Northeastern University researchers have discovered a new theoretical framework explaining how Weyl fermions interact in certain materials, challenging Albert Einstein's foundational theories after an 85-year search for these massless particles since Hermann Weyl first theorized their existence in 1929, according to News. The breakthrough, published in Nature Communications, represents a significant step toward resolving one of physics' greatest puzzles: uniting quantum mechanics with Einstein's theory of gravity.
The Elusive Weyl Fermions Finally Revealed
Wei-Chi Chiu, a postdoctoral researcher at Northeastern reporting to Arun Bansil, university distinguished professor of physics, tells researchers that Weyl fermions are "relativistic particles that had actually never been seen, or observed, until 2015," according to News. The discovery capped off decades of theoretical work, with Bansil's team predicting in June 2015 that tantalum arsenide (TaAs) crystalline material would host these fundamental particles.
The presence of Weyl fermions in TaAs was demonstrated through photoemission spectroscopy, according to News. These massless particles are considered basic building blocks of other subatomic particles, making their discovery crucial for understanding the quantum world's fundamental structure.
Challenging Einstein's View of Causality
The new theoretical framework developed by Northeastern researchers goes beyond Einstein's theory of relativity to probe these mysterious particles, according to News. Most significantly, the framework challenges Einstein's view of causality as time-ordered in spacetime, potentially overturning the traditional causality principle that states no object or signal can travel faster than the speed of light.
Meanwhile, separate research from Florida Atlantic University's Charles E. Schmidt College of Science has uncovered another surprising challenge to conventional physics. Warner A. Miller, a professor in the Department of Physics, discovered that light's polarization can behave unexpectedly when passing through curved space, according to Fau. The research, published in September 2024, found that the shift in light's polarization angle can become up to 10 times larger than what gravity alone would cause, even in extreme environments like near a black hole.
The Non-Reciprocity Phenomenon
"Non-reciprocity means that light behaves differently when it moves forward compared to when it goes backward," said Miller, according to Fau. "In other words, it doesn't 'undo' its twist, even if it retraces its path. This challenges the conventional belief that light always returns to its original state after traveling a closed loop, especially if its path is influenced only by gravity."
This discovery emerged from Miller's collaboration with scientists at the University of Seoul and Seoul National University, South Korea, according to Fau. By carefully choosing how light is measured, researchers could trigger this strange non-reciprocity effect, where light doesn't return to its original polarization state even when retracing its path.
Revolutionary Approaches to Quantum Gravity
Physicists at University College London have developed another novel approach to solving the persistent problem of uniting gravity with quantum mechanics, according to Livescience. Published in Reports on Progress in Physics, their research outlines a reformulation of gravity that could lead to a fully quantum-compatible description without invoking extra dimensions or exotic features required by string theory.
The approach reinterprets the gravitational field to mirror the structure of known quantum field theories, according to Livescience. "The key finding is that our theory provides a new approach to quantum gravity in a way that resembles the formulation of the other fundamental interactions of the Standard Model," study co-author Mikko Partanen told researchers.
A Century of Scientific Stagnation
Despite over 100 years since quantum mechanics and Einstein's general relativity shaped our understanding of the universe, the fundamental challenge remains unresolved, according to Thebrighterside. For over a century, these two theories have individually succeeded in their domains—quantum mechanics explaining the tiny world of particles, and general relativity describing gravity and spacetime fabric.
Jonathan Oppenheim, a physicist at University College London, has introduced a "postquantum theory of classical gravity" that takes a radically different approach, according to Sciencedaily. Rather than modifying Einstein's theory to fit quantum rules, Oppenheim's theory suggests keeping spacetime classical while modifying quantum theory itself. This approach predicts an intrinsic breakdown in predictability mediated by spacetime, resulting in random fluctuations that could make the weight of objects unpredictable if measured precisely enough.
The Path Forward
Since the 1970s, technological advances have provided powerful new tools for scientific discovery, yet major breakthroughs in fundamental physics remain elusive, according to Pmc. The spirit of curiosity that once ignited revolutionary explorations seems diminished, replaced by incremental improvements rather than paradigm-shifting discoveries.
However, these recent developments represent a potential renaissance in theoretical physics, according to Nautil. The convergence of multiple research teams challenging Einstein's theories through different approaches—from Weyl fermions to light polarization anomalies to hybrid quantum-classical models—suggests that the foundations of physics may finally be ready for their next revolutionary transformation.
The implications extend beyond theoretical physics. If successful, these approaches could unlock new technologies and fundamentally alter our understanding of reality itself, potentially resolving paradoxes that have puzzled scientists for decades while opening entirely new avenues for exploring the deepest mysteries of the universe.