All observables in nature measurable with a single unit of time

All observables in nature measurable with a single unit of time
by Clarence Oxford
Los Angeles CA (SPX) Dec 18, 2024

Brazilian researchers have introduced a thought-provoking perspective on a long-standing debate among physicists: how many fundamental constants are required to describe the universe? Their conclusion - just one, the "second" - could simplify how we understand physical measurements.

The study, published in Scientific Reports, was conducted by George Matsas and Vicente Pleitez from Sao Paulo State University (IFT-UNESP), Alberto Saa from the State University of Campinas (IMECC-UNICAMP), and Daniel Vanzella from the University of Sao Paulo (IFSC-USP). Their work revisits questions raised in a 2002 paper by Michael Duff, Lev Okun, and Gabriele Veneziano published in the Journal of High Energy Physics.

The researchers assert that the number of constants depends on the underlying space-time of the physical framework. In relativistic space-time, the system described by Einstein's theory of relativity, only one constant is needed: the "second," which defines time.

Revisiting the Constants Debate

In 1992, an informal conversation among Duff, Okun, and Veneziano at CERN revealed differences in opinion on the number of constants needed for measurements. Okun supported three units - meter, kilogram, and second - reflecting the MKS system. Veneziano argued for two: one for time and one for length. Duff suggested the number of constants could depend on the theoretical framework.

Physicist George Matsas explained, "The goal is to find the most fundamental description of physics possible. The question raised by Okun, Duff, and Veneziano is by no means trivial. As physicists, we're faced with the need to understand what's the minimum number of standards we need to measure everything."

The Brazilian researchers applied their reasoning to Galilean and relativistic space-times. Galilean space-time, central to Newtonian mechanics, requires rulers and clocks for measurements. In contrast, in relativistic space-time, the interrelation of space and time means only time-based measurements are needed. High-precision atomic clocks fulfill this role.

Space-Time and Measurement

Their work focused on Minkowski space-time, a model of relativity that is simple, empty, and isotropic. However, they believe their conclusions apply broadly to other relativistic space-times.

"In Galilean space-time, you need rulers and clocks to measure all the physical variables," Matsas explained. "In relativistic space-time, clocks are sufficient. High-precision clocks, such as the atomic clocks used today, are capable of meeting all measurement needs."

Even in the Newtonian framework, mass might not be fundamental. Daniel Vanzella commented, "Historically, the kilogram was defined as the mass of one liter of pure water at a given pressure and temperature. But from a fundamental point of view, it's not necessary. The mass of a body is given by the acceleration with which a particle is attracted when it's at a certain distance from the mass."

Rethinking the International System of Units

The International System of Units (SI) includes seven base units, but many can be derived from others. Since 2019, SI units have been tied to natural constants, such as the speed of light and Planck's constant.

In relativistic space-time, all physical quantities can be expressed in terms of the "second." This unit is derived from the radiation emitted when an electron transitions between specific energy states of caesium-133, corresponding to 9,192,631,770 oscillations. Matsas explained, "Any artifact capable of regularly counting 9,192,631,770 oscillations of this radiation will have measured 1s and can be considered an honest clock."

In conclusion, while the "second" is based on a natural constant, its adoption reflects both scientific precision and societal convenience. Vanzella remarked, "The verdict that an observable is or isn't a constant of nature is absolute because it's proclaimed by honest clocks. But the choice of which 'fundamental constant' is used to define them is a social and historical construction that depends on convenience."

Research Report:The study demonstrates that, fundamentally, time suffices to measure all physical quantities in relativistic space-time.