The Varieties of Scientific Experience is the published version of Carl Sagan’s 1985 Gifford Lectures given at the University of Glasgow. Capturing the lectures’ engaging tone, the volume consists of personal reflections on topics ranging from astrophysics and extraterrestrial life to human evolution and nuclear warfare. Sagan argues for the necessity of a worldview that adequately incorporates scientific knowledge and that, by consequence, is continually readjusting to account for new understandings of the cosmos and humanity’s place within it.
Sagan contends that the immensity of the universe (and the comparative smallness of humanity) must be incorporated into religious and philosophical thought. He suggests that too often western religions have preferred “a god of a tiny world and not a god of a galaxy, much less of a universe” (p. 30). In contrast, Sagan suggests that science is “informed worship” (p. 31) and that the continued use of scientific curiosity and intelligence is essential for the continued welfare of humanity.
Sagan illustrates how Copernicus’ scientific work contributed to the modern worldview by prompting a string of astronomical discoveries that challenged prevailing conceptions of the earth as the center of the cosmos. He further suggests that an analogical decentralization of humanity within world history has resulted from evolutionary scientific advances before arguing that this evolutionary decentralization should have implications for prevailing assumptions concerning both the place of divinity and humanity within the cosmos.
Sagan advocates a “skeptical scrutiny” based on scientifically verifiable evidence when dealing with questions concerning extraterrestrial intelligence (which he suggests is logically possible due to discoveries of organic matter throughout the cosmos) and the associated concept of “miracles” that appear contrary to the laws of physics (p. 145). Sagan’s insistence on evidence and human reason leads him to define natural theology—the topic to which the Gifford Lectures are dedicated—as “theological knowledge that can be established by reason and experience and experiment alone” (p. 147).
He notes that definitions of “god” proposed by Spinoza and Einstein broadly correspond to “the sum total of the physical laws of the universe,” and, if this is indeed the definition of “god,” then “no one can possibly be an atheist” (p. 149–150). Conversely, Sagan contends that proposed “proofs of the existence of God” offer no verifiable evidence of the common conception of god as a supernatural being residing in the sky who intervenes in the affairs of human life, before concluding with the words of Protagoras from the fifth-century B.C.: “About the gods I have no means of knowing either that they exist or that they do not exist” (p. 168).
Sagan concludes by examining the importance of a scientifically informed worldview in a rapidly changing world. He argues that in the modern world wisdom lies not in unchallenged tradition but “in the vigorous and skeptical and creative investigation of a wide variety of alternatives” (p. 194). Sagan is particularly concerned to demonstrate how such a worldview could confront nuclear proliferation and what he considers the unparalleled ability of humanity to destroy itself.