It is often stated that Light cannot escape the event horizon of a black hole and that is likely true. It is also believed that gravity propagates, like light, at light speed 'c'. Is there not a single cohort feeling a bit bothered that while "Light cannot escape the EH", gravity traveling like light at 'c' speed, escapes the EH with unfettered impunity? If gravity travels at 'c', perhaps when a BH occurs, it should 'wink' its self completely out of existence. There are a number of on-going experiments configured to detect gravity waves launched by supernova, neutron star, or BH collisions, etc; to date none have shown positive detection of gravity waves.
During supernova, a fraction of the original mass is liberated as energy by Mc2. If energy exhibits (emits) gravity (Einstein thought so), the loss in gravity due to stellar mass loss would be replaced by gravity emitted from the energy liberated buy the supernova thus leaving the net gravity arriving at Earth unchanged, and undetectable?
Spherical re-distribution of original stellar mass would still emit gravity; the remaining collapsed neutron star (or BH) core plus the mass fraction ejected radially into space would contribute to a 3-part sum in effect to mask the gravitational event. If gravity is wave like would not the wavelength of the waves be modified by doppler effects? Would doppler shifted gravity exhibit the same magnitude as Newtonian gravity?
If effects of a gravitational wave of receding ejecta is weakened at the observers post, perhaps that is offset by the increased effect of the advancing side of the ejecta wave front?, net sum zero? In other words, net gravitational attraction before and after the supernova event may appear to be unchanged?
To my knowledge, there is no proof or supporting measurement of the belief or assertion that gravity propagates at 'c' speed. What if gravity propagates at 'K>1' times 'c', then the bandwidth of the current gravity wave detection experiment(s) may not be adequate to detect or the event in the first place. Just a thought to consider in view of a dearth of gravity wave detection results to date.
Perhaps experimenters are seeking to detect a phenomenon that does not exist (DNE)? Perhaps gravity is instantaneous?
The value of 'G' has not been materially improved since having been computed from experimental data by Cavendish (circa 1798). Most measurements to establish the value of 'G' use Cavendish's torsional pendulum technique. At least three fairly recent measurements have been published with non-overlapping, albeit carefully established, error bounds. A possible reason for this enigmatic result:
My understanding is that according to special relativity that infinite flat planes of mass do not exhibit gravitational attraction. This would be because there is no field distortion between infinite flat plates to cause curvature of space, thus no mutual gravitational attraction. Here is my thought.
Engineers do not need to go to infinity to prove a point; EXAMPLE: Computation of thin wall and thick wall hoop stress; if the radius to a cylinder wall is >~10 times the wall thickness, the (simple) thin wall formula yields adequate results. Therefore an engineer does not need impossible infinite planes, just flat plates that are thin compared to width and length to detect a geometric influence on (measure of) the gravitational constant.
Therefore, finite flat plate shaped test masses may likely establish if gravity field distortion and mutual attraction would be actually reduced to zero (predicted by relativity) between infinite plane masses. Thus I suggest, configure a Cavendish G-test with flat plate test masses to see if the value of 'G' is being influenced by the shape of the test masses.
I would submit that a consistent starting point would be to use only spherical test masses. Cavendish used spheres, though maybe not for that reason. I seem to remember a variety of test mass shapes (spheres, cylinders, rods) being employed in recent tests. A smaller measured value of 'G' result would support the contention of zero attraction between infinite planes predicted by special relativity. See Science News; May 13, 2000 Vol 157, No.20 P-311; "Gravity gets measured to a greater certainty", by -P. Weiss.
The following link(s) provides an excellent explanation of the case for an accelerating expansion of the Universe based on data from 38 1a standard candle supernovae. In my opinion article is very clearly written and logically presented. The second link describes a supernova that seems to violate the "standard candle" characteristics of 1a supernova but/and includes explanation related to the case for accelerated expansion. (See NOTE: at bottom of this page).
Determination IF a system of dispersed diverging mass [the Universe] is 'closed' (eventually fall back in on its self) or 'open' (expand outward forever) requires knowledge of three parameters for each component of the system and the universal gravitational constant. The 3 parameters are: mass, position, and velocity.
By Newtonian or Relativistic physics there should have been one of two possible results: 'closed' OR 'open' Universe. Even in an 'open' Universe, the most remote supernovae should still be slowing down. When they looked, it was found that beyond some BLY that galaxies were not being slowed by gravity as expected but rather they were going 'faster' than closer galaxies. The determination is based on distance found from 1a brightness and recession velocity determined by 1a red shift. The 38 light curve data were first adjusted as described in Figure 1. Figure 4 seems to include 1a position uncertainty (in billions of LY); uncertainty looms larger for further distance. The Hubble constant (~20KM/s/MLY) is used to determine recession velocity.
I do not clearly understand how 1a recession velocity is distinguished from actual Universe expansion rate. I am also not clear on how relativity affects the apparent 1a velocity since the Hubble constant permits velocity greater than 'c'; it would seem that relativistic corrections required become very complex when the Hubble constant begins predicting recessional velocities greater than ~5% of the speed of light.
I would like to see data from the 'odd ball' supernova added onto charts from the 1st reference. The author notes that 100 times the 38 supernovae (3800) may be required to firm up the conclusion; 100 times more data would reduce the uncertainty to 1/10 that shown. I wonder if the '1a standard candle' will be revised. I also wonder if the Hubble constant may not be so constant over such great distances. I feel certain there will be more to come from the Perlmutter team at Lawrence Berkeley (soon, I hope). By any measure, the reference is a great article for those interested in the topic of dark energy accelerated expansion of the Universe.
March-2011 Astronomy 'Ask Astro' P-51 reply by Dragan Huterer (University of Michigan Ann Arbor) presents balanced discussion offering possibilities of a fifth force, modification to Einstein's relativity theory, or some other unknown explanation and that the truth is not yet known. Definitely worth a read.