system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why can't we see lasers from things like laser pointers until they've hit a surface?

I was fooling around at work with a laser thermometer and this crossed my mind. If the lasers are invisible to the human eye then why can we see them once they've hit a surface, such as a table?
gpt
You can only see light that enters your eyes. The light in a laser beam is traveling away from you and not entering your eyes so you can't see it. When it hits a surface, the light gets reflected and some of it does enter your eyes so you can see it. 

If you fill a room with smoke or fog then you can see the beam because the smoke/fog is scattering the light. Powerful enough lasers are visible in plain air because the air itself is scattering light.

Of course, this only applies to lasers that generate visible light. There's nothing you can do to see the light from an infrared laser with the naked eye.