Physicists have measured no change in time or space for any of the fundamental constants of nature.

Modern physics is based on two pillars. The force of gravity is explained by the theory of general relativity. The strong nuclear force and weak nuclear force are described in the Standard Model. Physicists can explain a lot of interactions.

Those theories are not fully explained. The numbers that appear within the equations are called fundamental constants. New predictions can only be made with the numbers in place. General relativity is based on two constants: the strength of gravity and the amount of energy in the vacuum of space time.

Problems with modern physics are related.

19 constants are required to plug into the equations in the standard model. The strength of the nuclear forces, the mass of nine fermions, and the constants that control how the particle interacts with other particles are included. We have to add seven more constants because the Standard Model doesn't always predict the neutrinos' mass.

All the physics of the universe is determined by 28 numbers.

 Not so constant 

Physicists think that having all these constants is artificial. As scientists, our job is to explain as many different phenomena as possible with as little starting assumptions as possible. Physicists believe that general relativity and the Standard Model are not the end of the story since they are incompatible with each other. They think there is a more fundamental theory that ties these two branches.

The more fundamental theory could have many fundamental constants. The set we see today could be the same one. It could have its own constants with the 28 being dynamic expressions of some underlying physics. The fundamental theory could explain itself in its entirety without having to be added by hand.

It would be a sign of physics beyond what we currently know if our fundamental constants are not really constant. We can get clues as to a more fundamental theory by measuring the variations.

Physicists have come up with a number of experiments to see if the constants stay the same.

Constants to the test 

Ultraprecise atomic clock is one test. The operation of an atomic clock is dependent on a number of factors. If any of the constants change, you can compare the clocks at different locations or observe the same clock for a long period of time.

The Oklo mine in Gabon is being tested. The site used to be a natural nuclear reactor for a few million years. The products of that radioactive process, which survive to the present day, would be different if any of the fundamental constants were different.

Astronomers have studied the light emitted by quasars, which are powered by black holes billions of light years away from us. The light from those quasars had to travel enormous distances to reach us, and they passed through many gas clouds to absorb some of it. quasars in one direction would look different from quasars in other directions if the fundamental constants were different.

Physicists can use the Big bang as a laboratory. Our knowledge of nuclear physics can be used to predict the amount of hydrogen and helium produced in the first 12 minutes of the Big bang. The properties of the light emitted when our universe cooled from a plasma to a neutral gas can be predicted with the help of Plasma physics. It would show up as a mismatch between theory and observation if the fundamental constants were not the same.

Nobody has ever seen any change in the fundamental constants. We can place very strict limits on their possible changes. The fine structure constant, which is a measure of the strength of the interaction, is the same throughout the universe.

Physicists continue to search for a new theory to replace the Standard Model, but it appears that the constants we know and love are here to stay.

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