WHAT IS TIME?

It’s a serious question. One scientists aren’t all that good at answering.

The legit-accepted definition in the scientific community is that time is “what clocks measure.”

This definition comes from the 1974 book, Physics by Donald G. Ivey and Patterson Hume. Ivey hosted The Nature of Things, a Canadian TV show in the 1960s, so he’s known for breaking complex science into simple takeaways.

But it’s hard not to think his definition of time borders on the obtuse.

Classical physics holds that time and space—equally difficult to describe—are separate forces of nature.

Einstein’s theory of special relativity intertwines the two in a single framework called spacetime.

The theory of special relativity is how we figure your watch runs in a time warp.

Still not much of an answer.

By 1927, British astronomer Arth Eddignton had identified the one-way direction of time flowing from the past towards the present. This became known as the “arrow of time.”

Steven Hawking gets in on the fun, too, because we need all the brilliant minds to still not totally explain what time is. Hawking is now mostly notable for begging us to avoid alien contact—they’d probably kill us—but he does a decent job of describing the three arrows of time:

The psychological arrow of time is our perception of time’s unstopping passage.

The thermodynamic or “heat and energy” arrow of time is distinguished by the growth of disorder, known as entropy, as stated in the second law of thermodynamics.

The cosmological arrow of time is distinguished by the expansion of the universe—i.e., the universe is approximately 13 billion years old—as measured from the Big Bang.

None of this is very satisfying in a concrete sense, which is probably why most conversations careen towards the metaphysical. The science of time is hard.

In the end, Ivey and Hume are right to keep it simple. Time is what clocks measure. Or, of course, watches.