The Quiet Galaxy

Explanations · They are there and we cannot see them

The simulation: the universe we observe is a computer model, and whoever is running it did not bother to include anyone else

Proposed by Nick Bostrom, as a general argument; applied to the Fermi question by many since, 2003 fc left alone

If a civilisation can run detailed simulations of minds and worlds, it will probably run many of them, and simulated people would then outnumber real ones by a wide margin. That is the simulation argument, and it concludes that unless such simulations are impossible or never run, we are more likely to be in one than not. Applied to the silence, the thought is simple: a simulation of a single civilisation on a single planet does not need to contain any others, and a sky full of stars is far cheaper to render than a galaxy full of neighbours. We see no one because the model stops at the edge of what we can check.

The philosopher Nick Bostrom published the argument in 2003. It does not claim we are in a simulation. It claims that one of three things must be true: almost no civilisation reaches the stage of being able to simulate minds in detail; almost none that reaches it chooses to run simulations of its own past; or we are almost certainly in a simulation, because simulated minds would vastly outnumber the real ones. The argument has been discussed ever since by philosophers, physicists and the public, and it has been attached to the Fermi question in an obvious way. A simulation has a budget. Modelling one planet's inhabitants in enough detail to fool them is expensive; modelling a galaxy of other civilisations, each with its own history and its own attempts at contact, is far more so. A simulator interested in us, or in a civilisation like us, would have every reason to leave the rest of the galaxy as scenery: real enough to look at, empty of anyone who might answer.

The idea has an older cousin in the planetarium hypothesis, which has its own page. In Stephen Baxter's version of it the universe is itself an artificial one, so the two overlap; the difference is in purpose. A planetarium is built on purpose to show us an empty sky, whereas in the general simulation argument the empty galaxy is simply a feature of the model's design, with no one hiding anything. The two make the same prediction about the silence and differ about what lies behind it.

The bearing on the Drake Equation is unusual. The explanation does not say any factor is small. It says the equation describes a model rather than a universe, and that the model need not obey the equation at all; whoever runs it decides how many civilisations it contains. For the catalogue's purposes the explanation leaves the factors unchanged and puts the silence down to our situation, which is why it sits in the "unseen" family.

The objections are of two kinds. Against the simulation argument itself: it assumes that simulated minds are possible and would be conscious, which is unknown; it assumes advanced civilisations would want to run such simulations; and some physicists have argued that simulating quantum physics is beyond ordinary computers. The paper most often cited for that, by Ringel and Kovrizhin in 2017, shows something much narrower: its abstract says that one common computing method cannot be made to work for certain quantum systems, and does not mention simulating the universe. The reading that it rules out a simulated universe came from press coverage and has been disputed. Against its use as an answer to the silence: it is not an explanation so much as a way of making the question go away, since a simulator could have included aliens as easily as not, and nothing about the simulation argument predicts an empty galaxy rather than a full one. An explanation that is compatible with every observation explains none of them. Its defenders reply that the same is true of the zoo hypothesis, which the field takes seriously, and that the simulation argument at least makes a definite claim about what the sky's emptiness would cost to produce.

What it says about the equation

Every explanation is a claim about one or more of the seven pieces that are multiplied to give the number of detectable civilisations. This one bears on 1 piece:

The test: what would strengthen or weaken it

Would strengthen it: A physical finding that the universe behaves as a discrete computation at the smallest scales; evidence of a boundary or shortcut in physical law that looks like a cost-saving measure; a demonstration that conscious minds can be simulated, which would make the argument's first premise true.

Would weaken it: A proof that simulating minds or physics at our level is impossible in principle; a detected civilisation, which would at least show the model included one; strong arguments that advanced civilisations would not run such simulations.

These two lines are what the record is read against when a new paper or discovery is logged. A result of the kind named here, published with its evidence, is what would settle it; a press claim on its own settles nothing.

The last reading

Once a week the records are read against the news, each against the test above. Open a line to see what that week held. Every reading ever made of this record is on the reading page.

  • 2026-10-16 Logged, no change By hand

    No physical finding of a discrete computation or a seam. Edge and Brown (Frontiers in Physics, 2026-04-21) answer Vazza's 2025 impossibility argument by saying it refutes a stronger claim than the one made, so the 'proof of impossibility' the weakening test names has not been given; a revised Wolpert preprint (2026-03-19) argues the question turns on the Church-Turing thesis. Logged Edge and Brown.

    Edge, 2026 source 1source 2

How seriously it is taken

The simulation argument is a respected piece of philosophy and widely discussed; its use as an answer to the Fermi question is common in popular writing and rare in the research literature, where it is regarded as untestable and as not predicting the silence in particular.

The papers that bear on it

Books, films and other work that take it up

Read next

Notes

Checked 2026-10-16. Bostrom's paper is in The Philosophical Quarterly 53, issue 211, pages 243-255 (April 2003), confirmed on Oxford's journal page (https://academic.oup.com/pq/article/53/211/243/1610975) and Bostrom's own site (https://simulation-argument.com/simulation/). Oxford lists the title as "Are We Living in a Computer Simulation?" while Bostrom's site uses "Are You Living in a Computer Simulation?"; this record keeps the author's. Corrected 2026-10-16: the body said some physicists argue that simulating our physics would need more computing than any physical computer could supply, with the 2017 paper by Ringel and Kovrizhin as the usual citation. That paper (Science Advances 3, e1701758, https://arxiv.org/abs/1704.03880) shows only that quantized gravitational responses block a particular computing method (a random-sampling method for simulating quantum systems) for certain systems of bosons; its abstract does not address simulating the universe, and Scott Aaronson explains why the press claim overreaches (https://scottaaronson.blog/?p=3482). The body now says so. Also reworded the sentence contrasting this idea with the planetarium page, because Baxter's planetarium paper is itself about an artificial universe (see the planetarium record's notes). No change to the id, family, bears_on or the would_strengthen and would_weaken lines.

Think this page gets the explanation wrong, or misses an objection? Say so, or read how disagreement gets folded in. The record itself is data/explanations/simulation.toml in the public repository. This page's address will never change; if the explanation is ever retired, the address will say what replaced it.