Are We Alone?


Since the early days of Project Ozma, the science of SETI has progressed greatly. Countless searches have been conducted—I found a list of about 80 searches till 1999 compiled by Jill Tarter of the SETI Institute.

While most SETI sky searches have studied the radio spectrum, some SETI researchers have considered the possibility that alien civilizations might be using powerful lasers for interstellar communications at optical wavelengths. The idea was first suggested by R. N. Schwartz and Charles Hard Townes, one of the inventors of the laser, in a 1961 paper published in the journal Nature titled ‘Interstellar and Interplanetary Communication by Optical Masers’.

It is not possible to cover all the major search efforts in one article but an excellent account can be found in Alan MacRobert’s article “SETI Searches Today”. Here I will describe just two of the searches. The first, called project SERENDIP, used an innovative approach that greatly boosted the availability of radio-telescope time for SETI scientists leading to the generation of enormous quantities of radio data. The second project, called SETI@home, was conceived out of the necessity to properly analyze this large volume of radio data.

It turned out, SETI@home is the first volunteer computing project that greatly mobilized the public’s interest in SETI research by tapping into the enormous processing power of millions of personal computers around the world. A new open source middleware system was developed for volunteer and grid computing called BOINC (Berkeley Open Infrastructure for Network Computing). Originally created to support SETI@home, BOINC has become a very useful platform for other distributed applications in areas as diverse as mathematics, medicine, molecular biology, climatology, environmental science, and astrophysics.


SERENDIP is the acronym for “Search for Extraterrestrial Radio Emissions from Nearby Developed Intelligent Populations”. Using the Arecibo L-band Feed Array (ALFA) on the Arecibo radio telescope in Puerto Rico, project SERENDIP is set up to search for potential signatures of extraterrestrial intelligence by scanning a very broad range of radio band frequencies.

Figure 13-1: The Arecibo Observatory, a radio telescope in Puerto Rico containing the largest curved focusing dish on Earth, making it the world’s most sensitive radio telescope. The telescope has featured in many fundamental discoveries in the field of astronomy. It has even made appearances in motion picture and television productions and got a lot of publicity in 1999 when it began to collect data for the SETI@home project.

The perpetual problem that SETI researchers face is how to get enough radio-telescope time for their admittedly chancy pursuits. SETI researchers at the University of California at Berkeley came up with the idea to piggyback an extra receiver onto the Arecibo radio telescope without interrupting the telescope’s routine work. Although scientists now have access to large amounts of telescope time, SERENDIP researchers do not have control over which targets to study and thus cannot conduct follow-up studies to confirm a possible extraterrestrial signal. Nevertheless, SERENDIP uses the world’s largest radio telescope to scan a good fraction of the celestial sphere. This means it can sample many billions stars in the Milky Way and many thousands of background galaxies.

Potentially interesting signals are run through false-alarm tests. Those that survive are stored. The most important test is whether a signal repeats itself when the same point on the sky is scanned again. Dedicated follow-up observations are conducted at the locations of the best candidate signals.

The most recently deployed SERENDIP spectrometer, SERENDIP V.v, was installed at the Arecibo Observatory in June 2009 and is currently operational.


The giant radio telescopes of today can pick up and record radio emissions with remarkable efficiency. But the SETI scientists often have to work with limited resources and inadequate computer time. They simply do not have the resources to thoroughly analyze of all the available data. As a result there is the risk that a true signal transmitted by intelligent beings, light years away from us, may remain hidden in the data (radio noise) and be completely ignored.

Then in 1994 David Gedye, a Seattle computer scientist, devised a brilliant scheme to create a dynamic “scientific computing ecosystem”. He realized that deeper analysis of SETI radio data would potentially be perfect for “distributed computing” if tens of thousands of volunteers using home computers can be engaged.

Enter SETI@home, a downloadable screensaver program that resides on a participant’s home computer. During the time when the computer is in an idle state, SETI@home fetches data files (“work units”) recorded by the SERENDIP radio receiver from the servers at UC-Berkeley. The participant’s computer analyzes the downloaded work units utilizing the algorithms built into SETI@home. Depending on the computer’s CPU and memory, it could take about 10 to 20 hours to analyze the data. When finished, the results are sent back to the UC-Berkeley servers. Any possible hits in the analysis are flagged. Another chunk of data is subsequently downloaded from the server, and the process continues.


Figure 13-2: SETI@home screen.

SETI@home analyzes only one narrow, 2.5-MHz segment of SERENDIP’s much wider band. The chosen segment is usually centered on the 1,420-MHz hydrogen line.

Figure 13-2 shows the SETI@home screen. Notice, it is divided into three sections: (1) the data-analysis window (upper left), (2) the data and user information (upper right), and (3) the frequency-power-time graph of the data as it is being analyzed (bottom). Data is analyzed using a mathematical technique called a Fast Fourier Transform (FFT) using which it is spread out over many channels. A signal of extraterrestrial origin will render itself as a spike that stands out in the background of random equal shaped signals in all FFT channels. The program flags the information for later analysis by UC-Berkeley scientists if the above criterion, and additional ones that takes into account the effect of the Earth’s rotation, are met.

Today, SETI@home remains the largest computational work effort ever performed. At its peak in 2002, around 500,000 people provided nearly 100 teraflops of computation per second analyzing radio signals from the Arecibo telescope. SETI@home created an entire new category of distributed computing, called volunteer computing, that has truly captured the public’s imagination. It has helped expanding the public’s understanding of SETI issues, mobilized enthusiasts and made them aware of how data is scientifically analyzed.

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