Classical physics says time is reversible because its laws hold true whether time flows forward or backward. Thermodynamics says time only flows forward, because were it to reverse, entropy of an isolated system could decrease which would violate the second law of thermodynamics.
So is time reversible or irreversible? The answer cannot be deduced from either classical physics or thermodynamics because both are flawed in their assumptions.
Classical physics only deals with deterministic systems whose past, present, and future are entirely contained in a single timeless equation. As a result, for such systems time does not exist except as spatial increments marking the various aspects of a static pattern frozen in eternity. Moving one way or another on a static pattern does not change it, and for this reason the laws of classical physics hold true regardless of whether the time variable is positive or negative. Because time is not an intrinsic part of deterministic systems, classical physics has nothing valid to say about the real nature of time.
Thermodynamics is a statistical science that calculates trends rather than individual events. This means it sweeps complex molecular motion under the rug and only makes observations about the resulting lump. It is important to remember that according to classical physics, molecular motion is deterministic, implying that thermodynamic systems must also be deterministic because they are merely collections of deterministic molecules. If the components of a system are time reversible, then so must the system itself.
So why does thermodynamics claim time is irreversible? Because due to the overwhelming complexity in keeping track of every deterministic molecule, it is forced to ignore this level of precision where reversibility resides.
The illusion of time irreversibility in thermodynamics arises from two problems:
1) its inability to calculate a system with absolute precision, which prevents it from mathematically confirming time symmetry, and
2) that its laws are based on incomplete statistical observations and assumptions.
Time symmetry or reversibility requires that the laws of a system in question do not change when time is reversed. In classical physics, this is easy to check because past and future of a system can be calculated with absolute precision. But thermodynamics cannot completely know the total characteristics of a system because its molecular details are too complex to take into account. So it cannot even compare the forward and reversed systems to check for symmetry because they are too complex. On this point alone, thermodynamics is therefore inconclusive about the nature of time.
Resorting to statistical observations, it forces a match between limited laboratory observation and mathematics by fatally assuming that instead of collections of deterministic particles, things are made of perfect fluids. This is done as a matter of practicality to smooth over the randomness of molecular motion, which unfortunately throws out its inherent deterministic and time reversible nature.
Assuming a perfect fluid is like assuming that each family in America has exactly 1.3 children, to match the national statistic. While this is a neat mathematical device, when it gets taken too seriously any family’s claim to have two children is seen as an impossibility because it would “violate the statistical law.”
Likewise, when time is reversed and entropy decreases, the resulting violation of the second law of thermodynamics should be no cause for alarm because the second law is only a unique statistical trend, not an absolute pillar of physics as its supporters claim. It seems universal only because the mathematics apparently support it, but remember that the math in thermodynamics is built upon the assumption that systems are made of perfect fluids.
While the systems to which science has restricted its observations do show increasing entropy, this says nothing about the ignored systems. What applies to the minority need not be universal for the majority. In truth, a decrease of entropy violates nothing because it is not an impossibility – it simply has lower probability than were the system to increase in entropy. Therefore, the mathematical and observational proof in thermodynamics are insufficient to claim that time is irreversible.
So how do we determine whether time is reversible or irreversible, being that classical physics and thermodynamics have now been eliminated from the debate? We see that thermodynamics is on the right track – stated another way, time seems irreversible because the future is more uncertain than the past. While the past can be clearly observed from observation of what transpired in a system, if calculations are unable to perfectly predict the future as well, the future will seem murkier. So the future seems always “in the making” which gives rise to an apparent forward flow of time.
But this murkiness of the future is only due to incomplete information concerning the individual particles of a thermodynamic system. Were we to know them in detail, we could indeed see that the future is as certain as the past and that time in that case is reversible. The nearsightedness of an observer says nothing about the intrinsic fuzziness of the object observed; that science cannot determine the future state of a system does not mean the system itself is nondeterministic.
It should now be clear that only nondeterministic systems are time irreversible. Time cannot be symmetric in systems whose future is not already contained in some tidy equation connecting it with the past.
Do such systems exist? Yes, quantum processes are nondetermistic by nature. What state a wave function collapses into cannot be predicted mathematically. Quantum mechanics is a lot like thermodynamics in the sense that its laws deal with the statistical trends of random processes, except there is one crucial difference: the unpredictability of a quantum system comes not from shallowness of an observer’s perception, but on the intrinsically nondeterministic nature of the system itself.
Then how exactly does time arise? By consciousness sequentially choosing which aspects of quantum wave functions to manifest as physical experience. Choice is nondeterministic because were it not, it would already be pre-decided, leaving no choice. Choice necessitates freewill, so the irreversibility of time ultimately stems from freewill being neither predictable nor easily undoable.
Perhaps this sounds like new age mumbo jumbo to you, but all this is self evident from the mathematics of quantum mechanics. There are no hidden variables in quantum theory, only those created on the spot by conscious selection. Nothing in quantum physics contradicts this idea.
The phase of a wave function is entirely “arbitrary” according to physics, and it is precisely this phase that creates huge consequences for how a time-dependent wave function evolves and interacts with other wave functions. In truth, this phase factor is not arbitrary, but deliberately chosen at some level of consciousness because being detached from the deterministic (statistical) parts of quantum theory, phase is left entirely at the discretion of choice. This shows how mind ultimately affects physical reality, not by violating its classical laws, but by working through nonlinear systems to amplify “arbitrary” quantum fluctuations into macroscopic effects.
Time dependent wave functions show how consciousness creates time. The only reason they appear to evolve through time is that they consist of multiple stationary states (wave functions independent of time) whose various phases change to produce a “moving” wave function. But these phases are chosen by consciousness, and since it is the phases that give rise to the seeming time-dependence of a wave function, it should be beyond debate at this point that consciousness creates time.
Furthermore, once a wave function has “collapsed” (one disc of the jukebox selected to be played), it cannot “uncollapse”. The collapse of a wave function is not time reversible because mathematics cannot calculate it equally well forwards and back. Only linear systems which are perfectly predictable are time reversible. So once more, time is irreversible when, and only when, it comes to quantum systems and freewill choice.
How does all this fit with the systems of classical physics? Classical systems are merely series of deterministic effects, while conscious choice is the original nondeterministic cause.
The interval between deterministic events is known as linear time, which is illusion for the simple fact that the span between first and last effect is redundant and thus nonexistent except to the observer choosing to observe it as real. Deterministic systems appear to move only because our consciousness slides its observational focal point along the eternally static pattern of the system, not because the system itself is changing.
As an analogy, the songs on a CD do not change with time because they all exist simultaneously as data on a disc, and any illusion of time between beginning and end of a song arises solely from them being played as such. When a CD is played, it progresses at a default sequence, direction, and speed – but these can be changed if one chooses to skip tracks, increase the speed, or listen to it backwards, all without actually changing the CD itself.
True time does not span intervals of deterministic sequences, but rather intervals of freewill choice. If consciousness were to choose to view the static pattern backwards, sideways, or in jumps, then that is perfectly permissible. The term “irreversible” only means that there exists a tendency for time to progress in the direction that conscious choices are made.
Thus, reality progresses in piecewise deterministic jumps. This can be compared to how road trips consist of roads and intersections. What roads have been traveled determine which new roads are available at an intersection, but not which particular road will be chosen. Quantum physics equations show what roads are available, but consciousness ultimately decides which to follow.
And so it is with reality – the choices we make determine what choices are available, but not which ones we’ll end up making. Thus, classical and quantum processes interact to give rise to the rich dynamic fractal we call life.