Cosmos

Sagan mentions many European figures who contributed to the development of modern science. These include Johannes Kepler, Isaac Newton, Charles Darwin, and Albert Einstein, among many others. He also acknowledges that so-called scientists were not always successful in their theories; science takes time and proof to progress.

Sagan traces the beginning of science as a discipline to the ancient Greeks (he does not mention the achievements of nonwhite scientists, for example those of ancient and medieval China or the Middle East—omissions typical of Sagan’s time). Thales of Miletus, whom the author calls the first Greek scientist, measured the heights of Egyptian pyramids using their shadows and the angle of the sun, and thus anticipated the method used by modern scientists to measure the height of the moon’s mountains. Anaximander of Miletus is one of the first people known to have conducted a true scientific experiment; his contributions include the fact that the moon shines by reflective light. Sagan also mentions Pythagoras, whose many contributions extend beyond the work that underpins geometry, the Pythagorean Theorem. Democritus invented the word atom for something that could not be cut or divided; he also hypothesized that the Milky Way consisted of unresolved stars. Aristarchus contributed the idea that the Earth is a planet.

Sagan singles out the Dutch mathematician Christiaan Huygens for his work on telescopes and in astronomy because this 17th-century astronomer discovered the rings of Saturn and pioneered the theory of light waves and centrifugal force. However, Sagan also places Huygens in context, arguing that his achievements would not have been possible outside the free-thinking environment of Holland, which was exceptionally permissive in comparison to other regions of Europe at the time.

Sagan is careful to demonstrate the progression of scientific discovery, tracing how earlier work influenced and led to future discoveries. It is notable that this history ignores national borders, indirectly supporting Sagan’s argument for our shared humanity. Sixteenth-century Danish astronomer, Tycho Brahe, is noted for his impressive observation of the planets over a number of years. Those closely recorded observations in turn became a major source of data for his German contemporary Johannes Kepler, who used them as part of his evidence to propose his three major laws regarding planetary orbits, which Sagan regards as foundational to planetary study. In turn, Kepler’s laws prompted 17th-century English mathematician Isaac Newton’s explication of the basic laws of gravity and inertia—a major step toward the recognition that a comparatively few mechanical laws actually control the workings of the cosmos.

Sagan often gestures as the applicability of Earth-based discoveries to extraplanetary life. For example, while Darwin’s theory of natural selection is fundamental to life on Earth, it also potentially expands to life in the cosmos. Similarly, Einstein’s theories of relativity and special relativity are among the most important considerations for the possibilities of space travel.

The author’s analysis of those participating in science is not limited to contributors who proved correct. Early 20th-century amateur astronomy enthusiast Percival Lowell’s incorrectly held that the surface of Mars features canals (presumably of intelligent origin), which in fact do not exist. Even otherwise successful scientists do not always get is right: Kepler’s idea that the workings of the planets marked God as geometrician also had to be shelved once he considered Tycho Brahe’s observations and his own detailed studies. Many scientists discussed as major contributors also advanced incorrect or incomplete ideas based upon their limited access to instruments of study or their immersion in ideas or assumptions accepted in their own time periods; these the author excuses as long as open scientific inquiry can continue. There is value in the process of exploration, even if first discoveries are not always correct discoveries.