I'm hoping to start a fairly regular set of postings on Quantum Mechanics and/or other weird science that fascinates me. However, if there's no interest (after all, it's outside the normal scope of all things dagblog), I'll drop it. With that in mind, I thought I'd start with an overview of Quantum Mechanics, talk about how it's really weird, and give my interpretation of it, all without delving into math or jargon. Well, I'll try to at least save any such delving for the comments section.

For those who find QM confusing, I offer up these quotes:

Those who are not shocked when they first come across quantum theory cannot possibly have understood it. - Niels Bohr

If you are not completely confused by quantum mechanics, you do not understand it. - John Wheeler

It is safe to say that nobody understands quantum mechanics. - Richard Feynman

Quantum mechanics makes absolutely no sense. - Roger Penrose

Now, for the two-cent tour of one of the simplest experiments that demonstrate the weirdness of quantum mechanics, the double slit experiment:

The experimental setup is quite simple. There's a light (or other particle) source, a card with two slits in it, and a detector. If you cover up one of the slits, you find that the majority of photons (or other particles) lands along the line connecting the source and the slit, with a predictable fall off the further you get from the intersection of that line and the detector. Do that with the other slit, and you find the same, simple, pattern, but moved as one would expect relative to that slit's location. So far, so good. Now, if you uncover both slits, you get what's known as an interference pattern. That is, you get a series of ripples (far more than just two), with alterations between a higher probability of finding a particle and a lower probability of finding a particle. As it stands so far, if we're just talking about light, this is not a new experiment. It's what led to the understanding (before Einstein's photoelectric effect experiment suggested otherwise) that light is a wave. If you've ever watched two sets of waves interact, you get this same sort of interference, so that's a nice, simple explanation. The only problem is, the explanation is wrong (or at least incomplete).

Let's switch the discussion from light (photons) to electrons. You get the same results. Now, the simplest explanation (and one that was posited) is that electrons passing through one slit are somehow interacting with electrons going through the other slit, and that interaction is responsible for the interference pattern. However, it's possible to send one electron through at a time. An electron can only go through one slit or the other, right? Well, you'd think so. However, if you do this experiment, one electron at a time, you still get that same interference pattern.

Bizarre, right? Well, how can we explain it?

That's where QM comes into play. It posits that these electrons have probability waves that describe their probable locations, and that these waves can interact with each other, even when they're describing a single particle. So, there's a probability the electron went through one slit, and a probability that it went through the other slit, and these probablities actually interact with each other!

But... What if we get creative and try to determine which slit the electron actually went through? Several ingenious experiments have been set up to do just that. Here's the catch, however: any experiment that reveals which slit the electron actually traveled through destroys the interference pattern on the detector end. In jargon (OK, so there's a little bit), we say it collapses the electron's probability wave. (Schrödinger's cat, see also.)

Now we're going to stray a bit from the world of physics into the world of metaphysics, because we're going to ask "what really happens"? Here's where there's a lot of disagreement (most of it amicable, however). For a sample of what I mean, check out this Wikipedia article. Personally, I'm keen on the many worlds interpretation, or maybe the many minds interpretation. Why? Well, essentially, this collapsing I just mentioned is caused by so-called "conscious observers" making an observation (or measurement). However, I'm not keen on putting consciousness in a special box with a pretty bow around it (as if the rest of quantum mechanics makes any sense!), so I've struggled with how it is that consciousness has the effect it does. I then considered the anthropic principle, which states that the universe is the way it is because otherwise we wouldn't be here to observe it. Let's put that another way: if you flip a fair coin 100 times, you're going to get a particular sequence of heads and tails. The odds of getting that particular sequence is 1:2^100, or (very) approximately 1:1,000,000,000,000,000,000,000,000,000,000. Yet, that's the sequence you got! Amazing, right? OK, not really, because any other sequence would've had the same odds, and you had to get one of them. Anyways, that's kinda-sorta the idea behind the anthropic principle. How does that relate to conscious observers collapsing probability waves? Well, it turns out that maybe we're not collapsing them, but we're uncollapsing ourselves (or, more technically, we're coupling our future experiences with that electron). I.e., when we make an observation of an electron, the self that might have had the electron going through slit A is decoupled from the self that might have had the electron going through slit B. Confused? Reread those quotes again.

I strongly welcome any comments, whether it's about what I've written, how I've written it, or how some other interpretation is even better.