> On 17 Apr 2019, at 01:41, 'Brent Meeker' via Everything List > <[email protected]> wrote: > > > > On 4/16/2019 7:56 AM, [email protected] <mailto:[email protected]> > wrote: >> >> >> On Monday, April 15, 2019 at 9:26:59 PM UTC-6, Brent wrote: >> >> >> On 4/15/2019 7:14 PM, [email protected] <javascript:> wrote: >>> >>> >>> On Friday, April 12, 2019 at 5:48:23 AM UTC-6, [email protected] <> wrote: >>> >>> >>> On Thursday, April 11, 2019 at 10:56:08 PM UTC-6, Brent wrote: >>> >>> >>> On 4/11/2019 9:33 PM, [email protected] <> wrote: >>>> >>>> >>>> On Thursday, April 11, 2019 at 7:12:17 PM UTC-6, Brent wrote: >>>> >>>> >>>> On 4/11/2019 4:53 PM, [email protected] <> wrote: >>>>> >>>>> >>>>> On Thursday, April 11, 2019 at 4:37:39 PM UTC-6, Brent wrote: >>>>> >>>>> >>>>> On 4/11/2019 1:58 PM, [email protected] <> wrote: >>>>>>> >>>>>>> >>>>>>> He might have been referring to a transformation to a tangent space >>>>>>> where the metric tensor is diagonalized and its derivative at that >>>>>>> point in spacetime is zero. Does this make any sense? >>>>>> >>>>>> Sort of. >>>>>> >>>>>> >>>>>> Yeah, that's what he's doing. He's assuming a given coordinate system >>>>>> and some arbitrary point in a non-empty spacetime. So spacetime has a >>>>>> non zero curvature and the derivative of the metric tensor is generally >>>>>> non-zero at that arbitrary point, however small we assume the region >>>>>> around that point. But applying the EEP, we can >>>>>> transform to the tangent space at that point to >>>>>> diagonalize the metric tensor and have its derivative as zero at that >>>>>> point. Does THIS make sense? AG >>>>> >>>>> Yep. That's pretty much the defining characteristic of a Riemannian >>>>> space. >>>>> >>>>> Brent >>>>> >>>>> But isn't it weird that changing labels on spacetime points by >>>>> transforming coordinates has the result of putting the test particle in >>>>> local free fall, when it wasn't prior to the transformation? AG >>>>> >>>> It doesn't put it in free-fall. If the particle has EM forces on it, it >>>> will deviate from the geodesic in the tangent space coordinates. The >>>> transformation is just adapting the coordinates to the local free-fall >>>> which removes gravity as a force...but not other forces. >>>> >>>> Brent >>>> >>>> In both cases, with and without non-gravitational forces acting on test >>>> particle, I assume the trajectory appears identical to an external >>>> observer, before and after coordinate transformation to the tangent plane >>>> at some point; all that's changed are the labels of spacetime points. If >>>> this is true, it's still hard to see why changing labels can remove the >>>> gravitational forces. And what does this buy us? AG >>> >>> You're looking at it the wrong way around. There never were any >>> gravitational forces, just your choice of coordinate system made fictitious >>> forces appear; just like when you use a merry-go-round as your reference >>> frame you get coriolis forces. >>> >>> If gravity is a fictitious force produced by the choice of coordinate >>> system, in its absence (due to a change in coordinate system) how does GR >>> explain motion? Test particles move on geodesics in the absence of >>> non-gravitational forces, but why do they move at all? AG >>> >>> Maybe GR assumes motion but doesn't explain it. AG >> >> The sciences do not try to explain, they hardly even try to interpret, they >> mainly make models. By a model is meant a mathematical construct which, >> with the addition of certain verbal interpretations, describes observed >> phenomena. The justification of such a mathematical construct is solely and >> precisely that it is expected to work. >> --—John von Neumann >> >> This is straight out of the "shut up and calculate" school, and I don't >> completely buy it. E.g., the Principle of Relativity and Least Action >> Principle give strong indications of not only how the universe works, but >> why. That is, they're somewhat explanatory in nature. AG > > Fine, then take them as explanations. But to ask that they be explained is > to misunderstand their status. It's possible that they could be explained; > but only by finding a more fundamental theory that includes them as > consequences or special cases. Whatever theory is fundamental cannot have an > explanation in the sense you want because then it would not be fundamental.
Indeed. And with Mechanism, any Turing-complete theory can be chosen as fundamental, because we can’t explain them from less (provably so). Then, physics becomes a sum on all histories, and the least action principle should be derivable from its quantum structure imposed by incompleteness on observation (defined by some variant of []p & p). We cannot explained what we are starting from. Bruno > > Brent > > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] > <mailto:[email protected]>. > To post to this group, send email to [email protected] > <mailto:[email protected]>. > Visit this group at https://groups.google.com/group/everything-list > <https://groups.google.com/group/everything-list>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
