SETI@home ("SETI at home") is a distributed computing (grid computing) project using Internet-connected computers, hosted by the Space Sciences Laboratory, at the University of California, Berkeley, in the United States. SETI is an acronym for the Search for Extra-Terrestrial Intelligence. SETI@home was released to the public on May 17, 1999.
The first of these goals is generally considered to have succeeded completely. The current BOINC environment, a development of the original SETI@home, is providing support for several computationally intensive projects in a wide range of disciplines.
The second of these goals has failed to date: no evidence for ETI signals has been shown via SETI@home. However, ongoing continuation is predicated on the assumption that the observational analysis is not an 'ill-posed' one. The remainder of this article deals specifically with the original SETI@home observations/analysis.
SETI@home searches for possible evidence of radio transmissions from extraterrestrial intelligence using observational data from the Arecibo radio telescope. The data are taken 'piggyback' or 'passively' while the telescope is used for other scientific programs. The data are 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 contain information. The crux of SETI@home is to have each chunk of data, from the millions of chunks resulting, analyzed off-site by home computers, and then have the software results reported back. Thus what appears an onerous problem in data analysis is reduced to a reasonable one by aid from a large, Internet-based community.
The software searches for four types of signals that distinguish them from noise:
There are many variations on how an ETI signal may be affected by the interstellar medium, and by relative motion of its origin compared to Earth. The potential 'signal' is thus processed in a number of 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.
Astronomer Seth Shostak (2004) has stated 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) nearly ten-year run without success in ETI detection.
While the project hasn't reached the goal of finding extraterrestrial intelligence, it has proved to the scientific community that distributed 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 'threats to project' below.)
Anybody with an Internet-active computer can participate in SETI@home by running a free program that downloads and analyzes radio telescope data.
Observational Data are recorded on 36 Gigabyte tapes at the Arecibo Observatory in Puerto Rico, each holding 15.5 hours of observations, which are then mailed to Berkeley (Korpela et al. 2001). Arecibo does not have a high bandwidth internet connection, so data must go by postal mail to Berkeley at first. Once there, it is divided in both time and frequency domains work units of 107 seconds of data (SETI@home 2001), or approximately 0.35 MB, which overlap in time but not in frequency (Korpela et al. 2001). These work units then get sent from the SETI@home server over the Internet to personal computers around the world to analyze.
The analysis software can search for signals with about one-tenth the strength of those sought in previous surveys, because it makes use of a computationally intensive algorithm called coherent integration that no one else has had the computing power to implement.
The initial software platform, now referred to as "SETI@home Classic", ran from 17 May 1999 to 15 December 2005. This program was only capable of running SETI@home; it was replaced by Berkeley Open Infrastructure for Network Computing (BOINC), which also allows users to contribute to other distributed computing projects at the same time as running SETI@home. The BOINC platform will also allow testing for more types of signals.
On 3 May 2006 new work units for a new version of SETI@home called "SETI@home Enhanced" started being distributed. Computers provide the power for even more computationally intensive work than when the project began. This new version is more sensitive by a factor of two with respect to Gaussian signals and to some kinds of pulsed signals than the original SETI@home (BOINC) software. This new application has been optimized to the point where it will run faster on some workunits than earlier versions. However, some workunits (the best workunits, scientifically speaking) will take significantly longer.
Notably, there have also been some distributions of the SETI@home applications that have been optimized for a particular type of CPU. They are referred to as "optimized executables" and have been found to run faster on systems specific for that CPU. As of 2007, most of these applications are optimized for Intel processors (and their corresponding instruction sets).
The results of the data processing are normally automatically transmitted when the computer is next connected to the internet; it can also be instructed to connect to the internet as needed.
As with any competition, attempts have been made to 'cheat' the system and claim credit for work that has not been performed. To combat cheats, the SETI@Home system sends every workunit to multiple computers, a value known as "initial replication" (currently 3). Credit is only granted for each returned workunit once a minimum number of results have been returned and the results agree, a value known as "minimum quorum" (currently 2). If, due to computation errors or cheating by submitting false data, not enough results agree, more identical workunits are sent out until the minimum quorum can be reached. The final credit granted to all machines which returned the correct result is the same, and is the lowest of the values claimed by each machine. The claimed credit by each machine for an identical workunit often varies due to very minor differences in floating point arithmetic on different processors.
Some users have installed and run SETI@home on computers at their workplaces — an act known as 'Borging', after the assimilation-driven Borg of Star Trek. In some cases, SETI@home users have misused company resources to gain work-unit results — with at least two individuals getting fired for running SETI@home on an enterprise production system . There is a thread in the newsgroup alt.sci.seti which bears the title "Anyone fired for SETI screensaver" and ran starting as early as 14 September 1999.
Other users collected large quantities of equipment together at home to create "SETI farms", which typically consist of a number of computers consisting of only a motherboard, CPU, RAM and power supply that are arranged on shelves as diskless workstations running either Linux or old versions of Windows "headless" (without a monitor).
The National Science Foundation has made it clear the Arecibo will close in 2011 without such funds, and therefore the present data stream for SETI@home would cease in that situation.
As of 16 October 2005, approximately one third of the processing for the non-BOINC version of the software was performed on work or school based machines (SETI@home, 2005). As a lot of these computers will give reduced privileges to ordinary users, it is possible that much of this has been done by network administrators.
To some extent, this may be offset by better connectivity to home machines and increasing performance of home computers.
BOINC allows unofficial clients and relies more on cross-checking.
However there are a few services which allow the user to manage all of their projects and computers running BOINC in one place, such as GridRepublic