Quarks and gluons are fundamental particles that are described by the theory of quantum chromodynamics (QCD), which is a part of the Standard Model of particle physics. Let's explore each of them:
Quarks: Quarks are elementary particles and the fundamental building blocks of matter. They are considered to be the smallest known particles in the universe. Quarks come in six different types or flavors: up, down, charm, strange, top, and bottom. Each flavor of quark has a corresponding antiparticle with opposite electric charge. Quarks have fractional electric charges and carry a property called color charge, which is associated with the strong nuclear force. Quarks are always found in combination with other quarks, forming composite particles called hadrons, such as protons and neutrons.
Gluons: Gluons are elementary particles that mediate the strong nuclear force, which is responsible for holding quarks together within hadrons. Gluons themselves carry color charge, similar to quarks. Unlike other forces, such as electromagnetism, the strong force becomes stronger as particles move farther apart, which is known as color confinement. Gluons can exchange color charge between quarks, effectively "gluing" them together. The strong force is also responsible for the binding energy within atomic nuclei.
Virtual particles: In quantum field theory, virtual particles are particles that are not directly observable as free particles but can exist momentarily as fluctuations in quantum fields. These particles play a role in the mathematical description of interactions between particles. According to the principles of quantum mechanics, virtual particles can be created spontaneously, borrow energy from the vacuum, and quickly annihilate. They are an inherent part of the quantum field theory framework and are invoked to explain certain phenomena, such as the behavior of particles in quantum tunneling and the interaction of charged particles with electromagnetic fields.
It's important to note that while virtual particles are used in calculations and theoretical descriptions, they are not directly detectable or observable in the same way as real particles. Their existence is inferred through their effects on measurable quantities.