01 August 2008

A taste of quantum mechanics: single photons doing unexpected things

Or, as they say in my home state of New Jersey, "quannum."

From what I can gather, some of you are interested in my posting more sciency stuff.

Well, here is one of the most beautiful and mysterious aspects of nature, something that really messed with our collective minds back in the 1910s-20s. Something that I was about to try to explain in my own words, but fortunately found a five-minute video that does it much better than I could.

In short, scientists are really confounded by the ways that little "bits" of light act if you shoot them -- even one at a time -- through two thin slits, and then let them whack the wall on the other side. Rather than just getting two clumps of photons, you get a wonderful rippled distribution of them. I guess you could imagine waves, such as water waves, making such a pattern. But photons? One at a time? What, are they colluding with each other as they decide where to fling themselves?

Physicists can now predict very accurately how light will act in a variety of circumstances. All this QM stuff has enabled a century's-worth of amazing new technology, such as, say, the laser, the transistor, you name it. But, frankly, the predictive equations have some pretty wacky philosophical underpinnings. There's still a lot of mystery to be worked out in those underpinnings.

There's self-conscious apology in how some of the equations were derived by the newly-minted Ph.D.s, in their 20s, about to gather up Nobel Prizes in the last century. I mean, it just doesn't make sense at the size-scale that we live in. French and Taylor put it like this in their QM textbook: "Finally, there is all the accumulated evidence that the Schrodinger equations work; they provide the basis for a correct analysis of molecular, atomic, and nuclear systems. Whatever questionable features there may be in the manner of their formulation are swept away in the evidence of their manifest success - a success of which we shall see many examples in this book."

Anyhow, here you are. Go learn yourself five minutes of science:



If this is up your alley, try this text, developed at MIT, which assumes you've had some physics & standard science-major math. Or, jump straight into this one, which was the Harvard QM text for a while.

Great, now I'm all sentimental for that lecture hall, which is at the Princeton Plasma Physics Lab where I had an internship after high school...

-g

ps And again, but with electrons:

1 comment:

Anonymous said...

Hey I recognise the material-you

put it so well-Daddy Vin