Are we alone in the universe? There are many sentient life forms waiting to be found. Will we be able to exchange knowledge when we meet them? Will we be able to recognize them as intelligent life forms when we meet them? We don't know what to expect when it comes to the search for life in the Universe. The speculation and theoretical studies into these questions are rich and varied.
The study was conducted by Nikolai Kardashev. Kardashev proposed a classification scheme for ranking a civilization's development while considering an important question related to the Search for Extraterrestrial Intelligence. The Kardashev Scale is one of the most influential concepts in SETI.
The first attempt to detect extraterrestrial communications was made in the United States in 1960. The experiment was conducted using a radio telescope at the National Radio Astronomy Observatory in Green Bank, West Virginia.
The two Sun-like stars were monitored for radio signals in the 1420 MHz range, corresponding to the frequencies of cold hydrogen gas in space. Ozma paved the way for more ambitious SETI efforts after the project failed to detect anything beyond radio static. Future surveys should be on the lookout for, that's what inspired astrophysicists worldwide.
Physicists in the Soviet Union formulated many of the seminal ideas that would endure until this day, at a time when a search for extraterrestrial intelligence was more a thought experiment than an actual discipline. One of the earliest and most consequential thinkers was Nikolai Kardashev.
Kardashev studied under the celebrated author of Intelligent Life in the Universe. The first general book on how humans could search for technologically capable beings in the universe was written by this book. Shklovskii's book became the inspiration for many scientists after it was published in 1966 in the West.
Kardashev was on his own for most of his formative years. His parents were both victims of the Great Purge in 1937 and 38 and he was sent to an orphanage. He was released into the care of his aunt, who died when he was 16. His father was shot while his mother worked in a labor camp.
Kadashev graduated from Moscow State University a year before, where he studied radio astronomy. He earned his PhD in 1962 from the Sternberg Astronomical Institute in Moscow. Kardashev's exposure to the fundamental premises of SETI led him to think about how radio astronomy could be used to detect transmissions that weren't from the ground.
One of his earliest contributions to SETI came in 1963, when he was studying a radio source located 8 billion light-years from Earth. The object was known to vary in intensity and send out irregular emissions. Kardashev suggested that this might be a deliberate attempt by extraterrestrials.
Astronomers learned that CTA-102 is an active quasar, which is variable in nature. Kardashev shared this theory and other imaginative ideas in a paper that would establish him among the astronomy community.
This paper was published in 1964. The purpose of the paper was to suggest what types of radio frequencies SETI researchers should be looking for. In keeping with the idea that there may be some civilizations billions of years older than humanity, it stood to reason that these civilizations would be able to harness levels of energy that were not humanly possible.
Kardashev proposed a three-level scale based on the amount of energy they could harness. This scale was included.
The odds of detecting a type I, II, or III civilization were described by Kardashev. He claimed that detecting a type I civilization was very unlikely, although they would still be able to receive communications. A type II or type III would be able to transmit a lot of information.
Kardashev estimated the power transmission levels of a type II civilization to be enough to transmit a lot of information within our universe. This ranged from a rate of 10 bits/s within a circle of 100,000 light-years from their star system, to 5 bits/s within a circle of 1 million light-years.
A Type III civilization would be capable of broadcasting at a rate of up to 13 bits per second over a range of 100,000 and 10 million light-years.
The Kardashev Scale established some constraints on the types of technosignatures that SETI researchers should be looking for. Scientists have come to theorize what types of technologies a type I, II, and III civilization would be capable of utilizing and what the resulting technosignatures would be, based on the power estimates established by the Scale.
The ability to harness 4 10 19 erg/sec of energy would imply access to fusion power and matter-antimatters. The form of renewable energy infrastructure is likely to be a technosignature. A constellation of space-based solar satellites would be visible using our current instruments.
The same techniques used by a type would be used by a type II civilization. Dyson suggested in 1960 that an advanced civilization could harness the energy of its star by building a massive system of satellites. Dyson said that these megastructures could be searched for by looking for large signatures of heat from them.
It has been suggested that a type II civilization would be able to lift stars. A Shkadov Thruster, also known as a Dyson structure, is a variation on the Shkadov Thruster that uses radiative force and gravitational attraction to achieve momentum and even relativistic velocities.
The type III civilization would be able to do these activities on a large scale. It has been suggested that the structures created by Galactic Civilizations could be used to counteract the expansion of the universe. Another idea is to watch quasars for signs of structures that could harness the power of SMBH.
Feeding matter onto an SMBH could be used to harness the energy they already put out. There are two possibilities for this scenario, one of which involves capturing the heat and energy generated by their jets.
Kardashev suggested criteria for how the estimated power of broadcasts could be differentiated from natural phenomena. As he said:
“The artificial sources would evidently 1) have to have very small angular dimensions (at least in the case of Type II civilizations);… 2) they would have to possess circular polarization, so that the effect of the Faraday rotation of the plane of polarization in the interstellar medium would not distort the information received; 3) they would have to exhibit variability in time without leading to statistical fluctuations… 4) finally, it is to be anticipated that certain details would be present in the spectrum of the source suspected of artificiality which would have been designed for the express purpose of emphasizing its artificial origin.”
The scientific value of the Scale is more qualitative than quantitative and it summarizes the challenges SETI researchers face. The Scale shows that the existence of a single type II civilization in our universe would not go unrecognized forever. The final section of Kardashev's paper addressed the implications of his Scale.
“The estimates arrived at show that should there exist even one type II civilization within the confines of the local system of galaxies, there will be a realistic possibility of securing an enormous quantity of information. The same holds for the existence of even one single type III civilization in the portion of the universe accessible to observation…
“Finally, it is entirely reasonable to assume that type II and type III civilizations would be in possession of information many orders of magnitude in excess of what we have available at the present tie. For that reason, they would have to be broadcasting practically continually, and this would also be the case for increasing the possibility of reception by type I civilizations.”
Kardashev estimated that advanced civilizations would be capable of broadcasting signals that type I civilizations would be able to receive. The transmissions would be broadcast continuously to ensure that they would be picked up and looped so that recipients wouldn't miss a beat.
Many additions and extensions have been suggested for the Scale since Kardashev's time. Adding classifications that fall between the three types was recommended by some. Civilizations that can harness the energy of the entire Universe or even collections of Universes are referred to as a type 0 rating.
The Scale should be redrawn using other metrics. The more advanced the species, the more information they would have at their level. The scale used the alphabet as a classification system, with each letter representing 10 million unique bits of information.
In his book, Entering Space: Creating a Spacefaring Civilization, Robert Zubrin described how a civilization could be measured.
“Adopting Kardashev’s scheme in slightly altered form, I define a Type I as a civilization that has achieved full mastery of all of its planet’s resources. A Type II civilization is one that has mastered its solar system, while a Type III civilization would be one that has access to the full potential of its galaxy.”
Perhaps John D. Barrow was the one who introduced the most radical reinterpretation. In his 1998 book, Impossibility: The Limits of Science and the Science of Limits, Barrow showed how technology has allowed us to extend our control over the environment.
Barrow thought that advanced species would grow to harness the full power of inner space, rather than being characterized by the amount of outer space it commands. The Barrow Scale is a reverse classification that consists of seven types.
Advanced civilizations would not focus on claiming more space and resources but would maximize the space they already occupy. They would stay within their solar system and harness the power of their sun rather than explore the universe. One scenario includes the possibility that they will convert all the matter in their system into computronium and arrange it in layers around the star.
Many assumptions used in the Kardashev Scale have been called into question. The belief is that extraterrestrial intelligence will have to colonize beyond its homeworld and home star. The Barrow Scale and other researchers have emphasized space maximization over expansion, which has challenged this.
The lack of observable evidence for advanced civilizations is one of the arguments against the Kardashev Scale. Since the Universe has been around for over 13 billion years, and our Solar System has only existed for over 4.5 billion years, it is likely that a few civilizations would have been able to achieve a type III level of development by now.
It would be very difficult for humans to ignore the signs of such a civilization. We haven't found any yet, that would indicate that either we are.
Nobody has emerged yet or nobody is out there. The idea of advanced life in our universe was raised by Carl Sagan and William I. Newman in their 1981 study.
The idea that civilizations will expand over distance is a criticism. This possibility was explored in detail by the author of the 1993 paper, The Fermi paradox: an approach based on percolation theory.
Civilizations would colonize outward rather than consistently and rapidly. Not all species would choose to go this route.
“Since it is possible, given a large enough number of extraterrestrial civilizations, one or more would have certainly undertaken to do so, possibly for motives unknowable to us. Colonization will take an extremely longtime, and will be very expensive.
“It is quite reasonable to suppose that not all civilizations will be interested in making such a large expenditure for a pay off far in the future. Human society consists of a mixture of cultures which explore and colonize, sometimes over extremely large distances, and cultures which have no interest in doing so.”
Considering the time and energy it would take to reach the nearest stars and the delays in sending messages, it makes sense for some species to forgo the expansion of the universe. Prof. Adam Frank and a team of exoplanet researchers from NASA made a similar argument in 2019.
The study was inspired by the book Aurora by Kim Stanley Robinson.
The other major assumption presented in Kardashev's original study has been criticized. One of the main tasks of such communication efforts would be to broadcast the existence of advanced civilizations.
Researchers and SETI scientists have explored the possibility that advanced intelligence would be compelled by the exact opposite motives. The Berserker Hypothesi, the Dark Forest Hypothesis, and various interpretations of the Great Filter are examples.
Concerns have been raised about the field of Messaging Extraterrestrial Intelligence, which is a separate field from SETI. Is it wise for humanity to be broadcasting its existence to the universe? Is it possible that intelligent life concluded the same thing a long time ago?
Concerns about extraterrestrial transmission have been raised by researchers. On Earth, governments commit cyberattacks on each other to get information. Similarly, hackers use computer viruses to trick people into giving them personal information.
Is it possible that alien civilizations are sending out messages that are designed to cripple our infrastructure or scam us?
After decades after Kardashev first published his seminal paper, academics, scientists, and regular people alike are referencing, citing, or attempting to expand on his famous Scale. Some of the assumptions and estimates he offered have been criticized, but this is to be expected from something as important as the Kardashev Scale. When human space exploration was just out of its cradle and barely walking, the theory was proposed.
The Kardashev Scale remains with us because of the fresh insight it offers, like so many other things that are fundamental to the field of SETI. Kardashev was one of the first people to think about how datememe datememe could be used to find evidence of aliens. Its influence can be seen in how it has helped to frame every discussion that has happened since about First Contact.
The legacies of SETI and astrophysics are dominated by the Scale that bears his name.
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