This is being done by the Ice Cube Neutrino observatory at the South Pole. Ice Cube uses the Earth as a shield, as is observing natural neutrinos coming in from the North (i.e., ones that transverse the entire Earth). Ice Cube may be able to directly image the Earth's core using neutrinos.
I would lay serious money that someone this morning is going over the Ice Cube specs and trying to figure out if it could be used to do timing to Fermilab or Cern. They are both, after all, in the field of view.
So ? Lunar Laser Ranging is done routinely at the few picosecond level with that level of detection. The Apollo LLR observatory sends Gigawatt pulses out (100 picoseconds long) and counts photons coming back, and does mm level Lunar ranging. A very low signal capture rate is perfectly adequate, as long as you have enough captured.
It's been done since the 1970's (Viking lander range measurements to Mars in 1976 were good to about 7 nanoseconds).
Now-a-days, really accurate delay measurements are at the picosecond level (Lunar Laser Ranging now can be done to a few picoseconds). GPS receivers do 50 nanosecond time delays with equipment that can fit in your phone.
As others have said, it's a matter of having fast enough electronics, and a fanatical attention to sources of error.
I think that the best proof of this would be to perform time of flight measurements around a triangle. This is commonly used in interferometry, as many errors (such as geodetic errors and clock errors) will "close" around a triangle, but the actual time of flight should not.
This is called the Sagnac effect, and is due to special relativity and the motion of the observers during the observations (it used to be called "retarded baseline" in VLBI). Now, an equilateral triangle with 700 km sides would only have a non-closing delay of 0.7 nanoseconds, which is too small, but one with 4500 km sides (roughly the US to Europe to Japan) would have a non-closing delay of 29 nanoseconds, which they could detect.
Here is something that struck me - in that whole, huge, author list I did not see a single geodesist or clock comparison person. (I can't claim to know them all, but I did work in those fields and do know most of the major players, plus their institutions.) If it were me, I would have brought in an expert in both GPS geodesy (there is a strong group in Switzerland, and another in France, not to mention Italy) and clock comparisons (several strong groups in France) as co-authors before I published the paper.
Neither geodesy nor clock synchronization are trivial at the accuracy they are claiming over the distances they used - true, fairly routine now-a-days, but not trivial. Since the whole paper hangs on that, a few practiced eyes from those fields could not have hurt.
Here is a prediction : Some theorist will come up with a theory (probably involving neutrino oscillations) explaining why v > c is only observed at short range, and the effect vanishes and v->c over distances like 160,000 light years. For bonus points, the short range of the effect will make it impossible to use it for causality violations.
where statistical and systematic are their estimates of these two different types of errors. Compare this to the current estimate of
(v c)/c = 2.5 ± 0.4 / 10**5
Note that both experiments found v > c. While I still think this is a systematic error, the fact that two groups found similar v > c for neutrinos make it seem a little more likely.
If you have faster than light travel, you can have causality violations. (In other words, you could prevent your own birth, change history, things like that.) True, it might require sending neutrino detectors off at a substantial fraction of the speed of light, but what is that compared to messing around with the course of history, not to mention the stock market and the pool on the Super Bowl ?
Article says that it's compared to light taking the same trip. That would imply it's the speed of light in whatever medium they're using.
They are almost certainly talking about the coordinate distance between the endpoints, and assuming that |x_2 - x_1| / c is the light travel time. (Where |x| is the magnitude of a vector and x_1 and x_2 are the position vectors of the endpoints. Now, it isn't (see my post below about relativistic coordinate systems) but that effect is picoseconds, not nanoseconds.
(Note : They may just be doing this for the press, but it is a common mistake in any case.)
One obvious error sources would be scale factor errors between (say) GPS measurements of position and the direct measurement of time of flight.* Unfortunately, these come in about about 10^-9, which is 4 orders of magnitude too small for this.
*Basically, GPS, or VLBI, or any modern measurement scheme, tells you where the end points are in some coordinate system. Coordinate systems are tricky things in general relativity, and the common relativistic coordinate system in harmonic gauge will NOT give you the right "proper time" (what the neutrinos should be measuring) if you just find the coordinate distance between two points and divide by c. These effects are of the order of GM/Rc^2 and v^2 / 2 c^2, both of which are no more than 10^-9 for observers resting on the surface of the Earth.
In this context that is called the Sagnac effect, and it only matters if they have a triangular measurement setup (in other words, velocity measurements between 3 points A, B and C, with A,B and C not on the same line). It's dominated by Earth rotation, BTW, if you are making measurements sitting on the Earth.
If they want to pursue this, a triangular measurement setup between 3 accelerators would actually be a really good thing for them to do.
60 ns / 2 ms is 3 x 10^-5. The speed of light has been verified to much better than that with photons (that would be a 7 orders of magnitude error on Mars ranging, for example, and about the same on LLR), so, if true, this is a neutrino issue.
This challenge is a practical demonstration of wireless power transmission. Practical systems employing power beaming would have a wide range of applications from lunar rovers and space propulsion systems to airships above the Earth. Another future application of power beaming would be the space elevator concept.
In 2009 the competitors drove their laser-powered devices up a cable one kilometer high, suspended from a helicopter, and LaserMotive LLC was awarded $900,000.
It turns out that it is really tough and actually somewhat dangerous to have a helicopter dangle a 1 km string perfectly vertical. This also "doesn't scale" (i.e., there is no way a helicopter is going to dangle a 5 km string for a longer test), and future competitions will be done horizontally, on the ground. (This also fits in with the idea of power beaming to rovers, say one exploring the always dark Shackleton Crater at the Lunar South pole, which is frankly a more realistic near-term prospect than a terrestrial space elevator.)
I believe there is still $ 2 million (USD) to be awarded, so slashdotters should get to it and go out there and take the Governments money.
Yes (although this is reverse engineering). In orbital dynamics, the easiest thing to change in the mean anomaly - i.e., where are you on the orbit. Orbital shape, size and orientation is harder to change (and, thus, easier to model). This is true both for initial errors, and for perturbations. Suppose you get the semi-major axis just a little off, say 300,000 km, or ~ 0.2%. Then you have the orbital period wrong by ~ 0.3%, and each year you build up an error of about 1.2 degrees of mean anomaly (longitude along the orbit). That's ~ 1.4 million km error per year, and it just keeps growing, to 135 million km now. This vehicle is subject to radiation pressure (from sunlight), and I imagine that the 135 million km is an mean anomaly error estimate derived from an estimate of the original orbit error, plus radiation pressure and other perturbations since then.
(300,000 km sounds in some ways like a big error for a spacecraft, but they sent this off by burning all of the fuel, and they may not have tracked it too carefully or for too long after that.)
There were a bunch of Lunar satellites in the Apollo era.
Apollo 12, 14, 15 and 17 LMs were deliberately impacted onto the Moon, again, to make Moon-quakes for the ALSEP seismometer network. Apollo 13 LM went into the Earth's atmosphere.
Apollo 15 and 16 released one "Particles and Fields subsatellite" each for lunar studies, and the Apollo 11 LM ascent stage (and, apparently, the Apollo 16 LM ascent stage), were left in Lunar orbit. There were also the Lunar Orbiters 1-5 and a similar number of unmanned Soviet Luna Lunar orbiters. Actually, the Apollo 10 decent stage was also left in Lunar orbit, and only the ascent stage sent into solar orbit. I don't know why that was done for Apollo 10. Apollo 16 had some problems, which may have been connected with the non-deorbit of its LM.
Anything without maneuvering capability left in a low lunar orbit has a lifetime measured in months, due to the roughness of the Lunar gravitational field (primarily the Mascons), and so these satellites are almost certainly long gone. (That is not true for the similar American and Soviet Mars orbiters, which are all probably still there, except maybe for 1 with a low periapse which may have decayed.) The orbit for the Apollo 16 subsatellite wasn't raised, for example, and it only lasted 35 days.
The main problem is going to be that Snoopy has a low mass to area ratio, and thus will be very subject to radiation pressure. It's orbit may not have changed much, but it could be anywhere along it (i.e., could have any mean anomaly).
There are also the Apollo 8, 10, 11 and 12 S-IVBs (3rd stage). (Starting with Apollo 13, the S-IVBs were impacted on the Moon to produce "Moonquakes" for the ALSEP seismometers). For all of those except for Apollo 8, there were also 4 large SLAs (panels) around the LM, which were ejected when the LM was retrieved just after TLI. (The Apollo-8 panels stayed on the S-IVB, as it had no LM.) In a real trivia, the Apollo 13-17 SLAs also should be out there, as the S-IVB was directed to hit the Moon after the LM was retrieved, and thus after they were ejected.
There was a claim that the S-IVB for Apollo 12 might have been found. I don't know if that was ever confirmed, though.
He had received decades of organized schooling from scientists, who I'd like to think make better teachers than birds.
Why ? I think that Dr Pepperberg would say it took a decade or so just to figure out how to teach him at all, which is a disadvantage the birds wouldn't have.
Flocks are social constructs, highly organized. They can include birds from other species (show me a human tribe that does that). That alone says that there is some active learning going on.
More to the point, however, if these flocks can start usefully communicating with the humans that they interact with, there will be very strong evolutionary pressure to improve the communication. That is what I see as the real significance here.
Slashdot Mirror
GPS is accurate to +-100ns.
I would really hope that they were using geodetic class GPS receivers and using carrier phase, which is accurate to picoseconds.
This is being done by the Ice Cube Neutrino observatory at the South Pole. Ice Cube uses the Earth as a shield, as is observing natural neutrinos coming in from the North (i.e., ones that transverse the entire Earth). Ice Cube may be able to directly image the Earth's core using neutrinos.
I would lay serious money that someone this morning is going over the Ice Cube specs and trying to figure out if it could be used to do timing to Fermilab or Cern. They are both, after all, in the field of view.
You can bet some people at Fermilab are looking at some old data really carefully this morning.
So ? Lunar Laser Ranging is done routinely at the few picosecond level with that level of detection. The Apollo LLR observatory sends Gigawatt pulses out (100 picoseconds long) and counts photons coming back, and does mm level Lunar ranging. A very low signal capture rate is perfectly adequate, as long as you have enough captured.
It's been done since the 1970's (Viking lander range measurements to Mars in 1976 were good to about 7 nanoseconds).
Now-a-days, really accurate delay measurements are at the picosecond level (Lunar Laser Ranging now can be done to a few picoseconds). GPS receivers do 50 nanosecond time delays with equipment that can fit in your phone.
As others have said, it's a matter of having fast enough electronics, and a fanatical attention to sources of error.
I think that the best proof of this would be to perform time of flight measurements around a triangle. This is commonly used in interferometry, as many errors (such as geodetic errors and clock errors) will "close" around a triangle, but the actual time of flight should not.
This is called the Sagnac effect, and is due to special relativity and the motion of the observers during the observations (it used to be called "retarded baseline" in VLBI). Now, an equilateral triangle with 700 km sides would only have a non-closing delay of 0.7 nanoseconds, which is too small, but one with 4500 km sides (roughly the US to Europe to Japan) would have a non-closing delay of 29 nanoseconds, which they could detect.
Here is something that struck me - in that whole, huge, author list I did not see a single geodesist or clock comparison person. (I can't claim to know them all, but I did work in those fields and do know most of the major players, plus their institutions.) If it were me, I would have brought in an expert in both GPS geodesy (there is a strong group in Switzerland, and another in France, not to mention Italy) and clock comparisons (several strong groups in France) as co-authors before I published the paper.
Neither geodesy nor clock synchronization are trivial at the accuracy they are claiming over the distances they used - true, fairly routine now-a-days, but not trivial. Since the whole paper hangs on that, a few practiced eyes from those fields could not have hurt.
Here is a prediction : Some theorist will come up with a theory (probably involving neutrino oscillations) explaining why v > c is only observed at short range, and the effect vanishes and v->c over distances like 160,000 light years. For bonus points, the short range of the effect will make it impossible to use it for causality violations.
Well, that is a good catch and very interesting.
Minos found an estimate of
(v c)/c = 5.1 ± 1.2 (statistical) ± 2.6 (systematic) / 10**5
where statistical and systematic are their estimates of these two different types of errors. Compare this to the current estimate of
(v c)/c = 2.5 ± 0.4 / 10**5
Note that both experiments found v > c. While I still think this is a systematic error, the fact that two groups found similar v > c for neutrinos make it seem a little more likely.
It's an easy calculation, and about 3 orders of magnitude (or more) too small.
If you have faster than light travel, you can have causality violations. (In other words, you could prevent your own birth, change history, things like that.) True, it might require sending neutrino detectors off at a substantial fraction of the speed of light, but what is that compared to messing around with the course of history, not to mention the stock market and the pool on the Super Bowl ?
That scale factor has been tested to much better than 5 orders of magnitude.
Article says that it's compared to light taking the same trip. That would imply it's the speed of light in whatever medium they're using.
They are almost certainly talking about the coordinate distance between the endpoints, and assuming that |x_2 - x_1| / c is the light travel time. (Where |x| is the magnitude of a vector and x_1 and x_2 are the position vectors of the endpoints. Now, it isn't (see my post below about relativistic coordinate systems) but that effect is picoseconds, not nanoseconds.
(Note : They may just be doing this for the press, but it is a common mistake in any case.)
One obvious error sources would be scale factor errors between (say) GPS measurements of position and the direct measurement of time of flight.* Unfortunately, these come in about about 10^-9, which is 4 orders of magnitude too small for this.
*Basically, GPS, or VLBI, or any modern measurement scheme, tells you where the end points are in some coordinate system. Coordinate systems are tricky things in general relativity, and the common relativistic coordinate system in harmonic gauge will NOT give you the right "proper time" (what the neutrinos should be measuring) if you just find the coordinate distance between two points and divide by c. These effects are of the order of GM/Rc^2 and v^2 / 2 c^2, both of which are no more than 10^-9 for observers resting on the surface of the Earth.
In this context that is called the Sagnac effect, and it only matters if they have a triangular measurement setup (in other words, velocity measurements between 3 points A, B and C, with A,B and C not on the same line). It's dominated by Earth rotation, BTW, if you are making measurements sitting on the Earth.
If they want to pursue this, a triangular measurement setup between 3 accelerators would actually be a really good thing for them to do.
60 ns / 2 ms is 3 x 10^-5. The speed of light has been verified to much better than that with photons (that would be a 7 orders of magnitude error on Mars ranging, for example, and about the same on LLR), so, if true, this is a neutrino issue.
My money would be on systematic error.
NASA has had a Centennial Challenge open in power beaming for some years now. From :
This challenge is a practical demonstration of wireless power transmission. Practical systems employing power beaming would have a wide range of applications from lunar rovers and space propulsion systems to airships above the Earth. Another future application of power beaming would be the space elevator concept.
In 2009 the competitors drove their laser-powered devices up a cable one kilometer high, suspended from a helicopter, and LaserMotive LLC was awarded $900,000.
It turns out that it is really tough and actually somewhat dangerous to have a helicopter dangle a 1 km string perfectly vertical. This also "doesn't scale" (i.e., there is no way a helicopter is going to dangle a 5 km string for a longer test), and future competitions will be done horizontally, on the ground. (This also fits in with the idea of power beaming to rovers, say one exploring the always dark Shackleton Crater at the Lunar South pole, which is frankly a more realistic near-term prospect than a terrestrial space elevator.)
I believe there is still $ 2 million (USD) to be awarded, so slashdotters should get to it and go out there and take the Governments money.
Yes (although this is reverse engineering). In orbital dynamics, the easiest thing to change in the mean anomaly - i.e., where are you on the orbit. Orbital shape, size and orientation is harder to change (and, thus, easier to model). This is true both for initial errors, and for perturbations. Suppose you get the semi-major axis just a little off, say 300,000 km, or ~ 0.2%. Then you have the orbital period wrong by ~ 0.3%, and each year you build up an error of about 1.2 degrees of mean anomaly (longitude along the orbit). That's ~ 1.4 million km error per year, and it just keeps growing, to 135 million km now. This vehicle is subject to radiation pressure (from sunlight), and I imagine that the 135 million km is an mean anomaly error estimate derived from an estimate of the original orbit error, plus radiation pressure and other perturbations since then.
(300,000 km sounds in some ways like a big error for a spacecraft, but they sent this off by burning all of the fuel, and they may not have tracked it too carefully or for too long after that.)
I know something about it because I was following it at the time, and because I am still involved in such stuff.
Here are some links to get you started
http://www.nasa.gov/mission_pages/apollo/missions/index.html
http://www.myspacemuseum.com/sitemap.htm
http://www.honeysucklecreek.net/msfn_missions/ALSEP/hl_alsep.html
There were a bunch of Lunar satellites in the Apollo era.
Apollo 12, 14, 15 and 17 LMs were deliberately impacted onto the Moon, again, to make Moon-quakes for the ALSEP seismometer network. Apollo 13 LM went into the Earth's atmosphere.
Apollo 15 and 16 released one "Particles and Fields subsatellite" each for lunar studies, and the Apollo 11 LM ascent stage (and, apparently, the Apollo 16 LM ascent stage), were left in Lunar orbit. There were also the Lunar Orbiters 1-5 and a similar number of unmanned Soviet Luna Lunar orbiters. Actually, the Apollo 10 decent stage was also left in Lunar orbit, and only the ascent stage sent into solar orbit. I don't know why that was done for Apollo 10. Apollo 16 had some problems, which may have been connected with the non-deorbit of its LM.
Anything without maneuvering capability left in a low lunar orbit has a lifetime measured in months, due to the roughness of the Lunar gravitational field (primarily the Mascons), and so these satellites are almost certainly long gone. (That is not true for the similar American and Soviet Mars orbiters, which are all probably still there, except maybe for 1 with a low periapse which may have decayed.) The orbit for the Apollo 16 subsatellite wasn't raised, for example, and it only lasted 35 days.
This was the founding of space archaeology.
The main problem is going to be that Snoopy has a low mass to area ratio, and thus will be very subject to radiation pressure. It's orbit may not have changed much, but it could be anywhere along it (i.e., could have any mean anomaly).
There are also the Apollo 8, 10, 11 and 12 S-IVBs (3rd stage). (Starting with Apollo 13, the S-IVBs were impacted on the Moon to produce "Moonquakes" for the ALSEP seismometers). For all of those except for Apollo 8, there were also 4 large SLAs (panels) around the LM, which were ejected when the LM was retrieved just after TLI. (The Apollo-8 panels stayed on the S-IVB, as it had no LM.) In a real trivia, the Apollo 13-17 SLAs also should be out there, as the S-IVB was directed to hit the Moon after the LM was retrieved, and thus after they were ejected.
There was a claim that the S-IVB for Apollo 12 might have been found. I don't know if that was ever confirmed, though.
"... which he describes as "better than most of what is being reported in mainstream media so far."
Well, duh. He was there. Eyewitness reports always have an advantage that way.
He had received decades of organized schooling from scientists, who I'd like to think make better teachers than birds.
Why ? I think that Dr Pepperberg would say it took a decade or so just to figure out how to teach him at all, which is a disadvantage the birds wouldn't have.
Flocks are social constructs, highly organized. They can include birds from other species (show me a human tribe that does that). That alone says that there is some active learning going on.
More to the point, however, if these flocks can start usefully communicating with the humans that they interact with, there will be very strong evolutionary pressure to improve the communication. That is what I see as the real significance here.