Thd USA is not the biggest economy in the world GDP (PPP) FYI it was passed out by China in 2014-15.
And FYI the USA was the biggest economy in the world GDP (PPP) approx from 1890 to 2014. This is when the USA panicked because it realised that it could not keep up the pace with a rate of economic growth one third that of China.
It is forecasted that China will pass out the USA in GDP (USD) by 2026.
And here is the evidence:
GDP(PPP) is a truer measure of a country'd economic global position because it accounts for each country's purchasing power.
For example if a US built Tesla sells for say $50K USD in the USA and an identical one built in China sells in China for say $30K USD equivalent. then the only varient is the purchasing power of the respective countries' currencies.
This is why the US GDP in USD is about $22.5 Trillion & China's is about $15.5 Trillion but in PPP the USA is still $22.5 Trillion while China is about $25 trillion GDP