Thread: Photons from Stars

When we look at a Star, we know the light has taken millions of years to reach us in some cases.
My question is How long can a photon last until its energy is spent
Also when it leaves its source does the photon expand its energy as it travels across the universe. As it can be seen from any point of the universe.
For instance lets say a star is 10 mtrs wide as it emits light, when it gets past 1000 mtrs do the photons split. As when you get to 1 million mtrs you can
still see the light from any point, and so on. How is this so.

Well infinitely. Photons don't decay. As they are travelling with the speed of light (since, they are light), the have no internal time. Light is just waves it might disperse, or decohere it doesn't decay.

I don't quite understand what you mean with your second part of the questions. A photon has a fixed energy. And sure it can be see from anywhere but this isn't easy. If I look deep into the sky with for instance a film, I might see 1 photon from a far away star, but millions from other sources. Their aparent magnetitude or brightness decreases over longer distances.

Thanks for that

For instance lets say a star is 10 mtrs wide as it emits light, when it gets past 1000 mtrs do the photons split. As when you get to 1 million mtrs you can
still see the light from any point, and so on. How is this so.

there are literally a near infinite quantity (saves writing all those zeros) of photons being emitted by a star. going in all directions. some will be parallel, some nearly and some not. we use really large telescopes to catch those photons that are parallel, least that is how i see it. the bigger the mirror the more we catch. that is why with a really long exposure we can see so far away.