Rarity of Complex Life in the Universe

7/29/2019 Rarity of Complex Life in the Universe

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How Rare is Complex Life in the Universe?

Jonathan Sunny Laxmi

Philosophy deals with the study of existence, knowledge, and the interaction between the

two. Psychology deals with the behavioral and social underpinnings of human behavior. Physics

deals with the nature of reality. How do these three interact?

It is only in answering this question that we can unravel the intricately interlaced natureof these three fundamental, interdependent areas of interest. Technology has allowed us to verify

beliefs about the universe through direct observation. From exploring the galaxies with advancedtelescopic technology, peering into the deep recesses of the universe, and analyzing patterns on a

cosmological and quantum level, we have a substantive trough of information supporting ourstrongest theory on all formationthe Big Bang. Using our knowledge about the universes

development coupled with the anthropic principle, which is the argument that any theoreticalbasis for physical explanations of the universe must account for the conscious life that observe

and abide by it, we can move our thoughts to the next logical question: Is there complex lifeelsewhere in the universe?

The question of how rare complex life is in the universe is one that has been debated for

several years, and has still not been completely answered to this day. Although it seems that thisissue has only become prevalent recently, through the publishing of Rare Earth, a book

explaining the possibility that we are alone as intelligent organisms in the galaxy, the issue of lifeand our existence has been around for some time. The Rare Earth controversy has its roots in

ancient Greece, where philosophers asked: Are there other worlds like ours harboring other lifelike us? (Darling 92). From this conception, we see that the Hellenic kosmos placed the Earth at

the center of many revolving spheres. Aristotle, Plato and other followers of this beliefestablished the idea that we were at the center of the universe and that there was nothing else out

there except forour sun and our moon. Later on, Copernicus soon realized that the solar system

was heliocentric through his observations and plotting of planetary and solar movement.Through the Copernican Revolution, questions of other bodies in space and the galaxy were soonquestioned, and within five hundred years, we came to know of the several other stars out there

in billions of other galaxies, and the lack of uniqueness of our own system and planet.

To redefine our understanding of our own planetary and solar system we began to look atEarths biological status. The two opinions developed during the 1920s and 1930s that were

widespread among biologists first, that either the steps leading to life were highly improbable,or second, that the planets of the solar system had formed in the wake of a near-collision between

the Sun and another star. This would have given an explanation to those trying to understand theformation of planets of our solar system because it would have shown that planets could only be

formed as a result of an incredibly unlikely encounter, therefore making life, and us, rare andunique. By the 1970s a new argument had surfaced which gave way to the present hypotheses

that exist today. Some astronomers, led by Michael Hart, spoke of a habitable zone around a star,which was a region in which an Earth-like planet would be able to support liquid water, and how

it was narrower than had been originally thought. Through his calculations, he figured that if theEarth had been just one percent farther from the Sun, it would have become permanently encased

in ice (Darling 94). Although this was later disproved through the discovery of the importanceof extra greenhouse heating, Hart brought up the concept of chaos theory (also known as the


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butterfly effect), which has proven itself apparent in several other situations. This theory pointsout that even the smallest change in initial conditions of a dynamical system can cause great

changes in the outcomes or eventual products.

To put all these concepts into application, Francis Drake proposed an equation in 1961,

which estimates the number of advanced civilizations (having intelligent life and being able tocommunicate) that might be present in the galaxy. Bias placed towards the potential existence ofintelligent, complex life elsewhere in the galaxy stems from the use of this equation. The Drake

Equation is presented as follows: N = R* fp x ne x fl x fi x fc x L. R is the average rate of starformation in our galaxy; fp is the fraction of those stars that have planets; ne is the average

number of planets that can potentially support life per star that has planets; f is the fraction ofthe above that actually go on to develop life at some point; fi is the fraction of the above that

actually go on to develop intelligent life; fc is the fraction of civilizations that develop atechnology that releases detectable signs of their existence into space; and L is the length of

time such civilizations release detectable signals into space. Although some of the equationselements can be figured out, such as the rate at which stars form in our galaxy, from fl onward,

there are no definitive quantities that scientists, astrobiologists, or physicists can attribute.Because we cannot pinpoint the fraction of planets that will go on to develop life, since the only

known example of this is Earth, we cannot infer much more objectively from the Drake equation.

The components of the Drake Equation are held separately from biological implicationsand the implications of what had to occur for Earth to be created. Peter D. Ward and David

Brownlee were the first two to truly shed light on the importance of a potential rare earthhypothesis. They put forth conditions to explain how life on earth, and the earth itself, must

have required a specific order of circumstances and conditions to come into existence, and howthere is a very small if any possibility of there being another planet with intelligent, complex life

like ours. In essence, aside from the complicated and complex processes in the actual evolution

and development of biological life on our planet, both Ward and Brownlee conclude that in orderfor complex life to exist on a planet, there are certain conditions, that our planet has met andanother planet must meet as well to have intelligent life. The planet must have a large, nearby

moon; it must experience the right level of catastrophic events to promote biological diversitywithout completely extinguishing life; it must be an Earth-like world in its stars continuously

habitable zone; the planetary system must contain a Jupiter-like world in a Jupiter-like orbit; theplanets orbit must be precise so that it does not fall out of orbit around a solitary, stable, Sun-

like star; the planet must have ongoing plate tectonics; and the planetary system must movewithin the Galactic Habitable Zone. (Darling 95) Physicist Lawrence Krauss of Case Western

Reserve University makes a valid point in saying that Ward and Brownlee summarize clearlythe developments over the past few decades that reveal the complexity of the evolution of

advanced life on earth. However, demonstrating the complexity of a process is different fromdemonstrating that the end result is rare (Darling 92).

Planets must have a large, nearby moon because if the Earth was spinning at the same

rate as it is now, and did not have a large moon, its obliquity would vary chaotically from zero toeighty-five degrees. Obliquity is the angle of tilt of Earths spin axis relative to the plane of its

orbit and is the cause of seasonal changes. For most of Earths history, Earths obliquity has notvaried from its twenty-three degree obliquity. It [the moon] causes lunar tides, it stabilizes the


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tilt of Earths spin axis, and it slows the Earths rate of rotation. Of these, the most important isits effect on its obliquity (Ward & Brownlee 223). This argument was derived from the work of

Jacques Laskar and his coworkers in 1993. It is this tilt, of course, that gives rise to the seasons:northern hemisphere summer occurs when the North Pole is tilted towards the Sun, while winter

occurs when the North Pole is tilted away from the Sun. Ward and Brownlee point out that

obliquities approaching 90 degrees would lead to extreme seasonal cycles, especially in polarcontinental interiors where the moderating effects of the ocean are small. Continents located nearthe equator would experience an unusual seasonal cycle with two summers and two winters each

year, but their climates would not be subject to the extremes of temperature that would occur athigh latitudes.

We cannot be sure that a moonless Earth would have prevented intelligent life from

arising. A moonless Earth's obliquity would vary chaotically depends on the planet's spin rateand initial obliquity, as well as on the masses and orbital periods of the other planets (Kasting

3). Models that have been made of Earth-Moon systems indicate that Earth may have beenspinning at a rapid rate initially and may have slowed down over time due to friction caused by

solar and lunar tides. Without the moon, tidal dissipation rate would have been smaller, and theEarths spin would not have decreased as fast. The only issue is that the very reason why the

Earth was spinning so fast was because of the presupposed Moon-forming impact, therefore notgiving a clear answer as to the true initial effects of the moon upon the Earth, or the full

consequences of a moonless Earth. It is extremely difficult to predict whether other Earth-likeplanets will be in the chaotic obliquity regime or not, so we cannot yet determine whether this is

a widespread problem for planetary habitability (Kasting 2-3). Even is a large moon is found ina separate planetary system for a planet, we cannot conclude that conditions for complex life

exist.

Another factor that plays into the Rare Earth hypothesis and that a specific set of

circumstances gave birth to the formation of Earth and its intelligent life is the creation of themoon itself. The giant impact hypothesis states that through young Earths collision with a Mars-sized body called Theia, the moon was formed. There is indirect evidence that comes from rocks

collected during the Apollo Moon landings, which show similar oxygen isotope compositions tothose of the Earth. When Theia grew to be the size of Mars it became too massive to stay in its

own Trojan orbit, so it began to fluctuate its orbit and hit the Earth. Because it is thought thatTheia struck the Earth at an oblique angle, we believe Theia was destroyed and a significant

portion of its planetary substance was ejected into space. Through computer simulation we haveestimated that about two percent of the original mass of Theia then became a ring of debris,

which then grouped together into the Moon between one and a hundred years after the impact.(Ward & Brownlee 229-234) Due to the randomness and specific circumstances of this event we

see how the Rare Earth hypothesis can be further supported. If it takes such a specific andrandom set of circumstances to create a large, nearby moon (which is hypothesized as a necessity

for intelligent life) then chances are, it is even less possible for there to be other planets that canhouse or support intelligent life in the galaxy.

The habitable zones discussed earlier in this paper play an important role in the Rare

Earth hypothesis. Earths location being a seemingly ideal distance from the sun gives furthersupport to the idea of a habitable zone. This zone represents a region where heating from a


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central star provides a planetary surface temperature at which a water ocean neither freezes overnor exceeds its boiling point (Ward & Brownlee 16-17) But not only is there a habitable zone

according to Ward and Brownlee, but also an Animal Habitable Zone. This zone is where aplanet has to have a mean surface temperature between 0 and 50C. They came to this

conclusion because 50C seems to be the upper limit above which animal life cannot exist.

Because water can exist on a planetary surface at temperatures up to the boiling point, a planetwith liquid water on its surface might be much too hot to allow animal life (Ward & Brownlee20). This further narrows the conditions under which complex life can actually exist, if it can

come to exist outside of our planet at all.

The location of a planetary system within a galaxy must be favorable to the developmentof life. Ward and Brownlee point out that not all regions of the Milky Way galaxy are equally

likely to harbor habitable planets. There are planets that are too close to the center of the galaxyand those that are too far. Those planets that are orbiting stars too close to the center of the

galaxy have a higher chance of being disturbed by close stellar encounters, and may findthemselves more susceptible to catastrophic events such as supernovae or gamma ray bursts.

Stars that are near the outer edge of the galaxy are less rich in metals than the sun, and thereforehave less of a chance of having orbiting planets in the first place. In order for there to be life, a

system must be close enough to the galactic center so that there are enough heavy elements canform rocky planets. Also, heavier elements may also need to be present as they form complex

molecules of life, such as iron or iodine. (Kasting 3-4) While any specific example of a heavierelement may not be necessary for all life, heavier elements in general become increasingly

necessary for complex life on Earth (both as complex molecules and as sources of energy(Brown 1).

Considering the topic of protection from hazardous impacts and extraneous objects, we

see the importance of the presence of a Jupiter-like world in a Jupiter-like orbit. This argument

derives largely from the work of George Wetherill in 1994. In general, Jupiter helps shield theinner Solar System from cometary impacts which originate from either the Oort Cloud or theKuiper Belt. Because Jupiter is so massive, more than three hundred times Earths size, it is able

to kick back most of the perturbed objects that are brought into orbit in the region occupied byplanets before it reaches the inner solar system. Wetherills studies suggest that if Jupiter was not

present the frequency of cometary impacts on Earth could have been as much as 1,000 to 10,000times the current value. (Kasting 1-2)

But unfortunately, the existence of Jupiter can prove to be a detriment to our planetary

system as well. Due to Jupiters large mass and gravity, the Earth has been hit occasionally byasteroids that have come from the asteroid belt. The large gravity of Jupiter makes it a double-

edged sword in this way. It was most likely an asteroid, not a comet, that killed off thedinosaurs 65 million years ago, as evidenced by the high concentrations of iridium in the

boundary layer clay. Indeed, the very existence of the asteroid belt is most likely a result ofJupiter's large gravity, which prevented a planet from forming in that region. So, to the extent

that asteroid impacts are a danger to life on Earth, Jupiter is a villain as well as a protector(Kasting 1-2). Recent studies in 2008 have shown that Jupiter acts more as a sniper in attracting

asteroids and other materials in space within the solar system than it does to protect it. Thisobservation dismisses the fact that a Jupiter-like planet is necessary for intelligent life to exist.


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Another concept important to the understanding of whether there is the possibility of

intelligent life elsewhere in the universe is the Fermi paradox. The Fermi paradox is the apparentcontradiction between high estimates of the probability of the existence of extraterrestrial

civilizations and the lack of evidence for, or contact with, such civilizations. This idea was

supposedly put forth by Enrico Fermi at a lunch in 1950, where he had wondered whereextraterrestrial life could be. Due to the extreme age of the universe and the amount of stars, it isintrinsically suggested that if the earth is typical, extraterrestrial life should be common. Enrico

Fermi questioned why, if a multitude of advanced extraterrestrial civilizations exist in the MilkyWay galaxy, evidence such as spacecrafts or probes are not seen (Wesson 161). There are

several reasons for why intelligent life may not have contacted us, including the idea that anintelligent race may have already destroyed itself, may not know how to communicate with us,

or just may be too distant from us within the galaxy to communicate. All these implications canbe answered by the fact that there may not be intelligent life out there, as the Rare Earth

hypothesis suggests. The chance of there being intelligent life is extremely low, and if there isintelligent life, we still do not know how to or if we will communicate with them.

It is important to remember that fifty years ago we did not have any idea about the

quantitative amounts used in the Drake equation. Although we are still missing definitiveknowledge to know the number of planets with intelligent life (N) in the Drake equation we have

calculated the amounts for the first three symbols in the equation. We know R, the rate of starformation, to be ten stars in our galaxy; fp to be .5, and ne to be 2 (with Mars being on the

edge of the habitable zone). (Bounama, Von Bloh, & Franck 747, 748) Through this we can seethat progress has been made with the Drake equation, and hopefully if we continue to work with

our observations, scientific deductions, and possibly any signs or communication we may receivefrom intelligent life in the future, we will understand better the concept of how rare complex life

really is in the universe.

(This paper was written by Jonathan Sunny Laxmi for Dr. Steven Soters New York University

Honors Seminar Class Life in the Universe. Dr. Steven Soter, is an astrophysicist currentlyholding the positions of scientist-in-residence for NYUs Environmental Studies Program and of

Research Associate for the Department of Astrophysics at the American Museum of NaturalHistory. He co-wrote Carl Sagan's 1980 astronomy documentary series Cosmos.)


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Works Cited

Bounama, Christine, and Werner Von Bloh, & Siegfried Franck. "How Rare Is Complex Life in

the Milky Way?." Astrobiology 7 (2007).

Brown, Ann. "Is Iron an Energy Source for Early Life on Anoxic Earth?." The Geological

Society of America (2005).

Darling, David. Life Everywhere: The Maverick Science of Astrobiology. New York: Basic

Books, 2001.

Kasting, James F.. "Peter Ward and Donald Brownlee's "Rare Earth"." Perspectives in Biology

and Medicine 44 (2001): 117-131.

Ward, Peter D., and Donald Brownlee. Rare Earth: Why Complex Life is Uncommon in the

Universe. New York: Copernicus, 2000.

Wesson, Paul S.. "Cosmology, Extraterrestrial Intelligence, and a Resolution of the Fermi-Hart

Paradox." Royal Astronomical Society 31(1990): 161-170.

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Rarity of Complex Life in the Universe