In the last post I talked about time travel to the past. What about time travel to the future?
There’s a boring sense in which we’re all moving into the future at the rate of one second per second. But that’s not what we mean. What about farther into the future than it takes from our point of view? What about Marty McFly traveling from 1985 to today (October 21, 2015) while remaining young. Is that possible?
Yes, it is.
In fact, I’ve been in a time machine that takes its passengers into the future. It cost me several hundred dollars, and it wasn’t very far into the future, but still — I did it.
And in all likelihood, so have you. This marvelous time traveling device is — … — (wait for it) —— … — a plane.
Yes, indeedy. Every time you fly in a plane you time travel to the future. Not much, but it happens.
Einstein’s special theory of relativity tells us that when we’re in motion time goes slower than when we’re stationary. (Of course, motion is relative, which leads a lot of people to puzzle over the so-called Twin Paradox; but we’ll leave that for another day.) General Relativity goes further and tells us that time also slows down when you’re sitting in a gravitational field. So your distance from a heavy body affects the rate at which time goes, and so does the speed at which you travel.
If you get in a plane, the Earth’s gravity is a tiny bit weaker, and you’re also going a tiny bit faster than when you’re walking (tiny in comparison to the speed of light, that is). But that tiny amount can produce a measurable difference in how much time passes for you — if your measurements are extremely precise, that is.
In 1971 a team of physicists demonstrated this by taking a few cesium-atom clocks on a flight around the world. They just bought the clocks a couple seats on commercial airline flights, flew around the world a couple times, and then compared the times to that recorded by the stationary (“twin”) clocks back home. (That’s the clocks there in the picture getting their in-flight peanuts from the flight attendant.)
Of course, the same thing happens (to an even even smaller extent) every time you drive in a car, or even walk. Whenever you move you’re time-traveling to the future. You get to dinner a bit faster (i.e., it takes you less time to get to that event) if you take stroll, rather than sitting in your house.
If you wanted to travel farther into the future, you’d just have to go faster. Once you get close to the speed of light, you’ll start to get some noticeable differences between the amount of time you’ve spent, and the amount of time your layabout friends have consumed.
This demonstrates a fairly general point: It is often the case that the dreams of science fiction turn out to be possible in principle, but so impractical that we lose interest in them.
For example, consider transmuting lead into gold: the dream of the alchemists. We can actually do it now. So why aren’t we excited?
Because it requires a particle accelerator that smashes together single atoms. It takes a huge amount of energy and results in only a few atoms of gold. Not so thrilling. Same thing with time travel. We all do it all the time. But the effects are much smaller than we might have wanted.
Still, you can truthfully tell your friends that you’re a time-traveler from the past. (I think I had a link to a story along these lines a while back.)