'Spooky Action at a Distance'

Even Einstein's confused

It’s safe to say that Einstein is considered one of the best brains in the business, so when a scientific problem arises that eludes even him, we know it’s going to be an interesting one. Quantum entanglement, or in Einstein’s words, ‘spooky action at a distance’, is a particularly mind-blowing example. Though my explanation will only ever be rudimentary, I’ll do my best to make some sense of it.

Essentially, quantum entanglement can be described as a relationship between two particles, like photons, whereby an action performed on one of the entangled particles will affect a response on the other. For example, when one photon is observed to be spining up, the other can be expected to be spin down. Moreover, this response seems to take place instantaneously, regardless of distance. In other words, it seems as though matter is transferred from one medium to another at a rate that’s faster than the speed of light - you’re right, Einstein; this is pretty spooky stuff. Now, at this point, many of us will begin to conjure vast and spine-tingling fantasies about parallel universes and time travel (I blame sci-fi), and I hate to be the one to burst the bubble, but it’s not actually quite as Back To The Future-esque as we might hope.

One of the primary rules of quantum physics is that all unobserved photons exist simultaneously in all possible vector states (like momentum or spin). When measured, however, photons will exhibit only one state. Boiled down to the absolute basics, then, quantum entanglement, is simply a matter of correlation between two entangled particles; once you observe the state of one particle, the state of the other is, at that moment in time, also already determined. Imagine that the movement of a photon is zero arbitrary units. Then, imagine that this photon decomposes, or that it is split by a laser beam into two entangled photons. When measured, the total movement will still be equal to zero. Remember that the vector state of each photon is not determined until the moment you observe it, so the particles could actually be moving at a rate greater than zero (or less than zero, depending on direction). If one of these photons is measured to be moving at a rate of -3 units, the other photon must be moving at +3 units. Likewise, if one photon is measured at +5 units, the other’s movement must be valued at -5 units. There is no magical transfer of information here; there is no parallel universe in existence; it’s simply that the state of one entangled atom is, by nature, ambiguous until the state of the other entangled atom is determined.

If you’re confused, (a) don’t worry - if Einstein couldn’t quite grasp it I’m sure you’ll forgive yourselves for feeling slightly befuddled and (b) check out Science Alert or Universe Today for slightly more in-depth explanations. Alternatively, check out Invisibilia on iTunes for the psychology side of entanglement. It’s pretty fascinating.


Lara Schull VII