Is Epstein's time-slowing explanation of gravity circular reasoning?

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Yogi, G is a coupling constant and it is used to change units of measure. It allows mass to be expressed a length, just in the same way as c allows time to be expressed as a length. You can set them to 1 and work in Planck units if you like. Yes, if you want a value in SI units you will have to measure it just as you do with c. There are also dimensionless constants (26 according to John Baez). These constants are used in the most accurate of all theories, QFT. Sure no-one knows why they have the values they do, or how to compute them from the theory, and that may mean the theory is incomplete in some sense, but it is the same with all theories.
 
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CRichard said:
Epstein's reasoning is then that you can fold this paper into a cone (which is allowed because it doesn't change the nature of spacetime) and then see that the straight line actually curves toward the wider end of the cone. This is how gravity comes about.

If I understand you correctly, this seems to violate time symmetry.
 
I enjoyed the debate between yogi and DaleSpam concerning the value of G.
yogi said:
Your missing the whole point - whatever units we use to express G - it will always measure the same - G appears to be temporally constant irrespective of the dimensions we use - but the units are significant - they show the fundamental tie between the physical thing (i.e., the law of Gravity) and its relationship to the cause that brings about the multiplying factor needed to make experimental measurements conform to the underlying theory. In the case of G, the units are cubic meters per sec squared per kgm - i.e., volumetric acceleration/kgm. And the volumetric acceleration of the universe within the limits of experimental error comports with the experimentally determined value of G - that is not numerology - it comes directly from Freidmann's equation.

That was the best explanation for G that I have read. Not to say that I think DaleSpame is wrong. What he is saying is of course correct, but it's not what makes the value of G meaningful.

Here is a case in point. The equivalence principle tells us that [itex]m_i = m_p = m_a[/itex]. If we could somehow change the ratio of [itex]m_a[/itex] to [itex]m_p[/itex] / [itex]m_i[/itex] then the measured value of G would change also, no matter what choice of units we used. In fact, this is precisely the way the equivalence principle can be experimentally tested. An example can be found in: "Experimental Measurement of the Equivalence of Active and Passive Gravitational Mass - L. B. Kreuzer". Start reading at the section titled "II. Theory".

Thanks for the interesting thread.