# what is space time???

i have heard these two words many times "space time" but what does it really means?

### 7 Answers

- Michael da ManLv 61 decade agoFavorite Answer
The space in front of your face right now will be different by the time you get to the end of this sentence. The molecules in it will be different. Dust motes will drift in and out of it. Its temperature will go up and down. That all means the space in front of you can only be described by 4 dimensions, length, width, height and time.

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- Anonymous1 decade ago
We perceive three spacial dimensions, and we experience the passage of time. In our minds, space and time are entirely different. But computers can be programmed to handle space and time in pretty much the same way in a four dimensional virtual space-time. Distances in 3D space are measured by taking the square root of (x^2 + y^ + z^2). In 4D space-time, the distance between two points is the square root of (x^2 + y^ + z^2 -ct^2).

The formulas of Einstein's general relativity are written for warped 4D space-time. The result is highly efficient computation of trajectories in gravitational fields at relativistic speeds. The same end result can be obtained by applying special relativity to small increments of time (an iterative numerical approach) in a flat 3D space, but the computer time required is much greater.

Edit: Jedi & rdcatchme: You guys really need to post a link to the source when you cut and paste someone else's work! Better yet, don't cut and paste. Instead, post the link and write your own original comments.

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- Anonymous1 decade ago
Imagine yourself inside a huge 3D box. It has length, depth, and height. The box is full of space. There is a point 'A' and a point 'B' located in that space. You want to go from 'A' to 'B.' To do so you must move through space which takes time.

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- 1 decade ago
Very in-depth topic, it's basically the relationship, and complete existance, of Space and Time. We used to think that they had nothing to do with each other, however, according to Albert Einstein's Theory of Relativity, they fit perfectly together. It's basically an abstract concept of how the universe operates, considering that it takes time to travel through space, and you have to have space to travel through for time to make sense!

I realize that this textbook answer probably doesn't make very much sense to you, as it did not to me when I first became interested in it, but this link: http://science.howstuffworks.com/time-dilation.htm provides an easy-to-understand way of thinking about it.... with a slightly humorous slant! (Page 2 talks about space-time more in-depth)

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- ShantLv 41 decade ago
The way how space and time are related. Without space, there would be no time, and with out time there would not be space. They are interdependent.

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- Anonymous1 decade ago
In physics, spacetime is any mathematical model that combines space and time into a single construct called the spacetime continuum. Spacetime is usually interpreted with space being three-dimensional and time playing the role of the fourth dimension. According to Euclidean space perception, the universe has three dimensions of space, and one dimension of time. By combining space and time into a single manifold, physicists have significantly simplified a large amount of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels.

In classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer. In relativistic contexts, however, time cannot be separated from the three dimensions of space because the rate at which time passes depends on an object's velocity relative to the speed of light, and also the strength of intense gravitational fields which can slow the passage of time, and as such is dependent on the state of motion of the observer and is therefore not universal.

Spacetimes are the arenas in which all physical events take place — an event is a point in spacetime specified by its time and place. For example, the motion of planets around the Sun may be described in a particular type of spacetime, or the motion of light around a rotating star may be described in another type of spacetime. The basic elements of spacetime are events. In any given spacetime, an event is a unique position at a unique time. Examples of events include the explosion of a star or the single beat of a drum.

A spacetime is independent of any observer.[3] However, in describing physical phenomena (which occur at certain moments of time in a given region of space), each observer chooses a convenient coordinate system. Events are specified by four real numbers in any coordinate system. The worldline of a particle or light beam is the path that this particle or beam takes in the spacetime and represents the history of the particle or beam. The worldline of the orbit of the Earth is depicted in two spatial dimensions x and y (the plane of the Earth orbit) and a time dimension orthogonal to x and y. The orbit of the Earth is an ellipse in space alone, but its worldline is a helix in spacetime.

The unification of space and time is exemplified by the common practice of expressing distance in units of time, by dividing the distance measurement by the speed of light.

The concept of spacetime combines space and time within a single coordinate system, typically with 4 dimensions: length, width, height, and time. Dimensions are components of a coordinate grid typically used to locate a point in space, or on the globe, such as by latitude, longitude and planet (Earth). However, with spacetime, the coordinate grid is used to locate "events" (rather than just points in space), so time is added as another dimension to the grid.

Formerly, from experiments at slow speeds, time was believed to be a constant, which progressed at a fixed rate; however, later high-speed experiments revealed that time slowed down at higher speeds (with such slowing called "time dilation"). Many experiments have confirmed the slowing from time dilation, such as atomic clocks onboard a Space Shuttle running slower than synchronized Earth-bound clocks. Since time varies, it is treated as a variable within the spacetime coordinate grid, and time is no longer assumed to be a constant, independent of the location in space.

Note that treating spacetime events with the 4 dimensions (including time) is the conventional view; however, other invented coordinate grids treat time as 3 additional dimensions, with length-time, width-time, and height-time, to accompany the 3 dimensions of space. When dimensions are understood as mere components of the grid system, rather than physical attributes of space, it is easier to understand the alternate dimensional views, such as: latitude, longitude, plus Greenwich Mean Time (3 dimensions), or city, state, postal code, country, and UTC time (5 dimensions). The various dimensions are chosen, depending on the coordinate grid used.

The term spacetime has taken on a generalized meaning with the advent of higher-dimensional theories. How many dimensions are needed to describe the universe is still an open question. Speculative theories such as string theory predict 10 or 26 dimensions (with M-theory predicting 11 dimensions; 10 spatial and 1 temporal), but the existence of more than four dimensions would only appear to make a difference at the subatomic level.

For physical reasons, a space-time continuum is mathematically defined as a four-dimensional, smooth, connected Lorentzian manifold (M,g). This means the smooth Lorentz metric g has signature . The metric determines the geometry of spacetime, as well as determining the geodesics of particles and light beams. About each point (event) on this manifold, coordinate charts are used to represent observers in reference frames. Usually, Cartesian coordinates are used. Moreover, for simplicity's sake, the speed of light 'c' is usually assumed to be unity.

A reference frame (observer) can be identified with one of these coordinate charts; any such observer can describe any event p. Another reference frame may be identified by a second coordinate chart about p. Two observers (one in each reference frame) may describe the same event p but obtain different descriptions.

Usually, many overlapping coordinate charts are needed to cover a manifold. Given two coordinate charts, one containing p (representing an observer) and another containing q (another observer), the intersection of the charts represents the region of spacetime in which both observers can measure physical quantities and hence compare results. The relation between the two sets of measurements is given by a non-singular coordinate transformation on this intersection. The idea of coordinate charts as 'local observers who can perform measurements in their vicinity' also makes good physical sense, as this is how one actually collects physical data - locally.

For example, two observers, one of whom is on Earth, but the other one who is on a fast rocket to Jupiter, may observe a comet crashing into Jupiter (this is the event p). In general, they will disagree about the exact location and timing of this impact, i.e., they will have different 4-tuples (as they are using different coordinate systems). Although their kinematic descriptions will differ, dynamical (physical) laws, such as momentum conservation and the first law of thermodynamics, will still hold. In fact, relativity theory requires more than this in the sense that it stipulates these (and all other physical) laws must take the same form in all coordinate systems. This introduces tensors into relativity, by which all physical quantities are represented.

Geodesics are said to be timelike, null, or spacelike if the tangent vector to one point of the geodesic is of this nature. The paths of particles and light beams in spacetime are represented by timelike and null (light-like) geodesics (respectively).

Hope I helped. :)

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- Anonymous1 decade ago
In physics, spacetime is any mathematical model that combines space and time into a single construct called the spacetime continuum. Spacetime is usually interpreted with space being three-dimensional and time playing the role of the fourth dimension. According to Euclidean space perception, the universe has three dimensions of space, and one dimension of time. By combining space and time into a single manifold, physicists have significantly simplified a large amount of physical theories, as well as described in a more uniform way the workings of the universe at both the supergalactic and subatomic levels.

In classical mechanics, the use of Euclidean space instead of spacetime is appropriate, as time is treated as universal and constant, being independent of the state of motion of an observer. In relativistic contexts, however, time cannot be separated from the three dimensions of space because the rate at which time passes depends on an object's velocity relative to the speed of light, and also the strength of intense gravitational fields which can slow the passage of time, and as such is dependent on the state of motion of the observer and is therefore not universal.

Contents [hide]

1 Concept with dimensions

2 Historical origin

3 Basic concepts

3.1 Time-like interval

3.2 Light-like interval

3.3 Space-like interval

3.4 Space-time intervals

4 Mathematics of space-times

4.1 Topology

4.2 Space-time symmetries

4.3 Causal structure

5 Spacetime in special relativity

6 Spacetime in general relativity

7 Quantized space-time

8 Spiralization and Compression Theory

9 Privileged character of 3+1 spacetime

10 See also

11 References

12 External links

[edit] Concept with dimensions

The concept of spacetime combines space and time within a single coordinate system, typically with 4 dimensions: length, width, height, and time. Dimensions are components of a coordinate grid typically used to locate a point in space, or on the globe, such as by latitude, longitude and planet (Earth). However, with spacetime, the coordinate grid is used to locate "events" (rather than just points in space), so time is added as another dimension to the grid.

Formerly, from experiments at slow speeds, time was believed to be a constant, which progressed at a fixed rate; however, later high-speed experiments revealed that time slowed down at higher speeds (with such slowing called "time dilation"). Many experiments have confirmed the slowing from time dilation, such as atomic clocks onboard a Space Shuttle running slower than synchronized Earth-bound clocks. Since time varies, it is treated as a variable within the spacetime coordinate grid, and time is no longer assumed to be a constant, independent of the location in space.

Note that treating spacetime events with the 4 dimensions (including time) is the conventional view; however, other invented coordinate grids treat time as 3 additional dimensions, with length-time, width-time, and height-time, to accompany the 3 dimensions of space. When dimensions are understood as mere components of the grid system, rather than physical attributes of space, it is easier to understand the alternate dimensional views, such as: latitude, longitude, plus Greenwich Mean Time (3 dimensions), or city, state, postal code, country, and UTC time (5 dimensions). The various dimensions are chosen, depending on the coordinate grid used.

The term spacetime has taken on a generalized meaning with the advent of higher-dimensional theories. How many dimensions are needed to describe the universe is still an open question. Speculative theories such as string theory predict 10 or 26 dimensions (with M-theory predicting 11 dimensions; 10 spatial and 1 temporal), but the existence of more than four dimensions would only appear to make a difference at the subatomic level.

[edit] Historical origin

The origins of this 20th century scientific concept began in the 19th century with fiction writers. Edgar Allan Poe stated in his essay on cosmology titled Eureka (1848) that "Space and duration are one." This is the first known instance of suggesting space and time to be one thing. Poe arrived at this conclusion after approximately 90 pages of reasoning but employed no mathematics. In 1895, in his novel, The Time Machine, H.G. Wells wrote, “There is no difference between time and any of the three dimensions of space except that our consciousness moves along it.” He added, “Scientific people…know very well that time is only a kind of space.”

While spacetime can be viewed as a consequence of Albert Einstein's 1905 theory of special relativity, it was first explicitly proposed mathematically by one of his teachers, the mathematician Hermann Minkowski, in a 1908 essay [1] building on and extending Einstein's work. His concept of Minkowski space is the earliest treatment of space and time as two aspects of a unified whole, the essence of special relativity. The idea of Minkowski Space also led to special relativity being viewed in a more geometrical way, this geometric viewpoint of spacetime being important in general relativity too. (For an English translation of Minkowski's article, see Lorentz et al. 1952.) The 1926 thirteenth edition of the Encyclopedia Britannica included an article by Einstein titled "space-time".[2]

[edit] Basic concepts

Spacetimes are the arenas in which all physical events take place — an event is a point in spacetime specified by its time and place. For example, the motion of planets around the Sun may be described in a particular type of spacetime, or the motion of light around a rotating star may be described in another type of spacetime. The basic elements of spacetime are events. In any given spacetime, an event is a unique position at a unique time. Examples of events include the explosion of a star or the single beat of a drum.

A spacetime is independent of any observer.[3] However, in describing physical phenomena (which occur at certain moments of time in a given region of space), each observer chooses a convenient coordinate system. Events are specified by four real numbers in any coordinate system. The worldline of a particle or light beam is the path that this particle or beam takes in the spacetime and represents the history of the particle or beam. The worldline of the orbit of the Earth is depicted in two spatial dimensions x and y (the plane of the Earth orbit) and a time dimension orthogonal to x and y. The orbit of the Earth is an ellipse in space alone, but its worldline is a helix in spacetime.

The unification of space and time is exemplified by the common practice of expressing distance in units of time, by dividing the distance measurement by the speed of light.

[edit] Time-like interval

For two events separated by a time-like interval, enough time passes between them for there to be a cause-effect relationship between the two events. For a particle travelling less than the speed of light, any two events which occur to or by the particle must be separated by a time-like interval. Event pairs with time-like separation define a positive squared spacetime interval (s2 > 0) and may be said to occur in each other's future or past.

The measure of a time-like spacetime interval is described by the proper time:

(proper time).

The proper time interval would be measured by an observer with a clock traveling between the two events in an inertial reference frame, when the observer's path intersects each event as that event occurs. (The proper time defines a real number, since the interior of the square root is positive.)

[edit] Light-like interval

In a light-like interval, the spatial distance between two events is exactly balanced by the time between the two events. The events define a squared spacetime interval of zero (s2 = 0).

Events which occur to or by a photon along its path (i.e., while travelling at c, the speed of light) all have light-like separation. Given one event, all those events which follow at light-like intervals define the propagation of a light cone, and all the events which preceded from a light-like interval defined a second light cone.

[edit] Space-like interval

When a space-like interval separates two events, not enough time passes between their occurrences for there to exist a causal relationship crossing the spatial distance between the two events at the speed of light or slower. Generally, the events are considered not to occur in each other's future or past. There exists a reference frame such that the two events are observed to occur at the same time.

For these space-like event pairs with a negative squared spacetime interval (s2 < 0), the measurement of space-like separation is the proper distance:

(proper distance).

Like the proper time of time-like intervals, the proper distance (Δσ) of space-like spacetime intervals is a real number value.

[edit] Space-time intervals

As can be seen, neither spacelike nor timelike intervals are invariant, but it is desirable to have invariants that can be used where events are not on light-like intervals. Spacetime entails a new concept of distance. Whereas distances in Euclidean spaces are entirely spatial and always positive, in special relativity the concept of distance is quantified in terms of the space-time interval between two events, which occur in two locations at two times:

(spacetime interval),

where:

c is the speed of light,

Δt and Δr denote differences of the time and space coordinates, respectively, between the events.

(Note that the choice of signs for s2 above follows the Landau-Lifshitz spacelike convention. Other treatments, including some within Wikipedia, reverse the sign of s2.)

Space-time intervals may be classified into three distinct types based on whether the temporal

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