The world of the small is very spooky
… at least it is to me. Recently a few researchers showed just how spooky it is by actually preforming Wheeler’s thought experiment. Wheeler’s thought experiment is really a test of the wave-particle duality of matter. I’ll give you the inside scoop.
Some Background About The Quantum World
First you need to know about particle interference patterns if you don’t already. It turns out that if you fire a beam of subatomic particles (like photons) at a wall with two slits and then look at the pattern the particles form on a screen behind this double slitted wall, you won’t just get two splotches of particles that look like the two slits. What you actually get is an interference pattern, just like that of a wave (like light, or water). Ok… weird. You might think, “Ok, well the particles must be interfering with each other, let’s just try firing one particle at a time“. To make things weirder, if you fire one particle at a time through this double slit, you get the same pattern! Each individual particle is interfering with itself! Now… to make things weirder still, if you set up a detector to try to measure which slit each individual particle passes through, you suddenly get the regular, dull pattern of two splotches of particles! It’s like the particle has a mind of its own and knows when you are looking and when you aren’t (this is not the case, of course). It will only interfere with itself when you’re not looking… as if being like a wave is taboo or something.
Wheeler’s Experiment
The next thing a physicist would try to do after realizing that (s)he had been outsmarted by quantum mechanics is to, well… fight back. Wheeler said to himself, “Let’s try to trick the particles into thinking we’re not looking when we actually are“. You can try to do this by only choosing to “look” or not (IE: measure which slit the particle passed through) after the particle passes through the double slit wall. This type of measurement is called Delayed Choice. This decision would have to be utterly random to work properly and physicists have figured out clever ways of doing this effectively.
So what happens? Do we trick the particles?
Turns out: NO. The particles have outsmarted us again. They behave exactly as they normally do depending on whether we’re looking or not, even if they don’t “know” we’re looking. They interfere when we’re not looking and just pass straight through the slits when we are. Spooooky! This is in complete agreement with the quantum mechanical (wave-particle duality) description of matter and it actually rules out many other theories.
This world just keeps getting weirder and weirder, doesn’t it? When you think about it though, what says that subatomic particles should behave like tennis balls, or rocks? It’s a completely different realm of reality. We find it spooky because we’ve adapted to the large scale laws of physics, and expect that when you throw a tennis ball through a hole in the wall, it will come straight out the other end no matter whether your eyes are open or closed. I’ll let you continue this philosophical tangent on your own.
