B Length, Time, and Velocity -- Which are fundamental quantities?

B
Thread starter Keith Koenig
Start date Mar 5, 2022
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Fundamental Length quantities Time Velocity

AI Thread Summary

The discussion centers on the fundamental nature of length, time, and velocity in physics, questioning the traditional view that length and time are fundamental while velocity is derived. Participants explore the implications of defining velocity as a fundamental quantity, especially in the context of a hypothetical federation of planets using a common system of units. They highlight that all three quantities are interdependent, asserting that time and length lose meaning without the context provided by velocity. The conversation also touches on the arbitrariness of choosing fundamental dimensions in different unit systems, suggesting that definitions may vary based on practical considerations. Ultimately, the dialogue emphasizes the philosophical aspects of defining fundamental quantities in physics.

May 12, 2022

David Lewis

Anko said:

Will any measurement be possible of a background in which there are no comparable differences?

It doesn't matter whether you can make the measurement in practice. To exist, a physical quantity only has to be hypothetically measurable.

jbriggs444 said:

Putting an engineer's hat on, we do not care whether the meter is fundamental, and the speed of light is derived or whether the speed of light is fundamental, and the meter is derived.

If the vacuum permittivity of free space is defined as a fundamental quantity, which has some advantages, I'm sure engineers would find the system unwieldy.