Suppose the Copenhagen interpretation is correct. And we reverse time, what happens. If a wave function has collapsed, and we found a particle somewhere. Now, I turn back time( just hypothetically), what would happen? Would the wave function uncollapse and would the particle then appear at some other location? THIS IS MY REALLY BURNING QUESTION: Let's suppose it does uncolapse, where then would we find the particle. Before experiment: Particle is at place A After experiment: The wave function has collapsed and the particle is now at location B Now I turn back time and... The wave function uncollapses( let's say it does), and it collapses again but before the experiment, since time is flowing backwards. Before the experiment we measured the particle so in time reverse that would collapse it. Would the particle again be at location A, or some new location C, because again it is wave of probbability, so is it certain that it will appear at A? If we turn back time after a wave function collapse will the past happen the same way?