What is needed is a

quantum theory of gravity: a theory which explains gravity at the macroscopic scale.

Such studies can yield new insights into the developing

quantum theory of gravity, and can also help establish ultimate limits on technology -- not based on the degree of scope or difficulty of an engineering challenge, but by compatibility with our core understanding of the fundamental laws of physics.

This leads on to a

quantum theory of gravity. He draws the reader along the mind-boggling route whose ultimate goal, he is convinced, will be a unified theory of physics.

And in the absence of an absolute spacetime structure, it is unclear to what extent full Hilbert space structure should be expected to play a fundamental role in the final

quantum theory of gravity (Barbour [1994b], p.

The

quantum theory of gravity explains the gravitational acceleration of matter as caused by the refraction of quantum waves by the time dependence and spatial inhomogeneities of the dynamical space flow [1].

He explores the general features that a

quantum theory of gravity is expected to show and gives an overview of the primary approaches.

"String theory is simply the only hope we currently have for a

quantum theory of gravity, and obviously gravity has to be quantized to be consistent with the rest of what we know about physics."

These phenomena are the corner stones of our present knowledge about the quantum nature of space-time, and it is of crucial importance to understand deeply their features and consequences in the quest for a

quantum theory of gravity. Unfortunately, these features are still poorly understood, and are experimentally out of reach in astrophysics.

Unlike the "point particles" of Quantum Field Theories, strings interact in a way that is almost uniquely specified by mathematical self-consistency, forming an allegedly valid

quantum theory of gravity. Since its launch as a dual resonance model (describing strongly interacting hadrons), ST has changed over the years to include a group of related superstring theories (SST) and a unifying picture known as the M-theory.