Introduction
Since ancient times, people have been interested in life on other planets and try to answer the question: “Are we alone in the Universe?” Cosmology and UFOlogy try to find some markers of life on other planets and prove that other forms of life exist in the Universe. The accounts of UFOs have varied, but there seems to be a common syndrome: strange objects in the sky, cylindrical or saucer-shaped, glowing or flickering lights, making beeping noises, darting about at incredible speeds, taking off at odd angles, suddenly standing still, or disappearing. There have been many reports of person encounters with humanoid creatures who came out of these saucers, and even incredible accounts of having been abducted, examined, taken to other galaxies, and then returned to earth.
History
Until 1572, astronomers viewed the ‘fixed’ stars — fixed and unchanging, that is, in position but also in brightness — as little more than a backdrop to the motions of the planets. In fact, of course, stars do have individual, or ‘proper’, motions across the sky, but the scale of interstellar distances is so immense that light from even the nearest stars takes years to reach us. As a result, proper motions are almost imperceptible, except over very long timescales; and so the Renaissance observer saw the stars in positions seemingly no different from those assigned them by Ptolemy. Another such nova shone forth in 1604, and this one generated alarm and despondency across Europe (Carroll, p. 11). For the first time in eight centuries, the slow-moving planets Jupiter and Saturn were in conjunction in the fateful ‘fiery trigon’ of the zodiac; and no sooner had they been joined there by Mars, than this new star blazed forth in their midst — the most ominous astrological event imaginable. No one could now doubt that changes occurred in the heavens. Indeed, there was talk of another nova that had appeared in the constellation of the Whale, but this was fainter, and had been seen by only a single observer before it faded and vanished. In 1638 the Whale was host to a second nova (or so it seemed); like its predecessor, it faded and vanished — but before its discoverer could publish his account of it, it astonished him by reappearing. It continued to vanish and reappear at intervals, and in 1667 Ismael Boulliau (1605–94) announced that this ‘wonderful star’ was reaching maximum brightness every 11 months: its behavior was to some extent predictable, and therefore law like (Carroll, p. 13). In these lists Herschel carefully compared stars with neighboring ones of similar brightness, so that a variation in one of the stars would reveal itself by disturbing the published comparisons (Carroll, p. 15). The solar system consists of the Sun, a smallish star resident in the suburbs of an average galaxy, and all the lesser objects that are gravitationally bound to it. The solar system has 8 planets and 166 moons. The Sun dominates its system completely; the second-largest object, Jupiter, has only 0.096% the mass and 2% the diameter of the Sun (Carroll, p. 18). There are nine planets and innumerable smaller bodies. Scientists can construct a scale model of the restricted solar system, consisting only of the Sun and the nine planets, to make it easier to grasp the scale of the system.
Discussion
Suppose that the Sun were the size of an orange. The Earth would then be about the diameter of a small BB pellet (1 mm) at a distance of 11 m from the orange. The moon is 0.25 mm in diameter, and located about an inch (2.5 cm) from the Earth. Jupiter is about 1 cm in diameter and resides 60 m, over half the length of a football field, from the orange. Tiny Pluto is only 0.2 mm in diameter, and its mean distance from the orange is 430 m, about four football fields. Yet even these staggering distances are just down the street, compared to separations in interstellar space (Carroll 23). The nearest star to the Sun, at a distance of 4.3 1t-yr, is Alpha Centauri, a star (more precisely, a stellar system) visible only in the Southern Hemisphere. On our scale model, Alpha Centauri is about 3000 km from the orange. Interstellar distances are really too large to be comprehended by human intuition, yet they are still small compared to the scale even of the galaxy. It is only through the symbolism of mathematics that scientists are able to understand the nature of the cosmos. As far as scientists can tell, almost all stars occur within galaxies. Galaxies are great clusters of stars, gas, and dust, which make up the fundamental population of the universe. Galaxies are divided into three major categories (Carroll, p. 65). Spiral galaxies are great disks of stars, with grand patterns of spiral arms threaded through them like the fins of a pinwheel.
The spirals themselves cannot be rigid objects, or they would have long since wound themselves up to a much greater degree than scientists observe; they are thought to consist of density waves which drift through the stars and gas like ripples on a pond. The spiral arms are delineated by their overabundance of bright, young stars and glowing gas clouds and may be the major location for star formation. Spirals have a range of masses, from a few billion to several hundred billion stars. The galaxy in which the Sun and its solar system are located is called the Milky Way galaxy, or just the Galaxy. Although scientists cannot, of course, observe it from the outside, the distribution of stars in our skies immediately shows that the Milky Way consists of a flat disk (Carroll, p. 76). Scientists cannot see its center in visible light because thick clouds of obscuring dust intervene between us and the core, but scientists know that the center of the Milky Way lies in the constellation Sagittarius and is one of the brightest radio sources in the Galaxy. Our inability to see our own Galaxy from the exterior inhibits detailed understanding of its structure (Carroll 65). Researchers estimate it to contain approximately 100 billion stars. The Sun is about 30,000 It-yr from the center, roughly two-thirds of the way to the visible edge of the galaxy. (Galaxies have no strict cutoff, but at some point become faint enough to define a boundary.) The solar system completes one revolution around the Galactic center in 200 million years. The universe is certainly a closed system; thus in any process, the entropy of the universe as a whole increases. The gasoline that was burned is changed in its composition and disappears forever as various combustion products, all of which are much less capable of conversion into work (Dodelson, p. 33). People eat, and most of the energy in their food is spent to maintain body temperature; only a fraction goes into driving biochemical processes, while the rest is radiated away into the atmosphere as waste heat. The difficulties of planets explorations are caused by the sun light and limited technological solutions (Baker, p. 65).
The stars make it possible for us to be aware that anything else exists. If all matter other than the Sun were dark, scientists would not even know, at least directly, of our own Galaxy, much less of the billions of other galaxies which inhabit the universe. Some light is emitted from very hot gas near the centers of galaxies, but most of the visible light in the universe, and much of the energy in other bands, originates directly or indirectly from stars (Dodelson, p. 98). The populations of stars make galaxies visible, but more than that, they enable us to measure the masses and compositions of the galaxies (Weinberg, p. 44). Certain kinds of bright stars provide a means to gauge the distances of galaxies; furthermore, when a massive star collapses, the resulting explosion is so brilliant that it can be seen across enormous distances, providing a means to measure the expanse that the light has crossed. Humbler, lower-mass stars have an equally important role to play in our cosmological investigations (Dodelson 44). Such stars can have ages comparable to the age of the universe itself. A star is a much simpler object, and much more amenable to observation, than is the universe as a whole, so that stars provide us with the best estimate for the age of the cosmos. Finally, stars play an active role in the evolving cosmos; their nuclear furnaces are the sole source of all the elements beyond lithium. As arguably the most important denizens of the universe, the stars are of great significance in the study of cosmology (Baker, p. 88).
If planets formed around one ordinary, unexceptional star, by a process which, to the extent that it is understood, does not require unusual conditions, then planetary systems must be abundant, especially around stars that lack binary partners. It is true that life is fairly sensitive, placing demands upon the conditions it requires, at least for the carbon-based life with which scientists are familiar. Life, as scientists understand it, requires reasonable stability of star and planet, the presence of a good solvent such as liquid water, and protection from disruptive radiation from the star, so that the weak chemical bonds that hold together the complex molecules of life are not broken. But under the right conditions, the great antiquity of life on Earth indicates that it develops readily (Dodelson, p. 77). Of the unknown billions of stars in the uncounted billions of galaxies, it is difficult to argue that there cannot be other planets that support life. Whether intelligent life would exist on such planets, scientists cannot, as yet, say. The development of intelligent life, or, at least, life forms that are capable of asking questions about the universe in which they live, does not even seem to have been inevitable on Earth.For many such cosmological questions, scientists have no definite answers. Scientists have come far from the geocentric, anthropocentric world of Aristotle. With the realization of our true place in the universe, humankind has been forced to accept humility. In exchange scientists have found that the universe of which we are a part is far larger, grander, and more fascinating than could have been imagined even a century ago (Dodelson, p. 44).
In order to search life on other planets, astronomers gather spectral data about stars and galaxies and examine the possibility of life and formation of Earth-like planets. The standard cosmological solutions and classical black hole solutions do not allow closed time-like curves. But these are by no means the only solutions to Einstein’s equations; might some solutions permit these unusual world lines? A new class of closed time-like curves associated with wormholes, discovered by Kip Thorne and collaborators, may seem to be a realization of the dreams of science-fiction writers, but such “time machines” occur only under extremely special conditions, and probably could not be traversed by any real particle (Dodelson, p. 98). A true world line is infinitesimally thin; any extended particle describes a world tube in space time. The world tubes found by Thorne are certainly too narrow for macroscopic particles and may not even be traversable by elementary particles. They also require a preexisting wormhole that is maintained in a very special state. ot seem to have much to do with the universe in which we live. No observations have ever detected an overall rotation of the universe, and certainly closed time-like curves are an uncomfortable property at best. The solution demonstrates, however, that the boundary conditions seem to be the way in which Mach’s principle is incorporated into general relativity. Those boundary conditions, in the real universe, may specify that classical closed time-like curves are not allowed. The main methodologies are based on direct search and indirect search. Direct methods search for unicellular life on plants of the solar system. Indirect search involves analysis of man-made electromagnetic radiation from coming from or spreading in cosmos (Baker, p. 75).
One possible resolution to the contradictions of time travel is provided by an alternative view of the wave-function, an exotic conjecture called the many-worlds interpretation. This interpretation of quantum mechanics, originally proposed by Hugh Everett, was developed to deal with the “measurement problem” in quantum cosmology. The Copenhagen interpretation depends upon a distinction between the observer and the system, a distinction which cannot be maintained in quantum cosmology. In the many-worlds interpretation, an infinite number of universes exist. These are not the usual kind of “parallel universes” of science fiction, nor are they the “child universes” of the chaotic inflation model (Oxlade, p. 87). They represent the set of universes in which all possible outcomes of all quantum process occur. When a measurement is made, no “collapse of the wave-function” takes place; rather, the probability of obtaining a given outcome is proportional to the number of universes in which that result is obtained. The issue of the meaning of the “collapse of the wavefunction” is avoided by requiring all possibilities to occur. As an illustration, return to Schrödinger’s cat. When the box is opened, the universe splits into those in which the cat is alive, and those in which it is dead. After the measurement, universes which were once indistinguishable can now be distinguished by whether the cat jumps from the box or not (Oxlade, p. 65). The many-worlds interpretation solves not only the “measurement problem” but the “grandfather paradox” as well. If a time-traveler murders his grandfather in the cradle, it merely means that now there are distinguishable universes. In one, the time traveler is never born. The universe containing the murderer and the dead infant continues along its own path. In the other universe, the murderer disappears the moment he travels into the past. The objection that the time-traveler and his grandfather are macroscopic, classical objects is inapplicable in this case, because ultimately quantum mechanics must apply to the universe as a whole if we are to solve the “measurement problem,” and therefore there is no such thing, strictly speaking, as classical behavior (Baker, p. 99).
The possibility that life may exist in other galaxies in the universe is a meaningful scientific hypothesis. Some astronomers have postulated the probabilities of life having evolved on other planets. The argument runs as follows: there may be at least one million planets in our galaxy alone. There are tens of billions of galaxies throughout the universe. If the conditions for life are present in these planetary systems, presumably higher forms could have evolved, and there may be intelligent forms which have developed advanced technological civilizations. It is reasonable to assume that life will spontaneously emerge on suitable planets, given adequate surface temperature and other conditions (Oxlade, p. 43). Organisms capable of photosynthesis can then develop, and it is estimated that after three to four billion years, other higher forms of life will or have evolved. This presupposes the presence of carbon, oxygen, nitrogen, hydrogen, and other elements. It is conceivable that such civilizations have advanced far beyond us and have conquered the technology to make space travel over infinite distances possible. Moreover, for a planet to be propitious for life, the necessary basic elements must be present, at least for the kinds of life with which scientists are acquainted, and many planets may contain far fewer elements. For life to be present, the planet must be at the right distance from its sun, that is, neither too far nor too near (Oxlade, p. 33). If the earth were closer to the sun, it would be too hot to support life, and if too far, glaciation would have taken place (Weinberg, p. T8). The zones that are habitable may be relatively limited. Thus the probabilities for life are, we are told, much smaller than those extrapolated by the optimists. Some astronomers differ from this pessimistic appraisal and believe that organic matter need not be based on carbon and water, as on our planet; they think that life grounded in silicon or other forms of chemistry might be possible, and that these forms of life might be able to survive extremely high or low temperatures. To assume that life on the planet earth is an entirely unique phenomena, they say, would be surprising (Oxlade, p. 54).
Still another speculative suggestion is that there may be cosmic clouds of organic material able to survive over long periods and/or that organic matter in spoors of life have been transmitted by meteors from different galaxies, enabling the evolutionary process to be repeated throughout the universe. Whatever the probabilities of these processes are is still uncertain at present (Weinberg, p. T8). What is of momentous significance to the human species is whether intelligent life exists elsewhere (Ryden 98). Radio telescopes have been monitoring the heavens and transmitting messages, but thus far, no identifiable messages have been received. One can neither confrere nor deny the hypothesis on a priori grounds at this stage of scientific inquiry. But this is all rather far removed from the question of whether the planet earth has been visited by ancient astronauts or is being visited today by UFOs. Aside from the question of probabilities is the empirical question of confirmation, and this can only be resolved by reference to the evidence (Baker, p. 43).
Modern UFOlogy began on June 24, 1947, when Kenneth Arnold reported that he saw a formation of nine disclike objects over Mt. Rainier, in the state of Washington. Arnold said that each disc resembled a “saucer skipping over water.” His claims were given worldwide attention, and subsequently “flying saucer” sightings have been reported by tens of thousands throughout the world. Believers run into the millions. In some years, UFO reports became epidemic, and public interest increased enormously (Weinberg, p. T8). These reports have come from most countries in the world, and from all strata of society. UFOlogy divides into two major camps: (1) UFO believers who are convinced that at least some of the UFOs are extraterrestrial in origin, and that knowledge of them is being systematically withheld from the public by national governments (but for what purpose is unclear). (2) Skeptics who have examined the evidence and have offered prosaic natural interpretations of the phenomena (Ryden, p. 98). Most UFO reports, they say, if carefully investigated, become IFOs–that is, Identified Flying Objects, objects in the sky that are commonly misperceived or misinterpreted. Most of the accounts can be explained as bright stars, the moon, or planets that stand out in the sky (Venus, Mars, Jupiter), meteors, weather and other balloons, helicopters, passenger or military planes, missile launches, reentering manmade rockets and satellites, searchlights, flares, fixed ground lights, and other visual anomalies–even birds, bolt lightning, kites, or unusual cloud formations. In some cases, sightings have been a prank or hoax (Baker, p. 12).
Summary
In sum, the search for life on other planets is still underdeveloped science based on suppositions and hypothetical predictions. Not all signs have been identified, primarily because there is no evidence corroborating the claims of the initial eyewitnesses. Thus an air of mystery attends those cases that still have not been fully explained to everyone’s satisfaction. Generally, the “sightings” are of strange lights or objects in the sky behaving in bizarre ways, hovering and darting about at unexpected angles. This is the age of air travel, so people are accustomed to look skyward and see balloons, helicopters, propeller and jet airplanes, rockets, and missiles-all phenomena that would have seemed strange in earlier centuries.
Works Cited
- Baker, D. Life on Other Planets. D.M.Baker, 1996.
- Carroll, A.M. Introduction to Modern Astrophysics. Benjamin Cummings; 2 edition, 2006.
- Dodelson, S. Modern Cosmology. Academic Press; 1 edition, 2003.
- Oxlade, Ch. The Mystery of Life on Other Planets. Topeka Bindery, 2002.
- Ryden, B. Introduction to Cosmology. Benjamin Cummings, 2002.
- Weinberg, S. Cosmology. Oxford University Press, USA, 2008.