Equation 1 · Part 8 · From Origins to Frontier: A History of Precision Cosmology
Denominator: D_A(z_*)
What this part means
The complete quantity below the fraction bar; it must be nonzero for this division.
Its job in the formula
occurs below the fraction bar. The quantity above the bar is divided by this expression; zero is excluded as a denominator.
Full expression→Denominator: D_A(z_*)→Article meaning
The passage around this formula
…on it: . where is the physical size of the sound horizon at recombination — how far a pressure wave in the primordial plasma could travel before the plasma became neutral and transparent — and is the angular diameter distance to that same epoch. Planck measures directly from the angular spacing of peaks in the CMB power spectrum to extraordinary precision; converting that angle into a present-day expansion rate requires assuming a cosmological model (matter content,…
Learn the underlying idea
A fraction a/b means a divided by b. The top number is the numerator; the bottom number is the denominator, and it cannot be zero.
Open the illustrated fractions: division written vertically guide →
Sources cited in the surrounding passage
These citations provide research context; check each source for the exact claim it supports.