Wheeler's Participatory Universe in Quantum Mechanics

"The universe does not exist 'out there' independently of us. We are inevitably involved in bringing about what appears to be happening. We are not merely observers. We are participants. In a strange sense, this is a participatory universe."

These are the words of theoretical physicist John Archibald Wheeler, also known for proposing the term 'black hole.' He is also known as the teacher of Richard Feynman.

This idea of a participatory universe stems from his own philosophy of 'It From Bit.' 'It,' representing all existence, refers to every particle, every field, and even spacetime itself. 'Bit' refers to the basic unit of information. It is the phrase that the world, which everything that exists constitutes, is born from information. This philosophy of his has been extended in modern times to 'It From Qbit,' the idea that the world emerges from qubits, the basic units of quantum information, and research into this is being advanced by many physicists around the world.

In quantum mechanics, no 'reality' exists before measurement. By performing a measurement, a 'reality' or 'actuality' emerges for the observer who performed that measurement.

What we call 'reality' or 'actuality' in our daily lives arises from the records of responses to questions based on a yes-no bit that we, as observers, pose to quantum objects and extract via measurement devices. In short, all physical things have an information-theoretic origin. In other words, the 'world' or 'universe' that refers to the exterior other than oneself as an observer is an idea that it emerges through our observations. This is the philosophy of Wheeler's participatory universe.

Wheeler often drew a conceptual diagram of the universe like Figure 1.

A large 'U' is written in this diagram, which symbolizes the Universe. It also corresponds to the initial 'U' of Unitarity, a fundamental property of quantum mechanics. The thin right side of the 'U' represents the beginning of the universe, which extends and connects to the thick left side of the 'U.' An eye is drawn there, symbolizing us as observers of the universe.

According to quantum mechanics, the history of the early universe is in a state of quantum superposition. By us in a later era observing the universe before our eyes, one of the past histories within it is picked up, and it is recognized by us as 'reality.' This is the meaning of the part where he says, 'The universe does not exist 'out there' independently of us. We are inevitably involved in bringing about what appears to be happening.' And Wheeler emphasizes that we are not mere observers, but participants who cause the 'reality' or 'actuality' of the universe to emerge. However, neither he nor modern quantum mechanics suggests that the observer's consciousness gives physical changes to the object. It is simply selecting one history that was already in the linear superposition of histories. This is where the way of thinking differs significantly from that of spiritual groups. In Wheeler's philosophy, it is correct that 'because it is consciousness that observes, the world is created (emerges) by consciousness,' but there is no spiritual meaning that 'if you change your consciousness, the world will also change.'

His philosophy of 'It From Bit,' and the modern 'It From Qbit,' is firmly taking root in modern physics through the progress of understanding quantum mechanics as information theory and through theories like the AdS/CFT correspondence, which is being studied as a concrete example of how spacetime emerges from quantum information.