have been directed towards public works of scale (such as from the Hoover Dam), military-industrial contracts, and the financial industry. Aging The U.S. population is aging, which has significant economic implications for GDP growth, productivity, innovation, inequality, and national debt, according to several studies. The average worker in 2019 was aged 42, vs. 38 in 2000. By 2030, about 59% of adults over 16 will be in the labor force, vs. 62% in 2015. One study estimated that aging since 2000 has reduced productivity between 0.25% and 0.7% per year. Since GDP growth is a function of productivity (output per worker) and the number of workers, both trends slow the GDP growth rate. Older workers save more, which pushes interests rates down, offsetting some of the GDP growth reduction but reducing the Federal Reserve's ability to address a recession by lowering interest rates. Means of addressing the aging trend include immigration (which theoretically brings in younger workers) and higher fertility rates, which can be encouraged by incentives to have more children (e.g., tax breaks, subsidies, and more generous paid leave). The Congressional Budget Office estimated in May 2019 that mandatory spending (e.g., Medicare, Medicaid, and Social Security) will continue growing relative to the size of the economy (GDP) as the population ages. The population aged 65 or older is projected to rise by one-third from 2019–2029. Mandatory program spending (outlays) in 2019 were 12.7% of GDP and are projected to average 14.4% GDP from 2025–2029. Entrepreneurship The United States has been a leader in technological innovation since the late 19th century and scientific research since the mid-20th century. In 1876, Alexander Graham Bell was awarded the first U.S. patent for the telephone. Thomas Edison's laboratory developed the phonograph, the first long-lasting light bulb, and the first viable movie camera. Edison's company would also pioneer (direct current based) electric power delivery and market it around the world, followed on by companies such as Westinghouse Electric Corporation which would rapidly develop alternating current power delivery. In the early 20th century, the automobile companies of Ransom E. Olds and Henry Ford popularized the assembly line. The Wright brothers, in 1903, made the first sustained and controlled heavier-than-air powered flight. American society highly emphasizes entrepreneurship and business. Entrepreneurship is the act of being an entrepreneur, which can be defined as "one who undertakes innovations, finance and business acumen in an effort to transform innovations