Categories: Physics

A new Approach Could Tease out the Connection Between Gravity and Quantum Mechanics

In physics, there are two main ways to model the universe. The first is the classical way. Classical models such as Newton’s laws of motion and Einstein’s theory of relativity assume that the properties of an object such as its position and motion are absolute. There are practical limits to how accurately we can measure an object’s path through space and time, but that’s on us. Nature knows their motion with infinite precision. Quantum models such as atomic physics assume that objects are governed by interactions. These interactions are probabilistic and indefinite. Even if we constrain an interaction to limited outcomes, we can never know the motion of an object with infinite precision, because nature doesn’t allow it.

These two theoretical worlds, the definite classical and indefinite quantum, each work extremely well. The classical for large, massive objects such as baseballs and planets, and the quantum for small, light objects such as atoms and molecules. But both of these approaches break down when we try to study massive but small things such as the interiors of black holes, or the observable universe in the earliest moments of the big bang. For that has all the properties of general relativity with all the properties of quantum theory. This theory is sometimes referred to as quantum gravity, but right now we don’t know it would work.

How different theories are related. Credit: B. Jankuloski

It’s difficult to study this theory because we don’t have any experiments to test it directly. But a new study proposes an experiment that could give us a glimpse of how quantum gravity might work.

The key is to have an object that is quantum in nature, but massive enough that classical gravity has an effect. To do this the team proposes using a super-cooled state of matter known as Bose-Einstein condensate. This occurs when certain groups of atoms are cooled so much that they effectively blur together in a single quantum state. If billions of atoms were cooled to a Bose-Einstein condensate, they would form a single quantum object with a mass roughly equal to that of a virus. Tiny, but massive enough for the effects of gravity to be studied.

The team proposes making such a condensate, then suspending it magnetically so that only gravity can interact with it. In their work, they show that if gravity works on a quantum level, then the shape of the condensate will shift slightly from its “weightless” Gaussian shape. If gravity only interacts on a classical level, then the condensate will remain Gaussian.

This approach could be done with our current technology. Unlike other proposed studies, this experiment would only rely on a basic property of quantum systems rather than more complex interactions such as entanglement. If the experiment can be performed, it could give us the first real look at the fundamental nature of quantum gravity.

Reference: Richard Howl, et al. “Non-Gaussianity as a Signature of a Quantum Theory of Gravity.” PRX Quantum 2.1 (2021): 010325.

Brian Koberlein

Brian Koberlein is an astrophysicist and science writer. He writes about astronomy and astrophysics on his blog. You can follow him on Mastodon @briankoberlein@mastodon.social.

Recent Posts

NASA Gets a Firm Grip on the Future of Space Exploration

As part of their ongoing mission to push the boundaries of space exploration, NASA’s cutting-edge…

7 hours ago

Yes, the Odds of an Asteroid Striking Earth Have Doubled. No, You Don’t Need to Worry

The odds of 2024 YR4 striking Earth in 2032 have doubled to 2.3%, but that's…

11 hours ago

Europa Clipper Tests its Star Tracker Navigation System

On October 14th, 2024, NASA's Europa Clipper mission launched atop a Falcon Heavy rocket from…

2 days ago

The Moon has Two Grand Canyons, Carved in Minutes by an Asteroid Impact

Our Moon continues to surprise us with amazing features. Scientists recently shared new information about…

3 days ago

Is Methane the Key to Finding Life on Other Worlds?

How would detecting methane help astronomers identify if exoplanets, or even exomoons, have life as…

3 days ago

Space Junk Could Re-Enter the Atmosphere in Busy Flight Areas

In the more than 60 years since the Space Age began, humans have sent more…

3 days ago