Quantum Computing and Quantum Cryptography are unrelated technologoies. Quantum crypto is indeed "unbreakable", but requires a single physical channel connecting source and destination. It will not carry over routers and absolutely cannot be used for normal internet email for instance.
Quantum computing would break a range of encryption techniques, especially most public-key techniques, but nothing known today rules out new and more robust digital encryption technologies being developed that Quantum Computers could not break, and I imagine plenty of people are working on them.
I think that's right. It's not a fundamental problem, but you need to find an energy-efficient way of getting the methane to the surface inside your pipes, without (a) wasting energy lifting ice or (b) losing the methane as bubbles rising to the surface outside your pipes.
It's not actually frozen methane as such. The freezing point of methane is much too cold for that. It's a clathrate essentially a form of ice with methane molecules trapped among the water molecules. It's stable at temperatures just above the normal freezing point of water, and high pressures. If the pressure is released (for example by bringing it to the surface) it decomposes into water and methane gas.
This effect is very small, as you would expect, since light is very fast. In fact it is so small that it gets mixed up with all the other small ways in which general relativity predict deviations from Newtonian gravity, like gravity waves. The net effect is that two spinning boies do VERY SLOWLY radiate their rotational energy away as gravity waves, and will eventually collide. For most reaosonable objects, however this will take longer than the lifetime of the universe. Only very dense objects rotating very fact (like binary neutron stars) actually show a measurable effect.
Someone once told me that LN2 is almost exactly as dangeous as boiling hot coffee -- a few drops won't hurt, but soak your sleeve in it and you in trouble, etc.
To take the second point. The Centre of Mass has to be in geostationary orbit. As several people have said, the cable is very non-uniform. It is thicker close to orbit, thinner near the ground and has a large mass attached somewhere outside geostationary orbit.
So, what happens if it is cut? Cut it at the bottom and almost nothing happens. The tension at the bottom is only enough for stability and load-carrying. So, cut it and the bottom end just flaps around until you catch it again.
Cut it below about 10000 km altitude and everything below the cut falls to the ground. The cable will almost certainly snap, in multiple places, or could be deliberately cut using explosives or something like thermite (the fal takes hours, there is plenty of time for cable control to press the big red button). The bits from lower altitudes fall at their terminal velocity in air (probably not all that fast) close to the bottom attachment point, the bits from higher up probably burn in the upper atmosphere, or at least get slowed to terminal velocity.
Cut it further up, and if cable control can move fast enough, they cut it at about 10000km and the bits above that altitude remain in orbit (an elliptical orbit that just misses the atmosphere). Also, the further up the cut is, the longer it all takes to happen.
Read the small print. The islands are only 5 nanometers high (and about ten times that wide). The head should sail right over it, a lofty 20 or 30 nm above the surface and still only "look down on" one island at a time.
A much harder problem will be head tracking. With uniform media, you just need the head to return reliably to the same place when you tell it to. Now you have to actually get the head over a pre-existing feature on the disk, which is much harder.
It was Cambridge (UK). The university is scattered through and around the town, and certainly doesn't have anything as centralized as a steam heating system (or, at that time, any central management worth a damn either). The network installation was further complicated by the fact that, in large parts of the town practically everything is a listed historical site of some kind, so huge and strange efforts had to be made not to damage anything. Rumours also mention problems around the Old Cavendish lab (in the town centre). Rutherford split the atom there in 1908 and parts of it are apparently still radio-active.Finally Cambeidge is basically built on a swamp and about 1m above sea-level, so if you dig a hole it tends to fill with water pretty quickly.
Switches for these speeds are still kind of large, awkward and pricy. We had a visiting lecturer from one of the major players in this level of kit talking here about 6 months ago, and their top-end product (he showed a photo) was a 48-way full bandwidth 10Gb switch, It filled two full height 19" racks, consumed 20kW and cost upwards of $2M.
Of course they've probably come down a but in the last few months...
Actually, burying pipe is the most expensive part..... I worked briefly for a university computing service a few years ago and they spent an absolute fortune to buy a network of yellow plastic pipe connecting all their buildings. A relatively trivial incidental expenditure was to pull some cable through it. When that sort of cable is obsolete, a further trivial expenditure will replace it, etc....
Nevertheless, current international standards define all the imperial units in terms of metric ones, so a mile is, by definition 1.609 2655 metres (or whatever it is). There is no standard mile, foot, inch or yard any more. The metre is defined by reference to the wavelength of a specific type of light amd the second by reference to the speed of light and the metre.
Matter of this type might make an interesting component of a ground based anti-balistic missile system. The bullet
would be microscopically small, but would have incredible mass and could hold significant kinetic energy, suitable for the
destruction of a warhead. The energy source for the prime mover could be any typical huge ground based power plant.
Because of the microscopic size of the projectile, air resistance would be insignificant relative to the kinetic energy.
Unfortunately, the target would offer little more resistance than the intervening air. You would drill a micron-sized hole right through the target warhead, depositing almost none of the strangelet's KE in the process. Like trying to shoot down a smoke-cloud with a rifle.
To explain a bit more, a system is only stable, if it can't get to a lower energy state without breaking some rule. Since one kind of quark can turn into another pretty freely, this favours systems made up to the lowest energy quarks, namely up. However, two things combine to make the proton stable (uud) rather than the particle with three up quarks, whose name I can't recall:
One is ordinary electrostatics. up quarks have positive charge (2/3 of a unit, as it happens), down quarks negative (-1/3) so cramming three u quarks together involves overcoming more electrostatic repulsion that forming a proton.
The other is a litle subtler. Many of you will be familiar with the idea of "shells" of electrons inside an atom, representing groups of possible energy levels for an electron, each able to hold just one electron. Something similar goes on in any compact collection of quarks: isolated baryon, atomic nucleus, strangelet or neutron star core. Each energy level can be occupied by at most one quark <emph>of each flavour</emph>. This favours structures with reasonably equal balances between the types of quarks. So a proton, uud with the us in the two lowest energy states and the d in the lowest state, ends up with lower total energy than uuu, which would have to use three enegry states.
OK. Now what happens when we try and compute the stable options for clusters of quarks.
With small numbers of quarks, we have to strike a balance between the fact that u are lighter and the goal of balancing u & d to keep the energy levels low and the electrostatic problems to a minimum. Solutions to this make up all the stable atomic nuclei from 1H (uud) to lead nuclei with 250--300 quarks of each type.
Somewhat larger stable clusters do not form, the electrostatic repulsion and the high energy states into which the quarks would be forced mean that they can lose energy by splitting into two smaller clusters, so they do, hence nuclear fission.
When cluster sizes get very large, then gravity starts to play a role. Solar mass sized clusters of u and d quarks (2 downs to 1 up, so the whole thing is neutral) can be stablized, despite the energy cost of all the down quarks, by the mutual gravitational attraction. The result is a neutron star. The fact that quarks are in different spatial locations also helps with the energy level problem.
It is suggested that collections of quarks intermediate in mass between nuclei and neutron stars may be stable, if they contain a significant portion of strange quarks. Although basically heavier and so more energetic than u and d quarks, they would be free to occupy the lowest energy levels. Estimates of how massive these clusters would need to be to be stable vary wildly. One the one hand people are looking for extra-compact neutron-star like objects on the other hand for "stranglets" a few microns across and massing tons.
Actually the received power levels are much LOWER than that.
10W at the antenna, say it's at 1cm wavelength (not sure about this, but it should be within a factor of 10). Thats a 250 wavelenth tranmitting dish, so the signal is spread over a 4 milli-radian diameter cone. At 7.5e12 m that is 9e20 m2 spot, so a 250m dish on Earth receives 125^2*pi / 9 e20 of the signal, which is about 5 e-16 W.about half a femtoWatt, ignoring any imperfections in either dish, noise, absorbtion, etc.
By radio astronomy standards this is actually quite a powerful signal. I think they work down to 10^2? W for fairly small values of ?. On the other hand, they need a 770Hx bandwidth here, which is relatively wide.
Someone else commented on the time it would take to dump 48Gb of data over this link. This fits the mision profile beautifully. They fly past Pluto/Charon in a few hours, recording frantically on all instruments, then the slowly download the results, which coasting out into interstellar space. This mission is a fly-past, not an orbiter.
Compare budgets. Manned Mars missions are currently being placed in the 20-50 billion $ range, relatively unambitious shuttle replacements at 10 bn, and space elevators are still at the "let's do some possibly related basic science and see if anything interesting drops out" stage. PKE is budgetted at US$500m. It's not making any real dent in the budgets for the kind of programs you like.
The trouble with one time pads is that you need to distribute them ahead of time.sender and receiver need to have the same one-time pads before transmission. Furthermore the PADs have to be generated by a true physical random process such as Brownian motion or radioactive decay. A random-number generator doesn't work. Finally if you have lots of possible senders and receivers, you need lots^2 of one time pads agreed before you start. Using the same PAD twice is a huge breach in security.
Quantum Encryption provides a provably secore way of distributing your one-time PAD or any shorter symmetric key that you might prefer.
You don't. You aim a beam of something else, protons, say (in the usual way with magnets) and then smash it into a carefully selected target. The collisions make lots of neutrinos (and other junk, but a few km or rock absorbs that) and they are travelling, pretty much, in the direction of the original beam.
I thought the latest idea was the the really heavy elements formed in neutron star collisions, which spray them out at close to light-speed in jets. Rare events, but they produce and scatter a lot if heavy elements, which are not all that common anyway.
Slashdot Mirror
Or, of course, silicone-geranium. Brightens up the garden without needing all that tedious watering.
Very interesting. Thanks for the link. Still a long way from implementation though.
Quantum Computing and Quantum Cryptography are unrelated technologoies. Quantum crypto is indeed "unbreakable", but requires a single physical channel connecting source and destination. It will not carry over routers and absolutely cannot be used for normal internet email for instance.
Quantum computing would break a range of encryption techniques, especially most public-key techniques, but nothing known today rules out new and more robust digital encryption technologies being developed that Quantum Computers could not break, and I imagine plenty of people are working on them.
L2 is quite unstable. Anything there which is not station-keeping will drift into an independent solar orbit quite quickly.
Only L4 and L5 are stable.
I think that's right. It's not a fundamental problem, but you need to find an energy-efficient way of getting the methane to the surface inside your pipes, without (a) wasting energy lifting ice or (b) losing the methane as bubbles rising to the surface outside your pipes.
It's not actually frozen methane as such. The freezing point of methane is much too cold for that. It's a clathrate essentially a form of ice with methane molecules trapped among the water molecules. It's stable at temperatures just above the normal freezing point of water, and high pressures. If the pressure is released (for example by bringing it to the surface) it decomposes into water and methane gas.
This effect is very small, as you would expect, since light is very fast. In fact it is so small that it gets mixed up with all the other small ways in which general relativity predict deviations from Newtonian gravity, like gravity waves. The net effect is that two spinning boies do VERY SLOWLY radiate their rotational energy away as gravity waves, and will eventually collide. For most reaosonable objects, however this will take longer than the lifetime of the universe. Only very dense objects rotating very fact (like binary neutron stars) actually show a measurable effect.
Someone once told me that LN2 is almost exactly as dangeous as boiling hot coffee -- a few drops won't hurt, but soak your sleeve in it and you in trouble, etc.
The Atlas V numbers are to GTO and I suspect the others are to LEO. I don't know exactly what difference that makes, but it's significant.
To take the second point. The Centre of Mass has to be in geostationary orbit. As several people have said, the cable is very non-uniform. It is thicker close to orbit, thinner near the ground and has a
large mass attached somewhere outside geostationary orbit.
So, what happens if it is cut? Cut it at the bottom and almost nothing happens. The tension at the bottom is only enough for stability and load-carrying. So, cut it and the bottom end just flaps around until you catch it again.
Cut it below about 10000 km altitude and everything below the cut falls to the ground. The cable will almost certainly snap, in multiple places, or could be deliberately cut using explosives or something like thermite (the fal takes hours, there is plenty of time for cable control to press the big red button).
The bits from lower altitudes fall at their terminal velocity in air (probably not all that fast) close to the bottom attachment point, the bits from higher up probably burn in the upper atmosphere, or at least get slowed to terminal velocity.
Cut it further up, and if cable control can move fast enough, they cut it at about 10000km and the bits above that altitude remain in orbit (an elliptical orbit that just misses the atmosphere).
Also, the further up the cut is, the longer it all takes to happen.
Steve
Could you move the experiment to a beam at CERN or somewhere if you could get funding there but not in Europe?
Read the small print. The islands are only 5 nanometers high (and about ten times that wide). The head should sail right over it, a lofty 20 or 30 nm above the surface and still only "look down on" one island at a time.
A much harder problem will be head tracking. With uniform media, you just need the head to return reliably to the same place when you tell it to. Now you have to actually get the head over a pre-existing feature on the disk, which is much harder.
It was Cambridge (UK). The university is scattered through and around the town, and certainly doesn't have anything as centralized as a steam heating system (or, at that time, any central management worth a damn either). The network installation was further complicated by the fact that, in large parts of the town practically everything is a listed historical site of some kind, so huge and strange efforts had to be made not to damage anything. Rumours also mention problems around the Old Cavendish lab (in the town centre). Rutherford split the atom there in 1908 and parts of it are apparently still radio-active.Finally Cambeidge is basically built on a swamp and about 1m above sea-level, so if you dig a hole it tends to fill with water pretty quickly.
Switches for these speeds are still kind of large, awkward and pricy. We had a visiting lecturer from one of the major players in this level of kit talking here about 6 months ago, and their top-end product (he showed a photo) was a 48-way full bandwidth 10Gb switch, It filled two full height 19" racks, consumed 20kW and cost upwards of $2M.
Of course they've probably come down a but in the last few months...
About 1000 DVD quality video channels, or a feature length movie in a few seconds, or a bit longer for some future HDTV standard.
Streaming digital holographic porn, anyone?
Actually, burying pipe is the most expensive part..... I worked briefly for a university computing service a few years ago and they spent an absolute fortune to buy a network of yellow plastic pipe connecting all their buildings. A relatively trivial incidental expenditure was to pull some cable through it. When that sort of cable is obsolete, a further trivial expenditure will replace it, etc....
Nevertheless, current international standards define all the imperial units in terms of metric ones, so a mile is, by definition 1.609 2655 metres (or whatever it is). There is no standard mile, foot, inch or yard any more. The metre is defined by reference to the wavelength of a specific type of light amd the second by reference to the speed of light and the metre.
Each shell groups a number of levels. Each level can only hold one electron.
Unfortunately, the target would offer little more resistance than the intervening air. You would drill a micron-sized hole right through the target warhead, depositing almost none of the strangelet's KE in the process. Like trying to shoot down a smoke-cloud with a rifle.
To explain a bit more, a system is only stable, if it can't get to a lower energy state without breaking some rule. Since one kind of quark can turn into another pretty freely, this favours systems made up to the lowest energy quarks, namely up. However, two things combine to make the proton stable (uud) rather than the particle with three up quarks, whose name I can't recall:
One is ordinary electrostatics. up quarks have positive charge (2/3 of a unit, as it happens), down quarks negative (-1/3) so cramming three u quarks together involves overcoming more electrostatic repulsion that forming a proton.
The other is a litle subtler. Many of you will be familiar with the idea of "shells" of electrons inside an atom, representing groups of possible energy levels for an electron, each able to hold just one electron. Something similar goes on in any compact collection of quarks: isolated baryon, atomic nucleus, strangelet or neutron star core. Each energy level can be occupied by at most one quark <emph>of each flavour</emph>. This favours structures with reasonably equal balances between the types of quarks. So a proton, uud with the us in the two lowest energy states and the d in the lowest state, ends up with lower total energy than uuu, which would have to use three enegry states.
OK. Now what happens when we try and compute the stable options for clusters of quarks.
With small numbers of quarks, we have to strike a balance between the fact that u are lighter and the goal of balancing u & d to keep the energy levels low and the electrostatic problems to a minimum. Solutions to this make up all the stable atomic nuclei from 1H (uud) to lead nuclei with 250--300 quarks of each type.
Somewhat larger stable clusters do not form, the electrostatic repulsion and the high energy states into which the quarks would be forced mean that they can lose energy by splitting into two smaller clusters, so they do, hence nuclear fission.
When cluster sizes get very large, then gravity starts to play a role. Solar mass sized clusters of u and d quarks (2 downs to 1 up, so the whole thing is neutral) can be stablized, despite the energy cost of all the down quarks, by the mutual gravitational attraction. The result is a neutron star. The fact that quarks are in different spatial locations also helps with the energy level problem.
It is suggested that collections of quarks intermediate in mass between nuclei and neutron stars may be stable, if they contain a significant portion of strange quarks. Although basically heavier and so more energetic than u and d quarks, they would be free to occupy the lowest energy levels. Estimates of how massive these clusters would need to be to be stable vary wildly. One the one hand people are looking for extra-compact neutron-star like objects on the other hand for "stranglets" a few microns across and massing tons.
Actually the received power levels are much LOWER than that.
10W at the antenna, say it's at 1cm wavelength (not sure about this, but it should be within a factor of 10). Thats a 250 wavelenth tranmitting dish, so the signal is spread over a 4 milli-radian diameter cone. At 7.5e12 m that is
9e20 m2 spot, so a 250m dish on Earth receives
125^2*pi / 9 e20 of the signal, which is about
5 e-16 W.about half a femtoWatt, ignoring any imperfections in either dish, noise, absorbtion, etc.
By radio astronomy standards this is actually quite a powerful signal. I think they work down to 10^2? W for fairly small values of ?. On the other hand, they need a 770Hx bandwidth here, which is relatively wide.
Someone else commented on the time it would take to dump 48Gb of data over this link. This fits the mision profile beautifully. They fly past Pluto/Charon in a few hours, recording frantically on all instruments, then the slowly download the results, which coasting out into interstellar space. This mission is a fly-past, not an orbiter.
Compare budgets. Manned Mars missions are currently being placed in the 20-50 billion $ range, relatively unambitious shuttle replacements at 10 bn, and space elevators are still at the "let's do some possibly related basic science and see if anything interesting drops out" stage. PKE is budgetted at US$500m. It's not making any real dent in the budgets for the kind of programs you like.
The trouble with one time pads is that you need to distribute them ahead of time.sender and receiver need to have the same one-time pads before transmission. Furthermore the PADs have to be generated by a true physical random process such as Brownian motion or radioactive decay. A random-number generator doesn't work. Finally if you have lots of possible senders and receivers, you need lots^2 of one time pads agreed before you start. Using the same PAD twice is a huge breach in security.
Quantum Encryption provides a provably secore way of distributing your one-time PAD or any shorter symmetric key that you might prefer.
You don't. You aim a beam of something else, protons, say (in the usual way with magnets) and then smash it into a carefully selected target. The collisions make lots of neutrinos (and other junk, but a few km or rock absorbs that) and they are travelling, pretty much, in the direction of the original beam.
I thought the latest idea was the the really heavy elements formed in neutron star collisions, which spray them out at close to light-speed in jets. Rare events, but they produce and scatter a lot if heavy elements, which are not all that common anyway.