With the laws of physics you can get Universes?

[jackmell]

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

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...art-universe-researchers-say/?intcmp=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]

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?

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]

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...art-universe-researchers-say/?intcmp=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

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]

according to the math universes can come into existence if just the right things happen

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.

A better way of stating is that based upon what we know about physics, the generation of new universes is entirely plausible

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

 

[Chalnoth]

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

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]

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.

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.

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

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.

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.

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]

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?

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]

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..

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]

Why? What evidence do we have to suggest the rules relevant when the Unvierse was born are similar to the rules now?

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.

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.

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 don't 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]

LQG gives a corrective term to Einstein's equations that rerpdocue GR on most scales but there is a crucial difference.

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]

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

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

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

 

[twofish-quant]

Why? What evidence do we have to suggest the rules relevant when the Unvierse was born are similar to the rules now?

None. But we can make up new rules and see what happens. Also, we can state that the rules that exist now are a *subset* of the big rule book, so we can eliminate all possible rules of physics which don't contain a given subset.

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.

Yup. People have thought of that

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

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."

Any "big cosmic rule changes" are going to leave some trace evidence of how the rules changed. Once you figure out how the rules changes, you could work backward to see what happened before...

For example, if you had a phase transition, it would impact the productions of gravity waves

http://arxiv.org/pdf/1112.0084v1.pdf

The other thing is that phase transitions are an important part of particle physics. One strategy is to look at the set of the "small rule book" after the phase transition, and then figure out the "big rule book" that created the phase transition. You can add the guess that the "big rule book" will turn out to be simpler than the "little rule book."

One other constraint is that if you start out with the assumption that the speed of light is some absolute limit, then one part of the universe that undergoes a "phase change' can't communicate with another part of the universe. This means differences in how different parts of the universe undergo phase changes, which then gives you fluctuations which we can see.

I have doubts we can understand how to create a Universe without changing qualitatively, the rules of Physics.

So change the rules. It turns out that there are limits on how you can change the rules without impacting something that we know.

 

[ImaLooser]

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

Yeah. Where did he get his degree?

 

[jackmell]

Because the laws of physics don't change. .

How can you say that? How do you know they don't change? Why would we think the laws of physics would be the same in the pre-existence before the Big Bang? Our laws are based on the dynamics of our Universe, space, time, energy, matter. But if these are all a consequence of the particular geometry and dynamics of our Universe, why would we think they would still apply outside (before) our Universe?

Now, one could turn that on me and ask how do I know they change? I don't but based on what can happen during phase-transitions in our universe and how these somtimes occur with rule-change, I don't think it's entirely unreasonable to suggest that if the Big Bang was a phase-transition, then perhaps it was acompanied by a change in rules and if so, then the physics we now see in the Universe could be different than the physics of the pre-existence and that is the basis for why I challenged the statement that with our physics, we can get Universes.

 

[Chalnoth]

How can you say that? How do you know they don't change?

Because if you write down some rules that do change with time, I can write down a different set of rules that describe the same system that don't change with time, just with different circumstances that change how the rules apply.

Said again: you can always factor a change in time into the circumstances the rules are describing.

 

[jackmell]

http://arxiv.org/pdf/1111.2107.pdf[/url]

May I say I like the sound of that even though I can't follow it? It just makes sense to me that our physics (GR) would precipitate into existence during a phase transition of some larger field, which in this case seems to be LQG. The reason it makes sense to me is that many phenomena in the Universe come into existence via critical-point phase transitions and I wonder if these mini-transitions we see in our world are echos of a grand transition that gave rise to our existence. However, since I can't follow the text, I'm not sure the author is proposing a phase-transition for this phenomenon.

Can you tell me if he is?

Anyway guys, that's my thesis: a larger system reached a critical-point, underwent a phase transition which gave rise to our Universe and the physics (QM, classical physics and GR) we observe. But that physics emerges only because of our Universe and since the pre-existence is separated from us by a critical point, we cannot use those physics to create other Universes. We need the larger system outside our Universe to do that. In my opinion anyway.