Archive for the ‘Physics’ category

Three Generations of Quarks are Needed To Avoid Anti-Matter

April 14, 2009

As we have already discussed, the reason we have particles without anti-particles is because of CP violation. CP-violation caused slightly more particles to be produced in the big bang then anti-particles. Then all the anti-particles annihilated with a particle leaving only the excess of particles we observe today.

However, it takes 3 generations of quarks to have CP violation. CP violation is encoded in the CKM Matrix, a 3 by 3 matrix. (N=3 for 3 generations of quarks). You need a overall phase in the CKM matrix to have cp-violation. If there were less then 3 generations of quarks, say 2, then the new 2 by 2 CKM matrix would have no overall phase and hence no CP-violation.

It was not too long ago when scientists had not suspected there were three generations of quarks. If there weren’t, we would have no CP-violation and no matter. It would have all been annihilated with the equal abundance of anti-matter.

By the way, in case you don’t know, the CKM matrix people won the Nobel Prize in physics last year.


Physics Quote Of The Day

March 9, 2009

Another one from Zee:  (I may adopt this one as my answer to the question “What is quantum field theory”)

Quantum field theory arose our of our need to describe the ephemeral nature of life.

He then goes on to discuss how it takes quantum field theory to explain why fundamental particles pop in and out of existence and shift from one to the other constantly then concludes:

So, I was more or less right: Quantum field theory is a response to the ephemeral nature of life.

The Higgs and Inflaton: Two Peas in a Pod

March 6, 2009

The Higgs Boson is an scalar particle that single handedly makes the whole standard model of particle physics make sense. One problem: nobody has detected that it actually exists.

The Inflaton is an scalar particle that single handedly makes the whole standard model of Cosmology/Big Bang make sense. One problem: nobody has detected that it actually exists.

Isn’t it amazing that a fundamental ingredient of two of the most experimentally successfully theories is a scalar particle which has never been detected? It is as if scalar particles have a Dr. Jekyll Mr. Hyde personality: The want to solve all our problems while at the same time cause everyone endless grief/time/money by escaping our detection!!!

They truly are two peas in a pod. 🙂

CP Violation May Explain Why No Antimatter

March 1, 2009

CP symmetry says that every interaction in particle physics must obey charge conjugation and parity. (If you don’t understand the above statement don’t worry, you just need to know such a symmetry exists.)

Though CP symmetry was thought to be an exact symmetry, it turns out it is violated by  weak interactions.  If CP was an exact symmetry, there should be just as much antimatter produced by the big bang as matter.  However, as we look around us we should be easily convinced this isn’t the case. 🙂

However, since CP is violated, there should have been slightly more matter produced than antimatter.  Soon after the big bang every antimatter particle then annihilated itself with a matter particle leaving only the excess of matter which is seen today.  This is probably why there is no antimatter.

How String Theory May Predict A 3+1 Dimensional World

February 28, 2009

Any compact universe should have strings that wind around, just like when you wind a string around a torus.

Well these winding strings, like a rubber band, want to compress any manifold down to the plank length. (At which point the dual momentum strings we discussed dually “push back” to prevent further collapse.) However, winding strings are oriented. Wrapping 3 times clockwise is different then 3 times counter-clockwise.

If we could have winding strings come in contact with anti-winding strings we would have the winding modes unwrap, and the universe expands. However, this process must be in equilibrium to keep the universe big for any length of time.

Well, a string sweeps out a 2 dimensional surface as it moves, so has a 2d interaction area. Same with a anti-winding string. So, the largest dimension where you could maintain long term expansion is a 2+2=3+1 dimensional space which would expand leaving the rest of the dimensions compactified.

This does something more, since it may take a long time before this equilibrium comes about, this could explain the high entropy in the universe.