What is the smallest thing in the universe?

The concept of the "smallest thing" in the universe is complex and depends on what we mean by "thing." Here's a breakdown:

Elementary Particles: These are the fundamental building blocks of matter, not made of anything smaller. Examples include:
- Quarks: These make up protons and neutrons.
- Leptons: These include electrons and neutrinos.
- Gauge Bosons: These mediate the fundamental forces (e.g., photons for electromagnetism, gluons for the strong force).
Point Particles: According to the Standard Model of particle physics, elementary particles are considered to be point particles, meaning they have no spatial extent or internal structure. This is a mathematical idealization; their true nature at extremely small scales is still being investigated.
Quantum Foam: At the Planck scale (around 10<sup>-35</sup> meters), the fabric of spacetime itself is theorized to become chaotic and foamy, with virtual particles popping in and out of existence. This realm is governed by quantum gravity, a theory we don't fully understand yet.
Strings (String Theory): String theory proposes that elementary particles are not point-like but are instead tiny, vibrating strings. These strings are incredibly small, on the order of the Planck length.