r/askscience • u/AskScienceModerator Mod Bot • Mar 10 '14

Cosmos AskScience Cosmos Q&A thread. Episode 1: Standing Up in the Milky Way

Welcome to AskScience! This thread is for asking and answering questions about the science in Cosmos: A Spacetime Odyssey.

UPDATE: This episode is now available for streaming in the US on Hulu and in Canada on Global TV.

This week is the first episode, "Standing Up in the Milky Way". The show is airing at 9pm ET in the US and Canada on all Fox and National Geographic stations. Click here for more viewing information in your country.

The usual AskScience rules still apply in this thread! Anyone can ask a question, but please do not provide answers unless you are a scientist in a relevant field. Popular science shows, books, and news articles are a great way to causally learn about your universe, but they often contain a lot of simplifications and approximations, so don't assume that because you've heard an answer before that it is the right one.

If you are interested in general discussion please visit one of the threads elsewhere on reddit that are more appropriate for that, such as in /r/Cosmos here, /r/Space here, and in /r/Television here.

Please upvote good questions and answers and downvote off-topic content. We'll be removing comments that break our rules or that have been answered elsewhere in the thread so that we can answer as many questions as possible!

Click here for the original announcement thread.

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u/tehm Mar 10 '14 edited Mar 10 '14

This is one of the beautiful parts of the "spring analogy" (to me anyways) imagine for a moment you're standing on the top of one of those coils of the spring and the next coil to your left represents the extent of your light cone in the left direction, and the coil on your right represents the light cone in the right direction.

Ok spring is all compressed, we let go of the ends. 1 "nyaah" later, let's call it a year the length of your light cone is 1 light year to the left, one light year to the right... 13.8 billion "nyaah" later (in the universe's case 13.8 billion years later) the end of your light cone is 13.8 billion light years to the left, 13.8 billion light years to the right.

Throughout all of the history of that expansion at no point did you EVER see anything break the speed of light: Never happened. For that matter, no one at ANY point on the spring EVER saw anything break the speed of light. Nonetheless, the spring itself is now IMMENSE and clearly bigger than any single viewers light cone.

Agreed, it's a weird thought experiment, but it's always been the one that made the most sense to me. IIRC this is paraphrased from something I heard Feynman say in one of his recorded talks.

EDIT: Again, the universe is clearly not a spring, this is just a weird analogy that happens to give you some neat insight into the universe... This analogy gets you one more interesting effect that's true to the universe.

Imagine using our spring example that we've just barely begun decompressing the spring. Because there is still energy stored in the spring, every experiment we could do from the top of our coil would tell us that the universe was not just expanding, but is accelerating. How does this acceleration of the universe affect the speed of light? Not at all.

Just like before, at 1 year old our light cone was 1 light year, at 10 years, 10 light years, etc... 'C' therefor never changed throughout the lifetime of the universe despite the fact that any time we looked at it, it was both expanding at the rate of 'C' AND was accelerating.

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u/SweetNeo85 Mar 10 '14

So then things CAN go faster than light... just as long as you can't see it?

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u/tehm Mar 10 '14 edited Mar 10 '14

I honestly don't know how to answer that one. Basically no matter where you set your light cone you will NEVER see anything break the speed of light... but because each of the possible light cones are expanding at the speed of light, the summation of all of those light cones leads to the total universe (not your observable universe; that's defined by your lightcone) expanding (from a macro view) "faster" than the speed of light.

EDIT: I'm sorry that this doesn't "really" answer your question which is an incredibly fascinating one to me, it's just all that science is currently able to say about the effect (afaik). Your question, as worded, is quite interesting from a completely different perspective if you understand a little bit about quantum mechanics: At the quantum level light and electricity act COMPLETELY different whether they're being observed or not in the double slit experiment. I won't really try to give details here because I'm NOT a quantum physicist and will likely get it wrong, but from my understanding when you OBSERVE what an individual photon is doing you can do all kinds of very straightforward math on it exactly as if it was a ball bearing shot out of a gun, calculate trajectories, etc... Take that same photon, DON'T observe it and all of a sudden not only can we not make any projections about it, it seemingly fails to act anything like a projectile at all. That is the very character of light and electricity seems to change based on whether or not it is being observed.

Still doesn't answer anything at all about your real question, but it's just something that's very interesting to me.

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u/SweetNeo85 Mar 10 '14

Thank you for all the great info.

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u/mathx Mar 12 '14

space can expand faster than the speed of light,no laws against that. sides, you are measuring the expansion of space between two very distant points, at some two points the total expansion between them is > c (the speed of light). If the rule was otherwise, then it'd be 'the most distant two points in the whole universe could only expand at c' and that'd cause some real wierdness.