As said by Oogway to Po
An interesting thought! We are in general so obsessed with past and future that we rarely take time to live the present. The older we get, more time we spend reflecting on either the future or the past. Present takes only a minuscule portion of our mental space. All our sense of self is derived from our knowledge of past and memories that we have acquired over the years. We identify and restrict ourselves accordingly based on our memories.
We have different kinds of epistemic access to past and future. We remember the past, but not the future. We also believe that by acting now, we can change the future but not the past. But as far is science is concerned, there should be no distinction between past and future. There are various interpretations of quantum mechanics suggests and all realities should exist simultaneously. Time is more of a feeling inside an observer rather than an objective physical reality existing on the outside. However as far as our reality is concerned, the difference is there, irrespective of whether science predicts it or not.
The implications of this interpretation are many, some of them being quite outrageous. What it means at the fundamental level is that there is no such thing as either past or future. There is no 'was' and there is no 'will be'. Everything is 'is'. This further paints a picture of an existence with no origins and no end. It all just exists now.
This view is more or less consistence with the data that we have and even with the Big-Bang like theories. There is a widely held belief among the experimental physicists, especially the astrophysicists, that space and time originated in some kind of a cataclysmic event, over a finite period of time in the past. We'll not go into the merits and demerits of this belief itself, but we have to take note of any interesting fact here. What this shows is that there are some highly educated and intellectual people who are ready to accept the fact that somewhere down the line there is bound to be the concept of a kind of existence without either time or space. But their hands are tied because they have no idea what to do in a situation like this. It's not just Relativity and Quantum Mechanics which don't work in this dreaded realm of no-space and no-time. But unfortunately every last straw of logic known to human race breaks down here. We just don't possess the ability to even digest a concept like that. We don't know what to make of it. No logical system of thinking exists that will work here. To make matters worse, there's not even a starting point, to start any kind of analysis!
But coming back to relative sanity, there is another diametrically opposite interpretation, consistent with the current theories, that can also be considered to be equally valid. What is says is that there is no such thing as present. What we perceive as present is a fuzzy area where past and future meet. Present is either an infinitesimal line dividing the past and future or like a band with a finite width. Both the viewpoints exist. However this second interpretation leans more towards the latter. The width of this band, representing our perception of the present, differs in general from person to person and depends upon how acute somebody's perception is.
Perhaps the core point to be gained from the second interpretation is the fact that it assumes there are at least two fundamental pieces at the bottom of the existence puzzle. While the first interpretations leans more towards the concept of Everything is One.
I'd like to conclude with some generalizations of our discussion above. Although we normally spend most of our time obsessing over either the past or the future, they are not really there, at least not within the realms of our perception. The more we obsess, the more we lose track of the present, perhaps the only thing that we can be sure to be really there. It's an established fact regarding our perception of time that the years pass by at a progressively faster rate, as we grow older with time. The accumulated dirt of years begins to cloud our vision of the present. The sharpness of our ability to perceive the present slowly decreases. For the same years spent, we live less and less, effectively losing our ability to live. Past exists only in the memories, and future is unknown. This is a very important fact to understand. All of our feeling of existence is nothing but a result of our ability to perceive light, sound and other kinds of input from the environment. In effect we are creatures of our sense organs. And all our senses function only in the present. We can neither smell nor hear the past, and likewise for the future. We are what we are now, not what we were or what we will be.