The physics that lets you forget your glasses are on your face | Explained Premium

Explore the mysteries of glass and its transparency with an assistant professor at IIT Kanpur.

When I am already getting late for my morning lecture, here at IIT Kanpur where I teach, that is the exact moment my spectacles choose to play hide-and-seek with me. Not in the kitchen nor near the washing machine; neither on the study table nor in the almirah. I struggled through every item on my bed: the winter blanket, the wet towel, and the wordy non-fiction book that helps me fall asleep last night, but to no avail.

As I debated myself if things really could disappear into thin air and, in frustration, placed my hand on my face, I realised the spectacles had been wearing me the whole time.

My students blamed me for the delay in starting the lecture that day, but the real problem lay with the glass – something that’s everywhere but is barely visible anywhere.

We are surrounded by glasses. More than half of us wear one at some point in our lives. You are probably reading this on a device whose screen is made of glass. Mirrors, windows, tables, bulbs, and probably the thing you use to drink water – they are all made of glass.

A transparent, shiny object that breaks easily, yet which all of us seem to be obsessed with. There are many mysteries about glass that physicists still struggle to answer. Glass is one of the more magical materials around us. It gives us the illusion of being in an open space even when we are not.

Imagine you are in a car with no glass windows but ones made of a steel frame. Would you still go for that long drive? Most solid things around us are opaque (including ourselves): light cannot pass through them. But glass is different: it feels like a solid and behaves like a solid – but is at the same time transparent to light.

How is it that we can see through glass?