Restrictions on scientific communication are nothing new—recall that Galileo was sentenced to house arrest by Church inquisitors in 1633 for supporting the Copernican theory. But serious threats to the freedom of scientific discourse have come to the forefront recently, after suspicions were raised of Chinese spying at U.S. national laboratories. These allegations triggered the imposition of new restraints and revived some old ones. So it is a good time for the scientific community to reflect on the evolution of such government controls in our time, to express support for regulations that are justified and to protest those that do harm.
After the outbreak of World War II, many physicists voluntarily censored themselves, with the result that papers about nuclear fission disappeared from the pages of the Physical Review starting in 1941. The government soon issued explicit restrictions on scientists and engineers privy to military secrets in the form of a classification system. Under that arrangement, information was labeled "Special Compartmentalized Information," "Top Secret," "Secret" or "Confidential," depending on the severity of damage to the nation should the material be compromised.
To accompany this system, government agencies introduced various levels of clearance. People seeking employment in organizations dealing with classified information or equipment surrendered some of their privacy by permitting a field investigator to talk about their past conduct with their neighbors and associates. In addition, inquiries into the subject's vulnerability to blackmail could be made, on the premise that such a liability might result from alcoholism, a drug habit or even money troubles. What is slightly more controversial—because it smacks of guilt by association—is the extent to which government investigators were allowed to inquire into people's political activities and, during the Cold War, their contacts with Communists or former Communists.
After the Cold War, it became much more difficult for government investigators to decide which associations were good and which were bad. I was once asked, for instance, as part of the renewal of my clearance, to submit copies of all my correspondence with my native country, Germany, which I left 61 years ago. The request turned out to apply to such a large pile that I was able to talk the investigators out of it. But even if investigators clear someone quickly and without hesitation, in the end, they have to make a leap of faith that the person will be loyal and responsible tomorrow as well as today.
Indeed, the clearance system is fundamentally based on trust, because, among other things, the cleared worker carries classified information in his or her head, something that cannot be censored. So it is imperative that a person given clearance play by the rules. Although certain security measures lessen the opportunity for misconduct, the system has had past failures: Aldrich Ames, John Walker and Ronald Pelton, for example, were all cleared. Yet they all succumbed to a desire for money and revealed military secrets to potential adversaries.
So classification and the accompanying clearance process have obvious shortcomings. But classification has worked reasonably well and is generally accepted as necessary and appropriate by the scientific community. In particular, it draws a well defined line between communications that are approved and those that are forbidden. But recent allegations of Chinese spying have brought on a worrisome shift in the nature of these governmental controls.