My Weekend at “Rat Fest”
David Deutsch talks to his fans at Rat Fest.
HOBOKEN, OCTOBER 4, 2025. “It feels a little cult-y.” That’s how I respond when Logan Chipkin asks what I think of “Rat Fest.”
Let me back up a bit: Last summer, I get an email from someone named Logan Chipkin, who founded something called the Conjecture Institute. He wants my permission to use an online conversation I recorded years ago with physicist David Deutsch.
Let me back up further: In 2011, The Wall Street Journal asks me to review Deutsch’s book The Beginning of Infinity. Deutsch contends that human knowledge can expand forever--as long as we don’t destroy ourselves or succumb to pessimism.
Deutsch rebuts my argument, in The End of Science, that science is bumping into limits. That should annoy me. But Deutsch defends his radical optimism with such “passion, imagination and quirky brilliance,” I tell Wall Street Journal readers, “that I couldn’t help but like his book.”
Then I interview Deutsch on the video-podcast site Blogginheads.tv. I ask him about quantum computing (which Deutsch pioneered), the many-worlds interpretation of quantum mechanics (Deutsch believes it, I don’t), artificial intelligence, the future of civilization yada yada. This 2011 dialogue is what Logan Chipkin wants my permission to use. I say sure.
When I express curiosity about the Conjecture Institute, Chipkin and I have a video chat. He’s a smart, clean-cut, confident young man, an intellectual hustler (and I mean that as a compliment, I’m a meme-peddler too). He founded the Conjecture Institute to promote critical rationalism, a philosophy conceived by philosopher Karl Popper and embraced by Deutsch.
Critical rationalism says knowledge advances when humans propose conjectures, criticize and test them, propose new conjectures, criticize them and so on. Recursive trial and error. That’s how species evolve and knowledge grows. Chipkin urges me to come to Rat (short for rationalism) Fest, the Conjecture Institute’s annual meeting, in Philadelphia the last weekend of September.
I take Amtrak to Philly and a taxi to the Cambria Hotel. The attendees—almost 80 in all, Chipkin says—are young, old, male, female, from the U.S. as well as Europe, Asia, Africa. Many have tech-related jobs.
Over three days Rat Festers give more than 30 talks, most just 15 minutes long, on physics, neuroscience, history, the arts, objectivism (Ayn Rand’s schtick), Bayesianism, the correspondence theory of truth, Christian transhumanism, artificial intelligence. Yeah, a real grab bag.
The low point is a one-hour zoom lecture by “skeptic” Michael Shermer. He rehashes his decade-old book The Moral Arc, which rehashes Steven Pinker’s bestseller The Better Angels of Our Nature, which says we’re becoming less racist, sexist and violent and more democratic.
Shermer doesn’t bother updating his everything-is-getting-better schtick for the Trump era, which some of us think is a step backward. When I ask Shermer about Trump during the Q&A, Shermer denounces left-wing “extremists” who denounce Trump’s “fascism.” Shermer adds that there are only two sexes, male and female.
The high point of Rat Fest is—well, there are lots of high points, talks that tickle my old brain. Zelalem Mekonnen tells us about Zara Yaqob, a 17th-century Ethiopian scholar who anticipated critical rationalism and feminism.
Lulie Tanett, wearing a “Beginning of Infinity” t-shirt, suggests you can use reason to pinpoint and overcome hidden, irrational fears. So… critical rationalism can help you be your own psychotherapist?
Dennis Hackenthal weighs the relative merits of “patches” versus “purges,” meaning incremental political reforms versus revolutions. Hackenthal asks Rat Festers which they prefer. More hands go up for incremental reform. Popper was an incrementalist, and, well, revolutions can get messy.
Zakary Mizell proposes that “progress” in art entails measurable, “objective” components. Jesse Nichols riffs on disobedience: Can you teach disobedience? If so, how? If you give your students an exam on disobediance, should they refuse to take it?
Zooming in from Australia, Brett Hall gives a one-hour talk on “AI and the Philosophy of Science.” Hall mocks AI “doomers” like Nick Bostrom and Eliezer Yudkowski, who warn that AI might destroy us. Hall’s take on AI is boosterish.
During the Q&A, I tell Hall that AI worries me, for two reasons: 1, It’s controlled by power-hungry zillionaires who are tight with Trump. 2, My students are using AI to do their thinking for them. I’m worried that AI, rather than catalyzing an exponential surge in knowledge, will exacerbate our era’s anti-intellectualism.
Hall assures me that things will be okay. He says AI, like calculators and other tools, will help us skip past boring chores so we can spend more time solving important problems requiring genuine creativity. I tell Hall I hope he’s right.
The conversation swirls and eddies before and after scheduled talks, through lunch and dinner. The vibe is wonky, upbeat, loosey-goosey, anti-authoritarian. I dig this shindig, it’s fun. So why do I call Rat Fest “cult-y”?
Because what binds this band of rebels together is veneration for Popper and Deutsch. Five folks give talks on physics, and all seem to assume as axiomatic that the many-worlds interpretation is true. Why? Because Deutsch says it’s true.
Aaron Stupple, author of a parenting guide called The Sovereign Child, talks about how to raise your kids without making them do things they don’t want to do. I tell Stupple I wish I’d read his book when my son and daughter were young, and I mean it, Stupple strikes me as wise. But it bothers me that Stupple was inspired by Deutsch, who has no kids.
A key tenet of critical rationalism is that knowledge is tentative, improvable, because all of us are fallible, we can never be sure we’re right. But Rat Festers cite Popper and Deutsch as if they are infallible.
Deutsch’s book The Beginning of Infinity suffers from this problem, too. Deutsch rejects appeals to authority but repeatedly appeals to Popper’s authority.
Popper himself, when I interviewed him in 1992, was a comically dogmatic denouncer of dogmatism. He kept insisting he was right and his critics wrong.
When I told Popper a former student accused him of not tolerating criticism, he responded: “It is completely untrue! I was happy when I got criticism! Of course, not when I would answer the criticism… and the person would still go on with it.” Then Popper would eject the student from the class.
Come on, that’s funny. It’s like a guru who preaches disobedience and then punishes devotees for not being disobedient in the right way.
For the Rat Fest finale, Deutsch zooms in from Oxford for a one-hour Q&A. He looms over us like Oz, a serene, elfin Oz minus smoke and bombast. He has an unearthly air about him. He answers questions about human suffering, quantum mechanics, time travel, AI, a science fiction novel he’s writing.
When it’s my turn, I bring up Trump. Someone has to! What matters more now! I ask Deutsch, Are Trump’s attacks on science and academia making you doubt your views on progress?
Not at all, Deutsch replies. We are fallible, he reminds me, that means we make mistakes. Civilizations have taken wrong turns in the past and collapsed, that can happen again. But Deutsch thinks things will work out. American scientists can come to Europe to continue their research, and maybe not all the research should continue.
Taking Amtrak home, I brood: When does optimism become delusional? Why do self-proclaimed rationalists often seem so wacky? Can you be skeptical without falling into self-contradiction, like Popper and Kuhn? At what point does veneration for a sage living or dead (Buddha, Jesus, Marx, Freud, Popper, Deutsch, Trump) become cult-y?
Two final points. Wait, three. 1, I’m grateful to Logan Chipkin and his fellow Rat Festers for provoking me. 2, Chipkin is thinking of renaming “Rat Fest,” calling it “Conjecture Con.” That would be a mistake, Logan, “Rat Fest” is cooler. 3, I welcome corrections of my account of Rat Fest, because I am, truly, fallible.
Further Reading:
See this lightly edited version of my 2011 review of The Beginning of Infinity; my 2011 video chat with Deutsch for Bloggingheads.tv; my 2018 Q&A with him for Scientific American; and a follow-up column in which I suggest that Deutsch’s belief in science’s infinitude “reflects wishful thinking rather than hardheaded realism.”
Rat Festers should check out Paul Feyerabend, whose philosophical style I prefer to Popper’s.
How AI Moguls Are Like Mobsters
Multiverses Are Pseudoscientific Bullshit
Conservation of Ignorance: A New Law of Nature
My Controversial Diatribe Against “Skeptics”