Final answer:
The amount of photons in a beam does not decrease with distance; however, their intensity decreases due to the spreading out over a larger area, following the inverse square law for light propagation.
Step-by-step explanation:
The question of whether the amount of photons in a beam decreases because of distance can be addressed with the inverse square law for light propagation. This physical principle states that as light travels away from its source, the intensity of light decreases in proportion to the square of the distance from the source. This means that if the distance is doubled, the intensity of light is reduced to one quarter. It's important to realize that while the intensity of the light decreases, the actual number of photons does not decrease; instead, they spread out over a larger area, which diminishes their density and thus the intensity we perceive.
For a visual example, consider two stars with the same luminosity. If one star is three times farther away than the other, it would appear nine times dimmer. This is because the light from the more distant star has to cover a larger area, following the inverse square law. The significance of this law is seen in how stars like Alpha Centauri A, which emits the same total energy as our Sun, appears billions of times fainter due to the vast distance between us and the star.