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Author Topic: Why do we need gravitons?  (Read 1753 times)

Offline stevewillie

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Why do we need gravitons?
« on: 31/08/2008 08:55:58 »
The graviton is the still unconfirmed particle carrier of the gravitational force. Why do we need it if gravity is already explained by General Relativity (GR)? Light has no mass. If it did, it could not travel at "the speed of light"(according to SR). GR explains the bending of a light beam near a massive body by the locally increased curvature of spacetime itself. Light is simply following the natural geodesic of spacetime. This explanation would also seem to hold for the gravitational attraction between masses.   


 

Offline graham.d

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Why do we need gravitons?
« Reply #1 on: 31/08/2008 09:51:08 »
It is a consequence of trying to fit General Relativity with Quantum Mechanics. The most accepted theory has all forces involve an exchange of particles. EM forces have the photon, Weak forces have W and Z Bosons, Strong forces have the Gluon and (it is thought) Gravitational forces have the graviton.

Of course this is just a theory but it has been a useful one so far. Whether it is necessary to have a concept of a graviton particle remains to be seen.
 

Offline Soul Surfer

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Why do we need gravitons?
« Reply #2 on: 31/08/2008 11:55:14 »
The thing that most people forget about gravitons as particles is the incredibly low frequencies associated with gravitational interactions compared with electromagnetic ones in the universe as it is now.

The energy associated with a quantum in electromagnetic radiation is Planck's constant times the frequency and it only becomes significant at around the frequencies associated with light  ie many terahertz  or millions of millions of cycles per second and even then the quanta are not very energetic individually.

The lowest frequency electromagnetic waves are in the Kilohertz region and individual quanta have such tiny energies that they are only detectable in largenumbers so classical analysis is good enough.  The very fastest gravitational interactions are rotating or binary neutron stars which can just about make it to the Kilohertz region  most gravitational interactions are in the cycles per year (The earth round the sun)or cycles per 200 million years  the sun and many other stars around their galaxy so assuming that the energy associated with individual gravitons is like electromagnetic  Planck's constant times the frequency the individual quanta involved have absolutely infinitesimally small energies and there are really vast numbers of them.
 

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Why do we need gravitons?
« Reply #2 on: 31/08/2008 11:55:14 »

 

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