Without getting into the arithmetic of exactly when the Chinese economy will become bigger than the American economy, I'd suggest that the raw measure of size is probably a bad substitute for the question we're actually interested in, which is economic, and thus geopolitical, power. If the Chinese economy were, today, the same size as the American economy, that would equal out to a GDP of about $10,000 per person. That's enough to make them a large market, but it doesn't make them the same market as the US. It means, for instance, that their consumption will still be focused on less advanced goods, and that internal investment will still require a huge percentage of GDP. America will still be a more advanced economy, even if it's not technically a larger one.
