… we have a radioactive substance that emits, on the average, a particle, an alpha particle, once every second on the average. Now, here I have a counter, and I close that counter, so it won’t count, except that I open it for half a second. If, in that half a second, a particle arrives, the probability is one half, then the same apparatus that I have already used can be coupled into other apparatus that will open a horrible door, which will let out some poison, which will kill the cat.
So, the quantum mechanical description is a probability distribution. After an hour, with the cat, the probability of cat being alive, one half, being dead, one half. And the correct description, I don’t know.
Now, here comes our observer, and looks. And his looking will either result in killing the cat for good, or for reviving it. And this finishes, Schrödinger …
I have no objection to any of this except that I say, I don’t need to look.
Prof. Edward Teller