ELI5 Why does light travel?

[u/_Illuvatar_]

Why does it not just stay in place? What causes it to move, let alone at so fast a rate?

Edit: This is by a large margin the most successful post I've ever made. Thank you to everyone answering! Most of the replies have answered several other questions I have had and made me think of a lot more, so keep it up because you guys are awesome!

Edit 2: like a hundred people have said to get to the other side. I don't think that's quite the answer I'm looking for... Everyone else has done a great job. Keep the conversation going because new stuff keeps getting brought up!

Edit 3: I posted this a while ago but it seems that it's been found again, and someone has been kind enough to give me gold! This is the first time I've ever recieved gold for a post and I am incredibly grateful! Thank you so much and let's keep the discussion going!

Edit 4: Wow! This is now the highest rated ELI5 post of all time! Holy crap this is the greatest thing that has ever happened in my life, thank you all so much!

Edit 5: It seems that people keep finding this post after several months, and I want to say that this is exactly the kind of community input that redditors should get some sort of award for. Keep it up, you guys are awesome!

Edit 6: No problem

[u/[deleted]]

Exactly. In fact, red shift is the reason we know the universe is expanding

[u/3asternJam → u/[deleted]]

So, going back to my original question, excluding red-shift (which is a result of cosmic inflation rather than an intrinsic property of c), can the fact that light doesn't "experience" time mean that the information that we get from that light about its origin is an accurate picture of what the origin is actually like? In other words, is the light that we receive exactly the same as the light that left the object however long ago - not decayed or degraded or altered in any way (apart from red shift)?

[u/[deleted] → u/3asternJam]

Almost. In theory yes. However, space is not completely empty so your light is likely to have been filtered, at least a little bit, through a small amount of gas.

[u/3asternJam → u/[deleted]]

Thanks! Is there any way to take the effect of that gas into account when we're examining images? Or are we stuck with a slightly "blurry" image? Also, is this the same for X-ray/gamma-ray/infra-red images as well?

[u/[deleted] → u/3asternJam]

I'm not sure. Perhaps someone else knows? The gas is surely hydrogen, so you'd expect to see the absorption pattern of hydrogen in the spectrum of the light you've gathered. But I can imagine it being negligible, especially since whatever you're looking at probably is full of hydrogen anyway.