Quote:
Originally Posted by CraigS
Hmm .. Steven .. just been doing some reading up … it seems that a basic difference between GR and QM/QFT is that GR theory is not dependent on any preferred type of space-time (ie: no frame of reference is 'special' over another), hence it is regarded as a 'background independent' theory.
In QM/QFT, however, the properties of the elementary particles have to do with their relationships to the state of the 'background' vacuum. Ie: the vacuum has different states which ultimately gives rise to the different properties of the elementary particles: ie: mass, position, momentum, spin, and charge.
Hence QFT is called a 'background dependent theory'.
If so, I think I can get this ..
Cheers
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Craig,
The vacuum is a field in the lowest or ground state. There are different types of vacuums, such as the quantum electrodynamic (QED) vacuum or the quantum chromodynamic (QED) vacuum.
The issue with gravity as a Quantum Field theory is that it is non- renormalizable. A gravitational interaction between 2 particles changes the particles from a state A to a state B. If you sum all the momenta going from state A to B you end up with infinite values. This is prevalent at the Planck scale. There is no way you can renormalize or "cut out" the infinite terms as you can with QED or QCD.
This is where string theory is an advantage. By making your strings larger than the Planck scale, the infinities are averted.
Regards
Steven