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The importance of being fundamental

Nature Physics volume 18, page 474 (2022)Cite this article

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A task group recommends values for many constants in fundamental theories of physics and chemistry. Eite Tiesinga and Peter Mohr tell some of the constants’ stories.

Another important constant is the Planck constant h and the related reduced Planck constant ħ. The Planck constant encapsulates the quantum aspects of nature and sets a fundamental limit on the accuracy with which both the position and momentum of an object can be measured. Its smallness, approximately 6.6 × 10−34 J Hz−1 in units of the international system of units (SI), reflects how tiny quantum effects are in our everyday world — they mainly appear at the atomic scale. Early in the twentieth century, h was determined by Max Planck to elucidate black-body radiation and later used by Albert Einstein to describe the photoelectric effect. It relates the energy of a quantum or photon of light to its frequency or colour. Since the redefinition of the SI in 2018, the Planck constant has been taken to be exact and helps define standard units.

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  1. Joint Quantum Institute, College Park, MD, USA

    Eite Tiesinga

  2. National Institute of Standards and Technology, Gaithersburg, MD, USA

    Eite Tiesinga & Peter Mohr

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  1. Eite Tiesinga
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  2. Peter Mohr
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Correspondence to Eite Tiesinga or Peter Mohr.

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Tiesinga, E., Mohr, P. The importance of being fundamental. Nat. Phys. 18, 474 (2022). https://doi.org/10.1038/s41567-022-01560-9

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