If you like that article, you may enjoy his latest book, which I listened to on audio.
http://www.amazon.com/The-Hidden-Realit ... 826&sr=1-1
Most of it is over my head, so a lot of techno-jargon had to wash over, but still enjoyable. In the book, Greene summarizes about 9 different multiverse theories. One involved imagining a cubic mile of swiss cheese where our universe was only one of the bubbles. In a truly infinite space, this means somewhere/elsewhere an identical twin to myself is typing this reply to your topic at this moment.
I was particularly interested in questions as to whether some (not all) of these "theories" are even part of science as mentioned in this quote from the article.
Years ago, Carl Sagan emphasized that extraordinary claims require extraordinary evidence. So, can we gather evidence supporting a proposal that invokes other universes?
Because the other universes would lie beyond what we can observe, it might seem that the answer is no, placing the multiverse outside the bounds of science. But that’s too quick.
Greene doesn't mention it, but a multiverse computer might provide evidence - a system that accesses computers in other universes to solve problems in less than a second that would take a decade on our systems alone? I bet the NSA already owns one.
Some of the numbers Greene bandies about are insane.
Today, the tally of possible universes stands at the almost incomprehensible 10^500, a number so large it defies analogy.
For comparison, the number known as Google 10^100 exceeds the number of sub-atomic particles in the known universe.
After reading that book about all I can really say is: