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Hubble constant, gravitational constant, Planck constant, Boltzmann constant, speed of light, π, dielectric constant of vacuum, permeability of vacuum, conductivity, resistivity, Coulomb constant, etc. The number of constant families is still expanding. Anyone who has studied basic science will encounter at least one physical constant, such as the speed of light or the mass of an electron. This is inevitable.

Scientists, especially physicists, must remember these constants (or at least become familiar with them) because they simplify many calculations. But when you stop and think about these constants and the properties of some aspect of the universe they describe, it's amazing. These huge numbers are not just meant to be computationally inconvenient.

We know a lot of constant values, but how do we get them? Are these constants created by scientists or do they exist naturally? What do they mean for physics? Do they change? If so, why do we call them constants?

What do these constants mean?

Hubble's constant tells us about the expansion of the universe and how fast stars are moving away from us, and ultimately helps us calculate the age of the universe. Nearly 100 years have passed since Edwin Hubble first calculated it in 1929, and scientists are still debating its actual value. With every leap in technology, and with every new (and more sophisticated) telescope, the Hubble constant "changes." Finding the exact value of Hubble's constant remains one of the greatest challenges of modern astronomy.

The gravitational constant, sometimes referred to as Newton's constant, is a constant of proportionality used in Newton's law of universal gravitation, denoted by G. The value of the gravitational constant does not change whether on Earth, Mars, or some distant planet thousands of light-years away.

Planck's constant gives the relationship between the frequency of a particle and its total energy, a breakthrough discovery in the physics world because one of these quantities is a property of the wave (frequency) and the other a property of the particle (energy). Thus, the wave-particle duality of matter was proved and finally paved the way for the development of quantum physics.

We can define individual constants by what they represent (physical quantities), but can we give several constants a global definition (meaning)? That is, we need to define certain quantities of the universe in units we specify, such as meters, newtons, light-years, and joules.

For example, the unit G of the gravitational constant is:

When G is multiplied by the masses of the two bodies and divided by the square of the distance between them, you get the unit of force, Newton (N). This is exactly what we need, because we want to know the gravitational force between two objects:

Therefore, the value of the constant will depend on the system of units we use.

Does this mean that constants are human-constructed? Absolutely not! This definition is about what a constant does, not what a constant is. Moreover, it cannot define all constants, since there are dimensionless constants, such as the famous pi.

Pi is an irrational number and transcendental number, which appears in many phenomena in nature. From the double helix of DNA, to the ripples of ponds when stones are thrown, to zebra stripes and leopard patterns, to the famous Heisenberg principle, to the structure of earthquake-resistant buildings, to the fluctuations of ocean waves-pi is everywhere. It gradually disappears at the center of the universe and appears in the most complex mathematics.

It's a constant, there's no unit, and we don't know why that's the case.

How are their values determined? There are some constants whose values are disputed, and errors will always exist, depending on the accuracy and sensitivity of our existing equipment. Constants are not created by scientists. They exist in the universe, and we measure them only through repeated experiments and observations.

There is another question that delves deeper into the mystery of constants. In a paper published in Nature on February 20, 1937, the famous physicist Paul Dirac posed a question that still puzzles physicists: If we look at the entire history of the universe, are all constants really constants? After all, all our measurements are made on Earth. What is constant here is constant elsewhere?

Paul Dirac's treatise Then there is evidence that the "ratio of the mass of the proton to the mass of the electron" is invariant. Over the years, teams of researchers from many countries have explored the farthest corners of the observable universe simply to determine whether the mass ratio of protons to electrons will change. Every time, the result is the same. The mass ratio remains unchanged.

Constants can change, such as Hubble's constant (Edwin Hubble measured an initial value more than seven times larger than the current value), but this is due to human error and equipment accuracy.

We cannot explain why these constants are the way they are, how they are determined by nature, or whether they can change over billions of years. We can only measure what already exists.

This article comes from Weixin Official Accounts: Laohu Science (ID: LaohuSci), Author: I am Lao Hu

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