It is also reported here and here that another group, the DAMA-LIBRA collaboration, have observed seperate evidence of dark matter, but this claim is more controversial. Galaxy collision seen by the CHANDRA space telescope In the passage of one galaxy through another, one might expect the dark matter of one galaxy to interact differently than its ordinary matter, and researchers at the University of Arizona are pretty sure this is exactly they saw. The strongest evidence yet for dark matter was reported last summer. In other words, the current model of the universe can be summed up byĭensity ord matter (4%) + Dens dark matter (22%) + Dens dark energy (74%) = 100% Putting the two together, cosmologists postulate that ordinary matter, dark matter and dark energy all add up to the critical density required for the geometry of the universe to be flat (which is what observation suggests). (From the point of view of theory, the phenomenon suggests that Einstein’s equations need an extra term, known technically as the ‘ positive cosmological constant’.) The physical cause for dark energy is thought to be some sort of vacuum energy, but nobody’s sure yet. It’s simply the name we give to whatever is causing the expansion of the universe to speed up (since 1998, it has been known that the expansion rate is currently increasing). But most physicists consider this unlikely, as the predictions of our theory of gravity match observation in so many other instances…ĭark energy is a lot more speculative, and a lot more recent. Of course, like the MOND crowd suggest, there is always the possibility is that our laws of gravity (both Newtonian and Einsteinian) are simply wrong. The idea was first postulated by Fritz Zwicky in the 1930s – today, the known motion of certain spiral galaxies suggests that dark matter makes up 22% of all matter/energy, while ordinary (visible) matter makes up only 4%. Instead, we include the possibility that some matter may be seen only by its gravitational effect on neighbouring matter. emit or reflect electromagnetic radiation). Put differently, we don’t insist that all existing matter must be ‘visible’ (i.e. Although we can’t see it, we’re pretty sure it exists, because its gravitational effect on visible matter can be seen. This is very common, so let’s have a post on it.ĭark matter is thought to account for 20% of all the matter/energy of the universe. Hoosier (below) is a bit confused between Dark Matter and Dark Energy, and unconvinced by the whole shebang.

Dark matter vs antimatter