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Saturday, November 10, 2012

What is a graviton?

If you've read anything about physics, then you will read many words ending with "ON" words like proton, neutron, gluon, photon, boson, fermion and on and on and on ... One of the words with which you might have found it "graviton". Let's be clear: At the moment, the graviton is a purely theoretical concept that walks the edge of the boundary between the domains of science and speculation seriously.

The spectacular success of quantum theory to describe three forces-electromagnetism and the strong and weak nuclear forces-provides an important impetus to try to attach it to the fourth force: gravity (What is gravity? ). In the same way the photon is known as the quantum particle of the electromagnetic force and the gluon quantum particle is the strong nuclear force, the "graviton" is the name given to hypothetical particle quantum gravity.

However, a quantum theory of gravity has been elusive until now. The theory of Einstein's general relativity has been the most successful description of gravity, but when he meets nonsense predicts the quantum world, with infinite impossible arising from the calculations. Infinities like these are the way of nature to say "back to the drawing board." And although theoretical physicists have a way to go to come up with such a model, it is still possible to calculate some of the properties of gravitons.

For example, we know that gravity is a rank-and-infinite range and distant galaxies can join. This means that the typical graviton have zero mass. In addition, the empty space has no electrical charge, which means that the graviton, which acts through empty space, must be electrically neutral.

Sophisticated thoughts tell us what should be the spin of the graviton in quantum mechanics. Although the Standard Model particles that make up matter have spin 1/2 particles and the same model "carriers" of the forces have a spin of 1, the graviton must have a spin of 2. (This comes from the fact that gravity appears as a result of the distribution of energy and momentum in the universe. In mathematical formalism of this is called a tensor. If you want to impress at a party, tell your friends that gravity originates due to energy-momentum tensor of rank two.)

Turns out this spin is a good help, because you can prove that any massless particle with spin 2 must act exactly as predicted to behave a graviton. Therefore, if we find a massless particle of spin 2, we know that is a graviton. This behavior with spin 2 also explains the fact that conventional gravity only attracts, unlike electromagnetism, which attracts and repels.

That has already been predicted in theory a massless particle superstrings and spin 2 is one of the reasons for the popularity of theory over the past decades. While the complexity of the theory has led to a decrease in community enthusiasm towards superstring in recent years, it remains an elegant way to bring gravity to the quantum world. In addition, newer theories that predict extra spatial dimensions can allow massive gravitons of spin 2.

The gravitons are theoretically acceptable idea, but not proven. So if you hear someone say "gravitons are particles that generate the gravitational force", keep in mind that it is a reasonable assumption, but by no means universally accepted. Before long that gravitons are considered part of the pantheon subatomic.

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