"With the laws of physics you can get Universes?"

jackmell

Hi guys. I like Cosmology even though I'm not a professional. I encountered this short Fox News story:

http://www.foxnews.com/scitech/2012/...ntcmp=features

I don't wish to address the God part of the story but rather the statement, "with the laws of physics you can get Universes."

I thought we cannot use the current laws of physics to create Universes. Rather we can only describe what happened shortly after it's creation by the current laws of physics. Is the Fox News story incorrect or am I not understanding this correctly?

Thanks,
Jack

TheEtherWind

Leave it to Fox News to always tie God into everything. Who is this "God" guy anyway? Never heard of him.

EngnrMatt

It sounds to me like they made a horrible attempt at spelling out something for the average joe that physicists have known for a very long time: quantum mechanics makes NO sense sometimes.

I recall reading that a property of electrons (can't remember if it was a reliable source or not though) is being able to just "pop" into existence and also, pop "out" just as well. With all the other strange phenomena in the world of physics though, it shouldn't be much of a surprise.

Drakkith

It's not that WE can create universes, it's that according to the math universes can come into existence if just the right things happen. Don't read too much into it though. We still have trouble explaining the laws within our own universe, let alone another one or creating another one. Just because the math of one theory says it can happen doesn't mean that it's true.

twofish-quant

There's a lot of progress trying to use what data we are finding to work backward to big bang t=0 and before. None of this is firm stuff, but people have come up with several difficult possibilities for "how the universe got created" and several different ways of testing these ideas.

The big piece of evidence is the "noise" from the "big bang". The big bang caused a lot of pressure waves to form and by looking at the shape of the pressure waves, we are getting a better idea of what may have caused it.

Chalnoth

A better way of stating is that based upon what we know about physics, the generation of new universes is entirely plausible. The main difficulty is that exactly how this occurs depends upon physics we don't yet know. So we can't make very many definitive statements. All that we can say is that based upon what we do know, it doesn't look hard to create new universes.

jackmell

May I ask what math? Not GR right? I was under the impression GR is only applicapable after the Big Bang and does not apply prior to it and thus cannot be used to describe how a Universe can come into existence.

What specifically, if I may ask, about what we know about physics can describe the generation of new universes?

Chalnoth

Well, the way the game is played is basically as follows:

We don't know the precise nature of physics that generates new universes, so we take current known physics, make some minimal extrapolations from it, and see if it's at all likely that such changes can result in new universes. Some of these attempts work, some don't. We don't know which, if any, of these models are close to reality, but we do know that there are quite a few different sorts of models that we can write down that produce new universes.

The primary takeaway from all this is not that we know how new universes are produced, but that based upon our current state of ignorance, we see no reason why it should be impossible.

twofish-quant

Just a terminology issue. I prefer use the term "big bang" to refer to what happened between t=0 and the time of CMB emission. Let's call what happened at t=0, "event zero." There are two sets of approaches....

1) There are quantum gravity people that are working on what may have happened at "event zero". You have people working on string theory and loop quantum gravity

2) People have come up with scenarios in which you can get a universe without an "event zero". For example, one scenario is that the universe as a whole has a large energy field that causes it to always expand, but because of random variations in the energy field, there are parts of it that "slow down" enough for stars and galaxies to develop, before speeding up again. These mechanisms avoid the problem of GR breaking down at event zero by having something happens that starts the clock just after "event zero".

What makes this "hard science" is that we are starting to get to the point where we can take observations to disprove/support some of these scenarios. For example, different gravity theories that produce different "event zeros" will leave different signatures in the cosmic microwave background.

The idea that there is this energy field that causes the universe to constantly accelerate would be totally nutty..... If we didn't see the universe accelerated becomes of some mystery energy field, and over the next few years we should have a much better idea of what that field is/isn't.

I prefer not to talk about "creating a new universe" but rather "having weird things happen in different parts of the big universe most of which we can't see." One of the big things is that we have very strong evidence that our part of the universe rapidly expanded at or shortly after "event zero" and this gives us enough clues to be able to piece together how other parts of the universe that we can't see may have expanded and expanded perhaps in a different way.

Also, it's not so much that we know the answer, but people are coming to the realization that we have enough data and ideas so that "what caused the big bang?" is no longer thought to be an unanswerable question. It's unknown, but increasingly people are thinking that it's not "unknowable."

jackmell

Thanks for those replies guys.
Can I ask you to give me a concrete example of this unless it's too techincal? I just don't understand how we can take current known physics and extrapolate it prior to it's very existence. Are you saying that physics as we know it is still applicable prior to the Big Bang and may be capable of being extrapolated to explain origins?

Chalnoth

I don't think anybody expects that the physical laws that were relevant when our region of the universe was being born bear no relationship at all to the physical laws we now know. Generally people expect that the relevant physical laws will be similar, at least in form, to the laws we know.

Some physicists have looked into the possibility that a particular manifestation of string theory was relevant at the time. Others have investigated what a universe described by Loop Quantum Gravity would do to the behavior of a universe around that time. Others have considered plain-old General Relativity and asked what would happen if there were different sorts of matter whose actions were important. Still others have attempted to abstract a little bit from the specific physical laws and simple ask questions of entropy, attempting to make use of some minimalistic assumptions about what the entropy of various states should probably be.

jackmell

Why? What evidence do we have to suggest the rules relevant when the Unvierse was born are similar to the rules now? Rather I suggest we have much indirect evidence to suggest they were not the same because the Big Bang appears to have been a critical-point phenomenon. A change in the rules often acompany such critical-point transitions, the canonical example being the freeziing point of water and the acompaning change in the rules of swimming.

I guess that was my point all along: I just do not understand how we can "extrapolate" our rules of Physics past the Big Bang critical point without anticipating that maybe, the rules change, and if that is a reasonable assumption then we cannot argue "with the laws of physics you can get Universes."

I have doubts we can understand how to create a Universe without changing qualitatively, the rules of Physics. However, I do not understand string theory and LQG and perhaps these represent the qualitative change I expect to see.

Chalnoth

Because the laws of physics don't change. Only the circumstances do. The effective laws of physics that would have been relevant in the early universe would only have been different in that the circumstances were different.

There is no such evidence.

skydivephil

I have doubts we can understand how to create a Universe without changing qualitatively, the rules of Physics. However, I do not understand string theory and LQG and perhaps these represent the qualitative change I expect to see.[/QUOTE]

LQG gives a corrective term to Einstein's equations that rerpdocue GR on most scales but there is a crucial difference. In Gr you can compress space time wihtout limit. In LGC there is a limit , once this limit is reached gravity becomes replusive and so the big bang is replaced by a big bounce. This big bang is not the beginning.
String theory I think is less well developed and different theorists have attempted to use it to model what happened at the big bang. The most famous is the colliding brane model of Turok and Steindhart, but I dont believe its the only possibility in string theory.
Does anyone know what the theory of causal sets has to say about the big bang? Is it also replaced with a bounce or something else?

Chalnoth

This isn't entirely accurate. As I understand it, nobody has yet managed to reproduce Einstein's equations using LQG.

skydivephil

i think the claim has been made, wehther its right or not is another issue

http://arxiv.org/pdf/1111.2107.pdf

Chalnoth

Hmm, interesting. Unfortunately I'm unable to find any responses to this article.