The Quantum Disco, Episode 1
Last week, in a comment on this blog, Marty Walpole challenged me to explain what quantum physics is in layman’s terms. Well I’m not one to let a challenge like that pass, so here goes… It’s going to take several posts…
Ted is a young quantum physicist, but he’s also single and determined to do something about it. He’s heard that there’s a good place to meet girls in the city, so he cranks up some Stevie Wonder on the stereo to get himself in a funked up party mood, and gets ready to head out.
As he sits on the subway, foot tapping to the beats of Superstition still in his head, Ted catches his reflection in the window. It’s dark in the tunnel, so it works pretty well as a mirror, reflecting the light from inside the carriage. Sometimes, Ted might think about the physics behind that, why some light passes through the window but some is reflected, but he’s preoccupied with more Darwinian thoughts for now so just checks himself out one last time before his stop.
Soon enough he arrives at the bar. There’s music playing, a few people dancing, busy enough to find shards of opportunities, but quiet enough to be able to talk. A good balance, he thinks. Ted isn’t that much of a dancer, he’s OK, but never going to stand out, so he’s relying on striking up a conversation. Like quantum mechanics, it’s a game of probability. Some lines, however witty, will have a staggeringly low success rate. “Fancy going halves on a bastard” could work- it’s not entirely beyond the realms of possibility, it’s just damn unlikely. Ted settles on the safe but slightly boring opener, “where are you from?”.
Ted knows that for each attempt, there’s a certain probability of success. For each encounter, there’s no way to predict the outcome, he can just guess that he has, say, a one in five chance of getting a (genuine) phone number. If he only speaks to five girls, there’s no guarantee he’ll get a number, but then again he might get one on his first shot. If he speaks to 100 girls, it’s quite likely that he’ll get about 20 phone numbers. It might be 18, or 25, but it’ll be around that many.
The point is that even though the outcome of any one encounter is unpredictable, take enough encounters into account and there’s going to be some predictability if you can figure out the probability of success. The more you take into account, the closer the actual number will be to the prediction. If Ted could somehow talk to 1,000,000 girls, he’ll get pretty close to 200,000 phone numbers.
It’s similar to the light passing through or reflecting off the window on the train. As each particle of light hits the window, there’s a specific probability that it’ll pass through, and a much smaller probability that it’ll be reflected. Even if Ted took the train during the day, his reflection would still be there, he just can’t see it because the light from outside is so much brighter that his eyes can’t pick out the reflection.
Now here are some weird ideas. When a particle of light (known as a photon, which I’ll talk about in another post) hits the window, even if there is nothing to distinguish it from all the other bits of light, how does it know whether to bounce off or pass through? Is there some interaction between all the particles that says, if six of us go this way, all you lot go the other? It’s completely random which ones pass through, but the proportion being reflected is always the same. Even if you fire one photon at a time, the proportions work come out the same way if you keep going long enough, just like Ted’s phone numbers.
Each girl Ted talks to has her own personality, which ultimately is the determining factor in terms of how well he does with each one. One of them, unbeknownst to Ted, even used to be a guy. But there’s no such distinction with the light bouncing off the window, somehow an exact number go each way.
Now if this seems a bit odd, get this. The amount of light reflecting off the glass varies if you increase the thickness of the window. I’m not talking about light being absorbed by thick glass, that should just mean that less light get’s through to the other side. But doing nothing to the surface of the glass and just increasing it’s thickness can increase the amount of reflected light. So a photon hits the glass and has to decide whether to bounce off or pass through. How does it know what to do?
These are tough questions, and we don’t have the answers. What we can do though is calculate probabilities and describe the ways things behave, rather than answer why they behave that way. We have an accurate and useful description of nature, but no explanation beyond this point. In a way it’s disappointing to be in this situation, but it leaves a bit of the magic of nature hidden away, for now at least.
Find out next time how Ted got on at the quantum disco.Explaining nano, Quantum Disco comment below, or link to this permanent URL from your own site.