observable
American-
A measurable property of a physical system, such as mass or momentum. In quantum mechanics, observables correspond to mathematical operators used in the calculation of measurable quantities. Operators that do not commute, having a nonzero commutator, correspond to observables that cannot be precisely measured at the same time, such as momentum and position.
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See also uncertainty principle
Other Word Forms
Etymology
Origin of observable
1600–10; < Latin observābilis remarkable, equivalent to observā ( re ) to observe + -bilis -ble
Explanation
Something observable can be perceived or detected — you can see it, hear it, or otherwise sense that it's there. An observable change in the temperature outdoors will make you run back in for your hat and gloves. If an observable hush falls over the dining room when your grandfather clears his throat, it's something that everyone notices. Observable differences between you and your twin sister might include different haircuts and the fact that you wear glasses but she doesn't. Observable things can be sensed (perceived with one of your five senses) or intuited.
Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
It is smaller than the width of a human hair by about the same factor that a human hair is smaller than the observable universe.
From The Wall Street Journal ● Oct. 23, 2026
Based on data gathered so far, scientists estimate that only about 1% of young stars display observable signs of this stage.
From Science Daily ● Oct. 7, 2026
"Vacuum fluctuations in free space are generally too weak to produce observable effects in macroscopic condensed-matter systems," said Prof. Zeng.
From Science Daily ● Oct. 3, 2026
Zhavoronkov said rentosertib has shown promising results in improving lung function and biological age, with the latter effect observable in the brain and other organs.
From The Wall Street Journal ● Sep. 7, 2026
By comparison, the total number of atoms in your body is about 1028, and the total number of elementary particles—protons and neutrons and electrons—in the observable universe is about 1080.
From "Cosmos" by Carl Sagan
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