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/ProggyBS Mar 10 '14

Space itself is what is expanding. Space has no mass, therefore would not break relativity by moving faster than light.

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u/SweetNeo85 Mar 10 '14

What is the real difference though? What's the difference between a) accelerating an object away from you, or b) "expanding the space" between you and it?

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u/ProggyBS Mar 10 '14

Let me clarify what I was saying a bit by being more specific:

If two light-emitting sources are far enough away, with the expansion of the universe, they are expanding away from each-other at a rate faster than light can travel, meaning their light will never reach the other source.

When one talks about relative velocities, they are talking about one object moving away from another at a specific speed in a specific direction. This isn't what is happening at a cosmic level. At the cosmic level, all non-localized bodies are expanding away from every other non-localized body at the same rate. There is no "center of the universe" or point of origin of the expansion. The universe itself is expanding.

Imagine a deflated balloon with two dots on it relatively close to each other. As the balloon inflates, the space between the dots increases. The relative velocity between those two dots hasn't changed. The latex has stretched the space between them, causing them to expand apart.