Hadrons (Greek for "stout" or "thick") are simply composite particles made of quarks held together by an electromagnetic force. They in turn are made up of baryons and mesons.
Baryons are made up of 3 quarks (so, protons and neutrons are the obvious examples but I gather there are others.) Protons are the only stable baryons.
Mesons are made up of a quark and an anti-quark. Examples created in particle physics experiments include pions and kaons. I'm not going to bother looking this up further. I tried and found a tangle of nuclear forces and gluons and colors and spinning bosons. I think all mesons are bosons. But not all bosons are mesons maybe? Aha, that logic class I took in college years ago to avoid math pays off.
Ok, it made me nuts so I did just look up a little more. Bosons are indeed mesons which means the Pauli Exclusion Principle does not apply to them because they are integer spin particles. As opposed to baryons which are Fermions and are half interger spin. If you are a Fermion, you can not simultaneously occupy the same quantum state with another...uh, particle?
Moving on...for the last time, here is the difference between dark matter and dark energy. They used to think the expansion of the Universe was slowing down and might reverse one day in the Big Crunch. Stephen Hawking talked about this in his book which apparently everyone claimed to have read but were really busy reading Jackie Collins. Then came the Hubble and they saw the Universe's acceleration is actually not only slowing down but is actually increasing over time. Over time, the expansion of the Universe has been confirmed from various sources such as study of the CMB and better measurements of supernovae. According to NASA, 70% of the Universe is dark energy. We can tell from the maths. Some people say though that Einstein's theories have some kind of as-yet-unknown gaffe in them. So dark energy is either a property of space, a new dynamic fluid, or a new theory of gravity.
Here is an easy way to explain dark energy: it's also referred to as repulsive gravity. It is much weaker than plain old gravity but more observable over large distances where it seems to take over.
Dark matter on the other hand is inferred to exist by its gravitational effects on visible matter. Some pioneering astronomers-Fritz Zwicky and later Vera Rubin-observed that some galaxies were spinning so fast they should fly apart. But they don't. The explanation for they don't would seem to be mass but we can't detect it. In fact, we are about 5 times short. It is not antimatter or we would see the unique gamma rays antimatter produces when it is annihilated. It is not composed of baryons as they are observable by their absorption of radiation. And because of the observed gravitational lensing, it's not massive black holes.
All told, regular matter only makes up about 5% of the universe so we are way off on something.
Here is some more info from Universe Today:
The case for dark matter can be appreciated by first looking at the solar system where, to stay in orbit around the Sun, Mercury has to move at 48 kilometers a second, while distant Neptune can move at a leisurely 5 kilometers a second. This principle doesn’t seem to apply in the Milky Way or in other galaxies we have observed. Broadly speaking, you can find stuff in the outer parts of a spiral galaxy that is moving at about the same orbital velocity as stuff that is quite close in to the galactic hub. This is puzzling, particularly since there doesn’t seem to be enough gravity in the system to hold onto the rapidly orbiting stuff in the outer parts – which should just fly off into space.
Hmmm, now I see why I have trouble keeping this shit straight. Hopefully this will help.
No comments:
Post a Comment