Physics (from Greek φυσική / physikê means science of nature) is the science concerned with the discovery and understanding of the fundamental laws which govern matter, energy, space, and time. Physics deals with the elementary constituents of the universe and their interactions, as well as the analysis of systems best understood in terms of these fundamental principles. Because physics treats the core workings of the universe, including the quantum mechanical details which underpin all atomic interactions, it can be thought of as the foundational science, upon which stands "the central science" of chemistry, and the earth sciences, biological sciences, and social sciences. Discoveries in basic physics have important ramifications for all of science.
Physics research is divided into two main branches: experimental physics and theoretical physics. Experimental physics focuses mainly on empirical research, and on the development and testing of theories against practical experiment. Theoretical physics is more closely related to mathematics, and involves generating and working through the mathematical implications of systems of physical theories, even where experimental evidence of their validity may not be immediately available.