Nothing external can be proved without possibility of doubt and argument. All perception is subjective. The 'past' is a term we use for memory or to explain what we observe because we need labels.
Logic decrees that perception can only happen in the present. The 'past' is not a place, a location where one can go or visit, the same as the 'future'. They are metaphors for what appears to our consciousness to occur.
Granted, however, that many seem to live in the past. Furthermore, much of humanity would seem to walk in a sleep state, to function under hypnosis, and that doesn't appear as very 'in the present'. Nevertheless, it cannot happen at any other time than now.