Photons, being massless particles, cannot be at rest. They always travel at the speed of light, which is approximately 299,792,458 meters per second (m/s) in a vacuum.

Here's why:

* Special Relativity: Einstein's theory of special relativity states that the speed of light in a vacuum is constant for all observers, regardless of their own motion.

* Energy and Momentum: Photons have energy and momentum, even though they have no mass. Their energy is directly proportional to their frequency, and their momentum is inversely proportional to their wavelength.

* Zero Rest Mass: Because they have no rest mass, they can't exist in a state of rest. They are always moving at the speed of light.

Let me know if you have any other questions!