Indeed, the standard mental picture of what the physical world is corresponds to a third intermediate viewpoint that could be termed the consensus view. From your subjectively perceived frog perspective, the world turns upside down when you stand on your head and disappears when you close your eyes, yet you subconsciously interpret your sensory inputs as though there is an external reality that is independent of your orientation, your location and your state of mind. It is striking that although this third view involves both censorship (like rejecting dreams), interpolation (as between eye-blinks) and extrapolation (say attributing existence to unseen cities) of your inside view, independent observers nonetheless appear to share this consensus view. Although the inside view looks black-and-white to a cat, iridescent to a bird seeing four primary colors, and still more different to a bee seeing polarized light, a bat using sonar, a blind person with keener touch and hearing, or the latest overpriced robotic vacuum cleaner, all agree on whether the door is open. The key current challenge in physics is deriving this semiclassical consensus view from the fundamental equations specifying the bird perspective. In my opinion, this means that although understanding the detailed nature of human consciousness is an important challenge in its own right, it is not necessary for a fundamental theory of physics.

This is one of the footnotes in the paper and captures something I find pretty significant - "understanding the detailed nature of human consciousness... is not necessary for a fundamental theory of physics." This statement is key and runs counter to so many world views.

Decoherence is an important factor in all of this "alternate universe" mumbo-jumbo. Decoherence is how you rig God's dice, so to speak. It is the interactions of the "environment" or "ensemble" on a probabilistic system that helps determine it's macroscopic state. For instance, if you direct a single quantum particle at a double-slit filter, it will produce a classical interference pattern. It has, seemingly, been able to pass through both slits simultaneously. If, however, you set up a device to detect the particle, it is now forced to "pick" a slit and no longer produces a visible interference pattern. It has, in essence, decohered due to the large numbers of interactions (entanglements) that occur between it and the measurement device.

One of the more interesting things about this is that decoherence has been observed on a "macroscopic". Researchers have recorded decoherence effects with "Buckyballs"/Buckminsterfullerene (C60) which is about 1nm in diameter. Suddenly we start seeing links between the quantum scale and the macroscopic where there was an obvious break before.

A couple other articles on decoherence:

After 8 years, the decision on how to try the alleged mastermind of the 9/11 attacks is creating a national debate. The Justice Department announced Friday five of the detainees at Guantanamo Bay will be transferred to New York to be tried in civilian court.