Quantum Physics Explained- Not!

Most recent answer: 10/22/2007

Q:
Can you please explain what is ’Quantum Physics’
- Greg (age 16)
Emmanuel College, Perth, WA, Australia
A:
We can say a few words about quantum physics, but a good starting explanation would take a few hours of lecture, which we can’t come close to matching in a short answer. We don’t know how long a complete explanation would take, because a satisfactory one really hasn’t yet been found.

In quantum mechanics, that state of any physical system, say a little collection of particles, is represented by a mathematical object that looks in many ways like a wave. Particles do not in general have well defined positions, velocities, etc. Only in special cases do they even have well-defined energies. They can have well-defined quantum states, it’s just that those states happen not to have the properties which we instinctively feel that physical things ought to have. That’s our problem, not theirs.

The way in which those states change with time follows a definite equation something like the equations governing classical waves. It has no randomness in it- the output state is completely determined by the input state, according to the equation. The problem is that the output states don’t look like anything we ever have seen. They have things in them like combined live/dead cats and versions of your brain which are combinations of having seen a live cat and having seen the cat dead.

So the best you can do with quamtum mechanics is to predict the probabilities of seeing each of the possible outcomes. Whether there’s another process, beyond the part we can describe with an equation, making nature choose just one outcome, or whether all the outcomes happen and there become more and more versions of us, no one knows. There are other possible interpretations as well, but all of them are just as weird.

Mike W.

(published on 10/22/2007)