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Heisenberg uncertainty principle
Intermediate
Position and momentum cannot both be known precisely.
ΔxΔp ≥ ħ/2The position and momentum cannot both be sharply defined: ΔxΔp ≥ ħ/2. It's a fundamental limit from the wave nature of matter.
An electron confined to 0.1 nm has Δp ≥ 5×10⁻²⁵ kg·m/s, speed spread about 10⁶ m/s.
Not due to measurement disturbance alone.
In more detail
The Heisenberg uncertainty principle states that the product of uncertainties in position and momentum is at least ħ/2. It is a fundamental limit on what can be known about a particle, not just a measurement error.
Real-world uses
- The uncertainty principle explains why atoms do not collapse.
- It sets limits on the sensitivity of precision measurements.
- Engineers designing electron microscopes and atomic clocks face limits on how precisely position and momentum can be known together.
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Frequently asked questions
Is it just a measurement problem?
No. It is a property of quantum systems, not only of how we measure them.
Does it apply to everyday objects?
Yes, but the uncertainties are too tiny to notice.
Does uncertainty mean the measurement is bad?
No. It is a property of quantum systems, not a flaw in the measurement.
Related topics in Quantum Mechanics
Davisson–Germer experiment · Wave–particle duality · Double slit with electrons · Energy–time uncertainty · Wavefunction · Born rule