Well, my Thanksgiving posting break lasted longer than I thought. Real life is a more fun place than the internet though, and I hope you were having lots of fun and food and were not on the internet to notice my absence.
Among the things I did this Thanksgiving was watch Dr. Horrible’s Sing-Along Blog for the first time. It is, as you know, a thing of surpassing brilliance. It warrants a few posts about its unique self-financed studio-conglomerate-free creation, because that model would probably work well in other arenas of creativity, not the least of which is science. That I’ll save for later. For now, if you haven’t watched it there’s places you can see it for free online, though I highly recommend ordering the DVD if you like it, because it will encourage other such productions as well as reward the cast and crew for a job well done.
Anyway, one of the things that Dr. Horrible is trying to create is a freeze ray. Really his version freezes time, but that’s a little outside of our current grasp. Maybe we’ll do better if our freeze ray only freezes things by cooling them down. Microwave ovens do the same thing in reverse, so how hard can it be? Pretty hard, of course. A ray will pretty much by definition pump energy into things and so more energy will mean more temperature in most cases. But there’s some cases where sufficient cleverness can save the day, Captain Hammer style.
Get a diffuse gas of atoms and shine lasers at it from all directions. The atoms will all have a particular set of frequencies that they like to absorb, while they’re effectively transparent to other frequencies. So tune your laser to shine light of a frequency just below that frequency the atoms like to absorb. The Doppler effect will come into play since these atoms are moving: atoms moving toward the source of the laser will see the light shifted up in frequency. This means they’ll absorb the light and be gradually slowed down just as though it were a pool ball being slowed by blowing on it opposite its direction of motion. But atoms moving more slowly don’t see the light shifted as strongly and aren’t affected by the light. By adjusting the light appropriately you can cool the atoms down gradually to very low temperatures.
Here’s a neat little Wikipedia diagram of it being done:
It’s a freeze ray! Well, sort of. There’s a lot of limitations. The atoms already have to be very cold and diffuse. Each laser tuning will only work for one particular atomic transition and so only one kind of atom at a time can be affected anyway. And the sample has to be hit from all sides to be effective. But it’s cooling, and it’s done with beams of light. Call it a baby step.