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  2. Expansion of the universe - Wikipedia

    en.wikipedia.org/wiki/Expansion_of_the_universe

    The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. [1] It is an intrinsic expansion, so it does not mean that the universe expands "into" anything or that space exists "outside" it. To any observer in the universe, it appears that all but the nearest galaxies ...

  3. 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 ...

  4. Inertial frame of reference - Wikipedia

    en.wikipedia.org/wiki/Inertial_frame_of_reference

    In classical physics and special relativity, an inertial frame of reference (also called inertial space, or Galilean reference frame) is a stationary or uniformly moving frame of reference. Observed relative to such a frame, objects exhibit inertia, that is, remain at rest until acted upon by external forces, and the laws of nature can be ...

  5. Comoving and proper distances - Wikipedia

    en.wikipedia.org/wiki/Comoving_and_proper_distances

    In standard cosmology, comoving distance and proper distance (or physical distance) are two closely related distance measures used by cosmologists to define distances between objects. Comoving distance factors out the expansion of the universe, giving a distance that does not change in time due to the expansion of space (though this may change ...

  6. Special relativity - Wikipedia

    en.wikipedia.org/wiki/Special_relativity

    e. In physics, the special theory of relativity, or special relativity for short, is a scientific theory of the relationship between space and time. In Albert Einstein 's 1905 paper, On the Electrodynamics of Moving Bodies, the theory is presented as being based on just two postulates: [p 1][1][2] The laws of physics are invariant (identical ...

  7. General relativity - Wikipedia

    en.wikipedia.org/wiki/General_relativity

    General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation ...

  8. Derivations of the Lorentz transformations - Wikipedia

    en.wikipedia.org/wiki/Derivations_of_the_Lorentz...

    In the fundamental branches of modern physics, namely general relativity and its widely applicable subset special relativity, as well as relativistic quantum mechanics and relativistic quantum field theory, the Lorentz transformation is the transformation rule under which all four-vectors and tensors containing physical quantities transform ...

  9. Mass in special relativity - Wikipedia

    en.wikipedia.org/wiki/Mass_in_special_relativity

    The relativistic mass is the sum total quantity of energy in a body or system (divided by c2). Thus, the mass in the formula is the relativistic mass. For a particle of non-zero rest mass m moving at a speed relative to the observer, one finds. In the center of momentum frame, and the relativistic mass equals the rest mass.