The past is a foreign country. Only 20 years ago the World Wide Web was an obscure academic thingamajig. All personal computers were fancy stand-alone typewriters and calculators that showed only text (but no newspapers or magazines), played no video or music, offered no products to buy. E-mail (a new coinage) and cell phones were still novelties. Personal music players required cassettes or CDs. Nobody had seen a computer-animated feature film or computer-generated scenes with live actors, and DVDs didn’t exist. The human genome hadn’t been decoded, genetically modified food didn’t exist, and functional M.R.I. was a brand-new experimental research technique. Al-Qaeda and Osama bin Laden had never been mentioned in The New York Times. China’s economy was less than one-eighth of its current size. CNN was the only general-interest cable news channel. Moderate Republicans occupied the White House and ran the Senate’s G.O.P. caucus.

Since 1992, as the technological miracles and wonders have propagated and the political economy has transformed, the world has become radically and profoundly new. (And then there’s the miraculous drop in violent crime in the United States, by half.) Here is what’s odd: during these same 20 years, the appearance of the world (computers, TVs, telephones, and music players aside) has changed hardly at all, less than it did during any 20-year period for at least a century. The past is a foreign country, but the recent past—the 00s, the 90s, even a lot of the 80s—looks almost identical to the present. This is the First Great Paradox of Contemporary Cultural History.

Think about it. Picture it. Rewind any other 20-year chunk of 20th-century time. There’s no chance you would mistake a photograph or movie of Americans or an American city from 1972—giant sideburns, collars, and bell-bottoms, leisure suits and cigarettes, AMC Javelins and Matadors and Gremlins alongside Dodge Demons, Swingers, Plymouth Dusters, and Scamps—with images from 1992. Time-travel back another 20 years, before rock ’n’ roll and the Pill and Vietnam, when both sexes wore hats and cars were big and bulbous with late-moderne fenders and fins—again, unmistakably different, 1952 from 1972. You can keep doing it and see that the characteristic surfaces and sounds of each historical moment are absolutely distinct from those of 20 years earlier or later: the clothes, the hair, the cars, the advertising—all of it. It’s even true of the 19th century: practically no respectable American man wore a beard before the 1850s, for instance, but beards were almost obligatory in the 1870s, and then disappeared again by 1900. The modern sensibility has been defined by brief stylistic shelf lives, our minds trained to register the recent past as old-fashioned.

Madonna to Gaga

Go deeper and you see that just 20 years also made all the difference in serious cultural output. New York’s amazing new buildings of the 1930s (the Chrysler, the Empire State) look nothing like the amazing new buildings of the 1910s (Grand Central, Woolworth) or of the 1950s (the Seagram, U.N. headquarters). Anyone can instantly identify a 50s movie (On the Waterfront, The Bridge on the River Kwai) versus one from 20 years before (Grand Hotel, It Happened One Night) or 20 years after (Klute, A Clockwork Orange), or tell the difference between hit songs from 1992 (Sir Mix-a-Lot) and 1972 (Neil Young) and 1952 (Patti Page) and 1932 (Duke Ellington). When high-end literature was being redefined by James Joyce and Virginia Woolf, F. Scott Fitzgerald and Ernest Hemingway, great novels from just 20 years earlier—Henry James’s The Ambassadors, Edith Wharton’s The House of Mirth—seemed like relics of another age. And 20 years after Hemingway published his war novel For Whom the Bell Tolls a new war novel, Catch-22, made it seem preposterously antique.