>One major aspect of the mystery of time is the fact that it doesn’t play the same role in quantum mechanics as other quantities, like position or momentum; phy

>One major aspect of the mystery of time is the fact that it doesn’t play the same role in quantum mechanics as other quantities, like position or momentum; physicists say there are no “time observables” There sort of is though. No fundamental force is time dependent per se. Here is a simple recipe: 1. Introduce a "clock system" to your experiment, whose job it is to be in state |t> at time t. Notice that the eigenstates of the clock system are the same as the quantum fourier transform. The clock Hamiltonian is thus easy to construct. 2. Change any time dependent term in the Hamiltonian into an interaction term between the original system and the clock system. In other words, rewrite H(t)|x> as H|t>|x>. 3. Solve as a time independent Hamiltonian. 4. Time is now an observable |t>. Oddly, it is now entangled with position states |x>. To make an analogy, instead of having a time dependent force you can imagine your experiment is being conducted on a train moving at constant speed, and the time dependent part is encoded in the curves of the track. Technically the particles of the experiment apply a reaction force on the clock system, but assuming your commuter train is several tons heavier than your subatomic particles this is irrelevant (except of course to get theoretical perfection one requires infinite mass). The entanglement aspect is just another way of saying that if you observe the 3:15 to Yuma at the station, this is highly correlated with observing the time 3:15 on the clock system. The rest of the article is interesting.