The timeless universe is the philosophical and ontological view that time and associated ideas are human illusions caused by our ordering of observable phenomena. Unlike most variants of presentism and eternalism, the timeless universe entirely rejects the notion of the reality of any time, arguing that it is exclusively a human illusion, and since the universe can know no time, no dimension of time can be permitted in any theoretical explanation of parts of the observable universe. All purported measurements of time must hence according to this view be correlation measurements between movements, as stated by physicist Ernst Mach in 1883:It is utterly beyond our power to measure the changes of things by time. Quite the contrary, time is an abstraction at which we arrive by means of the changes of things; made because we are not restricted to any one definite measure, all being interconnected.In a timeless universe the cosmos in its broadest definition is eternal, without beginning or end, and all physical processes operate within a timeless framework. Since fundamental problems related to time, such as the Arrow of time and time travel, are still among the great unsolved problems of physics, discussions of timeless universes revolve around proposed solutions to these fundamental problems and paradoxa, and the related fundamental problems of philosophy and science.