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Tuesday
Oct192010

The God particle...

Particle physics - also called high-energy physics - is the study of the fundamental constituents of matter and energy. The primary experimental tool is the particle accelerator: this is usually a multi-billion dollar state-of-the-art instrument that throws particles at each other at near the speed of light (see my previous post on the Large Hadron Collider). A typical experiment involves terabytes of data and hundreds of physicists. While the physics involved is now pretty well understood, the sociology of dealing with hundreds of ego-driven physicists still remains an interesting subject.

During the golden age of particle physics (1960-1980), the catalogue of all the forces of Nature and the building blocks of matter were charted and tabulated successfully. The result is a very elegant picture, with lots of symmetry and patterns. It is still elaborate enough however that discussing in too much detail would feel to a non-expert  like studying botany - not that there's anything wrong with botany. I'll summarize very briefly. All known matter is built from one of two types of particles: leptons (i.e. an electron), and quarks (i.e. a proton is made of quarks) - the naming scheme used in particle physics can get quite interesting. And all forces of Nature are traced to another category of particles called gauge bosons - yes, that's boson as in Bozo the Clown or the great Indian physicist Satyendra Bose: when two particles interact at a distance through a force, microscopically the process involves one of them spitting out the appropriate gauge boson and the other catching it. The back-reaction of throwing and catching the intermediary gauge boson results in a force on the two interacting particles. So, it's a zoo of particles in this microscopic quantum world, with leptons and quarks exchanging gauge bosons all the time; and thus the world goes around. We understand some aspects of this physics at a level of precision that is both gratifying and disturbing: in one famous measurable quantity, the theory predicts a number with 15 digit precision; the measurement agrees with it to all 15 digits… 

All is not rosy however with our understanding of this strange world of quantum particles. The highly successful theoretical framework that we currently have - called the Standard Model - requires the input of about two dozen parameters from experiment: numbers that we need to measure and depend on to be able to use the theory for predictions. For example, we need to measure and input into the equations of the Standard Model the mass and charge of the electron. This is somewhat of an ugly situation: the fewer "free" parameters a theory has, the better it is, the more fundamental. There's however another perhaps more important issue. The Standard Model predicts the existence of a particularly important particle - the Higgs particle. In the catalogue of the building blocks of matter that the Standard Model provides, all constituents have now been experimentally discovered - except for the Higgs… And the Higgs - popularly called the "God particle" - is a very very important missing link.

Let's add a bit of cosmology to the mix with a religious overtone. In the beginning, the universe was empty and void; and darkness was upon the face of the deep (i.e. dark energy). Then came about some matter from the Standard Model (see "graceful exit" in my previous post). However, temperatures were hot, very hot - too hot to have the Higgs around in large amounts. And all the other particles had no mass, they were massless much like the particle of light, the photon. Then the temperatures cooled down, and the Higgs particle condensed and filled the universe - like water vapor condensing at night on an open field. And there was much rejoicing. There was rejoicing because the Higgs particle interacts with the rest of the matter in the universe in a very interesting way: all other particles collide with the condensate of the Higgs that pervades space and, through this mechanism, acquire mass and substance… Hence, we get the proton, electron, then atoms, then us. So, the Standard Model requires a Higgs particle to make sense of the world we see around us. But we are yet to isolate one and identify it conclusively…

The Large Hadron Collider (LHC) - currently in operation in Switzerland - is hunting for the illusive Higgs. If we don't find it within the next few years, you will see particle physicists screaming and running around naked in the streets. If we do find it, but nothing else, the Standard Model would be complete for now - and depression will ensue on many physicists (including myself). Finally, if we find it in addition to a whole slew of new particles - perhaps candidates for dark matter - there will, once again, be much rejoicing. One last thing: there is a remote possibility that  the Higgs condensate IS the dark energy (see previous post on dark energy)… 

The accompanying video is a rap by the talented science journalist Kate McAlpine (known as alpinekat…) about the LHC. The words of the song actually have instructive physics content; it's worth to listen to carefully. Don't know however what to say about the dancing physicists… at least they're fully clothed. Check it out, and check out Kate McAlpine's webpage with more physics songs at: http://www.katemcalpine.com/

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