Speed ​​of light

The speed of light.In a vacuum it is by definition a universal constant with a value of 299,792,458 m / s (it usually approaches 3 · 108 m / s), or what is the same 9.46 · 1015 m / year; the second number is the one used to define the interval called light year. It is symbolized with the letter c, from the Latin celéritās (in Spanish speed or speed), and is also known as the Einstein constant. [Citation needed] The value of the speed of light in vacuum was officially included in the System International Units as a constant on October 21, 1983, thus turning the meter into a unit derived from this constant. The speed through a medium other than “vacuum” depends on its electrical permittivity, its magnetic permeability, and other electromagnetic characteristics. In material means, this speedit is less than “c” and is coded in the refractive index. In more subtle vacuum modifications, such as curved spaces, the Casimir effect, thermal populations, or the presence of external fields, the speed of light depends on the energy density of that vacuum


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  • 1 History
  • 2 Applications of Light
  • 3 Sources
  • 4 The fastest in the known universe


According to standard modern physics , all electromagnetic radiation (including visible light) propagates or moves at a constant speed in a vacuum, commonly known as “speed of light” (vector magnitude), rather than “speed of light “(scalar magnitude). This is a physical constant denoted as c. The speed c is also the speed of the propagation of gravity in the Theory of relativity . One consequence of the laws of electromagnetism (such as Maxwell’s equations ) is that the radiation rate celectromagnetic does not depend on the speed of the object emitting radiation. Thus, for example, light emitted from a rapidly moving light source would travel at the same speed as light from a stationary source (although the color, frequency, energy, and momentum of light will change; a phenomenon that known as the Doppler Effect ). If this observation is combined with the principle of relativity, it is concluded that all observers will measure the speed of light in a vacuum as one, regardless of the observer’s frame of reference or the speed of the light-emitting object. Because of this, ac can be viewed as a fundamental physical constant. This fact, then, can be used as a basis in the theory of relativity.special. The constant is the speed c, rather than the light itself, which is fundamental to special relativity. Thus, if the light is somehow slowed down to travel at a speed less than c, this will not directly affect the theory of special relativity. Observers traveling at high speeds will find that distances and times are distorted according to the Lorentz transformation. However, the transformations distort times and distances so that the speed of light remains constant. A person traveling at a speed close to c will also find that the colors of the light in front turn blue and back turn red.

Light Applications

The speed of light is of great importance for telecommunications. For example, since the Earth’s perimeter is 40,075 km (on the equator) and c is theoretically the fastest speed at which a piece of information can travel, the shortest period of time to reach the other end of the globe earth globe would be 0.067 s. Travel times are slightly longer today, in part because the speed of light is about 30% lower on an optical fiber, and there are rarely straight paths in global communications; In addition, delays occur when the signal passes through electrical switches or signal generators. In 2004, the typical delay in receiving signals from Australia or Japan to the US it was 0.18 s. Further, the speed of light affects the design of wireless communications. The finite speed of light became apparent to everyone in the control of communications between Houston Ground Control and Neil Armstrong, when he became the first man to set foot on the Moon: after every question, Houston he had to wait about 3 s for a response to return even though the astronauts responded immediately. Similarly, instant remote control of an interplanetary spacecraft is impossible because a spacecraft far enough from our planet it could take a few hours after it sends information to the ground control center and receives instructions. The speed of light can also influence short distances. In supercomputers the speed of light imposes a speed limit at which data can be sent between processors. If a processor operates at 1 GHz, the signal can only travel at a maximum of 300 mm in a single cycle. Therefore, the processors should be placed close to each other to minimize communication delays. If the frequencies of a watch continue to increase, the speed of light will eventually become a limiting factor for the internal design of individual chips.


[1] Speed ​​of Light

[2] Speed_light

The fastest in the known universe

Evidence-based evidence asserts that light is not the fastest thing in the universe, contradicting what Albert Einstein expressed in his Special Theory of Relativity in 1905.

In an experiment that threatens to tear down the basic tenet of relativity theory, and hence our current understanding of the universe, tiny particles called neutrinos appear to have traveled faster than light between Switzerland and Italy.

Neutrinos have traveled 730 kilometers underground from the European Laboratory for Particle Physics (CERN) in Geneva to the detector for the Opera experiment located under the Gran Sasso massif. To the surprise of the physicists working on the experiment, the particles have arrived earlier than expected.

Not long before: just 60 nanoseconds sooner than if they had traveled at the speed of light (a nanosecond is a million times shorter than a thousandth of a second). This difference means that neutrinos have gone 0.0025% faster than light.


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