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Originally Posted by Chris Hillman
Hi, Nereid!
Did you mean to write "non-quantum"? The standard characterization of gtr is that it is a relativistic classical field theory of gravitation, the one uniquely determined by various criteria, but also just one among many other such theories.
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Hi Chris.
Actually, I was being a little sloppy ... I simply meant it contains one of the two 20th century revolutions in physics, relativity (duh!). At a somewhat different level, I embedded a 'you can't grok this from your kinesthetic intuitions' meaning, which in turn hints at what you have written so forcefully about (crudely, you can't even begin to understand GR without the necessary math).
Quote:
Yes, with certain understandings:
1. assuming the "Pioneer effect" turns out to have some explanation other than a flaw in our understanding of the fundemental physics of gravitation at solar system scales,
2. assuming that several current mysteries in cosmology turn out to have some explanation than a a flaw in our understanding of the fundemental physics of gravitation at cosmological scales.
Try this
http://relativity.livingreviews.org/...6-3/index.html
then this:
http://arxiv.org/abs/0806.1731
Some other review papers are at http://relativity.livingreviews.org/...s/subject.html
Regarding the Pioneer effect, I favor developing the theory of "post-GPS" satellite navigation theories as per Coll and then designing a test; see
http://arxiv.org/abs/gr-qc/0507121
Right; in gtr "strong field regime" and "nonlinear regime" are usually used as an antonym to "weak-field gtr" and "linearized gtr". The latter pair are synonyms; see any gtr textbook. That is, the criterion for calling some scenario a "strong-field scenario" is basically the failure of weak-field gtr.
I hesitate to add "failure due to nonlinear effects" since that could easily be misunderstood, but for example: in linearized gtr, you can simply add two metric perturbations (each solving the linearized EFE) and obtain a new solution of the linearized EFE, but you can't simply add two Kerr objects and obtain an exact solution of the vacuum EFE modeling two massive objects.
(There are ways, using any of half dozen "solution generating techniques", to combine, in some sense, two exact solutions while accounting for nonlinear interactions. This are great fun for mathematicians, but sad to say, the results tend to be disappointing for physicists, e.g. when you combine two Kerr objects you will probably obtain a solution including a dubious "strong but massless strut" holding them apart, or something like that.)
To prevent possible misunderstanding:
The classic observations by Taylor of a binary pulsar (a neutron star tightly orbiting a more conventional object) have verified to impressive accuracy the prediction from gtr that the orbit should decay at a certain rate, due to gravitational radiation from the system slowly carrying off energy. This is usually taken as strong but indirect evidence that gravitational waves exist and carry energy, and in this respect at least behave as gtr predicts.
But naturally physicists want to check further detailed predictions by gtr, such as the behavior of test particles which encounter a gravitational wave. This is important because many competing gravitation theories predict behavior which would be forbidden in gtr. This is one motivation for LIGO/VIRGO and eventually LISA, the gravitational wave observatories. The other is that gravitational radiation should provide, as Kip Thorne puts it, "a new window on the Universe". LIGO/VIRGO are up and running. These instruments are designed to directly detect and study passing gravitational waves, roughly speaking by detecting very small variations in "length" (a thousandth of the diameter of proton, over several kilometers), and have been described as the most sensitive scientific instruments ever built. Noise like vibrations from tumbleweeds blowing over the mesa and trolleys in cities a hundred miles distant (to name just a handful of several dozen known sources of noise) has to be carefully eliminated. This is very difficult! So far, LIGO/VIRGO have failed to yield any confirmed encounters with gravitational waves, but this is generally expected to happen sometime "soon".
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Thanks!
If I may ask a follow-on question?
In what part of density-length parameter space are strong field regime effects detectable (with today's technology)? For example, how massive/big a lump of neutron star matter (degenerate nuclear matter) would you need, in your lab, to be able to distinguish weak from strong (assuming, of course, that you were not wiped out by the "neutronium's" return to local equilibrium)?