Problem 2 · Big Five
DISSOLVEDDark energy / Lambda
What's wrong (standard view): 69% accelerates. No mechanism.
The standard view
Sixty-nine per cent of the universe is unexplained acceleration
Type Ia supernovae, baryon acoustic oscillations and the CMB are jointly fit by adding a near-constant component, Λ, that accelerates the expansion. In ΛCDM this contributes about 69% of the energy density. There is no microphysical mechanism for it. The quantum field theory estimate of vacuum energy is too large by a factor of about 10120 — the worst prediction in the history of physics.
DESI DR2 (2025) has now found that w(z) — the dark-energy equation of state — is not constant with statistical significance: the data prefer a function that crosses the phantom divide. Recent analyses fit a sigmoidal Ξ(z) phenomenologically with four free parameters. ΛCDM disagrees with this at roughly 3 σ.
The ISST view
There is no dark energy. Apparent acceleration is a clock-rate contrast
ISST has no Λ and no quintessence. The expansion of the universe in the bare ISST background is not accelerating at all. What we measure as acceleration is the result of comparing clocks across the void/wall contrast of the cosmic web.
The mechanism is Wiltshire's timescape cosmology (Wiltshire 2007, 2013). Voids — large, low-density regions — and walls — the cosmic-web filaments and galaxy clusters that bound them — accumulate proper time at different rates because their gravitational potentials differ. A photon traversing the universe spends most of its path through voids; the average expansion rate inferred from supernovae is therefore a void-weighted quantity, not the bare expansion rate.
When you do the bookkeeping properly, the apparent acceleration falls out as a measurement artefact. ISST does not need a substance with negative pressure; it needs the void-fraction fv(z) as a function of redshift, which is what cosmic-web statistics already give us.
The mechanism
The Ξ(z) sigmoid, derived
The Wiltshire lapse links the bare expansion rate Hbare to the dressed (observed) one via where γw(z) depends on the void fraction at that redshift. Combined with the ISST sourcing of Ψ and the environment-dependent fs, the four parameters of the phenomenological Ξ(z) sigmoid (amplitude A, transition redshift ztr, slope n, present-day Hubble H0) come out from first principles to within 10% of the DESI fit (lab references: F53–F57, “T3 staged-MJ closure”, 18–19 April 2026).
Above: phenomenological Ξ(z) sigmoid (slate) and the ISST first-principles prediction (amber). The ΛCDM constant-w line is shown for comparison (dashed steel blue). DESI DR2 prefers the sigmoid over a constant at ~3 σ; ISST agrees with it.
Why this matters
A dissolution, not a discovery
The headline is not “we have a new dark energy candidate”. It is there is no dark energy to discover. The 69% has gone away. What was an ontological hole — a missing two-thirds of the universe — becomes a re-derivable consequence of the void-wall structure that the cosmic web has anyway.
One consequence: the Hubble constant. Planck measures H0 = 67.4 km/s/Mpc by fitting CMB peaks under ΛCDM. SH0ES measures 73.0 from local distance ladders. Under ISST the bare-dressed value is H0 = 61.79. Running the same physics through both measurement pipelines gives 62.8 on a Planck-template inversion (6.7% low vs 67.4) and 70.6 on a SH0ES-ladder inversion (3.4% low vs 73). One H0; two ladders read it differently. The structure of the tension is reproduced from a single value, but the literal numbers do not yet match observation cleanly — that is open work, flagged in the paper.
What would prove this wrong
The kill conditions
- DESI DR3 (2026/27) reverts to a strict cosmological constant w = −1 with the sigmoid disfavoured at ≥ 5σ.
- BOSS / DESI void-fraction measurements fv(z) are inconsistent with what ISST requires for the sigmoid closure.
- The Wiltshire lapse mechanism is shown to be incompatible with CMB acoustic peaks — i.e., the same void/wall contrast that gives Ξ(z) gives the wrong CMB.