...These multiverse theories all share the same fundamental defect: They can be neither confirmed nor falsified. Hence, they don't deserve to be called scientific, according to the well-known criterion proposed by the philosopher Karl Popper. Some defenders of multiverses and strings mock skeptics who raise the issue of falsification as "Popperazis"—which is cute but not a counterargument. Multiverse theories aren't theories—they're science fictions, theologies, works of the imagination unconstrained by evidence.
At their best, science fiction and theology can leave us awestruck before the unutterable strangeness and vastness of the cosmos. Multiverse theories used to arouse these emotions in me. When the Russian physicist Andrei Linde—one of the inventors of the inflation theory of cosmic creation—first explained his chaotic, self-reproducing, fractal, inflationary multiverse theory to me 20 years ago, my reaction was, "Wow! That's so cool!"
Multiverse theories don't turn me on anymore. Perhaps it's because of 9/11 and all its bloody consequences, especially the U.S. wars in Afghanistan and Iraq. Also, I have two teenage kids, and I'm worried about the enormous problems they're inheriting from my generation. Not only wars overseas but also global warming, species extinction, pollution, poverty, pandemics and so on.
Now, multiverse theories strike me as not only unscientific but also immoral, for two basic reasons: First, at a time when we desperately need science to help us solve our problems, it's irresponsible for scientists as prominent as Greene to show such a blithe disregard for basic standards of evidence. Second, like religious visions of paradise, multiverses represent an escapist distraction from our world.
I find two multiverse concepts especially loathsome...