21 June 2007

Quantum probability, and one and a half dead cat jokes

There exists such a thing as "quantum probability". Basically, it's like ordinary probability, except that instead of having probability density functions, you have wavefunctions. (Sometimes you have "discrete wavefunctions", which are wavefunctions that are concentrated on, say, the integers; I don't know if this is the right technical terminology. This doesn't seem to occur in actual quantum systems -- what with the world being continuous and all -- but that doesn't stop a mathematician!) These are annoying because wavefunctions are complex-valued and I can't keep nearly as many complex numbers straight in my head as real numbers. I'll probably have more to say about quantum probability in the future.

Anyway, I was walking down the street earlier today, lamenting this fact (after trying to do such computations in my head and failing) and I saw somebody wearing a T-shirt which said Schrodinger's cat is dead. I thought this was sad! Then after she walked past I saw that on the back of her shirt it said "Schrodinger's cat is not dead".

This joke's been done before, though. Griffiths' text on quantum mechanics has a picture of a live cat on the front and a dead cat on the back.

An ex of mine said that the only legitimate use of HTML's <blink> tag (which fortunately is used a lot less often than it was in, say, the late nineties) was the following:
Schrodinger's cat is NOT dead.

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