epsilon_0          = 8.85418782e-12 # Permittivity of free space
mu_0               = 1.25663706e-6  # Permeability of free space
speed_of_light     = 2.99792458e8   # Speed of light in vacuum
elementary_charge  = 1.60217663e-19 # Elementary charge
mass_electron      = 9.10938371e-31 # Electron mass
mass_proton        = 1.67262193e-27 # Proton mass
boltzmann_constant = 1.380649e-23  # Boltzmann constant