A fourth state of matter

By Paul Patton

Posted July 12, 2022

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Y: Today's Moment of Science is about the fourth state of matter.

D: Um--Yaël, everybody knows there are just three states of matter; solids, liquids, and gases.

Y: Don, suppose we take a solid, such as ice, and heat it. What will happen?

D: The ice will melt, of course, and become a liquid--water.

Y: And what happens if we heat the water?

D: It will boil and become a gas--water vapor.

Y: Now what happens if we heat up the gas?

D: Umm, it will get hotter?

Y: The gas will change to another state. Its atoms will break apart into negatively charged electrons and positively charged ions. This soup of electrons and ions is plasma-- the fourth state of matter. It was discovered by William Crookes in 1879.

D: That sounds exotic. Would anybody ever see plasma outside a science lab?

Y: Don! Don't you remember the plasma lamp in my office? The glowing streamers in the lamp are plasma. Plasma glows because when an electron moves to a lower orbit around an ion or atom, energy is released as light. Fluorescent tubes and neon lamps rely on glowing plasma too. Dr. Crookes discovery was very practical.

D: It sounds like plasma is rare except when people make it.

Y: Plasma only seems rare because we live in an unusual place.

D: And what place is that Yaël?

Y: The surface of Earth. In most other places plasma is everywhere. The sun and stars are made of it, and very thin plasma fills space. Plasma makes up ninety nine percent of matter in the visible universe. The fourth state of matter is its most common state.

A purple plasma ball with blue tendrils against a black background

A "soup" of electrons and ions becomes the fourth state of matter, plasma (Karen / flickr)

Everybody knows there are just three states of matter; solids, liquids, and gases. But today's Moment of Science is about a fourth state. Where does this fourth state come from?

Well, suppose we take a solid, such as ice, and heat it. What will happen? The ice will melt, of course, and become a liquid--water.

And what happens if we heat the water? It will boil and become a gas--water vapor.

Now what happens if we heat up the gas?

The gas will change to another state. Its atoms will break apart into negatively charged electrons and positively charged ions. This soup of electrons and ions is plasma-- the fourth state of matter. It was discovered by William Crookes in 1879.

And it might sound exotic, but plasma can be found more commonly than you might expect. Like in plasma lamps with glowing streamers. Plasma glows because when an electron moves to a lower orbit around an ion or atom, energy is released as light. Fluorescent tubes and neon lamps rely on glowing plasma too. Dr. Crookes discovery was very practical.

We might think of plasma as rare unless someone makes it, but it actually only seems rare because we live in an unusual place, the surface of Earth.

In most other places plasma is everywhere. The sun and stars are made of it, and very thin plasma fills space. Plasma makes up ninety nine percent of matter in the visible universe. The fourth state of matter is its most common state.

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