Two of cosmology's most precise measurements disagree on how fast the universe is expanding right now. Local distance-ladder measurements anchored in nearby Cepheid variable stars (the SH0ES program, Riess et al. 2022) give H₀ ≈ 73.0 ± 1.0 km/s/Mpc. CMB-anchored extrapolations from Planck 2020 give 67.4 ± 0.5 km/s/Mpc. The 5σ gap has not closed across a decade of refinement and systematic checks.
The standard model begins with a hot dense singular origin and assumes a single global expansion history with a fixed cosmological constant Λ. That structure forces every observer in every environment to measure the same H₀. There is no room for the answer to depend on where you happen to be sitting.
Replace the imaginary hot-dense-center with something physically simpler. SCT proposes that our visible universe is the thermalized debris field of a superluminal collision between two pre-existing parent pockets. The collision deposited the plasma we now see; the unthermalized parent-pocket structure beyond our horizon kept on existing, and that surrounding structure is the ongoing source of the gravitational mesh in which our patch is embedded.
Once you accept that picture, Λ stops being a fundamental constant. It becomes a derived quantity: Λ_eff(x,t) = κ · U_local(x,t) / U_parent(x,t), where U_local is the local pocket's gravitational binding energy and U_parent is the contribution from the surrounding parent-frame mesh (P17). That ratio depends on where and when you measure, which is the whole story.
We sit inside the KBC supervoid, a roughly 20% underdense region extending out to about 300 Mpc. Less local mass means less local binding energy, which raises the Λ_eff ratio and pushes the locally inferred H₀ about 2 to 3 km/s/Mpc above the cosmic average (P19). Independently, the parent-frame mesh has been progressively weakening since recombination through ordinary three-body ejection and dynamical friction (P14, P15, P16). That secular weakening adds another 2 to 3 km/s/Mpc to the gap between local inference and CMB inference (P18). The two contributions sum to the observed 6 km/s/Mpc tension, with no fitted parameters.
The local distance ladder and the CMB are not measuring the same H₀, because they are not sampling the same Λ_eff field. CMB photons traverse the entire post-recombination universe and report a volume-averaged expansion rate. SH0ES Cepheids and supernovae sit inside our local supervoid and report the locally enhanced rate. Both methods are correct. There is no single "true" H₀ anymore.
Environment-tagged H(z) measurements should reveal a systematic difference between void-direction sightlines and overdensity-direction sightlines after peculiar-velocity cleanup. SCT predicts void directions yield H₀ about 2 to 3 km/s/Mpc higher than cluster directions. DESI, Euclid, and Rubin/LSST will have the precision to test this within a few years. If the answer comes back uniform at the 1% level across all sky directions and environments, the M5 mechanism is wrong.