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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.
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.
For example, for visible light, the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200 000 km/s (124 000 mi/s); the refractive index of air for visible light is about 1.0003, so the speed of light in air is about 90 km/s (56 mi/s) slower than c.
Four-velocity. In physics, in particular in special relativity and general relativity, a four-velocity is a four-vector in four-dimensional spacetime [nb 1] that represents the relativistic counterpart of velocity, which is a three-dimensional vector in space. Physical events correspond to mathematical points in time and space, the set of all ...
As a wave, light is characterized by a velocity (the speed of light), wavelength, and frequency. As particles, light is a stream of photons . Each has an energy related to the frequency of the wave given by Planck's relation E = hf , where E is the energy of the photon, h is the Planck constant , 6.626 × 10 −34 J·s, and f is the frequency ...
A proton with that much energy would travel 1.665 × 10 15 times closer to the speed of light than the Oh-My-God particle did. As viewed from Earth and observed in Earth's reference frame, it would take about 3.579 × 10 20 years (2.59 × 10 10 times the current age of the universe) for a photon to overtake a Planck energy proton with a 1 cm lead.
The speed of light in vacuum is defined to be exactly 299 792 458 m/s (approx. 186,282 miles per second). The fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light. All forms of electromagnetic radiation move at exactly this same speed in vacuum.
Lorentz factor. where and v is the relative velocity between two inertial frames. For two frames at rest, γ = 1, and increases with relative velocity between the two inertial frames. As the relative velocity approaches the speed of light, γ → ∞. Time dilation (different times t and t' at the same position x in same inertial frame)