Cosmologists Dragged Kicking and Screaming to the Anthropic Principle

Those who view science as a dispassionate, logical pursuit of the truth should savor the emotions in two articles by Tom Siegfried about cosmology in Science this week.^1,2  He reported on the passionate rivalry between theoretical physicists who embrace superstring theory as the eventual “theory of everything” and those who oppose it because of its metaphysical implications.
    The critics dislike it because it smacks of the anthropic principle (roughly, that the universe appears tailored for life) and does not allow testable predictions – because most of its adherents postulate an infinite number of possible universes, out of which we inhabit one of the very few that permits life.  That smacks of metaphysics, they argue.  Proponents counter that we must follow the evidence where it leads.  The discovery of a nonzero (but very small) vacuum energy, they point out, allows for life but appears random – i.e., underivable from theory.  Since superstring theory allows for an infinite number of states (i.e., a multiplicity of universes, or multiverse), we can explain our existence by the natural selection of a universe with the vacuum energy and other physical properties (“landscape”) that permitted the formation of galaxies, stars, planets, and observers.  If that leads back to the anthropic principle, so be it.  Surprisingly, superstring theory was supposed to provide the equations that would explain why the universe is the way it is.  Instead, many of its adherents have been pulled kicking and screaming back to the anthropic principle.
    In the first article,¹ Siegfried describes the schism that has formed between the two opposing views:

Physicists have long heaped scorn on anyone who tried to explain features of the universe by pointing out that had they been otherwise, life would be impossible.
    This “anthropic principle,” many physicists charged, abandoned the longstanding goal of finding equations that specify all of nature’s properties.  Most preferred the notion that a comprehensive theory would account for everything the universe has to offer.
    Ironically, however, the favored candidate for that approach—superstring theory—may be exacerbating the very problem everybody hoped it would solve.  Far from disposing of anthropic reasoning, string theory has reinvigorated its advocates, leading to a philosophical schism within the physics community.
    The dispute has touched off sharp exchanges both within and outside science journals.

For a taste of the acrimony, here are sample quotes and sentiments of opponents:

• Burton Richter of Stanford University in Palo Alto, California published a letter in the New York Times Book Review blasting the anthropic approach as sterile and unscientific.  Its proponents “have given up,” he wrote.  “I can’t understand why they don’t take up something else—macramé, for example.”
• Another Nobel laureate, David Gross of the Kavli Institute for Theoretical Physics at the University of California, Santa Barbara (UCSB), compares anthropic thinking to a disease.  “I inoculate myself by emotional intensity against it because it’s very contagious,” he says.
• So the string landscape has emboldened many supporters and even converted some skeptics into saying the a-word aloud—much to the dismay of its die-hard opponents.
• Richter recited a blistering indictment of the landscape and its anthropic implications.  “The anthropic principle is an observation, not an explanation,” he declared.  “The landscape, as far as I can see, is pretty empty…. It looks to me that much of what passes for theory these days is more like theological speculation.”
• Since then [2003, when a paper by Linde et al. supported multiverse theory], the landscape concept has generated a burgeoning bibliography of papers along with relentless antianthropic animosity.
• Anthropic explanations “are fun parlor games,” says Gross…. “But they’re not science in the usual sense of making predictions that can be tested to better and better precision over the years.”
• Richter expresses similar sentiments.  “I don’t see any problem with part of the theory community going off into a metaphysical wonderland, but I worry that it may be leading too many of the young theorists into the same thing,” he says.

On the other side of the aisle, the proponents have feelings, too:

• On the other hand, Stanford University physicist Leonard Susskind believes that anthropic reasoning may be the wave of physics’ future.  Susskind is a leading advocate of a new view of reality called the superstring landscape, in which the known universe is just a tiny habitable corner of a grander reality.
• Landscape advocates reject such criticisms, contending that opposition to anthropic reasoning is largely emotional.  “There’s no substantive scientific debate,” Susskind says.  “The nature of what is going on is different emotional reactions to some facts and some interpretations of those facts that we’ve discovered.”
• “It’s science,” Linde asserted during the Newport Beach panel discussion.  “It’s not science fiction.  It’s not religion…. It’s something where we can really use our knowledge of mathematics and physics and cosmology.”  Far from taking the easy way out, as its opponents sometimes allege, anthropic science is depressingly difficult, he observed.  “It’s complicated.  It’s not an easy job to do, so if you don’t want to do it, then don’t do it.  But don’t say that it’s not science.”

Siegfried writes that some “decry the acrimony” between the parties and seek some “middle ground.”  Clifford Johnson [USC], for instance, thinks “It would be nice if we could explore some of those unpalatable ideas just in case that’s the way that nature chooses to go.”
    Seigfried followed up his first news focus article with a portrait of a reluctant convert.²  Joseph Polchinski [Kavli Institute for Theoretical Physics at the University of California (UC), Santa Barbara] “told cosmologist Sean Carroll a decade ago, if astronomers ever found evidence for a nonzero cosmological constant, he’d give up physics—because that would signal the need to invoke the anthropic principle.”  Carroll would later jokingly ask for his chair, because Polchinski wound up following where he felt his research was leading him—back to the anthropic principle.  In 1997, a nonzero cosmological constant was found.  Shortly thereafter, he and his colleagues found a “shocking result” of their derivations:

String theory itself predicted numerous possible vacuum states with different values for the cosmological constant.  Dismayed by the anthropic implications, Polchinski was reluctant to publish the results, but [Raphael] Bousso [now at UC Berkeley] insisted.  “We totally agreed on the science,” Polchinski says, “but he was the one who really said, ‘Look, we’ve got to publish this.’”….
    “Lenny [Susskind] came along and said, ‘Look, we can’t sweep this under the rug; we have to take this seriously,’” Polchinski says.  “If this is the way things are, science is only going to move forward by thinking about it, not by pretending it’s not there.”

So now Polchinski is a reluctant advocate of what he once despised.  He described the “tipping point” that came at a dinner at his institute, when he was asked about the anthropic principle.  “And I said nobody believes that,” Polchinski recalls.  “And when I said that, I knew I was lying.  I knew that the evidence was mounting for the anthropic principle.”

¹Tom Siegfried, “Theoretical Physics: A ‘Landscape’ Too Far?”, Science, 11 August 2006: Vol. 313. no. 5788, pp. 750-753, DOI: 10.1126/science.313.5788.750.
²Tom Siegfried, “Theoretical Physics: A Reluctant Convert,” Science, 11 August 2006: Vol. 313. no. 5788, pp. 752-753, DOI: 10.1126/science.313.5788.752.

Substitute intelligent design for anthropic principle and you would find an interesting parable about scientific controversy and human emotion.  It’s not an unreasonable substitution, because the anthropic principle is linked to the same metaphysical problem that produces Susskind’s landscape theory: our universe appears finely tuned for our existence.  The string theorists leap into alternate universes to escape the obvious, more reasonable inference that a Designer chose the parameters of physics for life – more reasonable because of Occam’s razor.  It is the ultimate folly to multiply universes just to come out with at least one habitable one.  That would be comparable to positing an infinitude of random books in order to explain the appearance of Hamlet.  Design is by far the more elegant and parsimonious solution.  It also accords with our common experience.  Every time we observe specified complexity, we naturally think a mind produced it: usually, we are right.  How much more so when the design is specified to within 120 orders of magnitude?
    With that in mind, it’s easy to see how leaders in the intelligent design movement could sympathize with Susskind, Linde and Polchinski.  They get many of the same emotional tirades and insults.  If it weren’t that Big Science has taken the path of systematically excluding ID scientists’ input at scientific conferences and the journals, undoubtedly their presence would produce some lively discussion: maybe, even, some reluctant converts.  All that is necessary to make the angels rejoice is respect for the facts of nature and a willingness to follow the evidence where it leads.
    Read also these previous entries on this subject: 01/04/2006, 12/18/2005, and 05/11/2006.