Scientists at Washington State University (WSU) have created what likely sounds like the impossible, a fluid with negative mass.
If your mind isn't yet completely blown, consider what happens to every object with positive mass (which is basically every physical object you have ever encountered) when you push it: it moves forwards. An object with negative mass should therefore act in the opposite way when you push it, by accelerating backwards. And that's exactly what happens to the fluid created at WSU.
“Once you push, it accelerates backwards,” explained Michael Forbes, a WSU assistant professor of physics and astronomy, in a press release. “It looks like the [fluid] hits an invisible wall.”
One crude way of trying to conceptualize it is as some kind of weird science version of a Chinese finger trap, which is a contraption that actually tightens its grip when you try to remove your fingers. It seems to do the opposite of what your intuition says it should do. But despite the fact that an object with negative mass might seem wonky, there's a scientific basis for it.
Technically speaking, matter should be able to have negative mass in the same way that an electric charge can be either negative or positive. The existence of objects with negative mass is also consistent with the theory of general relativity, and in certain speculative theories, negative mass might help to explain the construction of things like wormholes.
Forbes and his colleagues created the peculiar fluid by cooling rubidium atoms to just a hair above absolute zero, creating what is known as a Bose-Einstein condensate. Particles in this state are so cold and slow that they start synchronizing and moving in unison, and flow without losing energy, which means they transform into a superfluid. Researchers then used lasers that kicked the rubidium atoms back and forth and changed the way they spin, thus generating the negative mass effect.
More research will need to be done to confirm the conclusions of the experiment, but assuming everything checks out, the possible creation of stuff with negative mass has some mind-bending consequences. For instance, it would create ambiguity as to whether attraction should refer to force or the oppositely oriented acceleration for negative mass. Try to wrap your brain around that.
“It provides another environment to study a fundamental phenomenon that is very peculiar,” said Forbes.
The research appeared in the journal Physical Review Letters.