5. A FALSE SIGNAL
The history of SETI research is full of false positives.This Section tells you the story of a major discovery in the field of astronomy where, interestingly, the researchers initially could not rule out the possibility that their signal could be sent by intelligent beings from another world. Eventually, it proved to be a false SETI signal. But the research led to a Ph.D. and a Nobel Prize in physics.
In 1967, Antony Hewish, a radio astronomer in Cambridge University was designing a radio telescope to observe the scintillation (twinkling) of stars, particularly quasars. Stars appear to scintillate or twinkle because the light has to pass through the earth’s atmosphere to reach an observer on the Earth. Refraction of star light through the various layers of the atmosphere that are at different temperatures and densities cause them to twinkle, or scintillate. Luckily, the atmosphere is transparent to radio waves, so Hewish realized radio telescopes could be built around Cambridge to study his quasars!
Hewish’s graduate student Jocelyn Bell was responsible for operating the radio telescope and analyzing the data. In the summer of 1967, Bell observed an unusual signal at a wavelength of 3.7m, “scruff” as she called it, which manifested as sharp bursts of radio energy at a regular interval of 1.3 seconds, much faster than any known stellar rotation rates.
After extensive analysis, Hewish and Bell realized the pulses were arriving from outside our Solar System. The duration of a pulse was only 16 milliseconds. This short duration suggested that the source could be no larger than a small planet.
But if another planet was the source of these radio waves, as that planet orbited its alien “Sun”, the frequency of the radio waves would be higher when the planet moved towards us, and lower when it moved away. This ‘Doppler shift’ in frequency is the reason for the apparent change in pitch of a car or train as it races past an observer. But Hewish’s subsequent careful measurements indicated the change in the frequency could be explained as due to the motion of the Earth (motion of the observer) around our Sun. Thus the source of the radio waves could not be a planet.
Interestingly, Bell and Hewish first thought the signal could possibly be a beacon from an alien source and labeled it LGM for Little Green Men. This may sound rather amusing today, but imagine yourself in the shoes of Jocelyn Bell and her advisor Antony Hewish! In Bell’s own words “here was I trying to get a Ph.D. out of a new technique, and some silly lot of little green men had to choose my aerial and my frequency to communicate with us.” Soon Bell found another pulsing signal in a completely different part of the sky, slightly faster, with a pulse rate 1.2 per second. This meant the pulses must have a less exotic explanation. “It was very unlikely that two lots of little green men would both choose the same, improbable frequency, and the same time, to try signaling to the same planet Earth.”
With insights from theoretical astrophysicists, Hewish determined that the regularly patterned radio signals, or pulses, that Bell had detected were not caused by earthly interference or by any intelligent life forms trying to communicate with distant planets but rather were energy emissions from certain stars called pulsars. Fred Hoyle suggested that the pulsar could be the remnants of a supernova explosion. Thomas Gold of Cornell University in Ithaca, USA, suggested that the signals observed by Jocelyn Bell were coming from neutron stars, but that the neutron stars were spinning around an axis. The neutron star wouldn’t need to be emitting pulses of radiation, but could emit a steady radio signal if it swept around in circles like light from a lighthouse. When the pulsar ‘lighthouse’ was pointing toward the Earth we could detect the signal, which would appear as the short pulse that Bell had observed.
Antony Hewish was awarded (jointly with fellow astronomer Sir Martin Ryle) the 1974 Nobel Prize in Physics for his work in identifying pulsars as a new class of stars. This was the first time the prize had been given for observational astronomy. Jocelyn Bell was ignored by the Swedish Nobel committee in spite of her stellar contributions. She earned her Ph.D. in 1968. Pulsars appeared in the appendix of her dissertation.
Back to SETI. A completely new way of searching for an alien civilization based on the laws of physics, specifically, the Second Law of Thermodynamics, was conjured by physicist and mathematician Freeman Dyson in 1960. At first, the core idea will seem like a grandiose science fiction scheme (it was indeed inspired by science fiction) and its feasibility may be beyond our current engineering capabilities, but the underlying scientific logic is solid and its technological scope, awe inspiring.
1 Quasars or quasi-stellar radio sources, first detected in the 1960s, are a class of celestial objects called active galactic nuclei (AGN). They are the most distant and most luminous objects in the Universe and they are powered by a supermassive black hole located in the center of a Galaxy. While the nature of these objects was controversial until the early 1980s, there is now a scientific consensus that a quasar is a compact region in the center of a massive Galaxy surrounding a central supermassive black hole. Today we know most quasars are faint radio emitters. In addition to radio waves and visible light, quasars also emit ultraviolet rays, infrared waves, X-rays, and gamma-rays. Most quasars are larger than our solar system.