Life is process, process is change, and time measures change. Time enables life to occur.

Aristotle conceptualized time as the measure of change more than two thousand years ago. He theorized that the experience of time requires change, therefore without change there could be no time. Aristotle’s theory was a philosophical precursor to what Einstein later recognized as spacetime.

Einstein discovered that time is not merely the measure of change; it is inextricably intertwined with space in a four-dimensional field that serves as the underlying matrix for all movement and change in the macrocosmic universe.

Change assumes movement of some kind, movement assumes space in which to move. In spacetime, time becomes the measure not only of change, but of space itself.

Without space, there is no change, and without change, there is no time

Space and time are different aspects of the unified field that is spacetime. One cannot exist without the other. Time exists because existence in space and movement in space create time. Without existence or space in which to exist, there could be no time.

Spacetime spans the macrocosmic universe. It curves and rolls around concentrations of matter, bending in response to the gravitational forces of planets, stars, and galaxies. Light traveling across the universe rides those curves, bending and rolling according to the bends and rolls of spacetime.

Where spacetime curves around large concentrations of matter, time slows as though space becomes dense and thick. If an object travels through spacetime at great velocity, time for that object slows. Time and space exist in something like a zero-sum bond, with the velocity of travel through one increasing only at the other’s expense. The faster you move through space, the slower you move through time.

The entropy of space sets the direction of time

Physicists like to say that the Big Bang created spacetime. In the immediate aftermath of the Big Bang the universe was a place of extremely high pent-up or ordered energy[1] and consequently very low entropy. The universe has been expanding rapidly ever since, transforming that reserve of free energy into disordered random heat and steadily increasing the entropy of the universe.

Physicists also say that the unrelenting increase of entropy is what sets the direction of time. Time does not flow backward because total entropy in the universe cannot decrease.[2] A basic law of physics—the Second Law of Thermodynamics—pushes entropy to increase, with time, until the universe reaches some unimaginable state of thermodynamic equilibrium far in the distant future.

Spacetime is the matrix underlying the holodeck

The Big Bang created the space in which both change can occur and time can exist. It was necessary for both to exist together because neither could exist alone.

Spacetime became the fabric of the macrocosmic universe. It is the physical and temporal location where the laws of physics play out and the great illusion of the macrocosmic universe unfolds.

If all the world’s a stage, then spacetime is that stage.[3]

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[1] Also described as free energy available to do work in the universe.

[2] Does time also require an engine in addition to a direction? If time cannot go backward because total entropy in the universe cannot decrease, is there anything that makes time go forward? What makes time go at all?

[3] For one of many similar analogies, see Siegel (2017). “The Universe is a play, unfolding every time a particle interacts with another, and spacetime is the stage on which it all takes place.” https://www.forbes.com/sites/startswithabang/2017/01/28/ask-ethan-what-is-spacetime/?sh=71ce688350bd