What does the Alan Watts mean when he says the present is always changing the past?
The past can change, well the past in our mind can change and that is where the past lives. Each moment the past can change and slip away from us. The actual past and the actual events that happened cannot be altered, but our perception of them can be and that line is blurred more and more each passing moment. What was the actual past and what is our perception of it and which is real? They both exist only in the mind and the mind has flaws like everything else. So when we think about the past it may not be the actual past, we think now about the past and so if we remember the past differently than it actually was then it changes now, in this moment. Each passing moment it can change and degrade just due to the mind’s inability to store and keep detailed records of the past. So the past is altered and changed now, by us miss-remembering the events or the details of the past. This may be what he is talking about when he says that.