Rationale
My research has led me to the conclusion that simple life, like bacteria, is relatively pervasive in the Universe. The primary reason for this assertion is the rapidity within which life established itself on the Earth as soon as conditions made that possible. This occurred between 3.85 to 3.5 billion years ago as soon as the Earth ceased to be bombarded by devastating asteroids that would have sterilized the Earth and may have done so several times prior to this time. This is supported by Ward and Brownlee (2000) in Rare Earth: Why Complex Life Is Uncommon in the Universe, and by G.S. Kutter (1987) in The Universe and Life. Whereas both of these sources indicate that simple life is probably abundant in the Universe, they come to opposite conclusions on whether intelligent life exists elsewhere. As the title suggests, The Rare Earth hypothesis indicates that there are a plethora of factors that are required for a planet to be suitable for complex! life. Branching off of the Drake equation, Ward and Brownlee come to the conclusion that although simple life is probably abundant in our Galaxy, there are a multitude of factors that make it unlikely that intelligent life would evolve elsewhere. These factors include sterilizations of planets by meteor impact, the necessity of extremely stable conditions for complex life to evolve, including temperature, radiation levels, and water levels and the existence of a large moon to establish a beneficial and stable obliquity. In addition, the Earth's magnetic field helps to protect life from dangerous cosmic radiation. The presence of Jupiter helps to limit asteroid bombardment. They also believe that plate tectonics are an indispensable thermostatic process in the maintenance of a suitable global temperature and composition, and in establishing land masses. The rarity of plate tectonics on other planets greatly decreases the likelihood of life in the Universe. While simp! le life may well be pervasive, the time required with very tight environmental constraints that would enable simple life to survive and evolve into intelligent life is hugely significant. Based on the evolution of life on our planet, Ward and Brownlee suggest that billions of years are required for complex life to evolve. It is not a given as Darwin suggested that life will inevitable evolve into more complex forms. There is an indication in the fossil record of the Cambrian Explosion in which a tremendous number of "body types" evolved in a very short period of time. Actually, all of the body types that exist were developed by that time and no new body types have evolved since. How can this evolutionary "explosion" be explained? In the case of humanoid development there are other questions that are unresolved. In fact, very specific conditions are necessary for humanoid life to evolve, including a stretch of time living arboreally so that sensitive hands were developed and more unaccountably, the evolut! ion of the ability to be bipedal prior to leaving the trees. In addition, they suggest that very specific environmental demands are required for life to proceed to more complex life forms. In addition, more complex life forms are much more susceptible to extinction than simple life forms. All of these considerations lead Ward and Brownlee to propose the Rare Earth Hypothesis, that indicates that Earth is in fact very special and rare indeed and we may be the only intelligent life forms that exist in the Galaxy.
There are also discussions of habitability zones, the types of star systems that would be conducive to life, the inhospitable nature of parts of the Galaxy that are too densely populated, the development of the atmosphere, the necessity of having sufficient oxygen in the atmosphere for complex life to have more efficient energy conversion, the necessity of the existence of DNA or a suitable map, and how life began, including the possibility that life could have been "seeded" from space, most likely Mars. In the 3.8 billion years that life has had to evolve life has managed to propagate in incredibly diverse environments, including the extremophiles, which are organisms that live in extreme conditions. However it is surprising to me that all life is related in its DNA and came from the same source even though it has branched since. This strikes me as very difficult to assimilate that life is pervasive and yet in at least the 3.5 billion years that lif! e has been on Earth, only in the beginning did life originate? What special conditions existed to allow life to come into existence then but not to independently come into existence since? One strong suggestion for the lack of further evolution of life once it started is that life, once it formed, would have been able to out compete any other reproducing "cell" that came into existence. Another premise is that potentially multiple strands existed but all but one went extinct. Either of these hypotheses are plausible but not entirely convincing, so the question will remain, if simple life is as prevalent as Ward and Brownlee and Kutter suggest then why do all life forms on Earth, including the extremophiles share the same DNA source? In other words, why did life only produce one life form strand that survived or even left a record?
On the other hand, G.S. Kutter constructs his own Drake-like equation. In 1987, he predicted, based on a multitude of factors and the relative probabilities that could be assigned to those factors, that there are 100 advanced civilizations in our Galaxy. He is obviously much more optimistic, than Ward and Brownlee, that simple life will evolve into advanced life. His primary factors are 1) The probability that any given star in the Galaxy has planets suitable for supporting life, 2) The probability that on suitable planets life actually arises, 3) The probability that life, once it has arisen on a planet, evolves into complex multicelled forms, and 4) The probability that complex multicelled life evolves into intelligent beings with advanced technology. He states that "Life is not uncommon in the Universe. It probably has arisen tens of millions of times- perhaps even hundreds of millions of times- in our Galaxy alone. . .it appears conceivable that we are the ! only civilization with advanced technology presently existing in our Galaxy. However, just as likely, given the billions of galaxies that populate the observable part of the Universe, we are not entirely alone. Surely our kind has evolved, and survived, elsewhere also." (Kutter 1987) If, in fact, there were one hundred advanced civilizations in our Galaxy, this still presents a daunting problem. Given the size of the Galaxy, that means that the average civilization would still be 10,000 light years away. That means that having only been sending radio waves out for 80 years, and although they travel at the speed of light it would take another 9, 920 years before those first signals would reach them! That doesn't even address the fact that the radio waves would be so weak and dispersed that they would be undetectable. So in considering how we would detect advanced civilizations if they are out there we must consider the advantages of having space telescopes w! ith specialized detectors for receiving any extraterrestrial life signals.
Clearly, there are divergent points of view as to the likelihood that intelligent life exists. So in this unit, I propose to look at the likely probability of each of the factors that would be prerequisites for life as we understand it, and to analyze there relative merits based on current scientific data.
I also intend to introduce the recent discovery that there is a planet, Gliese 581c, that is an Earth like planet having 5 times the mass of the Earth and 1.5 times the diameter revolving around a red dwarf that is only 20.5 light years away. This is the first discovery of a terrestrial planet that is Earth like in the habitable zone of a star, and it greatly increases the probability of life existing in our Galaxy. In addition, scientists have indicated that a second terrestrial planet is also orbiting the Red Dwarf Gliese 581d slightly further out and eight time the mass of the Earth. Although it is slightly outside the habitable zone, scientists have suggested that Gliese 581d with its greenhouse gases may be the truly suitable planet, whereas Gliese 581c might have experience runaway greenhouse warming (W. Von Bloh, et. al, 2007).
It is only in the past decade or so that sensitive enough measurements could be made to prove the existence of planets outside our Solar System. The first extra solar planet was discovered in 1995 called 51 Pegasi by Marcy and Butler (although a radio telescope discovery around a dual star system may have indicated an inhabitable planet a few years earlier (Boss 1998)). The discover of 51 Pegasi was revolutionary and the 4.3 day orbit of the Jupiter sized planet convinced other scientists to reanalyze their six year old data for the existence of planets. And the revolution began. In the last 12 years 241 more planets have been discovered in over 181 solar systems, at an accelerating rate. As of April 2007 over 230 extrasolar planets had been discovered, but all of them were huge gaseous Jupiter-like planets circling far outside the habitable zones or too close to the stars that they revolve around. The difficulty of discovering planets exists because of the nature in wh! ich they are discovered. Most have been detected by their wobble which means that the planets must exert enough gravitational influence to detectably influence the motion of their star. In April two Earth-like terrestrial planet with masses five times and eight times the mass of the Earth respectively and with a diameter approximately 1.5 times that of the Earth were discovered that potentially with liquid oceans. The fact that these potentially habitable planets are so close to our Solar System and are able to be detected with our very limited technology, would seem to promise the existence of a plethora of such planets. There has been an explosion of extra solar planets and the technological advances are enabling astronomers to continue this tremendous advance. There are several NASA satellites in the process of being deployed or in the planning stages that promise the discovery of countless Earth like planets. It seems a simple matter of probability now that the first p! lanet has been found. If this is so, then it would seem all the more likely that advanced life forms would be able to evolve because our speculation about what is required for life could be reduced to verifiably similar environments. Gliese 581c and d basically guarantee that there are millions, and potentially billions, of Earth like planets.
There are four primary ways of detecting planets at the present time. The first two methods are dependent on the "wobble" in stars caused by the gravitational effects of action reaction which cause the stars position to move slightly when a planet revolves around it because only the center of mass moves in a straight line. The planet departs from the center of mass much more than the star but since the planet only reflects a minute amount of the starlight it is currently beyond our technology to detect. Therefore we must attempt to detect the very slight wobble of the luminous object, the star. The two methods of detecting this slight "wobble" are called the astrometric and the radial velocity method. The astrometric is a visual detection of the star's "wobble" when the orbital motion of the planet is perpendicular to ourselves. However, this change in motion is so small that it is extremely difficu! lt to detect, but current technology is advancing which is going to make this possible very soon. The advantage of detecting the EM waves directly is that this allows for spectography to analyze the spectra and determine the chemical composition of the atmosphere of the planets that are found. The second method that utilizes the stars "wobble" is called radial velocity. This method indirectly detects the change in the star's motion using the Doppler effect of the starlight when the orbits are parallel to ourselves. Since the star is oscillating slightly in its motion parallel to us, the motion towards us and away from us results in a change in the stars velocity which can be detected as the Doppler shift. Of the 242 planets that have been detected, the radial velocity method is how the majority of planets have been discovered, and it is the reason that all but two of those planets are huge Jupiter like planets because obviously more massive planet! s are going to cause stars to wobble more and therefore are detectible with our currently limited technology.
However, that technology is quickly evolving and there are many planned space satellites specifically designed to look for planets and search for extraterrestrial life. Satellites are far preferable to land based telescopes because of the undesirable effects of the atmosphere. Satellites avoid the distortions that prevent the precision measurements of the full spectrum of EM waves in space. The other two methods for searching for planets are the transit method and the coronagraphic method. The transit method is to use extremely sensitive optical satellites to detect the slight decrease of a star's luminosity when the planet crosses directly in front of the star. Although these occurrences are relatively rare they provide extremely accurate information about the planet's radius and mass and can determine if a planet is in the habitable zone of its star. The last method which is still being developed is the coronagraphic method. This extremely difficult opt! ical process involves the satellite blocking out the light of the star by optically eclipsing the star so that it can detect the planets which otherwise are too dim to be detected in the star's bright light. The impending deployment of satellites specifically with these capabilities will greatly increase our knowledge of the number of Earth-like or suitable planets there are for life in the habitable zones of stars in our Galaxy.
The only method for directly searching for intelligent life involves the attempt to detect intelligent electromagnetic signals. It is necessary to search as many different frequencies as possible so that the signals that might be sent are not missed. This is our best bet for verifying the existence of intelligent life because we simply do not have the technology to travel very far from this rock that we call home! Since the Galaxy is so huge, we are dependent on EM waves traveling at the speed of light to do the traveling for us. SETI (Search for Extra Terrestrial Intelligent life) is in the process of deploying a massive ground-based radio telescope to detect any possible signal from intelligent life.
This topic is very rich and timely. The greater our advances in technology, the more we will be able to discern about the cosmos. In recent decades science has seen the inclusion of cosmology as a verifiable science with tremendous amounts of data to offer to the scientific community. The advance of astronomy and cosmology has provided a boon of data for the entire scientific community in a time when high energy physics has been limited. It is my hope that the search for extraterrestrial life will gain the respectability that it deserves as a scientific endeavor. The search for intelligent life is the most compelling discovery that we could possible make. . . to know that we are not alone. Now that would be a truly awesome scientific realization.
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