Looking at stars yesterday set me to thinking if there was such a thing as a maximum distance that light can travel…?
Clearly stars are less bright than our sun and this must be a function of their distance from us (and also their initial brightness). But these distances are absolutely, mind-bendingly huge: we can see stars thats are hundreds of millions of light years away. And they are still visible not only after huge distances but also massive amount of time.
So is light not subject to “decay” or some form of “resistance” to travel that would mean there is a limit to how far (length) or how long (time) it could travel before it becomes completely unseen?
I realise I am using analogies that would be more relevant to sound or waves in a liquid so it may just be my incomprehension of the “light” phenomena and how it works that means ive missed the point… 😀
In: Physics
It’s important to remember that light is composed of individual photons, single ‘pieces’ of light that travel through space. Distant stars appear dimmer because *fewer* photons from them are hitting your eye, but not because anything is wrong with those photons themselves, the light itself.
For any star you can see, that’s pretty much all there is to it. The light travels and unless it hits something it is the same photon it was when it left that star a few years ago.
Still, on very very large distances, the gradual expansion of the universe comes into play. This causes those photons to have longer wavelengths- imagine a very short choppy wave in the ocean, but the ocean stretches somehow and the wave suddenly has more distance between peaks. Longer wavelengths mean the light is more “red” shifted. This is actually happening at all times in space right now, but only on massive distances and time scales.
The light from the most distant galaxies in our universe is so far shifted that we can’t see it with our eyes anymore and need special cameras designed for light at those wavelengths beyond what the human eye can see. The James Webb telescope that recently launched looks at these ancient, distant galaxies to learn more about them.
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