In Back to the Future, Marty McFly travels to the year 1955 to make sure his parents actually get together. (In the sequel he Marty goes 20 years into the future, which takes him to 2015.) My guess is that economist, if they had a Delorean with a flux capacitor, would travel back to 1973. Why? To put it in the word of Doctor Emmett Brown, it seems 1973 is a key temporal junction on the economic axis of the space-time continuum.
Greg Mankiw points to the most recent Economic Report of the President, which uses the year 1973 as a historical counterfactual. The report draws up an alternative history based on the previous trend of productivity, respectively, income growth, and the assumption of a static income distribution. In short, the insight of this thought experiment is: things went downhill after 1973. (I am still optimistic about hoverboards though.)
Of course, a lot of things happened in 1973. In terms of economic analysis three events play a key role in breaking with previous patterns. First, the energy crisis, primarily the increase in the oil price due to the Yom Kippur War and the OPEC embargo. Second, the US economy enters its first major post-war recession in November 1973. Third, stagflation undermines the Keynesian model of the Philips curve (there is no longer a stable trade-off between inflation and unemployment).