Another desperate attempt to find the Dark Matter gnome …
Astrophysicists Turn GPS Satellite Constellation into Giant Dark Matter Detector
If Earth is sweeping through an ocean of dark matter, the effects should be visible in clock data from GPS satellites.
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.
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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.
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They start with a different vision of what dark matter may consist of. Instead of small particles, another option is that dark matter may take the form of topological defects in space-time left over from the Big Bang. These would be glitches in the fabric of the universe, like domain walls, that bend space-time in their vicinity.
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Should the Earth pass through such a defect, it would change the local gravitational field just slightly over a period of an hour or so.
But how to detect such a change in the local field? To Roberts and co, the answer is clear. According to relativity, any change in gravity also changes the rate at which a clock ticks. That’s why orbiting clocks run a little bit slower than those on the surface.
If the Earth has passed through any topological defects in the recent past, the clock data from GPS satellites would have recorded this event. So by searching through geophysicists’ archived records of GPS clock timings, it ought to be possible to see such events.
That’s the theory. In practice, this work is a little more complicated because GPS timing signals are also influenced by other factors such as atmospheric conditions, random variations, and other things. All these need to be taken into account.
But a key signature of a topological defect is that its influence should sweep through the fleet of satellites as the Earth passes through it. So any other kinds of local timing fluctuation can be ruled out.
Roberts and co study the data over the last 16 years, and their results make for interesting reading. These guys say they have found no sign that Earth has passed through a topological defect in that time. “We find no evidence for dark matter clumps in the form of domain walls,” they say.
OOPS! Another negative result.