Matter

• 1. Defining The Physical Substance

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  Hydrogen in its plasma state is the most abundant ordinary matter in the universe. In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic particles. In everyday as well as scientific usage, matter generally includes atoms and anything made up of them, and any particles or combination of particles that act as if they have both rest mass and volume. However it does not include massless particles such as photons, or other energy phenomena or waves such as light or heat. Matter exists in various states also known as phases. These include classical everyday phases such as solid, liquid, and gas for example water exists as ice, liquid water, and gaseous steam but other states are possible including plasma Bose, Einstein condensates fermionic condensates and quark, gluon plasma.

• 2. Elementary Building Blocks

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  Usually atoms can be imagined as a nucleus of protons and neutrons and a surrounding cloud of orbiting electrons which take up space. However this is only somewhat correct because subatomic particles and their properties are governed by their quantum nature which means they do not act as everyday objects appear to act. They can act like waves as well as particles and they do not have well-defined sizes or positions. In the Standard Model of particle physics matter is not a fundamental concept because the elementary constituents of atoms are quantum entities which do not have an inherent size or volume in any everyday sense of the word. Due to the exclusion principle and other fundamental interactions some point particles known as fermions quarks leptons and many composites and atoms are effectively forced to keep a distance from other particles under everyday conditions. This creates the property of matter which appears to us as matter taking up space. The Standard Model groups matter particles into three generations where each generation consists of two quarks and two leptons. The first generation is the up and down quarks the electron and the electron neutrino; the second includes the charm and strange quarks the muon and the muon neutrino; the third generation consists of the top and bottom quarks and the tau and tau neutrino.

• 3. States And Phase Transitions

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  In bulk matter can exist in several different forms or states of aggregation known as phases depending on ambient pressure temperature and volume. A phase is a form of matter that has a relatively uniform chemical composition and physical properties such as density specific heat refractive index and so forth. These phases include the three familiar ones solids liquids and gases as well as more exotic states of matter such as plasmas superfluids supersolids Bose, Einstein condensates. A fluid may be a liquid gas or plasma. There are also paramagnetic and ferromagnetic phases of magnetic materials. As conditions change matter may change from one phase into another. These phenomena are called phase transitions and are studied in the field of thermodynamics. In nanomaterials the vastly increased ratio of surface area to volume results in matter that can exhibit properties entirely different from those of bulk material and not well described by any bulk phase. Degenerate matter refers to the ground state of a gas of fermions at a temperature near absolute zero. The Pauli exclusion principle requires that only two fermions can occupy a quantum state one spin-up and the other spin-down. Hence at zero temperature the fermions fill up sufficient levels to accommodate all the available fermions and in the case of many fermions the maximum kinetic energy called the Fermi energy and the pressure of the gas becomes very large and depends on the number of fermions rather than the temperature unlike normal states of matter.

• 4. Historical Philosophical Evolution

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  For much of the history of the natural sciences people have contemplated the exact nature of matter. The idea that matter was built of discrete building blocks the so-called particulate theory of matter appeared in both ancient Greece and ancient India. Early philosophers who proposed the particulate theory of matter include the Indian philosopher Kañada and the pre-Socratic Greek philosophers Leucippus and Democritus. In ancient India the Buddhist Hindu and Jain philosophical traditions each posited that matter was made of atoms paramanu pudgala that were eternal indestructible without parts and innumerable and which associated or dissociated to form more complex matter according to the laws of nature. The strongest developers and defenders of this theory were the Nyaya-Vaisheshika school with the ideas of the Indian philosopher Kanada being the most followed. In ancient Greece pre-Socratic philosophers speculated the underlying nature of the visible world. Thales c 624 BCE, c 546 BCE regarded water as the fundamental material of the world. Anaximander c 610 BCE, c 546 BCE posited that the basic material was wholly characterless or limitless: the Infinite apeiron. Anaximenes flourished 585 BCE d 528 BCE posited that the basic stuff was pneuma or air. Heraclitus c 535 BCE, c 475 BCE seems to say the basic element is fire though perhaps he means that all is change. Empedocles c 490, 430 BCE spoke of four elements of which everything was made: earth water air and fire. Meanwhile Parmenides argued that change does not exist and Democritus argued that everything is composed of minuscule inert bodies of all shapes called atoms a philosophy called atomism.

• 5. Cosmological Matter Distribution

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  Baryonic matter is the part of the universe that is made of baryons including all atoms. This part of the universe does not include dark energy dark matter black holes or various forms of degenerate matter such as those that compose white dwarf stars and neutron stars. Microwave light seen by Wilkinson Microwave Anisotropy Probe WMAP suggests that only about 4.6% of that part of the universe within range of the best telescopes that is matter that may be visible because light could reach us from it is made of baryonic matter. About 26.8% is dark matter and about 68.3% is dark energy. The great majority of ordinary matter in the universe is unseen since visible stars and gas inside galaxies and clusters account for less than 10 per cent of the ordinary matter contribution to the mass, energy density of the universe. In astrophysics and cosmology dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly but whose presence can be inferred from gravitational effects on visible matter. Observational evidence of the early universe and the Big Bang theory require that this matter have energy and mass but not be composed of ordinary baryons protons and neutrons. The commonly accepted view is that most of the dark matter is non-baryonic in nature. As such it is composed of particles as yet unobserved in the laboratory. Perhaps they are supersymmetric particles which are not Standard Model particles but relics formed at very high energies in the early phase of the universe and still floating about.

• 6. Antimatter And Annihilation

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  Antimatter is matter that is composed of the antiparticles of those that constitute ordinary matter. If a particle and its antiparticle come into contact with each other the two annihilate; that is they may both be converted into other particles with equal energy in accordance with Albert Einstein's equation E=mc^2. These new particles may be high-energy photons gamma rays or other particle, antiparticle pairs. The resulting particles are endowed with an amount of kinetic energy equal to the difference between the rest mass of the products of the annihilation and the rest mass of the original particle, antiparticle pair which is often quite large. Antimatter is not found naturally on Earth except very briefly and in vanishingly small quantities as the result of radioactive decay lightning or cosmic rays. This is because antimatter that came to exist on Earth outside the confines of a suitable physics laboratory would almost instantly meet the ordinary matter that Earth is made of and be annihilated. There is considerable speculation both in science and science fiction as to why the observable universe is apparently almost entirely matter in the sense of quarks and leptons but not antiquarks or antileptons and whether other places are almost entirely antimatter antiquarks and antileptons instead. In the early universe it is thought that matter and antimatter were equally represented and the disappearance of antimatter requires an asymmetry in physical laws called CP charge, parity symmetry violation which can be obtained from the Standard Model but at this time the apparent asymmetry of matter and antimatter in the visible universe is one of the great unsolved problems in physics.