Each of the periods of combinatorial innovation referred to in the previous section was accompanied by financial speculation. New technologies that capture the public imagination inevitably lead to an investment boom: Sewing machines, the telegraph, the railroad, the automobile ... the list could be extended indefinitely.
Perhaps the period that bears the most resemblance to the Internet boom is the so-called ``Euphoria of 1923,'' when it was just becoming apparent that broadcast radio could be the next big thing.
The challenge with broadcast radio, as with the Internet, was how to make money from it. Wireless World, a hobbyist magazine, even sponsored a contest to determine the best business model for radio. The winner was ``a tax on vacuum tubes'' with radio commercials being one of the more unpopular choices.4
Broadcast radio, of course, set off its own stock market bubble. When the public gets excited about a new technology, a lot of ``dumb money'' comes into the stock market. Bubbles are a common outcome. It may be true that it's hard to start a bubble with rational investors-but not it's not that hard with real people.
Though billions of dollars were lost during the Internet bubble, a substantial fraction of the investment made during this period still has social value. Much has been made of the miles laid of ``dark fiber.'' But it's just as cheap to lay 128 strands of fiber as a single strand, and the marginal cost of the ``excess'' investment was likely rather low.
The biggest capital investment during the bubble years was probably in human capital. The rush for financial success led to a whole generation of young adults immersing themselves in technology. Just as it was important for teenagers to know about radio during the 1920s and automobiles in the 1950s, it was important to know about computers during the 1990s. ``Being digital'' (whatever that meant) was clearly cool in the 1990s, just as ``being mechanical'' was cool in the 1940s and 1950s.
This knowledge of, and facility with, computers will have large payoffs in the future. It may well be that part of the surge in productivity observed in the late 1990s came from the human capital invested in facility with spreadsheets and web pages, rather than the physical capital represented by PCs and routers. Since the hardware, the software, and the wetware-the human capital-are inexorably linked, it is almost impossible to subject this hypothesis to an econometric test.