The Canadian Broadcasting Corporation has a smart and engaging radio show, Quirks & Quarks. Yesterday’s show focused on a big question: What happened at, and before, the Big Bang? Mavens queried included Robert Brandenberger, Paul Steinhardt, Justin Khoury, and of course me (otherwise it’s somewhat less likely that I’d be blogging about it, I guess). The blurb:
The Big Bang theory of the origin of our universe is widely accepted by the physics community. The idea that our universe started out as some infinitesimally small point, which expanded out to what we see today, makes a lot of sense. Except for one small thing. That initial point, called a singularity by physicists, is a physical impossibility. According to the models we have today, the temperature of the universe at that first moment would have had to be infinite, which mathematically makes no sense. Also, the singularity doesn’t do a good job of explaining where all the matter and energy we see today in the universe came from. So, physicists are increasingly starting to look at other branches of physics to see what they can do to replace the singularity with a more reasonable proposition, one which can actually be explained by existing science.
Listen here. As we’ve talked about on this very blog, the time is right to push our understanding of the universe back before the Big Bang and ask what was really happening. Current ideas are understandably vague, but the only way to improve them is to keep exploring.
One slight clarification, to those who listen: in the interview, I give an entropy-based argument against bouncing cosmologies. That’s appropriate for the ekpyrotic universe, but not necessarily for the most recent versions of the cyclic universe. In these models, the universe never really crunches; it keeps expanding, but at some point flares back to life — particles are created without space ever contracting. Some sort of thermodynamic sleight-of-hand is still being pulled — the entropy of the whole universe rises monotonically for all of eternity, which seems a bit fishy — but the argument is somewhat different.
Prof. Carroll,
I would very much like to hear any speculation you might have about how science will eventually describe the big bang…
NM
A real achievement would be to know definitely what was happening to the universe before nucelosynthesis.
Nice show… except for the constant stupid sound effects in the background! Gaahh!
If the sound effects help to make the science less intimidating and more accessible, I’m all in favor.
Nick, some of my thoughts on that are in this post.
Oh man, as long as physicists believe that there can be anything eternal explaining existence, how can we say to religious people there is no eternal god how created the universe?
I thought the presenter did a decent job, though I find the sound effects irritating as well.
It would have been nice to clarify (in such a program) the distinction between the ‘Big Bang Theory’ as used here, and the ‘Big Bang Theory’ as a synonym for an expanding universe cosmology, where the primordial nuclei were formed at BBN. In fact when the presenter mentions, learning about Big Bang theory in school and thinking it was accepted, I would think it was mostly in this second sense.
Sean,
Could expansion be due to micro quantum fluctuations, with the space created then falling into galactic black holes? That way, space expands, but the universe doesn’t. It would explain why everything is receding directly away from us, without all the problems of Inflation Theory.
We view time as going from past events to future ones, but if time exists as a dimension, then wouldn’t it be going the other direction? According to Big Bang Theory, the unit of time that is the universe, was in the future prior to the Big Bang and eventually it will be in the past, so it would seem to go from future to past. I realize this may seem incidential, but it raises the question of which is cause and which is effect, time, or the observation of it. Is time the basis of motion, or a consequence of it?
I recently came across a new theory by Peter Lynds, in which he describes his unique ideas about the origin of the universe. Fascinating reading; he has me convinced. The first link below is a summary of the Lynds theory (PDF). The second link is a paper titled: “Comparative Quantum Cosmology: Causality, Singularity, and Boundary Conditions,” written by four other researchers who discuss the Lynds theory in detail. The third link is Lynds’ paper itself, titled “On a finite universe with no beginning or end.”
http://www.peterlynds.net.nz/plcs.pdf
http://arxiv.org/abs/0710.5046
http://arxiv.org/abs/physics/0612053
Presumably in this discussion “big bang” means the beginning of the universe/multiverse. Perhaps it’s time to just call the beginning of the universe “the beginning of the universe,” and call the “big bang” the hot homogeneous space-like surface that serves as the initial condition for FRW cosmology. The point is these are not the same thing; the latter would be equated with reheating after inflation in the standard picture.
I think this makes it easier to communicate with the public. Now the “big bang” is a thing that actually happened, and the big questions become when/how did it happen and what happened before. I think this phrasing more cleanly separates things we understand from things that we do not, and has an advantage of presenting the picture in a way where big bang theory does not appear like a house built on sand (I think the other phrasing can lend a layperson to think the validity of big bang theory may depend on the nature of the “big bang,” which in this phrasing depends on the beginning of the universe, which is something we might be far from understanding). Another advantage is this avoids any discussion of an initial singularity, which is not necessary and not believed by most physicists anyway.
I just came across this paper by Aguirre et al – “Towards observable signatures of other bubble universes”
http://arxiv.org/abs/0704.3473
If predictions on the existence of bubble universe effecting the CMB can be derived from eternal inflation, then we will indeed have potentially some real knowledge about ” Before the Big Bang”.
On the other hand I am very dubious about the statistical arguments on parameter values due to the multiverse. Ultimately we are examining a sample of one, and if we have an infinite or very large finite population of universes, then we must consider the words of Spike Milligan in the Goon Show where he replied to the question “What are you doing here?” with the deeply philosophical statement “everybody’s got to be somewhere”.
Wow I just went to the CBC site and you can even download the show in OGG format.
Sean,
The ill-justified view that I have generally taken about the big bang, whether bouncing or not is that the special conditions of a very small, hot universe allows a “low entropy boundary condition” or rather produces produces low entropy with high probability. This sounds ridiculous stated like that and it probably is, I have never looked at it properly: Perhaps I should play with a toy “quantum gas” model to see if there is any merit in it at all. Of course real cosmologists do not find the problem to be easy so I have little faith that my intuitive idea really works. If it does then a bouncing universe with low entropy “boundary conditions” at the narrow points makes as much sense as a big bang. Perhaps this is also one of those cases also where the vagaries of the interface between quantum and classical statistics is important. In which case there is some hope that the answer might be essentially fairly simple.
Any illumination that you can give to someone who has spent too much time idly musing on this subject while falling asleep and none actually reading papers or doing maths would be much appreciated (I ‘ll start by reading your links).
I agree that the model/event distinction for meanings of the term “Big Bang” is a crucial one. I definitely made it during our conversation, but sometimes it’s hard for them to squeeze everything in.
maninalift, why should you assume that the early universe (or any time in the universe’s history) is hot and dense? That’s one of those facts we’re trying to explain, not something given a priori. Moreover, if you take a star and squeeze it to make a black hole, it will become hot and dense, but nowhere near smooth.
I am not assuming the early universe is hot and dense.
The stupid thing that I am saying is that somehow extreme compactness promotes correlation so that that of all of the possible solutions to your physics, the ones that are low-entropy at compact points are relatively common.
Though I state that it is stupid, I can’t shake-off a sort of belief in it which is why I need to disillusion myself by playing with some simple model.
If this were true though, it would not be an assumption that the early universe is dense but rather a consequence of being dense that the universe is early, since a low entropy point looks to an inhabitant of the universe like an early time.
And what I’m asking is, why should there ever be “extreme compactness”?
Again, what you’re getting at seems to not be empirically true: when you squeeze matter to an extremely compact state, it doesn’t smooth out. But there’s still the question of why it should ever be compact in the first place.
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“In these models, the universe never really crunches; it keeps expanding, but at some point flares back to life — particles are created without space ever contracting.”
Which version is that? Space does contract in every version of the cyclic model that I have ever seen.
Not really. In the “Einstein frame” the universe crunches, but that’s not the frame that actually describes the motion of test particles. In the matter frame (in the versions of cyclic cosmology I’m familiar with) the universe just keeps growing, but the energy density increases.
Sean,
As space expands, does the speed of light increase? It would seem to me that if C doesn’t increase proportionally, it is measuring a stable dimension of space and the expansion would have to be a conventional increase in volume, but that doesn’t square with Inflation Theory. ?
Dear Norm,
Thanks. I’m glad you liked it.
“…the time is right to push our understanding of the universe back before the Big Bang and ask what was really happening.”
Dear Sean,
I very much agree, although there is a “but” there which I do not think many appreciate yet, and it is related to questioning what was happening “before” the big bang, as well as to the question of whether the past is finite or infinite. The past cannot be infinite and the universe have no beginning (if so, it would be impossible for it to evolve forward, not only to where we find ourselves today, but at all). However, the universe can also not have had a beginning at some finite time in the past (if so, what caused it, and what caused that, and so on…). Both ideas result in very real contradiction. Moreover, it demonstrates that there must be something going deeply wrong with our regular ideas and assumptions about time, cause and cosmology.
Any model that posits either a universe with a beginning at some finite time in the past, or a universe with an infinite past, cannot even potentially offer an answer to the question of the origin of the universe, as both ideas are faulty.
Best wishes
Peter
“In the matter frame (in the versions of cyclic cosmology I’m familiar with) the universe just keeps growing, but the energy density increases.”
OK, right, I see what you are saying. Still, in the Steinhardt-Turok paper you linked to, they put great emphasis on the *contraction*; they argue that this is ok because they have a scalar with w > 1, which squashes all anisotropies when the universe *contracts*. So it does seem that an interpretation involving contraction is, in their eyes, an important part of the physics of their model.
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Sean, in order to make this interesting we could agree on a bet:
I bet x dollars that in y years there will be no observations of anything before Big Bang. x could be symbolic 1USD (or a 1000 if you like) and y could be 5, 10 or 20 years for example. The bet should really go on for millions of years, but since we’re mortals then a limit must be set..
Carls conjecture ( 😉 ) states that there will never be made any observations of anything before BB. Such speculations should therefore be shaved away by Occams razor.
I hold that the BB represents the event when the universe started to exist (“created from” nothing). So it is impossible to observe anything “before” BB.
Carl
Peter Lynds,
So how do you propose to get out of that box?
What if space is infinite and stable, otherwise the speed of light would have to fluctuate, as space expanded or contracted, but we wouldn’t be able to tell, because the speed of light would always be proportional.
While time isn’t an actual dimension, but a property of motion, like temperature, rather then a basis for it, like space. Consider; If two atoms collide, it creates an event in time. While the atoms proceed through this event and on to others, the event goes the other way. First it is in the future, then in the past. (The motion of the earth, relative to the sun, goes through the series of events that are days and years, while these units of time go from being in the future to being in the past.)
So which is the real direction? If time is a fundamental dimension, then physical reality proceeds along it, from past events to future ones. On the other hand, if time is a consequence of motion, then physical reality is simply energy in space and events are constantly being reordered and go from being future potential to receding into past circumstance. To the hands of the clock, the face goes counterclockwise.
Even in the Big Bang model, the entire universe is a unit of time that goes from being in the future to being in the past. So what is more real, the energy that is present, or the units of time that pass by?