The Sun and Earth from the ISS. While Earth’s light is less than a second old, the Sun’s is more than eight minutes old. Image credit: NASA / International Space Station.

How do photons experience time?

We see them change in wavelength, energy and in their electric and magnetic fields over time. So how do they experience it?

“Everyone has his dream; I would like to live till dawn, but I know I have less than three hours left. It will be night, but no matter. Dying is simple. It does not take daylight. So be it: I will die by starlight.” –Victor Hugo

Traveling at the speed of light, photons emitted by the Sun take a little over eight minutes to reach the Earth. The 93 million mile (150 million km) journey across the expanse of empty space is no obstacle to this light, but it means that when we look at the Sun, we’re seeing it as it was a short time in the past, not as it is instantaneously from our perspective. If the Sun were to wink out of existence right now, we wouldn’t know it — not from its light, not from its gravity — until eight minutes later. But what about from the photon’s point-of-view? We know that if you travel close to the speed of light, Einstein’s theory of special relativity kicks in, and time dilates while lengths contract. Photons, however, don’t move close to the speed of light but rather at it. So how much has a photon emitted by the Sun aged by time it reaches the Earth?