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It would not go on for ever. Its intensity falls off by 1/distance^2, but interstellar dust and gas absorbs the light as well.

For comparision: the Sun can no longer be seen by the naked eye if you are further away than 50 light years.

Astronomers shine lasers at the Moon, where they reflect off the mirrors left there by three Apollo missions. It is used to measure the distance to the Moon with centimeter precision. However, typically a dozen photons are collected when the light pulse comes back...

If you shined a flash light into the sky the light beam would diffract. This means the light beam would bounce off objects (in this case the Earth's atmosphere which contains all sorts of gasses) into different directions and some of the light will even be absorbed by those objects and be turned into some other form of energy such as heat. But if there were nothing to block the light beam (such as empty space), then the light beam will travel forever until it hits something.

Hypothetically, forever. Light doesn't "fizzle out" by itself. Realistically, however, light will gradually become absorbed or scattered by the interstellar medium (gas and dust). Typically, when a photon it absorbed, it's re-emitted at a lower energy, meaning that over time and huge distances it will become redder and redded, eventually becoming infrared light.

yea the light particles will travel forever or until something blocks it path. although the light won't be visible from space or any other point from outside the atmosphere (with naked eye) because a flashlight does not give off enough light particles at one time like a star does

so a ways as all of us understand, mild does no longer decay. it quite is to no longer say that it won't be ready to be absorbed via hindrances alongside its path. Even in deep area there is interstellar rely that would soak up mild. mild intensity, inspite of the undeniable fact that, is a diverse tale. jointly as a single photon won't decay, in case you're taking a mild source, including a much off galaxy, its brightness is inversely proportional to its distance squared. additionally, you're able to evaluate the outcomes of advance. it quite is been shown that there is an significant 'redshift' for distant products, suggesting an acceleration of the universe's advance This redshift decreases the potential of a given photon, yet won't injury it. it quite is subsequently that we see the cosmic microwave history radiation (CMBR) as microwaves, incredibly than the gamma rays they are literally. it incredibly is likewise why the sky isn't constantly superb, because of the fact jointly as the universe itself must be countless, we can basically ever be conscious a bubble of it out to a distance of 13-20ish billion years, the place at its very factor we can see what the universe replaced into like at its delivery.

In COMPLETE vacuum the light would continue travelling for ever and ever. However, does complete vacuum exist? Because vacuum as we know it has something like 1 atom per cubic meter.

OK, so if you shinned a light into space would it continue travelling for ever and ever? No, for the reason I said above, vacuum as we know it has something like 1 atom per cubic meter. It would continue travelling for a long time, maybe millions or even billions of years - although those 1 atoms per cubic meter would eventually absorb the light.

It would keep traveling as long as nothing comes in its way. Also there is a slight friction with air and light which makes it a tiny bit slower. But yea, it would keep going until it hits something.

It will travel until the light has hit enough space dust and debris that all the light has been absorbed.

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IT WOULD GO ON FOR ETERNITY AS LONG AS IT HAS AN INFINITE ENREGY SOURCE