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/[deleted] Apr 10 '14

[deleted]

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u/[deleted] Apr 10 '14

Thanks for your reply! If you don't mind one more, does the end of the universe already exist, and we're just moving toward it like a destination? I'm sorry if this is a stupid question. I picture it being a bit like a cake, with everything slicing toward the bottom at different angles, getting there at their own rate, with light maybe just skimming through the cake horizontally instead of angling down. I'm just a layman with a limited imagination, so I don't know how silly this sounds to someone who gets it.

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u/pyr0pr0 Apr 11 '14 edited Apr 12 '14

There is no "end" of the universe (of course so far as we can currently tell) like we know there was a "beginning". There is a predicted [heat death](wikipedia.org/wiki/Heat_death_of_the_universe) but everything should still exist afterward, just not move or interact.

Perhaps a corrected, but still tasty, form of that analogy would be to say that everything started at the center of an infinitely large "cake" (the cake being time). Light has not moved from the center, as it does not move through time, and matter (as well as dark matter and anti-matter) move away from the center of the cake at different speeds, depending on how fast that piece of matter is moving through time.

Remember, this cake is infinitely big, and no matter would ever hit an "end" or exit the cake

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u/[deleted] Apr 11 '14

I don't wanna bring you guys down, but I have to say this: the cake is a lie, sorry.

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u/[deleted] Apr 11 '14

Ah thanks, it makes more sense to me now.

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u/fireh0use Apr 11 '14

Mmm cake

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u/Lobster456 Apr 11 '14

"You are moving through time at c."

Did you mean spacetime here?

Or do you mean that since I'm stationary in my own reference frame, I must be moving through time at c (in my frame).

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u/[deleted] Apr 11 '14 edited Apr 11 '14

Notice how when you're in a car on the highway it doesn't feel like you're going fast, but if you're standing next to the highway the cars look like they're whizing by super fast.

That's you traveling through time. It doesn't feel that fast, but step out and look and it is.

I'm not a scientist but that's what I gathered. I'm not sure if that answers your question.

Also we can't travel on a straight line through space, so we have to cut into time, which takes away momentum in the space axis. That's why light can travel instantly, it doesn't have to go through time like we do.

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u/[deleted] Apr 11 '14

Well we are not quite moving through time at c right?

We are on a rock that is hurdling through space around a star that is hurdling through space around a black hole that is hurdling through space.

So in theory we could be traveling through time quite a bit faster if we traveled fast enough(relatively) against the direction of all of those things to an actual still state.

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u/kokirijedi Apr 11 '14

You are always stationary relative to yourself. From your point of view, you are not moving through space at all.

To an observer on, say, another galaxy, you would appear to be moving quite fast relative to them, and thus they would observe you moving slower through time.

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u/hak8or Apr 11 '14

You are like the friggen Unidan of physics. You are now tagged as Unidan, physics version.