zeptometers

A zeptometer (symbol zm) is a unit of length in the International System of Units (SI). It denotes 10^-21 meters. The prefix zepto- means one sextillionth, so a zeptometer is one thousandth of an attometer (10^-18 meters). The next smaller prefix is yocto- (10^-24 meters).

Zeptometers are used primarily in physics to describe scales far smaller than atomic and nuclear dimensions. They arise in discussions of subnuclear distances and in theoretical models or high-energy processes where the relevant length scales are well below a femtometer. For reference, typical nuclear sizes are on the order of 1 to a few tens of femtometers (10^-15 meters), which is many orders of magnitude larger than a zeptometer.

In practice, measurements at the zeptometer scale are extraordinarily challenging. Experimental results at these scales are usually interpreted through indirect methods that relate energy, momentum transfer, or scattering observables to spatial scales, rather than through direct ruler-like measurements.

Related SI prefixes include the adjacent attometer (10^-18 m) and yoctometer (10^-24 m). The zeptometer thus sits in a range far beyond everyday measurement and is most commonly encountered in theoretical discussions or specialized high-energy physics contexts.