or if you prefer
Scientists have created a fluid with negative mass – but what does it tell us?
Prof Peter Engels, from Washington State University (WSU), and colleagues cooled rubidium atoms to just above the temperature of absolute zero (close to -273C), creating what's known as a Bose-Einstein condensate.
In this state, particles move extremely slowly, and following behaviour predicted by quantum mechanics, acting like waves.
They also synchronise and move together in what's known as a superfluid, which flows without losing energy.
To create the conditions for negative mass, the researchers used lasers to trap the rubidium atoms and to kick them back and forth, changing the way they spin.
Weird. I'd heard about this before as something-that's-not-technically-impossible, but never figured we'd actually create the stuff.