According to string theory, matter is made up of strings.
A theory of theories – CERN Courier
The Power of Mirror Symmetry - Ideas
How Quantum Pairs Stitch Space-Time
Is this the only universe?
Symmetry is a Guide to Reality
Full article: The string theory landscape: a tale of two hydras
String theory: simple yet elegant – Physics World
A new model of quantum gravity from the building blocks of grand unified theories - Highlighted Articles - Physics Open - Journal - Elsevier
String Theory Explained: A Brief Overview for Starters
String Theory Explained : r/Physics
String Theorists Simulate the Big Bang
The Sound of Symmetry Max Planck Institute for Gravitational Physics (Albert Einstein Institute)
String Theory Meets Loop Quantum Gravity
The Shape of Inner Space: String Theory and the Geometry of the Universe's Hidden Dimensions: 9780465020232: Yau, Shing-Tung, Nadis, Steve: Books