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2012年北航SDL TRADOS杯研究生科技英语翻译比赛原文

The Fermi–Hart Paradox: Where are the Aliens?

Fermi is reported to have mused over lunch that there could not be intelligent life forms elsewhere than Earth because they would have colonized space and already be here. Conversely, the presence of life on the Earth implies its presence elsewhere. This problem, though it originated with Fermi, has been worked on by many people, most notably Hart. Over the years, the absence of evidence for aliens has emerged as one of the few solid data in the field of exobiology. In this section, we therefore confine our attention to the Fermi–Hart paradox and how it may be resolved.

An immediate suggestion for a resolution is, of course, that alien civilizations are sparse in the universe. Indeed, Tipler and others have argued that human civilization may be unique and that we are truly alone. This view is distasteful to many, and some researchers such as Clarke and Sagan have reached the opposite conclusion, that life (and by implication civilization) is common. The reason for this divergence of opinion lies simply in a lack of data.

Drake’s formula is the traditional way to quantify the frequency of extraterrestrial civilizations. It involves a product of probabilities, ranging from the astrophysical (e.g. the fraction of stars which have habitable planets) to the sociological (e.g. the relative timescale for the development of technology). However, each of the component probabilities is poorly known, so the result has a high degree of uncertainty. The nearest technological civilization to us may be around a nearby star, or in one of the most remote galaxies.

It is important to realize in the application of Drake’s formula that there is a continuum of systems to which it can be applied: the stars of the Milky Way, the local group of galaxies, or all of the objects in the visible universe. To order of magnitude, there are as many galaxies in that part of the universe accessible to observation as there are stars in the Milky Way. Signals from extraterrestrial civilizations involve, for their detection, a balance between the number of sources (which goes up approximately as the cube of the distance) and the signal strength (which goes down for electromagnetic radiation as the square of the distance). This is like the situation we encountered before in regard to Olbers’ paradox. The American program on the Search for Extraterrestrial Intelligence has concentrated on nearby stars, but previous Russian surveys focused on distant galaxies. The fact that no signals have been detected from either class of objects brings us back to the Fermi–Hart paradox.

It actually makes little difference to the veracity of this paradox whether we consider the detection of signals from extra-terrestrial civilizations or other evidence of their existence. It has been estimated, for example, that a technologically advanced race could populate the Milky Way with robotic devices in a period of about of approximately

yr, which is small compared to the Galactic age

yr. The fact that we have found no evidence of aliens in our solar

system reinforces the fact that we have received no signals from them. A few researchers, such as the radio astronomer Verschuur, have suggested that the money spent on S.E.T.I. (Search for Extraterrestrial Intelligence) might be better spent on alleviating problems on our own troubled planet. While most scientists would probably not go this far, it is becoming more imperative to face up to the question: Are we alone?

（选自Paul S. Wesson著Weaving the Universe: Is Modern Cosmology Discovered or Invented? World Scientific Publishing Co. Pte. Ltd. 2011）