On 29 Sep 1999, Anders Sandberg wrote:
> Isn't this an old story? I recall some claims along these lines last > year. There are some papers on xxx.lanl.gov on the deviations; they > have apparently been explained. >
The confusing text from the "popular press" is
| When they published their observations in the journal
| Physical Review Letters, discussion is exactly what
| Anderson's team got. "When you hear that something's
| wrong with gravity you get pretty interested," says
| Edward Murphy, an astronomer at Johns Hopkins
| University who published a possible explanation in a
| recent issue of the same journal. Anderson's team noted
| that in the near-vacuum, low-gravity environment of
| space, the small amount of heat radiating out from the
| probes' electrical systems might provide enough push to
| account for the speed change. But then they calculated
| that heat would dissipate equally in all directions with
| no net effect. Murphy, who has worked on other probes,
| says they missed a design detail; heat vents are located
| on the side facing away from the sun, so they don't heat
| up in the solar radiation. Murphy says his calculations
| show that the slight, constant nudge of heat from the vent
| could provide "half or more of the total explanation."
| Jonathan Katz, an astronomer at Washington University
| in St. Louis, thinks he's worked out where the rest of the
| push is coming from. The probes rely on small
| plutonium-powered nuclear reactors called RTGs for
| their electricity. Katz calculates that some of the excess
| heat given off by the RTGs would bounce off the back of
| the probes' radio antennas, providing enough of a shove
| toward the sun to explain the deceleration. Interesting
| ideas, says Anderson, but "our estimate is that they fail
| by a factor of five or more."
|
So some people think they have a handle on it but others aren't convinced it seems.
Regarding the cosmological constant and accelerating expansion, I think I've seen two differing opinions in the last week. One (Nature?) saying its real and putting constraints on the shape of the Universe and another (Science News?) saying its an illusion and once more data is in the effect will disappear. At any rate it would be *really* strange to see an effect on our space probes due to changes in the cosmological constant over a ~10-20 year period.
I will lay money on the table with really favorable odds however that in case (1) nobody has proposed a baby-SI observer in our solar system providing extra "gravity"; or in case (2) changes in stellar composition due to SI mining activities (early universe, no mining, late universe potentially lots of mining) causing variations in the expected composition & brightness of the supernova being used as distance measuring tools have been considered as possible explanations...
Robert