Surveying the Landscape

/ by Joshua Roebke /

Physicists weigh in on a controversy of universal proportions.

cosmiclandscape.jpg Credit: Mark Weiss

The world of high energy physics is currently embroiled in a controversy that, as Stanford professor Leonard Susskind points out, resembles the debate between evolution and intelligent design in its intensity.

At issue is “the landscape,” the possibly infinite set of solutions to the equations of string theory that arise when one tries modeling our universe. But string theory does not, as of yet, provide an internal mechanism to determine which solution applies to our particular universe.

The easiest solution is to say that we must live in a universe that supports life—we exist, right?— but that puts our very existence at the center of the problem. This notion is known as the anthropic principle. 

The real conflict arises when some of the theorists try to whittle away at the landscape by evoking the Anthropic Principle.

Some physicists see this as a blessing, a quick fix to the landscape, meaning that somewhere in the infinite solutions to string theory, our universe exists. Detractors criticize their colleagues for resorting to the equivalent of throwing their hands up at a difficult impasse, essentially giving up on physics itself. They believe that string theory will only be robust when it offers its own self-selection mechanism.

The conflict has spurred conferences, panels, and blog posts. Three new books are wading into the conflict: Hiding in the Mirror by Lawrence Krauss (Viking), The Cosmic Landscape by Leonard Susskind (Little, Brown), and Not Even Wrong by Peter Woit (Jonathan Cape, out in spring 2006). For a quick primer on this divisiveness, we ve contacted a few of the heavyweights of physics to get their reactions to the idea of the landscape and the use of the Anthropic Principle.  Here’s their scale of opinion:

“The possible existence of a huge landscape is a fascinating development in theoretical physics that forces a radical rethinking of many of our assumptions. My gut feeling is that it may well be right.” –Nina Arkani-Hamed, Harvard University

“Those who dislike the anthropic principle are simply in denial.” –Andrei Linde, Stanford University

“No amount of philosophizing, sloganeering or crying over spilled milk can answer the question. What is needed is much more open-minded exploration of the universe and of the mathematical Landscape.” –Leonard Susskind, Stanford University

“The issue of whether a fundamental theory will specify uniquely the constants of physics—or whether what we call the laws are just parochial bylaws in our cosmic patch—is a key one for 21st-century physics—a less poetic version of Einstein’s question: ‘Did God have any choice?’” –Martin Rees, Cambridge University

“I think it’s quite plausible that the landscape is real.” –Max Tegmark, MIT

“For many years, anthropic arguments have been ridiculed as handwaving and unpredictive, but now the tide has turned.” –Alexander Vilenkin, Tufts University

“Anthropic reasoning runs so much against the historic goals of theoretical physics that I resisted it long after realizing its likely necessity. But now I have come out.” –Joe Polchinski, University of California at Santa Barbara

“Today, the landscape is the best logical explanation for dark energy. But it is not very satisfying and I hope that we will soon have a better one.” –Juan Maldacena, Institute for Advanced Studies, Princeton University

“Mother Nature is what she is. It’s our job to try to understand her as she is, not as we wish she were.” –Jacques Distler, University of Texas

“I just don’t have anything incisive to say. I hope we will learn more.” –Ed Witten, Fields Medal winner, Institute for Advanced Studies, Princeton University

“It’s healthy to be skeptical of it even if it is true, so that new discoveries are not viewed as already explained by anthropic reasoning.” –Cumrun Vafa, Harvard University

“It’s the triumph of imagination over knowledge.” –Frank Wilczek, Nobel Prize Winner, MIT

“One version of the anthropic principle that is certainly wrong is the one that says ‘The universe must behave in such a way as to keep me happy.’” –Sean Carroll, University of Chicago

“Anthropic Lack of Principles.” –Lubos Motl, Harvard University, from his blog

“The problem with the landscape is very simple: It’s not science.” –Peter Woit, Columbia University

“If the landscape turns out to be the main physical implication of the grand edifice of string theory, what was touted 20 years ago as a Theory of Everything would then instead have turned quite literally into a Theory of Nothing.” –Lawrence Krauss, Case Western Reserve University, from his book.

“Unfortunately, what I think about many of these cosmology ideas cannot be printed in many cases.” –Robert Laughlin, Nobel Prize Winner, Stanford University

Originally published December 12, 2005

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