Tag Archives: SETI

FAST completed

Time rolls by. When I wrote New Eyes on the Universe I pictured FAST – the Five-hundred-meter Aperture Spherical radio Telescope – as an instrument for the mid-term future. Construction of the telescope began in March 2011 but I thought its remote location in a karst sinkhole in Guizhou Province, combined with the technical difficulty of operating such a large device, would cause innumerable delays. In September 2016, however, the telescope saw first light. Chinese scientists are now calibrating the telescope, and by 2019 it should be doing astronomy.

FAST is a staggering telescope. It consists of 4450 triangular reflecting panels that combine to form a collection area more than twice as large as the famous 300m Arecibo telescope in Puerto Rico. If it works to its design specifications, FAST will be twice as sensitive as Arecibo, observe three times more sky than Arecibo, and be able to survey the sky 5–10 times faster than Arecibo.

Such a vast instrument has the potential to make a number of discoveries in pure astronomy, but a further intriguing possibility lies in its use for SETI: scientists interested in the search for extraterrestrial intelligence will be able to “piggyback” on pure science projects and comb the data for signals.

FAST

FAST lies in a natural basin in the Guizhou Province of China. The telescope is undoubtedly an impressive astronomical instrument, but its name is a slight misnomer: although the reflector diameter is 500m only a 300m diameter circle is used at any one time. (Credit: Asianewsphoto)

A SETI simulation

In a former life, back when computers were powered by steam and the Web was only a twinkle in Tim Berners-Lee’s eye, I helped develop simulations for teaching and learning physics. Years have gone by since I last coded a physics simulation, but I still find enjoy using them and I’m convinced that the best ones can really improve a student’s understanding of physical theory. I’m not alone in that belief. For example the Nobel laureate Carl Wieman, who has long argued that metrics for assessing the quality of an academic’s teaching should sit alongside metrics for assessing the quality of an academic’s research, founded PhET Interactive Simulations to improve the way physics is taught and learned. (PhET stands for “Physics Education Technology”, but since Wieman founded it in 2002 the project has expanded to include biology, chemistry and earth sciences.) The simulations that PhET release allow students to see in real time the effect of changing the value of a physical variable; these software-based experiments allow students to play safely, quickly and cheaply with systems, and can help inculcate a deeper understanding of the underlying physics. The simulations don’t have to be particularly complicated to be of value. A basic simulation of a wave on a string, for example, will allow students to change the values for frequency, wavelength and amplitude – and the students will immediately be able to visualise and understand what those terms mean. Simulations don’t necessarily replace textual descriptions – there has to be a pedagogic scaffold surrounding the simulations – but they certainly bring texts to life.

In writing Where is Everybody? I toyed with the idea of developing simulations to illustrate some of the points I wanted to make. When discussing the challenges faced by SETI scientists I couldn’t help but think that readers would get the point more readily if they were able to visualise the search space. What is the effect on likely detection if we double the range over which we believe radio signals from an extraterrestrial civilisation can be detected? What happens if we treble the range, or half it? What is the effect on likely detection if we increase the lifespan over which a civilisation is likely to transmit, or decrease the time over which a civilisation is motivated to listen? How important to the SETI endeavour is the rate at which radio civilisations come into existence? A reader could of course answer these questions by working through the mathematics. But not all readers have a mathematical background. A simulation would handle the mathematics for the reader, and allow everyone – even the math-phobic – to explore these questions.

I no longer have the time to devote to coding simulations. However I recently discovered that Roger Guay has already produced a gorgeous-looking simulation, called Alien Civilization Detection, that allows us all to play with various factors associated with SETI.

ACD introductory screen

The introductory screen from Roger Guay’s app Alien Civilization Detection (Credit: Roger Guay)

Roger’s simulation features a concise introduction that first outlines the problem of detection and then explains why his simulation is of only a “small” (10000 x 8000 light year) region of the Galaxy. Interactive tabs at the bottom of the simulation present useful information on the Drake equation, a slider that illustrates timescales, and example analyses. Screen tools at the side of the simulation allow you to change its appearance (and toggle some “fun facts”; did you know, for example, that firelight from the last of the Stone Age people is now just a quarter of the way to the centre of the Galaxy?).

Instructions for ACD

Some of the features in the Alien Civilization Detection simulation. (Credit: Roger Guay)

The simulation itself presents the viewer with a number of dials. We can set the typical maximum distance for radio detection, from 600 light years to 2000 light years. We can set the timespan over which a civilization will broadcast, from 160 years up to 2000 years; similarly, we can set the timespan over which a civilisation will be actively listening. The view can be either “Earth-centric” or “Galaxy-centric”. Press the green “Start” button, or the space bar, and watch as this small part of the Galaxy fills with radio signals. We see civilizations appear; we see civilisations that are currently both listening and transmitting; we see civilisations that are listening but no longer transmitting; and we see the ever-weakening signals from civilisations that are no longer listening, no longer transmitting. A counter keeps track of the elapsed time along with the number of potential detections that could have been made during that time.

ACD-typical run showing detection potential

Screenshot of a typical run of the Alien Civilization Detection app. Note the detection potential! (Credit: Roger Guay)

It’s rather hypnotic to watch civilisations pop into existence, transmit radio waves into the cosmos, and then cease transmitting or listening (perhaps they die?) before those waves cross the path of another civilisation. Occasionally, though, there is the chance for detection. Those rare events are what SETI scientists hope to see.

I viewed the simulation on a Mac, but I believe that a Windows version is in the pipeline. If you would like to contact Roger to discuss the simulation, his email address is irog@icloud.com. And if you would like to download the app, you can do so via this Dropbox link.

Enjoy!

Listening to Gliese 581

The first modern SETI experiment – Frank Drake’s observations at Green Bank in 1960 – focused on two specific stars: Epsilon Eridani and Tau Ceti. Six decades later, astronomers have targeted another star for SETI observations: Gliese 581. This red dwarf star, which is about 20 light years distant, is not an unreasonable target: it has planets, two of which may be superEarths that are on the edge of the star’s habitable zone. What makes this particular SETI study interesting, however, is that it uses a technique that hasn’t been tried before in a SETI context: very long baseline interferometry (VLBI).

Hayden Rampadarath, and three colleagues from Curtin University in Australia, used the Australian Long Baseline Array (ALBA) in their work. This is a collection of three radio telescopes, separated by several hundred kilometres, which (once the signals from the different telescopes are combined) has an angular resolution that’s similar to the Hubble Space Telescope. The team used ALBA to observe Gliese 581 for a total of eight hours in  June 2007, tuning in to frequencies near the waterhole. They discovered 222 candidate SETI signals, all of which were quickly excluded (and probably come from communications with geostationary satellites).

The interest in this paper is not that the study rules out Gliese 581 as a candidate for hosting extraterrestrial intelligence: it doesn’t. (While ALBA would pick up a transmission beamed directly to us from an Arecibo-type instrument, it obviously wouldn’t pick it up if the transmitter was pointing somewhere else or happened to be idle on the days when they looked. And ALBA wouldn’t pick up ‘leakage’ radio transmissions of the type that we typically broadcast.) No, the interest in this paper is that it demonstrates how SETI scientists can use VLBI as part of a targeted search strategy. What’s really exciting is that soon we’ll have interferometers with much more sensitivity than ALBA. The forthcoming Square Kilometer Array, in addition to being a revolutionary tool for astronomy, has the potential to enhance SETI enormously: imagine this great instrument listening to planets identified by Kepler

You can find a preprint of Rampadarath’s paper here.