The agent causing this expansion is termed as dark energy and it violates the strong energy condition
. Cosmological observations reveal that our universe is approximately homogeneous and isotropic at large scales  described by the standard FRW model.
The Null Energy Condition
(NEC) in the bulk imposes some constraints on the class of non-relativistic field theories dual to the hyperscaling violating backgrounds, namely, that the critical exponents must satisfy [72, 75]
From above, it is clear that the energy density of anisotropic fluids ([p.sub.[phi]] = [p.sub.z] = [p.sub.t] tangential stress) violates the weak energy condition
Secondly, the plot of weak energy condition
(WEC), dominant energy condition
(DEC), and strong energy condition
(SEC) for non-interacting and interacting cases is shown in Figures 7 and 8, respectively.
It possesses negatively large pressure which violates the strong energy condition
(p + 3[rho] < 0, where p and [rho] are pressure and energy density, respectively) but its complete characteristics are still not known.
Abreu and Sasaki  studied the effects of null energy condition
(NEC) and weak energy condition
(WEC) with noncommutative wormhole.
Yurtsever, "Wormholes, time machines, and the weak energy condition
," Physical Review Letters, vol.
As ordinary matter, DM satisfies the strong energy condition
. Dark energy, instead, is more peculiar still, given that it does not share the clustering properties of ordinary matter or DM, as it violates the strong energy condition
The energy density of null dust satisfies the null energy condition
The time machine spacetime discussed in [35-39] violated the weak energy condition
(WEC) and the strong energy condition
(SEC) is violated in [40-43].
Moreover, since [rho]([phi]) = -(3/4)[[beta].sup.2](t) is negative for real nonzero values of [beta](t), the weak energy condition
is not respected by a real nonzero [[phi].sub.[mu]].
Soma, "Lorentzian wormholes in higher-derivative gravity and the weak energy condition
," Physical Review D, vol.