Matter is generally defined as anything that exists, making up everything in the observable universe. This includes all objects you can see and touch, molecules in the air, and distant stars. While matter takes on vastly different forms—such as a solid ice cube, a liquid ocean, or superheated plasma—all these forms share fundamental commonalities. Exploring these shared properties reveals the unified nature of our physical reality.
The Universal Requirements: Mass and Volume
The most fundamental commonality for all matter is that it must possess mass and occupy space, which is referred to as volume. Mass quantifies the amount of matter in an object; it is also a measure of an object’s inertia. Inertia is the inherent resistance a body has to a change in its state of motion, meaning a more massive object is harder to accelerate. This intrinsic property is constant regardless of where the object is located in the universe.
It is important to distinguish mass from weight, which is the force of gravity acting on an object. An astronaut’s mass remains the same whether they are on Earth or the Moon, but their weight changes dramatically because the gravitational force is different. Every piece of matter, from a single molecule of gas to a planet, has this property of inertia.
All matter also occupies space, which is its volume. This is easy to see with a solid object, but it is equally true for gases and even plasma, the superheated, ionized state of matter. A gas will expand to fill its container, while plasma, which is similar to a gas but electrically conductive, also lacks a fixed shape or volume. Even in these fluid states, the constituent particles occupy a three-dimensional space, preventing other matter from occupying the same location at the same time.
The Shared Building Blocks: Atomic Structure
Regardless of whether matter is an element or a complex compound, all ordinary matter is ultimately constructed from atoms. These atoms, the smallest units that retain the chemical properties of an element, share a remarkably consistent internal architecture. This universal structure consists of a dense central nucleus surrounded by a cloud of much lighter, negatively charged electrons. The nucleus itself contains positively charged protons and electrically neutral neutrons.
The composition of the atom determines the type of element, as the number of protons defines the element’s identity. However, the fundamental building blocks—protons, neutrons, and electrons—are identical across all forms of matter. For example, an atom of oxygen shares the same type of electron as an atom of carbon, only the quantity and arrangement are different. The nucleus is held together by the strong nuclear force, which is immensely powerful but acts only over extremely short distances.
The electrons are bound to the nucleus by the electromagnetic force, which is the attraction between the positively charged protons and the negatively charged electrons. This force gives atoms their size and allows them to interact with other atoms to form molecules and compounds. This common set of particles and the forces that govern their interactions ensure that the microscopic foundation of all matter throughout the universe is the same.
Governing Principles: Physical Laws and Conservation
Beyond its physical makeup, all matter is universally governed by the same fundamental laws of physics. These laws dictate how all matter behaves, moves, and interacts, ensuring a predictable universe. One set of these principles is described by Newton’s laws of motion, which state that an object’s velocity will not change unless acted upon by an external force. The force required to change the motion of any piece of matter is directly proportional to its mass, illustrating the deep connection between mass and behavior.
Furthermore, all matter that possesses mass is subject to the law of universal gravitation. This law states that every mass in the universe attracts every other mass with a force that depends on the product of their masses and the distance between them. This force governs everything from an apple falling to Earth to the orbital paths of galaxies. It is a universal interaction that binds all matter together across cosmic distances.
Another unifying principle is the law of conservation of mass-energy. This law, derived from the theory of special relativity, asserts that the total amount of mass and energy in an isolated system remains constant. Matter cannot be created or destroyed, only transformed into different forms of matter or energy. This principle applies to all physical and chemical changes, confirming that all matter is part of a single, closed energetic system.