Superfluid With ‘Negative Mass’ Just Been Created by Physicists From Washington State University

Behaviour of superfluid. Image credits: 44833/Pixabay

A team of researchers from Washington State University has created a fluid with negative mass. Stunned? We are too.

But hypothetically speaking, matter can have negative mass. Well, it can be in the same sense that an electric charge can be either negative or positive.

So when you push it, and unlike every other physical object in the world, instead of accelerating in the direction it was pushed, it accelerates backward. This could potentially help scientists to know the strange behavior of black holes and neutron stars.

The phenomenon is rarely created in laboratory conditions and can be used to explore some of the more challenging concepts of the cosmos, said Michael Forbes, an assistant professor of physics and astronomy at the University of Washington.

Isaac Newton’s Second Law of Motion is force equals an object’s mass times its acceleration or often written as the formula F=ma.

If we rewrite it as acceleration is equal to a force divided by the object’s mass, and make the mass negative, it would have negative acceleration. Just imagine sliding a glass across a table and having it push back against your hand.

In other words, if you push an object, it will accelerate in the direction you’re pushing it. Mass will accelerate in the direction of the force.

“That’s what most things around us do,” said Forbes, hinting at the bizarreness to come. “With negative mass, if you push something, it accelerates toward you.”

a helium superfluid
A superfluid is a phase of matter capable of flowing endlessly without energy loss. Image credits: IIT Indore

The team created the conditions for this strange negative mass by- cooling rubidium atoms to just a fraction above absolute zero, what is known as a Bose-Einstein condensate.

In this state, particles move extremely slowly and, following the principles of quantum mechanics, behave like waves. It is as predicted by Satyendra Nath Bose and Albert Einstein.

Particles also synchronize and move in unison as what is known as a superfluid, which flows without losing energy.

Led by Peter Engels, WSU professor of physics and astronomy, the team created these conditions by using lasers to slow the particles. They made them colder and allowing hot, high energy particles to escape like steam, cooling the material further.

The team used lasers to keep this superfluid at the icy temperatures, but also to trap it in a tiny bowl-like field. This bowl-like field measured less than 100 microns across.

At this point, the rubidium superfluid has regular mass. Breaking the bowl will allow the rubidium to rush out, expanding as the rubidium in the center pushes outward.

To create negative mass, the researchers applied a second set of lasers that kicked the atoms back and forth and changed the way they spin. Now when the rubidium rushes out fast enough, if behaves as if it has negative mass.

“Once you push, it accelerates backwards,” said Forbes, who acted as a theorist analyzing the system. “It looks like the rubidium hits an invisible wall.”


The researchers successfully attempted to avoid some of the underlying defects encountered in previous attempts to understand negative mass.

What’s a first here is the exquisite control we have over the nature of this negative mass, without any other complication,” said Forbes.

This superfluid provides a platform to engineer experiments to study analogy in astrophysics, like neutron stars, and cosmological phenomena like black holes and dark energy, where experimenting are merely impossible.

It provides another environment to study a fundamental phenomenon that is very peculiar,” Forbes said.

So hopefully it won’t be long before we see the experiment recreated.

In conclusion, physics just keeps getting weirder, and now we’re much excited to see what happens next. Or what does it hold further?

The research was published in Physical Review Letters, where it is featured as an “Editor’s Suggestion.”


Source WSU Sciencealert

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