Re: Open poll on "What changes for special and general relativity?"
- From: "Juan R." <juanrgonzaleza@xxxxxxxxxxxxxxxxxxxx>
- Date: Mon, 26 Nov 2007 04:00:44 +0000 (UTC)
On Nov 21, 5:37 pm, Doug Sweetser <dougsweet...@xxxxxxxxx> wrote:
3) Spacetime is not fundamental just a derived framework.
Spacetime needs events, events need spacetime.
Are you repeating the main general relativity point that physical
events do not happen over a spacetime background (but spacetime is a
dynamical actor)? Or do you mean anything else?
6) Gravity is a force like electrodynamics. Thus, geometric General
Relativity arises like an approximation.
If true, it would be hard to sell because everything would have to be
utterly perfect and pristine (from a clod with experience).
Currently, there are ungeometrical theories of gravity thought to be
empirically undistinguishable from general relativity.
An example is the field theory of gravity (FTG) developed in recent
years in basis to early ideas given by Feynman and others.
9) Irreversibility is real. Thus Minkowskian view is just approximated
one.
Time cannot have an arrow because it is a scalar, but spacetime can
have a handedness. When Lorentz symmetry goes local, irreversibility
is a handjob.
The popular expression "time arrow" does not mean that time may be
thought like a vector or similar.
It is a statement about time-asymmetry usually related to a semigroup
description.
14) E^2 =/= {mc^2}^2 + {pc}^2
I would NEVER write it this way, since we observe E, we observe p, and
we calculate m. In curved spacetime, the value of any 4-vector
contraction will change in ways we understand. {mc^2}^2 = E^2 -
{pc}^2 in flat spacetime.
I wrote the standard expression in loop quantum gravity literature.
Check the L. Smolin reference [2].
Smolin proposes {c = 1}
E^2 == m^2 + p^2 + {l_p * E^3} + ...
since the l_p is of Planck order, the difference with Lorentzian SR
formula will be observable only beyond certain upper limit.
Lee Smolin proposes in several places a set of high-energy experiments
would measure deviations from special relativity of that kind.
It is just another proposal.
18) Equivalence principle may arise from some other more fundamental
principle.
The equivalence principle is too simple to arise from something else.
I believe the active, passive and inertial masses are all equivalent.
The equality between the three masses corresponds to the _weak_
version of the principle.
As noticed by an online review of Feynman lecture notes on gravitation
[3]
{BLOCKQUOTE
This is a more fundamental approach than the usual differential
geometric
framework and shows what the [strong] equivalence principle really
means
in terms of fundamental symmetries. Highly recommended for a modern
field theory viewpoint of GR.
}
This non-fundamental aspect of the equivalence is also remarked by
John Preskill and Kip S. Thorne on the Foreword to the book [3].
However, Preskill and Thorne go beyond Feynman's own way of thinking
and write
{BLOCKQUOTE
A quite different approach to deducing the form of the gravitational
interaction was developed by Weinberg [...] Weinberg showed that the
theory of an interacting massless spin-2 particle can be Lorentz
invariant
only if the particle couples to matter (including itself) with a
universal
strength; in other words, only if the strong principle of equivalence
is
satisfied. In a sense, Weinberg's argument is the deepest and
most powerful of all, since the property that the graviton couples to
the energy-momentum tensor is derived from other, quite general,
principles.
Once the principle of equivalence is established, one can proceed to
the
construction of Einstein's theory
}
In my opinion we may be still missing more deepest and powerful
arguments to establish the strong principle of equivalence.
doug
[2] Phys. Rev. D 2003, 67, 044017.
[3] http://www.amazon.com/Feynman-Lectures-Gravitation-Richard-Phillips/dp/0813340381
========
I follow http://canonicalscience.com/guidelines.txt
.
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- From: Juan R.
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- From: Doug Sweetser
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