At the 'now' moment, the future and past coincide but as time moves on and the 'now' moment changes we can make some deductions on the nature of these aspects of time.
The future remains unknowable because it is yet to come into existence but the past has been experienced and can be accessed by a brain working in the three dimensions of time via memory. That is not all, the invention of writing has been crucial in the recording of the past, replacing an oral tradition of passing on history as stories where what had been forgotten or unexplained was replaced with imaginings that through embellishment became unicorns, angels and gods.
The human brain has a great capacity for storing life's experiences and across the world this amount of information allows for a considerable recording of the past. I suggest that this information will be passed on to successive generations meaning that each of us is an encyclopedia of the earths history. Why then do I know so little? Because you don't need to access all this data in day to day life although some of it may be retrieved and appear in dreams. Images you never knew you had.
What of the future? At every point in the universe, except the origin, there will be an older part where development has been longer. If one could instantly travel to this older part you may glimpse THEIR future but because of the vicissitudes of nature it may be a vision of scientific advancement or a sterile desert of stagnation.
You can never know your own future. The 'imaginary' time working of your brain allows you to predict or anticipate what comes next but you cannot know for sure which leads me to nature's greatest paradox. How come there can be no 'now' moment, the present, without there being a non-existent future?
The answer, of course, can be found in my inexpensive booklet: Spiritual Man: An Introduction to Negative Dimensions