You cannot simultaneously know a particle's position and momentum to arbitrary precision.
Try this
1
Δx · Δp ≥ ℏ/2 — pin down position and momentum gets fuzzier = minimum Δp ≈ 5.27e-26 kg·m/s
Heisenberg's uncertainty principle
ℏ ≈ 1.055 × 10⁻³⁴ J·s. Squeeze Δx towards zero and Δp must blow up to keep the product above ℏ/2.
This isn't about clumsy instruments. A particle simply doesn't *have* a perfectly sharp position and momentum at the same time — the limit is built into the quantum description of nature.
Watch out
It's not 'measuring one disturbs the other' in a billiard-ball sense. Even an unmeasured particle has linked spreads in position and momentum; observing just forces the trade-off into the open.
Uncertainty principle
It's not a measurement limitation — it's a property of the universe.