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Faster-than-light ( superluminal or supercausal) travel and communication are the conjectural propagation of matter or information faster than the speed of light ( c ). The special theory of relativity implies that only particles with zero rest mass (i.e., photons) may travel at the speed of light, and that nothing may travel faster.
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). [Note 3] According to the special theory of relativity, c is the upper limit for the speed at which ...
No-communication theorem. In physics, the no-communication theorem or no-signaling principle is a no-go theorem from quantum information theory which states that, during measurement of an entangled quantum state, it is not possible for one observer, by making a measurement of a subsystem of the total state, to communicate information to another ...
Cherenkov radiation ( / tʃəˈrɛŋkɒf / [1]) (also known as Čerenkov or Cerenkov radiation [2]) is electromagnetic radiation emitted when a charged particle (such as an electron) passes through a dielectric medium (such as distilled water) at a speed greater than the phase velocity (speed of propagation of a wavefront in a medium) of light ...
Speed of sound. The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. More simply, the speed of sound is how fast vibrations travel. At 20 °C (68 °F), the speed of sound in air is about 343 m/s (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn ), or 1 km in 2.91 s or one mile in 4.69 s.
Theorized. 1967. A tachyon ( / ˈtækiɒn /) or tachyonic particle is a hypothetical particle that always travels faster than light. Physicists believe that faster-than-light particles cannot exist because they are inconsistent with the known laws of physics. [ 1][ 2] If such particles did exist they could be used to send signals faster than light.
Lighthouse paradox. Observed distance traveled by light (from left to right) as light source rotates. At a sufficient distance, the speed at which the beam "moves" may exceed the speed of light. The lighthouse paradox is a thought experiment in which the speed of light is apparently exceeded. The rotating beam of light from a lighthouse is ...
Light fixtures bring a daylight glow and ambiance to any room, but they have to work correctly in order to be functional and safe. While most light bulb problems can be solved with a bulb swap ...