# Do photons at light speed stop time?

18 March 2014

## Question

Does time stop for photons travelling at the speed of light?

Tamela - He's probably been studying relatively longer than I have, but I'll do my best. So, absolutely right. If the particle is approaching a speed of light and had a clock on it, we as observers of that particle going extremely fast would see that time slows down and approaches this sort of eventual stopping. It is impossible to imagine the frame of reference at the speed of light- special relativity doesn't really deal with that. It takes the speed of light as a constant and that's regardless of what speed you're going at. So, even if you're 99% at the speed of light, you're still measuring c as c. So in that sense, it is difficult to answer what kind of time is the photon experiencing. But just to say that if you were a particle, maybe at 99% at the speed of light, in your own frame of reference, time is moving normally. You have a much faster ticking clock compared to the observer that sees that time has nearly slowed down. Actually, you've probably heard of this, but we've experimentally confirmed time dilation here on Earth. There was an experiment back in the '70s that put these atomic clocks on commercial aircraft and had them fly around the Earth, both in the eastward direction and the westward direction, and we're able to compare, once they got back on Earth with sort of naval observatory clocks. Actually, there was this difference because they were moving faster than the Earth's rotation at some point.

Chris - The great pyramids also distort time because they're very massive and so, they bend space time. So, time travels at a different rate.

Tamela - Exactly, yeah.

Chris - Yes, which that really does blow my mind - the whole concept of you going near something very massive and time changes. So, you go to Egypt, sit next to a pyramid and actually, time is distorted. So maybe the Egyptians were on to something when they said that they were going to try and make their pharaohs immortal because relative to the rest of us they are ageing more slowly.

Tamela - To extend this even further, if you go to a black hole and kind of start falling into a black hole, you're observer is seeing that time has nearly stopped for you as you fall towards it because you've warped that time so much. So yeah, lots of interesting things going on.