Symmetry, the FNAL/SLAC run online magazine funded by the DOE, today is running a piece of multiverse mania entitled Is this the only universe?. It’s a rather standard example of the pseudo-scientific hype that has flooded the popular scientific media for the last 10-15 years.
Besides the usual anthropic argument for the size of the CC, the evidence for the multiverse is string theory:
For further evidence of a multiverse, just look to string theory, which posits that the fundamental laws of physics have their own phases, just like matter can exist as a solid, liquid or gas. If that’s correct, there should be other universes where the laws are in different phases from our own—which would affect seemingly fundamental values that we observe here in our universe, like the cosmological constant. “In that situation you’ll have a patchwork of regions, some in this phase, some in others,” says Matthew Kleban, a theoretical physicist at New York University.
No mention is made of the fact that there is no evidence for string theory, with the multiverse given as the usual argument for why this is so.
Kleban also claims the theory is testable in this way:
it may be possible to experimentally induce a phase change—an ultra-high-energy version of coaxing water into vapor by boiling it on the stove. You could effectively prove our universe is not the only one if you could produce phase-transitioned energy, though you would run the risk of it expanding out of control and destroying the Earth. “If those phases do exist—if they can be brought into being by some kind of experiment—then they certainly exist somewhere in the universe,” Kleban says.
No word on how to do that.
Nomura says the way to test the idea is by looking at the universe’s spatial curvature (which, according to Planck is zero within the experimental uncertainties). According to Nomura, the implications for the multiverse of possible more accurate measurements of the spatial curvature are
- If it remains zero, that’s consistent with the multiverse.
- If it is negative, that’s “strong evidence of a multiverse”.
- If it is positive, that’s a problem for some multiverse models, but not evidence against the multiverse, because you can’t have evidence against the multiverse:
a positively curved universe would show that there’s something wrong with our current theory of the multiverse, while not necessarily proving there’s only one. (Proving that is a next-to-impossible task. If there are other universes out there that don’t interact with ours in any sense, we can’t prove whether they exist.)
Kleban and Nomura are quite excited by this, because the multiverse has the wonderful implication that we can all give up on trying to find a better fundamental theory and do something more useful with our lives:
If there were different universes with different phases of laws, we might not need to seek fundamental explanations for some of the properties our universe exhibits.