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Warn moderators| Author : | Topic: Spacetime | Bottom |
| experi-momentum Posts : 13  |
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 space-time 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. experi-momnentum |
| saucer admin Posts : 673 A Good Tautology is Hard to Find!  |
- Privileged character of 3+1 spacetime A number of scientists and philosophers have written about spacetime, and concepts have evolved as more theories have been deduced and tested by mathematical analysis or experimentation. Other writers have been limited by the scientific evidence available at the time. For example, in the latter 20th century, experiments with "atom-smasher" particle accelerators had revealed that individual protons accelerated to high speeds were gaining the mass equivalent to a car at rest, requiring ever-increasing amounts of energy to accelerate the protons even faster. While the passage of Time slowed at high speeds, the mass of the particles increased. Writers from previous eras were not aware of that evidence. - |
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