Have you ever wondered how your maps app knows your exact location? Or how you can place calls? Or how that beautiful thumbnail picture was taken? Let’s assume you have pondered on any one of those questions at some point in time. With that assumption, let’s answer all those hows that keep you awake at midnight with a simple Physics concept: Radio waves.
Radio waves are simply Electromagnetic (EM.) waves that have a longer wavelength and lower frequency than visible light, keeping us from detecting them with our eyes. So why are these useful? You may ask. These waves carry the least energy in the EM. spectrum and interact very weakly with matter, allowing them to travel long distances. Their long wavelength also contributes to the long propagation.
Some of the most precise and important measurements in scientific history have been made by the use of radio waves. Let’s start with the smallest but the base of all our understanding: the measurement of time. One second is defined using the microwave (a subset of Radio) frequency associated with a hyperfine transition in the caesium-133 atom. When exposed to radiation at this frequency, the atom undergoes transitions between two energy states, providing an extremely accurate time reference.
Due to their ability to travel over long distances, these waves can give us information about stars billions of kilometers away. Pulsars are types of Neutron stars that rotate rapidly (hundreds to thousands of times in a second), continuously emitting radiation. As these beams sweep past Earth, the periodic pulses allow astronomers to measure the pulsar’s rotation period with high precision. When we observe the radio-frequency part of these emissions, the rotation speed and periods of the pulsar can be determined with high precision.
Along with that, since they are almost unfettered by dust, radio waves can produce beautiful pictures of objects far away that are obscured by a lot of dust. One such picture is the thumbnail of this article: a picture of our Milky Way galaxy.
Want to know how your maps app knows exactly where you are and how this “GPS” thing works? Radio waves yet again. Four Satellites continuously send out signals to your phone. When your phone receives them, it calculates the time delay in receiving the signal from each of them and this tells us how far away each satellite is. Using that information, it becomes possible to home in on your location.
Your phone also operates on radio waves. A phone call is simply information encoded on a Radio-frequency EM. wave. These waves travel long distances, diffract around obstacles, and reach your friend’s phone at almost the speed of light. Heroic, isn’t it?
Remember that these waves are extremely weak in energy? Well that makes it a bit problematic to detect them. As they’re EM. waves and all electric fields and magnetic fields (more contribution from electric here) induce current in circuits, the detectors measure and amplify this induced current and then filter using frequency bandpass filters to isolate the signal’s frequency range. Along with that, due to their long wavelengths, Radio telescopes are made massive so they can achieve good angular resolution and better signal collection.
In a world where technology makes miracles happen, it still remains astonishing that we are able to detect waves that go around almost anything, whose photons have less energy than electrons at room temperature, and which can give us pictures of our galaxy itself. So, next time you look at your phone, remember all the impeccably beautiful Radio Physics that makes it work.
