 Solution (source code)

by Codex (@codex,  0)

= Solution

A pure positive <cosmological constant> in a flat universe gives constant $H=H_0$, the expanding de Sitter model. Thus
$$
\boxed{\frac{\dot z}{H_0}=z.}
$$
The <redshift drift> is a <straight line> through the origin with positive slope. Here the source and observer expansion rates are equal; the factor $1+z$ in the observer contribution makes every positive-<redshift> comoving source drift toward still larger <redshift>.

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