Video-calls in public are mathematically rude
The physics that makes video-calls fundamentally annoying
Back in 2010, during the Apple’s reveal of iPhone 4, Steve Jobs proudly presented FaceTime as the new way of talking to each other, which seemed to come straight from the future. Yet more than 15 years later, video calls are not exactly as common as he must have expected, even though they are much more common than I wish they were.
The problem with video calls is that they create a bad user experience for pretty much everyone within a 3-5 meter radius, unless the perfect conditions are met – people on both ends of the call are in quiet private spaces with no people around them. Otherwise, someone for sure will be disturbed, even if they don’t explicitly show it.
There is a straightforward mathematical mechanism that makes video calls more annoying than other types of communication, such as texting or audio calls.
In the following, I’ll explain exactly how it works.
Building blocks of a Video call
A video call relies on the following four components:
a camera 📷 – to record your image;
a screen 📱 – to show you the person you’re talking to;
a microphone 🎤 – to record your voice;
a speaker 🔈 – to hear the voice of the other person.
To make the illustration more simple, let’s consider just a bare phone, without any earphones, since that’s how the most annoying video calls are made. That’s what I observe regularly in regional trains and public transport in Italy, Switzerland and the UK. Things are a little different with earphones, but just a little. I might discuss those aspects in another post in the future.
Video vs Audio
There is a fundamental difference between the video and audio components of a video call, and this difference is what defines the level of discomfort that a video call creates.
▶ Video is transmitted by photons of light that travel in straight lines and get absorbed as soon as they hit any surface. So when you’re watching a video, it can hardly disturb anyone else, unless you’re watching it at extreme brightness in a dark place. And even in that case they can simply turn their head away and isolate themselves from the light if it disturbs them.
▶ Audio, on the other hand, travels in all directions, like concentric circles around you, and gets reflected from hard surfaces, bouncing back and forth many times, traveling at much longer distances. Therefore, audio is able to disturb way more people around you than video. And unlike photons, sound waves have long enough wavelength to propagate through materials, so it’s almost impossible to completely isolate yourself from unwanted sounds, even when you close your ears. The best you can do is reduce its intensity by moving further away from it or putting something soundproof into your ears. Both require much more effort than simply turning your head away from someone’s screen.
This is why being mindful of the acoustic noise that you create is so important. Unless you actually want to be rude to the people around, of course.
The inverse-square law
The thing that makes video calls fundamentally annoying is the way sound behaves. Like I said earlier, it propagates as concentric waves in all directions. Since we live in 3D space, all directions means that the wavefront of the sound emitted by your phone has a shape of a sphere that is expanding from its centre.
According to the law of conservation of energy, as that sphere is expanding, the original energy of the soundwave gets stretched over its surface, making the amplitude of the sound smaller as it expands. This is why sound gets quieter as you move away from the source. But the crucial detail is that this decrease of loudness is not linear. It’s quadratic, speaking in mathematical terms. And here is why…
If you studied geometry at school, you might remember the formula for the surface area of a sphere:
