Why The Recent Signal From Proxima Centauri That Seemed Promising is Highly Unlikely
Astronomers have conducted calculations to assess the probability of the signal originating from an advanced alien civilization, and the results are discouraging.
On April 29, 2019, the Parkes Radio Telescope in Australia initiated its mission of monitoring radio signals from Proxima Centauri, the nearest star to our Sun located just over 4 light-years away. The primary objective was to detect signs of solar flares. It began this endeavor with a 30-minute listening session, subsequently shifting its focus to a distant quasar for recalibration before resuming observations.
During this campaign, the telescope amassed a total of 26 hours of data. However, upon conducting a more in-depth analysis, astronomers stumbled upon an unusual occurrence – a solitary, unmodulated signal at a frequency of 982.02 MHz, which manifested five times within the data.
The initial report of this signal surfaced in The Guardian, a British newspaper, last year, sparking speculation about the potential implications for the existence of an advanced civilization inhabiting Proxima Centauri. This red dwarf star, well-known for hosting an Earth-sized planet within its habitable zone, raised questions about extraterrestrial signals.
Nonetheless, researchers have consistently downplayed the likelihood of this scenario. They insist that, at the very least, the signal should be observed again before any definitive conclusions can be drawn. Regrettably, despite various search efforts, this signal has remained elusive and has not recurred.
Now, Amir Siraj and Abraham Loeb from Harvard University in Cambridge, Massachusetts, have undertaken the task of calculating the probability that the signal originated from a civilization based in Proxima Centauri, even in the absence of additional observations. Their assessment indicates that the odds are exceedingly low, effectively ruling out the possibility, provided that the assumptions underlying their calculations hold true.
The fresh signal was stumbled upon by scientists associated with the Breakthrough Listen project, an international initiative of astronomers dedicated to the quest for signs of extraterrestrial intelligence. This endeavor is generously funded by the billionaire Yuri Milner, and they have denoted this signal as Breakthrough Listen Candidate 1, or BLC1.
What makes this signal intriguing is that it deviates from the typical characteristics of natural occurrences. Natural sources often produce broad-spectrum noise, whereas BLC1 exhibits all the attributes of a technosignature—something that arises from a technologically advanced civilization.
The most probable origin of this signal is, by far, Earth. Such signals are commonly attributed to terrestrial radio interference from nearby sources like mobile phones, microwave ovens, passing vehicles, aircraft, satellites, and the like. However, the team scrutinizing this signal has yet to identify a definitive source. What adds to the mystery is that the signal’s frequency subtly fluctuates over time, which aligns with the behavior of a signal originating from a rotating or orbiting object. This has heightened the intrigue surrounding it.
This is where the work of Siraj and Loeb becomes particularly relevant. Their approach is rooted in the Copernican Principle, which posits that Earth does not occupy a privileged position in the universe, nor does it exist at any specific point in time. In other words, observations made from Earth are no more extraordinary than those made from anywhere else in the universe.
The Copernican Principle has a rich history, stemming from the 14th-century astronomer Nicolaus Copernicus, who asserted that Earth does not hold a central position in the universe and instead revolves around the Sun. Nearly three decades ago, astronomer Richard Gott applied this principle to demonstrate, with a 95% degree of confidence, that our species is likely to endure for a minimum of 200,000 years but will not persist for more than 8 million years.
The fundamental idea is that humanity had a commencement and will ultimately meet its conclusion. At present, we exist somewhere in the middle of this timeline, without any particular privilege of being close to the beginning or the end. In mathematical terms, we are improbable to be within the first 2.5% of humanity’s existence or its final 2.5%. Consequently, with 95% confidence, we find ourselves in the middle.
Subsequently, it becomes a matter of applying the numbers. We know that our species has been in existence for around 200,000 years, which must account for at least 2.5% of the total duration. This implies, with 95% confidence, that humanity should endure for at least another 200,000 years but no longer than 8 million years.
Indeed, Gott employed the same rationale to propose that the likelihood of encountering signs of intelligent life elsewhere in our galaxy is exceedingly slim, even if we assume that such civilizations exist. Given that we have possessed radio communication capabilities for just over a century, the probability of this timeframe overlapping with another civilization’s similar capability is infinitesimal. As Gott puts it, “A targeted radio search of 1,000 nearby stars is not likely to succeed.”
Applying a similar argument, Siraj and Loeb assess the probability that our civilization’s radio capabilities coincide with those of another civilization in the Proxima Centauri system. Unfortunately, the results are not encouraging. They conclude that if Breakthrough Listen Candidate 1 were generated by a technologically advanced civilization, it would violate the Copernican Principle by eight orders of magnitude. As a result, they assert that “this rules out, a priori, Breakthrough Listen Candidate 1 (BLC1) as a technological radio signal from the Alpha Centauri system.”
The Theory of Panspermia
Indeed, considering the vast number of potentially habitable planets throughout the galaxy, the notion that two adjacent stars would simultaneously host advanced civilizations appears exceedingly improbable.
However, there could be other influencing factors, such as panspermia, which proposes that life is disseminated from space. This concept enhances the likelihood of neighboring stars supporting advanced life concurrently. Nevertheless, this argument is intricate, as life on Earth originated approximately 4.5 billion years ago, well before the Sun and Proxima Centauri became close neighbors.
Certainly, the Copernican Principle doesn’t entirely rule out the possibility that the signal detected at Parkes originates from another civilization. It’s just that the probability of it being an unintended terrestrial signal is considerably higher by orders of magnitude. For now, astronomers can only turn their radio telescopes back toward Proxima Centauri and await further developments.
Ref: The Copernican Principle Rules Out BLC1 as a Technological Radio Signal from the Alpha Centauri System: arxiv.org/abs/2101.04118
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