Thread: big bang

For mainstream physics what are possible causes to kick off the big bang?

I'm not really a believer in multiple Universes, but one theory is that the Big Bang is the expansion of our Universe off of a different Universe. Otherwise, there are no solid theories on WHY or WHAT started the Big Bang.

Here is why I am confused: If the Big Bang was the "start" of time and the universe (the start of space time), then there was nothing before it. Maybe all that matter was stuck in that infinitely small point for trillions of years or maybe just a couple hours - but it wouldn't make any difference because if there was no space, if there was no entropy, then there is no way to measure time, so "before" the Big Bang isn't something that can be measured. If there was no entropy before the Big Bang, then how did things become offset to lead to the expansion of the Universe? Nothing should have kicked off the Big Bang because a change in the state of the energy should have been impossible.

Obviously our current understanding of physics and how the Universe expands isn't to the point where your question can be correctly answered.

I think right now the one theory that has the most strength (IMO) is the theory of our Universe expanding off a different Universe even though I don't like that idea, I don't quite buy the "multiverse" idea yet. There had to be a "first" Universe, right?!?

This question has lead me toward where I stand with religion, although I'm not going into that here.

The point is that there was no "trillions of years" as there was no time and if there was how would you measure that it was trillions of years?
Time as well as space began at the big bang ( or at least the big bangers would have you believe that ).

Originally Posted by stereobot

Here is why I am confused: If the Big Bang was the "start" of time and the universe (the start of space time), then there was nothing before it. Maybe all that matter was stuck in that infinitely small point for trillions of years or maybe just a couple hours - but it wouldn't make any difference because if there was no space, if there was no entropy, then there is no way to measure time, so "before" the Big Bang isn't something that can be measured. If there was no entropy before the Big Bang, then how did things become offset to lead to the expansion of the Universe? Nothing should have kicked off the Big Bang because a change in the state of the energy should have been impossible.

Obviously our current understanding of physics and how the Universe expands isn't to the point where your question can be correctly answered.

I think right now the one theory that has the most strength (IMO) is the theory of our Universe expanding off a different Universe even though I don't like that idea, I don't quite buy the "multiverse" idea yet. There had to be a "first" Universe, right?!?

This question has lead me toward where I stand with religion, although I'm not going into that here.

Originally Posted by tom

The point is that there was no "trillions of years" as there was no time and if there was how would you measure that it was trillions of years?
Time as well as space began at the big bang ( or at least the big bangers would have you believe that ).

Yeah I understand that there was no "time" before the Big Bang, that was my point - that "Before the Big Bang" time was non existent. I just expressed that poorly in my post. I don't know why I made it more complicated than it should have been.

My point about confusion (really more just a lack of understanding) is if there was no space, then there was no time, so there was no possible entropy. If there is no entropy, then nothing "within" the energy prior to the Big Bang would have (or should have) changed to offset whatever was there with the resulting expansion/ big bang.

I know this is something that is still unsolved, so I'm not looking for an answer, but I think the closest answer given our knowledge of physics is that our universe expanded off another universe, maybe one with a different set of physics that allowed our Universe to branch off of it.

To the best of my knowledge, some physicists are under the impression that the natural quantum fluctuations you see at the smallest level of space-time (the Casimir effect, basically how virtual particles pop in and out of existence in time-frames that are barely comprehensible) could have "kicked off" the Big Bang. It's often referred to as the "energy of empty space", and apparently it accounts for much more energy than the normal mass and energy we are all familiar with. Some cosmologists have suggested that our Universe arose from such a quantum "foam" in which these particle-anti particle pairs are blipping in and out of existence and occasionally their overall energy would reach a non-zero value, thus having an energy component. While the quantum "foam" obviously exists in our Universe, and space and time are quantized to a certain degree, we do not yet know enough about the earliest stages of the Universe to suggest whether or not this quantum "foam" hypothesis may have been the lead-in to our current Universe (if I am wrong, please correct me, I still have a lot to learn!). My one argument with this position is that the space-time we are familiar with are quantized, but since the Big Bang was an expansion of both space and time, basically the beginning of such, I really don't know how those fluctuations could have lead to it. Anyone have any info on the topic?

@John

The quantum fluctuations accounted for the earliest moments where matter started to fall into each other, however that isn't (to the best of my knowledge and understanding) and couldn't have been what kicked off the Big Bang. "Prior" to the Big Bang, if there was no space-time there would have been no entropy, so by definition quantum fluctuations would have been impossible. There would had to have been an initial kick of space time coming into existence before quantum fluctuations could have been possible.

However, physicists do not yet know how or why the Big Bang was kicked off, so maybe there wasn't an initial point before the initial quantum fluctuations. Actually, there is the part of M-theory where "branes" could have collided and kicked off the initial expansion where the quantum fluctuations could start.

I still have a lot to learn too, I wouldn't trust anyone who thinks they don't

@stereobot

That's something I've thought of as well. Seeing as there was effectively no space-time at T=0, then those quantum fluxes that we're all familiar with may not have been occuring, as there really wasn't anything to flux. For all I know there may be physicists saying differently, but to the best of my knowledge, without space-time, the Casimir effect does not occur. Although I am aware that particles are allowed to "come from nothing" on the scale of the Planck Time, I think that may only be applicable for an already expanded Universe. Do you know of any good sources of info into this particular subject?

P.S. To me, this is one of those motivating mysteries in science. We can say quite a lot about the Universe's early history and even it's current composition and the like, yet it is still a mystery how it began from T=0. Definitely one of those mysteries that keeps you up at night in a very good way.

I agree. Even if our universe did start with the collision of branes, where did the branes come from? If universes are expanding off each other then there still had to be a start.

I am almost finished with "Fabric of the Cosmos" by Brian Green (Greene?). I HIGHLY recommend it, especially for you since it covers a lot about what we are discussing and I think it would help your understanding of early stages of the universe. It certainly helped mine - I didn't understand much before I read it (I guess compared to many people, especially the Ph.D's out there, I still don't), you are already further along than I was.

The book is great, starts with basic physics (not just "gravity makes object fall to Earth" but why the basic physics work) and ends with expansion theories, string theory, branes, etc. It is just over 500 pages. He covers "time" and the arrow of time, everything. It has taken me MONTHS to get through it since I frequently have to re-read pages so I understand the concepts, but I have learned so much. He does a great job of explaining things to the reader without getting into the mathematics of the theories.

I think your understanding of the Casimir effect might be a bit off, I believe the Casimir effect has more to do with the level of energy when two objects are extremely close to each other. There is actually an electro magnetic energy level at that point that repels the two objects - that energy prevents gravity from making the two objects lock into each other. I'm sure I'm missing some details there, I might be incorrect all together.

I've actually read The Fabric of the Cosmos as well as The Elegant Universe, and both are quite amazing and I loved them dearly. Brian Greene is by far one of my favorite authors and scientists. I had to take a month or so to read either one, because I found myself re-reading them constantly to make sure I had it down.

You're actually correct. I was misusing the term "Casimir Effect" to refer to the energy of empty space. Effectively, the way I learned it, the Casimir Effect relates to how you can have two uncharged metal plates close together and because there is more empty space outside of them than between them, they will actually be forced together. Definitely an interesting part of reality, I would say. The reason I used that term is actually because saying "the energy of empty space" can sometimes get redundant XP.

Overall, when it comes to the brane hypothesis, I'm definitely rooting for it in the sense that I find it compelling, although I am unaware of any evidentiary support. Either way, the cosmos does give us a lot of "what if" and "how" questions for us to answer. I'm looking forward to more data coming in.

I often tend to agree with a quote I once heard, although I can't remember who it was from, that said "I think the Universe is just something that happens from time to time." I always liked that one.

I think to get anywhere with the space and time of the big bang, you have to forget about concepts like space and time. You have to forget about anything relating to the universe that we see from OUR perspective. Because the universe goes well beyond the perspective of any human being. There are so many elements to the equation of the start of the universe that we don't know about and probably won't every know about because, none of our senses are set up to detect them and our brains are not set up to understand them.