Courtesy Photo and graphic by author plus Wikimedia CommonsThis is a perfect post for Halloween. A really scary story involving quantum physics. Let me begin by saying that this stuff is absolutely mind-boggling. I’m not even sure I can explain it. Albert Einstein himself – the bravest theoretical physicist there ever was - called it “Spooky action at a distance”, that’s how much it scared him. What’s even more disturbing is that scientists now are reporting that this spooky action has gotten even spookier! I’m talking back-from-the-dead-zombie spooky! Let me feebly try to explain.
One dark and stormy night there were two sub-atomic particles – photons, let’s say – that are joined together like a two-headed freak show turtle. Wait, probably a bad analogy – how about this: like a set of identical twins? That works. Think of twins, Larry and Ralph. They’ve interacted with each other since birth, acting exactly the same way no matter where they were. If Larry ate a cheeseburger for lunch, Ralph had one, too. Anyway, in the world of quantum mechanics, this joining of two particles is called entanglement.
At quantum levels all rules of physics are thrown out like a rotting pumpkin on All Saints Day. As I understand it, particles don’t really exist in one particular spot or state on the time-space continuum –but rather in all their probable states at the same time. It has to do with a deal called superposition, and is all about probability. Which means until they’re measured or observed in some way, they live in a constant state of uncertainty. Once one of them gets measured, and a value is placed on it, the uncertainty is eliminated, and at that point it locks into some sort of “existence”. I think so anyway. But – and this is a really big but – just by measuring it, the particle dies. Or it’s state of uncertainty dies– I’m not sure which. Something gets killed. Does this make any sense? Not to me, but I’ll continue anyway.
So, with an entangled pair of particles, things get kind of weird. When two particles are entangled – i.e. physically interacting - with some sort of correlation (or anti-correlation), – that interaction remains no matter where they are located in relation to each other. You measure a value in one of the entangled particles, you can be certain the other particle instantly has the same value. In a correlated pair, if you see that one particle has an up spin, you’ll know right away the other has an up spin, too. In a normal world analogy, if you see Larry bobbing for apples at a party tonight, you’ll know Ralph is somewhere with a wet head.
This theory has been successfully tested several times on pairs of entangled photons separated by 80 some miles. It would matter not a whit if they were separated by a 100 billion lightyears, some unexplained force tying them together, would give the same results.
Now here comes the really scary part. Quantum physicists are now predicting that the same kind thing can happen when the two entangled particles don't even exist at the same time. This is called an entanglement swap. It involves removing a particle from one entangled pair, and using it to create a new pair with another particle removed from a different entangled pair. I know. Blah, blah, blah. But let’s see if I can help you (and me) understand.
Let’s start with an entangled pair of photons, our old pals “Larry and Ralph” again. You decide to measure Larry’s spin. It’s a down spin. So far so good. But unfortunately, your measurement leaves his twin Ralph, all alone. “You’re dead to me!” Ralph screams! And Larry is dead because you gave him a value (his spin). Ralph now wanders about by himself (with the same down spin as Larry of course). This is called disengagement. A little later, you create another entangled pair of photons, this time named “Jane and Sally”. They’re not very happy– always bickering, always fighting over whether they’re actually particles or packets of waves – you know, the usual photon sibling stuff. Anyway, after a while they become disengaged (somehow evidently without measuring and killing one – I’m confused here). Anyway, Jane leaves in a huff and eventually ends up hooking up with the very lonely Ralph. They’ve now done the old entanglement swap.
This leaves us with one dead photon, Larry, and one abandoned photon, Sally. They come from two different disengaged pairs and couldn’t be more unrelated. But, thanks to the screwy world of quantum mechanics Larry has somehow returned from the dead and is suddenly now entangled with Sally. They are an entangled pair. Sally wasn’t even alive when Larry died! But now she’s stuck in a paired entanglement with a stupid zombie. Now that's frightening. I’m sure Einstein is spinning in his grave.
If my telling of this bizarre quantum tale hasn’t scrambled your brains, or made the hairs on the back of your neck stand up, you can try to learn more at the below links.
SOURCES AND LINKS
New Scientist story
Scientific American story
Niels Bohr – the genius responsible for this stuff
Schrodinger’s Cat A cat's both dead and alive until you look inside the box.