A group of Brazilian researchers has proposed an innovative approach to resolve an ongoing debate in theoretical physics regarding the number of fundamental constants necessary to describe the observable universe. The question of how many fundamental constants are required is crucial, as these constants serve as the basic standards for measuring all physical quantities. The research, published by scientists from several Brazilian institutions, offers a fresh perspective that could significantly impact our understanding of the fundamental framework of the universe.
The controversy regarding the number of fundamental constants began in 2002 with an influential article by physicists Michael Duff, Lev Okun, and Gabriele Veneziano in the Journal of High Energy Physics. This article reignited a decades-old debate among physicists about the number of constants required to measure the physical world accurately. However, the roots of the debate stretch back further, beginning in the early 1990s during informal discussions between the three scientists.
The debate gained traction in 1992 when Okun, Veneziano, and Duff met at CERN, the European Organization for Nuclear Research, where they realized they held different views about the number of fundamental constants. Their discussion continued through the years, and in the summer of 2001, they revisited the topic, ultimately deciding to formalize their differing opinions in an academic article. Okun’s position, which is aligned with the traditional view, emphasized the need for three basic unitsāmeter (length), kilogram (mass), and second (time)āto measure all physical quantities. This idea reflects the MKS system (meter, kilogram, second) that is the basis for the International System of Units (SI).
Veneziano, in contrast, argued that under certain conditions, only two unitsātime and lengthāwould be necessary. Duff, meanwhile, maintained that the number of constants could vary depending on the specific theory or framework being applied. This disagreement raised important questions about the nature of physical constants and their role in the measurement system, prompting further investigations into the issue.
The recent work by the Brazilian researchers aims to resolve this debate by introducing a novel idea: the number of fundamental constants required depends on the type of space-time in which the physical theories are formulated. They distinguish between two types of space-time: Galilean space-time, which is associated with classical mechanics and Isaac Newton’s laws of motion, and relativistic space-time, which underpins Albert Einstein’s theory of general relativity. By analyzing these two types of space-time, the researchers suggest that the number of fundamental constants can vary depending on the underlying structure of space-time itself.
The Brazilian team’s primary argument is that in Galilean space-time, rulers and clocks are necessary to measure all physical quantities. In this framework, both length and time are treated as independent variables, and thus two fundamental constants are required. On the other hand, in relativistic space-time, which is the framework of modern physics, time and space are so intricately connected that only a single constantāthe standard of timeācan be used to define all physical quantities. This observation suggests that, in a relativistic space-time, the number of fundamental constants can be reduced to just one.
The researchers focus on Minkowski space-time, a simple form of relativistic space-time that is empty, homogeneous, and isotropic. In this idealized model, time and space are unified into a four-dimensional continuum, where the standard of time can serve as the basis for measuring all physical quantities. They argue that in such a space-time, high-precision clocks, such as atomic clocks, are sufficient to measure everything, making other constants like length and mass unnecessary in certain contexts.
This viewpoint provides a new perspective on the traditional understanding of fundamental constants. While mass has long been considered a necessary standard for measurement, the Brazilian researchers challenge this assumption. Historically, the kilogram was defined based on a standard massāone liter of pure water at a specific temperature and pressure. However, from a more fundamental standpoint, they argue that mass is not an essential constant. Instead, mass can be determined through the acceleration of a body under the influence of a gravitational field, as described by Newton’s laws of motion. This insight highlights that while mass is useful for practical purposes, it may not be as fundamental as previously thought.
The debate about the number of fundamental constants is not just a theoretical exercise; it has practical implications for the way we measure and understand the physical world. The International System of Units (SI), which is the global standard for measurements, currently uses seven basic units: meter (length), second (time), kilogram (mass), kelvin (temperature), ampere (electric current), candela (light intensity), and mole (amount of substance). These units are essential for everyday measurements, such as determining the size of objects, the duration of events, or the intensity of light.
However, the Brazilian researchers argue that many of these units are redundant, as they can be expressed in terms of others. For example, the unit of mass, the kilogram, is currently defined in terms of the Planck constant and the speed of light. Similarly, temperature and electric current can be related to fundamental constants such as the Boltzmann constant and the elementary charge. This redundancy raises the question of whether all seven units are truly necessary, or whether some could be eliminated or redefined based on a smaller set of fundamental constants.
The researchers also point out that while the current definition of the second is based on the energy difference between two states of the caesium-133 atom, this definition is essentially based on a natural constant. The second is defined as the time it takes for the caesium-133 electron to oscillate 9,192,631,770 times between these two energy levels. This definition underscores the idea that time itself can be standardized using a constant of nature, making it the only unit required to express all other physical quantities in a relativistic space-time.
The concept of a “fundamental constant” is not purely theoretical. It reflects a choice of measurement standard that is influenced by practical considerations and historical context. For example, the decision to define the second based on the caesium-133 atom is the result of a long-standing effort to create reliable, precise measurements for scientific and technological purposes. Similarly, the adoption of the kilogram as the standard unit of mass has been shaped by the need for a consistent and universally accepted measure of weight.
The Brazilian team’s work is a significant contribution to the ongoing debate about the number of fundamental constants. Their findings suggest that in a relativistic space-time, a single constantāthe standard of timeāmay be sufficient to measure all physical quantities. This insight could lead to a reevaluation of the way we define and use physical constants, with implications for both theoretical physics and practical measurement systems.
The research team, including George Matsas, Vicente Pleitez, Alberto Saa, and Daniel Vanzella, represents a cross-disciplinary effort that combines theoretical physics, mathematics, and measurement science. Their work provides a fresh perspective on a long-standing issue, offering new insights into the nature of space-time and the role of fundamental constants in our understanding of the universe.
Ultimately, the Brazilian researchers’ proposal underscores the importance of revisiting fundamental assumptions in physics. As our understanding of the universe deepens, it is essential to remain open to new ideas that challenge established conventions and offer alternative frameworks for thinking about the physical world. The search for the most fundamental description of the universe is ongoing, and contributions like this one will continue to shape the future of theoretical physics and our understanding of the cosmos.
The study isĀ publishedĀ in the journalĀ Scientific Reports.
Source: FAPESP