From the viewpoint of cosmological evolution it seems that the optical variation of QSOs becomes more violent with the cosmologicaltime, and finally it connects itself with that of active galaxies.
从宇宙演化的角度来看，类星体的光变随着宇宙时愈演愈烈，最后与活动星系相接。
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Another exception is the "cosmological arrow of time," which points forward from the Big Bang in the direction of the universe's expansion.
To return to the arrow of time, there remains the question: why do we observe that the thermodynamic and cosmological arrows point in the same direction?