Wednesday, 5 December 2007

the very weird world of quantum physics

Quantum physics goes against a lot of what we "know" to be true, and has long fascinated me (in a very non-expert kind of way!).

Quantum physics deals with atomic and sub-atomic particles and radiation, and the relationship between them. The word "quantum" (= "a small discrete unit of energy or mass") is based on the fact that radiation, such as light, while generally regarded as a continuous wave, can be considered to be composed of discrete energy packets which behave like particles.

There are many curious aspects of quantum physics which seem very unusual, even impossible:

  • In the world we experience every day, things are solid, and they are either in one place or another. But in the quantum world, things are composed of very small particles surrounded by relatively large spaces, and we cannot be sure where a particle may be - we can only say where it probably will be (Heisenberg's uncertainty principle).
  • In our world, things are there whether we know about them or not. The tree really does crash down in the forest, whether anyone sees it, hears it or cares, or not. But in the quantum world, things aren't necessarily "there" until we observe them - and when we observe them we change them. And if we measure some aspects of a particle (say its position) we may be unable to measure other aspects (say its velocity) - it just can't be done.
  • In the "normal" world, things happen because of detectable cause and effect. You push a barrow and it moves, don't push it and it stays still - and if you are too far away from it, you can't push it. But in the quantum world, action can happen "at a distance", with no discernible connecting forces. Particles which have once become "entangled" (they have each been created or affected by some process which leads to them being linked) remain linked even across great distances, so that what happens to one will affect what happens to the other, even if there is no physical connection between them. It's impossible, but it's been proved to occur.

The combination of these and other findings of quantum physics can lead to bizarre outcomes, where measuring a particle beam in one part of a laboratory changes the state of an entangled beam in another part of the laboratory, even though the only connection between the two beams occurred in the past and some distance away.

Einstein famously was suspicious of quantum physics because it seemed too peculiar, and because it was difficult to see how it could be integrated into his theory of relativity to create a "grand unified theory of everything". Yet it has been experimentally proven, and forms the basis of much modern physics.

However a view is coming into vogue that there may be an even more fundamental understanding of physics (just as quantum physics is more fundamental than the classical physics that we are all familiar with), that will one day be discovered to explain the quantum peculiarities in a simple and logical (and non-peculiar!) way. The key seems to be in using a different form of mathematics than we usually use.

I have read a few research scientists who say that inspiration and a general feeling of the "fitness" of things play a big part in their developing of ideas, which they then flesh out using the familiar route of scientific hypothesis, data and hypothesis-testing. I find it interesting that we somehow expect the world to be logical, ordered, mathematical and explicable, even if we believe it to have occurred by random chance.

Check out Quantum Physics and Entanglement in Wikipedia, or new theories and speculations in New Scientist and a science forum.

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