In Mathematics

Space is a set, with some particular properties and usually some additional structure. It is not a formally defined concept as such, but a generic name for a number of similar concepts, most of which generalize some abstract properties of the physical concept of space.

In particular, a vector space and specifically a Euclidean space can be seen as generalizations of the concept of a Euclidean coordinate system. Important varieties of vector spaces with more imposed structure include Banach space and Hilbert space. Distance measurement is abstracted as the concept of metric space and volume measurement leads to the concept of measure space.

As far as the concept of dimension is defined, although three-dimensional space is the most commonly thought of dimensional space, the number of dimensions for a space to exist need not be three: it can also be zero, one, two, more than three, finite or infinite, and with some definitions, a non-integer value. Mathematicians often study general structures that hold regardless of the number of dimensions

Halloween Costume

The Black market

The Black market or underground market is the part of economic activity involving illegal dealings, typically the buying and selling of merchandise or services illegally. The goods themselves may be illegal to sell ; the merchandise may be stolen; or the merchandise may be otherwise legal goods sold illicitly to avoid tax payments or licensing requirements, such as cigarettes or unregistered firearms. It is so called because "black economy" or "black market" affairs are conducted outside the law, and so are necessarily conducted "in the dark", out of the sight of the law.

Black markets develop when the state places restrictions on the production or provision of goods and services. These markets prosper, then, when state restrictions are heavy, such as during a period of prohibition, price controls and/or rationing. However, black markets are currently present in any known economy.

Halloween Costumes

White tea

Young leaves (new growth buds) that have undergone no oxidation; the buds may be protected from sunlight to avoid formation of chlorophyll. White tea is produced in lesser quantities than most other styles, and can be correspondingly more expensive than tea from the same plant processed by other methods. It is less well known in countries outside of China, though this is altering with increased western interest in natural or finest teas.

Halloween Costumes

People mover

A people mover or automated people mover is a completely automated, grade-separated transit system. The term is normally used only to describe systems serving relatively small areas such as airports, downtown districts or theme parks, but is sometimes useful to considerably more complex automated systems. The term does not involve any particular technology, and a people mover may use technologies such as monorail, duorail, automated guide way transit or maglev. Propulsion may engage conventional on-board electric motors, linear motors or cable traction.

A few complex APMs deploy fleets of small vehicles over a track network with off-line stations, and supply near non-stop service to passengers. These taxi-like systems are more frequently referred to as personal rapid transit. Other complex APMs have related characteristics to mass transit systems, and there is no clear cut difference between a complex APM of this type and an automated mass transit system.

Halloween Costumes

In Physics

Space is one of the few fundamental quantities in physics, meaning that it cannot be defined via other quantities because there is nothing more fundamental known at present. Thus, similar to the definition of other fundamental quantities, space is defined via measurement. Currently, the standard space interval, called a standard meter or simply meter, is defined as the distance traveled by light in a vacuum during a time interval of 1/299792458 of a second. This definition coupled with present definition of time makes our space-time to be Minkowski space and makes special relativity theory to be absolutely correct by definition.

In classical physics, space is a three-dimensional Euclidean space where any position can be described using three coordinates. Special and general relativity uses space-time rather than space; space-time is modeled as a four-dimensional space with the time axis being imaginary in special relativity and real in general relativity, and currently there are many theories which use more than four-dimensional spaces.

Before Einstein's work on relativistic physics, time and space were viewed as independent dimensions. Einstein's discoveries have shown that due to relativity of motion our space and time can be mathematically combined into one symmetric object — space-time.

Halloween Costumes