We investigated students' epistemological views of physics with a specific focus on physics laboratory work. The roles of experiments in physics have been underemphasized in previous epistemology research and there is a need for a broad view of epistemology that systematically incorporates experiments into discussions about the structure, methodology, and validity of scientific knowledge. An epistemological framework incorporating these features guided the development of an open-ended survey, which was administered to students in algebra-based and calculus-based introductory physics courses, an upper-division physics lab, as well as to physics Ph.D. students. We identified several differences in students' epistemological views of physics. Regarding the roles of experiments in physics courses, introductory students viewed experiments as supplemental tools for conceptual learning and problem solving, while higher-level students valued unique things experiments provide, including experiments as opportunities to emphasize the empirical nature of physics and the development of scientific and professional skills. Regarding views on the relationship between theory and experiment, introductory students heavily emphasized experiment testing theory. However, higher-level students recognized a holistic cyclical relationship: experiment inspires theory, theory guides experiment, experiment tests theory, and theory explains experiment.