To understand degenerate matter, we’ve got to step back and look at regular normal matter first. If you’ve had even a rudimentary physics education (high-school level or higher), you’ll be aware of the gas laws. Pressure and volume are proportional to temperature, so that if you increase the temperature, the gas will try to expand (and if it is prevented by expanding by being sealed in a container, the pressure rises). These principles explain how a hot air balloon flies, how refrigerators and air conditioners work, why scuba divers need pressure regulators, and numerous other everyday events.
These laws come about as a natural consequence of the fact that a gas is made of swarms of tiny molecules, moving freely and colliding with each other. When you model their interactions with each other, they average out statistically into the laws we’ve been talking about. Pressure is just the sum of the tiny forces exerted by the individual molecules as they collide with each other and the walls of whatever contains the gas. Temperature is a measure of the average speed of the molecules. But if you apply truly extreme amounts of heat and pressure to a gas, higher even than what is found at the core of the Sun, then the true nature of the particles begins to manifest, and the effects of quantum mechanics start appearing. When this happens, these classical physical laws stop working and we say that the gas is in a degenerate state.
Heisenberg’s Uncertainty Principle is based upon the idea that the quantum nature of things makes it impossible to ever measure the position and momentum of a particle with absolute accuracy (although you can get close enough that this only matters at the atomic scale). It states that the uncertainties of these two attributes are proportional to each other, so that the more precisely you measure something’s position, the less certain you can be about its momentum, and vice versa.
But if you increase the pressure of a gas enough, if you squeeze it so tightly that the electrons around each atom start running out of space to move, then you create a very strange situation. Because the individual electrons are now restrained into an extremely tiny space, you can potentially know their position very accurately indeed. Heisenberg’s uncertainty principle forces them to compensate by making the variability in their momentum get extremely large, and this manifests in an increase in pressure. Meanwhile, the atoms stop moving independently of each other, preventing the temperature from having any effect on pressure. The result is that the link between pressure and temperature is broken – you can change one with practically no effect on the other The degenerate matter is now incredibly dense, and an almost perfect conductor of heat. White dwarf stars (which are made of electron-degenerate matter, with a very thin surface shell of unburned hydrogen and helium) demonstrate this effect well – every single point, whether deep in the core of near the surface, is at the same temperature. If more material is added (perhaps scooped up gravitationally from a companion star), it actually shrinks as the pressure increases because the temperature cannot climb – if the particles cannot move faster, then there’s no mechanism to prevent the volume from reducing!
Written by Allen Versfeld
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