## October 15th: Weak

There are four forces that govern the Universe: Gravitation, that acts on mass/energy; Electromagnetic force, that bounds together atoms and molecules and dictates the law of light; Strong Interaction, that makes atomic nuclei and hadrons; * Weak *Interaction, that describes beta decay and the life of sub-atomic particles called left-handed fermions.

The last sentence might have given it away: one of the four fundamental forces of nature was theorised and described by Enrico Fermi.

Fermi left many contributions to theoretical physics: for example, he demonstrated self-sustained nuclear fission, he worked with Paul Dirac to define the statistic of electrons (and in general of fermions), he described the probability of quantum decay from an isolated quantum state to another (the Golden Rule).

But most importantly he changed the way we do physics. He was not only a theoretical physicist: he was practical and stayed comfortably behind a console. He gave the name to back-of-envelope calculations –sometimes called Fermi’s problem– quick estimations essential to applied physics and engineering to check that the dimensions for a specific application have the right units and fall in the expected bulk number.

More importantly for me, as an Italian, he reformed the way physics was studied in Italy. Physics in Italy became so important and relevant as it is today thanks to Fermi, Segre’, Amaldi, Majorana and all the other great minds of “via Panisperna”.

If you are not totally hooked on Fermi and his achievement, there is also the fact that half the sci-fi literature out there is based on Fermi’s Paradox, the contradiction between the high probability of extraterrestrial life and no encounter recorded to date. He made the math to demonstrate why it is weird that we haven’t yet met any other civilised forms of life out there. If you like sci-fi, maybe you should read a bit more Fermi.

If you wondering what’s going on here, I explained it on this blog post: Inking Science