German-born Swiss physicist Albert Einstein is granted an American visa.

A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate causes of phenomena, and usually frame their understanding in mathematical terms. They work across a wide range of research fields, spanning all length scales: from sub-atomic and particle physics, through biological physics, to cosmological length scales encompassing the universe as a whole. The field generally includes two types of physicists: experimental physicists who specialize in the observation of natural phenomena and the development and analysis of experiments, and theoretical physicists who specialize in mathematical modeling of physical systems to rationalize, explain and predict natural phenomena.

Albert Einstein was a German-born theoretical physicist who is best known for developing the theory of relativity. Einstein also made important contributions to quantum mechanics. His mass–energy equivalence formula E = mc², which arises from special relativity, has been called "the world's most famous equation". He received the 1921 Nobel Prize in Physics for his services to theoretical physics, and especially for his discovery of the law of the photoelectric effect.

A travel visa is a conditional authorization granted by a polity to a foreigner that allows them to enter, remain within, or leave its territory. Visas typically include limits on the duration of the foreigner's stay, areas within the country they may enter, the dates they may enter, the number of permitted visits, or if the individual can work in the country in question. Visas are associated with the request for permission to enter a territory and thus are, in most countries, distinct from actual formal permission for an alien to enter and remain in the country. In each instance, a visa is subject to border control at the time of actual entry and can be revoked at any time. Visa evidence most commonly takes the form of a sticker endorsed in the applicant's passport or other travel document but may also exist electronically. Some countries no longer issue physical visa evidence, instead recording details only in border security databases.