Modern Definition of Time & Length Units

  • Context: Undergrad 
  • Thread starter Thread starter LeoYard
  • Start date Start date
  • Tags Tags
    Length Time Units
Click For Summary

Discussion Overview

The discussion revolves around the modern definitions of time and length units, specifically the second and the meter, as well as the practical realization of these units in everyday measurements.

Discussion Character

  • Conceptual clarification, Technical explanation

Main Points Raised

  • Some participants reference the current definitions of the second and meter as outlined in the International System of Units, noting the specific scientific criteria involved.
  • One participant suggests that the realization of these units can vary based on individual perception and practical measurement methods, such as estimating height.
  • Another participant expresses uncertainty about the specifics of how these units are physically implemented, indicating a need for clarification.
  • A later reply proposes that the original poster may be inquiring about the physical implementation of a meter or a second in practical terms.

Areas of Agreement / Disagreement

Participants generally agree on the definitions provided in part (a), but there is uncertainty and lack of consensus regarding the interpretation and implications of part (b).

Contextual Notes

There is ambiguity in the phrasing of part (b), which may lead to different interpretations of how time and length units are realized in practice. The discussion does not resolve these interpretations.

Who May Find This Useful

This discussion may be useful for individuals interested in the definitions and practical applications of measurement units in physics and everyday life.

LeoYard
Messages
16
Reaction score
0
a) What is the modern definition of the time unit and the length unit?

b) How people actually Materially realize these units ?


(a) in the wiki, it reads:

Second:
Under the International System of Units, the second is currently defined as the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom.[1] This definition refers to a caesium atom at rest at a temperature of 0 K (absolute zero). The ground state is defined at zero magnetic field.

Meter: Today, it is defined as 1⁄299 792 458 of a light-second.

Would anybody like to answer question (b) ?
 
Physics news on Phys.org
I think in question b you are asking how you, I, or anyone else measures time or length. How we individually realize these units varies from person to person. I can look at a person and say oh, he is 6 feet tall. He is not actually exactly 6 feet tall, but i think he is around that height. I hope that answers your question.
 
Wiki has it correct for part (a).

I'm not quite sure what you are asking in part (b).
 
perhaps the OP is wondering how we actually physically implement a meter, or a second.
 

Similar threads

Undergrad Replacing the Measurement standards (SI units)
  • · Replies 58 ·
2
Replies
58
Views
10K
Undergrad Why do we still use seconds and meters as SI base units?
  • · Replies 2 ·
Replies
2
Views
4K
High School Discrete definitions of Physics Standard Units
  • · Replies 5 ·
Replies
5
Views
3K
Undergrad Trouble understanding the SI definition of 1 second
  • · Replies 56 ·
2
Replies
56
Views
7K
Undergrad Time Measurement in Extremely Curved Space Regions
  • · Replies 95 ·
4
Replies
95
Views
8K
Graduate How is the wavelength of emitted EM radiation measured?
  • · Replies 14 ·
Replies
14
Views
2K
Graduate When and Why Was the Definition of the Meter Changed?
  • · Replies 101 ·
4
Replies
101
Views
13K
Graduate Why can't we define a kg as a multiple of the electron mass
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Why Are Standards Definitions So Complicated?
  • · Replies 21 ·
Replies
21
Views
4K
Undergrad Permittivity/Permeability, the speed of light, and the meter
  • · Replies 12 ·
Replies
12
Views
4K