Unifying gravity and the Standard Model with quantum mechanics
Reminder: Have you read the preceding page on Quantum Field Theory?
In speculative theories of quantum gravity, the graviton is a hypothetical elementary particle that mediates the force of gravitation in the framework of quantum field theory (QFT). In QFT, the fundamental forces are mediated by the exchange of particles - the photon for electromagnetism, the gluon for the strong nclear force, W and Z bosons for the weak nuclear force - and if such a similar particle exists for gravity, QFT would describe all of the known forces. [1]
In this regard, three American scientists claim to have discovered a way of simplifying Richard Feynmann’s complex diagrams governing particle collisions, revealing features of the natural world that were implicit in current theories, but were obscured in the swarms of Feynmann diagrams. The methodology of this technique is unitary, since it required that the probabilities of all possible outcomes add up to 100%.
Most striking of all their revelations is a possible way to incorporate the force of gravity into the Standard Model, which had hitherto resisted all previous attempts to explain it. According to this model, the graviton behaves like a ‘double copy’ of the gluon, and each graviton behaves like two gluons stitched together, working like the contestants in a three legged race[2]. Thus:
If correct, this may perhaps provide an avenue for uniting the presently separate theories of general relativity with quantum mechanics. However, we should note that it is only when trying to make a theory of gravity consistent with quantum mechanics that a need for quanta (gravitons) arises at all.[3] Different commentators have different ways of looking at this.
On the one hand, there is a view that general relativity, which describes gravity in terms of the curvature of spacetime, doesn't need gravitons.[4] On the other, there is the view that in order to prove the existence of the graviton in general relativity, physicists must somehow be able to link the particle to the curvature of the space-time continuum and calculate the gravitational force involved in much the same way as Einstein did with light (and, as we now know, its individual photons).
[1] Source: https://en.wikipedia.org/wiki/Graviton
[2] Zvi Bern, Lance J Dixon and David A Kosower, “Loops, trees and the search for new physics”, Scientific American, May 2012, 20 esp at 23,26. If correct, this may perhaps provide an avenue for uniting general relativity with quantum mechanics.
[3] Professor Brian Cox, “What on earth is wrong with gravity?” BBC 2008.
[4] Q: Why does “curved space-time” cause gravity? Online post on 11 December 2010 by “The Physicist”.
On the one hand, there is a view that general relativity, which describes gravity in terms of the curvature of spacetime, doesn't need gravitons.[4] On the other, there is the view that in order to prove the existence of the graviton in general relativity, physicists must somehow be able to link the particle to the curvature of the space-time continuum and calculate the gravitational force involved in much the same way as Einstein did with light (and, as we now know, its individual photons).
[1] Source: https://en.wikipedia.org/wiki/Graviton
[2] Zvi Bern, Lance J Dixon and David A Kosower, “Loops, trees and the search for new physics”, Scientific American, May 2012, 20 esp at 23,26. If correct, this may perhaps provide an avenue for uniting general relativity with quantum mechanics.
[3] Professor Brian Cox, “What on earth is wrong with gravity?” BBC 2008.
[4] Q: Why does “curved space-time” cause gravity? Online post on 11 December 2010 by “The Physicist”.