We don't have enough nukes to blow the Earth into space dust. We have enough to wipe out human civilization, and, if we used them carefully, probably enough to wipe out human life (and most othger large animals with us). I doubt we have enough to wipe out all life on land, and I'm sure we don't have enough to seriously damage the structure of the planet.
Also, delivering them to an asteroid is significantly more difficult than delivering them to another spot on Earth
As several people have observed, the attacker in this case used his "split into multi-files" trick to hide the necessary information in the directory structure of the disk. This is just barely ruled out by the "one compressed file" rule. However, suppose you hid the data in the filename of one file. For example write a program like
echo $1 | cat - $1
(about 20 bytes) and use the first 21 bytes of the raw file as the name of the compressed file.
This is in the same spirit as this attempt (hide the data in the directory) but avoids breaking the one compressed file rule.
This had crossed my mind. It would actually be easy to do with this fibre -- just pump it down from one end. If you don't do this, I imagine you do at least want to fill the central space with clean dry nitrogen, or something, rather than mucky ambient air.
The proposed mission puts 20 or so small nukes into independent orbits around the asteroid. I imagine the controlling processors would learn its exact mass profile pretty quickly. They also use a whole series of nudges to get it on target. The whole process takes a couple of years, so there no hurry.
The only real problem would be if the asteroid turned out not to be solid enough to deflect in one piece.
Read the article. The scenario envisaged is an unmanned launch disguised as a Mars or similar mission. This is "lost" and makes a rendezvous with the asteroid where it unloads 20 or so small nukes into orbits around the asteroid (ideally an otherwise unidentified one about 100m across). The nukes are used to alter the orbit of the asteroid, exploding when the sun is between Earth and the asteroid, leaving just one final course correction to be done in the final month of so before impact, shifting it from a near-miss to a collision.
In their simulations an average of 15 blasts was enough to hit a medium sized city.
Once the final blast is done, it could probably be nudged into a nearby ocean or something up to the last few days, but a hitherto unsuspecting opponent would probably not be able to launch a nuke beyond Earth orbit (an ICBM will not do) fast enough to do this themselves.
Budget, less than 100 billion $ for the first one, much less for subsequent ones.
We are broadcasting less and less radio power into space as time passes. More and more data is being transmitted on narrow beams, or by wire or fibre or at high frequencies that don't escape the atmosphere much. Even without some "magical" replacement for radio, it is imaginable that higher tech civilizations would radiate relatively little radio energy omnidirectionally into space.
Also, our present detection systems would not detect Earth's boradcast emmision at stellar distances. The SETI experiments hope instead to detect a deliberate beacon transmission aimed at us.
Possibly so, but my intuition is that these should be easier to resolve. Scalability needs bigger molecules and more precise spectral control of the NMR setup, but this doesn't seem improbable. Decoherence could be partly resolved by quantum error correction, and partly, perhaps, by careful choice of solvent, temperature, sample size, etc.
I admit that this is no more than gut feeling, though, I am neither a chemist nor a physicist.
To nitpick, EUV is not actually a laser technology at all. The laser is just used as a heater to get really, really hot xenon gas, which then radiates thermally.
More seriously, the distinction between EUV and soft X-ray is putely a marketing one. This technique was called soft X-ray until X-rays got a bad name.
I was not proposing a near future development, just speculating. Since you are a radio interferometrist, let me ask you a question: are radio astronomy sources actually coherent in any sense? That is, are the radio photons being detected at the two antennae in VLBI actually in phase for a reason, or are you relying on some statistical property of the large numbers of photons.
If the former, then optical VLBI is indeed in trouble. You'd have to quantum-mechanically preserve the photons phase information (without observing it) recombine them later and observe the combination to get useful interference. This might not be impossible -- you essentially need quantum teleportation, which is known to be possible.
If the latter, then you just need a big enough light-bucket and a bright enough source. This would limit the application of optical VLBI, but not rule it out. A 10000km baseline optical interferomter, for instance, would have a 1mm resolution for detail on the surface of the sun, for instance
You can compress your number a bit! Call it H (for halting). Consider the following compression scheme: if TM(n) halts after at most 10000n steps then omit digit n. This is computable in compression and expansion, and will reduce the amount of data needed to transmit the first N digits of H quite a lot, even if you have to send the decompressor over first.
For W_UTM, no such compression exists. If you want to send, N bits of W_UTM to someone, then, including sending the decompressor program, you HAVE to send them at least N bits of data.
Light from an extrasolar planet has been detected, in a sense, by a group of astronomers. What they did was to use the fact that the reflected light from the planet is blue-shifted when the planet is moving towards us in its orbit and red-shifted when it's moving away. It also varies in brightness in a characteristic way depending on how much of the planet we can see.
Essentially the researchers used very sophisticated image processing software to detect this "signature" pattern of colour and brightness variations in the light of the star (before processing the signal was 20000 times fainter than the noise). They can't point to any one photon and say "this is reflected light from the planet" but they can say statistically that reflected light is almost certainly present in their data.
You're right. There is no realistic prospect of interferometry with Gemini using any current technique. The point of building the two telescopes identical was to cut down on design costs, to allow exhchange of instruments and so on.
It is interesting to speculate on how one might do real long baseline optical interferometry, by
analogy with the techniques used in radio astronomy. Essentially you would need to record the phase of the incoming light at (point in the image of) each telescope as well as its intensity. This phase calculation would need to be stable over the duration of the recording, requiring something like a laser whose phase didn't drift by more than a few femtoseconds per hour -- a clock accurate to 1 part in 10^18 or so. This will give a rather large (petabytes/second/pixel) dataset.
Once you have done that you need to track the relative movement of the two telescopes to within a fraction of a wavelength, which will require allowing for the Earth's rotation, tidal distortion, thermal expansion and contraction of the rock, special and general relativistic effects from the Earth's rotation and gravity and probably much more. A better approach might be to observe a known source near the target star and try and calibrate from that. Using three or more telescopes also helps.
Then it just comes down to a comparatively well-understood, if enormous, computing task, to combine the datasets from all the telescopes and synthesise an image.
In a word, no. Only black holes in the last fraction of their life-span produce enough Hawking radiation to be noticed, and there is no obvious source for black holes small enough to be decaying now.
These black holes may have formed from large clumps of matter relatively soon after the big bang, or from very early, super-large, short-lived stars. They could then have grown by absorbing matter from their vicinities in the relatively dense universe of the time.
It seems unlikely that black holes make up much of the dark matter in the universe, although they could be a part. We know by looking at the way galaxies rotate and move, that most of the dark matter is in galaxies, but reasonably evenly distributed through them rather than collected at the center. If this was small black holes we'd notice their Hawking radiation. If it was bigger ones, we'd notice their gravity in various ways.
Finally the X-ray signatures could possibly be other small and very hot objects, but we don't know of anything that could be that small and that hot except matter falling into a black hole.
By and large they are still there, they have just cleaned out most of the matter in their immediate vicinities, so that they are no longer very easy to detect -- bloack holes are mainly detectable by the energy given off by the matter in the process of falling in, which gets VERY hot.
Black holes do radiate Hawking radiation, but most big ones radiate less than they absorb from the cosmic microwave background (let alone any remaining infall), so they are mostly still growing. Only when the universe is much, much, much older will they radiate away their mass and evaporate.
It now seems that most large galaxies have a pretty big (millions of solar masses) central black hole. One theory is that the black hole came first and the galaxy accumulated around it.
What society gains is clear in kind, although debatable in amount, or relative value. By limiting (for a period) who may perform these operations, society encourages the inventors to publicise them, so that everyone knows (in principle) that they exist, and could possibly be licensed, and so that after the patent period expires, everyone can use them. In addition, the prospect of a monopoly period encourages the sometimes laborious process of filling in all the details of the original idea and making it usable, which might otherwise not be worthwhile.
This is the claimed benefit of patents, whether of mathematics or of a mechanical design or of a DNA sequence. It is basically a decision for politicians what the cost/benefit analysis is for patents in a particular domain, what the period should be, what the "obviousness" test should be, and so on. In this case, I think the UK has called it better than the US, but I don't really see how algorithm patents are different in kind to other patents.
No, you have misremembered. Hydrogen liquefies at roughly 30K at 1 atmosphere, and liquid hydrogen is used as a rocket fuel (the shuttle external tank is mostlyu full of liquid hydrogen, for instance).
If you want to liquefy hydrogen at room temperature then you do need rather extreme pressures, such as those found in Jupiter. In fact, Jupiter is big enouygh (probably) to squeeze hydrogen into a liquid metallic state, which is really interesting. A liquid of protons in a sea of electrons.
As it stands, lead is almost certainly a better choice of superconductor, since both require liquid helium coolant and the plastic is probably more expensive. The point, however is that this opens the door to a new kind of superconductor. the first metallic superconductor was mercury at roughly 1K, we eventually got up to wierd (and expansive) alloys that superconduct at about 30K (liquid hydrogen coolant could be used).
The first ceramic superconductors worked only at 30 or 40 K, but we quickly got up to over 100K. Unfortunately, they're murder to form into wires, or anything else useful.
Now this group has opened the door, we can expect many more superconducting polymers. The ideal result would be one that is easy to make and form, and can carry high currents or operate in high magnetic fields and liquid nitrogen temperatures.
Even if that is not achieved this new class of superconductors might have interesting or useful properties.
I've seen a detailed proposal for a 15g man rated coilgun capable of launching 1 ton into (very) LEO. It's a 250 mile long fiberglass vacuum tube surrounded by a electromagnets. A launch takes 15GW of electrical power for about 30 seconds. The passenger rides in a crash couch (obviously at 15g) in front of a superconducting coil. For the first 25s, the thrust is forwards. For the next 5s the thrust is upwards, as the end of the gun bends up a convenient mountain. Shortly before the payload reaches them, the muzzle doors open, and the thrust is then backwards (air resistance) for the few seconds it takes to clear most of the atmosphere. Aerodynamic control surfaces on the projectile bend the orbit into an ellipse whose perigee just grazes the atmosphere, with apogee just above. Finally a very small rocket firing 45 minutes later raises the perigee to stabilize the orbit long enough for pickup by an inter-orbital shuttle.
It seemed a completely plausible design, although the failure mode analysis was likely to be tricky.
There were a series of articles in Nature last summer about the ultimate physical limits of comnputation. Specifically one of them looked at the ultimate 1kg laptop. If you want serial processing, then the answer is a very carefully structured 1kg black hole, which can do about 10^16 quantum bit operations on a 10^16 qbit "word" in the 10^-19 second lifetime of the black hole. Of course the power consumption, cooling and containment problems are rather severe. If you don;t play clever games with reversible computation and very very strong mirrors, then you need a supernova to power the thing.
The problem is that when you tug on a rope what you actually do is send a "wave" of compression and stretching down the rope, and it takes time for the wave to reach the other end and be felt.
The same happens if you push on a rod.
The speed of this wave is determined by the stiffness and mass of the rope or rod. The stiffer and lighter, the faster it travels. So, you say, make your rod or rope stiff enough and light enough and it should travel faster than light!
In fact you can't do that. The stiffness of a rope or rod is determined by the strength of the forces between the atoms that make it up, which are determined by electromagnetic effects (same as light). The fact that these effects only transmit information between the atoms at the speed of light puts an absolute limit of how stiff a rope or rod you can make, and ensures that the waves always travel slower than light.
Just as understanding the electromagnetic properties of electrons (which we do pretty well) does not let us immediately understand all of chemistry (which is basically just an application of the EM properties of electrons), so even a complete understanding of quantum chomodynamics will not let us instantly understand all the properties of nuclei. On the other hand, if our partial understanding of QCD makes a prediction, which we can then verify, then we make progress with QCD, and the better our understanding of QCD the closer we come to understanding how it can interact with gravity, which is the unified field theory you wanted.
By the way, I suspect the left-handed nuclei are wildly unstable states (so are the right-handed ones) so making molecules containing them is proabably not feasible
This really is what's going on, and everyone is doing it. Memory speeds are advancing much more slowly than CPU speeds. To fight this, we see more or faster cache, more levels of cache (expect L3 to start showing up soon on IA32) cleverer cache controllers and cleverer compilers. Real benchmarks (see for instance http://www.specbench.org) show improvements from memory OR CPU speed-ups, so neither is totally bottle-necking the other at this stage.
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We don't have enough nukes to blow the Earth into space dust. We have enough to wipe out human civilization, and, if we used them carefully, probably enough to wipe out human life (and most othger large animals with us). I doubt we have enough to wipe out all life on land, and I'm sure we don't have enough to seriously damage the structure of the planet.
Also, delivering them to an asteroid is significantly more difficult than delivering them to another spot on Earth
As several people have observed, the attacker in this case used his "split into multi-files" trick to hide the necessary information in the directory structure of the disk. This is just barely ruled out by the "one compressed file" rule. However, suppose you hid the data in the filename of one file. For example write a program like
echo $1 | cat - $1
(about 20 bytes) and use the first 21 bytes of the raw file as the name of the compressed file.
This is in the same spirit as this attempt (hide the data in the directory) but avoids breaking the one compressed file rule.
Steve
This had crossed my mind. It would actually be easy to do with this fibre -- just pump it down from one end. If you don't do this, I imagine you do at least want to fill the central space with clean dry nitrogen, or something, rather than mucky ambient air.
The proposed mission puts 20 or so small nukes into independent orbits around the asteroid. I imagine the controlling processors would learn its exact mass profile pretty quickly. They also use a whole series of nudges to get it on target. The whole process takes a couple of years, so there no hurry.
The only real problem would be if the asteroid turned out not to be solid enough to deflect in one piece.
Read the article. The scenario envisaged is an unmanned launch disguised as a Mars or similar mission. This is "lost" and makes a rendezvous with the asteroid where it unloads 20 or so small nukes into orbits around the asteroid (ideally an otherwise unidentified one about 100m across). The nukes are used to alter the orbit of the asteroid, exploding when the sun is between Earth and the asteroid, leaving just one final course correction to be done in the final month of so before impact, shifting it from a near-miss to a collision.
In their simulations an average of 15 blasts was enough to hit a medium sized city.
Once the final blast is done, it could probably be nudged into a nearby ocean or something up to the last few days, but a hitherto unsuspecting opponent would probably not be able to launch a nuke beyond Earth orbit (an ICBM will not do) fast enough to do this themselves.
Budget, less than 100 billion $ for the first one, much less for subsequent ones.
We are broadcasting less and less radio power into space as time passes. More and more data is being transmitted on narrow beams, or by wire or fibre or at high frequencies that don't escape the atmosphere much. Even without some "magical" replacement for radio, it is imaginable that higher tech civilizations would radiate relatively little radio energy omnidirectionally into space.
Also, our present detection systems would not detect Earth's boradcast emmision at stellar distances. The SETI experiments hope instead to detect a deliberate beacon transmission aimed at us.
I don't happen to have any moderator points just now, but thanks for a really clear and informative post.
Possibly so, but my intuition is that these should be easier to resolve. Scalability needs bigger molecules and more precise spectral control of the NMR setup, but this doesn't seem improbable. Decoherence could be partly resolved by quantum error correction, and partly, perhaps, by careful choice of solvent, temperature, sample size, etc.
I admit that this is no more than gut feeling, though, I am neither a chemist nor a physicist.
Of course this article is not about ion trap QC.
It's about NMR based QC, using multiple 13C atoms in a molecule as multiple q-bits.
To nitpick, EUV is not actually a laser technology at all. The laser is just used as a heater to get really, really hot xenon gas, which then radiates thermally.
More seriously, the distinction between EUV and soft X-ray is putely a marketing one. This technique was called soft X-ray until X-rays got a bad name.
I was not proposing a near future development, just speculating. Since you are a radio interferometrist, let me ask you a question: are radio astronomy sources actually coherent in any sense? That is, are the radio photons being detected at the two antennae in VLBI actually in phase for a reason, or are you relying on some statistical property of the large numbers of photons.
If the former, then optical VLBI is indeed in trouble. You'd have to quantum-mechanically preserve the photons phase information (without observing it) recombine them later and observe the combination to get useful interference. This might not be impossible -- you essentially need quantum teleportation, which is known to be possible.
If the latter, then you just need a big enough light-bucket and a bright enough source. This would limit the application of optical VLBI, but not rule it out. A 10000km baseline optical interferomter, for instance, would have a 1mm resolution for detail on the surface of the sun, for instance
You can compress your number a bit! Call it H (for halting). Consider the following compression scheme: if TM(n) halts after at most 10000n steps then omit digit n. This is computable in compression and expansion, and will reduce the amount of data needed to transmit the first N digits of H quite a lot, even if you have to send the decompressor over first.
For W_UTM, no such compression exists. If you want to send, N bits of W_UTM to someone, then, including sending the decompressor program, you HAVE to send them at least N bits of data.
Light from an extrasolar planet has been detected, in a sense, by a group of astronomers. What they did was to use the fact that the reflected light from the planet is blue-shifted when the planet is moving towards us in its orbit and red-shifted when it's moving away. It also varies in brightness in a characteristic way depending on how much of the planet we can see.
Essentially the researchers used very sophisticated image processing software to detect this "signature" pattern of colour and brightness variations in the light of the star (before processing the signal was 20000 times fainter than the noise). They can't point to any one photon and say "this is reflected light from the planet" but they can say statistically that reflected light is almost certainly present in their data.
You're right. There is no realistic prospect of interferometry with Gemini using any current technique. The point of building the two telescopes identical was to cut down on design costs, to allow exhchange of instruments and so on.
It is interesting to speculate on how one might do real long baseline optical interferometry, by
analogy with the techniques used in radio astronomy. Essentially you would need to record the phase of the incoming light at (point in the image of) each telescope as well as its intensity. This phase calculation would need to be stable over the duration of the recording, requiring something like a laser whose phase didn't drift by more than a few femtoseconds per hour -- a clock accurate to 1 part in 10^18 or so. This will give a rather large (petabytes/second/pixel) dataset.
Once you have done that you need to track the relative movement of the two telescopes to within a fraction of a wavelength, which will require allowing for the Earth's rotation, tidal distortion, thermal expansion and contraction of the rock, special and general relativistic effects from the Earth's rotation and gravity and probably much more. A better approach might be to observe a known source near the target star and try and calibrate from that. Using three or more telescopes also helps.
Then it just comes down to a comparatively well-understood, if enormous, computing task, to combine the datasets from all the telescopes and synthesise an image.
In a word, no. Only black holes in the last fraction of their life-span produce enough Hawking radiation to be noticed, and there is no obvious source for black holes small enough to be decaying now.
These black holes may have formed from large clumps of matter relatively soon after the big bang, or from very early, super-large, short-lived stars. They could then have grown by absorbing matter from their vicinities in the relatively dense universe of the time.
It seems unlikely that black holes make up much of the dark matter in the universe, although they could be a part. We know by looking at the way galaxies rotate and move, that most of the dark matter is in galaxies, but reasonably evenly distributed through them rather than collected at the center. If this was small black holes we'd notice their Hawking radiation. If it was bigger ones, we'd notice their gravity in various ways.
Finally the X-ray signatures could possibly be other small and very hot objects, but we don't know of anything that could be that small and that hot except matter falling into a black hole.
By and large they are still there, they have just cleaned out most of the matter in their immediate vicinities, so that they are no longer very easy to detect -- bloack holes are mainly detectable by the energy given off by the matter in the process of falling in, which gets VERY hot.
Black holes do radiate Hawking radiation, but most big ones radiate less than they absorb from the cosmic microwave background (let alone any remaining infall), so they are mostly still growing. Only when the universe is much, much, much older will they radiate away their mass and evaporate.
It now seems that most large galaxies have a pretty big (millions of solar masses) central black hole. One theory is that the black hole came first and the galaxy accumulated around it.
What society gains is clear in kind, although debatable in amount, or relative value. By limiting (for a period) who may perform these operations, society encourages the inventors to publicise them, so that everyone knows (in principle) that they exist, and could possibly be licensed, and so that after the patent period expires, everyone can use them. In addition, the prospect of a monopoly period encourages the sometimes laborious process of filling in all the details of the original idea and making it usable, which might otherwise not be worthwhile.
This is the claimed benefit of patents, whether of mathematics or of a mechanical design or of a DNA sequence. It is basically a decision for politicians what the cost/benefit analysis is for patents in a particular domain, what the period should be, what the "obviousness" test should be, and so on. In this case, I think the UK has called it better than the US, but I don't really see how algorithm patents are different in kind to other patents.
No, you have misremembered. Hydrogen liquefies at roughly 30K at 1 atmosphere, and liquid hydrogen is used as a rocket fuel (the shuttle external tank is mostlyu full of liquid hydrogen, for instance).
If you want to liquefy hydrogen at room temperature then you do need rather extreme pressures, such as those found in Jupiter. In fact, Jupiter is big enouygh (probably) to squeeze hydrogen into a liquid metallic state, which is really interesting. A liquid of protons in a sea of electrons.
As it stands, lead is almost certainly a better choice of superconductor, since both require liquid helium coolant and the plastic is probably more expensive. The point, however is that this opens the door to a new kind of superconductor. the first metallic superconductor was mercury at roughly 1K, we eventually got up to wierd (and expansive) alloys that superconduct at about 30K (liquid hydrogen coolant could be used).
The first ceramic superconductors worked only at 30 or 40 K, but we quickly got up to over 100K. Unfortunately, they're murder to form into wires, or anything else useful.
Now this group has opened the door, we can expect many more superconducting polymers. The ideal result would be one that is easy to make and form, and can carry high currents or operate in high magnetic fields and liquid nitrogen temperatures.
Even if that is not achieved this new class of superconductors might have interesting or useful properties.
I've seen a detailed proposal for a 15g man rated coilgun capable of launching 1 ton into (very) LEO. It's a 250 mile long fiberglass vacuum tube surrounded by a electromagnets. A launch takes 15GW of electrical power for about 30 seconds. The passenger rides in a crash couch (obviously at 15g) in front of a superconducting coil. For the first 25s, the thrust is forwards. For the next 5s the thrust is upwards, as the end of the gun bends up a convenient mountain. Shortly before the payload reaches them, the muzzle doors open, and the thrust is then backwards (air resistance) for the few seconds it takes to clear most of the atmosphere. Aerodynamic control surfaces on the projectile bend the orbit into an ellipse whose perigee just grazes the atmosphere, with apogee just above. Finally a very small rocket firing 45 minutes later raises the perigee to stabilize the orbit long enough for pickup by an inter-orbital shuttle.
It seemed a completely plausible design, although the failure mode analysis was likely to be tricky.
There were a series of articles in Nature last summer about the ultimate physical limits of comnputation. Specifically one of them looked at the ultimate 1kg laptop. If you want serial processing, then the answer is a very carefully structured 1kg black hole, which can do about 10^16 quantum bit operations on a 10^16 qbit "word" in the 10^-19 second lifetime of the black hole. Of course the power consumption, cooling and containment problems are rather severe. If you don;t play clever games with reversible computation and very very strong mirrors, then you need a supernova to power the thing.
This is actually quite an insightful question.
The problem is that when you tug on a rope what you actually do is send a "wave" of compression and stretching down the rope, and it takes time for the wave to reach the other end and be felt.
The same happens if you push on a rod.
The speed of this wave is determined by the stiffness and mass of the rope or rod. The stiffer and lighter, the faster it travels. So, you say, make your rod or rope stiff enough and light enough and it should travel faster than light!
In fact you can't do that. The stiffness of a rope or rod is determined by the strength of the forces between the atoms that make it up, which are determined by electromagnetic effects (same as light). The fact that these effects only transmit information between the atoms at the speed of light puts an absolute limit of how stiff a rope or rod you can make, and ensures that the waves always travel slower than light.
Just as understanding the electromagnetic properties of electrons (which we do pretty well) does not let us immediately understand all of chemistry (which is basically just an application of the EM properties of electrons), so even a complete understanding of quantum chomodynamics will not let us instantly understand all the properties of nuclei. On the other hand, if our partial understanding of QCD makes a prediction, which we can then verify, then we make progress with QCD, and the better our understanding of QCD the closer we come to understanding how it can interact with gravity, which is the unified field theory you wanted.
By the way, I suspect the left-handed nuclei are wildly unstable states (so are the right-handed ones) so making molecules containing them is proabably not feasible
This really is what's going on, and everyone is doing it. Memory speeds are advancing much more slowly than CPU speeds. To fight this, we see more or faster cache, more levels of cache (expect L3 to start showing up soon on IA32) cleverer cache controllers and cleverer compilers. Real benchmarks (see for instance http://www.specbench.org) show improvements from memory OR CPU speed-ups, so neither is totally bottle-necking the other at this stage.