Matter

In common usage, Matter is anything that has both mass and volume (takes up space). A more rigorous definition is used in science: matter is what atoms and molecules are made of. Matter is commonly said to exist in four states (or phases): solid, liquid, gas and plasma; other phases, such as Bose–Einstein condensates, also exist.

Matter, in the scientific definition, constitutes about 4% of the energy of the observable universe. The remaining energy is theorized to be due to exotic forms, of which 23% is dark matter and 73% is dark energy.

It is the opposite of Antimatter

Definitions of matter

Common definition

The common definition of matter is anything that has both mass and volume (occupies space).For example, a car would be said to be made of matter, as it occupies space, and has mass.

The observation that matter occupies space goes back to antiquity. However, an explanation for why matter occupies space is recent, and is argued to be a result of the exclusion principle. Two particular examples where the exclusion principle clearly relates matter to the occupation of space are white dwarf stars and neutron stars, discussed further below. For a wider discussion, you should research the Pauli exclusion principle.

BIPM definition

The international standards organization Bureau International des Poids et Mesures uses the terminology "amount of substance", rather than "matter". To quote the SI brochure:

Amount of substance is defined to be proportional to the number of specified elementary entities in a sample, the proportionality constant being a universal constant which is the same for all samples. The unit of amount of substance is called the mole, symbol mol, and the mole is defined by specifying the mass of carbon 12 that constitutes one mole of carbon 12 atoms. By international agreement this was fixed at 0.012 kg, i.e. 12 g.

• 1. The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12; its symbol is "mol".
• 2. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.”

Scientific definition

A definition of "matter" that is based upon its physical and chemical structure is: matter is what atoms and molecules are made of, meaning anything made of protons, neutrons, and electrons. This definition is consistent with the BIPM definition of "amount of substance" above, but is more specific about the constituents of matter (and unconcerned about the unit mole). Further discussion appears below in the discussion section and in the description of the quarks and leptons definition. As an example of matter under this definition, genetic information is carried by a long molecule called DNA, which is copied and inherited across generations. It is matter under this definition because it is made of atoms, not by virtue of having mass or occupying space.