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a) Briefly explain what is meant by "particle horizon" and "event horizon" in cosmology.
b) Calculate the physical particle horizon, RH (t), at time t. Assume a flat FRW universe which
is dominated by a fluid that gives rise to scale factor evolution
a(t) = ao ()*,
to
where n is a constant with 0 <n< 1, and a (to) = ao.
n

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