Time isn’t quite as straightforward as we think. We tend to work by the clock, punching in at 9 and heading home at 5, and in that span our experience of time doesn’t change (though it seems to slow down before the weekend). In reality, though, according to our understanding of physics and general relativity, time changes. Time dilates. Here’s how it works:
1. The speed of light is constant.
The speed of light is an important number in physics and lies at the basis of many of our theories. It is used in equations as the number c, and the value is 299,792,458 meters per second. The speed of light is a constant, which means it never changes.
2. Velocity factors into time dilation.
Nothing can go faster than the speed of light. As such, when something begins to move faster, it experiences time differently than something that moves more slowly. This speed is relative to the speed of light, so something that moves closer to the speed of light experiences slower time.
3. What does this look like in the real world?
Two atomic clocks were synced up and one went for a speedy ride in a plane while the other stayed on the ground. When the clock that was moving faster came back, it was slightly behind the one that hadn’t gone anywhere. In addition, astronauts “fall behind” our time since they’re moving faster in the International Space Station than we do on Earth.