What is quantum entanglement?
In: Physics
Ooh boy. This is one of the most misunderstood concepts in all of physics and it’s very hard to eli5 but I’ll try my best. Quantum entanglement is when particles interact in such a way that their quantum states become linked in such a way that you can’t describe the particles individually. The result is that when you observe the state of one particle, you instantly know the state of the other, because they’re intertwined. For example, if you measure one particle to have spin up, you instantly know the other particle is spin down. This occurs no matter how far away the particles are. The state isn’t determined until you actually measure one of the particles. Once you measure the system, you break the entanglement.
Here’s the part that most people have trouble understanding, which is that you *cannot* use this to communicate faster than light because no information is being transferred. There’s no causal relationship, it’s merely a correlation. Also, it’s not a magical state that forces the two particles to always have opposite states. It only means that the next time you measure both particles, there will be a 100% chance that they are opposite. But if you change one of the particles, nothing happens to the other one. They just aren’t in a correlated state anymore.
Here’s an analogy I really like to sum it all up: Imagine that you know that a friend of yours only has 2 hats, and if he wears one, the other one is on his shelf in his home. You then meet your friend, and see which hat he wears, thus instantly telling you the position of the other hat. Has any FTL communication occurred? No, course not, the information that you gained “traveled” on top of your friends head at whatever speed he was moving at when he left his house to meet you, and then you combine it with a previously established fact (the correlation between the two hats). Entanglement is roughly the same as this, and really not all that much stranger.
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