Will the Milky Way and Andromeda Collide Despite the Expanding Universe?

[buddhakan]

I am a molecular biologist but cosmology is my "hobby". I have some questions about some seeming inconsistencies I have heard on TV treatments of cosmological topics. Here is the first: I hear the the Milky Way and the Andromeda galaxy will collide in 2.5 - 3 billion years. If the universe is expanding at an accelerating rate, and every object in the universe is receding from every other object (which I also hear often), then how is this collision possible?

 

[russ_watters]

Every object is not receding from every other. Some objects are close enough together that they are gravitationally bound to each other, defeating expansion.

 

[emc2cracker]

That means our local group of galaxies will eventually be all of the universe we can see. However it remains to be seen if the expansion will continue, some are holding out that maybe dark energy will weaken at some point thus giving gravity a chance to pull everything back together. Personally I think we can only go on what we see and that is to assume expansion will continue.