There is a long-standing problem in physics concerning the flow of time. All known physical laws -- except one: the second law of thermodynamics -- are "temporally symmetric" that is, they operate equally well whether time is flowing forwards or backwards. Take a movie of any physical phenomenon and run it backwards and everything you see will be consistent with physics. But the Second Law is not really a fundamental law, it is just the statement of the empirical observation that time seems to flow in one direction and not the other, so the deeper question of why this should be so has remained a mystery.
Actually, it's not mysterious at all once you get past the quantum-physics mystery conspiracy, which insists on presenting QM in false and misleading terms. In particular, the QMMC focuses on measurement and entanglement as if they were two distinct physical phenomena, one simple and familiar, the other alien and inscrutable. In fact, measurement and entanglement are one and the same physical process. Once you realize this, the answer to the arrow-of-time "dilemma" becomes obvious: time appears to flow in one direction because the perception of the flow of time relies on the formation of records of "past" events, which is to say, the formation of classical information, which requires "measurements", which requires particles to become entangled with each other. It is possible to reverse this process, but only by bringing all the particles in an entangled ensemble physically together, which is possible in principle but not in practice. (See section 5.4 in the link above for more details.)
This result has recently been (re)discovered by a card-carrying physicist.
It's really starting to annoy me how many physicists get press by making these kinds of "breakthroughs". All this stuff was figured out in the mid-90's. You'd think that now nearly fifteen years on the word would have gotten out, but it hasn't. It's really kind of weird. I seriously doubt that there's a conscious QM Mystery Conspiracy, and yet here we are. Why people should still be scratching their heads about the arrow of time and "spooky action at a distance" in 2009 is the biggest mystery of all.