What is smaller than an atom?

Smaller than an atom are subatomic particles and, at even smaller scales, the fundamental forces and potentially other things we're still discovering. Here's a breakdown:

Subatomic Particles: Atoms are made up of three primary types of subatomic particles:

• Protons: Positively charged particles found in the atom's nucleus.
• Neutrons: Neutrally charged particles also found in the atom's nucleus. Protons and neutrons together constitute almost all of an atom's mass.
• Electrons: Negatively charged particles that orbit the nucleus in electron shells. They have significantly less mass than protons and neutrons.

These three particles are themselves composite particles, meaning they are made of even smaller constituents.

Constituents of Protons and Neutrons:

Protons and neutrons are composed of smaller particles called quarks. There are six types (or "flavors") of quarks: up, down, charm, strange, top, and bottom. Protons are made of two up quarks and one down quark, while neutrons are made of one up quark and two down quarks. Quarks are held together by the strong force, mediated by gluons.

Fundamental Forces:

These aren't "particles" in the same way, but they are fundamental interactions that govern the behavior of matter at the subatomic level:

• Strong Force: The strongest of the four fundamental forces, responsible for holding quarks together within protons and neutrons, and for binding protons and neutrons together in the nucleus.
• Electromagnetic Force: Responsible for interactions between electrically charged particles, including the attraction between electrons and the nucleus.
• Weak Force: Responsible for radioactive decay and certain types of particle transformations.
• Gravitational Force: The weakest of the four fundamental forces, but significant at macroscopic scales, it governs the attraction between objects with mass.

Beyond the Standard Model:

The current understanding of fundamental particles and forces is encapsulated in the Standard Model of particle physics. However, the Standard Model doesn't explain everything. There are phenomena it doesn't account for, leading scientists to theorize about entities even smaller and more fundamental, such as:

• Supersymmetric particles: Hypothetical particles that are partners to the known particles in the Standard Model.
• Dark matter: A mysterious substance that makes up a significant portion of the universe's mass but doesn't interact with light or ordinary matter in the same way.
• Dark energy: A mysterious force accelerating the expansion of the universe.

In short, the realm smaller than an atom is a complex and fascinating world of fundamental particles, forces, and mysteries yet to be fully understood. Research continues to push the boundaries of our knowledge at these incredibly small scales.