This is something of a new direction. For a long time I have been a fan of Peter Woit's blog Not even wrong, which comments on theoretical physics and string theory in particular. Recently, he posted some comments on an article in Die Zeit, (a VERY erudite German news magazine publication with a distinguished history) about the current state of theoretical physics.
Since no English translation is available, some people posted machine translations. They were good proof of the old joke that if you take the English idiom "Out of sight, out of mind" into French and back, what you get is "blind idiot".
Anyhow, I have made a better translation (and I do welcome corrections and suggestions to improve it and if Zeit asks me to remove it I will) and am posting it here. The article was by Max Rauner, a science journalist, whose other work can be googled.
According to Susskind we live "in an infinitely small bag in an enormous Megaverse". Our world would therefore be only a nice anthropic niche, nearby which there are innumerable other universes. Some of them are empty and boring, others exist for a few milliseconds, a handful have brought forth stars, planets and even life. The concept of multi or megverses has been around for a while. What is new is that, meanwhile, not only a few philosophically inspired cranks believe in it, but to a certain extent the guiding elite of theoretical physics. For Leonard Susskind, and others who agree with him, it is certain: “If philosophers and physicists look back in one hundred years, they will describe today as that time, in which the concept of a single universe was replaced in favor of the concept of a Multiverse.”
But if Kopernikus’ theory was a transgression, the Multiverse is a deep depression. This puts mankind on a completely insignificant, accidental island in the cosmic ocean. The only comfort that remains for us is that nevertheless there are organisms on this island, who are intelligent enough to argue about it.
Scientifically seen, the major problem for this conception is whether it can be proved: How are we to know whether the Multiverse theory is actually correct? Even if there really were many other universes, we could never observe them. Is this science? Or does physics thereby become an esoteric system, in which much is only postulated, but nothing proven or can be refuted? The philosopher Karl Popper maintained that scientific theories should be so constituted that they can be disproved in principle, and are therefore falsifiable. If one gives up this guiding principle, a basic tenant of natural science is staggered.
Therefore, criticism of Susskind’s thesis has been severe. "I consider the assumptions to be dangerous", say Paul Steinhardt of Princeton University. "Science would come to a depressing end." The string theoretician Brian Greene feared, the idea could prevent scientist from seeking for deeper explanations. And the cosmologist Lee Smolin of the Perimeter of Institute in Waterloo, Canada, grumbles: "Lenny Susskind has gone astray, and he will see that he has done so. "It is good when one presents ideas, however if one has a theory, that neither explains anything nor predicts anything, then one is not doing science."
But the Multiverse theory has advocates who are just as prominent. "Our whole universe is a fruitful oasis within the surrounding Multiverse", says the astrophysicist Sir Martin Rees, president of the venerable British Royal Society. Andrei Linde of Stanford University, who sometimes charms his colleagues with magic tricks, has already simulated the Multiverse on a computer and placed pictures of it on his Website ("Kandinsky Universe"). Even the Nobel Prize winner Steven Weinberg, a solid, highly estimated theoretician, is open to the idea. "I am not convinced yet of the Multiverse, but I take the possibility seriously."
The controversy was overdue. With all its successes physics today has no answer to the fundamental question: Why is the world so constituted as we have found it? Or, in the words of Einstein: "Could God have created the world differently?" In the meantime we know that laws of nature and natural constants are so finely adjusted that the smallest deviations would have had fatal consequences, in any case for the existence of humans. But physics has never even gotten close to an explanation of this astonishing fact.
Until today two great theories stand next to each other like marriage partners who sleep in separate beds: Einstein’s theory of relativity and quantum theory. With the one can understand space, time and cosmological structures, with the other, the behavior of atoms and elementary particles. Both are extremely efficient in their range, but they cannot be reconciled. In the Big Bang they also fail, because the conditions are too extreme. Moreover, the theories cannot explain why the velocity of light is approximately 300000 kilometers per second and a hydrogen atom weighs 1.67 x 10-27 kilograms. Physicists must insert dozens of such natural constants by hand into their equations.
"As a young physicists I hoped to find beauty and elegance in the laws of nature", remembers Leonard Susskind. Just as his father, a plumber, somehow aesthetically ran pipes at right-angles or parallel, so he then imagined physics. "Instead I found a depressing disorder." That was end of the sixties. In the seventies the situation improved, in the eighties the physicists became euphoric. A new theory gave hope. It described elementary particles no longer as point-like particles, but as vibrating strings or threads. These strings are, to be sure, too small ever to be directly observed (approximately 10-33 centimeters), but with this trick, mathematical infinities in the equations could be avoided. Even the gravitation force from relativity theory found its place in this abstract model. So far however, string theory is so complicated that many characteristics of the Multiverse remain in the dark. For example it postulates eleven dimensions, of which some are microscopically "rolled up", so that we observe only three special dimensions.
Michio Kaku compares string theory in his new book In the Parallel Universe with a small, beautiful pebble, which the physicists find in a trek through the desert: "As we swept the sand aside, we see that it really was the point of an enormous pyramid, which lay buried under tons of sand. After decades we discover mysterious hieroglyphics, hidden chambers and tunnels. One day we will penetrate the lowest level and finally push open the gate."
What Kaku so optimistically describes is the dream of the Grand Unified Theory. But that has now collapsed - says Susskind, who meantime has picked up a white beard and a bald spot: "Beauty became the beast." According to Susskind’s computations, string theory at present has 10500 solutions, which is for all practical purposes, infinite. Until Susskind’s book The Cosmic Landscape is published in German, some additional orders of magnitude could be added to the number of universes. Instead of talking about a pyramid, the Stanford professor now sketches the picture of an endless, imaginary landscape as a model of our cosmos. In this landscape there are mountains, valleys and highlands. And in each valley is another universe. Some look like ours, most exist only briefly before, again, in the same valley another new universe is born. Only unfortunately, one cannot move from one valley into another one. Whether other universes actually exist can never be determined.
Such unobservable theories produce cold sweat on the forehead of the physicist Lee Smolin. If physics gives the principle up of observability, then Smolin warns, it comes close to being a religious theory, such as, for instance, the creationist teachings of Intelligent Design. "The danger stands directly outside our door", says Smolin. For the Catholic Church the Multiverse theory is not particularly compatible with religion. In his much commented on attack on Evolution in the past year the Viennese Cardinal Christoph Schönborn also explicitly scourged the Multiverse hypothesis. For him, it contradicts the overwhelming evidence for nature’s purpose and design.
If there are enough universes, some of them must be habitable.
Such attacks leave hard bitten physicists such as Steven Weinberg cold. "It is nice that cosmology gets a bit of the attention which Evolution is enjoying these days" Weinberg said, sarcastically commenting on Schönborn’s statements. The speculative nature of the Mutiverse theories have a special attraction for atheistically oriented scientists such as Weinberg. They have been beating their heads against the wall in vain till now on the question of why the cosmos has been created with stars, planets and occasionally, also intelligent life. The almost unbelievable fine tuning of natural constants in favor of a habitable universe dissolves in the Mutiverse theory to everyone’s satisfaction. According to it, the existence of a philanthropic universe is a pure consequence of statistics: Among 10500 universes there simply must be one like ours, just as someone gets six lucky numbers in Lotto (Powerball) if enough people play. Martin Rees compares the Multiverse with a large clothing store. "If the selection of clothes is large enough, it is not surprising that we find something that fits" - namely, our own universe.
Could God have created the world differently? Yes, answer the Multi-World theoreticians and pile on: He used all the available space. It is only regrettable, that this concept leads to an inflationary arbitrariness in the description of reality.
How can physics progress? Whoever will not admit to being satisfied that either our universe is pure coincidence or the loving God has arranged all as we find it, has the choice between three possibilities.
The principle hope: String theory is not near finished, perhaps the physicists overlooked something. "It is much too early, to give up", says Princeton professor Paul Steinhardt, who has put forward his own theory of an eternally returning, cyclic universe. Who knows, perhaps still everything will come to good at the end, and one day an extended string theory will describe exactly one universe, i.e. ours.
The escape forward. Assume that the Multiverse actually exists. Then, to be sure the other universes exist outside of our own, and even the best telescope could never see it. But, perhaps one day other predictions can be derived from the theory, which one could empirically test at least in our universe. At the European research lab CERN in Geneva in 2007 the Large Hadron Collider (LHC) is to go into operation. Perhaps this gigantic particle accelerator could find a hint of the hidden spatial dimensions, which the theory predicts.
Finally the possibility of a mistake remains. For example, Peter Woit believes "String theory is simply wrong". Woit, a mathematician at Columbia University in New York, runs the anti-string blog Not Even Wrong and sets forth the challenge that: "A correct theory should have a limited number of solutions." As alternative candidates for such a theory some researchers are discussing loop quantum gravity, which is being developed among other places at the Albert-Einstein-Institute in Potsdam. According to it, space-time is developed from tiny pellets. It gets along without the many dimensions and universes of string theory. The problem is clear: So far this theory also delivers no empirically examinable predictions.
German physicists are playing almost no role in the increasingly heated debate over the Multiverse. Perhaps they are missing the socialization of the Bronx, where Leonard Susskind and Steven Weinberg attended the same High School. But in this country (Germany) philosophical analysis is treasured. Reiner Hedrich of the University of Gießen got a grant from the German Research Council, to analyze the arguments of the physics debate. Anyone who visits the philosopher hears classical music in the background. "The theory of the Multiverse is reasonable in its logic", says Hedrich, "however not reasonably enough to be science." The research program reminds him of the Greek philosophers before Socrates: it is "Metaphysical thinking about nature”
In any case, Smolin has his own theory of universes. Universes could come into being in black holes as baby universes and afterwards, be destroyed in a kind of Darwinian selection process. Smolin assures that the theory is refutable by the observation of neutron stars. But other researchers doubt that.
Newton said, Hypothesis non fingo, I fabricate no hypotheses **. His modern colleagues hold back a bit less. It almost seems as if the dreaming up of new universes has become a pastime. A kind of finger exercise, until the LHC finally goes into operation. However, it would be too simple, to so regard the bizarre worlds of the cosmologists and string theoreticians. "As long as no one has a better idea, one has to continue trying", says the Giessener philosopher Reiner Hedrich, “even if the assumptions appear paradoxical: "Keep trying, knowing that it does not describe reality."
Until the cosmologists regain firm ground under their feet, one will have to make do with another measure for the reliability of a theory: Royal Society president Martin Rees would bet his dog on the Multiverse thesis, Andrei Linde of Stanford University would bet even his life. And in November, in a publication with the title “Life in the Multiverse” Steven Weinberg announced that he already has enough confidence in the theory “to bet both Andrei Linde’s life and Martin Rees' dog on it".
** translation for fingo as fabricate suggested by Who said...see comments.