Wednesday, February 11, 2009

Multiverse theory and the two die allegory

In my last post, I described an allegory I'd created that illustrates why life on Earth, even if it is extremely unlikely, does not serve as evidence that God exists. (I emphasize "if" because there is actually no empirical data I know of that has established this probability.)

The same allegory can be used to understand a thought experiment which is one of my favorites. I forget where I read it and who it's by, but it serves as a proof of multiverse theory. That's the theory that says that there are infinite parallel universes. At each moment, every decision or random act that's possible happens in one of those multiple universes.

So, here's the thought experiment: Find a reliable pistol, load it, put it to your head, and pull the trigger. There is a high probability that you'll have just killed yourself, but a small probability that the gun will fail. Repeat this several times. For good measure, after you've pulled the trigger a few times, fire it at the wall to make sure that the gun really works; then put it to your head and pull the trigger a few more times.

If the multiverse theory is wrong, you're almost definitely going to die. In fact, you probably died at the first pull of the trigger.

But if multiverse theory is right, then at every pull of the trigger, you die in the vast majority of universes — but live in the very few in which the gun failed. "Very few" of infinity is infinity, so you're still alive in infinite universes. Moreover, you only go on testing out the experiment and analyzing its results in those [rare] universes in which you're alive. (That's where the evolution allegory comes in.)

The result is that, if you're still alive after having tried to kill yourself a couple hundred times, you can be relatively sure that multiverse theory is correct. You'd have a very, very small chance of being alive if it's not correct, but a 100% chance of being alive if it is.

The kicker, of course, is that you can't communicate with any of the other parallel universes. So while you can be fairly sure that multiverse theory is right, that information doesn't help the versions of you that are dead. Also, since outside observers haven't eliminated all versions of themselves in which you're dead, they won't be able to share your knowledge: even if multiverse theory is right, the chance that an outside observer is in the right universe to see you alive is the same as the chance that the gun has failed. So even if they do see you live, there's no way for them to know if that's because multiverse theory is right or if you're just very, very lucky.

Needless to say, for both your sake if multiverse theory is wrong and for your loved ones' sakes even if it's right, I highly recommend not trying this out.


Big said...

Is it considered a corruption of the test and any results if you run the test on a kitten instead of on yourself?

Yuval Shavit said...

That's a different experiment.