Bojo in Nature Physics July issue, probing before bigbang with quantum cosmology

[dilletante]

If Bojo is correct and our present universe is a bounce from a previous collapsed one, doesn't that imply that the likelihood is that our present universe will undergo a crunch? Ignoring of course the possibility that we are a baby universe, for which there is no evidence.

The alternative seems to be that we are the last of a series of cyclic universes, which would be awfully convenient.

Therefore might we conclude that identifying enough matter to theorize an end to expansion might be one test of the validity of the bounce theory, and the lack of such a discovery an argument against the theory?

 

[marcus]

Therefore might we conclude that identifying enough matter to theorize an end to expansion might be one test of the validity of the bounce theory, and the lack of such a discovery an argument against the theory?

Logically your argument seems to point in the direction of a prior black hole collapse.

Or else I suppose the ONE bounce model where the prior phase of the universe takes an indefinitely long time to collapse and our post-bounce phase spends an indefinitely long time expanding

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

I don't know of any evidence for or against the BLACK HOLE ORIGIN version.
So since present observations suggest we will not have crunch, and your reasoning seems to disfavor the cyclic picture (which I never liked anyway ) it does seem that your argument makes BH-origin more plausible.
I don't see why you seem to avoid that conclusion in your post.

But I also don't know of anything that rules out the One-bounce picture. Indeed Bojowald referred to that possibility in his paper, if I remember right.

Anyway, you've raised an interesting issue, Dilly.
Thanks

 

[dilletante]

it does seem that your argument makes BH-origin more plausible.
I don't see why you seem to avoid that conclusion in your post.

Hmm, you are right, my argument does favor the one thing I rejected, silly me. I did find a couple of interesting articles on the possibilities of baby universes -- one is just an article in Slate about Andrei Linde:

http://www.slate.com/id/2100715
"When I invented chaotic inflation theory, I found that the only thing you needed to get a universe like ours started is a hundred-thousandth of a gram of matter," Linde told me in his Russian-accented English when I reached him by phone at Stanford. "That's enough to create a small chunk of vacuum that blows up into the billions and billions of galaxies we see around us."

Seems that Linde developed much of his theories in the 1980's so I am not sure if they are out of date:
http://www.stanford.edu/%7Ealinde/

Another seems to be a more serious proposal by some Japanese physicists arguing that a universe can be created in a lab from a magnetic monopole:

http://www.citebase.org/fulltext?format=application%2Fpdf&identifier=oai%3AarXiv.org%3Agr-qc%2F0602084

 

[marcus]

Hmm, you are right, my argument does favor the one thing I rejected, silly me. I did find a couple of interesting articles on the possibilities of baby universes -- one is just an article in Slate about Andrei Linde:

http://www.slate.com/id/2100715
"When I invented chaotic inflation theory, I found that the only thing you needed to get a universe like ours started is a hundred-thousandth of a gram of matter," Linde told me in his Russian-accented English when I reached him by phone at Stanford. "That's enough to create a small chunk of vacuum that blows up into the billions and billions of galaxies we see around us."

Seems that Linde developed much of his theories in the 1980's so I am not sure if they are out of date:
http://www.stanford.edu/%7Ealinde/

Another seems to be a more serious proposal by some Japanese physicists arguing that a universe can be created in a lab from a magnetic monopole:

http://www.citebase.org/fulltext?format=application%2Fpdf&identifier=oai%3AarXiv.org%3Agr-qc%2F0602084

you seem to be focusing on the question "what could a baby universe be made out of?"

say you have a BH of a few solar mass, or a million or billion solar mass, as some BH are that massive----in any case it is almost nothing (a drop in the bucket) compared with the whole universe. so where does all that energy/mass come from?

From the very start, inflation scenarios have assumed some kind of exotic matter like an "inflaton" scalar field----basically that amounts to a constant energy density (similar to the "dark energy" that is supposed to be causing accelerated expansion today)

since the scalar field energy density is constant---it violates energy conservation Law. As space expands there are more and more cubic meters of space and each cubic meter has the same amount of energy (because of constant density) so there is more and more energy.

Conventional cosmology has loose ends like this----little things happen all the time that violate global energy conservation. The "dark energy" thing going on today violates, because a constant energy density and space is expanding. People have ways of explaining away the puzzles, but it really isn't all that clear. They do the best they can.

Inflation scenarios were invented to solve some puzzles, but they contain their own puzzles, like seeming to create energy out of nothing.
Dark energy was invented to explain today's observed acceleration, but it contains the same puzzle.

So you don't have to go to Japan and listen to a man talk about magnetic monopoles. this trouble with energy-from-nothing is in all kinds of models---it is a daily experience.
this means that "baby universes" are not stranger or more contradictory than anything else----from the energy sufficiency viewpoint. A solar mass BH has enough stuff to start a universe (or at least that is not any more incredible than darkenergy or inflation.)

There is one theory that I've been learning more about lately that has the right amount of inflation happen without needing an "inflaton" exotic matter field. this is Martin Reuter's.
It is less "mythical" than the others I've seen.

And Bojowald's picture CAN simply be a ONE-BOUNCE CYCLIC, with one indefinitely long contracting phase, one bounce, one expanding phase that goes on forever. That doesn't violate energy rules in any really obvious overt way. So Bojowald is at least spared from having to address this issue.

 

[dilletante]

since the scalar field energy density is constant---it violates energy conservation Law. As space expands there are more and more cubic meters of space and each cubic meter has the same amount of energy (because of constant density) so there is more and more energy.

There is one theory that I've been learning more about lately that has the right amount of inflation happen without needing an "inflaton" exotic matter field. this is Martin Reuter's.
It is less "mythical" than the others I've seen.

And Bojowald's picture CAN simply be a ONE-BOUNCE CYCLIC, with one indefinitely long contracting phase, one bounce, one expanding phase that goes on forever. That doesn't violate energy rules in any really obvious overt way. So Bojowald is at least spared from having to address this issue.

I may be missing something but the reason I don't like the idea of a ONE-BOUNCE CYCLIC is because it seems to require two theories for the origin of a universe. The "bounce explains universe number two, but now you have to come up with a different theory for how universe number one, the contracting one, came into being. Assuming it didn't start out fully formed and infinitely large.

The conservation of dark energy is something that bugs me. I can only conceive of 3 possibilities, the third of which is inane:
1) The law of conservation of energy is incorrect.
2) Dark energy does not exist and we need a Reuter-like solution for inflation.
3) Dark energy pre-existed and is what the universe is expanding into.

It seems safe to discard 1) and 3).

 

[marcus]

I may be missing something but the reason I don't like the idea of a ONE-BOUNCE CYCLIC is because it seems to require two theories for the origin of a universe. The "bounce explains universe number two, but now you have to come up with a different theory for how universe number one, the contracting one, came into being. Assuming it didn't start out fully formed and infinitely large.

The conservation of dark energy is something that bugs me. I can only conceive of 3 possibilities, the third of which is inane:
1) The law of conservation of energy is incorrect.
2) Dark energy does not exist and we need a Reuter-like solution for inflation.
3) Dark energy pre-existed and is what the universe is expanding into.

It seems safe to discard 1) and 3).

I appreciate the way you are wrestling with these difficult questions, which I would describe as mentally vigorous. the conservation of energy thing bugs me too. There is something about it at John Baez site. We talk about it here sometimes. It seems that GR does not have a global energy conservation law! (nor does it have one official global time-clock, things have their own time that is proper to them but there is no comprehensive time). When one works with the universe as a whole, so far that means working within the GR context! So we have to get along without a complete energyconservation idea. It works locally in some particular frame of reference or in some region you can isolate from the rest, but not globally.

All the violations of energy conservation I know of share the aspect that it would be impossible to exploit them by any imaginable "perpetual motion" machine and thus to extract useful work. In the reference frame of the machine energy would be conserved basically so you couldn't get anything from it. Sometimes this seems amusing in a tantalizing way.

I'm glad you come to the same tentative conclusion that I do---which would be #2 among your alternatives.

About what you say at the beginning. I don't look to cosmology in particular or science in general to explain for me why the universe exists---or if it was simply always there---or if and how it came into "being". I just take for granted that it exists and I want to know about it.

that includes pushing back to time and events prior to bang

So the ONE BOUNCE CYCLIC is basically as good as any other, in this respect, for me. It has no more and no less untied loose ends.

however I have this unavoidable feeling that the black hole origin picture is more FUN. More fun to think about universes evolving so that they manage to produce lots of stars and thus lots of stellarcollapse black holes and thus lots of babies. it has the evolution angle that Smolin wrote about in the book Life of the Cosmos.
and its just fun to think about . this should not influence me as a sober critical person but it probably does.