A new research paper has raised significant questions regarding the longstanding assumption that gravity may be elucidated through quantum entanglement. This finding, if validated, could make the quest to comprehend gravity and its relationship with quantum physics even more complex.
The debate traces back to a proposal made in 1957 by Nobel laureate Richard Feynman, who posited that if gravity could lead to quantum entanglement between two massive objects, then gravity itself must exhibit quantum characteristics. This notion has gained momentum recently as advancements in precision measurement have made experimental tests of this idea more feasible.
However, a recent study conducted by Richard Howl and Joseph Aziz from Royal Holloway, University of London, challenges this fundamental assumption. Their calculations suggest that classical gravity, the framework introduced by Albert Einstein, could produce entanglement under specific circumstances, contradicting the traditional view that a purely classical gravitational field cannot convey quantum information.
Historically, physicists believed that entanglement necessitated faster-than-light information transfer, which is deemed unphysical. Yet, Howl and Aziz employed a novel approach by integrating quantum field theory (QFT) with classical gravity, demonstrating that quantum communication could still occur.
The authors stated, “Although entanglement can be used to provide evidence for the quantum nature of gravity, this is not unambiguous and is fundamentally a phenomenological issue: it depends on the parameters and form of the experiment.” They emphasized that the critical factor lies not in hypothetical graviton propagators but rather in virtual matter propagators, which are integral to the quantum field description of particles like electrons.
This nuanced perspective carries profound implications. For years, scientists have proposed conducting “tabletop experiments” to validate Feynman”s hypothesis, aiming to observe gravitationally induced entanglement as evidence of quantized gravity. However, the latest findings imply that such experimental outcomes could be ambiguous, potentially arising from either quantum gravity or classical gravity interacting with quantum fields.
The research team remarked, “Here we show that local classical theories of gravity can, in fact, generate quantum communication and, thus, entanglement.” They further explained that while classical gravity was thought to operate solely through local operations and classical communication (LOCC), considering matter through the lens of quantum field theory reveals that classical gravitational interactions can indeed lead to quantum communication.
Although this may complicate the search for a definitive experimental signature of quantum gravity, it does not render such endeavors futile. The team noted that both classical and quantum gravity models would yield entanglement at varying strengths based on factors such as mass, distance, and duration of the experiment. With meticulous measurements, scientists might still be able to differentiate between the two scenarios.
As such, Feynman”s envisioned experiment remains as intriguing and challenging as ever. The study has been published in the journal Nature.
