How is it possible for us to see through objects (like air, water, and windows) and not through others (like wood, steel, and window blinds)?
Light is a form of electromagnetic wave energy oscillating in a particular frequency range and energy level. There are many more frequencies (and energy levels) in the spectrum of electromagnetic waves. X-rays are electromagnetic waves at a higher frequency than light. Radio waves from cell phones, radio, and Bluetooth devices are also electromagnetic waves at a lower frequency than light. We can’t see the waves that are above or below light frequencies because our eyes were not designed to see them.
We say that an object is opaque if we can’t see through it and transparent when we can see through it. When some light passes through an object, we say that it is translucent. Wood is opaque to visible-light frequencies, but it is transparent to electromagnetic waves in other frequency ranges. For that reason, we can listen to the radio or use our cell phones or wi-fi inside our houses. Our bodies are partially transparent to X-rays. That allows doctors to use X-rays to check for broken bones.
If our eyes were sensitive to radio waves and not light frequencies, we would be able to see through most solid objects. Then we would not only lose our car keys, but we would also lose our car–and our house too! The things we need to see would be invisible, and all of the electromagnetic waves around us would fill our vision with confusion.
Electromagnetic waves of different frequencies can pass through some materials but not others because of their wavelengths and the energy levels of the electrons in the atoms of the materials. So X-rays can pass through skin and muscle better than through bones. Radio waves can pass through wood, but not through steel. Light can pass through clear glass, but not wood or steel or cookie dough.
The complexity of this system allows us to see those things we need to see, like solid objects that our bodies cannot pass through. It also enables us to see through objects that we can pass through, like the air or water. It even allows us to see through objects which can protect us, like glass windows in our homes and cars. At the same time, it enables us to have cell phones, MRIs, and wireless headphones which use electromagnetic waves that can pass through objects without being seen. This very complex system took some incredible engineering by a Master Engineer.
–Roland Earnst © 2018
The Bluetooth logo consists of a combination of Harald Bluetooth’s initials H and B from the Scandinavian alphabet of his day.