Gravity, Particle Physics, and an Ultimate 'Theory of Everything'

Gravity's revenge in the theory of everything.

For nearly a century, physics has stretched in a tug-o-war between the science of the very big and the indescribably small. For planets and galaxies, gravity is easily noticed. But in the realm of microparticle interactions, gravity is weak because the size of the matter is tiny. Too small, many believed, for it to have a meaningful role in major cosmic events like particle formation — where electromagnetic and nuclear forces are much more potent.

However, physicists are rethinking gravity's place in the basic blocks of nature, assigning the cosmic force a small but critical role in explaining how fundamental particles could come into being, according to a recent study published in the journal Universe.

Gravity particle physics

A duo of physicists from the Institute of Gravitation and Cosmology at the People's Friendship University of Russia (RUDN University) are revisiting the idea of giving gravity a role in the creation of particles. For typical elementary particles (like electrons), the force of electromagnetic pull is 10^40 times more powerful than the pull of gravity.

From a conventional perspective, including gravity in the description of an electron's behavior in proximity to an atom's nucleus is a lot like including the effect of a mosquito on a windshield when discussing a car crash.

Regardless, study authors Vladimir V. Kassandrov and Ahmed Alharthy suspect the mosquito might have more bite than we thought — at least in the unconscionably small level called the Planck scale.

Physicists used semi-classical models to include gravity

"Gravity can potentially play an important role in the microworld, and this assumption is confirmed by certain data," said Kassandrov in a blog post shared on RUDN University's website.

Surprisingly, the scientific consensus on solutions for fundamental field theory equations in curved spacetime (effectively what gravity is) leaves a tiny space for gravity to have a non-zero influence. As distances between particles shrink, the force of gravity becomes comparable to that of attracted charges.


In some models, the tiny effects of gravity might also reinforce solitary waves forming in quantum fields.

The pair of physicists used semi-classical models for electromagnetic field equations, switching out equations that typically removed gravity from consideration and applying ones that left room to modify some quantities without adversely affecting others.

Some scenarios suggested a role for gravity in particle physics

This switch-and-swap method enabled the scientists to define the charge and mass of known elementary particles, and look for solutions capable of describing particle formation.

Unfortunately, the duo didn't find a distinct case where gravity played a necessary role — at least for particles we know exist.

Some scenarios — where the distance between particles was reduced to roughly 10^-33 meters for charged objects of mass 10^-5 grams — showed solutions.

While these parameters might not describe something found generally throughout the universe, the physicists' answer did find limits on a spectrum related to hypothetical semi-quantum particles — known as maximons.


Merging hypothetical cases in physics

While hypothetical overlaps might seem far-fetched, it represents a major accomplishment in theoretical physics. Often in science — which is based on empirical observation — we know nothing of new phenomena until we witness them. Not so for theoretical physics. Einstein's theory of gravity predicted the existence of black holes, which no one had observed before.

If particle physicists confirm the existence of maximons, and astronomers discover boson stars, we have pre-formed ideas about how gravity plays a role in their behavior — merging hypothetical cases about physics and bringing us closer to even further discoveries about the fundamental forces of the universe.

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