In the June issue of Scientific American, theoretical physicist Yasunori Nomura discusses an idea he's had to resolve one of the big problems with the Cosmological Inflation theory. I hope that I understand him well enough to adequately summarize his argument.
The starting point is that a fraction of a second after the Big Bang singularity, the nascent universe experiences a moment of incredibly fast expansion that flattens out space-time, accounting for the near-perfect flatness of space seen today. The problem is that the phase change from the inflation phase to normal expansion can't be perfect: Parts of space keep inflating, almost instantly becoming bigger than the "normal" universe. Bits of space-time keep bubbling out of the perpetual inflation, creating new universes in a "multiverse."
Unfortunately, it follows that in such an endlessly multiplying Multiverse, anything imaginable -- no matter how improbable it may seem -- not only happens, it happens an infinite number of times. This makes the whole notions of probability and prediction meaningless.
Nomura, however, tries to link inflation with another theory that seems to predict everything: the Many Worlds interpretation of quantum mechanics. In this interpretation, every possible outcome of a quantum mechanical event actually happens, in an endlessly splitting "tree" of diverging universes. The math works; it's just hard to imagine the universe actually functioning this way.
Nomura also draws on a similarity he sees between the event horizon of a black hole and the "event horizon" of the observable universe. Just as no matter or energy can pass from the interior of a black hole to the outside (but information possibly can), nothing beyond a particular distance can ever affect us because it's receding faster than the speed of light.
Nomura thinks the bubbling multiple universes of inflation theory do not exist in a super-energetic but otherwise ordinary, larger space-time. Rather, he thinks they exist in the probability "space" of Many Worlds quantum mechanics. Even if every possible outcome in some sense occurs, they still have different mathematical probabilities. (How, I don't know. I just take mathematicians' word for it.)
Now, I tend to roll my eyes when another theoretical physicist says his Great Idea will Revolutionize Everything if the math pans out. Nomura, however, says his theory has produced a testable prediction: The universe should include observable areas of negatively curved space. (He doesn't spell out how one detects negatively curved space, but I presume the effect would resemble that of a negative gravitational field. Perhaps "gravitational" lensing, but the lens is concave instead of convex?) If the "conventional" inflation theory is correct and all the multiple universes exist in a wider space, any instances of negative special curvature can still exist, but the curvature should be much less -- so much less that Nomura doubts they could be detected at all.
So, that's one more thing for the deep-space astronomers to look for. Kudos to Nomura for producing a theory that can be tested.
Also, unrelated: I just heard that LIGO detected another pulse of gravitational waves.