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2. List of unsolved problems in astronomy - Wikipedia

   en.wikipedia.org/wiki/List_of_unsolved_problems...

   Since 2003, Jean-Pierre Luminet, et al., and other groups have suggested that the shape of the universe may be the Poincaré dodecahedral space. Is the shape unmeasurable, the Poincaré space, or another 3-manifold? Cosmic inflation: Is the theory of cosmic inflation in the very early universe correct? If so, what are the details of this epoch?

3. Shapiro time delay - Wikipedia

   en.wikipedia.org/wiki/Shapiro_time_delay

   In a 1964 article entitled Fourth Test of General Relativity, Irwin Shapiro wrote: [1] 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 ...

4. Theory of relativity - Wikipedia

   en.wikipedia.org/wiki/Theory_of_relativity

   The theory transformed theoretical physics and astronomy during the 20th century, superseding a 200-year-old theory of mechanics created primarily by Isaac Newton. [ 3 ] [ 4 ] [ 5 ] It introduced concepts including 4- dimensional spacetime as a unified entity of space and time , relativity of simultaneity , kinematic and gravitational time ...

5. 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 ...

6. 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.

7. Theoretical astronomy - Wikipedia

   en.wikipedia.org/wiki/Theoretical_astronomy

   The Deep Space Network, or DSN, is an international network of large antennas and communication facilities that supports interplanetary spacecraft missions, and radio and radar astronomy observations for the exploration of the Solar System and the universe. The network also supports selected Earth-orbiting missions.

8. Quantum field theory in curved spacetime - Wikipedia

   en.wikipedia.org/wiki/Quantum_field_theory_in...

   In theoretical physics, quantum field theory in curved spacetime (QFTCS) [1] is an extension of quantum field theory from Minkowski spacetime to a general curved spacetime. This theory uses a semi-classical approach; it treats spacetime as a fixed, classical background, while giving a quantum-mechanical description of the matter and energy ...

9. Four-tensor - Wikipedia

   en.wikipedia.org/wiki/Four-tensor

   In special relativity, one of the simplest non-trivial examples of a four-tensor is the four-displacement = (,,,) = (,,,) a four-tensor with contravariant rank 1 and covariant rank 0.