I am skeptical of the multiverse idea. Of course I am a complete amateur, but other scientists are too. As Brian Greene says,



He does defend the possibility, and even though falsifiability will be difficult, he goes on,



http://www.thedailybeast.com/newsweek/2 ... verse.html

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.

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.

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:

I read Hawking's book The Grand Design which defends the multiverse. I quoted some critical reviews of the book before, essentially saying it's a bunch of unfalsifiable speculation.

I'm going to be a holdout like Einstein was about some of the implications of quantum theory, until someone gives me a good reason otherwise.

My recollection from Greene's book is some of the multiverse theories are unfalsifiable, but others could indeed be proved by certain observations or experiments.

You mention "unfalsifiable speculation", which leads me to a related topic, the use of the word "theory" in science. Remember a frequent critique of Evolution is "it's only a theory", therefore completely unproven. But this is rejected by scientists saying those critics do not understand the technical use of the word "theory" in science, that it really means a huge amount of data and experimentation supports any given scientific theory.

However it seems when we move to "theoretical physics", this definition of the word breaks down. We have String "theory" even though no one knows if a string exists. Or several multiverse "theories" which are completely outside of any detection system that can be imagined and therefore questionable as to whether they are even science.

So doesn't this tend to weaken the defense of Evolution as a "theory"? Shouldn't these areas of physics be considered "hypothetical physics"? Even that may not be enough, since a hypothesis implies some method of experimentation or proof. Perhaps the term "speculative physics" would preserve the scientific definition of "theory" instead of negating it?

I haven't read this book, but see this description:



I think if anyone is trying to argue that evolution is "only a theory" they are indicating that they don't know much about it, and are just trying to score a rhetorical point. There's not much you can do there.