American physicist Herbert Callen observed that even though a survey conducted by the American Physical Society Committee on the Applications of Physics reported (in the "Bulletin of the APS") in 1971 that industry leaders desired a greater emphasis on more practical subjects, such as thermodynamics as opposed to the more abstract statistical mechanics, academia subsequently went the other way. British physicist Paul Dirac, who had relocated to the United States in the 1970s, opined to his colleagues he doubted the wisdom of educating so many undergraduates in science when so many of them had neither the interest nor the aptitude. Quantitative historian Peter Turchin noted intensifying competition among graduates, whose numbers were larger than what the economy could absorb, a phenomenon he termed elite overproduction, led to political polarization, social fragmentation, and even violence as many became disgruntled with their dim prospects despite having attained a high level of education. Income inequality, stagnating or declining real wages, and growing public debt were contributory factors. Turchin argued that having a youth bulge and massive young population with university degrees were the key reasons for the instability of the 1960s and 1970s and predicted that the 2020s would see the pattern repeat itself. Having a youth bulge can be seen as one factor among many in explaining social unrest and uprisings in society.