Matter

**Matter** is any substance that has mass and takes up space by having volume. All such objects in the cosmos are composed of atoms which are made up of interacting subatomic particles. Matter exists in states or phases of solid, liquid, and gas (for example water exists as ice, liquid water, and steam) and the fourth state plasma. Exotic states include Bose–Einstein condensates, fermionic condensates, and quark–gluon plasma.

Matter has a special relationship with energy called mass–energy equivalence whereby matter and energy can be used interchangeably and often is. The principle is described by the physicist Albert Einstein's famous formula: E=mc2.

Approximate matter/energy in the universe
 0.5%

Based on its physical and chemical structure, matter is made up of molecules, which are made up of atoms, which are made up of protons, neutrons, and electrons.

Using the Standard Model of Elementary Particles, all matter is made up of fermions which are made up of quarks and leptons. Leptons (the most famous being the electron), and quarks (of which baryons, such as protons and neutrons, are made) combine to form atoms, which in turn form molecules.

According to the theory of supersymmetry (SUSY), every particle in the Standard Model has a supersymmetric heavier twin. For example, quarks would have a heavier partner particle called a squark, which is short for supersymmetric quark. The supersymmetric partner of an electron is called a selectron. It's possible these super-partners are the source of dark matter. Just after the Big Bang, particles and their super-partners were indistinguishable. Each pair co-existed as single massless entities. As the universe expanded and cooled, though, this supersymmetry broke down. Partners and super-partners went their separate ways, becoming individual particles with a distinct mass all their own.

Baryonic matter does not include dark energy, dark matter, black holes or various forms of degenerate matter. Therefore only about 5% of the universe is made of baryonic matter. Hadronic matter can include 'ordinary' baryonic matter, or quark matter and degenerate matter.

Bosons (which include photons and the force carriers gluons) are massless (with zero rest mass) and are therefore not matter. Other energy phenomena such as light and gravitational waves are also massless, and also don't have mass-energy equivalence.

The forces of nature are mediated by elementary particles:

* electromagnetism by the photon
* the strong interaction by gluons
* the weak interaction by the W and Z bosons
* gravitation by the graviton which is the hypothetical quantum of gravity and a massless state of a string.

The Randall-Sundrum (RS) brane theory in Type 0 tries to address why the force of gravity appears to be so much weaker than other fundamental forces such as the electromagnetic force and the strong and weak nuclear force. According to the RS theory, gravity may be weak because it is concentrated in another dimension. Our visible universe with its three dimensions of space and one dimension of time is a visible brane (where particles in the Standard Model reside). Another brane may reside a short distance away in another spatial dimension. It is on this other hidden brane that gravitons may reside. Gravity may actually be as strong as the other forces, but it is diluted as it 'leaks' into our visible brane. Photons that are responsible for our eyesight are stuck to the visible brane, and thus we are not able to see the hidden brane. In Type I it is discovered as the 5th dimension.

A tachyon has complex or imaginary rest mass and is not massless. It can only be superluminal and travel faster than c. They speed up as they lose energy. At zero energy they have infinite velocity and are present everywhere in the universe at the same time (transcendental tachyon). Albert Einstein said that special relativity implies that faster-than-light particles could be used to communicate backwards in time. The Higgs boson also has an imaginary mass in its uncondensed phase.

### Hierarchy of matter

#### Molecular

Matter at the highest level is made of molecules and their bonds. The bonds include ionic (electrons are transferred), covalent (electrons are shared equally), polar covalent (electrons are shared unequally), diatomic (molecules with two atoms), and hydrogen bonds.

#### Atomic

These are individual atoms, ions, and isotopes.

#### Subatomic

These are protons, electrons and neutrons within atoms themselves. The strong interaction binds neutrons and protons to create atomic nuclei, where it is called the nuclear force. The weak interaction or force is the mechanism of interaction between subatomic particles that is responsible for the radioactive decay of atoms. Electromagnetism is the interaction that occurs between particles with electric charge via electromagnetic fields.

#### Elementary or fundamental

These are subatomic particles that are not composed of other particles. The Standard Model recognizes seventeen distinct particles—twelve fermions (divided into quarks and leptons) and five bosons.

#### Quantum

These are 1D quantum strings and foam, which make up the indivisible spacetime packets or *quanta* that form a universe. This is the fabric of reality.

### Exotic matter

Exotic energy and matter are found naturally in neutron stars or black holes or cosmic events such as supernovas or the Big Bang. All these matter types have an associated exotic energy.