Warp wrote:
>   With quantum gravity the direction seems reversed: They have formed the
> theory of a gravitational quantum *first*, and now they are really hard
> trying to discover it somehow.

The problem is that both relativity and QED (quantum electrodynamics - 
quantum mechanics for non-nuclear interactions) seem to be very accurate in 
their appropriate timescales. But QED assumes absolute time (AFAIK), and 
relativity assumes continuously differentiable space (and hence energy 
levels), so we know we can't resolve those two into one theory without 
changing one or the other. (At least, that's my understanding of the problem.)

The approach that QED uses has been successfully applied to nuclear 
interactions with the strong and weak nuclear forces, as well as 
interactions between quarks (quantum chromodynamics). In other words, it 
looks like every force *except* gravity behaves like 
two-dimensional-probability "waves" traveling at the speed of light on average.

Hence the assumption that gravity is likely to also play by that rule, with 
gravitons mediating the effects of gravity on the small scale with 
statistical properties making it look smooth and consistent and "not 
quantum" over larger scales.

tl;dr - relativity and quantum are mathematically incompatible, and quantum 
accurately describes everything *except* gravity, so the assumption is 
gravity is wrong.

-- 
Darren New, San Diego CA, USA (PST)
   You know the kamikaze monsters in Serious Sam
     with the bombs for hands, that go AAAAAHHHHHHHH!
   I want that for a ring tone.

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