- #1
Fra
- 4,104
- 606
I think I raised this before but I am curious to hear the reflections from all of you about one simple thing. The context of my question is the quest for a deeper theory of QG, along the lines of an intrinisic measurement theory, but the principal question can be easily phrased in terms of classical geometry.
As we know, long before Riemann, curvatures was formulated in terms of, an imagined external embedding space. But Riemann seeked an "instrinsic formulation" with "intrinsic curvature measures" of differential geometry that was not referencing to these external objects.
He sort of succeeded, but of course Riemann was not going an instrinsic measurement theory, his constructs were fully of mathematical realist types.
One thing has bothered me since way back, and I get even more bothered by the fact that a lot of people seem to not see this as a big issue.
If we now consider _information_ about geometry, we know from Riemann that an inside observer can _in principle_ infer the geometry by making "measurements" with sticks and rods, or light rays or something similar. So far so good. But this totally ingores the quantity of information required to define say a local chart, not to mention an atlas.
In particular if one imagines an inside observer, like an ant crawling on the surface - how this this ant (which must be infinitely small, in order to not violate the manifold iabstraction)
1) construct sticks and rods
2) store map information
It seems clear to me, that we currently do not yet have an instrinsic theory of information. It seems already from this general starting point, that the complexity of the _visible_ manifold must somehow be bounded by the complexity of the inside observer - right?
Somehow, this is also partly the essence of an ultimate implementation of a holographic principle and bound?
Does this have any implications on what it means to "quantize gravity" or wether we can make sense of something like a "hilbert space" for the gravitational field? Because the hilbert space itself would be constrained by our "ant" analogy, or?
I don't exepect any full solutions but I'm curious how you people "consider" this type of question? do you dismiss it as philosophical things of no relation to physics? or do you think it is trying to tell us something?
/Fredrik
As we know, long before Riemann, curvatures was formulated in terms of, an imagined external embedding space. But Riemann seeked an "instrinsic formulation" with "intrinsic curvature measures" of differential geometry that was not referencing to these external objects.
He sort of succeeded, but of course Riemann was not going an instrinsic measurement theory, his constructs were fully of mathematical realist types.
One thing has bothered me since way back, and I get even more bothered by the fact that a lot of people seem to not see this as a big issue.
If we now consider _information_ about geometry, we know from Riemann that an inside observer can _in principle_ infer the geometry by making "measurements" with sticks and rods, or light rays or something similar. So far so good. But this totally ingores the quantity of information required to define say a local chart, not to mention an atlas.
In particular if one imagines an inside observer, like an ant crawling on the surface - how this this ant (which must be infinitely small, in order to not violate the manifold iabstraction)
1) construct sticks and rods
2) store map information
It seems clear to me, that we currently do not yet have an instrinsic theory of information. It seems already from this general starting point, that the complexity of the _visible_ manifold must somehow be bounded by the complexity of the inside observer - right?
Somehow, this is also partly the essence of an ultimate implementation of a holographic principle and bound?
Does this have any implications on what it means to "quantize gravity" or wether we can make sense of something like a "hilbert space" for the gravitational field? Because the hilbert space itself would be constrained by our "ant" analogy, or?
I don't exepect any full solutions but I'm curious how you people "consider" this type of question? do you dismiss it as philosophical things of no relation to physics? or do you think it is trying to tell us something?
/Fredrik