When 2 becomes 1 – Healed !!!!!!!!

You may recall from previous posts that describing a quantum particle’s state is characterised by the wave  function- a partial differential equation describing the wave-like properties of a quantum particle (we keep saying quantum particle to indicate that such complexities are not required when considering a classical particle). Imagine the wave function as a  machine, the type where you put things in and get something else out. A classic machine.

“Spooky action at a distance.” — Albert Einstein

Into this machine we can throw different information (for example the degrees of freedom within a quantum system), then (ignoring the inner workings) out of the machine comes a crisp mathematical expression offering a complete probabilistic description of the particles options. Everything a particle may do, expressed in a probabilistic expression.

We have been considering all the information we need to feed the machine about a particle to arrive at this description of its universe, but what happens if some of the information we need is in fact the information about another particle? There you have it, after less than 300 words we have quantum entanglement.

Let’s enrich our understanding with an example. Quantum particles posses a quality known as spin. It isn’t quite the same as the dictionary definition of the word – that is the Physicists favourite game, to alter the meaning of words – but in this instance it isn’t too far away either. For those who are interested, quantum spin is a form of angular momentum carried by particles; which for the really astute is what omega represents in a classical system in my post on simple harmonic motion.

For the purposes of our illustration let the spin take one of two values; up or down (these expressions used in particle physics). The spin can be one of these two values here, the choice is binary. A photon; the quantum of light, is indeed a particle which may possess one of these two spin values. If you take a laser, and aim it correctly at a certain type of crystal you can create pairs of photons which become entangled – that is to say the qualities one possess has a direct consequence on the other. It is observed that if we measure the spin one of the photons as up, the other will certainly be down.

There is more to the above – intuitively it might seem as though it makes sense, if two photons are fired off near to each other that they have some sort of influence on each other but the effects of quantum entanglement  are not interested in how close they are to one another. The same phenomena will be measured even when the particles are separated by great distances; this is what elevates quantum mechanics to being spooky action at a distance.

There are a couple of things worth illuminating at this point. Firstly, we are not suggesting that the particles are sending messages to each other, while we may not be able to fully explain how quantum entanglement works we are reasonably sure there are no secret messages.

Secondly, whilst we are saying that the particles will have opposite spin we are not saying we can accurately predict the spin of both of them; we can just say A if we already know B. Finally, whilst we may strive to understand to understand how nature works it is unwise, particularly at the present, to attempt to understand why nature works in that way. Indeed a question of why nature does something may in itself have no meaning, but let us climb out of the philosophical rabbit hole and progress.

The result embodies the weird world of particle physics; not only are we impacting the properties of electrons by measuring it the electrons are impacting each other without even being in the same place. What can our little human minds even trust? I love it.

Next time I will be doing a brief run through of the quantum numbers, which I hope will be interesting in its own right and serve as a useful reference article to have on the site.

Reference – https://rationalisingtheuniverse.org/