Now on top of this all, the energy density of a fusion system is *tiny*, so you need to build *enormous* reactors.
And that's where it falls apart. There is simply no way, under any reasonable development line, that the cost of building the plant, and servicing its debt, can possibly be made up by the electricity coming out. PV, one of the worst power sources in terms of cents/kWh, is currently running at about 15 to 20 cents/kWh. A fusion reactor almost certainly cannot be built that will produce power at under ten times that cost.
I think your post as a whole was very interesting, especially the numbers, but this last section suddenly became very handwavy. Do you have numbers for the last part also? Some of what you say there is quite suprising. Especially the energy density part: Am I completely mistaken in remembering that high power vs. low occupied land area was one of the advantages of fusion? By volume, ITER will produduce about 500 MW for 840 m^3 of reactor, or 0.6 MW/m^3. Area-wise, the ITER facilities will cover 40 hectar, which gives it a power footprint of 1.25 kW/m^2, comparable to coal. And it's unlikely that a reactor with 10 times more power would need ten times the area of the facilities, so that number would get better for larger reactors, especially one's that aren't full-blown research bases.
The main difficulty of a tokamak is plasma confinement, but this is a problem that benefits from the square-cube law because insulation goes up with volume, and the magnetic field curvature goes down. So a larger reactor could use higher densities and higher temperatures than a small one, and would be overall more efficient. So the power density would go up with reactor size.
As you say, an important question is what the final cost per energy will be. Here you basically pull a number of about 200 cents/kWh out from thin air. How do you arrive at that number? What size and type of reactor is is based on? (As a side note, solar power does not look like one of the worst power sources cost-wise in this table.
I'll also note that while progress has been slow compared to the first optimistic guesses, it is still being made.
It's common to hear someone say that "fusion power was 30 years away in the seventies, it's 30 years away now, and it will stay 30 years away"" or similar, and sadly, there is some truth to that (though perhaps it's 30 years now (estimated time for the DEMO full power-plant is 2033)). I think one of the reasons is that funding keeps decreasing, far below the optimistic projections of the 70s. The MIT fusion project made this graph to illustrate: https://i.imgur.com/sjH5r.jpg
It's a bit like when you're downloading a file, and while the download keeps making progress, the estimated time left stays put because the download speed keeps going down. I've had that happen a few times, and it requires an exponentially falling download speed. With fusion, the situation isn't quite that bad, but when you consider the sort of funding levels people were imagining before, it isn't surprising that they thought we would have fusion power by the year 2000.
One interesting way of putting this is to say that fusion power isn't a constant amount of time away, but about 50 billion dollars of funding away. To put those 50 billion dollars in context, fossil fules have received 594 billion dollars in subsidies in the USA since 1950. So partially fusion is difficult, and partially we're not trying very hard.
Lets be honest, if copyright did not exist and people were all expected to give everything away for free and starve
It's hard to be honest about what would happen if copyright didn't exist, because we don't know. But we do know that not having copyright doesn't mean that one has to "give everything away for free and starve". Many other alternative means of compensation have been proposed, but we haven't really tested any of them seriously, which is why we aren't sure how it would compare to the current copyright system, quality and amount-wise.
My favorite alternative means of compensation is up-front payment, like we have everywhere else in society. This model has gained quite a bit of steam lately through Kickstarter. Basically, the author asks for the full payment for his work before he performs it, rather than extracting it gradually over years afterwards. The author creates a Kickstarter page detailing his plan for, say, a new work, with some information about what it would be about, and states a price he wants for writing it (say 50,000€), possibly with some stretch goals (bonus chapter after 100,000€, for example). Potential readers then choose how much money they want to commit. Once enough money to reach the author's price has been reached, he gets the money, and starts working. If too much time passes (time-limit is commonly 90 days with Kickstarter) without the goal being reached, then the potential readers get their money back, and the author must try some other approach.
The advantage of this approach is that since the author has already been paid before he does the work, he does not need to control copying: copies are free, and can be shared freely. The more copies are shared, and the more people who enjoy his work, the easier it will be for him to gather money for his work. What is today called piracy would now just be free advertisement.
The disadvantage of this system is that it will be hard for unknown authors to find people willing to fund them. Probably, their first book would need to be written for free in order to get enough interested readers for this approach to work. On the other hand, in practice authors already write their first book for free under the current system (they need something to show the editor in order to be funded), so this is not a serious disadvantage.
Projects of more than $1,000,000 are regularly funded through Kickstarter, and more than 50,000 projects have been funded during the 4 years since its founding. So a Kickstarter-inspired model of up-front payment really looks like it could work, and I think it's worth a try.
Here's a good article about how prisons that treat prisoners well (except for the lack of freedom part) give much lower reoffense rates by building character rather than destroying it.
I recommend youtube-dl. It's an easy-to-use open source command line tool for downloading videos from youtube and many other sites. It's a part of the package repositories of most linux distributions also. I usually start a download (youtube-dl link-to-video-page), and then immediately point mplayer at the in-progress file. So there's no delay compared to watching it in the browser, but seeking is much faster, and you get to use a decent player. And if the connection is slow, you just wait a bit.
If you prefer not to use a command-line tool, there are firefox extensions that do this kind of thing, like netvideohunter and downloadhelper, but they are a bit sleazy and support fewer sites, I think. They also can't be automated the way youtube-dl can.
Estimating the exact rate at which GRBs occur is difficult, but for a galaxy of approximately the same size as the Milky Way, the expected rate (for long-duration GRBs) is about one burst every 100,000 to 1,000,000 years. Only a small percentage of these would be beamed towards Earth. Estimates of rate of occurrence of short-duration GRBs are even more uncertain because of the unknown degree of collimation, but are probably comparable
So they are mostly seen very far away due to volume effects. There are far more galaxies >100 Mly away than galaxies 100 Mly away, for example.
In theory, all we need to do is find a black hole and look with unreasonably high resolution and sensitivity at a point slightly more than 0.5 black hole radii away from its horizon (i.e. 1.5 schwarzchild radii from the center). The black hole acts as a lens, and at that point light is deflected by 180 degrees, letting us look back at ourselves as the earth was 2d years ago, where d is the distance to the hole in lightyears. In fact, by looking even closer to the point 0.5 black hole radii away, you can get to a point where light is deflected by 540 degrees, giving us an even fainter and more distorted image of ourselves a few minutes after the second image, and so on in infinity. In practice, even the first image will be so faint that it probably won't contain even a single photon, and would be washed out by the noise in the environment of the black hole (and between us and it) even if it did. But it's a fun through experiment.
Certainly not the flooding of the Mediterranean that was recorded in Sumerian legends and thence made it's way into Christian myths?
Isn't it unrealistic that the Zanclean flood, that ended the Mediterranean's latest dry phase 5.33 million years ago (that's about 2 million years before the evolution of Australopitthecus afarensis), should be recorded in Sumerian legends? Perhaps you're thinking of the Black Sea deluge, which might have occured somewhere between 7400 BD and 5600 BC (if it happened at all).
I have also seen articles decline in quality, but I wonder how big a problem this is. What fraction of articles does this apply to? And what fraction of articles are getting better at the same time? And when an article declines, does it stabilize at some quality level? If so, what is that level? Perhaps one even has something more complicated going on, like a slow overall increase in the level of an article, but with significant short-time fluctuations, just like global temperatures? I read wikipedia extensively, both at work and for fun, and at least in the topics I visit, the average article quality is very high. And in my fields of expertise, the error rate is also very small. I think this indicates that either the fraction of articles that tend to decline in quality are very small, or that the level at which the quality stabilizes is very high.
It's a fundamental problem for them, but one which they can do little about without changing their most basic policies.
I think it's also the reason for Wikipedia's success: More articles recruit more editors, which leads to more articles, etc.. Its predecessor, Nupedia, was written more according to your wishes, but because of its strict focus on experts and quality, it never got the network effects going that have driven Wikipedia's enormous growth. Wikipedia's success, and both in the number of articles and the quality it has achived (and its quality is, on average, pretty good) is quite the miracle, and if you had asked me, or most others, whether "an encyclopedia anyone can edit" could work, I think the answer would have been that it would get bogged down in trolling and sabotage. I guess most people are more constuctive than we give them credit for, and the "armies of editors" approach seems to be a very good strategy.
Lately, Wikipedia's balance seems to have shifted away from the initial inclusionism ("allow imperfect and incomplete articles, someone (not necessarily the same person) will improve them and add sources later") towards deletionism ("if an article isn't good enough (yet), delete it; if information isn't sourced (yet), delete it"). While the intentions behind this is good, namely getting more reliable articles, I think it might be counterproductive, as aggressive deletion policies probably hurt editor recruitment, and hence lowers the pool from which expertise can be drawn. I speculate that part of the reason for the slowdown in Wikipedia's growth the last few years might be this deletionism trend, though the fact that many important topics already have articles probaby is more important.
When I saw this article's headline, I first thought it was about this, but this is clearly something quite different. Do you know anything about the hydrogen sulphite idea discussed in the video?
The scales on the figures in the article, for example, don't actually go down to 100 GeV -- the left hand edge (log scale) appears to be 1 TeV.
Sorry, my third link was to the wrong article. It should have been this one. That's the one that covers the whole energy range, and which shows the magnitude and location of the W-boson resonance.
SLAC is apparently capable of generating 1/2 an ampere of beam current. That's basically 10^19 electrons/second, which knocks five orders of magnitude off your estimate of 1 event per 300000 years to one per 3 years.
Wow, I was off by a lot! I don't know how noisy environments accelerators are, but I think one would need many times more events per year to be able to detect this. It would be really nice.. But I'm skeptical.
That seems as though it is low enough that IF there were any sort of actual resonance, it might knock another order of magnitude off and get one at least several events per year, maybe more.
From the figure on page 3 in the article, it seems like the W resonance is at 6 PeV/c^2 for a stationary neutrino being impacted by a moving electron, or vice versa. I think that makes sense from a momentum convervation point of view. I haven't done relativistic kinematics in a long while, but the available energy in a collision is E_a^2 = 2 E_1 E_2 + (m_1c^2)^2 + (m_2c^2)^2, so for a massless impactor (m_1=0) hitting an stationary electron (m_2 = m_e, E_2 = m_e c^2) to have 80 GeV/c^2 (W mass) of available energy, we need E_1 = sqrt((E_a^2-E_2^2)/(2E_2)) = 6.3 PeV/c^2. If you go significantly below that energy, there isn't enough available energy to produce a W without violating momentum conservation. So I don't think there's much hope for an accelerator electron getting this resonance with the cosmic neutrino background.:/ Unless I've missed something crucial here. But perhaps we'll have a breaktrough in accelerator technology that will let us reach these levels at some point. If we hit the resonance, the scattering rate will be of the order 1e-31, 13 orders of magnitude higher than what I used in my back-of-the-envelope calculation. But we aren't likely to hit those energies soon, I think.
My Ph.D. advisor (Larry Biedenharn) spent a decade or so looking hard at muon catalyzed fusion so I learned a lot about it then even though my research was in completely different stuff). The primary block point was the huge cost per muon to create muons via e.g. nuclear cross sections and pion decay.
Yes, I've been interested in muon catalyzed fusion myself. It's such a nice idea. A way to reduce the cost of muon production would be very nice.
Yes, the accelerated beam is a rapidly moving detector. My point is that it is a rapidly moving detector with a woefully tiny volume. I'm no expert on this - I used this page for neutrino cross sections. Both inelastic and elastic scattering seems to be proportional to collision energy.
Neutrinos of several PeV/c^2 are regularly observed in neutrino observatories. At these energies, the Earth is able to act as a somewhat effective neutrino shield, resulting in a significant deficiency in high-enery (>60 TeV) neutrino flux from the direction of the ground (i.e. the direction shielded by the Earth). That says something about how difficult even extremely high energy neutrinos are to detect: Even a detector the size of the Earth lets through quite a bit of them.
It seems you're right that having enough energy to create W-bosons in the collision frame does give the cross section a huge boost, though. There is a really nice figure showing this on page 3 of the article From eV to EeV: Neutrino Cross-Sections Across Energy Scales (note: That figure only shows one of several possible scattering processes - see page 40 for more details). But as the other poster pointed out, to get 100 GeV/c^2 in the collision frame, you need much higher energy when only one particle is moving. In this figure, that point seems to be about 6 PeV. So extragalactic ultra-high-energy neutrinos aren't that far away from that point. But particles in our accelerators have far too low energy.
I think you are overestimating the scattering cross section of even GeV neutrinos. An electron neutrino with 10 GeV in the rest frame of an electron has a scattering cross section of about 2e-44 m^2. There are about 112 electron neutrinos per cm^3, so the (lab frame) scattering rate is about 2e-44 m^2 * c *112/cm^3 = 6.7e-28/s per electron. The number of protons per beam in LHC is about 1e14. Assuming the number of electrons per beam in SLAC etc. is roughly the same, we get about 1e-13/s scatterings total in the beam. So to get a single scattering one would expect to have to wait about 300000 years (assuming I didn't mess up this back-of-the-envelope calculation).
This is the reason why neutrino detectors are so huge - they have to overcome the tiny scattering rate with a huge number of potential targets. That's why the article is saying one would have to accelerate a whole neutrino detector.
AdBlock ("souled-out" 2 Google/Crippled by default)
AbBlock Plus sold out, not AdBlock. Several things call themselves "AdBlock", but as far as I know none of them have sold out. The AdBlock Plus sellout resulted in a fork called AdBlock Edge, which is equivalent to AdBlock Plus, but without the "acceptable" ads "feature".
What array libraries do you recommend for numerical programing in C++? I'm used to fortran and numpy arrays, which are very similar. Something that allows convenient slicing of multidimensional arrays, and is as fast as fortran arrays, would be really nice to know about.
In my experience they are the norm rather than the exception. I work on a program that takes 12 hours on 320 cores to complete (and that's when we still only have a small fraction of our expected amount of data). If it were all written in python, it would take weeks to months instead.
The big thing Fortran has over C is proper support for multidimensional arrays, with powerful slicing operations built into the language. It was the inspiration for numpy arrays. My first languages were C++ and C, but when I do scientific programming, my languages of choice are now python and fortran (with f2py making it very easy to glue them together). Fortran is horrible at text processing, and has an almost absent standard library, but for scientific use, good arrays make up for that - especially when you can use python in the non-performance-critical parts.
C++ has some multidimensional array classes, but none of them are as convenient as fortran arrays. Especially when it comes to slicing. At least that's how it was the last time I checked.
Why should the author work so hard to earn such a meager sum? He would be better off doing a 9-5 job with little risk and making roughly the same income.
$100,000 was just an example. I chose it because it seemed like a quite good salary (2-3 times higher than what I earn as a scientist) if he can manage one of these projects per year. But the author sets the price himself. If he doesn't feel like working for $100,000, then he can ask for $400,000 instead. Of course, the higher his demand, the harder it will be to find enough people to meet it.
What you are suggesting that once pizza sales for the day exceed a certain fixed threshold above the cost, say $1500 (or $500 profit), the pizza owner should give out free pizza to the remaining customers.
No. I'm saying that before making each pizza the pizza house owner should ask to be paid. He sets the price himself so that he covers his costs for running the restaurant + any amount of profits he wants. And only when he's paid does he make the pizza. That sounds quite a bit like a normal pizza restaurant, doesn't it?
In your pizza description, you seem to assume that the pizza chef makes tons of pizzas beforehand, and then tries to get paid afterwards. But that is a paid-after-the-fact model (like our current copyright model), not an upfront payment model.
Just to be clear: The author is not employed by somebody who sets an arbitrary price per creative work that he has to slavishly accept. This isn't the case of the state telling everybody that they must work for $100,000 per book or something. Every author is his own boss, and directly asks his potential audience to finance him, choosing the amount he asks for completely freely. This system does not rely on any invervention from external powers at all. So no special laws to force authors or the public to behave in certain ways.
There were lots of interesting talks related to this on the 30th chaos communication conference. This one for example. That whole video is well worth a watch (as are the other ones from the conference). Though, the border between backdoor and exploit can be a bit fuzzy: Did these phone companies just make a mistake, or did they willingly collaborate?
On the internet it's often hard to know if people are serious or just joking, but this reply assumes you were serious. First of all, the grandparent wasn't talking about dictating anything. He was making a suggestion in the hopes that others would find it interesting. With enough people agreeing, perhaps one could democratically agree to make it so. Nothing about a single person dictating anything.
Secondly, the grandparent wasn't taking about dictating how anything should be sold. He was discussing alternatives to monopoly on distribution. Right now we enforce an artificial monopoly on the distribution of works. This is done to encourage authors to create new works. The idea is that they will prevent others from making copies (via their monopoly), and make money by selling copies of their work. But that's only one way one could make money on one's creative output, and it might not be the best one. The grandparent pointed out several alternatives. What they have in common is that they can all function without artificial monopolies on distribution.
For example, with a Kickstarter-type method, an author would describe his plan for a new book on the site, and set his price for writing it (say $100,000). If enough people choose to buy in, he would write the book and publish it. At that point, he would already be fully compensated, and would have no need to prevent people from sharing the book. In fact, the more widely the book is shared, the more exposure he will get, and the more people will be willing to finance his next book, letting him set the next price higher. Sure, a new author would have a hard time getting people to finance him - he would probably have to write the first book for free, and use that to show his worth. But that's pretty similar to the current way of doing things, where you need to have written something very substantial by the time you approach a publisher anyway.
Getting paid up-front not only ensures that creative people are encouraged to create - it does so without putting the public in a straightjacket like the current system does. I think it's pretty neat that the internet has made the kickstarter-type approach viable (and it does seem to be viable, in the 4 years since it was started, more than 50,000 projects have been funded like that, many of them at more than $1,000,000). It probably wouldn't have worked at the time when copyright was first created. So I think this is a case of new technology allowing a better solution to a social problem.
Getting paid up-front ensures that the artist gets paid while freeing up our culture so that anyone can use it without restrictions. In fact, with a kickstarter-like model, it will be in the artist's best interests to make everyone share as many copies of his work as possible, as the more people enjoy it, the more will be willing to contribute to his next project. That's exactly the opposite of the copyright model, where it's in the artist's interest to persecute sharing.
I've written more about this on slashdot previously. I host a copy of that here if anybody's interested.
Every time the U.S. tries to stop being the world policeman and something bad happens (like the genocide in Rwanda), the world asks "where was the U.S.? Why didn't you stop it?"
[citation needed]
How about letting the UN do what international policing is needed? That way there is a world consensus behind the policing that gets done, instead of a single country doing what's at best vigilantism. And as a bonus, the USA won't be creating so many enemies of itself all the time.
Yes, I think so. A planet the size of Earth with a moon the size of Titan would be even more of a double-planet than the Earth-Moon system is. And at least in the solar system such large moons are very uncommon for anything but the tiniest bodies.
Slashdot Mirror
Now on top of this all, the energy density of a fusion system is *tiny*, so you need to build *enormous* reactors.
And that's where it falls apart. There is simply no way, under any reasonable development line, that the cost of building the plant, and servicing its debt, can possibly be made up by the electricity coming out. PV, one of the worst power sources in terms of cents/kWh, is currently running at about 15 to 20 cents/kWh. A fusion reactor almost certainly cannot be built that will produce power at under ten times that cost.
I think your post as a whole was very interesting, especially the numbers, but this last section suddenly became very handwavy. Do you have numbers for the last part also? Some of what you say there is quite suprising. Especially the energy density part: Am I completely mistaken in remembering that high power vs. low occupied land area was one of the advantages of fusion? By volume, ITER will produduce about 500 MW for 840 m^3 of reactor, or 0.6 MW/m^3. Area-wise, the ITER facilities will cover 40 hectar, which gives it a power footprint of 1.25 kW/m^2, comparable to coal. And it's unlikely that a reactor with 10 times more power would need ten times the area of the facilities, so that number would get better for larger reactors, especially one's that aren't full-blown research bases.
The main difficulty of a tokamak is plasma confinement, but this is a problem that benefits from the square-cube law because insulation goes up with volume, and the magnetic field curvature goes down. So a larger reactor could use higher densities and higher temperatures than a small one, and would be overall more efficient. So the power density would go up with reactor size.
As you say, an important question is what the final cost per energy will be. Here you basically pull a number of about 200 cents/kWh out from thin air. How do you arrive at that number? What size and type of reactor is is based on? (As a side note, solar power does not look like one of the worst power sources cost-wise in this table.
I'll also note that while progress has been slow compared to the first optimistic guesses, it is still being made.
It's common to hear someone say that "fusion power was 30 years away in the seventies, it's 30 years away now, and it will stay 30 years away"" or similar, and sadly, there is some truth to that (though perhaps it's 30 years now (estimated time for the DEMO full power-plant is 2033)). I think one of the reasons is that funding keeps decreasing, far below the optimistic projections of the 70s. The MIT fusion project made this graph to illustrate: https://i.imgur.com/sjH5r.jpg
It's a bit like when you're downloading a file, and while the download keeps making progress, the estimated time left stays put because the download speed keeps going down. I've had that happen a few times, and it requires an exponentially falling download speed. With fusion, the situation isn't quite that bad, but when you consider the sort of funding levels people were imagining before, it isn't surprising that they thought we would have fusion power by the year 2000.
One interesting way of putting this is to say that fusion power isn't a constant amount of time away, but about 50 billion dollars of funding away. To put those 50 billion dollars in context, fossil fules have received 594 billion dollars in subsidies in the USA since 1950. So partially fusion is difficult, and partially we're not trying very hard.
Lets be honest, if copyright did not exist and people were all expected to give everything away for free and starve
It's hard to be honest about what would happen if copyright didn't exist, because we don't know. But we do know that not having copyright doesn't mean that one has to "give everything away for free and starve". Many other alternative means of compensation have been proposed, but we haven't really tested any of them seriously, which is why we aren't sure how it would compare to the current copyright system, quality and amount-wise.
My favorite alternative means of compensation is up-front payment, like we have everywhere else in society. This model has gained quite a bit of steam lately through Kickstarter. Basically, the author asks for the full payment for his work before he performs it, rather than extracting it gradually over years afterwards. The author creates a Kickstarter page detailing his plan for, say, a new work, with some information about what it would be about, and states a price he wants for writing it (say 50,000€), possibly with some stretch goals (bonus chapter after 100,000€, for example). Potential readers then choose how much money they want to commit. Once enough money to reach the author's price has been reached, he gets the money, and starts working. If too much time passes (time-limit is commonly 90 days with Kickstarter) without the goal being reached, then the potential readers get their money back, and the author must try some other approach.
The advantage of this approach is that since the author has already been paid before he does the work, he does not need to control copying: copies are free, and can be shared freely. The more copies are shared, and the more people who enjoy his work, the easier it will be for him to gather money for his work. What is today called piracy would now just be free advertisement.
The disadvantage of this system is that it will be hard for unknown authors to find people willing to fund them. Probably, their first book would need to be written for free in order to get enough interested readers for this approach to work. On the other hand, in practice authors already write their first book for free under the current system (they need something to show the editor in order to be funded), so this is not a serious disadvantage.
Projects of more than $1,000,000 are regularly funded through Kickstarter, and more than 50,000 projects have been funded during the 4 years since its founding. So a Kickstarter-inspired model of up-front payment really looks like it could work, and I think it's worth a try.
Here's a good article about how prisons that treat prisoners well (except for the lack of freedom part) give much lower reoffense rates by building character rather than destroying it.
I recommend youtube-dl. It's an easy-to-use open source command line tool for downloading videos from youtube and many other sites. It's a part of the package repositories of most linux distributions also. I usually start a download (youtube-dl link-to-video-page), and then immediately point mplayer at the in-progress file. So there's no delay compared to watching it in the browser, but seeking is much faster, and you get to use a decent player. And if the connection is slow, you just wait a bit.
If you prefer not to use a command-line tool, there are firefox extensions that do this kind of thing, like netvideohunter and downloadhelper, but they are a bit sleazy and support fewer sites, I think. They also can't be automated the way youtube-dl can.
From the Wikipedia article
Estimating the exact rate at which GRBs occur is difficult, but for a galaxy of approximately the same size as the Milky Way, the expected rate (for long-duration GRBs) is about one burst every 100,000 to 1,000,000 years. Only a small percentage of these would be beamed towards Earth. Estimates of rate of occurrence of short-duration GRBs are even more uncertain because of the unknown degree of collimation, but are probably comparable
So they are mostly seen very far away due to volume effects. There are far more galaxies >100 Mly away than galaxies 100 Mly away, for example.
In theory, all we need to do is find a black hole and look with unreasonably high resolution and sensitivity at a point slightly more than 0.5 black hole radii away from its horizon (i.e. 1.5 schwarzchild radii from the center). The black hole acts as a lens, and at that point light is deflected by 180 degrees, letting us look back at ourselves as the earth was 2d years ago, where d is the distance to the hole in lightyears. In fact, by looking even closer to the point 0.5 black hole radii away, you can get to a point where light is deflected by 540 degrees, giving us an even fainter and more distorted image of ourselves a few minutes after the second image, and so on in infinity. In practice, even the first image will be so faint that it probably won't contain even a single photon, and would be washed out by the noise in the environment of the black hole (and between us and it) even if it did. But it's a fun through experiment.
Certainly not the flooding of the Mediterranean that was recorded in Sumerian legends and thence made it's way into Christian myths?
Isn't it unrealistic that the Zanclean flood, that ended the Mediterranean's latest dry phase 5.33 million years ago (that's about 2 million years before the evolution of Australopitthecus afarensis), should be recorded in Sumerian legends? Perhaps you're thinking of the Black Sea deluge, which might have occured somewhere between 7400 BD and 5600 BC (if it happened at all).
I have also seen articles decline in quality, but I wonder how big a problem this is. What fraction of articles does this apply to? And what fraction of articles are getting better at the same time? And when an article declines, does it stabilize at some quality level? If so, what is that level? Perhaps one even has something more complicated going on, like a slow overall increase in the level of an article, but with significant short-time fluctuations, just like global temperatures? I read wikipedia extensively, both at work and for fun, and at least in the topics I visit, the average article quality is very high. And in my fields of expertise, the error rate is also very small. I think this indicates that either the fraction of articles that tend to decline in quality are very small, or that the level at which the quality stabilizes is very high.
It's a fundamental problem for them, but one which they can do little about without changing their most basic policies.
I think it's also the reason for Wikipedia's success: More articles recruit more editors, which leads to more articles, etc.. Its predecessor, Nupedia, was written more according to your wishes, but because of its strict focus on experts and quality, it never got the network effects going that have driven Wikipedia's enormous growth. Wikipedia's success, and both in the number of articles and the quality it has achived (and its quality is, on average, pretty good) is quite the miracle, and if you had asked me, or most others, whether "an encyclopedia anyone can edit" could work, I think the answer would have been that it would get bogged down in trolling and sabotage. I guess most people are more constuctive than we give them credit for, and the "armies of editors" approach seems to be a very good strategy.
Lately, Wikipedia's balance seems to have shifted away from the initial inclusionism ("allow imperfect and incomplete articles, someone (not necessarily the same person) will improve them and add sources later") towards deletionism ("if an article isn't good enough (yet), delete it; if information isn't sourced (yet), delete it"). While the intentions behind this is good, namely getting more reliable articles, I think it might be counterproductive, as aggressive deletion policies probably hurt editor recruitment, and hence lowers the pool from which expertise can be drawn. I speculate that part of the reason for the slowdown in Wikipedia's growth the last few years might be this deletionism trend, though the fact that many important topics already have articles probaby is more important.
When I saw this article's headline, I first thought it was about this, but this is clearly something quite different. Do you know anything about the hydrogen sulphite idea discussed in the video?
The scales on the figures in the article, for example, don't actually go down to 100 GeV -- the left hand edge (log scale) appears to be 1 TeV.
Sorry, my third link was to the wrong article. It should have been this one. That's the one that covers the whole energy range, and which shows the magnitude and location of the W-boson resonance.
SLAC is apparently capable of generating 1/2 an ampere of beam current. That's basically 10^19 electrons/second, which knocks five orders of magnitude off your estimate of 1 event per 300000 years to one per 3 years.
Wow, I was off by a lot! I don't know how noisy environments accelerators are, but I think one would need many times more events per year to be able to detect this. It would be really nice.. But I'm skeptical.
That seems as though it is low enough that IF there were any sort of actual resonance, it might knock another order of magnitude off and get one at least several events per year, maybe more.
From the figure on page 3 in the article, it seems like the W resonance is at 6 PeV/c^2 for a stationary neutrino being impacted by a moving electron, or vice versa. I think that makes sense from a momentum convervation point of view. I haven't done relativistic kinematics in a long while, but the available energy in a collision is E_a^2 = 2 E_1 E_2 + (m_1c^2)^2 + (m_2c^2)^2, so for a massless impactor (m_1=0) hitting an stationary electron (m_2 = m_e, E_2 = m_e c^2) to have 80 GeV/c^2 (W mass) of available energy, we need E_1 = sqrt((E_a^2-E_2^2)/(2E_2)) = 6.3 PeV/c^2. If you go significantly below that energy, there isn't enough available energy to produce a W without violating momentum conservation. So I don't think there's much hope for an accelerator electron getting this resonance with the cosmic neutrino background. :/
Unless I've missed something crucial here. But perhaps we'll have a breaktrough in accelerator technology that will let us reach these levels at some point. If we hit the resonance, the scattering rate will be of the order 1e-31, 13 orders of magnitude higher than what I used in my back-of-the-envelope calculation. But we aren't likely to hit those energies soon, I think.
My Ph.D. advisor (Larry Biedenharn) spent a decade or so looking hard at muon catalyzed fusion so I learned a lot about it then even though my research was in completely different stuff). The primary block point was the huge cost per muon to create muons via e.g. nuclear cross sections and pion decay.
Yes, I've been interested in muon catalyzed fusion myself. It's such a nice idea. A way to reduce the cost of muon production would be very nice.
Oops, I mistakenly used the same link twice. The last link was supposed to be this:
http://arxiv.org/pdf/1305.7513v1
It is well worth a look through.
Yes, the accelerated beam is a rapidly moving detector. My point is that it is a rapidly moving detector with a woefully tiny volume. I'm no expert on this - I used this page for neutrino cross sections. Both inelastic and elastic scattering seems to be proportional to collision energy.
Neutrinos of several PeV/c^2 are regularly observed in neutrino observatories. At these energies, the Earth is able to act as a somewhat effective neutrino shield, resulting in a significant deficiency in high-enery (>60 TeV) neutrino flux from the direction of the ground (i.e. the direction shielded by the Earth). That says something about how difficult even extremely high energy neutrinos are to detect: Even a detector the size of the Earth lets through quite a bit of them.
It seems you're right that having enough energy to create W-bosons in the collision frame does give the cross section a huge boost, though. There is a really nice figure showing this on page 3 of the article From eV to EeV: Neutrino Cross-Sections Across Energy Scales (note: That figure only shows one of several possible scattering processes - see page 40 for more details). But as the other poster pointed out, to get 100 GeV/c^2 in the collision frame, you need much higher energy when only one particle is moving. In this figure, that point seems to be about 6 PeV. So extragalactic ultra-high-energy neutrinos aren't that far away from that point. But particles in our accelerators have far too low energy.
I think you are overestimating the scattering cross section of even GeV neutrinos. An electron neutrino with 10 GeV in the rest frame of an electron has a scattering cross section of about 2e-44 m^2. There are about 112 electron neutrinos per cm^3, so the (lab frame) scattering rate is about 2e-44 m^2 * c *112/cm^3 = 6.7e-28/s per electron. The number of protons per beam in LHC is about 1e14. Assuming the number of electrons per beam in SLAC etc. is roughly the same, we get about 1e-13/s scatterings total in the beam. So to get a single scattering one would expect to have to wait about 300000 years (assuming I didn't mess up this back-of-the-envelope calculation).
This is the reason why neutrino detectors are so huge - they have to overcome the tiny scattering rate with a huge number of potential targets. That's why the article is saying one would have to accelerate a whole neutrino detector.
AdBlock ("souled-out" 2 Google/Crippled by default)
AbBlock Plus sold out, not AdBlock. Several things call themselves "AdBlock", but as far as I know none of them have sold out. The AdBlock Plus sellout resulted in a fork called AdBlock Edge, which is equivalent to AdBlock Plus, but without the "acceptable" ads "feature".
You're ignoring the problem that the two sides are on different continental plates..
No, they're not.
What array libraries do you recommend for numerical programing in C++? I'm used to fortran and numpy arrays, which are very similar. Something that allows convenient slicing of multidimensional arrays, and is as fast as fortran arrays, would be really nice to know about.
In my experience they are the norm rather than the exception. I work on a program that takes 12 hours on 320 cores to complete (and that's when we still only have a small fraction of our expected amount of data). If it were all written in python, it would take weeks to months instead.
The big thing Fortran has over C is proper support for multidimensional arrays, with powerful slicing operations built into the language. It was the inspiration for numpy arrays. My first languages were C++ and C, but when I do scientific programming, my languages of choice are now python and fortran (with f2py making it very easy to glue them together). Fortran is horrible at text processing, and has an almost absent standard library, but for scientific use, good arrays make up for that - especially when you can use python in the non-performance-critical parts.
C++ has some multidimensional array classes, but none of them are as convenient as fortran arrays. Especially when it comes to slicing. At least that's how it was the last time I checked.
Why should the author work so hard to earn such a meager sum? He would be better off doing a 9-5 job with little risk and making roughly the same income.
$100,000 was just an example. I chose it because it seemed like a quite good salary (2-3 times higher than what I earn as a scientist) if he can manage one of these projects per year. But the author sets the price himself. If he doesn't feel like working for $100,000, then he can ask for $400,000 instead. Of course, the higher his demand, the harder it will be to find enough people to meet it.
What you are suggesting that once pizza sales for the day exceed a certain fixed threshold above the cost, say $1500 (or $500 profit), the pizza owner should give out free pizza to the remaining customers.
No. I'm saying that before making each pizza the pizza house owner should ask to be paid. He sets the price himself so that he covers his costs for running the restaurant + any amount of profits he wants. And only when he's paid does he make the pizza. That sounds quite a bit like a normal pizza restaurant, doesn't it?
In your pizza description, you seem to assume that the pizza chef makes tons of pizzas beforehand, and then tries to get paid afterwards. But that is a paid-after-the-fact model (like our current copyright model), not an upfront payment model.
Just to be clear: The author is not employed by somebody who sets an arbitrary price per creative work that he has to slavishly accept. This isn't the case of the state telling everybody that they must work for $100,000 per book or something. Every author is his own boss, and directly asks his potential audience to finance him, choosing the amount he asks for completely freely. This system does not rely on any invervention from external powers at all. So no special laws to force authors or the public to behave in certain ways.
There were lots of interesting talks related to this on the 30th chaos communication conference. This one for example. That whole video is well worth a watch (as are the other ones from the conference). Though, the border between backdoor and exploit can be a bit fuzzy: Did these phone companies just make a mistake, or did they willingly collaborate?
On the internet it's often hard to know if people are serious or just joking, but this reply assumes you were serious. First of all, the grandparent wasn't talking about dictating anything. He was making a suggestion in the hopes that others would find it interesting. With enough people agreeing, perhaps one could democratically agree to make it so. Nothing about a single person dictating anything.
Secondly, the grandparent wasn't taking about dictating how anything should be sold. He was discussing alternatives to monopoly on distribution. Right now we enforce an artificial monopoly on the distribution of works. This is done to encourage authors to create new works. The idea is that they will prevent others from making copies (via their monopoly), and make money by selling copies of their work. But that's only one way one could make money on one's creative output, and it might not be the best one. The grandparent pointed out several alternatives. What they have in common is that they can all function without artificial monopolies on distribution.
For example, with a Kickstarter-type method, an author would describe his plan for a new book on the site, and set his price for writing it (say $100,000). If enough people choose to buy in, he would write the book and publish it. At that point, he would already be fully compensated, and would have no need to prevent people from sharing the book. In fact, the more widely the book is shared, the more exposure he will get, and the more people will be willing to finance his next book, letting him set the next price higher. Sure, a new author would have a hard time getting people to finance him - he would probably have to write the first book for free, and use that to show his worth. But that's pretty similar to the current way of doing things, where you need to have written something very substantial by the time you approach a publisher anyway.
Getting paid up-front not only ensures that creative people are encouraged to create - it does so without putting the public in a straightjacket like the current system does. I think it's pretty neat that the internet has made the kickstarter-type approach viable (and it does seem to be viable, in the 4 years since it was started, more than 50,000 projects have been funded like that, many of them at more than $1,000,000). It probably wouldn't have worked at the time when copyright was first created. So I think this is a case of new technology allowing a better solution to a social problem.
Getting paid up-front ensures that the artist gets paid while freeing up our culture so that anyone can use it without restrictions. In fact, with a kickstarter-like model, it will be in the artist's best interests to make everyone share as many copies of his work as possible, as the more people enjoy it, the more will be willing to contribute to his next project. That's exactly the opposite of the copyright model, where it's in the artist's interest to persecute sharing.
I've written more about this on slashdot previously. I host a copy of that here if anybody's interested.
Every time the U.S. tries to stop being the world policeman and something bad happens (like the genocide in Rwanda), the world asks "where was the U.S.? Why didn't you stop it?"
[citation needed]
How about letting the UN do what international policing is needed? That way there is a world consensus behind the policing that gets done, instead of a single country doing what's at best vigilantism. And as a bonus, the USA won't be creating so many enemies of itself all the time.
Yes, I think so. A planet the size of Earth with a moon the size of Titan would be even more of a double-planet than the Earth-Moon system is. And at least in the solar system such large moons are very uncommon for anything but the tiniest bodies.