- #36
PAllen
Science Advisor
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I wonder if the following scenario clarifies any of these interpretational questions.
Suppose we compare our universe to one in which gravity only affects matter with either color or e/m charge (in particular, neither photons nor neutrinos are affected by gravity). In such a universe, you could unambiguously distinguish measurements of gravity from measurement of what background geometry there is for spacetime.
Comparing that universe to ours, you can say with equal justification, that gravity is no longer a force, instead mass/energy interacts with geometry as specified by GR; or that geometry has become unobservable because it is indistinguishable from gravity as determined by GR. If this is what Mentz114 is getting at, then I suspect few would have any disagreement. This distinction is purely philosophic, and there is no objective criterion you can use to say one is a more economic viewpoint than the other. Purely a matter of taste.
Suppose we compare our universe to one in which gravity only affects matter with either color or e/m charge (in particular, neither photons nor neutrinos are affected by gravity). In such a universe, you could unambiguously distinguish measurements of gravity from measurement of what background geometry there is for spacetime.
Comparing that universe to ours, you can say with equal justification, that gravity is no longer a force, instead mass/energy interacts with geometry as specified by GR; or that geometry has become unobservable because it is indistinguishable from gravity as determined by GR. If this is what Mentz114 is getting at, then I suspect few would have any disagreement. This distinction is purely philosophic, and there is no objective criterion you can use to say one is a more economic viewpoint than the other. Purely a matter of taste.