This blog post explores how the scientific principles behind the Singularity—a pivotal point in technological advancement—and supercritical fluids impact our daily lives and industries.
“The Singularity is coming!” This phrase echoed across the internet after many witnessed the shocking Go match between Google’s AlphaGo and Lee Sedol, a 9-dan professional. The term gained fame as the title of a book by Ray Kurzweil, Google’s director of engineering, who describes the Singularity as the point when human-made technology surpasses human capabilities. In other words, the author argues that the singularity is the point where human technology and human capabilities become equal, and that beyond this singularity, unforeseen events will occur. These unforeseen events refer to a future where artificial intelligence surpasses human expectations, learning and evolving independently, capable of thinking and making decisions like humans.
However, the term singularity itself is a broader concept frequently used in mathematics and science, referring to the point at which competing elements achieve equilibrium, beyond just the balance between technology and humans. For example, in mathematics, the characteristics of an equation can be determined by the ratio of two variables within it. When the magnitudes of these two factors achieve an extremely delicate equilibrium, a situation arises where the characteristics of the equation become indefinable. This point is called the singularity of the equation. Understanding the term singularity from this broader perspective of a balance point reveals that every substance around us has its own singularity—a point called the critical point where the characteristics of liquid and gas are in equilibrium. And once this critical point is crossed, it exhibits useful properties we never imagined.
All matter can exist in three states. Consider water. At low temperatures, it exists as ice, a solid state. As the temperature rises, it melts into water, a liquid, and becomes even hotter, it boils and turns into steam, a gas. Thus, the three states of matter—solid, liquid, and gas—change depending on temperature. Moreover, the state of matter changes not only with temperature but also with pressure. A spray can contains liquid under very high pressure, but when sprayed, it is expelled into the air as an invisible gas. Thus, whether a substance exists as a solid, liquid, or gas is determined by both temperature and pressure. While this is a common phenomenon around us, it becomes even more fascinating when examined scientifically: each state can only be maintained at specific temperatures and pressures. We easily observe water in its solid state melting into a liquid and then vaporizing into a gas in daily life, yet behind this lies the complex interplay between molecules.
So how do temperature and pressure change a state? First, let’s understand what temperature and pressure signify. Temperature indicates how fast the molecules—the tiny particles composing matter—move. That is, at low temperatures, molecules move slowly, and at high temperatures, they move rapidly. Conversely, pressure indicates the distance between molecules. High pressure means the substance is compressed, reducing the distance between molecules, while low pressure increases the distance between them. However, regulating the distance between molecules through pressure produces an additional effect. Molecules possess an inherent tendency to attract each other, as the strength of this attractive force increases when molecules are closer together. Thus, higher pressure brings molecules closer, intensifying their mutual attraction and tendency to cluster together. Conversely, lower pressure weakens the force pulling molecules toward each other.
Now, let’s return to water. At low temperatures, the water molecules that compose it move sluggishly. These slow-moving molecules cannot overcome the mutual attraction and escape, causing them to clump together. This results in a solid state where they are completely immobilized—ice. When the temperature of ice rises, allowing the molecules to move more briskly, they remain clustered in large groups but can partially overcome the mutual attraction, enabling some molecular movement. This is the liquid state of water. If the temperature rises further, the molecules move so rapidly that the attractive forces can no longer hold them together. They become free to move about randomly, forming the gaseous state: water vapor. To summarize, the state of a substance is determined by which force prevails in the competition between the attractive force between molecules and the speed of the molecules. The attractive force increases with higher pressure, and the speed of the molecules increases with higher temperature. Therefore, the state of a substance changes depending on temperature and pressure.
Now, let’s try turning water vapor back into a liquid without lowering the temperature. Increasing pressure brings water molecules closer together. This also increases the force of attraction between them. If pressure is raised sufficiently, the mutual attraction becomes strong enough to hold even rapidly escaping molecules, causing the substance to revert to a liquid. But does increasing pressure always turn a gas into a liquid?
To answer upfront: no. Increasing pressure reduces the distance between molecules and strengthens their mutual attraction. But there is a definite limit to how strong this attraction can become. This is because once molecules are compressed until they touch each other with no gaps left, they cannot get any closer. In contrast, temperature can be raised indefinitely until problems arise within the molecules themselves or they break down. Therefore, once a specific temperature is exceeded, the competition between pressure and temperature ends. No matter how much pressure is increased, it cannot create a molecular attraction strong enough to capture the rapidly moving molecules, so the gas does not become a liquid. This final equilibrium point, just before the competition between temperature and pressure breaks down, is called the critical point. This can also be seen as a singularity of the substance.
However, just because a substance cannot become a liquid beyond the critical point’s temperature and pressure does not mean it exists as a gas beyond that point. Beyond the critical point, while it is not liquid enough to form a liquid, the distance between molecules becomes very close, causing them to attract each other with strong forces. Therefore, even though the molecules are not clustered together like in a liquid, they cannot move around completely freely like in a gas. A substance that has crossed the critical point and is neither liquid nor gas is called a supercritical fluid.
Supercritical fluids exhibit properties rarely seen in ordinary liquids or gases, notably extremely low viscosity and a high solubility for other substances. Low viscosity means high penetrating power. This can be easily understood by recalling that when water is poured onto sand, it permeates every nook and cranny between the grains and flows out below, whereas honey, which has higher viscosity than water, barely flows and only slightly soaks into the sand.
In short, using a supercritical fluid as an extraction solvent allows it to penetrate everywhere, dissolving the desired target material. When pressing sesame seeds to extract sesame oil, an antioxidant called lignin doesn’t dissolve. However, using supercritical fluid for extraction can increase its yield by over 10,000 times. Sesame oil extracted this way is actually sold commercially. Furthermore, supercritical fluid is utilized in the decaffeination process of coffee to selectively remove only the caffeine. Beyond this, numerous pharmaceutical companies are researching the use of supercritical fluids to extract active ingredients from substances like herbs. Supercritical fluids are also actively employed as a medium for producing nanoparticles or inducing highly specialized chemical reactions. Thus, supercritical fluids have established themselves as a core material in advanced technology, and their range of applications continues to expand.
