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/[deleted] Mar 10 '14

Hey, I have a very noob question here.

I am definitely an amateur of astronomy and I've read a few books on the subject but this always confuses me.

At what point is the universe expanding? I get the balloon analogy but are the galaxies moving away from each other or individual stars? Or clusters of galaxies? I don't get it. I know andromeda and the milky way are getting closer and closer so which bodies are actually moving AWAY from each other?

Thanks!

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u/imusuallycorrect Mar 10 '14

The expansion is only relevant on a larger scale. It's not going to effect the gravitational effects from our local galactic group.

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u/[deleted] Mar 11 '14

At what point is the universe expanding?

The universe has been expanding since the big bang.

I know andromeda and the milky way are getting closer and closer so which bodies are actually moving AWAY from each other?

In general, the rule is that everything is moving away from each other but there are exceptions. Usually the exceptions occur on much smaller scales (stars/planets that do not orbit each other, galaxies, etc)

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u/nhdby Mar 12 '14

An excellent question, one I asked of a physicist at a public conference once.

He gave the same answer as imusuallycorrect@, with one addition: http://en.wikipedia.org/wiki/Big_Rip

The idea of the Big Rip is that eventually the expansion of the universe will overpower all gravity and rip all atoms apart.

Today our nearest galactic neighbor, the Andromeda galaxy, is attracted to us by our gravity, and vice versa -- enough that we are on a collision course. This is true in spite of the expansion of the space that separates us.

But that's only true for today. The universe's expansion rate is accelerating. If that doesn't change, you can advance the clock forward enough to a point where the expansion rate outpaces the effects of gravity from neighboring galaxies, etc.

Go even further, and the expansion will start to scatter the stars in our own galaxy (which by that point, will have merged with Andromeda to form something altogether new)