The objectively real world may be separate from and indifferent to sense perception, but sense perception isn’t indifferent to the objective world. Sense perceptions are caused by an interaction of our sense organs and the world. Surely from repeated patterns of sense perception we can draw some correct inferences about the external world?
When we go back in time, we worry about changing the past. But we expect this person from the future to tell us all the stuff so we can fuck around with (for them) things that already happened.