He suggests that there really are only two options: The existence of zillions of universes, so many that we cannot comprehend the number (To get an idea of the size of the number there are only 10^80 atoms in the whole of our universe), or there is only one universe and it was intentionally designed by a cosmic intelligence.
Some time ago New Scientist ran an interview with Susskind by Amanda Gefter. Here's an excerpt:
Gefter:So even if you accept the multiverse and the idea that certain local physical laws are anthropically determined, you still need a unique mega-theory to describe the whole multiverse? Surely it just pushes the question [of the source of fine-tuning] back?Nuclear physicist David Heddle responds:
Susskind: Yes, absolutely. The bottom line is that we need to describe the whole thing, the whole universe, or multiverse. It's a scientific question: is the universe on the largest scales big and diverse or is it homogeneous [i.e. Is it many universes or just one]? We can hope to get an answer from string theory and we can hope to get some information from cosmology.
There is a philosophical objection called Popperism that people raise against the landscape [multiverse] idea. Popperism [named for philosopher Karl Popper] is the assertion that a scientific hypothesis has to be falsifiable, otherwise it's just metaphysics.
Other worlds, alternative universes, things we can't see because they are beyond horizons, are in principle unfalsifiable and therefore metaphysical - that's the objection. But the belief that the universe beyond our causal horizon is homogeneous is just as speculative....
Gefter: If we do not accept the landscape idea are we stuck with intelligent design [ID]?
Susskind: I doubt that physicists will see it that way. If, for some unforeseen reason, the landscape turns out to be inconsistent - maybe for mathematical reasons, or because it disagrees with observation - I am pretty sure that physicists will go on searching for natural explanations of the world.
But I have to say that if that happens, as things stand now, we will be in a very awkward position. Without any explanation of nature's fine-tunings we will be hard pressed to answer the ID critics. One might argue that the hope that a mathematically unique solution will emerge is as faith-based as ID.
Susskind's answer shows that his book should be subtitled String Theory and the Possible Illusion of Intelligent Design. He has done nothing whatsoever to disprove fine-tuning. Nothing. He has only countered it with a religious speculation in scientific language, a God of the Landscape.I think Heddle is correct. A fundamental theory that predicted all the physical constants would be a "win" for ID. It would nullify the only real threat to cosmological intelligent design, the hypothesis that there are an infinitude of universes all with different laws of physics.
Snatching victory from the jaws of defeat, he tells us that we should embrace the String Theory landscape, not in spite of its ugliness, but rather because of it. Physics should change its paradigm and sing praises to inelegance.
Out with Occam's razor, in with Rube Goldberg. Out with reductionism, in with lots of free parameters. Why? Because if we don't (according to Susskind) there really is no way to explain the fine-tuning, except by Intelligent Design.
The subtext (at times explicit) in Susskind's book is that fine-tuning is real, in the sense that our universe really does exist on a knife's edge, so much so that it demands attention. The only possible way that it is an illusion is if our universe is but one of an unimaginable number of universes.
To save materialism from the spectre of theism, Susskind argues that we must explain this fine-tuning, and his landscape [i.e. that there are zillions of universes] has the best chance of playing the role of a white knight.
Susskind's argument demonstrates the desperation of materialists who wish to escape the conclusion that there is an intelligence behind the cosmos. He's willing to jettison the traditional scientific criteria of testability, falsifiability and Occam's razor and blindly accept on faith, without any empirical evidence, that there exists a nearly infinite number of other worlds.
With so much cosmological variety, he believes, one of those other worlds just has to possess the extraordinary complex of features required to support life, and our universe happens to be that world. Thus, our universe is not so extraordinary after all.
Susskind's interview makes it plain that the battle over intelligent design is not one between science and religion but rather between two different philosophical views of the world: Naturalism and Supernaturalism.
Susskind says that our universe certainly appears to be intricately well-ordered and intelligently planned for living things, but that the appearance of purpose and design are, in fact, simply illusions.
The intelligent design theorist counters that the only evidence to which we have access, or even could have access, tells us that this universe is the only one there is, and that the supposition that our world is the only world is in any event the most parsimonious hypothesis.
Thus, we think we see purpose and intentional engineering in the fabric of the cosmos because these things are really there, and the only reason one would have for failing to accept that conclusion is an a priori metaphysical commitment to atheism. Unfortunately, a priori commitments are not conducive to a scientific approach to the search for truth.
Should anyone question why all parties seem to agree that the universe at the very least appears to be deliberately fine-tuned, I commend either or both of the following: Modern Physics and Ancient Faith by physicist Stephen Barr and Nature's Destiny by biologist Michael Denton.