As much as it's about theoretical physics, it's also about the progress of any ordinary life, which begins with seemingly endless possibilities and then dwindles until death forecloses further choice. I wish I'd seen Sally Hawkins and Rafe Spall in the London debut, but the director Michael Longhurst has found very fine replacements in Gyllenhaal and Wilson. They have a lovely time playing with the script and with each other -- Wilson with her pointy, pouty features and wonderfully manic energy, Gyllenhaal with his bushy beard and earthier charms. He relies perhaps a bit heavily on blokiness and she on intensity, but they ably vary the mood of each new scene. And though the play fixes on physics, rest assured the chemistry is ample. If Longhurst's direction is somewhat invisible...he has created an environment in which the actors feel comfortable taking risks and chances and turns.