Let's be more precise in use of "informal language" in gravity theory.

Science, order, and creativity - Google Books Result

books.google.com/books?isbn=0415171822...

David Bohm, F. David Peat - 2000 - Philosophy - 316 pages

Weyl's story shows the enormous power of informal language, which forms a significant part of the tacit infrastructure of science. ...

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Niels Bohr: Reflections on Subject and Object - Google Books Result

books.google.com/books?isbn=1930832001...

Paul McEvoy - 2001 - Philosophy - 540 pages

He then asked Bohm in essence what was special about the Aharonov-Bohm effect. Bohmreplied that it is a contribution to clarifying the informal language that ...

History of Twentieth-Century Philosophy of Science Book 7

www.philsci.com/book7-4.htm - Cached

He later refers to such supplementary description as informal language. Bohm's conclusion that mathematical physics must be supplemented with informal ...

Subject: Re: nonlocalizability of the gravity energy

Zielinski wrote:

*Well yes and no. Free test objects move along Minkowski geodesics that are justified by an action principle that leads to the GR field equations, but at the same time there is no deeper physical explanation.*

I replied: No, free massive test objects move along timelike geodesics (inside local light cone) of curved space-time. Locally only inside the small LIF they appear to move on Minkowski geodesics (in segments small compared to radii of curvature).

Z:

*But I think Jack has a point when he says that there is an explanation for flat space geodesic motion in GR, even if it has a distinctly formal feel to it.*

I replied: Formally, in the tetrad formalism. The gravity field (meaning #3) is the motion of an LIF described by a SO1,3 Lorentz group 4-vector e^I, I = 0 (timelike), 1,2,3 (spacelike) of Cartan 1-forms each of which is GCT scalar invariant!

e^I is a SPIN 1 gravity field (meaning #3)

Einstein's SPIN 2 gravity curvature field (meaning #2)

ds^2 = e^IeI = (Minkowski)IJe^Ie^J = guv(LNIF)e^u(LNIF)e^v(LNIF)

however, adding Lorentz group SPINS

1 + 1 = 0, 1, 2

i.e. in terms of dimensions of the finite irreducible representations (2S + 1)

3x3 = 1 + 3 + 5

so what happened to spin 0 Brans gravity and repulsive spin 1 anti-gravity?

Higgs mechanism gives them large mass. Are they part of the nuclear force?

In sense of renormalization group running of the coupling constant ---> Salam's strong short-range Yukawa gravity?

You can actually show that free test objects move along geodesics in GR. A Minkowski manifold is just a special case.

On 8/29/2011 7:07 AM,

*Minkowski spacetime has inertial forces built in because our experience is that spacetime is locally almost exactly flat (and Minkowski spacetime is an idealization of that local experience) and inertia is a fact of our local experience. So using Minkowski spacetime to "explain" inertia is no explanation at all because it is simply assumed. At best, it becomes what Wheeler identifies as a "non-dynamical" boundary condition for cases where cosmic matter density is less than critical and it is imposed as an asymptotic condition at infinity. But cosmic matter density is NOT less than critical. That, now, is a measured fact, not speculation. So inertial reaction forces are in fact due to gravity in our universe.*

I don't get Jim's point

*.*There is no Machian model that can explain the rest mass of the elementary particles the way the Higgs mechanism and QCD do in a quantitative fashion. Maybe the hologram theory can do it. That is speculation. However, it must be a future boundary. It can't be a past boundary.