This book provides the reader with a detailed and captivating account of the story where, for the first time, physicists ventured into proposing a new force of nature beyond the four known ones - the electromagnetic, weak and strong forces, and gravitation - based entirely on the reanalysis of existing experimental data. Back in 1986, Ephraim Fischbach, Sam Aronson, Carrick Talmadge and their collaborators proposed a modification of Newton’s Law of universal gravitation. Underlying this proposal were three tantalizing pieces of evidence: 1) an energy dependence of the CP (particle-antiparticle and reflection symmetry) parameters, 2) differences between the measurements of G, the universal gravitational constant, in laboratories and in mineshafts, and 3) a reanalysis of the Eötvos experiment, which had previously been used to show that the gravitational mass of an object and its inertia mass were equal to approximately one part in a billion. The reanalysis revealed that, contrary to Galileo’s position, the force of gravity was in fact very slightly different for different substances. The resulting Fifth Force hypothesis included this composition dependence and also added a small distance dependence to the inverse-square gravitational force. Over the next four years numerous experiments were performed to test the hypothesis. By 1990 there was overwhelming evidence that the Fifth Force, as initially proposed, did not exist. This book discusses how the Fifth Force hypothesis came to be proposed and how it went on to become a showcase of discovery, pursuit and justification in modern physics, prior to its demise. In this new and significantly expanded edition, the material from the first edition is complemented by two essays, one containing Fischbach’s personal reminiscences of the proposal, and a second on the ongoing history and impact of the Fifth Force hypothesis from 1990 to the present.

In No Easy Answers, Allan Franklin offers an accurate picture of science to both a general reader and to scholars in the humanities and social sciences who may not have any background in physics. Through the examination of nontechnical case studies, he illustrates the various roles that experiment plays in science. He uses examples of unquestioned success, such as the discoveries of the electron and of three types of neutrino, as well as studies that were dead ends, wrong turns, or just plain mistakes, such as the "fifth force," a proposed modification of Newton's law of gravity. Franklin argues that science is a reasonable enterprise that provides us with knowledge of the natural world based on valid experimental evidence and reasoned and critical discussion, and he makes clear that it behooves all of us to understand how it works.

Beyond Einstein: Perspectives on Geometry, Gravitation, and Cosmology explores the rich interplay between mathematical and physical ideas by studying the interactions of major actors and the roles of important research communities over the course of the last century.

Selectivity and Discord addresses the fundamental question of whether there are grounds for belief in experimental results. Specifically, Allan Franklin is concerned with two problems in the use of experimental results in science: selectivity of data or analysis procedures and the resolution of discordant results.By means of detailed case studies of episodes from the history of modern physics, Franklin shows how these problems can be—and are—solved in the normal practice of science and, therefore, that experimental results may be legitimately used as a basis for scientific knowledge.

A history of the attempts to test the predictions of Newtonian Gravity, describing in detail recent experimental efforts to verify both the inverse-square law and the Equivalence Principle. Interest in these questions has increased in recent years, as it has become recognised that deviations from Newtonian gravity could be a signal for a new fundamental force in nature. This is the first book devoted entirely to this subject, and will thus be useful to both graduate students and researchers interested in this field. It describes the ideas that underlie searches for such deviations, focusing on macroscopic tests. A comprehensive bibliography of some 450 entries supplements the text.

A leading astronomer and gifted teacher takes readers on a wondrous tour—"perfect for anyone who enjoyed Astrophysics for People in a Hurry" (Publishers Weekly)—of how science confronts the big questions about the origins, destiny, and fundamental nature of our universe Humans have learned a lot about the world around us and the universe beyond. We have made powerful insights and created profound theories about the universe and everything in it. Surely the ultimate theory must be waiting, just beyond our current knowledge. Well, maybe. In Into the Unknown, astrophysicist Kelsey Johnson takes us to the edge of scientific understanding about the universe: What caused the Big Bang? What happens inside black holes? Are there other dimensions? She doesn’t just celebrate what we know but rather what we don’t, and asks what it means if we never find that knowledge. Exploring the convergence of science, philosophy, and theology, Johnson argues we must reckon with possibilities—including those that may be beyond human comprehension. The very places where we run smack into total ignorance are the places where the most important questions—about the philosophy of knowledge, the nature of our cosmos, and even the existence of God—await. As accessible as it is profound, Into the Unknown invites each of us to join in the great quest for knowledge.