Since the coupling charge and the response coefficient for gravity are identical, it follows that gravity can only operate in a single directional sense, because changing the sign of m for a particle would reverse the sense of both the coupling and the response, leaving the particle’s overall behavior unchanged. In other words, if we considered gravitation to apply a repulsive force to a certain particle by setting the particle’s coupling charge to -m, we would also set its inertial coefficient to -m, so the particle would still accelerate into the applied force.

— 2.2  Force Laws and Maxwell’s Equations

— Reflections on Relativity

— mathpages

2013.06.09 Sunday ACHK

So one can show that all of physics of M-theory, if studied in the light-cone gauge, is equivalent to an ordinary non-gravitational matrix model – a quantum mechanical model with matrix degrees of freedom.

The eigenvalues of the X^i matrices may be viewed as the positions of the gravitons (or their superpartners) in 11 dimensions; a threshold (zero-binding-energy) bound state of several such eigenvalues (which can be proved to exist, a remarkable property of SU(N) supersymmetric quantum mechanics) are gravitons that carry a higher number of units of the quantized light-like (longitudinal) momentum.

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— Physics Stack Exchange
   
— answered Mar 6 ’11 at 8:02

— Lubos Motl

2013.06.06 Thursday ACHK