If everything is travelling out from the big bang - how is it that we are going to collide with the Andromeda galaxy?
-------------------------------------------------------
answers:
az_lender say: Same reason why you crash into the earth if you fall out of bed. Gravity !
-
aladdinwa say: Nothing is "traveling out from the big bang". Space, itself is expanding. However, objects which are gravitationally bound to each other can overcome the expansion of space. The Andromeda Galaxy and the Milky Way Galaxy are gravitationally bound to each other.
-
Jeffrey K say: The Big Bang was not an explosion of matter in empty space. It was the expansion of space itself. Gravity can pull things together against this expansion. The gravity of the Milky Way and Andromeda galaxies are pulling them together.
-
Ronald 7 say: We are catching up
-
Pearl L say: i dont think we are
-
cosmo say: The Universe is expanding more-or-less uniformly on scales 100 million lightyears. On scales smaller that that (which includes our local group of galaxies with M31), local regions will contract under self-gravity if their average density is higher than the "critical density".
-
Raymond say: Nothing is "travelling out from the Big Bang".
Space is expanding. Period. Things that are fixed in space appear to move away from each other simply because there is more and more space between them, not because they are flying away from each other.
Space expands everywhere, including inside individual photons of light (this is what causes cosmological redshift).
The rate of expansion is very small on the local scale. It is cumulative (= if you consider long enough distances, you can measure it). Over a length of 2 metres (the height of a man), the rate of expansion is the size of one atom over a lifetime of 70 years. Natural growth is very sufficient to compensate for that.
Over a million parsecs (3.26 million light-years), the rate is a very slow 70 km/s. Every second, there is 70,000 metres worth of space that is added.
Meanwhile, things move on their own, mostly due to gravity. Both our Galaxy and the Andromeda galaxy belong to the Local Group. The Group is help together by gravity, so that all objects in the Group (including our Galaxy) are in some kind of orbit around the barycentre (centre of mass) of the Local Group.
Because of our orbit around the barycentre and Andromeda s orbit, the distance between the two galaxies is decreasing faster than the amount of new space being added by expansion.
It is a bit like two cars going in the same direction, on the highway, the one in front going 90 km/h (a bit over 55 mph) and the one behind going at 120 km/s (75 mph). Eventually, they will collide even though both are going in the same direction at high speed.
-
neb say: It’s simple. I walk toward my coffee pot every morning, overcoming the expansion of space. The reason I can do that is the expansion rate is so small over short distances that I can easily overcome it by exerting forces that direct my motion.
The expansion rate is also pretty small over millions of light years distance. A galaxy can easily overcome the expansion with a relatively low velocity due to many forces that have operated on the galaxy over its life time.
-
Sharon say: galactic clusters not isolated galaxies
-
Starrysky say: Local gravitational forces might bend the paths a little bit. Over billions of years, the bends get tighter. Galaxies form into clusters, then might collide (or go separate ways). Astronomers have a prediction that it might happen in 5 billion years or so. But humans (as we know them now) won't be around to see it.
-
poldi2 say: The gravity within our Local Group of galaxies (Milky Way, Andromeda, and dozens of other smaller galaxies) is stronger than the expansion of the universe).
-
duke_of_urls say: Gravity is stronger than the expansion of space.
So, if 2 masses are close enough AND have enough mass, the gravitational attraction between them will be stronger than the expansion of space between them.
-
CarolOklaNola say: The Andromeda I Galaxy cluster may have more mass than the Milky Way Galaxy Local Cluster and BOTH are part of the Virgo 81 super cluster. Gravity and mass is why clusters and super clusters and sheets and voids form while Space is expanding in all directions, NOT "...traveling out from the big bang...". THAT is a FALSE premise.
BTW, there are something like 16 Andromeda galaxies. I assume you mean M31 and M32.
I usually ignore the coffee pot. I am ayea person.
-