How fast are laser beams

Bouncing lasers off mirrors on the lunar surface is an old trick. Astronauts walking on the moon first left reflectors behind in This laser, visible to the naked eye at night, produces ten pulses per second. Out of the thousands of photons bombarding the moon, few will return to Earth and be captured by the telescope. A round trip journey of roughly , km that takes 2.

While traveling through the vacuum of space, laser beams are invisible unless shot directly into your eye. The vacuum of space does not have anything to reflect the light back into your eye. Sign in Register. Enter e-mail address Show Enter password Remember me. Sign in to Unlock all the content on the site Manage which e-mail newsletters you want to receive Read about the big breakthroughs and innovations across 13 scientific topics Explore the key issues and trends within the global scientific community.

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Each flash of light is an isolated event, and they only create the illusion of movement collectively. Now, imagine shining a laser pointer straight out into infinite space. You don't see the laser dot projected anywhere because there is no end to this room. Now, imagine you are shining the light parallel to an infinite wall. Turn your wrist so the laser pointer intersects the wall. At what point does the laser pointer intersect the wall?

It can't be at infinity, because that would take infinite time. But it also can't be right next to you — it has to be at some point between you and infinity.

But according to Nemiroff, if you choose a finite point where the light should be, the beam must always be just beyond that point, one step closer to infinity. In fact, the spot of light must always be in two places at once. Because the photon must be in two places at once, Nemiroff explained, something very bizarre happens: Two points of light appear on the wall, moving in opposite directions — one away from you and one toward you.

One point of light is traveling more slowly than the speed of light, while the other appears to be moving faster. As with the laser pointer projected onto the ceiling, this is an illusion. It is not a single photon traveling faster than the speed of light. This creates a burst of light, which Nemiroff calls a "photonic boom" because it is similar to the sonic boom that occurs when an object exceeds the speed of sound and overtakes sound waves.

Nemiroff provided the technical details for this scenario in a paper that is now available on the preprint website arXiv. In the paper, Nemiroff argues that these photonic booms exist in nature.