The participatory anthropic principle (PAP) was proposed by the physicist John Archibald Wheeler when he said that people exist in a “participatory universe.” In Wheeler’s (extremely controversial) view, an actual observer is needed to cause the collapse of the wavefunction, not just bits and pieces bouncing into each other.
This stance goes significantly further than the strict tenets of the Copenhagen interpretation, but it can’t be completely dismissed when you look in depth at the quantum evidence. If you never look at the quantum system, then for all intents and purposes it always stays a quantum system. Schrödinger’s cat really is both alive and dead until a person looks inside the box.
To John Barrow and Frank Tipler (in their popular and widely controversial 1986 book The Anthropic Cosmological Principle), this means that the universe itself comes into being only if someone is there to observe it. Essentially, the universe requires some form of life present for the wavefunction to collapse in the first place, meaning that the universe itself could not exist without life in it.
Most physicists believe that the PAP approach places humans in a crucial role in the universe, a stance which went out of favor when Copernicus realized Earth wasn’t the center of the universe. As such, they dismiss this interpretation in favor of those where humans aren’t necessary components of the universe.
This is an especially strong statement of a concept known as the anthropic principle. Recent discoveries in string theory have caused some theoretical physicists who were once strongly opposed to any form of anthropic principle to begin to adopt weaker versions of the anthropic principle as the only means of making predictions from the vast array of string theory possibilities.
