The primary goal of studying the history of physics is to reconstruct the many discoveries made by physicists going back to antiquity. There has never been a point in human history when mankind didn’t desire to know more about the universe. Many physicists have contributed to our collective knowledge by using observations and math to explain exactly how ordinary events occur. As such, we shall trace the history of universal thought and demonstrate the key developments that have led to the state of our understanding now.

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## An early point in physics

The history of physics is deeply rooted in antiquity and the distant past. Archaeologists have shown without a reasonable doubt that ancient individuals had keen powers of observation. We know this because of megalithic structures like “Stonehenge” that have survived to the present day as physical monuments. Men throughout prehistory recognized this burning curiosity about the universe and attempted to recreate specific events, laying the groundwork for the first step in the scientific method: cautious observation.

In addition, the first tools to measure time arose at this time in human history. Among the first ones were the **Ishango bone**, the **Abri Blanchard bones**, and even **Stonehenge **and **Carnac stones**. The description of specific astronomical processes was the first step in the development of physics. However, we have a far more exact understanding of the physics of antiquity. The passing of time was also a major factor. The **sundial**, **gnomon**, and **clepsydra **(water clock) are all devices with ancient origins.

Many traction devices, including war machines, such as the catapult, may trace their ancestry back to Archimedes.

Greek knowledge was formed by physicists like Archimedes, Thales of Miletus, and Eratosthenes, going well beyond the mere measurement of time. Most of these philosophers have contributed to our knowledge of the universe since they were interested in matter and its processes. The Greek term **atomos **means “indivisible,” which is where we get our modern name “atom.” **Democritus **(460 BC–370 BC) was right in thinking that matter consists of discrete particles separated by empty space. He called those smallest and inseparable units “atoms.”

Democritus explained the atom, saying that the bodies we see as hard and massive owe their coherence to more hooked, more intimately linked corpuscles. According to him it is smooth and round corpuscles that form the bodies of a liquid and the rest of nature.

Many traction devices, as well as certain war machines, such as the catapult, may trace their ancestry back to **Archimedes **(287–212 BC), who is now considered the creator of static mechanics. However, his contributions to the field of fluid mechanics have brought him the most attention. “Archimedes’ principle” states that every body submerged in a liquid (or a gas) gets a push, which is exerted from bottom to top, and equal to the weight of the volume of liquid displaced. This discovery is said to have occurred after Archimedes yelled “Eureka!” (I have found it).

The term “thrust” in Archimedes’ principle was coined for this particular propulsion mechanism. Although we cannot possibly include every ancient physicist here, it is important to at least highlight **Eratosthenes** (276–194 BC). Using just a stick and some basic math, Eratosthenes determined the size of the Earth.

At midday in Alexandria, Eratosthenes measured the angle of the Sun’s beams with a vertical stick and found it at 7 degrees, lending credence to the assumption that the Sun’s rays were parallel. Similarly, in Syene, a city south of Alexandria, almost on the same meridian, the Sun’s rays did not create any shadows (0 degrees) at the same time of day. Eratosthenes calculated the Earth’s circumference as 25,072 miles (40,349 kilometers) using a proportionate relationship (assuming that Earth was a 360-degree globe), which is off by around 10 percent from the estimate we have today.

Observation, hypothesis testing, and the use of mathematical tools to create theories are the means by which physics advances and information is accumulated.

## Advances in physics

As the Middle Ages settled in, conflicts proliferated. The collected Greek knowledge of Antiquity is lost due to invasions, conquests, and wars; nonetheless, certain thinkers, such as **Boethius **(480–524 AD), maintained some scientific heritages of antiquity via the Quadrivium. The golden age of scientific progress by Arab-Muslims occurred while the West was in a dark age, and it was during this time that the Greeks’ scientific works were carried on by the Arab-Muslims. In particular, they preserved the written records of discoveries and expanded upon them, laying the groundwork for a civilization based on knowledge.

Algebra and the work of mathematicians like **Averroes **(1126–1198) show how the introduction of the zero by the Arabs sparked a revolution in mathematics and paved the way for advancements in the field. When astronomer **Alhazen **(965–1039) created the first water telescope, he ushered in a new era of discovery that would profoundly alter the field. When asked why the Moon seems bigger at particular times or why the Moon shines, Alhazen was able to provide a rational explanation.

Alhazen also made the first recorded mention of refraction, a concept that later scientists would develop. Alhazen proposed the concept of inertia in mechanics, which was eventually adopted by Galileo; he also discussed the attraction of masses, which was mostly adopted by Isaac Newton a few centuries later. During the Renaissance, several scientists made groundbreaking contributions to the field of physics.

The next major figure is **Galileo Galilei **(1564–1642), an astronomer and physicist who achieved widespread renown thanks to innovations like the telescope. The study of dynamics allowed him to fathom the paths taken by the planets, an insight he gained in the course of his career. Aside from that, Galileo came up with the concept of inertia, which says that a body is either at rest or in uniform rectilinear motion if it is not subjected to any force or to forces whose resultant is zero. A few years later, Newton’s First Law would be based on this idea. **René Descartes** (1596–1650) devoted more time and energy to the study of optics, eventually formulating the mathematical expression of the rule of refraction of light and, of course, the law of reflection.

It is safe to say, however, that physicist **Isaac Newton**‘s (1643–1723) contributions were the most significant of the 17th century. By contributing to several disciplines, including optics, mechanics, and mathematics, Newton radically altered our view of the universe. With his work on the refraction of light, Newton built upon the discoveries made by Descartes (and **Willebrord Snellius**) by demonstrating that a prism separates light into its component colors before recombining them to generate white light. He also invented the Newton telescope, which outperformed Galileo’s in terms of clarity of image, and investigated diffraction.

Isaac Newton developed a mathematical theory of mechanics that used vectors to represent the forces responsible for the motion of things. With the help of his friend, the astronomer **Edmund Halley** (1656–1742), he was able to formulate three rules that would become known as “Newton’s Laws,” and he also succeeded in explaining how gravity worked by stating the law of universal gravitation, both of which were published in Newton’s book *The Mathematical Principles of Natural Philosophy*.

Finally, **Gottfried Leibniz** (1646–1716) was a major figure in the field of physics at the time. His theoretical findings on the conservation of energy and the theoretical modeling of spatial and temporal dimensions were immensely helpful to subsequent scientists.

## Physical sciences after Newton

Understanding energy and motion (kinematics and dynamics) led to the development of thermodynamics, a science that brings together previously separated fields of study. Named after the ancient Greek words for heat (**thermos**) and power (**dunamis**), this subfield of physics studies the connections between motion and energy (heat is only a means of transporting energy). The advancement of industry (during the industrial period) and the improvement of steam engines can be credited to this new subject of physics.

James Maxwell (1831–1879) introduced yet another new physics field, electromagnetism. This new field brought together electricity and magnetism, and it did so with straightforward experiments (and theoretical and mathematical analysis): a moving electric current in a wire produces a magnetic field. When free electrons flow, they generate an electric current and a magnetic field.

The measurement of light’s speed was the century’s most significant discovery.

The measurement of light’s speed using an interferometer by **Edward Morley** (1838–1923) and Albert **Abraham Michelson** (1852–1931), who shared the Nobel Prize in Physics, was unquestionably the century’s most significant discovery. Their discovery shook the dynamics of physics by finding that the speed of light was constant across all reference frames of the same medium. This meant that the speed of light was the same for all observers no matter their speed of motion.

But in reality, the dynamics of physics dictate that an observer traveling in the same direction as a photon at high speed should perceive the photon going more slowly for that observer than for an observer at rest (in the same reference frame). Only **George FitzGerald**‘s (1851–1901), and later **Hendrik Lorentz**‘s (1853–1928) notion of length contraction was able to account for this. This assumption directly contradicted the principles of classical mechanics until Einstein made it explicit.

## The physics world has been forever changed by Einstein

This unexpected finding was never made compatible with mechanics until Albert Einstein (1879–1955). In 1905, Einstein presented his theory of special relativity, which demonstrated that motion results from a distortion of space and time even if the speed of light remains constant. As a result, Einstein demonstrated that space and time are not fixed, but rather expand and contract, as shown by the imagined experiment of **Paul Langevin**‘s (1872–1946) twins, the ages of which would vary depending on whether or not they had traveled at high speed (according to some reference frame).

Reconciling special relativity with a theory of gravity was now possible thanks to the general theory of relativity that Einstein developed between 1907 and 1915. Indeed, Albert demonstrated that, in his view, gravity was only a warping of space-time. When a body, like a ball, was put on a rubber sheet, the sheet would sink and the latter would attract the former because of the gravitational lines created by this deformation, or geodesics.

Ernest Rutherford (1871–1937) paved the way for unprecedented breakthroughs in nuclear physics through his work in quantum mechanics.

Because of general relativity, the application of Newtonian physics turned out to be limited; it would no longer apply to objects traveling at very high velocities. General relativity also opened the door to novel ideas, such as the newly discovered black hole. Edwin Hubble (1889–1953), a physicist, would also demonstrate that galaxies are moving away from one another (contrary to what Newtonian physics led us to assume), thereby giving rise to the concept of the expansion of the universe in the wake of an event later dubbed the “Big Bang.”

Ernest Rutherford (1871–1937) paved the way for unprecedented breakthroughs in nuclear physics via his work in quantum mechanics. Rutherford uncovered radioactivity and ionizing radiation like alpha and beta particles. The nucleus, which combines the atom’s positive charges and gives it its mass, was discovered thanks to an experiment Rutherford performed on gold.

## Modern physics

The field of physics today has a stable basis on which to build and make crucial advances. But the fundamental differences between quantum physics and general relativity have yet to be reconciled. The notion of a **theory of everything** and a **master equation**, which is the subject of considerable inquiry by physicists at the present time, stems from the fact that all the discoveries of the previous two centuries appear to go to the same point, to converge. Advances in the field of physics are facilitated by computers and machinery, which allow for faster and more accurate progression.

The **Large Hadron Collider (LHC) **at CERN (European Organization for Nuclear Research) still promises to reveal many new and exciting things about the nature of matter and the early universe. In part because of developments in mathematics, computing, and technology, the physical sciences keep making strides and adding chapters to the book that is the history of this beautiful field of study.