"from the beginning that has no beginning and the end that has no end, from the Circle of the Roundness, give us your power, oh Great Spirit."
(from a Sioux Sun Dance prayer)
The "present" does not exist and the "past" and the "future" are the same thing.
The "present" must be infinitely small, for if it had any dimension it would over-lap into the "past" on one side and the "future" on the other and therefore would not be the "present." In order for it not to extend both into the "past" and the "future," it must be infinitely small and therefore non-existent.
Visualize the "present" as a ring which slides along a cord labeled "past" on one end and "future" on the other. Since "past" and "future" are both infinite, they must be equal and therefore have at least an implied measurement.
As the ring moves along the cord into the "future," the "past" is getting longer and the "future" shorter. That's impossible since they are both permanently equal.
Therefore time must be a circle. For only if time were an endless circle would "past" and "future" be both infinite and equal.
Time is not a straight-forward phenomenon at all. It is rather like a river, with swift currents and slow currents - even eddies and backwashes.
The sub-conscious is more in tune with this than the intellect is. (Some people more than others.) Recognition of these variables and inconsistances is the only clue we have to understand such mental phenomena as deja vu, prophesy and nostalgia.
Time is different things to different people and even to the same people under different conditions of receptivity. No one can understand another person's "time," for each person has a different subliminal perception of the movement of the ring.
The pain of nostalgia is an individual's confrontation with his/her own personal time-frame.
Physical "time" is merely our convenient measurement of physical events - the movement of heavenly bodies or the decay of atoms. But personal time moves in a personal way - spurts, drags, lunges, zig-zags, circles, reverses, leap-frogs, both forward and backward.
Nostalgia is the pain of a backward leap; a forward leap is variously called deja vu, ESP, transcendence or, by the Indians, "vision" or prophesy.
Everything is a great circle - birth, life, death, even time. Some of us call it "Indian Standard Time" - IST.