scuq.constants

scuq.constants provides a deliberately small set of physical constants as native SCUQ quantities. It does not import SciPy and does not mirror the full scipy.constants database.

Data provenance

The measured value in the initial set is pinned to the 2022 CODATA recommended values published in version 9.0 of the NIST Reference on Constants, Units, and Uncertainty (May 2024). The exact values follow the SI defining constants published by the BIPM.

The SI fixes the numerical values of c, h, e, k_B, and N_A exactly. Their SCUQ standard uncertainty is therefore zero. In contrast, the fine-structure constant alpha is measured and carries the CODATA 2022 standard uncertainty.

Shared electromagnetic uncertainty

Vacuum permeability, vacuum permittivity, and vacuum impedance are derived from the same uncertain fine-structure input:

\[\begin{split}\mu_0 &= \frac{2\alpha h}{e^2 c},\\ \epsilon_0 &= \frac{1}{\mu_0 c^2},\\ Z_0 &= \mu_0 c.\end{split}\]

They are consequently physically dependent SCUQ expressions, not three independent measurements. Calculations containing more than one of these constants retain this shared dependency during uncertainty propagation.

Example

from scuq.constants import alpha, epsilon_0, mu_0, Z_0
from scuq.ucomponents import Context

context = Context()
print(context.value_uncertainty_unit(alpha))
print(context.value_uncertainty_unit(mu_0))
print(context.value_uncertainty_unit(epsilon_0))
print(context.value_uncertainty_unit(Z_0))

The module-level constants are protected against augmented assignment and direct changes to their stored value or unit. Ordinary arithmetic remains available and returns regular scuq.quantities.Quantity expressions.

API

Curated physical constants represented as uncertainty-aware quantities.

The measured values in this module are pinned to the 2022 CODATA recommended values published in NIST Reference on Constants, Units, and Uncertainty, version 9.0 (May 2024). The exact constants use the defining values of the International System of Units (SI), 9th edition.

Only the fine-structure constant is introduced as an independent uncertain input. Vacuum permeability, vacuum permittivity, and vacuum impedance are derived from that shared input and the exact defining constants. Consequently, SCUQ retains their physical dependence during uncertainty propagation.

References

NIST

https://physics.nist.gov/constants

BIPM

https://www.bipm.org/en/measurement-units/si-defining-constants

scuq.constants.CODATA_RELEASE = '2022 CODATA recommended values'

Pinned release used for measured physical constants.

scuq.constants.CODATA_SOURCE = 'https://physics.nist.gov/constants'

Official NIST source for the pinned CODATA release.

scuq.constants.SI_DEFINITION_SOURCE = 'https://www.bipm.org/en/measurement-units/si-defining-constants'

Official BIPM source for exact SI defining constants.

class scuq.constants.PhysicalConstant(unit, value)[source]

Bases: Quantity

A Quantity protected against in-place mutation.

Physical constants participate in ordinary SCUQ arithmetic exactly like other quantities. Arithmetic returns ordinary Quantity objects, while augmented assignment and direct changes to the stored unit or value raise TypeError. This protects the module-level objects from accidental process-wide modification.

Parameters:
__init__(unit, value)[source]

Default constructor.

Parameters:

  • unit – The corresponding unit.

  • value – The value assigned

instances of ucomponents.UncertainInput as values.

__setstate__(state)[source]

Restore a pickled constant while preserving its protection.

scuq.constants.SPEED_OF_LIGHT = Quantity(m*s^(-1), 299792458.0)

Speed of light in vacuum, exactly 299 792 458 m/s in the SI.

scuq.constants.PLANCK_CONSTANT = Quantity(J*s, 6.62607015e-34)

Planck constant, exactly 6.626 070 15e-34 J s in the SI.

scuq.constants.ELEMENTARY_CHARGE = Quantity(C, 1.602176634e-19)

Elementary charge, exactly 1.602 176 634e-19 C in the SI.

scuq.constants.BOLTZMANN_CONSTANT = Quantity(J*K^(-1), 1.380649e-23)

Boltzmann constant, exactly 1.380 649e-23 J/K in the SI.

scuq.constants.AVOGADRO_CONSTANT = Quantity(mol^(-1), 6.02214076e+23)

Avogadro constant, exactly 6.022 140 76e23 1/mol in the SI.

scuq.constants.FINE_STRUCTURE_CONSTANT = Quantity(1, 0.0072973525643 +/- 1.1e-12)

Fine-structure constant with its CODATA 2022 standard uncertainty.

scuq.constants.VACUUM_MAGNETIC_PERMEABILITY = Quantity(H*m^(-1), 1.2566370612628149e-06 +/- 1.8942496682311442e-16 [NC])

Vacuum magnetic permeability derived from 2 * alpha * h / (e**2 * c).

scuq.constants.VACUUM_ELECTRIC_PERMITTIVITY = Quantity(F*m^(-1), 8.854187818840059e-12 +/- 1.3346767221268747e-21 [NC])

Vacuum electric permittivity derived from 1 / (mu_0 * c**2).

scuq.constants.VACUUM_IMPEDANCE = Quantity(u"Ω", 376.73031340987586 +/- 5.6788176410469925e-08 [NC])

Vacuum impedance derived from mu_0 * c.