Economists: The countdown to the US financial crisis has begun.

Kent Smetters, head of the budget modeling project at the University of Pennsylvania's Wharton School, believes that the "doomsday" will arrive in the United States between 2045 and 2050, which is a critical point for the U.S. economy. By that time, the interest costs on the federal government's national debt will become so huge that even massive tax increases will not help. Smetters states that at that point, the U.S. government will be forced into either explicit or implicit default, both of which will have catastrophic consequences. Explicit default would make the U.S. a global deadbeat. Implicit default could theoretically be achieved through debt monetization or by cutting social security and medicare expenditures. Smetters said, "This is when panic begins to spread, and it is a time when trust in the government is lost. This is also the reason for the destruction of other societies. Looking back at Rome, France, Spain, Britain, and Germany, almost every empire has collapsed due to debt."