Do Photons Have A Limit?

[TheoreticalCheckmate]

Why does light , even on a dark night just seem to disappear ? Why doesn't it just continue on into space forever. Please explain.

[Sensei]

Why does light , even on a dark night just seem to disappear ? Why doesn't it just continue on into space forever. Please explain.

 

That's not entirely correct.

 

Photons are going in space forever, but until being absorbed by some particle or molecule. In Earth environment we have air atmosphere with molecules of Nitrogen and Oxygen and a few others in much smaller concentration that interfere with light.

 

Scientists are pointing strong laser at Moon, where is retroreflector, leaved by Apollo astronauts,

http://en.wikipedia.org/wiki/Retroreflector

and some photons come back to Earth ~2.6 seconds later.

 

Are you familiar with inverse square law?

http://en.wikipedia.org/wiki/Inverse-square_law

Even if beam of laser has f.e. diameter 1 mm here on Earth, after traveling millions of km, it would be spread across large area.

When you can see laser beam, like in dirty air or water, you can be sure that distance laser will travel in straight line will be much smaller than with crystal pure, or vacuum.

Edited March 5, 2015 by Sensei

[swansont]

Why does light , even on a dark night just seem to disappear ? Why doesn't it just continue on into space forever. Please explain.

 

You only see things if the light makes it into your eyes — it has to scatter off something. If there's nothing to scatter it, it will seem to disappear. If there are things to scatter it, then you have to realize that light from a source diverges; if it's a point source it gets weaker as 1/r², so you can rapidly get to the point where very little light will scatter and return to you. Combined with your eye's dynamic range — dim images will be seemingly lost if there's something bright in your field of view, causing your iris to close — the light seems to disappear.