Solution

ID: past-exam-of-the-mathematics-course-of-the-university-of-cambridge/2009/iii/paper-66/1/v/solution

Assume both densities are nonnegative and , so a nonzero pressureless matter component exists. Their ratio obeys
Thus matter domination gives
At fixed , the early expansion rate does depend on the present dark energy fraction: increasing it reduces . There is no contradiction with negligible early dark energy, since the leading expression is simply . At fixed physical matter density, that leading rate is independent of the negligible component.
The endpoint has no matter, so the ratio argument does not apply. Its Hubble parameter is : it diverges for , is constant for , and tends to zero for .

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