What Is The World Made Of?

According to Carlo Rovelli in Reality Is Not What It Seems (Allen Lane, 2016), p. 168:

Newton thought that reality was space, time and particles;
Faraday and Maxwell added fields;
Einstein 1905 united space and time;
Einstein 1915 united space-time and fields as covariant fields;
quantum mechanics referred to space-time and quantum fields;
quantum gravity has just covariant quantum fields.

It is not surprising that covariant fields generate space-time because surely space and time are relationships in any case. Newtonian space was relationships between particles and Newtonian time was relationships between relationships between particles. Now particles are regarded as quanta of fields.

What is counter-intuitive is that there are quanta of space. Mathematically, the number one can be divided into endless smaller fractions but apparently a volume of space cannot be divided into endless smaller volumes.

Addendum: Quantum gravity is a theory of fields but not yet a unified field theory.