questions about the origin of singularity = nothing

Just to add a slightly different angle to this:The thing is... the singularity is not a thing, it's a place: like the North Pole. How big is the North Pole? It has no size whatsoever, but nobody disputes its existance. It is the origin of lines of longitude. The big bang singularity is the origin of lines of time. How can you go north from the North Pole? You can't, you can only go south. But there is no barrier or edge preventing you from going further north; the question just doesn't make sense or apply. In the same way, you can't think of before the big bang, because from the the big bang, all directions lead to "after" the big bang. At time=0, our common understanding of time has disappeared and no longer applies: there is no "before", only "after". Just as our common understanding of north disappears at the north pole: there is no north (or east or west), only south.If we live in a "closed" universe, this analogy is even better, because just as the circles of latitude grow from zero size from the north pole, reach a maximum (the equator) and then shrink bank to zero size at the south pole, so too the universe grows from zero size, reaches a maximum then shrinks to zero size again in a "big crunch". The idea is not to look at the lines of latitude, but look at the whole earth: although the lines of latitude begin and end with zero size at the two poles, there is no edge or boundary. Looking at the earth as a whole, we understand that asking what's north of the north pole and south of the south pole makes no sense. In the same way, when we look at the universe not as three-dimensional slices (which is all our eyes and minds can do) but as a four-dimensional whole, we realise that although we can have a beginning of time (big bang) and end of time (bug crunch), asking what happend "before" the big bang and "after" the big crunch simply doesn't make sense... it's not evading the question.General Relativity (the mathematics which gives us big bang cosmology) only deals in 4 dimensions (3 space + 1 time). So to understand what it is telling us, we have to think in 4 dimensions, which is neither easy nor intuitive when we are so used to a world that appears to be 3-dimensional.

I was talking Standard Model FRW cosmology with a hint of Hartle-Hawking NB proposal but I'm trying to get across a basic mathematical truth about the geometry of space-time. It doesn't really matter what model you stick in there. Exactly the same priciples will apply, whether your target space is 4, 10, 11, or 26 dimensional. The important point is that time is simply a coordinate... just because it may start somewhere, it does not necessarily introduce an "edge" or "boundary" that would beg the question of "what came before?".Anyway, the original point was about the singularity being of zero size, and we seem to have drifted off that (my fault!). Again, you need to think in higher dimensions. I've used the north pole analogy... now a slighlty different one: take a box. It has eight vertices. Each vertex is a "point" of zero size, zero volume. Does that mean that we can't fit things in the box? It is the box that contains the things... the vertices are just limits of where those contained things can be. The big bang singularity is simply a vertex to the 4-dimensional universe.Hmmm, I'm not to happy with this analogy... I'll work on it :-)

This idea of creation out of nothing is a complete misunderstanding. Also, it's playing into this misunderstanding to say that the big bang was a "starting" point. It's just "a" point. Our simple notions of time, before and after, only apply in this very quiet region of the universe where we live.Caveat for the technical: the following is related to a closed FRW universe...The universe didn't appear out of nothing. It just "is". There is, at one point in the universe, a thing called the initial "big bang" singularity, and at another point a thing called the final "big crunch" singularity. These are just two points, not beginnings or endings. There are some very strange inhabitants of this universe, called humans. They cannot see the four dimensional nature of this universe, and are restricted to a three dimensional view. They "age" along lines joining the two singularities, and invent terms such as "before", meaning points in the universe closer to the initial singularity than their "now" and "after" meaning points in the universe closer to the final singularity than their "now". To the universe, this is all very mysterious, especially as these terms have no meaning close to either singularity. But that's ok, because none of the humans' "now" points are anywhere near either singularity: the humans only live in the middle bit of the universe, well away from either singularity. The universe is still confused though, because these humans keep asking what happened "before" the big bang. But if you are at the big bang, how can you get any closer to it? Do these humans really know what they're asking? "how did the big bang come out of nothing?" What do they mean, nothing??? If they stood at the big bang they would see the entire universe stretching out around them. There is no nothing. The universe concludes that it must be very sad to be a human, restricted to this narrow 3-dimensional view, suffering from all these worries just because they can't see clearly... oh well.Sorry, got carried away there :-)

Be careful here, because we're in danger of confusing "nothing". This is certainly not nothing. You've got mathematics, also physics, and a bunch of quantum fields, and a background space-time for it all to live in. This is hardly nothing. This is the universe. The universe cannot comes from this, as it already includes this! "Nothing" in my book is an absence of: definitely space-time, definitely quantum fields, possibly physics... hmmm, mathematics... well God sometimes appears to be a mathematician, so I'll allow mathematics :-)

Just to add to what I've just said, when a lay-person asks about creation from "nothing", they are almost certainly implying some form of naive absolute nothing. So when physicists all-to-often reply with the pair-creation argument, they are not addressing the real concern. You cannot pair-create without a universe in which to pair-create. And if you want to pair-create universes, you still need some form of super-arena for your physics. Is this nothing?

It's a good stalling tactic, but never ultimately satisfying :-) Exactly. I think this model should be understood before trying to looking at more esoteric theories. Once you've got the essence of no-boundary, it all becomes much more clear. If you can grasp that, you can grasp anything that string theory throws your way! There are very few pictures I have ever seen that are more satisfying than no-boundary in a closed FRW universe.

Huh? I can only assume you are objecting to my anthropomorphising of the universe... it's a literary technique used for effect and emphasis.Just in case you're objecting to the science, it's called General Relativity, and it's just the way it is... sorry.

Where I did I suggest it was? We can do science, however, so at worst my scenario is a scientific hypothesis. I did not think I was implying either...

Yes, "no boundary" works with a closed universe. Observational evidence points to a flat universe, with W=1. If it is truly flat, then this is an infinite universe like the open universe. However, one of the benefits of inflation is that it explains this flatness as a product of the inflation. You can start with any value of W and inflation pushes it close to 1. So the universe is quite possibly closed. The observed acceleration does not change this. We are beyond the original three scenarios of the FRW universe now.

Sorry, I'm being a little loose with my definitions. I'm talking about W distinct from the accelerative factor (cosmological constant, quintessence, whatever). We can have a closed universe that has accelerative expansion... this is just like de Sitter space. And yes, this is like the inflationary period, just much much much less dramatic! Don't think of W changing, but whatever it is that is causing the expansion.

Closed and big crunch are synonymous in a classic FRW universe, which is what we used to believe in (no cosmological constant, no quintessence) That is why you (and most of us) still put the two concepts together. But add a cosmological constant type device and everything changes...I'd forgotten the Turok thing. It post-dates my time in the field. I've only spoken with him a couple of times. Seemed a nice guy. He joined the department not long after I left. Don't worry, when you look at the number of papers published in this field, you only ever hear of a fraction of a percent of the stuff that goes on. Check out the daily lists of hep-th and gr-qc at xxx.lanl.gov.

That's right SG, start with the basics

SG has alreay covered this, but just to emphasise: thermodynamics is very much secondary to Relativity. In its usual guise it is merely a probablistic statement, applies locally, and has no application to considerations of the universe as a whole.When time is simply an internal aspect of the universe, the beginning of time does not imply a beginning of the universe. If the universe is created (and as a Christian I believe it is) then that creation not only involves the beginning of time, but its middle and end.

Hi Chirop, Are you asking if the universe could have existed "forever"?Absolutely, but "forever" is a little naive... take the space-time of an electrically charged black hole - the Reissner-Nordtrom solution. It has an infinite number of sub-universes all connected by an infinite corridor, and each sub-universe is eternal: no beginning and no end. The key point is that there is no universal time. The question is not "has the universe existed forever?" but "does the universe contain any time lines that extend infinitely far back?". This is perhaps one of the hardest things to appreciate in GR, that time is purely local and has no global meaning... "Will the universe go on forever?" "well, which bit of it?"Every time line (in the kind of universe we live in) is predicted to begin in a singularity by the Hawking-Penrose singularity theorems. But these do not take into account quantum gravity, which could smooth off the singularity (into a nice North Pole as I describe it in my globe anaogy but really the Hartle-Hawking no-boundary proposal), or just as easily open up the geometry into an infinite past, perhaps revealing a larger embedding universe.This message has been edited by cavediver, 02-11-2006 06:12 PM

Intuition and the universe have very little in common. Does your intuition provide a better understanding of the workings of time than GR? Can you explain what YOU mean by "the unverse has always existed"?Simply stating something is so is not really part of what most of us call science...This message has been edited by cavediver, 02-11-2006 08:15 PM