Why Can't We Measure Time in Length Units: The Case for Keeping Separate Units for Time and Distance

In everyday communication, it is crucial to use agreed-upon units of measurement for effective understanding. Although it is possible to call units of measurement anything we want, adhering to conventional standards ensures clear and accurate communication.

Dimensions of Measurement: Time vs. Length

Time and length, or distance, are fundamentally different dimensions, and thus, they require distinct units of measurement to describe them accurately. Attempting to unite these dimensions would complicate measurement and lead to confusion. Historically, units of measurement have evolved to reflect these differences, ensuring precision and clarity in various contexts.

A Historical Angle: Variations in Measurement Units

The standardization of units for different dimensions was not always the case. For instance, in one of the cgs (centimeter-gram-second) system variants, capacitance was denoted in centimeters instead of farads. One centimeter represented the capacitance of a sphere with a radius of 1 centimeter, approximately 1.113 picofarads. Such variations highlight the importance of consistent and widely accepted units in scientific and practical applications.

Practical Examples of Time and Distance Equivalencies

While time and distance measurements are inherently dimensional, there are contexts where the use of time for indicating distance can be practically useful. For example, hiking associations often announce the length of a walk in terms of expected travel time. This can be advantageous for hikers, as it provides a more intuitive understanding of the effort required. Similarly, the distance between cities can sometimes be described using travel time instead of miles or kilometers, which can be easier to grasp for travelers.

Connecting Time and Distance: The Speed of Light

A fundamental conversion constant that can link time and distance is the speed of light. The light-second, light-minute, and other units related to light travel distances provide an interesting link between these dimensions. The light-second is defined as the distance light travels in vacuum during one second, which is approximately 299,792.458 kilometers.

This conversion can be further scaled down for practical use. For example, a light-nanosecond is about 299.792458 millimeters, or approximately 30 centimeters. While this concept is fascinating, the practical challenges arise when considering the scale. Reasonable human-scale times translate to quite large distances, making the units unwieldy. One second, for instance, is comparable to the distance a car travels from new until it is junked, whereas reasonable human-scale lengths correspond to unnoticeably brief intervals.

The Importance of Separate Units for Time and Distance

Despite the theoretical possibility of unit conversions, separating time and distance into distinct units remains the most practical approach. Devices for measuring time do not operate the same way as devices for measuring distance. Although the readouts can be scaled from one to the other, maintaining separate dimensions simplifies measurement and avoids confusion.

In conclusion, while time and distance can be linked through fundamental constants like the speed of light, the practical benefits of keeping them as separate units outweigh the theoretical advantages. Standard units for different dimensions ensure clarity and precision in scientific and everyday contexts.