Researchers at Washington State University have created a fluid "that has the properties of negative mass," reports New Atlas. When you push it, it accelerates towards you.
The team made the Bose-Einstein condensate by slowing down rubidium atoms with lasers, which cools them to just slightly above absolute zero and keeps them confined to a bowl-shaped area of about 100 microns across. Next, the scientists hit those atoms with another set of lasers that changed how they spin, a phenomenon known as "spin orbit coupling." That gives the rubidium the properties of a substance with negative mass when it's allowed to flow out of the bowl shape, which, according to the researchers, makes it look like it's hitting 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," says Forbes. "It provides another environment to study a fundamental phenomenon that is very peculiar."