- Email: [email protected]
An iconic approach to communicating musical concepts in interstellar messages
Acta Astronautica 67 (2010) 1406–1409
Contents lists available at ScienceDirect
Acta Astronautica journal homepage: www.elsevier.com/locate/actaastro
An iconic approach to communicating musical concepts in interstellar messages Douglas A. Vakoch a,b, a b
Department of Clinical Psychology, California Institute of Integral Studies, 1453 Mission Street, San Francisco, CA 94103, USA Center for SETI Research, SETI Institute, 515 North Whisman Road, Mountain View, CA 94043, USA
a r t i c l e i n f o
abstract
Article history: Received 21 February 2009 Accepted 6 January 2010 Available online 27 January 2010
Some characteristics of terrestrial music may be meaningful to extraterrestrial civilizations by virtue of the connection between acoustics and mathematics—both of which might be known by technologically advanced extraterrestrial intelligence. For example, a fundamental characteristic of terrestrial polyphonic music is found the number of tones used various scales, insofar as the number of tones represents a compromise between competing musical demands; the number of tones in a scale, however, also reflects some of the perceptual characteristics of the species developing that music. Thus, in the process of communicating something about the structure of terrestrial music through interstellar messages, additional information about human perceptual and cognitive processes can also be conveyed. This paper also discusses methods for sending signals that bear information through the form of the very frequencies in which the signals are transmitted. If the challenges of creating intelligible messages are greater than often thought, the advantage of reduced conventionality of encoding the message by using an iconic format of this sort may be of significant value. Such an approach would allow the incremental introduction of musical concepts, somewhat akin to the step-by-step tutorials in mathematics and logic that form the basis of Freudenthal’s Lincos. & 2010 Elsevier Ltd. All rights reserved.
Keywords: Search for Extraterrestrial Intelligence SETI Interstellar communication Interstellar messages Interstellar music Universal music Polyphonic music Iconicity Cognitive modeling of music
1. Introduction Some proposals for interstellar messages have begun with systematic expositions of presumably universal mathematical and scientific concepts in an incremental manner from simple to complex. Indeed, the flexibility of this approach is suggested by Freudenthal’s Lincos, which progresses from basic arithmetic to discuss such varied notions as time, space, and human behavior [2]. In the current paper, an analogous approach based on a step-bystep exposition of basic principles is suggested as a means Corresponding author. Department of Clinical Psychology, California Institute of Integral Studies, 1453 Mission Street, San Francisco, CA 94103, USA. Tel.: + 1 415 575 6244; fax: +1 415 575 1266. E-mail addresses: [email protected], [email protected].
0094-5765/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2010.01.006
of constructing messages that bear structural similarities to terrestrial music, in the process reflecting something about the perceptual and cognitive nature of the composers of that music. Perhaps the most widely known example of the use of music for interstellar communication is the Voyager recording, which contains encoded images, sounds, and music of Earth. Although the primary intended audience of this recording was terrestrial, this effort at expanding people’s ideas of how we might communicate over interstellar distances also attempted to provide clues that might enable any extraterrestrial intelligence that intercepts the recording in the distant future to begin to understand its content. For example, the recording’s introduction to the actual musical selections was made via pictorial images of the sort of instruments used to play the music, as well as
D.A. Vakoch / Acta Astronautica 67 (2010) 1406–1409
a graphic representation of the musical score. The hope was that this would provide clues to help the recipients comprehend how the music was physically produced. The suggestion of using music to communicate with intelligence beyond Earth has a much longer history than the Voyager recordings. The 17th-century European genre of the imaginary voyage provided a context for exploring a variety of contemporary proposals for universal language schemes. For example, the English prelate Francis Godwin described a voyage to the Moon, in which the terrestrial adventurer encountered strange lunarians who communicated through a musical language. The inspiration for this tonal language, however, was thoroughly terrestrial—based on the Chinese language as described by Jesuit missionaries recently returned to Europe. In the case of Godwin’s lunar ‘‘language,’’ the musical system was actually simply a method for translating letters of the alphabet into particular musical notes. However, it did preview more truly universal language proposals of the next two centuries [3]. But would music really be intelligible to intelligent beings evolved independently of humans on other planets? Are the mathematical and acoustical foundations of terrestrial music sufficient to provide a basis for interstellar communication?
2. Universal scales? The astronomer Sebastian von Hoerner provided one argument in favor of the possible universality of at least some aspects of music. He posited that if extraterrestrial intelligence had indeed developed music, the form of this music might share certain features with terrestrial music [12]. Particularly interesting is his analysis of the number of notes in musical scales. Von Hoerner suggested that the use of a 12-tone scale in Western music is not completely arbitrary. Rather, this number of notes yields one of only a handful of possibilities for a workable foundation for polyphonic music. Specifically, polyphonic music must meet two competing demands, which always entails a compromise. First, an octave needs to be divisible into equal parts to allow for modulations from one key to another. Second, the tones corresponding to these divisions should have harmonic frequency ratios to one another. Any attempt to satisfy both of these conditions, however, requires some compromise. Equal intervals do not provide exactly harmonic tones, thus one must be content with relatively close matches that use only some of all possible harmonics. For example, classical Western music uses a 12-tone scale that allows for 5 harmonics. But according to von Hoerner, a 12-tone scale does not exhaust the ‘‘good compromises’’ for polyphonic music. One might also use a 31-tone scale or a 5-tone scale. The choice among these scales might provide a clue about the sensory functioning of the intelligence using these scales. Those beings with more sensitive auditory processing than humans might make use of the finer divisions of the 31-tone scale. In contrast, extraterrestrials with less sensitive auditory systems may be more likely to use a mere 5 tones. While the choice between scales may not be
1407
dictated by biology (as suggested by the existence of 5tone, 12-tone, and 31-tone scales among human cultures), sensory apparatus may sometimes restrict the range of a species’ musical scales. 3. A didactic approach As noted above, the recordings onboard the Voyager spacecraft included musical selections, which were drawn from a range of terrestrial cultures. The hope of the recordings’ creators was that the structure of the music might be intelligible to extraterrestrials because of universal characteristics of the music. The present paper assumes a more skeptical stance and suggests that music as experienced by humans may need to be taught in order to be intelligible to extraterrestrials. Previous proposals for interstellar messages have suggested beginning a message with a primer based on basic mathematics and science, which any civilization capable of radio communication is anticipated to have in common with us [1,2,4]. Similarly, one could start to communicate terrestrial ideas about music by initially presenting an essential ‘‘vocabulary’’ and ‘‘syntax’’ of music. There are many possible ways to construct such introductory primers, in part dependent on what are assumed to be the as the essential elements of musical expression. For example, to describe some of our notions of music, we might communicate features such as pitch, dynamics, tone color, and duration. Such a tutorial might initially isolate individual components of musical expression in a somewhat artificial manner, only later introducing their complex interactions as heard in fully developed music. In most discussions of interstellar messages, one of the most fundamental differences between the interstellar composition and traditional forms of art created for human audiences is overlooked. The actual physical medium of radio waves through which interstellar messages are conveyed is at frequencies beyond the range of human sight or hearing. In contrast, the medium of traditional art is directly perceptible to humans. While the signals bearing interstellar messages can be transduced into a range that is perceptible to humans, in their raw forms, such signals are invisible, inaudible, and intangible to a human audience. Although the electromagnetic signals used to convey interstellar music may be imperceptible to beings on either end, nevertheless, aspects of music can be conveyed very directly in physical properties of the signals that can be measured accurately by instrumentation. For example, like music, interstellar signals are of a specific frequency that can vary over time. If desired, such signals could be modulated, directly conveying our notions of rhythm and melody, ‘‘for example, if we want to communicate something about rhythm, we should rhythmically vary the signal itself’’ [11]. 4. Cognitive modeling Messages using this didactic approach can be based on an expressly cognitive model of human music perception,
1408
D.A. Vakoch / Acta Astronautica 67 (2010) 1406–1409
which has several advantages: a cognitive model is empirically testable, it may be linked to parallel messages providing an account of human perception and cognition, and it provides multiple levels at which decryption might occur [6]. By illustrating progressively more complex rules that specify how terrestrial musical melodies are generated, and by doing so through radio signals that directly mimic these melodies, extraterrestrials are presented with two means of understanding human music perception. First, extraterrestrials may be able to comprehend the musical content we attempt to convey, because they can follow our intended ‘‘chain of reasoning,’’ or in this case, the ‘‘musical tutorial.’’ However, if they cannot comprehend this content as an artistic expression, they may still be able to infer something about our cognitive and perceptual systems based on the patterning of the message we send. Thus, even without comprehending the musical intent of such a message, the recipients might gain some understanding of human information-processing capabilities, because we are providing a message that is meant to describe our cognitive processes, by making the form of the message reflect these capabilities. This is an extension of the author’s earlier proposal that the form of the message should reflect its meaning [9].
5. A direct approach Some of the structural characteristics of music – temporal modulations of transmissions at precise frequencies – can be used to communicate basic scientific information [7]. One critique of prior suggestions for interstellar messages is that these messages often rely on conventions of representation that may be unique to a single species’ model of the physical universe. This criticism does not call into question the actual existence of physical reality. Rather, it points out that one species’ conceptualizations and theoretical models about reality may not necessarily be readily comprehensible by a species relying on very different models—even though the two species may be studying the same underlying reality [10]. For instance, pictorial representations of atoms might rely on the Bohr model, in which electrons circle the atom’s nucleus much like planets orbit a star. Nevertheless, this is only one way of representing atomic structure, and it is not immediately obvious that even other species with advanced knowledge of chemistry will use models that are directly commensurable with ours [9]. One potential solution to the above problem would be to attempt to communicate our concepts of chemistry through signals that directly mimic physical phenomena related to the chemical concepts we are conveying [7]. For example, one might transmit electromagnetic signals at frequencies corresponding to some subset of those spectral lines that are uniquely associated with energy emissions from certain chemical elements. Thus, a hydrogen atom might be represented more directly by signaling at some of the frequencies at which this element naturally emits. These frequencies may be rather far from each another, so the actual process of transmission might involve starting with a single frequency and slowly
drifting the signal to another frequency associated with the emission spectrum of that element. Following this approach, one could transmit for awhile at each frequency of a characteristic emission line, then move on to the next target frequency until each has been transmitted. Given the wide range of frequencies accessible to some radio telescopes, a significant range of chemical concepts could be communicated in this manner. For example, the SETI Institute’s Allen Telescope Array covers a range of 4.5 octaves, with frequencies ranging between 0.5 and 11.2 GHz. Once we are able to convey individual chemical constituents, we might then describe the process by which these constituents combine to form more complex molecules. Since the early days of the search for extraterrestrial intelligence (SETI), astronomers have suggested searching at or near frequencies associated with strong emission lines of the constituents of water—hydrogen (H + ) and hydroxyl (OH ). Although frequencies associated with hydrogen and hydroxyl emission spectra have often been suggested as ‘‘magic frequencies’’ to help narrow searches – with some advocating searches within the ‘‘water hole’’ that spans the range of frequencies between 1420 and 1640 MHz – others have not suggested using these frequencies as icons of the constituents themselves. To see how we might represent iconically the chemical equation H + +OH -H2O in an interstellar message, consider Fig. 1. At the left side of the figure, a transmission at or near the hydrogen line (1420 MHz) appears, and as time passes (moving from left to right in the figure), this first signal is joined by another signal sent at the frequency associated with the strongest hydroxyl line (1640 MHz). After each of these two signals is well established, additional signals slowly drift away from the hydrogen and hydroxyl lines, combining at the frequency associated with the 22 GHz water maser line. The intended message is that hydrogen and hydroxyl combine to form water. As an alternative to the transmission represented in Fig. 1, one might simply have the transmissions at 1420 and 1640 MHz end, and immediately begin a transmission at 22 GHz. Given rapid advances in technology, it is
Fig. 1. An iconic interstellar message representing the combination of hydrogen and hydroxyl to form water (H + +OH -H2O).
D.A. Vakoch / Acta Astronautica 67 (2010) 1406–1409
reasonable to assume that this entire range of frequencies could be detected by even rudimentary technological civilizations with radio telescopes. For example, a modest expansion of the existing Allen Telescope Array would make narrowband signals detectable within this entire frequency range. A process analogous to that used to describe chemical concepts could also be used to communicate musical concepts. Though the initial form of the message might focus on basic parameters of music, eventually one might transmit at multiple frequencies, creating a sort of ‘‘interstellar symphony’’ [8], with the frequencies of the signals having the kind of relationship to one another identified by von Hoerner for well-tempered polyphonic music. This approach would mark a significant shift from the traditional approach that messages should be encoded in a form that bears no direct relationship to the content of the message. While the traditional procedure may be efficient from an information theoretic perspective, it does not take into account that the process of decoding such messages may be significantly more challenging than typically anticipated. As noted above, the particular form of the musical tutorial might provide information about the cognitive functioning of a species [6]. For instance, Narmour has posited that as humans begin to hear even very few notes played sequentially, they begin to form strong anticipations of the sort of tones that are likely to follow [5]. One of the parameters that influence these anticipations is the size of the intervals between notes (from a relatively small interval—yielding notes ‘‘close together,’’ to relatively large intervals—resulting in notes ‘‘far apart’’). Similarly, the parameter of direction of pitch (increasing, decreasing, or remaining stable) can create expectations about subsequent notes. By structuring a musical primer to reflect such ‘‘cognitive primitives’’ of music perception as interval size and pitch direction, one could introduce a basic vocabulary that reflects both components of music and parameters of human auditory perception. By conveying this information directly in the form of the electromagnetic signal, clues would be provided about our intended meaning as well as about the senders of the message, all in a form that may be
1409
more intelligible than many previously proposed formats for interstellar communication.
Acknowledgments The author gratefully acknowledges the following support of this research: The John Templeton Foundation, though its Grant #1840, ‘‘Construction of Interstellar Messages Describing the Evolution of Altruistic Behavior;’’ President Joseph Subbiondo, Academic Vice President Judie Wexler, and Clinical Psychology Department Chair Katie McGovern of the California Institute of Integral Studies for sabbatical and ongoing research leaves; CEO Thomas Pierson and Director of SETI Research Jill Tarter of the SETI Institute for support of research on SETI and Society; and Jamie Baswell, as well as Harry and Joyce Letaw, for financial support through the SETI Institute’s Adopt a Scientist program. References [1] C.L. DeVito, Languages, science and the search for extraterrestrial intelligence, Leonardo 25 (1992) 13–16. [2] H. Freudenthal, Lincos: Design of a Language for Cosmic Intercourse; Part I, North-Holland, Amsterdam, 1960. [3] J. Knowlson, Universal Language Schemes in England and France 1600–1800, University of Toronto Press, Toronto, 1975. [4] P. Morrison, Interstellar communication, in: A.G.W. Cameron (Ed.), Interstellar Communication: A Collection of Reprints and Original Contributions, W. A. Benjamin, New York, 1963. [5] E. Narmour, The Analysis and Cognition of Basic Melodic Structures: The Implication-Realization Model, University of Chicago Press, Chicago, 1990. [6] D.A. Vakoch, Cognitive modeling of music perception as a foundation for interstellar message composition. Paper IAA-00-IAA.9.2.10 presented at the SETI: Interdisciplinary Connections Review Meeting, 51st International Astronautical Congress, Rio de Janeiro, Brasil, October 2000. [7] D.A. Vakoch, An iconic approach to communicating chemical concepts to extraterrestrials, SPIE Proceedings 2704 (1996) 140–149. [8] D.A. Vakoch, The music of the spheres, Sky & Space 11 (3) (1998) 24. [9] D.A. Vakoch, Signs of life beyond Earth: a semiotic analysis of interstellar messages, Leonardo 31 (1998) 313–319. [10] D.A. Vakoch, Technology as a manifestation of intelligence: does shared technology imply shared science and mathematics? [Abstract.], Astrobiology 8 (2) (2008) 391. [11] D.A. Vakoch, To the stars, silently, Leonardo 37 (2004) 265. [12] S. von Hoerner, Universal music?, Psychology of Music 2 (1974) 18–28.
Contents lists available at ScienceDirect
Acta Astronautica journal homepage: www.elsevier.com/locate/actaastro
An iconic approach to communicating musical concepts in interstellar messages Douglas A. Vakoch a,b, a b
Department of Clinical Psychology, California Institute of Integral Studies, 1453 Mission Street, San Francisco, CA 94103, USA Center for SETI Research, SETI Institute, 515 North Whisman Road, Mountain View, CA 94043, USA
a r t i c l e i n f o
abstract
Article history: Received 21 February 2009 Accepted 6 January 2010 Available online 27 January 2010
Some characteristics of terrestrial music may be meaningful to extraterrestrial civilizations by virtue of the connection between acoustics and mathematics—both of which might be known by technologically advanced extraterrestrial intelligence. For example, a fundamental characteristic of terrestrial polyphonic music is found the number of tones used various scales, insofar as the number of tones represents a compromise between competing musical demands; the number of tones in a scale, however, also reflects some of the perceptual characteristics of the species developing that music. Thus, in the process of communicating something about the structure of terrestrial music through interstellar messages, additional information about human perceptual and cognitive processes can also be conveyed. This paper also discusses methods for sending signals that bear information through the form of the very frequencies in which the signals are transmitted. If the challenges of creating intelligible messages are greater than often thought, the advantage of reduced conventionality of encoding the message by using an iconic format of this sort may be of significant value. Such an approach would allow the incremental introduction of musical concepts, somewhat akin to the step-by-step tutorials in mathematics and logic that form the basis of Freudenthal’s Lincos. & 2010 Elsevier Ltd. All rights reserved.
Keywords: Search for Extraterrestrial Intelligence SETI Interstellar communication Interstellar messages Interstellar music Universal music Polyphonic music Iconicity Cognitive modeling of music
1. Introduction Some proposals for interstellar messages have begun with systematic expositions of presumably universal mathematical and scientific concepts in an incremental manner from simple to complex. Indeed, the flexibility of this approach is suggested by Freudenthal’s Lincos, which progresses from basic arithmetic to discuss such varied notions as time, space, and human behavior [2]. In the current paper, an analogous approach based on a step-bystep exposition of basic principles is suggested as a means Corresponding author. Department of Clinical Psychology, California Institute of Integral Studies, 1453 Mission Street, San Francisco, CA 94103, USA. Tel.: + 1 415 575 6244; fax: +1 415 575 1266. E-mail addresses: [email protected], [email protected].
0094-5765/$ - see front matter & 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.actaastro.2010.01.006
of constructing messages that bear structural similarities to terrestrial music, in the process reflecting something about the perceptual and cognitive nature of the composers of that music. Perhaps the most widely known example of the use of music for interstellar communication is the Voyager recording, which contains encoded images, sounds, and music of Earth. Although the primary intended audience of this recording was terrestrial, this effort at expanding people’s ideas of how we might communicate over interstellar distances also attempted to provide clues that might enable any extraterrestrial intelligence that intercepts the recording in the distant future to begin to understand its content. For example, the recording’s introduction to the actual musical selections was made via pictorial images of the sort of instruments used to play the music, as well as
D.A. Vakoch / Acta Astronautica 67 (2010) 1406–1409
a graphic representation of the musical score. The hope was that this would provide clues to help the recipients comprehend how the music was physically produced. The suggestion of using music to communicate with intelligence beyond Earth has a much longer history than the Voyager recordings. The 17th-century European genre of the imaginary voyage provided a context for exploring a variety of contemporary proposals for universal language schemes. For example, the English prelate Francis Godwin described a voyage to the Moon, in which the terrestrial adventurer encountered strange lunarians who communicated through a musical language. The inspiration for this tonal language, however, was thoroughly terrestrial—based on the Chinese language as described by Jesuit missionaries recently returned to Europe. In the case of Godwin’s lunar ‘‘language,’’ the musical system was actually simply a method for translating letters of the alphabet into particular musical notes. However, it did preview more truly universal language proposals of the next two centuries [3]. But would music really be intelligible to intelligent beings evolved independently of humans on other planets? Are the mathematical and acoustical foundations of terrestrial music sufficient to provide a basis for interstellar communication?
2. Universal scales? The astronomer Sebastian von Hoerner provided one argument in favor of the possible universality of at least some aspects of music. He posited that if extraterrestrial intelligence had indeed developed music, the form of this music might share certain features with terrestrial music [12]. Particularly interesting is his analysis of the number of notes in musical scales. Von Hoerner suggested that the use of a 12-tone scale in Western music is not completely arbitrary. Rather, this number of notes yields one of only a handful of possibilities for a workable foundation for polyphonic music. Specifically, polyphonic music must meet two competing demands, which always entails a compromise. First, an octave needs to be divisible into equal parts to allow for modulations from one key to another. Second, the tones corresponding to these divisions should have harmonic frequency ratios to one another. Any attempt to satisfy both of these conditions, however, requires some compromise. Equal intervals do not provide exactly harmonic tones, thus one must be content with relatively close matches that use only some of all possible harmonics. For example, classical Western music uses a 12-tone scale that allows for 5 harmonics. But according to von Hoerner, a 12-tone scale does not exhaust the ‘‘good compromises’’ for polyphonic music. One might also use a 31-tone scale or a 5-tone scale. The choice among these scales might provide a clue about the sensory functioning of the intelligence using these scales. Those beings with more sensitive auditory processing than humans might make use of the finer divisions of the 31-tone scale. In contrast, extraterrestrials with less sensitive auditory systems may be more likely to use a mere 5 tones. While the choice between scales may not be
1407
dictated by biology (as suggested by the existence of 5tone, 12-tone, and 31-tone scales among human cultures), sensory apparatus may sometimes restrict the range of a species’ musical scales. 3. A didactic approach As noted above, the recordings onboard the Voyager spacecraft included musical selections, which were drawn from a range of terrestrial cultures. The hope of the recordings’ creators was that the structure of the music might be intelligible to extraterrestrials because of universal characteristics of the music. The present paper assumes a more skeptical stance and suggests that music as experienced by humans may need to be taught in order to be intelligible to extraterrestrials. Previous proposals for interstellar messages have suggested beginning a message with a primer based on basic mathematics and science, which any civilization capable of radio communication is anticipated to have in common with us [1,2,4]. Similarly, one could start to communicate terrestrial ideas about music by initially presenting an essential ‘‘vocabulary’’ and ‘‘syntax’’ of music. There are many possible ways to construct such introductory primers, in part dependent on what are assumed to be the as the essential elements of musical expression. For example, to describe some of our notions of music, we might communicate features such as pitch, dynamics, tone color, and duration. Such a tutorial might initially isolate individual components of musical expression in a somewhat artificial manner, only later introducing their complex interactions as heard in fully developed music. In most discussions of interstellar messages, one of the most fundamental differences between the interstellar composition and traditional forms of art created for human audiences is overlooked. The actual physical medium of radio waves through which interstellar messages are conveyed is at frequencies beyond the range of human sight or hearing. In contrast, the medium of traditional art is directly perceptible to humans. While the signals bearing interstellar messages can be transduced into a range that is perceptible to humans, in their raw forms, such signals are invisible, inaudible, and intangible to a human audience. Although the electromagnetic signals used to convey interstellar music may be imperceptible to beings on either end, nevertheless, aspects of music can be conveyed very directly in physical properties of the signals that can be measured accurately by instrumentation. For example, like music, interstellar signals are of a specific frequency that can vary over time. If desired, such signals could be modulated, directly conveying our notions of rhythm and melody, ‘‘for example, if we want to communicate something about rhythm, we should rhythmically vary the signal itself’’ [11]. 4. Cognitive modeling Messages using this didactic approach can be based on an expressly cognitive model of human music perception,
1408
D.A. Vakoch / Acta Astronautica 67 (2010) 1406–1409
which has several advantages: a cognitive model is empirically testable, it may be linked to parallel messages providing an account of human perception and cognition, and it provides multiple levels at which decryption might occur [6]. By illustrating progressively more complex rules that specify how terrestrial musical melodies are generated, and by doing so through radio signals that directly mimic these melodies, extraterrestrials are presented with two means of understanding human music perception. First, extraterrestrials may be able to comprehend the musical content we attempt to convey, because they can follow our intended ‘‘chain of reasoning,’’ or in this case, the ‘‘musical tutorial.’’ However, if they cannot comprehend this content as an artistic expression, they may still be able to infer something about our cognitive and perceptual systems based on the patterning of the message we send. Thus, even without comprehending the musical intent of such a message, the recipients might gain some understanding of human information-processing capabilities, because we are providing a message that is meant to describe our cognitive processes, by making the form of the message reflect these capabilities. This is an extension of the author’s earlier proposal that the form of the message should reflect its meaning [9].
5. A direct approach Some of the structural characteristics of music – temporal modulations of transmissions at precise frequencies – can be used to communicate basic scientific information [7]. One critique of prior suggestions for interstellar messages is that these messages often rely on conventions of representation that may be unique to a single species’ model of the physical universe. This criticism does not call into question the actual existence of physical reality. Rather, it points out that one species’ conceptualizations and theoretical models about reality may not necessarily be readily comprehensible by a species relying on very different models—even though the two species may be studying the same underlying reality [10]. For instance, pictorial representations of atoms might rely on the Bohr model, in which electrons circle the atom’s nucleus much like planets orbit a star. Nevertheless, this is only one way of representing atomic structure, and it is not immediately obvious that even other species with advanced knowledge of chemistry will use models that are directly commensurable with ours [9]. One potential solution to the above problem would be to attempt to communicate our concepts of chemistry through signals that directly mimic physical phenomena related to the chemical concepts we are conveying [7]. For example, one might transmit electromagnetic signals at frequencies corresponding to some subset of those spectral lines that are uniquely associated with energy emissions from certain chemical elements. Thus, a hydrogen atom might be represented more directly by signaling at some of the frequencies at which this element naturally emits. These frequencies may be rather far from each another, so the actual process of transmission might involve starting with a single frequency and slowly
drifting the signal to another frequency associated with the emission spectrum of that element. Following this approach, one could transmit for awhile at each frequency of a characteristic emission line, then move on to the next target frequency until each has been transmitted. Given the wide range of frequencies accessible to some radio telescopes, a significant range of chemical concepts could be communicated in this manner. For example, the SETI Institute’s Allen Telescope Array covers a range of 4.5 octaves, with frequencies ranging between 0.5 and 11.2 GHz. Once we are able to convey individual chemical constituents, we might then describe the process by which these constituents combine to form more complex molecules. Since the early days of the search for extraterrestrial intelligence (SETI), astronomers have suggested searching at or near frequencies associated with strong emission lines of the constituents of water—hydrogen (H + ) and hydroxyl (OH ). Although frequencies associated with hydrogen and hydroxyl emission spectra have often been suggested as ‘‘magic frequencies’’ to help narrow searches – with some advocating searches within the ‘‘water hole’’ that spans the range of frequencies between 1420 and 1640 MHz – others have not suggested using these frequencies as icons of the constituents themselves. To see how we might represent iconically the chemical equation H + +OH -H2O in an interstellar message, consider Fig. 1. At the left side of the figure, a transmission at or near the hydrogen line (1420 MHz) appears, and as time passes (moving from left to right in the figure), this first signal is joined by another signal sent at the frequency associated with the strongest hydroxyl line (1640 MHz). After each of these two signals is well established, additional signals slowly drift away from the hydrogen and hydroxyl lines, combining at the frequency associated with the 22 GHz water maser line. The intended message is that hydrogen and hydroxyl combine to form water. As an alternative to the transmission represented in Fig. 1, one might simply have the transmissions at 1420 and 1640 MHz end, and immediately begin a transmission at 22 GHz. Given rapid advances in technology, it is
Fig. 1. An iconic interstellar message representing the combination of hydrogen and hydroxyl to form water (H + +OH -H2O).
D.A. Vakoch / Acta Astronautica 67 (2010) 1406–1409
reasonable to assume that this entire range of frequencies could be detected by even rudimentary technological civilizations with radio telescopes. For example, a modest expansion of the existing Allen Telescope Array would make narrowband signals detectable within this entire frequency range. A process analogous to that used to describe chemical concepts could also be used to communicate musical concepts. Though the initial form of the message might focus on basic parameters of music, eventually one might transmit at multiple frequencies, creating a sort of ‘‘interstellar symphony’’ [8], with the frequencies of the signals having the kind of relationship to one another identified by von Hoerner for well-tempered polyphonic music. This approach would mark a significant shift from the traditional approach that messages should be encoded in a form that bears no direct relationship to the content of the message. While the traditional procedure may be efficient from an information theoretic perspective, it does not take into account that the process of decoding such messages may be significantly more challenging than typically anticipated. As noted above, the particular form of the musical tutorial might provide information about the cognitive functioning of a species [6]. For instance, Narmour has posited that as humans begin to hear even very few notes played sequentially, they begin to form strong anticipations of the sort of tones that are likely to follow [5]. One of the parameters that influence these anticipations is the size of the intervals between notes (from a relatively small interval—yielding notes ‘‘close together,’’ to relatively large intervals—resulting in notes ‘‘far apart’’). Similarly, the parameter of direction of pitch (increasing, decreasing, or remaining stable) can create expectations about subsequent notes. By structuring a musical primer to reflect such ‘‘cognitive primitives’’ of music perception as interval size and pitch direction, one could introduce a basic vocabulary that reflects both components of music and parameters of human auditory perception. By conveying this information directly in the form of the electromagnetic signal, clues would be provided about our intended meaning as well as about the senders of the message, all in a form that may be
1409
more intelligible than many previously proposed formats for interstellar communication.
Acknowledgments The author gratefully acknowledges the following support of this research: The John Templeton Foundation, though its Grant #1840, ‘‘Construction of Interstellar Messages Describing the Evolution of Altruistic Behavior;’’ President Joseph Subbiondo, Academic Vice President Judie Wexler, and Clinical Psychology Department Chair Katie McGovern of the California Institute of Integral Studies for sabbatical and ongoing research leaves; CEO Thomas Pierson and Director of SETI Research Jill Tarter of the SETI Institute for support of research on SETI and Society; and Jamie Baswell, as well as Harry and Joyce Letaw, for financial support through the SETI Institute’s Adopt a Scientist program. References [1] C.L. DeVito, Languages, science and the search for extraterrestrial intelligence, Leonardo 25 (1992) 13–16. [2] H. Freudenthal, Lincos: Design of a Language for Cosmic Intercourse; Part I, North-Holland, Amsterdam, 1960. [3] J. Knowlson, Universal Language Schemes in England and France 1600–1800, University of Toronto Press, Toronto, 1975. [4] P. Morrison, Interstellar communication, in: A.G.W. Cameron (Ed.), Interstellar Communication: A Collection of Reprints and Original Contributions, W. A. Benjamin, New York, 1963. [5] E. Narmour, The Analysis and Cognition of Basic Melodic Structures: The Implication-Realization Model, University of Chicago Press, Chicago, 1990. [6] D.A. Vakoch, Cognitive modeling of music perception as a foundation for interstellar message composition. Paper IAA-00-IAA.9.2.10 presented at the SETI: Interdisciplinary Connections Review Meeting, 51st International Astronautical Congress, Rio de Janeiro, Brasil, October 2000. [7] D.A. Vakoch, An iconic approach to communicating chemical concepts to extraterrestrials, SPIE Proceedings 2704 (1996) 140–149. [8] D.A. Vakoch, The music of the spheres, Sky & Space 11 (3) (1998) 24. [9] D.A. Vakoch, Signs of life beyond Earth: a semiotic analysis of interstellar messages, Leonardo 31 (1998) 313–319. [10] D.A. Vakoch, Technology as a manifestation of intelligence: does shared technology imply shared science and mathematics? [Abstract.], Astrobiology 8 (2) (2008) 391. [11] D.A. Vakoch, To the stars, silently, Leonardo 37 (2004) 265. [12] S. von Hoerner, Universal music?, Psychology of Music 2 (1974) 18–28.