Context: https://www.reddit.com/r/askscience/comments/uruuh8/if_spaceships_actually_shot_lasers_in_space/?utm_medium=android_app&utm_source=share
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If you mean, why light dissipates over *distance* it’s because of the inverse square law.
Imagine you have a light bulb and a square light sensor that is 1 meter x 1 meter and you put the sensor 1 meter away from the bulb and it measures some number.
Next, imagine 4 lines going from the light bulb to each corner of your sensor. It forms a pyramid shape, right?
Let’s leave those lines where they are, but we back up the sensor to 2 meters away. And now it’s measuring 1/4th of what we had before… why is that??
Because while we doubled the distance, that pyramid doubled both in width & height. Our sensor stayed a 1 meter square, but all those photons are now spread over a 2 meter x 2 meter square.
If we moved out to 3 meters from the bulb, we would measure 1/9th the amount of light because those photons are spread over a 3×3 meter area.
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