--- title: "What Isn't There (Surprisingly Hard)" description: "List the things that never happen in the world you observe, then ask why they were so hard to notice: an exercise in turning absences into expectations you can test." type: Activity tags: [course, student-facing, problem, section-3, observation, negative-evidence, perception] status: stable problem: section: 3 session: 14 identification: probable kind: discussion generated: by: "claude/opus-5" at: "2026-09-16T00:00:00Z" sources: - id: winfree-handout-2002 resource: "https://web.archive.org/web/20020420212713/http://eebweb.arizona.edu/Faculty/Winfree/handout_479.htm" title: "The Art of Scientific Discovery (ECOL 479/579): course handout, archived 20 April 2002" author: "Arthur T. Winfree" - id: winfree-sas08-2002 resource: "https://web.archive.org/web/20030114040501/http://eebweb.arizona.edu/faculty/winfree/SAS/SAS08/SAS08.html" title: "Adventure of the Rainbow Moon (Adventures in Discovery column, SAS E-Bulletin, 11 January 2002)" author: "Arthur T. Winfree" - id: winfree-sas09-2002 resource: "https://web.archive.org/web/20030114041305/http://eebweb.arizona.edu/faculty/winfree/SAS/SAS09/SAS09.html" title: "Adventure of the Rainbow Moon: crucial experiment this afternoon in Tucson (SAS E-Bulletin, 25 January 2002)" author: "Arthur T. Winfree" - id: judson-1980 resource: "https://archive.org/details/searchforsolutio00juds" title: "The Search for Solutions (chapter 4, 'Chance')" author: "Horace Freeland Judson" - id: anderson-1990 resource: "https://doi.org/10.1063/1.2810433" title: "Some Thoughtful Words (Not Mine) on Research Strategy for Theorists" author: "Philip W. Anderson" - id: doyle-silver-blaze-1892 resource: "https://www.gutenberg.org/files/834/834-h/834-h.htm" title: "The Memoirs of Sherlock Holmes: 'Silver Blaze' (Project Gutenberg eBook #834)" author: "Arthur Conan Doyle" - id: aosd-syllabus resource: "https://github.com/tyson-swetnam/aosd/blob/main/docs/assets/aosd_syllabus.pdf" title: "The Art of Scientific Discovery: original course syllabus (PDF)" author: "Arthur T. Winfree" --- # What Isn't There (Surprisingly Hard)

This work is licensed under a Creative Commons Attribution 4.0 International License. *[Section 3](../section3.md), session 14. The same session continues the [chemical pattern-formation lab](chemical-pattern-formation-lab.md); the next session discusses [Rainbow Moon](rainbow-moon.md).* !!! abstract "The problem" Reconstructed from the syllabus: the original text is lost, so this follows the item's name, its place in the schedule, and Winfree's framing of the same idea in a later column. Some absences are easy to notice. As Winfree put it, "I bet you never saw a stone fall upwards, and you would have noticed." Others are not. He passed on two he had only been told: that no fish blinks both eyes at once (though sharks do), and that certain animals, sharks among them, never get any kind of cancer. 1. Over a week, list things that **never happen**, or are **never there**, in the world you observe: in the sky, on the walk to class, in your chemical observations. Aim for absences you had never registered until you went looking. 2. For each, ask: how much can you work out about why you never saw it, and what deliberate observations could settle the questions that raises? 3. Sort the list. Which cannot happen? Which happen where you were never placed to see them? Which has nobody checked? Which were you merely told? Then the question that gives the exercise its name: why is this so surprisingly hard? ## Why it is in the course Section 3 is "Observations and Questions". Session 14 pairs "More chemical observations" with this item, one session before the Rainbow Moon, with Judson's *Chance* and Anderson on research strategy as readings. The syllabus gives only a name and a warning: surprisingly hard. In Winfree's words from a later column, "Other things that never happen are hard to notice." Working out why is the point of the exercise. It also returns to session 04's "distinguishing things we know vs only imagine": "I never saw it", "it never happens" and "I was told it never happens" are three different claims. ## Where it comes from The editors found no published puzzle with this name. The archived course handout lists it for session 14, but its problem descriptions lived in a companion document that was never archived. Winfree's clearest statement of the idea opens his column "Adventure of the Rainbow Moon" (Society for Amateur Scientists E-Bulletin, 11 January 2002), written about three months after the session. It shows how he framed the theme, not the exercise as set. He contrasts easy absences with hard ones, then poses a hard one: nobody remembers seeing the Moon behind the colour band of a rainbow. The follow-up (25 January 2002) describes engaging "the absence of an experience that 'ought' to be remembered, but isn't". Winfree had seen a Rainbow Moon himself in Tucson on 6 September 2001, a month before the class discussed it. The idea is old. Holmes makes the point in Conan Doyle's "Silver Blaze" (1892), where the curious incident is the dog that did nothing in the night-time. Nothing in Winfree's materials mentions the story; it is an aside here, not the source. ??? tip "Hints" - Start with the easy absences (stones never fall up) and ask why those were easy. What did you already know that let you notice them? - Separate "I have never seen it", "nobody has ever seen it" and "it cannot happen". Which kind is each entry, and what observation would move it from one kind to another? - For absences that survive, ask what enforces them: geometry, timing, physics, selection. - To catch something that does not happen, first name a specific thing that *could* happen, then look for it. ??? success "Resolution" There is no single answer; the resolution is seeing *why* it is hard. An absence is not an experience. You can notice that something is missing only once you hold a definite expectation that it should be there. The remedy is to manufacture expectations and test them: predict when and where the missing thing should appear, then go and look. Winfree did that with his own example. Predicting when the Moon should stand in a rainbow led him to a month of sextant measurements and several small discoveries about the Moon's motion. The geometry belongs on the [Rainbow Moon](rainbow-moon.md) page. The other half of the lesson is Winfree's hedge: he introduced his fish and cancer examples with "I have been told" and "I have also heard". An absence reported at second hand is a claim to check, not a fact. ## Sources - **Arthur T. Winfree**, *The Art of Scientific Discovery* (ECOL 479/579): course handout, archived 20 April 2002 — [Wayback Machine](https://web.archive.org/web/20020420212713/http://eebweb.arizona.edu/Faculty/Winfree/handout_479.htm){target=_blank} 🔓 - **Arthur T. Winfree**, "Adventure of the Rainbow Moon", Adventures in Discovery column, SAS E-Bulletin (11 January 2002) — [Wayback Machine](https://web.archive.org/web/20030114040501/http://eebweb.arizona.edu/faculty/winfree/SAS/SAS08/SAS08.html){target=_blank} 🔓 - **Arthur T. Winfree**, "Adventure of the Rainbow Moon: crucial experiment this afternoon in Tucson", SAS E-Bulletin (25 January 2002) — [Wayback Machine](https://web.archive.org/web/20030114041305/http://eebweb.arizona.edu/faculty/winfree/SAS/SAS09/SAS09.html){target=_blank} 🔓 - **Horace Freeland Judson**, *The Search for Solutions* (1980), chapter 4, "Chance" — [Internet Archive](https://archive.org/details/searchforsolutio00juds){target=_blank} 🔓 *(borrow)* - **Philip W. Anderson**, "Some Thoughtful Words (Not Mine) on Research Strategy for Theorists", *Physics Today* 43(2), 9 (1990) — [doi:10.1063/1.2810433](https://doi.org/10.1063/1.2810433){target=_blank} 🔒 (very likely the session's "Anderson on research strategy"; not read by the editors) - **Arthur Conan Doyle**, "Silver Blaze", in *The Memoirs of Sherlock Holmes* (1892) — [Project Gutenberg](https://www.gutenberg.org/files/834/834-h/834-h.htm){target=_blank} 🔓 - **Arthur T. Winfree**, *The Art of Scientific Discovery*: original course syllabus — [PDF](https://github.com/tyson-swetnam/aosd/blob/main/docs/assets/aosd_syllabus.pdf){target=_blank} 🔓 !!! note "How sure are we that this is Winfree's problem?" The syllabus gives only the name and its place in session 14, just before the Rainbow Moon. No text of the problem survives, so the reading is **probable**, not confident. - **Likeliest: an exercise in noticing things that never happen.** It matches the "hard to notice" framing of Winfree's Rainbow Moon column, and the schedule runs straight from this item to that case. Against it: the column dates from January 2002, about three months after the session, so it shows Winfree's framing of the theme, not the exercise as set. - **Negative evidence and the dog in the night-time.** This site's earlier guess. The classic illustration, but no Winfree source mentions it, so it is rejected as the identification. - **A perceptual absence such as the eye's blind spot**, leading into session 15's "Mother Nature as magician; hallucinations". It fits the theme, but nothing in the archived material supports it. --- *Back to [Section 3](../section3.md) · [All problems](index.md) · [The schedule](../syllabus.md#section-3-observations-and-questions)*