Identified Flying Objects: A Multidisciplinary Scientific Approach to the UFO Phenomenon

by Michael P. Masters

A paper by Earman et al. (2009) titled Do the Laws of Physics Forbid the Operation of Time Machines? sought an answer to this question of whether backward time travel is impossible, using a broad approach rooted in physics, history, and philosophy. This review paper examined the vast amount of literature concerning backward time travel research, with a specific focus on more critical studies whose results suggest that time travel to the past is not possible. This included more skeptical approaches like Stephen Hawking’s Chronology Protection conjecture (which is the idea that the laws of physics prevent time travel for macroscopic objects as a result of perceived causality violations),7 as well as similar other disparaging studies of time machines under classical general relativity, semi-classical quantum gravity, quantum field theory on curved spacetime, and Euclidean quantum gravity.8 The results of this research, as well as an earlier investigation by Earman (1995),9 demonstrated that these anti-time travel studies, including Hawking’s Chronology Protection Conjecture, are not actually as prohibitive as they may seem: Our verdict on the question of our title is that no result of sufficient generality to underwrite a confident ‘yes’ has been proven.10 Although, these authors also highlight the current difficulty associated with assessing the potentiality of backward time travel, devoid of a unified theory of gravity and quantum mechanics: Perhaps in the not too distant f...