© Robert Ehrlich
CRC Press, Taylor & Francis Group (2022)
For a 32 min video summarizing many of the ideas in this book, see:
Preface and Acknowledgments
This book is a scientific detective story. The crime is speeding, that is the breaking of the cosmic speed limit of 299,792,458 meters per second, which is the exact value of the speed of light in vacuum. Any perpetrator violating that cosmic speed limit would be committing a very serious crime according to nearly all physicists – perhaps the worst crime in over a century, if not ever. Unlike most detective stories, where the mystery is the identity of the perpetrator, here the main uncertainty is whether the crime has in fact been committed by a well-known subatomic particle, the neutrino. Of course, physicists continually discover new particles, so it is also possible that some as-yet-unobserved species of particle is the guilty party. Whether the speed violator is a neutrino or some new particle it would be called a tachyon.
This detective story is also a memoir written by a “tachyon hunter,” who has been pursuing these beasts for over two decades. My pursuit of them has been in the face of extreme skepticism from most of my physics colleagues. The skeptics note correctly that no superluminal neutrinos or other particles have ever been observed, and there have been many false sightings. Despite that history, considerable circumstantial evidence has been published in physics journals that some neutrinos are probably tachyons. The term circumstantial is used here exactly the way it is used in law, meaning evidence that relies on an inference to connect it to a conclusion of fact. Moreover, it has long been recognized that some circumstantial criminal evidence, such as DNA on the murder weapon, can be considerably stronger than direct evidence, such as eye-witness testimony of the murder.
As you probably know, Albert Einstein, in his 1905 special theory of relativity, prohibited faster-than-light particle speeds. Fifty-seven years later three physicists, O. M. P. Bilaniuk, V. K. Deshpande, and E. C. G. Sudarshan rediscovered a loophole in relativity. The trio noted that Einstein recognized that superluminal speeds were banned only for particles that were initially moving slower than light. Therefore, hypothetical tachyons would not conflict with relativity provided that, from the moment of their creation, they always moved faster than light. In this case, the speed of light, instead of being an upper limit to speed, would represent a two-way barrier. Normal matter like electrons, protons, or human beings, would forever be on the slower-than-light side of the barrier, and tachyons would forever be on the faster-than-light side.
Even though we slower-than-light creatures could never catch up to and capture a tachyon, that does not mean we could not observe its superluminality. If a single subatomic particle were found to have traveled a known distance from its source to a detector in less time than light, the particle would be a tachyon. As we have noted, there already is a good tachyon candidate among one of the well-known particles, namely the “ghostly” neutrino. Neutrinos are special because their measured speed has always been found to be very close to that of light. Secondly, there are reasons to believe their speed slightly differs from light, making them either a bit faster or slower. Even if only a handful of neutrinos were found to move a tiny bit faster-than-light, it would be a very big deal in the world of physics. It would be a much bigger deal than when airplanes first broke the sound barrier, which some “experts” thought was impossible.
Should you find yourself in the “Who cares?” category, I would note that if neutrinos are tachyons, the assumptions of theoretical physics would be turned upside down. Even the order of cause and effect could be switched. Suppose, for example, Alice sends Bob a message using a beam of tachyons. She could do this by simply modulating the beam into a series of long and short pulses using Morse code. Relativity tells us that some observers would say the tachyon message really went from Bob to Alice, and that we cannot say who is right. Furthermore, such a switch between sender and receiver of a message might even allow Alice to send messages to her earlier self. For now, these wild speculations remain in the category of science fiction unless the existence of tachyons should be surely demonstrated in an experiment.
Of course, extraordinary claims, such as superluminal neutrinos, require extraordinary evidence, which an ongoing experiment in Germany known as KATRIN might conceivably provide. This experiment is designed to measure the mass of neutrinos rather than their speed. If neutrinos really are tachyons, then their mass would be an imaginary number. Note that “imaginary” is here used in its mathematical sense, meaning that the square of the neutrino mass is negative. Imaginary mass particles would have the extremely weird property of speeding up when they lose energy. In fact, on losing all its energy, a tachyon would be moving at infinite speed, and travel through the entire universe in no time at all. While the KATRIN experiment’s initial results have not shown neutrinos are tachyons, nor do they exclude the possibility. Eventually, KATRIN may yield a definitive result on the matter, however, as the experiment accumulates more data, and the measurement uncertainty in the neutrino mass shrinks. Even if the
experiment ultimately fails to show that one (of three) types of neutrinos are tachyons, it will not thereby prove that tachyons do not exist. All that a negative result can do is set limits of some kind, whether the search is for tachyons, extraterrestrial civilizations, or hidden extra dimensions.
Tachyons are just one of many crazy ideas in science, some of which defy expectation and turn out to be true. My affinity for crazy ideas in science has motivated much of my research and led me to write several books on that very theme for the general reader. All that the present book will require of you, aside from skills and knowledge you probably learned in high school, is a deep curiosity about our very strange universe and an openness to unconventional ideas. In many places, the book crosses the blurry line between science fact and science fiction. Doing so is appropriate, because ideas gleaned from science fiction have often led physicists to research subjects such as tachyons, extraterrestrials, and time travel.
I wrote this book as a retired 83-year-old physics professor who is nearing the end of his journey through time. In my remaining time on this planet before the atoms of my body return to the stardust from whence they came, I can only hope that I live to see a definitive result from the KATRIN experiment. Even if that experiment yields the result nearly all physicists expect, namely no evidence of neutrinos being tachyons, I believe that my detective story should be of interest to many readers. As the story unfolds, we shall come across important lessons for anyone interested in pursuing their own unconventional ideas in science. To accompany the book, I have created a fun and a bit tacky (tachy?) website: Ehrlich.physics.gmu.edu. Whether you are a novice or an expert you will find much to explore there, including a list of over eighty questions (with answers) about tachyons and time travel, and many links to various resources on those two closely related subjects.
I am indebted to all the people who reviewed sections of this book and made helpful suggestions, including John Todd and Dublin artist Sinead McDonald. Many of my George Mason University colleagues were also helpful in reviewing the book including Political Scientist Jim Pfiffner, Space Scientist Art Poland, Geologist Doug Mose, Astronomer Harold Geller, and Science Communication specialist Kathy Rowan. Their comments helped me understand which sections needed extensive work to make them more understandable to non-scientists. Several reviewers including former Mason colleagues, Economist Jim Bennett, Historian Peter Stearns and retired Librarian Ian Fairclough made detailed stylistic
and substantive comments on the entire book. Jim even reviewed two drafts of the book. I especially thank my friend of over 60 years physicist Donald Gelman for his tremendously helpful comments.
Many other physicists were extremely helpful during my research on tachyons. They include Mason physics colleagues Maria Dworzecka and Robert Ellsworth, who were appropriately skeptical of some of my half-baked ideas. My collaborations with Man Ho Chan and Ulrich Jentschura led to the publication of three (out of a total of 18) articles about tachyons, which I could not have written alone. Special thanks go to Alan Chodos: his help in better understanding the physics of tachyons has been invaluable. Alan’s work with Alan Kostelecky, Robertus Potting and Evalyn Gates on neutrinos as tachyons got me initially interested in the subject, and it was in part his encouragement that led me to write this book. Alan has also very kindly agreed to handle the final editing in the event of my death or incapacitation.
Although my tachyon research has not involved me in any experiments, most of my work has relied on analyses of experimental work published by others. The work of three specific groups has been most helpful. First, I am indebted to Masayuki Nakahata and the other members of the Kamiokande Collaboration who detected the neutrino burst from supernova SN 1987A. The inclusion in their 1988 Physical Review article of neutrino data taken in the hours before and after the main burst, was invaluable in discovering important evidence showing that some neutrinos may be tachyons.
Second, I am grateful to Antonio Eridato and the other members of the OPERA group at CERN, who announced their “neutrino anomaly” to the world in 2011. They did so even though they knew from the outset that it probably was not truly due to faster-than-light neutrinos. The neutrino anomaly, even though it later proved to be a phantom of the OPERA, reawakened in me an interest in the subject that I had studied over a decade earlier.
Finally, I especially wish to thank the KATRIN Collaboration, which has been conducting an incredible experiment to measure the electron neutrino mass with far higher precision than previous measurements. Group leader of KATRIN, Guido Drexlin, has been particularly kind to me. Diana Parno, one of the people in charge of their data analysis, and Hamish Robertson were also very kind in keeping me informed of the experiment’s status. I particularly appreciate Diana’s willingness to discuss details of the data analysis with me, as well as her
reassurance that they were taking my prediction for the experiment seriously. I am also very thankful to Hamish Robertson for reading and correcting several errors chapter 5 dealing with the KATRIN experiment. This experiment could not have come along at a better time, and I thank the KATRIN people for inviting me to give several seminars at KIT. I also am grateful that they did not treat me as a crackpot: even though I suspect that they were extremely dubious about my prediction for the experiment’s results.
I want to thank all the reviewers of my tachyon papers, especially those who criticized them severely and often recommended against publication – thereby giving me the time and incentive to improve them. In a similar vein, I am indebted to someone or something responsible for a mysterious seemingly automated message I received on November 22, 2015. I seriously wondered if this could have been a message from the future. Whatever its source, I interpreted the “message” as a sign that I was on the right track in my research, and I should keep at it. Most of all, I thank my wife Elaine for being my best friend and soulmate for 60 years and counting, and for her serving as a good sounding board for my ideas.
Finally, I thank God, about whose existence I am devoutly agnostic, for putting all those clues out there suggesting that neutrinos might be tachyons. Through those clues I believe that I was able to see through the excellent “camouflage” that allowed tachyons to remain hidden for over a century. Alternatively, if the KATRIN experiment should not support my prediction for it, and it has all been a magnificent delusion, I can only admire God for his great sense of humor and interpret His actions as being merely mischievous, not malicious. As Einstein once said, “Subtle is the Lord, but malicious He is not.”