Physicists Say The Entire Universe Might Only Need One Constant – Time

If you've spent a little time wondering about how the cosmos works (as you should) you have likely stumbled across one of the so-called "constants" of the universe.

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These are physical quantities which cannot be derived through theory, and must be gained through going out there and measuring them through experiment. Classic examples include the speed of light, Planck's constant, and the fine-structure constant (note; this last one weirds people out the most).

The conditions of the universe can be described through its “fundamental constants” – fixed quantities in nature, such as the gravitational constant (called G) or the speed of light (called C)," Martin Rees, Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge explains in a piece for The Conversation.

"There are about 30 of these representing the sizes and strengths of parameters such as particle masses, forces or the universe’s expansion. But our theories don’t explain what values these constants should have. Instead, we have to measure them and plug their values into our equations to accurately describe nature."

Physicists have worked to pin down the exact values of these constants, and how they relate to each other, with some being measured more precisely than others. The International System of Units now use seven base units (seconds, meters, kilograms, amperes, kelvins, moles, and candela). But how many of these constants do we need to describe the universe around us? According to a recent paper, the answer is only one; time.

The paper is the most recent result of a conversation which took place in a cafeteria at CERN, back in 1992. There, three physicists (Michael J. Duff, Lev B. Okun, and Gabriele Veneziano) realized that they couldn't agree exactly how many constants are necessary in order to describe the universe. This discussion led to a three papers in 2002 with three different suggestions; three constants, two constants, and zero constants. Okun's paper argued that three basic units were needed to measure all physical quantities of the universe; length, mass, and time. Veneziano argued that two was enough; length and time, while Duff believed that the numbers of constants varied depending on the theoretical model.

"The goal is to find the most fundamental description of physics possible," George Matsas, lead author on the new paper, explained in a statement. "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."

In the recent paper, the team attempted to figure out how many constants are needed to describe two different types of spacetime. These are the Galilean version used by Isaac Newton, and Minkowski spacetime, a relativistic spacetime solution to Einstein's equations.

In Galilean spacetime, before things got messy, space and time are distinct and separate from each other. Time is absolute, and agreed upon by all observers, and distances are independent of time, and the one cannot be derived by the other. The authors explain that other units, such as mass, can be defined using just these two constants.

Looking at Minkowski spacetime, which the authors believe can be applied to relativistic spacetime in general, they found that you don't even need length.

“In Galilean space-time, you need rulers and clocks to measure all the physical variables. In relativistic space-time, however, clocks are sufficient,” Matsas explained.

"This is because in relativity, space and time are so interrelated that a single unit is sufficient to describe all quantities. High-precision clocks, such as the atomic clocks used today, are capable of meeting all measurement needs."

To do away with length, the team uses a clock experiment first proposed by Canadian physicist Bill Unruh. In Minkowski spacetime, space and time are not independent of each other, meaning that one can be derived from the other. In the three clock experiment, two observers are placed at different ends of a rod you want to measure. One has two clocks, the other one. The observer with two synchronized clocks sends it along the rod to the second observer, who then synchronizes his own clock to the received clock at the end of its journey. He then sends the clock back to the first observer. Remember that in relativistic spacetime, time is altered by your velocity. Using these time measurements, it is then possible to define length, without reference to any other constant (for example, the speed of light).

In summary, the team suggests that any unit can in fact be measured in terms of one constant, seconds, currently defined as "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom."

While this is interesting and intriguing, don't expect the other constants to disappear, because they are still useful and convenient to use.

“Historically, based on a standardization effort adopted during the French Revolution (1789-1799), the kilogram was defined as the mass of one liter of pure water at a given pressure and temperature. In practical terms, it’s very convenient to have a mass standard, but from a fundamental point of view, it’s not necessary,” Daniel Vanzella, from the São Carlos Institute of Physics at the University of São Paulo, added. "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."

The study is published in Nature Scientific Reports.