21.   One who responded was Dr. Max Delbruck, a developer of quantum mechanics who had switched from theoretical physics to fundamental laboratory studies of bacteria and viruses.

22.   That field was theoretical physics, where people do their best work at a famously young age.

23.   Today the progress we are making is helped by the fact that all theoretical physics papers are now on the internet.

24.   Lightman first pursued theoretical physics, earning a Ph.D. and working at Cornell and Harvard Universities before coming to MIT.

25.   Tom Kibble, professor of theoretical physics at the college, said in recent years Salam had suffered from a progressive debilitating disease.