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  2. Energy–momentum relation - Wikipedia

    en.wikipedia.org/wiki/Energy–momentum_relation

    This equation holds for a body or system, such as one or more particles, with total energy E, invariant mass m 0, and momentum of magnitude p; the constant c is the speed of light. It assumes the special relativity case of flat spacetime [ 1 ] [ 2 ] [ 3 ] and that the particles are free.

  3. Speed of light - Wikipedia

    en.wikipedia.org/wiki/Speed_of_Light

    v. t. e. The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second (approximately 300,000 kilometres per second; 186,000 miles per second; 671 million miles per hour).

  4. Length contraction - Wikipedia

    en.wikipedia.org/wiki/Length_contraction

    An observer at rest observing an object travelling very close to the speed of light would observe the length of the object in the direction of motion as very near zero. Then, at a speed of 13 400 000 m/s (30 million mph, 0.0447 c ) contracted length is 99.9% of the length at rest; at a speed of 42 300 000 m/s (95 million mph, 0.141 c ), the ...

  5. Cosmic inflation - Wikipedia

    en.wikipedia.org/wiki/Cosmic_inflation

    e. In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the very early universe. Following the inflationary period, the universe continued to expand, but at a slower rate. The re-acceleration of this slowing expansion due to dark energy began after the universe was ...

  6. 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.

  7. Photon - Wikipedia

    en.wikipedia.org/wiki/Photon

    The "time" axis gives the angular frequency (rad⋅s −1) and the "space" axis represents the angular wavenumber (rad⋅m −1). Green and indigo represent left and right polarization. In empty space, the photon moves at c (the speed of light) and its energy and momentum are related by E = pc, where p is the magnitude of the momentum vector p.

  8. Lorentz factor - Wikipedia

    en.wikipedia.org/wiki/Lorentz_factor

    Its initial value is 1 (when v = 0); and as velocity approaches the speed of light (v → c) γ increases without bound (γ → ∞). α (Lorentz factor inverse) as a function of velocity—a circular arc. In the table below, the left-hand column shows speeds as different fractions of the speed of light (i.e. in units of c). The middle column ...

  9. Rømer's determination of the speed of light - Wikipedia

    en.wikipedia.org/wiki/Rømer's_determination_of...

    By timing the eclipses of Jupiter's moon Io, Rømer estimated that light would take about 22 minutes to travel a distance equal to the diameter of Earth's orbit around the Sun. [1] Using modern orbits, this would imply a speed of light of 226,663 kilometres per second, [2] 24.4% lower than the true value of 299,792 km/s. [3]