Quantum Mechanics

John Clark (jonkc@worldnet.att.net)
Tue, 24 Aug 1999 12:58:56 -0400

Anders Sandberg <asa@nada.kth.se>

>Heisenberg only showed that measurement uncertainties will
>always be larger than a certain level, essentially
>placing a limit on how well we (or anything else) can distinguish
>quantum states.

But it's much deeper than just a measurement problem. Take the old 2 slit experiment for example, it's not that the photon goes through one slit and we just don't know which one, it must go through the left slit only, and the right slit only, and both slits, and no slit at all, and it must do all these things at the same time.

Shine a light on 2 closely spaced slits and it will produce a complex interference pattern on a film, even if the light beam is so weak the photons (or any other particle) are sent out one at a time. If a particle goes through one slit it wouldn't seem to matter if the other slit, the one it didn't go though, was there or not, but it does.

Even stranger, place a polarizing filter set at 0 degrees over one slit, and one set at 90 degrees over the other, the interference pattern disappears. Now place a third filter set at 45 degrees one inch in front of the film and 10 light years from the slits. The interference pattern comes back, even though you didn't decide to put the filter in front of the film until 10 years after the photons passed the slits! Heisenberg's Uncertainty Principle does not enter into any of this. Quantum Mechanics may or may not be a good idea but one thing is certain, it's the law.

John K Clark jonkc@att.net