Thursday, 26 January 2017

The meaning of the particle waves

So far we've explained that according to quantum theory every particle has an associated wave. The shape of the wave depends upon several factors, and determines- among other things- the energy of the particle.

There have been lots and lots and lots of experiments that have proved that the idea of a particle having an associated wave is a good way to model the way in which nature works. The predictions of quantum theory agree with experiments to an astonishing degree of precision.

What is less clear is what the wave actually is, and how it is associated with the particle. Indeed, it is possible that the wave and the particle are two manifestations of the same thing, and that the thing acts like a particle in some circumstances and like a wave in others. There is nothing in everyday life that is a good analogy of this mixture of a wave and a particle, and that is one of the reasons why quantum theory is mysterious.

The mainstream interpretation of quantum theory is that the wave represents the probability of the particle materialising in a given place, and there is a lot of experimental evidence to support this. If you imagine the example of the wave that you send down a long rope by twitching one end of the rope. At any given time there are parts of the rope either side of the moving ripple that are completely undisturbed, and the ripple itself gets gradually larger, reaches a maximum, then gets smaller. If the ripple on the rope were the matter wave of an electron say, what that would mean is that there was no chance whatsoever of the electron appearing either side of the ripple. The chances of the electron appearing would gradually increase as you approach the maximum peak of the ripple then gradually decreased as you passed downs the other side of it.

What is very important to understand is that this interpretation does not assume that the electron even has a position until it materialises by interacting with other matter. The interpretation assumes that the electron is somehow smeared out until it materialises. We will consider this in more detail in the next post.

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