Cold light.... what about this problem???

I have been reading a couple of books regarding one of Hubbles greatest discoveries, the fact that the universe is expanding. Simply put, it states that quote, "every galaxy is moving away from every other galaxy." This tied with the Big Bang seems to indicate that all matter would have been thrown apart from itself (much as the example they use drawing galaxies on a ballon and then blowing it up. They all move apart). If that is the case then why is the M31 racing towards the Milky Way rather than away from it? Why do other galaxies murge if they should be moving apart from one another? Am I taking the concept of "moving away" to literal? Does it have to do with the warping of space time? My head hurts again.

See what happens when someone with an I.Q. of 136 suddenly tries to grasp an idea at 180+.

Paul Atkinson
AstroPro Products

The idea that "everything is moving away from each other" is somewhat of an over-simplification. The expansion of the universe is not about the motion of any particular star, cluster, galaxy, or other object, but with the universe as a whole. While a group of objects may be moving towards each other, in the average, things are moving apart because space itself is expanding.

It can give you a headache to try and picture it. A classic analogy is to compare the 3D universe to the 2D surface of a balloon. Cover the balloon with dots to represent galaxies. As the balloon is blown up (an expanding 2D universe), everything on the balloon's surface moves away from everything else. It gets more complex when you factor in the motion of individual objects. Replace the dots with ants, for example, and some ants will be moving towards each other even as the balloon gets larger. On the average, though, this motion is superimposed over the gradual expansion.

So, M31 can be rushing towards us while at the same time the entire universe is expanding.

Hi Paul,

It is not that difficult. Although space itself is expanding as a whole, on "small" scales (eg galaxy clusters) the force of gravity is sufficiently strong to prevent galaxies from being carried along as the space between them expands. Hence M31 is approaching us because the gravitational attraction between the Milky Way and M31 is sufficiently strong to draw them together.

cheers,

Maurice