Last Updated：2025/11/23
(physics, philosophy) The hypothetical observer in a thought experiment in which Wigner, absent when his friend observes the state of a particle (in some versions, Schrödinger's cat) as it collapses from quantum superposition, concludes that both the particle and his friend remain in quantum superposition until Wigner himself learns the result of the observation.
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Wigner's friend
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Source Word
Wigner's friend
Proper noun
(physics,
philosophy)
The
hypothetical
observer
in
a
thought
experiment
in
which
Wigner,
absent
when
his
friend
observes
the
state
of
a
particle
(in
some
versions,
Schrödinger's
cat)
as
it
collapses
from
quantum
superposition,
concludes
that
both
the
particle
and
his
friend
remain
in
quantum
superposition
until
Wigner
himself
learns
the
result
of
the
observation.
Japanese Meaning
（物理学・哲学の文脈）ウィグナーの友人とは、ウィグナーが不在の間に彼の友人が粒子（またはシュレディンガーの猫）の状態を観測するという思考実験における仮想の観測者であり、ウィグナーが観測結果を知らない限り、観測された対象（粒子や友人）が量子重ね合わせ状態にあると解釈される状況を示す概念です。
Sense（1）
(physics,
philosophy)
The
hypothetical
observer
in
a
thought
experiment
in
which
Wigner,
absent
when
his
friend
observes
the
state
of
a
particle
(in
some
versions,
Schrödinger's
cat)
as
it
collapses
from
quantum
superposition,
concludes
that
both
the
particle
and
his
friend
remain
in
quantum
superposition
until
Wigner
himself
learns
the
result
of
the
observation.
