Kardashev scale

From Wikipedia, the free encyclopedia

The Kardashev scale is a method of measuring a civilization's level of technological advancement, based on the amount of energy a civilization is able to use for communication,^[1] proposed by Russian astrophysicist Nikolai Kardashev. The scale has three designated categories:

• A Type I civilization—also called a planetary civilization—can use and store all of the energy which reaches its planet from its parent star.
• A Type II civilization—also called a stellar civilization—can harness the total energy of its planet's parent star (the most popular hypothetical concept being the Dyson sphere—a device which would encompass the entire star and transfer its energy to the planet(s)).
• A Type III civilization—also called a galactic civilization—can control energy on the scale of its entire host galaxy.^[2]

The scale is hypothetical, and regards energy consumption on a cosmic scale. It was proposed in 1964 by the Soviet astronomer Nikolai Kardashev. Various extensions of the scale have since been proposed, including a wider range of power levels (types 0, IV and V) and the use of metrics other than pure power.

Definition

In 1964, Kardashev defined three levels of civilizations, based on the order of magnitude of power available to them:

Type I

Technological level of a civilization that can harness all the energy that falls on a planet from its parent star (for Earth-Sun system, this value is close to 7x10¹⁷ watts), which is more than five orders of magnitude higher than the amount presently attained on earth, with energy consumption at ≈4×10¹⁹ erg/sec (4 × 10¹² watts).^[1] The astronomer Guillermo A. Lemarchand stated this as a level near contemporary terrestrial civilization with an energy capability equivalent to the solar insolation on Earth, between 10¹⁶ and 10¹⁷ watts.^[3]

Type II

A civilization capable of harnessing the energy radiated by its own star—for example, the stage of successful construction of a Dyson sphere—with energy consumption at ≈4×10³³ erg/sec.^[1] Lemarchand stated this as a civilization capable of utilizing and channeling the entire radiation output of its star. The energy utilization would then be comparable to the luminosity of our Sun, about 4×10³³ erg/sec (4×10²⁶ watts).^[3]

Type III

A civilization in possession of energy on the scale of its own galaxy, with energy consumption at ≈4×10⁴⁴ erg/sec.^[1] Lemarchand stated this as a civilization with access to the power comparable to the luminosity of the entire Milky Way galaxy, about 4×10⁴⁴ erg/sec (4×10³⁷ watts).^[3]

Energy consumption estimated in three types of

civilizations defined by Kardashev scale.

Current status of human civilization

Total World, Annual Primary Energy Consumption.

 

According to the astronomer Carl Sagan, humanity is going through a phase of technical adolescence, "typical of a civilization about to integrate the type I Kardashev scale."

At the current time, Humans have not yet reached Type 1 civilization. Physicist and futurist Michio Kaku suggested that humans may attain Type I status in 100–200 years, Type II status in a few thousand years, and Type III status in 100,000 to a million years.^[4]

Carl Sagan suggested defining intermediate values (not considered in Kardashev's original scale) by interpolating and extrapolating the values given above for types I (10¹⁶ W), II (10²⁶ W) and III (10³⁶ W), which would produce the formula

${\displaystyle K={\frac {\log _{10}P-6}{10}}}$,

where value K is a civilization's Kardashev rating and P is the power it uses, in watts. Using this extrapolation, a "Type 0" civilization, not defined by Kardashev, would control about 1 MW of power, and humanity's civilization type as of 1973 was about 0.7 (apparently using 10 terawatt (TW) as the value for 1970s humanity).^[5]

In 2012, total world energy consumption was 553 exajoules (553×10¹⁸ J=153,611 TWh),^[6] equivalent to an average power consumption of 17.54 TW (or 0.7244 on Sagan's Kardashev scale).

Observational evidence

In 2015, a study of galactic mid-infrared emissions came to the conclusion that "Kardashev Type-III civilizations are either very rare or do not exist in the local Universe".^[7]

On October 14, 2015, the detection of an unusual light curve for star KIC 8462852 raised speculation that a Dyson Sphere (Type II civilization) may have been discovered.^{[8][9][10][11][12]} The SETI Institute's initial radio reconnaissance of KIC 8462852, however, found no evidence of technology-related radio signals from the star.^[13][14][15]

In 2016, Paul Glister, author of the Centauri Dreams website, described a signal apparently from the star HD 164595 as requiring the power of a Type I or Type II civilization, if produced by extraterrestrial lifeform.^[16] However, in August 2016 it was discovered that the signal's origin was most likely a military satellite orbiting the Earth.^[17]

Energy development

Type I civilization methods

• Large-scale application of fusion power. According to mass–energy equivalence, Type I implies the conversion of about 2 kg of matter to energy per second. An equivalent energy release could theoretically be achieved by fusing approximately 280 kg of hydrogen into helium per second,^[18] a rate roughly equivalent to 8.9×10⁹ kg/year. A cubic km of water contains about 10¹¹ kg of hydrogen, and the Earth's oceans contain about 1.3×10⁹ cubic km of water, meaning that humans on Earth could sustain this rate of consumption over geological time-scales, in terms of available hydrogen.
• Antimatter in large quantities would have a mechanism to produce power on a scale several magnitudes above our current level of technology.^{[citation needed]} In antimatter-matter collisions, the entire rest mass of the particles is converted to radiant energy. Their energy density (energy released per mass) is about four orders of magnitude greater than that from using nuclear fission, and about two orders of magnitude greater than the best possible yield from fusion.^[19] The reaction of 1 kg of anti-matter with 1 kg of matter would produce 1.8×10¹⁷ J (180 petajoules) of energy.^[20] Although antimatter is sometimes proposed as a source of energy, this does not appear feasible. Artificially producing antimatter—according to current understanding of the laws of physics—involves first converting energy into mass, which yields no net energy. Artificially created antimatter is only usable as a medium of energy storage, not as an energy source, unless future technological developments (contrary to the conservation of the baryon number, such as a CP violation in favour of antimatter) allow the conversion of ordinary matter into anti-matter. Theoretically, humans may in the future have the capability to cultivate and harvest a number of naturally occurring sources of antimatter.^[21][22][23]
• Renewable energy through converting sunlight into electricity—either by using solar cells and concentrating solar power or indirectly through wind and hydroelectric power. There is no known way for human civilization to use the equivalent of the Earth's total absorbed solar energy without completely coating the surface with human-made structures, which is not feasible with current technology. However, if a civilization constructed very large space-based solar power satellites, Type I power levels might become achievable—these could convert sunlight to microwave power and beam that to collectors on Earth.

Figure of a Dyson swarm surrounding a star

Type II civilization methods

• Type II civilizations might use the same techniques employed by a Type I civilization, but applied to a large number of planets in a large number of planetary systems.
• A Dyson sphere or Dyson swarm and similar constructs are hypothetical megastructures originally described by Freeman Dyson as a system of orbiting solar power satellites meant to enclose a star completely and capture most or all of its energy output.^[24]
• Perhaps a more exotic means to generate usable energy would be to feed a stellar mass into a black hole, and collect photons emitted by the accretion disc.^[25][26] Less exotic would be simply to capture photons already escaping from the accretion disc, reducing a black hole's angular momentum; this is known as the Penrose process.
• Star lifting is a process where an advanced civilization could remove a substantial portion of a star's matter in a controlled manner for other uses.
• Antimatter is likely to be produced as an industrial byproduct of a number of megascale engineering processes (such as the aforementioned star lifting) and, therefore, could be recycled.^{[citation needed]}
• In multiple-star systems of a sufficiently large number of stars, absorbing a small but significant fraction of the output of each individual star.

Type III civilization methods

• Type III civilizations might use the same techniques employed by a Type II civilization, but applied to all possible stars of one or more galaxies individually.^[2]
• They may also be able to tap into the energy released from the supermassive black holes which are believed to exist at the center of most galaxies.
• White holes, if they exist, theoretically could provide large amounts of energy from collecting the matter propelling outwards.
• Capturing the energy of gamma-ray bursts is another theoretically possible power source for a highly advanced civilization.
• The emissions from quasars can be readily compared to those of small active galaxies and could provide a massive power source if collectable.

Civilization implications

There are many historical examples of human civilization undergoing large-scale transitions, such as the Industrial Revolution. The transition between Kardashev scale levels could potentially represent similarly dramatic periods of social upheaval, since they entail surpassing the hard limits of the resources available in a civilization's existing territory. A common speculation^[27] suggests that the transition from Type 0 to Type I might carry a strong risk of self-destruction since, in some scenarios, there would no longer be room for further expansion on the civilization's home planet, as in a Malthusian catastrophe. Excessive use of energy without adequate disposal of heat, for example, could plausibly make the planet of a civilization approaching Type I unsuitable to the biology of the dominant life-forms and their food sources. If Earth is an example, then sea temperatures in excess of 35 °C (95 °F) would jeopardize marine life and make the cooling of mammals to temperatures suitable for their metabolism difficult if not impossible. Of course, these theoretical speculations may not become problems possibly through the applications of future engineering and technology. Also, by the time a civilization reaches Type I it may have colonized other planets or created O'Neill-type colonies, so that waste heat could be distributed throughout the planetary system.

Extensions to the original scale

Many extensions and modifications to the Kardashev scale have been proposed.

• Types 0, IV, and V Kardashev rating: The most straightforward extension of the scale to even more hypothetical Type IV beings who can control or use the entire universe or Type V who control collections of universes. This would also include Type 0 civilizations, who do not rank on the Kardashev scale. The power output of the visible universe is within a few orders of magnitude of 10⁴⁵ W. Such a civilization approaches or surpasses the limits of speculation based on current scientific understanding, and may not be possible.
  • Zoltán Galántai has argued that such a civilization could not be detected, as its activities would be indistinguishable from the workings of nature (there being nothing to compare them to).^[28]
  • In his book Parallel Worlds, Michio Kaku has discussed a Type IV civilization that could harness "extragalactic" energy sources such as dark energy.^[29]
• Kardashev alternative rating characteristics: Other proposed changes to the scale use different metrics such as 'mastery' of systems, amount of information used, or progress in control of the very small as opposed to the very large.
• Planet mastery (Robert Zubrin): Metrics other than pure power usage have also been proposed. One is 'mastery' of a planet, system or galaxy rather than considering energy alone.^[30]
• Information mastery (Carl Sagan): Alternatively, Carl Sagan suggested adding another dimension in addition to pure energy usage: the information available to the civilization.
  • He assigned the letter A to represent 10⁶ unique bits of information (less than any recorded human culture) and each successive letter to represent an order of magnitude increase, so that a level Z civilization would have 10³¹ bits.
  • In this classification, 1973 Earth is a 0.7 H civilization, with access to 10¹³ bits of information.
  • Sagan believed that no civilization has yet reached level Z, conjecturing that so much unique information would exceed that of all the intelligent species in a galactic supercluster and observing that the universe is not old enough to exchange information effectively over larger distances.
  • The information and energy axes are not strictly interdependent, so that even a level Z civilization would not need to be Kardashev Type III.^[5]
• Microdimensional mastery (John Barrow): John D. Barrow, going by the fact that humans have found it more cost-effective to extend any abilities to manipulate their environment over increasingly smaller dimensions rather than increasingly larger ones, reverses the classification downward from Type I-minus to Type Omega-minus:
  • Type I-minus is capable of manipulating objects over the scale of themselves: building structures, mining, joining and breaking solids;
  • Type II-minus is capable of manipulating genes and altering the development of living things, transplanting or replacing parts of themselves, reading and engineering their genetic code;
  • Type III-minus is capable of manipulating molecules and molecular bonds, creating new materials;
  • Type IV-minus is capable of manipulating individual atoms, creating nanotechnologies on the atomic scale and creating complex forms of artificial life;
  • Type V-minus is capable of manipulating the atomic nucleus and engineering the nucleons that compose it;
  • Type VI-minus is capable of manipulating the most elementary particles of matter (quarks and leptons) to create organized complexity among populations of elementary particles; culminating in:
  • Type Omega-minus is capable of manipulating the basic structure of space and time.^[31]
• According to this scale, humans, having wide expertise in various branches of chemistry and biology, have passed the stage of Type III-minus. Type IV-minus technologies (that have had practical and widespread applications) have been seen in areas like nanotechnology, semiconductors, materials science and genetic engineering, whereas Type V-minus has seen large scale application in the field and subfields of nuclear physics. Type VI-minus has had tentative research in the field of particle physics with particle colliders such as the Large Hadron Collider.
• Civilizational range (Robert Zubrin): Robert Zubrin adapts the Kardashev scale to refer to how widespread a civilization is in space, rather than to its energy use.
  • In his definition, a Type I civilization has spread across its planet.
  • A Type II has extensive colonies in its respective stellar system, and
  • A Type III has colonized its galaxy.^[30]

Criticism

It has been argued that, because we cannot understand advanced civilizations, we cannot predict their behavior. Thus, the Kardashev scale may not be relevant or useful for classifying extraterrestrial civilizations. This central argument is found in the book Evolving the Alien: The Science of Extraterrestrial Life.^[32]

Active SETI

From Wikipedia, the free encyclopedia

A representation of the 1679-bit Arecibo message.

Active SETI (Active Search for Extra-Terrestrial Intelligence) is the attempt to send messages to intelligent extraterrestrial life. Active SETI messages are usually sent in the form of radio signals. Physical messages like that of the Pioneer plaque may also be considered an active SETI message. Active SETI is also known as METI (Messaging to Extra-Terrestrial Intelligence). The term METI was coined by Russian scientist Alexander Zaitsev, who denoted the clear-cut distinction between Active SETI and METI:^[1][2]

The science known as SETI deals with searching for messages from aliens. METI deals with the creation and transmission of messages to aliens. Thus, SETI and METI proponents have quite different perspectives. SETI scientists are in a position to address only the local question “does Active SETI make sense?” In other words, would it be reasonable, for SETI success, to transmit with the object of attracting ETI’s attention? In contrast to Active SETI, METI pursues not a local and lucrative impulse, but a more global and unselfish one – to overcome the Great Silence in the Universe, bringing to our extraterrestrial neighbors the long-expected annunciation “You are not alone!”

In 2010, Douglas A. Vakoch of the SETI Institute addressed concerns about the validity of Active SETI alone as an experimental science by proposing the integration of Active SETI and Passive SETI programs to engage in a clearly articulated, ongoing, and evolving set of experiments to test various versions of the Zoo Hypothesis, including specific dates at which a first response to messages sent to particular stars could be expected.^[3]

On 13 February 2015, scientists (including Douglas Vakoch, David Grinspoon, Seth Shostak, and David Brin) at an annual meeting of the American Association for the Advancement of Science, discussed Active SETI and whether transmitting a message to possible intelligent extraterrestrials in the Cosmos was a good idea;^[4][5] That same week, a statement was released, signed by many in the SETI community including Berkeley SETI Research Center director Andrew Siemion, advocating that a "worldwide scientific, political and humanitarian discussion must occur before any message is sent".^[6] On 28 March 2015, an essay with a different point of view was written by Seth Shostak and published in the New York Times.^[7]

Rationale for METI

In the paper Rationale for METI, transmission of the information into the Cosmos is treated as one of the pressing needs of an advanced civilization. This view is not universally accepted, and it does not agree to those who are against the transmission of interstellar radio messages, but at the same time are not against SETI searching. Such duality are called The SETI Paradox.

Radio message construction

The lack of an established communications protocol is a challenge for METI.

First of all, while trying to synthesize an Interstellar Radio Message (IRM), we should bear in mind that Extraterrestrials will first deal with a physical phenomenon and, only after that, perceive the information. At first, ET's receiving system will detect the radio signal; then, the issue of extraction of the received information and comprehension of the obtained message will arise. Therefore, above all, the Constructor of an IRM should be concerned about the ease of signal determination. In other words, the signal should have maximum openness, which is understood here as an antonym of the term security. This branch of signal synthesis can be named anticryptography.

To this end, in 2010, Michael W. Busch created a general-purpose binary language,^[8] later used in the Lone Signal project^[9] to transmit crowdsourced messages to extraterrestrial intelligence.^[10] Busch developed the coding scheme and provided Rachel M. Reddick with a test message, in a blind test of decryption.^[8] Reddick decoded the entire message after approximately twelve hours of work.^[8] This was followed by an attempt to extend the syntax used in the Lone Signal hailing message to communicate in a way that, while neither mathematical nor strictly logical, was nonetheless understandable given the prior definition of terms and concepts in the hailing message.^[11]

Also characteristics of the radio signal such as wavelength, type of polarization, and modulation have to be considered.

Over galactic distances, the interstellar medium induces some scintillation effects and artificial modulation of electromagnetic signals. This modulation is higher at lower frequencies and is a function of the sky direction. Over large distances, the depth of the modulation can exceed 100%, making any METI signal very difficult to decode.

Error correction

In METI research, it is implied that any message must have some redundancy, although the exact amount of redundancy and message formats are still in great dispute.

Using ideograms, instead of binary sequence, already offers some improvement against noise resistance. In faxlike transmissions, ideograms will be spread on many lines. This increases its resistance against short bursts of noise like radio frequency interference or interstellar scintillation.

One format approach proposed for interstellar messages was to use the product of two prime numbers to construct an image. Unfortunately, this method works only if all the bits are present. As an example, the message sent by Frank Drake from the Arecibo Observatory in 1974 did not have any feature to support mechanisms to cope with the inevitable noise degradation of the interstellar medium.

Error correction tolerance rates for previous METI messages

• Arecibo Message (1974) : 8.9% (one page)
• Evpatoria message (1999) : 44% (23 separate pages)
• Evpatoria message (2003) : 46% (one page, estimated)

Examples

The 1999 Cosmic Call transmission was far from being optimal (from our terrestrial point of view) as it was essentially a monochromatic signal spiced with a supplementary information. Additionally, the message had a very small modulation index overall, a condition not viewed as being optimal for interstellar communication.

• Over the 370,967 bits (46,371 bytes) sent, some 314,239 were “1” and 56,768 were “0”—5.54 times as many 1's as 0's.
• Since frequency shift keying modulation scheme was used, most of the time the signal was on the “0” frequency.
• In addition, “0” tended to be sent in long stretches (white lines in the message).

Realized projects

These projects have targeted stars between 17 and 69 light-years from the Earth. The exception is the Arecibo message, which targeted globular cluster M13, approximately 24,000 light-years away.

The first message to reach its destination will be RuBisCo Stars, which should reach Teegarden's star, a brown dwarf in 2021.

• The Morse Message (1962)^[12]
• Arecibo message (1974)
• Cosmic Call 1 (1999)
• Teen Age Message (2001)
• Cosmic Call 2 (2003)
• Across the Universe (2008)
• A Message From Earth (2008)
• Hello From Earth (2009)
• RuBisCo Stars (2009)^[13]
• Wow! Reply (2012) ^[14]
• Lone Signal (2013)
• A Simple Response to an Elemental Message (2016)

Potential risk

Active SETI has been heavily criticized due to the perceived risk of revealing the location of the Earth to alien civilizations, without some process of prior international consultation. Notable among its critics is scientist and science fiction author David Brin, particularly in his article "expose."^[21]

However, Russian and Soviet radio engineer and astronomer Alexander L. Zaitsev has argued against these fears.^[22][23] Indeed, Zaitsev argues that we should consider the risks of not reaching out to extraterrestrial civilizations.^[24]

To lend a quantitative basis to discussions of the risks of transmitting deliberate messages from Earth, the SETI Permanent Study Group of the International Academy of Astronautics^[25] adopted in 2007 a new analytical tool, the San Marino Scale.^[26] Developed by Prof. Ivan Almar and Prof. H. Paul Shuch, the San Marino Scale evaluates the significance of transmissions from Earth as a function of signal intensity and information content. Its adoption suggests that not all such transmissions are created equal, thus each must be evaluated on a case-by-case basis before establishing blanket international policy regarding Active SETI.

In 2012, Jacob Haqq-Misra, Michael Busch, Sanjoy Som, and Seth Baum argued that while the benefits of radio communication on Earth likely outweigh the potential harms of detection by extraterrestrial watchers, the uncertainty regarding the outcome of contact with extraterrestrial beings creates difficulty in assessing whether or not to engage in long-term and large-scale METI.^[27]

In 2015, João Pedro de Magalhães proposed transmitting an invitation message to any extraterrestrial intelligences watching us already in the context of the Zoo Hypothesis and inviting them to respond. By using existing television and radio channels, de Magalhães argued this would not put us in any danger, "at least not in any more danger than we are already if much more advanced extraterrestrial civilizations are aware of us and can reach the solar system." ^[28]

Douglas Vakoch, president of METI, argues that passive SETI itself is already an endorsement of active SETI, since "If we detect a signal from aliens through a SETI program, there’s no way to prevent a cacophony of responses from Earth."^[29]

Beacon proposal

One proposal for a 10 billion watt interstellar SETI beacon was dismissed by Robert A. Freitas Jr. to be infeasible for a pre-Type I civilization on the Kardashev scale.^[30] As a result, it has been suggested that civilizations must advance into Type I before mustering the energy required for reliable contact with other civilizations.^{[citation needed]}

However, this 1980s technical argument assumes omni-directional beacons which may not be the best way to proceed on many technical grounds. Advances in consumer electronics have made possible transmitters that simultaneously transmit many narrow beams, covering the million or so nearest stars but not the spaces between.^[31] This multibeam approach can reduce the power and cost to levels that are reasonable with current mid-2000s Earth technology.

Once civilizations have discovered each other's locations, the energy requirements for maintaining contact and exchanging information can be significantly reduced through the use of highly directional transmission technologies.

In 1974, the Arecibo Observatory transmitted a message toward the then-apparent position of the M13 globular cluster about 25,000 light-years away, for example, and the use of larger antennas or shorter wavelengths would allow transmissions of the same energy to be focused on even more remote targets, such as those attempted by Active SETI.

Communication with extraterrestrial intelligence

From Wikipedia, the free encyclopedia

NASA SETI (Search for Extraterrestrial Intelligence) Microwave Observing Project sites.

Communication with extraterrestrial intelligence (a.k.a. CETI) is a branch of the search for extraterrestrial intelligence that focuses on composing and deciphering interstellar messages that theoretically, could be understood by another technological civilization.^[1] This field of study once was known as exosemiotics. The best-known CETI experiment of its kind was the 1974 Arecibo message composed by Frank Drake.

There are multiple independent organizations and individuals engaged in CETI research; the generic application of abbreviations CETI and SETI (search for extraterrestrial intelligence) in this article should not be taken as referring to any particular organization (such as the SETI Institute).

CETI research has focused on four broad areas: mathematical languages, pictorial systems such as the Arecibo message, algorithmic communication systems (ACETI), and computational approaches to detecting and deciphering "natural" language communication. There remain many undeciphered writing systems in human communication, such as Linear A, discovered by archeologists. Much of the research effort is directed at how to overcome similar problems of decipherment that arise in many scenarios of interplanetary communication.

On 13 February 2015, scientists (including Douglas Vakoch, David Grinspoon, Seth Shostak, and David Brin) at an annual meeting of the American Association for the Advancement of Science, discussed Active SETI and whether transmitting a message to possible intelligent extraterrestrials in the cosmos was a good idea.^[2][3] That same week, a statement was released, signed by many in the SETI community, that a "worldwide scientific, political, and humanitarian discussion must occur before any message is sent".^[4] On 28 March 2015, a related essay was written by Seth Shostak and published in The New York Times.^[5]

History

In the 19th century there were many books and articles about the possible inhabitants of other planets. Many people believed that intelligent beings might live on the Moon, Mars, and Venus.^{[citation needed]}

Since travel to other planets was not possible at that time, some people suggested ways to signal the extraterrestrials even before radio was discovered. Carl Friedrich Gauss^[when?] suggested that a giant triangle and three squares, the Pythagoras, could be drawn on the Siberian tundra. The outlines of the shapes would have been ten-mile-wide strips of pine forest, the interiors could be rye or wheat.

The Pythagoras

Joseph Johann Littrow^[when?] proposed using the Sahara as a blackboard. Giant trenches several hundred yards wide could delineate twenty-mile-wide shapes. Then the trenches would be filled with water, and then enough kerosene could be poured on top of the water to burn for six hours. Using this method, a different signal could be sent every night.

Meanwhile, other astronomers were looking for signs of life on other planets. In 1822, Franz von Gruithuisen thought he saw a giant city and evidence of agriculture on the moon, but astronomers using more powerful instruments refuted his claims. Gruithuisen also believed he saw evidence of life on Venus. Ashen light had been observed on Venus, and he postulated that it was caused by a great fire festival put on by the inhabitants to celebrate their new emperor. Later he revised his position, stating that the Venusians could be burning their rainforest to make more farmland.^[6]

By the late 1800s, the possibility of life on the moon was put to rest. Astronomers at that time believed in the Kant-Laplace hypothesis, which stated that the farthest planets from the sun are the oldest—therefore Mars was more likely to have advanced civilizations than Venus. It was evident that Venus was shrouded perpetually in clouds, so the Venusians probably would not be very good astronomers.^{[citation needed]} Subsequent investigations focused on contacting Martians. In 1877 Giovanni Schiaparelli announced he had discovered "canali" ("channels" in Italian, which occur naturally, and mistranslated as "canals", which are artificial) on Mars—this was followed by thirty years of Mars enthusiasm.^{[citation needed]}

The inventor Charles Cros was convinced that pinpoints of light observed on Mars and Venus were the lights of large cities. He spent years of his life trying to get funding for a giant mirror with which to signal the Martians. The mirror would be focused on the Martian desert, where the intense reflected sunlight could be used to burn figures into the Martian sand.^{[citation needed]}

Inventor Nikola Tesla mentioned many times during his career that he thought his inventions such as his Tesla coil, used in the role of a "resonant receiver", could communicate with other planets,^[7][8] and that he even had observed repetitive signals of what he believed were extraterrestrial radio communications coming from Venus or Mars in 1899. These "signals" turned out to be terrestrial radiation, however.

Around 1900, the Guzman Prize was created; the first person to establish interplanetary communication would be awarded 100,000 francs under one stipulation: Mars was excluded because Madame Guzman thought communicating with Mars would be too easy to deserve a prize.^[9]

Eventually the Martian canals proved illusory.

Mathematical and scientific languages

Lincos (Lingua cosmica)

Published in 1960 by Hans Freudenthal, Lincos: Design of a Language for Cosmic Intercourse, expands upon Astraglossa to create a general-purpose language derived from basic mathematics and logic symbols.^[10] Several researchers have expanded further upon Freudenthal's work. A dictionary resembling Lincos was featured in the Carl Sagan novel Contact and film adaptation.

Astraglossa

Published in 1963 by Lancelot Hogben, "Astraglossa" is an essay describing a system for combining numbers and operators in a series of short and long pulses. In Hogben's system, short pulses represent numbers, while trains of long pulses represent symbols for addition, subtraction, etc.^[11]

Carl Sagan

In the 1985 science fiction novel Contact, Carl Sagan explored in some depth how a message might be constructed to allow communication with an alien civilization, using prime numbers as a starting point, followed by various universal principles and facts of mathematics and science.

Sagan also edited a nonfiction book on the subject.^[12] An updated collection of articles on the same topic was published in 2011.^[13]

Arrival (film)

In 2016, McGill University Linguistics Professor, Jessica Coon, spoke with Business Insider about how 2016 sci-fi blockbuster, Arrival, properly portrayed how humans might actually communicate with aliens.^[14] To create this language, film producers consulted with Wolfram Research Founder and CEO, Stephen Wolfram - creator of the computer programming language known as the Wolfram Language - and his son, Christopher. Together, they helped analyze approximately 100 logograms that ultimately served as the basis for the alien language utilized throughout the film. This work, along with many other thoughts with regard to artificial intelligence communication has been documented in an interview published by Space.com.^[15] During production, Wolfram's personal copy of Lincos: Design of a Language for Cosmic Intercourse was also on set.

A language based on the fundamental facts of science

Published in 1992 by Carl Devito and Richard Oehrle, A language based on the fundamental facts of science is a paper describing a language similar in syntax to Astraglossa and Lincos, but which builds its vocabulary around known physical properties.^[16]

Busch general-purpose binary language used in Lone Signal transmissions

In 2010, Michael W. Busch created a general-purpose binary language ^[17] later used in the Lone Signal project^[18] to transmit crowdsourced messages to extraterrestrial intelligence (METI). This was followed by an attempt to extend the syntax used in the Lone Signal hailing message to communicate in a way that, while neither mathematical nor strictly logical, was nonetheless understandable given the prior definition of terms and concepts in the Lone Signal hailing message.^[19]

Name	Designation	Constellation	Date sent	Arrival date	Message
Gliese 526	HD 119850	Boötes	July 10, 2013	2031	Lone Signal

Pictorial messages

Pictorial communication systems seek to describe fundamental mathematical or physical concepts via simplified diagrams sent as bitmaps. These messages presume that the recipient has similar visual capabilities and can understand basic mathematics and geometry. A common critique of these systems is that they presume a shared understanding of special shapes, which may not be the case with a species with substantially different vision, and therefore a different way of interpreting visual information. For instance, an arrow representing the movement of some object could be interpreted as a weapon firing.

Pioneer probes

The two Pioneer plaques were launched on Pioneer 10 and Pioneer 11 in 1972 and 1973, depicting the location of the Earth in the galaxy and the solar system, and the form of the human body.

Voyager probes

Launched in 1977, the Voyager probes carried two golden records that were inscribed with diagrams depicting the human form, our solar system, and its location. Also included were recordings of images and sounds from Earth.

The Arecibo message

The Arecibo message, transmitted in 1974, was a 1679 pixel image with 73 rows and 23 columns. It shows the numbers one through ten, the atomic numbers of hydrogen, carbon, nitrogen, oxygen, and phosphorus, the formulas for the sugars and bases in the nucleotides of DNA, the number of nucleotides in DNA, the double helix structure of DNA, a figure of a human being and its height, the population of Earth, a diagram of our solar system, and an image of the Arecibo telescope with its diameter.

Cosmic Call messages

The Cosmic Call messages consisted of a few digital sections - "Rosetta Stone", copy of Arecibo Message, Bilingual Image Glossary, the Braastad message, as well as text, audio, video, and other image files submitted for transmission by everyday people around the world. The "Rosetta Stone" was composed by Stephane Dumas and Yvan Dutil and represents a multi-page bitmap that builds a vocabulary of symbols representing numbers and mathematical operations. The message proceeds from basic mathematics to progressively more complex concepts, including physical processes and objects (such as a hydrogen atom). The message is designed with a noise resistant format and characters that make it resistant to alteration by noise. These messages were transmitted in 1999 and 2003 from Evpatoria Planetary Radar under scientific guidance of Alexander L. Zaitsev. Richard Braastad coordinated the overall project.

Star systems to which messages were sent, are the following:^[20]

Name	Designation HD	Constellation	Date sent	Arrival date	Message
16 Cyg A	HD 186408	Cygnus	May 24, 1999	November 2069	Cosmic Call 1
15 Sge	HD 190406	Sagitta	June 30, 1999	February 2057	Cosmic Call 1
	HD 178428	Sagitta	June 30, 1999	October 2067	Cosmic Call 1
Gl 777	HD 190360	Cygnus	July 1, 1999	April 2051	Cosmic Call 1
	Hip 4872	Cassiopeia	July 6, 2003	April 2036	Cosmic Call 2
	HD 245409	Orion	July 6, 2003	August 2040	Cosmic Call 2
55 Cnc	HD 75732	Cancer	July 6, 2003	May 2044	Cosmic Call 2
	HD 10307	Andromeda	July 6, 2003	September 2044	Cosmic Call 2
47 UMa	HD 95128	Ursa Major	July 6, 2003	May 2049	Cosmic Call 2

Multi-modal messages

Teen-Age Message

The Teen-Age Message, composed by Russian scientists (Zaitsev, Gindilis, Pshenichner, Filippova) and teens, was transmitted from the 70-m dish of Evpatoria Deep Space Center to six star systems resembling that of the Sun on August 29 and September 3 and 4, 2001. The message consists of three parts:

Section 1 represents a coherent-sounding radio signal with slow Doppler wavelength tuning to imitate transmission from the Sun's center. This signal was transmitted in order to help extraterrestrials detect the TAM and diagnose the radio propagation effect of the interstellar medium.

Section 2 is analog information representing musical melodies performed on the theremin. This electric musical instrument produces a quasi-monochromatic signal, which is easily detectable across interstellar distances. There were seven musical compositions in the First Theremin Concert for Aliens. The 14-minute analog transmission of the theremin concert would take almost 50 hours by digital means; see The First Musical Interstellar Radio Message.

Section 3 represents a well-known Arecibo-like binary digital information: the logotype of the TAM, bilingual Russian and English greeting to aliens, and image glossary.

Star systems to which the message was sent are the following:^[20]

Name	HD designation	Constellation	Date sent	Arrival date
	197076	Delphinus	August 29, 2001	February 2070
47 UMa	95128	Ursa Major	September 3, 2001	July 2047
37 Gem	50692	Gemini	September 3, 2001	December 2057
	126053	Virgo	September 3, 2001	January 2059
	76151	Hydra	September 4, 2001	May 2057
	193664	Draco	September 4, 2001	January 2059

Cosmic Call 2 (Cosmic Call 2003) message

The Cosmic Call-2 message contained text, images, video, music, the Dutil/Dumas message, a copy of the 1974 Arecibo message, BIG = Bilingual Image Glossary, the AI program Ella, and the Braastad message.

Algorithmic messages

Algorithmic communication systems are a relatively new field within CETI. In these systems, which build upon early work on mathematical languages, the sender describes a small set of mathematic and logic symbols that form the basis for a rudimentary programming language that the recipient can run on a virtual machine. Algorithmic communication has a number of advantages over static pictorial and mathematical messages,^{[citation needed]} including: localized communication (the recipient can probe and interact with the programs within a message, without transmitting a reply to the sender and then waiting years for a response), forward error correction (the message might contain algorithms that process data elsewhere in the message), and the ability to embed proxy agents within the message. In principle, a sophisticated program when run on a fast enough computing substrate, may exhibit complex behavior and perhaps, intelligence.

CosmicOS

CosmicOS, designed by Paul Fitzpatrick at MIT, describes a virtual machine that is derived from lambda calculus.

Logic Gate Matrices

Logic Gate Matrices (a.k.a. LGM), developed by Brian McConnell, describes a universal virtual machine that is constructed by connecting coordinates in an n-dimensional space via mathematics and logic operations, for example: (1,0,0) <-- an="" arbitrarily="" as="" be="" class="noprint Inline-Template" complex="" computing="" describe="" executed="" instructions="" it.="" may="" method="" on="" one="" style="margin-left: 0.1em; white-space: nowrap;" substrate="" sup="" the="" this="" to="" using="" well="">[clarification needed]

Natural language messages

This research focuses on the event that we receive a signal or message that is either not directed at us (eavesdropping) or one that is in its natural communicative form. To tackle this difficult, but probable scenario, methods are being developed that first, will detect if a signal has structure indicative of an intelligent source, categorize the type of structure detected, and then decipher its content: from its physical level encoding and patterns to the parts-of-speech that encode internal and external ontologies.^[21][22]

Primarily, this structure modeling focuses on the search for generic human and inter-species language universals to devise computational methods by which language may be discriminated from non-language and core structural syntactic elements of unknown languages may be detected.^[23] Aims of this research include: contributing to the understanding of language structure and the detection of intelligent language-like features in signals, to aid the search for extraterrestrial intelligence.^[24][25]

The problem goal is therefore to separate language from non-language without dialogue, and learn something about the structure of language in the passing. The language may not be human (animals, aliens, computers...), the perceptual space may be unknown, and we cannot presume human language structure, but must begin somewhere. We need to approach the language signal from a naive viewpoint, in effect, increasing our ignorance and assuming as little as possible.^[26][27]

If a sequence can be tokenized, that is, separated into "words", an unknown human language may be distinguished from many other data sequences by the frequency distribution of the tokens. Human languages conform to a Zipfian distribution, while many (but not all) other data sequences do not. It has been proposed that an alien language also might conform to such a distribution (^[26]). When displayed in a log-log graph of frequency vs. rank, this distribution would appear as a somewhat straight line with a slope of approximately -1. SETI scientist Laurance Doyle explains that the slope of a line that represents individual tokens in a stream of tokens may indicate whether the stream contains linguistic or other structured content. If the line angles at 45°, the stream contains such content. If the line is flat, it does not.^[28][29]

SETI researchers

• Frank Drake (SETI Institute): SETI pioneer, composed the Arecibo message.
• Dr John Elliott (SETI Research UK): research into developing strategies, which are based on receiving a 'natural' language message, that look at developing algorithms to detect if an ET signal has intelligent-like structure and if so, then how to decipher its content. Author of many papers in this area and a contributor to SETI's book on interstellar communication. Other contributions include message design and construction; member of: International Academy of Astronautics, SETI Permanent Study Group; International Task Group for the Post-detection identification of unknown radio signals.^{[21][22][23][24][25][26][27]}
• Laurence Doyle (SETI Institute): studies animal communication, and has developed statistical measures of complexity in animal utterances as well as human language.
• Stephane Dumas: developed Cosmic Call messages, as well as a general technique for generating 2-D symbols that remain recognizable even if corrupted by noise.
• Yvan Dutil: developed Cosmic Call messages with Stephane Dumas.
• Paul Fitzpatrick (MIT): developed CosmicOS system based on lambda calculus
• Brian McConnell: developed framework for algorithmic communication systems (ACETI) from 2000-2002.
• Marvin Minsky (MIT AI researcher): Believes that aliens may think similarly to humans because of shared constraints, permitting communication.^[30] First proposed the idea of including algorithms within an interstellar message.
• Carl Sagan (deceased): co-authored the Arecibo message and was heavily involved in SETI throughout his life.
• Douglas Vakoch (METI): studies CETI and has published numerous articles, as well as an upcoming book from MIT Press about interstellar communication.
• Alexander Zaitsev (IRE, Russia): composed Teen Age Message with Boris Pshenichner, Lev Gindilis, Lilia Filippova, et al., composed Bilingual Image Glossary for Cosmic Call 2003 Message, Scientific Manager of transmitting from Evpatoria Planetary Radar the Cosmic Call 1999, the Teen Age Message 2001, and the Cosmic Call 2003, Scientific consultant for A Message From Earth project.,^{[31][32][33][34]}
• Michael W. Busch: (Lone Signal) created the binary encoding system for the ongoing Lone Signal hailing message.
• Jacob Haqq Misra: (Lone Signal) is the chief science officer for the ongoing Lone Signal active SETI project.

Connections with Interspecies Communication

John C. Lilly worked on teaching dolphins English (successful with rhythms, not with understandability, given their different mouth/blowhole shapes) and identifying whether extraterrestrial signals contain communication.

Laurance Doyle compares the complexity of cetacean and human languages to help determine whether specific signal from space is complex enough to represent a message that needs to be decoded.

Brenda McCowan studies signal complexity of humpback whales and extraterrestrial signals.

Robert Freitas has used density of brain processing (Sentience Quotient) to compare the difficulty of communicating with animals, including cetaceans, and extraterrestrials.

Self-explanatory languages such as Lincos have been tried with radio waves to extraterrestrials, but not sound waves or other signals on earth. They presume recipients patient enough to analyze repetitive mathematical signals in order to understand the content, and may presume note-taking ability based upon things such as opposable thumbs.