physical constant
Let an agent explain physical constants and their roles, relay values, uncertainties and the 2019 SI redefinition from metrology references, describe dimensionless and context-specific constants, and distinguish fundamental constants from material constants and mathematical constants.
Research draft, second pass
A second pass drafted this model: the structure a model of this thing needs, and what is known about it in the world. The line under this one says how the second half was obtained - researched against sources, or recalled without web access, in which case nothing here was read anywhere and every claim is a lead to verify. Unreviewed either way.
written by Claude from model knowledge without web access - no source was read, every claim is a lead to verify
Researched by: Claude
Purpose and description
Let an agent explain physical constants and their roles, relay values, uncertainties and the 2019 SI redefinition from metrology references, describe dimensionless and context-specific constants, and distinguish fundamental constants from material constants and mathematical constants.
A physical quantity whose value is believed to be universal and unchanging in time, such as the speed of light, the Planck constant, the elementary charge, the gravitational constant and the fine-structure constant, some dimensionless and some fixed by definition in the SI since 2019, together with derived and context-specific constants such as coupling constants, constants of motion in mechanics, the Oort constants in galactic astronomy and the ebullioscopic constant in chemistry; constants are determined by measurement and tabulated by CODATA.
What it is for: Not applicable; quantities in physics.
It can be explain the concept; relay values and uncertainties; describe kinds of constants; distinguish related notions.
Distinguishing features
Universal
Unchanging
Measured or defined
Some dimensionless
What it looks like
Not a visible object; numerical values.
Physical character
speed of light: 299792458 m/s - exact by definition
Planck constant: 6.62607015e-34 J s - exact since 2019
fine-structure constant: about 1/137.036 dimensionless
gravitational constant: 6.674e-11 m^3/(kg s^2) - measured
How it is recognised
Universal unchanging physical quantity
Speed of light, Planck constant, fine-structure constant, coupling constants, Oort constants, ebullioscopic constant
Mathematical constants such as pi are not physical; material constants depend on the substance
Related models
is a kind of - in registry terms
is a kind of - in registry terms
is tabulated by - in recommended values
defines - since 2019
In practice
Families and kinds
fundamental constants such as c, h, e, G and k
dimensionless constants such as the fine-structure constant
coupling constants of the fundamental interactions
constants of motion as conserved quantities
astronomical constants such as the Oort constants
chemical constants such as the ebullioscopic constant
Standards and regulation
CODATA recommended values
SI Brochure and the 2019 redefinition
IUPAC and IAU constant tables
Failure modes and hazards
Using outdated values
Confusing physical with mathematical or material constants
Presenting speculative variation of constants as established
Also called
Where this came from
wikidata · CC0 1.0
Drafted structure
Bundle to layer to finding to question, as the second pass will find it: 4 bundles · 8 layers · 8 findings · 16 questions.
Understand What physical constants are.
Science.
Definition
Definition.
Definition
Definition.
- What is a physical constant, and how do fundamental, dimensionless and context-specific constants differ? definition
- Is the question about a physical constant, a mathematical constant or a material property? boundary
List
Main constants.
List
List.
- What are the main constants, their symbols, values and units? measurement
- Which entry fits the specific constant? action
Measure Measurement and definition.
Science.
Determination
Determination.
Determination
Determination.
- How are constants measured, and how does CODATA combine results and uncertainties? provenance
- Which references are standard? provenance
SI
SI redefinition.
SI
SI.
- How did the 2019 redefinition fix h, e, k and the Avogadro constant, and what changed? provenance
- Which sources are cited? provenance
Apply Constants in fields.
Application.
Physics
Physics and astronomy.
Physics
Physics.
- How are coupling constants, constants of motion and the Oort constants used? provenance
- Which entry fits the specific constant? action
Chemistry
Chemistry.
Chemistry
Chemistry.
- What are the ebullioscopic and cryoscopic constants, and how are they used? provenance
- Which entry fits ebullioscopic constant? action
Context Questions and history.
Context.
Questions
Open questions.
Questions
Questions.
- Why do constants have the values they do, and is there evidence they vary, with positions attributed? provenance
- Which entry fits fine-tuned universe? action
History
History.
History
History.
- How were the major constants discovered and measured historically? provenance
- Which entry fits the history of physics? action
What the second pass must settle
- Should the fine-structure constant and coupling constant be separate primary entries?
- How should CODATA tables be linked?
- The registry entry has merged aliases naming context-specific constants and a textbook chapter; should they be split off?