Quantum mechanics formulations started in the early 1900s and the caught the eye of physicists around the world, with more and more acceptability being given to it. The Copenhagen Interpretation by Niels Bohr and Heisenberg in 1925-27 is the widely accepted form of quantum mechanics. It has changed the very nature of physics and it has radically changed our understanding of the universe and our place in it.
Quantum mechanics ushered in the era of the "participatory universe" where the observer, the observed and the act of observation all are interlinked. This shattered the ideas of classical physics, where an independent observer can observe the universe independently and understand it. According to Quantum Mechanics, the observer is affecting the universe by the mere act of observation and affects not only the present but the past as well, thereby changing our notion of the linearity of time.
So, we can no longer think of the universe from the point of view of independent observation; it is not independent (each part of the universe is connected to each other) and we are not independent observers. Rather we shape the universe by our observation and action.