sure you can ask it! and it's a good question, and similar to many which cause heated debate in QM (essentially - the model works beautifully, but what does it

sure you can ask it! and it's a good question, and similar to many which cause heated debate in QM (essentially - the model works beautifully, but what does it _mean_?). Basically I don't have the answer. All I can say is that when an anti-particle is created, that is IDENTICAL to - per our model - a particle travelling back in time and being destroyed at the production point. Now we know the model works extremely well. It describes the system to a very high degree of accuracy, and can be used to make predictions about how that system evolves. So - if the model is correct (let's assume it is), and anti-particle production -> moving forward in time == particle moving backwards -> destruction, which is it that we are observing? Basically, I think most physicists would say these two scenarios are the same thing, just expressed (or observed) in two different ways. Edit: actually this highlights an important distinction between the quantum and macro-worlds. Things can only happen in one direction in the macro-world thanks to entropy (everything -> disorder). Whereas in the quantum world there's no such restriction, and things can happen in either direction.