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Is Earth Weighed Down By Dark Matter?
Nerval's Lobster writes "There may be a giant ring of dark matter invisibly encircling the Earth, increasing its mass and pulling much harder on orbiting satellites than anything invisible should pull, according to preliminary research from a scientist specializing the physics of GPS signaling and satellite engineering. The dark-matter belt around the Earth could represent the beginning of a radically new understanding of how dark matter works and how it affects the human universe, or it could be something perfectly valid but less exciting despite having been written up by New Scientist and spreading to the rest of the geek universe on the basis of a single oral presentation of preliminary research at a meeting of the American Geophysical Union in December. The presentation came from telecom- and GPS satellite expert Ben Harris, an assistant professor of mechanical and aerospace engineering at the University of Texas- Arlington, who based his conclusion on nine months' worth of data that could indicate Earth's gravity was pulling harder on its ring of geostationary GPS satellites than the accepted mass of the Earth would normally allow. Since planets can't gain weight over the holidays like the rest of us, Harris' conclusion was that something else was adding to the mass and gravitational power of Earth – something that would have to be pretty massive but almost completely undetectable, which would sound crazy if predominant theories about the composition of the universe didn't assume 80 percent of it was made up of invisible dark matter. Harris calculated that the increase in gravity could have come from dark matter, but would have had to be an unexpectedly thick collection of it – one ringing the earth in a band 120 miles thick and 45,000 miles wide. Making elaborate claims in oral presentations, without nailing down all the variables that could keep a set of results from being twisted into something more interesting than the truth is a red flag for any scientific presentation, let alone one making audacious claims about the way dark matter behaves or weight of the Earth, according to an exasperated counterargument from Matthew R. Francis, who earned a Ph.D. in physics and astronomy from Rutgers in 2005, held visiting and assistant professorships at several Northeastern universities and whose science writing has appeared in Ars Technica, The New Yorker, Nautilus, BBC Future and others including his own science blog at Galileo's Pendulum."
It's standard not to write all the technicalities down in a scientific presentation. They usually last 30 to 45 minutes. There is no way, even for a scientific mind, to follow all the technicalities in 45 minutes when it took several months for the speaker to grasp the subject. Nobody in the audience would understand anything aside from the coauthors. Imagine your 20 hours advanced graduate course on physics condensed in 45 minutes with no simplification at all.
Disclosure: I'm a mathematician, not a physicist.
Let's wait for the proceeding or the full paper even though it's true we should be skeptical at this point.
> geostationary GPS satellites
A what now?
You laugh at the power of Lord Cthulhu, the Great and Glorious One. You try to come up with "scientific" theories and fancy math but the truth will become apparent to you very soon.
Your screams of terror will be like the song of angels to me.
Dedicated Cthulhu Cultist since 4523 BC.
No, this research wasn't even published, it's a conference talk and a PR release. Go read the actual link, at the bottom of the long post, where Matthew Francis dishes it out. Here it is again in case you missed it:
http://galileospendulum.org/2014/01/02/no-dark-matter-is-not-messing-up-gps-measurements/
The later link from Dr Francis points out that the calculation has yet to be adjusted for the gravitational contributions of the Moon or Sun, and that it also doesn't make any relativistic corrections.
Those omissions puts the dark matter claim on par with "hey guys I haven't looked at it from far away but from right here it looks the Earth is pretty flat, yeah?"
For geostationary satellites, drag is unlikely. The upper altitude limit for atmospheric drag is considered to be 2000km, geostationary are at 36 thousands km high.
The earth mass is computed from the semi axis and the (sideral) period of any satellite (including the moon) orbiting earth: http://en.wikipedia.org/wiki/Standard_gravitational_parameter which gives you the standard gravitational parameter. To get the mass, you need to measure the gravitational constant which is harder but can be done with Cavendish experiment: http://en.wikipedia.org/wiki/Cavendish_experiment.
planets can't gain weight over the holidays like the rest of us
Actually they do. It's estimated that the Earth gains at least 164,000 kg per day from meteoric accretion. (Barker, J.L. and Anders, E. "Accretion rate of cosmic matter from iridium and osmium contents of deep-sea sediments." Geochimica et Cosmochimica Acta 32, 627-645 (1968))
You never really know how close to the edge you can go until you fall off.
I work with GPS a lot, and there are many MANY people around the world who spend their entire lives making sure that there are very precise measurements of where those satellites are and how good predictions of where they'll be going are. These orbit calculations take into account the pressure of light from the sun on the satellites along with several other very small effects, so if there was some large extra mass in a ring around the earth it would have been noticed many years ago. I think this guy needs to recheck his calculations.
I don't trust this whole "theory of gravity." Obviously, this "theory" is just an unknowable guess and therefore doesn't have the full consensus of "science". I say we need to teach the controversy that the reason we stay on the earth is because some supreme being wants us there. Birds and planes only work because when their wings are outstretched they make a holy cross.
Teach the controversy. Don't believe "theories".
Slow Down Cowboy! It's been 1 hour, 47 minutes since you last successfully posted a comment
It's not just a hypothesis. It's a hypothesis that fits some data, from GPS satellites and the Juno probe. It's solid enough to present as an idea to other scientists.
It's not solid enough to present as an idea to the general public, but unfortunately that's what popular science publications do for a living. They want "news"; their readers want to be the first ones to hear about exciting new developments. So they publish highly speculative material without the kinds of caveats, qualifications, and context that other scientists in the field bring automatically.
I have a love-hate relationship with them. They're helpful in drumming up public interest in science, playing up the romantic parts that help young proto-scientists engage with the field before the years of drudge work that go into actually becoming a scientist. And they help keep people feeling good about science and voting to fund it. But they mis-inform as much as they inform, and real scientists are continually having to provide the context that the magazines frequently refuse to.
(New Scientist is better than most daily newspapers, but worse than Science News. Frequency of publication seems to make a big difference: the longer your readership is willing to wait for accurate information, and the less they demand to have it ten seconds before the next guy, the more informative they are. Web-only sources are generally the worst.)