Researchers at Hiroshima University have developed a realistic, highly sensitive method to detect the Unruh effect—a long-predicted phenomenon at the crossroads of relativity and quantum theory. Their novel approach opens new possibilities for exploring fundamental physics and for developing advanced technologies.
The work is published in Physical Review Letters on July 23, 2025.
The Fulling-Davies-Unruh effect, or simply the Unruh effect, is a striking theoretical prediction at the profound intersection of Albert Einstein's Theory of Relativity and Quantum Theory.
"In quantum theory, even the vacuum seethes with tiny energy fluctuations, where particles and antiparticles briefly appear and vanish. Remarkably, the Unruh effect shows how these 'vacuum ripples' are perceived depends on the observer's motion. A stationary observer sees nothing, but an observer undergoing acceleration perceives them as real particles with a thermal energy distribution—a 'quantum warmth,'" said Noriyuki Hatakenaka, professor emeritus at Hiroshima University.
The counterintuitive result emphasizes the important connection between these two pillars of modern physics. If scientists could experimentally verify the Unruh effect, it would not only bridge the gap between general relativity and quantum mechanics but also provide profound insights into the nature of spacetime itself. Yet the experimental verification of the Unruh effect has been a long-standing and significant challenge in fundamental physics.
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