Why are quarks considered fundamental particles?

Quarks are considered fundamental particles because they cannot be broken down into smaller particles.

Quarks are one of the basic building blocks of matter, along with leptons. They are the smallest particles that we know of and are considered fundamental because they cannot be divided or broken down into smaller particles. This is based on our current understanding of particle physics, which is encapsulated in the Standard Model. The Standard Model is a theory that describes three of the four known fundamental forces in the universe: electromagnetism, strong nuclear force, and weak nuclear force. It also classifies all known elementary particles.

Quarks are unique in that they carry a fractional electric charge, unlike leptons and other particles which carry a whole electric charge. They also participate in all four fundamental interactions: gravity, electromagnetism, strong nuclear force, and weak nuclear force. This makes them an integral part of the structure and dynamics of matter.

There are six types of quarks known as 'flavours': up, down, charm, strange, top, and bottom. Up and down quarks form protons and neutrons, which in turn form the nuclei of atoms. The other four types of quarks are produced in high-energy environments, such as in particle accelerators.

Quarks are always found in combinations of two or three, forming particles known as hadrons. This is due to a property known as colour confinement, which states that quarks cannot exist independently. This is another reason why quarks are considered fundamental: they are the smallest particles that we can observe, as they cannot be isolated.

In conclusion, quarks are considered fundamental particles because they are the smallest known particles, they participate in all four fundamental interactions, and they cannot be broken down into smaller particles. This is based on our current understanding of particle physics, as described by the Standard Model.