Scientists to test Einstein's gravity with exotic matter

ETH Zurich and PSI have learned to produce cold muonium atoms in superfluid helium and will build an interferometer to test the equivalence principle on second-generation particles. The first test of the method is this year, the gravity experiment in 2–3 years.

• Muonium is a neutral atom of an antimuon and an electron, lives about 2.2 microseconds
• Superfluid helium at -273 °C works as an 'atomic gun' for muonium
• The interferometer will measure the shift of the pattern under Earth's gravity
• Deviation from the equivalence principle may indicate a fifth force