Long before scientists measured the speed of light, they had to work hard to define the very concept of "light". One of the first to think about this was Aristotle, who considered light to be a kind of mobile substance spreading in space. His ancient Roman colleague and follower Lucretius Carus insisted on the atomic structure of light.
By the 17th century, two main theories of the nature of light were formed - corpuscular and wave. Newton was among the adherents of the first. In his opinion, all light sources emit the smallest particles. In the process of "flight" they form luminous lines - rays. His opponent, the Dutch scientist Christian Huygens, insisted that light is a kind of wave motion.
As a result of centuries of disputes, scientists have come to a consensus: both theories have the right to life, and light is the spectrum of electromagnetic waves visible to the eye.
A bit of history. How the speed of light was measured
Most ancient scientists were convinced that the speed of light is infinite. However, the results of the studies of Galileo and Hooke admitted its limit, which was clearly confirmed in the 17th century by the outstanding Danish astronomer and mathematician Olaf Roemer.
He made his first measurements by observing the eclipses of Io, a satellite of Jupiter at a time when Jupiter and the Earth were located on opposite sides relative to the Sun. Roemer recorded that as the Earth moved away from Jupiter at a distance equal to the diameter of the Earth's orbit, the lag time changed. The maximum value was 22 minutes. As a result of calculations, he received a speed of 220, 000 km / s.
50 years later, in 1728, thanks to the discovery of aberration, the English astronomer J. Bradley "refined" this figure to 308, 000 km / s. Later, the speed of light was measured by French astrophysicists Francois Argo and Leon Foucault, who received 298, 000 km / s at the "exit". An even more accurate measurement technique was proposed by the creator of the interferometer, the famous American physicist Albert Michelson.
Michelson's experiment in determining the speed of light
The experiments lasted from 1924 to 1927 and consisted of 5 series of observations. The essence of the experiment was as follows. A light source, a mirror and a rotating octahedral prism were installed on Mount Wilson in the vicinity of Los Angeles, and after 35 km on Mount San Antonio - a reflecting mirror. First, the light through the lens and the slit fell on a prism rotating with the help of a high-speed rotor (at a speed of 528 rps).
The participants in the experiments could adjust the speed of rotation so that the image of the light source was clearly visible in the eyepiece. Since the distance between the peaks and the rotation frequency were known, Michelson determined the value of the speed of light - 299796 km / s.
Scientists finally decided at the speed of light in the second half of the 20th century, when masers and lasers were created, characterized by the highest stability of the radiation frequency. By the beginning of the 70s, the measurement error dropped to 1 km / s. As a result, on the recommendation of the XV General Conference on Weights and Measures, held in 1975, it was decided to assume that the speed of light in a vacuum is now equal to 299792, 458 km / s.
Is the speed of light achievable for us?
It is obvious that the exploration of the distant corners of the Universe is unthinkable without spaceships flying at great speed. Desirable at the speed of light. But is this possible?
The light speed barrier is one of the consequences of the theory of relativity. As you know, an increase in speed requires an increase in energy. The speed of light would require almost infinite energy.
Alas, the laws of physics are categorically against this. At a spaceship speed of 300, 000 km / s, particles flying towards it, for example, hydrogen atoms, turn into a deadly source of powerful radiation equal to 10, 000 sievert / s. It's about the same as being inside the Large Hadron Collider.
According to scientists at Johns Hopkins University, while in nature there is no adequate protection from such a monstrous cosmic radiation. Erosion from the effects of interstellar dust will complete the destruction of the ship.
Another problem with light speed is time dilation. At the same time, old age will become much more prolonged. The visual field will also undergo a curvature, as a result of which the trajectory of the ship will pass, as it were, inside a tunnel, at the end of which the crew will see a shining flash. Absolute pitch darkness will remain behind the ship.
So in the near future, mankind will have to limit their high-speed "appetites" 10% of the speed of light. This means that the closest star to the Earth - Proxima Centauri (4, 22 light years) will take about 40 years to fly.