You can say that everything we see is matter, not just things we see but it encompasses things that we don’t see too but what is matter actually?
What is Matter?
There are two things that exists in the Universe, matter and wave. If it is not one, then it is the other. Since we are just talking about just matter, let us start with its definition. Matter is recognized primarily by two properties – occupying space and having non-zero mass. So, anything that occupies space and has mass (rest mass) is called matter.
Although we refer to things as matter and wave distinctly, duality principle dictates that any particle can behave as matter as well as wave. When things are in quantum level, we don’t actually distinguish between these two but rather consider matter as well as wave property simultaneously. So, everything is matter in a sense.
But, let us not complicate things. In our view, in our surrounding anything that has mass and occupies space is a matter. Everything we see including the gases and some materials which cannot be seen but has those properties are matter.
Non Zero Mass
Mass is the amount of matter contained by a body. It is an intrinsic property of a material. It is a physical quantity that represents how much matter is contained in a body. It is measured in kilograms, grams, ounce. pounds, etc. Every matter has its own rest mass. Rest mass is simply mass of a body when it is completely at rest and is a term introduced by the theory of relativity, since mass is velocity dependent.
Occupation of Space
Space is a three dimensional surrounding which extends indefinitely. Any object that exists in space has three dimensions and they are called matter if they have mass too. But, there are two (like graphene, silicene) and one dimensional (like nano rods and nano wires) objects too in the world, does it mean that they are not matter? These materials are just called two or one dimensional for other reason, yet they have a non-zero volume in space, they occupy space and are matter.
Types of Matter
There are two types of matter on the basis of their composition – baryonic matter and non-baryonic matter.
Matter which are made up of Baryons, material composed of three quarks, are called baryonic matter. Almost all the materials that we see are made up of baryonic matter. Protons, neutrons, etc. are baryons and they make up mostly everything we see in our daily life.
Matter which are not made up of baryons are called non-baryonic matter. Mesons, leptons, dark matter, black holes, etc are some examples of non-baryonic matter. Among these types of non-baryonic matter, dark matter represents nearly 84% of total matter. Thus most of the matter in the Universe is non-baryonic.