The Nobel Prize in Physics has been awarded since 1901 for groundbreaking discoveries in the field. These discoveries can be generally divided into three types:

Theoretical discoveries – theoretical predictions of physical phenomena or the formation of theories that explain unexpected outcomes observed in past experiments.

Empirical discoveries – observation of a new phenomenon through experimentation or experiments that prove for the first time a previously suggested theory.

Development of novel scientific or technological tools that made a significant impact on physical research or in different industries.

In this article I will review several examples of discoveries that entitled their proprietors to a Nobel Prize in Physics. Some of these discoveries were previously mentioned in this section, and some I will discuss very briefly. Of course this is only a partial list, since it is impossible to go over all Nobel Prizes ever awarded (over 100). Should any of the readers request a more detailed account of any of the topics discussed here, I will try to fulfill these requests soon.

Quantum mechanics

The principles of modern physics are based on the laws of quantum mechanics, and at higher energies, the laws of the Theory of Relativity. Since quantum theory has been developed only in the last century, many of the first Physics Nobel Prize laureates were scientists who articulated the underlying fundamentals of this field. Among these most notable are:

(1) Max Planck, who was awarded the 1918 Nobel Prize in Physics "in recognition of the services he rendered to the advancement of physics by his discovery of energy quanta".

It was the problem of black-body radiation that enticed Planck to propose a hypothesis that is considered by many the birth of quantum mechanics. A "black body" is an idealized physical entity whose magnitude of radiation depends exclusively on its temperature. Planck tried to explain how the intensity of the electromagnetic radiation emitted by such a black body correlates with its temperature and with the frequency of the radiation (the color of the emitted light). The problem was that when trying to answer this question using classical physical theory, assuming that electromagnetic radiation behaves as a wave with continuous levels of energy, the theoretical computations proved to be inconsistent with experimental observations. In fact, these calculations made no sense at all, since they implied that a black body emits infinite amounts of energy. In order to overcome this, Planck made an assumption that electromagnetic radiation is not a continuous form of energy but rather can be emitted only in quantized form, i.e. only in certain discrete magnitudes (quanta). Following this "simple" assumption, the experimental observations were perfectly complemented by the modified theoretical computations. Planck's groundbreaking theory is well accepted today, and the energy quanta he had described were later discovered to be photons.

For further reading about black body radiation, click here.

(2) Louis de Broglie (1929), "for his discovery of the wave nature of electrons".

Until Planck hypothesized that light is composed of energy quanta, physicists divided the world into waves and particles. Electromagnetic radiation spread in space according to wave functions, while particles behaved like tiny "marbles" that moved according to the laws of Newton. After Planck had suggested that light is not solely a wave and that its particle nature should also be considered, de Broglie made the opposite journey by attributing wave-like properties to electrons, which until then were thought of as simple particles. This hypothesis is one of the most important premises of quantum theory, which provides a probabilistic description of where a particle is to be found in space at a given time according to this particle's wave function.

(3) Werner Heisenberg (1932), "for the creation of quantum mechanics...".

The above citation speaks for itself. In fact, the laws of quantum mechanics evolved simultaneously from two distinct yet corresponding mathematical approaches, one advocated by Heisenberg and the other by Erwin Schrodinger. Heisenberg was awarded the Nobel Prize in Physics since his theory led to our understanding of how an electromagnetic spectrum is emitted by different atoms, for example the hydrogen atom. One of Heisenberg's most notable contributions was his Uncertainty Principle, according to which certain pairs of physical properties cannot be measured simultaneously to high precision. The most prominent example is that of position and velocity: since precise measurement of the velocity of a particle requires that we bounce other particles off of it, this immediately affects its location, which now cannot be determined to high precision. The implications of the Uncertainty Principle on quantum theory and the way it governs our world are enormous.

For further reading about the uncertainty principle, click here.

(4) Wolfgang Pauli (1945), "for the discovery of the Exclusion Principle, also called the Pauli Principle".
Pauli's exclusion principle is one of the most important laws in quantum mechanics. According to the exclusion principle, two identical electrons cannot occupy the same quantum state. A quantum state is the set of properties (quantum numbers) that describe a quantum system. These include spin, angular momentum, energy, etc. This principle has a tremendous effect on nature. For instance, different chemical substances are composed of electrons that orbit a nucleus at various energy levels. Intuitively, one may expect that all electrons should occupy the lowest energy state, thus reducing the energy level of the whole system. However, this assumption is refuted by Pauli's principle, according to which no two electrons in a single atom can occupy the same quantum state, i.e. they must differ in at least one of their quantum numbers.

The exclusion principle is not unique to electrons. There are two types of particles in nature: fermions, including electrons, which follow the exclusion principle, and bosons (e.g. photons), that can occupy the same quantum state.

High energy physics

Also known as particle physics, this branch of physics studies the most fundamental structures in nature, how they interact, and how they may predict the existence of new particles. The findings that were made along the years in this field consolidated into what is known today as the Standard Model. Several Nobel Prizes were awarded to physicists that contributed to the development and substantiation of the Standard Model. These can be divided into three categories: proposal of theories concerning particle interactions, actual discovery of predicted particles and development of particle sensors that enabled experimental research in this field.

Here are some examples for Nobel Prizes awarded for the discovery of new particles:

(1) James Chadwick (1935), "for the discovery of the neutron".

While studying radiation, Chadwick came across neutron radiation, and realized that this is a proton-like particle which lacks an electric charge. The discovery of neutron radiation contributed directly to the construction of the first atom bomb (The Manhattan Project).

(2) Carl David Anderson (1936), "for his discovery of the positron".

Anderson discovered the positron, which is the antiparticle of the electron. He used a Wilson cloud chamber (for which Wilson was awarded a Nobel Prize himself) to detect positrons that reached Earth's atmosphere from space through cosmic radiation.

(3) Emilio Gino Segre & Owen Chamberlain (1959), "for their discovery of the antiproton".

The antiproton, which is the antiparticle of the proton, is produced only at extremely high energies, equivalent to a temperature of 10 trillion (1x1013) Kelvin, and thus can only be generated in particle accelerators.

And many more...

And here are some examples of Nobel Prizes awarded for the development of experimental techniques that enabled the discovery of new particles:

(1) Charles Wilson (1935), "for his method of making the paths of electrically charged particles visible by condensation of vapour".

Charles Wilson invented the cloud chamber, a device used for the detection of ion particles that pass through it. Basically, a cloud chamber is a sealed container that contains very high humidity levels, i.e. it is saturated with water vapors. When a charged particle passes, it ionizes the air atoms inside the chamber. The resulting ions serve as condensation nuclei for the water vapors, which condense into a trail of water drops along the path taken by the charged particle, which can now be detected.

(2) Donald Glaser (1960), "for the invention of the bubble chamber".

A bubble chamber is similar to a cloud chamber, only that it contains liquid rather than gas. The liquid is in a superheated state, meaning that it is heated slowly above its boiling temperature. In this way the liquid does not evaporate, since the energetic cost of producing a gas bubble by breaking the surface tension of the liquid is greater than the energetic gain of phase transformation from liquid to gas. When a particle enters the chamber, it breaks the liquid's surface tension along its path, allowing liquid to evaporate. In this manner, a trail of gas bubbles forms within the liquid along the path of the particle.

A bubble chamber, with bubble trails left behind the particles that moved along the chamber.

(3) Georges Charpak (1992), "for his invention and development of particle detectors, in particular the multiwire proportional chamber".
In contrast to the previously discussed particle detectors, which are characterized by a slow read-out, the multiwire chamber is a modern and efficient device with an electronic read-out. This chamber is composed of electric wires that are laid out in a manner that gives rise to small mini-chambers. An electric potential exists between the two ends of each mini-chamber. The wires are isolated from each other by a non-conductive gas which prevents any electric current between them. When a charged particle enters through the chamber it ionizes the gas, rendering it conductive and allowing an electric current to pass. The greater the energy of the particle - the more gas atoms it ionizes, leading to an increased current. This means that a multiwire chamber enables measurement of not only the path of a particle, but also its energy.

The division of the chamber into many mini-chambers allows for accurate tracking of the path of the particle. A magnetic field is often applied so that the path is curved in a manner that provides information about the mass and charge of the particle (this is also true for a bubblechamber).

Scheme of a multiwire chamber. The two plates serve as cathodes while the thin wires are anodes, with electric potential between them. A particle that enters each mini-chamber ionizes the gas, allowing electric current to pass between the anode and the cathode.

And many more...

Several theoreticians in the field of high energy physics were also awarded with Nobel Prizes, the most prominent being Sin-Itiro Tomonaga, Julian Schwinger, and Richard Feynman (1965), "for their fundamental work in quantum electrodynamics". This theory, commonly abbreviated QED, was the first to postulate how particles interact with each other and solved many unanswered theoretical issues such as the difference between the calculated mass of an electron and its actual mass.

Condensed matter physics/Solid-state physics

As the name implies, solid-state physics studies solids and their unique properties. The first years of the 20th century saw a plethora of studies on the structure of matter and many important traits of solids were discovered, including their structure and basic electric properties. In later years and until these very days, much of the research has been dedicated to the unique electric properties that are attributed to a collective effect of all the electrons in a solid. In fact, many studies are being focused on the properties of electrons, whereas the solid only serves as the experimental system that "traps" the electrons and endows them with properties that are somewhat different than those of free electrons. I will discuss one example from each one of these issues.

Crystal structure

Most solids we know are in crystal form. The atoms are arranged in an orderly and repeated pattern in space, this in order to achieve the lowest energetic state. The distance between the atoms and the crystal shape they form depends on electrostatic forces that are applied on the atoms after they become ionized, that is to say after one or more of the electrons leave their atom and start moving inside the solid.

Crystals were given much attention at the beginning of the 20th century. The technique developed to study their structure relies on the diffraction pattern of radiation directed at the crystal, characterized by interference of the waves as a result of bouncing off the crystal. Initially, X-rays were employed in this method. The invention of X-ray crystallography was honored with 2 Nobel Prizes.

In 1914, The Nobel Prize in Physics was awarded to Max von Laue, "for his discovery of the diffraction of X-rays by crystals". A year later, it was awarded to William Henry Bragg and to his son, William Lawrence Bragg, "for their services in the analysis of crystal structure by means of X-rays".  Thus, the first Prize was awarded for the discovery of the phenomenon, and the second one for devising a method to exploit it in the study of crystal structures.

It should be mentioned that the work of Prof. Ada Yonath of the Weizmann Institute, for which she was awarded the Nobel Prize in Chemistry in 2009, is based on this technique.

Several examples of naturally-occurring crystals.

 

The atomic structure of the simplest crystal; the atoms are arranged in cubes where each corner of a cube is occupied by one atom.

Superconductivity

Superconductivity is an example of a collective effect of many electrons in a material. The material itself serves as a mediator between the different electrons, and affects the technical aspects of the phenomenon (the energy gap, the type of superconductor, etc.). The phenomenon itself, however, arises from the traits of electrons. Several Nobel Prizes in Physics have been awarded for the study of this phenomenon:

(1) The Nobel Prize was awarded in 1972 to Bardeen, Cooper and Schrieffer, "for their jointly developed theory of superconductivity, usually called the BCS-theory".

(2) In 1973 it was awarded to Brian David Josephson, "for his theoretical predictions of the properties of a supercurrent through a tunnel barrier...".

(3) In 1987, the Nobel Prize was awarded to J. Georg Bednorz and K. Alexander Muller, "for their important break-through in the discovery of superconductivity in ceramic materials".

This refers to superconductors in high temperatures (tens of Kelvins). This remains a very lively field of research to this day, as attempts are being made to increase the critical temperature of superconductors in order to make them more available for everyday use.

Technological advancement

The Nobel Prize in Physics, as the name implies, is awarded for breakthroughs in physics, rather than in engineering. Nevertheless, the prize has been awarded several times for technological innovations that were not aimed directly at advancing physics research (as in the case of particle detectors) but provided more industrial benefits by introducing innovative approaches for exploiting physical principles.

The most prominent example is probably the transistor. A separate article will soon be available on this website, discussing in detail the different types of transistors. It is well known that this invention practically changed the modern world. The manufacturing of transistors from semiconductors enabled their mass production at very small sizes (tens of nanometers) and at a low price, paving the way to the technological revolution of the last decades. Today, each one of us is the proud owner of millions, if not billions of transistors, as the transistor is the key active component in practically all modern electronic devices.

The transistor was invented in 1947 by William Shockley, John Bardeen and Walter Brattain, endowing them with the 1956 Nobel Prize in Physics.

Click here to see a picture of the first transistor, made from a semiconductor.

Click here to read about the story behind the invention of the transistor.

In 2000, another Nobel Prize in Physics was awarded for technological (more precisely electronic) breakthroughs. Zhores Alferov and Herbert Kroemer were honored "for developing semiconductor heterostructures used in high-speed- and opto-electronics" and Jack Kilby "for his part in the invention of the integrated circuit". The former two developed a new type of semiconductor in which a two-dimensional electron gas is formed (article available soon), enabling the production of transistors that work at extremely high frequencies. This invention is an integral part of the cellular phones we use today. Kilby's development, the integrated circuit, made the production of the electronics more efficient and less expensive.

Albert Einstein

No discussion of Nobel Prizes in Physics can be complete without mentioning Albert Einstein whose contribution to the evolution of modern physics was unprecedented, transforming him from a "mere" physicist to a household name. Most people know that Einstein was a Nobel Prize laureate, but under the false presumption that it was his Theory of Relativity for which he was bestowed with the honor. In fact, Einstein was awarded with the Nobel Prize in 1921 "for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect". This discovery provided a direct proof for Max Planck's assumption that light can be emitted only in quantized form, making it a milestone in the evolution of quantum mechanics.

Summary

The above list is obviously a very partial one. Many fields in the science of physics were not mentioned, such as discoveries in astronomy, ion traps, laser cooling, magnetic resonance and many more. The idea behind this article was to introduce to the reader the types of studies for which the Noble Prize in Physics has been awarded throughout the years, and their immense contribution to our understanding of the universe and how these findings can be implemented in the development of technological innovations.

In the future we will do our best to add articles that are directly related to these topics.

Yaron Gross
Department of Condensed Matter Physics
Weizmann Institute of Science

 

A note to the reader

If you find these explanations insufficiently clear or if you have further questions on this topic, please write about this in our forum, and we will relate to your comments. Your suggestions and constructive criticism are always welcome.

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