Eli5: If a laser is shined into space will it continue to infinity (if it doesn’t hit a solid object)?


Seems like a gargantuan, if not infinite amount of energy would be required for this to occur

In: 10

Technically yes, it doesn’t just stop somewhere. However, the beam will widen and so lose strength.

If it does not hit *anything*, yes.

It does not need a solid object, even a gas molecule could take out energy from a light wave.

That said, it actually takes no energy at all. It’s pretty easy. The conservation of energy says, that as long as you do not have any force counteract, there is not energy needed to continue whatever you are doing.

A laser beam consist of photons. Space is almost empty but not completely empty. There are a few atoms per cubic meter in interstellar and intergalactic space. So your beam gets eroded when your photons collide with some atoms. Eventually photon count on your beam reaches to zero and you have no longer have a laser beam.

It doesn’t take more energy to go further because it doesn’t use any up traveling. It’s just a clump of energy that happens to be moving in the same direction.

Same as how you can see stars for a super long distance, but it requires less energy because it’s only moving in a specific direction instead of everywhere.

It won’t. Outer space isn’t a perfect vacuum. Some of the photons of light will hit stray bits of matter and scatter and be absorbed. Eventually, it won’t be much of a beam anymore. Light has a finite velocity so it cannot literally travel to infinity without an infinite amount of time.