A Series About Time: Reality or an Illusion? Part II: Physicists Point of View

As an operational definition of time, we use a number of repetitions of a standard cyclical event (the phases of the moon, movement of the sun, radiation cycles of a 133Cs atom). This is very useful, as well as in daily life as in advanced experiments. To describe an event, typically we use location (position in space) and time.

Light takes time to travel; therefore, what we experience is already the past. Our belief what is happening now has already happened according to the clock. The sun shines, but the light we see left the sun 8 minutes ago. And there is time our brain needs to reconstruct what we see and sense, which takes about eighty milliseconds. The past is the set of events that can send light signals to an entity, and the future is the set of events to which an entity can send light signals.

But how about the present, how about now? A now would be a class of instances that occur at the same time. But because Einstein showed that time is relative to a reference frame, there are different nows for different reference frames, so the notion of now is not frame-free and thus is not objective.

There is something essential about the Now which is just outside the realm of science.

Einstein

Einstein’s theory of relativity has had the most significant impact on our understanding of time. The theory implies that two synchronized clocks will disagree on their readings once they move relative to each other or undergo different gravitational forces. Because of this latter influence, a clock in a car parked near your apartment building runs slower than the stationary clock in an upper floor apartment because the upper floor feels a weaker gravitational force from the earth. Clocks at the top of Mount Everest pull ahead of those at sea level by about 30 microseconds a year. The following example can explain the effect of speed. If you move away from a clock with a certain speed, the light of the clock will take longer to reach you. So it appears that the clock will move slower. The faster you move, the slower the clock will be. Theoretically, if you would travel at the speed of light, the clock would not move at all. Effects on time by speed and gravitation are called time dilation effects. They affect all clocks, even biological ones.

Till now it was believed that time and space existed by themselves, even if there was nothing — no Sun, no Earth, no stars — while now we know that time and space are not the vessel for the universe, but could not exist at all if there were no contents, namely, no Sun, no Earth, and other celestial bodies.

Einstein

But then, in his Nobel Prize acceptance speech, Einstein backtracked on this and said time and space could continue to exist without the Sun, Earth, and other celestial bodies. He claimed that, although relativity theory does rule out Maxwell’s aether and Newton’s absolute space, it does not rule out some other underlying substance that is pervasive in space. All that is required is that if such a substance exists, then it must obey the principles of relativity. Soon he was saying this substance is space-time itself — a field whose curvature is what we call gravitational force.

This can sound strange, but we are slowly moving into the realm of philosophy, where the ideas are getting even more interesting. The theoretical physicist Max Tegmark (and others) say that time is not as a line, but time is as a branching tree. At each next instant, the universe splits into new universes, all of which have a common past. So, there is one you now in our universe, but at the next instant, for any of the, say, 9,999 things that could happen now in the next instant here, there come into existence 9,999 new universes, each with its own counterpart of you, and so on for the next instant in each of those universes. Each counterpart of you has the same right to be called the real you as any other. These branches of time do not show up in ordinary human experience. This hypothetic realm containing every possible `now` is called Platonia or World of Forms.

Rovelli posits that reality is just a complex network of events on which we project sequences of past, present, and future. The whole universe obeys the laws of quantum mechanics and thermodynamics, out of which time emerges. Forward in time is the direction in which entropy increases and in which we gain information. Einstein showed us that time is just a fourth dimension and that there is nothing special about ‘now’. The malleability of space and time means that two events occurring far apart might even happen in one order when viewed by one observer, and in the opposite order when viewed by another. At our level, each of those events looks like the interaction of particles at a particular position and time; but time and space themselves really only manifest out of their interactions and the web of causality between them.

To put it in other words, time is not a cause, but a product. Rovelli argues that our perception of time’s flow depends entirely on our inability to see the world in all its detail. (Rovelli, 2019)

In the third and last part about time, I will discuss about time from the philosophical point of view.

Interesting links:

A Series About Time: Reality or an Illusion? Part I: History and Culture

A Series About Time: Reality or an Illusion? Part III: Philosophical Point of View

Reference

Rovelli, C. (2019). The Order of Time. Riverhead Books.

You think this is a worthy blog and you want to read more?