1. A Universal Problem
Los Alamos Laboratories, New Mexico, 1945. It is lunchtime.
Our gaze is directed towards a quiet corner of the otherwise busy
refectory hall. A cluster of crop-haired physicists are seated around
a large circular table. In twos and threes they huddle together in
deep conversation. Snippets of their discourse drift into range. The
discussion topics vary wildly: the weather, the ending of the war,
a weekend hike, the solution to a particular integral equation, and
the many other problems of their work. At some moment, no one
is quite sure how or why it happened, one of the physicists, Enrico
Fermi,1 asks a question about extraterrestrial life. “What’s that,
Fermi?” a voice queries. “I was just thinking” repeated Fermi, “if
the galaxy is full of extraterrestrial civilizations, then why are there
no extraterrestrial beings on Earth—walking amongst us now?"
“Don’t be absurd Fermi,” one of the group counters. “The galaxy
is huge, and it would take longer than the age of the universe to
colonize it—surely?"
“Are you so certain?” rejoins Fermi. “Let’s do a back of the
envelope calculation.” There is a flurry of movement among our
huddle of physicists. Fermi is famous for his order of magnitude
calculations. “Let’s assume that there are 1010 stars in our galaxy
and that each star is on average, oh, say, 6 light years from
its nearest neighbor,” Fermi begins.2 “Let’s also assume that a
spaceship has been developed that uses standard rocket power
to propel it at speeds of, oh, let’s say, 30 kilometers per second
or one-ten-thousandth the speed of light.3 So, travel time being
distance divided by speed gives about 65,000 years to move from
any one star to its next nearest companion. A long time by human
standards for sure, but small fry compared to the age of the galaxy.”
“Not an exactly profound result,” someone mumbles, but a
series of sharp glances and furrowed brows quells the interrupter.
“Now, as I see it,” Fermi continues, ignoring the young
upstart, “any reasonable colonization strategy would work like
5
6 Rejuvenating the Sun and Avoiding Other Global Catastrophes
a fission process. One spaceship sets off from the home planet.
When it reaches the next nearest star, two new spaceships are
made, and these are sent off to the next two nearest stars, where
the same doubling process continues. In this way, after 33 generations,
every star in the galaxy should have been visited, since 233 is
about 1010. So, as I see it, the total time required to visit every star
in the galaxy should be of order 33 x 65,000, or 2 million years.4
Two million years, why compared to the age of the Sun (which is
something like 4.5 billion years old) this is a mere nothing. Even
on a geological time scale, this is peanuts. A civilization that arose
on a planet orbiting a star formed, say, a billion years before our
Sun formed, could have easily colonized the entire galaxy. So, I
ask again, where are they?"
A hush falls over his audience. Fermi has them in a bind. The
younger physicists at the table are racking their brains in the hope
of finding a loophole in the argument, hoping to score points with
their companions. But no one can come up with a counter answer.
Dealing with Fermi
The lunchtime conversation as just described may never have
actually happened, but it is loosely based upon a story recounted
by planetary astronomer Carl Sagan. Real or not, however, it is
an anecdote that has become encased in legend. Where and when
Fermi first raised the topic is not so much the issue; the point is
that Fermi’s Paradox – as his question has become known – is a
real problem that correspondingly requires a solution. A paradox,
the dictionary indicates, is a statement that seems contradictory
but contains an element of truth. In this manner Fermi’s question
does require a few points of qualification: it is only a paradox if
extraterrestrial beings actually exist and are capable of, and of a
mind to, explore and possibly attempt to colonize the galaxy. We
shall argue later in this chapter and indeed throughout this book
that Fermi’s Paradox is answered, in fact, in terms of a no-needto-colonize
principle at work within the galaxy. Indeed, it is the
viewpoint of this author that extraterrestrial civilizations will first
engineer their parent stars into long-lived states, rather than—or,
indeed, instead of—embarking on galactic colonization programs.
A Universal Problem 7
This being said, it seems worthwhile at this stage to spend a little
time reviewing a few of the basic issues that arise from a consideration
of Fermi’s question in general.
As of the time of this writing, we do not know if any other
life forms exist beyond Planet Earth—intelligent or otherwise. We
do, however, have knowledge of one fact, and it is that there
are currently no extraterrestrial intelligent beings making their
presence clearly known to us on Earth. There is also no clear
evidence for extraterrestrial beings ever having visited Earth in the
past. This latter point, while true as it stands, should be tempered
by recalling the well-known maxim: absence of evidence is not
evidence of absence.
With these very limited facts to deal with, however, what
might be said in answer to Fermi’s question? Well, it is probably
fair to say that a very impressive and a very diverse array of
solutions have been offered over the years,5 and they range from
the extreme idea that there are absolutely no intelligent life forms,
other than us, in the entire galaxy (and universe), to the idea that
advanced civilizations are everywhere in the galaxy, but they are
being very careful to avoid contact with us. There is also the
idea that we happen to live in a very special epoch, which argues
that the conditions necessary for a galaxy-colonizing civilization
to emerge have not, as of yet, been satisfied. All such explanations
are indeed possible solutions to Fermi’s Paradox, although some
of the arguments seem much more compelling than others.
Perhaps the most incredible and thought-provoking solution
to the paradox is that no alien civilizations exist. As Stephen J.
Gould once aptly put it, “Perhaps we are only an afterthought, a
kind of cosmic accident, just one bauble on the Christmas tree of
evolution.”6 The suggestion that we live in some special epoch
is one in general to be wary of, no matter how compelling the
argument might sound, since it runs against the basic tenant of the
so-called Copernican Principle which, under admittedly different
circumstances, many astronomers take to be an underlying axiom
of their work. This principle, while sounding profound, is essentially
a straightforward statement concerning special conditions.
Just as Nicolaus Copernicus, in 1543, argued that Earth is not
located at the center of the universe but is instead a planet in
orbit around the Sun (which he believed was located at the center
8 Rejuvenating the Sun and Avoiding Other Global Catastrophes
of the universe), the Copernican Principle in general says that we
shouldn’t assume that there is anything special about our existence
or our location in the galaxy (and the universe). The point behind
this principle is that the conditions that have resulted in our
existence, while wholly remarkable and exceptionally special in
their development, should operate elsewhere in the galaxy, and,
consequently, there is no specific reason why other life forms
shouldn’t have come into existence on planets orbiting other stars
within our galaxy (and in other galaxies).
There is a caveat to the Copernican Principle that is worth
considering at this stage. Although it makes good scientific
sense to avoid special-case explanations for any given observed
phenomena, there are circumstances where special conditions
must hold true for some specific phenomenon to be observable in
the first place. This set of circumstances is often referred to as
the Anthropic Principle.7 Our existence as intelligent observers,
for example, is special in that the convoluted set of events leading
up to our emergence are not likely to have happened much earlier
than they did. That is, the fact that we observe the Solar System
to be 4.56 billion years old is in part a necessary reflection of
the time required for us to appear. If the time for us to evolve
on Earth is Tus, then we know0 Tms), but that the longer the evolutionary
process proceeds the more likely it is that an intelligent observer
is going to appear, then the appearance time TIN for intelligent life
should be TIN ≈ Tms. In other words, intelligent observers are most
likely going to appear at the exact same time that their parent star
destroys their home planet. According to this line of reasoning the
existence of extraterrestrial life forms is, in fact, highly unlikely.
Carter suggests that our existence (Tus < Tms < Tav) indicates that
our presence is the result of a set of highly improbable evolutionary
circumstances, not likely to be repeated anywhere else in
the galaxy—ever! So, in some sense, we are special, albeit apparently
improbable, after all.
The Drake Equation
When a physicist or mathematician writes down an equation, it
is usually because it makes a very definite and precise statement
about some particular set of circumstances. When we write down
the Drake equation, however, which expresses the possible number
of extraterrestrial civilizations N within our galaxy, we ultimately
write down an equation that expresses our total ignorance. This
statement is not made as an indictment of SETI pioneer Frank
Drake,8 who first discussed the equation now named after him,
but a comment upon the fact that we simply don’t know, even to
order of magnitude, what actual numbers to place in the equation.
(This is actually a counter example to Fermi’s maxim discussed
in Note 1.) There are at least seven terms that can be included
in the Drake equation. The first term accounts for the formation
rate of stars R* in the mass range ∼0.5 M to ∼1.3 M We shall
explain in Chapter 4 why this particular mass range is important.
Having formed a star, there is then a term fP that accounts for
the fraction of those stars that actually have planets. A third term
nL then accounts for the number of planets that reside in the
habitability zone (again, discussed in Chapter 4) where life might
possibly exist. Three other fractional terms are then introduced:
fI, which accounts for those planets in the habitability zone that
actually evolve life; fI, the fraction of those life forms evolved that
actually acquire an advanced ‘intelligence,’ and fE, the fraction
10 Rejuvenating the Sun and Avoiding Other Global Catastrophes
of those intelligent species that develop advanced technologies
(such as radio transmitters producing signals that we might detect).
A final term L is introduced to account for the lifetime of the
civilization ended by natural or self-destruction. Drake’s equation
is the product of all these terms:
N = R∗ fP nL fL fI fE L (1.1)
The simplicity of Equation (1.1) is, as mentioned above, deceptive.
Surely, all we have to do now is plug in reasonable numbers for all
of the terms, and we have our estimate for N. This would be true, of
course, if we actually knew with any certainty what values to give
for the various terms. The only term that astronomers can place a
reasonably good value on is that for R*, the star formation rate. The
second astronomical term fP is beginning to be constrained through
the ever-increasing number of extrasolar planets being discovered.
This latter constraint, however, is currently not especially helpful,
since only gas and ice-giant Jupiter- to Neptune-like planets have
been discovered with any certainty. As of this writing there is no
clear idea how many of the presently detected planetary systems
might contain terrestrial planets in a habitable zone.9
The available observations suggest that the star formation
rate R* has been decreasing ever since the formation of our galaxy
(thought to be at least 13 billion years old). This has a number
of interesting consequences. The metals (by which astronomers
mean all the elements other than hydrogen and helium) that are
vitally important for making terrestrial-like planets and ultimately
allowing life to come about are all produced through fusion
reactions (see Chapter 3) within the cores of massive stars and
their end stages as supernovae. Most of the metals were produced,
therefore, in a strong initial burst of star formation in the first
few 100 million years of the galaxy forming. Consequently it is
possible that at least some terrestrial planets may have formed
very early on, allowing for the possibility that some extraterrestrial
civilizations may have existed for billions of years prior to the
formation of our Solar System. This is a thought-provoking possibility
indeed, and one that makes the absence of extraterrestrials
on Earth – here and now – all the more intriguing, as Fermi noted.
A Universal Problem 11
There is an interesting mix of terms in Equation (1.1), and
these speak to its hidden complexity. Although the first three
terms are essentially astronomical in nature, the terms fL and fI
are determined according to biological constraints. The last two
terms, fE and L, depend upon the sociology of the intelligent life
that has evolved. All we can say currently is that N is at least equal
to one—i.e., philosophical issues aside, we exist. As to whether N,
after a final tally is made (which begs the question, “how would
we know?”), will still be equal to one or if it will be as large as,
say, one million is completely unclear at the present time. Either
way, even finding out that N = 2 would have profound effects upon
human society.
“Hey! Over Here!"
A number of researchers have suggested that rather than the actual
beings from an advanced extraterrestrial civilization exploring
(or colonizing) the galaxy, they might send out self-replicating
machines instead. These so-called von Neumann10 machines are
almost mythical beasts, endowed with superior engineering skills
and an intelligence that far exceeds those of, say, a mere human
being. With these machines we break with the traditional science
fiction precedent and submit that just because such mechanisms
can be dreamed of does not mean that they will ever be constructed
(for galactic exploration, that is). If a civilization wants to actually
communicate its existence or colonize the galaxy, then the use of
self-replicating machines is an inherently difficult way of trying to
do it. Highly advanced robotic and artificially intelligent systems
will almost certainly be developed, and they will also probably be
used to explore and help colonize a home planetary system, but
only under circumstances where profits – commercial and social
as well as scientific – can be extracted.
Having argued the above it should be noted, however, that
there are actually good reasons for sending spacecraft into interstellar
space. The difference between spacecraft and Von Neumann
machines, however, are that the former are passive and relatively
cheap, while the latter are invasive, arguably aggressive, and
highly expensive. Neither object actually provides any return of
12 Rejuvenating the Sun and Avoiding Other Global Catastrophes
information, but the simple, slow spacecraft method provides
an exceptionally efficient means of providing a large amount of
information, to any potential finder, in one simple dose. Indeed,
when the speed at which any communication proceeds is not of
overriding importance, Christopher Rose and Gregory Wright11
argue that “inscribed matter” messages (Figure. 1.1) are far more
Figure 1.1. The plaque carried aboard the Pioneer 10 and 11 spacecraft, both
of which are now traveling into interstellar space. The plaque was designed
by Frank Drake in collaboration with Carl and Linda Sagan and carries a
wealth of ‘inscribed’ information. Two human figures are shown to scale
by the spacecraft, and a diagram (to the lower right) shows which planet in
our solar system the spacecraft came from. The set of ‘star’ lines towards
the center right of the plaque indicate the position of our Sun with respect
to nearby pulsars—each pulsar being identified by the binary value of its
spin period. The two circles to the upper right of the plaque correspond
to the atomic hydrogen molecule. The plaque is about 15cm x 23cm in
size. While not actually aimed at any specific star system, Pioneer 10 is
currently heading in the direction of the constellation of Taurus. Pioneer 11
is heading towards the constellation of Aquila. (Image courtesy of NASA)
A Universal Problem 13
cost-effective and efficient than any other mode of communication.
Indeed, Rose and Wright comment that “Carefully
searching our own planetary backyard may be as likely to reveal
evidence of extraterrestrial civilizations as studying distant stars
through telescopes.”12
Caveat
One of the central tenets of the Fermi Paradox is that there
is no evidence that extraterrestrial beings or, for that matter,
autonomous extraterrestrial spacecraft (such as von Neumann
machines) have ever visited our solar system. Although this last
statement is true as it stands, there is, of course, the issue of recognition.
How can we be sure that all the correct places have been
searched when we don’t actually know what it is we are looking
for? Physicist Stephen Wolfram has recently argued, in fact, that
recognizing extraterrestrial intelligence may even be impossible—
at least, that is, with current search strategies.12
In spite of Wolfram’s pessimism, various programs have
been initiated in recent years to address the visitation issue. For
example, Search for Extraterrestrial Artifacts (SETA) and Search
for Extraterrestrial Visitation (SETV) programs have joined the
multitude of Search for Extraterrestrial Intelligence (SETI) initiatives
already in place. But to date no credible artifacts or visitation
data have been found.
The ability to search for and potentially recognize extraterrestrial
artifacts, such as spacecraft with inscribed, informationladen
messages will, presumably, improve with time. As humans
explore more of the Solar System in greater and greater detail,
the chances of our finding any embedded artifacts will improve.
Since longevity of survival is paramount for any inscribed message
platform, Alexey Arkhipov of the Institute for Radio Astronomy
in the Ukraine has suggested that the best first-place to look for
such objects is our Moon.13 The Moon, Arkhipov argues, provides
shielding from a large fraction of the micro-meteoroid flux, a
stable land mass (large impact cratering events aside) that has no
atmospheric or biological factors to corrode or disturb equipment.
14 Rejuvenating the Sun and Avoiding Other Global Catastrophes
Arkhipov has also suggested that an “Astroinfect Principle”
could be at play within our galaxy.14 Specifically, Arkhipov notes
that the winds associated with stars might eject space debris
(literally, the small scraps of paint, fuel pellets, fecal matter, and
exotic alloy flecks blasted by meteoroid impacts upon spacecraft
in orbit around Earth) into interstellar space, and these alien scraps
might just be detectable in, say, the lunar regolith. Ian Morrison
writes that “For perhaps 7 billion years there have been enough
heavy elements within the interstellar medium for planets to form
and intelligent life to arise. If, in this period, one such civilization
came into existence every 100,000 years, then 70,000 advanced
civilizations might have come and gone. Could one of them have
left any evidence of their existence?”15 One can always argue
about the numbers of possible extraterrestrial civilizations, but it
is intriguing, and indeed sobering, to think that the past heights
of advanced extraterrestrial intelligences within our galaxy might
only be betrayed to us by the garbage that they left behind.
Types of Civilizations
Russian astrophysicist Nicolai Kardashev has proposed a threetiered
system of civilization classification. His scheme is based
upon how much energy a specific civilization can draw upon.16
Using Earth and the Sun as the basic measure of energy being
consumed and energy potentially available, Kardashev suggests the
following designations:
• Type I A civilization that can draw upon and consume ∼1017
joules of energy per second. Earth presently corresponds to just
such a civilization.
• Type II A civilization capable of harnessing and using the entire
energy output from its parent star. In the case of our Solar
System, this would correspond to the consumption of about
4 x 1030 J/s worth of energy. A civilization capable of building
a so-called Dyson sphere (discussed in more detail in the next
chapter) about their parent star would correspond to a Type II
civilization.
A Universal Problem 15
• Type III A civilization that can draw upon the energy available
on a galactic scale. This corresponds to an energy consumption
rate of something like 1041 J/s.
Although the actual amount of power available to a civilization
will no doubt vary from one stellar system to the next, the basic
idea of the scale advancement is clear, with the classification type
increasing each time the energy consumption rate jumps from
planetary to parent star to multiple star to galactic. It seems that
there is no Type III civilization currently in existence within our
Milky Way galaxy, and there is currently no evidence to indicate
that any Type II civilizations exist (but see Chapter 2).
Moving Forward
In the highly charged game of debating the existence of extraterrestrial
civilizations one has eventually to – openly or obliquely –
make a statement about how one is going to proceed. We
are going to assume, since we have no real proof, that life is
probably abundant throughout our galaxy (and other galaxies),
and that many advanced civilizations exist with technologies
well in advance of our own. We shall also proceed on the basis
that no advanced civilization has ever attempted, or perhaps
more strongly, has never needed to colonize the galaxy. These
working assumptions we will attempt to bolster in the next several
chapters. Mostly, however, we will proceed on the basis that it is
unlikely that galactic colonization is ever likely to be advanced
upon pure economic grounds. Likewise, we will argue that any
civilization that survives against self-destruction would have no
overriding reason to leave their home planet (or more exactly their
planetary system) because of ecosystem collapse. To survive in the
long-term requires that a civilization must live in at least partial
harmony with its surroundings and have a stable, well-supplied,
and well-nourished population. Anything less will inevitably lead
to strife and ultimately self-destruction.17 There are, it seems,
fundamental limits to communication and space travel speed that
cannot be broken. Specifically, for example, let us assume that
space travel will never proceed at speeds anywhere near that of
the speed of light.3 The advanced civilizations that do exist, we
16 Rejuvenating the Sun and Avoiding Other Global Catastrophes
suppose, will explore their immediate planetary systems and will
carefully utilize all the properties and resources available to them.
These civilizations may also build small worlds that orbit their
parent star, and they may even build O’Neill and Dyson sphere-like
structures (described in the next chapter). In this fashion so-called
Kardashev Type II civilizations might eventually be discovered,
but we suppose that Kardashev Type III civilizations, utilizing the
entire energy of their host galaxy, will not be found.18
With all the above being laid out, what is the solution to
Fermi’s Paradox being developed in this book? In a nutshell, it
is this: although the galaxy contains many (or even just a few;
it matters very little at this stage) advanced civilizations, they
are not among us now because they have never had a need to
move away from their home planet (or more precisely, their home
planetary system). In addition, for civilizations more ancient than
our own, star-engineering has eliminated the imperative towards
galactic colonization resulting from the gigantism experienced by
non-engineered stars at the end of their main-sequence phase.
We will argue in the following chapters that advanced civilizations
will not be forced to seek new planetary systems as a result
of their parent stars reaching the end of their main sequence phase.
Indeed, advanced societies will invest their superior skills and
knowledge into the engineering of their parent star. They will
literally control their own destiny and, thus, have no need to
seek new havens beyond the reaches of their immediate planetary
system. The interstellar exploration that any advanced extraterrestrial
civilizations might ultimately undertake will most likely
be purely parochial and predominantly scientific fact-gathering
missions.
Notes and References
1. Enrico Fermi (1901–54), an Italian-American physicist, is principally
known for his pioneering research relating to the modern day understanding
of atomic structure. In 1926 he described the statistical
law (now called Fermi-Dirac statistics) that governs the behavior
of particles subject to the Pauli Exclusion Principle. Fermi was
one of the key scientists behind the Manhattan Project leading to
A Universal Problem 17
the development of the first atomic bomb. Fermi was also famous
amongst his peers for his approach to making ‘ballpark estimates’
of unknown quantities. Essentially, Fermi argued, that even if you
don’t know the order of magnitude answer to a question, you can still
proceed to estimate the answer by making a series of assumptions
about the numbers going into the answer. The law of probability then
dictates that while some estimates will be too big, others will be
too small and correspondingly the eventual result should be about
right. There is a very enjoyable and highly recommended introductory
chapter on solving Fermi problems in the book by John Adam, Mathematics
in Nature: Modeling Patterns in the Natural World. Princeton
University Press, Princeton (2003).
2. Observations indicate that the Sun is 8,000 pc from the galactic center
about which it orbits with a speed of 230 km/s. From these two
quantities the galactic year is evidently some 200 million (Earth)
years long. Kepler’s third law further tells us that for the Sun’s orbital
radius and orbital period to have the values that they do, the amount
of matter interior to the Sun’s orbit must amount to about 1011 solar
masses. Now, astronomers have also discovered that about 90 percent
of this mass is in the form of dark matter that neither emits nor
absorbs electromagnetic radiation. The amount of mass in terms of
observable matter (i.e., stars) is of order 1010 M therefore. Some of
this mass is in the form of the gas and dust of the interstellar medium,
some is in the form of hard-to-observe Jupiter-like planets, and some
will be in the form of brown and white dwarf stars. Our estimate of
1010 stars in the galaxy is probably conservative since most stars have
masses of only a few tenths that of the Sun. The average separation of
stars is based upon the observed density of about 0.1 stars per cubic
parsec volume of space. With this density the typical star separation
will be about 2 pc (or ∼6 light-years). If we had assumed that there
are 1011 stars in the galaxy with an average separation of 2 pc then
the colonization time increases to about 2.5 million years—a change
that has no effect upon Fermi’s argument.
3. The speed of light c = 3 x 108 m/s is a universal constant that defines a
limiting speed within our Universe. Our estimate for the speed of an
interstellar probe is relatively modest. The New Horizons spacecraft,
launched in January of 2006, on its way to study the dwarf planet
Pluto will reach a top speed of about 16 km/s. Even at this speed it
will take more than nine years to reach Pluto and the Kuiper Belt
beyond. If this current upper speed limit of 16 km/s is used in the
Fermi calculation (as per Note 2) the galaxy colonization time is
18 Rejuvenating the Sun and Avoiding Other Global Catastrophes
doubled to about four million years – a change that has no significant
effect upon the argument being presented.
4. A variety of interstellar colonization models have been proposed and
developed over the years and, according to the various input assumptions
adopted, a range of colonization times emerge. Typically the
galactic colonization time for a single motivated civilization is found
to fall between 107 and 109 years. While these colonization times
are 10 to 1,000 times larger than our Fermi estimate, they do not
significantly change the argument. The timescales are still such that
one would expect aliens to be actively found within our solar system
in the here and now.
5. A good – but now a little dated – survey of solutions to Fermi’s
Paradox is given by Michael Hart, An explanation for the absence
of extraterrestrials on Earth. Quarterly Journal of the Royal Astronomical
Society, 16, 128–135 (1975).
6. S. J. Gould, Wonderful Life, Norton, New York (1989). The famed
evolutionary biologist Ernst Mayer (1904–2005) has also pointed out
that eyes, for example, have evolved on numerous occasions since life
first appeared on Earth, while intelligence (such as ours) has evolved
just once. This clearly indicates that the evolution of eyes is highly
probable, while the evolution of intelligence, in spite of its great
adaptive value, is not. Mayer discusses this point in Extraterrestrial:
Science and Alien Intelligence, E. Regis Jr. (ed), Cambridge University
Press, Cambridge (1985). In contrast to the evolutionary argument,
one could also explain our (apparent) uniqueness in terms of religious
doctrine.
7. There are a number of forms of the Anthropic principle. The socalled
weak form is being presented in this book. By far the most
comprehensive guide to the historical development and application of
the Anthropic principle is that by John Barrow and Frank Tipler, The
Anthropic Cosmological Principle, Oxford University Press, Oxford
(1986).
8. In 1960 Frank Drake (b. 1930 - ) used a radio telescope at the National
Radio Astronomy Observatory in Greenbank, Maryland to listen-in
to possible radio transmissions from the nearby Sun-like stars Tau
Ceti and Epsilon Eridani. Nicknamed Project Ozma, this was the first
dedicated radio survey in the search for extraterrestrial intelligence
(SETI). Drake developed his famous equation in 1961 on the number
of possible extraterrestrial civilizations. The purpose of the equation
was (and still is) to focus attention towards the crucial questions that
might determine the chances of SETI’s success.
A Universal Problem 19
9. It is entirely possible that, in principle, life could exist within the
upper atmospheres of Jupiter-like planets having orbits that place
them close-in to their parent star. Life could also, in principle, exist
on a moon in orbit around a Jovian planet. The moon Europa that
orbits Jupiter in our solar system, for example, has a global ocean
that may harbor life (see Chapter 4). Enceledus, in orbit around
Saturn, is another candidate moon that may potentially support life
given that subsurface liquid water is thought to be an important
component in shaping a number of its observed surface features. The
potential number of Earth-like planets within our galaxy is not easily
estimated, but recent observational results suggest that they may, in
fact, be very plentiful.
10. John von Neumann (1903–1957) was the Hungarian-American mathematician
responsible for the development of game theory and the
mathematical foundations of quantum mechanics. He was a pioneer
of computer science and was a key player in the development of the
theory of electronic computation. Barrow and Tipler (Note 7) have
especially argued that we (that is, humanity on planet Earth) must
be unique in the galaxy since no Von Neumann-like machines have
ever visited the solar system.
11. Christopher Rose and Gregory Wright, Inscribed matter as an
energy-efficient means of communication with an extraterrestrial
civilization. Nature, 431, 47–49 (2004). Commenting on the paper by
Rose and Wright, Woodruff Sullivan III [Message in a bottle, Nature,
431, 27–28 (2004)] notes that it has been estimated that all of the
written and electronic information that now exists on Earth constitutes
about 1019 bits of information. If one used scanning tunneling
microscopy, as suggested by Rose and Wright, to encode this information
in nanometer squares of xenon atoms placed on a nickel
substrate, then the entire written knowledge of humanity could be
inscribed within 1 gram of material. Certainly this methodology
encodes a fantastic amount of information in a very small package,
but as Sullivan argues, “We do not know if such a package, even if
efficiently sent, would ever be recognized and opened.” The point is,
of course, that there are times when arguments based upon economics
and efficiency, which are little more than the ‘spoiled children’ of
guesswork and ideology anyway, are not enough. Sometimes, the
inefficient and more expensive approach will return better dividends.
12. Wolfram’s views have been nicely described by Marcus Chown [The
alien within your computer, Astronomy Now, 20 (7), 32–35, July
(2006)]. With respect to electromagnetic communications, Wolfram
argues that advanced civilizations will use methods that are far more
20 Rejuvenating the Sun and Avoiding Other Global Catastrophes
complicated and much less structured than the forms we are accustomed
to using. In this sense, Wolfram suggests, SETI radio surveys
that only ‘search’ for extraneous periodic signals are probably doomed
to failure at the very outset.
13. A. V. Arkhipov, in Progress in the Search for Extraterrestrial Life.
G. S. Shostak (ed.). ASP Conference Series, 74, 259–267 (1995).
Arkhipov, in fact, argues in his article that, “Landing on the moon
would be for ET visitors a necessity rather than a convenience.”
14. A. V. Arkhipov, New arguments for panspermia. The Observatory,
116, 396-397 (1996). Arkhipov argues that microorganismcontaminated
space debris can potentially form a large, – of order
1-pc in size – non-sterile zone (NSZ) around a star supporting an
intelligent, space-exploring civilization. The passage of another star
(and its accompanying) planets through a NSZ could result in the
planets being infected by space-borne microbes. Arkhipov argues that
something like 200,000 stars capable of supporting planetary systems
will have passed within 1.5 pc of the Sun since its formation 4.5
billion years ago. We will pick up the theme of stellar encounters in
the next chapter.
15. I. Morrison, SETI in the new millennium. Astronomy and
Geophysics, 47, 4.12–4.16 (2006). Morrison points out in this review
article that, to date, only a very small fraction of the radio spectrum
and galaxy has been studied at radio frequencies. The next major
step forward for radio SETI is likely to be the completion of the
Square Kilometre Array (SKA), a project currently under design study
(http://skatelescope.org/).
16. N. Kardashev, Transmission of information by extraterrestrial
civilizations, Soviet Astronomy-AJ, 8 (2), 217 – 221 (1964).
17. Here I am betraying a somewhat humanistic philosophy which may
not be a required dictate for of all civilizations. It is not inconceivable
that a civilization (either terrestrial or extraterrestrial) might
maintain a rigidly enforced birth control and euthanasia program
to ensure its long-term survival. This process is (arguably) fair; all
individuals get some allotted time to enjoy a full and happy life,
but no individual is allowed to overexploit the resources needed to
support the current and future generations. It is possible that highly
aggressive and secular societies – such as our own could be characterized
– will never achieve long-term survival. To face an extended
future or to journey to nearby star systems may require a more
non-materialistic, non-commercial, and inherently spiritual outlook.
Some of these issues are nicely explored in Mary Doria Russell’s
fictional book The Sparrow [Black Swan, 1998]. Secular societies
A Universal Problem 21
certainly achieve many great triumphs, but they never live up to their
full potential. We will pick up on these themes again in Chapter 7.
18. James Annis, an astrophysicist at Fermilab in the United States, has
conducted a study of the brightness characteristics of several hundred
elliptical and spiral galaxies in search of potential Type III civilizations
[Placing a limit on star-fed Kardashev type III civilizations,
Journal of the British Interplanetary Society, 52, 33–36 (1999)], but
no candidate civilizations were revealed. Indeed, Annis goes further
and uses the available galactic survey data to estimate that the time
required to produce a Type III civilization cannot be less than 300
billion years. Since the Universe is only 13 to 14 billion years old, it
seems clear that Type III civilizations simply can’t exist within our
present universe.
2. It’
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