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As a field, Extraterrestrial Intelligence Research suffers from quite significant constraints. Besides the uncertainty involved (e.g. is there life beyond Earth that we can actually communicate with?), There are the limitations imposed by technology and the very nature of space and space. time. For example, scientists are forced to face the possibility that by the time a message is received by an intelligent species, the civilization that sent it will be long dead.
Harvard astronomers Amir Siraj and Abraham Loeb address this question in a new study recently published online. Drawing inspiration from Copernicus’ principle, which states that humanity and Earth are representative of the norm (not an outlier), they calculated that if transmissions from Earth were heard by an alien technological civilization ( ETC), it would take about 3000 years to get a response.
Their study, titled “Smart Responses to Our Technology Signals Will Not Happen in Less Than Three Millennia,” was recently published online and is being considered for publication. While Siraj is a concurrent undergraduate and graduate student in astrophysics at Harvard, Professor Loeb is Frank B. Baird Jr., professor of science, director of the Harvard Institute for Theory and Computing (ITC), president from Revolutionary Starshot Siraj advisory board, bestselling author and academic advisor.
Loeb is also renowned for theorizing that the interstellar object ‘Oumuamua, which flew over Earth in 2017, could have been an alien glowing sail. This theory was first put forward in a 2018 article he co-wrote with postdoctoral researcher Shmuel Bialy (ITC). The arguments presented there have since been developed in Loeb’s most recent book, Alien: the first sign of intelligent life beyond Earth.
Professor Loeb recently joined forces with Dr Frank Laukien and other colleagues to launch Project Galileo, a multinational non-profit dedicated to the study of Unidentified Aerial Phenomena (UAP). Siraj is the Director of Interstellar Object Studies for this project, and he and Loeb have published extensively on topics ranging from black holes and meteors to panspermia and interstellar objects (many of which were on the subject of ‘Oumuamua ).
For the purposes of this study, Siraj and Loeb focused on a particular aspect of SETI, which they dubbed alien response intelligence research (SETRI). By this, they designate ETIs who would be motivated to send a message to Earth in response to the detection of technological activity on our planet (aka “technosignatures”). This answers a question of growing importance to the SETI community.
In short, does humanity have a chance to hear from an ETC before our civilization collapses or is wiped out by a natural disaster? As Siraj told Universe Today via email:
“It is important to estimate the response time of responding extraterrestrial intelligences (ETRIs) because such an estimate informs about the nature of effective SETI searches – as well as the implications of a confirmed signal if we ever receive one. The question we try to answer in our article is, when can we expect our first cosmic conversation to take place? “
This establishes the first parameter of their study, which was the time during which humanity issued detectable signatures. Of all the potential technosignatures that have been considered to date, the most likely and most widely studied by SETI researchers are still radio transmissions. In accordance with the Copernican Principle, we can assume that ETIs are also engaged in the search for signs of intelligence other than their own.
“The Copernican principle asserts that it is unlikely that we are living in a privileged time and therefore the probability that another habitable planet like Earth is currently going through an analogue of our first century of radio communication, given a few billion years of its history, is less than one in ten million, ”said Loeb. “Therefore, a response is only expected in a sufficiently large volume, containing more than ten million stars.”
It is also safe to assume that an ETI would see radio signals as possible technosignature and actively listen to them. The first long-range radio broadcast took place in 1901, when Italian inventor Guglielmo Marconi sent the first transatlantic broadcast from Cornwall, England, to St. John’s, Newfoundland. Since then, humans have sent radio transmissions into space without thinking about the consequences.
This means that if there is a civilization within a hundred light years of Earth with sensitive radio telescopes, they may have heard of us before. In short, we may have already “started a conversation” with an intelligent species and are just waiting for a response. Beyond that, said Siraj, they went with a number of parameters that were consistent with the Copernican principle and the conditions under which life is known to flourish:
“[W]We considered ETIs capable of communicating via electromagnetic radiation, located on Earth-like planets orbiting Sun-like stars (aka “life as we know it”). In addition, we considered radio signals (which at the speed of light) as well as physical probes, which would move more slowly. We used the Copernicus Principle, which is inherently optimistic about the prevalence of life in the Universe, to establish a lower bound on the expected response time of ETRIs.
Transmission technologies can extend beyond radio waves to include other types of electromagnetic (EM) radiation, such as microwave lasers, x-rays, gamma rays, etc. As the only constraint is the speed of light – 299,792,458 m / s (1,079 million km / h; 670.6 million mph) – it remains the fastest option available. It also means that humans would only have to wait until the 22nd century for a transmission from a civilization located a hundred light years away.
That being said, it is also possible that an ETC may choose to explore our planet more closely rather than sending a forwarded response. In this regard, Siraj and Loeb considered possibilities such as the Traveler 1 and 2 missions, New Horizons, and the Pioneer 10 and 11 spatialship. All of these robotic missions have or will enter interstellar space (or will enter in the near future) and could one day be intercepted by an ETC.
It is for this reason that the Pioneer Plaques and the Golden Records were created. However, it will be millions of years before any of these missions reach even the closest star systems to Earth. This means that if a civilization sent a probe to investigate Earth in response to radio signals from a hundred years ago, it wouldn’t arrive for hundreds of thousands of years. As Loeb explained:
“Although this latter method of response results in physical contact with extraterrestrial objects, it takes millions of years to travel a hundred light years. This means that we still have a waiting time as long as the time that has passed since humans first appeared on Earth before witnessing chemical-powered devices in response to our radio broadcasts.
Other possible concepts, such as directed energy propulsion (at the Revolutionary Starshot), could complete the transit in much less time – at 20% the speed of light, it would reach Alpha Centauri in just 20 years. However, such concepts are effective in reaching the nearest star systems, but not stars 1000 light years away in a reasonable amount of time. As a last parameter, they took into account the number of planets likely to host an ETC.
“The Copernican principle states that it is unlikely that we are living in a privileged time and therefore the probability that another habitable planet like Earth is currently going through an analogue of our first century of radio communication, given a few billion years of its history, is less than one in ten million, ”said Loeb. From there, they determined that a response could only be expected in a sufficiently large volume, containing over ten million stars.
Assuming that our galaxy is relatively homogeneous in terms of the distribution of stars in its disk, this translates into a volume of 1 billion cubic light years (ly3) or a thousand light years in any direction. This, in turn, implies a round trip time of over two thousand years. This basically means that if an ETC knows about us and wants to talk, we wouldn’t hear from them until 4000 CE at the earliest. Or as Siraj summed it up:
“We have discovered that the fact that we have only existed as a technological civilization for about a hundred years means that, at the moment, we should not expect to receive a response from an alien civilization in response to our own signals. . In other words, it is extremely unlikely that we can strike up a cosmic conversation.
This conclusion is supported by previous research (conducted with the help of Dr. Frank Drake himself!) Which indicated that within various parameters a call and response scenario would take longer than duration. average life of a civilization. In other words, any signal we receive from an ETC (whether it is a response or an attempt to ‘start a conversation’) is likely to have been sent by a species that s ‘has since been extinct.
This, according to Siraj, is the most important aspect of their study, namely that civilizations have a life expectancy (over which they have some control). In essence, this underscores the importance of ensuring that humanity does not succumb to self-destruction or cataclysmic fate. “The big takeaway here is that we had better pull ourselves together and find a way to survive in the long term if we ever want to participate in a cosmic conversation! “
Further reading: arXiv
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