c·t = CONST, THAT CLICKS EPISODE 49 ／ Part VI — examining the procedure
Nearly four in ten cannot be closed by data
There were only
four kinds of door
Every question opened in 48 episodes and not closed, laid out.
And telling which kind a door is turned out to be a result in itself.
Two episodes remain. This time: the doors left open — every question opened in 48 episodes and not closed. Laid out together, what emerges is that there are only four kinds of door, and nearly four in ten of them cannot be closed by data. Telling which kind a door is has been what this series was doing all along.
01Doors opened and not closed
| Ep. | Question | What would close it | Kind |
|---|---|---|---|
| 18 | Does one bit \(\leftrightarrow\) 1.96 fm mean anything? | ── | coincidence |
| 29 | Does MOND survive on other datasets? | clusters and the CMB | observation |
| 34 | Does conformal gravity have a CMB prediction? | the calculation is unestablished | calculation |
| 36 | Is the "band of coincidences" real? | a larger sample | observation |
| 38 | Which contour for the conformal factor is right? | a first-principles derivation | calculation |
| 38 | Is there a theory with a ghost in neither place? | an existence or impossibility proof | calculation |
| 40 | What is the entropy of a gravitational field without a horizon? | an agreed definition | definition |
| 41 | What explains the low initial entropy? | measuring \(r\) | observation |
| 42 | Does information come out of black holes? | a mechanism | calculation |
| 43 | Is spacetime discrete? | quadratic Lorentz violation | observation |
| 43 | Does \(G\) transform under a conformal transformation? | ── (a choice of convention) | definition |
| 44 | What is the \(6\sigma\) in \(^4\)He's \(\lambda\) transition? | replication and systematics | observation |
| 46 | Which way does the Hubble tension fall? | the distance ladder and the CMB | observation |
| 47 | How many fundamental constants are there? | ── (a choice of convention) | definition |
| 48 | Can sensory beauty be measured? | ── (outside this tool) | not measurable |
| 48 | What fixes the prior in naturalness? | ── (a choice of prior) | definition |
02The core — there are only four kinds of door
| Kind | Count | Character |
|---|---|---|
| observation | \(6\) | data decides. It will close one day |
| calculation | \(4\) | a proof or derivation decides. In principle it closes |
| definition | \(4\) | a choice of convention. Data will not close it |
| coincidence / not measurable | \(2\) | not worth pursuing / outside the tool. Cannot be closed |
The main point of this episode
Six of the sixteen — nearly four in ten — cannot be closed by data.
"Open problems in physics" brings to mind the ones waiting on measurements,
but conventions and things outside the tool are about as numerous.
── Telling which kind of door it is, is already a result.
Figure: the sixteen doors sorted by kind. The observational ones have expected dates; the definitional ones do not close however long you wait. Move the slider forward in years — however far you go, some remain.
03When will the observational doors close?
| What is measured | Current value | Instrument | Timescale |
|---|---|---|---|
| Primordial gravitational waves \(r\) | \(<0.036\) | LiteBIRD / CMB-S4 | 2030s |
| Dark energy \(w(z)\) | \(-1.03\pm0.03\) | Euclid / DESI / Rubin | late 2020s |
| Variation of \(\alpha\) | \(|\Delta\alpha/\alpha|<1.4\times10^{-8}\) | optical and nuclear clocks | 2020s |
| The Hubble constant | \(67.4\) versus \(73.0\) | JWST / standard sirens | late 2020s |
| Black hole spins and mergers | model-dependent | LISA / Einstein Telescope | 2030s |
| Discreteness of spacetime (quadratic) | \(E_{\rm QG,2}>10^{11}\) GeV | CTA and others | late 2020s |
Most of the six observational doors are expected to settle in the 2020s and 2030s — readers of this series will see the answers within their lifetimes.
04The definitional doors do not close
Conclusion of §04
Without choosing the convention, the sentence is not finished (Episode 3).
── Choose, then measure. Reverse the order and you cannot see that the answer depends on the convention.
Episode 37 §05 (is \(\alpha\) constant?) and Episode 43 §02 (a smallest length) were exactly that.
05What did not change
| Statement | First stated | Since |
|---|---|---|
| \(c\cdot t=\)const is a notation, not new physics | Episode 3 | reconfirmed in Episode 46 |
| Extrapolated at face value it contradicts nucleosynthesis | previous series | unmoved |
| Dimensionful is bookkeeping, dimensionless is physics | Episode 3 | the SI drew the same line (Ep. 47) |
| Name what you compare to, or it is not yet a sentence | Episode 3 | it bit twice, in Eps. 37 and 43 |
For every door that opened, one stayed shut.
(1) The count of sixteen is this series' own. What counts as "one door" is arbitrary — split them finely and there are more, merge them and fewer, and §02's percentage moves with it. The substance is the structure "there are four kinds", not the count (the same caution as Episode 46 §03).
(2) §03's timescales are expectations based on published programme goals. Programmes slip, and target sensitivities are not always reached — the instruments and dates are the outlook as of writing (2026), not promises, and even an item marked "settles" may return an intermediate result that settles nothing.
(3) The four placed under "closed by calculation" may be an optimistic sorting. The black hole information problem (Episode 42) has been "about to be solved" for half a century, and whether "in principle it closes" is even the right description is itself uncertain.
(4) The definitional doors should not be dismissed. A choice of convention is not settled by data, but it changes what can be measured — whether \(G\) transforms changed the entire meaning of the statement about a smallest length (Episode 43). "Not settled by observation" is not "unimportant".
(5) This list covers only the doors this series opened. Physics has far more open problems (quantum gravity, the identity of dark matter, the baryon asymmetry, the measurement problem…) and this document does not survey them — it is the restricted list of "opened in 48 episodes and not closed".
Exercises
- Into how many kinds do the open doors fall?
Show the answer
Four — closed by observation (6), closed by calculation (4), fixed by definition (4), coincidence or not measurable (2). Telling which kind a door is, is already a result. - What fraction cannot be closed by data?
Show the answer
Nearly four in ten (6 of 16, 38 per cent) — the four definitional ones plus the two that are coincidence or unmeasurable. "Open problems in physics" brings to mind the observational ones, but conventions and things outside the tool are about as numerous. Per caveat (1), this depends on how one counts. - Which observational door is likely to close first?
Show the answer
The variation of \(\alpha\) (optical and nuclear clocks, 2020s), along with dark energy \(w(z)\) and the Hubble constant (both late 2020s) — readers of this series will see the answers within their lifetimes. Per caveat (2), these are outlooks, not promises. - Do the definitional doors not matter?
Show the answer
They do. Without choosing the convention the sentence is not finished (Episode 3) — choose, then measure. Reverse the order and you cannot see that the answer depends on the convention. "Not settled by observation" is not "unimportant" (caveat 4). - (Harder) What never changed across 48 episodes?
Show the answer
Four things — (i) \(c\cdot t=\)const is a notation, not new physics (Episode 3, reconfirmed in 46); (ii) extrapolated at face value it contradicts nucleosynthesis (previous series); (iii) dimensionful is bookkeeping and dimensionless is physics (the SI drew the same line in Episode 47); (iv) name what you compare to or it is not yet a sentence (it bit twice, in Episodes 37 and 43). For every door that opened, one stayed shut.
Summary: there were only four kinds of door
The questions opened in 48 episodes and left unclosed come to sixteen, and they fall into four kinds — closed by observation (6), closed by calculation (4), fixed by definition (4), coincidence or not measurable (2).
Most of the six observational ones are expected to settle in the 2020s and 2030s — primordial gravitational waves (LiteBIRD / CMB-S4), dark energy \(w(z)\) (Euclid / DESI / Rubin), the variation of \(\alpha\) (optical clocks), the Hubble constant (JWST / standard sirens), black hole ringdowns (LISA / Einstein Telescope), the discreteness of spacetime (CTA). Readers of this series will see the answers within their lifetimes.
But six of the sixteen — nearly four in ten — cannot be closed by data. "Open problems in physics" brings to mind the ones waiting on measurements, yet conventions and things outside the tool are about as numerous — and telling which kind of door it is, is already a result.
The definitional doors must not be dismissed. Without choosing the convention, the sentence is not finished (Episode 3) — choose, then measure; reverse the order and you cannot see that the answer depends on the convention. Episode 37's "is \(\alpha\) constant?" and Episode 43's "a smallest length" were exactly that.
Finally, what never moved across 48 episodes: that \(c\cdot t=\)const is a notation and not new physics; that extrapolated at face value it contradicts nucleosynthesis; that dimensionful is bookkeeping and dimensionless is physics; and that naming what you compare to is what makes a sentence. For every door that opened, one stayed shut.
This document is Episode 49 of "c·t = const, That Clicks" (the fourth of Part VI), written for physics-minded high-school and university readers. It collects the places in Episodes 1 to 48 marked "unresolved", "unsettled" or "not measurable"; there are no new computations (the tally is in kenshou/calc53.py) — for details see the endnotes of each episode. The count of sixteen is this series' own, and what counts as "one door" is arbitrary — split them finely and there are more, merge them and fewer, and §02's percentage moves with it; the substance is the structure, not the count. §03's timescales are expectations based on published programme goals; programmes slip and target sensitivities are not always reached — the instruments and dates are the outlook as of writing (2026), not promises, and an item marked "settles" may still return an intermediate result. The four placed under "closed by calculation" may be an optimistic sorting — the black hole information problem has been "about to be solved" for half a century. The definitional doors should not be dismissed: a choice of convention is not settled by data but changes what can be measured (whether \(G\) transforms changed the meaning of the smallest-length statement entirely) — "not settled by observation" is not "unimportant". This list covers only the doors this series opened; physics has far more open problems (quantum gravity, dark matter, the baryon asymmetry, the measurement problem…) which this document does not survey. ── To make a PDF, use your browser's Print dialogue (sliders freeze and answers are hidden in the print version).