We feel the presence of a deep past, a long history. Of the past, present, and future, the past feels largest; the past has substantial dimension in our imagination. The future feels finite in a way the past does not. But still, we think of the future as also having dimension, and of ourselves as capable of imagining "far into the future." The present? The present has no dimension. The present is evanescent, the instant between past and future. The moment one begins to think, the present vanishes. (One is no longer "in the moment.") The present is in a perpetual state of vanishing, that's what the present does. It can never be measured. It has no duration.
Another view: the present is a Heisenbergian paradox: as light is both particle and wave, the present is simultaneously an instant that can neither be fixed nor measured and a phenomenon with duration.
This presupposes that present and past are not divided by a dimensionless line; instead, the present is a gradient shading into the past, becoming less present and more past as time elapses. (If one can, indeed, be in the moment, the moment must have dimension, for what else could one be "in"?)
Does the present shade into the future? Does the gradient work the other way, making the present a point atop a bell curve? That doesn't seem right. The present cannot shade into the future unless time elapses, and time elapsing will always create a gradient toward the past.
So you see the problem.
Geologic dating of rocks as 3 billion years old. Radiation from the Big Bang traveling 13 billion years to reach Earth. Deep.
Heisenberg's uncertainty principle states that one can measure the position or the momentum of a subatomic paricle, but one can never measure both at the same time. Measure one and the other becomes unmeasurable.