TOKYO  For years, Japan has been readying itself for the day that it is eclipsed economically by China. But as a result of the global slowdown, Japan’s difficulty in managing its economy and China’s rise  on vivid display Thursday as Beijing celebrated the 60th anniversary of the founding of the People’s Republic  that day may come sooner than anyone predicted.

Though recent wild currency swings could delay the reckoning, many economists expect Japan to cede its rank as the world’s second-largest economy sometime next year, as much as five years earlier than previously forecast.

At stake are more than regional bragging rights: the reversal of fortune will bring an end to a global economic order that has prevailed for 40 years, with ramifications across arenas from trade and diplomacy to, potentially, military power.

China’s rise could accelerate Japan’s economic decline as it captures Japanese export markets, and as Japan’s crushing national debt increases and its aging population grows less and less productive  producing a downward spiral.