WTF is the speed of gravity

[KrazyHorse]

Note that I'm pulling the above out of my ass, given how much I know about QED et al.

[KrazyHorse]

Remember that we have no data points for quantum levels of gravitation (right?) so all you require is that on everyday scale at low velocity it reduces to Newt gravity...

[Ethelred]

Originally posted by Frogger


You can't describe gravity on a quantum scale? I'm pretty sure you can. What would the problem be? Just use QED, slap on coupling constant. Only problem is that when you hit large scales it breaks down, no?

Isn't Quantum Chromo Dynamics more complex than QED? That would imply that a quantum theory of gravity would be more complex yet.

[KrazyHorse]

Nah, isn't QCD more complex just because they have evidence of it being more complex? Like the fact that there are a kajillion diferent colours of force carriers, etc.?

On everyday scale, grav. is quite simple...behaves exactly EM except weaker and there's no repulsion...

[Rogan Josh]

Originally posted by Ethelred
Isn't Quantum Chromo Dynamics more complex than QED? That would imply that a quantum theory of gravity would be more complex yet.

QCD is based on the symmetry group SU(2) - so called because it is represented by the set of special (determinant=1), unitary 2x2 matrices. QED is base on U(1) - unitary 1x1 matrices (ie. any number 'a' for which |a|^2=1).

This introduces quite a few more complexities - for example, the gluon (the QCD force carrier) itself carries colour charge; the photon by contrast is neutral.

Gravity is probably based apon some more complex symmetry group. My money is on local supersymmetry, which is an extremely complicted group with fermionic generators. So quantum gravity will be quite different from (and quite a bit more complex than) QED.

But. Frogger, if you can write down a consistent theory of quantum gravity I am sure we would all be interested......