Plasma

Everything around you is made up of matter — of atoms and molecules. These particles can be arranged in different ways, and this changes the characteristics of the matter. Particles arranged close together make up solid structures, such as ice, or a book. Particles that are a bit further apart and can move more freely make up liquids, like water, or blood in your body. And particles that are floating around loosely without a fixed structure make up gases, such as steam, or the air you breathe.

These are the three basic states of matter that exist in nature. They are easy to observe everywhere around you. But there is a fourth state of matter you might be less familiar with! Let’s visit Sir William Crookes in 1879, as he’s about to discover it. Crookes is carrying out an experiment with a device he’s invented.

The device, today known as a Crookes tube, is a glass bulb that contains air at very low pressure. The bulb is connected to a source of electrical energy. When Crookes connects the tube to electricity, the inside of it starts to glow! It seems something happens to the gas inside the tube that makes it behave differently to any known solids, liquids, or gases. Crookes concludes that the gas inside the tube must have turned into a new state of matter.

Because of its glow, he calls it radiant matter. Scientists continue to study this newly-discovered state of matter. About 50 years later, another scientist, Irving Langmuir, gives it a new name — plasma. What exactly is plasma and how does it differ from other states of matter? Plasma is much unlike liquids or solids.

It’s less dense and has very different characteristics. It seems to be much more similar to gas — plasma has no fixed shape or volume. It can spread easily and indefinitely, unless it’s put in some sort of a container. But plasma is different from gas in important ways. The molecules and atoms of gas don’t carry any charge.

But when high energy, such as heat or electricity, is applied to a gas, the molecules and atoms of gas break apart. Then the gas turns into a cloud of freely floating, negatively and positively charged particles — electrons and ions. The gas becomes ionised. And ionised gas is actually no longer a gas at all — it's plasma! Because particles in plasma are charged, it can do things gases cannot — like conduct electricity and interact with magnetic fields.

Plasma also glows, because when the charged particles in plasma interact with each other, they give off light. Despite being discovered so late, plasma is the most common state of matter in the universe. The sun is in fact a giant ball of plasma. So are all the other stars in the universe. And if you’ve ever seen glowing, colourful lights in the sky, known as auroras, you were looking at plasma too!

On Earth, natural plasma occurs most commonly as lightning. Lightning forms when the difference in electric charge, between the ground and the sky, is large enough to ionise the air between them. The air turns into plasma and forms a column that conducts electricity — a lightning bolt. We have also learned how to create plasma ourselves, and have been putting it to use for many different purposes - from plasma cutters used in manufacturing to cut metals, to fluorescent light bulbs, neon signs, and plasma TVs. Not only is plasma the most common state of matter in the universe, it’s becoming increasingly common in our everyday lives too!