It has long since occurred to me that all that exists in reality must be capable of existing in the mind, however all things that exist in the mind must not necessarily exist in reality. Since Einstein's theories of special and general relativity, and even before, we know that time exists in a four-dimensional continuum along with space.
This implies that there exists a past,. However, by proving that there exists a past, we have thus proved that there exists a future, namely our present is another time's past.
This argument lends itself greatly to the philosophical ideology of determinism. That is to say that, if the past cannot be changed, than we can similarly suggest that the future cannot be changed. Ergo, there exists no freewill (as this is, in part, an illusion).