Short answers, pulled from the story.
Matter is defined as something that has mass and volume, yet at the atomic level it is mostly empty space. The nucleus of an atom is so small that if the atom were the size of a football stadium, the nucleus would be a marble on the 50-yard line. The rest of the volume is occupied by a cloud of electrons whizzing around at incredible speeds.
The ancient Indian philosopher Kanada proposed that all matter was composed of paramanu, or atoms, which were eternal and indestructible. Simultaneously, the pre-Socratic philosophers Leucippus and his student Democritus developed a similar theory called atomism in ancient Greece. These thinkers argued that the universe is built from discrete building blocks rather than continuous elements.
The electron was discovered by J. J. Thomson in 1897, shattering the idea of the atom as an indivisible, solid sphere. This discovery revealed that atoms had internal structures composed of negatively charged electrons orbiting a positive nucleus. It opened the door to the 20th century study of matter moving from macroscopic mechanics to the microscopic realm of quantum mechanics.
Ordinary baryonic matter makes up only about 4.6% of the universe according to observations from the Wilkinson Microwave Anisotropy Probe. Dark matter accounts for about 26.8% of the universe and does not emit or reflect light, yet its presence is inferred from its gravitational effects on visible matter. Dark energy makes up the remaining 68.3% and is a mysterious force accelerating the expansion of the universe.
The Big Bang should have produced equal amounts of matter and antimatter, which would have annihilated each other leaving only energy. A slight asymmetry in the early universe known as CP violation allowed a small excess of matter to survive the annihilation. This phenomenon explains why stars and galaxies exist today rather than the universe being a sea of radiation.
Plasma is the fourth state of matter and is the most abundant form of ordinary matter in the universe found in stars and interstellar space. At temperatures near absolute zero matter can form Bose-Einstein condensates where atoms lose their individual identity. In the cores of white dwarf stars and neutron stars matter exists as degenerate matter where the Pauli exclusion principle creates immense pressure.