Physics Databases

Overview

Access physical constants and reference data from authoritative databases. Never hardcode physical constants — always query from scipy.constants (CODATA 2018) or NIST APIs.

CRITICAL: Always Use Database Values

• NEVER type physical constants from memory
• ALWAYS use scipy.constants or NIST lookup
• Constants change between CODATA editions (e.g., 2014 → 2018 → 2022)

Core Workflows

1. CODATA Physical Constants (scipy.constants)

from scipy import constants as const

# Fundamental constants
print("=== Fundamental Constants (CODATA 2018) ===")
print(f"Speed of light:       c  = {const.c:.10e} m/s")
print(f"Planck constant:      h  = {const.h:.10e} J·s")
print(f"Reduced Planck:       ℏ  = {const.hbar:.10e} J·s")
print(f"Boltzmann constant:   k  = {const.k:.10e} J/K")
print(f"Gravitational const:  G  = {const.G:.10e} m³/(kg·s²)")
print(f"Elementary charge:    e  = {const.e:.10e} C")
print(f"Electron mass:        mₑ = {const.m_e:.10e} kg")
print(f"Proton mass:          mₚ = {const.m_p:.10e} kg")
print(f"Neutron mass:         mₙ = {const.m_n:.10e} kg")
print(f"Vacuum permittivity:  ε₀ = {const.epsilon_0:.10e} F/m")
print(f"Vacuum permeability:  μ₀ = {const.mu_0:.10e} H/m")
print(f"Avogadro number:      Nₐ = {const.N_A:.10e} mol⁻¹")
print(f"Gas constant:         R  = {const.R:.10e} J/(mol·K)")
print(f"Stefan-Boltzmann:     σ  = {const.sigma:.10e} W/(m²·K⁴)")
print(f"Fine structure:       α  = {const.fine_structure:.10e}")
print(f"Rydberg constant:     R∞ = {const.Rydberg:.10e} m⁻¹")
print(f"Bohr radius:          a₀ = {const.physical_constants['Bohr radius'][0]:.10e} m")
print(f"Standard gravity:     g  = {const.g:.6f} m/s²")
print(f"Standard atmosphere:  atm= {const.atm:.2f} Pa")

2. Unit Conversions

# Energy conversions
print("\n=== Energy Conversions ===")
print(f"1 eV  = {const.eV:.10e} J")
print(f"1 cal = {const.calorie:.6f} J")
print(f"1 BTU = {const.Btu:.6f} J")
print(f"1 erg = {const.erg:.10e} J")

# Length conversions
print("\n=== Length Conversions ===")
print(f"1 Å   = {const.angstrom:.10e} m")
print(f"1 au  = {const.au:.6e} m")  # astronomical unit
print(f"1 ly  = {const.light_year:.6e} m")
print(f"1 pc  = {const.parsec:.6e} m")

# Temperature
print(f"\n0°C = {const.zero_Celsius:.2f} K")

# Pressure
print(f"\n1 atm = {const.atm:.2f} Pa")
print(f"1 bar = {const.bar:.2f} Pa")
print(f"1 torr = {const.torr:.6f} Pa")

3. Look Up Any CODATA Constant

# Search by name
def find_constant(keyword):
    """Search CODATA constants by keyword."""
    results = []
    for name, (value, unit, uncertainty) in const.physical_constants.items():
        if keyword.lower() in name.lower():
            results.append((name, value, unit, uncertainty))
            print(f"  {name}")
            print(f"    = {value:.10e} {unit}")
            print(f"    ± {uncertainty:.4e}")
    return results

print("Searching for 'Bohr':")
find_constant("Bohr")

print("\nSearching for 'magnetic moment':")
find_constant("magnetic moment")

4. Materials Project API

# pip install mp-api
# Requires API key: https://materialsproject.org/api

def query_materials_project(formula, api_key=None):
    """
    Query Materials Project for material properties.
    Set MP_API_KEY environment variable or pass api_key.
    """
    try:
        from mp_api.client import MPRester
        import os

        key = api_key or os.environ.get('MP_API_KEY')
        if not key:
            print("Set MP_API_KEY environment variable")
            return None

        with MPRester(key) as mpr:
            docs = mpr.summary.search(formula=[formula])
            for doc in docs[:5]:
                print(f"  {doc.material_id}: {doc.formula_pretty}")
                print(f"    Space group: {doc.symmetry.symbol}")
                print(f"    Energy above hull: {doc.energy_above_hull:.4f} eV/atom")
                print(f"    Band gap: {doc.band_gap:.3f} eV")
                print(f"    Density: {doc.density:.3f} g/cm³")
            return docs
    except ImportError:
        print("Install mp-api: pip install mp-api")
        return None

# Example: query_materials_project("Si")

5. Particle Data Group (PDG)

# Key particle properties (from PDG 2024)
# These are reference values — for precision work, check pdg.lbl.gov

particles = {
    'electron': {
        'mass_MeV': 0.51099895,
        'charge': -1,
        'spin': 0.5,
        'lifetime': 'stable',
    },
    'proton': {
        'mass_MeV': 938.27208816,
        'charge': +1,
        'spin': 0.5,
        'lifetime': 'stable (> 10^34 years)',
    },
    'neutron': {
        'mass_MeV': 939.56542052,
        'charge': 0,
        'spin': 0.5,
        'lifetime_s': 878.4,  # ~14.6 minutes
    },
    'muon': {
        'mass_MeV': 105.6583755,
        'charge': -1,
        'spin': 0.5,
        'lifetime_s': 2.1969811e-6,
    },
    'pion_charged': {
        'mass_MeV': 139.57039,
        'charge': +1,
        'spin': 0,
        'lifetime_s': 2.6033e-8,
    },
    'W_boson': {
        'mass_GeV': 80.3692,
        'charge': +1,
        'spin': 1,
    },
    'Z_boson': {
        'mass_GeV': 91.1876,
        'charge': 0,
        'spin': 1,
    },
    'Higgs': {
        'mass_GeV': 125.20,
        'charge': 0,
        'spin': 0,
    },
}

# Always cite: "Particle Data Group, Phys. Rev. D 110, 030001 (2024)"
# For precision values: https://pdg.lbl.gov

6. Astronomical Constants

# Solar system data (IAU 2015 values)
print("\n=== Astronomical Constants ===")
print(f"Solar mass:    M☉ = 1.98892e30 kg")
print(f"Solar radius:  R☉ = 6.9634e8 m")
print(f"Solar luminosity: L☉ = 3.828e26 W")
print(f"Earth mass:    M⊕ = 5.9722e24 kg")
print(f"Earth radius:  R⊕ = 6.3781e6 m")
print(f"Moon mass:     M☾ = 7.342e22 kg")
print(f"AU:            1 AU = {const.au:.6e} m")

# For precise values, use astropy:
# from astropy import constants as astro_const
# print(astro_const.M_sun)

Quick Reference

Constant	Symbol	Value	scipy.constants
Speed of light	c	2.998×10⁸ m/s	const.c
Planck	h	6.626×10⁻³⁴ J·s	const.h
Boltzmann	k_B	1.381×10⁻²³ J/K	const.k
Gravitational	G	6.674×10⁻¹¹ m³/(kg·s²)	const.G
Elementary charge	e	1.602×10⁻¹⁹ C	const.e
Electron mass	m_e	9.109×10⁻³¹ kg	const.m_e
Proton mass	m_p	1.673×10⁻²⁷ kg	const.m_p
Avogadro	N_A	6.022×10²³ mol⁻¹	const.N_A
Gas constant	R	8.314 J/(mol·K)	const.R
1 eV	—	1.602×10⁻¹⁹ J	const.eV
1 Å	—	1.0×10⁻¹⁰ m	const.angstrom

Tips

1. Always from scipy import constants as const — never type values manually
2. Check units: const.physical_constants['Bohr radius'] returns (value, unit, uncertainty)
3. For astrophysics: use astropy.constants for additional astronomical constants
4. For materials: use mp-api to query the Materials Project database
5. Cite your source: "CODATA 2018 via scipy.constants" or "PDG 2024"