Uncertain future: Is Andromeda going to collide with the Milky Way or not?

In 2012, astronomers announced a startling result: The had used Hubble to very carefully measure the motion of the Andromeda galaxy, and found that it appeared to heading very nearly directly toward the Milky Way at 100 kilometers per second. They predicted that in about 4 billion years the two galaxies would collide, and chaos would ensue.