|
|||
The Heisenberg Principle says that it is not possible to precisely know the position of a particle and its velocity at the same time. The more accurately you measure one, the less you'll know about the other. The product of the error in the two measurements can never be less than Planck's Constant. This is not a statement about our incompetence in building measurement equipment, it's a fundamental statement about the characteristics of matter. At the scale of atoms and sub-atomic particles, reality is fuzzy. The Heisenberg principle applies to all objects no matter their size, but the amount of the error is so tiny that at "normal" scales (whatever that means) it is too small to be perceptible. But when you start messing around with atoms and electrons, it becomes a real phenomenon. It is, for instance, a critical part of semiconductor theory, and if it were not true then MOSFETs would not work (and there would be no computers like the one I'm typing this on). Velocity is a speed and a direction, so velocity is a vector, while speed is a scalar. Temperature turns out to be kinetic energy at the particle level. The speed a particle is trying to travel is a function of the temperature it is at. So when objects are very cold, they have a low speed, which means they have a low velocity. When they are extremely cold, their speed is very, very low, and thus their velocity is very low. Which means that the error in the measurement of the velocity cannot be very large, since it can't drastically exceed the speed. This means that the universe is doing a good job of measuring the velocity of those particles, which therefore means that their position must be indistinct, to keep Heisenberg happy. So when you cool atoms of, say, rubidium waaaay down and keep them in a bunch, their apparent diameter grows drastically and they overlap. You can do this with hundreds of atoms at once, and the result is what appears to be a sort of super-atom of rubidium rather than a whole bunch of atoms near each other. This isn't fusion; it's still rubidium. It's just that the dividing line between the atoms breaks down. That's a BEC, and it is a fundamental state of matter which is different than solid, liquid, gas, plasma, or neutronium. But to do this you have to achieve extremely low temperatures indeed. Liquid helium is scaldingly hot by comparison. To achieve it, they use a variation on Maxwell's Demon. What they do is start with a cloud of atoms which are near the temperature they want, and then extract out all the hotter ones and leave the coldest ones behind. This used to be done in a laser trap, where intersecting beams of laser light would create a quantum zone where it required too much energy to escape, so the atoms in question were trapped. The hotter ones had enough energy to cross the hump, the colder ones could not. Leave it for long enough and pretty soon your BEC forms. (Of course, it's a lot more difficult than I just made it sound.) Now some folks have figured out how to do the same thing using a EM field generated by a special IC. This is pretty neat, because the laser-trap method is difficult. No-one really knows what kinds of things might be possible with BECs; they may have all sorts of miraculous characteristics. No-one knew that fullerenes might be useful in superconductors and semiconductors when they were first discovered, either. Pure research is pretty cool, even when it's frigid. (discuss) |
|||
