Popular MechanicsScientists Get One Step Closer to Unraveling the Secrets of Quantum GravityDarren Orf
Mon, December 1, 2025 at 8:30 AM EST
3 min read
Scientists Get One Step Closer to Quantum Gravity koto_feja - Getty ImagesHere’s what you’ll learn when you read this story:
*For close to a century, scientists have been trying to marry Albert Einstein’s General Theory of Relativity and quantum theory—our two best bets on understanding the universe on a macroscopic and microscopic level.
*A new study mathematically explores that even if gravity is not quantum (and is instead classical), it can still quantum-entangle particles—just not with as strong of a correlation as quantum gravity.
*This work doesn’t attempt to disprove quantum gravity, but exploring gravitationally induced entanglement could lead to an experimental confirmation (or refutation) further down the line.
Today, our conception of the universe is governed by two big theoretical frameworks. Albert Einstein’s General Theory of Relativity describes the universe of the very big—the movement of planets and the propagation of gravity across space-time. Quantum theory, on the other hand, describes the universe of the very small, where forces are quantized. For example, the electromagnetic force’s quantum is the photon, while bosons and gluons are the quanta for the weak and strong force, respectively.
You might’ve noticed that gravity isn’t included in this list of forces and their associated smallest pieces. While scientists theorize that quantum gravity must also have a force carrier (called a graviton), we’ve never actually seen one. This summer, Nature reported a growing effort among scientists to discern once and for all if quantum gravity exists as our theoretical understanding and experimental capabilities improve. One of the most exciting efforts exploring this idea comes from the University of London, where physicists Joseph Aziz and Richard Howl are investigating whether classical gravity could induce quantum entanglement—a phenomenon where two particles become linked, and the measurement of one influences the other.
“With the other interactions, we quantized them assuming they live within an independent background of classical space and time,” Howl, whose paper was
published in late October in the journal Nature, told Physics World. “But with quantum gravity, arguably you cannot do this [because] gravity describes space−time itself rather than something within space−time.”
Quantum theory postulates that entanglement occurs via the exchange of virtual gravitons. As Space.com explains, these gravitons don’t really exist, but due to “wacky world of quantum physics,” such particles are mathematically allowed for an extremely limited amount of time. The idea behind Aziz and Howl’s work is that gravity can remain classical while still mediating quantum entanglement.
“You could think about the gravitational interaction as more general than just the mediation of the gravitational field,” Howl told Space.com, “and there could be quantum processes associated with it, virtual matter processes, and in that case even if the gravitational field is classical the gravitational interaction could still potentially entangle matter.”
Howl notes that this idea doesn’t mean quantum gravity doesn’t exist—in fact, he thinks there’d be methods for distinguishing between these two methods of entanglement. Quantum gravity would have stronger correlations, meaning that one could easily discern the state of one particle in an entanglement pair using the information of the other. In a classical entanglement scenario, the correlation would be weaker due to the nature of probabilities. This study helps form the parameters, establishing these effects for future experiments.
“There’s nothing to say you can’t do [an experiment] in theory,” Howl told Space.com, “but you have to eliminate all decoherence [things that would cause the superposition to collapse] and it is an incredibly difficult challenge.”
Luckily, difficult challenges are well-known obstacles for physicists trying to merge the two most powerful theories in the history of science.
https://www.yahoo.com/news/articles/scientists-one-step-closer-unraveling-133000564.html
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