Cavynaut said:
I might be wrong, but I think that the point is that you cannot possibly know whether the cat is alive or dead until you open the box and observe it. It's as though the observer somehow creates the reality that he/she observes. By seeing the state of the cat, a probability wave is collapsed and the universe at large is then informed of the state of the cat (through greater and greater probability waves).
Yup, the point of the thought experiment is an attempt to bridge the quantum world of the microscopic and the classical world of the macroscopic.
Physicists are happy with the idea that a microscopic particle can be described as a superposition of two, or more, states. They are also (fairly) happy with the idea that the act of observation can cause the "collapse" of the wave function into one of those states.
One nice analogue of this process is what you can do with polarised light. If you have enough polaroid sunglasses you might be able to try this at home.
If you shine a light through the lens of polaroid sunglasses, you convert the light into a linearly polarised state. What you can now do is to put another pair of sunglasses into the path/beam and slowly turn them through 90°. You should see the light grow darker until, at 90°, nothing (or at least a very good approximation of nothing) gets through.)
Now comes the sneaky part.
Get a third pair of polaroid sunglasses, and stick a lens between the other two pairs. Turn it through 45° from the first (or halfway between the firts and second) and Hey Presto! you have light getting through again!
Why?
If you have read this far, you're probably wondering why I'm boring you with talk about sunglasses, and not superpositions of wavefunctions.
Well, this is exactly what we have done in this little experiment.
First of all, with the first lens we have generated linearly polarised light with a polarisation of (for the sake of simplicity) 0°. With the third (or intermediate) lens at 45°, we are effectively measuring the linear polarisation at 45°. It turns out that light with a polarisation of 0° can be thought of as a superpostion of light with a polarisation of 45° and light with a polarisation of 315°, hence making the measurement can collapse some of the light into the 45° polarisation. Now when we put the polaroid lens with a polarisation of 90° into the beam we can see that the 45° beam is actually a superposition of light with polarisations of 0° and 90°, and hence some of the light will make it through.
We can now see the very real effect of "collapsing" a wavefunction, and how something everyday can be thought of as a superposition of states. The
problem with quantum mechanics is to determine the point at which measurement (and hence collapse) occurs. The point of the cat is that it is very much a macroscopic object, not a funny little thing like an electron or photon. Whilst we can easily think of photons being in a superpostion of two completely different states (like we did above) it is somewhat harder to think of a cat as being a superposition of dead and alive.
So the question is, "Do we need a conscious observer to collapse a wavefunction by making a measurement, or is there something subtler at play here?" Answers on a postcard, please.