SETI@home instance of volunteer computing
SETI@home ("SETI at home") is a project of the Berkeley SETI Research Center to analyze radio signals with the aim of searching for signs of extraterrestrial intelligence. Until March 2020, it was run as an Internet-based public volunteer computing project that employed the BOINC software platform. It is hosted by the Space Sciences Laboratory at the University of California, Berkeley, and is one of many activities undertaken as part of the worldwide SETI effort.
SETI@home software was released to the public on May 17, 1999, making it the third large-scale use of volunteer computing over the Internet for research purposes, after Great Internet Mersenne Prime Search (GIMPS) was launched in 1996 and distributed.net in 1997. Along with MilkyWay@home and Einstein@home, it is the third major computing project of this type that has the investigation of phenomena in interstellar space as its primary purpose.
In March 2020, the project stopped sending out new work to SETI@home users, bringing the crowdsourced computing aspect of the project to a stop. At the time, the team intended to shift focus onto the analysis and interpretation of the 20 years' worth of accumulated data. However, the team left open the possibility of eventually resuming volunteer computing using data from other radio telescopes, such as MeerKAT and FAST.As of November 2021, the science team has analysed the data and removed noisy signals (Radio Frequency Interference) using the Nebula tool they developed and will choose the top-scoring 100 or so multiplets to be observed using the Five-hundred-meter Aperture Spherical Telescope, to which they have been granted 24 hours of observation time.Procedure details
SETI@home searches for possible evidence of radio transmissions from extraterrestrial intelligence using observational data from the Arecibo radio telescope and the Green Bank Telescope. The data is taken "piggyback" or "passively" while the telescope is used for other scientific programs. The data is digitized, stored, and sent to the SETI@home facility. The data are then parsed into small chunks in frequency and time, and analyzed, using software, to search for any signals—that is, variations which cannot be ascribed to noise, and hence contain information. Using volunteer computing, SETI@home sends the millions of chunks of data to be analyzed off-site by home computers, and then have those computers report the results. Thus what appears a difficult problem in data analysis is reduced to a reasonable one by aid from a large, Internet-based community of borrowed computer resources.
The software searches for five types of signals that distinguish them from noise:
Spikes in power spectra
Gaussian rises and falls in transmission power, possibly representing the telescope beam's main lobe passing over a radio source
Triplets – three power spikes in a row
Pulsing signals that possibly represent a narrowband digital-style transmission
Autocorrelation detects signal waveforms.There are many variations on how an ETI signal may be affected by the interstellar medium, and by the relative motion of its origin compared to Earth. The potential "signal" is thus processed in many ways (although not testing all detection methods nor scenarios) to ensure the highest likelihood of distinguishing it from the scintillating noise already present in all directions of outer space. For instance, another planet is very likely to be moving at a speed and acceleration with respect to Earth, and that will shift the frequency, over time, of the potential "signal." Checking for this through processing is done, to an extent, in the SETI@home software.
The process is somewhat like tuning a radio to various channels, and looking at the signal strength meter. If the strength of the signal goes up, that gets attention. More technically, it involves a lot of digital signal processing, mostly discrete Fourier transforms at various chirp rates and durations.Results
To date, the project has not confirmed the detection of any ETI signals. However, it has identified several candidate targets (sky positions), where the spike in intensity is not easily explained as noise spots, for further analysis. The most significant candidate signal to date was announced on September 1, 2004, named Radio source SHGb02+14a.
While the project has not reached the stated primary goal of finding extraterrestrial intelligence, it has proved to the scientific community that volunteer computing projects using Internet-connected computers can succeed as a viable analysis tool, and even beat the largest supercomputers. However, it has not been demonstrated that the order of magnitude excess in computers used, many outside the home (the original intent was to use 50,000–100,000 "home" computers), has benefited the project scientifically. (For more on this, see § Challenges below.)
Astronomer Seth Shostak stated in 2004 that he expects to get a conclusive signal and proof of alien contact between 2020 and 2025, based on the Drake equation. This implies that a prolonged effort may benefit SETI@home, despite its (present) twenty-year run without success in ETI detection.
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