Photons do not emit photons. In fact, photons don't interact with each other at all. But if you send a very short pulse of light (visualized as the thin spherical shell in the video) at an object, the photons in that pulse will hit the object at different times depending on how far away the scattering surface is from the source of the light. After they reflect from the surface, these photons will also take different amounts of time to travel to the camera (your eye). If you can measure the time the photons enter the camera very accurately, you'll see different parts of the scene light up at different times.
This would be very close to watching the light pulse travel across the scene...except for that second effect: that the parts of the scene are different distances from the camera.
>In fact, photons don't interact with each other at all.
They can. It's a non-classical concequence of Quantum Electrodynamics. If you are interested in the cross-sections, check out Berestetskii et al., 1982.
This would be very close to watching the light pulse travel across the scene...except for that second effect: that the parts of the scene are different distances from the camera.