Quantum physics is regarded by many as the most powerful predictive theory science has produced.
Quantum mechanics developed in the last century to deal with the tiniest parts of nature. It seemed that classical physics, which applied to everything from stars to grains of sand, should have sufficed. But it didn’t. A whole new theory was needed. To it we owe modern bombs and modern computers. It’s been called the most empirically powerful and accurate theory ever developed.
But quantum theory has been a pain, or at any rate a challenge, for philosophers since its beginning. In the first place, the quanta turn out to be neither particles, or waves --- each of which classical physics could deal with --- but something that shares the properties of both, in a way that is impossible to picture. This used to bother people more than it does now. There is a consensus that if we can understand things mathematically, or at least physicists can, we don’t need picture them.
More worrisome is the strange role for the observer in quantum mechanics. The idea seems to be that the systems move along from quantum state to quantum state in predictable and unproblematic ways as long as there is no observer. But these quantum states are just probabilities about what’s happening. But as soon as there is an observer, things have to resolve themselves one way or the other. And this seems to not be determined by the quantum state.
So, to use Schrödinger’s famous example, you put a cat in a box with bottle of gas rigged up so that if a particle ends up in one place, it will be released and the cat will die, but if doesn’t’ end up in that place, the cat will be OK.
Quantum theory tells us exactly what the probabilities are, but not what happens. But when someone opens the box and looks in, the cat is alive or dead. Some how the observer forces the world make up its mind in some way the laws of quantum physics don’t.
Well some physicists, and some philosophers, say that what happens is the world splits, with the cat living in some and not in others, matching the probabilities. I think that is really weird.
These problems have been around for almost a century. Lately, in the past quarter century, attention has focused on yet another problem, entanglement. And what some physicists say about entanglement makes us philosophers feel like we’ve been kicked back inside of Plato’s cave, that our familiar world, spread out in space and changing through time, is being downgraded to an illusion.
Here’s how I understand it. Suppose that Ken and I are particles generated by some subatomic process. We fly off in opposite directions at close the speed of light. After a while we each raise one of our hands---simultaneously, relative to an observer at the place where we began.
It seems like there is a 50-50 chance we will raise the same hand. But it turns out that we do so ¾ of the time. Somehow, what one of us does depends on what the other does. Our states are entangled, even if after a few minutes we are thousands or even millions of miles apart. But how?
We can’t be influencing each other, because no signal can go faster than the speed of light, and get from me to Ken, or Ken to me, in time to coordinate out actions. It seems like this better-than-chance correlation would be a miracle.
But that’s the way quanta really seem to work. Quantum physicists know this. But they don’t believe in miracles, so they are finding it hard to explain.
And some of their attempts at explaining I really find upsetting. Our guest, Jenann Ismael, uses the analogy of a kaleidoscope to explain one idea.
When you look into a kaleidiscope, you see one thing --- a red piece of glass, say, in one position, and another exactly symmetrical thing in another position. As you turn the end of the kaleidoscope, the symmetry remains.
So you ask yourself how their positions remain coordinated ---- some hidden connection perhaps? Some entanglement?
But in fact, the hidden connection is just identity. Because of the mirrors, you are seeing the same piece of red glass twice over.
So one idea, one I really find philosophically distressing, is that our life in space and time is a little bit like living in a kaleidoscope. There are other dimensions, ones we can’t perceive, and along those dimensions, things, like the Ken particle and the John particle, that seem after a few minutes to be millions of miles apart, are quite close together --- maybe they are even the same thing.
It is like we live in Plato’s cave, or Ismael’s Kaleidoscope, seeing shadows or mirror images, with no way of knowing what the true relations between the causes of those images are.