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[–] TrivialGravitas 0 points 2 points (+2|-0) ago 

So this question requires picking a reference frame, the obvious one is going to be 'relative to the local galactic supercluster'

as it turns out we're headed toward the center of it at about 1000 km/s http://www.scientificamerican.com/article/how-fast-is-the-earth-mov/

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[–] syllovespan [S] 0 points 1 points (+1|-0) ago 

Thanks for the link, the other article I saw had it a just slightly faster. Still, 870,200 miles per hour, 20+ million miles per day, for billions of years. The party is at the Great Attractor but we don't get to see it for now because of the Zone of Avoidance. I'm too small to comprehend this vastness but I love thinking about it.

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[–] TrivialGravitas 0 points 1 points (+1|-0) ago 

we're moving towards it substantially faster than we were billions of years ago. Both because the attraction is stronger as we get closer and because the acceleration rate is still really slow.

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[–] Charlie_Prime 0 points 2 points (+2|-0) ago  (edited ago)

To calculate movement, you must decide what that movement will be relative to.

Relative to my computer monitor, I am sitting still. At this same instant relative to the sun, I am moving very fast.

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[–] syllovespan [S] 0 points 0 points (+0|-0) ago 

How about relative to other galaxies? I was thinking in terms of the front-end speed of the Milky Way itself. I envision our galaxy moving through space like a big old frisbee, it has rotation and forward velocity (speed?, not sure if used the term velocity correctly here). Because gravity allows us to feel like we're sitting still, many forget or perhaps don't realize that we are heading toward somewhere in this vast universe at speeds that are probably difficult if not impossible to grasp.

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[–] Charlie_Prime 0 points 2 points (+2|-0) ago 

My point was that you need to pick a galaxy to measure against.

Each one will be different.

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[–] RayLomas 0 points 1 points (+1|-0) ago 

Well, first we need to decide what frame of reference we use. If we pick the CMB rest frame, then according to wikipedia it's 552 ± 6 km/s. Keep in mind that CMB rest frame is a convenient, but still an arbitrary choice.

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[–] gcb 0 points 1 points (+1|-0) ago 

The most common theory is that the universe is expanding. If that is true, then everything is getting further and further away from everything else. Relative speed would be a function of the distance between the two objects - closer object would have a slower relative than comparing two distant object.

Expansion is of course just one theory. This article for example indicates otherwise.

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[–] syllovespan [S] 0 points 1 points (+1|-0) ago 

I have a difficult time squaring in my non-scientist mind that all galaxies are moving away from each other yet we're headed for a collision with Andromeda.

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[–] The_Cat 0 points 2 points (+2|-0) ago 

It's Hubble's law, and is actually based on observation. Everything in the universe moves away from each other. The further two objects are apart, the faster they're moving away. The expression is ridiculously simple:

v = H*D

where v is velocity, D is distance and H is Hubble's constant. H is about 21 km/s / Mly. This is also the only form which respects the Copernican principle. Because no matter where you go in the universe, Hubble's law will hold in exactly that form1.

Andromeda is one of only a handful of exceptions. It's so close to us that local gravity is actually stronger than the expansion of the universe. So in billions of years, Andromeda and the Milky Way will collide and merge, while the rest of the universe moves away.

1 Note: While that form is correct for the entire universe, Hubble's constant is getting larger throughout time, so the expansion is accelerating.