Tuesday, January 24, 2006

Ceci N'est Pas Une Second Wave/Particle Post

I started writing the follow up to my last post, and found the following to be true:
  • My post was becoming incredibly cluttered with sidetracks about physics and reality and such.
  • I was writing it as if everyone reading either knew about these things, or clicked on the links to find out about them, in either case ending up with the same understanding of them that I have.
  • Given the degree to which some have loudly complained that my discussions of such things are rudely opaque, this seemed to be a bad assumption, therefore...
  • ...being as how I generally have great affection for my audience and do not wish them to feel alienated, I thought I would provide a little bonus post to talk about some things which seem like they are scary and math-y/technical, but which are in fact cool and full of narrative.
  • If you already know about such things, and/or don't care, and/or you are not feeling alienated, you may skip this post.


So...the cat in the box that's both dead and alive: I have not yet explicitly mentioned Schrödinger's Cat, but it's come up in the comments, and the concepts involved are relevant. It is, for instance, the particular result that Physicists feel compelled to explain by introducing the concept of many universes. Here it is: experiments with very small particles, like electrons and photons, in the early part of the 20th century, revealed that these particles had a wave nature. This was relatively soon after physicists had discovered that light and energy had a particle nature, whereas classical physics had said that light and energy came in waves. Physicists in the first part of the last century had a lot of problems making up their minds.

One of the things these indecisive scientists discovered about particles was that one couldn't accurately measure the particle's velocity and position at the same time. That is, one could know where it was, but not exactly where it was going. Or know where it was going, but not exactly where it was. This is the Heisenberg Uncertainty Principle. This is a very powerful result, and it shattered the classical idea of Determinism--in this case, the belief that if you knew the velocity and position of every particle in the universe, you could know what was going to happen in the future--the weather tomorrow, whether that coin flip that I left right in the middle of my last post was going to end up heads or tails, etc. It turned out that you simply could never know the velocity and position of even one particle in the universe, let alone all of them. Even God was subject to Heisenberg.

This has all manner of repercussions in discussions of free will and fate and Philosophy in general which will be ignored by me right now. The upshot is that electrons are tricky bastards. You can track them for days, and still not know exactly where they are. Say you spot an electron somewhere (they are very small, so it's not like you can just put a tracking device on the thing; you have to put a detector some place and hope one passes by). The fact that you can't quite know where it was going (since you knew where it was) means that you're going to have to take a guess. So all you can do is narrow it down to a general area, based on what it was doing the last time you saw it. Think of this like watching a person entering a dark room: you know his path walking up to the doorway, but then he walks through the door and disappears. You know for sure he's now inside the room, and you could maybe make a pretty good guess where he is based on where he was headed, but that's about all you know. He could have stopped or changed direction after he's run into a chair because nobody bothered to turn on the goddamn light. Erwin Schrödinger more or less quantified this phenomenon with what is known as the Wave Function. It basically shows you the probability that a particle will be in a particular place given where you last saw it (actual Quantum Physicists are now having a freak out from this definition of the Wave Function. Fuck them. They are not important right now). Basically, it will be highly likely to be in some places and extremely unlikely to be in others.

Okay, put that aside for a moment and consider the Double Slit Experiment. For this you'll need a visual aid. Here's a really cool one. Here's a lower tech version, if that doesn't work for you (you have to scroll down a little to get to the pictures). The reason Classical Physicists thought light was a wave was because it acted like one. If you turned on a light, and shined it through a barrier with two slits in it, it created an interference pattern on the wall behind it. This is what waves do--think of waves in the ocean. If two waves that are at their peak combine, they make a wave with a peak twice as high. If both waves meet when they're both at their lowest point, they'll make a trough twice as deep. And if two waves meet when one is at a peak and one is at a trough, they'll cancel each other out and the result will be smooth. So everyone was going along all happy with light being a wave until the late 19th century, when Max Planck realized that light had to come in small packets which he called 'quanta', because all the experiments with light and heat only made sense if energy came in discrete quantities. I won't expound on this, but it's kind of mind-blowing. I mean, hell, I've installed dimmer switches in my house, it sure looks to me like light is a relatively continuous quantity--I turn the switch, the light gets brighter. But this isn't quite what's going on. Light seems like it's analog, but it's digital--it comes in steps. They're very, very small steps, but they are steps nonetheless.

This threw the Physicists into a tizzy--I mean, what the fuck, right? (This was nothing compared to what was about to hit them.) Light acts like a wave. If light were a particle it would act like a particle when you shined it through a barrier with two slits in it--there would be no interference pattern, there'd just be two bright spots where the light shined through. "Well," they reasoned, "if light is a particle, we should be able to see which slits the particles are going through." So they set up the experiment again (I am being fast and loose with the time frame here), except this time they put some detectors by the slits to see which slit the particles were going through. As soon as they did that, light started acting like a particle. The interference pattern on the wall behind the double-slit barrier went away and was replaced by two bright splotches of light. As soon as the detectors were removed, the interference pattern returned. This was just too much. The Physicists, after having their entire foundation of what reality was crumble underneath them, all went out for a collective three-day crack-and-whore bender (or whatever it was they smoked in those days). When they came back from their lost weekends, they were left with only one reasonable conclusion: particles simply have no reality until you observe them. It's not just that a particle of light (or an electron--the double slit experiment has been verified with a particle as large as a bucky ball) can be in many places with varying probabilities, it's that it is in all of these places until an observation is made.

I should add here that many Physicists thought that this interpretation of the phenomenon was crap. Einstein was among them, saying famously that "God does not play dice with the universe" (to which I say, no duh: God is clearly playing Settlers of Catan with the universe). He spent much of the rest of his life trying to prove it. One of the results of this pursuit is what is known as the ERP Paradox, which postulates instantaneous exchange of information across unlimited distances. According to Einstein's own theory of Special Relativity, this is impossible, and all tests of the ERP Paradox have shown that this phenomenon is real. Quantum Physics is full of ironies like this. Another of these little ironies is Schrödinger's Cat (you were wondering when I was going to get back to that). Schrödinger also thought that this interpretation of his wave function, that it showed where a given particle could be with given probability, was complete bollocks. He created the thought experiment of the cat in a box to prove it. He imagined that there was an opaque, sound-proof box containing a cat, a canister of cyanide gas, and a hammer connected to a Geiger Counter. There was also a piece of radioactive material in the box, and it was such that the probability that a piece of the particle would decay in the span of an hour was exactly 50%. If this happened, the Geiger Counter would detect the radioactive decay, and trigger the hammer, which would smash the glass, letting out the gas and killing the cat. After an hour, you would look in and see how the cat was doing. But wait! Particle decay is a quantum event, which means that, according to the favored interpretation, the particle has neither decayed nor not decayed until an observation is made. But since you've created a system in which the life of the cat is connected to the decay of the particle, the cat is in the exact same condition--neither alive nor dead--until an observation is made. That is, until you lift the lid of the box and see if the cat is still alive.

"Clearly," said Schrödinger, "no reasonable person would ever believe in a cat that was both alive and dead at the same time. I mean, come on, have you ever seen one?" "No dude...wait...that's totally awesome!" replied the Physicists, who somehow had become stoner surfers from Long Beach between the last paragraph and this one, "The cat is totally alive and dead at the same time! It exists in some never-before-observed state of being. That totally rocks!" Then they all went out to score dime bags from their dealers, hitting the grocery store for some Fritos before going back to their labs to finish watching The Wizard of Oz with Pink Floyd's Dark Size of the Moon as the soundtrack. For his part, Schrödinger returned home, having had enough irony for one day.

Here I'd like to defer to L., in her wifely guise of "Mrs. Transient Gadfly," in which she states the whole paradox of this quite nicely:
That there is no reality outside of our representation/observation/interpretation of it is, well, our approach to media, politics, art, philosophy, narrative, reading, writing, the world in general, and everything else there is in the universe -- absolutely...except that freaking cat...who though i believe in every every important, representational, constructed, intent, and purpose way is neither/both alive/dead in my heart of hearts, i secretly can't convince myself that really REALLY he isn't actually one or the other.


Before I finish, I want to make a little nod to Dan, who started this whole thing off. He made a couple of arguments for the possibility of many universes actually being a simpler model of reality than one fuzzy universe, a topic which I would like to address, but my posts are just getting way too damn long. Hopefully some day I'll get there. I've never met Dan, and I wouldn't know him if he fell on me (unless, of course, I were warned in advance that the person who would be, in just a moment, falling on me were to be Dan), but he's joined the dialog here at OaO, so I've added his blog, Until Today, to the blogroll at the left. Welcome, Dan.

Finally, L. also made reference in her comments on Sam's post as to how Quantum Physicists get steamed every time somebody in another field uses their models as metaphor for something else. Here is what I have to say to them: shut the hell up. Physics is metaphor. It is not reality. It is map, not territory, the same way Math is, the same way Anthropology is, the same way Art is, the same way Philosophy is. In 50 years, somebody will, within the established framework of Physics, prove this, and the Physicists will be shocked and amazed, and that person will win the Nobel Prize. Then everybody will go back to their labs where, quite surprisingly, they'll still be watching Judy Garland and listening to Floyd. So tomorrow or the next day, whenever I get back to Part II of the post, when I'll be making a bunch of metaphors that would make any real scientist cringe, I'll point back to this paragraph. Physicists have been, over the last century, galloping headlong towards the idea that everything everyone else already understood about everything macro, in every other intellectual discipline--that there is no truth, only good metaphor; that nothing is but that observing makes it so--holds for any level of reality you care to look at. Sooner or later, we'll all run into each other.

Next: brazenly pseudo-scientific quasi-intellectual babble!
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3 comments:

dan said...

"Welcome, Dan."

Thanks!

I'm not that clumsy, so it's unlikely that I'll fall on you anytime soon. I'm pretty sure that you and I are rarely on the same coast, let alone in the same US state, thus further decreasing the odds that I will, in fact, fall onto or even run into you. However, if I did fall on you, I, too, wouldn't know you except that you were someone I just fell on to, and that would be embarrassing enough that I'd probably try to get as far away from you as possible as quickly as possible. That wouldn't likely be my reaction if we were to meet in some other capacity (though, no guarantees).

I promise not to respond to the rest of your post until I've read it and the external links several times. (Ask most people who have had a class with me/had me in a class -- I have trouble not responding, even if I don't know what I'm talking about).

Sam said...

I learned a great deal there. Something is nagging me about that cat, though. You see, I totally buy that the cat is neither dead nor alive until we observe it, but there's something about saying it's dead and not-dead at the same time that's troubling. That seems like a sort of logical deduction from within the very paradigm of logic that the particle/wave results ought to be breaking down.

We don't know what's up with the cat until we look - sure. But that's reallly all there is to say.

Alas, I don't think I myself am making this point very clealry, but I feel certain that there is a point there to make.

Transient Gadfly said...

You seem to be making a distinction there between the cat being alive and the cat being not dead. Which I guess is a distinction that I've never seen made, but given the terms of the experiment is perhaps important, now that I think about it.