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The Wu experiment was a
particle In the Outline of physical science, physical sciences, a particle (or corpuscule in older texts) is a small wikt:local, localized physical body, object which can be described by several physical property, physical or chemical property, chemical ...
and
nuclear physics Nuclear physics is the field of physics that studies atomic nuclei and their constituents and interactions, in addition to the study of other forms of nuclear matter. Nuclear physics should not be confused with atomic physics, which studies the ...
experiment conducted in 1956 by the
Chinese American Chinese Americans are Americans of Han Chinese ancestry. Chinese Americans constitute a subgroup of East Asian Americans which also constitute a subgroup of Asian Americans. Many Chinese Americans along with their ancestors trace lineage from ...
physicist
Chien-Shiung Wu ) , spouse = , residence = , nationality = ChineseAmerican , field = Physics , work_institutions = Institute of Physics, Academia SinicaUniversity of California at BerkeleySmith CollegePrinceton UniversityColumbia UniversityZhejiang Unive ...
in collaboration with the Low Temperature Group of the US
National Bureau of Standards The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sci ...
. The experiment's purpose was to establish whether or not conservation of
parity Parity may refer to: * Parity (computing) ** Parity bit in computing, sets the parity of data for the purpose of error detection ** Parity flag in computing, indicates if the number of set bits is odd or even in the binary representation of the r ...
(''P''-conservation), which was previously established in the
electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
and strong interactions, also applied to
weak interaction In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, ...
s. If ''P''-conservation were true, a mirrored version of the world (where left is right and right is left) would behave as the mirror image of the current world. If ''P''-conservation were violated, then it would be possible to distinguish between a mirrored version of the world and the mirror image of the current world. The experiment established that conservation of parity was violated (''P''-violation) by the weak interaction, providing a way to operationally define left and right without reference to the human body. This result was not expected by the physics community, which had previously regarded parity as a
conserved quantity In mathematics, a conserved quantity of a dynamical system is a function of the dependent variables, the value of which remains constant along each trajectory of the system. Not all systems have conserved quantities, and conserved quantities are ...
.
Tsung-Dao Lee Tsung-Dao Lee (; born November 24, 1926) is a Chinese-American physicist, known for his work on parity violation, the Lee–Yang theorem, particle physics, relativistic heavy ion (RHIC) physics, nontopological solitons, and soliton star ...
and
Chen-Ning Yang Yang Chen-Ning or Chen-Ning Yang (; born 1 October 1922), also known as C. N. Yang or by the English name Frank Yang, is a Chinese Theoretical physics, theoretical physicist who made significant contributions to statistical mechanics, integrab ...
, the theoretical physicists who originated the idea of parity nonconservation and proposed the experiment, received the 1957
Nobel Prize in physics ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
for this result.
Chien-Shiung Wu ) , spouse = , residence = , nationality = ChineseAmerican , field = Physics , work_institutions = Institute of Physics, Academia SinicaUniversity of California at BerkeleySmith CollegePrinceton UniversityColumbia UniversityZhejiang Unive ...
's role in the discovery was mentioned in the Nobel prize acceptance speech, but was not honored until 1978, when she was awarded the first
Wolf Prize The Wolf Prize is an international award granted in Israel, that has been presented most years since 1978 to living scientists and artists for ''"achievements in the interest of mankind and friendly relations among people ... irrespective of natio ...
.


History

In 1927,
Eugene Wigner Eugene Paul "E. P." Wigner ( hu, Wigner Jenő Pál, ; November 17, 1902 – January 1, 1995) was a Hungarian-American theoretical physicist who also contributed to mathematical physics. He received the Nobel Prize in Physics in 1963 "for his con ...
formalized the principle of the conservation of
parity Parity may refer to: * Parity (computing) ** Parity bit in computing, sets the parity of data for the purpose of error detection ** Parity flag in computing, indicates if the number of set bits is odd or even in the binary representation of the r ...
(''P''-conservation), the idea that the current world and one built like its mirror image would behave in the same way, with the only difference that left and right would be reversed (for example, a clock which spins clockwise would spin counterclockwise if a mirrored version of it were built). This principle was widely accepted by physicists, and ''P''-conservation was experimentally verified in the
electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
and strong interactions. However, during the mid-1950s, certain decays involving
kaon KAON (Karlsruhe ontology) is an ontology infrastructure developed by the University of Karlsruhe and the Research Center for Information Technologies in Karlsruhe. Its first incarnation was developed in 2002 and supported an enhanced version of ...
s could not be explained by existing theories in which ''P''-conservation was assumed to be true. There seemed to be two types of kaons, one which decayed into two
pion In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: ) is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more gene ...
s, and the other which decayed into three pions. This was known as the puzzle. Theoretical physicists
Tsung-Dao Lee Tsung-Dao Lee (; born November 24, 1926) is a Chinese-American physicist, known for his work on parity violation, the Lee–Yang theorem, particle physics, relativistic heavy ion (RHIC) physics, nontopological solitons, and soliton star ...
and
Chen-Ning Yang Yang Chen-Ning or Chen-Ning Yang (; born 1 October 1922), also known as C. N. Yang or by the English name Frank Yang, is a Chinese Theoretical physics, theoretical physicist who made significant contributions to statistical mechanics, integrab ...
did a
literature review A literature review is an overview of the previously published works on a topic. The term can refer to a full scholarly paper or a section of a scholarly work such as a book, or an article. Either way, a literature review is supposed to provid ...
on the question of parity conservation in all fundamental interactions. They concluded that in the case of the
weak interaction In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, ...
, experimental data neither confirmed nor refuted ''P''-conservation. Shortly after, they approached
Chien-Shiung Wu ) , spouse = , residence = , nationality = ChineseAmerican , field = Physics , work_institutions = Institute of Physics, Academia SinicaUniversity of California at BerkeleySmith CollegePrinceton UniversityColumbia UniversityZhejiang Unive ...
, who was an expert on
beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...
, with various ideas for experiments. They settled on the idea of testing the directional properties of beta decay in
cobalt-60 Cobalt-60 (60Co) is a synthetic radioactive isotope of cobalt with a half-life of 5.2713 years. It is produced artificially in nuclear reactors. Deliberate industrial production depends on neutron activation of bulk samples of the monoisoto ...
. Wu realized the potential for a breakthrough experiment and began work in earnest at the end of May 1956, cancelling a planned trip to
Geneva Geneva ( ; french: Genève ) frp, Genèva ; german: link=no, Genf ; it, Ginevra ; rm, Genevra is the List of cities in Switzerland, second-most populous city in Switzerland (after Zürich) and the most populous city of Romandy, the French-speaki ...
and the
Far East The ''Far East'' was a European term to refer to the geographical regions that includes East and Southeast Asia as well as the Russian Far East to a lesser extent. South Asia is sometimes also included for economic and cultural reasons. The ter ...
with her husband, wanting to beat the rest of the physics community to the punch. Most physicists, such as close friend
Wolfgang Pauli Wolfgang Ernst Pauli (; ; 25 April 1900 – 15 December 1958) was an Austrian theoretical physicist and one of the pioneers of quantum physics. In 1945, after having been nominated by Albert Einstein, Pauli received the Nobel Prize in Physics fo ...
, thought it was impossible. Wu had to contact Henry Boorse and Mark W. Zemansky, who had extensive experience in
low-temperature physics In physics, cryogenics is the production and behaviour of materials at very low temperatures. The 13th IIR International Congress of Refrigeration (held in Washington DC in 1971) endorsed a universal definition of “cryogenics” and “cr ...
, to perform her experiment. At the behest of Boorse and Zemansky, Wu contacted
Ernest Ambler Ernest Ambler (November 20, 1923 – February 17, 2017) was a British-American physicist who served as the Acting Under Secretary for Technology in the Department of Commerce (1988–89), as director of the United States' National Bureau of Stan ...
, of the
National Bureau of Standards The National Institute of Standards and Technology (NIST) is an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical sci ...
, who arranged for the experiment to be carried out in 1956 at the NBS' low-temperature laboratories. After several months of work overcoming technical difficulties, Wu's team observed an asymmetry indicating parity violation in December 1956. Lee and Yang, who prompted the Wu experiment, were awarded the Nobel prize in physics in 1957, shortly after the experiment was performed. Wu's role in the discovery was mentioned in the prize acceptance speech, but was not honored until 1978, when she was awarded the inaugural
Wolf Prize The Wolf Prize is an international award granted in Israel, that has been presented most years since 1978 to living scientists and artists for ''"achievements in the interest of mankind and friendly relations among people ... irrespective of natio ...
. Many were outraged, from her close friend Wolfgang Pauli, to Lee and Yang, with 1988 Nobel Laureate
Jack Steinberger Jack Steinberger (born Hans Jakob Steinberger; May 25, 1921December 12, 2020) was a German-born American physicist noted for his work with neutrinos, the subatomic particles considered to be elementary constituents of matter. He was a recipient ...
labeling it as the biggest mistake in the Nobel committee's history. Wu did not publicly discuss her feelings about the prize, but in a letter she wrote to Steinberger, she said, "Although I did not do research just for the prize, it still hurts me a lot that my work was overlooked for certain reasons."


Theory

If a particular interaction respects parity symmetry, it means that if left and right were interchanged, the interaction would behave exactly as it did before the interchange. Another way this is expressed is to imagine that two worlds are constructed that differ only by parity—the "real" world and the "mirror" world, where left and right are swapped. If an interaction is parity symmetric, it produces the same outcomes in both "worlds". The aim of Wu's experiment was to determine if this was the case for the weak interaction by looking at whether the decay products of cobalt-60 were being emitted preferentially in one direction or not. This would signify the violation of parity symmetry because if the weak interaction were parity conserving, the decay emissions should be emitted with equal probability in all directions. As stated by Wu et al.: The reason for this is that the cobalt-60 nucleus carries
spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...
, and spin does not change direction under parity (because angular momentum is an
axial vector In physics and mathematics, a pseudovector (or axial vector) is a quantity that is defined as a function of some vectors or other geometric shapes, that resembles a vector, and behaves like a vector in many situations, but is changed into its ...
). Conversely, the direction that the decay products are emitted ''is'' changed under parity because momentum is a
polar vector In physics and mathematics, a pseudovector (or axial vector) is a quantity that is defined as a function of some vectors or other geometric shapes, that resembles a vector, and behaves like a vector in many situations, but is changed into its op ...
. In other words, in the "real" world, if the cobalt-60 nuclear spin and the decay product emissions were both in roughly the same direction, then in the "mirror" world, they would be in roughly opposite directions, because the emission direction would have been flipped, but the spin direction would not. This would be a clear difference in the behaviour of the weak interaction between both "worlds", and hence the weak interaction could not be said to be parity symmetric. The only way that the weak interaction could be parity symmetric is if there were no preference in the direction of emission, because then a flip in the direction of emissions in the "mirror" world would look no different from the "real" world because there were equal numbers of emissions in both directions anyway.


Experiment

The experiment monitored the decay of
cobalt-60 Cobalt-60 (60Co) is a synthetic radioactive isotope of cobalt with a half-life of 5.2713 years. It is produced artificially in nuclear reactors. Deliberate industrial production depends on neutron activation of bulk samples of the monoisoto ...
(60Co) atoms that were aligned by a uniform magnetic field (the polarizing field) and cooled to near
absolute zero Absolute zero is the lowest limit of the thermodynamic temperature scale, a state at which the enthalpy and entropy of a cooled ideal gas reach their minimum value, taken as zero kelvin. The fundamental particles of nature have minimum vibration ...
so that thermal motions did not ruin the alignment. Cobalt-60 is an
unstable In numerous fields of study, the component of instability within a system is generally characterized by some of the outputs or internal states growing without bounds. Not all systems that are not stable are unstable; systems can also be mar ...
isotope of cobalt that decays by
beta decay In nuclear physics, beta decay (β-decay) is a type of radioactive decay in which a beta particle (fast energetic electron or positron) is emitted from an atomic nucleus, transforming the original nuclide to an isobar of that nuclide. For ...
to the stable isotope nickel-60 (60Ni). During this decay, one of the
neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...
s in the cobalt-60 nucleus decays to a
proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
by emitting an
electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no kn ...
(e) and an
electron antineutrino The electron neutrino () is an elementary particle which has zero electric charge and a spin of . Together with the electron, it forms the first generation of leptons, hence the name electron neutrino. It was first hypothesized by Wolfgang Pauli ...
(e). The resulting nickel nucleus, however, is in an
excited state In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers to a ...
and promptly decays to its ground state by emitting two
gamma ray A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...
s (γ). Hence the overall nuclear equation of the reaction is: :^_\text \rightarrow ^_\text + e^- + \bar_e + 2 Gamma rays are photons, and their release from the nickel-60 nucleus is an
electromagnetic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
(EM) process. This is important because EM was known to respect parity conservation, and therefore they would be emitted roughly equally in all directions (they would be distributed roughly "isotropically"). Hence, the distribution of the emitted electrons could be compared to the distribution of the emitted gamma rays in order to compare whether they too were being emitted isotropically. In other words, the distribution of the gamma rays acted as a
control Control may refer to: Basic meanings Economics and business * Control (management), an element of management * Control, an element of management accounting * Comptroller (or controller), a senior financial officer in an organization * Controllin ...
for the distribution of the emitted electrons. Another benefit of the emitted gamma rays was that it was known that the degree to which they were ''not'' distributed perfectly equally in all directions (the "anisotropy" of their distribution) could be used to determine how well the cobalt-60 nuclei had been aligned (how well their spins were aligned). If the cobalt-60 nuclei were not aligned at all, then no matter how the electron emission was truly distributed it would not be detected by the experiment. This is because an unaligned sample of nuclei could be expected to be oriented randomly, and thus the electron emissions would be random and the experiment would detect equal numbers of electron emissions in all directions, even if they were being emitted from each individual nucleus in only one direction. The experiment then essentially counted the rate of emission for gamma rays and electrons in two distinct directions and compared their values. This rate was measured over time and with the polarizing field oriented in opposite directions. If the counting rates for the electrons did not differ significantly from those of the gamma rays, then there would have been evidence to suggest that parity was indeed conserved by the weak interaction. If, however, the counting rates were significantly different, then there would be strong evidence that the weak interaction does indeed violate parity conservation.


Materials and methods

The experimental challenge in this experiment was to obtain the highest possible polarization of the 60Co nuclei. Due to the very small magnetic moments of the nuclei as compared to electrons, strong magnetic fields were required at extremely low temperatures, far lower than could be achieved by liquid helium cooling alone. The low temperatures were achieved using the method of
adiabatic demagnetization Magnetic refrigeration is a cooling technology based on the magnetocaloric effect. This technique can be used to attain extremely low temperatures, as well as the ranges used in common refrigerators. A magnetocaloric material warms up when a ma ...
. Radioactive cobalt was deposited as a thin surface layer on a crystal of cerium-magnesium nitrate, a paramagnetic salt with a highly anisotropic
Landé g-factor In physics, the Landé ''g''-factor is a particular example of a ''g''-factor, namely for an electron with both spin and orbital angular momenta. It is named after Alfred Landé, who first described it in 1921. In atomic physics, the Landé ''g ...
. The salt was magnetized along the axis of high g-factor, and the temperature was decreased to 1.2 K by pumping the helium to low pressure. Shutting off the horizontal magnetic field resulted in the temperature decreasing to about 0.003 K. The horizontal magnet was opened up, allowing room for a vertical solenoid to be introduced and switched on to align the cobalt nuclei either upwards or downwards. Only a negligible increase in temperature was caused by the solenoid magnetic field, since the magnetic field orientation of the solenoid was in the direction of low g-factor. This method of achieving high polarization of 60Co nuclei had been originated by Gorter and Rose. The production of gamma rays was monitored using equatorial and polar counters as a measure of the polarization. Gamma ray polarization was continuously monitored over the next quarter-hour as the crystal warmed up and anisotropy was lost. Likewise, beta-ray emissions were continuously monitored during this warming period.


Results

In the experiment carried out by Wu, the gamma ray anisotropy was approximately 0.6. That is, approximately 60% of the gamma rays were emitted in one direction, where as 40% were emitted in the other. If parity were conserved in beta decay, the emitted electrons would have had no preferred direction of decay relative to the nuclear spin, and the asymmetry in emission direction would have been close to the value for the gamma rays. However, Wu observed that the electrons were emitted in a direction preferentially opposite to that of the gamma rays with an asymmetry significantly greater than the gamma ray anisotropy value. That is, most of the electrons favored a very specific direction of decay, specifically opposite to that of the nuclear spin. The observed electron asymmetry also did not change sign when the polarizing field was reversed, meaning that the asymmetry was not being caused by remanent magnetization in the samples. It was later established that parity violation was in fact maximal. The results greatly surprised the physics community. Several researchers then scrambled to reproduce the results of Wu's group, while others reacted with disbelief at the results.
Wolfgang Pauli Wolfgang Ernst Pauli (; ; 25 April 1900 – 15 December 1958) was an Austrian theoretical physicist and one of the pioneers of quantum physics. In 1945, after having been nominated by Albert Einstein, Pauli received the Nobel Prize in Physics fo ...
upon being informed by Georges M. Temmer, who also worked at the NBS, that parity conservation could no longer be assumed to be true in all cases, exclaimed "That's total nonsense!" Temmer assured him that the experiment's result confirmed this was the case, to which Pauli curtly replied "Then it must be repeated!" By the end of 1957, further research confirmed the original results of Wu's group, and ''P''-violation was firmly established.


Mechanism and consequences

The results of the Wu experiment provide a way to operationally define the notion of left and right. This is inherent in the nature of the weak interaction. Previously, if the scientists on Earth were to communicate with a newly discovered planet's scientist, and they had never met in person, it would not have been possible for each group to determine unambiguously the other group's left and right. With the Wu experiment, it is possible to communicate to the other group what the words left and right mean exactly and unambiguously. The Wu experiment has finally solved the
Ozma problem ''The Ambidextrous Universe'' is a popular science book by Martin Gardner, covering aspects of symmetry and asymmetry in human culture, science and the wider universe. It culminates in a discussion of whether nature's conservation of parity (the ...
which is to give an unambiguous definition of left and right scientifically. At the
fundamental Fundamental may refer to: * Foundation of reality * Fundamental frequency, as in music or phonetics, often referred to as simply a "fundamental" * Fundamentalism, the belief in, and usually the strict adherence to, the simple or "fundamental" idea ...
level (as depicted in the
Feynman diagram In theoretical physics, a Feynman diagram is a pictorial representation of the mathematical expressions describing the behavior and interaction of subatomic particles. The scheme is named after American physicist Richard Feynman, who introduc ...
on the right), Beta decay is caused by the conversion of the negatively charged ()
down quark The down quark or d quark (symbol: d) is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. Together with the up quark, it forms the neutrons (one up quark, two down quarks) and protons (two up q ...
to the positively charged ()
up quark The up quark or u quark (symbol: u) is the lightest of all quarks, a type of elementary particle, and a significant constituent of matter. It, along with the down quark, forms the neutrons (one up quark, two down quarks) and protons (two up quark ...
by emission of a boson; the boson subsequently decays into an electron and an electron antineutrino: : → + + . The quark has a
left Left may refer to: Music * ''Left'' (Hope of the States album), 2006 * ''Left'' (Monkey House album), 2016 * "Left", a song by Nickelback from the album ''Curb'', 1996 Direction * Left (direction), the relative direction opposite of right * L ...
part and a
right Rights are law, legal, social, or ethics, ethical principles of Liberty, freedom or entitlement; that is, rights are the fundamental normative rules about what is allowed of people or owed to people according to some legal system, social convent ...
part. As it walks across the spacetime, it oscillates back and forth from right part to left part and from left part to right part. From analyzing the Wu experiment's demonstration of parity violation, it can be deduced that only the left part of down quarks decay and the weak interaction involves only the left part of quarks and leptons (or the right part of antiquarks and antileptons). The right part of the particle simply does not feel the weak interaction. If the down quark did not have mass it would not oscillate, and its right part would be quite stable by itself. Yet, because the down quark is massive, it oscillates and decays. Overall, as J_\text=5, the strong magnetic field vertically polarizes the nuclei such that J_=J_\text=+5. Since J_\text=4 and the decay conserves
angular momentum In physics, angular momentum (rarely, moment of momentum or rotational momentum) is the rotational analog of linear momentum. It is an important physical quantity because it is a conserved quantity—the total angular momentum of a closed syst ...
, J_=J_ + J_ + J_=+5 implies that J_=J_=+1/2. Thus, the concentration of
beta ray A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β ...
s in the negative-z direction indicated a preference for left-handed quarks and electrons. From experiments such as the Wu experiment and the Goldhaber experiment, it was determined that massless neutrinos must be left-handed, while massless antineutrinos must be right-handed. Since it is currently known that neutrinos have a small mass, it has been proposed that right-handed neutrinos and left-handed antineutrinos could exist. These neutrinos would not couple with the weak
Lagrangian Lagrangian may refer to: Mathematics * Lagrangian function, used to solve constrained minimization problems in optimization theory; see Lagrange multiplier ** Lagrangian relaxation, the method of approximating a difficult constrained problem with ...
and would interact only gravitationally, possibly forming a portion of the
dark matter Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not ab ...
in the universe.


Impact and influence

The discovery set the stage for the development of the
Standard Model The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions - excluding gravity) in the universe and classifying a ...
, as the model relied on the idea of symmetry of particles and forces and how particles can sometimes break that symmetry. The wide coverage of her discovery prompted the discoverer of fission
Otto Robert Frisch Otto Robert Frisch FRS (1 October 1904 – 22 September 1979) was an Austrian-born British physicist who worked on nuclear physics. With Lise Meitner he advanced the first theoretical explanation of nuclear fission (coining the term) and firs ...
to mention that people at Princeton would often say that her discovery was the most significant since the
Michelson–Morley experiment The Michelson–Morley experiment was an attempt to detect the existence of the luminiferous aether, a supposed medium permeating space that was thought to be the carrier of light waves. The experiment was performed between April and July 1887 ...
that inspired Einstein's
theory of relativity The theory of relativity usually encompasses two interrelated theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical phenomena in ...
. The
AAUW The American Association of University Women (AAUW), officially founded in 1881, is a non-profit organization that advances equity for women and girls through advocacy, education, and research. The organization has a nationwide network of 170,000 ...
called it the “solution to the number-one riddle of atomic and nuclear physics.” Beyond showing the distinct characteristic of weak interaction from the other three conventional forces of interaction, this eventually led to general
CP violation In particle physics, CP violation is a violation of CP-symmetry (or charge conjugation parity symmetry): the combination of C-symmetry (charge symmetry) and P-symmetry ( parity symmetry). CP-symmetry states that the laws of physics should be the ...
, the violation of the charge conjugation parity symmetry. This violation meant researchers could distinguish matter from antimatter and create a solution that would explain the existence of the universe as one that is filled with matter. This is since the lack of symmetry gave the possibility of matter-antimatter imbalance which would allow matter to exist today through the
Big Bang The Big Bang event is a physical theory that describes how the universe expanded from an initial state of high density and temperature. Various cosmological models of the Big Bang explain the evolution of the observable universe from the ...
. In recognition of their theoretical work, Lee and Yang were awarded the
Nobel Prize for Physics ) , image = Nobel Prize.png , alt = A golden medallion with an embossed image of a bearded man facing left in profile. To the left of the man is the text "ALFR•" then "NOBEL", and on the right, the text (smaller) "NAT•" then " ...
in 1957. To further quote the impact it had, Nobel laureate
Abdus Salam Mohammad Abdus Salam Salam adopted the forename "Mohammad" in 1974 in response to the anti-Ahmadiyya decrees in Pakistan, similarly he grew his beard. (; ; 29 January 192621 November 1996) was a Punjabi Pakistani theoretical physicist and a ...
quipped,
If any classical writer had ever considered giants (
cyclops In Greek mythology and later Roman mythology, the Cyclopes ( ; el, Κύκλωπες, ''Kýklōpes'', "Circle-eyes" or "Round-eyes"; singular Cyclops ; , ''Kýklōps'') are giant one-eyed creatures. Three groups of Cyclopes can be distinguish ...
) with only the left eye. newould confess that one-eyed giants have been described and
ould have Ould is an English surname and an Arabic name ( ar, ولد). In some Arabic dialects, particularly Hassaniya Arabic, ولد‎ (the patronymic, meaning "son of") is transliterated as Ould. Most Mauritanians have patronymic surnames. Notable pe ...
supplied me with a full list of them; but they always sport their solitary eye in the middle of the forehead. In my view what we have found is that space is a weak left-eyed giant.
Wu's discovery would pave the way for a unified
electroweak force In particle physics, the electroweak interaction or electroweak force is the unified description of two of the four known fundamental interactions of nature: electromagnetism and the weak interaction. Although these two forces appear very differe ...
that Salam proved, which is theoretically described to merge with the strong force to create a total new model and a
Grand Unified Theory A Grand Unified Theory (GUT) is a model in particle physics in which, at high energies, the three gauge interactions of the Standard Model comprising the electromagnetic, weak, and strong forces are merged into a single force. Although this ...
.


See also

* ''
The Ambidextrous Universe ''The Ambidextrous Universe'' is a popular science book by Martin Gardner, covering aspects of symmetry and asymmetry in human culture, science and the wider universe. It culminates in a discussion of whether nature's conservation of parity (the ...
'' by
Martin Gardner Martin Gardner (October 21, 1914May 22, 2010) was an American popular mathematics and popular science writer with interests also encompassing scientific skepticism, micromagic, philosophy, religion, and literatureespecially the writings of Lewis ...
; book containing a lengthy popular discussion of parity and the Wu experiment *
Fermi's interaction In particle physics, Fermi's interaction (also the Fermi theory of beta decay or the Fermi four-fermion interaction) is an explanation of the beta decay, proposed by Enrico Fermi in 1933. The theory posits four fermions directly interactin ...


References


Further reading

*{{cite web , last1=Martin , first1=W. C. , last2=Coursey , first2=J. , last3=Dragoset , first3=R. A. , date=July 1997 , title=The Fall of Parity , url=https://www.nist.gov/pml/general/parity/index.cfm , publisher= NIST Physical Measurement Laboratory Electroweak theory Physics experiments 1956 in science 1956 in Washington, D.C. Asymmetry