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A fifth force of nature? Subatomic particles are defying the laws of physics

Scientists at the US Energy Department’s Fermilab in Batavia, Illinois may be on the brink of an astonishing breakthrough. Observations of a mysterious “wobble” in muons – subatomic particles similar to electrons – may open up a new chapter of physics. The unusual activity could potentially represent a fifth force of nature.

For years, physicists have tried to decode the intricacies of the universe on the most fundamental scale: the subatomic level. This is the world beyond what we can perceive, where particles smaller than atoms come into play. Atoms, which we can consider as the basic units of matter, interact to form molecules, the constituents of solids, gases, and liquids.

Finding a fifth force of nature

The cornerstone theory that describes the universe’s mechanics at this scale is the Standard Model of particle physics. Conceived in the early 1970s, the Standard Model proposes that everything in existence is an outcome of interactions between a handful of fundamental particles. These interactions are mediated by four foundational forces of nature: the strong force, the weak force, the electromagnetic force, and gravity.

Throughout the 20th century, the Standard Model emerged as a robust theory, demonstrating uncanny accuracy in predicting diverse phenomena. However, it’s not without its blind spots. Some profound questions, like the constituents of dark matter and the reason for the observed imbalance between matter and antimatter, remain unanswered.

Studying subatomic particles

To shed light on these enigmas, scientists at Fermilab embarked on a remarkable journey, diving deep into the world of muons. These particles, comparable to electrons but with a mass 200 times greater, come into existence when cosmic rays interact with the Earth’s atmosphere. Being magnetic, muons exhibit a “wobble” or “precess” when exposed to intense magnetic fields.

The Fermilab’s “Muon g-2” experiment plunged these particles into a vast, donut-shaped superconducting magnetic storage ring, cooled to a staggering -268°C (-450°F). 

As muons raced around this ring at almost the speed of light, they revealed their dance by interacting with other subatomic particles, thereby altering their wobble. Detectors meticulously tracked this wobble, comparing the observed behavior to predictions from the Standard Model.

Fascinating possibilities 

Brendan Casey, a senior scientist at Fermilab and a principal investigator of the study, noted, “We are looking for an indication that the muon is interacting with something that we do not know about.” This “something” could span from previously unknown subatomic particles and forces to unprecedented properties of space-time. 

Casey even suggests the possibility of violating the Lorentz invariance, which claims the constancy of physical laws throughout the universe. “That would be insane and revolutionary,” he said.

Strong evidence 

The revelations in the Fermilab mirror findings from 2021, but are even more convincing as they are supported by over four times the data. This bolsters the case for a departure from the Standard Model.

“With all this new knowledge, the result still agrees with the previous results, and this is hugely exciting,” said Dr. Rebecca Chislett of University College London.

“Results further reinforce our team’s previous precise measurements of the muon’s anomalous magnetic moment, reaching unprecedented accuracy in testing the Standard Model and probing deeper into the subatomic world.”

This potential fifth force of nature serves as a pivotal milestone on the journey to fully understanding the subatomic realm.

The forces of nature

The forces of nature are fundamental interactions that govern how objects and particles interact with each other in the universe. These forces include:

Gravitational force

Gravitational force is a fundamental force of nature that causes any two masses to be attracted to each other. It’s what keeps planets in orbit around the sun, causes apples to fall from trees, and holds galaxies together.

This force is described by Sir Isaac Newton’s law of universal gravitation and further refined by Albert Einstein’s theory of general relativity. Both of these theories have been tested extensively and have been found to predict the behavior of objects under the influence of gravity quite accurately. However, under certain extreme conditions, general relativity offers more accurate predictions than Newtonian gravity.

Electromagnetic force

The electromagnetic force governs the interactions between charged particles and is responsible for a vast range of phenomena observed in the universe.

The electromagnetic force can be attractive or repulsive. It acts between objects with electric charge. Like charges (e.g., two positive charges or two negative charges) repel each other, while opposite charges (a positive and a negative) attract each other.

It is mediated by photons, which are quanta of the electromagnetic field. These are the same photons that make up visible light, as well as other forms of electromagnetic radiation like radio waves, X-rays, and ultraviolet light.

The electromagnetic force plays a crucial role in determining the structure and behavior of molecules and solids. It is responsible for chemical bonds, the behavior of electrical circuits, the operation of electronic devices, the transmission of light and radio waves, and many other phenomena that we encounter in daily life.

Weak nuclear force

The weak nuclear force, often simply called the weak force or weak interaction, is responsible for certain types of particle interactions, particularly those involved in the process of radioactive decay.

The most well-known effect of the weak force is beta decay. In beta-minus decay, for instance, a neutron inside an atomic nucleus is transformed into a proton while emitting an electron and an antineutrino. Conversely, in beta-plus decay, a proton can be converted into a neutron, with the emission of a positron and a neutrino.

The weak force plays a crucial role in the fusion processes that power the Sun and other stars. The proton-proton chain reaction, which is the dominant energy-producing process in the Sun, involves weak interactions to produce deuterium (a type of hydrogen nucleus), positrons, and neutrinos.

The weak interaction, along with the electromagnetic and strong nuclear force, is described within the framework of the Standard Model of particle physics. The Standard Model provides a unified description of these three forces, with gravity being the only fundamental force not yet integrated into this framework.

Despite its name, the weak force is considerably stronger than gravity, but its effects are typically masked in everyday life due to its short range and the specific types of particles it affects.

Strong nuclear force

The strong nuclear force, often simply called the strong force or strong interaction, is primarily responsible for holding the protons and neutrons together within atomic nuclei.

The primary role of the strong nuclear force is to bind protons and neutrons (collectively referred to as nucleons) together within the atomic nucleus. This is particularly remarkable considering that protons are positively charged and would repel each other due to electromagnetic forces.

However, the strong force is much stronger than the electromagnetic force at short distances, overcoming the repulsive electromagnetic force between protons and binding them together inside the nucleus.

The strong nuclear force is essential for the stability of atomic nuclei and, by extension, the existence of atoms, molecules, and matter as we know it.

These forces govern everything from the structure of atoms to the motion of galaxies, and their underlying principles are described by modern physics, including the theory of relativity and quantum field theory.


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