There’s a truism in investing that the last one into a market is the first one out. And that certainly seems to be the case today, with Japan’s Nikkei index crashing off the back of two things: First, hints from the Federal Reserve that the U.S. economy is improving enough to justify a slow pull-back from the central bank’s market-goosing asset buying program known as “quantitative easing;” and second, that the Chinese economy is slowing down even more than we thought.

For some time now, I’ve been writing that the global equity markets have been inflated by central banks — and that this was a bubble that would eventually pop once people realized that monetary policy, rather than the real economy, was behind the boom.

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Well, folks, that time may be here. Behavioral economist Peter Atwater, whose firm Financial Insyghts focuses on the market implications of consumer sentiment, certainly thinks so. “I would offer that Abenomics” — i.e. Japanese prime minister Shinzo Abe’s plan to goose his nation’s economy with a combination of monetary policy and fiscal and structural reforms — “was the ‘subprime’ of policy-making,” says Atwater. It’s a useful analogy: Subprime loans were the top of a real estate bubble that had been building for years in the U.S., and Japan’s version of quantitative easing is coming at the end of three years of money dumps by the U.S. Federal Reserve, each of which has had a smaller effect on the markets than those that came before. Sounds like a bubble to me.

So, where do we go from here? Atwater and other folks like the smart guys at Capital Economics in London believe that the Nikkei will continue to be vulnerable and that Japan’s attempts to lower the value of it’s currency in order to boost exports and real economic activity may be at an end. In fact, you might even see the yen start to rise, especially if there’s another crisis in the euro-zone, which is looking very possible and even likely.

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The U.S. will continue to be the prettiest house on the ugly block that is the global economy. U.S. markets have fallen, but they are probably the least vulnerable of the major global markets right now. Private sector GDP growth in the U.S. is actually over 3%; it’s the government, as per usual, that’s slowing things down.

But the second half of the year may not be as bright as the first, at least in terms of stock markets. I spoke earlier today with Mohamed El-Erian, the head of the world’s largest bond trader, PIMCO, a prescient investor who has been tip-toing away from risk for a while now. I asked him whether this was truly the bursting of the central bank bubble. His thoughful answer was “We don’t know yet.” But he also pointed out that in a recent Financial Times column he had defined a “brand” as something that divorces prices from fundamentals – that’s why, for example, Apple and Facebook share prices overshot their fundamentals by so much. For years now, we’ve come to trust the brand known as “central banking” to deliver us from the real economy. But how much longer can central bankers deliver tomorrow’s growth today? That’s the big unanswered question that will be moving markets in the days and weeks to come.