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The Question
(Submitted June 08, 1997)
Force carrying particles for electromagnetic radiation, the weak/strong nuclear
forces and gravity have been either discovered or postulated. What are the
experimental difficulties in "discovering" gravitons?
The Answer
There is a strong analogy between the photon and the graviton. EM forces
are propagated by virtual photons, and of course we detect 'real' photons in
the form of (classical) EM radiation. Similarly, since the graviton must be
massless (since gravity has an infinite range), the graviton can only be
'detected' analogously to the way that the photon is detected, i.e., in the
detection of 'classical' gravity waves. Part of the idea of unification theory
is that at high enough energies all four forces 'merge', and can be propagated
by the same particle (i.e., this has been shown to be the case for the EM and
weak interaction, and hence they are often referred to collectively as the
electro-weak interaction). But I think you would need a particle accelerator
bigger than the size of the Earth to get to energies high enough for all of the
forces to be unified.
Andy Ptak
for Ask a High-Energy Astronomer
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