Gerald Feinberg and the Birth of Tachyon Physics
Gerald Feinberg was an American theoretical physicist whose 1967 paper permanently changed the way the physics community thinks about faster-than-light particles. By constructing a rigorous quantum field theory framework for superluminal objects, he transformed what had been a speculative curiosity into a legitimate branch of theoretical physics. He is the reason the word tachyon exists.
Early Life and Education
Gerald Feinberg was born on May 27, 1933 in New York City. He showed extraordinary aptitude for science from an early age, growing up alongside his childhood friend Steven Weinberg, who would go on to share the 1979 Nobel Prize in Physics. Feinberg attended the Bronx High School of Science, a public magnet school that has produced an astonishing number of future Nobel laureates. He then enrolled at Columbia University, where he would spend essentially his entire academic career.
Feinberg earned his bachelor’s degree from Columbia in 1953 and completed his Ph.D. there in 1957 under the supervision of T.D. Lee. He joined the Columbia physics faculty and remained there for the rest of his life, rising to the rank of full professor and becoming one of the department’s most respected theorists.
The Muon Neutrino and Early Contributions
Before his work on tachyons, Feinberg made a prediction that would prove central to one of the great experimental discoveries in particle physics. In 1958, he proposed that the neutrino associated with muon decay might be distinct from the neutrino associated with electron interactions. This was a bold claim at a time when only one type of neutrino was known.
In 1962, Leon Lederman, Melvin Schwartz, and Jack Steinberger conducted an experiment at Brookhaven National Laboratory that confirmed Feinberg’s prediction. They demonstrated that the muon neutrino (nu-mu) is indeed a separate particle from the electron neutrino (nu-e). This discovery, which earned the three experimentalists the 1988 Nobel Prize in Physics, would not have been pursued without Feinberg’s theoretical groundwork.
Feinberg also contributed important work on parity violation in weak interactions, radiative corrections to beta decay, and the general properties of symmetry in quantum field theory.
Predecessors: Bilaniuk, Deshpande, and Sudarshan
Feinberg was not the first physicist to seriously consider faster-than-light particles. In 1962, five years before Feinberg’s landmark paper, Olexa-Myron Bilaniuk, V. K. Deshpande, and E. C. George Sudarshan published a paper titled “Meta Relativity” in the American Journal of Physics. In it, they showed that special relativity does not actually forbid the existence of particles that always travel faster than light. The theory only forbids a massive particle from being accelerated through the light barrier.
Bilaniuk and Sudarshan classified particles into three categories:
- Bradyons (or tardyons): particles with real mass that always travel slower than light
- Luxons: massless particles (like photons) that always travel exactly at light speed
- Tachyons: particles with imaginary mass that always travel faster than light
The key insight was that the light speed barrier works both ways. Just as a bradyon cannot be accelerated to reach the speed of light, a tachyon cannot be decelerated to reach it. The speed of light is an asymptotic barrier, not a universal speed limit in the way it is popularly understood.
However, Bilaniuk and Sudarshan’s work remained relatively obscure. It was Feinberg who brought widespread attention to the concept and developed it into a full quantum field theoretic framework.
The 1967 Paper: “Possibility of Faster-Than-Light Particles”
Feinberg’s seminal paper was published in Physical Review (volume 159, pages 1089-1105) on July 25, 1967. The paper’s title was deliberately cautious: “Possibility of Faster-Than-Light Particles.” Feinberg was not claiming that tachyons exist. He was demonstrating that their existence is not ruled out by fundamental physics.
The paper made several critical contributions:
Coining the Name
Feinberg coined the term tachyon from the Greek word tachys (fast), giving a memorable and precise name to what Bilaniuk and Sudarshan had called “meta-particles.” The name stuck immediately and has been the standard term in physics ever since.
A Quantum Field Theory for Tachyons
While Bilaniuk and Sudarshan worked within classical special relativity, Feinberg went further. He attempted to construct a full quantum field theory for scalar particles with imaginary mass. He wrote down the Lagrangian, derived the propagator, and analyzed the commutation relations for a tachyonic field. This was essential because quantum field theory, not classical mechanics, is the proper framework for describing fundamental particles.
Feinberg’s analysis revealed deep subtleties. He found that the naive quantization of a tachyon field led to problems with causality and the spin-statistics theorem. These difficulties hinted at deeper issues that are still debated in theoretical physics today, particularly in the context of tachyon condensation in string theory.
The Reinterpretation Principle
One of the most important ideas in Feinberg’s paper was his formalization of the reinterpretation principle, which addressed a troubling consequence of tachyonic travel: the possibility of backward-in-time signaling and the resulting tachyonic antitelephone paradox.
According to special relativity, if a particle travels faster than light, there exist reference frames in which the particle travels backward in time. This appears to violate causality. The reinterpretation principle resolves this by treating a negative-energy tachyon traveling backward in time as a positive-energy anti-tachyon traveling forward in time. Under this reinterpretation, no observer ever sees a particle moving into the past. Instead, they see an antiparticle being emitted where the original particle would have been absorbed, and vice versa.
This principle is analogous to the Feynman-Stueckelberg interpretation of antiparticles in ordinary quantum field theory, where a negative-energy electron moving backward in time is reinterpreted as a positive-energy positron moving forward in time.
Experimental Predictions
Feinberg also discussed how one might detect tachyons experimentally. He noted that a charged tachyon would emit Cherenkov radiation even in vacuum, since it would always exceed the speed of light. This provided a concrete experimental signature that experimentalists could search for, and it remains one of the primary detection strategies studied today.
Why the Paper Was Revolutionary
Feinberg’s 1967 paper was groundbreaking for several reasons. Before its publication, faster-than-light particles were largely considered the province of science fiction and crackpots. Serious physicists did not invest time in the topic. Feinberg, as a well-respected Columbia professor with established credentials in mainstream particle physics, lent the subject instant credibility.
The paper demonstrated that tachyons do not violate the principles of special relativity when properly understood. It provided a mathematical framework rigorous enough for other theorists to build upon, criticize, and refine. It also connected the purely theoretical concept to potential observable phenomena, bridging the gap between abstract theory and experimental research.
After Feinberg’s paper, dozens of physicists began publishing follow-up studies on tachyon properties, tachyon interactions, and experimental search strategies. The topic became a recognized, if speculative, branch of theoretical physics.
Beyond Tachyons: Other Contributions
Feinberg’s intellectual range extended well beyond tachyon physics. Throughout the 1970s and 1980s, he worked on a wide variety of problems:
- Long-range forces between atoms and molecules: Feinberg made important contributions to the theory of Casimir-type and van der Waals interactions at large separations, work that connects to the broader study of the Casimir effect.
- Neutrino physics: He continued to work on neutrino interactions and their role in astrophysics, a topic that intersects with the ongoing question of whether neutrinos could have tachyonic properties.
- Futurism and philosophy of science: Feinberg wrote two books for general audiences. The Prometheus Project (1969) explored how humanity might use science and technology to shape its future. Consequences of Growth (1977, co-authored with Robert Shapiro) examined the long-term implications of technological development.
- Exotic matter and exotic states: He studied the theoretical properties of unusual forms of matter, including what he called “exotic atoms” and states involving long-lived particles.
Death and Legacy
Gerald Feinberg died on April 21, 1992, at the age of 58, from cancer. His passing cut short a career that had been remarkably productive and far-ranging.
His legacy in physics is secured primarily by two contributions: his prediction of the muon neutrino, which was confirmed experimentally and led to a Nobel Prize for the discoverers, and his formalization of tachyon theory, which opened an entire field of study. Every modern paper on superluminal particles, tachyon condensation in string theory, or the physics of imaginary mass builds on the foundation that Feinberg laid in 1967.
The word tachyon itself stands as a lasting monument to Feinberg’s work. It has entered not only the technical vocabulary of physics but also the broader culture, appearing in countless works of science fiction and popular science. Whenever someone asks whether faster-than-light travel is possible, they are asking a question that Gerald Feinberg was the first to take truly seriously.