The physics version of chicken-egg problem is fields vs particles.

Is the universe made of fields or particles? 🧵

To understand the concept of fields, we go back to its origin -- magnets.

A magnet will exert a pull on all magnets around it.

One way to understand this pull is that a magnet creates a magnetic field around it, and other magnets feel and respond to this field.

It gets more interesting if I spin magnet.

As the north and south poles of the magnet move around, its pull on other magnets must also change periodically.

But how does the news about the constantly changing location of the poles reach other magnets?

Solving the equations of electromagnetic theory gives the answer: spinning the magnet creates a stream of ripples in the magnetic field.

These ripples travel outward updating the magnetic field everywhere.

You have seen these ripples -- they go by the name of light.

Electromagnetic fields then appear to have a life of their own.

They permeate all of space like an invisible sea. The waves in this sea are light.

The field mediates interactions between far-away magnetic or electrical objects, with light acting as the messenger.

This was the understanding before quantum theory.

With the advent of quantum, particles took center stage.

Light was revealed to be as much of a particle as an electron.

But it was soon realised that particles could not be all there is. Fields had to be part of the story.

To describe electrons zooming around freely, the quantum theory of particles would suffice.

But to describe how electrons interact, one needed the mediation of fields.

The quantum theory of electromagnetic field was developed to accomplish this.

This theory also related fields and particles.

We saw light first as a ripple in a field and then as a quantum particle.

It is both -- turns out that a ripple in a quantum field is precisely a particle.

For electromagnetic field, the particle is a photon aka light-particle

Electrons too are ripples on a quantum field (called the Dirac field).

The quantum picture is that the electromagnetic interaction between electrons is mediated by the exchange of photons.

This is what the famous Feynman diagrams depict.

All the forces in nature (except gravity) were found to be fully describable as quantum fields.

Everything in the universe, including ourselves, is built out of quantum fields!

...Or is it?

One school of thought maintained that we can rid physics of fields.

The idea is not to worry about how interactions between particles are mediated.

Instead, use principles like symmetries and causality to try to constrain the results of any experiment involving particles completely

tl/dr: Particles are enough, fields are extra.

This is the bootstrap paradigm: the theory should pick itself up by its own bootstraps.

In its first iteration, the bootstrap program fizzled out after some initial success.

Quantum field theory won out.

But in the last 15 or so years, bootstrap has been making a comeback!

Are fields essential to our understanding of nature, or are particles sufficient?

The last word is yet to be said, but we are learning new things constantly!

(Of course in the end it is strings all the way down! ;))