Observer (quantum physics)
Encyclopedia
In quantum mechanics
, "observation" is synonymous with quantum measurement and "observer" with a measurement apparatus and observable
with what can be measured. Thus the quantum mechanical observer does not
necessarily present or solve any problems over and above the (admittedly difficult) issue of measurement in quantum mechanics
. The quantum mechanical observer is also intimately tied to the issue of observer effect.
A number of interpretations of quantum mechanics, notably "consciousness causes collapse", give the observer a special role, or place
constraints on who or what can be an observer. For instance, Fritjof Capra
writes:
However, other authorities downplay any special role of human observers
Critics of the special role of the observer also point out that observers can themselves be observed, leading to paradoxes such as that of Wigner's friend
; and that it is not clear how much consciousness is required
("Was the wave function waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer for some highly qualified measurer - with a PhD?").
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
, "observation" is synonymous with quantum measurement and "observer" with a measurement apparatus and observable
Observable
In physics, particularly in quantum physics, a system observable is a property of the system state that can be determined by some sequence of physical operations. For example, these operations might involve submitting the system to various electromagnetic fields and eventually reading a value off...
with what can be measured. Thus the quantum mechanical observer does not
necessarily present or solve any problems over and above the (admittedly difficult) issue of measurement in quantum mechanics
Measurement in quantum mechanics
The framework of quantum mechanics requires a careful definition of measurement. The issue of measurement lies at the heart of the problem of the interpretation of quantum mechanics, for which there is currently no consensus....
. The quantum mechanical observer is also intimately tied to the issue of observer effect.
A number of interpretations of quantum mechanics, notably "consciousness causes collapse", give the observer a special role, or place
constraints on who or what can be an observer. For instance, Fritjof Capra
Fritjof Capra
Fritjof Capra is an Austrian-born American physicist. He is a founding director of the Center for Ecoliteracy in Berkeley, California, and is on the faculty of Schumacher College....
writes:
"The crucial feature of atomic physics is that the human observer is not
only necessary to observe the properties of an object, but is necessary
even to define these properties. ... This can be illustrated with the
simple case of a subatomic particle. When observing such a particle, one
may choose to measure — among other quantities — the particle's
position and its momentum"
However, other authorities downplay any special role of human observers
"Of course the introduction of the observer must not be misunderstood to imply that some kind of subjective
features are to be brought into the description of nature. The observer has, rather, only the function of
registering decisions, i.e., processes in space and time, and it does not matter whether the observer is an
apparatus or a human being; but the registration, i.e., the transition from the "possible" to the "actual,"
is absolutely necessary here and cannot be omitted from the interpretation of quantum theory."
Critics of the special role of the observer also point out that observers can themselves be observed, leading to paradoxes such as that of Wigner's friend
Wigner's friend
Wigner's friend is a thought experiment proposed by the physicist Eugene Wigner; it is an extension of the Schrödinger's cat experiment designed as a point of departure for discussing the Quantum mind/body problem.- The thought experiment :...
; and that it is not clear how much consciousness is required
("Was the wave function waiting to jump for thousands of millions of years until a single-celled living creature appeared? Or did it have to wait a little longer for some highly qualified measurer - with a PhD?").