Thursday, May 25, 2006

Quantum Misunderstandings

Ever since that incredibly poor movie came out, I've been seeing a steady rise in the number of brutal misunderstandings of quantum mechanics. I'd like to explain a little bit about quantum mechanics and big fucking things. Like, say, a mote of dust.

I'm not exactly a quantum physicist, but I am a relatively intelligent armchair scientist who has done a lot of reading. So, take that into account.

Okay. The basic misunderstanding is that there is some kind of gross quantum uncertainty. Which means that you can, say, see the various potentials in any situation. In theory, talented people (or people who pay $$$ to frauds) can learn to abuse this situation and, say, get parking spaces in lots that should be full. Or draw only aces. Or anything else that has a low probability of happening.

Unfortunately, this is not possible.

Let's approach it from the bottom. Quantum. IE, extremely small. So small that it granulizes time. Granulates? Time doesn't flow at that scale: it jitters along like a three year old on fourteen espressos.

The piece that gets misunderstood is this whole "uncertainty principle". As you know, Bob, the uncertainty principle states that you can know velocity or location but not both. More correctly, the more you know about one, the less you know about the other.

People are hopped up on the idea that you "can't understand quantum mechanics". Personally, I think that's bullcrap, but I'll assume it is true for the sake of this argument. However, one thing that is clear is the math behind this stuff. You can't ignore the math just because people think it's impossible to visualize. That's like saying blind people can't get run over by cars.

When you want to analyse a quantum structure, you have a couple mathematical options. Because I'm most familiar with Feynmann diagrams, let's discuss those. It should be noted that all of the mathematical models show the same basic result, although they reach it in very different ways.

And that result is that the more stuff you put in the equation, the more stable it is from an external point of view. The equations get bogged down, but that much is clear.

Sure, inside the soup it's a mess. But once you get a few dozen atoms, the probabilities become either infinitessimal or unavoidable. There may be a 43% chance that particle A emits a photon that escapes, and a 23% chance that particle B emits a photon, and so on... but the chance that photons escape generally approaches either 1 or 0. The number of photons which escape also tends to quickly approach a set number, relatively speaking. This is true of all interactions.

You can think of it as surface area. The smaller the surface area, relative to the number of atoms, the more predictable the result. the surface area is the part that interacts with the rest of the world. Including, say, your eyeball. So the mess inside gets lumped into a statistical probability. We don't know what the pieces we can't see are doing, specifically, but their outcome will always be the same because the probabilities, when compiled, are very, very close to absolute.

Similarly, when we interact with the surface area, we affect the parts we can't see... and they react. How, exactly? Which particles do what? Who can say? But the probability is functionally absolute. It gets done.

Also, these interactions begin to take an absurd quanta of time, meaning that they start to take actual time. In essence, the more particles you stick together, the slower and more predictable the actions.

This means that when you have something with as many atoms as, say, a dust molecule, there is no fucking quantum uncertainty. There is simply a giant spike of probability which is something like 99.99999999999999999999999999999999999999999999% that the dust molecule will act exactly like a friggin' dust molecule.

Okay, lets assume you like the idea that a "quantum waveform doesn't collapse until it is measured", like a certain movie posits. Let's also assume you're a damn dirty solipsist, so you're the only one doing the measuring.

Certain new age frauds would have you believe you can control this waveform.

First, they're wrong. I'll get to this in a minute.

Second, if you could control it, you'd have to do it blind, since if you measure it, the waveform collapses. How can you give yourself a parking space or make someone fall in love with you if you can't scan the final potentials and select the one that matches?

Okay, back to them being wrong:

You cannot control quantum probability. Your senses cannot interact on a quantum level. Why? First, because they operate too slowly. They use millions of those kinds of interchanges to perceive even the teeniest little perception. This means they're not operating in quantum time, but in something closer to picoseconds. IE, much, much, much, much, much slower.

Second, because they don't perceive small enough. The things they perceive are so large that quantum uncertainty has no effect on them.

Third, your brain simply cannot process that kind of information on a scale large enough to change what kind of day you're having. You might be able to, say, make a chunk of radium decay unusually fast, assuming you have already broken the laws of physics twice to get this far.

Also, you cannot "see but not measure". The idea is idiocy. The whole reason measuring changes the quantum field is because of the "seeing" part. It doesn't matter whether you consciously recognize a given situation - you've still measured it. This is, of course, totally irrelevant because at the scale you can see, there is no quantum uncertainty.

Trying to control these things with your senses is like trying to eat soup with an exploding thermonuclear bomb.

Quantum mechanics is a lot of fun. But it doesn't tell you why people act like they do. It doesn't let you modify reality. And it certainly doesn't govern our daily lives in any way.

Please! Stop the pain! Don't abuse quantum mechanics!



-Edit:

Ooh! Ooh!

Think of it this way:

If you have a hundred particles, you can measure half of them for position and half of them for velocity and get an extremely close approximation of exactly what the group as a whole is doing.

6 comments:

Corvus said...

What movie are you referencing?

Patrick Dugan said...

I suspect its "What The Bleep Do We Know?", which features, amoung other things, a magical black kid.

I suppose I was guilty of abusing the uncertainty principle just a bit in my last post.

So hey, whats the deal with quantum gravity?

I'm not going to give up on the Penrose Hypothesis just yet, as the sort of calibrations it supposes happen on a subconscious level, in other words, its a computation that builds up over a high distribution to alter a thought, not a thought that handles a quantum computation. Its non-commutative in that sense, and I suspect more literal ones as well.

Craig Perko said...

Got it in one, Patrick.

Anyway, you're welcome to believe whatever you'd like. I just read a whole book which was based around this misunderstanding, so I'm touchy on the matter.

The Penrose hypothesis is probably false, but even if it is true, it's not something humans can control and not something external. IE, no parking spaces magically appearing.

Duncan said...

Quantum mechanics are fun, but are relegated to little things. Quantum encryption works on single photons. Quantum computers are strings only a few molecules long (I don't think they've gotten much above 8). Quantum uncertainty only applies to single particles (or very small groups).

Isn't it interesting how probability holds the universe together? Without probability, matter wouldn't tend to be matter. Think about it.

As an aside... I don't see why The Uncertainty Principle is so hard to understand. Think of it like this: You roll a marble down a path. While the marble is rolling, you take a picture. If you take a picture using a very fast film (action shot!) you wind up with a very focused marble. You can see the position, but little of the direction (or velocity) is described in the picture. The faster the film, say a bullet cam, the clearer the position, but the less you can tell of the velocity. A slower film produces a blurred marble. You can judge the velocity, but the exact position of the marble is harder to tell.

Patrick Dugan said...

The other sense I was referring to was how some models of quantum behavior are based on non-commutative geometry.

Craig Perko said...

Duncan: that works for a casual look, but it isn't perfect. If you take a velocity photograph of a rolling marble, you can tell where it is because it is at the end of the trail.

It's more like bing able to take a picture of the amount of map someone in an RTS has explored. The less time you let the game run, the more accurately you can tell where they are. As more game progresses, you can determine what directions they are exploring and what they're doing, but not where they are inside that explored map.

Of course, you can only take one picture per game. :)