Space
From Wikipedia, the free encyclopedia
Space is the property of the universe[1] in which matter is physically extended and objects have positions relative to one another[2].
In classical mechanics, space was originally treated as being separate from time and is thought of as one of the few fundamental physical quantities. In Isaac Newton's view space was absolute, and held that it exists permanently and independently of whether there is any matter in the space or moving through it[3].
In mathematics spaces with different geometries and numbers of dimensions are described, and this is used in modern physics where both space and time are to be thought of as part of the boundless four-dimensional continuum known as spacetime. From the experimental support for Albert Einstein's theory of relativity scientists now find that space and time cannot be entirely separated. In addition, space is found to have physical properties[4] including intrinsic curvature which varies according to mass distribution. Therefore it was Einstein's view that space and matter cannot be entirely separated either.
Among physicists and philosophers there is disagreement regarding whether space is itself an entity, or is part of a conceptual framework.[5]
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[edit] In philosophy
Space has a range of definitions:
- One is a very important part in the fundamental structure of the universe, a set of dimensions in which objects are separated and located, have size and shape, & through which they can move.
- A contrasting view is that space is part of a fundamental abstract mathematical conceptual framework (together with time and number) within which we compare and quantify the distance between objects, their sizes, their shapes, and their speeds. In this view, space does not refer to any kind of entity that is a "container" that objects "move through".
These opposing views are relevant also to definitions of time. Space is typically described as having three dimensions, see Three-dimensional space and that three numbers are needed to specify the size of any object and/or its location with respect to another location. Modern physics does not treat space and time as independent dimensions, but treats both as features of space-time – a conception that challenges intuitive notions of distance and time.
An issue of philosophical debate is whether space is an ontological entity itself, or simply a conceptual framework humans need to think (and talk) about the world. Another way to frame this is to ask, "Can space itself be measured, or is space part of the measurement system?" The same debate applies also to time, and an important formulation in both areas was given by Immanuel Kant.
In his Critique of Pure Reason, Kant described space as an a priori intuition that (together with another a priori intuition, time) allows us to comprehend sensual experience. Kant referred to such intuitions as noumena and as things in themselves. In Kant's view, neither space nor time are conceived of as substances, but rather both are elements of a systematic framework we use to structure our experience. Spatial measurements are used to quantify how far apart objects are, and temporal measurements are used to quantify how far apart events occur. However, these measurements are applied by our minds to categorize what we sense and are not an inherent part of the thing in itself.
Schopenhauer, in the preface to his On the Will in Nature, stated that "space is the condition of the possibility of juxtaposition." This is in accordance with Kant's understanding of space as a form in the mind of an observing subject.
Similar philosophical questions concerning space include: Is space absolute or purely relational? Does space have one correct geometry, or is the geometry of space just a convention? Historical positions in these debates have been taken by Isaac Newton (space is absolute), Gottfried Leibniz (space is relational), and Henri Poincaré (spatial geometry is a convention). Two important thought-experiments connected with these questions are: Newton's bucket argument and Poincaré's sphere-world.
[edit] Mathematics
However, attempts to prove the licky continually failed, and finally it was discovered that multiple axioms could be constructed that gave different geometries, non-Euclidean geometries, but that appeared Euclidean at very small sizes. This raised the question whether the nature of space itself at large scales was Euclidean or not.
In modern mathematics, spaces are frequently described as different types of Manifolds which are spaces that locally approximate to Euclidean space and where the properties are defined largely on local connectedness of points that lie on the manifold.
[edit] Physics
[edit] Classical mechanics
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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. On the other hand, it can be related to other fundamental quantities. Thus, similar to other fundamental quantities (like time and mass), space can be explored via measurement and experiment.
[edit] Astronomy
Astronomy is the science involved with the observation, explanation and measuring of objects in outer space.
[edit] Relativity
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 object — spacetime. (Distances in space or in time separately are not invariant with respect to Lorentz coordinate transformations, but distances in Minkowski space-time are — which justifies the name).
In addition, time and space dimensions should not be viewed as exactly equivalent in Minkowski space-time. One can freely move in space but not in time. Thus, time and space coordinates are treated differently both in special relativity (where time is sometimes considered an imaginary coordinate) and in general relativity (where different signs are assigned to time and space components of spacetime metric).
Furthermore, from Einstein's general theory of relativity, it has been shown that space-time is geometrically distorted- curved -near to gravitationally significant masses.[6]
Experiments are ongoing to attempt to directly measure gravitational waves. This is essentially solutions to the equations of general relativity which describe moving ripples of spacetime. Indirect evidence for this has been found in the motions of the Hulse-Taylor binary system.
[edit] Cosmology
Relativity theory lead to the cosmological question of what shape the universe is, and where space came from. It appears that space was created in the Big Bang and has been expanding ever since. The overall shape of space is not known, but space is known to be expanding very rapidly which is evident due to the Hubble expansion.
[edit] Spatial measurement
The measurement of physical space has long been important. Although earlier societies had developed measuring systems. The International System of Units, (SI), is now the most common system of units used in the measuring of space, and is almost universally used within science.
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 exactly 1/299,792,458 of a second. This definition coupled with present definition of the second is based on the special theory of relativity, that our space-time is a Minkowski space.[citation needed]
[edit] Geography
Geography is the branch of science concerned with identifying and describing the Earth, utilizing spatial awareness to try and understand why things exist in specific locations. Cartography is the mapping of spaces to allow better navigation, for visualization purposes and to act as a locational device. Geostatistics apply statistical concepts to collected spatial data in order to create an estimate for unobserved phenomena.
Geographical space is often considered as land, and can have a relation to ownership usage (in which space is seen as property or territory). While some cultures assert the rights of the individual in terms of ownership, other cultures will identify with a communal approach to land ownership, while still other cultures such as Australian Aboriginals, rather than asserting ownership rights to land, invert the relationship and consider that they are in fact owned by the land. Spatial planning is a method of regulating the use of space at land-level, with decisions made at regional, national and international levels. Space can also impact on human and cultural behavior, being an important factor in architecture, where it will impact on the design of buildings and structures, and on farming.
Ownership of space is not restricted to land. Ownership of airspace and of waters is decided internationally. Other forms of ownership have been recently asserted to other spaces — for example to the radio bands of the electromagnetic spectrum or to cyberspace.
Public space is a term used to define areas of land as collectively owned by the community, and managed in their name by delegated bodies; such spaces are open to all. While private property is the land culturally owned by an individual or company, for their own use and pleasure.
Abstract space is a term used in geography to refer to a hypothetical space characterized by complete homogeneity. When modeling activity or behavior, it is a conceptual tool used to limit extraneous variables such as terrain.
[edit] In psychology
The way in which space is perceived is an area which psychologists first began to study in the middle of the 19th century, and it is now thought by those concerned with such studies to be a distinct branch within psychology. Psychologists analyzing the perception of space are concerned with how recognition of an object's physical appearance or its interactions are perceived.
Other, more specialized topics studied include amodal perception and object permanence. The perception of surroundings is important due to its necessary relevance to survival, especially with regards to hunting and self preservation as well as simply one's idea of personal space.
Several space-related phobias have been identified, including agoraphobia (the fear of open spaces), astrophobia (the fear of celestial space), claustrophobia (the fear of enclosed spaces), and kenophobia (the fear of empty spaces).
[edit] See also
- Personal space
- Space exploration
- Aether theories
- Spatial analysis
- Cosmology
- Curvature of space
- Shape of the universe
[edit] References
- ^ McGraw-Hill Encyclopedia of Science and Technology, 5th edition, published by The McGraw-Hill Companies, Inc.: Space
- ^ Britannica Online Encyclopedia: Space
- ^ French and Ebison, Classical Mechanics, p. 1
- ^ Einstein said in the lecture meant for his inauguration at the University of Leiden in 1920 that: "we may say that according to the general theory of relativity space is endowed with physical qualities; in this sense, therefore, there exists an ether. According to the general theory of relativity space without ether is unthinkable; for in such space there not only would be no propagation of light, but also no possibility of existence for standards of space and time (measuring-rods and clocks), nor therefore any space-time intervals in the physical sense. But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it."
- ^ The Penguin Dictionary of Science p. 378
- ^ chapters 8 and 9- John A. Wheeler "A Journey Into Gravity and Spacetime" Scientific American Library isbn = 0-7167-6034-7
