Where Grey Matter meets Dark Matter

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Episode 27 - 20 June 2010

People get addicted to all sorts of stuff: heroin, glue-sniffing, gambling, TV, eating, caffeine, making long lists, using archaic forms of common words, et cetera.

You can divide them roughly into two categories: substance addictions and behavioural addictions. The first uses chemicals to stimulate certain brain responses, while the other is all about doing certain activities that give your brain the juice it wants. But regardless of the how or why, the point is that you get to the point where you can't be without it.

But addiction is not necessarily a disorder; you could be addicted to all sorts of things, but if you have the money and time to indulge yourself (and you don't become a sociopath) then you can get by just fine. But if it starts to affect your job, your health, your housing situation, your better half or lesser fractions, or anything that is generally considered important, then it's probably a disorder.

But addictions are nothing if difficult to get off. That's the point. Your biology has become dependent on some stuff, and unless you get it, your instincts are going to tell you to get more of it, any way you can. This can be bad.

There's really nothing funny or cute about addictions... except for this:


  • Here's a list of criteria for substance dependence: http://www.behavenet.com/capsules/disorders/subdep.htm
  • A paper about how harmful drug addiction can be: Nutt, David (2007), `Development of a rational scale to assess the harm of drugs of potential misuse', Lancet, 369, pp. 1047-1053.
  • Here's a report about compulsive eating, with a cute picture of a mouse. It's probably dead now.
  • Did you men think those hours spent gaining xp were just fun and games? Wrong. (Men are weak.)


Photo: Jeff Keyzer. Source: Wikipedia

Light amplification by stimulated emission radiation. Yep, a laser. The trusty old ray gun from sci-fi brought to life in a hand-held, battery-powered amusement for your pet. Do we need to give examples of where you might have seen lasers before?

It's the 'stimulated emission' part that makes the laser, but what is stimulated emission, you ask. First, let's lay down an axiom - things (like electrons, protons, aeroplanes and obese people) try to be in as low an energy state as possible. There, now we can move on.

All electrons have some energy, and the energy of the electrons in a material is characteristic of that particular thing. Now when a high energy electron loses energy (as we assume they try to do), then they give off light. Now if you could convince a whole heap of these electrons to lose the same amount of energy at the same time, then you would have a nice burst of monochromatic light. There are energy states called 'meta-stable' that allow electrons to teeter on the edge, ready to drop off and emit light but just needing a little push. Now we get to the stimulated emission.

Source: Wikipedia.

If an electron is in one of these meta-stable states and a photon of the right energy comes along, then it can provide the kick needed to get the electron over the edge. Now one of the quirks of the universe is that if the electron drops down, it will have the same phase as the photon that kicked it, and it will travel in the same direction. This is stimulated emission, in an electron shell.

So now that we've liberated an electron and got a couple of photons, those photons can now kick two more electrons, making four photons - which can liberate eight electrons, and the cascade begins. Where does the first electron come from? Well, the meta-stable state isn't perfect, and sooner or later an electron will lose energy all by itself and get the process going. Rad.

So there you have it: coherent, colimated, monochromatic light. There are some finicky details about how you get the light all going in the correct direction, and not just in any of the 4\pi steradians. You can use mirrors.

Lasers can be found everywhere, and are so ubiquitous that we forget just how awesome they are. They're just not awesome to shine in your eyes. Not awesome.



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