Sample Physics Book from Wikipedia… love the Wiki!

Hmm… looks way better in the PDF form than here…



Atom 1

Atomic nucleus 5

Boson 11

Electric charge 11

Electron 13

Elementary particle 15

Fermion 18

Googolplex 19

Hadron 19

Lepton 20

Neutron 21

Nucleus (physics) 22

Proton 22

Quark 23

Universe 25

Up quark 34


Article Sources and Contributors 35

Image Sources, Licenses and Contributors 36

Article Licenses

License 37Atom 1



Lithium atom modelShowing nucleus with four neutrons


three protons (red) and,

orbited by three electrons (black).


Smallest recognised division of a chemical element


Mass: 1.66 x 10(−27) to 4.52 x 10(−25) kg

Electric charge: zero

An atom is the basic unit that makes up all matter. There are many different types of atoms, each with its own name,

mass and size. These different types of atoms are called chemical elements. Examples of elements are hydrogen and

gold. Atoms are very small, but the exact size changes depending on the element. Atoms range from 0.1 to 0.5

nanometers in width.[1] One nanometer is around 100,000 times smaller than the width of a human hair.

[2] This

makes atoms impossible to see without special tools. Equations must be used to see the way they work and how they

interact with other atoms.

Atoms come together to make molecules or particles: for example, two hydrogen atoms and one oxygen atom

combine to make a water molecule, a form of a chemical reaction.

Atoms themselves are made up of three kinds of smaller particles, called protons, neutrons and electrons. The

protons and neutrons are in the middle of the atom. They are called the nucleus. The nucleus is surrounded by a

cloud of electrons with a negative charge which are bound to the nucleus by an electromagnetic force.

Protons and neutrons are made up of even smaller particles called quarks. Electrons are elementary or fundamental

particles; they cannot be split into smaller parts.

The number of protons, neutrons and electrons an atom has determines what element it is. Hydrogen, for example,

has one proton, no neutrons and one electron; the element sulfur has 16 protons, 16 neutrons and 16 electrons.

Atoms move faster when in gas form (as they are free to move) than liquid and solid matter. In solid materials the

atoms are tightly next to each other so they vibrate [3], but are not able to move (there is no room) as atoms in liquids

do.Atom 2


The word “atom” comes from the Greek ἀτόμος, indivisible [4], from ἀ-, not, and τόμος, a cut. The first historical

mention of the word atom came from works by the Greek philosopher Democritus, around 400 BC.[5] Atomic theory

stayed as a mostly philosophical subject, with not much actual scientific investigation or study, until the

development of chemistry in the 1600s.

In 1777 French chemist Antoine Lavoisier defined the term element for the first time. He said that an element was

any basic substance that could not be broken down into other substances by the methods of chemistry. Any substance

that could be broken down was a compound.


In 1803, English philosopher John Dalton suggested that elements were tiny, solid spheres made of atoms. Dalton

believed that all atoms of the same element have the same mass. He said that compounds are formed when atoms of

more than one element combine. According to Dalton, in a compound, atoms of different elements always combine

the same way.

In 1827, British scientist Robert Brown looked at pollen grains in water and used Dalton’s atomic theory to describe

patterns in the way they moved. This was called Brownian Motion. In 1905 Albert Einstein used mathematics to

prove that the seemingly random movements were down to the reactions of atoms, and by doing so he conclusively

proved the existence of the atom.[6] In 1869 scientist Dmitri Mendeleev published the first version of the periodic

table. The periodic table groups atoms by their atomic number (how many protons they have. This is usually the

same as the number of electrons). Elements in the same column, or period, usually have similar properties. For

example helium, neon, argon, krypton and xenon are all in the same column and have very similar properties. All

these elements are gases that have no colour and no smell. Together they are known as the noble gases.


The physicist J.J. Thomson was the first man to discover electrons. This happened while he was working with

cathode rays in 1897. He realized they had a negative charge, unlike protons (positive) and neutrons (no charge).

Thomson created the plum pudding model, which stated that an atom was like plum pudding: the dried fruit

(electrons) were stuck in a mass of pudding (protons). In 1909, a scientist named Ernest Rutherford used the

Geiger–Marsden experiment to prove that most of an atom is in a very small space called the atomic nucleus.

Rutherford took a photo plate and surrounded it with gold foil, and then shot alpha particles at it. Many of the

particles went through the gold foil, which proved that atoms are mostly empty space. Electrons are so small they

make up only 1% of an atom’s mass.


Ernest Rutherford in 1910, shortly before

he won the Nobel Prize for physics.

In 1913, Niels Bohr introduced the Bohr model. This model showed that

electrons orbit the nucleus in fixed circular orbits. This was more accurate

than the Rutherford model. However, it was still not completely right.

Improvements to the Bohr model have been made since it was first


In 1925, chemist Frederick Soddy found that some elements in the periodic

table had more than one kind of atom.[8] For example any atom with 2

protons should be a helium atom. Usually, a helium nucleus also contains two

neutrons. However, some helium atoms have only one neutron. This means

they are still helium, as the element is defined by the number of protons, but

they are not normal helium either. Soddy called an atom like this, with a

different number of neutrons, an isotope. To get the name of the isotope we

look at how many protons and neutrons it has in its nucleus and add this to the

name of the element. So a helium atom with two protons and one neutron is

called helium-3, and a carbon atom with six protons and six neutrons is calledAtom 3

carbon-12. However, when he developed his theory Soddy could not be certain neutrons actually existed. To prove

they were real, physicist James Chadwick and a team of others created the mass spectrometer.

[9] The mass

spectrometer actually measures the mass and weight of individual atoms. By doing this Chadwick proved that to

account for all the weight of the atom, neutrons must exist.

In 1937, German chemist Otto Hahn became the first person to create nuclear fission in a laboratory. He discovered

this by chance when he was shooting neutrons at a uranium atom, hoping to create a new isotope.[10] However, he

noticed that instead of a new isotope the uranium simply changed into a barium atom. This was the world’s first

recorded nuclear fission reaction. This discovery eventually led to the creation of the atomic bomb.

Further into the 20th century physicists went deeper into the mysteries of the atom. Using particle accelerators they

discovered that protons and neutrons were actually made of other particles, called quarks.

The most accurate model so far comes from the Schrödinger equation. Schrödinger realized that the electrons exist in

a cloud around the nucleus, called the electron cloud. In the electron cloud, it is impossible to know exactly where

electrons are. The Schrödinger equation is used to find out where an electron is likely to be. This area is called the

electron’s orbital.

Structure and parts


The complex atom is made up of three main particles; the proton, the neutron and the electron. The isotope of

Hydrogen Hydrogen-1 has no neutrons, and a positive hydrogen ion has no electrons. These are the only known

exceptions, all other atoms have at least one proton, neutron and electron each.

Electrons are by far the smallest of the three, their mass and size is too small to be measured using current

technology.[] They have a negative charge. Protons and neutrons are similar sizes[] Protons are positively charged

and neutrons have no charge. Most atoms have a neutral charge; because the number of protons (positive) and

electrons (negative) are the same, the charges balance out to zero. However in ions (different number of electrons)

this is not always the case and they can have a positive or a negative charge. Protons and Neutrons are made out of

quarks, of two types; up quarks and down quarks. A proton is made of two up quarks and one down quark and a

neutron is made of two down quarks and one up quark.


The nucleus is in the middle of an atom. It is made up of protons and neutrons. Usually in nature, two things with the

same charge repel or shoot away from each other. So for a long time it was a mystery to scientists how the positively

charged protons in the nucleus stayed together. They solved this by finding a particle called a Gluon. Its name comes

from the word glue as Gluons act like atomic glue, sticking the protons together using the strong nuclear force. It is

this force which also holds the quarks together that make up the protons and neutrons.Atom 4

A diagram showing the main difficulty in nuclear fusion, the fact that

protons, which have positive charges, repel each other when forced


The number of neutrons in relation to protons defines

whether the nucleus is stable or goes through

radioactive decay. When there are too many neutrons or

protons, the atom tries to make the numbers the same

by getting rid of the extra particles. It does this by

emitting radiation in the form of alpha, beta or gamma

decay.[11] Nuclei can change through other means too.

Nuclear fission is when the Nucleus splits into two

smaller nuclei, releasing a lot of stored energy. This

release energy is what makes nuclear fission useful for

making bombs and electricity, in the form of nuclear

power. The other way nuclei can change is through nuclear fusion, when two nuclei join together, or fuse, to make a

heavier nucleus. This process requires extreme amounts of energy in order to overcome the electrostatic repulsion

between the protons, as they have the same charge. Such high energies are most common in stars like our Sun, which

fuses hydrogen for fuel.


Electrons orbit or go around the nucleus. They are called the atom’s electron cloud. They are attracted towards the

nucleus because of the electromagnetic force. Electrons have a negative charge and the nucleus always has a positive

charge, so they attract each other. Around the nucleus some electrons are further out than others. These are called

electron shells. In most atoms the first shell has two electrons, and all after that have eight. Exceptions are rare, but

they do happen and are difficult to predict.[12] The further away the electron is from the nucleus, the weaker the pull

of the nucleus on it. This is why bigger atoms, with more electrons, react more easily with other atoms. The

electromagnetism of the nucleus is not enough to hold onto their electrons and they lose them to the strong attraction

of smaller atoms [13]

Radioactive decay

Some elements, and many isotopes, have what is called an unstable nucleus. This means the nucleus is either too big

to hold itself together[] or has too many protons, electrons or neutrons. When this happens the nucleus has to get rid

of the excess mass or particles. It does this through radiation. An atom that does this can be called radioactive.

Unstable atoms continue to be radioactive until they lose enough mass/particles that they become stable. All atoms

above atomic number 82 (82 protons) are radioactive.[]

There are three main types of radioactive decay; alpha, beta and gamma.


• Alpha decay is when the atom shoots out a particle having two protons and two neutrons. This is essentially a

helium nucleus. The result is an element with atomic number two less than before. So for example if a beryllium

atom (atomic number 4) went through alpha decay it would become helium (atomic number 2). Alpha decay

happens when an atom is too big and needs to get rid of some mass.

• Beta decay is when a neutron turns into a proton or a proton turns into a neutron. In the first case the atom shoots

out an electron, in the second case it is a positron (like an electron but with a positive charge). The end result is an

element with one higher or one lower atomic number than before. Beta decay happens when an atom has either

too many protons, or too many neutrons.

• Gamma decay is when an atom shoots out a gamma ray, or wave. It happens when there is a change in the energy

of the nucleus. This is usually after a nucleus has already gone through alpha or beta decay. There is no change in

the mass, or atomic number or the atom, only in the stored energy inside the nucleus.Atom 5

Every radioactive element or isotope has something called a half life. This is how long it takes half of any sample of

atoms of that type to decay until they become a different stable isotope or element.[15] Large atoms, or isotopes with

a big difference between the number of protons and neutrons will therefore have a long half life.




Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – Tachyon

Other websites

• General information on atomic structure (

• Atomic structure timeline (

Atomic nucleus

The nucleus of an atom is the very small dense part of an atom, in its center made up of nucleons (protons and

neutrons). The size (diameter) of the nucleus is between 1.6 fm (10-15 m) (for a proton in light hydrogen) to about 15

fm (for the heaviest atoms, such as uranium). These sizes are much smaller than the size of the atom itself by a factor

of about 23,000 (uranium) to about 145,000 (hydrogen). Almost all of the mass in an atom is made up from the

protons and neutrons in the nucleus with a very small contribution from the orbiting electrons. The word nucleus is

from 1704, meaning “kernel of a nut”. In 1844, Michael Faraday used nucleus to describe the “central point of an

atom”. The modern atomic meaning was proposed by Ernest Rutherford in 1912.[1] The use of the word nucleus in

atomic theory, however, did not happen immediately. In 1916, for example, Gilbert N. Lewis wrote, in his famous

article The Atom and the Molecule [2], that “the atom is composed of the kernel and an outer atom or shell”.Atomic nucleus 6

A drawing of the helium atom. In the nucleus, the protons are in red and neutrons

are in purple.


Nuclear makeup

The nucleus of an atom is made up of

protons and neutrons (two types of baryons)

joined by the nuclear force. These baryons

are further made up of sub-atomic

fundamental particles known as quarks

joined by the strong interaction.

Isotopes and nuclides

The isotope of an atom is based on the

number of neutrons in the nucleus. Different

isotopes of the same element have very

similar chemical properties. Different

isotopes in a sample of a chemical can be

separated by using a centrifuge or by using a

mass spectrometer. The first method is used

in producing enriched uranium from regular

uranium, and the second is used in carbon


The number of protons and neutrons together determine the nuclide (type of nucleus). Protons and neutrons have

nearly equal masses, and their combined number, the mass number, is about equal to the atomic mass of an atom.

The combined mass of the electrons is very small when compared to the mass of the nucleus; protons and neutrons

weigh about 2000 times more than electrons.


The discovery of the electron by J. J. Thomson was the first sign that the atom had internal structure. At the turn of

the 20th century the accepted model of the atom was J. J. Thomson’s “plum pudding” model in which the atom was a

large positively charged ball with small negatively charged electrons embedded inside of it. By the turn of the

century physicists had also discovered three types of radiation coming from atoms, which they named alpha, beta,

and gamma radiation. Experiments in 1911 by Lise Meitner and Otto Hahn, and by James Chadwick in 1914

discovered that the beta decay spectrum was continuous rather than discrete. That is, electrons were ejected from the

atom with a range of energies, rather than the discrete amounts of energies that were observed in gamma and alpha

decays. This was a problem for nuclear physics at the time, because it indicated that energy was not conserved in

these decays. The problem would later lead to the discovery of the neutrino (see below).

In 1906 Ernest Rutherford published “Radiation of the α Particle from Radium in passing through Matter”[3]

. Geiger

expanded on this work in a communication to the Royal Society[4] with experiments he and Rutherford had done

passing α particles through air, aluminum foil and gold foil. More work was published in 1909 by Geiger and

Marsden[5] and further greatly expanded work was published in 1910 by Geiger,

[6] In 1911-2 Rutherford went before

the Royal Society to explain the experiments and propound the new theory of the atomic nucleus as we now

understand it.Atomic nucleus 7

Around the same time that this was happening (1909) Ernest Rutherford performed a remarkable experiment in

which Hans Geiger and Ernest Marsden under his supervision fired alpha particles (helium nuclei) at a thin film of

gold foil. The plum pudding model predicted that the alpha particles should come out of the foil with their

trajectories being at most slightly bent. He was shocked to discover that a few particles were scattered through large

angles, even completely backwards in some cases. The discovery, beginning with Rutherford’s analysis of the data in

1911, eventually led to the Rutherford model of the atom, in which the atom has a very small, very dense nucleus

consisting of heavy positively charged particles with embedded electrons in order to balance out the charge. As an

example, in this model nitrogen-14 consisted of a nucleus with 14 protons and 7 electrons, and the nucleus was

surrounded by 7 more orbiting electrons.

The Rutherford model worked quite well until studies of nuclear spin were carried out by Franco Rasetti at the

California Institute of Technology in 1929. By 1925 it was known that protons and electrons had a spin of 1/2, and in

the Rutherford model of nitrogen-14 the 14 protons and six of the electrons should have paired up to cancel each

others spin, and the final electron should have left the nucleus with a spin of 1/2. Rasetti discovered, however, that

nitrogen-14 has a spin of one.

In 1930 Wolfgang Pauli was unable to attend a meeting in Tübingen, and instead sent a famous letter with the classic

introduction “Dear Radioactive Ladies and Gentlemen”. In his letter Pauli suggested that perhaps there was a third

particle in the nucleus which he named the “neutron”. He suggested that it was very light (lighter than an electron),

had no charge, and that it did not readily interact with matter (which is why it had not yet been detected). This

desperate way out solved both the problem of energy conservation and the spin of nitrogen-14, the first because

Pauli’s “neutron” was carrying away the extra energy and the second because an extra “neutron” paired off with the

electron in the nitrogen-14 nucleus giving it spin one. Pauli’s “neutron” was renamed the neutrino (Italian for little

neutral one) by Enrico Fermi in 1931, and after about thirty years it was finally demonstrated that a neutrino really is

emitted during beta decay.

In 1932 Chadwick realized that radiation that had been observed by Walther Bothe, Herbert L. Becker, Irène and

Frédéric Joliot-Curie was actually due to a massive particle that he called the neutron. In the same year Dmitri

Ivanenko suggested that neutrons were in fact spin 1/2 particles and that the nucleus contained neutrons and that

there were no electrons in it, and Francis Perrin suggested that neutrinos were not nuclear particles but were created

during beta decay. To cap the year off, Fermi submitted a theory of the neutrino to Nature (which the editors rejected

for being “too remote from reality”). Fermi continued working on his theory and published a paper in 1934 which

placed the neutrino on solid theoretical footing. In the same year Hideki Yukawa proposed the first significant theory

of the strong force to explain how the nucleus holds together.

With Fermi and Yukawa’s papers the modern model of the atom was complete. The center of the atom contains a

tight ball of neutrons and protons, which is held together by the strong nuclear force. Unstable nuclei may undergo

alpha decay, in which they emit an energetic helium nucleus, or beta decay, in which they eject an electron (or

positron). After one of these decays the resultant nucleus may be left in an excited state, and in this case it decays to

its ground state by emitting high energy photons (gamma decay).

The study of the strong and weak nuclear forces led physicists to collide nuclei and electrons at ever higher energies.

This research became the science of particle physics, the most important of which is the standard model of particle

physics which unifies the strong, weak, and electromagnetic forces.

Modern nuclear physics

A light nucleus can contain hundreds of nucleons which means that with some approximation it can be treated as a

classical system, rather than a quantum-mechanical one. In the resulting liquid-drop model, the nucleus has an

energy which arises partly from surface tension and partly from electrical repulsion of the protons. The liquid-drop

model is able to reproduce many features of nuclei, including the general trend of binding energy with respect to

mass number, as well as the phenomenon of nuclear fission.Atomic nucleus 8

Superimposed on this classical picture, however, are quantum-mechanical effects, which can be described using the

nuclear shell model, developed in large part by Maria Goeppert-Mayer. Nuclei with certain numbers of neutrons and

protons (the magic numbers 2, 8, 20, 50, 82, 126, …) are particularly stable, because their shells are filled.

Much of current research in nuclear physics relates to the study of nuclei under extreme conditions such as high spin

and excitation energy. Nuclei may also have extreme shapes (similar to that of American footballs) or extreme

neutron-to-proton ratios. Experimenters can create such nuclei using artificially induced fusion or nucleon transfer

reactions, employing ion beams from an accelerator. Beams with even higher energies can be used to create nuclei at

very high temperatures, and there are signs that these experiments have produced a phase transition from normal

nuclear matter to a new state, the quark-gluon plasma, in which the quarks mingle with one another, rather than

being segregated in triplets as they are in neutrons and protons.

Modern topics in nuclear physics

Spontaneous changes from one nuclide to another: nuclear decay

If a nucleus has too few or too many neutrons it may be unstable, and will decay after some period of time. For

example, nitrogen-16 atoms (7 protons, 9 neutrons) beta decay to oxygen-16 atoms (8 protons, 8 neutrons) within a

few seconds of being created. In this decay a neutron in the nitrogen nucleus is turned into a proton and an electron

by the weak nuclear force. The element of the atom changes because while it previously had seven protons (which

makes it nitrogen) it now has eight (which makes it oxygen). Many elements have multiple isotopes which are stable

for weeks, years, or even billions of years.

Nuclear fusion

When two light nuclei come into very close contact with each other it is possible for the strong force to fuse the two

together. It takes a great deal of energy to push the nuclei close enough together for the strong force to have an

effect, so the process of nuclear fusion can only take place at very high temperatures or high densities. Once the

nuclei are close enough together the strong force overcomes their electromagnetic repulsion and squishes them into a

new nucleus. A very large amount of energy is released when light nuclei fuse together because the binding energy

per nucleon increases with mass number up until nickel-62. Stars like our sun are powered by the fusion of four

protons into a helium nucleus, two positrons, and two neutrinos. The uncontrolled fusion of hydrogen into helium is

known as thermonuclear runaway. Research to find an economically viable method of using energy from a

controlled fusion reaction is currently being undertaken by various research establishments (see JET and ITER).

Nuclear fission

For nuclei heavier than nickel-62 the binding energy per nucleon decreases with the mass number. It is therefore

possible for energy to be released if a heavy nucleus breaks apart into two lighter ones. This splitting of atoms is

known as nuclear fission.

The process of alpha decay may be thought of as a special type of spontaneous nuclear fission. This process

produces a highly asymmetrical fission because the four particles which make up the alpha particle are especially

tightly bound to each other, making production of this nucleus in fission particularly likely.

For certain of the heaviest nuclei which produce neutrons on fission, and which also easily absorb neutrons to initiate

fission, a self-igniting type of neutron-initiated fission can be obtained, in a so-called chain reaction. [Chain reactions

were known in chemistry before physics, and in fact many familiar processes like fires and chemical explosions are

chemical chain reactions]. The fission or “nuclear” chain-reaction, using fission-produced neutrons, is the source of

energy for nuclear power plants and fission type nuclear bombs such as the two that the United States used against

Hiroshima and Nagasaki at the end of World War II. Heavy nuclei such as uranium and thorium may undergo

spontaneous fission, but they are much more likely to undergo decay by alpha decay.Atomic nucleus 9

For a neutron-initiated chain-reaction to occur, there must be a critical mass of the element present in a certain space

under certain conditions (these conditions slow and conserve neutrons for the reactions). There is one known

example of a natural nuclear fission reactor, which was active in two regions of Oklo, Gabon, Africa, over 1.5 billion

years ago. Measurements of natural neutrino emission have demonstrated that around half of the heat emanating

from the earth’s core results from radioactive decay. However, it is not known if any of this results from fission


Production of heavy elements

As the Universe cooled after the big bang it eventually became possible for particles as we know them to exist. The

most common particles created in the big bang which are still easily observable to us today were protons (hydrogen)

and electrons (in equal numbers). Some heavier elements were created as the protons collided with each other, but

most of the heavy elements we see today were created inside of stars during a series of fusion stages, such as the

proton-proton chain, the CNO cycle and the triple-alpha process. Progressively heavier elements are made during the

evolution of a star. Since the binding energy per nucleon peaks around iron, energy is only released in fusion

processes occurring below this point. Since the creation of heavier nuclei by fusion costs energy, nature resorts to the

process of neutron capture. Neutrons (due to their lack of charge) are readily absorbed by a nucleus. The heavy

elements are created by either a slow neutron capture process (the so-called s process) or by the rapid, or r process.

The s process occurs in thermally pulsing stars (called AGB, or asymptotic giant branch stars) and takes hundreds to

thousands of years to reach the heaviest elements of lead and bismuth. The r process is thought to occur in supernova

explosions because the conditions of high temperature, high neutron flux and ejected matter are present. These stellar

conditions make the successive neutron captures very fast, involving very neutron-rich species which then

beta-decay to heavier elements, especially at the so-called waiting points that correspond to more stable nuclides

with closed neutron shells (magic numbers). The r process duration is typically in the range of a few seconds.

Related pages

• List of particles

• Radioactivity

• Nuclear fusion

• Nuclear fission

• Nuclear medicine

• Nuclear physics

• Atomic number

• Atomic mass

• Isotope

• Liquid drop model

• Semi-empirical mass formulaAtomic nucleus 10


[1] Nucleus – Online Etymology Dictionary (


[3] Philosophical Magazine (12, p 134-46)

[4] Proc. Roy. Soc. July 17, 1908

[5] Proc. Roy. Soc. A82 p 495-500

[6] Proc. Roy. Soc. Feb. 1, 1910

Other websites

• The Nucleus – a chapter from an online textbook (


• – Study of the NUCLEAR STRUCTURE by R. Kolessin (

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – Tachyon

Template:Nuclear TechnologyBoson 11


A boson is a particle which has a whole number spin (‘spin’ is a quality assigned to subatomic particles).

A photon is an example of a boson as it has a spin of 1.

Bosons are different from Fermions, which are particles that make up matter, because they obey Bose-Einstein

statistics. (This means that you can put two of them in the same place at the same time).

“Gauge bosons” carry forces. There are three known gauge bosons which are fundamental particles. For example, the

photon carries the electromagnetic force. The four gauge bosons are as follows: photons for electromagnetism,

gluons for strong force, and W and Z bosons for weak force. Other theoretical gauge bosons are predicted, such as

gravitons for gravity. The Higgs boson is another fundamental particle of a type called a scalar boson.

Paul Dirac named this class of particles “bosons” in honor of a famous scientist called Satyendra Nath Bose.

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – Tachyon

Electric charge


Electricity · Magnetism

Electric charge is a basic property of electrons, protons and other subatomic particles. Electrons are negatively

charged while protons are positively charged. Things that are negatively charged and things that are positively

charged pull on (attract) each other. This makes electrons and protons stick together to form atoms. Things that have

the same charge push each other away (they repel each other). This is called the Law of Charges. It was discovered

by Charles Augustin de Coulomb. The law that describes how strongly charges pull and push on each other is called

Coulomb’s Law.

Things that have equal numbers of electrons and protons are neutral. Things that have more electrons than protons 

are negatively charged, while things with fewer electrons than protons are positively charged. Things with the same 

charge repel each other. Things that have different charges attract each other. If possible, the one with too many 

electrons will give enough electrons to match the number of protons in the one that has too many protons for its loadElectric charge 12

of electrons. If there are just enough electrons to match the extra protons, then the two things will not attract each

other anymore. When electrons move from a place where there are too many to a place where there are too few, that

transfer makes an electrical current.

When a person shuffles his feet on a carpet and then touches a brass doorknob, he or she may get an electrical shock.

If there are enough extra electrons then the force with which those electrons push each other away may be enough to

make some of the electrons jump across a gap between the person and the doorknob. The length of the spark is a

measure of voltage or “electrical pressure.” The number of electrons that move from one place to another per unit of

time measured as amperage or “rate of electron flow.”

If a person gets a positive or negative charge, it may make the person’s hairs stand up because the charges in each

hair push it away from the others.

Electric charge felt when one gets a shock from a doorknob or other object usually is between 25 thousand and 30

thousand volts. However the amperage involved is incredibly low so the flow of electrons through the person’s body

can not cause physical harm. On the other hand, when clouds accumulate electrical charges they have even higher

voltages and the amperage (the number of electrons that will flow in the lightning strike) can be very high. That

means that electrons can jump from a cloud to the earth (or from the earth to a cloud), and if those electrons go

through a person then that person will be burned and may die.

Historical experiment

Electric charge is the fundamental properties of sub atomic particles, that provides an electric field between them.

Let a piece of glass and a piece of resin–neither of which exhibits any electrical properties–be rubbed together and

left with the rubbed surfaces in contact. They will still exhibit no electrical properties. Let them be separated. They

will now attract each other.

If a second piece of glass is rubbed with a second piece of resin, and if the pieces be then separated and suspended in

the neighborhood of the former pieces of glass and resin, it may be observed:

1) that the two pieces of glass repel each other.

2) that each piece of glass attracts each piece of resin.

3) that the two pieces of resin repel each other.

These phenomena of attraction and repulsion are called Electrical phenomena and the bodies which exhibit them are

said to be ‘electrified’, or to be ‘charged with electricity’.

Besides being electrified by friction, bodies may be electrified in many other ways.

When two substances are rubbed together and an electrical charge is produced, one of them will give electrons to the

other. The reason is that the atoms in the two substances have unequal power to attract electrons. So the one that is

more able to attract electrons will rob electrons from the one that has a lower attractive force. In one pair of

substances rubbed together, the one made of glass may either give or take electrons. What happens depends on the

nature of the other member of that pair.

If a body electrified in any manner whatever behaves as the glass does when rubbed with resin, that is, if it repels the

glass and attract the resin, the body is said to be ‘vitreously’ electrified, and if it attracts the glass and repels the resin

it is said to be ‘resinously’ electrified. All electrified bodies are found to be either vitreously or resinously


It is the established practice of men of science to call the vitreous electrification positive, and the resinous

electrification negative. The exactly opposite properties of the two kinds of electrification justify us in indicating

them by opposite signs but the application of the positive sign to one rather than to the other kind must considered as

a matter of arbitrary (random choice) convention (agreement), just as it is a matter of convention in mathematical

diagrams to reckon positive distance towards the right hand.Electric charge 13

No force, either of attraction or of repulsion (the opposite of attraction), can be observed between an electrified body

and a body not electrified.

The above experiment is described by James Clerk Maxwell in his magnum opus (great work) A Treatise on

Electricity and Magnetism.


An electron is a very small piece of matter and energy. Its symbol is e


The electron is a subatomic particle. It is believed to be an elementary particle because it cannot be broken down into

anything smaller.[1] It is negatively charged,

[2] and may move almost at the speed of light.


Electrons take part in gravitational, electromagnetic and weak interactions.

[4] The electricity that powers radios,

motors, and many other things consists of many electrons moving through wires or other conductors.


The Niels Bohr model of the atom. Three electron

shells about a nucleus, with an electron moving

from the second to the first level and releasing a


Electrons have the smallest electrical charge. This electrical charge

equals the charge of a proton, but has the opposite sign. For this

reason, electrons are attracted by the protons of atomic nuclei and

usually form atoms. An electron has a mass of about 1/1836 times a

proton.[] One way to think about the location of electrons in an atom is

to imagine that they orbit at fixed distances from the nucleus. This

way, electrons in an atom exist in a number of electron shells

surrounding the central nucleus. Each electron shell is given a number

1, 2, 3, and so on, starting from the one closest to the nucleus (the

innermost shell). Each shell can hold up to a certain maximum number

of electrons. The distribution of electrons in the various shells is called

electronic arrangement (or electronic form or shape). Electronic

arrangement can be shown by numbering or an electron diagram. (A

different way to think about the location of electrons is to use quantum

mechanics to calculate their atomic orbitals.)

The electron is one of a class of subatomic particles called leptons. The electron has a negative electric charge. The

electron has another property, called spin. Its spin value is 1/2, which makes it a fermion.

While most electrons are found in atoms, others move independently in matter, or together as cathode rays in a

vacuum. In some superconductors, electrons move in pairs. When electrons flow, this flow is called electricity, or an

electric current.

An object can be described as ‘negatively charged’ if there are more electrons than protons in an object, or ‘positively

charged’ when there are more protons than electrons. Electrons can move from one object to another when touched.

They may be attracted to another object with opposite charge, or repelled when they both have the same charge.

When an object is ‘grounded’, electrons from the charged object go into the ground, making the object neutral. This is

what lightning conductors do.Electron 14

Chemical reactions

Electrons in their shells round an atom are the basis of chemical reactions. Complete outer shells, with maximum

electrons, are less reactive. Outer shells with less than maximum electrons are reactive. The number of electrons in

atoms is the underlying basis of the chemical periodic table.



Electric charge can be directly measured with a device called an electrometer. Electric current can be directly

measured with a galvanometer. The measurement given off by a galvanometer is different from the measurement

given off by an electrometer. Today laboratory instruments are capable of containing and observing individual


‘Seeing’ an electron

In laboratory conditions, the interactions of individual electrons can be observed by means of particle detectors,

which allow measurement of specific properties such as energy, spin and charge.[6] In one instance a Penning trap

was used to contain a single electron for 10 months.[] The magnetic moment of the electron was measured to a

precision of eleven digits, which, in 1980, was a greater accuracy than for any other physical constant.[7]

The first video images of an electron’s energy distribution were captured by a team at Lund University in Sweden,

February 2008. The scientists used extremely short flashes of light, called attosecond pulses, which allowed an

electron’s motion to be observed for the first time.[8][] The distribution of the electrons in solid materials can also be



The antiparticle of the electron is called a positron. This is identical to the electron, but carries electrical and other

charges of the opposite sign. When an electron collides with a positron, they may scatter off each other or be totally

annihilated, producing a pair (or more) of gamma ray photons.

History of its discovery

The effects of electrons were known long before it could be explained. The Ancient Greeks knew that rubbing amber

against fur attracted small objects. Now we know the rubbing strips off electrons, and that gives an electric charge to

the amber. Many physicists worked on the electron. J.J. Thomson proved it existed,[10] in 1897, but another man

gave it the name ‘electron’.[11]

Other pages

• Proton

• Neutron


[1] Purcell, Edward M. 1985. Electricity and Magnetism. Berkeley Physics Course Volume 2. McGraw-Hill. ISBN 0-07-004908-4.

[3] For instance, as beta particles, and in the inner electron shells of elements with a large atomic number. US Dept. of Energy: (http://www.

[4] Anastopoulos, Charis 2008. Particle or Wave: the evolution of the concept of matter in modern physics. Princeton University Press.

pp261–262. ISBN 0691135126.

[5] Pauling, Linus C. 1960. The nature of the chemical bond and the structure of molecules and crystals: an introduction to modern structural

chemistry (3rd ed). Cornell University Press. pp4–10. ISBN 0801403332.

[6] Grupen, Claus 1999. “Physics of Particle Detection”. AIP Conference Proceedings, Instrumentation in Elementary Particle Physics, VIII. 536.

Istanbul: Dordrecht, D. Reidel Publishing Company. pp. 3–34. doi:10.1063/1.1361756.

[10] Davis & Falconer, J.J. Thomson and the Discovery of the ElectronElectron 15

[11] Shipley, Joseph T. 1945. Dictionary of word origins. The Philosophical Library. p133.

Other websites

• “The Discovery of the Electron” ( American Institute of Physics, Center

for History of Physics.

• “Particle Data Group” ( University of California.

• Bock, R.K.; Vasilescu, A. (1998). The Particle Detector BriefBook (

ParticleDetector/BriefBook/) (14th ed.). Springer. ISBN 3-540-64120-3.

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – Tachyon

Elementary particle

Standard Model of elementary particles.

1 GeV/c


 = 1.783×10-27 kg. 1 MeV/c


 = 1.783×10-30 kg.

In physics, an elementary particle or

fundamental particle is a particle not made

up of smaller particles, and so, it can’t be

broken into anything smaller. Elementary

particles are either bosons (if they have a

characteristic called spin of -1, 0, or 1) or

fermions (if their “spin” is -½ or ½). The

Standard Model is the most accepted way to

explain how all particles behave, and the

forces that affect these particles.

Atoms are not elementary particles because

they are made of subatomic particles

(particles smaller than an atom) like protons

and neutrons. Protons and neutrons are not

elementary particles because they are made

up of even smaller particles called quarks

joined together by other particles called

gluons because they “glue” the quarks

together in the atom. Quarks are elementary

because quarks cannot be broken down any


PropertiesElementary particle 16

Every elementary particle has at least three important properties: “mass”, “charge”, and “spin”. Each property has a

number value. The properties are:

• Mass: A particle has mass if it takes energy to increase (accelerate) how fast it is moving. The table to the right

gives the mass of each elementary particle. Special relativity tells us that energy equals mass times a constant, the

square of the speed of light. If distance and time are measured so that light travels one unit of distance in one unit

of time, then mass equals energy. This is why the masses in the table to the right are given in units of energy over

the speed of light squared, MeV/c2 (that is pronounced megaelectronvolts over “c” squared). All particles with

mass produce gravity. (Strangely, particles without mass also produce gravity. See general relativity for more

information.) Though mass is not always conserved (neither increased nor decreased), mass plus energy is almost

always conserved because of the e=mc2 concept.

• Charge: An electron has charge -1. A proton has charge +1. A neutron has an average charge 0. Normal quarks

have charge of ⅔ or -⅓. If one particle has a negative charge, and another particle has a positive charge, the two

particles are attracted to each other. If the two particles both have negative charge, or both have positive charge,

the two particles are pushed apart. At short distances, this force is much stronger than the force of gravity which

pulls all particles together. Charge has always been conserved in all measured experiments.

• Spin: The angular momentum or constant turning of a particle has a particular value, called its spin number,

which is a natural number (positive whole number) times ½. Spin is always conserved in all reactions that do not

involve the weak force. Subatomic particles with “spin” are not spinning in the usual sense, but instead “spin” in

quantum physics is a more abstract concept invented by scientists to describe what is really going on with the


Mass and charge are properties we can see in everyday life, because gravity and electricity affect things that humans

can see and touch. But spin is affects only the very, very small world of subatomic particles. And so we do not see

their effect in our everyday life.


Fermions (named after the scientist,Enrico Fermi) have a spin number of -½ or ½, and are either quarks or leptons.

There are 12 different types of fermions (not including antimatter. Each type is called a “flavor.” The flavors are:

• Quarks: up, down, strange, charm, bottom, top. Quarks come in three pairs, called “generations.” One member of

each pair has a charge of ⅔. The other member has charge -⅓.

• Leptons: electron, muon, tau, electron neutrino, mu neutrino, tau neutrino. The neutrinos have charge 0, hence

the neutr- prefix. The other leptons have charge -1. Each neutrino is named after its corresponding original lepton:

the electron, muon, and tauon.

Six of the 12 fermions are thought to last forever: up and down quarks, the electron, and the three kinds of neutrinos

(which constantly switch flavor). The other fermions decay. That is, they break down into other particles a fraction

of a second after they are created. Fermi-Dirac statistics is a theory that describes how collections of fermions

behave. Essentially, you can’t have more than one fermion in the same place at the same time.Elementary particle 17


Bosons (named after the Indian physicist Satyendra Nath Bose (1894-1974)) have spin numbers that are integers

(e.g. -1, 0, 1). Although most bosons are made of more than one particle, there are two kinds of elementary bosons:

• Gauge bosons: gluons, W

+ and W- bosons, Z

0 bosons, and photons. These bosons carry 3 of the 4 fundamental

forces, and have a spin number of 1;

• Higgs boson: Physicists believe that massive particles have mass (that is, they are not pure bundles of energy like

photons) because of the Higgs interaction.

The photon and the gluons have no charge, and are the only elementary particles that have a mass of 0 for certain.

The photon is the only boson that does not decay. Bose-Einstein statistics is a theory that describes how collections

of bosons behave. Unlike fermions, it is possible to have more than one boson in the same space at the same time.

Standard Model

The Standard Model includes all of the elementary particles described above. All these particles except the Higgs

boson have been observed in the laboratory.

The Standard Model does not talk about gravity. If gravity works like the three other fundamental forces, then

gravity is carried by the hypothetical boson called the graviton. (The Higgs boson and graviton have yet to be found,

and are not included in the table above.)

The first fermion to be discovered, and the one we know the most about, is the electron. The first boson to be

discovered, and also the one we know the most about, is the photon. The theory that very accurately explains how

the electron, photon, electromagnetism, and electromagnetic radiation all work together is called quantum


Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – TachyonFermion 18


A fermion is one of the things that everything is made of. Fermions are really small and do not weigh much.

Fermions can be thought of as the building blocks of matter because atoms are made up of fermions.

An electron (a particle of electricity) is a fermion, but a photon (a particle of light) is not. Fermions are particles with

spin numbers that are 1/2, 3/2, 5/2, etc. (Spin is a made-up name that scientists use to describe a phenomenon that

they can not totally understand–it does not literally spin). Paul Dirac named them fermions in honor of a famous

scientist called Enrico Fermi.

Fermions are special because you cannot put two of them in the same place at the same time, if they have the same

quantum numbers, such as spin. Scientist have given the name Pauli exclusion principle to this behavior. Fermions

obey Fermi-Dirac statistics. This behavior is different to particles in the opposite class called bosons. An example of

a boson is a photon. Unlike fermions, you can have many bosons in the same place at the same time.

Most well known fermions have spin of 1/2. An example of a type of fermion with a spin of 1/2 is the electron. The

electron belongs to a group of fermions called Leptons.

Fundamental fermions (fermions that are not made up of anything else) are either quarks or leptons. There are 6

different types of quarks (called “flavours”) and 6 different types of leptons. These are their names:

• Quarks — up, down, charm, strange, top, bottom

• Leptons — electron, muon, tau, electron neutrino, muon neutrino, tau neutrino

Each of these fermions also has an anti-particle associated with it, so there are a total of 24 different fundamental

fermions. The anti-particle is similar to the original particle, but with opposite electrical charge. The “up”, “charm”,

and “top” quarks have electrical charge of +2/3. Their anti-particles have charge -2/3 (anti-up, anti-charm, anti-top).

The other three quarks (down, strange and bottom) have charge -1/3, and their anti-particles have charge +1/3. The

electron, muon, and tau leptons all have charge of -1, and their anti-particles (anti-electron or “positron”, anti-muon,

anti-tau) have charge +1. All the neutrinos and anti-neutrinos have charge 0. The main difference between quarks or

leptons with the same charge is in how much they weigh.

The supersymmetric counterpart of any fermion is called a “sfermion.”

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – TachyonGoogolplex 19


A googolplex is the number 10Googol(1010100). A googolplex can not be written down. This is because there are not

enough atoms in the universe to use to write it down on. In fact, it would take a trillion times more atoms to write

down a googolplex. It was thought of by the nephew of mathematician Edward Kasner.

Google named their headquarters, Googleplex, after the googolplex.

Also see

• Graham’s number


A hadron is a kind of composite particle that is affected by the strong interaction that is made of quarks held

together by strong force. There are two kinds of hadrons. One kind are baryons, which are made of three quarks. The

other kind are mesons, which are made of one quark and one anti-quark.

List of Hadrons

Known to Exist


• Proton

• Neutron


• Pion

• Kaon

Not yet Known to Exist

• Tetraquark

• Pentaquark

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – TachyonLepton 20


The six basic leptons: electrons, muons, tauons,

electron neutrinos, mu neutrinos, and tau

neutrinos, respectively

Leptons are elementary particles with spin 1/2 (a fermion) that are not

affected by strong nuclear force. They are a family of particles that are

different from the other known family of fermions, the quarks.

Electrons are a well-known example that are found in ordinary matter.

There are six leptons: the electron, muon, and tau particles and their

associated neutrinos. The different varieties of the elementary particles

are commonly called “flavors”, and the neutrinos here are considered to

have distinctly different flavor. Of the six leptons, three have electrical charge and three do not. The best known

charged lepton is the electron (e). The other two charged leptons are the muon (µ) and the tau (τ), which are like

electrons but much bigger. The charged leptons are all negative.

The superparticle of a lepton is called a “slepton.”

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – TachyonNeutron 21


A picture of a neutron. The ‘u’ stands for an up quark,

and the ‘d’ stands for a down quark.

Neutrons, with protons and electrons, make up an atom. Neutrons

and protons are found in the nucleus of an atom.[][][] Unlike

protons, which have a positive charge, or electrons, which have a

negative charge, neutrons have zero charge.[][1] Neutrons bind

with protons with the residual strong force.

Neutrons were predicted by Ernest Rutherford,

[2] and discovered

by James Chadwick,

[][3] in 1932.[] Atoms were fired at a thin pane

of beryllium. Particles emerged which had no charge, and he

called these ‘neutrons’.

Neutrons have a mass of 1.675 × 10-24


[] which is a little heavier

than the proton.[] Neutrons are 1839 times heavier than electrons.[]

Like all hadrons, neutrons are made of quarks. A neutron is made

of two down quarks and one up quark.

[][] One up quark has a

charge of +2/3, and the two down quarks each have a charge of

-1/3. The fact that these charges cancel out is why neutrons have a

neutral (0) charge. Quarks are held together by gluons.


Neutrons can be found in almost all atoms alongside protons and electrons, hydrogen-1 being the single common

exception. The number of them in the atom does not change the element, unlike protons. However, it does change

some characteristics of the element or ore. The number of them in an atom determines what isotope this compound


Atomic reactions

Neutrons are the key to nuclear chain reactions, nuclear power and nuclear weapons.



Other pages

• Proton

• ElectronNeutron 22

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – Tachyon

Nucleus (physics)

The nucleus is the middle part of an atom. It is made of protons and neutrons, and is surrounded by the electron

cloud. The nucleus has most of the mass of an atom, though it is only a very small part of it.

Neutrons have no charge and protons are all positively charged. Because the nucleus is only made up of protons and

neutrons it is positively charged. Things that have the same charge repel each other. Unless there was something else

holding the nucleus together it could not exist because the protons would push away from each other. The nucleus is

actually held together by a force called the strong nuclear force.

The strong nuclear force is a force that can only act over extremely short ranges.


A picture of a proton. The ‘u’ stands for an up quark,

and the ‘d’ stands for a down quark.

A proton is part of an atom.

[] They are found in the nucleus of an

atom along with neutrons.

[] The periodic table groups atoms

according to how many protons they have. A single atom of

hydrogen (the lightest kind of atom) is made up of an electron

moving around a proton. Most of the mass of this atom is in the

proton, which is almost 2000 times heavier than the electron.

Protons and neutrons make up the nucleus of every other kind of

atom. In any one element, the number of protons is always the

same. An atom’s atomic number is equal to the number of protons

in that atom.

Protons are made of quarks.

[] A proton is believed to be made up

of 3 quarks, two up quarks and one down quark.

[] One down quark

has a charge of -1/3, and two up quarks have a charge of +2/3

each. This adds to a charge of +1. A proton has a very small mass.

The mass of the proton is about one atomic mass unit. The mass of

the neutron is also about one atomic mass unit. The size of a proton is determined by the vibration of the quarks that

are in it, and these quarks effectively form a cloud. This means that a proton is not so much a hard ball as an area that

contains quarks.Proton 23


Other pages

• Proton decay

• Neutron

• Electron

• Quarks

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – Tachyon


Six of the particles in the Standard Model are quarks (shown in purple). Each of

the first three columns forms a generation of matter.

A quark is a tiny particle which makes up

protons and neutrons. Atoms are made of

neutrons, protons, and electrons. It was once

thought that neutrons, protons and electrons

were fundamental particles. Fundamental

particles can not be broken up into anything

smaller. After the invention of the particle

accelerator, it was discovered that electrons

are fundamental particles, but neutrons and

protons are not. Neutrons and protons are

made up of quarks, which are held together

by gluons.

There are six types of quarks. The types are

called flavours. The flavours are up, down,

strange, charm, top, and bottom. Up,

charm and top quarks have a charge of +2



while down, strange and bottom quarks have

a charge of -1


. Each quark has a matching

antiquark. Antiquarks have a charge

opposite to that of their quarks; meaning

that up, charm and top antiquarks have a charge of -2

3 and that down, strange and bottom antiquarks have a charge of




.Quark 24

A picture of a neutron. The ‘u’ stands for an up

quark, and the ‘d’ stands for a down quark. A

neutron is made of three quarks, and is a baryon

(baryons are a type of hadron). The colors used

do not matter; just which quarks are there.

Only up and down quarks are found inside atoms of the normal matter.

Two up quarks and one down make a proton (2

3 + 2

3 – 


3 = +1 charge)

while two down quarks and one up make a neutron (2

3 – 


3 – 


3 = 0

charge). The other four flavours are not seen naturally on Earth, but

they can be made in particle accelerators. Some of them may also exist

inside of stars.

When two or more quarks are held together by the strong nuclear force,

the particle formed is called a hadron. Quarks that make the quantum

number of hadrons are named ‘valence quarks’. The two families of

hadrons are baryons (made of three valence quarks) and mesons (which

are made from a quark and an antiquark).

When quarks are stretched farther and farther, the force that holds them

together becomes bigger. When it comes to the point when quarks are

separated, they form two sets of quarks.

The idea (or model) for quarks was proposed by physicists Murray

Gell-Mann and George Zweig in 1964. Other scientists began

searching for evidence of quarks, and succeeded in 1968.

The superparticle of a quark is called a “squark.”

Other websites

• Basic quark site [1]

Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – Tachyon


[1] 25


Physical cosmology

Universe · Big Bang

Age of the universe

Timeline of the Big Bang

Ultimate fate of the universe

Early universe

Inflation · Nucleosynthesis

GWB · Neutrino background

Cosmic microwave background

Expanding universe

Redshift · Hubble’s law

Metric expansion of


Friedmann equations

FLRW metric

Structure Formation

Shape of the universe

Structure formation


Galaxy formation

Large-scale structure

Galaxy filamentsUniverse 26


Lambda-CDM model

Dark energy · Dark matter


Timeline of

cosmological theories

Timeline of the Big


Future of an expanding





2dF · SDSS



WMAP · Planck


Isaac Newton ·

Einstein · Hawking ·

Friedman · Lemaître

· Hubble · Penzias ·

Wilson · Gamow ·

Dicke · Zel’dovich ·

Mather · Rubin ·


The universe is commonly defined as everything that exists.

[1] It includes all kinds of physical matter and energy,

the planets, stars, galaxies, and all the contents of space.


Astronomers can use telescopes to look at very distant galaxies. Like this they see what the universe looked like a

long time ago. This is because the light from distant parts of the universe takes a very long time to reach us. From

these observations, it seems the physical laws and constants of the universe have not changed.


Many people in history had ideas to explain the universe. Most early models had the Earth at the centre of the

Universe. Some ancient Greeks thought that the Universe has infinite space and has existed forever. They thought it

had a set of spheres which corresponded to the fixed stars, the Sun and various planets. The spheres circled about a

spherical but unmoving Earth.

Over the centuries, better observations and better ideas of gravity led to Copernicus’s Sun-centred model. This was

hugely controversial at the time, and was fought long and hard by authorities of the Christian church (see Giordano

Bruno and Galileo).

The invention of the telescope in the Netherlands, 1608, was a milestone in astronomy. By the mid-19th century they

were good enough for other galaxies to be distinguished. The modern optical (uses visible light) telescope is still

more advanced. Meanwhile, the Newtonian dynamics (equations) showed how the Solar System worked.Universe 27

The improvement of telescopes led astronomers to realise that the Solar System is in a galaxy made of millions of

stars, the Milky Way, and that other galaxies exist outside it, as far as we can see. Careful studies of the distribution

of these galaxies and their spectral lines have led to much of modern cosmology. Discovery of the red shift showed

that the Universe is expanding (see Hubble).

High-resolution image of the Hubble ultra deep field. It

shows a variety of galaxies, each made of billions of

stars. The equivalent area of sky that the picture

occupies is shown in the lower left corner. The

smallest, reddest galaxies, about 100, are some of the

most distant galaxies to have been photographed. They

formed shortly after the Big Bang.

Big bang

The most used scientific model of the Universe is known as the

Big Bang theory. The Universe expanded from a very hot, dense

phase called the Planck epoch, in which all the matter and energy

of the Universe was concentrated. Several independent

experimental measurements support the expansion of space and,

more generally, the Big Bang idea. Recent observations support

the idea that this expansion is happening because of dark energy.

Most of the matter in the Universe may be in a form which cannot

be detected by present methods. This has been named dark matter.

Just to be clear, dark matter and energy have not been detected

directly (that is why they are called ‘dark’). Their existence is

inferred by deduction from observations which would be difficult

to explain otherwise.

Current thinking in cosmology is that the age of the Universe is

13.73 (± 0.12) billion years,[4] and that the diameter of the

Universe is at least 93 billion light years, or 8.80 ×1026 metres.


According to general relativity, space can get bigger faster than the

speed of light, but we can view only part of the universe because of the speed of light. We cannot see space beyond

the limitations of light (or any electromagnetic radiation).

Etymology, synonyms and meaning

The word Universe comes from the Old French word Univers, which comes from the Latin word universum.

[5] The

Latin word was used by Cicero and later Latin authors in many of the same senses as the modern English word is


A different interpretation (way to interpret) of unvorsum is “everything rotated as one” or “everything rotated by

one”. This refers to an early Greek model of the Universe. In that model, all matter was in rotating spheres centered

on the Earth; according to Aristotle, the rotation of the outermost sphere was responsible for the motion and change

of everything within. It was natural for the Greeks to assume that the Earth was stationary and that the heavens

rotated about the Earth, because careful astronomical and physical measurements (such as the Foucault pendulum)

are required to prove otherwise.

The most common term for “Universe” among the ancient Greek philosophers from Pythagoras onwards was το παν

(The All), defined as all matter (το ολον) and all space (το κενον).[6]Universe 28

Broadest meaning

The broadest word meaning of the Universe is found in De divisione naturae by the medieval philosopher Johannes

Scotus Eriugena, who defined it as simply everything: everything that exists and everything that does not exist.

Time is not considered in Eriugena’s definition; thus, his definition includes everything that exists, has existed and

will exist, as well as everything that does not exist, has never existed and will never exist. This all-embracing

definition was not adopted by most later philosophers, but something similar is in quantum physics.


Definition as reality

See also: Reality and Physics

Usually the Universe is thought to be everything that exists, has existed, and will exist.[7] This definition says that

the Universe is made of two elements: space and time, together known as space-time or the vacuum; and matter and

different forms of energy and momentum occupying space-time. The two kinds of elements behave according to

physical laws, in which we describe how the elements interact.

A similar definition of the term Universe is everything that exists at a single moment of time, such as the present or

the beginning of time, as in the sentence “The Universe was of size 0”.

In Aristotle’s book The Physics, Aristotle divided το παν (everything) into three roughly analogous elements: matter

(the stuff of which the Universe is made), form (the arrangement of that matter in space) and change (how matter is

created, destroyed or altered in its properties, and similarly, how form is altered). Physical laws were the rules

governing the properties of matter, form and their changes. Later philosophers such as Lucretius, Averroes,

Avicenna and Baruch Spinoza altered or refined these divisions. For example, Averroes and Spinoza have active

principles governing the Universe which act on passive elements.

Space-time definitions

It is possible to form space-times, each existing but not able to touch, move, or change (interact with each other. An

easy way to think of this is a group of separate soap bubbles, in which people living on one soap bubble cannot

interact with those on other soap bubbles. According to one common terminology, each “soap bubble” of space-time

is denoted as a universe, whereas our particular space-time is denoted as the Universe, just as we call our moon the

Moon. The entire collection of these separate space-times is denoted as the multiverse.

[] In principle, the other

unconnected universes may have different dimensionalities and topologies of space-time, different forms of matter

and energy, and different physical laws and physical constants, although such possibilities are currently speculative.

Observable reality

According to a still-more-restrictive definition, the Universe is everything within our connected space-time that

could have a chance to interact with us and vice versa.

According to the general idea of relativity, some regions of space may never interact with ours even in the lifetime of

the Universe, due to the finite speed of light and the ongoing expansion of space. For example, radio messages sent

from Earth may never reach some regions of space, even if the Universe would exist forever; space may expand

faster than light can traverse it.

It is worth emphasizing that those distant regions of space are taken to exist and be part of reality as much as we are;

yet we can never interact with them, even in principle.[8] The spatial region within which we can affect and be

affected is denoted as the observable universe.

Strictly speaking, the observable universe depends on the location of the observer. By traveling, an observer can

come into contact with a greater region of space-time than an observer who remains still, so that the observable

universe for the former is larger than for the latter. Nevertheless, even the most rapid traveler may not be able to

interact with all of space. Typically, the observable universe is taken to mean the universe observable from ourUniverse 29

vantage point in the Milky Way Galaxy.

Basic data on the Universe

The Universe is huge and possibly infinite in volume. The matter which can be seen is spread over a space at least 93

billion light years across.

[9] For comparison, the diameter of a typical galaxy is only 30,000 light-years, and the

typical distance between two neighboring galaxies is only 3 million light-years.

[10] As an example, our Milky Way

Galaxy is roughly 100,000 light years in diameter,[11] and our nearest sister galaxy, the Andromeda Galaxy, is

located roughly 2.5 million light years away.[12] There are probably more than 100 billion (1011) galaxies in the

observable universe.[13] Typical galaxies range from dwarf galaxys with as few as ten million[14] (107

) stars up to

giants with one trillion[] (1012) stars, all orbiting the galaxy’s center of mass. Thus, a very rough estimate from these

numbers would suggest there are around one sextillion (1021) stars in the observable universe; though a 2003 study

by Australian National University astronomers resulted in a figure of 70 sextillion (7 x 1022).[15]

The universe is thought to be mostly made of dark energy and

dark matter, both of which are not understood right now. Less

than 5% of the universe is ordinary matter.

The matter that can be seen is spread throughout the

universe, when averaged over distances longer than 300

million light-years.[16] However, on smaller length-scales,

matter is observed to form ‘clumps’, many atoms are

condensed into stars, most stars into galaxies, most galaxies

into galaxy groups and clusters and, lastly, the largest-scale

structures such as the Great Wall of galaxies.

The present overall density of the Universe is very low,

roughly 9.9 × 10−30 grams per cubic centimetre. This

mass-energy appears to consist of 73% dark energy, 23%

cold dark matter and 4% ordinary matter. The density of

atoms is about a single hydrogen atom for every four cubic

meters of volume.[17] The properties of dark energy and

dark matter are not known. Dark matter slows the expansion

of the Universe. Dark energy makes its expansion faster.

The Universe is old, and changing. The best good guess of the Universe’s age is 13.73±0.12 billion years old, based

on what was seen of the cosmic microwave background radiation.

[] Independent estimates (based on measurements

such as radioactive dating) agree, although they are less precise, ranging from 11–20 billion years[18] to 13–15

billion years.[19]

The universe has not been the same at all times in its history. This getting bigger accounts for how Earth-bound

people can see the light from a galaxy 30 billion light years away, even if that light has traveled for only 13 billion

years; the very space between them has expanded. This expansion is consistent with the observation that the light

from distant galaxies has been redshifted; the photons emitted have been stretched to longer wavelengths and lower

frequency during their journey. The rate of this spatial expansion is accelerating, based on studies of Type Ia

supernovae and other data.

The relative amounts of different chemical elements — especially the lightest atoms such as hydrogen, deuterium

and helium — seem to be identical in all of the universe and throughout all of the history of it that we know of.[20]

The universe seems to have much more matter than antimatter.

[21] The Universe appears to have no net electric

charge, and therefore gravity appears to be the dominant interaction on cosmological length scales. The Universe

also appears to have neither net momentum nor angular momentum. The absence of net charge and momentum

would follow if the universe were finite.[22]Universe 30

The elementary particles from which the Universe is

constructed. Six leptons and six quarks comprise most of the

matter; for example, the protons and neutrons of atomic nuclei

are composed of quarks, and the ubiquitous electron is a lepton.

These particles interact via the gauge bosons shown in the

middle row, each corresponding to a particular type of gauge

symmetry. The Higgs boson (as yet unobserved) is believed to

confer mass on the particles with which it is connected. The

graviton, a supposed gauge boson for gravity, is not shown.

The Universe appears to have a smooth space-time

continuum made of three spatial dimensions and one

temporal (time) dimension. On the average, space is very

nearly flat (close to zero curvature), meaning that Euclidean

geometry is experimentally true with high accuracy

throughout most of the Universe.[23] However, the universe

may have more dimensions and its spacetime may have a

multiply connected global topology.[]

The Universe seems to be governed throughout by the same

physical laws and physical constants.

[24] According to the

prevailing Standard Model of physics, all matter is

composed of three generations of leptons and quarks, both

of which are fermions. These elementary particles interact

via at most three fundamental interactions: the electroweak

interaction which includes electromagnetism and the weak

nuclear force; the strong nuclear force described by

quantum chromodynamics; and gravity, which is best

described at present by general relativity.

The idea of special relativity is thought to hold in all of the universe, provided that the spatial and temporal length

scales are sufficiently short; otherwise, general relativity must be applied. There is no explanation for the particular

values that physical constants appear to have throughout our Universe, such as Planck’s constant h or the

gravitational constant G. Several conservation laws have been identified, such as the conservation of charge,

conservation of momentum, conservation of angular momentum and conservation of energy.

Theoretical models

General theory of relativity

Accurate predictions of the universe’s past and future require an accurate theory of gravitation. The best theory

available is Albert Einstein’s general theory of relativity, which has passed all experimental tests so far. However,

since rigorous experiments have not been carried out on cosmological length scales, general relativity could

conceivably be inaccurate. Nevertheless, its predictions appear to be consistent with observations, so there is no

reason to adopt another theory.

General relativity provides of a set of ten nonlinear partial differential equations for the spacetime metric (Einstein’s

field equations) that must be solved from the distribution of mass-energy and momentum throughout the universe.

Since these are unknown in exact detail, cosmological models have been based on the cosmological principle, which

states that the universe is homogeneous and isotropic. In effect, this principle asserts that the gravitational effects of

the various galaxies making up the universe are equivalent to those of a fine dust distributed uniformly throughout

the universe with the same average density. The assumption of a uniform dust makes it easy to solve Einstein’s field

equations and predict the past and future of the universe on cosmological time scales.

Einstein’s field equations include a cosmological constant (Lamda: Λ),[25][26] that is related to an energy density of 

empty space.[27] Depending on its sign, the cosmological constant can either slow (negative Λ) or accelerate (positive 

Λ) the expansion of the universe. Although many scientists, including Einstein, had speculated that Λ was zero,


recent astronomical observations of type Ia supernovae have detected a large amount of dark energy that is 

accelerating the universe’s expansion.[29] Preliminary studies suggest that this dark energy is related to a positive Λ,Universe 31

although alternative theories cannot be ruled out as yet.[30]

Solving Einstein’s field equations

See also: Big Bang

The distances between the spinning galaxies increase with time, but the distances between the stars within each

galaxy stay roughly the same, due to their gravitational interactions. This animation illustrates a closed Friedmann

universe with zero cosmological constant Λ; such a universe oscillates between a Big Bang and a Big Crunch.

Big Bang model

The prevailing Big Bang model accounts for many of the experimental observations described above, such as the

correlation of distance and redshift of galaxies, the universal ratio of hydrogen:helium atoms, and the ubiquitous,

isotropic microwave radiation background. As noted above, the redshift arises from the metric expansion of space; as

the space itself expands, the wavelength of a photon traveling through space likewise increases, decreasing its

energy. The longer a photon has been traveling, the more expansion it has undergone; hence, older photons from

more distant galaxies are the most red-shifted. Determining the correlation between distance and redshift is an

important problem in experimental physical cosmology.

Other experimental observations can be explained by combining the overall expansion of space with nuclear and

atomic physics. As the universe expands, the energy density of the electromagnetic radiation decreases more quickly

than does that of matter, since the energy of a photon decreases with its wavelength. Thus, although the energy

density of the universe is now dominated by matter, it was once dominated by radiation; poetically speaking, all was

light. As the universe expanded, its energy density decreased and it became cooler; as it did so, the elementary

particles of matter could associate stably into ever larger combinations. Thus, in the early part of the

matter-dominated era, stable protons and neutrons formed, which then associated into atomic nuclei. At this stage,

the matter in the universe was mainly a hot, dense plasma of negative electrons, neutral neutrinos and positive nuclei.

Nuclear reactions among the nuclei led to the present abundances of the lighter nuclei, particularly hydrogen,

deuterium, and helium. Eventually, the electrons and nuclei combined to form stable atoms, which are transparent to

most wavelengths of radiation; at this point, the radiation decoupled from the matter, forming the ubiquitous,

isotropic background of microwave radiation observed today.

Chief nuclear reactions responsible for the relative amounts of light

atomic nuclei observed in the universe.

Other observations are not clearly answered by known

physics. According to the prevailing theory, a slight

imbalance of matter over antimatter was present in the

universe’s creation, or developed very shortly

thereafter. Although the matter and antimatter mostly

annihilated one another, producing photons, a small

residue of matter survived, giving the present

matter-dominated universe.

Several lines of evidence also suggest that a rapid

cosmic inflation of the universe occurred very early in its history (roughly 10−35 seconds after its creation). Recent

observations also suggest that the cosmological constant (Λ) is not zero and that the net mass-energy content of the

universe is dominated by a dark energy and dark matter that have not been characterized scientifically. They differ in

their gravitational effects. Dark matter gravitates as ordinary matter does, and thus slows the expansion of the

universe; by contrast, dark energy serves to accelerate the universe’s expansion.Universe 32


Some people think that there is more than one Universe. They think that there is a set of universes called the

multiverse. By definition, there is no way for anything in one universe to affect something in another. The multiverse

is not yet a scientific idea because there is no way to test it. An idea that cannot be tested is not science.

Further reading

• Edward Robert Harrison 2000. Cosmology 2nd ed. Cambridge University Press.

• Misner C.W., Thorne K. Wheeler, J.A. (1973). Gravitation. San Francisco: W.H. Freeman. pp. 703–816.

ISBN 978-0-7167-0344-0. The classic text for a generation.

• Rindler W. (1977). Essential relativity: special, general, and cosmological. New York: Springer Verlag.

pp. 193–244. ISBN 0-387-10090-3.

• Weinberg S. (1993). The first three minutes: a modern view of the origin of the Universe (2nd updated ed.). New

York: Basic Books. ISBN 978-0465024377. OCLC 28746057 [31]. For lay readers.

• ——– 2008. Cosmology. Oxford University Press. Challenging.

Related pages

• Anthropic principle

• Big Bang

• Cosmology

• Multiverse

• Omniverse

• Reality


[5] The Compact Edition of the Oxford English Dictionary, volume II, Oxford: Oxford University Press, 1971, p.3518.

[6] Liddell and Scott, pp.1345–1346.

[8] Even with most of the visible universe, we cannot interact with it in practice. A relatively simple task, so it might seem, would be to

communicate within our own galaxy. Even if we knew how to send a message successfully, it would be about 200,000 years before a reply

could come back from the far end of the Milky Way, whose diameter is 100,000 light years. galaxy.

[10] Rindler (1977), p.196.

[22] Landau and Lifshitz 1975. p361

[23] WMAP Mission: Results – Age of the Universe (

[25] Einstein A. 1917. “Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie”. Preussische Akademie der Wissenschaften,

Sitzungsberichte 1917 (part 1): 142–152.

[26] Rindler (1977), pp. 226–229.

[27] Landau and Lifshitz (1975), pp. 358–359.

[29] Hubble Telescope news release (

[30] BBC News story: Evidence that dark energy is the cosmological constant (

[31] 33

Other websites

• Is there a hole in the universe? ( at HowStuffWorks

• Age of the Universe ( at Space.Com

• Stephen Hawking’s Universe ( – Why is the universe the

way it is?

• Cosmology FAQ (

• Cosmos – An “illustrated dimensional journey from microcosmos to macrocosmos” (


• Illustration comparing the sizes of the planets, the sun, and other stars (


• Logarithmic Maps of the Universe (

• My So-Called Universe ( – Arguments for and against an

infinite and parallel universes

• Parallel Universes ( by Max Tegmark

• The Dark Side and the Bright Side of the Universe ( Princeton

University, Shirley Ho

• Richard Powell: An Atlas of the Universe ( – Images at various scales,

with explanations

• Multiple Big Bangs (

• Universe – Space Information Centre (

• Exploring the Universe ( at

• The Size Of The Universe, understand the size of the universe by starting with humans and going up by powers of

ten (



• The Known Universe ( created by the American Museum

of Natural HistoryUp quark 34

Up quark

Two up quarks (u) and one down quark (d) form a proton

Up quarks are subatomic particles that help

make up many larger particles, like protons.

Up quarks have a charge of +2/3, and are the

lightest of the six types (flavours) of quarks.

Like all fermions (non force-carrying

particles), Up quarks have a spin of 1/2.

They are affected by all four of the

fundamental forces, which are gravity,

strong force, weak force, and

electromagnetism. Like all quarks, Up

quarks are elementary particles, which

means that they are so small that scientists

believe that they can not be divided any


Protons (which have a total charge of +1)

are made of two up quarks (which have a

charge of +2/3) and one down quark (which

have a charge of -1/3). Neutrons (which

have a total charge of 0) are made of one up

quark, and two down quarks. Up quarks can

also be used to create more complex particles, such as pions.


“Up quark” ( Wikipedia. 17 December 2010. Retrieved 17 December


Particles in Physics

Elementary: Fermions: Quarks: up – down – strange – charm – bottom –


Leptons: electron – muon – tau – neutrinos

Bosons: Gauge bosons: photon – W and Z bosons – gluons

Composite: Hadrons: Baryons: proton – neutron – hyperon

Mesons: pion – kaon – J/ψ

Atomic nuclei – Atoms – Molecules

Hypothetical: Higgs boson – Graviton – TachyonArticle Sources and Contributors 35

Article Sources and Contributors

Atom Source:  Contributors: 2602:306:CD8B:1E70:C19:2142:495E:845D, A7x, Allemandtando, American Eagle, Arjenvreugd,

Az1568, Barras, Blockinblox, Bluegoblin7, Chenzw, Claimgoal, Clementina, Coffsneeze, Cometstyles, DJDunsie, Darrien, Diego Grez, DrJimothyCatface, Dweller, EchoBravo, Eptalon,

Evanherk, Fairfield, FrancoGG, Freshstart, GblDave, Gordonrox24, Grain, Griffinofwales, Gwib, Huji, Imthebest, Intelati, Isis, Kansan, Kenvancleve, Leifanator, LilHelpa, Listlistlist, Majorly,

Mark91, Mat, Maya, Mentifisto, Mercy, Mh7kJ, Minor Contributer, Nifky?, Nishkid64, ONaNcle, Peddy, PhnomPencil, PiRSquared17, Piccolo, Pmlineditor, Pure Evil, Racepacket, Razorflame,

Ricky81682, Rockrocks434323, Rothorpe, RyanCross, Savh, Selket, Sesna2, Sonia, Suisui, Synergy, TBloemink, Tango, Tegel, Tenth Plague, The Flying Spaghetti Monster, The angel jean, The

life of brian, Tholly, Uvzz, Vector, Vogone, Voyajer, WFPM, Wannabe Wiki, Webkid, Wiooiw, Yoshiha40,, 171 anonymous edits

Atomic nucleus Source:  Contributors: American Eagle, Auntof6, Kumioko, Morgankevinj AWB, Peterdownunder, PiRSquared17,

Wannabe Wiki, 5 anonymous edits

Boson Source:  Contributors: Auntof6, Creol, DJDunsie, Illuminating Friend, JacobParker100, MeggyinRussia, Mh7kJ, Racepacket,

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Electric charge Source:  Contributors: Barras, Blockinblox, Creol, JDPhD, Osiris, Patrick0Moran, Ruslik0, Sertion, Sesna2, Soryusu,

Srleffler, Tbennert, The Flying Spaghetti Monster, Werieth, 13 anonymous edits

Electron Source:  Contributors: Aflm, Auntof6, Belinda, Chenzw, Clarkcj12, Clementina, Djsasso, Egmontaz, Juliancolton, Jusjih,

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Elementary particle Source:  Contributors: Auntof6, Benmccanna, Meriga, Osiris, Ruslik0, Sesna2, Simeon, Tygrrr, Werieth, WikiJon,

Yakiv Gluck, Zedshort, 12 anonymous edits

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Googolplex Source:  Contributors: Albacore, American Eagle, Art LaPella, Barras, Berek, Bob.v.R, EvillyG00d, Fairfield, Foxj,

Freshstart, Hazard-SJ, I wish you knew I was sorry, Liam.gloucester, Nataly8, NonvocalScream, Philosopher, PiRSquared17, Pmlineditor, Ruy Pugliesi, Sonia, The Flying Spaghetti Monster,

Tygrrr, 27 anonymous edits

Hadron Source:  Contributors: Auntof6, EhJJ, Griffinofwales, Mh7kJ, Nifky?, Ruslik0, RyanCross, Sesna2, Shustov, Synergy, 11

anonymous edits

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Sesna2, The Rambling Man, Tygrrr, 11 anonymous edits

Neutron Source:  Contributors: AnakngAraw, DJDunsie, Exert, Freshstart, Llb43, Macdonald-ross, Nifky?, Ora Stendar, PhnomPencil,

Pmlineditor, Ruslik0, Sesna2, Sir James Paul, Sosme88, The Flying Spaghetti Monster, WashingManwithwings, Zakkazzakkaz, 26 anonymous edits

Nucleus (physics) Source:  Contributors: Berek, Blockinblox, Gordonrox24, Isis, King of Hearts, Mh7kJ, Ora Stendar, Srleffler, Stauros,

Tygrrr, Wiooiw, 3 anonymous edits

Proton Source:  Contributors: -Midorihana-, Ajraddatz, AnakngAraw, Archer7, Blockinblox, Bluemask, Creol, DJDunsie, DaGizza,

Geeksluvpi, Geni, Isis, Lord Truth, O.Koslowski, Ruslik0, Savh, Sesna2, Synergy, 29 anonymous edits

Quark Source:  Contributors: 2012rc, Archer7, DJDunsie, Fairfield, Frankie1969, Freshstart, Gutworth, Liquid daisies, Maurice

Carbonaro, Mh7kJ, Neurolysis, Nifky?, PiRSquared17, Razorflame, Richard n, Ricky81682, Ruslik0, Schneb78, Sesna2, Tanthanyes, Tree Biting Conspiracy, Tygrrr, Werdan7, 26 anonymous


Universe Source:  Contributors: AnakngAraw, Angela, Anonymous Dissident, Archer7, Azcolvin429, Blockinblox, CRRaysHead90,

Chenzw, Chris Roy, Claus Ableiter, Creol, Cymru.lass, Diego Grez, Eptalon, Fairfield, Freshstart, Giggy, Griffinofwales, Grunny, Gwib, Isis, Jcaraballo, Jessicagirl, JetLover, Jonas D. Rand,

Jusjih, Lcawte, Macdonald-ross, Metalic, Mh7kJ, Niteowlneils, ONaNcle, Osiris, PhnomPencil, PiRSquared17, Ruslik0, ScienceApologist, Sikilai, Sir James Paul, Tango, Tholly, Werieth, Xilien,,, 67 anonymous edits

Up quark Source:  Contributors: DJDunsie, Morgankevinj AWB, Sesna2Image Sources, Licenses and Contributors 36

Image Sources, Licenses and Contributors

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