China's economy, depending on your bias, will surpass the US by 2020, 2030, 2050 – or never.

Yet China's economy might already be bigger than the US's.

The point isn't to fish for hate mail, but to demonstrate how disorienting the world has become. Remember how two years ago most people said the subprime crisis was containable, Asia was immune to global turmoil, and the Goldman Sachs alumni could do no wrong? Well, think again.

Many took exception to a previous column I wrote which claimed that the US economy is worth $14trn and China's just $3.3trn. Most argued the US figure – from the World Bank – was overstated. Others wondered if the Chinese figure was too high. Some argued it was too low.

All this makes you consider our goalposts. The methods used to calculate gross domestic product may not be valid as the global economy swoons.

Take China. At its most basic level, GDP is the total market value of final goods and services a nation produces in a given year. Andy Xie, a Shanghai-based independent economist, puts China's GDP at $4.1trn to $4.3trn. Xie isn't alone. Some put the figure at $4.4trn. If correct, China has just about caught up with Japan, the second-biggest economy.

Or is China really a shell of its claimed size? You have to wonder about a place that every couple of years finds an economy the size of Austria it wasn't aware of, as it did in late 2005. In January, China suddenly said its economy overtook Germany's to become the third-largest in 2007.

Not surprisingly, many readers will doubt the brawn of China's economy. The skepticism is over how any country can announce such huge revisions and be believed. Some also point to a lack of transparency and the quality of Chinese goods. Looking at the US, there is cause to doubt the size of the world's biggest economy. The reason? Wall Street.

Economies that are highly reliant on financial flows "are less transparent", says Glenn Maguire, chief Asia economist at Société Générale SA in Hong Kong. "That means any economy that has depended on financial services for growth. Financial-sector profits were responsible for most of the growth in US profits in this cycle."

When you have a mispricing of asset values on a national or international scale, it's hard to know what's real and what isn't – what genuinely is floating around in the financial ether, and what is not. And when do we stop referring to economies such as the US as "industrialised"? One is hard pressed to name many products that are actually made in America.

That leaves services, the value of which is devilishly hard to measure. Chinese officials who think they can trade in $682bn of US government debt for tangible goods that will be loaded onto ships and delivered to Shanghai are dreaming.

So, the size of the US economy could be a figment of statisticians' imagination. So could China's. It's no longer clear what to believe. Making sense of the world is getting harder by the day.

William Pesek is a Bloomberg News columnist. Frank Lee is off this week