I took a quantum optics course once. It's true what you say that entanglement can't be used to communicate (by itself), hence no problems with relativity, speed

I took a quantum optics course once. It's true what you say that entanglement can't be used to communicate (by itself), hence no problems with relativity, speed of light etc. This is known as the No-communication theorem: https://en.wikipedia.org/wiki/No-communication_theorem https://en.wikipedia.org/wiki/No-communication_theorem But together with a conventional communications channel (e.g. radio signals), you can use quantum entanglement to create a secure communications channel. This combination is called quantum teleportation (as opposed to just quantum entanglement): https://en.wikipedia.org/wiki/Quantum_teleportation https://en.wikipedia.org/wiki/Quantum_teleportation