Yonatan Zunger’s Blog

Again, not yet the big politics post. Instead, some interesting things:

Grigory Perelman declined the Fields Medal, as he has declined a host of other honors and awards in the past, for his proof of Thurston’s Geometrization Conjecture. This conjecture basically states that there are eight basic pieces, and some simple surgery rules, out of which all possible three-dimensional compact surfaces can be built, and therefore we can classify all 3D compact surfaces. A compact surface is roughly speaking one that fits into a finite region; for example, in two dimensions, the surface of a sphere is compact, as is the surface of a donut, but a flat plane isn’t. Proving Thurston’s Conjecture also proves the Poincaré Conjecture, which roughly states that the only 3D compact surface that has no holes in it that you could wrap a string around (like you could wrap a string around the inner hole of the surface of a donut, and it couldn’t shrink because it would get “caught”) is a 3-dimensional sphere. It’s a major problem in mathematics that has been open for over a century, and Thurston’s conjecture is a regular tool of various fields of physics and applied math.

And perhaps even more excitingly, a smoking gun for the existence of Dark Matter has been found. A team pointed the Chandra X-ray observatory, the Hubble Space Telescope and various other telescopes at a place where two clusters of galaxies had collided and gone through each other. They could clearly see that the “luminous” part of the galaxies had gone past one another and were well-separated, but 90% of the mass — as visible by its gravitational effects on light — was somehow still in the middle, and completely transparent. Apparently, the luminous matter had kept on going, but there was so much dark matter that the two big lumps from each galaxy cluster had rammed into each other and come to a stop. This confirms the existence of what’s technically known as non-baryonic cold dark matter. “Dark” means that it isn’t luminous or visible to the eye; “cold” means that it isn’t a gas of photons or neutrinos, since those disperse much more quickly; “non-baryonic” means that it isn’t made of any ordinary kind of matter, and we know that because of how transparent it is relative to its mass. (In fact, its transparency tells us that whatever it is doesn’t interact electromagnetically very much, or perhaps at all.) Previous investigations have suggested that the universe is about 70% dark energy (which is not visible to the eye, but unlike dark matter, doesn’t form clumps or shapes; it’s just uniformly spread out), 27% dark matter, and 3% luminous matter; this experiment confirms the dark matter / luminous matter ratio, and all previous hypotheses about the dark matter, very beautifully.

Now, the next question is just what it is made of…