In the years since the terrorist attacks of 11 September 2001, there has been anecdotal evidence that young foreign scientists have become more hesitant about studying and working in the United States. Tougher visa rules announced earlier this year seemed to discourage them further (see Nature 422, 96–97; 2003). A survey by the American Institute of Physics (AIP) now shows that those rules, and perhaps the general climate of suspicion in the United States towards foreign scientists, has led to a reduction in the number of young physicists entering the country.

The proportion of foreign physics students in the United States had risen steadily since 1971, when 21% of all first-year graduate students came from abroad. It reached a peak of 55% for the 2000–01 academic year, but has since dropped by 10%.

The AIP survey shows that visa difficulties have played a large part in the decline. In 2002, about 20% of foreign applicants accepted to physics graduate programmes in the United States were initially denied entry into the country. The group experiencing the biggest problems hasn't been from the Middle East, but rather from China, which provides the largest number of foreign physics graduate students.

Visa problems haven't yet discouraged foreign students from applying, but they probably will unless the rules are relaxed. And if the decline in foreign students continues, it could have profound effects on physics employment in the United States. Many foreign physicists stay on past their training, so there may be fewer talented people to fill physics posts after graduate school.

This may well lead to more opportunities for those students who do make it into the US physics programme. But the drop in competition and international collaboration means that those who find these jobs could be celebrating bitter-sweet victories.