Friday, 7 September 2007

The Great Quantum Suicide/Prayer experiment

One of the wackier ideas I've come across recently is the Quantum Suicide thought experiment. For a full explanation look here

It concerns one of the interpretations of Quantum Mechanics, (a subject I studied a long time ago at University & wasted many late evenings in pointless discussions of its philosophical implications).

In the "Many Worlds" interpretation of Quantum Mechanics, all possible outcomes of an event occur in separate parallel universes. Consider a radioactive atom that has a 50/50 chance of decaying in any given second. We are unable to predict which of these outcomes will happen, only the chance of one or the other. Albert Einstein didn't like this idea, and was often quoted as saying "God does not play at dice". (Well, coin-tossing in this case). Enter the Many Worlds Interpretation (MWI) to the rescue. In fact at the end of a second, there are two parallel universes, one in which the atom has decayed, and one in which it hasn't.

Now imagine a physicist who wants to test if the Many Worlds Interpretation is correct, as opposed to there being One World, where the outcome is determined by God (or whatever) tossing a coin. The way to test it is to rig up the radio-active atom to a detector, which, if it detects the decay, fires a gun. The physicist sits in a chair facing the gun. At the end of the first second, there are two parallel universes, one with a dead physicist, and one with a live physicist. Clearly, the physicist's consciousness only continues in the universe where he is alive. Now the physicist repeats the experiment for 1000 repetitions. The chance of getting 1000 coin tosses in a row coming up heads is so astronomically small that if there is but one Universe, then the physicist is going to be dead by the end as sure as eggs are eggs. But in the Many Worlds Interpretation, all outcomes always happen, so at the end of 1000 seconds, there is one universe with a live physicist, and 999 with dead ones.

Now the physicist returns home elated after his day's work, and says to his wife:

"Hi, dearest, I'm home, and guess what? I've proved that many worlds interpretation is true - and I'm going to be famous".

However, his devoutly religious wife knew about the experiment and also knew that barring miracles, her husband would be dead before the end of the day. And so she prayed to her God to intervene and save her husband's wife. So even though it dampens her husband's enthusiasm, she replies:

"No you haven't proved it's true, I've just proved that prayer works. It's a miracle!!".

(Sadly in 999 other universes, the grieving wife is left wondering if God exists at all).

What should our physicist do? Should he:

(a) Divorce his religious nutter of a wife, publish his findings and get the Nobel prize?
(b) Start believing in the same God that his wife believes in?
(c) Go back to the lab and try and figure out what went wrong with the experiment?

[ Clue: what would be the most scientific thing to do?]

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