In 1967, a young Irish student named Jocelyn Bell Burnell detected a strange signal coming from the radio telescope she was working with. It was a series of short pulses every 1.3 seconds, which occurred every day at the same time according to sidereal time (a timing system based on the Earth’s rotation relative to the stars rather than the Sun). This indicated that the signal came from outer space. But the 1.3 second interval between pulses was much shorter and more regular than any pulsed source known at the time. Nothing like this had ever been detected before, and as Bell Burnell later admitted, the thought crossed her mind: had she picked up signals from an alien civilization? Neither she nor her thesis supervisor brought up the idea in public, but the press was still filled with stories of little green men trying to communicate with humans.
A few months later, astronomers Thomas Gold and Fred Hoyle identified the origin of these signals, or at least offered an explanation that did not involve extraterrestrials: neutron stars. The existence of these objects had been predicted in 1933 by Walter Baade and Fritz Zwicky as the last evolutionary stage of a supernova. These objects emit radiation along their magnetic poles which, due to their rapid rotation, we see only intermittently, much like the beam from a lighthouse on the coast.
Sherlock Holmes, the famous character created by British author Arthur Conan Doyle, said that “when you have eliminated the impossible, whatever remains, however improbable, must be the truth”. The detective was making a logically correct statement that the improbable is statistically greater than the impossible. But it is precisely this fallacy of logic that makes Sherlock Holmes’ argument so misleading, and by far the cause of so many false reports of extraterrestrial discoveries in the news. The universe is stranger than we can imagine, and it would be arrogant to assume that we already know all the possible non-extraterrestrial phenomena that could lead to a given astronomical observation.
A very good example is ‘Oumuamua, a strange elongated object that passed through our solar system a few years ago. ‘Oumuamua appeared as a reddish, pulsating, very faint spot in the sky. It was not a normal object. It was about 400 meters long (1,312 ft) and 40 meters wide (131 ft) and rotated at high speed. Its first observers, a team of astronomers from the University of Hawaii, gave it its name, which roughly means “distant first messenger”. Besides its shape, observers were baffled by its trajectory and high speed, which increased as it moved away from the Sun, in violation of Kepler’s second law of planetary motion. This behavior has also been observed in comets due to what is called outgassing, when heat from the Sun melts their ice and releases gases that propel comets forward, creating their beautiful tails. But ‘Oumuamua had no tail.
Renowned Harvard University astrophysicist Avi Loeb has come out to say that ‘Oumuamua was an extraterrestrial object, specifically that it could be a thin artificial solar sail accelerated by the pressure of solar radiation. But scientists from the University of Arizona have concluded, after detailed analysis, that it could be a fragment of a dwarf planet or a Pluto-like asteroid that was blasted into space. interstellar by the force of an impact. Pluto also has a reddish tint due to radiation that turns its surface methane into hydrocarbons and could accelerate like comets through the outgassing of nitrogen ice, which is very abundant on these types of objects. But this outgassing would be invisible. Again, this may or may not be a correct or complete explanation, but it does show that there are perfectly plausible natural explanations for ‘Oumuamua without resorting to extraterrestrials.
Tabby’s Star is another good example. Discovered by Tabetha Boyajian in 2011, this star showed very unusual dips in light that had never been seen before and for which there was no logical explanation. After ruling out several hypotheses, a few scientists have suggested the possibility of an extraterrestrial megastructure that might be blocking its light, something akin to what are known as Dyson spheres, hypothetical structures that completely encompass a star to capture light. most of its influence. This theory was based on the fact that no known natural phenomenon could easily explain the sightings, and for a time the idea was very popular. The largest radio telescopes in the world quickly pointed in its direction, not to mention the antennas of the SETI (Search for Extraterrestrial Intelligence) network. Since then, new data has shown that light dips do not affect all colors equally, as one would expect from an opaque structure, and are quite similar to the effect produced by cosmic dust, which allows more red light to pass through than blue. There’s still a lot to explain, but current assumptions point to cosmic dust from a recently destroyed planet or satellite as the most likely cause.
But let’s not completely destroy our hopes of discovering extraterrestrial life and consider a few discoveries that still don’t have satisfactory natural explanations. Many readers may have heard of the Wow! signal, a strange narrowband radio signal detected in August 1977 by Big Ear, the Ohio State University radio telescope. No simple explanation has yet been offered for this signal, and no other similar signal has ever been detected again. Or have they? On April 29, 2019, the Parkes Radio Telescope was pointing at our nearest stellar neighbor, a star known as Proxima Centauri, when it detected an emission peak at a frequency of 982.002 MHz that gradually shifted to higher frequencies over the next three hours.
The signal went undetected for over a year until a student working on the alien research project Breakthrough Listen looked at the data again. There are many sources of radio signals in the sky and most are made by humans. But Breakthrough Listen has detailed protocols for filtering them out. This signal passed through the filters due to its frequency motion and the fact that it was only detected when the telescope was pointing at Proxima Centauri and not at another point in the sky. This is especially exciting because Proxima Centauri has a planetary system that includes a planet with a mass similar to Earth, which is located the right distance from Proxima to allow liquid water to be on its surface. If an increase in frequency means the signal is getting closer, does that mean there’s an invading fleet of Proximans coming our way? There are several good reasons to think not. For example, Proxima Centauri is a red dwarf that is dangerously active, with multiple flares and coronal mass ejections, so a planetary atmosphere is unlikely to survive its outbursts. Moreover, the signals are spaced in regular frequency intervals and these seem to be multiples of frequencies commonly used in the oscillators of our electronic devices. This tips the scales on the boring side, even if the specific source of the interference has not been identified. On the other hand, the fact that the signal cannot be detected when the telescope is not pointed at Proxima Centauri is certainly odd.
The fact is that the observation of the universe does not stop surprising us with new phenomena, and although the extraterrestrial idea returns regularly, in any case, a natural culprit is ultimately always found. Does this mean that we will never be able to confirm the existence of extraterrestrials based on our observations of the sky? When will we be able to say that a new clue is unequivocal proof of extraterrestrial life? Believe me, if the clue was delivered by extraterrestrials, the evidence would pile up. Most scientists want there to be extraterrestrials; they want it more than anyone, and they’ll be the first to jump for joy when the most likely interpretation of the data points to alien lifeforms. It’s not happening right now, but millions of dollars, many hours of work, and a lot of effort are going into trying to make it happen, so that we can one day finally announce that we’re not the only intelligent beings in all space-time.