I live in Australia, where people vote with
pencils, piles of paper, eyeballs, and
telephones. Thanks to massively parallel
processing we usually know who's going to form
the next government by bedtime on election night.
The first-past-the-post tallies are invariably
known on the night, but the winners are decided
by a rather complicated algorithm to avoid the
Nader effect, so the closest electorates take
weeks to count. The government has to get its
legislation passed by the senate, which uses
an even more complicated algorithm, and often
takes a month to determine.
But it doesn't matter. Really important
politics, such as abolishing slavery, liberating
women, banning alcohol, or providing public
funding for education, happens over decades or
centuries. Even on such an immediate issue as
building a dam on the Franklin River, political
debate took years. Urgent decisions such as
going to war would usually be decided the same
way by any party that might win an election.
Voting machines gain only speed, while only
accuracy counts.
Apparently Craig also has problems reading licenses. The GPL
requires you provide the source to the customers not to everyone.
It also requires you to grant those customers the right to
redistribute the source to anyone they want, so the effect is very
similar, particularly in the context of trade secrets or copyright,
which Craig Mundie was discussing at that point. Mundie was
strategically ambiguous as to which of the two he meant.
Hang, draw and quarter him by all means, but only after due process.
What I find neat about diamagnetic levitation (what's holding up
that frog in its blob of water) is that the force acts within each
atom of the levitatee, so the net force on each of the frog's atoms
becomes zero (gravity is exactly counteracted).
I have thought occasionally that this would be a perfect way to
cushion acceleration. After five to ten pages of solid algebra, the
mind can wander to some really interesting places - you can forget
about the really big problems with interstellar transport, and get to
(or rather away from) work on the details.
I once had to discuss whether it is practical to escape the solar
system by sailing on the pressure of sunlight, as an exercise in an
atom optics course. Unless you have a (really) ridiculously large
sail, you need to pick up energy while you are close to the sun; the
pressure on your sail follows an inverse square law. So you need a
large acceleration. I estimated 10 g at the time. That does bad things
to jet pilots, who experience it for just an instant while ejecting.
With a diamagnetic cushion, which acts on the water in your body, you
might be able to push harder. Designing cockpit instruments which
would not be affected by a 10 T magnetic field, not to mention building
the magnet, is left as an exercise.
BTW, it should be pointed out that Berry is a very serious
physicist - my favorite textbook on quantum theory has a whole
appendix on geometric phase, which is based on a paper he published in
1984. And it is quite possible to levitate a ferromagnet with
magnetic fields - I have heard of it being done as an undergraduate
experiment. You just need feedback.
Andrew Tridgell metioned at a Canberra Linux User Group meeting a few years ago that at first, when the SAMBA project website consisted of one page, it was served by a "cat foo" line in inetd.conf on some machine at ANU; foo was a file containing some http response headers and the page. He figured this would be simpler than installing and configuring apache. I don't think you can get much simpler than that.
I strongly recommend against putting these questions in the interview; they are FAQs, and the answers can be found in any number of places without consulting a Nobel laureate. I give a few references below.
Before I discuss the quantum examples, I should mention that there is a very general reason to believe faster than light communication is impossible: according to the theory of relativity, it is entirely equivalent to communicating backwards in time, which brings up deep questions about free will and killing your grandmother. For details of this and and lots of other mind bending features of the universe, try reading Spacetime Physics by Taylor and Wheeler, a great introduction to the special theory of relativity at a level a good high school student should be able to understand.
There has been quite a lot of noise about transmitting information faster than at light speed (with twin photons, tunnelling or whatever means). All (serious ?) scientists say that this is not possible, no matter if experiments show something else (or are these all faulty ?).
The short answer to this is that since any measurement on one member of a set of (maximally) entangled particles will give a random result, you can't possibly derive any information from that measurement alone; you might as well flip a coin, and avoid the trouble of setting up the entanglement. On the other hand, if you can communicate with the person who has the other entangled particle, the classically impossible correlations between measurements the pair of you you might make allow you to do a number of things you couldn't do otherwise, like provably secure key distribution, dense coding and quantum teleportation.
For a popular science discussion, see Schrodinger's kittens and the search for reality : solving the quantum mysteries by John Gribbin. If you want it from the horses' mouths, try Bennett and Shor's review (IEEE Transactions on Information Theory 44 (6), p2724 (1998)).
Also, why do physicians claim that faster than light information transport by tunneling does not transport the information faster than light ?
They don't; physicists do. This is a somewhat ill posed question, in that a phenomenon (like an electron tunneling through a barrier, or the edge of a shadow travelling along a surface) can not transmit information by itself. You have to be able to control it so different things will happen depending on what you want to send. If you want to communicate using an electron tunneling through a barrier, you can modulate either the energy of the electron or the height of the barrier. These changes will take time to propagate from your position, and for all situations people have thought about so far, this happens slower than light.
If the Australian government implements its mandatory filtering scheme, many of us will want to circumvent it on occasion. For instance an overzealous classification board could ban bugtraq, or I might want to distribute my private webpage to those who request it, even though it might be inappropriate for broadcast on the TV or radio. Although Australian censors have been sensible so far, and pretty good at resisting political pressure, they could break down under load, like the US patent examiners.
Of course, circumventing the filters would be illegal, and because you don't agree with the law is not necessarily a reason to break it. On the other hand, one could argue governments have no business restricting personal communication (evidently a lot of people don't agree). Do you intend to obey the filtering laws? Would you encourage others to do so?
As far as symmetric ciphers go, I don't know of any algorithms to break them using a quantum computer. It doesn't seem to be an especially difficult problem, however, and I wouldn't be surprised if the NSA or someone had already written up a few to crack 3DES, Blowish, etc.
As far as I can see quantum computers are not a huge threat to symmetric ciphers, which can only be attacked statistically, not by solving a set mathematical problem. The defining feature of public key cyphers is what makes them vulnerable - since everyone knows the public key, the attacker (Eve) has enough information for a break without any intercepts of cipertext. Once she knows the public key, in principle she can determine the secret key with pencil and paper. Quantum computers just make it practical.
This is not the case for symmetric cyphers - Eve knows nothing until she has some ciphertext, and with most cyphers that plaintext could in theory have been encrypted with any key. The only reason symmetric ciphers can be broken at all is that Eve can guess characteristics of the plaintext, and might discover some way these are reflected in characteristics of the ciphertext. If she doesn't have enough plaintext, or it doesn't have enough structure, then even in principle there is no way for her to break the cipher, since the ciphertext she has could be the result of encrypting many different messages with different keys. Symmetric cypher designers have a large space to explore to find ciphers where the cyphertext does not reveal characteristics of the plaintext, and say with DES it took decades before any attacks better than brute force were revealed in public. For short enough messages, even a substitution cypher is secure.
It is hard to see how a quantum computer would significantly speed up the statistical calculations used to break symmetric cyphers. Grover's search algorithm could speed up brute force searches, but only by a square root, doubling the key length would make the cypher as secure as it would be otherwise. With the attack on RSA, doubling the key length would only increase the difficulty of attack by a constant factor, which doesn't do you much good.
There have been plans to do this for a while, with a group of satelites in orbit around the sun. The acronym for it is LISA. The big advantage is that the arms of the interferometer can be a lot longer, which is the simplest way to make it more sensitive. Here is the first page google threw back at me.
And you thought $3.5e8 was a lot of money...
The big risk with building gravity wave detectors is if they don't detect anything. This would be a really surprising result if it were true, so no one would believe it unless more experiments with bigger instruments were done to confirm it. But getting money to repeat an experiment which didn't work the first time would be next to impossible, so everyone could be left in a frustrating situation.
It was experiments like this that actually proved that neutrinos exist.
That's only true for very large values of prove. If you believe in conservation of momentum, you just need to look at the beta decay of a random nucleus near you and notice that the two bits you can find afterwards (the nucleus and an electron) aren't going in opposite directions. This means the nucleus must have spat out something else to conserve momentum.
Because you can't find the missing bit (i.e. it doesn't interact with any of your detectors) you strongly suspect it's neutral. By measuring the bits you can see and doing some arithmetic, you can find out its energy and momentum, and then some basic relativity tells you that it has very little mass and is travelling close to the speed of light.
Hence you might decide to call the missing particle a little neutral thing, but since an Italian found it first, it's known as a neutrino. So in fact neutrinos were first discovered by analysing their production, not their absorption.
Unexplained gaps in our basic theories of physics are not new. For centuries after classical mechanics was developed by Galileo, Newton, Kepler et al., no one had a convincing argument that the techniques of calculus it relied on were valid. This led someone (I think it was Bishop Berkeley) to suggest that science was just as much a matter of faith as Christianity.
Of course, astronomical observations eventually agreed with the theory so well that no one really doubted it; though it took some time for calculations to reach a precision which would account for all the observations. It was not until the 19th century that Cantor et al. put calculus on a rigorous foundation, and moved the controversy on to really bizarre matters like the axiom of choice.
Another good example is the inconsistency of electromagnetic theory and Newtonian mechanics in the second half of the 19th century. It was 50 years from Maxwell's calculation of a (constant) value for the speed of light from his laws of electromagnetism before Einstein found a consistent theory with special relativity. In this case it turned out that the assumptions underlying the original theory were wrong.
So although some areas of modern physics lack a generally accepted explanation, particularly in quantum mechanics with renormalisation and non-locality, this is not at all an alarming situation to be in, it just means that physics is still in progress, as it always has been. I don't think anyone expects to have all the answers any time soon.
Slashdot Mirror
I live in Australia, where people vote with pencils, piles of paper, eyeballs, and telephones. Thanks to massively parallel processing we usually know who's going to form the next government by bedtime on election night. The first-past-the-post tallies are invariably known on the night, but the winners are decided by a rather complicated algorithm to avoid the Nader effect, so the closest electorates take weeks to count. The government has to get its legislation passed by the senate, which uses an even more complicated algorithm, and often takes a month to determine.
But it doesn't matter. Really important politics, such as abolishing slavery, liberating women, banning alcohol, or providing public funding for education, happens over decades or centuries. Even on such an immediate issue as building a dam on the Franklin River, political debate took years. Urgent decisions such as going to war would usually be decided the same way by any party that might win an election. Voting machines gain only speed, while only accuracy counts.
Alan Cox wrote:
Apparently Craig also has problems reading licenses. The GPL requires you provide the source to the customers not to everyone.
It also requires you to grant those customers the right to redistribute the source to anyone they want, so the effect is very similar, particularly in the context of trade secrets or copyright, which Craig Mundie was discussing at that point. Mundie was strategically ambiguous as to which of the two he meant.
Hang, draw and quarter him by all means, but only after due process.
What I find neat about diamagnetic levitation (what's holding up that frog in its blob of water) is that the force acts within each atom of the levitatee, so the net force on each of the frog's atoms becomes zero (gravity is exactly counteracted).
I have thought occasionally that this would be a perfect way to cushion acceleration. After five to ten pages of solid algebra, the mind can wander to some really interesting places - you can forget about the really big problems with interstellar transport, and get to (or rather away from) work on the details.
I once had to discuss whether it is practical to escape the solar system by sailing on the pressure of sunlight, as an exercise in an atom optics course. Unless you have a (really) ridiculously large sail, you need to pick up energy while you are close to the sun; the pressure on your sail follows an inverse square law. So you need a large acceleration. I estimated 10 g at the time. That does bad things to jet pilots, who experience it for just an instant while ejecting. With a diamagnetic cushion, which acts on the water in your body, you might be able to push harder. Designing cockpit instruments which would not be affected by a 10 T magnetic field, not to mention building the magnet, is left as an exercise.
BTW, it should be pointed out that Berry is a very serious physicist - my favorite textbook on quantum theory has a whole appendix on geometric phase, which is based on a paper he published in 1984. And it is quite possible to levitate a ferromagnet with magnetic fields - I have heard of it being done as an undergraduate experiment. You just need feedback.
Andrew Tridgell metioned at a Canberra Linux User Group meeting a few years ago that at first, when the SAMBA project website consisted of one page, it was served by a "cat foo" line in inetd.conf on some machine at ANU; foo was a file containing some http response headers and the page. He figured this would be simpler than installing and configuring apache. I don't think you can get much simpler than that.
Before I discuss the quantum examples, I should mention that there is a very general reason to believe faster than light communication is impossible: according to the theory of relativity, it is entirely equivalent to communicating backwards in time, which brings up deep questions about free will and killing your grandmother. For details of this and and lots of other mind bending features of the universe, try reading Spacetime Physics by Taylor and Wheeler, a great introduction to the special theory of relativity at a level a good high school student should be able to understand.
There has been quite a lot of noise about transmitting information faster than at light speed (with twin photons, tunnelling or whatever means). All (serious ?) scientists say that this is not possible, no matter if experiments show something else (or are these all faulty ?).
The short answer to this is that since any measurement on one member of a set of (maximally) entangled particles will give a random result, you can't possibly derive any information from that measurement alone; you might as well flip a coin, and avoid the trouble of setting up the entanglement. On the other hand, if you can communicate with the person who has the other entangled particle, the classically impossible correlations between measurements the pair of you you might make allow you to do a number of things you couldn't do otherwise, like provably secure key distribution, dense coding and quantum teleportation.
For a popular science discussion, see Schrodinger's kittens and the search for reality : solving the quantum mysteries by John Gribbin. If you want it from the horses' mouths, try Bennett and Shor's review (IEEE Transactions on Information Theory 44 (6), p2724 (1998)).
Also, why do physicians claim that faster than light information transport by tunneling does not transport the information faster than light ?
They don't; physicists do. This is a somewhat ill posed question, in that a phenomenon (like an electron tunneling through a barrier, or the edge of a shadow travelling along a surface) can not transmit information by itself. You have to be able to control it so different things will happen depending on what you want to send. If you want to communicate using an electron tunneling through a barrier, you can modulate either the energy of the electron or the height of the barrier. These changes will take time to propagate from your position, and for all situations people have thought about so far, this happens slower than light.
If the Australian government implements its mandatory filtering scheme, many of us will want to circumvent it on occasion. For instance an overzealous classification board could ban bugtraq, or I might want to distribute my private webpage to those who request it, even though it might be inappropriate for broadcast on the TV or radio. Although Australian censors have been sensible so far, and pretty good at resisting political pressure, they could break down under load, like the US patent examiners.
Of course, circumventing the filters would be illegal, and because you don't agree with the law is not necessarily a reason to break it. On the other hand, one could argue governments have no business restricting personal communication (evidently a lot of people don't agree). Do you intend to obey the filtering laws? Would you encourage others to do so?
As far as I can see quantum computers are not a huge threat to symmetric ciphers, which can only be attacked statistically, not by solving a set mathematical problem. The defining feature of public key cyphers is what makes them vulnerable - since everyone knows the public key, the attacker (Eve) has enough information for a break without any intercepts of cipertext. Once she knows the public key, in principle she can determine the secret key with pencil and paper. Quantum computers just make it practical.
This is not the case for symmetric cyphers - Eve knows nothing until she has some ciphertext, and with most cyphers that plaintext could in theory have been encrypted with any key. The only reason symmetric ciphers can be broken at all is that Eve can guess characteristics of the plaintext, and might discover some way these are reflected in characteristics of the ciphertext. If she doesn't have enough plaintext, or it doesn't have enough structure, then even in principle there is no way for her to break the cipher, since the ciphertext she has could be the result of encrypting many different messages with different keys. Symmetric cypher designers have a large space to explore to find ciphers where the cyphertext does not reveal characteristics of the plaintext, and say with DES it took decades before any attacks better than brute force were revealed in public. For short enough messages, even a substitution cypher is secure.
It is hard to see how a quantum computer would significantly speed up the statistical calculations used to break symmetric cyphers. Grover's search algorithm could speed up brute force searches, but only by a square root, doubling the key length would make the cypher as secure as it would be otherwise. With the attack on RSA, doubling the key length would only increase the difficulty of attack by a constant factor, which doesn't do you much good.
And you thought $3.5e8 was a lot of money...
The big risk with building gravity wave detectors is if they don't detect anything. This would be a really surprising result if it were true, so no one would believe it unless more experiments with bigger instruments were done to confirm it. But getting money to repeat an experiment which didn't work the first time would be next to impossible, so everyone could be left in a frustrating situation.
That's only true for very large values of prove. If you believe in conservation of momentum, you just need to look at the beta decay of a random nucleus near you and notice that the two bits you can find afterwards (the nucleus and an electron) aren't going in opposite directions. This means the nucleus must have spat out something else to conserve momentum.
Because you can't find the missing bit (i.e. it doesn't interact with any of your detectors) you strongly suspect it's neutral. By measuring the bits you can see and doing some arithmetic, you can find out its energy and momentum, and then some basic relativity tells you that it has very little mass and is travelling close to the speed of light.
Hence you might decide to call the missing particle a little neutral thing, but since an Italian found it first, it's known as a neutrino. So in fact neutrinos were first discovered by analysing their production, not their absorption.
Unexplained gaps in our basic theories of physics are not new. For
centuries after classical mechanics was developed by Galileo, Newton,
Kepler et al., no one had a convincing argument that the techniques of
calculus it relied on were valid. This led someone (I think it was
Bishop Berkeley) to suggest that science was just as much a matter of
faith as Christianity.
Of course, astronomical observations eventually agreed with the theory
so well that no one really doubted it; though it took some time for
calculations to reach a precision which would account for all the
observations. It was not until the 19th century that Cantor et
al. put calculus on a rigorous foundation, and moved the controversy
on to really bizarre matters like the axiom of choice.
Another good example is the inconsistency of electromagnetic theory
and Newtonian mechanics in the second half of the 19th century. It
was 50 years from Maxwell's calculation of a (constant) value for the
speed of light from his laws of electromagnetism before Einstein found
a consistent theory with special relativity. In this case it turned
out that the assumptions underlying the original theory were wrong.
So although some areas of modern physics lack a generally accepted
explanation, particularly in quantum mechanics with renormalisation
and non-locality, this is not at all an alarming situation to be in,
it just means that physics is still in progress, as it always has
been. I don't think anyone expects to have all the answers any time
soon.