The cosmological equations are
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(Weinberg 1972, p. 614) and
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where R is the distance scale,
is the cosmological constant, and

is the universe's radius of curvature. The qualitative behavior of R(t) is determined from (1), and the three resulting solution regimes are called the de Sitter, Friedmann-Lemaître Cosmological Model, and
Defining
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and integrating (1) gives
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(1) and (2) can be rewritten as
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and
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Taking
gives
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which can be rewritten as
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
(1)
(Weinberg 1972, p. 614) and

(2)
where R is the distance scale,
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
(3)
is the universe's radius of curvature. The qualitative behavior of R(t) is determined from (1), and the three resulting solution regimes are called the de Sitter, Friedmann-Lemaître Cosmological Model, and
Defining

(4)
and integrating (1) gives
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(5)
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(6)
(1) and (2) can be rewritten as
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(7)
and

(8)
Taking


(9)
which can be rewritten as
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(10)
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