What Matter Means in Physics

By 

Andrew Zimmerman Jones

Andrew Zimmerman Jones

Math and Physics Expert

• M.S., Mathematics Education, Indiana University
• B.A., Physics, Wabash College

Andrew Zimmerman Jones is a science writer, educator, and researcher. He is the co-author of "String Theory for Dummies."

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Updated on May 06, 2019

Matter has many definitions, but the most common is that it is any substance which has mass and occupies space. All physical objects are composed of matter, in the form of atoms, which are in turn composed of protons, neutrons, and electrons.

The idea that matter consisted of building blocks or particles originated with the Greek philosophers Democritus (470-380 BC) and Leucippus (490 BC).

Examples of Matter (and What Isn't Matter)

Matter is built from atoms. The most basic atom, the isotope of hydrogen known as protium, is a single proton. So, although subatomic particles aren't always considered forms of matter by some scientists, you could consider Protium to be the exception. Some people consider electrons and neutrons to also be forms of matter. Otherwise, any substance built of atoms consists of matter. Examples include:

• Atoms (hydrogen, helium, californium, uranium)
• Molecules (water, ozone, nitrogen gas, sucrose)
• Ions (Ca2+, SO42-)
• Polymers and Macromolecules (cellulose, chitin, proteins, DNA)
• Mixtures (oil and water, salt and sand, air)
• Complex Forms (a chair, a planet, a ball)

While protons, neutrons, and electrons are the building blocks of atoms, these particles are themselves based on fermions. Quarks and leptons typically aren't considered forms of matter, although they do fit certain definitions of the term. At most levels, it's simplest to state simply that matter consists of atoms.

Antimatter is still matter, although the particles annihilate ordinary matter when they contact each other. Antimatter exists naturally on Earth, although in extremely small quantities.

Then, there are things that either have no mass or at least have no rest mass. Things that are not matter include:

• Light
• Sound
• Heat
• Thoughts
• Dreams
• Emotions

Photons have no mass, so they are an example of something in physics that is not comprised of matter. They are also not considered "objects" in the traditional sense, as they cannot exist in a stationary state.

Phases of Matter

Matter can exist in various phases: solid, liquid, gas, or plasma. Most substances can transition between these phases based on the amount of heat the material absorbs (or loses). There are additional states or phases of matter, including Bose-Einstein condensates, fermionic condensates, and quark-gluon plasma.

Matter Versus Mass

Note that while matter has mass, and massive objects contain matter, the two terms are not exactly synonymous, at least in physics. Matter is not conserved, while mass is conserved in closed systems. According to the theory of special relativity, matter in a closed system may disappear. Mass, on the other hand, may never have been created nor destroyed, although it can be converted into energy. The sum of mass and energy remains constant in a closed system.

In physics, one way to distinguish between mass and matter is to define matter as a substance consisting of particles that exhibit rest mass. Even so, in physics and chemistry, matter exhibits wave-particle duality, so it has properties of both waves and particles.

Visible Light Spectrum

The visible light spectrum is the section of the electromagnetic radiation spectrum that is visible to the human eye. Essentially, that equates to the colors the human eye can see. It ranges in wavelength from approximately 400 nanometers (4 x 10 -7 m, which is violet) to 700 nm (7 x 10-7 m, which is red).1 It is also known as the optical spectrum of light or the spectrum of white light.

Wavelength and Color Spectrum Chart

The wavelength of light, which is related to frequency and energy, determines the color perceived by the human eye. The ranges of these different colors are listed in the table below. Some sources vary these ranges pretty drastically, and their boundaries are somewhat approximate, as they effectively blend into each other. Additionally, the edges of the visible light spectrum blend into the ultraviolet and infrared levels of radiation.

How White Light Is Split Into a Rainbow

Most light that we interact with is in the form of white light, which contains many or all of these wavelength ranges. Shining white light through a prism causes the wavelengths to bend at slightly different angles due to optical refraction. The resulting light is split across the visible color spectrum.

This is what causes a rainbow, with airborne water particles acting as the refractive medium. The order of wavelengths can be remembered by the mnemonic "Roy G Biv" for red, orange, yellow, green, blue, indigo (the blue/violet border), and violet. If you look closely at a rainbow or spectrum, you might notice that cyan also appears between green and blue. Most people cannot distinguish indigo from blue or violet, so many color charts omit it.

By using special sources, refractors, and filters, you can get a narrow band of about 10 nanometers in wavelength that is considered monochromatic light.2 Lasers are special because they are the most consistent source of narrowly monochromatic light that we can achieve. Colors consisting of a single wavelength are called spectral colors or pure colors.

Colors Beyond the Visible Spectrum

The human eye and brain can distinguish many more colors than those of the spectrum. For example, purple and magenta are the brain's way of bridging the gap between red and violet. Unsaturated colors such as pink and aqua are also distinguishable, as well as brown and tan.

However, some animals have a different visible range, often extending into the infrared range (wavelength greater than 700 nanometers) or ultraviolet (wavelength less than 380 nanometers).3 For example, bees can see ultraviolet light, which is used by flowers to attract pollinators. Birds can also see ultraviolet light and have markings that are visible under a black (ultraviolet) light. Among humans, there is variation between how far into red and violet the eye can see. Most animals that can see ultraviolet can't see infrared.

The Visible Light Spectrum
Color	Wavelength (nm)
Red	625 - 740
Orange	590 - 625
Yellow	565 - 590
Green	520 - 565
Cyan	500 - 520
Blue	435 - 500
Violet	380 - 435

 

What Is Time?

Time is familiar to everyone, yet it's hard to define and understand. Science, philosophy, religion, and the arts have different definitions of time, but the system of measuring it is relatively consistent.

Clocks are based on seconds, minutes, and hours. While the basis for these units has changed throughout history, they trace their roots back to ancient Sumeria (Sumer, an area that is now southern Iraq). The modern international unit of time, the second, is defined by the electronic transition of the cesium atom. But what, exactly, is time?

What is time, exactly? Physicists define time as the progression of events from the past to the present into the future. Basically, if a system is unchanging, it is timeless. Time can be considered to be the fourth dimension of reality, used to describe events in three-dimensional space. It is not something we can see, touch, or taste, but we can measure its passage.

Physics equations work equally well whether time is moving forward into the future (positive time) or backward into the past (negative time.) However, time in the natural world has one direction, called the arrow of time. The question of why time is irreversible is one of the biggest unresolved questions in science.

One explanation is that the natural world follows the laws of thermodynamics. The second law of thermodynamics states that within an isolated system, the entropy of the system remains constant or increases. If the universe is considered to be an isolated system, its entropy (degree of disorder) can never decrease. In other words, the universe cannot return to exactly the same state in which it was at an earlier point. Time cannot move backward.