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September 7, 2010

CATEGORY: Blog [back]
TOPIC: The Big-Bang versus the Big-Bang [refresh]

FQXi Administrator Anthony Aguirre wrote on Nov. 13, 2007 @ 20:50 GMT

"Big-bang" versus "Big bang"

I spend a good bit of time thinking about what happened in the period of time between the Big-Bang and the Big-Bang. No, I'm not crazy (or at least not with respect to this issue). Rather, the problem is that the term "Big-bang" is often used -- both by professionals in the field and in the popular press -- to discuss two quite different things.

One thing is the "big bang theory" or "big-bang model" in which the observable universe expanded and cooled from a nearly uniform, ultra-hot and ultra-dense bath of radiation and a smattering of particles. This theory is very well-confirmed observationally, back to temperatures of billions of degrees (at which times the model can be probed via nucleosynthesis).

The second thing is the "big-bang singularity" by which is generally meant an early-time edge of the spacetime region that can be treated using the reasonably well-understood physics of classical general relativity and quantum field theory.

These two different ideas are conflated because in the original formulations of "big-bang cosmology" these notions went hand-in-hand: extrapolating the big-bang theory back in time led inexorably to the big-bang singularity. And singularity theorems proven by Hawking, Penrose and others made this connection quite tight by showing that under what seemed like rather general conditions, the initial singularity is unavoidable.

However, in the modern cosmological theories developed over the past 20 years (inflation, and also many of its rivals), this connection does not exist. In particular, in inflation the creation of a hot, homogeneous region occurs through 'reheating' at the end of inflation, but may happen an indefinite time after an initial cosmological singularity -- if there even was one! Moreover, nearly all of the classic singularity theorems fail to apply to inflation because they assume properties of matter (essentially that it is gravitationally attractive) that inflation violates.

Thus when discussing inflation -- or the cyclic model, etc. -- it is crucial to distinguish between these meanings. Otherwise you get a lot of rather frustrating debate (see this for a current example) about whether we can gain evidence of what happened "before the big bang". If this means "before a hot, homogeneous radiation-dominated phase", then the answer is clearly yes: the current CMB tests of inflation are doing exactly that. If "before the big-bang" means before some cosmological singularity, this is a very different proposition, and the answer may or may not be yes, and depends a lot on what sort of singularity you are talking about.

Some of the most interesting cases lie in between. For example, believers in the string theory landscape (among others) believe in a picture in which inflation occurs eternally, and creates infinitely many "bubble universes", each of which is spatially infinite inside. The genesis of one of these bubbles is not quite a big-bang in either of the above senses, and yet entails the "creation of a universe", and there are fascinating questions about whether other bubbles would have any observable in ours (I think perhaps they might)

So I'd like to make two pleas. First, let's all try to make this distinction clear both within the scientific community and in communications with the general public. We don't do ourselves any favors by having newscasts etc. discussing how cosmologists are debating "whether there was a big-bang" when they all agree on the basic cosmological model and are debating, say, the cyclic versus inflationary cosmology. (Imagine biologists debating lateral transfer of DNA and calling it a debate about whether evolution happened...not wise.)

Second, to make this easier, we could use a new name for a huge, hot, homogeneous, region that could in principle evolve into our universe, however it was created. I've recently used the term 'hotzone'. 'Hotpocket' might be better but runs into trademark issues and does not accord the creation of the universe the respect it deserves (with all due respect to the folks at Nestle foods). But I there have got to be better ideas out there. Any proposals?

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paul valletta wrote on Nov. 25, 2007 @ 20:40 GMT

One can use modern terminology WRT big-bang, bigger-bang and BIGGEST-Bnag, information_age ?

I suggest: Giga-Bang, Mega-Bang spawns Mega-verse's ? while big-bang, at least locally can be traced to an initial point, or Monostate, within our Mono-verse, which of corse is the embedding of "singularity" .

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Gevin wrote on Dec. 4, 2007 @ 06:04 GMT

Those using the term "before the big bang" are using it to gain attention to their work and that kind of sensationalism would be difficult to stop. The term big bang should continue to refer generically to a past that is increasingly dense and hot, while we convey that the observed history of our universe is not an explosion or a history of existence itself. The past is just another place in time, not so different from the outer cosmic event horizon.

I think Vilenkin is using the term O-region in a way that would be consistent with the clarification you are wanting to make. It wouldn't refer specifically to just that stage prior to the singularity (thinking in reverse), but it respects the orientation of the observer in a way that shouldn't be left out of the description. A "hot bubble" works in the same way but doesn't have a great deal of appeal.

I think simply setting up common language for all stages of the cosmos would be a significant accomplishment and improvement. I have always liked referring to the singularity itself as Alpha, and presently refer to the final state of an accelerating universe (empty space) as Omega.

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Gevin wrote on Dec. 4, 2007 @ 06:15 GMT

Anthony, in respect to the period between Alpha and the disintegration of uniformity and symmetry, I recommend approaching Alpha as a charged singularity, in our case the positive half of a neutral whole. Alpha is a symmetry of being perfectly positive, but in a reference beyond itself is the ultimate asymmetry or the most imbalanced state in reality, all positive apart from all negative. The big bang results of the collision between a positive and a negative singularity, which is still happening.

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Hi Vue wrote on Dec. 4, 2007 @ 20:38 GMT

The CMBR has, historically, always been hooked up tightly with the term "Big Bang." Keep "Big Bang" associated with the event(s) understood to have produced the CMBR, and apply some new, completely different name to any putative prior bang(s).

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MG wrote on Jan. 15, 2008 @ 03:59 GMT

Is there anyone out there willing to think outside the box? What if Joao Magueijo is on to something with a universe capable of C^2? What about William Tiller's ideas of a energy-velocity universe with positve energy and negative energy, C^1 and C^2?

Maxwell could use imaginary solutions in his equations to express the mathmatics of EM. Why stop there?

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