Frank WIlczek (photo by Andrei Linde)
When a physicist tells you that they have an idea for a lab experiment that may be able to detect the existence of quantum parallel worlds, the standard reaction is to smile, nod and move slowly away (even though the proposals for experiments can sometimes be intriguing). But when the physicist in question is Nobel Laureate (and FQXi member) Frank Wilczek, it's probably a good idea to take him seriously. His tentative idea -- which he tells me about in the August Podcast -- is that it may be possible to detect energy leaking back and forth between alternative realities. You can listen to the podcast here.
If you follow Wilczek on twitter then you'll know that he's recently been musing about "Multiversailty" in a review paper for Classical and Quantum Gravity (arXiv:1307.7376). (If you don't follow him on twitter, then you should: @FrankWilczek.) The term "multiverse" can be used to describe the idea from cosmology that faraway regions are governed by different laws and contain different substances. In the podcast we run through Wilczek's thoughts on the cosmological multiverse and its use as an explanation for why certain physical parameters are surprisingly well suited for life. He cautions that such anthropic lines of reasoning can be dangerous -- but then also gives an example, from axion cosmology, of how to use anthropic arguments to make testable predictions.
But his newest ideas are based on thoughts about a different type of multiverse: the multiple parallel worlds first predicted to exist by Hugh Everett III as a reaction to the apparent indeterminacy of the quantum world. The classic example used to highlight this is the paradox of Schrodinger's cat, shut in a box with a vial of poison (or a bomb, or some other gruesome deadly device) that will be smashed (or triggered) if a radioactive atom decays. While the box remains unopened, the atom exists in a quantum superposition state in which it has both decayed and not decayed -- leaving the unfortunate cat caught in a ghostly limbo between life and death. Everett's contribution was to argue that, when the lid is opened, reality splits into two: in one world the cat lives; in the other, the physicist is arrested for cruelty to animals.
Everett's ideas are now over 50 years old, and have gained many respectable followers. But whether or not you believe in it seems to be down to a matter of faith. At least, there did not seem to be any simple lab experiment that could be carried out to test whether such alternative realities (each with alternate you-s) exist.
But, thanks to a very savvy question from one of Wilczek's followers on twitter, the Nobel Laureate is thinking about whether such a test could be devised. Having tweeted his Multiversality paper, Wilzcek was asked where the power to generate such parallel worlds would come from. Wouldn't they violate energy conservation?
Puffy the cat, contemplating energy conservation
Wilczek has carried out a short calculation to prove that the answer is no -- they would not. You can hear him explain why not in the podcast. It comes down to the fact that energy is not a substance in quantum mechanics that is shared out between universes (one with a happy and one with a sad cat owner), but an "operator" (something which changes a physical state to another physical state). That means that you do not simply sum the energies of the universes by adding one to the other, as though they are numbers, but take a weighted average -- which will always conserve energy overall.
So does that mean that parallel universes never trade energy? If they did, we may be able to detect them in lab experiments. It is this possibility that Wilczek hopes to investigate in the coming months. Is there a way that some tiny fluctuating amounts of energy may leak back and forth between parallel worlds, while preserving overall energy conservation? And how could we detect it in the lab, given that experimental physicists are getting better and better at maintaining quantum effects in ever larger objects?
We wish Wilczek luck is his investigation!
Listen to the podcast to find out more.
I have posted two versions of Wilczek's interview on the podcast page, www.fqxi.org/community/podcast. The first, which is included in the main edition, features both myself and Brendan (with a cameo from Puffy the cat), while the second is my extended interview with Wilczek. Regarding the first version, please rest assured that no cats were harmed in the making of the podcast (although Brendan did follow Puffy round with a mic, which might have annoyed him).