Fluid With "Negative Mass" Moves Backwards When Pushed Forwards

This fluid fights back. alekime/Shutterstock

Fluids are weird, no matter the context. They never behave like they’re supposed to, the naughty things – and scientists apparently quite like creating newer and quirkier versions of them all the time. To wit, the latest member of the circus is a so-called superfluid that, when pushed, accelerates backwards in the opposite direction.

A team at Washington State University (WSU) have been doing that old-fashioned sciencey thing – playing with lasers – and used it to cool some rubidium atoms. Although lasers are traditionally associated with heating things or destroying planets, their careful application can cause atoms to emit energy and thus cool down over time.

The troublemakers at WSU did this and managed to get the rubidium atoms down to near-absolute zero, the coldest temperature possible. At this temperature, the atoms behaved less like particles and more like waves, an effect first predicted by physicists extraordinaire, Satyendra Nath Bose and Albert Einstein.

The torture of these atoms was, however, not yet complete. Atomic nuclei, along with individual elementary particles, spin around – a bit like little planets or ballerinas. Changing a particle’s spin changes how it behaves and interacts with its environment, so the WSU manipulators once again used lasers to alter the spin of these considerably chilly rubidium nuclei.

Ultimately, this caused them to behave as if they had negative mass. This, ladies and gentlemen, is a considerably weird property to have.

You, right now, have positive mass – no offense. Your constituent parts all add up to a certain number of kilograms, and you are warping the fabric of space-time as a consequence. This is normal.

True negative mass is some shadowy reflection of positive mass. It’s like saying you weigh minus kilograms – it doesn’t appear to make sense, and for quite a while, the concept was just that – hypothetical.

How about some negative energy to go with that negative mass? Discovery UK via YouTube

This team appear to have created negative mass, in that it behaves in very much the opposite way to normal mass. If you push a ball, the momentum you impart upon it pushes it forwards in the direction of applied force.

This new rubidium fluid moves backwards when you push it, because it apparently has negative mass. In reality, this is not true negative mass, but something called negative effective mass, which is mass that behave as if it is negative mass – so not the genuine article, but pretty weird stuff nonetheless. “It looks like the rubidium hits an invisible wall,” co-author Michael Forbes, a WSU assistant professor of physics and astronomy, said in a statement.

It’s likely that negative mass already exists elsewhere, but as reported in the journal Physical Review Letters, this experiment allows the researchers to carefully control a version of it and probe its characteristics. The new fluid also opens up a new avenue of analysis for strange astronomical features, like black holes and dark energy, which cannot be directly experimented with.

More than anything, though, we’re pretty sure it’s designed to mess with your head.

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