The speed of light in a vacuum is a physical constant.
The speed of light is the distance that electromagnetic waves that are part of the visible spectrum travel per unit of time . It is a physical constant: that is, a value that does not register changes in a physical process despite the advance in time.
Originating from the Latin word velocĭtas , speed is a physical magnitude that refers to the space traveled by someone or something in a certain time. In the international system, the unit of speed is the meter per second .
Light , meanwhile, is the radiation in the electromagnetic spectrum that humans can perceive through sight. This radiation implies a propagation of particles or energy through space.
What is the speed of light
The speed of light is 299,792,458 meters per second , measured in a vacuum (space that has no matter). The symbol of this constant is c , since the Latin word celéritās was taken into account.
It is important to consider that, when the measurement is not made in a vacuum, electromagnetic factors influence. Therefore, if the medium is material, the speed of light is lower than c . By taking the speed of light in a vacuum and dividing it by the speed of light in a specific physical medium, the quotient obtained is called the refractive index .
It should be noted that the recognition as a constant of the measured value of the speed of light in a vacuum took place in 1983 . From this definition, it was also established that the meter is a unit that derives from said physical constant, establishing that it is the distance that light travels in a vacuum within a period of 1/299,792,458 seconds .
The refractive index of a medium affects the speed of light.
Some considerations
The movement of visible light through a vacuum takes place at a constant speed. This constant, which as we indicated above is called c , is equal to the speed with which gravitational waves propagate according to the general theory of relativity proposed by Albert Einstein .
Taking into account the principles of each Maxwell equation and the rest of the laws that explain the phenomena of electromagnetism , the speed of light has nothing to do with the speed of the source of the radiation. Therefore, the light emitted by a body that is still moves with the same speed as that emitted by an element that is moving at high speed. However, according to the so-called relativistic Doppler effect , the frequency of light emitted by a moving object does change.
It can be stated that, beyond the frame of reference that the observer has and the speed with which the light source moves, all observers will measure the speed of light in a vacuum with the same value.
The set of links known as Lorentz transformations explain the relationships between the calculations of a physical magnitude made by different observers. These transformations introduce a distortion of distances and times, causing the speed of light to remain constant.
It should be considered that, if information could move faster than c in a certain reference frame, the causal ordering would be violated since the effect would be observed first and then the cause. At this point the concept of light cone is important, which allows us to represent space-time under the theory of special relativity .
The light cone describes how a beam of light evolves over time. Propagation occurs to and from a point in regions defined by this cone.
The speed of light is relevant in telecommunications.
The importance of the speed of light in telecommunications
Fiber optic communications allow information to be transmitted by sending light waves. The signals are enclosed in the fiber, which functions as a conductor, and travel at high speed due to the low refractive index of the materials used.
The laws of refraction and reflection of light indicate why light remains in the duct, while Snell's law explains the change in trajectory when it passes from a transparent medium to another with a lower speed of propagation.
As we already saw, the speed of light indicates that, in a vacuum, photons (elementary particles of light) move at almost 300,000 kilometers per second. Due to the refractive index, light travels slower through air and water, for example.
In the case of fiber optics , light reaches a maximum speed that, in theory, is close to 204,218 kilometers per second . In any case, interference and bandwidth for the transmission of information must also be considered.
It is important to mention that, upon reaching a server or a computer, the light beams are converted into electrical signals that travel at a speed much lower than the speed of light. For some time we have been working on the development of a technology known as integrated optics that would avoid this transformation, allowing data packets to remain as light waves at all stages.