was spacetime really created with the Big Bang?

[gib65]

This is a good question for Marvin.

 

I'm just wondering if this theory is debated at all, or if there's any solid proof. I've heard theories saying that the BB was the result of two "branes" colliding, in which case there'd have to be space and time all ready.

[insane_alien]

The correct answer is, we don't know since we can't work back to the beginning(if there was one) we can get close(we think) but the laws of physics have not been tested/break down under those conditions.

 

not sure what the current consensus is, seems to change every other week.

[Azukre]

Yes, the Big Bang is something that simply "seems to have happened". There are multiple ideas as to what happened.

 

The only thing we can be quite positive about is that it didn't just randomly occur without a cause, we just don't know what the cause is for sure, because obviously, we cannot separate ourselves from the confines of this universe and peer beyond it.

 

The fact that the Big Bang "seems to have happened" implies to me, that there is existence beyond what we call "the universe".

[iNow]

The fact that the Big Bang "seems to have happened" implies to me, that there is existence beyond what we call "the universe".

 

This, I suppose, is one interpretation. I suggest that we speculate too much when our theories break down. Our understanding of t_null is so limited and sporadic that our imaginations try to fill the gaps.

 

Let's do ourselves a favor and better understand the t₀ of the inflationary model before we speculate what exists "beyond what we call the universe."

 

 

 

A Mathematician, an engineer and a physicist were traveling through Scotland when they saw a black sheep through the window of the train.

 

"Aha", says the engineer, "I see that Scottish sheep are black."

 

"Hmm", says the physicist, "You mean that some Scottish sheep are black".

 

"No", says the mathematician, "All we know is that there is at least one sheep in Scotland, and that at least one side of that one sheep is black!"

[Martin]

 

was spacetime really created with the Big Bang?

 

This is a good question for Martin.

 

I'm happy with the range of opinion already expressed by Azukre, Alien, iNow.

 

I know of no scientific reason to believe that time began at the start of expansion (bigbang). If someone just fancies that---if they just LIKE the idea---then of course they can believe it. But there are no scientific grounds for claiming that AFAIK.

 

I have no belief or opinion about conditions before start of expansion. there are several models. At least one model, which has a bounce, fits the data as well as classic 1915 General Relativity, which breaks down.

Since there are (at least) two models which are fairly simple (no elaborate extras like bouncing branes) and which are equally good fit to observation, you can take your choice.

 

You can either use a model which breaks down at that point---so no time evolution is described back past that point.

 

Or you can use a model which does not break down and has a bounce---so it describes a contracting phase that preceded the expansion.

 

And there may be other models that are also simple and fit observation, that I dont know about.

 

In the future we will probably have observations that favor one model over the other(s), so there will be grounds for preferring. right now I can't think of any reason to prefer, besides personal taste/philosophy.

 

I expect gammaray and UHECR observations may change the picture by giving some clues as to quantum geometry of spacetime (i.e. quantum gravity). Auger observatory has started reporting. GLAST satellite is scheduled for launch next year. Auger observes ultra high energy cosmic rays. GLAST will observe gammaray bursts. there are some other gammaray telescopes in operation, like MAGIC---a new kind of telescope called IACT=imaging air cherenkov telescope. there is room for more neutrino astronomy too.

 

People are rapidly expanding what they can see. I expect that before many years have passed there will be reasons to prefer one or another quantum cosmology model. then we will no longer be so undecided. And perhaps there will be a better answer to your question

[Sayonara]

Whatever happened to Gasperini and Veneziano's work on the pre-bang universe?

[Martin]

Whatever happened to Gasperini and Veneziano's work on the pre-bang universe?

 

it hasnt been cited much lately---dearth of RECENT Veneziano pre-bb papers that are getting citations by others.

it's funny how this kind of thing happens.

theories seem to fade and dwindle in the eyes of active research colleagues who are the only ones whose opinion matters.

 

Maybe nobody ever comes and officially puts an end for reason A B and C

 

they just gradually don't get cited in the current literature so much.

 

the great source, to watch this, is SLAC-Stanford SPIRES database

which tells you the citation counts up front and will even present papers in a ranked list

 

===============

also I was listening to the online videos of talks at a January 2007 workshop at the SantaBarbara institute (David Gross director, very posh)

and the workshop was about this very thing, resolving singularities so you could see before bang or past hole.

and they were DISMISSING Veneziano's pre-bb stuff and not even including it in the workshop! yet this institute is a major string theory stronghold!

they didnt seem to think worth more than a quick dismissive comment. so apparently string theorists don't think it is cool anymore.

 

however this is unreliable scuttlebut I just caught in passing, in the video of a discussion

 

the only real thing is the citation counts, and even that could be a false indicator.