Although the conductivity of free space is indeed zero, electromagnetic waves can still propagate through it due to the presence of electric and magnetic fields. The propagation of electromagnetic waves is governed by Maxwell's equations, which describe the behavior of electric and magnetic fields and their interactions.
Maxwell's equations consist of four fundamental equations:
Gauss's Law for Electric Fields: This equation relates the electric flux through a closed surface to the charge enclosed by that surface. It states that the divergence of the electric field is proportional to the charge density.
Gauss's Law for Magnetic Fields: This equation states that the magnetic field does not have any isolated magnetic charges (monopoles). The magnetic flux through any closed surface is always zero.
Faraday's Law of Electromagnetic Induction: This equation describes how a changing magnetic field induces an electric field. It states that the curl of the electric field is proportional to the rate of change of the magnetic field.
Ampère's Law with Maxwell's Addition: This equation relates the circulation of the magnetic field around a closed loop to the electric current flowing through that loop and the rate of change of the electric field. Maxwell's addition includes the displacement current term, which accounts for the fact that a changing electric field can create a magnetic field.
When these equations are solved, they yield wave solutions known as electromagnetic waves. In free space, where there are no charges or currents, these equations simplify and lead to the existence of electromagnetic waves propagating with a constant speed, known as the speed of light. This speed is approximately 299,792,458 meters per second (or about 186,282 miles per second) in a vacuum.
In summary, even though free space has zero conductivity, the interaction between the electric and magnetic fields allows for the self-sustaining propagation of electromagnetic waves. These waves do not rely on the movement of charges to propagate, making them capable of traveling through empty space.