Eli5 If you shine a laser up in the sky for ~3 seconds, does the beam eventually fizzle out or does it keep going until it hits an object?

Question

Eli5 If you shine a laser up in the sky for ~3 seconds, does the beam eventually fizzle out or does it keep going until it hits an object?

In: 5

Answer 1

Both, actually. It fizzles out precisely because it’s hitting stuff as the laser propagates through the atmosphere. If the beam was perfectly collimated, then yes, there’s nothing internal to the laser that would cause the beam to spread out and diffuse. But in reality, the laser gets bent by air at different temperatures, absorbed by water vapor, particles in the atmosphere, etc…