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Detectability of Extraterrestrial Technological Activities

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Author Topic: Detectability of Extraterrestrial Technological Activities  (Read 735 times)
Jennifer Murdoch
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« on: February 04, 2010, 01:17:15 pm »

Detectability of Extraterrestrial Technological Activities


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                             THE ELECTRONIC JOURNAL OF

                        Volume 5, Number 5 - December 1993

       The Electronic Journal  of  the Astronomical Society of the Atlantic
       (EJASA) is published monthly by  the  Astronomical  Society  of  the
       Atlantic, Incorporated.  The   ASA  is  a  non-profit   organization
       dedicated to the  advancement  of amateur and professional astronomy
       and space exploration, as well as  the  social and educational needs
       of its members.


                            Guillermo A. Lemarchand [1]

                    Center for Radiophysics and Space Research
                    Cornell University, Ithaca, New York, 14853

            1 - Visiting Fellow under ICSC World Laboratory scholarship

            Present address:  University of Buenos Aires,
                              1425 - Buenos Aires,

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Jennifer Murdoch
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Posts: 5235

« Reply #1 on: February 04, 2010, 01:17:29 pm »

    This paper  was  originally  presented  at the  Second  United
           Nations/European Space Agency Workshop on Basic Space Science

             Co-organized by The Planetary Society in cooperation with
          the Governments of Costa Rica and Colombia, 2-13 November 1992,
                      San Jose, Costa Rica - Bogota, Colombia


       If we want  to  find  evidence for the existence of extraterrestrial
       civilizations (ETC), we must work  out an observational strategy for
       detecting this evidence  in order to establish the various  physical
       quantities in which it involves.  This information must be carefully
       analyzed so that  it  is neither over-interpreted nor overlooked and
       can be checked by independent researchers.

                                      Page 1

       The physical laws  that govern the Universe are the same everywhere,
       so we can use our knowledge of these  laws  to  search  for evidence
       that would finally   lead   us   to   an  ETC.   In   general,   the
       experimentalist studies a   system   by   imposing  constraints  and
       observing the system's response to a controlled stimulus.

       The variety of these constraints  and  stimuli  may  be  extended at
       will, and experiments  can  become  arbitrarily  complex.    In  the
       problem of the  Search  for Extraterrestrial Intelligence (SETI), as
       well as in conventional astronomy,  the  mean  distances are so huge
       that the "researcher" can only observe what is received.   He or she
       is entirely dependent  on  the carriers of information that transmit
       to him or her all he or she may learn about the Universe.
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Jennifer Murdoch
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« Reply #2 on: February 04, 2010, 01:17:39 pm »

Information carriers, however, are  not  infinite  in  variety.  All
       information we currently have about the Universe  beyond  our  solar
       system has been  transmitted  to  us  by  means  of  electromagnetic
       radiation (radio, infrared, optical,  ultraviolet, X-rays, and gamma
       rays), cosmic ray particles (electrons and atomic nuclei),  and more
       recently by neutrinos.

       There is another possible physical carrier, gravitational waves, but
       they are extremely difficult to detect.

       For the long  future  of humanity, there have also been speculations
       about interstellar automatic probes  that  could  be  sent  for  the
       detection of extrasolar life forms around the nearby stars.

       Another set of   possibilities   could   be   the    detection    of
       extraterrestrial artifacts in  our  solar system, left here by alien
       intelligences that want to reveal their visits to us.

       Table 1 summarizes the possible "information  carriers" that may let
       us find the evidence of an extraterrestrial civilization,  according
       to our knowledge  of  the  laws  of  physics.  The classification of
       techniques in Table  1  is  not  intended  to  be  complete  in  all

       Thus, only a few fundamental particles have been listed.  No attempt
       has been made  to  include any antiparticles.  This  classification,
       like any such  scheme,  is also quite arbitrary.  Groupings could be
       made into different "astronomies".
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Jennifer Murdoch
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« Reply #3 on: February 04, 2010, 01:18:01 pm »

 Page 2

                               TABLE 1: Information Carriers

                                        | Radio Waves
                                        | Infrared Rays
                      |-                | Optical Rays
                      | Photon Astronomy| Ultraviolet Rays
                      |                 | X-Rays
           Boson      |                 | Gamma Rays
           Astronomy  |                 |-
                      | Graviton Astronomy: Gravity Waves
                      |-                     |-
                                             | Neutrinos
                    |-           |-  Fermions| Electrons   |-
                    | Atomic     |           | Protons     | Cosmic
                    | Microscopic|           |-            | Rays
                    | Particles  |   Heavy Particles       |-
          Particle  |            |-
          Astronomy |                      |-
                    | Macroscopic Particles|       Meteors, meteorites,
                    | or objects           |       meteoritic dust
                    |-                     |-
                        | Space Probes
           Direct       | Manned Exploration
           Techniques   |  ET  Astroengineering  Activities  in  the  Solar

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Jennifer Murdoch
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« Reply #4 on: February 04, 2010, 01:18:13 pm »

The methods of collecting this information  as  it  arrives  at  the
       planet Earth make it immediately obvious that it  is  impossible  to
       gather all of  it  and measure all its components.  Each observation
       technique acts as an information filter.   Only  a fraction (usually
       small) of the complete information can be gathered.   The  diversity
       of these filters  is  considerable.   They  strongly  depend  on the
       available technology at the time.

       In this paper a review of the advantages  and  disadvantages of each
       "physical carrier" is examined, including the case that the possible
       ETCs are using them for interstellar communication purposes, as well
       as the  possibility  of  detection  activities  of  extraterrestrial

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Jennifer Murdoch
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« Reply #5 on: February 04, 2010, 01:18:29 pm »

 Classification of Extraterrestrial Civilizations

       The analysis of  the  use  of  each  information  carrier are deeply
       connected with the assumption of  the  level  of  technology  of the
       other civilization.

       Kardashev (1964) established a general criteria regarding  the types
       of activities of   extraterrestrial   civilizations   which  can  be
       detected at the present level of development.  The most general
       parameters of these activities are  apparently ultra-powerful energy
       sources, harnessing of  enormous solid masses, and the  transmission
       of large quantities of information of different kinds through space.

       According to Kardashev, the first two parameters are a prerequisite
       for any activity of a supercivilization.  In this way, he suggested

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Jennifer Murdoch
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« Reply #6 on: February 04, 2010, 01:18:41 pm »

                                      Page 3

       the following classification     of     energetically    extravagant

           TYPE I:   A level "near" contemporary  terrestrial  civilization
                    with an  energy  capability  equivalent  to  the  solar
                    insolation on Earth, between 10exp16 and 10exp17 Watts.

           TYPE II:  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 4x1026 Watts.

           TYPE III:  A civilization with access to the power comparable
                      to the luminosity of the entire Milky Way galaxy,
                      about 4x10exp37 Watts.

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Jennifer Murdoch
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« Reply #7 on: February 04, 2010, 01:18:51 pm »

Kardashev also examined  the  possibilities  in cosmic communication
       which attend the investment of most  of  the  available  power  into
       communication.  A Type II civilization could transmit  the  contents
       of one hundred  thousand  average-sized  books  across the galaxy, a
       distance of one  hundred  thousand   light   years,   in   a   total
       transmitting time of one hundred seconds.  The transmission  of  the
       same information intended  for  a  target  ten  million  light years
       distant, a typical intergalactic distance, would take a transmission
       time of a few weeks.

       A Type III civilization could transmit the same information over a
       distance of ten billion light years, approximately the radius of the
       observable Universe, with a transmission time of just three seconds.

       Kardashev and Zhuravlev (1992) considered  that the highest level of
       development corresponds to the highest level of utilization of solid
       space structures and the highest level of energy consumption.

       For this assumption, they considered the temperature  of solid space
       structures in the  range  3  Kelvin  s T s 300 K, the consumption of
       energy in the  range  1 Luminosity  (Sun)  s  L  s  10exp12  L(Sun),
       structures with sizes up to 100 kiloparsecs (kpc),  and distances up
       to Dw 1000 mega-parsecs (mpc).  One parsec equals 3.26 light years.
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Jennifer Murdoch
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« Reply #8 on: February 04, 2010, 01:19:07 pm »

  Searching for these  structures  is  the  domain  of millimeter wave
       astronomy.  For the 300 Kelvin technology, the maximum emission
       occurs in the infrared region (15-20 micrometers) and searching is
       accomplished with infrared observations from Earth and space.  The
       existing radio surveys of the sky  (lambda  =  6 centimeters (cm) on
       the ground and lambda = 3 millimeters (mm) for the Cosmic Background
       Explorer (COBE) satellite) place an essential limit on the abundance
       of ETC 3   Kelvin   technology.   The  analyzes  of   the   Infrared
       Astronomical Satellite (IRAS)   catalog  of  infrared  sources  sets
       limitations on the abundance of 300 Kelvin technology.

               Information Carriers and the Manifestations of Advanced
               Technological Civilizations

               Boson and Photon Astronomy

       Electromagnetic radiation carries  virtually  all the information on
       which modern astrophysics    is    built.     The   production    of
       electromagnetic radiation is directly related to the physical

                                      Page 4

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Jennifer Murdoch
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« Reply #9 on: February 04, 2010, 01:19:24 pm »

 conditions prevailing in   the  emitter.   The  propagation  of  the
       information carried by electromagnetic  waves  (photons) is affected
       by the conditions  along  its  path.   The trajectories  it  follows
       depend on the local curvature of the Universe, and thus on the local
       distribution of matter  (gravitational lenses), extinction affecting
       different wavelengths unequally,   neutral  hydrogen  absorbing  all
       radiation below the  Lyman  limit  (91.3  mm),  and  absorption  and
       scattering by interstellar  dust,  which  is  more  severe  at short

       Interstellar plasma absorbs  radio  wavelengths  of  kilometers  and
       above, while the  scintillations  caused  by  them   become  a  very
       important effect for  the  case  of  ETC  radio messages (Cordes and
       Lazio, 1991).

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Jennifer Murdoch
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« Reply #10 on: February 04, 2010, 01:19:35 pm »

 The inverse Compton effect lifts low-energy photons to high energies
       in collisions with relativistic electrons,  while  gamma  and  X-ray
       photons lose energy  by  the direct Compton effect.   The  radiation
       reaching the observer  thus bears the imprint of both the source and
       the accidents of its passage though space.

       The Universe observable  with  electromagnetic  radiation  is  five-
       dimensional.  Within this   phase,  four  dimensions   -   frequency
       coverage plus spatial,  spectral,  and temporal resolutions - should
       properly be measured logarithmically with each unit corresponding to
       one decade (Tarter,  1984).  The fifth  dimension  is  polarization,
       which has four possible states:  Circular, linear,  elliptical,  and

       This increases the volume of logarithmic phase space fourfold.
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Jennifer Murdoch
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« Reply #11 on: February 04, 2010, 01:19:49 pm »

It is useful  to  attempt to estimate the volume of the search space
       which may need to be explored to detect an ETC signal.  For the case
       of electromagnetic waves, we have a "Cosmic Haystack" with an eight-
       dimensional phase space.  Three spatial  dimensions  (coordinates of
       the source), one  dimension  for  the  frequency  of  emission,  two
       dimensions for the   polarization,   one   temporal   dimension   to
       synchronize transmissions with receptions, and one dimension for the
       sensitivity of the receiver or the transmission power.

       If we consider  only  the microwave  region  of  the  spectrum  (300
       megahertz (MHz) to  300 gigahertz (GHz)), it is easy  to  show  that
       this Cosmic Haystack  has  roughly  10exp29  cells,  each  of 0.1 Hz
       bandwidth, per the number of directions  in  the  sky  in  which  an
       Arecibo (305-meter) radio  telescope  would need to  be  pointed  to
       conduct an all-sky  survey, per a sensitivity between 10exp(-20) and
       10exp(-30) [W m-2], per two polarizations.   The  temporal dimension
       (synchronization between transmission   and   reception)   was   not
       considered in the   calculation.    The  number  of  cells  increase
       dramatically if we  expand  our  search  to  other  regions  of  the
       electromagnetic spectrum.  Until now, only a small  fraction  of the
       whole Haystack has been explored (w 10exp(-15) - 10exp(-16)).

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Jennifer Murdoch
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« Reply #12 on: February 04, 2010, 01:20:04 pm »

      Page 5

            TABLE 2: Characteristics of the Electromagnetic Spectrum

              (All the numbers that follows each 10 are exponents.)
       Spectrum      Frequency          Wavelength        Minimum Energy
       Region        Region [Hz]        Region [m]        per photon [eV]

        Radio         3x106-3x1010       100-0.01          10-8 - 10-6
        Millimeter    3x1010-3x1012      0.01-10-4         10-6 - 10-4
        Infrared      3x1012-3x1014      10-4-10-6         10-4 - 10-2
        Optical       3x1014-1015        10-6-3x10-7       10-2 - 5
        Ultraviolet   1015-3x1016        3x10-7-10-8       5 - 102
        X-rays        3x1016-3x1019      10-8-10-11        102 - 105
        Gamma-rays    r3x1019            s10-11            r105

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Jennifer Murdoch
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« Reply #13 on: February 04, 2010, 01:20:16 pm »

Radio Waves

       In the last  thirty  years,  most  of  the  SETI  projects have been
       developed in the radio region of  the  electromagnetic  spectrum.  A
       complete description of the techniques that all the present and
       near-future SETI programs are using for detecting extraterrestrial
       intelligence radio beacons  can be found elsewhere  (e.g.,  Horowitz
       and Sagan, 1993).  The general hypothesis for this kind of search is
       that there are   several   civilizations  in  the  galaxy  that  are
       transmitting omnidirectional radio  signals  (civilization Type II),
       or that these civilizations are beaming these kind  of  messages  to
       Earth.  In this  section  we  will discuss only the detectability of
       extraterrestrial technological manifestations in the radio spectrum.
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Jennifer Murdoch
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« Reply #14 on: February 04, 2010, 01:20:29 pm »

Domestic Radio Signals

       Sullivan et al (1978) and Sullivan (1981) considered the possibility
       of eavesdropping on  radio emissions  inadvertently  "leaking"  from
       other technical civilizations.  To better understand the information
       which might be derived from radio leakage, the case  of  our  planet
       Earth was analyzed.   As  an  example,  they  showed that the United
       States Naval Space  Surveillance   System   (Breetz,  1968)  has  an
       effective radiated power of 1.4x10exp (10) watts into a bandwidth of
       only 0.1 Hz.   Its  beam  is  such  that  any  eavesdropper  in  the
       declination range of zero to 33 degrees (28 percent of the sky) will
       be illuminated daily  for  a  period of roughly seven seconds.  This
       radar has a detectability range of  leaking  terrestrial  signals to
       sixty light years  for an Arecibo-type (305-meter)  antenna  at  the
       receiving end, or  six  hundred light years for a Cyclops array (one
       thousand dishes of 100-meter size each).

       Recently Billingham and Tarter (1992) estimated the maximum range at
       which radar signals from Earth could be detected by a search similar
       to the NASA High Resolution Microwave  Survey  (HRMS)  assumed to be
       operating somewhere in  the  Milky  Way galaxy.  They  examined  the
       transmission of the  planetary  radar  of  Arecibo and the ballistic
       missile early warning  systems  (BMEWS).   For  the  calculation  of
       maximum range R, the standard range equation is:

               R=(EIRP/(4PI PHImin))exp(1/2)

                                      Page 6
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