Is it linear, as many of us perceive it, or is it cyclic? Or is it an illusion altogether imposed by our limited human perspective?
Are we going up and to the right to some lofty endpoint? Or are we looping back around?
When Nestorius challenged the Catholic Church on the nature of Jesus Christ as both man and God, there arose a schism. Following the Council of Ephesus, Nestorius was declared a heretic. His followers went east to the Byzantines. In the West, the Church cemented new dogma: Jesus Christ was the Son of God, and a man born of the Virgin Mary, only to be born once, to die and be resurrected once, and only to return once more at the Final Judgment. No more saviors were coming. Jesus' birthday became very important. They set the calendar by it, kind of. They hadn't been keeping close track of the years until then. And we may have lost some years here and there since 431 A.D.
The point is, linear time became dogma around 431 in the Western Christian world, and it has been ever since. Outside of this sphere of dogma, we do not believe time is linear. We have no evidence that it is.
We do have evidence of cycles in nature. A seed becomes a tree becomes seeds and so on. A chicken lays an egg that becomes a chicken that lays eggs. These are not paradoxes if we do not hold time as linear.
Many cultures have developed what we in the West call creation myths. These do not imply linear time any more than a child's birth or a sunrise. Rather, these beginnings are part of the cycle, along with growth, decay, and endings, leading to new beginnings along the way.
Many physicists strive to discover what was before the Big Bang. The creation myths often conjure a formless void as preceding this universe. Which void can easily have followed a period of growth and decay. We would be none the wiser. In fact, we will be none the wiser if we hold to a belief in a linear timeline. Is this why we rush? Why we fail to enjoy ourselves?
With nothing to strive for, I feel inordinately relaxed and grateful. This is a beautiful place and time to be, here and now. It always has been and I suspect it always will be.
John Locke agreed with Isaac Newton that time and space are aspects of objective reality, independent of the mind. Today, Locke and Newton appear to have been as woefully myopic as Descartes, who famously held thought as the source of existence.
While we may be capable of stringing the moments we experience together into a timeline, this does not imply that time exists inherently, objectively, or independent of the mind. As Einstein once said, "People like us, who believe in physics, know that the distinction between past, present, and future is only a stubbornly persistent illusion."
We typically perceive past events as influencing or causing present and future events. But physics does not support the arrow of time. The laws of classical physics and quantum mechanics are invariant under time reversal. Even the oft-cited second law of thermodynamics, which says the entropy increases with time, doesn't specify or care which direction time is moving. An ice cube is likely to be more melted ten minutes from now, or ten minutes ago.
This unfounded belief in the arrow of time may spring from a tautology at the root of logic and thus science: that of causality. Few question causality. We take it as true that similar causes have similar effects, though this is unfalsifiable, unproven, and (it would seem) unprovable. We accept this, agree to it, and then go on our merry way none the wiser. Hoffman goes so far as to propose that belief in causality and our perception of spacetime may be advantageous adaptations, useful fictions that make one fitter, and more likely to make babies.
Steven Kaufman might say that time is a tool we use to measure change, while space is the underlying dynamic structure of physical reality.