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

twofish-quant

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.

Yup. People have thought of that

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

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.

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

Yeah. Where did he get his degree?

jackmell

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

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

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.