Algorithmic Homophily

1. The claim, as it now stands

Two claims, which the first version of this paper did not separate, and separating them is most of what the revision is for.

The observation. Practitioners inside a given medium converge in technical opinion faster than the underlying evidence justifies, and the convergence is experienced as consensus rather than as narrowing. I still hold this at roughly the confidence I started with.

The explanation. That ranking algorithms optimising for engagement are the cause. This is the part that broke, and it broke cleanly rather than partially, which is the good kind of wrong.

2. The observation, and why it is hard to see

Convergence is invisible from inside because the mechanism that produces it also produces its own corroboration. The same opinion arriving from eleven directions reads as eleven independent confirmations. It is one confirmation, resampled.

  what it feels like        what it is
A  B  C  D  E             A —+
|  |  |  |  |                 |
+—+—+—+—+             B —+— one source,
|                    C —+   eleven arrivals
v                    D —+
consensus               E —+

The engineering consequence is specific: technology choices acquire the appearance of settled practice before the evidence exists, and the papers, benchmarks and postmortems that would test them arrive two years later, by which point the choice is load-bearing. Section 5.10 of this document is a retracted paper of mine that was produced exactly this way.

3. The mechanism, under rewrite

The original argument ran as follows. Ranking optimises for engagement. Engagement correlates with agreement, because disagreement costs attention and produces exit. Therefore a ranked feed converges on your priors, and does so faster the more you use it. The cache analogy did real work here: a cache with a hit-rate objective and no invalidation policy will happily serve stale entries forever, because staleness is not on the objective.

The mailing list result falsifies the necessity of ranking. Whatever produces the convergence is present when ranking is absent.

The candidate replacement, which I am not yet confident enough to state as the paper’s position: the binding term is selection, not ranking. Choosing whom to read is already a filter, it is applied once and revisited almost never, and it is applied on criteria (clarity, seniority, agreeableness) that correlate with existing agreement. Ranking then accelerates a process that subscription already started. If that is right, the paper’s advice barely changes and its target changes completely: the intervention belongs at the subscription boundary rather than at the feed.

I do not yet have a way to distinguish the selection account from a third possibility, which is that professional communities converge for ordinary social reasons that have nothing to do with media at all. Until I can, this section stays marked.

4. What the revision does not change

The observation in Section 1 survives the correction, and so does the practical advice, which is why the paper is being revised rather than retracted. Advice that survives the falsification of its own mechanism should be treated with suspicion, and I am treating it with suspicion: it may be surviving because it stands on its own, or because it was never load-bearing on the mechanism in the first place.

5. The practice, offered at 0.60

• Write down what would change your mind before reading. This is the same discipline the retirement conditions on this site enforce, applied to consumption rather than to publication. It is the only intervention in this list I am confident about, because its value does not depend on which mechanism is correct.
• Audit the subscription boundary, not the feed. If the selection account is right, this is where the whole effect enters. Once a quarter, list who you read and ask which of them has told you something you did not want to hear.
• Prefer artefacts with provenance. A postmortem, a benchmark with a methodology, a paper with a retirement condition. These are harder to resample, because the source is attached.
• Count arrivals, not sources. When a position reaches you from many directions, the useful question is how many distinct pieces of evidence sit behind it, which is usually one.

6. The strongest objection

7. What this paper does not claim

It does not claim consensus is wrong; most consensus is correct and cheaply acquired. It does not claim engagement optimisation is malicious. It does not, as of the August 2026 revision, claim that ranking causes the effect, and any quotation of the earlier version saying so should be treated as withdrawn. And it does not claim a fixed timeline for the rewrite, because the replacement mechanism is not yet good enough to publish.