Entanglement is a correlation. A common example is putting clothing into boxes and moving them a light-year apart: if our box contains a left-hand glove, then w

Entanglement is a correlation. A common example is putting clothing into boxes and moving them a light-year apart: if our box contains a left-hand glove, then we know the other box has a right-hand glove (and vice-versa). However, there's no way to create a radio using this correlation, since we can't effect whether we got the left/right glove: - If we chose it before travelling, that would (a) require measuring which is which (i.e. opening the boxes), and (b) require choosing our message ahead of time, when the boxes are together (which isn't faster-than-light communication; e.g. we could just as well write our message inside the other box; no radio needed) - If we re-arrange the fabric of our glove after measuring it, that would have no effect on the other glove (our actions would de-correlate them). The reason this glove analogy breaks down is that gloves can be explained by "local hidden variables": i.e. if we see a left-handed glove, that could have been in the box all along; nothing weird. The weirdness occurs in the correlations between different measurements. For example, if we put the clothing on our hand, we're measuring which glove it is (left or right hand); if we instead put it on our foot, we would measure which sock it is (left or right foot). Handed-ness is completely (anti)correlated: if both are measured as gloves, we always get one left-hand and one right-hand; likewise if they're both measured as socks. Handed-ness and footed-ness are uncorrelated: if one piece of clothing is measured as a glove, and the other as a sock, there's no correlation between left-hand/right-hand and left-foot/right-foot. Where it gets weird is when measuring somewhere in-between, e.g. if we measure 2/3 glove and 1/3 sock; and the other is measured 1/3 glove and 2/3 sock: their handedness/footedness is more correlated than classical physics can explain (in practice we measure the polarisation of light, which can be measured horizontally, vertically, or some angle in-between!). Experiments have ruled out "local hidden variables", like "it was always an X" (e.g. something like "the box always contained an 80/20 mixture of glove/foot, with respective left/right mixtures of 50/50 and 20/40"). Quantum physics correctly predicts those experiments (e.g. using "superpositions of left/right handedness/footedness") See e.g. https://en.wikipedia.org/wiki/CHSH_inequality https://en.wikipedia.org/wiki/CHSH_inequality