if the universe is moving and expanding,why is The Andromeda in a collision course with the Milky Way?

Question

If most astronomers agree the universe is moving away from each other and expanding,then why do they also agree that our galaxy the Milky Way and The Andromeda Galaxy are heading straight at each other.

Answer 1

The easiest way to understand this is the following, in my opinion:

Imagine the universe is a big balloon. The balloon is filled with confetti. Air is being pumped into the balloon.

Because air is being pumped into the balloon, if the confetti spreads out to fill the balloon each piece of confetti will get farther, on average, from another piece. However, just because this happens *on average* does not mean that a single piece of confetti may not get closer to another piece. The confetti is flying around inside and some may get closer to others than they had been in the past.

Answer 2

When two Gravitational mass systems are gravitating toward each other theri relative velocity and accelerations increases.
Therefore a relative velocity increases their relative masses change accordingly.

When Galaxies expand their radius vector relative to the Universe they are experiencing a mass structure change.

The motion of the Galaxies can occur as a function of whether the Galaxiy is gaining mass faster than it receives mass,or whether the galaxy is lossing mass faster than it receives. It is all relative.

Mass structures such as stars and Galaxies tend to be gathered together because of the Gravity phenomena.
The purpose of gravity is to assembe masses together to form a more stable structure.

There fore Galaxies tend to expand as well as contract. The reason is due to mass losses or mass gains into their structures.

Answer 3

Gravity.
They are not all moving in the same direction.