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Are they still doing crowd sourcing on processing the captured data? I remember running their screen saver for a few years, where they would send out data packets to be processed, and then capture the results.
I used to have seven or eight PC’s running the SETI software.
This reminds me of a quote from some general I read somewhere “We’re alone, or we’re not. Either way, it boggles the mind.”
Coincidentally, in the US this weekend a restored version of “Close Encounters of the Third Kind” is playing in about 900 theaters. It’s probably hard for younger Ricochetti to imagine the level of hype that picture got when released in late 1977. Partly this was because “Star Wars” had opened six months earlier and become an unprecedented box office phenomenon, so the expectations were the director of “Jaws” should easily be able to top it. (He didn’t.)
But partly it was a function of Columbia Pictures’ buildup campaign, rather unusual in that they sought the endorsement of prestigious figures like Ray Bradbury, the Dalai Lama, Carl Sagan and the secretary general of the United Nations. In short, it was a pretentious campaign meant to convince the public that this was more than just a movie, but something akin to a religious experience. Widespread SETI publicity in the Seventies was part of that background.
It has been speculated since that Spielberg, like most people, underestimated how long it would take to identify a provable extraterrestrial signal; that he wanted to be proven to be a prophet when that day came, be it in 1979 or 1982 or 1985.
This is the SETI@Home project, which has been run by UC Berkeley since 1999. The project is still running, and you can download and run the software. It has since been extended into an open infrastructure which allows running other computationally-intense tasks in the background.
In the 1990s and early 2000s, most personal computers, when not processing user tasks, simply whiled away their time in an “idle loop” which did nothing. Thus, it made sense to replace the idle loop with a task that mopped up all of that otherwise wasted compute time to do something useful. In the late ’80s I spent three years of computer time trying to figure out whether the number 196 ever formed a palindrome!
These days, most computers have intelligent power management, which means that when they’re idle, rather than just running what amounts to a:
heck: goto heck;
loop, they reduce the clock speed and power down, which doesn’t just lower energy consumption, it reduces the heat generated by the processor, which in turn reduces cooling requirements and increases component life. With such machines, a compute-bound background task or screen saver makes less sense, and as a result programs like SETI@Home are less frequently used today.
I’m still doing it, since 2001. As John explained.
John, Here’s a real dumb question..
You mention that there’s basically an infinite number of possible frequencies a signal could be sent on, so we could be listening in the right direction but not be on the right frequency.
Isn’t there some way to have a receiver that simply picks up everything, regardless of frequency? After all, the signal is passing through, so why can’t it be detected regardless of what frequency the receiver is tuned to?
Radio signals have traditionally been thought of as having a single principal frequency, or “carrier wave”, which contains most of the energy of the transmission. Information is transmitted in a variety of ways: by turning the carrier wave off and on, as when transmitting Morse or teletype code, by varying the intensity of the carrier (amplitude modulation, or AM radio), or shifting its frequency up and down through a range which is small compared to the carrier frequency (frequency modulation, or FM radio). This is because it is very easy to generate a carrier signal with a tuned circuit, and to pick it out of the background noise with another tuned circuit set to the same frequency as the carrier. When you “tune” a simple radio, you’re adjusting a tuned circuit to correspond to the carrier frequency of the transmitter to which you wish to listen.
This is a tremendous simplification of the set of all possible electromagnetic signals. A pure carrier wave has the waveform of a simple sine wave, but it’s possible for an electromagnetic signal to have any waveform whatsoever. It is possible to represent an arbitrary waveform as the sum of a series of sine waves by means of a Fourier transform, decomposing the signal into a spectrogram. A device which does this is, not surprisingly, called a spectrograph. SETI observations have mostly used electronic spectrographs operating in the microwave band (where signals propagate efficiently over interstellar distances and aren’t absorbed by the Earth’s atmosphere). These spectrographs have, over time, grown from the hundred-channel unit of project SERENDIP to the billion channel spectrum analysers used in current work. Inherent in all of this work, dating back to Project Ozma in 1960, is that the most likely alien signal will be a “beacon” consisting of a carrier wave on a single, precisely-controlled frequency. Such a signal is economical to generate and transmit, is easily distinguished from background noise, and, importantly, is not generated by any known natural process. Detecting such a signal would mean that it is either artificially-generated or the result of a novel astrophysical source never before observed.
But there is another way to go about receiving a radio signal. With sufficiently high performance electronics (something which was only a dream until recently), it is possible to build a “software-defined radio”. This dispenses entirely with tuned circuits, and simply connects the antenna to an analogue-to-digital converter, which produces a digital signal representing the waveform sampled at a sufficiently high rate to represent it faithfully. Software then processes these waveform data with algorithms which extract the signal from them, depending upon how it is encoded. Running the sampled waveform through a Fourier transform algorithm, for example, produces a spectrogram of the signal, but many other transformations and modulations are possible.
Software-defined radio is now practical for carrier frequencies up to those used in amateur radio and military communications, but we’re not yet at the point where it can operate in the microwave bands examined by most SETI projects. The advent of software-defined radio at SETI frequencies is one of the anticipated technological breakthroughs that will dramatically increase the performance of SETI without any need to upgrade the antenna hardware.
It should be noted that SETI researchers are not unanimous in assuming a narrow-band beacon is the most effective signal for interstellar communications. That assumption dates from the days when such signals were the only kind we could easily produce and detect, which was long before the advent of technologies such as spread-spectrum and broadband communications. In the following talk, James Benford, who knows a thing or two about microwave communication, argues that a cost-optimised interstellar beacon is more likely to be a pulsed or spread spectrum transmission, and that by searching exclusively for narrow-band beacons we may be looking in the wrong place. If this view is correct, the advent of software-defined radio will be extremely important in searching for such signals.
Thanks so much John.
Historical note. Phil Morrison was my undergrad advisor at Cornell in 1959 and I was taking classes from him when he was working on the paper cited above.
While radio SETI is important, I think SETI may have more luck looking for artifacts of civilization rather than communication signals.
We are in our infancy when it comes to communication technology. It is entirely possible that broadcast radio emissions are a tiny blip in the lifespan of a civilization, We ourselves are in the process of going cosmically ‘dark’ as we move away from powerful broadcast signals towards fiber and cable. Tuned narrowband communications are very rapidly giving way to spread spectrum, encrypted communications which can be very hard to pick out from noise in a foreign signal. And we’ve only been at the point where we can communicate over large distances for a tiny fraction of our civilized existence, which in turn is only a tiny fraction of the age of the universe.
With telescopes like the James Webb observatory coming online, and with increasingly large telescopes on earth with adaptive optics, it seems more likely that we will discover civilizations by looking for pollution in the atmospheres of exoplanets, Dyson spheres around stars, perhaps the signatures of relativistic spaceships or beamed power used to accelerate them, etc. Communication technologies may change rapidly, but huge civilizations require huge amounts of energy or make huge changes to their solar systems, and that’s the kind of thing we might be able to detect.
Do you think that Dyson spheres are a real possibility?
Fascinating. Thank you.
My dad worked at NRAO in Green Bank, WV back when SETI was active on the 40m telescope. Those guys were pretty fun to talk to as a 17 year-old high school senior.
“The Ringworld is unstable!”
A Dyson Sphere, probably not. An actual solid sphere around the sun would not be gravitationally stable. But the modern conception of a Dyson sphere is more like a Dyson swarm – a vast collection of solar collectors, habitats or other artifacts, each disconnected from the others and in its own orbit. Put enough of them in orbit around the star, and we could detect it as a dimming of the star, coupled with an increase in infrared radiation that shouldn’t exist for a star of that type.
For example, you may have heard of Tabby’s Star, which is a star that The Kepler mission was observing, looking for planetary transits that cause slight dimming of the star when the planet passes in front. That’s how we have detected most of our exoplanets. But Tabby’s star is strange – it has weird, non-periodic transits much bigger than a planet should be able to cause. And the transits are oddly-shaped, which would not be the case for a transiting spherical object.
In addition, Tabby’s star has been constantly dimming for decades, which is unheard of in a main sequence star. Now, no one is saying that it’s aliens, but to this point we do not have a satisfactory explanation for what is going on there. But this is exactly the type of signature you might see if a civilization were in the process of building out a giant dyson swarm. Other features are missing, howver, such as an increase in infra-red radiation,
Whatever it is, it’s something rare as Kepler has looked at over 70,000 stars and we have not seen another one remotely similar.
We now have a catalog of thousands of exoplanets that Kepler has discovered. Now that we know where they are and when they will transit, we can begin to look at how the star’s spectra changes when the planet passes in front. With the new generation of telescopes coming online, we should soon be able to measure the composition of the atmospheres of earth-like planets in the habitable zones of those stars. If we find planets with oxygen-rich atmospheres or other chemicals like methane, it will be a strong marker for life. We can then target those planets for more detailed measurements.
My own guess is that life is relatively common in the universe, but intelligent, technological civilizations may be extremely rare. In that case, my money is on us discovering life somewhere else in the cosmos long before we pick up communications from ET.
Dang. It’s been the main event on my bucket list. First contact. Hubby and I may not have but a couple decades to go yet. Dang. So we shouldn’t hold our breath, I guess :(
Incredible. Thanks, Dan.
I’ve always expected that if and when we detect intelligent aliens it will be a) in some part of the observational phase space we’ve opened up looking for something else entirely and b) obvious in retrospect that we’d made many “pre-discovery observations” which we didn’t know how to interpret at the time.
The discovery of pulsars is an excellent example of this: as soon as radio astronomy observations with high time resolution began to be made, we discovered something so strange that nobody could, at the time, think of a natural process that could account for it. In that case, it turned out to be spinning neutron stars rather than aliens, but it’s an example of how when you look in a new place, you often find things you never imagined existed.
Tabby’s star (KIC 8462852) is another example: it’s the result of the Kepler spacecraft conducting a long-term staring survey of transits on a large number of stars. Once again, we looked in a corner of the observational phase space we’d never probed before, and something distinctly odd popped out. The jury’s still out on this one.
Another mystery, less well known to non-specialists, is the “fast radio bursts”. First detected in 2007, they are millisecond-length pulses in the radio band which seem to come from distant sources at extragalactic distances. Their discovery was accidental, and exploration of them is opening up another part of the phase space: transient radio events distributed across the whole sky. The first observations seemed never to repeat, but more recently a source (FRB 121102) has been found which does repeat. Nobody knows the cause of these bursts. A recent paper has noted that the properties of fast radio bursts are almost precisely what you’d expect from transient observations of microwave-propelled light sails used by advanced extragalactic civilisations to propel interplanetary or interstellar craft as leakage from the propulsion beam happens to sweep across the Earth.
^That^
(Why I read Ricochet — The occasional word from people who know about what they are talking (as opposed to the bloviating about current events, about which no one actually knows anything).)
In my own unschooled rumination on seti (not to be confused with SETI) I was stuck at the point of, “If they’re civilized, the BEMs (more politely LGMs) must have radio.” Several posts have given thoughtful work-arounds on that. But the one I would toss out is the fact that potential sources being a bazillion light years away means that ANY observation of which we are capable is observing conditions a bazillion years ago. Thus, if there is any correlation between the appearance of us and our development of technology coupled with a sufficient disconnect from the lower levels of Maslow’s Hierarchy to permit serious seti, and the age of the galaxy and/or the universe, it may simply be too soon to see anything but possibly the BEM equivalent of the stone age, or less.
This is a common misconception as regards most current and past SETI projects. With the exception of a very few and extremely limited searches for signals from other galaxies and star clusters, which would require such power to generate that they could be sent only by a civilisation so far advanced compared to our own that we could scarcely imagine their capabilities or motives (the energy needed to send such a signal would require, at the minimum, harnessing the entire energy output of one or more stars), almost all SETI observations are sensitive only to signals from a distance of around 1000 light years, which includes around one million stars. A signal from a civilisation at this distance would have taken at most 1000 years to reach Earth, so the sender need only be in advance of terrestrial technology by that amount.
This is a tiny sample of the galaxy—there are around two hundred billion stars in the Milky Way galaxy, so the stars we can observe with current SETI technology is 1/200000 of those in the galaxy, or 0.0005%.
The estimation of a maximum detection range of 1000 light years makes the assumption that the signals we’re looking for are those we could generate with our own existing technology and with a budget comparable to “big science” projects such as the Large Hadron Collider or the International Space Station. If the sending civilisation were transmitting a stronger signal, this would increase the range at which it can be detected, but only slowly due so the inverse square law (if you double the distance, you need a signal four times stronger to remain detectable).
There are stars similar to the Sun which are billions of years older, so a gap of 1000 years in technology is no barrier to finding another communicating civilisation. One key factor in determining how many communicating civilisations exist within a range where we can detect them is how long each civilisation transmits its beacon. Even if civilisations are common, if each transmits for much less than 10,000 years, it’s unlikely that two will overlap within a 1000 light year radius. So one of the assumptions of the SETI endeavour is the optimistic assumption that once a civilisation develops the technology to communicate, it will remain at that level of technology for a long time compared to recorded human history.
It’s worth noting that for our own species, this “longevity” parameter in the Drake equation is currently zero—we have never yet deliberately transmitted a signal which would be detectable by a SETI search conducted by beings in another star system.
Most excellent. But “deliberately” is a very big word; are we not radiating, rather promiscuously, signals that would be interpreted as “intelligent?” Even back episodes of, say, The Beverly Hillbillies?” More problematic is that thousand year figure; we’ve not had a civilization last nearly that long, much less a technology, and the returns are from from being counted on the question of whether we are capable. You may argue that the latter is more political than scientific, but it is no less real.
But it’s not as if we have one big transmitter beaming The Beverley Hillbillies. There are thousands, each sending out a different signal. I have to guess that’s going to work out to something like white noise. Guessing again, I’m betting that is going to be similar to the radio noise produced by stars.
Put that on top of most of the signals not being powerful enough to go very far, in terms of being heard against the background noise.
This is what, in the SETI community, is called “leakage radiation”: transmissions which propagate into space that were not intended as a beacon to other civilisations. Significant leakage from the Earth only dates from the years after World War II, when television broadcasting in the VHF and later UHF bands became common and high-power military radars were deployed for anti-aircraft surveillance and ballistic missile warning. (Earlier radio broadcasts were at frequencies which are bent by the Earth’s ionosphere and do not escape into space in large quantities.)
The Earth is increasingly going “radio silent” as high power broadcasting is being replaced by cable and fibre optic distribution and satellite broadcasting. Unlike a terrestrial radio transmitter which leaks its signals along the horizon, a communication satellite aims its antennas at the Earth and leaks very little signal to space. Military radars continue to be used, but their signals are intermittent and detecting them would require the listener to searching at just the right place and right time.
The fact is that if there were planets radiating leakage energy to the extent the Earth presently does, none of the SETI searches to date or presently planned would have detected it. That would require at least a massive antenna array as envisioned by Project Cyclops plus the luck to happen to be listening when the beam from one of the leakage sources happened to sweep past the Earth. And even so, the distance at which even so grandiose a system (recall that the budget estimate for Cyclops was comparable to the Apollo project) could detect Earth-scale leakage was estimated to be less than 100 light years, within which there are around 150,000 stars.