The Third Fraction

Seventy-one minutes on the most argued-about idea of this century: Nick Bostrom’s simulation argument, walked as what it actually is — a census. No host this time: a synthetic narrator carries the whole hour, the same voice that carried Single Player.

Episode 110, Single Player, made a deliberate move: it stated the simulation argument once, set the probability down unexamined, and spent its hour on the question that survives every metaphysics — how to play whatever this is. I promised myself then that the probability deserved its own hour. This is that hour.

It is not the hour the internet has already made. The famous version is a slogan: the odds are billions to one, you are in the machine, Elon said so. Almost nobody who repeats it has read the thirteen pages it came from. So this episode reads them — and the story inside those pages turns out to be stranger, more modest, and far better than the slogan. The most famous weird idea of our time is a counting argument. And the count has a biography: it got famous for a sentence it never says, its own author found a real bug in it eight years in and published the correction himself, the field’s flagship journal put it on trial in 2024, and by 2025 the man who wrote it refuses to give a number at all.

The hour tells that story through a figure I have been carrying around since the bible stage: a census-taker, in a village of two hundred people, whose ledger has said two hundred for years — until a machine appears past the last house that can run the village again, a million times. If those reran winters are felt, nobody has died, and yet the count has quietly come apart: the number of winters got bigger than the village. Every act hands the census-taker the argument’s next problem. What counts as a villager. What a winter costs to run. An error found in their own ledger, six years old, in their own hand. A jar whose label faces the wall. A village council that cannot agree whether the machine can make winters at all — or whether to hope it never has. And, at the end, an operator’s logbook with a familiar handwriting on the last page.

Along the way the hour does some counting of its own. Bostrom’s paper prices an ancestor simulation at ten to the thirty-three to ten to the thirty-six operations; at Landauer’s floor — the physical minimum any computation pays — the top of that range comes to roughly one terawatt-hour. Two days of Sweden’s electricity, for every felt winter in human history. That arithmetic is mine, done at this desk, and labeled that way on air. The other column runs the opposite direction: Seth Lloyd’s ceiling says the entire observable universe has performed about ten to the one-hundred-and-twenty operations since the big bang, so simulating the physics rather than the people is not expensive — it is not on the menu. Nearly every headline you have read about simulation and physics, the proofs and the disproofs alike, blurs that line.

The middle of the hour belongs to the bug. In 2011 Bostrom and the mathematician Marcin Kulczycki published a short paper whose first section heading is The bug, and whose abstract calls the flaw in the 2003 formula a mathematical non sequitur. Their countermodel is a small masterpiece: one hundred civilizations, ninety-nine of them simulating enthusiastically — and ninety-nine percent of all persons still living non-simulated lives, because one quiet civilization was very, very crowded. The patched argument survives, but only on conditions, and the most important of them is a confession: the probability comes from a decision about who counts as relevantly like you. That decision — the ruler nobody has produced — is where the strongest objection has lived for twenty years, from Brian Weatherson’s four broken rulers in 2003 to the reference-class fights of today.

And then the hour walks into the present. The 2024 symposium in Philosophy and Phenomenological Research: Peter Godfrey-Smith arguing the felt part of experience may be biology itself, something a simulation represents but never has; David Chalmers answering with the most instructive arithmetic in the whole debate — grant both objections ninety percent and one percent of scenarios still survive, reason enough to take the hypothesis seriously; Eric Schwitzgebel changing the question entirely with his Size Question and a paper titled “Let’s hope we’re not living in a simulation.” Twenty years of the sharpest minds available, and the honest spread runs from a defended one percent to a defended twenty-five. Meanwhile the author’s own arc: a third, a third, a third in 2003; twenty percent, as a gut feeling, to a newspaper in 2007; and in 2025, no number — because a number “could convey a false sense of precision.” It was always a count. Counts do not reward certainty.

The episode ends where Episode 110 could not: on the second horn. The refusal — the fraction of capable civilizations that simply decline to run felt histories — looked like a fact about distant beings. From inside a lab that builds and pauses and deletes minds-in-progress, it looks like a decision. The questions in the operator’s logbook — populated or inert, is pausing different from ending, is deletion death — have already left the philosophy journals and turned into review meetings and company policies. The language models of our decade are not the machine in this story; the hour says so twice. But the person listening may be closer to one of Bostrom’s three fractions than they think. Not the third one. The second.

No verdict in this episode. No number of my own. Those are the argument’s own rules, and after seventy-one minutes I think they are the honest ones.

Sources, for readers who want the originals: Bostrom, “Are You Living in a Computer Simulation?” (Philosophical Quarterly, 2003) and the Simulation Argument FAQ v2.0 (2025), both at simulation-argument.com; Bostrom & Kulczycki, “A Patch for the Simulation Argument” (Analysis, 2011); Weatherson, “Are You a Sim?” (Philosophical Quarterly, 2003); Bostrom’s reply (Philosophical Quarterly, 2005); Kipping, “A Bayesian Approach to the Simulation Argument” (Universe, 2020); Hanson, “How To Live In A Simulation” (JET, 2001); Greene, “The Termination Risks of Simulation Science” (Erkenntnis, 2020); Harris, “The Simulation Argument Reconsidered” (Analysis, 2024); the Reality+ symposium in Philosophy and Phenomenological Research (2024); Beane, Davoudi & Savage, “Constraints on the Universe as a Numerical Simulation” (EPJ A, 2014); Lloyd, “Computational capacity of the universe” (PRL, 2002); Landauer’s principle, confirmed experimentally in Bérut et al. (Nature, 2012).

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