Hi Julian
I'm glad to see you flying the Machian flag, and also taking a stand against infinity. I'm with you in both cases.
I find shape dynamics intriguing, and agree with the basic premise that the gravitational degrees of freedom are conformal. I'm struggling with whether they are 3-d or 4-d conformal. I tend to the latter position, but am willing to learn.
Best wishes
george
MAX PLANK:
An important scientific innovation rarely makes its way by gradually winning over and converting its opponents; it rarely happens that Saul becomes Paul. What does happen is that its opponents gradually die out and that the growing generation is familiarized with the idea from the beginning.
Dr. Barbour,
thank you for thought provoking essay. I read it today the second time, because of Daniel Waagner Fonteles Alves, whose essay I found more accessible than yours. The concept of shape dynamics is new to me but my immediate instinct is that this is the right way to go.
You write, " A closed geometry is needed to model a universe as a whole. A closed three-geometry is much harder to imagine, but is mathematically possible. "
I happen to visualize 3-geometry very well, even though call it 4D geometry, because I insist on considering not just the 3D surface, but the 4D object as a whole. My approach to physics is visual and, in line with your holistic approach, I see the universe as a hypersphere, on the 3D surface of which we live. I found that this 4D perspective dispels the paradoxes that plague contemporary physics and makes the workings of the universe, from its smallest components to largest structures, appear to make perfect sense.
I especially appreciate your holistic view, because I conceive of space, energy and time as 3 aspects of one and the same, a process, with either one being the expression of the other two. To me it appears that shape dynamics is the best way to model such processes evolving and interacting locally.
I wonder if Alpha shape is a hypersphere -? because, topologically, 4D allows for most symmetries in comparison to all other spaces, and as a space with even number of dimensions, also permits more rotations than the next runner-up, 3D.
I very much hope that you would find time to comment on my essay, even though the ratings are already closed ( http://fqxi.org/community/forum/topic/1547 ) I would very much value your feedback.
Congratulations on making the finalists list!
Julian Barbour: "I believe that Shape Dynamics (developed in the last 13 years with my collaborators and presented in my Perimeter colloquium PIRSA:12050050 at the recent workshop) does explain the origin of local inertial frames and why all of Einstein's conclusions in special relativity hold in them. It is not challenging special relativity but explaining from relational Machian first principles why its conclusions are correct. The intriguing aspect of this work is that the explanation of why special relativity is correct of necessity singles out a definition of absolute simultaneity in the universe as a whole while showing that, just as Einstein concluded, there is no way it can be detected locally."
So, Julian Barbour, absolute simultaneity is what happens "in the universe as a whole" but locally Nature is deceiving us and, as a result, we fiercely sing "Divine Einstein" and "Yes we all believe in relativity, relativity, relativity"?
Pentcho Valev
Julian
I noticed a reference to a Discover article just now on another blog (Is Einsteins's work....)
The error Einstein (and indeed most other people) made was to presume there is duration in physical existence. This results in the misuse of x = vt. So, having introduced a non existent variable into physical existence (ie reified time), then that has to be explained. That was achieved via another common error, which is to conflate physical existence with the observation of physical existence. That is, what Einstein explained as being variations in timing because 'everything is relative' is the differential in the time taken for light to travel from the point where it was created (ie where physical existence occurred) to the observer.
Without becoming an historian and reading everything, I can track the formal reification of time back to Poincaré and his flawed concept of simultaneity, in narrative form 1898 and in numerical form 1900. He picked up on local time which Lorentz was using by 1895, essentially correctly, after Voigt and Doppler, but associated it with his misunderstanding of simultaneity. In addition they all thought their thinking was correct because the first hypothesis was dimension alteration, a false reaction to Michelson, so the concept that timing devices could not keep 'proper' time when being caused to change momentum seemed valid.
Paul
