# Scientists create fluid that seems to defy physics

Imagine something that reacts totally opposite to the way it should. That's what scientists at Washington State University have created, and it could help them better understand our universe.

## 'Negative mass' reacts opposite to any known physical property we know

Newton's cradle, seen here, illustrates Isaac Newton's Second Law of Motion, which states that a force is equal to its mass times acceleration. But scientists have created a fluid that seems to defy that law. (Shutterstock)

Imagine something that reacts totally opposite to the way it should. That's what scientists at Washington State University have created, and it could help them better understand our universe.

When we push on an object, we know intuitively that — adhering to Isaac Newton's Second Law of Motion — it will move away. But imagine taking your child to the park, putting him or her on a swing and pushing — only to have the swing move toward you and not away.

Physicists at Washington State University (WSU) have created a fluid with this sort of property, called a negative mass.

## How it was created

The theory of negative mass has been around for some time. Just like an electric charge can be positive or negative, it is believed the same should hold true for mass. But no such naturally occurring substance has ever been found.

The researchers at WSU were able to create it by using a laser to cool rubidium atoms to just above absolute zero (–273 C). This slows the atoms to the point where they're almost immobile, called a superfluid. And, as opposed to moving as individual atoms, they act as one, moving as a wave, as predicted by quantum mechanics. If the atoms were released , they would rush out as expected.

However, then a second laser was applied that changed the way the atoms spin. Once the rubidium rushed out, it acted as though it had hit a wall and accelerated backward.

At the top, the cloud of gas is seen before it begins to demonstrate its negative mass. The cloud begins to expand (middle) and finally expands in the opposite direction. (Michael Forbes/WSU)

"It's just strange. You push something and you see it go in the wrong direction," said Canadian researcher Michael Forbes of WSU, and co-author of the study. "It's a new way of studying physics here, and a phenomenon that's really counterintuitive to everyday life."

And while it does seem counterintuitive, it's not a violation of physics.

"It's not like we violated some laws of physics," Forbes said. "These objects are not going to create a black hole or anything like that."

## Practical applications

Forbes said creating negative mass allows him to study matter that he's unable to study in any other way. His studies focus around neutron stars, small and extremely dense stars. The neutrons in the crust of the star form a superfluid similar to the ones created in this kind of experiment. This can help answer questions as to why the neutron in these stars behave the way they do.

This creation may have practical applications as well.

"Once new quantum ideas and phenomenon are discovered, there's a fairly short timescale before those tend to be developed into quantum technologies which can be used to create high-precision measurements or improve navigational devices and things like that," Forbes said.

For example, earlier experiments have resulted in our phones having compasses.

And there's a lot of money being put into developing quantum technology, he said.

As to what possible technologies this new creation may lead to, Forbes said it's too early to tell.

"We don't know where this is going yet … but once you start understanding these behaviours, then you can use them to engineer devices, engineer measurement techniques, and then they can find their way into consumer devices."

Nicole Mortillaro

Senior Reporter, Science

Nicole has an avid interest in all things science. As an amateur astronomer, Nicole can be found looking up at the night sky appreciating the marvels of our universe. She is the editor of the Journal of the Royal Astronomical Society of Canada and the author of several books.

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