Equation 6 · Part 1 · From Origins to Frontier: A History of Precision Cosmology

Symbol r_*

r_*

r_*

What this part means

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 —.

Its job in the formula

$r_*$ is a part of this expression. Its role is fixed by the surrounding article and by the operations shown in the formula.

Full expressionSymbol r_*Article meaning

Where the article explains it

where $r_*$ 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 $D_A(z_*)$ is the angular diameter distance to that same epoch.

The passage around this formula

where $r_*$ 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 $D_A(z_*)$ is the angular diameter distance to that same epoch. Planck measures $\theta_*$ directly from the angular…

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Learn the underlying idea

A subscript is a label attached below a symbol. It often selects a time step, component, category, or member of a sequence.

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Sources cited in the article section

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