One of the coolest things I’ve learned this year has to do with time. I don’t mean how to make it stand still when I’m drinking a Frappuccino, or run faster during ads and trailers at the movie theater, but something even harder to imagine. When it comes to Einstein, my flailing intellect can only grasp his ideas with scrabbling fingernails, but here’s what I understand.
Time is a property of the universe, just like mass or energy. It’s not the fixed, immutable thing we perceive it as. We commonly employ adages like, “A watched pot never boils,” or “Time flies when you’re having fun,” but we all understand these to be figures of speech: acknowledgments of the subjective feel of time despite its constancy. In fact, the passage of time does vary, and it does so in two main ways. Hold on to your seat: here’s the freakiest, wildest thing I’ve learned lately.
Time moves more slowly the closer you are to a massive object. Yep, read that last sentence again; it’s worth it! Gravity affects how time moves, so the closer you are to Earth, or any other massive object, the slower time moves. GPS satellites actually take this into account and correct for it. If they didn’t, GPS devices would become unreliable pretty quickly. Of course such differences are extremely slight, but astronauts like Chris Hadfield who’ve spent extended time in space, are infinitesimally younger than they would have been had they stayed on Earth.
The other way you can change your interaction with time is to travel really really fast. The closer you get to the speed of light, the slower time passes for you. Any self-respecting science fiction fan knows this of course. If you left Earth in a ship that could travel close to the speed of light, you would come back to Earth after one year to find that many years had passed for the people you left behind. I won’t embarrass myself by trying to explain or give equations to support this, but the ideas are verifiable by people a lot smarter than me.
I used to amuse myself by trying to get an obsessive/compulsive friend wound up about the idea of a base ten clock. “Why,” I would ask keenly, “should we tolerate all this 60 seconds, 12 hours nonsense? Why not divide the day into ten segments, then divide those into ten segments? That way calculations involving time could be done with decimals.” Although maniacal about metric and other expressions of logic in measurement, my friend remained unmoved.
Time is fixed; we can’t mess with it. This conclusion, drawn from observation of a hard-liner, is borne out by 5000 years of history. It was the ancient Egyptians who first divided day and night into 12 hours each. The love of the number 60 came from the Sumerians, who used a base 60 numbering system called sexagecimal, which doesn’t refer to a hot night with a mathematician. The Greeks introduced minutes and seconds, and once mechanical clocks were invented around the 14th century, these divisions of time got standardized. Essentially, our concept of time is so unquestioning that constructs around it have lasted for 5000 years.
With our great cleverness in inventing digital watches and cesium clocks, we’re surer than ever that time is objective, immutable. Is it? A friend recently described a dangerous mishap he witnessed on the ski trails, and tried to convey how time slowed down at the instant between when he saw something bad was going to happen, and when it actually happened. This is a commonly reported experience in a crisis, and while I’ve never experienced it, it makes me wonder: what’s happening there? What if we could control that? Further muddying the temporal waters, there are about eight minutes per decade that have an extra second, in order that atomic clocks stay synced with astronomical time. (Fortunately for me this is a blog and not a live talk, so no one can ask me to explain that.)
We go through our days relying on a myriad of unexamined assumptions about how the universe works. This is a good thing: otherwise we’d never get anything done. The nature of time is one such principle. There’s no practical reason for non-physicists to think much about it, but it’s one of those arcane concepts that’s fun to shake up now and then.