Physicists increasingly doubt that time has any independent existence. Let’s look at this afresh.
We could start with a paradox known as “the Arrow,” first described 2,500 years ago by the philosopher Zeno of Elea. Beginning logically with the premise that nothing can be in two places at once, he reasoned that an arrow is only in one specific location at every moment of its trajectory. Logically, then, motion per se is not what is really occurring; rather, it is a series of separate events. This may be a first indication that the forward motion of time – of which the movement of the arrow is an embodiment – is not a feature of the external world, but a projection of something within us, as we tie together things that we are observing.
Philosophers, who have long questioned the reality of time, argue that the past exists only as ideas in the mind, which themselves are neuroelectrical events occurring strictly in the present moment. The future is similarly nothing more than a mental construct, an anticipation, a grouping of thoughts. Because thinking itself occurs strictly in the “now,” where is time? But does time exist apart from human concepts of motion and events? Or is it all an “eternal now” that includes our mind’s tendency to think and daydream?
Physicists, for their part, find that all working models for reality – from Newton’s laws and Einstein’s field equations through quantum mechanics – have no need for time. They are all time-symmetrical. Time is a concept looking for a function – except when we’re speaking about a change, as in acceleration. But change is not the same thing as time.
Scientifically, time appears to be indispensable in just one area: thermodynamics, whose second law has no meaning at all without the passage of time. Thermodynamics’ second law describes entropy (the process of going from greater to lesser structure, like the bottom of your clothes closet).
Consider a glass containing club soda and ice cubes. At first, there is definite structure. Ice is separate from the liquid, and so are the bubbles. But return later and the ice has melted, the soda has gone flat and the contents of the glass have merged into a structureless oneness. Barring evaporation, no further change will occur.
This evolution away from structure and activity toward sameness, randomness and inertia is entropy. In classical science, entropy does not make sense without a directionality of time, because it is a non-reversible mechanism. In fact, entropy defines the arrow of time. Without entropy, time need not exist at all.
But many physicists question this “conventional wisdom” regarding entropy. Instead of the act of structure-loss and disorganization representing a concrete directionality to time, it can just as well be seen as a demonstration of random action. Things move. Molecules move. They do so in the here-and-now. Their motions are haphazard. Before long, an observer will notice the dissipation of the previous organization. Why should they then assign arrows to it? Shouldn’t we regard such random entropy as an example of the non-essentiality or unreality of time, rather than the other way around?