PIMCO’s Mohamed El-Erian says what’s happening in Japan is key to what will happen with the bond market in the U.S. El-Erian tells CNBC that the latest stage of the stock market rally seems to have been driven by Japan’s big stimulus efforts, and by the notion in general that central banks around the globe are “all in” in terms of bolstering markets. El-Erian says he thinks that over the next few months we’ll find that Japan central bank policies are becoming “increasingly ineffective”, however. He says markets have priced in the idea that central bank growth will give way to genuine growth — which means the big issue is whether or not that transition actually occurs before the effectiveness of central bank policies runs out. If the transition doesn’t go smoothly in Japan and other areas, El-Erian says we could be in for a “hell of a lot more volatility”.