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Observers and consciousness
· Open question
Open questionNobody knows the answer.
The open question of what counts as an "observer" in physics, and whether consciousness plays any special role.
See it on the Science map →How it works
In quantum theory, a particle's outcome seems to become definite only when measured. That raises a question: what counts as measuring? Most physicists say any interaction with the environment does, so a Geiger counter or a stray air molecule will do; this process is called decoherence. A minority, following John von Neumann and Eugene Wigner, once suggested consciousness completes the measurement. Observers also matter in cosmology's anthropic reasoning and in the simulation argument.
Why it matters
It sits where physics meets philosophy of mind. How it is answered decides whether minds are ordinary physical systems or something special in nature's laws.
How we know
Experiments show detectors with no human present behave just like watched ones, and decoherence is well measured. No experiment shows consciousness affects outcomes. What consciousness is remains scientifically unexplained.
Still a mystery
Why a single outcome appears at all, and how subjective experience arises from matter, are both unsolved.
Connections (3)
▸The measurement problem raises the role of Observers and consciousnessOpen question
The relationship
Quantum theory describes a particle as a spread of possibilities until it is measured, then gives one definite result. The theory never says exactly what counts as a measurement. That gap invites the question of whether an observer, and maybe a conscious one, has a special role, or whether any physical interaction counts.
How the link was found
John von Neumann (1932) showed the cut between system and observer could be placed anywhere. Fritz London and Edmond Bauer (1939) and Eugene Wigner (1961) suggested consciousness might complete it; Wigner later dropped the idea.
Is it proven?
Decoherence theory (Zeh 1970, Zurek in the 1980s) explains, with experiments to back it, why interactions with surroundings hide quantum effects. Photon experiments in 2019 tested Wigner's-friend scenarios. None show consciousness is needed.
Open questions and mysteries
Decoherence explains why we never see blends, but not why one specific outcome occurs. Interpretations such as many-worlds and pilot waves still answer that differently.
▸The anthropic principle depends on Observers and consciousnessPhilosophy
The relationship
The anthropic principle explains features of the universe by noting that observers must exist to see them. That makes it depend on what counts as an observer: a human, any life, any conscious mind? Different choices give different predictions, and some choices lead to bizarre results such as random fluctuating brains.
How the link was found
Brandon Carter (1973) introduced it; Nick Bostrom's 2002 book Anthropic Bias analyzed the "reference class problem" of which observers count.
Is it proven?
Selection effects are real; statisticians correct for them routinely. But no agreed definition of observer exists for cosmology, so the dependence is philosophical.
Open questions and mysteries
Why we are not "Boltzmann brains", lone minds from random fluctuations, is a real puzzle in some cosmological models.
▸Observers and consciousness is central to The simulation hypothesisPhilosophy
The relationship
Bostrom's argument counts observers: if simulated minds vastly outnumber biological ones, a typical observer is simulated. That only works if a simulation can contain genuine conscious observers. So the whole hypothesis hinges on what consciousness is and whether it can run on a computer.
How the link was found
Nick Bostrom (2003) made the assumption explicit, calling it substrate independence: the idea that minds depend on information processing, not on biology.
Is it proven?
Not proven. Science has no accepted explanation of consciousness, so whether simulated minds would be conscious cannot be tested now.
Open questions and mysteries
If consciousness requires biology or something non-computable, as some philosophers argue, the simulation argument fails.