← INDEX — ROMAN LAUNCHED 30 AUGUST 2026
4.9 % · 26.5 % · 68.5 %
DARK
EUCLID & ROMAN: MAPPING DARK MATTER AND DARK ENERGY
Ordinary matter is about a twentieth of the universe.
BEGIN — CHAPTER 01 →CH.01 / 08 — ZWICKY, 1933
A cluster moving too fast to hold together
Zwicky: at least 400 times.
Planck: 4.9 / 26.5 / 68.5.
THE UNIVERSE'S BUDGET, PLANCK 2018
Ωb = Ωbh² / h² · Ωc = Ωch² / h² · ΩΛ ≈ 1 − Ωm
Budget.
CH.02 / 08 — RUBIN AND FORD, 1970–1980
Galaxies that spin too fast at the edge
Rubin & Ford.
NGC 3198.
CIRCULAR SPEED AND THE MASS INSIDE
v² = G M(<R) / R · vvis² = vgas² + Υ vdisk² · vhalo² = 4πGρ₀Rc² [1 − (Rc/R) arctan(R/Rc)]
Circular speed.
INSTRUMENT 1 · A DARK HALO FOR NGC 3198
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SPARC data.
CH.03 / 08 — SUPERNOVAE, 1998
The expansion is speeding up
Riess, Perlmutter.
Nobel 2011.
LUMINOSITY DISTANCE
E(z) = √(Ωm(1+z)³ + Ωk(1+z)² + ΩΛ) · dL = (1+z) (c/H₀) Sk(∫₀z dz′/E) · μ = 5 log₁₀(dL/10 pc)
Luminosity distance.
INSTRUMENT 2 · HOW FAR IS THE SUPERNOVA?
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Model curves.
CH.04 / 08 — EUCLID, 2023–
Weighing the dark by the way it bends light
Weak lensing.
Euclid.
AVERAGING AWAY THE SHAPES
eobs ≈ eint + γ · σ(ē) = σε / √N · S/N = γ √N / σε
Shape noise.
INSTRUMENT 3 · WHY A BILLION GALAXIES
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Ellipses.
Q1 and DR1.
Why lensing.
CH.05 / 08 — ROMAN, 2026–
Hubble's mirror, two hundred Hubbles' view
Roman.
Roman status.
FoV table.
Webb link.
CH.06 / 08 — AN OPEN QUESTION, 2025–2026
Is dark energy changing? Not settled
DESI DR2.
Dovekie.
Sigma.
CH.07 / 08 — LEGACY
Ninety years of measuring what cannot be seen
Effects, not the thing itself.
CH.08 / 08 — REFERENCES