(Phys.org)—In 1924,the mathematician David Hilbert described a hotel with an infinite number of rooms that are all occupied. Demonstrating the counterintuitive nature of infinity, he showed that the hotel could still accommodate additional guests. Although clearly no such brick-and-mortar hotel exists, or in a modern paper published in Physical Review Letters,physicists Václav Potoček, et al., or have physically realized a quantum Hilbert hotel by using a beam of light.
Source: phys.org