Beyond the three states of matter (solid, liquid and gas) exists 2 more states - Plasma and the Bose-Einstein condensate.
In physics, plasma is an electrically conducting medium in which there are roughly equal numbers of positively and negatively charged particles, produced when the atoms in a gas become ionized. It is sometimes referred to as the fourth state of matter, distinct from the solid, liquid, and gaseous states. The uniqueness of the plasma state is due to the importance of electric and magnetic forces that act on a plasma in addition to such forces as gravity that affect all forms of matter. Since these electromagnetic forces can act at large distances, a plasma will act collectively much like a fluid even when the particles seldom collide with one another. Nearly all the visible matter in the universe exists in the plasma state, occurring predominantly in this form in the Sun and stars and in interplanetary and interstellar space. Auroras, lightning, and welding arcs are also plasmas; plasmas exist in neon and fluorescent tubes, in the crystal structure of metallic solids, and in many other phenomena and objects. The Earth itself is immersed in a tenuous plasma called the solar wind and is surrounded by a dense plasma called the ionosphere. A plasma may be reduced in the laboratory by heating a gas to an extremely high temperature, which causes such vigorous collisions between its atoms and molecules that electrons are ripped free, yielding the requisite electrons and ions. Artificially created plasmas have many practical uses. For example, electricity turns the gas in the tube of a neon sign into a plasma that gives off light. Electric rockets may someday use plasma fuels for long trips through space.
The Bose-Einstein condensate represents a fifth phase of matter beyond solids. It is a phase of matter, in the sense that solid, liquid, gas and plasma are phases of matter. Bose-Einstein condensates form from matter that has been cooled to near absolute zero. They were predicted in the 1920s by Satyendra Nath Bose and Albert Einstein based on Bose's work on rules for deciding when two photons should be counted up as either identical or different. Einstein formalized and generalized these ideas, and the result of their efforts is the so called Bose-Einstein statistics. This is the description of the statistics of identical particles that can share a quantum energy level with each other (as opposed to Fermi-Dirac statistics, which describe identical particles of which you can only put one in each energy level). One of the results that one can derive from this statistics is the existence of stimulated emission of photons, which is the effect that is used in creating lasers. Einstein also applied the statistics to atoms instead of photons, and discovered that at a certain very low temperature, all of the atoms tend to drop into the lowest accessible energy level. The effect can be understood in broad outline by considering the Heisenberg Uncertainty Principle which states, roughly, that it is impossible to know both a particle's velocity and a particle's position simultaneously with certainty. When a group of atoms is cooled to a low enough temperature, however, their velocities become very certain; they must be moving very slowly, or, stated more technically, they must have low quantum energy levels. This causes their positions to "smear out", effectively causing the individual atoms to overlap each other. In a Bose-Einstein condensate, the many overlapping atoms can be considered to be a single super-atom, with all of its constituent atoms sharing a single quantum state. The Bose-Einstein condensate therefore is a rare example of the uncertainty principle in action in the macroscopic world. Bose-Einstein condensates are extremely fragile. The slightest interaction with the outside world can be enough to warm them past the condensation threshold, causing them to break back down into individual atoms again; it will likely be some time before any practical applications are developed for them.
No comments:
Post a Comment