If the universe is expanding, how can milkyway and andromeda collide?

Question

Universe is expanding means that galaxies are moving apart, then how can milkyway and andromeda collide?

Answer 1

the appearance of the cosmos seemingly expanding does not in any way, shape, or form give validity to the big bang model. in all honesty my human friends, the big bang has many a problem. nor does it prove that the hubble constant is actually the case. nature is another word for illusion. (to human eyes). it is my consummate thought that a revolution in cosmology is on the brink of happening in our time (some would say it is already happening - to them i would say just hang'a'round a while - lol). which will yet again peel off another layer of fact and truth about the mysterious and lovely cosmos.

as the great democritus once said : "i would rather understand one cause than be king of persia!"

on matters of cosmological order and the fundamental pillars of all things, i to concur.

Answer 2

Edwin Hubble discovered that the farther away a galaxy is from us the faster it is moving away from us. This is the pattern one would expect if the whole universe were expanding. But that also means that really close galaxies are hardly moving away at all. And Andromeda is one of the closest so that its own gravitational attraction with our own galaxy is stronger than the very small motion away from us that the expanding universe would cause.

Answer 3

Space is different than matter.   The galaxies are matter.  And although space may be expanding, it isn't expanding fast enough to change the fact that the two galaxies are on a collision course.

Answer 4

When we say galaxies are moving apart, we are are speaking of averages taken over distances of 100s of millions of light-years.  When look at smaller scales, like that of our local group of galaxies, we find that some galaxies are moving towards one another.

Also, it should be noted that the expansion of space isn't some force that is "pulling" galaxies away from one another, in opposition to gravity.  The concept of expanding space arises from general relativity, which is simply Einstein's theory of gravity.  This theory allows us to describe the motion of matter in terms of expanding or contracting space,  provided that the matter is subject to no forces except gravity.

Answer 5

It's quite natural for galaxies to collide even though the universe is expanding. What happens is that there is a battle between the forces of gravity trying to pull the two galaxies  together and the expansion of the universe trying to pull them apart.

With galaxies that start out quite close together, it is almost always gravity that wins, so in the end the galaxies will collide. This will most likely happen to the Milky Way and the Andromeda galaxy (our nearest large neighbor) in a few billion years.

Answer 6

The general expansion of the universe is indeed making most galaxies recede from one another.

But the galaxies in our Local Group (Andromeda, us, and about 2 dozen others) are all gravitationally bound together, so the expansion of the universe isn't enough to pull them apart.

The galaxies in a galaxy cluster will remain near each other even as the universe expands.

It might help if you remember that the galaxies are not actually moving.  The space between the galaxies is expanding, driving them apart.

But in clusters, the gravity holding them together is stronger than the space expansion trying to drive them apart.

Answer 7

Gravity has began to take effect after about 13.5 billion years. I believe one day all matter will stop and begin collapsing back in on itself. Then, BIG BANG all over again. Like a balloon blowing up, then releasing air, over and over.