Answer the following question given this paragraph: 

Over 2500 years ago Aristotle proposed two laws of physics governing motion. One for ‘Earthly bodies’ (objects on Earth) that states objects naturally go in straight lines and one for ‘Heavenly bodies’ (objects in space) that states objects naturally go in circles. This idea held steady for 2,000 years until Isaac Newton, in a triumph of brilliance, declared that there is one law of physics that governs motion and he unified “earthly” bodies and “heavenly” bodies with the The Universal Law of Gravitation. Newton used the universal law of gravity to prove that the moon is accelerating towards Earth just as a body on Earth is falling towards it. The acceleration of both the moon and the object on Earth is calculated using the same formula. This theory is so well regarded that it has been used to hypothesize the existence of black holes and dark matter, later verified by observation. The search to unify the laws of physics into one theory continues today and is often referred to as the yet undiscovered Grand Unified Theory (GUT).


Q: The as yet undiscovered grand unified theory is a search to unify laws of what branch of science?


A:
physics