In classical mechanics, space and time are different categories and refer to absolute space and time. That conception of the world is a four-dimensional space but not the one that was found necessary to describe electromagnetism. The four dimensions of spacetime consist of events that are not absolutely defined spatially and temporally, but rather are known relative to the motion of an observer. Minkowski space first approximates the universe without gravity; the pseudo-Riemannian manifolds of general relativity describe spacetime with matter and gravity. Ten dimensions are used to describe string theory, and the state-space of quantum mechanics is an infinite-dimensional function space.
The concept of dimension is not restricted to physical objects. High-dimensional spaces frequently occur in mathematics and the sciences. They may be parameter spaces or configuration spaces such as in Lagrangian or Hamiltonian mechanics; these are abstract spaces, independent of the physical space we live in.
- In mathematics
- In physics
- Networks and dimension
- In literature
- In philosophy
- More dimensions
- See also
- Further reading
- External links
The dimension of Euclidean n-space En is n. When trying to generalize to other types of spaces, one is faced with the question "what makes En n-dimensional?" One answer is that to cover a fixed ball in En by small balls of radius ε, one needs on the order of ε−n such small balls. This observation leads to the definition of the Minkowski dimension and its more sophisticated variant, the Hausdorff dimension, but there are also other answers to that question. For example, the boundary of a ball in En looks locally like En-1 and this leads to the notion of the inductive dimension. While these notions agree on En , they turn out to be different when one looks at more general spaces.
A tesseract is an example of a four-dimensional object. Whereas outside mathematics the use of the term "dimension" is as in: "A tesseract has four dimensions", mathematicians usually express this as: "The tesseract has dimension 4", or: "The dimension of the tesseract is 4".
Although the notion of higher dimensions goes back to René Descartes, substantial development of a higher-dimensional geometry only began in the 19th century, via the work of Arthur Cayley, William Rowan Hamilton, Ludwig Schläfli and Bernhard Riemann. Riemann's 1854 Habilitationsschrift, Schläfli's 1852 Theorie der vielfachen Kontinuität, Hamilton's 1843 discovery of the quaternions and the construction of the Cayley algebra marked the beginning of higher-dimensional geometry.
The rest of this section examines some of the more important mathematical definitions of the dimensions.
Dimension of a vector spaceEdit
ManifoldsEditA connected topological manifold is locally homeomorphic to Euclidean n-space, and the number n is called the manifold's dimension. One can show that this yields a uniquely defined dimension for every connected topological manifold.
For connected differentiable manifolds, the dimension is also the dimension of the tangent vector space at any point.
In geometric topology, the theory of manifolds is characterized by the way dimensions 1 and 2 are relatively elementary, the high-dimensional cases n > 4 are simplified by having extra space in which to "work"; and the cases n = 3 and 4 are in some senses the most difficult. This state of affairs was highly marked in the various cases of the Poincaré conjecture, where four different proof methods are applied.
An algebraic set being a finite union of algebraic varieties, its dimension is the maximum of the dimensions of its components. It is equal to the maximal length of the chains of sub-varieties of the given algebraic set (the length of such a chain is the number of "").
Each variety can be considered as an algebraic stack, and its dimension as variety agrees with its dimension as stack. There are however many stacks which do not correspond to varieties, and some of these have negative dimension. Specifically, if V is a variety of dimension m and G is an algebraic group of dimension n acting on V, then the quotient stack [V/G] has dimension m−n.
For an algebra over a field, the dimension as vector space is finite if and only if its Krull dimension is 0.
Lebesgue covering dimensionEdit
The inductive dimension of a topological space may refer to the small inductive dimension or the large inductive dimension, and is based on the analogy that (n + 1)-dimensional balls have n-dimensional boundaries, permitting an inductive definition based on the dimension of the boundaries of open sets.
Hilbert spacesEditEvery Hilbert space admits an orthonormal basis, and any two such bases for a particular space have the same cardinality. This cardinality is called the dimension of the Hilbert space. This dimension is finite if and only if the space's Hamel dimension is finite, and in this case the above dimensions coincide.
Spatial dimensionsEditClassical physics theories describe three physical dimensions: from a particular point in space, the basic directions in which we can move are up/down, left/right, and forward/backward. Movement in any other direction can be expressed in terms of just these three. Moving down is the same as moving up a negative distance. Moving diagonally upward and forward is just as the name of the direction implies; i.e., moving in a linear combination of up and forward. In its simplest form: a line describes one dimension, a plane describes two dimensions, and a cube describes three dimensions. (See Space and Cartesian coordinate system.)
|Example co-ordinate systems|
TimeEditA temporal dimension is a dimension of time. Time is often referred to as the "fourth dimension" for this reason, but that is not to imply that it is a spatial dimension. A temporal dimension is one way to measure physical change. It is perceived differently from the three spatial dimensions in that there is only one of it, and that we cannot move freely in time but subjectively move in one direction.
The equations used in physics to model reality do not treat time in the same way that humans commonly perceive it. The equations of classical mechanics are symmetric with respect to time, and equations of quantum mechanics are typically symmetric if both time and other quantities (such as charge and parity) are reversed. In these models, the perception of time flowing in one direction is an artifact of the laws of thermodynamics (we perceive time as flowing in the direction of increasing entropy).
The best-known treatment of time as a dimension is Poincaré and Einstein's special relativity (and extended to general relativity), which treats perceived space and time as components of a four-dimensional manifold, known as spacetime, and in the special, flat case as Minkowski space.
Additional dimensionsEditIn physics, three dimensions of space and one of time is the accepted norm. However, there are theories that attempt to unify the four fundamental forces by introducing more dimensions. Most notably, superstring theory requires 10 spacetime dimensions, and originates from a more fundamental 11-dimensional theory tentatively called M-theory which subsumes five previously distinct superstring theories. To date, no experimental or observational evidence is available to confirm the existence of these extra dimensions. If extra dimensions exist, they must be hidden from us by some physical mechanism. One well-studied possibility is that the extra dimensions may be "curled up" at such tiny scales as to be effectively invisible to current experiments. Limits on the size and other properties of extra dimensions are set by particle experiments[clarification needed] such as those at the Large Hadron Collider.
At the level of quantum field theory, Kaluza–Klein theory unifies gravity with gauge interactions, based on the realization that gravity propagating in small, compact extra dimensions is equivalent to gauge interactions at long distances. In particular when the geometry of the extra dimensions is trivial, it reproduces electromagnetism. However at sufficiently high energies or short distances, this setup still suffers from the same pathologies that famously obstruct direct attempts to describe quantum gravity. Therefore, these models still require a UV completion, of the kind that string theory is intended to provide. In particular, superstring theory requires six compact dimensions forming a Calabi–Yau manifold. Thus Kaluza-Klein theory may be considered either as an incomplete description on its own, or as a subset of string theory model building.
In addition to small and curled up extra dimensions, there may be extra dimensions that instead aren't apparent because the matter associated with our visible universe is localized on a (3 + 1)-dimensional subspace. Thus the extra dimensions need not be small and compact but may be large extra dimensions. D-branes are dynamical extended objects of various dimensionalities predicted by string theory that could play this role. They have the property that open string excitations, which are associated with gauge interactions, are confined to the brane by their endpoints, whereas the closed strings that mediate the gravitational interaction are free to propagate into the whole spacetime, or "the bulk". This could be related to why gravity is exponentially weaker than the other forces, as it effectively dilutes itself as it propagates into a higher-dimensional volume.
Some aspects of brane physics have been applied to cosmology. For example, brane gas cosmology attempts to explain why there are three dimensions of space using topological and thermodynamic considerations. According to this idea it would be because three is the largest number of spatial dimensions where strings can generically intersect. If initially there are lots of windings of strings around compact dimensions, space could only expand to macroscopic sizes once these windings are eliminated, which requires oppositely wound strings to find each other and annihilate. But strings can only find each other to annihilate at a meaningful rate in three dimensions, so it follows that only three dimensions of space are allowed to grow large given this kind of initial configuration.
Extra dimensions are said to be universal if all fields are equally free to propagate within them.
Networks and dimensionEdit
One of the most heralded science fiction stories regarding true geometric dimensionality, and often recommended as a starting point for those just starting to investigate such matters, is the 1884 novella Flatland by Edwin A. Abbott. Isaac Asimov, in his foreword to the Signet Classics 1984 edition, described Flatland as "The best introduction one can find into the manner of perceiving dimensions."
The idea of other dimensions was incorporated into many early science fiction stories, appearing prominently, for example, in Miles J. Breuer's The Appendix and the Spectacles (1928) and Murray Leinster's The Fifth-Dimension Catapult (1931); and appeared irregularly in science fiction by the 1940s. Classic stories involving other dimensions include Robert A. Heinlein's —And He Built a Crooked House (1941), in which a California architect designs a house based on a three-dimensional projection of a tesseract; and Alan E. Nourse's Tiger by the Tail and The Universe Between (both 1951). Another reference is Madeleine L'Engle's novel A Wrinkle In Time (1962), which uses the fifth dimension as a way for "tesseracting the universe" or "folding" space in order to move across it quickly. The fourth and fifth dimensions were also a key component of the book The Boy Who Reversed Himself by William Sleator.
"Space has Four Dimensions" is a short story published in 1846 by German philosopher and experimental psychologist Gustav Fechner under the pseudonym "Dr. Mises". The protagonist in the tale is a shadow who is aware of and able to communicate with other shadows, but who is trapped on a two-dimensional surface. According to Fechner, this "shadow-man" would conceive of the third dimension as being one of time. The story bears a strong similarity to the "Allegory of the Cave" presented in Plato's The Republic (c. 380 BC).
Simon Newcomb wrote an article for the Bulletin of the American Mathematical Society in 1898 entitled "The Philosophy of Hyperspace". Linda Dalrymple Henderson coined the term "hyperspace philosophy", used to describe writing that uses higher dimensions to explore metaphysical themes, in her 1983 thesis about the fourth dimension in early-twentieth-century art. Examples of "hyperspace philosophers" include Charles Howard Hinton, the first writer, in 1888, to use the word "tesseract"; and the Russian esotericist P. D. Ouspensky.
Topics by dimensionEdit
|This article needs additional citations for verification. (May 2010)|
- "Curious About Astronomy". Curious.astro.cornell.edu. Retrieved 2014-03-03.
- "MathWorld: Dimension". Mathworld.wolfram.com. 2014-02-27. Retrieved 2014-03-03.
- Yau, S-T and Nadis, S.; The Shape of Inner Space, Basic Books, 2010, Chapter 4.
- Fantechi, Barbara (2001), "Stacks for everybody" (PDF), European Congress of Mathematics Volume I, Progr. Math. 201, Birkhäuser, pp. 349–359
- Fractal Dimension, Boston University Department of Mathematics and Statistics
- Bunde, Armin; Havlin, Shlomo, eds. (1991). Fractals and Disordered Systems. Springer.
- Bunde, Armin; Havlin, Shlomo, eds. (1994). Fractals in Science. Springer.
- CMS Collaboration, "Search for Microscopic Black Hole Signatures at the Large Hadron Collider" (arxiv.org)
- Brandenberger, R., Vafa, C., Superstrings in the early universe
- Scott Watson, Brane Gas Cosmology (pdf).
- Song, Chaoming; Havlin, Shlomo; Makse, Hernán A. (2005). "Self-similarity of complex networks". Nature 433 (7024). arXiv:cond-mat/0503078v1. Bibcode:2005Natur.433..392S. doi:10.1038/nature03248.
- Daqing, Li; Kosmidis, Kosmas; Bunde, Armin; Havlin, Shlomo (2011). "Dimension of spatially embedded networks". Nature Physics 7 (6). Bibcode:2011NatPh...7..481D. doi:10.1038/nphys1932.
- Prolegomena, § 12
- Banchoff, Thomas F. (1990). "From Flatland to Hypergraphics: Interacting with Higher Dimensions". Interdisciplinary Science Reviews 15 (4): 364. doi:10.1179/030801890789797239.
- Newcomb, Simon (1898). "The Philosophy of Hyperspace". Bulletin of the American Mathematical Society 4 (5): 187. doi:10.1090/S0002-9904-1898-00478-0.
- Kruger, Runette (2007). "Art in the Fourth Dimension: Giving Form to Form – The Abstract Paintings of Piet Mondrian" (PDF). Spaces of Utopia: an Electronic Journal (5): 11.
- Pickover, Clifford A. (2009), "Tesseract", The Math Book: From Pythagoras to the 57th Dimension, 250 Milestones in the History of Mathematics, Sterling Publishing Company, Inc., p. 282, ISBN 9781402757969 .
- Katta G Murty, "Systems of Simultaneous Linear Equations" (Chapter 1 of Computational and Algorithmic Linear Algebra and n-Dimensional Geometry, World Scientific Publishing: 2014 (ISBN 978-981-4366-62-5).
- Edwin A. Abbott, Flatland: A Romance of Many Dimensions (1884) (Public domain: Online version with ASCII approximation of illustrations at Project Gutenberg).
- Thomas Banchoff, Beyond the Third Dimension: Geometry, Computer Graphics, and Higher Dimensions, Second Edition, W. H. Freeman and Company: 1996.
- Clifford A. Pickover, Surfing through Hyperspace: Understanding Higher Universes in Six Easy Lessons, Oxford University Press: 1999.
- Rudy Rucker, The Fourth Dimension, Houghton-Mifflin: 1984.
- Kaku, Michio (1994). Hyperspace, a Scientific Odyssey Through the 10th Dimension. Oxford University Press. ISBN 0-19-286189-1.
- Krauss, Lawrence M. (2005). Hiding in the Mirror. Viking Press. ISBN 0670033952.
|Wikiquote has quotations related to: Dimension|
|Wikimedia Commons has media related to Dimensions.|
- Copeland, Ed (2009). "Extra Dimensions". Sixty Symbols. Brady Haran for the University of Nottingham.