02 August 2006

What's in a Name

I've just come to realise that the term "Feynman boson" is not exactly nonsensical as it seems. But before I delve into that, I shall briefly recount how I came to name this blog as such.

A couple of months back, when I decided, somewhat on the whim, to establish a blog, I was momentarily held back when I was required to decide on the name of the blog. Since I could not come up with anything sensible at that moment, my mind searched for absurdly creative names.

(You can skip the next paragraph if you wish.)

At that time, my statistical physics course has steered into spin-statistics theorem, touching on what a boson is. At the same time, our SPS project has ventured into scalar fields, more specifically, the Higgs boson. Now, the Higgs boson is a particle predicted in theory (due to symmetry), by Peter Higgs, but is yet to be observed experimentally. It is a very important particle in that it was supposedly responsible for giving mass to other particles.

The Higgs boson is obviously named after Peter Higgs. So I thought, Higgs has his boson. Since Richard Feynman is my favourite scientist, why not name a boson after him? And hence the name of this blog...

Recently, while looking up certain facts about Feynman on Wikipedia, I came across this paragraph:

After the success of quantum electrodynamics, Feynman turned to quantum gravity. By analogy with the photon, which has spin 1, he investigated the consequences of a free massless spin 2 field, and was able to derive the Einstein field equation of general relativity, but little more.

Now, a boson is a particle which has integer spin, i.e. spin-0, spin-1, spin-2 and so on. Gravity, in quantum field theory, is described by a spin-2 particle known as the graviton (the equivalent of photon in electromagnetic interactions). In particle physics, a force is actually an exchange of these particles, so when there is electromagnetic or gravitational force between two bodies, these two bodies exchange photons or gravitons respectively.

I'm not sure if Feynman is the first person to derive Einstein field equations from quantum field theory. Now, assuming it is, this particle, this graviton, can then also be named after Feynman. And since gravitons are spin-2 particles, this meant that they are bosons. So Feynman bosons are actually gravitons.

Gravitons have never been observed experimentally. The currently accepted theory for gravity is Einstein's general theory of relativity. In it, gravity is actually not a force, but a result of the geometry of spacetime. There is no particle involved. On the other hand, in quantum field theory where gravitons are hypothesized to exist, there is currently no model that can meaningfully describe the gravitational force. It is the only particle in quantum field theory responsible for interactions not to be observed, which may be a hint that the quantum field theory may not be the ultimate theory that can unify all four fundamental forces.

The attempt at finding a model of quantum field theory that can describe gravity (and hence incorporate gravitons) is collectively known as quantum gravity, and so far the success has been limited. Right now, the superstring theory holds greater hope in this aspect.

Perhaps this is what "Feynman boson" means... barking up the wrong tree.

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