Speed of light a laser beam is swept quickly across a distant object, the spot of light can move faster than "c", although the initial movement of the spot is delayed because of the time it takes light to get to the distant object at the speed "c". However, the only physical entities that are moving are the laser and its emitted light, which travels at the speed "c" from the laser to the various positions of the spot. Similarly, a shadow projected onto a distant object can be made to move faster than "c", after a delay in time. In neither case
Variable speed of light of light is not constant. In quantum field theory the Heisenberg uncertainty relations indicate that photons can travel at any speed for short periods. In the Feynman diagram interpretation of the theory, these are known as "virtual photons", and are distinguished by propagating off the mass shell. These photons may have any velocity, including velocities greater than the speed of light. To quote Richard Feynman "...there is also an amplitude for light to go faster (or slower) than the conventional speed of light. You found out in the last lecture that light doesn't go only in straight lines; now, you