", "cause", etc.

From my recent posting to the "Big Bang" thread: _at most_ we can trace evidence back to a "singularity". That is to say, whether there is sufficient evidence to trace universal causality back to a "singularity" or not, we certainly cannot meaninfully discuss anything "prior" to said hypothetical "singularity".

My main point being that since "causality", "before" and similar concepts have meaning only within the concept of "time" as we hold it, and since "time" is considered as only beginning with "space" in the Big Bang, it is meaningless to discuss a concept of "before" the "Big Bang".

Likewise, it is meaningless to ask "what is outside of the universe," since "universe" is defined as the superset of all matter/energy/time/space/etc.

If someone else has significantly different definitions of "before" "time" and "universe" that solve this semantic absurdity, please share with the rest of us...

As "Eh" so clearly stated in his prior posting: "A universe created from nothing: The idea here that the entire universe emerged as a quantum fluctuation in the void. Nothing physical existed prior to the big bang, but the laws of physics clearly did, allowing for such a fluctuation to bring about the universe. This of course deifies any arbitrary laws of physics."

If God is the creator, who created God?
If the laws of physics caused the BigBang, then what caused the laws of physics?
If the world rides on the back of a giant cosmic turtle, then what's below the cosmic turtle?

The only answer to any of these questions is, "It's turtles all the way down!" IMHO, when the only possible answer to a question is an absurd paradox, then this is an indication that the question -- as phrased -- is itself absurd and the only possible resolution is to consciously re-examine terms and re-phrase the question.

So, sorry to say, but IMHO the question "what caused the Big Bang" is meaningless for current definitions of the terms "caused" and "Big Bang".

...to be honest, I don't quite know how one would begin re-defining terms to resolve the evident paradox...

...invoking the "cyclical universe" theory of sequential expansions and contractions does not seem to resolve the issue, since one could always ask what started the sequence...

...just one more excellent reason to remain a Skeptic, instead of falling into the tragic certainty of a dogma about "ultimate causes".

keyser_soze

BIG BANG. Hmmm. Don't know, don't follow it. Don't know that I buy it, but at least the price is better than the goddidit theory(what price your mind?). Personally I don't worry about the "where'd it come from" as it is presently unknowable.

fando

String theory (now Membrane theory) provides a very weird explanation for the Big Bang: the collision of special 'branes' or spacetimes with certain properties. The best site to learn about this stuff is http://superstringtheory.com/ under cosmology. This stuff is wildly theoretical.

Besides that, there really is not much that can be said about the 'creation' of the universe without having a foundation to describe the environment 'prior' to the Planck Time. The physics that will allow us to do so is widely thought to be quantum gravity, which sort of fills in the cracks between Quantum Field Theory and General Relativity.

These ideas are venerable by now and pretty much conjecture. Basically, these ideas were arrived at by hand-waving extrapolation of very basic models of the universe. For instance, the Oscillating universe idea was conjured from assumptions that our universe was comfortably closed (that it is dense enough to halt expansion and contract) and that the universe has a phoenix-like ability to be reborn after collapsing in a big crunch. Credulity is involved here, this is the genesis of new ideas in science.

That's why we need a framework like quantum gravity. Otherwise, we won't be able to understand the very weird stuff that goes on. Remember that your intuition, the stuff you understand clearly, is limited by what you have experienced personally. Realistically, your intuition is limited to classical physics, and therefore your intuitive understanding is limited to grasping things like Newton's laws of motion and maybe relativity. On the other hand, don't expect to understand the probabilistic nature of the quantum world in any deep way. The quantum world is simply not experienced by us directly. We resort to logic and re-training our intuition in order to understand new and unfamiliar physics. We will need to do this for systems where time has a very different meaning than we're used to, and this seems to be the case for the environment on the scale of Planck Lengths and Planck Times.

Tim Thompson

Seen strictly from the point of view of classical, general relativity, time as a coordinate variable comes into existence with the "bang". So, even when we have a good intuitive idea of what we mean by "before" the "bang", the question can't be answered in classical terms, since we are being asked to describe that which does not exist (i.e., "time" before the "bagng").

However, once one considers quantum theories of gravity, the problem with "before" the "bang" goes away. Time makes as much sense on one side of a quantum event as it does on the other. The trick is figuring out the right way to quantize general relativity, a task currently generating much heat, if little light.

There is a "pre big bang" scenario based on string theory. There is a "cyclic universe" idea based on the multi-dimensional foundation of string theory. Those are the two developed ideas about what comes "before" the "bang". I don't doubt there are other ideas available from other quantizing schemes, but I am unaware of them if they exist.

Do an internet search on "quantum cosmology" or "quantum gravity" and you'll find a few reputable sources, even if they aren't all that articulate for non-scientists.

• Welcome to the home page of Maurizio Gasperini, devoted to pre-big bang cosmology, based on string theory. It is an index of links to research papers on the topic.
• Paul J. Steinhardt's Homepage. Steinhardt is rthe cheif architect of the cyclic universe hypothesis. Links to research papers and other material for non-scientists.
• Quantum Gravity from the Cambridge Relativity Group. More or less non scientist targeted material on quantum cosmology & string theory.
• Ned Wright's Cosmology Tutorial. Not much about quantum cosmology, but the best source on the web for classical cosmology & relativity, accesible to non-scientists. See especially the Fads & Fallacies pages, where he takes to task various questionable alternatives to big bang cosmology.

Infidelettante

So, as I understand it there was BB because we see the universe expanding and that leads to the conclusion that at one time everything there is now fit into very, very little space...no wait, not at one time because there wasn't any time and there was no space so it couldn't have fit in...at some...point, everything that makes the universe was so close together that it was all the same and there didn't seem to be much of it and it was really hot and then it began moving outward no expanding it began expanding and is still expanding even faster all the time and will go on expanding untill everything is cold and dark and may even get eaten by massive black holes untill there is nothing left and then God is going to be really lonely...again. Great!

keyser_soze

Beats the "god came from nowhere" and "created everything cause he was bored" theory. At least universal expansion is observable via information. God is observable only in the minds of nut's and child kidnappers. (right jab, followed by a feint and then a kick to the groin)

Infidelettante

As I wrote it my post amusingly [one hopes] posits that indeed God came from nowhere and created everything because he was bored and may get the chance to do it all over again if things go accordingly causeing no end of regret that as he does not exist nor does eternal life you and I are precluded from ever having this exchange again. Do not make me call my lawyer.