© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

24.1.1  Eavesdropping

What if we wish to discover extraterrestrial civilizations which are not deliberately attempting to make their presence known to us by posting a cosmic signpost? Xenologists generally agree that probably one of the best ways to do this is to attempt to monitor the putative culture’s "technological garbage."^80,57 (But note Sagan and Sullivan.³¹⁹²) As any first-year anthropology student is well aware, that which is thrown away often bears much information about the thrower.

From the xenological standpoint there are two basic constraints on this mode of contact. First, since the effluents of technical civilization must cross interstellar distances to be detectable, said effluents must be of such character as not to suffer undue attenuation during transit. Second, the technology of the wasting culture must be sufficiently advanced and sufficiently energy-rich so that the flux of garbage into interstellar space is great enough to be detectable far from the original source. The only serendipitous effluents which satisfy both of these requirements are electromagnetic waves (radio, microwaves, etc.).

Even a backwoods emergent Type I civilization such as humanity emits enough electromagnetic garbage to be detectable over interstellar distances. Assuming for the moment that our planet represents a fairly typical primitive planetary culture, the radio spectrum of Earth indicates the presence of technological activity at the hands of presumably sentient beings. Carl Sagan explains the reasoning behind this conclusion:

Since the Earth is at a temperature of roughly 300 K, we would expect it to have an emission spectrum following the blackbody curve, except for some absorption by the atmosphere. Further, the curve should be centered at about 10 microns in the infrared and fall off inversely as the square of the wavelength to ward very long wavelengths. What we find is a truly remarkable peak in the meter band. The amount of radio emission is extremely striking. Indeed, it is so large that if one observed only at meter-band frequencies and assumed the emission to be of thermal origin, the deduced blackbody temperature of the Earth would be about 40,000,000 K. This is an example of extreme disequilibrium. That is, the Earth’s radio radiation is not characteristic of thermodynamic equilibrium. The strong disequilibrium component is due to the activities of the modicum of intelligence residing on the planet.³²⁸⁷

Woodruff T. Sullivan and his colleagues have completed an extensive survey of all sources of radio leakage on our planet. The video carrier in TV broadcasting is responsible for most of the radiative wastage. Even though power emitted from antennas on tall towers is deliberately concentrated downward to avoid waste, a thin sheet nevertheless escapes over the horizon as leakage radiation into space. This amounts to a total effective radiated power of about 10,000 megawatts/Hz for the TV video carrier, 400 megawatts/Hz from FM broadcasting, and about 200 megawatts/Hz from BMEWS-type military radars.

According to Sullivan, the Arecibo radio dish used by NRAO in Puerto Rico, if operated by inquisitive aliens on another world looking back at Earth, could detect a. strong UHF television station at a range of 1.8 light-years. BMEWS radar could be picked up out to 18 light-years using an Arecibo-type radiotelescope. The construction of a system similar to the proposed Cyclops SETI network (see description next section) would permit detection of video carriers out to 25 light-years (which encompasses about 300 stars) and BMEWS radar out to 250 light-years (covering about 200,000 stars). Our hypothetical extraterrestrial observers who were able to detect video carrier waves would recognize them as artificial, although an additional four orders of magnitude of antenna sensitivity would be required to pick up actual program material.

After carefully monitoring the intensity and frequency variations of terrestrial transmitters for several years, distant ET scientists could deduce an incredible number of important facts about Earth:

1. The complete orbit of our world;
2. The existence of station broadcast schedules influenced by the sun;
3. The presence of an ionosphere and perhaps a troposphere;
4. The size, rotation rate, and axis of rotation of the Earth;
5. A complete map of the stations;
6. The mass and distance to the moon;
7. The size of the radiating antennas; and
8. Various cultural inferences concerning our civilization.

Sullivan elaborates further:

The deductions that might be made from this wealth of information can only be conjectured, but certainly the extraterrestrial "humanists" and scientists would all have their favorite theories concerning (i) the purposes of these transmitters, as well as their physical structure; (ii) the nature of this planet’s relationship to the sun, as well as its geography, geology, and atmosphere; and (iii) the nature of this civilization’s biology, sociology, commerce, politics, economics, philosophy, technology, and science. We feel that far more could be deduced about our culture than one would at first think. For instance, political spheres of influence could be measured quite accurately by noting the frequencies and other technical conventions of stations. Furthermore, the varying broad cast schedules of stations (set by policies of national networks in most cases) would sharply delineate political boundaries, as distinct from spheres of influence. Further possible deductions are left to the imagination of the reader.³¹⁰

As technology advances and a civilization enters the Type II stage, the waste products of an aspiring society may become even more readily apparent. For instance, if we place in Earth-orbit a series of gigawatt-capacity solar power satellites (as many proponents of space industrialization have urged), the minor lobes of the spaceborne transmission antenna radiation will make humanity highly visible on the galactic scene. Incessant radio traffic between interplanetary or interstellar ships, or between such vessels and their home planets, will contribute to the "garbage." (A gradual increase in strength of such a signal. together with a spectral blueshift might be taken to indicate the approach of a high-velocity starship towards our solar system.^1381,49,3138) Powerful defensive radars probably would be detectable anywhere in the Galaxy using a Cyclops-type radiotelescope array.

Let us assume a mature Type II culture which has spread itself around the parent star in the traditional Dyson Sphere configuration. Viewed from interstellar distances, the optical characteristics of the sun itself may appear drastically altered. Independent of specific engineering details, the Second Law of Thermodynamics requires that a technically advanced society that exploits the entire energy output of its stellar primary must re-radiate every bit of that energy in some degraded form to maintain thermal equilibrium. If the shell lies at the radius of Earth and the central star is like Sol, the mean temperature of the Dyson Sphere will be 250-300 K. The waste energy will come off as heat, down in the infrared portion of the spectrum around 7-10 microns. This waste is not easily concealed from nosy interstellar neighbors.*

One writer has suggested that beings based on a hotter biochemistry than our own might construct Dyson Spheres with a higher waste-heat temperature. The infrared emissions could run as high as 2-5 microns, which "would look deceptively like red giant or supergiant stars."⁶⁷³ Marvin Minsky at MIT offers a different viewpoint: In his opinion, radiative emissions at any temperature above the natural 3 K background is wasteful and a squandering of scarce energy resources. According to Minsky, "the higher the civilization, the lower the infrared radiation. We should look for extended sources of 4 K radiation. There should be very few natural such sources."²² (4 K corresponds to a wavelength of about 700 microns.)

Indeed, in recent times a number of large infrared objects with solar-system-sized dimensions and temperatures below 1000 K have been discovered by astronomers,^3109,3108 including object T in the constellation Taurus and object R in Monoceros.¹³⁴⁴ But regardless of our secret hopes, says Iosef Shklovskii, a noted Soviet astrophysicist, "we must assume all astronomical phenomena natural until proven otherwise."¹⁵ Shklovskii’s well-known "Principle of Naturalness," while questioned by some,³¹⁷⁷ is widely accepted by working xenologists.

As before, much information may be concealed in the effluents of Type II societies. Soviet xenologists have given much thought to the question of "civilization detectors" and remote cybernetic analysis of advanced extraterrestrial cultures. Kardashev has suggested a way to distinguish Dyson Spheres from dust clouds across interstellar distances -- the two have distinctly differently shaped emission spectra.²² If the Type II society is viewed as a complex cybernetic system then, according to Soviet radioastronomer B.N. Panovkin, much information about how the civilization actually works may be derived from its electromagnetic effluents:

[If we consider] the radiation associated with life activity as an output of this system, on the basis of an analysis of radiation one can draw certain conclusions as to the functional structure of the system and its internal organization. For example, based on the properties of radiation it can be established that a system belongs to a wide class of objects in which feedback is present. From this class, after a more detailed analysis, a narrower sub class of systems can be discriminated in which homeostasis is manifested. From the class of homeostatic objects one can isolate a group of objects possessing even more complicated functional properties -- for example, "systems logic," etc. Ultimately, in principle it is possible to isolate a class of objects which (regardless of their physical structure) can be recognized as equivalent, let us say, to our earth civilization in terms of their functional properties and their manifestations.²⁵

When at last we come to an analysis of the expected appearance of the "garbage" generated by the technological activities of a Type III galactic civilization, we leap ahead at least ten orders of magnitude in available energy and complexity. Such a society should be capable (see Chapter 19) of directly altering the physical characteristics of entire galaxies. According to Freeman Dyson, the acknowledged premier speculator on the topic of galactic technology, "tame" galaxies should appear far differently than "wild" ones still in the natural state. Such taming appears largely to be absent from the Milky Way. Says Dyson:

It seems to me clear that we could turn the galaxy upside down if we wanted to, within a million years; there’s nothing in the world of physics to stop us from doing that. There may be good reasons for not doing it, and there may be good reasons why other intelligent species are not doing it.... I have the feeling that if an expanding technology had ever really got loose in our galaxy, the effects of it would be glaringly obvious. Starlight, instead of wastefully shining all over the galaxy, would be carefully dammed and regulated. Stars, instead of moving at random, would be grouped and organized. We don’t see any traces of this when we look in the sky, which is peculiar. Nothing like a complete technological takeover has occurred in our galaxy.. . .To search for evidence of technological activity in the galaxy might be like searching for evidence of technological activity on Manhattan Island. If an Indian from 400 years ago were to come paddling into New York harbor, he might not understand what he sees, but he would at least notice there is something there.^1558,1450

Despite the apparently "wild" state of the Milky Way, astronomers have discovered a number of highly unusual and inexplicable phenomena in the heavens.³¹³⁵ Perhaps the best-known of these is the galaxy M87, also called Virgo A. M87 is a giant elliptical galaxy located about 50 million light-years from Earth. Photographs clearly show a string of bright knots -- the "galactic jet" -- extending outward from the nuclear regions. Like a giant searchlight beam, the jet stretches 5000 light-years in length and measures 500 light-years thick. Astronomers believe that this artifact has existed only for a few millions of years, and that its total energy is approximately 10⁵¹ joules. If we consult Table 19.2 in the chapter on high technology, we find that this is sufficient energy to engage in a galactic transport operation at a speed of 40,000 meter/second, or about 0.01%c.

Other celestial oddities are known. Stephan’s Quintet is a congregation of five separate galaxies in the constellation Serpens, each connected to the others by mysterious gaseous "bridges." Many Seyfert galaxies (characterized by intense radiation emissions from their core regions) exhibit highly unusual shapes, often including jet-like structures emanating from the nucleus. Object 3C273 and several other quasars also have elliptical jets or tails extruding from the main body. (The tails are visually dim, but emit 90% of the total radio energy.¹²¹⁴) There are spectacular "radio galaxies" such as Cygnus A in which 0.01% of the total galactic mass has been catastrophically converted into radio wave energy by means unknown.¹³³⁸ But perhaps most startling of all are the famous Ring Galaxies,³¹⁶⁴ of which about 16 have been discovered to date.^3159,3110 These monstrous halos of stars are known to be dynamically unstable stellar aggregations with astronomically ephemeral lifetimes of only 100 million years -- which implies fairly recent assembly. Scientists already have devised a number of theories of formation,³¹¹¹ but xenologists continue to hope.

A few speculators have pinned their hopes on some of the recently discovered marvels of the astronomical zoo, in particular the pulsars. (See Kardashev,¹³²⁰ McDonough,¹³⁸⁴ Verschuur,¹³³⁷ and Spaceflight¹¹⁷³.) Pulsars are objects which emit regular pulses of radio energy at extremely regular intervals.** These intervals range from 1-30 seconds for different objects. Pulsars are so regular that a variety of putative intelligent functions have been assigned to them by some xenologically-inclined writers. These range from artificial extraterrestrial acquisition beacons (the so-called LGM or "Little Green Men" theory) to waste energy from the exhaust from pulsed x-ray lasers used in some advanced starship propulsion system. The orthodox explanation is that pulsars are fast-spinning neutron stars with asymmetrical surface "hot spots" or polar fusion of infalling gas that traces round and round like a revolving searchlight.³¹³⁹

While it is most probable that pulsars arise by natural causes, it is quite possible that advanced technical communities may still he exploiting them as navigational buoys or galactic chronometers. To make proper use of a spinning neutron star, a Type III civilization should have available the technology required physically to rotate the spin axis of the object. ETs will need to orient the pulsar’s flashes towards certain specific preferred directions -- say, into the plane of interstellar trade routes -- since natural pulsars may have random orientations. To shift the axis of a spinning neutron star of 1 solar mass and a period of 1 second through a full right-angle turn (90°) will require at least 3 x 10²⁹ joules. If reorientation is accomplished in a single century, 8 x 10¹⁹ watts of power must be expended continuously over that time. If the alien engineers are in a real hurry and choose to do it in only 10 years, then 8 x 10²¹ watts are needed. The energies required to meet either of these schedules is well within the means of a Type II civilization, and a Type III galactic society would have no trouble at all.

Another favorite cosmological object for xenological speculation is the quasar.^1557,1814 This fascinating phenomenon has a bluish starlike visual appearance and is characterized by strong ultraviolet and (usually) radio emissions. A large spectral redshift seems to indicate that quasars are very very far away -- perhaps at cosmological distances (billions of light-years) -- and their lack of proper motion against the background field of stars tends to support this conclusion.

However, quasars also vary in brightness over time periods as brief as a single day.²⁶³⁸ If it is true that no material disturbance can travel faster than the speed of light, then the maximum size of the primary quasar energy source should be on the order of a light-day in diameter. Assuming this is correct, quasars would have to be considerably closer, perhaps even within our Ga1axy,¹⁴⁸² because it is difficult to visualize the generation of galactic energies in a solar-system-size volume of space. And if quasars were really close, their computed total energy would drop to approximately of an oversized globular cluster -- perhaps interpretable as a consortium of advanced Type II civilizations.

Quasars exhibit rapid fluctuations in radio brightness, in optical bright ness, in polarization of visible light emissions, and so forth.^1488,1486 Parts of quasars appear to be flying apart at velocities greater than the speed of light,^1485,3166 although several explanations have been offered to avoid violations of Relativity theory.³¹⁶⁵ Different spectral absorption lines often exhibit different redshifts.¹⁵⁵⁶ A few quasars, such as the BL Lacertae objects, frequently display uncorrelated variations in the radio and visible spectrums (e.g., radio power increases while visible power decreases).³¹⁶⁰ Still more surprising, "BL Lacs" and many other quasistellar objects emit radiation with the spectral characteristics of a nonthermal source (non-black-body), which implies "that the powerhouse inside must be generating radio power by a rather exotic mechanism.^3151,3295

While such unusual behavior certainly is not "clearly artificial," to the best of my knowledge no serious studies have yet been done in which quasar emission signatures are analyzed for information content and periodicities of the sort which might be expected of the transmissions or electromagnetic "garbage" of advanced alien civilizations. Quasars, most likely are not extraterrestrial acquisition beacons, but still it is useful always to bear in mind the First Law of Serendipity: To find anything, one must first be looking for something.

* It might be possible to hide by arranging all waste heat to be radiated in a tight nonisotropic beam, straight up out of the Galactic Plane so that only a very few stars could ever hope to have any knowledge of the existence of the civilization by means of eavesdropping.

** For example, pulsar CP1919 in Vulpecula has a period of exactly 1.33730109 seconds.¹³⁸⁴

Last updated on 6 December 2008