What existed before the big bang?

[marcus]

Hi everyone! I have 3 questions :

If the big bang was a quantum event (as suggested by some entries in this thread) - doesn't that require quantum field to exist before the big bang? Wouldn't this make it likely that quantum field exists "outside" the big bang universe? My question 1 : Does anybody have more information on the topic of quantum field before and outside of big bang universe?

The only other big bang origin I have heard of is from singularity - Question 2 : Is there a mainstream big bang theory that creates the quantum field out of the big bang?

Question 3 : Are there other mainstream theories on relationship of big bang and quantum field?

Thanks for putting up with my ignorance! :)

the mainstream about the quantum beginnings of expansion is MANY STREAMS. it is too early to try to sum up and say that there is a consensus. I suggest you SAMPLE one of the quantum bang theories.

Don't for god sake rely on secondhand popular science journalism, if you read that you should ALSO go directly to primary sources and GET WHAT YOU CAN. skip the technicalities and read the summaries and conclusions.

Here is a sample:


http://arxiv.org/abs/gr-qc/0602086
Quantum Nature of the Big Bang
Abhay Ashtekar, Tomasz Pawlowski, Parampreet Singh
4 Pages, 2 Figures. Minor changes to match the published version...
Phys.Rev.Lett. 96 (2006) 141301

"Some long standing issues concerning the quantum nature of the big bang are resolved in the context of homogeneous isotropic models with a scalar field. Specifically, the known results on the resolution of the big bang singularity in loop quantum cosmology are significantly extended as follows: i) the scalar field is shown to serve as an internal clock, thereby providing a detailed realization of the `emergent time' idea; ii) the physical Hilbert space, Dirac observables and semi-classical states are constructed rigorously; iii) the Hamiltonian constraint is solved numerically to show that the big bang is replaced by a big bounce. Thanks to the non-perturbative, background independent methods, unlike in other approaches the quantum evolution is deterministic across the deep Planck regime."

This was published in Physical Review Letters which is a legitimate science journal, not pop sci. If you can understand one paragraph in ten, or one paragraph in twenty, you are getting something worthwhile already. If more, then so much the better. There will usually be some conclusions at the end of a scientific article that are expressed in general language (but may be heavily qualified and intentionally vague so as not to go out on a limb)

when they say "solved numerically" they mean run their model in a computer. they plot some graphs to show visually what they got.

NOTHING ABOUT THIS HAS BEEN SHOWN EXPERIMENTALLY OR EMPIRICALLY BY OBSERVATIONS YET

but some aspects of these models are testable and it is beginning to be time to winnow out some of these models. wolram recently found an article by some people figuring out how to test and possibly exclude some alternative ('braneworld' type) models. It is going to be a slow process, but what else can you do.

Our tradition is the slow empirical tradition. Pure inspiration does not fly. Even if you are Einstein----he proposed General Relativity in 1915 and already it was tested in 1919 with an astronomical test that could have shot it down. the tradition is you DONT BELIEVE, you take proposed theories one by one and try to shoot them down by empirical observation.

I think Ashtekar's quantum bounce model of the bang is great but I don't believe it. I just wait (as patiently as I can) for testing to check it.

 

[CosmologyHobbyist]

Thanks very much for your answer, Marcus. I did read the Ashketar paper before I posted (I'll read it again now!); I suppose I was trying to find a synopsis of current views.

 

[marcus]

Thanks very much for your answer, Marcus. I did read the Ashketar paper before I posted (I'll read it again now!); I suppose I was trying to find a synopsis of current views.

In the braneworlds picture, branes bump together repeatedly
search arxiv.org for author name Steinhardt
braneworld cosmology is very different from loop quantum gravity cosmology. (and there are other attempts too, Hawking had a quantum cosmology back in the 1980s which no one works on much but which he has popularized)

I do not know of a synopsis that harmonizes the diverse ideas.

but there is some "high level diplomacy" in the works.

In January 2007 there will be a workshop at KITP (a top string theory location) in Santa Barbara about "Quantum Spacetime Singularities" and string-cosmology people will be there but also martin Bojowald.

Bojowald is a loop guy. So the loop cosmology and stringy cosmology people will be comparing notes for a week or so on how they handle the big bang. to my mind there is no way to judge ahead of time what might, if anything, come of it

they both eliminate singularity----that is, have theories that don't fail at that point, but they are so different

to try to make a combined synopisis would somehow be unjust to both

 

[CosmologyHobbyist]

Thanks again, Marcus. I meant "summary" when I said "synopsis", and you gave me an excellent list of things to look into.

 

[hellfire]

In the braneworlds picture, branes bump together repeatedly
search arxiv.org for author name Steinhardt
braneworld cosmology is very different from loop quantum gravity cosmology. (and there are other attempts too, Hawking had a quantum cosmology back in the 1980s which no one works on much but which he has popularized)

I do not know of a synopsis that harmonizes the diverse ideas.

You might be interested in this.

 

[marcus]

You might be interested in this.

Yes! I knew of that paper! it is a strange offbeat paper because it USES the cushioning effect of LQG repulsive gravity (which I personally tend to think as having a good chance of being real) to

cushion the collision of two imaginary objects (which I personally tend to think are pure fantasy)

so it is in a way like "a real toad in an imaginary garden"

this was how a poet once defined what a poem does.

I didnt want to mention that paper----which I think is the exception that proves the rarity of crossover. there is ALMOST no crossover between loop cosmology and braneworlds----and the one exception that one knows about (both you and I) is this strange paper where loop gravity is the quantum padding between two branes so they don't even have to touch when they collide and rebound

In case anyone is reading and hasnt seen this paper that hellfire was referring to:

http://arxiv.org/abs/hep-th/0407115
Loop Quantum Gravity and the Cyclic Universe
Martin Bojowald, Roy Maartens, Parampreet Singh
6 pages, 4 figures; v2: minor changes to match PRD version
Phys.Rev. D70 (2004) 083517
"Loop quantum gravity introduces strong non-perturbative modifications to the dynamical equations in the semi-classical regime, which are responsible for various novel effects, including resolution of the classical singularity in a Friedman universe. Here we investigate the modifications for the case of a cyclic universe potential, assuming that we can apply the four-dimensional loop quantum formalism within the effective four-dimensional theory of the cyclic scenario. We find that loop quantum effects can dramatically alter the near-collision dynamics of the cyclic scenario. In the kinetic-dominated collapse era, the scalar field is effectively frozen by loop quantum friction, so thatthe branes approach collision and bounce back without actual collision.

 

[drakken1985]

Perhaps Mathmatically Zero is the answer. Negative would not be possible implying "before". But that for reasons yet to be discovered zero became positive and BOOM! the universe started with a singularity that was unstable. Perhaps there are a million, million billion zeros each second in this and other diamensions of non-reality that stay stable and no booms, along with other million, million billion zeros becoming unstable.

 

[hurk4]

Before and after our BB

i all ways wonder this. what existed before the big bang?

What else than an ever existing swinging " Infinity-verse" ?

 

[Chronos]

I am prejudiced in favor of the net zero energy universe model - it preserves causality, IMO.

 

[hurk4]

before and after our bb

I am prejudiced in favor of the net zero energy universe model - it preserves causality, IMO.

To me N.Z.E.U.M. preserves incomprehensibility. Symmetry is elegant and beautiful, but isn't like throwing away the baby and the bathwater? Is N.Z.E.U.M. the only way (if it really is?) to preserve causality?
"If you are to describe the 'truth', leave elegance to the taylor."
(Albert Einstein)

 

[Chronos]

I admit believing NZE is necessary to preserve causality in an FRW universe.

 

[hurk4]

Before and after the BB

I admit believing NZE is necessary to preserve causality in an FRW universe.

To me belief seems like a 'well' adapted boundary/frontier. Interest in what is behind or beyond seems to stop there. I don't want to live in such a prison.

 

[string querry]

Possible Pre Big Bang Scenarios

i just came up with a theory. another universe. maybe when a
universe ends it explodes in a big bang and creates another universe. what do you guys think?

My understanding is that experts like Hawking describe three posible scenarios. 1) The big bang singularity, whatever its cause, or lack thereof, began as a unique event with "creation of everything out of nothing" which jibbed well with othrodox Christians because of the the book of Hebrews says something akin to "it is by faith that we believe God created everything that is seen from what is not seen" and was interpreted by orthodox theologians as meaning creation 'ex nihilo' (out of nothing)

the second scenario is that some other universe existed, with unknown properties and collapsed into a black hole time of effect until so much "stuff" was packed into the singularity that it exploded into the big bang.

Scenario three is that the universe is in a continuous oscillation of collapsion. expansion with infinite big bangs/big crunches. But this teory is kind of pooched if the new data on universal expansions is correct that the expansion rate is actually accelerating, meaning that the universe will never collapse regardless of <> omega mass (or whatever it's called, fravity of the total mass of the universe overcoming the inertia of the expansion) On the other hand, until we know why the expansion is accelerating, its kind of illogical to assume that the acceleration is permanent; perhaps there will, for some reason, be an eventually deceleration. Until there is more data, such theories require almost as much blind faith as religion (no snub intended)