China is far from replacing the US as the world's lone superpower either economically or militarily.
The United States is by far the world's largest debtor nation,
with half our debt obligations being owed to foreign creditors.
As a U.S. taxpayer, this means that an increasing portion of your taxes will go to supporting foreign governments (as interest payments) BEFORE even one penny is spent to support our own.
In speculative market prices yes. So was the Tokyo years ago more valuable that US East Coast.
In real physical terms measured by PPP, China economy is about half of America and growing fast. Also having larger population accustomed to lower standard of living might make you stronger (as it did with Soviet Russia versus Germany).
"Its GDP per capita is $900 compared to the US $35,200."
China
http://www.odci.gov/cia/publications/factbook/geos/ch.html
Population: 1,298,847,624 (July 2004 est.)
GDP: $6.449 trillion (2003 est.)
GDP per capita: $4965
United States
http://www.odci.gov/cia/publications/factbook/geos/us.html
Population: 293,027,571 (July 2004 est.)
GDP: $10.99 trillion (2003 est.)
GDP per capita: $37505