In an act that defies physics as we know, Washington State University physicists have just created a fluid with negative mass. Apply pressure to the liquid and instead of accelerating in the direction it was pushed (like every other physical object in the world), it accelerates backward. Michael Forbes, a WSU assistant professor of physics and astronomy, believes the phenomenon can be used to explore some of the more challenging concepts of the cosmos.
“Hypothetically, matter can have negative mass in the same sense that an electric charge can be either negative or positive,” the University’s website notes. “People rarely think in these terms, and our everyday world sees only the positive aspects of Isaac Newton’s Second Law of Motion, in which the force is equal to the mass of an object times its acceleration, or F=ma.”
This explains why mass will typically accelerate in the direction of the force that is pushing it.
“That’s what most things that we’re used to do,” Forbes said. “With negative mass, if you push something, it accelerates towards you.”
In order to create this bizarre reaction, Forbes and his colleagues created the conditions for negative mass by cooling rubidium atoms to just below absolutely zero—creating a Bose-Einstein condensate. In this state, particles move extremely slowly and behave like waves. They also move in unison as a superfluid, which can flow without losing energy.
WUS professor of physics and astronomy Peter Engels and his team created these conditions using lasers to slow the particles, making them colder and allowing high-energy particles to escape like steam. The lasers trapped the atoms as if they were in a bowl; and breaking the bowl would allow the rubidium to rush out, expanding as the rubidium in the center pushes outward. To create negative mass, researchers applied a second set of lasers and kicked the atoms back and forth to change the way they spin.
“Once you push, it accelerates backwards,” Forbes commented. “It looks like the rubidium hits an invisible wall.”
“What’s a first here is the exquisite control we have over the nature of this negative mass, without any other complications,” he added.
The control gives researchers a new tool for studying cosmological phenomena like black holes—or even dark energy. However, it remains to be seen whether the escaping superfluid created by the team will be reliable (or accurate) enough to test the boundaries of negative mass in the lab. It will also be necessary for other teams to replicate the results independently.