Enrico Fermi
Fermi wrote a paper "On the Origin of Cosmic Radiation" in which he proposed that cosmic rays arose through material being accelerated by magnetic fields in interstellar space, which led to a difference of opinion with Teller. Fermi examined the issues surrounding magnetic fields in the arms of a spiral galaxy. He mused about what is now referred to as the "Fermi paradox": the contradiction between the presumed probability of the existence of extraterrestrial life and the fact that contact has not been made.
Toward the end of his life, Fermi questioned his faith in society at large to make wise choices about nuclear technology. He said:
Fermi paradox
The theories and principles in the Drake equation are closely related to the Fermi paradox. The equation was formulated by Frank Drake in 1961 in an attempt to find a systematic means to evaluate the numerous probabilities involved in the existence of alien life. The speculative equation considers the rate of star formation in the galaxy; the fraction of stars with planets and the number per star that are habitable; the fraction of those planets that develop life; the fraction that develop "intelligent" life; the fraction that have detectable, technological intelligent life; and finally the length of time such communicable civilizations are detectable. The fundamental problem is that the last four terms are completely unknown, rendering statistical estimates impossible.