The Moon, the planet Jupiter, and the star Aldebaran form a long, skinny triangle in the eastern sky at first light tomorrow. Jupiter looks like a brilliant star, to the upper right of the Moon. Fainter Aldebaran is the same distance to the lower left of the Moon.
The three bodies are at different distances from Earth. That means we see them as they looked at different times: a little more than a second ago for the Moon, 40 minutes for Jupiter, and 65 years for Aldebaran.
That’s how long it takes the light to reach Earth from our perspective. But from the perspective of the light itself, there’s no difference at all.
Light travels in “packets,” known as photons. They move at the speed of light — 186,000 miles per second. Albert Einstein’s theory of special relativity says that, as measured by an outside observer, time doesn’t pass for anything moving at lightspeed. From a photon’s perspective, it’s born, it races through space, and it dies in the same instant.
Relativity says that clocks tick at different rates for objects that are moving at different velocities. But an object needs to move at a big fraction of the speed of light for the effect to become noticeable. And at the speed of light, the clock wouldn’t tick at all.
So, on our clocks, a photon that leaves Aldebaran tonight will travel 65 years to reach Earth. But for the photon itself, when it hits the eye of a skywatcher in 2088, no time will have passed at all.
Script by Damond Benningfield