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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.
This is one of the most stupid arguments I have ever read. You state your opinion, then argue that the concept is wrong since it conflicts with your opinion. Look into muon showers caused by cosmic rays hitting Earth's atmosphere. Taking into account the speed they are traveling and the half-life of a muon, they should never reach the surface. But they do, since they are moving near the speed of light and the time dilation involved means that time is happening much slower from the particle's frame of reference. There is no mechanism involved to slow down.
Think of a coordinate system with the three usual dimensions (x, y and z) and then one other dimension orthogonal to the other three, this extra dimension is time (t).
An object at rest describes a vector where x= y = z = 0 and t = c (the speed of light).
As an object moves the vector rotates to point in a new direction and therefore the resolution of the (now rotated) vector on the t dimension is smaller than when the object was at rest. Therefore as the object moves time passes more slowly for the object. When the object moves at speed c, time stops for the object.
I leave it for others to translate this model to a gravitational field (it's been too long and I've forgotten).
Is there something the EU member want to do that the current GPS network cannot or declines to do?
Yes. Not have an important piece of technology controlled by a (potential) rival nation. Maybe not an ideal reason but NIH is sometimes a strong motivation.
...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.
I said, look into it. In other words, read about it and see if it supports your opinion or contradicts it. Muons are created in particle accelerators. The ones created are moving fairly slowly compared to cosmic rays. We can measure the half life of them before they decay, which is 2.2 microseconds. The ones created by cosmic rays hitting the atmosphere are moving at a speed where the muon should go about 450m before decaying. Yet, they reach the Earth's surface from 60-100 km up where they are created in the atmosphere. The reason they last that long and can move that far is due to time dilation, since they are moving at relativistic speeds.
So I was wondering about the time slowing effect of the speed of the satellites vs. our on the surface of the Earth closeness time slowing effect. So the effects partly cancel each other out. General relativity is the norm/aka the general rule (with gravity comes acceleration) and special relativity is the special case one I learned in high school where speed with no acceleration slows down time. I really love this stuff.
This guys explains it well I believe:
https://www.quora.com/If-an-at...
Quote:
"Keith Norfolk
Keith Norfolk, former Educational Specialist at European Space Agency
Answered Aug 22, 2017 Author has 250 answers and 87.4k answer views
There are actually two effect that (partly) cancel each other. Yes, the satellite is moving at a particular speed and than means that from Earth its clock will run slower (according to special relativity). However it is also higher in the Earth’s gravitational field and this is the domain of general relativity is needed (special relativity is only valid in inertial reference frames (i.e. no acceleration and no gravitational differences). According to general relativity, time deep in a gravitational well will run slower and so, reversing the reasoning, time for the satellite (that is higher in the gravitational well) will run faster.
From the point of view of an observer on Earth the two effects partly cancel each other but not fully and so there is a time rate difference for the satellite and the observer on Earth. This is why GPS satellite clocks have to be set to the ‘wrong’ rate in the factory so that they will run at the right rate when operating on orbit.
Curiously, the higher the satellite is, the greater the rate differential is for the gravitational effect. However the higher the satellite is the slower its orbital velocity will be and so the smaller the special relativistic effect will be. So, there should be an orbit at which the two effects exactly cancel each other out. Now that would make an interesting question!
By the way, it is not that there is Special Relativity on the one hand and General Relativity on the other. Special Relativity, as I said earlier, is only valid if there is no acceleration. General Relativity allows for situations where acceleration (e.g. gravitational fields) are present. Special relativity is a special case not the general case. That’s where the two names come from!"
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.
I'd love to find a source of ephemerides for their satellites. It'd be interesting to plug it into the GPS coverage software I wrote back in the '80s. Just to see for myself how "useless" the Galileo system is because of this $11B screw-up.
CUR ALLOC 20195.....5804M
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)
Yes. GPS has low reliability and is controlled by a lunatic. By having an alternative, high-precision, system that actually works and is not controlled by a lunatic, you have what's called a benefit.
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)
At this point with all the overwhelming evidence, most would agree that Einstein is probably correct. The reason they keep doing things like this is to see if they can find something unusual or unexpected. It's often the weird / unexplained phenomena that leads to new theories or even technology that we can use. So yes, it seems redundant but it's how new things are discovered.
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.