How do Electromagnetic Waves Travel

The reason why you are able to read this page right now is that the light receptors in your retina are receiving the visible waves from the electromagnetic spectrum that are traveling from the screen towards your eyes and your brain is interpreting the electrical signals generated as a result of it.

Nothing can travel faster than electromagnetic waves and they are the fastest information and energy carrying mechanism in the universe. If you are flummoxed about how light from galaxies, billions and billions of kilometers away, reaches us, keep reading ahead. I unravel the underlying mechanism which makes the travel of light possible.

Unlike sound waves which require a material medium to travel, electromagnetic waves can travel through vacuum, as they are manifestations of pure electromagnetic energy.

Every wave is transverse with two mutually perpendicular components. These two components are the electric field (E) and magnetic field (E) that oscillate in a direction, which is perpendicular to the direction of wave travel.

Every light wave transports energy and has momentum. The energy carried by the wave is dependent on its frequency (number of waves passing per second). The electromagnetic spectrum is made up of waves of different frequencies, ranging from low-frequency radio waves, microwaves, infrared, visible, high energy x-rays, to gamma rays.

To fully comprehend what makes light waves travel, you must study the Maxwell's equations of electromagnetism. Where there is a charge, there is an electric field pervading space around it. Whenever such a charge or charged object oscillates or accelerates, the electric field associated with it, changes.

It is a fact of observation that every changing electric field or conductor with increasing amount of electric current coursing through it, gives rise to a changing magnetic field. A changing magnetic field in turn gives rise to a changing electric field.

Imagine this process of an oscillating electric field giving rise to a magnetic field and an oscillating magnetic field giving rise to another electric field continuing ad infinitum in space and time, and what you get is an electromagnetic wave. That is how light travels and that is how we can see objects around us.

Depending on the frequency of oscillation of the initial electric field, electromagnetic disturbances of varying frequencies and energies are created. All such waves travel at a constant velocity in vacuum. Electronics is devoted to creation of transmitter circuits which can create waves of specific frequencies.

The transmitter in your cell phone creates an oscillating electric field of high frequency which acts as the precursor that gives rise to electromagnetic waves being propagated in space.

All space around you is filled with changing electric fields. Even the electrons traveling through your brain and nervous system create weak electromagnetic signals which can be actually measured. We are surrounded by 'electromagnetic music' of sorts, of varying frequencies.

So the key thing to remember here is the fact that a changing electric field creates a magnetic field and a changing magnetic field gives rise to an electric field. These two phenomena, described by Maxwell's equations of electromagnetism, make the passage of electromagnetic waves across space possible, with no need for a material medium.

One could perceive the waves as disturbances in the all-pervading electromagnetic field, traveling at a constant speed of 2.99792458 x 10⁸ m/s. To completely understand the beautiful mechanism of electromagnetic radiation and its propagation, you must study Maxwell's theory. A recommended book to start exploring this subject further is part II of the 'Feynman Lectures on Physics'.