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LONDON — Albert Einstein once said, “Logic will get you from A to B. Imagination will take you everywhere.” Now, thanks to the creative power of University College London physicists, a new theory is challenging the longstanding discrepancy between Einstein’s theory of general relativity and quantum theory. This new theory reconciles the concepts of gravity and quantum mechanics, while still holding onto the famous physicist’s understanding of spacetime.
At the core of modern physics lie these two fundamental pillars: quantum theory, governing the behavior of the tiniest particles, and Einstein’s theory of general relativity, explaining gravity through the bending of spacetime. However, these theories clash, presenting a challenge that has persisted for over a century.
Scientists traditionally believed that reconciling these theories required modifying Einstein’s theory to fit within quantum theory, as attempted by leading theories like string theory and loop quantum gravity. However, the new theory is challenging this consensus.
In the theory termed a “postquantum theory of classical gravity,” rather than altering spacetime, quantum theory undergoes modification. This suggests that spacetime might not be governed by quantum theory at all. Instead, the theory predicts unpredictable fluctuations in spacetime larger than those predicted by quantum theory, causing objects’ apparent weights to become unpredictable under precise measurements.
A simultaneous paper is also exploring the theory’s implications and proposes an experiment to test it. This experiment involves precisely measuring the weight of a one-kilogram mass over time at the International Bureau of Weights and Measures in France. If fluctuations in measurements surpass expected limits, it could refute the theory.
For five years, the UCL research group has scrutinized and tested this theory.
“Quantum theory and Einstein’s theory of general relativity are mathematically incompatible with each other, so it’s important to understand how this contradiction is resolved. Should spacetime be quantized, or should we modify quantum theory, or is it something else entirely?” questions study author Jonathan Oppenheim, professor of physics and astronomy at UCL, in a university release. “Now that we have a consistent fundamental theory in which spacetime does not get quantized, it’s anybody’s guess.”
Study co-author Zach Weller-Davies, who as a PhD student at UCL helped develop the experimental proposal and made key contributions to the theory itself, emphasized the experimental implications.
“In both quantum gravity and classical gravity, spacetime must be undergoing violent and random fluctuations all around us, but on a scale which we haven’t yet been able to detect,” explains Weller-Davies. “But if spacetime is classical, the fluctuations have to be larger than a certain scale, and this scale can be determined by another experiment where we test how long we can put a heavy atom in superposition of being in two different locations.”
Study co-author Dr. Barbara Šoda expressed hope that these experiments could settle the debate about pursuing a quantum theory of gravity.
“Because gravity is made manifest through the bending of space and time, we can think of the question in terms of whether the rate at which time flows has a quantum nature, or classical nature,” notes Dr. Šoda. “And testing this is almost as simple as testing whether the weight of a mass is constant, or appears to fluctuate in a particular way.”
The theory’s origins lie in resolving the black hole information problem, allowing for information destruction due to a breakdown in predictability, a departure from standard quantum theory.
This novel theory not only challenges current paradigms but also offers new perspectives for experimental testing, potentially reshaping our understanding of gravity and spacetime.
The study is published in the journal Physical Review X.
