Wednesday, August 30, 2006

Physics topics for beginners part 3: the Heisenberg uncertainty principle

Lots of people have heard of the Heisenberg uncertainty principle, but most people who haven't studied physics have an incorrect idea of what it means. The way it is usually stated is that the better you know the position of something the less well you know its velocity. What the Heisenberg uncertainty principle means, fundamentally, is that things smaller than an atom are not particles like we are used to, in that they are spread out over space. When they interact you can treat them like particles, they have a size and shape, but they exist in more than one place at a time (or rather they might exist in more than one place at a time).

A better way to look at it is to think of subatomic particles (like electrons) not as particles, but as an energy field (that term made me wince but there is no better way to put it without using physics jargon). The less space it takes up, the more concentrated it is. If you think about it this way the uncertainty principle is pretty obvious: the smaller the area of the field the better you know the position, the more concentrated the energy the higher energy you would measure at a point inside the position. The energy is proportional to (the square of) the speed, so with a higher energy the particle will move faster, but you don't know what direction it is moving, so it's probably bouncing around wildly in there, and you have less and less certainty about the velocity (which is the speed and the direction of motion). It is easy to see how it works the other way too.

This isn't quite how it really works, but it is a good intuitive description that clears up a lot of the misconceptions about the Heisenberg uncertainty principle. It, unfortunately, says nothing about free will, moral certainty or the existence of the universe. All it says is that if you look at really small things they get fuzzy.

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