Natural Science Forum / Physics / Research / April 2005

The claim that String theorist make is that the relativistic interpretation
of space time is not the most fundamental way of looking at the problem of
gravity. In general relativity gravitational action is mediated by space
time itself.  Specifically the curvature of space time manifolds due to the
distribution of energy in a given space.  In string theory the background
space time is fixed and (usually) flat and has 11 or more dimensions.
forces, fields and particles are all represented by vibrational modes of
the strings.  As it turns out one of these modes would have the feature's
predicted for a graviton*.  In the view of string theory it is the action
of theses stringgy gravitons which gives rise to gravity.  

* The reason that string theory has not been universally accepted as the
theory of everything including quantum gravity is that there is more than
one string theory.  Furthermore string theories only seem to work in a
universe that is "super symmetric" and no experimental proof exist to back
up any of it's claims.  

Loop quantum gravity and other so called canonical theories of quantum
gravity are more like general relativity in that they look at gravity as
being a consequence of the geometry of space time.  This seems to leave no
room for a graviton or particles scattering and interacting in a way that
most physicist are comfortable with.  This is the main reason I see for
canonical quantum gravitational theories not getting very far.  

Some other theories of quantum gravity are

Discrete Lorentzian quantum gravity - Is as old as a set of paper's by
Hartland S. Snyder which appeared in physical review in 1947. Since then
other have worked to add dynamics to his flat quantized space time.

Process physics - This interesting idea says that all the universe can be
treated as a large neural network and what we as physicist do is simply
look for the program that network is running...

Sakharov induced gravity- This theory says that we should not quantize the
gravitaional field.  The quantum gravitational field does not exist and
simply arises from what is left over from other forces. That gravity is a
sort of van der wall force.

By way of qualifying myself to answer this question..

Myself and Alexander Klimets have been working in parallel on quantum
gravity and have reached many of the same conclusions by following
different mathematical paths.  Such speaks to the logical underpinings of
our works.

The problem with all of the above is iron clad incontravertable positive
experimental results that no one can deny are valid + negative results for
the other theories predictions.  When that happens the matter will be
settled.