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The history of physics


Over time, people have always wanted to improve their understanding of the universe. The history of physics main objective is to retrace the various discoveries made by physicists since prehistoric times. Thus, through the ages, we will show what have been the major evolutions which have made it possible to found our current knowledge of the universe.

The physical sciences in the beginning

We know that physics takes root only in prehistoric times and in antiquity. Thanks to archaeologists, we know with certainty that prehistoric men were good observers. Monuments, such as that of the megalithic “Stonehenge” provide us with proof of this. The men of prehistory knew this ardent desire to know more about our universe and tried to reproduce certain phenomena, they thus founded the first element of a scientific process which is the observation.

Also, the first objects used to measure time saw their appearance during this period of our history. The bone of Ishango, the bone of the Blanchard shelter, but also Stonehenge, and Carnac were the first instruments that could measure time. This is the beginning of physics: the description of certain astronomical mechanisms. The physics of antiquity, for its part, is known to us in a much more precise way. Time was also a major concern. The gnomon, the clepsydra and the sundial are legacies from antiquity.

But beyond the measurement of time, a Greek knowledge was formed with physicists such Archimedes, Thales of Milet, or even Erasthostène. Interested in matter and its phenomena, most of these philosophers have thus advanced our understanding of the universe. The word "atom" comes from the Greek "atomon" meaning "indivisible". Indeed, Democritus (-460 - -370 BC) assumes that matter is made up of particles separated by a vacuum. These particles which are said to be non-breaking, because considered as the smallest elements will be called atoms. "Finally, the bodies that we see hard and massive, owe their coherence to more hooked, more intimately linked bodies ... On the contrary, they are smooth and round bodies that form bodies of a liquid and fluid nature" he says. . Archimedes (-287 - -212 BC) is referred to today as the founder of static mechanics: he is at the origin of many traction machines, but also some of war, like the catapult.

But it is mainly through his work on fluid mechanics that he is known. Having shouted "Eureka" according to the legend, he discovers the properties of bodies immersed in a fluid, and thus states the "Archimedes principle": Any body immersed in a liquid (or a gas) receives a thrust, which s 'exerts from bottom to top, and that is equal to the weight of the volume of liquid displaced. This push will be called the "Archimedes push". We will not cite here all the physicists of Antiquity, but it is nevertheless advisable to be interested in Eratosthenes. The latter calculated the circumference of the Earth from standing stones and using simple mathematics. Indeed, assuming the rays of the Sun to be parallel, he manages to measure at noon in Alexandria the angle of the solar rays with the vertical (menhir) and finds 7 °. At the same time in Syene, a city located almost on the same meridian, the Sun's rays do not form any angle in a well. Using a proportionality relationship, he deduced the Earth's circumference of 40,349 km, an error of 10% from the value measured today with precision. Thus physics progresses and knowledge accumulates through observation, the formulation of hypotheses, and the development of theories using mathematical tools.

A constant progression

The Middle Ages set in, and wars multiply. Invasions, conquests, wars ... and the accumulated Greek knowledge of Antiquity is lost except for a few philosophers, such as Boethius, who keep some scientific heritage from Antiquity through the Quadrivium. While the West is plunged into a period of oblivion, the Arab-Muslim civilization continues the work initiated by the Greeks, in particular by preserving the writings of discoveries, and by resuming these works to deepen them and thus found a civilization of knowledge. : it is the golden age of Arab-Muslim progress. The invention of zero by the Arabs caused an upheaval in the mathematical sciences and allowed progress in the field, as illustrated by algebra and scientists such as Averroes (1126-1198). Astronomy is also deepened by the invention of a first water telescope by the astronomer physicist Alhazen (965-1039). The latter manages to explain optical phenomena such as the Moon which appears larger in the sky at certain times, or even why the Moon shines. He is also the first to speak of the phenomenon of refraction, an idea which will be taken up by physicists in the following centuries. In mechanics, Alhazen states the principle of inertia, which will later be taken up by Galileo, and also speaks of the attraction of masses, an idea that will be mainly taken up by Isaac Newton centuries later. The Renaissance saw many scientists revolutionize the world of physical science. Comes Galileo (1564-1642), the astronomer-physicist who became very famous for many inventions such as the astronomical telescope. His work in dynamics teaches him to understand the movement of planets. Also, it states the principle of inertia which states that if an object is not subjected to any force or to forces whose resultant is zero, then the body in question is either at rest or in uniform rectilinear motion. This principle will constitute Newton's first law a few years later. René Descartes (1596-1650), for his part, worked more on optics and mathematically expressed the law of refraction of light, and obviously that of reflection.

But the major progress of the 17th century was surely the work of the scientist Isaac Newton (1643-1723). He works in many fields, such as optics, mechanics and mathematics, and revolutionizes our understanding of the Universe. Newton continues the work of Descartes (and Snell) on the refraction of light: he shows that a prism decomposes light into several colors, and that it is these colors which form white light. He is also studying diffraction and will be the inventor of Newton's telescope which will allow better sight and visibility than Galileo's astronomical telescope. In mechanics, Isaac Newton explains the motion of bodies mathematically, using vectors to model forces. Thus he establishes three laws which will be called later the "laws of Newton" and manages to explain the functioning of gravity by stating the law of universal gravitation, which he will publish in his work "The principles of philosophy natural "thanks to his friend the astronomer Halley (1656-1742). Finally Leibniz (1646–1716) was an important physicist of the moment: his theoretical discoveries on the conservation of energy and the theoretical modeling of spatial and temporal dimensions will have been of great use to the scientists who will follow.

Post-Newtonian physical sciences

We better understand energy and dynamics: kinematics and dynamics, a branch will then be created which unites the two sub-fields: thermodynamics. As its name suggests, which comes from the ancient Greek "thermos": heat, and "dunamis": power (hence the name dynamic), this branch of the physical sciences relates movement and energy ( heat is only a means of transporting energy). With this new branch of physics, industry will make progress (precisely in the industrial age) and steam engines will develop. Another new branch also appears: electromagnetism, with Maxwell (1831–1879). This new branch unifies electricity with magnetism, and this with simple experiments (as well as in theory with mathematics): an electric current flowing in a wire generates a magnetic field. It is the movement of free electrons that creates a magnetic field, at the same time as an electric current. But the most important discovery of the century will undoubtedly be that of the measurement of the speed of light using the interferometer by two Nobel Prize winners: Edward Morley (1838-1923) and Albert Abraham Michelson (1852-1931) . They note that the speed of light is the same in all the frames of reference of the same medium, a discovery which creates an upheaval in the dynamics. Indeed, an observer moving at a high speed, and an observer being stationary, in a certain frame of reference, will see a photon pass at the same speed, which is contrary to the dynamics of physics: an observer moving in the same sense of the photon at a high speed, should see it progress less quickly than an observer at rest (in a certain frame of reference) [1]. This can only be explained with the principle of length contraction, which Fitzgerald (1851-1901) and Lorentz (1853-1928) are at the origin. Classical mechanics are therefore contradicted.

It was not until Einstein (1879-1955) to reconcile this surprising discovery with mechanics. In 1905, he published his special theory of relativity which proves that if the speed of light does not change, a movement follows from a deformation of space and time. Thus he shows that space and time are not constants, but dilate and contract, hence the imagined experience of the Langevin twins (1872-1946) whose old age would be different depending on whether they were travel at high speed or not (in relation to a certain benchmark) [1]. General relativity developed between 1907 and 1915 by Einstein will reconcile special relativity with a theory of gravitation. Indeed Albert shows that gravitation is according to him only a deformation of space-time. Like a ball that we put on a rubber sheet, the deformation of the latter would generate an attraction because a body follows the gravitational lines that we call geodesics.

General relativity will reduce the field of application of Newtonian mechanics, the latter no longer working for bodies moving at very high speed. It will also lead to new concepts, such as the black hole, which have recently been detected. Also the physicist Hubble (1889-1953) will show that the galaxies move away from each other (contrary to what Newtonian mechanics could lead us to believe) hence the idea of ​​the expansion of the Universe, continued at an event that will be named "Big Bang". In the field of quantum mechanics, Ernest Rutherford (1871-1937) will lead to extraordinary discoveries in nuclear physics. He discovered ionizing rays like radioactivity, alpha rays, and beta rays. His experience with the gold atom will highlight the existence of a nucleus bringing together the positive charges of the atom and responsible for its mass.

Nowadays

Physics therefore has a solid foundation in order to allow new discoveries and new inventions. It still remains to resolve the incompatibility between quantum mechanics and general relativity, which are radically different. All the discoveries of the last two hundred years seem to lead to the same point, to converge, hence the idea of ​​a theory of everything, and of a master equation which is currently the subject of intense research by physicists. . Computers and machines allow physics to move faster and more accurately. Recently the opening of the LHC ("Large Hardron Collider") at CERN ("European Council for Nuclear Research", officially: "European Organization for Nuclear Research") will allow the secrets of matter and perhaps even to reconstitute the Universe at its beginnings, in short, it promises us many surprises. Thanks to mathematics, computer science, and technology, the physical sciences continue to advance, and the history of this magnificent science continues to be written ...

[1] We always speak of movement with respect to a frame of reference (solid considered as fixed)

Bibliography

- Jean Rosmorduc, A History of Physics and Chemistry. Points Sciences, 1985.

- Jean Perdijon, History of physics. Dunod, 2008.


Video: An Animated Story of Physics - Dara O Briains Science Club - Albert Einstein - BBC (September 2021).