In his book The Hitchhiker’s Guide to the Galaxy the author Douglas Adams’ character Ford Prefect states that ‘time is an illusion, lunchtime doubly so’. It turns out that Douglas Adams was more prescient than he perhaps imagined.
In contemporary quantum physics the nature of time is hotly debated and is generally unknown – an illusion perhaps. In her YouTube video Sabine Hossenfelder presents an overview of the current scientific understanding of What is Time.
It turns out that time is an enigma. We all think we know what it is, but our imaginings have no basis in science. We know that we can recall the past and only anticipate the future but beyond this our certainty evaporates.
From a scientific perspective time is imagined as a coordinate of the spacetime of General Relativity, Einstein’s theory of gravity. For macroscopic systems this kind of time may be adequate, but it seems that at the atomic scale where quantum theory applies, elementary particles operate without a knowledge of time. Indeed, they behave the same whether time runs forward or backward.
In our macroscopic world we measure time using clocks of various kinds. In this way we are made aware of the passage of time and the notion of causality where an action precedes a result. In the quantum world this relationship does not hold, we often see the consequence of an action occurring before its cause.
A scientific hero of mine, Emmy Noether discovered that the physical principle of the conservation of energy was the consequence of time reversal symmetry. She also discovered other physical conservation laws that were the consequence of other symmetries, Noether’s Theorem. This theorem is at the center of modern theories of the four forces of nature.
When it comes to clocks, we must take extreme measures to synchronize them together to establish a universal time. We are all familiar with the time zones of our daily lives, particularly when scheduling when to watch a sports event in another zone. What our human experience is mostly blind to is that clocks are subject to Einstein’s relativity, both special and general.
If we put an extremely accurate atomic clock in an aircraft and fly it at high speed, we notice that it seems to run slower than a matching atomic clock that is kept on the ground because of Special Relativity. We also note that an atomic clock that is carried into space some distance above the earth runs faster than one on the surface because of General Relativity. Both effects must be accounted for in the GPS satellites that we rely on for navigation. The system would otherwise be very inaccurate without the correction.
There does seem to be some connection between the direction of the flow of time and entropy, but entropy does not seem to be an explanation of the nature of time, especially when causality is compromised.
So far, our scientific explanations for the nature and origin of time have not yet produced a solution with wide acceptance in the scientific community. Some day we may have an answer, but it doesn’t appear that the answer will happen soon.
