I have a couple more minutes left, and just let me tell you about non-electromagnetic messengers, and they come in several different flavors. First the high-energy cosmic rays, which are detected in same principle as high-energy gamma rays. Except that here we have a whole lot of particle detectors on the ground and they detect secondary and tertiary and untiary products of cosmic rays as the fast particles decay and slower ones. This is actually quite amazing because cosmic rays arrived to us over a large range of energies. And the most energetic ones are about 10 to 21 electron volts. That is the kinetic energy of a baseball moving at 100 miles an hour. And in one particle. So no wonder that they can actually leave substantial signature in the atmosphere. The biggest cosmic ray observatory now is in Argentina. It's called Pierre Auger, named after a nuclear physicist and it does both of these things which is radiation as well as particles from the showers they're collected and detected in particle detectors. There are others, there's one called Milagro in New Mexico, and I'm going to Mexico, Mexico, which is essentially a big swimming pool of super clear water with a lot of quantum multipliers looking for flashes. The same principle is now used to find neutrinos. Neutrinos don't interact very much, but occasionally they do. And the way this is done is, you get large tank of some fluid, which tends to be pure water, deep underground, and this is to shield from all other particles, and whole lot of photomultiplier tubes looking at the volume. So every once in a while, a really energetic neutrino knocks something, interacts with interface. And that then behaves just like a detection of a cosmic ray. So the big sphere on the left is in Canada, in Sudbury Mine. The one on the right is even bigger. It's called Super-Kamiokande. It's in Japan. You can see there these technicians in a little rubber dinghy fixing the individual photomultiplier tubes. These things are big and the reason why they have to be big is because neutrinos don't interact very much so you need a lot of targets. And they work with detected neutrinos from the sun, from Supernova 1987A, and maybe even some other things. But the queen of this is called the IceCube Neutrino Observatory which uses a chunk of few kilometers of purest ice available. Very transparent, right on south pole. So they drilled tunnels, put photomultiplier tubes in strings. Then let if freeze again. The neutrinos come, knock out electrons or something and by series of which photomultipliers light up and also how far the cone spreads, you can tell the direction, you can tell the edge. Now here's a cute thing about this. They don't count anything coming from above. They're only looking for neutrinos coming from below because the only thing that can go through planet earth would be neutrinos. Cosmic rays can generate fake signals coming from above. So you actually use whole planet Earth as shielding the telescope too. And one final thing is another part of Caltech's glory, which is opening of gravitational wave astronomy. And Caltech and MIT are principle players in the first gravitational observatory, which is working on some level, not finding anything yet. People expect to see things in next few years, getting quite ready for that. The way this is done is, again, top-notch experimental physics. Essentially, you have some heavy mirrors hanging in long vacuum tubes. And you bounce laser around them to measure their positions with kai precision. Gravitational waves come through jigor space-time and move those mirrors back and forth a little bit. That has to be then detected and all spurius signals filtered out. The precision with which these things are measured is many orders of magnitude smaller than size of individual atoms. Look and they're many, many kilograms in size. So this really is a fantastically precise physics experiment.
