  The Einstein-Aether (EA) theory belongs to a class of modified gravity
theories characterized by the introduction of a time-like unit vector field,
called aether. In this scenario, a preferred frame arises as a natural
consequence of a broken Lorentz invariance. In the present work we have
obtained and analyzed some exact solutions allowed by this theory for two
particular cases of perfect fluid, both with
Friedmann-Lemaitre-Robertson-Walker (FLRW) symmetry: (i) a fluid with constant
energy density ($p=-\rho_0$), and (ii) a fluid with zero energy density
($\rho_0=0$), corresponding to the vacuum solution with and without
cosmological constant ($\Lambda$), respectively. Our solutions show that the EA
and GR theories do not differentiate each other only by the coupling constants.
This difference is clearly shown because of the existence of singularities that
there are not in GR theory. This characteristic appears in the solutions with
$p=-\rho_0$ as well as with $\rho_0=0$, where this last one depends only on the
aether field. Besides, we consider the term of the EA theory in the
Raychaudhuri equation and discuss the meaning of the strong energy condition in
this scenario and found that this depends on aether field. The solutions admit
an expanding or contracting system. A bounce, a singular, a constant and an
accelerated expansion solutions were also obtained, exhibiting the richness of
the EA theory from the dynamic point of view of a collapsing system or of a
cosmological model. The analysis of energy conditions, considering an effective
fluid shows that the term of the aether contributes significantly for the
accelerated expansion of the system for the case in which the energy density is
constant. On the other hand, for the vacuum case ($\rho_0=0$), the energy
conditions are all satisfied for the aether fluid.
