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  2. Four-velocity - Wikipedia

    en.wikipedia.org/wiki/Four-velocity

    The history of an object traces a curve in spacetime, called its world line. If the object has mass, so that its speed is necessarily less than the speed of light, the world line may be parametrized by the proper time of the object. The four-velocity is the rate of change of four-position with respect to the proper time along the curve. The ...

  3. Multiple time dimensions - Wikipedia

    en.wikipedia.org/wiki/Multiple_time_dimensions

    Dunne suggested that, in the context of a "block" spacetime as modelled by General Relativity, a second dimension of time was needed in order to measure the speed of one's progress along one's own timeline. This in turn required a level of the conscious self existing at the second level of time.

  4. Spacetime - Wikipedia

    en.wikipedia.org/wiki/Spacetime

    In physics, spacetime, also called the space-time continuum, is a mathematical model that fuses the three dimensions of space and the one dimension of time into a single four-dimensional continuum. Spacetime diagrams are useful in visualizing and understanding relativistic effects, such as how different observers perceive where and when events ...

  5. Time in physics - Wikipedia

    en.wikipedia.org/wiki/Time_in_physics

    is the corresponding change of coordinates.) The speed of light c can be seen as just a conversion factor needed because we measure the dimensions of spacetime in different units; since the metre is currently defined in terms of the second, it has the exact value of 299 792 458 m/s. We would need a similar factor in Euclidean space if, for ...

  6. iPad Air (4th generation) - Wikipedia

    en.wikipedia.org/wiki/IPad_Air_(4th_generation)

    The iPad Air (4th generation), informally referred to as iPad Air 4, is a tablet computer developed and marketed by Apple Inc. It was announced by Apple on September 15, 2020. Pre-orders began on October 16, 2020, and shipping began a week later on October 23, 2020, alongside the iPhone 12 and iPhone 12 Pro .

  7. Schwarzschild coordinates - Wikipedia

    en.wikipedia.org/wiki/Schwarzschild_coordinates

    In the theory of Lorentzian manifolds, spherically symmetric spacetimes admit a family of nested round spheres.In such a spacetime, a particularly important kind of coordinate chart is the Schwarzschild chart, a kind of polar spherical coordinate chart on a static and spherically symmetric spacetime, which is adapted to these nested round spheres.

  8. Minkowski space - Wikipedia

    en.wikipedia.org/wiki/Minkowski_space

    Hermann Minkowski (1864–1909) found that the theory of special relativity could be best understood as a four-dimensional space, since known as the Minkowski spacetime. In physics, Minkowski space (or Minkowski spacetime) (/ m ɪ ŋ ˈ k ɔː f s k i,-ˈ k ɒ f-/ [1]) is the main mathematical description of spacetime in the absence of gravitation.

  9. Shapiro time delay - Wikipedia

    en.wikipedia.org/wiki/Shapiro_time_delay

    Because, according to the general theory, the speed of a light wave depends on the strength of the gravitational potential along its path, these time delays should thereby be increased by almost 2 × 10 −4 sec when the radar pulses pass near the sun. Such a change, equivalent to 60 km in distance, could now be measured over the required path ...