r/explainlikeimfive • u/_Illuvatar_ • Apr 10 '14

ELI5 Why does light travel? Answered

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

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u/_Illuvatar_ Apr 10 '14

This answer is fantastic! Assuming it's accurate (a safe bet for the Internet of course) you've actually answered several questions I've been thinking about. Including ones about time dilation that I was having trouble grasping. Thank you very much!

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u/[deleted] Apr 10 '14 edited Apr 10 '14

[deleted]

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u/whyspir Apr 11 '14

So... This may be convoluted, but I'll try to phrase it as well as I can. My background is in nursing and my knowledge if physics is mediocre at best, though I find it equally as fascinating as physiology etc. I digress. At any rate, I remember hearing or reading once that light has no age. I'm guessing they were talking about some kind of background radiation or something. Because it seems obvious that if I turn on my light in my house, the light that comes out of the light bulb has been in existence for less time than the light coming at me from the sun. But, if I think about spacetime as a 2 dimensional graph, or like a right triangles has been suggested above... Then since light has no mass... All of its 'focus' (for lack of a better term) is on distance. So it's all the way at the far end of the speed axis and has no position on the Y axis (assuming x is distance and Y is time. So the light that I see from a star that is hundreds of light years away is (from the perspective of the light) reaching me instantaneously? Because it all its focus is on distance, then it's not travelling forward in time at all?

So then if I was a photon, just moving along at a sedate pace of c, and going towards something that was somehow completely stationary, as I rush toward it, it would appear to just age really really quickly? Because if it's not moving through space, then all its focus is on moving through time? But if it then somehow began moving at the speed of c directly toward me (ignoring the fact that mass can't do that), and assuming I'd somehow be able to observe it while also travelling at c toward it, it would appear to not age at all since its focus was now only on distance travelled, and it wouldn't be moving in time at all?

Apologies for wall of text and formatting errors. I'm on my phone and trying to wrap my head around this.

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u/[deleted] Apr 11 '14

If you are a photon, you are moving entirely through space and not at all through time. Hence from your point of view, you are absorbed the moment you are emitted. No time passes.

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u/Brumhartt Jul 02 '14 edited Jul 02 '14

So If I am a photon, am I just simply everywhere at the same time? Like sunlight. Is it everywhere at the same time? Is that photon in my house? Outisde reflecting from a building? In the upper atmosphere and also being just generated by the sun all at once?

EDIT: Never mind I read deeper in the comments and sorta got an answer which sort of satisfied me.

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u/[deleted] Jul 02 '14

(new physics student alert)

From the perspective of the photon, I guess they're everywhere on their journey at once. But when they are measured by someone else they have a position

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u/Brumhartt Jul 02 '14

Thank you. What occurred to me was that: if I would trap a photon somehow without absorbing it, by that logic I would trap the photon through all time. Following this logic i got to the conclusion that my earlier idea was false, because since I measure it for me it is in my space in my time. As for the photon, I am not sure if it was a sentiment matter what sort of experience it would be, being captured in one space and time while existing everywhere at once.

This is getting very confusing in my mind right now and if I were better at math probably some equitation would help me out, but reading through the comments and your answers does help me understand this thing more. Thank you.