Why send a message back in time, but lock it so that no one can ever read the contents? Because it may be the key to solving currently intractable problems. It turns out that an unopened message can be exceedingly useful. This is true if the experimenter entangles the message with some other system in the laboratory before sending it.
Quantum theory is one of the great achievements of 20th century science, yet physicists have struggled to find a clear boundary between our everyday world and what Albert Einstein called the “spooky” features of the quantum world, including cats that could be both alive and dead, and photons that can communicate with each other across space instantaneously.