Physics—the study of matter and energy, time and space, and their interactions and interconnections—is often regarded as the most fundamental of the natural sciences. An understanding of physics is essential for an understanding of many aspects of chemistry, which in turn provides a foundation for understanding a variety of biological processes. Physics also plays an important role in most branches of engineering; and the field of astronomy, essentially, is physics applied on the largest of scales. As science has progressed over the last century or so, the boundaries between the different scientific disciplines have become blurred and new interdisciplinary fields—such as chemical physics, biophysics, and engineering physics—have arisen. For these reasons, and because of the excellent training in critical thinking and problem solving provided by the study of physics, this subject represents an indispensable gateway to the other natural sciences and a valuable component of a liberal arts education.