Dark Energy, Dark Matter, And The Fate of The Universe

In many ways, we don't actually know what dark matter and dark energy are. In some sense, they are just placeholders for a complete explanation. This seems to make is a little hard to see how we can really look for evidence for dark energy and dark matter. We do know a little about them though and have a few reasons for thinking that both things exist in very large quantities.


The main reason that we think that they must exist is that "the expansion of the Universe has not been slowing due to gravity, it has been accelerating." If there were no dark energy and dark matter, then we would expect the universe to be slowing down, since gravity attracts and pulls, not pushes. However, the galaxies seem to be speeding up, so something must be responsible for this.



Another reason that we think that dark energy and matter exist is due to the fact that "galaxies are rotating with such speed that the gravity generated by their observable matter could not possibly hold them together." So something must be giving them extra mass to hold the galaxies together. Dark energy and dark matter is supposed to do the job of that.

Lastly, the fact that our universe is flat supports the existence of dark energy. This is because the total matter density of our universe is not enough on its own to make the universe flat so something else has to be there.

If dark matter and energy really do exist, then there will be some interesting consequences for the fate of the universe. Galaxies will continue to accelerate and will get farther and farther away from each other. I think it is unclear what the outcome for between for individual solar systems, or even planets and molecules. Will solar systems begin to start spreading apart too? Could this even happen at the level of the atom. This seems like it will largely depend on how dark matter and dark energy work, but it seems to me that if it can cause galaxies to accelerate away from each other, it could cause smaller things to do so as well. This would mean that there will be a pretty catastrophic end to the universe. Everything will end up tearing apart and there won't really be much left except for dark matter and energy. Maybe the extra mass that dark matter gives would prevent this though. Even if all non-dark matter isn't also caused to spread apart by dark energy, it will be interesting to see what the effect that even larger distances between galaxies will have on galaxies way down the road. Maybe they can just drift on forever.

http://home.web.cern.ch/about/physics/dark-matter
http://science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy/
http://wfirst.gsfc.nasa.gov/about/darkenergy.jpg