You may not remember the Intel 432, a truly fascinating chipset which flopped more miserably than the Itanic.
Speak for yourself. I remember it quite well. A most humngous beast from over 20 years ago. It had some weird features, including some amazingly long instructions. I remember a competition to find the longest valid instruction. The winner was something like 400 bits long! IIRC, the iapx-432 was essentially an ADA processor.
I never actually saw a complete working 432 system. I do remember seeing a chip, and an extremely large one for the day, encased in acrylic resin and worn as pendant.
ake a few oceanography and geology classes. In near term climate change next 10-200 years global climate change will cool and warm various places. Your point is more valid for long term climate change (millions of years)
Thank you for your clarification. Note, however, that I very carefully did not set any time scale on the changes outlined in my posting. I did, however, say that other factors need to be taken into account. Very important factors are the time scales on which particular mechanisms operate.
If the climate shifts, we will most certainly both freeze and fry in different places. Such a shift refers to changes in the patterns of energy on Earth, not changes to the total energy in the planetary system. Some places get hot, others cold. People will move.
Yes and no. The energy input to the planet as a whole may remain roughly constant but that doesn't mean that the heat stored in the planet will remain the same.
Consider a perfectly ordinary greenhouse with no heating other than sunlight. The temperature inside is markedly hotter than that of a similarly sized and shaped volume outside, even though the energy input is essentially the same.
For a more extreme example, compare Venus and the Earth. Despite Venus being closer to to sun, less energy is deposited in its atmosphere and surface than we get in our atmosphere and surface layers. The reflectivity of the Venusian clouds is so much higher than the reflectivity of the Earth's. Nonetheless, despite getting more energy it is much colder near the Earth's surface than it is near the Venusian surface.
Conclusion: it's entirely possible for everywhere to get hotter. It's also entirely possible for everywhere to get colder. You can't conclude, purely on energy input grounds, that either will be the case, or that a redistribution of temperature variations will take place. If you take into account other factors it does indeed seem likely that some places will become cooler and others warmer, but those other factors must be evaluated properly.
Ever tried to modulate a high energy laser? I do not mean semiconductor toys. Even in space their useable distance can hardly exceed a few million km. I am talking about something real which can be seen a few ae from Earth - CO2, HF or HI eximer or the high end crystals. The only way to modulate them is a combination of two polarization cells which are controlled by electric field. The switching speed for this is rather lame. It is a few kbit at best and you have to fire it in short pulses so that the cell does not boil off. It is much easier to introduce a signal into a high power microwave beam. We have been learning on how to do this for more then a century now. We are yet to learn how to do this with light at power levels that make it useable for very long distance communications.
Emphasis added to the above quote so you can more easily see the inconsistency.
Now I'm not saying it is the best way of modulating a laser beam, but you could use an external flexible mirror to switch the beam on to or away from the receiver. Diverting the beam a matter of arc minutes would be enough.
Does a 100W gold laser count as high power? If so, go to a Pink Floyd concert to see one being modulated in public.
TWINKLE broke the 512bit RSA key. Bernstein has a proposal on how a machine could break a 1024bit key. For all we know, the NSA may have found better methods - which are able to factor 2048bit keys in a short timespan.
Garbage.
TWINKLE hasn't yet been built and, in its original form, probably never will be.
The first known factorization of a 512-bit hard integer was performed by "The Cabal". As far as anyone knows, that integer (rsa-512) has never been used as the public modulus of an RSA key.
The only 512-bit integer known to me to have been used as the public modulus of an RSA key and subsequently factored.is the stage-10 challenge in Simon Singh's The Codebook.
Both of these numbers, and a couple more which are at least as big, were factored by the general number field sieve running on a collection of quite ordinary computer.
I've already given you a goodly collection of keywords to type into a search engine, but the following may also be of use if you want to learn more: Lenstra, Montgomery, Franke, Leyland, "te Riele", CWI, "Simon Singh", Granlund, NFSNET, Shamir.
A more interesting application might be genetically modifying a plant disease which could introduce GM RNA into drug-producing plants, crippling their ability to reproduce or even produce the drug chemicals themselves. A revamped War on Drugs would then be fought by plant diseases that spread among Coca plants or Poppies rendering them harmless.
Be careful of what you ask for. You might get it.
In retaliation for spreading such diseases, those who would rather their coca trees or opium poppies not be infected may be moved to spray your cotton or corn fields.
It's not too big to be a supergiant planet. It's the same size as jupiter.
Same diameter, near enough, but much more massive. The article says it has a mass about a twentieth of that of the Sun. Jupiter has a mass about 1/1047 that of the Sun. From which we can conclude that the object has about fifty times the mass of Jupiter and is about fifty times as dense.
Let me say that you are right but I still have some doubt. After the collison the reference frame is still moving along with the photon so the momentum is zero after the collison.
Nope. After the collision the reference frame isn't still moving "along with the photon", even assuming that a single photon could be created, which it can't. Let's assume it does, though, and see what conclusion we draw.
First off, the reference frame was that of the centre of mass of the electron/positron pair. We know, pace Einstein, that frame is travelling at less than the speed of light with respect to anything else in the universe. After the collision, the frame is still moving the same with respect to the universe, but a photon has been created. In the reference frame the electron positron pair had zero net momentum. By conservation of momentum, the photon must therefore also have zero momentum. This point you seem to agree on. However, the momentum of a photon is proportional to its energy (p=E/c). If it has zero momentum, it has zero energy. Voila! Conservation of mass-energy has been violated. We've reached a contradiction and something has gone wrong somewhere. The error lies in the assumption that a single photon can be produced. To remedy the error you have to add at least one more photon so that energy and momentum can be simultaneously conserved.
The original poster said was useless, not is useless. At the time Einstein created relativity, and afterwards when the Nobel committee was thinking about giving hin a prize, it was indeed almost useless, especially his general theory.
I'm pretty sure that if the radiation exposure isn't enough to kill you, the chemical toxicity of Plutonium would be.
Wrong on both counts. Others have already commented on the radiation. As an ex-chemist I'll restrict myself to pointing out that plutonium has similar chemical toxicity to lead. It's a heavy metal and you don't want to go around eating it for the sake of it, but it really isn't that poisonous. The UPPU club has some members still alive almost sixty years after ingesting their plutonium.
Yes you can conserve momentum with a single photon except in head on collison. It is true however that there are always two photon.
Consider that the electron is moving in south east direction and positron in north east. When they collide their north - south momentum will cancel out. Now the only remaining momentum is in the east direction. This momentum will be the momentum of the photon moving in the east direction.
The reason the momentum cant be conserved during head on collison is that the resultant momentum has to be zero and single photon will have a mometum.
Errm, no you can't.
Einstein told us that as far as the laws of physics are concerned, one reference frame is as good as another. Now imagine you are sitting near to the the center of mass of the electron and positron and moving along with it. In your frame you see the two particles moving towards a head-on collision and with no net momentum. After the collision you will see at least one photon (by conservation of mass-energy) with zero net momentum (by conservation of momentum). The only way to get net zero momentum is by having at least two photons, travelling in suitable directions, since every photon carries momentum.
If you bring conservation of angular momentum into play, there is another wrinkle. The electron and positron each have a half-unit of intrinsic angular momentum, called "spin" for brevity. A photon has unit spin. So the two initial particles can have either net zero spin (the two angular momenta are equal, opposite and cancel) or net unit spin. After the collision, the photons each have unit spin and so the net spin is either zero or two, depending on whether the spins are opposite or aligned respectively.
Spot the problem?
If the initial total spin of the two particles is unity, three photons have to be created to ensure that all the conservation laws are satisfied.
In the center of mass frame of reference, the three photons have equal momenta (and so have equal energy and are directed at an angle of 120 degrees from each other) and two of them have spins which are oppositely aligned.
That raises the question: What could they possibly find on another planet that's valuable enough to import? ...
The only plausible case I've seen is importing He3 from the moon for fusion fuel. However, I saw one estimate that it would take a strip mining operation on the moon on a scale similar to all of coal mines on earth to glean enough of that rare isotope to supply our energy needs. Even that seems unlikely to be economically feasible.
The lunar surface has very low concentrations of He3 and is not an ideal source of it. The only benefits of mining He3 on the moon seems to be that it is easy to get to.
A far better source of He3 lies in the atmospheres of Jupiter and Saturn. It's not presently clear which is the more favourable. Jupiter is closer but has a deeper gravity well to haul the stuff out of. It also has worse weather, by and large, and a much nastier ionizing radiation problem on the way in and out.
You are exaggerating somewhat, but I have heard that anyone in the U.K. who doesn't pay their TV fee gets harrassed mightily, even if they don't have a TV.
I live in the UK and I've heard that too. OTOH, I spent several years without a TV set and was not harassed, mightily or otherwise. Once a year or so a letter would arrive asking me whether I had a TV set and/or licence for it. I'd reply that I had a set, that it was broken and couldn't receive broadcasts and that therefore I didn't need a licence. No real hassle.
To explain for the benefit of non-Brits: the licence is not for the set but for the ability to receive broadcasts. As my receiver was nonfunctional I didn't need the licence. I only kept the set in the house in order to screw with the brains of the bureaucrats. Eventually I got married, my wife had a fully functional TV set and I ditched the bureaucrat teaser.
I'm just wondering when we're going to start putting in ram for the sake of having more ram. Won't more ram eventually become unnecessary with all the bottlenecks computers have?
Perhaps, but not yet by a long way.
For instance, I presently want to find linear dependencies in a sparse bit matrix which has something over 8.1 million rows and columns. Even with a sparse representation, the computation requires over 2 gigabytes of active memory. In my field of interest (integer factorization) having access to machines with several gigabytes is almost an entry requirement. There are a number of other fields which need much more RAM than this if the programs aren't to be paging themselves into torpidity. Numerical simulation and large database access are a couple of examples.
Why aren't they using conventional storage standards, RAM, and disk space are all in megabytes (1024 vs 1000 debating aside) saying something is *bit (giga,mega,kilo) implies a rate connectivity doesn't it?
They are using conventional storage standards. Memory chips have been measured in (multiples of) bits for decades. When I started paying attention, around 1980 or so, the state of the art was something like 4k or 16k bits for DRAM and those chips were 1-bit wide. Even 8-bit wide chips were, and still are, quoted with storage capacity in bits. Again from the early days, an EEPROM with 2048 words of 8-bits each was described as a 16k device.
Further down in the article it is stated that "The flash chip is designed to let consumer electronics designers put up to 16 gigabytes of data on a single memory card". Note that they use the conventional units, bytes, for memory cards.
Remember, different conventions in different fields. You may think its silly, but that's life and you'd better get used to it.
And, since you ask: no, bits doesn't necessarily imply a rate connectivity. Raw connections are usually rated in bits per second but high level data streams, such as ftp download speeds, are often quoted in bytes per second. I do not know whether there is a parallel here between comms and storage in the different conventions used to specify what the raw technology gives you and what is built out of that technology. I would be interested to learn whether it is more than coincidence.
Energy and water are the requirements for life as we know it. Energy alone isn't enough - if it was the Sahara desert would be booming with life.
The Sahara desert is booming with life. Just because you can't always see it easily doesn't mean it's not there. It is completely infested with bacteria. There's a good smattering of plants of various kinds. Arthropods are relatively common. There's even a goodly smattering of birds and mammals.
The reason, of course, is that there is water in the Sahara desert. Less than there is in, say, Amazonia or the Pacific but plenty for life to get along nonetheless.
Paul
Re:transistor development driven by commerce
on
Antarctic Telescope?
·
· Score: 1
And only to get it working one had to have radio, based on decades of research of electromagnetism, in turn based on reseach of electricity, based on research of physics... etc etc etc.
Completely correct. But no quantum mechanics, which is the point under discussion. Radio, in the form of the spark transmitter at least, long predates Bohr's quantum theory let alone quantum mechanics. I don't know exactly when the point contact diode was invented but it certainly predates the work of Schrodinger, Heisenberg, Dirac, et al.
Paul
Re:transistor development driven by commerce
on
Antarctic Telescope?
·
· Score: 1
Transistors were probably developed with more commercial support than not (it's tough to do the accounting). It did benefit from the prior (academic) discovery/invention of quantum mechanics, but it's possible it would have been transistors could have been discovered anyway. I've known at least one person who argued that you could invent the transistor without quantum mechanics, though it certainly helps.
The semiconductor diode was certainly invented without the benefit of quantum mechanics so it is not entirely unreasonable that transistors might have been.
Back when my grandfather was a young man (he was born in 1892) people would listen to radio broadcasts with a receiver built in part around what was then called a "crystal and cat's whisker". We now call such devices "point contact diodes". It is entirely reasonable, in my view, that transistors could have been developed following empirical investigations of the behaviour of point contact diodes and analogies drawn from thermionic triodes, which are only thermionic diodes with a controllable electric field between the anode and cathode.
Slashdot Mirror
You can tell I'm a child of the seventies. (Well, the sixties actually but I never grew up.)
I only checked out the first couple of pages, but I can reveal that I presently own a mercury maze, a 4x4x4 Rubik cube, a Mastermind, ...
I've owned several others but they're are no longer in my posession, and recognize the rest.
Paul
I know: don't feed the trolls, but I can't let this pass.
If the US space program is a purely civilian effort, why is DoD bankrolling it to such an extent?
Paul
In places that abide by the Berne Convention, since it was made. Most everywhere follows the Convention.
It is actually rather difficult to produce a video that isn't copyrighted.
Paul
Speak for yourself. I remember it quite well. A most humngous beast from over 20 years ago. It had some weird features, including some amazingly long instructions. I remember a competition to find the longest valid instruction. The winner was something like 400 bits long! IIRC, the iapx-432 was essentially an ADA processor.
I never actually saw a complete working 432 system. I do remember seeing a chip, and an extremely large one for the day, encased in acrylic resin and worn as pendant.
Paul
Thank you for your clarification. Note, however, that I very carefully did not set any time scale on the changes outlined in my posting. I did, however, say that other factors need to be taken into account. Very important factors are the time scales on which particular mechanisms operate.
Paul
Yes and no. The energy input to the planet as a whole may remain roughly constant but that doesn't mean that the heat stored in the planet will remain the same.
Consider a perfectly ordinary greenhouse with no heating other than sunlight. The temperature inside is markedly hotter than that of a similarly sized and shaped volume outside, even though the energy input is essentially the same.
For a more extreme example, compare Venus and the Earth. Despite Venus being closer to to sun, less energy is deposited in its atmosphere and surface than we get in our atmosphere and surface layers. The reflectivity of the Venusian clouds is so much higher than the reflectivity of the Earth's. Nonetheless, despite getting more energy it is much colder near the Earth's surface than it is near the Venusian surface.
Conclusion: it's entirely possible for everywhere to get hotter. It's also entirely possible for everywhere to get colder. You can't conclude, purely on energy input grounds, that either will be the case, or that a redistribution of temperature variations will take place. If you take into account other factors it does indeed seem likely that some places will become cooler and others warmer, but those other factors must be evaluated properly.
Paul
Emphasis added to the above quote so you can more easily see the inconsistency.
Now I'm not saying it is the best way of modulating a laser beam, but you could use an external flexible mirror to switch the beam on to or away from the receiver. Diverting the beam a matter of arc minutes would be enough.
Does a 100W gold laser count as high power? If so, go to a Pink Floyd concert to see one being modulated in public.
Paul
Garbage.
TWINKLE hasn't yet been built and, in its original form, probably never will be.
The first known factorization of a 512-bit hard integer was performed by "The Cabal". As far as anyone knows, that integer (rsa-512) has never been used as the public modulus of an RSA key.
The only 512-bit integer known to me to have been used as the public modulus of an RSA key and subsequently factored.is the stage-10 challenge in Simon Singh's The Codebook.
Both of these numbers, and a couple more which are at least as big, were factored by the general number field sieve running on a collection of quite ordinary computer.
I've already given you a goodly collection of keywords to type into a search engine, but the following may also be of use if you want to learn more: Lenstra, Montgomery, Franke, Leyland, "te Riele", CWI, "Simon Singh", Granlund, NFSNET, Shamir.
Paul
Be careful of what you ask for. You might get it.
In retaliation for spreading such diseases, those who would rather their coca trees or opium poppies not be infected may be moved to spray your cotton or corn fields.
Paul
Same diameter, near enough, but much more massive. The article says it has a mass about a twentieth of that of the Sun. Jupiter has a mass about 1/1047 that of the Sun. From which we can conclude that the object has about fifty times the mass of Jupiter and is about fifty times as dense.
Paul
You're welcome. I'm not a physicist either, but I sometimes play one on Slashdot. I'm not entirely sure what I am.
Paul
Which is why ortho- and para-positronium have significantly different lifetimes.
Paul
Nope. After the collision the reference frame isn't still moving "along with the photon", even assuming that a single photon could be created, which it can't. Let's assume it does, though, and see what conclusion we draw.
First off, the reference frame was that of the centre of mass of the electron/positron pair. We know, pace Einstein, that frame is travelling at less than the speed of light with respect to anything else in the universe. After the collision, the frame is still moving the same with respect to the universe, but a photon has been created. In the reference frame the electron positron pair had zero net momentum. By conservation of momentum, the photon must therefore also have zero momentum. This point you seem to agree on. However, the momentum of a photon is proportional to its energy (p=E/c). If it has zero momentum, it has zero energy. Voila! Conservation of mass-energy has been violated. We've reached a contradiction and something has gone wrong somewhere. The error lies in the assumption that a single photon can be produced. To remedy the error you have to add at least one more photon so that energy and momentum can be simultaneously conserved.
Paul
The original poster said was useless, not is useless. At the time Einstein created relativity, and afterwards when the Nobel committee was thinking about giving hin a prize, it was indeed almost useless, especially his general theory.
Paul
Wrong on both counts. Others have already commented on the radiation. As an ex-chemist I'll restrict myself to pointing out that plutonium has similar chemical toxicity to lead. It's a heavy metal and you don't want to go around eating it for the sake of it, but it really isn't that poisonous. The UPPU club has some members still alive almost sixty years after ingesting their plutonium.
Paul
Consider that the electron is moving in south east direction and positron in north east. When they collide their north - south momentum will cancel out. Now the only remaining momentum is in the east direction. This momentum will be the momentum of the photon moving in the east direction. The reason the momentum cant be conserved during head on collison is that the resultant momentum has to be zero and single photon will have a mometum.
Errm, no you can't.
Einstein told us that as far as the laws of physics are concerned, one reference frame is as good as another. Now imagine you are sitting near to the the center of mass of the electron and positron and moving along with it. In your frame you see the two particles moving towards a head-on collision and with no net momentum. After the collision you will see at least one photon (by conservation of mass-energy) with zero net momentum (by conservation of momentum). The only way to get net zero momentum is by having at least two photons, travelling in suitable directions, since every photon carries momentum.If you bring conservation of angular momentum into play, there is another wrinkle. The electron and positron each have a half-unit of intrinsic angular momentum, called "spin" for brevity. A photon has unit spin. So the two initial particles can have either net zero spin (the two angular momenta are equal, opposite and cancel) or net unit spin. After the collision, the photons each have unit spin and so the net spin is either zero or two, depending on whether the spins are opposite or aligned respectively.
Spot the problem?
If the initial total spin of the two particles is unity, three photons have to be created to ensure that all the conservation laws are satisfied.
In the center of mass frame of reference, the three photons have equal momenta (and so have equal energy and are directed at an angle of 120 degrees from each other) and two of them have spins which are oppositely aligned.Paul
That raises the question: What could they possibly find on another planet that's valuable enough to import?
...
The only plausible case I've seen is importing He3 from the moon for fusion fuel. However, I saw one estimate that it would take a strip mining operation on the moon on a scale similar to all of coal mines on earth to glean enough of that rare isotope to supply our energy needs. Even that seems unlikely to be economically feasible.
The lunar surface has very low concentrations of He3 and is not an ideal source of it. The only benefits of mining He3 on the moon seems to be that it is easy to get to.
A far better source of He3 lies in the atmospheres of Jupiter and Saturn. It's not presently clear which is the more favourable. Jupiter is closer but has a deeper gravity well to haul the stuff out of. It also has worse weather, by and large, and a much nastier ionizing radiation problem on the way in and out.
Paul
I live in the UK and I've heard that too. OTOH, I spent several years without a TV set and was not harassed, mightily or otherwise. Once a year or so a letter would arrive asking me whether I had a TV set and/or licence for it. I'd reply that I had a set, that it was broken and couldn't receive broadcasts and that therefore I didn't need a licence. No real hassle.
To explain for the benefit of non-Brits: the licence is not for the set but for the ability to receive broadcasts. As my receiver was nonfunctional I didn't need the licence. I only kept the set in the house in order to screw with the brains of the bureaucrats. Eventually I got married, my wife had a fully functional TV set and I ditched the bureaucrat teaser.
Paul
Perhaps, but not yet by a long way.
For instance, I presently want to find linear dependencies in a sparse bit matrix which has something over 8.1 million rows and columns. Even with a sparse representation, the computation requires over 2 gigabytes of active memory. In my field of interest (integer factorization) having access to machines with several gigabytes is almost an entry requirement. There are a number of other fields which need much more RAM than this if the programs aren't to be paging themselves into torpidity. Numerical simulation and large database access are a couple of examples.
Paul
They are using conventional storage standards. Memory chips have been measured in (multiples of) bits for decades. When I started paying attention, around 1980 or so, the state of the art was something like 4k or 16k bits for DRAM and those chips were 1-bit wide. Even 8-bit wide chips were, and still are, quoted with storage capacity in bits. Again from the early days, an EEPROM with 2048 words of 8-bits each was described as a 16k device.
Further down in the article it is stated that "The flash chip is designed to let consumer electronics designers put up to 16 gigabytes of data on a single memory card". Note that they use the conventional units, bytes, for memory cards.
Remember, different conventions in different fields. You may think its silly, but that's life and you'd better get used to it.
And, since you ask: no, bits doesn't necessarily imply a rate connectivity. Raw connections are usually rated in bits per second but high level data streams, such as ftp download speeds, are often quoted in bytes per second. I do not know whether there is a parallel here between comms and storage in the different conventions used to specify what the raw technology gives you and what is built out of that technology. I would be interested to learn whether it is more than coincidence.
Paul
The reason, of course, is that there is water in the Sahara desert. Less than there is in, say, Amazonia or the Pacific but plenty for life to get along nonetheless.
Paul
Completely correct. But no quantum mechanics, which is the point under discussion. Radio, in the form of the spark transmitter at least, long predates Bohr's quantum theory let alone quantum mechanics. I don't know exactly when the point contact diode was invented but it certainly predates the work of Schrodinger, Heisenberg, Dirac, et al.
Paul
The semiconductor diode was certainly invented without the benefit of quantum mechanics so it is not entirely unreasonable that transistors might have been.
Back when my grandfather was a young man (he was born in 1892) people would listen to radio broadcasts with a receiver built in part around what was then called a "crystal and cat's whisker". We now call such devices "point contact diodes". It is entirely reasonable, in my view, that transistors could have been developed following empirical investigations of the behaviour of point contact diodes and analogies drawn from thermionic triodes, which are only thermionic diodes with a controllable electric field between the anode and cathode.
Paul
Do you seriously believe that there are no Linux boxes in Redmond? If so, I suggest you wake up and start paying attention.
Paul
Paul