Uncertainty principle
The uncertainty principle, stated by Heisenberg in 1927, says that certain pairs of properties cannot both have sharp values at the same time. Position and momentum are the standard pair: the more precisely one is fixed, the less precisely the other is. This is a property of quantum systems themselves, not a limitation of instruments, and it follows mathematically from the way quantum states are represented. Energy and time obey a related relation, which is why short-lived states do not have a precisely defined energy.
Why it matters
It puts a hard limit on what can be simultaneously true of a system, not merely on what can be known about it.
Also written: uncertainty, Heisenberg uncertainty principle
Where it comes up
Read about Uncertainty principle on Wikipedia
Sources
- Uncertainty principle English Wikipedia
- The Uncertainty Principle Stanford Encyclopedia of PhilosophySeparates the several distinct claims that travel under this one name.
- Heisenberg / Uncertainty AIP Center for History of Physics
