Can you spot the quantum physics around your house? Premium

The electrons in metallic objects have an effective temperature of tens of thousands of degrees celsius because of the Fermi energy, a concept that illustrates how much quantum physics controls the properties of everyday objects in our homes.

“Sir, what is this Fermi energy? I can’t find a reasonable explanation. Which electrons have this energy and why?”

A visibly annoyed Hardik, one of my students, asked this as I started my class the other day. Hardik is one of a few undergraduate students taking a physics department elective course in IIT Kanpur, where I teach. 

That copper, a garden-variety material that runs through the network of wires in our homes and lines the bottom of a few cooking utensils, has electrons at effectively at least 50,000° C was as surprising as it was worrisome for the students. And my insistent logic to prove this by assertion was not helping.

Forty-five degree celsius is already hot enough for the humans of Kanpur to curse at passersby. To imagine we are carrying “50,000-degree electrons” in our pockets should be difficult to contemplate. Water boils at 100° C; aluminium melts at 600° C, and 5,000° C is around the surface temperature of the sun. How then can we make sense of 50,000° C, that too inside everyday objects?

I could see why my students were upset.

Quantum physics is often understood to be the physics of things that can both be ‘located and absent’ at a place, things that tunnel through walls, and things that can act across very large distances in an instant. But this is also a romantic conception that takes for granted, and thus overlooks, quantum physics’s role in shaping the fascinating properties of the objects in our daily lives. Indeed, it offers a host of counterintuitive principles to grapple with, but it also makes some of the most quantitatively accurate predictions that we can actually test.

Take the Fermi energy of electrons in copper, for example. Quantum physics tells us that electrons are not particles like the little marbles that we play with. Instead, they are treated as waves, like the ones you see on a surface of water or that you create when you pluck a guitar string.