I am not a lawyer, (nor do I play one on TV), but I am a Canadian. Perhaps our attitude towards such things as health care may explain this mouse ruling. Americans tend to mock our system as left-wing and socialist, but given a choice between being sick (or being a patentable mouse) in Canada or the U.S., my choice is clear.
Warning: The contents of this post are non-flamable.
I respect Stallman's right to earn money off of his works. But I've seen a lot of posts here that say "where is the on-line version" of his book. Why are they being modded down? It's an opinion that directly relates to the article.
Slashdot minds want to know!
"Ye can Mod me doon, but ye cannae take awey me Karma!" Wait, actually, you can...
I thought he treated the interview as the joke that it was. Hence the "good show" comment, for answering in kind.
Personally, I laughed at the questioners who were asking what they thought, to them, were "serious" questions. I'm no fan, but I admire Bill for never stooping to anyone's level, and at the same time, plugging his wife's website.
Current line in Vegas for number of replies to this story by 3:00 p.m. EDT are
100->499 50:1
400->499 5:1
500->599 4:1
600->699 2:1
700->799 2:1
800->899 1:1
900->999 1:2
1000+ 1:10
I know I'm responding to an AC, but I hope that your grandmother didn't die alone. And I even hope that you don't die alone.
Never mind about life millions of light-years away, life that's dead by the time we might hear its "Hello, world". Concentrate on the life around you, before its gone.
Warning: the following post contains material that can be considerd possible flamebait. You have been warned!
The reason that SETI@HOME has been embraced by the computer community at large is that the computer community has a large segment of individuals who
- have seen every Star Trek episode aired.
- live in eternal hope that their computer will be the one that provides evidence of extra-terrestrial life.
- don't care a tinker's cuss for a cure to cancer, because it doesn't affect them.
SETI@home Prepares to Revisit its Best Signals by Amir Alexander
A Special Day at Arecibo Sometime early in 2003 the giant radio telescope at Arecibo will take a day off from its normal astronomical duties. For 24 hours it will devote all of its immense observational capacity to a single goal: searching for steady repeating signals from space, the telltale signs of intelligent transmissions.
Needless to say, SETI research at Arecibo is not limited to that one single day. The SETI@home receiver, mounted 500 feet above the enormous dish, scans the skies throughout the year in search of intelligent transmission. On most days, however, the receiver sits passively on its perch, and scans whichever part of the sky the telescope happens to point to. Over time, the receiver scans the entire celestial band visible from Arecibo. It can never, however, go back and listen attentively to a particular promising signal, to determine whether it might possible be an intelligent transmission.
This, however, is precisely what the radio telescope will do on that special day. Rather than searching the vastness of space at random, it will focus its attention on a list of 100 most promising locations, handed to the telescope operators by SETI@home scientists. All of these are locations in the sky where SETI@home had detected radio signals at least twice before.
Signal Types
Gaussians are the power curves produced when the Arecibo beam scans a steady celestial radio source. The signal is weak at first, strong when it is at the center of the beam, and then fades again. This produces a bell shaped power curve known as a gaussian.
A perfect gaussian
Spikes represent any celestial radio signal of a fixed frequency that is distinguishable above the background noise.
Triplets are a set of 3 equally spaced spikes. Whereas gaussians represent a constant signal from space, triplets may represent a series of pulses transmitted at fixed time intervals.
Scores, Stars, and Multiplets In preparation for those very special 24 hours, SETI@home scientists have been making a concerted effort to compile the best list of signals. Since more than 5 billion(!) gaussians, spikes, and triplets have been detected so far by SETI@home users around the world, coming up with a list of the 100 most promising signals has been no easy task. First, the least reliable signals must be weeded out in a process called "data integrity check", and those that are most likely the result of detection or computer error are eliminated. Then all signals are compared to a database of known Radio Frequency Interference (RFI) sources. These are strong human-made radio transmissions generated by radars, satellites, and the like, which operate in the vicinity of Arecibo. If a SETI@home signal appears to match a known RFI source, then it too is removed from the list.
Once these obvious "false alarms" are eliminated, however, SETI@home scientists are still left with several billion signals. Each must therefore be assigned a score, representing the likelihood that it is, in fact, an alien transmission. The top 100 scorers will have their day at Arecibo, where they will earn a repeat visit to their location by the giant radio telescope.
To determine a signal's ranking in this multitude, the first step is to give it an individual or "detection" score. The factors that go into calculating this, naturally depend on the type of signal. Gaussians will be ranked according to how well their curve matches a perfect gaussian generated by the Arecibo dish, as well as by their strength. The stronger the signal, the more likely it is to be located once again. Triplets and spikes are not restricted to a particular shape, but their score also improves with their strength.
Another factor that contributes to a signal's score is its location in the sky. A signal that comes from the direction of a known star or galaxy will be given preference over one that appears to emerge from empty space. To check for this, the SETI@home crew relied on the Hipparcus catalogue - the most comprehensive list of celestial objects available. Hipparcus lists no less than 33,000 main sequence stars within Arecibo's observation band, and all of these are compared with each signal. To these are added the numerous distant galaxies that dot the skies at Arecibo's latitude, on the assumption that a signal might just possibly originate from one of them as well.
When it comes to scoring signals, however, not all stars are equal. This is because, according to SETI wisdom, some stars are more likely to host a communicating alien civilization than others. Thus, for example, only main-sequence stars are considered for signal-scoring purposes, excluding red giants and white dwarfs. Short-lived stars, whose lifespan is only a few million years, are also excluded from consideration, since complex life would not have had time to evolve in such an environment. Nearby stars, on the other hand, get "extra credit" in their scoring, since it would be comparatively easier to communicate with civilizations in our galactic neighborhood than with those in distant parts of our galaxy or beyond. Finally, the more similar a star is to our own Sun, the higher its score, since it would be more likely to host a civilization similar to ours.
The extrasolar planets discovered in recent years are also factored into the equation: a signal originating from the direction of a star with known planets will certainly receive special attention. The ideal signal, in other words, would originate from the direction of a nearby main-sequence Sun-like star with known planets.
So far we have only dealt with unique events - separate signals that have been detected by Arecibo at different times. But a signal that has been detected only once and never again is not a good candidate for an extraterrestrial communication. Consider the "Wow!" signal for example: detected in 1977, it was (and still is!) by far the strongest and clearest transmission ever detected by SETI. It was, however, never heard from again despite repeated efforts, and as a result we are still not sure what it truly was.
The Star Factor
The formula used to rank the different stars according to the likelihood that they would host a communicating civilization is:
N is a normalizing factor, 1.65x10^7 bv is b-v color bv0 is b-v color of the bluest star in the catalog (-0.41) bv_sun is the b-v color of the sun (+0.65) par is the parallax in milliarcseconds
The formula was developed by SETI@home scientist Eric Korpela.
Because of this experience, SETI@home scientists insist that signals must be persistent and reliable to be strong candidates for an extraterrestrial transmission. Only signals that have been detected more than once in the same location on separate SETI runs are to be considered. These signals, composed of two, and sometimes three separate observations, are referred to as "multiplets" by the SETI@home team.
But not only repeated signals of the same type are considered. In some cases a particular kind of signal, say a gaussian, was detected at a given location during one pass of the Arecibo dish, while a different kind of signal, say a triplet, was detected coming from the same direction during a later pass. SETI@home scientists combine the two (or more) signals into a single candidate, and refer to it as a "metacandidate."
Now that we have ranked all the different gaussians, spikes, triplet, multiplets, and metacandidates, each according to its own set of criteria, we are well on our way to selecting the "winning" signals that will be tested at Arecibo. A major problem nonetheless remains. A signal's "detection score" effectively compare gaussians to other gaussians and triplets to other triplets, and determines which ones are most likely to represent intelligent transmissions. But in order to come up with a list of the 100 best signals overall, it is also necessary to compare gaussians to triplets, and spikes to metacandidates, and decide which are the most promising. To resolve this, each signal is assigned not only a "detection score," which is specific to each type of signal, but also a "metascore," which can be compared with all the different types of signals. The 100 signals with the best metascores are the ones that Arecibo will aim for.
That Magical Frame of Reference One characteristic of a radio signal will immediately make it stand out in the crowd, and send it to the top of the list of candidates for re-observation: if it remains at a fixed and steady frequency. Almost all celestial signals vary in frequency over time. That is because they originate on moving celestial bodies, whose velocity relative to the Earth changes constantly. This causes the signal's detection frequency on Earth to vary as well, in a phenomenon known as "Doppler drift."
In their analysis, SETI@home scientists compensate for the Doppler drift: they take into account the motions of the Earth around the Sun, including the effects of the Moon and the giant planets, arriving at a figure known as the "barycentric" frequency. That is the frequency at which the signal would be detected if the receiver was placed not on Earth, but at the center of gravity ("barycenter") of the Solar System.
Even so, because of the motion of the transmitting body, the barycentric frequency does drift and scientists cannot compensate for the motions of this unknown body. If, however, the barycentric frequency of a signal remains steady, this almost certainly means that it is designed to compensate for the movements of its own host planet. In other words, it would point to a deliberate intelligent design. This is a unique, and indeed "magical" state of affairs. SETI@home scientists like to refer to the frame of reference in which celestial signals are sent and received at a steady frequency as a "Magical Frame of Reference."
And so, the SETI@home crew, along with millions of users around the world, awaits the day at Arecibo when it will put its most promising results to the test. As is usual with SETI, the odds of finally detecting an alien transmission are long. Nevertheless, those 24 hours at Arecibo may represent one of the best opportunities yet to find that elusive signal.
SETI@home Takes Stock of Its Most Promising Signals by Amir Alexander
I. Millions and Millions For almost three years now SETI@home users have been processing data on their home computers. Millions of Gaussians, spikes, triplets, and pulsed signals, have been detected by SETI@home's three and a half million users, and sent back to Berkeley for further analysis. It is time, the SETI@home crew in Berkeley decided, to take stock of what has been accomplished so far. Which of this plethora of signals is the most likely to be that epoch-making transmission we have been waiting for?
A perfect gaussian as it would appear on a SETI@home screen. Sorting through this mass of data is no easy matter: with so many candidate signals, how does one decide which is the most promising? To simplify matters a bit, the SETI@home scientists decided to start by sorting through the gaussians, and leave the other signals for later. "Gaussians", it will be recalled, are the bell-shaped power curves that are typical of continuous signals coming from space. When the Arecibo radio telescope's detection beam scans the sky, any continuous transmission from space first appears as a faint signal on the margin of the beam, then grows in strength as it approaches the beam's center, and finally fades away as the beam moves on to other regions of the sky. This pattern produces the characteristic gaussian shape. Since most SETI scientists believe that an alien transmission would indeed announce itself in the form of a gaussian, it seemed natural to start with these. Even this choice, however, left the SETI@home team with no less than 20 million candidates to choose from.
II. Why Some Gaussians are More Equal than Others As a first step in selecting the most promising signals, each gaussian was assigned a score, defined as its peak power divided by chi square. The first element simply indicates the maximum strength of the signal. Naturally, if a signal is strong, it is a better candidate for further analysis. The second element, chi square, is a measure of how closely the detected signal resembles a perfect gaussian. The smaller chi square is, the better the fit, and consequently, the higher the gaussian score.
But while processing the signals in this manner, the SETI@home scientists detected a disturbing pattern: the number of gaussians found, it seemed, was dependent on the speed at which Arecibo's beam was traveling through the sky at the time the signal was detected. This speed, known as the telescope's "slew rate," can vary significantly, depending on what the telescope is observing at the time. For the SETI@home sky survey it would have been best if the telescope had been pointed constantly straight up, and would traverse all points at a fixed speed. But since the big dish is always being used for various scientific observations and experiments, it is a fact of life for SETI that the slew rate varies significantly over time.
An analysis of all the gaussians clearly showed that the faster the telescope's slew rate, the more gaussians it detected. The reason for this was clear to SETI scientists early on. At faster rates, it takes the beam a shorter time to scan a point in the sky than at slower rates. When a received signal is then analyzed by the SETI@home program on a user's computer, the program breaks down the continuous signal into measured "points," each lasting a fixed number of seconds. These points are represented by the blocks on your screen. A short signal (fast slew rate) would have fewer points than a long signal (slow slew rate). When the program then proceeds to search for gaussians in the data, it looks for close fits between the measured points and a perfect guassian. Naturally, it is much easier to fit a small number of points onto a gaussian curve than it is to fit a large number of points onto the same curve. As a result, the SETI@home client was much more likely to detect gaussians in short signals (fast slew rates) than in long signals (slow slew rates). These fast signals, however, were in a sense "lower quality" gaussians, because they were based on a fit of fewer points. Not all gaussians, it seems, are truly equal...
This discovery posed a significant problem: if not all gaussians are truly of the same quality, how should SETI@home go about ranking them? How do we ensure that the best candidates to be a "real" signal do indeed get the highest scores? To address this, project scientist Eric Korpela devised a mathematical function that would compensate for the "slew rate" distortion. This "normalizing" function excluded all but the best gaussians at the fast slew rates, while preserving most of the gaussians from the slow slew rates. As a result, the same number of gaussians would now be included from any slew-rate, effectively eliminating it as a selection factor.
III. Multiplets and Frequencies The slew rate correction left SETI@home scientists with "only" 1.25 million gaussians with a score of 1.0 or higher to process and rank. These were the strongest and best fitting gaussians of the lot. But if a signal, no matter how strong and clear, is detected in the skies only once, how can we ever hope to know what it is? One need only think of the famous "Wow!" signal to appreciate the problem: the most promising signal ever detected by SETI was heard just once and never again, and as a result remains an enigma to this day. If we are to believe that a signal is coming from an alien civilization, then we must be able to detect it repeatedly.
For this reason, the SETI@home team set a final and demanding test for the remaining gaussians. A signal must be detected at least twice on two separate passes for it to be considered a likely candidate for an alien transmission.
Although this standard sounds straightforward enough, applying it is far from simple. For how does one know whether a signal detected today is the "same" one detected on a previous pass months ago? After some deliberation, the SETI@home team decided on the following criteria:
First - the two signals must come from the same direction in the sky, to within 10 arc minutes. Location, of course, is the primary indication that the two signals are one and the same.
Second - the two signals must be detected at least 900 seconds apart. This is to ensure that the two are indeed separate detections, rather than a continuous one.
Third - the "barycentric" frequency of the two signals must be the same, within 125 Hertz.
This last criterion requires some explanation. A signal coming from space will most likely not be received at a steady frequency. Because both the Earth and the presumed alien planet will be in motion around their stars, they will also be in motion in relation to each other, and their relative speed will be changing constantly. As a result, the frequency of a transmission received on Earth will drift, either increasing or decreasing, depending on the relative motions of the two planets. The SETI@home program installed on users' computers takes this effect, known as "Doppler drift," into account, and searches each data set at different drift rates. When SETI Scientists want to determine the true frequency of a transmission they must first compensate for this drift rate. This corrected frequency is known as the "detection frequency."
Even this, however, is not enough. The reception frequency is also affected by the Earth's movement within the Solar System. In other words, the same signal might be detected at different frequencies depending on the position and direction of the Earth at the time of detection. To compensate for this SETI scientists must take into account not only the Earth's exact position and movement at the time of the detection, but also the position of the Moon, the gravitational effects of the giant outer planets, and the direction the telescope is pointing. When all these are accounted for, the resulting frequency is the one that would have been received at a fixed point at the center of gravity (or "barycenter") of our Solar System. That is the barycentric frequency, used to determine whether two signals detected at different times could, in fact, be one and the same.
When the gaussians detected by SETI@home are checked against these exacting standards, the vast majority fail the test. Of the 1.25 million only 1397 qualify as being likely cases of multiple detections. They are, appropriately, labeled "multiplets."
Having a "mere" 1397 candidate signals is a vast improvement over having one and a quarter million signals, not to mention the 20 million gaussians we started out with. But even so it is too many. The SETI@home team still needs to narrow the list further, to around 25 most promising signals. This list they can then present at Arecibo, and arrange for dedicated telescope time to go back and check each of the signals separately.
Finding the few best signals out of millions of possibilities is a tough task, and there is always the danger of missing that one true signal hiding among so many false ones. The people at SETI@home are working hard to make sure this doesn't happen. And if their choices prove correct, then there is always the chance that one of these anonymous gaussians will in fact bear a message from the stars.
Samaritans are people from Samaria. The "Good Samaritan" was a guy from Samaria who happened to take care of an injured man by the side of the road, which was more than could be said for the other passers by. Maybe these Samritans are just a bunch of people from Samaria?
Any similarity between The Samaritans and a story from the bible is strictly coincidental.
CBC is an institution in Canada, celebrating its 50th anniversary. For those lucky Americans who live close to the border, CBC has offered excellent hockey coverage, as well as superior Olympic Games coverage.
A comparable traincam on-line would have cost a minimum of US$360, approximately $550 Canadian, and would still have required a train car to mount it in and some assembly. Purchasing a traincam built into a railcar cost even more.
It sounds like there are products out there that already do exactly what this guy's camera does. And they probably do things a lot better (i.e. take power from the rails, offer a "swivel" camera so you can take pictures front, back, or side) - but you get what you pay for. As interesting as this is, I don't see how he did things any better. To me, it's just a miniature version of Junkyard Wars, except:
- he's not competing against anyone else
- there's no prize
- there's no time limit
- he did the basic equivalent of destroying a perfectly working car in order to construct a motorcyle that weighs twice as much, and only runs in one gear
- he doesn't get to meet Cathy Rodgers
There's a site called JavaRanch, which has some useful forums for the serious Java developer. If you participate in their "Open Source Projects" forum, you'll be entered into a draw to win a copy of the book.
Also, one of the authours (Ted Husted) will be on-line to answer questions. Note that you need to register - No Anonymous Cowards!
Slashdot Mirror
Can you hear me now?
Gut!
Can you hear me now?
Gut!
I am not a lawyer, (nor do I play one on TV), but I am a Canadian. Perhaps our attitude towards such things as health care may explain this mouse ruling. Americans tend to mock our system as left-wing and socialist, but given a choice between being sick (or being a patentable mouse) in Canada or the U.S., my choice is clear.
Warning: The contents of this post are non-flamable.
I'll post this as myself - I'm not going to hide.
I respect Stallman's right to earn money off of his works. But I've seen a lot of posts here that say "where is the on-line version" of his book. Why are they being modded down? It's an opinion that directly relates to the article.
Slashdot minds want to know!
"Ye can Mod me doon, but ye cannae take awey me Karma!"
Wait, actually, you can...
And I WON'T post as a Coward!
"Ye can Mod me doon, but ye cannae take awey me Karma!"
No, wait, actually, you can...
I thought he treated the interview as the joke that it was. Hence the "good show" comment, for answering in kind.
Personally, I laughed at the questioners who were asking what they thought, to them, were "serious" questions. I'm no fan, but I admire Bill for never stooping to anyone's level, and at the same time, plugging his wife's website.
Good show, Bill.
Current line in Vegas for number of replies to this story by 3:00 p.m. EDT are
100->499 50:1
400->499 5:1
500->599 4:1
600->699 2:1
700->799 2:1
800->899 1:1
900->999 1:2
1000+ 1:10
...or did he manage sound flippant? He seemed to treat this whole thing as a joke.
Good show, Bill!
That's EXACTLY what I'm talking about!
I know I'm responding to an AC, but I hope that your grandmother didn't die alone. And I even hope that you don't die alone.
Never mind about life millions of light-years away, life that's dead by the time we might hear its "Hello, world". Concentrate on the life around you, before its gone.
Warning: the following post contains material that can be considerd possible flamebait. You have been warned!
The reason that SETI@HOME has been embraced by the computer community at large is that the computer community has a large segment of individuals who
- have seen every Star Trek episode aired.
- live in eternal hope that their computer will be the one that provides evidence of extra-terrestrial life.
- don't care a tinker's cuss for a cure to cancer, because it doesn't affect them.
They do filter them out first.
SETI@home Prepares to Revisit its Best Signals
0 .01)^3
by Amir Alexander
A Special Day at Arecibo
Sometime early in 2003 the giant radio telescope at Arecibo will take a day off from its normal astronomical duties. For 24 hours it will devote all of its immense observational capacity to a single goal: searching for steady repeating signals from space, the telltale signs of intelligent transmissions.
Needless to say, SETI research at Arecibo is not limited to that one single day. The SETI@home receiver, mounted 500 feet above the enormous dish, scans the skies throughout the year in search of intelligent transmission. On most days, however, the receiver sits passively on its perch, and scans whichever part of the sky the telescope happens to point to. Over time, the receiver scans the entire celestial band visible from Arecibo. It can never, however, go back and listen attentively to a particular promising signal, to determine whether it might possible be an intelligent transmission.
This, however, is precisely what the radio telescope will do on that special day. Rather than searching the vastness of space at random, it will focus its attention on a list of 100 most promising locations, handed to the telescope operators by SETI@home scientists. All of these are locations in the sky where SETI@home had detected radio signals at least twice before.
Signal Types
Gaussians are the power curves produced when the Arecibo beam scans a steady celestial radio source. The signal is weak at first, strong when it is at the center of the beam, and then fades again. This produces a bell shaped power curve known as a gaussian.
A perfect gaussian
Spikes represent any celestial radio signal of a fixed frequency that is distinguishable above the background noise.
Triplets are a set of 3 equally spaced spikes. Whereas gaussians represent a constant signal from space, triplets may represent a series of pulses transmitted at fixed time intervals.
Scores, Stars, and Multiplets
In preparation for those very special 24 hours, SETI@home scientists have been making a concerted effort to compile the best list of signals. Since more than 5 billion(!) gaussians, spikes, and triplets have been detected so far by SETI@home users around the world, coming up with a list of the 100 most promising signals has been no easy task. First, the least reliable signals must be weeded out in a process called "data integrity check", and those that are most likely the result of detection or computer error are eliminated. Then all signals are compared to a database of known Radio Frequency Interference (RFI) sources. These are strong human-made radio transmissions generated by radars, satellites, and the like, which operate in the vicinity of Arecibo. If a SETI@home signal appears to match a known RFI source, then it too is removed from the list.
Once these obvious "false alarms" are eliminated, however, SETI@home scientists are still left with several billion signals. Each must therefore be assigned a score, representing the likelihood that it is, in fact, an alien transmission. The top 100 scorers will have their day at Arecibo, where they will earn a repeat visit to their location by the giant radio telescope.
To determine a signal's ranking in this multitude, the first step is to give it an individual or "detection" score. The factors that go into calculating this, naturally depend on the type of signal. Gaussians will be ranked according to how well their curve matches a perfect gaussian generated by the Arecibo dish, as well as by their strength. The stronger the signal, the more likely it is to be located once again. Triplets and spikes are not restricted to a particular shape, but their score also improves with their strength.
Another factor that contributes to a signal's score is its location in the sky. A signal that comes from the direction of a known star or galaxy will be given preference over one that appears to emerge from empty space. To check for this, the SETI@home crew relied on the Hipparcus catalogue - the most comprehensive list of celestial objects available. Hipparcus lists no less than 33,000 main sequence stars within Arecibo's observation band, and all of these are compared with each signal. To these are added the numerous distant galaxies that dot the skies at Arecibo's latitude, on the assumption that a signal might just possibly originate from one of them as well.
When it comes to scoring signals, however, not all stars are equal. This is because, according to SETI wisdom, some stars are more likely to host a communicating alien civilization than others. Thus, for example, only main-sequence stars are considered for signal-scoring purposes, excluding red giants and white dwarfs. Short-lived stars, whose lifespan is only a few million years, are also excluded from consideration, since complex life would not have had time to evolve in such an environment. Nearby stars, on the other hand, get "extra credit" in their scoring, since it would be comparatively easier to communicate with civilizations in our galactic neighborhood than with those in distant parts of our galaxy or beyond. Finally, the more similar a star is to our own Sun, the higher its score, since it would be more likely to host a civilization similar to ours.
The extrasolar planets discovered in recent years are also factored into the equation: a signal originating from the direction of a star with known planets will certainly receive special attention. The ideal signal, in other words, would originate from the direction of a nearby main-sequence Sun-like star with known planets.
So far we have only dealt with unique events - separate signals that have been detected by Arecibo at different times. But a signal that has been detected only once and never again is not a good candidate for an extraterrestrial communication. Consider the "Wow!" signal for example: detected in 1977, it was (and still is!) by far the strongest and clearest transmission ever detected by SETI. It was, however, never heard from again despite repeated efforts, and as a result we are still not sure what it truly was.
The Star Factor
The formula used to rank the different stars according to the likelihood that they would host a communicating civilization is:
score=
N*(bv-bv0)*exp(0.5*(bv-bv_sun)^2)/(par+
where
N is a normalizing factor, 1.65x10^7
bv is b-v color
bv0 is b-v color of the bluest star in the catalog (-0.41)
bv_sun is the b-v color of the sun (+0.65)
par is the parallax in milliarcseconds
The formula was developed by SETI@home scientist Eric Korpela.
Because of this experience, SETI@home scientists insist that signals must be persistent and reliable to be strong candidates for an extraterrestrial transmission. Only signals that have been detected more than once in the same location on separate SETI runs are to be considered. These signals, composed of two, and sometimes three separate observations, are referred to as "multiplets" by the SETI@home team.
But not only repeated signals of the same type are considered. In some cases a particular kind of signal, say a gaussian, was detected at a given location during one pass of the Arecibo dish, while a different kind of signal, say a triplet, was detected coming from the same direction during a later pass. SETI@home scientists combine the two (or more) signals into a single candidate, and refer to it as a "metacandidate."
Now that we have ranked all the different gaussians, spikes, triplet, multiplets, and metacandidates, each according to its own set of criteria, we are well on our way to selecting the "winning" signals that will be tested at Arecibo. A major problem nonetheless remains. A signal's "detection score" effectively compare gaussians to other gaussians and triplets to other triplets, and determines which ones are most likely to represent intelligent transmissions. But in order to come up with a list of the 100 best signals overall, it is also necessary to compare gaussians to triplets, and spikes to metacandidates, and decide which are the most promising. To resolve this, each signal is assigned not only a "detection score," which is specific to each type of signal, but also a "metascore," which can be compared with all the different types of signals. The 100 signals with the best metascores are the ones that Arecibo will aim for.
That Magical Frame of Reference
One characteristic of a radio signal will immediately make it stand out in the crowd, and send it to the top of the list of candidates for re-observation: if it remains at a fixed and steady frequency. Almost all celestial signals vary in frequency over time. That is because they originate on moving celestial bodies, whose velocity relative to the Earth changes constantly. This causes the signal's detection frequency on Earth to vary as well, in a phenomenon known as "Doppler drift."
In their analysis, SETI@home scientists compensate for the Doppler drift: they take into account the motions of the Earth around the Sun, including the effects of the Moon and the giant planets, arriving at a figure known as the "barycentric" frequency. That is the frequency at which the signal would be detected if the receiver was placed not on Earth, but at the center of gravity ("barycenter") of the Solar System.
Even so, because of the motion of the transmitting body, the barycentric frequency does drift and scientists cannot compensate for the motions of this unknown body. If, however, the barycentric frequency of a signal remains steady, this almost certainly means that it is designed to compensate for the movements of its own host planet. In other words, it would point to a deliberate intelligent design. This is a unique, and indeed "magical" state of affairs. SETI@home scientists like to refer to the frame of reference in which celestial signals are sent and received at a steady frequency as a "Magical Frame of Reference."
And so, the SETI@home crew, along with millions of users around the world, awaits the day at Arecibo when it will put its most promising results to the test. As is usual with SETI, the odds of finally detecting an alien transmission are long. Nevertheless, those 24 hours at Arecibo may represent one of the best opportunities yet to find that elusive signal.
SETI@home Takes Stock of Its Most Promising Signals
by Amir Alexander
I. Millions and Millions
For almost three years now SETI@home users have been processing data on their home computers. Millions of Gaussians, spikes, triplets, and pulsed signals, have been detected by SETI@home's three and a half million users, and sent back to Berkeley for further analysis. It is time, the SETI@home crew in Berkeley decided, to take stock of what has been accomplished so far. Which of this plethora of signals is the most likely to be that epoch-making transmission we have been waiting for?
A perfect gaussian as it would appear on a SETI@home screen.
Sorting through this mass of data is no easy matter: with so many candidate signals, how does one decide which is the most promising? To simplify matters a bit, the SETI@home scientists decided to start by sorting through the gaussians, and leave the other signals for later. "Gaussians", it will be recalled, are the bell-shaped power curves that are typical of continuous signals coming from space. When the Arecibo radio telescope's detection beam scans the sky, any continuous transmission from space first appears as a faint signal on the margin of the beam, then grows in strength as it approaches the beam's center, and finally fades away as the beam moves on to other regions of the sky. This pattern produces the characteristic gaussian shape. Since most SETI scientists believe that an alien transmission would indeed announce itself in the form of a gaussian, it seemed natural to start with these. Even this choice, however, left the SETI@home team with no less than 20 million candidates to choose from.
II. Why Some Gaussians are More Equal than Others
As a first step in selecting the most promising signals, each gaussian was assigned a score, defined as its peak power divided by chi square. The first element simply indicates the maximum strength of the signal. Naturally, if a signal is strong, it is a better candidate for further analysis. The second element, chi square, is a measure of how closely the detected signal resembles a perfect gaussian. The smaller chi square is, the better the fit, and consequently, the higher the gaussian score.
But while processing the signals in this manner, the SETI@home scientists detected a disturbing pattern: the number of gaussians found, it seemed, was dependent on the speed at which Arecibo's beam was traveling through the sky at the time the signal was detected. This speed, known as the telescope's "slew rate," can vary significantly, depending on what the telescope is observing at the time. For the SETI@home sky survey it would have been best if the telescope had been pointed constantly straight up, and would traverse all points at a fixed speed. But since the big dish is always being used for various scientific observations and experiments, it is a fact of life for SETI that the slew rate varies significantly over time.
An analysis of all the gaussians clearly showed that the faster the telescope's slew rate, the more gaussians it detected. The reason for this was clear to SETI scientists early on. At faster rates, it takes the beam a shorter time to scan a point in the sky than at slower rates. When a received signal is then analyzed by the SETI@home program on a user's computer, the program breaks down the continuous signal into measured "points," each lasting a fixed number of seconds. These points are represented by the blocks on your screen. A short signal (fast slew rate) would have fewer points than a long signal (slow slew rate). When the program then proceeds to search for gaussians in the data, it looks for close fits between the measured points and a perfect guassian. Naturally, it is much easier to fit a small number of points onto a gaussian curve than it is to fit a large number of points onto the same curve. As a result, the SETI@home client was much more likely to detect gaussians in short signals (fast slew rates) than in long signals (slow slew rates). These fast signals, however, were in a sense "lower quality" gaussians, because they were based on a fit of fewer points. Not all gaussians, it seems, are truly equal...
This discovery posed a significant problem: if not all gaussians are truly of the same quality, how should SETI@home go about ranking them? How do we ensure that the best candidates to be a "real" signal do indeed get the highest scores? To address this, project scientist Eric Korpela devised a mathematical function that would compensate for the "slew rate" distortion. This "normalizing" function excluded all but the best gaussians at the fast slew rates, while preserving most of the gaussians from the slow slew rates. As a result, the same number of gaussians would now be included from any slew-rate, effectively eliminating it as a selection factor.
III. Multiplets and Frequencies
The slew rate correction left SETI@home scientists with "only" 1.25 million gaussians with a score of 1.0 or higher to process and rank. These were the strongest and best fitting gaussians of the lot. But if a signal, no matter how strong and clear, is detected in the skies only once, how can we ever hope to know what it is? One need only think of the famous "Wow!" signal to appreciate the problem: the most promising signal ever detected by SETI was heard just once and never again, and as a result remains an enigma to this day. If we are to believe that a signal is coming from an alien civilization, then we must be able to detect it repeatedly.
For this reason, the SETI@home team set a final and demanding test for the remaining gaussians. A signal must be detected at least twice on two separate passes for it to be considered a likely candidate for an alien transmission.
Although this standard sounds straightforward enough, applying it is far from simple. For how does one know whether a signal detected today is the "same" one detected on a previous pass months ago? After some deliberation, the SETI@home team decided on the following criteria:
First - the two signals must come from the same direction in the sky, to within 10 arc minutes. Location, of course, is the primary indication that the two signals are one and the same.
Second - the two signals must be detected at least 900 seconds apart. This is to ensure that the two are indeed separate detections, rather than a continuous one.
Third - the "barycentric" frequency of the two signals must be the same, within 125 Hertz.
This last criterion requires some explanation. A signal coming from space will most likely not be received at a steady frequency. Because both the Earth and the presumed alien planet will be in motion around their stars, they will also be in motion in relation to each other, and their relative speed will be changing constantly. As a result, the frequency of a transmission received on Earth will drift, either increasing or decreasing, depending on the relative motions of the two planets. The SETI@home program installed on users' computers takes this effect, known as "Doppler drift," into account, and searches each data set at different drift rates. When SETI Scientists want to determine the true frequency of a transmission they must first compensate for this drift rate. This corrected frequency is known as the "detection frequency."
Even this, however, is not enough. The reception frequency is also affected by the Earth's movement within the Solar System. In other words, the same signal might be detected at different frequencies depending on the position and direction of the Earth at the time of detection. To compensate for this SETI scientists must take into account not only the Earth's exact position and movement at the time of the detection, but also the position of the Moon, the gravitational effects of the giant outer planets, and the direction the telescope is pointing. When all these are accounted for, the resulting frequency is the one that would have been received at a fixed point at the center of gravity (or "barycenter") of our Solar System. That is the barycentric frequency, used to determine whether two signals detected at different times could, in fact, be one and the same.
When the gaussians detected by SETI@home are checked against these exacting standards, the vast majority fail the test. Of the 1.25 million only 1397 qualify as being likely cases of multiple detections. They are, appropriately, labeled "multiplets."
Having a "mere" 1397 candidate signals is a vast improvement over having one and a quarter million signals, not to mention the 20 million gaussians we started out with. But even so it is too many. The SETI@home team still needs to narrow the list further, to around 25 most promising signals. This list they can then present at Arecibo, and arrange for dedicated telescope time to go back and check each of the signals separately.
Finding the few best signals out of millions of possibilities is a tough task, and there is always the danger of missing that one true signal hiding among so many false ones. The people at SETI@home are working hard to make sure this doesn't happen. And if their choices prove correct, then there is always the chance that one of these anonymous gaussians will in fact bear a message from the stars.
Gabriel's written 1000 poems in the last two years, which is about 1000 poems more than you have.
[sarcasm]
I bet youse hasn't written a grammatically correct post in their life.
[/sarcasm]
Samaritans are people from Samaria. The "Good Samaritan" was a guy from Samaria who happened to take care of an injured man by the side of the road, which was more than could be said for the other passers by. Maybe these Samritans are just a bunch of people from Samaria?
Any similarity between The Samaritans and a story from the bible is strictly coincidental.
500GB - how many Libraries of Congress is that?
CBC is an institution in Canada, celebrating its 50th anniversary. For those lucky Americans who live close to the border, CBC has offered excellent hockey coverage, as well as superior Olympic Games coverage.
A comparable traincam on-line would have cost a minimum of US$360, approximately $550 Canadian, and would still have required a train car to mount it in and some assembly. Purchasing a traincam built into a railcar cost even more.
It sounds like there are products out there that already do exactly what this guy's camera does. And they probably do things a lot better (i.e. take power from the rails, offer a "swivel" camera so you can take pictures front, back, or side) - but you get what you pay for. As interesting as this is, I don't see how he did things any better. To me, it's just a miniature version of Junkyard Wars, except:
- he's not competing against anyone else
- there's no prize
- there's no time limit
- he did the basic equivalent of destroying a perfectly working car in order to construct a motorcyle that weighs twice as much, and only runs in one gear
- he doesn't get to meet Cathy Rodgers
Yeah, but do you write commercial web-apps? Ones that are complex? What's your definition of "Good"?
There's a site called JavaRanch, which has some useful forums for the serious Java developer. If you participate in their "Open Source Projects" forum, you'll be entered into a draw to win a copy of the book.
Also, one of the authours (Ted Husted) will be on-line to answer questions. Note that you need to register - No Anonymous Cowards!
Maybe the researchers should see the world is bigger than the US
Good joke! Oh, wait, you were actually serious...
Actually, didn't he have two tablets? One was running Commandments, the other was running Commandments with the expansion pack.
...Welcome to Slashdot...
Here is an earlier Slashdot article. It mentions that the current database (as of Nov 10) has 200 titles
Next thing you'll know we'll be crying for an open source API, so that we can link in with the game and create our own UI.
Or maybe a scripting language that allows one to create a program for building a house, rather than saving the house data itself.
Mmmmm, scripting... (drool)
It'll never float.
You were warned.