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Up Quark

The up quark, along with its counterpart the down quark, form the protons and neutrons of atoms, and is therefore one of the main constituents of matter. The up and down quarks comprise the first generation of quarks and are the least massive. The up quark is a fermion, and therefore obeys the Pauli exclusion principle

Its existence was first proposed in 1964 independently by Murray Gell-Mann and George Zweig to explain the dozens of different “elementary” particles discovered in the first half of the 20th Century, in a theory known as the Eightfold Way. The up and down quarks were first observed by the Stanford Linear Accelerator Center in 1968.

Charm Quark

The charm quark is the third most massive quark, and is found in “charmed” hadrons like D mesons or charmed Sigma baryons. The charm and strange quarks comprise the second generation of quarks, and are only present in high-energy environments such as cosmic rays or particle accelerators. The charm quark will decay into its counterpart the strange quark or to a down quark. The charm quark is a fermion, and therefore obeys the Pauli exclusion principle.

Its existence was proposed by various scientists around 1964, and was first discovered at the Stanford Linear Accelerator Center and the Brookhaven National Laboratory in 1970.

Top Quark

The top quark is the most massive quark, and most massive elementary particle. The top and bottom quarks comprise the third generation of quarks, and are only present in high-energy environments such as cosmic rays or particle accelerators. The top quark will decay into a bottom quark, or very rarely a strange quark or a down quark. In fact, it decays so quickly that it has no time to interact with other quarks, and therefore never forms any baryons. The top quark is a fermion, and therefore obeys the Pauli exclusion principle

The top and bottom quarks were first proposed by Makoto Kobayashi and Toshihide Masukawa in 1973 (for which they shared a Nobel Prize in 2008). It was discovered by experiments at Fermilab in 1995.

Down Quark

The down quark, along with its counterpart the up quark, form the protons and neutrons of atoms, and is therefore one of the main constituents of matter. The up and down quarks comprise the first generation of quarks and are the least massive. The down quark is a fermion, and therefore obeys the Pauli exclusion principle

Its existence was first proposed in 1964 independently by Murray Gell-Mann and George Zweig to explain the dozens of different “elementary” particles discovered in the first half of the 20th Century, in a theory known as the Eightfold Way. The up and down quarks were first observed by the Stanford Linear Accelerator Center in 1968.

Strange Quark

The strange quark is the fourth most massive quark, and is found in “strange” hadrons like kaons and Sigma baryons. The charm and strange quarks comprise the second generation of quarks, and are only present in high-energy environments such as cosmic rays or particle accelerators. Strange quarks are one of the components (along with up and down quarks) of strange matter, which may form the cores of neutron stars or even entire stars themselves (quark stars). The strange quark will decay into the up quark. The strange quark is a fermion, and therefore obeys the Pauli exclusion principle

Its existence was first proposed in 1964 independently by Murray Gell-Mann and George Zweig to explain the dozens of different “elementary” particles discovered in the first half of the 20th Century, in a theory known as the Eightfold Way. When up and down quarks were first observed by the Stanford Linear Accelerator Center in 1968, it confirmed the Eightfold Way classification and also the existence of strange quarks.

Bottom Quark

The bottom quark is the second most massive quark, and is found in various B mesons or paired with its own antiparticle. The top and bottom quarks comprise the third generation of quarks, and are only present in high-energy environments such as cosmic rays or particle accelerators. The bottom quark will decay into a charm quark or an up quark. The bottom quark is a fermion, and therefore obeys the Pauli exclusion principle

The top and bottom quarks were first proposed by Makoto Kobayashi and Toshihide Masukawa in 1973 (for which they shared a Nobel Prize in 2008). Bottom quarks were first observed at Fermilab in 1977.

Electron

The electron is an elementary particle with a negative charge whose interactions account for the vast majority of the phenomenon we observe in our day-to-day lives. Electrons bound around atomic nuclei form a “shell” which will repel the shells of other atoms, creating the physical interactions of matter at human scales. Also, the behavior and interactions of electrons bound in atomic orbitals produces chemistry, while the behavior of free electrons is responsible for electricity and modern technology such as computers or television. The electron and the electron neutrino form the first generation of leptons. The electron has mass, though it's exponentially less massive than the quarks. The electron is a fermion, and therefore obeys the Pauli exclusion principle.

Electricity and magnetism have long been observed, but it wasn't until the 1700s that the concept of charge was introduced. By the mid-19th century various experiments with cathode rays isolated and observed the behavior of these particles, and the electron term was coined in 1894. These discoveries led up to the formation of atomic theory in the early 20th century.

Muon

The muon is a subatomic particle with the same properties as an electron but with over 200 times the mass. The muon and the muon neutrino represent the second generation of leptons, and are only present in high-energy environments such as cosmic rays or particle accelerators. Due to its larger mass, it is less affected by electromagnetic forces, which along with their near-relativistic speeds, allow them to travel to the surface and penetrate long distances into the Earth's crust after being produced by cosmic rays hitting the Earth's upper atmosphere. Muons decay into an electron and some combination of two neutrinos. The muon is a fermion, and therefore obeys the Pauli exclusion principle.

The muon was discovered in 1936 by Carl D. Anderson and Seth Neddermeyer at Caltech, when they observed particles in cosmic radiation that carried a negative charge but did not respond as strongly to magnetic fields as electrons.

Tau

The tau is a subatomic particle with the same properties as an electron but with over 3000 times the mass. The tau and the tau neutrino represent the third generation of leptons, and are only present in high-energy environments such as cosmic rays or particle accelerators. Due to its larger mass, it is less affected by electromagnetic forces, and the tau is so massive that it is the only lepton which can decay into hadrons such as pions (pairs of quarks). The tau is a fermion, and therefore obeys the Pauli exclusion principle.

The tau was first detected in 1974 by Martin Lewis Perl at the Stanford Linear Accelerator Center, when discrepancies in energy hinted at the existence of new particles. Perl along with Frederick Reines shared the 1995 Nobel Prize for the discovery.

Electron Neutrino

The neutrinos are subatomic particles that, while common, are nearly undetectable because they only interact with gravity and the weak nuclear force. Neutrinos are produced in large quantities in weak interactions, such as the changing of quark flavors or the decay of particles, and have an extremely small but non-zero mass. The electron neutrino is produced along with its counterpart, the electron, in weak interactions. The electron and the electron neutrino form the first generation of leptons. The electron neutrino is a fermion, and therefore obeys the Pauli exclusion principle.

The electron neutrino was first proposed in the beginning of the 20th century to explain why electron emissions from beta decay (the transformation of a proton to a neutron or vice versa inside an atomic nucleus) were different than predicted. The particle was first observed by Clyde Cowan and Frederick Reines in 1956.

Muon Neutrino

The neutrinos are subatomic particles that, while common, are nearly undetectable because they only interact with gravity and the weak nuclear force. Neutrinos are produced in large quantities in weak interactions, such as the changing of quark flavors or the decay of particles, and have an extremely small but non-zero mass. The muon neutrino is produced along with its counterpart, the muon, in weak interactions. The muon and the muon neutrino form the second generation of leptons. The muon neutrino is a fermion, and therefore obeys the Pauli exclusion principle.

The muon neutrino was discovered by Leon M. Lederman, Melvin Schwartz, and Jack Steinberger at Brookhaven National Laboratory in 1962.

Tau Neutrino

The neutrinos are subatomic particles that, while common, are nearly undetectable because they only interact with gravity and the weak nuclear force. Neutrinos are produced in large quantities in weak interactions, such as the changing of quark flavors or the decay of particles, and have an extremely small but non-zero mass. The tau neutrino is produced along with its counterpart, the tau, in weak interactions. The tau and the tau neutrino form the third generation of leptons. The tau neutrino is a fermion, and therefore obeys the Pauli exclusion principle.

The tau neutrino was first hypothesized in the 1970s, after the discovery of its counterpart, the tau. It wasn't discovered until the year 2000, via the DONUT experiment at Fermilab which was specifically built to detect it.

Gluon

Gluons are a set of 8 particles which carry the strong nuclear force (or color charge) between quarks. Gluons interact with themselves to produce field structures called “flux tubes” in a process called confinement. As a result of the interaction, quarks can only form hadrons in specific configurations and gluons are restricted within them, making the strong nuclear force the shortest-ranged of all forces.

Gluons were first discovered at the PLUTO detector in the 1970s, by detecting the decay of hadrons into other hadrons.

Gluon

Gluons mediate the strong nuclear force, but unlike the photon and the electromagnetic force, the gluon also interacts with itself. As a result, while the strong nuclear force is several magnitudes stronger than any of the other forces, its influence does not extend beyond extremely short-ranged interactions between quarks.

Quarks

Quarks interact with all four fundamental interactions. They interact with the strong nuclear force via gluons, which allows them to form hadrons and atomic nuclei. They also interact with the electromagnetic force via photons, which is what gives atoms their charge. The weak interaction allows quarks to transform into other “flavors” of quarks, such as a down quark transforming into an up quark or vice versa.

Quarks interact with the Higgs field, and therefore have mass.

THE STANDARD MODEL

of particle physics


Particles


Interactions

Leptons

Leptons do not interact with the strong nuclear force, unlike quarks, but do interact with gravity and the weak force. While electrons, muons, and tau carry electric charge and interact with the electromagnetic force, the neutrinos do not.

Leptons interact with the Higgs field, and therefore have mass, though in ways that are complex and arcane.

Photon

The photon is a subatomic particle that is the mediator of the electromagnetic force, and comprises all forms of electromagnetic radiation, from infrared to x-rays to radio waves and visible light. The photon has no mass, and therefore travels at 3.00 x 10^8 m/s in vacuum, otherwise known as the speed of light. Photons are created whenever electromagnetic interactions take place, such as electrons jumping energy levels around the atomic nucleus, or reactions like antimatter annihilation or nuclear fusion.

While explanations for the phenomenon of light have existed since antiquity, modern theories of light were first formulated in the 17th century. Rene Descartes chose to describe light as a wave due to its refractive properties through mediums, while Pierre Gassendi (and later Issac Newton) chose to describe light as a particle due to its travel in straight lines through vacuum. In the 19th century Michael Faraday first proposed the relationship between light, electricity, and magnetism by observing the travel of light through magnetic fields. It wasn't until the early 20th century that Max Planck and Albert Einstein chose to describe light as both a particle and a wave, which led to the development of Quantum theory.

W and Z Bosons

The W and Z bosons are the mediators of the weak nuclear force, which is responsible for particle decay and the transformation of particles into other particles. Most notably, the weak force is essential for nuclear and stellar fusion, as it allows protons to transform into neutrons and vice versa. The W+ and W- bosons carry electric charges and are each other's antiparticle, while the Z boson is neutral. The W and Z bosons have significant mass and short lifetimes, thereby making the weak force very short-ranged.

The weak nuclear force was first proposed in the 1930s by Enrico Fermi to explain the properties of beta decay (the decay of a neutron to a proton). In 1968, Sheldon Glashow, Steven Weinberg, and Abdus Salam proposed a unified theory of electromagnetic and weak interactions called the electroweak theory, for which they shared the 1979 Nobel Prize. The bosons were first observed at CERN in 1983, for which Carlo Rubbia and Simon van der Meer shared the 1983 Nobel Prize.

Higgs Boson

The Higgs boson is the particle form of the Higgs field, an underlying scalar field that permeates the entire universe and gives mass to particles that interact with it. The Higgs field is a necessary mediator to describe the particulars of the weak interaction, especially how the W and Z bosons gain mass. The mechanism is described as being a kind of medium which gives “drag” to particles that move through it, slowing them down and preventing them from traveling at the speed of light.

The Higgs was first proposed by three separate papers in 1964, and named for one of its authors, Peter Higgs. This formed a part of the Standard Model of particle physics, which unified all the fundamental forces and particles (except gravity) and performed calculations with incredible accuracy. However, the Higgs itself wasn't observed until 2012 at CERN's Large Hadron Collider, a particle accelerator built specifically to detect it. Currently, the specific properties of the Higgs boson aren't established, and it is unknown whether there is a single Higgs boson (like the photon) or multiple Higgs bosons (like the W and Z bosons). Peter Higgs and Francois Englert shared the 2013 Nobel Prize for the discovery of the Higgs.

Graviton

The graviton is a hypothetical particle which is the force carrier for the force of gravity. It would need to be massless since gravity has infinite range, and propagate in space similarly to the electromagnetic force. Gravity waves have been observed at specialized detectors, but the particle itself interacts too weakly with other particles for it to ever be directly observed at particle accelerators.

Photon

Electromagnetism is responsible for almost all everyday interactions, as well as the processes involved in chemistry, classical physics, and the workings of most modern technologies. The photon interacts with everything that has an electric charge, such as quarks and leptons. However, the photon itself has no charge, so therefore it does not interact with itself in normal energies. This, along with its relativistic speed, allows photons to propagate extreme distances through space.

W and Z Bosons

The weak nuclear force interacts with all fermions (quarks and leptons) and allows them to change their flavor, which isn't permitted by the strong nuclear force or the electromagnetic force. The W bosons have charge, which allows them to interact with the electromagnetic force, while the Z does not. The W and Z bosons have mass, which makes them short-ranged, and they also interact with themselves.

Higgs Boson

The Higgs field interacts with leptons and the W and Z bosons, giving them all mass. Massive objects must move at a speed below the speed of light, because of the interference from the Higgs.

Graviton

Gravity is the weakest of the fundamental forces, but one with profound impact over the structure of the universe. Gravity allows particles with mass to warp the “fabric” of time and space, propagating across infinite distances and pulling the contents of the universe together to form galaxies, stars, and planets. Therefore, it affects all other particles, however weakly, by curving the very space they inhabit.

The Standard Model

The Standard Model of particle physics is a “theory of almost everything”. It is the sum of our understanding of the fundamental building blocks of the universe, and is currently the best description we have of the subatomic world. It describes the universe as consisting of a set of particles, as either the “material” of the universe (fermions) or the particles that interact with them (bosons), and it can predict their interactions with incredible accuracy and consistency.

However, the theory of general relativity is currently our best description of gravity, yet it is incompatible with the standard model. Moreover, observations of the mass of distant galaxies, and the rate of expansion of the universe, suggest to us that the particles of the standard model account for less than 5% of the content of the universe. Therefore, the standard model is not a true “theory of everything”.

The foundations of the Standard Model were laid in the 1964 with the first theories of Quarks, and subsequently with the theory of electroweak interaction in 1967. With the discovery of the Higgs Boson in 2012 (a particle first predicted in the 1960s), the standard model remains our strongest theory of the subatomic universe.

THE UNIVERSE

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Scroll Down to Begin Time

At the beginning of time, the universe was a singularity.

Everything that ever was, confined to a single point.

Infinitely dense, and infinitely hot.

Without time and without space.

Until it went...

...bang.

The Beginning of Time

PLANCK EPOCH

The universe is so hot and so dense that our current understanding of physics is inadequate to describe any of its properties. All four fundamental forces are unified into a single force, and measurements of time and distance are meaningless.

10-43 seconds

GRAND UNIFICATION EPOCH

Gravity separates from the other fundamental forces as the universe cools.

10-36 seconds

INFLATIONARY EPOCH

The strong nuclear force separates, cascading a series of events which leads to a theoretical "inflation field" that begins to push the universe outwards.

The effects of this force are immediate, and the universe undergoes an exponential expansion.

...from smaller than a Planck length, the shortest possible measurement of distance...

...to several centimeters across, about the size of a grapefruit.

10-32 seconds

ELECTROWEAK EPOCH

The rapid expansion from the inflationary epoch leaves the universe extremely hot but nearly empty, as the original material from the big bang is distributed evenly but thinly across an exponentially larger universe.

The high energy background immediately repopulates the universe with new particles, as the electroweak force separates and the Higgs field is created.

10-12 seconds

QUARK EPOCH

The universe cools enough for the four fundamental forces to take their present forms, and the universe becomes dominated by a thick "soup" of quarks, gluons, and leptons known as quark-gluon plasma.

Soon, it becomes cold enough for quarks and gluons to form new structures.

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A Proton

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10-6 seconds

HADRON EPOCH

The quark gluon plasma cools enough for quarks and gluons to form hadrons, including baryons like protons and neutrons.

Hadrons are composite particles made from multiple quarks via gluons and the strong nuclear force. They include mesons (a quark paired with an antiquark), baryons (three quarks), or even more complex particles that contain 4 or even 5 quarks.

At the end of the hadron epoch, the universe cools enough for quarks and anti-quarks to interact and annihilate each other, leaving very few hadrons behind.

1 second

LEPTON EPOCH

After most of the hadrons have annihilated each other, leptons and anti-leptons dominate the matter content of the universe.

Until they too annihilate each other, ending the lepton epoch.

10 seconds

PHOTON EPOCH

Once the majority of leptons and anti-leptons annihilate each other, the universe becomes dominated by photons.

The remaining electrons in the universe form a loose cloud which prevents photons from propagating, keeping everything in equilibrium as the universe still continues to expand and cool.

3 Minutes

NUCLEOSYNTHESIS

Between 3 and 20 minutes after the big bang, the universe is at the right temperature to initiate fusion between baryons.

Two protons cannot fuse because of their positive charges, as the repulsion of the electromagnetic force would push against the attraction strong nuclear force and make the pairing energetically impossible.

However, neutrons have no charge and can therefore interact with protons without interference, which allows a neutron to fuse with a proton to produce a deuteron. There are no stable neutron - neutron pairs.

And deuterium can fuse further to form an alpha particle, a stable nucleus with two protons and two neutrons, better known as the nucleus of helium.

20 minutes after the big bang, the universe becomes too cold for nucleosynthesis to continue. Free neutrons have either formed into helium or decayed to protons, and the ratio of hydrogen to helium in the universe is more than 3 to 1.

As the violence of the big bang subsides, the universe finds equilibrium and stabilises.

...as it continues to expand and cool...

...for minutes, hours, days...

...and years and years...

...and hundreds of thousands of years.

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377,000 Years

RECOMBINATION

Electrons can form tenative bonds with atomic nuclei as their electromagnetic attraction keeps the electron in an "orbit" around the positively-charged nucleus. However, in high-energy environments the electron would easily be dislodged by an energetic photon, which would also produce another photon that might dislodge another electron, and so on.

300 thousand years after the big bang, the universe has finally cooled enough for electrically neutral atoms to form.

As soon as recombination became energetically favorable, almost all the free protons and electrons in the universe spontaneously formed neutral atoms.

Without free electrons to block their propagation, photons can now travel freely throughout space. For the first time, the universe becomes transparent.

This initial burst of free photons is still detectable today, though billions of years of traveling through expanding space has reduced it to a barely detectable buzz at the lowest frequencies, known as cosmic microwave background radiation.

380,000 years after the big bang...

...the universe is simple, and dark.

Still hot, but constantly cooling.

Over 40 million light years across,

and always expanding.

But this is only the beginning...

Stay tuned for part 2!