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Wayward Satellites Test Einstein's Theory of General Relativity (scientificamerican.com)
An anonymous reader quotes a report from Scientific American: In August 2014 a rocket launched the fifth and sixth satellites of the Galileo global navigation system, the European Union's $11-billion answer to the U.S.'s GPS. But celebration turned to disappointment when it became clear that the satellites had been dropped off at the wrong cosmic "bus stops." Instead of being placed in circular orbits at stable altitudes, they were stranded in elliptical orbits useless for navigation. The mishap, however, offered a rare opportunity for a fundamental physics experiment. Two independent research teams -- one led by Pacome Delva of the Paris Observatory in France, the other by Sven Herrmann of the University of Bremen in Germany -- monitored the wayward satellites to look for holes in Einstein's general theory of relativity.
Einstein's theory predicts time will pass more slowly close to a massive object, which means that a clock on Earth's surface should tick at a more sluggish rate relative to one on a satellite in orbit. This time dilation is known as gravitational redshift. Any subtle deviation from this pattern might give physicists clues for a new theory that unifies gravity and quantum physics. Even after the Galileo satellites were nudged closer to circular orbits, they were still climbing and falling about 8,500 kilometers twice a day. Over the course of three years Delva's and Herrmann's teams watched how the resulting shifts in gravity altered the frequency of the satellites' super-accurate atomic clocks. In a previous gravitational redshift test, conducted in 1976, when the Gravity Probe-A suborbital rocket was launched into space with an atomic clock onboard, researchers observed that general relativity predicted the clock's frequency shift with an uncertainty of 1.4 x 10-4. The new studies, published last December in Physical Review Letters, again verified Einstein's prediction -- and increased that precision by a factor of 5.6. So, for now, the century-old theory still reigns.
Einstein's theory predicts time will pass more slowly close to a massive object, which means that a clock on Earth's surface should tick at a more sluggish rate relative to one on a satellite in orbit. This time dilation is known as gravitational redshift. Any subtle deviation from this pattern might give physicists clues for a new theory that unifies gravity and quantum physics. Even after the Galileo satellites were nudged closer to circular orbits, they were still climbing and falling about 8,500 kilometers twice a day. Over the course of three years Delva's and Herrmann's teams watched how the resulting shifts in gravity altered the frequency of the satellites' super-accurate atomic clocks. In a previous gravitational redshift test, conducted in 1976, when the Gravity Probe-A suborbital rocket was launched into space with an atomic clock onboard, researchers observed that general relativity predicted the clock's frequency shift with an uncertainty of 1.4 x 10-4. The new studies, published last December in Physical Review Letters, again verified Einstein's prediction -- and increased that precision by a factor of 5.6. So, for now, the century-old theory still reigns.
...does there need to be an "answer" to the US GPS? Is there something the EU member want to do that the current GPS network cannot or declines to do?
Yes: when President Clinton opened the high-resolution GPS up to all users (instead of just military) in May 2000, he reserved the right of the U.S. to selectively turn off the GPS system in the event of war or another national emergency (specific words were: "capability to selectively deny GPS signals on a regional basis when our national security is threatened"). The Europeans at that point committed to making their own system, which they could control, and turn of when they think it's necessary, not us.
There are a lot of reasons for having their own system, including control. But regardless of the reasons, right now there are pieces of five different positioning systems in operation right now. There's GPS (US), GLONAS (Russia), Galileo (Europe), Beidou (China), and QSZZ (Japan). New crops of GPS units, including the very impressive ZED-F9P chip from U-Blox, can see all of these satellites, allowing for more accurate and faster fixes. Also more satellites provides more redundant information for weeding out any bad satellite data, overcoming deliberate jamming, or when a country intentionally degrades the signal. Apparently recently near Georgia and South Carolina there was some GPS jamming going on as part of a naval exercise. Having more systems to work with mitigates this somewhat, although they all use similar frequencies to GPS's L1, L2, and L5 bands.
And recently the FCC has finally allowed American users of GPS receivers to be able to use these other satellites. Odds are your phone is now using GPS, Galileo, and Glonass for positioning. It's a really a win win for those that rely on this technology. I can't see a downside, either for end users or countries to have more of these systems up and running, other than cost.
That isn't an opinion, that is a prediction. A prediction that is reliable for particles of any given speed. A reliable prediction.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
It's also much higher precision - by an order of magnitude. The US system cannot be trivially upgraded, you have to replace all of the satellites.
It's a small world and it smells funny; I'd buy another if it wasn't for the money; Take back what I paid (SoM)
Apparently this data can be found in RINEX format here: ftp://gssc.esa.int/gnss/data/h....
Despite these satellites being lost as far as the constellation usability is concerned, the ESA plans to have the system completed by 2020, and that would mean 100% coverage across Europe and most of the world. Right now my phone uses Galileo as well as GPS and Glonas. I just noticed that Glonas reports nearly 100% coverage of the globe right now also.
Some of the GPS units I'm working right including the U-Blox M8T with RTKLIB and the ZED-F9P (integrated RTK) see satellites from GPS, Glonass, Galileo, Beidou, and QZSS. In fact I was able to briefly get an RTK fix on my M8T (Reach RS+) using only Beidou observation data from my base unit, apparently. With cheap receivers like the ZED-F9P, lots of satellite constellations, it's really a golden age for low-cost, high-accuracy GNSS work for agriculture, drones, etc.
Your opinion is that muon showers are reaching the Earth due to time dilation therefore proving that time dilation is real.
It's not his opinion, it is established scientific fact. A muon at rest decays with a lifetime of 2.2 microseconds. Travelling at the speed of light this means that, without any time dilation, the muon would travel 3e8*2.2e-6 = 660m. However, muons are typically generated at around 15 km about the surface and we also see a lot coming it at angles meaning that they have travelled even further than this.
Looking at muons produced directly overhead, which have the shortest distance to travel, without time dilation this is well over 22 lifetimes and so the probability of survival of 1.35e-10. This will be even lower for muons produced at non-vertical angles and so have to travel further. We observe a rate of 1 muon per second per cubic centimetre at the Earths surface so to produce this rate without time dilation we would need such a high intensity of cosmic rays (comparable to early accelerator beam intensities) hitting the atmosphere that plane travel and mountain climbing would be death sentences from the massive radiation at altitude.
The lack of acute radiation sickness in pilots and mountain climbers therefore conclusively rules out that the muon lifetime does not change with relative speed. From our point of view the muon's lifetime is dilated by relativity. From the muon's point of view, the thickness of the atmosphere is Lorentz contracted making it appear far thinner to the muon.