There is a philosophical, or metaphysical position that can be taken–maybe its a scientific hypothesis–that the past cannot in fact exist. Everything that can possibly exist exists now. Things now may be expressive of some conceivable or describable past state of affairs, yes:but that's different from saying this this former state actually somehow exists in the form of "the past". Even in our memory[...]there is no past:no scenes preserved with all their sights and sounds. Merely fleeting states of mind, myriad points assembled for a moment to make a new picture (but "picture" is wrong too, too full, too fixed) of what we think are former states of things: things that once were, or may have been the case.

Is the very mechanism for the universe to come into being meaningless or unworkable or both unless the universe is guaranteed to produce life, consciousness and observership somewhere and for some little time in its history-to-be? The quantum principle shows that there is a sense in which what the observer will do in the future defines what happens in the past—even in a past so remote that life did not then exist, and shows even more, that 'observership' is a prerequisite for any useful version of 'reality'.

the past has no existence except as it is recorded in the present. (...) we would seem forced to say that no phenomenon is a phenomenon until it is an observed phenomenon. The universe does not 'exist, out there' independent of all acts of observation. Instead, it is in some strange sense a participatory universe

How can the past and future be, when the past no longer is, and the future is not yet? As for the present, if it were always present and never moved on to become the past, it would not be time, but eternity.

In the emerging picture of mankind in the universe, the future (if it exists) will surely entail discoveries about space and time which will open up whole new perspectives in the relationship between mankind, mind, and the uni-verse.… But what is now? There is no such thing in physics;it is not even clear that ‘now’ could ever be described, let alone explained, in terms of physics.… Notions such as ‘the past,’ ‘the present’ and ‘the future’ seem to be more linguistic than physical.… There is no universal now, but only a personal one—a ‘here and now.’ This strongly suggests that we look to the mind, rather than to the physical world, as the origin of the division of time into past, present, and future.…There is none of this in physics.… No physical experiment has ever been performed to detect the passage of time. As soon as the objective world of reality is considered, the passage of time disappears like a ghost into the night.

The truth is that the past exists no more than the future, even though it feels as though it does.

The past is an interpretation. The future is an illusion.
The world does not move through time as if it were a straight line, proceeding from the past to the future.
Instead, time moves through and within us, in endless spirals. Eternity does not mean infinite time, but simply timelessness.

PAST, n. That part of Eternity with some small fraction of which we have a slight and regrettable acquaintance. A moving line called the Present parts it from an imaginary period known as the Future. These two grand divisions of Eternity, of which the one is continually effacing the other, are entirely unlike. The one is dark with sorrow and disappointment, the other bright with prosperity and joy. The Past is the region of sobs, the Future is the realm of song. In the one crouches Memory, clad in sackcloth and ashes, mumbling penitential prayer; in the sunshine of the other Hope flies with a free wing, beckoning to temples of success and bowers of ease. Yet the Past is the Future of yesterday, the Future is the Past of to-morrow. They are one — the knowledge and the dream.

In reality, time doesn't pass; we pass. Time itself is invariant. It just is. Therefore, past and future aren't separate locations, the way New York and Paris are separate locations. And since the past isn't a location, you can't travel to it.

The past did affect the present and the future, in ways you could see and a million ones you couldn't. Time wasn't a thing you could divide easily; there was no defined middle or beginning or end. I could pretend to leave the past behind, but it would not leave me.

Past, n. That part of Eternity with some small fraction of which we have a slight and regrettable acquaintance. A moving line called the Present parts it from an imaginary period known as the Future. These two grand divisions of Eternity, of which the one is continually effacing the other, are entirely unlike. The one is dark with sorrow and disappointment, the other bright with prosperity and joy. The Past is the region of sobs, the Future is the realm of song. In the one crouches Memory, clad in sackcloth and ashes, mumbling penitential prayer; in the sunshine of the other Hope flies with a free wing, beckoning to temples of success and bowers of ease. Yet the Past is the Future of yesterday, the Future is the Past of to-morrow. They are one--the knowledge and the dream.

The past is a ghost, the future is a dream, and all we ever have is now.

I don't think the human mind can comprehend the past and the future. They are both just illusions that can manipulate you into thinking there's some kind of change.

The past is a ghost, the future a dream and all we ever have is now.