IIF. Schrödinger’s Cat.

1. The Schrödinger’s Cat Experiment. 

In the last section (IIE), we introduced the idea that quantum mechanics allows many simultaneously existing courses of events.  This seemingly nonsensical state of affairs was illustrated in a particularly acute and dramatic form by Schrödinger (who never really had full confidence in the theory he discovered!).

A cat is placed in a large box.  In with the cat is a bottle of cyanide that can be broken upon receiving an electrical signal from outside the box.  A half-silvered mirror experiment, as in section IIE, is set up near the box.  A single light wave function is put through the apparatus.  The electrical circuitry is set up so that if the V detector (but not the H detector) detects the wave function, nothing happens.  But if the H detector (but not the V detector) detects the wave function, an electrical signal is sent to the box, the bottle of cyanide is broken and the cat dies.  In quantum mechanics, both these possibilities happen at the same time.  Thus the mathematics of quantum mechanics seems to imply that the cat is both alive and dead at the same time!

2. Two Problems.

There are actually two problems or puzzles presented by this example.  The first is: Since both possibilities occur in the mathematics (and since we put unquestioning faith in the mathematics), why don’t we see both possibilities at once?  And then, assuming we can solve this first puzzle, the second one is: How is the one alternative we actually perceive chosen?  The first puzzle has a solution of sorts within the mathematics of quantum mechanics (IIIA3).  But the second does not.

3. State of the Observer. 

To make the second problem even more acute, we will introduce an observer into the experiment.  Then the two possibilities are:

[V,yes][H,no][cat alive][observer’s brain perceives cat alive]

and

[V,no][H,yes][cat dead][observer’s brain perceives cat dead]

where [observer’s brain perceives cat alive] means the neurons of the brain fire in a pattern corresponding to perceiving a live cat.  The two states of the brain are treated equally by quantum mechanics so it offers no clue about which state of the brain will correspond to the contents of our awareness.

4. The Central Problem in Understanding Quantum Mechanics.

The state of affairs just illustrated is the central problem of quantum mechanics.  There are only two possible ways to solve it:  Either the wave function and/or the mathematics of conventional quantum mechanics give an incomplete description of physical reality; or there is something about the process of being aware that we have not taken into account.  Because the mathematics of quantum mechanics works so well in every other respect, and because it is very difficult to make additions or corrections to the theory (section IIIB3 and IIIB4) we opt for the second possibility (section IIIE).