Standard Model

 From Wikipedia, the free encyclopedia
https://en.wikipedia.org/wiki/Standard_Model

The Standard Model of particle physics is the theory describing three of the four known fundamental forces (electromagnetic, weak and strong interactions) excluding gravity in the universe and classifying all known elementary particles. It was developed in stages throughout the latter half of the 20th century, through the work of many scientists worldwide, with the current formulation being finalized in the mid-1970s upon experimental confirmation of the existence of quarks. Since then, proof of the top quark (1995), the tau neutrino (2000), and the Higgs boson (2012) have added further credence to the Standard Model. In addition, the Standard Model has predicted various properties of weak neutral currents and the W and Z bosons with great accuracy.

Although the Standard Model is believed to be theoretically self-consistent and has demonstrated huge successes in providing experimental predictions, it leaves some phenomena unexplained. It falls short of being a complete theory of fundamental interactions. For example, it does not fully explain baryon asymmetry, incorporate the full theory of gravitation as described by general relativity, or account for the universe's accelerating expansion as possibly described by dark energy. The model does not contain any viable dark matter particle that possesses all of the required properties deduced from observational cosmology. It also does not incorporate neutrino oscillations and their non-zero masses.

The development of the Standard Model was driven by theoretical and experimental particle physicists alike. The Standard Model is a paradigm of a quantum field theory for theorists, exhibiting a wide range of phenomena, including spontaneous symmetry breaking, anomalies, and non-perturbative behavior. It is used as a basis for building more exotic models that incorporate hypothetical particles, extra dimensions, and elaborate symmetries (such as supersymmetry) to explain experimental results at variance with the Standard Model, such as the existence of dark matter and neutrino oscillations.

Historical background

See also: History of quantum field theory, History of subatomic physics, Julian Schwinger, and John Clive Ward

In 1954, Chen Ning Yang and Robert Mills extended the concept of gauge theory for abelian groups, e.g. quantum electrodynamics, to nonabelian groups to provide an explanation for strong interactions. In 1957, Chien-Shiung Wu demonstrated parity was not conserved in the weak interaction. In 1961, Sheldon Glashow combined the electromagnetic and weak interactions. In 1967 Steven Weinberg and Abdus Salam incorporated the Higgs mechanism into Glashow's electroweak interaction, giving it its modern form.

The Higgs mechanism is believed to give rise to the masses of all the elementary particles in the Standard Model. This includes the masses of the W and Z bosons, and the masses of the fermions, i.e. the quarks and leptons.

After the neutral weak currents caused by Z boson exchange were discovered at CERN in 1973, the electroweak theory became widely accepted and Glashow, Salam, and Weinberg shared the 1979 Nobel Prize in Physics for discovering it. The W^± and Z⁰ bosons were discovered experimentally in 1983; and the ratio of their masses was found to be as the Standard Model predicted.

The theory of the strong interaction (i.e. quantum chromodynamics, QCD), to which many contributed, acquired its modern form in 1973–74 when asymptotic freedom was proposed (a development which made QCD the main focus of theoretical research) and experiments confirmed that the hadrons were composed of fractionally charged quarks.

The term "Standard Model" was first coined by Abraham Pais and Sam Treiman in 1975, with reference to the electroweak theory with four quarks. According to Steven Weinberg, he came up with the term and used it in 1973 during a talk in Aix-en-Provence in France.

Particle content

The Standard Model includes members of several classes of elementary particles, which in turn can be distinguished by other characteristics, such as color charge.

All particles can be summarized as follows:

Elementary particles

Elementary fermionsHalf-integer spinObey the Fermi–Dirac statistics

Elementary bosonsInteger spinObey the Bose–Einstein statistics

Quarks and antiquarksSpin = 1/2Have color chargeParticipate in strong interactions

Leptons and antileptonsSpin = 1/2No color chargeElectroweak interactions

Gauge bosonsSpin = 1Force carriers

Scalar bosonsSpin = 0

Three generations Up (u), Down (d) Charm (c), Strange (s) Top (t), Bottom (b)

Three generations Electron ( e− ), [†] Electron neutrino ( ν e) Muon ( μ− ), Muon neutrino ( ν μ) Tau ( τ− ), Tau neutrino ( ν τ)

Four kinds Photon ( γ ; electromagnetic interaction) W and Z bosons ( W+ , W− , Z ; weak interaction) Eight types of gluons ( g ; strong interaction)

Unique Higgs boson ( H0 )

Notes:
[†] An anti-electron (
e⁺
) is conventionally called a “positron”.

Fermions

The Standard Model includes 12 elementary particles of spin 1⁄2, known as fermions. According to the spin–statistics theorem, fermions respect the Pauli exclusion principle. Each fermion has a corresponding antiparticle.

Fermions are classified according to how they interact (or equivalently, by what charges they carry). There are six quarks (up, down, charm, strange, top, bottom), and six leptons (electron, electron neutrino, muon, muon neutrino, tau, tau neutrino). Each class is divided into pairs of particles that exhibit a similar physical behavior called a generation (see the table).

The defining property of quarks is that they carry color charge, and hence interact via the strong interaction. The phenomenon of color confinement results in quarks being very strongly bound to one another, forming color-neutral composite particles called hadrons that contain either a quark and an antiquark (mesons) or three quarks (baryons). The lightest baryons are the proton and the neutron. Quarks also carry electric charge and weak isospin. Hence they interact with other fermions via electromagnetism and the weak interaction. The remaining six fermions do not carry color charge and are called leptons. The three neutrinos do not carry electric charge either, so their motion is directly influenced only by the weak nuclear force and gravity, which makes them notoriously difficult to detect. By contrast, by virtue of carrying an electric charge, the electron, muon, and tau all interact electromagnetically.

Each member of a generation has greater mass than the corresponding particle of any generation before it. The first-generation charged particles do not decay, hence all ordinary (baryonic) matter is made of such particles. Specifically, all atoms consist of electrons orbiting around atomic nuclei, ultimately constituted of up and down quarks. On the other hand, second- and third-generation charged particles decay with very short half-lives and are observed only in very high-energy environments. Neutrinos of all generations also do not decay, and pervade the universe, but rarely interact with baryonic matter.

Gauge bosons

Interactions in the Standard Model. All Feynman diagrams in the model are built from combinations of these vertices. q is any quark, g is a gluon, X is any charged particle, γ is a photon, f is any fermion, m is any particle with mass (with the possible exception of the neutrinos), m_B is any boson with mass. In diagrams with multiple particle labels separated by / one particle label is chosen. In diagrams with particle labels separated by | the labels must be chosen in the same order. For example, in the four boson electroweak case the valid diagrams are WWWW, WWZZ, WWγγ, WWZγ. The conjugate of each listed vertex (reversing the direction of arrows) is also allowed.

In the Standard Model, gauge bosons are defined as force carriers that mediate the strong, weak, and electromagnetic fundamental interactions.

Interactions in physics are the ways that particles influence other particles. At a macroscopic level, electromagnetism allows particles to interact with one another via electric and magnetic fields, and gravitation allows particles with mass to attract one another in accordance with Einstein's theory of general relativity. The Standard Model explains such forces as resulting from matter particles exchanging other particles, generally referred to as force mediating particles. When a force-mediating particle is exchanged, the effect at a macroscopic level is equivalent to a force influencing both of them, and the particle is therefore said to have mediated (i.e., been the agent of) that force. The Feynman diagram calculations, which are a graphical representation of the perturbation theory approximation, invoke "force mediating particles", and when applied to analyze high-energy scattering experiments are in reasonable agreement with the data. However, perturbation theory (and with it the concept of a "force-mediating particle") fails in other situations. These include low-energy quantum chromodynamics, bound states, and solitons.

The gauge bosons of the Standard Model all have spin (as do matter particles). The value of the spin is 1, making them bosons. As a result, they do not follow the Pauli exclusion principle that constrains fermions: thus bosons (e.g. photons) do not have a theoretical limit on their spatial density (number per volume). The types of gauge bosons are described below.

• Photons mediate the electromagnetic force between electrically charged particles. The photon is massless and is well-described by the theory of quantum electrodynamics.
• The
  W⁺
  ,
  W⁻
  , and
  Z
  gauge bosons mediate the weak interactions between particles of different flavours (all quarks and leptons). They are massive, with the
  Z
  being more massive than the
  W^±
  . The weak interactions involving the
  W^±
  act only on left-handed particles and right-handed antiparticles. The
  W^±
  carries an electric charge of +1 and −1 and couples to the electromagnetic interaction. The electrically neutral
  Z
  boson interacts with both left-handed particles and right-handed antiparticles. These three gauge bosons along with the photons are grouped together, as collectively mediating the electroweak interaction.
• The eight gluons mediate the strong interactions between color charged particles (the quarks). Gluons are massless. The eightfold multiplicity of gluons is labeled by a combination of color and anticolor charge (e.g. red–antigreen). Because gluons have an effective color charge, they can also interact among themselves. Gluons and their interactions are described by the theory of quantum chromodynamics.

The interactions between all the particles described by the Standard Model are summarized by the diagrams on the right of this section.

Higgs boson

Main article: Higgs boson

The Higgs particle is a massive scalar elementary particle theorized by Peter Higgs in 1964, when he showed that Goldstone's 1962 theorem (generic continuous symmetry, which is spontaneously broken) provides a third polarisation of a massive vector field. Hence, Goldstone's original scalar doublet, the massive spin-zero particle, was proposed as the Higgs boson, and is a key building block in the Standard Model. It has no intrinsic spin, and for that reason is classified as a boson (like the gauge bosons, which have integer spin).

The Higgs boson plays a unique role in the Standard Model, by explaining why the other elementary particles, except the photon and gluon, are massive. In particular, the Higgs boson explains why the photon has no mass, while the W and Z bosons are very heavy. Elementary-particle masses, and the differences between electromagnetism (mediated by the photon) and the weak force (mediated by the W and Z bosons), are critical to many aspects of the structure of microscopic (and hence macroscopic) matter. In electroweak theory, the Higgs boson generates the masses of the leptons (electron, muon, and tau) and quarks. As the Higgs boson is massive, it must interact with itself.

Because the Higgs boson is a very massive particle and also decays almost immediately when created, only a very high-energy particle accelerator can observe and record it. Experiments to confirm and determine the nature of the Higgs boson using the Large Hadron Collider (LHC) at CERN began in early 2010 and were performed at Fermilab's Tevatron until its closure in late 2011. Mathematical consistency of the Standard Model requires that any mechanism capable of generating the masses of elementary particles must become visible at energies above 1.4 TeV; therefore, the LHC (designed to collide two 7 TeV proton beams) was built to answer the question of whether the Higgs boson actually exists.

On 4 July 2012, two of the experiments at the LHC (ATLAS and CMS) both reported independently that they had found a new particle with a mass of about 125 GeV/c² (about 133 proton masses, on the order of 10×10⁻²⁵ kg), which is "consistent with the Higgs boson". On 13 March 2013, it was confirmed to be the searched-for Higgs boson.

Theoretical aspects

Main article: Mathematical formulation of the Standard Model

Construction of the Standard Model Lagrangian

Parameters of the Standard Model

Technically, quantum field theory provides the mathematical framework for the Standard Model, in which a Lagrangian controls the dynamics and kinematics of the theory. Each kind of particle is described in terms of a dynamical field that pervades space-time. The construction of the Standard Model proceeds following the modern method of constructing most field theories: by first postulating a set of symmetries of the system, and then by writing down the most general renormalizable Lagrangian from its particle (field) content that observes these symmetries.

The global Poincaré symmetry is postulated for all relativistic quantum field theories. It consists of the familiar translational symmetry, rotational symmetry and the inertial reference frame invariance central to the theory of special relativity. The local SU(3)×SU(2)×U(1) gauge symmetry is an internal symmetry that essentially defines the Standard Model. Roughly, the three factors of the gauge symmetry give rise to the three fundamental interactions. The fields fall into different representations of the various symmetry groups of the Standard Model (see table). Upon writing the most general Lagrangian, one finds that the dynamics depends on 19 parameters, whose numerical values are established by experiment. The parameters are summarized in the table (made visible by clicking "show") above.

Quantum chromodynamics sector

Main article: Quantum chromodynamics

The quantum chromodynamics (QCD) sector defines the interactions between quarks and gluons, which is a Yang–Mills gauge theory with SU(3) symmetry, generated by T^a. Since leptons do not interact with gluons, they are not affected by this sector. The Dirac Lagrangian of the quarks coupled to the gluon fields is given by

$${\displaystyle {\mathcal{L}}_{\text{QCD}}=\sum _{\psi }{\overline{\psi }}_i\left(i{\gamma }^{\mu }({\mathrm{\partial }}_{\mu }{\delta }_{ij}-i{g}_s{G}_{\mu }^a{T}_{ij}^a)\right){\psi }_j-\frac{1}{4}{G}_{\mu \nu }^a{G}_a^{\mu \nu },}$$

where

• ψ
  _i is the Dirac spinor of the quark field, where i = {r, g, b} represents color,
• γ^μ are the Dirac matrices,
• G^a
  _μ is the 8-component (${\displaystyle a=1,2,\dots ,8}$) SU(3) gauge field,
• T^a
  _ij are the 3 × 3 Gell-Mann matrices, generators of the SU(3) color group,
• G^a
  _μν represents the gluon field strength tensor,
• g_s is the strong coupling constant.

Electroweak sector

Main article: Electroweak interaction

The electroweak sector is a Yang–Mills gauge theory with the symmetry group U(1) × SU(2)_L,

$${\displaystyle {\mathcal{L}}_{\text{EW}}=\sum _{\psi }\overline{\psi }{\gamma }^{\mu }\left(i{\mathrm{\partial }}_{\mu }-g^{\prime }\frac{1}{2}{Y}_{\text{W}}{B}_{\mu }-g\frac{1}{2}{\overrightarrow{\tau }}_{\text{L}}{\overrightarrow{W}}_{\mu }\right)\psi -\frac{1}{4}{W}_a^{\mu \nu }{W}_{\mu \nu }^a-\frac{1}{4}{B}^{\mu \nu }{B}_{\mu \nu },}$$

where

• B_μ is the U(1) gauge field,
• Y_W is the weak hypercharge – the generator of the U(1) group,
• W→_μ is the 3-component SU(2) gauge field,
• τ_L→ are the Pauli matrices – infinitesimal generators of the SU(2) group – with subscript L to indicate that they only act on left-chiral fermions,
• g' and g are the U(1) and SU(2) coupling constants respectively,
• ${\displaystyle W^{a\mu \nu }}$ (${\displaystyle a=1,2,3}$) and ${\displaystyle B^{\mu \nu }}$ are the field strength tensors for the weak isospin and weak hypercharge fields.

Notice that the addition of fermion mass terms into the electroweak Lagrangian is forbidden, since terms of the form ${\displaystyle m\overline{\psi }\psi }$ do not respect U(1) × SU(2)_L gauge invariance. Neither is it possible to add explicit mass terms for the U(1) and SU(2) gauge fields. The Higgs mechanism is responsible for the generation of the gauge boson masses, and the fermion masses result from Yukawa-type interactions with the Higgs field.

Higgs sector

Main article: Higgs mechanism

In the Standard Model, the Higgs field is a complex scalar of the group SU(2)_L:

$${\displaystyle \phi =\frac{1}{\sqrt{2}}\left(\begin{array}{c}{\phi }^{+}\\ {\phi }^0\end{array}\right),}$$

where the superscripts + and 0 indicate the electric charge (Q) of the components. The weak hypercharge (Y_W) of both components is 1.

Before symmetry breaking, the Higgs Lagrangian is

$${\displaystyle {\mathcal{L}}_{\text{H}}={\phi }^{†}\left({\mathrm{\partial }}^{\mu }-\frac{i}{2}\left(g^{\prime }{Y}_{\text{W}}{B}^{\mu }+g\overrightarrow{\tau }{\overrightarrow{W}}^{\mu }\right)\right)\left({\mathrm{\partial }}_{\mu }+\frac{i}{2}\left(g^{\prime }{Y}_{\text{W}}{B}_{\mu }+g\overrightarrow{\tau }{\overrightarrow{W}}_{\mu }\right)\right)\phi -\frac{{\lambda }^2}{4}{\left({\phi }^{†}\phi -v^2\right)}^2,}$$

which up to a divergence term, (i.e., after partial integration) can also be written as

$${\displaystyle {\mathcal{L}}_{\text{H}}={\left|\left({\mathrm{\partial }}_{\mu }+\frac{i}{2}\left(g^{\prime }{Y}_{\text{W}}{B}_{\mu }+g\overrightarrow{\tau }{\overrightarrow{W}}_{\mu }\right)\right)\phi \right|}^2-\frac{{\lambda }^2}{4}{\left({\phi }^{†}\phi -v^2\right)}^2.}$$

The Higgs self-coupling strength λ is approximately 1⁄8. This is not included in the table above because it can be derived from the mass (after symmetry breaking) and the vacuum expectation value.

Yukawa sector

The Yukawa interaction terms are

$${\displaystyle {\mathcal{L}}_{\text{Yukawa}}={\overline{U}}_{\mathrm{L}}{G}_{\mathrm{u}}{U}_{\mathrm{R}}{\phi }^0-{\overline{D}}_{\mathrm{L}}{G}_{\mathrm{u}}{U}_{\mathrm{R}}{\phi }^{-}+{\overline{U}}_{\mathrm{L}}{G}_{\mathrm{d}}{D}_{\mathrm{R}}{\phi }^{+}+{\overline{D}}_{\mathrm{L}}{G}_{\mathrm{d}}{D}_{\mathrm{R}}{\phi }^0+\mathrm{h}.\mathrm{c}.,}$$

where G_u,d are 3 × 3 matrices of Yukawa couplings, with the ij term giving the coupling of the generations i and j, and h.c. means Hermitian conjugate of preceding terms.

Fundamental interactions

Main article: Fundamental interaction

The Standard Model describes three of the four fundamental interactions in nature; only gravity remains unexplained. In the Standard Model, such an interaction is described as an exchange of bosons between the objects affected, such as a photon for the electromagnetic force and a gluon for the strong interaction. Those particles are called force carriers or messenger particles.

The four fundamental interactions of nature

Property/Interaction	Gravitation	Electroweak		Strong
		Weak	Electromagnetic	Fundamental	Residual
Mediating particles	Not yet observed (Graviton hypothesised)	W+, W− and Z0	γ (photon)	Gluons	π, ρ and ω mesons
Affected particles	All particles	Left-handed fermions	Electrically charged	Quarks, gluons	Hadrons
Acts on	Stress energy tensor	Flavour	Electric charge	Color charge
Bound states formed	Planets, stars, galaxies, galaxy groups	—	Atoms, molecules	Hadrons	Atomic nuclei
Strength at the scale of quarks (relative to electromagnetism)	10−41 (predicted)	10−4	1	60	Not applicable to quarks
Strength at the scale of protons/neutrons (relative to electromagnetism)	10−36 (predicted)	10−7	1	Not applicable to hadrons	20

Gravity

See also: Quantum gravity and Gravity

Despite being perhaps the most familiar fundamental interaction, gravity is not described by the Standard Model, due to contradictions that arise when combining general relativity, the modern theory of gravity, and quantum mechanics. However, gravity is so weak at microscopic scales, that it is essentially unmeasurable. The graviton is postulated as the mediating particle.

Electromagnetism

See also: Electromagnetism and Quantum electrodynamics

Electromagnetism is the only long-range force in the Standard Model. It is mediated by photons and couples to electric charge. Electromagnetism is responsible for a wide range of phenomena including atomic electron shell structure, chemical bonds, electric circuits and electronics. Electromagnetic interactions in the Standard Model are described by quantum electrodynamics.

Weak nuclear force

See also: Weak interaction and Electroweak interaction

The weak interaction is responsible for various forms of particle decay, such as beta decay. It is weak and short-range, due to the fact that the weak mediating particles, W and Z bosons, have mass. W bosons have electric charge and mediate interactions that change the particle type (referred to as flavour) and charge. Interactions mediated by W bosons are charged current interactions. Z bosons are neutral and mediate neutral current interactions, which do not change particle flavour. Thus Z bosons are similar to the photon, aside from them being massive and interacting with the neutrino. The weak interaction is also the only interaction to violate parity and CP. Parity violation is maximal for charged current interactions, since the W boson interacts exclusively with left-handed fermions and right-handed antifermions.

In the Standard Model, the weak force is understood in terms of the electroweak theory, which states that the weak and electromagnetic interactions become united into a single electroweak interaction at high energies.

Strong nuclear force

See also: Strong interaction, Nuclear force, and Quantum chromodynamics

The strong nuclear force is responsible for hadronic and nuclear binding. It is mediated by gluons, which couple to color charge. Since gluons themselves have color charge, the strong force exhibits confinement and asymptotic freedom. Confinement means that only color-neutral particles can exist in isolation, therefore quarks can only exist in hadrons and never in isolation, at low energies. Asymptotic freedom means that the strong force becomes weaker, as the energy scale increases. The strong force overpowers the electrostatic repulsion of protons and quarks in nuclei and hadrons respectively, at their respective scales.

While quarks are bound in hadrons by the fundamental strong interaction, which is mediated by gluons, nucleons are bound by an emergent phenomenon termed the residual strong force or nuclear force. This interaction is mediated by mesons, such as the pion. The color charges inside the nucleon cancel out, meaning most of the gluon and quark fields cancel out outside of the nucleon. However, some residue is "leaked", which appears as the exchange of virtual mesons, that causes the attractive force between nucleons. The (fundamental) strong interaction is described by quantum chromodynamics, which is a component of the Standard Model.

Tests and predictions

The Standard Model predicted the existence of the W and Z bosons, gluon, top quark and charm quark, and predicted many of their properties before these particles were observed. The predictions were experimentally confirmed with good precision.

The Standard Model also predicted the existence of the Higgs boson, which was found in 2012 at the Large Hadron Collider, the final fundamental particle predicted by the Standard Model to be experimentally confirmed.

Challenges

See also: Physics beyond the Standard Model

 

Unsolved problem in physics:

• What gives rise to the Standard Model of particle physics?
• Why do particle masses and coupling constants have the values that we measure?
• Why are there three generations of particles?
• Why is there more matter than antimatter in the universe?
• Where does dark matter fit into the model? Does it even consist of one or more new particles?

Self-consistency of the Standard Model (currently formulated as a non-abelian gauge theory quantized through path-integrals) has not been mathematically proven. While regularized versions useful for approximate computations (for example lattice gauge theory) exist, it is not known whether they converge (in the sense of S-matrix elements) in the limit that the regulator is removed. A key question related to the consistency is the Yang–Mills existence and mass gap problem.

Experiments indicate that neutrinos have mass, which the classic Standard Model did not allow. To accommodate this finding, the classic Standard Model can be modified to include neutrino mass.

If one insists on using only Standard Model particles, this can be achieved by adding a non-renormalizable interaction of leptons with the Higgs boson. On a fundamental level, such an interaction emerges in the seesaw mechanism where heavy right-handed neutrinos are added to the theory. This is natural in the left-right symmetric extension of the Standard Model and in certain grand unified theories. As long as new physics appears below or around 10¹⁴ GeV, the neutrino masses can be of the right order of magnitude.

Theoretical and experimental research has attempted to extend the Standard Model into a unified field theory or a theory of everything, a complete theory explaining all physical phenomena including constants. Inadequacies of the Standard Model that motivate such research include:

• The model does not explain gravitation, although physical confirmation of a theoretical particle known as a graviton would account for it to a degree. Though it addresses strong and electroweak interactions, the Standard Model does not consistently explain the canonical theory of gravitation, general relativity, in terms of quantum field theory. The reason for this is, among other things, that quantum field theories of gravity generally break down before reaching the Planck scale. As a consequence, we have no reliable theory for the very early universe.
• Some physicists consider it to be ad hoc and inelegant, requiring 19 numerical constants whose values are unrelated and arbitrary. Although the Standard Model, as it now stands, can explain why neutrinos have masses, the specifics of neutrino mass are still unclear. It is believed that explaining neutrino mass will require an additional 7 or 8 constants, which are also arbitrary parameters.
• The Higgs mechanism gives rise to the hierarchy problem if some new physics (coupled to the Higgs) is present at high energy scales. In these cases, in order for the weak scale to be much smaller than the Planck scale, severe fine tuning of the parameters is required; there are, however, other scenarios that include quantum gravity in which such fine tuning can be avoided. There are also issues of quantum triviality, which suggests that it may not be possible to create a consistent quantum field theory involving elementary scalar particles.
• The model is inconsistent with the emerging Lambda-CDM model of cosmology. Contentions include the absence of an explanation in the Standard Model of particle physics for the observed amount of cold dark matter (CDM) and its contributions to dark energy, which are many orders of magnitude too large. It is also difficult to accommodate the observed predominance of matter over antimatter (matter/antimatter asymmetry). The isotropy and homogeneity of the visible universe over large distances seems to require a mechanism like cosmic inflation, which would also constitute an extension of the Standard Model.

Currently, no proposed theory of everything has been widely accepted or verified.

Geological engineering

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Geological_engineering 

 

Example of infrastructure engineering (tunnel) and natural hazard engineering (rockfall protection), two subdisciplines of geological engineering

Geological engineering is a discipline of engineering concerned with the application of geological science and engineering principles to fields, such as civil engineering, mining, environmental engineering, and forestry, among others. The work of geological engineers often directs or supports the work of other engineering disciplines such as assessing the suitability of locations for civil engineering, environmental engineering, mining operations, and oil and gas projects by conducting geological, geoenvironmental, geophysical, and geotechnical studies. They are involved with impact studies for facilities and operations that affect surface and subsurface environments. The engineering design input and other recommendations made by geological engineers on these projects will often have a large impact on construction and operations. Geological engineers plan, design, and implement geotechnical, geological, geophysical, hydrogeological, and environmental data acquisition. This ranges from manual ground-based methods to deep drilling, to geochemical sampling, to advanced geophysical techniques and satellite surveying. Geological engineers are also concerned with the analysis of past and future ground behaviour, mapping at all scales, and ground characterization programs for specific engineering requirements. These analyses lead geological engineers to make recommendations and prepare reports which could have major effects on the foundations of construction, mining, and civil engineering projects. Some examples of projects include rock excavation, building foundation consolidation, pressure grouting, hydraulic channel erosion control, slope and fill stabilization, landslide risk assessment, groundwater monitoring, and assessment and remediation of contamination. In addition, geological engineers are included on design teams that develop solutions to surface hazards, groundwater remediation, underground and surface excavation projects, and resource management. Like mining engineers, geological engineers also conduct resource exploration campaigns, mine evaluation and feasibility assessments, and contribute to the ongoing efficiency, sustainability, and safety of active mining projects 

History

While the term geological engineering was not coined until the 19th century, principles of geological engineering are demonstrated through millennia of human history.

Tunnel of Eupalinos aqueduct tunnel in Samos, Greece, which is a famous example of ancient tunnel and survey engineering.

Ancient engineering

One of the oldest examples of geological engineering principles is the Euphrates tunnel, which was constructed around 2180 B.C. – 2160 B.C... This, and other tunnels and qanats from around the same time were used by ancient civilizations such as Babylon and Persia for the purposes of irrigation. Another famous example where geological engineering principles were used in an ancient engineering project was the construction of the Eupalinos aqueduct tunnel in Ancient Greece. This was the first tunnel to be constructed inward from both ends using principles of geometry and trigonometry, marking a significant milestone for both civil engineering and geological engineering 

Geological engineering as a discipline

Overhead view after the Vajont dam catastrophe (1963), where a massive landslide filled the water reservoir and caused a devastating overtopping wave. This engineering failure was partly a result of poor consideration of the mountain's geological conditions.

Although projects that applied geological engineering principles in their design and construction have been around for thousands of years, these were included within the civil engineering discipline for most of this time. Courses in geological engineering have been offered since the early 1900’s; however, these remained specialized offerings until a large increase in demand arose in the mid-20th century. This demand was created by issues encountered from development of increasingly large and ambitious structures, human-generated waste, scarcity of mineral and energy resources, and anthropogenic climate change – all of which created the need for a more specialized field of engineering with professional engineers who were also experts in geological or Earth sciences.

Notable disasters that are attributed to the formal creation of the geological engineering discipline include dam failures in the United States and western Europe in the 1950’s and 1960’s. These most famously include the St Francis dam failure (1928), Malpasset dam failure (1959), and the Vajont dam failure (1963), where a lack of knowledge of geology resulted in almost 3,000 deaths between the latter two alone. The Malpasset dam failure is regarded as the largest civil engineering disaster of the 20th century in France and Vajont dam failure is still the deadliest landslide in European history.

Education

Post-secondary degrees in geological engineering are offered at various universities around the world but are concentrated primarily in North America. Geological engineers often obtain degrees that include courses in both geological or Earth sciences and engineering.  To practice as a professional geological engineer, a bachelor's degree in a related discipline from an accredited institution is required. For certain positions, a Master’s or Doctorate degree in a related engineering discipline may be required. After obtaining these degrees, an individual who wishes to practice as a professional geological engineer must go through the process of becoming licensed by a professional association or regulatory body in their jurisdiction.

Canadian institutions

In Canada, 8 universities are accredited by Engineer’s Canada to offer undergraduate degrees in geological engineering. Many of these universities also offer graduate degree programs in geological engineering. These include:

• Queen’s University (Department of Geological Sciences and Geological Engineering) (1975 – present),
• École Polytechnique (1965 – present),
• Université Laval (1965 – present),
• Université du Québec à Chicoutimi (1983 – present),
• University of British Columbia (1965 – present),
• University of New Brunswick (jointly administered by Department of Earth Sciences and Department of Civil Engineering) (1984 – present),
• University of Saskatchewan (1965 – present), and
• University of Waterloo (1986 – present).

American institutions

In the United States there are 13 geological engineering programs recognized by the Engineering Accreditation Commission (EAC) of the Accreditation Board for Engineering and Technology (ABET). These include:

• Colorado School of Mines (1936 – present),
• Michigan Technological University (1951 – present),
• Missouri University of Science and Technology (1973 – present),
• Montana Technological University (1972–present),
• South Dakota School of Mines and Technology (1950 – present),
• The University of Utah (1952 – present),
• University of Alaska-Fairbanks (1941 – present),
• University of Minnesota Twin Cities (1950 – present),
• University of Mississippi (1987 – present),
• University of Nevada, Reno (1958 – present),
• University of North Dakota (1984 – present),
• University of Texas at Austin (1998 – present), and
• University of Wisconsin – Madison (1993 – present).

Other institutions

Universities in other countries that hold accreditation to offer degree programs in geological engineering from the EAC by the ABET include:

• Escuela Superior Politécnica Del Litoral, Guayaquil, Ecuador (2018 – present),
• Istanbul Technical University, Istanbul, Turkey (2009 – present),
• Universidad Nacional de Ingeniería, Rímac, Peru (2017 – present), and
• Universidad Politécnica de Madrid, Madrid, Spain (2014 – present).

Specializations

In geological engineering there are multiple subdisciplines which analyze different aspects of Earth sciences and apply them to a variety of engineering projects. The subdisciplines listed below are commonly taught at the undergraduate level, and each has overlap with disciplines external to geological engineering. However, a geological engineer who specializes in one of these subdisciplines throughout their education may still be licensed to work in any of the other subdisciplines.

Mountain lake showing surface water. Geoenvironmental engineers (subdiscipline of geological engineering) work on managing drinking water supplies and remediation of contaminated surface water and groundwater.

Geoenvironmental and hydrogeological engineering

Geoenvironmental engineering is the subdiscipline of geological engineering that focuses on preventing or mitigating the environmental effects of anthropogenic contaminants within soil and water. It solves these issues via the development of processes and infrastructure for the supply of clean water, waste disposal, and control of pollution of all kinds. The work of geoenvironmental engineers largely deals with investigating the migration, interaction, and result of contaminants; remediating contaminated sites; and protecting uncontaminated sites. Typical work of a geoenvironmental engineer includes:

• The preparation, review, and update of environmental investigation reports,
• The design of projects such as water reclamation facilities or groundwater monitoring wells which lead to the protection of the environment,
• Conducting feasibility studies and economic analyses of environmental projects,
• Obtaining and revising permits, plans, and standard procedures,
• Providing technical expertise for environmental remediation projects which require legal actions,
• The analysis of groundwater data for the purpose of quality-control checks,
• The site investigation and monitoring of environmental remediation and sustainability projects to ensure compliance with environmental regulations, and
• Advising corporations and government agencies regarding procedures for cleaning up contaminated sites.

A tunnel under construction by conventional excavation methods with a pilot tunnel through tunnel face and a drill jumbo positioned near the face. Rock engineers and geotechnical engineers (subdisciplines of geological engineering) are involved with the design and construction of underground excavations.

Geotechnical and rock engineering

Geotechnical engineering is the subdiscipline of geological engineering that deals with safely excavating, stabilizing, and monitoring the rock and soil surrounding underground excavations and surface construction, as well as managing ground natural and induced settlement of buildings, stability of slopes and fills, and probable effects of landslides and earthquakes on human infrastructure. Geotechnical engineers focus their work primarily around geomechanical deformation properties of rocks and soils which are then applied to ongoing problems in fields such as rock mechanics, soil mechanics, and natural hazard mitigation and prevention. They work in designing and monitoring a variety of construction projects in urban and rural settings, including roads, railways, tunnels, dams, caverns, surface and underground mines, sewers, underground utilities, deep geological repositories for long-term nuclear waste storage, onshore infrastructure, and offshore infrastructure. In addition, geotechnical engineering also focusses on slope stability and risk assessment of projects which could be the subject of natural disasters such as earthquakes, floods, and landslides. Some geotechnical engineers also work in the restoration or expansion of historical infrastructure for uses in transportation and tourism.

An active open pit mine. Mineral and energy resource engineers (subdiscipline of geological engineering) are involved with mining from orebody discovery to mine design, production, and closure.

Mineral and energy resource exploration engineering

Mineral and energy resource exploration (commonly known as MinEx for short) is the subdiscipline of geological engineering that applies modern tools and concepts to the discovery and sustainable extraction of natural mineral and energy resources. A geological engineer who specializes in this field may work on several stages of mineral exploration and mining projects, including exploration and orebody delineation, mine production operations, mineral processing, and environmental impact and risk assessment programs for mine tailings and other mine waste. Like a mining engineer, mineral and energy resource exploration engineers may also be responsible for the design, finance, and management of mine sites.

A Ground Penetrating Radar (GPR) being used to conduct a geophysical survey. Geophysical engineers (subdiscipline of geological engineering) use multiple geophysical techniques to noninvasively investigate the Earth's subsurface at all scales and use the results in a variety of engineering projects.

Geophysical engineering (applied geophysics)

Geophysical engineering is the subdiscipline of geological engineering that applies geophysics principles to the design of engineering projects such as tunnels, dams, and mines or for the detection of subsurface geohazards, groundwater, and pollution. Geophysical investigations are undertaken from ground surface, in boreholes, or from space to analyze ground conditions, composition, and structure at all scales. Geophysical techniques apply a variety of physics principles such as seismicity, magnetism, gravity, and resistivity. This subdiscipline was created in the early 1990’s as a result of an increased demand in more accurate subsurface information created by a rapidly increasing global population. Geophysical engineering and applied geophysics differ from traditional geophysics primarily by their need for marginal returns and optimized designs and practices as opposed to satisfying regulatory requirements at a minimum cost 

Job responsibilities

Geological engineers are responsible for the planning, development, and coordination of site investigation and data acquisition programs for geological, geotechnical, geophysical, geoenvironmental, and hydrogeological studies. These studies are traditionally conducted for civil engineering, mining, petroleum, waste management, and regional development projects but are becoming increasingly focused on environmental and coastal engineering projects and on more specialized projects for long-term underground nuclear waste storage. Geological engineers are also responsible for analyzing and preparing recommendations and reports to improve construction of foundations for civil engineering projects such as rock and soil excavation, pressure grouting, and hydraulic channel erosion control. In addition, geological engineers analyze and prepare recommendations and reports on the settlement of buildings, stability of slopes and fills, and probable effects of landslides and earthquakes to support construction and civil engineering projects. They must design means to safely excavate and stabilize the surrounding rock or soil in underground excavations and surface construction, in addition to managing water flow from, and within these excavations.

Geological engineers also perform a primary role in all forms of underground infrastructure including tunnelling, mining, hydropower projects, shafts, deep repositories and caverns for power, storage, industrial activities, and recreation. Moreover, geological engineers design monitoring systems, analyze natural and induced ground response, and prepare recommendations and reports on the settlement of buildings, stability of slopes and fills, and the probable effects of natural disasters to support construction and civil engineering projects. In some jobs, geological engineers conduct theoretical and applied studies of groundwater flow and contamination to develop site specific solutions which treat the contaminants and allow for safe construction. Additionally, they design means to manage and protect surface and groundwater resources and remediation solutions in the event of contamination. If working on a mine site, geological engineers may be tasked with planning, development, coordination, and conducting theoretical and experimental studies in mining exploration, mine evaluation and feasibility studies relative to the mining industry. They conduct surveys and studies of ore deposits, ore reserve calculations, and contribute mineral resource expertise, geotechnical and geomechanical design and monitoring expertise and environmental management to a developing or ongoing mining operation. In a variety of projects, they may be expected to design and perform geophysical investigations from surface using boreholes or from space to analyze ground conditions, composition, and structure at all scales 

Professional associations and licensing

Professional Engineering Licenses may be issued through a municipal, provincial/state, or federal/national government organization, depending on the jurisdiction. The purpose of this licensing process is to ensure professional engineers possess the necessary technical knowledge, real-world experience, and basic understanding of the local legal system to practice engineering at a professional level. In Canada, the United States, Japan, South Korea, Bangladesh, and South Africa, the title of Professional Engineer is granted through licensure. In the United Kingdom, Ireland, India, and Zimbabwe the granted title is Chartered Engineer . In Australia, the granted title is Chartered Professional Engineer. Lastly, in the European Union, the granted title is European Engineer. All these titles have similar requirements for accreditation, including a recognized post-secondary degree and relevant work experience.

Canada

In Canada, Professional Engineer (P.Eng.) and Professional Geoscientist (P.Geo.) licenses are regulated by provincial professional bodies which have the groundwork for their legislation laid out by Engineers Canada and Geoscientists Canada. The provincial organizations are listed in the table below.

Regulatory body responsible for awarding licenses for professional engineering and geosciences in each province and territory of Canada

Province	Regulatory Body
Alberta	Association of Professional Engineers and Geoscientists of Alberta
British Columbia	Association of Engineers and Geoscientists of British Columbia
Manitoba	Engineers Geoscientists of Manitoba
New Brunswick	Association of Professional Engineers and Geoscientists of New Brunswick
Newfoundland and Labrador	Professional Engineers and Geoscientists of Newfoundland and Labrador
Northwest Territories	Northwest Territories and Nunavut Association of Professional Engineers and Geoscientists
Nova Scotia	Association of Professional Engineers of Nova Scotia
Nunavut	Northwest Territories and Nunavut Association of Professional Engineers and Geoscientists
Ontario	Professional Engineers Ontario
Prince Edward Island	Association of Professional Engineers of Prince Edward Island
Quebec	Ordre des ingénieurs du Québec
Saskatchewan	Association of Professional Engineers and Geoscientists of Saskatchewan
Yukon	Engineers of Yukon

United States

In the United States, all individuals seeking to become a Professional Engineer (P.E.) must attain their license through the Engineering Accreditation Commission (EAC) of the Accreditation Board for Engineering and Technology (ABET). Licenses to be a Certified Professional Geologist in the United States are issued and regulated by the American Institute of Professional Geologists (AIPG) 

Professional Societies

Professional societies in geological engineering are not-for-profit organizations that seek to advance and promote the represented profession(s) and connect professionals using networking, regular conferences, meetings, and other events, as well as provide platforms to publish technical literature through forms of conference proceedings, books, technical standards, and suggested methods, and provide opportunities for professional development such as short courses, workshops, and technical tours. Some regional, national, and international professional societies relevant to geological engineers are listed here:

• American Geophysical Union (AGU)
• American Geosciences Institute (AGI)
• American Rock Mechanics Association (ARMA)
• Association of Environmental and Engineering Geologists (AEG)
• Association for Mineral Exploration (AME)
• Atlantic Geoscience Society (AGS)
• Canadian Dam Association (CDA)
• Canadian Federation of Earth Sciences (CFES)
• Canadian Geophysical Union (CGU)
• Canadian Geotechnical Society (CGS)
• Canadian Institute of Mining, Metallurgy and Petroleum (CIM)
• Canadian Society of Petroleum Geologists (CSPG)
• Canadian Rock Mechanics Association (CARMA)
• European Association of Geoscientists & Engineers (EAGE)
• European Geosciences Union (EGU)
• Geological Association of Canada (GAC)
• Geological Society of America (GSA)
• Geoscience Information Society (GSIS)
• Institute of Materials, Minerals and Mining (IOM3)
• International Association for Engineering Geology and the Environment (IAEG)
• International Association of Hydrogeologists (IAH)
• International Council on Mining and Metals (ICMM)
• International Society for Rock Mechanics and Rock Engineering (ISRM)
• International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE)
• International Tunnelling Association (ITA)
• International Union of Geological Sciences (IUGS)
• Mineralogical Association of Canada (MAC)
• Mining Association of Canada (MAC)
• Prospectors and Developers Association of Canada (PDAC)
• Society for Mining, Metallurgy & Exploration (SME)
• Society of Exploration Geophysicists (SEG)
• Tunnelling Association of Canada (TAC)
• U.S. Geological Survey (USGS)
• U.S. National Mining Association (NMA)

Distinction from engineering geology

Engineering geologists and geological engineers are both interested in the study of the Earth, its shifting movement, and alterations, and the interactions of human society and infrastructure with, on, and in Earth materials. Both disciplines require licenses from professional bodies in most jurisdictions to conduct related work. The primary difference between geological engineers and engineering geologists is that geological engineers are licensed professional engineers (and sometimes also professional geoscientists/geologists) with a combined understanding of Earth sciences and engineering principles, while engineering geologists are geological scientists whose work focusses on applications to engineering projects, and they may be licensed professional geoscientists/geologists, but not professional engineers. The following subsections provide more details on the differing responsibilities between engineering geologists and geological engineers.

Engineering geology

Engineering geologists are applied geological scientists who assess problems that might arise before, during, and after an engineering project. They are trained to be aware of potential problems like:

• landslides,
• faults,
• unstable ground,
• groundwater challenges, and
• floodplains.

They use a variety of field and laboratory testing techniques to characterize ground materials that might affect the construction, the long-term safety, or environmental footprint of a project. Job responsibilities of an engineering geologist include:

• collecting samples and surveys,
• conducting lab tests on samples,
• assessing in situ soil or rock conditions at many scales,
• preparing reports based on testing and on-site observations for clients, and
• creating geological models, maps, and sections.

Geological Engineering

Geological engineers are engineers with extensive knowledge of geological or Earth sciences as well as engineering geology, engineering principles, and engineering design practices.  These professionals are qualified to perform the role of or interact with engineering geologists. Their primary focus, however, is the use of engineering geology data, as well as engineering skills to:

• Design advanced exploration programs, environmental management or remediation projects including:
  • Groundwater extraction and sustainability,
  • Natural hazard mitigation systems,
  • Energy resource exploration and extraction,
  • Mineral resource exploration and extraction, and
  • Environmental remediation.
• Design Infrastructure, including:
  • Surface works,
  • Foundations,
  • Tunnels,
  • Dams,
  • Caverns, and
  • Other construction that interfaces with the ground.
• Oversee components of mining including:
  • Advanced resource assessment and economics,
  • Mineral processing,
  • Mine planning, and
  • Geomechanical and geotechnical stability.

In all these activities, the geological model, geological history, and environment, as well as measured engineering properties of relevant Earth materials are critical to engineering design and decision making.