#428 – Sean Carroll: General Relativity, Quantum Mechanics, Black Holes & Aliens

5602.361 - 5624.018 Sean Carroll

That's right. All of quantum mechanics, all different versions, require a kind of arrow of time. It might be different in every kind. But the quantum measurement process is irreversible. You can measure something, it collapses, you can't go backwards. If someone tells you the outcome, if I say I've measured an electron, its spin is clockwise. And they say, what was it before I measured it?