Exotic fifth state of matter made on the International Space Station

By Jonathan O’Callaghan

NASA/JSC

AN EXOTIC fifth type of matter has been created in one of the coldest places in the universe – a device on board the International Space Station (ISS).

The Cold Atom Laboratory (CAL) was launched to the ISS in 2018 to investigate a strange kind of matter, known as a Bose-Einstein condensate (BEC). This suitcase-sized device chills atoms of rubidium and potassium in a vacuum chamber, using laser light to slow their movement. Magnetic fields then contain the resulting cloud of atoms, which is cooled to nearly absolute zero at -273°C, producing a BEC.

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This chilly substance was initially theorised by Albert Einstein and Satyendra Nath Bose in the early 1920s as the fifth state of matter, following solids, liquids, gases and plasma. It is a supercooled gas that no longer behaves as individual atoms and particles, but rather an entity in a single quantum state.

“This is pretty remarkable because this gives you a macroscopic-sized quantum mechanical object,” says Maike Lachmann at Leibniz University Hannover in Germany.

BECs have been produced in a variety of experiments on Earth since 1995, but these are hindered by gravity, which collapses the clouds in a split second. The microgravity environment of the ISS keeps them stable for multiple seconds, allowing them to be studied in more detail.

Robert Thompson at NASA’s Jet Propulsion Laboratory and his colleagues have been operating the CAL remotely and have published their first results. While mostly just a demonstration that the machine works, there are some tantalising glimpses of what might be possible one day.

“It’s more of a technological achievement,” says Thompson. “But in the future, it will enable a wide spectrum of science.”

The initial results show that BECs behave differently in orbit. The team found that about half of the atoms form into a halo-like cloud around the main body of the BEC. On the ground, these atoms would simply fall due to gravity, but in microgravity on the ISS, the cloud remains suspended (Nature, s41586-020-2346-1 DOI: 10.1038/s41586-020-2346-1).

In the near future, the researchers hope to use the experiment to watch atoms collide on a quantum level. They also want to probe ripples in space-time called gravitational waves by monitoring disturbances in the movement of the atoms.

Looking further ahead, the experiment could also tackle ideas like Einstein’s equivalence principle, which says that all masses in a given gravitational field accelerate in the same way. Tests in microgravity could reveal whether there are any violations of the principle. “It’s usually unwise to bet against Einstein,” says Thompson. “But it’s always important to test these things.”