Abstract
For exploring the physics behind the accelerating universe a crucial question
is how much we can learn about the dynamics through next generation
cosmological experiments. For example, in defining the dark energy behavior
through an effective equation of state, how many parameters can we
realistically expect to tightly constrain? Through both general and specific
examples (including new parametrizations and principal component analysis) we
argue that the answer is 42 - no, wait, two. Cosmological parameter analyses
involving a measure of the equation of state value at some epoch (e.g. w_0) and
a measure of the change in equation of state (e.g. w') are therefore realistic
in projecting dark energy parameter constraints. More elaborate
parametrizations could have some uses (e.g. testing for bias or comparison with
model features), but do not lead to accurately measured dark energy parameters.
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