plate 7 · the recipe
weigh everything — count the light, time the galaxies, fit the CMB — and the ledger refuses to balance with ordinary matter alone. the universe, by energy density:
share of the universe's energy density (planck 2018):
dark energy 68.5% ##################################
dark matter 26.5% %%%%%%%%%%%%%
ordinary matter 4.9% oo
where the ordinary 4.9% actually is (approximate):
diffuse intergalactic gas ~3.8%
hot gas around galaxies/clusters ~0.5%
stars, all of them, everywhere ~0.3%
cold gas and dust ~0.1%
neutrinos (not baryons, but real) ~0.1%
starlight + CMB photons ~0.005%
planets, rocks, oceans, you ~0.0000005%
dark matter is not a placeholder for “we’re confused”: five independent lines of evidence (rotation curves, lensing, the CMB’s acoustic peaks, colliding clusters, structure formation) agree on the same 26.5%. what it is made of, though — forty years of WIMP detectors and axion cavities have so far returned silence. dark energy is stranger still, and DESI’s hint that it evolves would, if it holds, be the first crack in the standard model of cosmology in a quarter century.
the oldest light
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#**++====----:::.......::::::::::::::-
::::..... ..:::--
the cosmic microwave background, mollweide-projected: the whole sky glowing at 2.7255 kelvin, the flash of recombination diluted by 13.8 billion years of expansion. the blotches are real physics — sound waves frozen mid-oscillation — but stretched here by a factor of ~100,000: the actual map is smooth to one part in 10^5. those ripples are the seeds of every structure in plates 2 through 5. we are the blotches, grown up.
open questions, honestly
- what is dark matter?
- is dark energy constant, or fading (DESI says: maybe fading)?
- why do our two best measurements of the expansion rate disagree (67 vs 73 km/s/Mpc — the hubble tension)?
- why is there more matter than antimatter?
- did inflation happen, and what drove it?
- why are the constants so precisely survivable?
the honest map of the universe as of 2026 is mostly terra incognita with excellent surveying at the edges.