Exploring the Idea of an 'Almost Nothing' Universe

[Garth]

As a point of information: the sum total of gravitational, matter and scalar field energies in SCC is zero, and always was.

Garth

 

[Mike2]

I think the point Thor raised is at least shared by some mainstreamers. The idea that the Universe may have appeared out of nothing and contains zero net energy, was first suggested by Edward Tryon in the 1970s. He proposed it might have appeared out of nothing as a vacuum fluctuation allowed by quantum theory. Steven Hawking, among others, has since echoed this sentiment. From a QT perspective, this is a very consistent explanation. The universe, as a quantum fluctuation, could only persist as long as it has by maintaining a near perfect balance between positive and negative energy. It is appealing at a certain level. I like symmetry in nature. I try to resist explanations that are intuitively correct, but don't always succeed. But I do still insist on observational evidence.

How can existence be a flucuation of a field that doesn't exist yet? Doesn't that presuppose the existence of a field before existence itself arose?

Question: wouldn't a singularity be the perfect symmetry? It would still be a singularity no matter how you look at it, in any dimension, right?

 

[marcus]

... The idea that the Universe may have appeared out of nothing and contains zero net energy, was first suggested by Edward Tryon in the 1970s. He proposed it might have appeared out of nothing as a vacuum fluctuation allowed by quantum theory. Steven Hawking, among others, has since echoed this sentiment. ...

Chronos it occurs to me that we may be seeing the beginnings of an interesting discussion among quantum cosmologists
and one to which observational evidence may eventually be applied.

1. On the one hand there is quite an upsurge of work in LQC (what looks like exponential growth of postings at arxiv with a lot of new people entering the field) and in Loop cosmology one sees a real bounce, from a real contraction phase prior to the onset of expansion.

The prior does not have to represent a comparable amount of energy because there will be inflation, but it does not have to represesnt precisely zero either. It can be the collapse of a stellarmass black hole or it can be the contraction of a universe. But whether small or large, Loop extrapolates back and sees something there.

People are busy on the phenomenology end trying to determine what traces in the CMB to look for. the 3 recent talks by Parampreet Singh summarizing recent papers by a number of people are a good survey of that.

If the real bounce models are wrong then it may be possible to prove that they are wrong. But there is another part of the story as well:

2. On the other hand there is Hawking and Hartle and Villenkin and that group going back to the 1980s with the "Euclidean Path Integral" or "Euclidean Quantum Gravity", and the idea of the universe arising from a little accidental hiccup.

Oh excuse me, it says, and makes a little fluctuation...and the rest is history.

And this rather (to me) vague notion has been revitalized and given a very concrete form by Ambjorn Jurkiewicz and Loll and the Causal Dynamical Triangulations (CDT) model. CDT doesn't have a prior contraction.

======
so we have two strong competitors with very specific models of what used to be called "big bang"

both models are singularity-free

both groups of authors use the word bounce (but I don't see the AJL model doing a real bounce, as I picture what a proper bounce is, I see it more as an accidental self-creative hiccup)

one model says there was something there which contracted, and it says how to extrapolate back to it----and it explains how inflation starts, at bouncetime, without finetuning.

the other model does NOT see a prior contracting stage! AJL and Hawking before them do NOT have that. So it seems to me there is a real difference and a possible contest

The division is not perfectly clearcut. Some LQG people may not agree with Bojowald and the Loop cosmologists and they may not think it is meaningful to talk about a prior contracting stage, but that is something that the Loop people will have to work out. Right now the ranks of the Loop cosmologists are growing.

An important factor in both the LQC and the CDT is that they have actual models of where the "singularity" used to be, models they can program and that they run in the computer with various choices to see what if any difference, and so on. Both are very concrete approaches in this.

Another complication is that LQC is a minisuperspace version (but it behaves very well in the semiclassical limit----it approximates classical Friedmann behavior once it gets away from the bouncetime) and CDT is more of a full model.

 

[marcus]

this is bound to cause confusion especially for people who have gotten into a mental rut of only being able to picture things happening in a Newtonian absolute space

in the CDT model there is no space in which the hiccup occurs
the hiccup is about the appearence of space and its subsequent expansion.

in their computer model they do not set up a simulation of space and then have that be an arena in which space appears
what they establish is a combinatorial setup which allows, with some probablility, eventually, a simplex to appear, and with some probability not to immediately go away again but to accumulate other simplexes
and (roughly like a crystal growing from a tiny seedcrystal)

for a spacetime to crystalize out of nowhere, because the spacetime is the where----there is no larger encompassing space

so the setup is combinatorial-----that means on the level of abstract relationship. There are n-tuples of natural numbers like (1, 2, 3) and
(2,3,1) and (1,2) that show how some very finite simple things can be related to each other.

the initial setup is combinatorial-----and conventional 4D space only EMERGES from this, as more and more simplexes accumulate and finally some resemblance of a macroscopic world takes shape.

the interesting thing, to me, is the 10 years or so they spent trying different combinatorial setups and having the 4D space of our everyday experience NOT emerge.

If I ever put a picture of Renate Loll up on the wall, or Jan Ambjorn, it will be because of those 10 years when they didnt give up. they kept on trying to discover combinatorial rules that would work. to me, it shows guts.

 

[marcus]

either one or both of CDT and LQC could be wrong
both are getting extremely interesting results
both will pretty clearly be brought to the point where definite versions of them make unequivocal predictions
and they will be checked against the real universe
I expect to be able to watch, and feel lucky to.

it's a striking contrast that CDT does not have a prior contraction
and LQC does have (maybe we will be able to spot other
clear differences)

here is Martin Bojowald (who originated LQC) with Alejandro Perez

http://perimeterinstitute.ca/images/marseille/marseille017.JPG

here is Renate Loll (co-originator of CDT) talking to Thomas Thiemann
http://perimeterinstitute.ca/images/marseille/marseille028.JPG

 

[Mike2]

either one or both of CDT and LQC could be wrong
both are getting extremely interesting results
both will pretty clearly be brought to the point where definite versions of them make unequivocal predictions
and they will be checked against the real universe
I expect to be able to watch, and feel lucky to.

I'm not so sure of that. It may be that these efforts will only apply to very tightly curled up space and we will not be able to compare with reality. It might be that more than one effort will give the same low energy results. Then what do we do?

 

[Chronos]

The bounce model may well be correct. What leaves me feeling empty is it evades the bigger issue. Is it more palatable to accept that 'something' has been around for eternity or that 'something' arose from 'nothing' at some distant, though finite time in the past? It's the cosmic version of chicken and egg. All objects in the observable universe appear to have originated in the finite past, and from a state much different than the current state. We can say, with some confidence, that stars originated from primordial gas clouds and those primordial gas clouds originated from an extraordinarily dense and hot precursor state [a hot big bang]. It would be pretty tough to know those things with any confidence were not those precursor states, or strong evidence thereof, still around for us to observe. Unfortunately, aside from the CBR, there is little if anything left to observe of the state prior to recombination. If we lived in a much older universe [say where the CMB was nearly absolute zero, primoridial hydrogen was nearly depleted, and all first generation stars had long since expired], even stellar evolution would be a mystery.

The answer may well be hidden inside black holes. Perhaps they do bud off new universes in an endless, eternal cycle. Which leads to an immediate problem. What happens to those universes when black holes merge, or evaporate? Is this universe in a death spiral with another incredibly massive black hole in another, vastly larger universe? Or perhaps our mother universe is in imminent peril in grandma universe. Are we embedded and imperiled by an infinite sequence of progressively larger black holes?

Let's also examine the proposition that baby universes are 'safe' once born. Protected by their personal event horizon, matter in the baby universe persists, even if mom bites the dust. It looks suspiciously like we are back to free energy, i.e., creation ex nihilo: at least from the perspective of the total mass in whatever omniverse, megaverse, or multiverse it is in which we live.

 

[wolram]

I am very unsure of this, but i guess space time can only support
a limited range of energies, and that black holes are a result of
energy surplus, not a result of distorted space time, if one wants
to talk about spin foams, there must be an energy limit that causes
them to break down, if this is so then what we think of as a BH is
the destruction of space time not some type of gateway to other
worlds.

 

[marcus]

...The answer may well be hidden inside black holes. Perhaps they do bud off new universes in an endless, eternal cycle. Which leads to an immediate problem. What happens to those universes when black holes merge, or evaporate? Is this universe in a death spiral with another incredibly massive black hole in another, vastly larger universe? Or perhaps our mother universe is in imminent peril in grandma universe. Are we embedded and imperiled by an infinite sequence of progressively larger black holes?
...

we are used to the fact that the passage of time obscures the past and that the remote past is automatically dim
but I am stunned to realize that the remote past of some 13 billion years ago is staring us in the face in the form of the CMB

so perhaps we will be able to see traces of even older events
perhaps traces of a bounce
or perhaps there was no bounce
but a coming into existence a la Ambjorn and Loll, a la CDT.

or something else.

if universes do inflate out from each black hole pit
then I agree they seem imperiled by evaporation and by mergers

have to go, will think more about and reply later