The familiar states of matter—solid, liquid, and gas—govern nearly every physical experience on Earth. Physics defines a fourth fundamental state, plasma, which is far less common in our daily lives. This leads many to question if this lesser-known state of matter is truly as abundant as some scientific claims suggest. The answer is counterintuitive to our terrestrial experience: plasma is the most prevalent form of ordinary matter in the universe.
What Exactly Is Plasma
Plasma is an ionized gas, often referred to as the fourth state of matter. It is distinct from solid, liquid, and gas due to its unique physical properties. Plasma is created when enough energy is supplied to a neutral gas to strip electrons from atoms or molecules, a process called ionization. This leaves behind a mixture of positively charged ions and negatively charged electrons, creating a highly energetic “soup” of particles.
The presence of these free electric charges fundamentally changes the material’s behavior compared to a neutral gas. Plasma becomes an excellent electrical conductor, easily carrying an electric current. The charged particles also respond strongly to magnetic fields, which govern the plasma’s motion and allow for collective behavior over large distances. This makes plasma a highly reactive, electrically conductive medium whose dynamics are dominated by electromagnetic forces.
The Universal Confirmation Why Plasma Dominates
The abundance of plasma is a consequence of the extreme conditions found throughout the cosmos. Estimates consistently show that well over 99% of all visible, or baryonic, matter in the universe exists in the plasma state. This dominance is due to the intense energy and high temperatures naturally prevalent in space.
Every star, including our Sun, is a sphere of superheated, fully ionized plasma. Temperatures within stars are high enough to keep all electrons stripped from their atoms. Stars contain the vast majority of the universe’s baryonic mass, making them the largest reservoir of plasma. The space between stars is also filled with this ionized matter.
The interstellar medium (ISM), the material between star systems, and the intergalactic medium (IGM), the material between galaxies, are both composed of tenuous plasma. Although these regions are sparse, they are so vast that they collectively account for a substantial portion of the universe’s total baryonic mass. High-energy radiation from distant objects is often sufficient to keep the scattered atoms in an ionized state. In terms of volume, the universe is almost entirely filled with a plasma medium, with neutral gas, liquids, and solids representing only a tiny fraction of the total space.
Plasma’s Presence Closer to Home
While the extreme conditions of space are necessary for plasma’s universal dominance, it also occurs naturally on Earth and is harnessed for various technological applications. One dramatic terrestrial example is lightning, which forms when a large electrical charge builds up and ionizes a channel of air, momentarily creating a hot, conductive plasma path. The light and energy released from this plasma is what we perceive as a lightning bolt.
The celestial light displays known as the aurora borealis and aurora australis are also a form of plasma. They occur when charged particles from the solar wind (a stream of plasma) are funneled by Earth’s magnetic field toward the poles. These particles collide with atoms in the upper atmosphere, exciting them and causing them to glow with the characteristic colors.
Humans have learned to create and control plasma for numerous devices. Low-pressure plasma is used in fluorescent light bulbs and neon signs, where an electrical current excites a gas to a plasma state, causing it to emit visible light. Controlled fusion research aims to replicate the Sun’s energy generation process. This involves creating and containing hot, dense plasma using powerful magnetic fields. These examples show that plasma, despite its cosmic origins, is a state of matter we regularly interact with and utilize.