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The Global Positioning System consists of 31 Earth-orbiting satellites, each carrying an atomic clock that sends a highly accurate timing signal to the ground. Anybody with an appropriate receiver can work out their position to within a few meters by comparing the arrival time of signals from three or more satellites.
And this system can easily be improved. The accuracy of GPS signals can be made much higher by combining the signals with ones produced on the ground. Geophysicists, for example, use this technique to determine the position of ground stations to within a few millimeters. In this way, they can measure the tiny movements of entire continents.
This is an impressive endeavor. Geophysicists routinely measure the difference between GPS signals and clocks on the ground with an accuracy of less than 0.1 nanoseconds. They also archive this data providing a detailed record of how GPS signals have changed over time. This archival storage opens the possibility of using the data for other exotic studies.
Today Benjamin Roberts at the University of Nevada and a few pals say they have used this data to find out whether GPS satellites may have been influenced by dark matter, the mysterious invisible stuff that astrophysicists think fills our galaxy. In effect, these guys have turned the Global Positioning System into an astrophysical observatory of truly planetary proportion.
The theory behind dark matter is based in observations of the way galaxies rotate. This spinning motion is so fast that it should send stars flying off into extra-galactic space.
But this doesn't happen. Instead, a mysterious force must somehow hold the stars in place. The theory is that this force is gravity generated by invisible stuff that doesn't show up in astronomical observations. In other words, dark matter.
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(Score: 2) by dry on Tuesday May 09 2017, @06:12AM
While it was the rotation curves of galaxies that originally led to the theory of dark matter, it also explains other puzzling observations, the large scale structure of the universe, some observations about the cosmic background radiation and some gravitational lensing. So it's not just based on the rotation curves of galaxies.
People who go on about it being a kludge forget that other kludges have turned out to be true, including a similar one about weird matter that was hypothesized to make the equations of fusion work, namely the neutrino (originally called the neutron). Even the neutron itself was a kludge originally.