In 1997 the science agent and impresario John Brockman orchestrated a debate about my book The End of Science on his website,, a forum where eggheads—let's call them Edgeheads--chitchat about science-related stuff. I summarized my argument that pure science is bumping up against fundamental limits and hence yielding diminishing returns; science will probably never again yield insights into nature as profound as quantum mechanics and relativity, the Big Bang, natural selection and genetics.

As evidence that scientists were hitting the wall, I pointed out the proliferation of what I called "ironic science," highly speculative ideas—notably string theory, which some proponents called a "theory of everything"--that can never be empirically confirmed.

Edgeheads politely swatted away my meme. "I believe [Horgan] is wrong," physicist Lee Smolin wrote, because science's picture of reality is "full of holes, unanswered fundamental questions and, in some cases, basic inconsistencies" that will surely be resolved. Smolin insisted that string theory, contrary to my disparagement of it as science fiction with equations, offers "a growing list of experimental predictions." Brockman, who's a funny guy, called the debate "The End of Horgan?"

Some Edgeheads have belatedly, tentatively, slipped a foot onto the end-of-science bandwagon. Every year since 1998, shortly after New Year's Day Brockman has posted Edgeheads' reactions to a Big Question. Brockman just published more than 170 answers to this year's question: What scientific idea is ready for retirement?

Physicist Martin Rees, former head of England's Royal Society, suggests jettisoning the idea that "We'll Never Hit Barriers To Scientific Understanding." Although he loads his little essay with caveats, Rees writes: "We humans haven't changed much since our remote ancestors roamed the African savannah. Our brains evolved to cope with the human-scale environment. So it is surely remarkable that we can make sense of phenomena that confound everyday intuition: in particular, the minuscule atoms we're made of, and the vast cosmos that surrounds us. Nonetheless—and here I'm sticking my neck out—maybe some aspects of reality are intrinsically beyond us, in that their comprehension would require some post-human intellect—just as Euclidean geometry is beyond non-human primates."

Yeah, like I said in 1997, we face cognitive limits, because "we are animals, designed by natural selection not for discovering deep truths of nature but for breeding."

Citing Rees, physicist Peter Woit says on his blog "Not Even Wrong" that some Edgeheads "sound like John Horgan, announcing we’re reaching the limits of science." Indeed, Woit (a long-time string-basher) and several other physicists, including Marcelo Gleiser, Frank Tipler and Paul Steinhardt, express some of the same frustration with particle physics and cosmology that I did back 17 years ago. Steinhardt's essay is especially noteworthy, because he is one of the inventors of inflation, a popular theory of cosmic creation.

Steinhardt complains that string theory and inflation have devolved into a "theory of anything," because they "predict" not only what we observe in our universe but also every other kind of conceivable universe. Unlike other prominent physicists (see for example the Edge essay by Sean Carroll, who wants to retire "falsifiability"), Steinhardt realizes that a theory that predicts everything does not really predict anything.

"Science is useful insofar as it explains and predicts why things are the way they are and not some other way," Steinhardt writes. "The worth of a scientific theory is gauged by the number of do-or-die experimental tests it passes. A Theory of Anything is useless because it does not rule out any possibility and worthless because it submits to no do-or-die tests."

Yeah! Like I said!

This is the second year in a row that the end-of-science meme has popped up in the responses to Brockman's annual question. Last year physicist Lawrence Krauss, among others, fretted over "new limits looming on our ultimate ability to probe nature."

Back in 1997, Lee Smolin chastised me for my pessimism. But facing the limits of science represents not pessimism but realism.