The Multiverse and 'No boundary' conditions approach in cosmology

[Suekdccia]

TL;DR

Questions about the Multiverse hypothesis and the 'No boundary' conditions approach in cosmology

Summary: Questions about the Multiverse hypothesis and the 'No boundary' conditions approach in cosmology

I have some questions about James Hartle and Stephen Hawking's 'No-boundary' proposal:

- In their approach multiple histories would exist. These histories could yield universes with different constants or laws. But would these histories yield radically fundamental constants and laws?

- In Max Tegmark's hypothesis of Mathematical Universe Hypothesis he says that there are no initial/boundary conditions and because of that, there is a vast multiverse where each universe is governed by at least one different mathematical structure. This hypothesis proposes that every mathematical structure exists as a universe.
Since Hartle and Hawking's proposal also says that there are no specified boundary/initial conditions, then, could it yield histories corresponding to the universes proposed by Tegmark? Could their proposal yield universes governed by all mathematical structures?

- If the answer to #2 is basically 'yes', then, couldn't we find histories of universes governed by different fundamental theories in their approach? For example, we could find universes governed by the standard model, by quantum mechanics, by classical mechanics, by M-theory or string theory, by inflation, by causal networks...etc, correct?

 

[PeterDonis]

Moderator's note: Moved to cosmology forum.

 

[Ehyeh Asher Ehyeh]

The problem with allowing yourself to confuse the symbology with the reality as Tegmark does is that you can create absurd entities and concepts that are in truth impossible. Mathematics is just a system that manipulates symbols according to rule sets, it's not the precedent, but the descriptor. The Universe is not made up of numbers anymore than a blackboard is the numbers written on it.

 

[PeterDonis]

Since Hartle and Hawking's proposal also says that there are no specified boundary/initial conditions, then, could it yield histories corresponding to the universes proposed by Tegmark?

No, because Hartle and Hawking's proposal still assumes a particular mathematical structure, a particular quantum extension of General Relativity. They do not claim that other mathematical structures also exist, as Tegmark does.