Official websites use .gov A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
In this letter Heidelberger forcefully expressed his concern for the freedom of science and of international scientific exchange, which in the early 1950s, at the height of McCarthyism, was threatened by travel restrictions imposed on scientists with leftist or pacifist political leanings.