Does a beam of light travel forever, or will it eventually run out?

[taiwan_girl]

So while a beam of light will in theory travel through a vacuum forever, in the context of light from the stars reaching our planet, much of it will have been deflected or refracted along the way.

This means that when light from distant objects does eventually arrive at our eyes (or our telescopes), we’re only actually seeing a fraction of the light that was originally emitted.

and

Put all these things together – deflection, refraction and redshift – and a more nuanced answer to the question would be that yes, in a vacuum, light will in theory travel forever.

But from a practical point of view – and certainly for observers here on Earth – there are impediments to that which mean that, over time, light will eventually, or at least appear to, wear thinner. This is known as attenuation.

That said… light will still be around very faintly even then. Which is why we are still able to detect the Cosmic Microwave Background, or CMB.

First mapped by NASA’s COBE (Cosmic Background Explorer) satellite in 1989, the CMB consists of light emitted during the Big Bang itself.

It’s light, in other words, that’s been travelling across the Universe for 13.8 billion years.

https://www.skyatnightmagazine.com/space-science/does-a-beam-of-light-travel-forever

[89th]

Interesting questions, and even if we had perfect answers the practicality of it is "ok, neat."

[Axtremus]

Light can travel forever and still may never ever actually reach a certain point in space because space itself may expand faster than the speed of light.