Robertson uncertainty relation
A commutator constrains two outcome spreads in the same state.
Key knowledge
For self-adjoint observables A and B in a normalized state, with the products and finite variances defined, ΔA ΔB ≥ ½|⟨[A,B]⟩|, where [A,B] = AB − BA.
Values and equations
ΔA ΔB ≥ ½|⟨[A,B]⟩|; [A,B] = AB − BA
- A, B
- Self-adjoint observables with their respective physical units
- ΔA, ΔB
- Standard deviations in the same normalized state
- ⟨[A,B]⟩
- Commutator expectation; unit [A][B]
Conditions and scope
- Finite-dimensional Hermitian matrices satisfy the domain requirement; unbounded operators need a suitable common domain for AB and BA.
- This bounds ensemble spreads in one state; it is not a general measurement-error versus disturbance formula.
Sources · 1
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
Evidence and review
Section 10.4 displayed inequality and Cauchy–Schwarz argument.
2026-10-10 · State-spread Robertson bound only; the source's unrestricted wave-function domain shorthand is narrowed.
Entry details
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- physics-robertson-uncertainty
- Revision
- university-reference.1
- Structured reference record
- University reference · University core expansion