Many worlds

Mon Jan 24, 2011

Ever since reading Max Tegmark’s article in Scientific American on the many worlds version of quantum mechanics, which mentioned David Lewis' plurality of worlds, I have been wanting to learn more.

In high school, I was very good at chemistry but avoided physics at all costs, for no apparent reason, so I have a large deficit in that area. A good plan might be to read the textbook Physics for Future Presidents by Richard Muller at UC Berkeley. But that will have to wait for some vacation in the future.

Instead, when I saw Colin Bruce’s new book on “the many worlds of quantum”, I decided to make it my bedtime reading for this week [NB: that was written in May 2003 and I have made little to no progress since then!].

There is in fact a brief mention in the book of David Lewis, occasioned by his paper “How many Lives Has Schrödinger’s Cat?". So, I actually decided to first read Lewis' paper and the commentary by David Papineau later in the same issue of the Australasian Journal of Philosophy.

The basic issue seems to be that if there truly are many worlds branching off from each other all the time (something also called the “no-collapse” theory), this has great impact on our thinking about decisions, ethics, and our philosophy of life in general. Have you ever thought “I could kill myself” when you realize you made a carelessly wrong decision a while back? Well, even if you make the right decision “here in this world”, there will be another world (in fact many such worlds) where you made the other — wrong — decision and suffer the consequences. So, what difference does it really make if you make the right decision “here”? As long as the plurality of worlds is a harmless abstraction introduced to make it easier to think about the semantics of modal expressions in natural language, for example, such considerations may not be very disturbing. But if all those worlds are really real, we have a lot of thinking to do. Of course, some philosophers and some physicists have been thinking about this for a while, but it’s all new stuff to me.

Lewis points out a truly disturbing thought: in many worlds, we eventually die of course and maybe that’s fine since we don’t have any further experiences in those worlds (we may of course worry about the people and the world we leave behind in those worlds). But there is always a (however small) chance that we do not die but barely continue to live, albeit maimed and disabled. Since those are the only worlds where we continue to have experiences, we all can expect to live horrible lives at some point. Lewis writes:

“What you should predominantly expect, if the no-collapse hypothesis is true, is cumulative deterioration that stops just short of death. … How many lives has Schrödinger’s cat? If there are no collapses, life everlasting. But soon, life is not at all worth living. That, and not the risk of sudden death, is the real reason to pity Schrödinger’s cat.”

David Papineau’s commentary in the AJP tries to soothe these worries, but clearly there is much to figure out. Colin Bruce reports that “although [Lewis'] words are light, I am told by those who worked with him that he was terrified by this hypothesis [Fn: Sebastian Sequoia-Jones, pc to Bruce, March 2004]. By a cruel coincidence, he died suddenly and unexpectedly from diabetes within weeks of giving that lecture — at least in our version of reality. His paper is about to be published posthumously as I write. He must have died a badly frightened man, and the psychological impact on his colleagues was considerable.”

I am now halfway through Bruce’s book and somewhat overmatched by the strangeness of the quantum world, but I’ll continue working through it and cannot see how one can’t be fascinated by this area of inquiry. I wish I had paid more attention in high school. The fact that I did in some other worlds doesn’t help me much “here”.

Some other pointers: the entry in the Stanford Encyclopedia of Philosophy on “Many-Worlds Interpretation of Quantum Mechanics”, the Everett FAQ, Max Tegmark’s “Welcome to my crazy universe”, and a recent Fresh Air interview with physicist Brian Greene, who just wrote a book called The Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos.