Example image of eyePlorer eyePlorer map for 'Free space': Classical physics Maxwell's equations Vacuum Ampere International System of Units Metre Absolute zero Speed of light Vacuum permeability Vacuum permittivity Electromagnetic force Farad Fine-structure constant Henry Newton (unit) Electromagnetic radiation Electromagnetic spectrum Radio waves Visible spectrum Impedance of free space Ohms Superposition principle Vacuum state Casimir effect Lamb shift Spontaneous emission Symmetry breaking Higgs mechanism QCD vacuum Precision tests of QED Reduction to practice Operational definition Ultra high vacuum Outer space Pascal (unit) Atmosphere (unit) Cosmic dust Cosmic noise Density Matter Cosmic microwave background radiation Interplanetary medium Interstellar medium Free-space optical communication United States Patent and Trademark Office Mathematical descriptions of the electromagnetic field Permeability (electromagnetism) Permittivity Sinusoidal plane-wave solutions of the electromagnetic wave equation Free-space path loss