Several authors have recently explored the idea that physical constants such as c and G might vary over time and have formulated theories describing this variation that can address a range of cosmological problems .
Such work typically invokes a generic parameterization which assumes a power-law variation with the expansion scale factor , R .
This work offers alternative , physically motivated definitions for the parameters c , G , and h 
based on the Machian premise that these dimensional quantities reflect global dynamics of the expansion geometry .
Together with a postulated conservation law and equations of motion , the implications of this theory for Friedmann models are examined , and found to yield several interesting conclusions including : ( 1 ) natural solutions to the horizon , flatness , and lambda problems , ( 2 ) the prediction of a flat , \Omega _ { 0 } = 1 universe , ( 3 ) different forms for some cosmological scaling laws , ( 4 ) an apparent fit to observations of Type Ia supernovae without invoking a cosmological constant , ( 5 ) equivalence between our Universe and a black hole and apparent consistency of the model with the Holographic Principle , and ( 6 ) potentially testable predictions for the time variation of physical parameters , including values for \dot { c _ { 0 } } and \dot { h _ { 0 } } that are small but non-zero today and a value for \dot { G } that was negative and nonzero during radiation domination and decayed to effectively zero upon the epoch of matter domination .
While this work does not attempt to provide the complete theoretical foundation that must ultimately underlie any theory that could naturally marry traditional physics with the notion of time-varying physical parameters , it is written in the hope that it might stimulate further progress towards this end .