What Is Time? Quantum Mechanics, General Relativity Place Fundamental Limits On Our Ability To Measure Time

What is time? The complexity of this deceptively simple question was aptly highlighted in the fourth century by Saint Augustine when he said: “If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know.”

You’d think nearly 1,600 years later, we’d know better, but despite our best efforts, we haven’t gone beyond witticisms like “time is what happens when nothing else does.” We still can’t define what time is, we still don’t know what gives direction to the arrow of time, and we have no idea if the flow of time from the past to the present to the future is something that is highly subjective or an essential quality of reality.

Read: The Arrow Of Time: Why Do We Remember The Past But Not The Future?

As if things weren’t complicated enough, the picture is further muddled when we take the principles of quantum mechanics and general relativity into consideration. A study published in the latest edition of the Proceedings of the National Academy of Sciences, which has done so, has now revealed a fundamental limitation in our ability to measure time.

“Our findings suggest that we need to re-examine our ideas about the nature of time when both quantum mechanics and general relativity are taken into account,” study lead author Esteban Castro from the University of Vienna and the Austrian Academy of Sciences said in a statement.

The study builds upon two fundamental properties of the universe. One, that at its deepest level, nature is inherently uncertain (as described by Heisenberg's uncertainty principle), and two, that the flow of time is disrupted by the presence of masses or sources of energy (as described by Einstein’s general theory of relativity).

If we combine the two, we find that the more precise a clock is, the larger its energy uncertainty. The larger the uncertainty in energy, the larger the uncertainty in the flow of time in the clock's neighbourhood. Therefore, the more precise a given clock is, the more it “blurs” the flow of time measured by neighbouring clocks.

“Putting the pieces together, the researchers showed that clocks placed next to one another necessarily disturb each other, resulting eventually in a ‘blurred’ flow of time,” the University of Vienna said in the statement. “This limitation in our ability to measure time is universal, in the sense that it is independent of the underlying mechanism of the clocks or the material from which they are made.”

For the time being, it would seem that when it comes to explaining the nature of time, Saint Augustine is closer to truth than anyone else.