How is done the calculation of the minimum number of movement to solve any configuration of Rubik's Cube?

Question

I have read a few weeks ago that some mathematical researchers have discover that the minimum number of movements to solve any initial configuration of a Rubik's cube has been downsized to 20.

How do they calculate such a number ?

Thanks.

Answer 1

See the discussion and references on the associated Wikipedia page Optimal solutions for Rubik's Cube

Answer 2

See http://www.cube20.org/