Time goes in only one direction

Physicists say that entropy sets the direction of time. A broken teacup falls apart; it does not spring back together. Heat spreads and dissipates; it does not increase without a source of new heat. Unless the second law of thermodynamics is false, aggregate entropy in the universe can only increase, not decrease. Entropy advances inexorably—the force that points the arrow of time toward the future.

All things in spacetime therefore move only in one direction ultimately. That has been true since at least the Big Bang, the immediate result of which was a universe of very low entropy. Exploding from perhaps a microscopic singularity, the universe became almost instantaneously a massive macrocosm of ordered, compressed, very hot energy. That macrocosm has been expanding and expending that energy since, and there was ever only one direction for it to go—toward a state of lower heat and higher entropy.

But what makes time go at all?

My question is different from the one answered by entropy. I want to know not why time goes in one direction, but simply why time goes.

When you wind a pendulum clock, there is only one direction for the springs to go. They unwind; they do not wind up if left alone. They do not move if left alone, unless and until the pendulum moves. What swings the pendulum? What starts the clock?

If the universe could go in only one direction after the Big Bang, why did it go? Why didn’t the universe stand still without moving forward or backward? Why did the universe go in any direction?

Microcosmic quantum reality is not time as we know it

A physicist might say that the universe is a place of constant quantum activity, with so much inherent quantum evolution of systems or general quantum fluctuation that it is impossible for the universe ever to stand still. The universe must go; the quantum state of the universe demands it.

But the microcosmic quantum world may not follow the arrow of time or depend on entropy in the way prescribed in the macrocosmic world. A quantum wave function describes the probability amplitudes of different possibilities, all of which can remain in a state of superposition in the microcosm. Schrödinger’s cat can be both dead and alive. Without a single, unique state, it has no definite history of unique moments following one after the other. Instead, the cat exists in a state of constant possibility evolving into more possibilities.

It is not until the cat interacts with the macroscopic world that its fate is known—or that it has any fate at all. Without the macrocosm, the quantum world is little more than a soup of constant interaction and simultaneous possibility. And that quantum soup does not have a direct relationship with time or forward direction. At the quantum level there very likely is no time and no direction in time; there is only the quantum wave function.

Time requires more

The quantum microcosm underlies the grand sweep of history, but it is not history. History requires more than a quantum puzzle of entangled superpositions; it requires change and movement, actual unique events, a macrocosmic world evolving over billions of years. History and time assume a quantum wave function that results in more than superpositions with constantly changing probability amplitudes, but instead produces a stream of unique macrocosmic outcomes, a stream of history.

Time measures change and movement

Probability is a function of time, measuring the likelihood of change and movement. At its core the quantum wave function is a probability distribution that both calculates abstract possibilities in superposition and measures the likelihood of detecting an actual event[1] in a particular location and time. It effectively assumes the existence of time as a medium in which probabilities have the potential to resolve into outcomes.[2]

The quantum wave function exists in two phases. In the first phase, when a system is isolated, the wave function exists as superpositioned probability amplitudes evolving according to the deterministic rules of the Schrödinger equation. In the second phase, when a system is not isolated, when the wave function interacts with something distinct from itself—something in the macroscopic world—it evolves in a new and more random way. Instead of a microcosmic wave function of probability amplitudes, it becomes a set of actual probabilities that resolve into one unique outcome in the macrocosm. Essentially, the dice are thrown, resulting in a unique moment in time and history.[3]

We don’t know why or how interaction with the macroscopic world causes probability amplitudes to resolve into outcomes. We don’t know if quantum wave functions “collapse” to produce unique outcomes or if the universe splits into “many worlds” at every quantum intersection. We know only that the universe includes some form of interaction between the macrocosmic and quantum worlds that results in probabilities becoming outcomes—that produces a stream of outcomes.

Quantum wave functions as we know them interact with the macrocosm and resolve calculable sets of probabilities into unique outcomes. Each outcome influences another wave function and another set of probabilities, which resolves again into a new unique outcome. That is how the macrocosm functions today. That is how history progresses. That is how time works.

How did a quantum soup become a macrocosm of history and time?

Perhaps before the Big Bang there was only quantum fluctuation or isolated quantum evolution, with no history and no time. A world of possibilities and probabilities only, without direction, without outcomes, without resolution. There was no spacetime and no macrocosmic world, perhaps only a universal state of complete, unbroken entanglement.

In such a pre-Big Bang universe, there could have been no possible interaction between a macrocosmic world and the microcosmic quantum world. There was only one thoroughly entangled universe with no interactive mechanism for possibilities to become outcomes. Wave functions that interact with a macrocosm, driving the universe forward, resolving probabilities into outcomes—did not exist at all.

Yet that timeless quantum world eventually fluctuated into an explosive state that produced the Big Bang. The result was a macrocosmic world of massive, organized energy with very low entropy, a disentangled universe waiting for a new form of quantum interaction.

Did the Big Bang create both the arrow of time and the engine of time?

If interaction with the macroscopic world causes quantum wave functions to resolve into outcomes, did the state of low entropy that followed the Big Bang set the stage for that macroscopic interaction? Did the Big Bang create just enough separation and disentanglement in the universe to start the chain of collapses and unique outcomes that we know as history? Just enough of whatever it took to cause quantum wave functions to resolve into unique events, pushing all other possible outcomes into the realm of imagination or many worlds? Is the wave function the engine of time?

Does the wave function create the great illusion?

It may be reasonable to think of microcosmic quantum reality as a world of possibilities only—a world where all things are possible, a world that mathematically defines the probabilities of all outcomes. But a world without a mechanism for turning probabilities into outcomes.

It is the macrocosmic world that is about outcomes. The great illusion that is the macrocosmic world may be the mechanism by which the universe creates outcomes. Perhaps when quantum fluctuation caused the Big Bang and created spacetime, that new macrocosm became a Petri dish for a new form of quantum interaction that enabled probabilities to resolve into outcomes, starting the clock of history and birthing the great illusion that we live in today.

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[1] Which may or may not be equivalent to the likelihood of an event occurring in a particular location and time.

[2] A probability and outcome assume movement and change. Something is probable and then something occurs. Does the concept of probability have meaning without the possibility of a future outcome? Perhaps. But is difficult to conceive of a world of probability that would not eventually, in some way, experience an outcome.

[3] Roger Penrose has suggested that this result, called quantum state-vector reduction, could be explained as a gravitational phenomenon in a yet-to-be-specified theory of quantum gravity. “My own point of view is that as soon as a ‘significant’ amount of space-time curvature is introduced, the rules of quantum linear superposition must fail. It is here that the complex-amplitude superpositions of potentially alternative states become replaced by probability-weighted actual alternatives—and one of the alternatives indeed actually takes place.” Penrose (1989), p. 475 (emphasis in original).

Beneath the surface of the great illusion, the universe is seemingly a soup of quantum interaction generating a constant flow of illusory experience on the four-dimensional stage of spacetime. We and all other entities in the universe play out our existence as part of this great drama.

Is the play all about us? Probably not.

For most of our recent existence, we humans have imagined that the great drama is mostly about us. We see ourselves at the center of the universe, brought into existence by a creator who stages the play for our benefit.

We know now that we are not the center. The sun does not orbit around us as we once thought. Our sun’s system is one of hundreds of millions in the Milky Way galaxy, which is one of hundreds of millions of galaxies in the universe. The likelihood that this great expanse exists for our sake seems vanishingly remote.

Are we in the cast?

So if the universe does not exist for our sake, do we at least have a role in the great drama? Absolutely.

We even have an important role, one that we share with all other entities alongside us in the universe.

We make choices. We make decisions. We act and interact. And by doing so, we turn probabilities into reality.

The universe presents us with options every moment of our existence, and from those options we make choices. Every choice transforms a host of probable possibilities into a single outcome. Sometimes we choose the most probable outcome; sometimes we do not. But every choice, action, or moment of awareness adds a unique outcome to the stream of outcomes that shape the drama of the universe.

The play is driven by probabilities, not certainties

We live in uncertainty, both in the macrocosmic world of the great illusion and the microcosmic world of quantum reality. It is not a practical uncertainty, driven by unknowns, but a fundamental uncertainty driven by quantum interaction. The core of our reality is not an endless stream of cause and effect pushing the universe down a wholly determined path. Our universe is about a flow of probabilities and interactions, with every interaction affecting the next set of probabilities. The future can never be predicted definitively in the way we once imagined; it is possible only to know the probabilities for the future. That is fundamental, and it cannot be changed.

Our choices and experiences define future probabilities

Every choice and every experience eliminates other potential options from contention. By choosing among the options and experiencing each moment presented to us, we create information about the universe.[1] Constantly. That is what we do.

Not just us. Every creature or organism that moves or acts or chooses or experiences, even in a rudimentary way—turns left instead of right, flies or walks, jumps or dives, slithers or stays at rest—creates information about the world. Every one of those actions or experiences define what the world is instead of what it could have been.

A philosophizing physicist might suggest that we and other entities help collapse the quantum wave function of the universe. That perhaps every choice or experience collapses the wave function of probabilities for that moment into a single outcome. And that every outcome then affects the distribution of probabilities in the wave function for the next moment.[2]

We help create the future

Like all the other creatures or entities that inhabit the universe, we help transform the universe from probability to reality. We create information about the universe that turns the future into the present. That is our role. The universe needs us to do that.

So we are in the play and the cast. Our role is vital. But it is not unique to us.

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[1] “At any one time, we have precisely one conscious experience out of vastly many possible conscious experiences. Every conscious experience therefore delivers a massive reduction of uncertainty, since this experience is being had, and not that experience, or that experience, and so on. And reduction of uncertainty is—mathematically—what is meant by ‘information’” Seth (2021), p. 56.

[2] A set of probabilities prior to an interaction results in an outcome from the interaction. That outcome then changes the state reflected in the wave function for the very next moment. The world is presented with a new wave function, a new set of probabilities that influences a new interaction and outcome. And the process repeats itself. On and on. Forever. This is how quantum mechanics might describe creating the future.

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