Moment of Science: Time Dilation

Last week, we touched upon E=mc2, and how Einstein’s theory of relativity turned the world of physics upside-down. Now, we’re using that theory to show why the very concept of time may not be what you think it is.

The story goes that a teenaged Einstein boarded a tram in Bern, Switzerland after a day’s work, and looked up at this intricate clock. The thought consumed him: What would happen if the tram were moving away at the speed of light? Your watch would keep going like nothing happened, but if you look back at the tower, it appears as if the clock freezes and time stops, since the light coming from it is moving at the same speed as the observer. On a larger scale, those twinkling stars at night are giving off light that can technically be a glimpse many years into the past, since it does take a set amount of time to get here. Einstein had a dilemma: either Newton’s laws of motion were wrong, or the speed of light wasn’t constant. He ended up tweaking Newton’s theories by saying that time has to slow down for lightspeed to remain constant.

Welcome to the mind-bending world of “time dilation” and for the second week in a row, don’t panic, we’re gonna walk you through it. All this formula says is that time is relative to how you look at it. That dilation calculation takes the time if you weren’t moving, and uses that handy little bit below the line to figure out the fraction of the speed of light you ARE moving at. It’s easier in action: Let’s say you’re in a spaceship moving at 10% of the speed of light for an entire year. That math works out so that you experience nearly 44 hours less time having passed, compared to if you’d been stuck on Earth the whole time. How about 99% the speed of light? One year to you would be 7 years on Earth, like “dog years” for humans.

But wait, there’s more! Speed is one factor... gravity can be another. All those sci-fi shows about time slowing down around a black hole have some truth to them... keyword, some. A strong enough gravitational field can bend spacetime, and NASA says if put a clock 10 km above a black hole with same mass as our Sun, it would take 70 Earth minutes to read a full 60 on the clock. Closer to home, GPS satellites could give you results inaccurate by miles if they didn’t account for time dilation. Their orbital speed means they have to knock off 7 microseconds a day to make it work, but add 45 microseconds to account for the pull of Earth’s gravity (and lack thereof). That gravity also means someone living high in the Rockies all their life is technically younger than someone in Toledo, and unless you’ve spent most of your life upside-down, your head is just the tiniest bit older than your feet.

Good science fiction is grounded in good, if not downright weird, science, and if you have any further questions, I hear NASA has email these days.

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