"Philosophy has not kept up with modern developments in science, particularly physics."
- Stephen Hawking, The Grand Design, pg 5
"The universe itself has no single history, nor even an independent existence."
- Stephen Hawking, The Grand Design, pg 6
Our everyday world-of-the-large confirms to our visual senses a reality that is not found present in the quantum world of subatomic orders and microscopic perplexities unseen, unknown and downright curious even to our adjusted scientific observations. We find ourselves in quantum worlds that violate everything that we sense and know in the world-of-the-large made up of a lifetime of experiences that tell us of our own version of reality. A reality that is naive and incompatible with the modern world of physics, and the quantum paradoxes that will confront our subjective form of model-dependent realism which we have attributed qualities of reality and truth to that cannot be supported at the particle level of quantum theory.
Model-dependent realism applies not only to scientific models but also to the conscious and subconscious mental models we create in order to interpret and understand our everyday world. There is no way to remove the observer in us from our perceptions of the world created either by our sensory processing and by the way we think and reason. Our models of realism are shaped by our interpretive structures, experiences and personal histories. It is the way that we perceive things. Some of us more acutely, more perceptively, more uniquely. In a sense, we see in 2D, our brain interprets in 3D, and we feel in 4D. But nevertheless, we build mental pictures, or models, of what we see, sense, and feel.
In the case of subatomic particles we cannot see them but our studies from science confirm to us that they exist. And that they exist unlike anything else we can compare them to in the macro worlds of our experiences. From these observations have come a wealth of information that gives to us the chemical world of the elements, their microscopic bonds of covalence, mutual attraction and non-attraction, nuclear forces, electron clouds and atomic charges. Continuing down to the sub-sub-atomic world-of-the-small we observe the even further perplexing minutia of quarks, leptons, neutrinos, muons, gluons, bosons as the very, very, tiny forces of the universe. Elements and forces that contain a duality of nature to them... a duality that can at once be observed and explained as a wave pattern or as an individual particle.
Starting with Isaac Newton's classical models of physics, then James Clerk Maxwell's theory of electro-magnetism (which also includes the properties of light as an electro-magnetic wave particle called a photon; hence EM particles travel at the speed of light), and finally with Albert Einstein's General Theory of Relativity (dealing with gravity, space-time, and light) we come to the field of study known as quantum physics. Which takes each of the above theories to the microscopic level:
From these discoveries science can study the quantum nature of the universe as it looks at the gravitational affects of solar systems upon their parts; the hot surfaces of stars and their massive nuclear interactions within; how time-and-space are bent and ripped apart within black holes; and even construct histories of the universe backwards to its formative event known as the early primodial universe condensed to less than the size of a pin prick; containing no time as we know it (considered at this stage as a spatial dimension because of intense gravitational warpage); undoing all the natural laws of today's quantum physics because of its immense deflation; and scientifically indescribable when telling of the universe's initial state of chaos before its intense and immediate inflationary birth by the term "singularity."
- Per Maxwell we study the behavior of atoms and molecules in interaction with one another;
- Per Newton the study of gravity at the subatomic level affecting subatomic bonds; and,
- Per Einstein the quantum effects of gravity brought to bear upon particles warping space-time and thus creating gravitational warpage and dimensionality. That is, space-time is not flat but is curved and distorted by the effects of mass and energy upon one another making both space and time are intertwined within one another.
From these discoveries science can study the quantum nature of the universe as it looks at the gravitational affects of solar systems upon their parts; the hot surfaces of stars and their massive nuclear interactions within; how time-and-space are bent and ripped apart within black holes; and even construct histories of the universe backwards to its formative event known as the early primodial universe condensed to less than the size of a pin prick; containing no time as we know it (considered at this stage as a spatial dimension because of intense gravitational warpage); undoing all the natural laws of today's quantum physics because of its immense deflation; and scientifically indescribable when telling of the universe's initial state of chaos before its intense and immediate inflationary birth by the term "singularity."
By mathematic formula, and through scientific observation, quantum physics has found that our universe can have any possible history. And that it can have all possible histories simultaneously (the concept of multi-verses). However, in Einstein's theory, time still had a linear point of origin and was different from space. But when quantum theory is added to Einstein's theory of relativity, in extreme cases like that of black holes, or as the beginning point of early primodial universes, dimensional warpage can occur to such a great extent that time behaves like another dimension of space. Consequently, there can only be three effective dimensions of space and none of time (as a quality different from space). Time did not exist. It was however all of one beginning and ending intermingling with space as space-time. It was neither linear, compressed or stretched. It had no existence except as a spatial dimension (just as space had no separate existence unbound from time). They each were all one surface without boundary (called the no-boundary condition).
For the Christian theologian or philosopher this has important bearings to the biblical understanding of ex nihilo creation, meaning that in the beginning God created the world. In a sense, from the standpoint of quantum physics, this is not true. The universe already existed as a singularity with no beginning. There was no nothing to be created by YHWH (Yahweh) and the great I AM. The early universe was already present in its eternity-less form of pure energy and light. In a form we describe as small but within itself could be described neither as small nor large because there was nothing to compare it too. Space did not exist. The concept of large did not exist. Just as time did not exist. It was ageless. Pure. Filled with potentiality. Raw. And unformed like the metaphysical concepts we struggle to apply to describe this state of cosmic history.
But in another sense, the traditional Christian understanding of Genesis says that creation was formed from nothing. And in its formation it had a beginning. Perhaps this could be modified to mean that God sparked the universe from its state as a singularity into that of an inflationary universe. But in the classic sense of God being God, the traditional preference still posits that the universe could not exist even as a singularity without the hand of God giving to it its formless form and potential purpose. Who then sparked its creation as an energetic light event (from darkness, light!) and gave to it its cataclysmic birth. If not, we then confuse God and the universe as one essence and being (a form of pantheism). Or may speak of God and the universe as co-dependent upon one another, and mutually enabling each other's constructive being and essence (panentheism; held by process theology). However, the classic theistic standpoint still holds that God and His creation are separate from one another, and more importantly, that the one is born of God and not the other way around (thus, classic theism's postmodern equivalent is known as relational theism and is a synthetic blended position between classic theism and process theology).
Hence, God created the universe as a singularity, fashioning it into its many multiple versions of itself by creating from it an infinite series of multiverses bubbling into instant cosmic universes chaotically inflating and deflating with a rapidity too quick even for the human eye to behold in a blinding array-event of light and energy. Fashioning the universe we have today with just enough irregularity to give to us the necessary building blocks for life and necessary matter. This also will allow for the idea of indeterminacy which Einstein had noted when thinking of the quantum fluctuations of the universe and remarked that it was as if God were playing dice. In the Christian understanding of creation (and evolution) we call this idea the freedom (or, free will) that we observe within nature. Of its randomness, its indeterminate structure, its chaotic form of structure and development/sustenance of life systems. Even at the quantum level it can be shown that a single particle has no preference for its path, but takes every possible path simultaneously, giving to it different possible states of travel. We might pin down its location by our act of observing it, but in-between our observations, it takes all possible paths (according to Richard Feynman's Sum of Histories).
Consequently, we can describe the collapse of quantum space as that of a state of singular infinities. Where the universe doesn't just have one single history, but every possible history, each with its own probabilities and potentialities. And that our observations of its current state affects its past and determines the different histories of the universe, just as our observation of particles can affect their history and outcome. (However, in quantum reality this is not so... we are simply seeing one version of the many infinite versions of the universe's simultaneous forms). In the Newtonian sense, the past was assumed to exist as a definite series of events. In the quantum sense this is no longer true. It is affected and affecting. Almost circular because every probability had been explored. But more importantly, it describes to us the indeterminacy of nature, which is an important concept to think about when thinking of sin and this world's lament under the reign of sin. God gave to His creation the beauty of indeterminacy to offset the effects of sin's destruction upon creation (and humanity by extension). Without indeterminacy sin would have devolved God's majestic creative order without hope or help. But with it, God has wisely out-maneuvered the sustaining effects of sin upon His creation and creative purpose. (Curiously, some of the more subtle poems by men who have observed this same effect we simply thought fools for saying as such to our hastily pronounced errors... we can even find these same similar poetic observations in the Psalms and Proverbs.)
In the next article on quantum physics we will explore a little further the aspects of particle indeterminacy, probabilities and histories. If only to show the infinite largeness and wisdom of God as our Creator and Redeemer. Though creation is indeterminate and uncertain the Christian believer still understands that God is its mover and shaker. Without His will, determination, and divine action, even quantum's indeterminacy and uncertainty would boil away for naught, never giving to any multiverse its exquisite divine character of singularity and uniqueness. This then is the Christian understanding of creation.
R.E. Slater
May 30, 2012
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Other related articles that I've written may be found here:
QUANTUM PHYSICS, INDETERMINACY & MULTIVERSES
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Addendum: How It All Works
...In the quantum world of physics we have at-the-last but two interactions - one composed of matter particles and antiparticles (generally described as fermions), and the other composed of force particles (generally described as bosons, gluons and photons) - which interaction may either be absorbed or recoiled from in a series of quantum collisions that changes the motion and constitution of the particle itself. Thus, quantum electrodynamics (QED) says that all interactions between charged particles and antiparticles (fermions) can be described as an exchange of force particles which then forms the basis for quantum (force) field theory. From this postulation quantum physics then looks at how force particles can interact with each other starting with the weak nuclear forces ( of bosons W and Z), the strong nuclear forces of gluons (g), and than that of gravitational force particles (not pictured in the Standard Model below). The last force particle is the photon (or light) particle which is an included as an electrodynamic force particle.
When combined we get the following formulas:
Electromagnetism (EM) + Light/Photons = QED, Quantum Electrodynamics
QED + Weak Nuclear Forces (WNF) = EWF, Electroweak Nuclear Forces
The Strong Nuclear Force of quarks, or Quantum Electro-Chromodynamics = QCD (chromo for the colored/colorless pairs and triads of quarks and antiquarks, known as mesons and baryons)
QED + WNF + QCD = GUT, the Grand Unification Theory (quantum physics holy grail)
G - gravitational forces are the weakest of the four forces but is long-range and has the greatest effective range of all the forces. And because it is accumulative as an attractive force it means that it can add up and dominate all the other forces. We see this strength in the destructive force of black holes which rips apart all the quantum bonds of atoms and molecules as it draws in stars and cosmic matter into its event horizon and condenses them into infinitesimal singularities. The standard model cannot unify the first three forces (EM, WNF, SNF) with gravity. Hence, they are treated separately from gravity. In fact, gravity is not even included in the Standard Model's table of interactions.
QED + WNF + QCD + G = TOE, the Theory of Everything (later replaced by M-Theory's supersymmetries and other quantum postulations)
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| The Standard Model showing three generations of matter particles (fermions) and force-carrying particles. |
Study of the Four Quantum Forces
from Wikipedia.com
1 - The Electromagnetic Force (QED)
Electromagnetism is the branch of science concerned with the forces that occur between electrically charged particles. In electromagnetic theory these forces are explained using electromagnetic fields. Electromagnetic force is one of the four fundamental interactions in nature, the other three being the strong interaction, the weak interaction and gravitation.
Electromagnetism is the interaction responsible for practically all the phenomena encountered in daily life, with the exception of gravity. Ordinary matter takes its form as a result of intermolecular forces between individual molecules in matter. Electrons are bound by electromagnetic wave mechanics into orbitals around atomic nuclei to form atoms, which are the building blocks of molecules. This governs the processes involved in chemistry, which arise from interactions between the electrons of neighboring atoms, which are in turn determined by the interaction between electromagnetic force and the momentum of the electrons.
Electromagnetism manifests as both electric fields and magnetic fields. Both fields are simply different aspects of electromagnetism, and hence are intrinsically related. Thus, a changing electric field generates a magnetic field; conversely a changing magnetic field generates an electric field. This effect is called electromagnetic induction, and is the basis of operation for electrical generators, induction motors, and transformers. Mathematically speaking, magnetic fields and electric fields are convertible with relative motion as a 2nd-order tensor or bivector.
Electric fields are the cause of several common phenomena, such as electric potential (such as the voltage of a battery) and electric current (such as the flow of electricity through a flashlight). Magnetic fields are the cause of the force associated with magnets.
In quantum electrodynamics, electromagnetic interactions between charged particles can be calculated using the method of Feynman diagrams, in which we picture messenger particles called virtual photons being exchanged between charged particles. This method can be derived from the field picture through perturbation theory.
The theoretical implications of electromagnetism led to the development of special relativity by Albert Einstein in 1905.
The Photon (Light)
The Photon is an electromagnetic force particle. In physics, a photon is an elementary particle, the quantum of light and all other forms of electromagnetic radiation, and the force carrier for the electromagnetic force. The effects of this force are easily observable at both the microscopic and macroscopic level, because the photon has no rest mass; this allows for interactions at long distances. Like all elementary particles, photons are currently best explained by quantum mechanics and exhibit wave–particle duality, exhibiting properties of both waves and particles. For example, a single photon may be refracted by a lens or exhibit wave interference with itself, but also act as a particle giving a definite result when its position is measured.
The modern concept of the photon was developed gradually by Albert Einstein to explain experimental observations that did not fit the classical wave model of light. In particular, the photon model accounted for the frequency dependence of light's energy, and explained the ability of matter and radiation to be in thermal equilibrium. It also accounted for anomalous observations, including the properties of black body radiation, that other physicists, most notably Max Planck, had sought to explain using semiclassical models, in which light is still described by Maxwell's equations, but the material objects that emit and absorb light, do so in amounts of energy that are quantized (i.e., they change energy only by certain particular discrete amounts and cannot change energy in any arbitrary way). Although these semiclassical models contributed to the development of quantum mechanics, many further experiments[2][3] starting with Compton scattering of single photons by electrons, first observed in 1923, validated Einstein's hypothesis that light itself is quantized. In 1926 the chemist Gilbert N. Lewis coined the name photon for these particles, and after 1927, when Arthur H. Compton won the Nobel Prize for his scattering studies, most scientists accepted the validity that quanta of light have an independent existence, and Lewis' term photon for light quanta was accepted.
In the Standard Model of particle physics, photons are described as a necessary consequence of physical laws having a certain symmetry at every point in spacetime. The intrinsic properties of photons, such as charge, mass and spin, are determined by the properties of this gauge symmetry. The photon concept has led to momentous advances in experimental and theoretical physics, such as lasers, Bose–Einstein condensation, quantum field theory, and the probabilistic interpretation of quantum mechanics. It has been applied to photochemistry, high-resolution microscopy, and measurements of molecular distances. Recently, photons have been studied as elements of quantum computers and for sophisticated applications in optical communication such as quantum cryptography.
2 - The Weak Nuclear Force (WNF)
Weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental forces of nature, alongside the strong nuclear force, electromagnetism, and gravity. It is responsible for the radioactive decay of subatomic particles and initiates the process known as hydrogen fusion in stars. Weak interactions affect all known fermions; that is, particles whose spin (a property of all particles) is a half-integer.
In the Standard Model of particle physics the weak interaction is theorised as being caused by the exchange (i.e., emission or absorption) of W and Z bosons; as such, it is considered to be a non-contact force. The best known effect of this emission is beta decay, a form of radioactivity. The Z and W bosons are much heavier than protons or neutrons and it is the heaviness that accounts for the very short range of the weak interaction. It is termed weak because its typical field strength is several orders of magnitude less than that of both electromagnetism and the strong nuclear force. Most particles will decay by a weak interaction over time. It has one unique property – namely quark flavour changing – that does not occur in any other interaction. In addition, it also breaks parity-symmetry and CP-symmetry. Quark flavour changing allows for quarks to swap their 'flavour', one of six, for another.
The weak force was originally described, in the 1930s, by Fermi's theory of a contact four-fermion interaction: which is to say, a force with no range (i.e., entirely dependent on physical contact[1]). However, it is now best described as a field, having range, albeit a very short range. In 1968, the electromagnetic force and the weak interaction were unified, when they were shown to be two aspects of a single force, now termed the electro-weak force. The theory of the weak interaction can be called Quantum Flavordynamics (QFD), in analogy with the terms QCD and QED, but in practice the term is rarely used because the weak force is best understood in terms of electro-weak theory (EWT).[2]
Weak interactions are most noticeable when particles undergo beta decay, and in the production of deuterium and then helium from hydrogen that powers the sun's thermonuclear process. Such decay also makes radiocarbon dating possible, as carbon-14 decays through the weak interaction to nitrogen-14. It can also create radioluminescence, commonly used in tritium illumination, and in the related field of betavoltaics.[3]
3 - The Strong Nuclear Force (QCD)
In particle physics, the strong interaction (also called the strong force, strong nuclear force, or color force) is one of the four fundamental interactions of nature, the others being electromagnetism, the weak interaction and gravitation. At atomic scale, it is about 100 times stronger than electromagnetism, which in turn is orders of magnitude stronger than the weak force interaction and gravitation.
The strong interaction is observable in two areas: on a larger scale (about 1 to 3 femtometers (fm)), it is the force that binds protons and neutrons (nucleons) together to form the nucleus of an atom. On the smaller scale (less than about 0.8 fm, the radius of a nucleon), it is also the force (carried by gluons) that holds quarks together to form protons, neutrons and other hadron particles.
In the context of binding protons and neutrons together to form atoms, the strong interaction is called the nuclear force (or residual strong force). In this case, it is the residuum of the strong interaction between the quarks that make up the protons and neutrons. As such, the residual strong interaction obeys a quite different distance-dependent behavior between nucleons, from when it is acting to bind quarks within nucleons.
The strong interaction is thought to be mediated by gluons, acting upon quarks, antiquarks, and other gluons. Gluons, in turn, are thought to interact with quarks and gluons because all carry a type of charge called "color charge." Color charge is analogous to electromagnetic charge, but it comes in three types rather than one, and it results in a different type of force, with different rules of behavior. These rules are detailed in the theory of quantum chromodynamics (QCD), which is the theory of quark-gluon interactions.
4 - The Gravitational Force (G)
Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their masses. Gravitation is most familiar as the agent that gives weight to objects with mass and causes them to fall to the ground when dropped. Gravitation causes dispersed matter to coalesce, and coalesced matter to remain intact, thus accounting for the existence of the Earth, the Sun, and most of the macroscopic objects in the universe.
Gravitation is responsible for keeping the Earth and the other planets in their orbits around the Sun; for keeping the Moon in its orbit around the Earth; for the formation of tides; for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; and for various other phenomena observed on Earth.
Gravitation is one of the four fundamental interactions of nature, along with electromagnetism, and the nuclear strong force and weak force. Modern physics describes gravitation using the general theory of relativity by Einstein, in which it is a consequence of the curvature of spacetime governing the motion of inertial objects. The simpler Newton's law of universal gravitation provides an accurate approximation for most physical situations.
Quantum Gravity
Quantum gravity (QG) is the field of theoretical physics which attempts to develop scientific models that unify quantum mechanics (describing three of the four known fundamental interactions) with general relativity (describing the fourth, gravity). It is hoped that development of such a theory would unify into a single mathematical framework all fundamental interactions and to describe all known observable interactions in the universe, at both subatomic and cosmological scales.
Such a theory of quantum gravity would yield the same experimental results as ordinary quantum mechanics in conditions of weak gravity (gravitational potentials much less than c2) and the same results as Einsteinian general relativity in phenomena at scales much larger than individual molecules (action much larger than reduced Planck's constant), but moreover be able to predict the outcome of situations where both quantum effects and strong-field gravity are important (at the Planck scale, unless large extra dimension conjectures are correct).
If the theory of quantum gravity also achieves a grand unification of the other known interactions, it is referred to as a theory of everything (TOE).
Motivation for quantizing gravity comes from the remarkable success of the quantum theories of the other three fundamental interactions, and from experimental evidence suggesting that gravity can be made to show quantum effects.[1][2][3] Although some quantum gravity theories such as string theory and other unified field theories (or 'theories of everything') attempt to unify gravity with the other fundamental forces, others such as loop quantum gravity make no such attempt; they simply quantize the gravitational field while keeping it separate from the other forces.
Observed physical phenomena can be described well by quantum mechanics or general relativity, without needing both. This can be thought of as due to an extreme separation of mass scales at which they are important. Quantum effects are usually important only for the "very small", that is, for objects no larger than typical molecules. General relativistic effects, on the other hand, show up mainly for the "very large" bodies such as collapsed stars. (Planets' gravitational fields, as of 2011, are well-described by linearized gravity except for Mercury's perihelion precession; so strong-field effects—any effects of gravity beyond lowest nonvanishing order in φ/c2—have not been observed even in the gravitational fields of planets and main sequence stars). There is a lack of experimental evidence relating to quantum gravity, and classical physics adequately describes the observed effects of gravity over a range of 50 orders of magnitude of mass, i.e., for masses of objects from about 10−23 to 1030 kg.
Comparison of Electromagnetic and gravitational fields
Sources of electromagnetic fields consist of two types of charge – positive and negative. This contrasts with the sources of the gravitational field, which are masses. Masses are sometimes described as gravitational charges, the important feature of them being that there is only one type (no negative masses), or, in more colloquial terms, 'gravity is always attractive'.
The relative strengths and ranges of the four interactions and other information are tabulated below:
Quantum Field Theories
Quantum field theory (QFT) provides a theoretical framework for constructing quantum mechanical models of systems classically parametrized (represented) by an infinite number of degrees of freedom, that is, fields and (in a condensed matter context) many-body systems. It is the natural and quantitative language of particle physics and condensed matter physics. Most theories in modern particle physics, including the Standard Model of elementary particles and their interactions, are formulated as relativistic quantum field theories. Quantum field theories are used in many contexts, and are especially vital in elementary particle physics, where the particle count/number may change over the course of a reaction. They are also used in the description of critical phenomena and quantum phase transitions, such as in the BCS theory of superconductivity.
In perturbative quantum field theory, the forces between particles are mediated by other particles. The electromagnetic force between two electrons is caused by an exchange of photons. Intermediate vector bosons mediate the weak force and gluons mediate the strong force. There is currently no complete quantum theory of the remaining fundamental force, gravity, but many of the proposed theories postulate the existence of a graviton particle that mediates it. These force-carrying particles are virtual particles and, by definition, cannot be detected while carrying the force, because such detection will imply that the force is not being carried. In addition, the notion of "force mediating particle" comes from perturbation theory, and thus does not make sense in a context of bound states.
In QFT, photons are not thought of as "little billiard balls" but are rather viewed as field quanta – necessarily chunked ripples in a field, or "excitations", that "look like" particles. Fermions, like the electron, can also be described as ripples/excitations in a field, where each kind of fermion has its own field. In summary, the classical visualization of "everything is particles and fields", in quantum field theory, resolves into "everything is particles", which then resolves into "everything is fields". In the end, particles are regarded as excited states of a field (field quanta). The gravitational field and the electromagnetic field are the only two fundamental fields in Nature that have infinite range and a corresponding classical low-energy limit, which greatly diminishes and hides their "particle-like" excitations. Albert Einstein, in 1905, attributed "particle-like" and discrete exchanges of momenta and energy, characteristic of "field quanta", to the electromagnetic field. Originally, his principal motivation was to explain the thermodynamics of radiation. Although it is often claimed that the photoelectric and Compton effects require a quantum description of the EM field, this is now understood to be untrue, and proper proof of the quantum nature of radiation is now taken up into modern quantum optics as in the antibunching effect.[1] The word "photon" was coined in 1926 by physical chemist Gilbert Newton Lewis (see also the articles photon antibunching and laser).
In the "low-energy limit", the quantum field-theoretic description of the electromagnetic field, quantum electrodynamics, does not exactly reduce to James Clerk Maxwell's 1864 theory of classical electrodynamics. Small quantum corrections due to virtual electron positron pairs give rise to small non-linear corrections to the Maxwell equations, although the "classical limit" of quantum electrodynamics has not been as widely explored as that of quantum mechanics.
Presumably, the as yet unknown correct quantum field-theoretic treatment of the gravitational field will become and "look exactly like" Einstein's general theory of relativity in the "low-energy limit", or, more generally, like the Einstein-Yang-Mills-Dirac System. Indeed, quantum field theory itself is possibly the low-energy-effective-field-theory limit of a more fundamental theory such as superstring theory. Compare in this context the article effective field theory.
String Theory
String theory is an active research framework in particle physics that attempts to reconcile quantum mechanics and general relativity. It is a contender for a theory of everything (TOE), a self-contained mathematical model that describes all fundamental forces and forms of matter.
String theory posits that the electrons and quarks within an atom are not 0-dimensional objects, but rather 1-dimensional oscillating lines ("strings"). The earliest string model, the bosonic string, incorporated only bosons, although this view developed to the superstring theory, which posits that a connection (a "supersymmetry") exists between bosons and fermions. String theories also require the existence of several extra dimensions to the universe that have been compactified into extremely small scales, in addition to the four known spacetime dimensions.
The theory has its origins in an effort to understand the strong force, the dual resonance model (1969). Subsequent to this, five different superstring theories were developed that incorporated fermions and possessed other properties necessary for a theory of everything. Since the mid-1990s, in particular due to insights from dualities shown to relate the five theories, an eleven-dimensional theory called M-theory is believed to encompass all of the previously distinct superstring theories.
Many theoretical physicists (e.g., Stephen Hawking, Edward Witten, Juan Maldacena and Leonard Susskind) believe that string theory is a step towards the correct fundamental description of nature. This is because string theory allows for the consistent combination of quantum field theory and general relativity, agrees with general insights in quantum gravity (such as the holographic principle and Black hole thermodynamics), and because it has passed many non-trivial checks of its internal consistency.[1][2][3][4] According to Hawking in particular, "M-theory is the only candidate for a complete theory of the universe."[5] Nevertheless, other physicists, such as Feynman and Glashow, have criticized string theory for not providing novel experimental predictions at accessible energy scales.[6]
M-Theory
In theoretical physics, M-theory is an extension of string theory in which 11 dimensions are identified. Because the dimensionality exceeds that of superstring theories in 10 dimensions, proponents believe that the 11-dimensional theory unites all five string theories (and supersedes them). Though a full description of the theory is not known, the low-entropy dynamics are known to be supergravity interacting with 2- and 5-dimensional membranes.
This idea is the unique supersymmetric theory in eleven dimensions, with its low-entropy matter content and interactions fully determined, and can be obtained as the strong coupling limit of type IIA string theory because a new dimension of space emerges as the coupling constant increases.
Drawing on the work of a number of string theorists (including Ashoke Sen, Chris Hull, Paul Townsend, Michael Duff and John Schwarz), Edward Witten of the Institute for Advanced Study suggested its existence at a conference at USC in 1995, and used M-theory to explain a number of previously observed dualities, initiating a flurry of new research in string theory called the second superstring revolution.
In the early 1990s, it was shown that the various superstring theories were related by dualities which allow the description of an object in one super string theory to be related to the description of a different object in another super string theory. These relationships imply that each of the super string theories is a different aspect of a single underlying theory, proposed by Witten, and named "M-theory".
Originally the letter M in M-theory was taken from membrane, a construct designed to generalize the strings of string theory. However, as Witten was more skeptical about membranes than his colleagues, he opted for "M-theory" rather than "Membrane theory". Witten has since stated that the different interpretations of the M can be a matter of taste for the user, such as magic, mystery, and mother theory.[1]
M-theory (and string theory) has been criticized for lacking predictive power or being untestable. Further work continues to find mathematical constructs that join various surrounding theories. However, the tangible success of M-theory can be questioned, given its current incompleteness and limited predictive power.
Supersymmetry
In particle physics, supersymmetry (often abbreviated SUSY) is a symmetry that relates elementary particles of one spin to other particles that differ by half a unit of spin and are known as superpartners. In a theory with unbroken supersymmetry, for every type of boson there exists a corresponding type of fermion with the same mass and internal quantum numbers, and vice-versa.
There is no direct evidence for the existence of supersymmetry.[1] It is motivated by possible solutions to several theoretical problems. Since the superpartners of the Standard Model particles have not been observed, supersymmetry, if it exists, must be a broken symmetry, allowing the superparticles to be heavier than the corresponding Standard Model particles.
If supersymmetry exists close to the TeV energy scale, it allows for a solution of the hierarchy problem of the Standard Model, i.e., the fact that the Higgs boson mass is subject to quantum corrections which — barring extremely fine-tuned cancellations among independent contributions — would make it so large as to undermine the internal consistency of the theory. In supersymmetric theories, on the other hand, the contributions to the quantum corrections coming from Standard Model particles are naturally canceled by the contributions of the corresponding superpartners. Other attractive features of TeV-scale supersymmetry are the fact that it allows for the high-energy unification of the weak interactions, the strong interactions and electromagnetism, and the fact that it provides a candidate for dark matter and a natural mechanism for electroweak symmetry breaking. Therefore, scenarios where supersymmetric partners appear with masses not much greater than 1 TeV are considered the most well-motivated by theorists[2]. These scenarios would imply that experimental traces of the superpartners should begin to emerge in high-energy collisions at the LHC relatively soon. As of September 2011, no meaningful signs of the superpartners have been observed[3][4], which is beginning to significantly constrain the most popular incarnations of supersymmetry. However, the total parameter space of consistent supersymmetric extensions of the Standard Model is extremely diverse and can not be definitively ruled out at the LHC.
Another theoretically appealing property of supersymmetry is that it offers the only "loophole" to the Coleman–Mandula theorem, which prohibits spacetime and internal symmetries from being combined in any nontrivial way, for quantum field theories like the Standard Model under very general assumptions. The Haag-Lopuszanski-Sohnius theorem demonstrates that supersymmetry is the only way spacetime and internal symmetries can be consistently combined.[5]
In general, supersymmetric quantum field theory is often much easier to work with, as many more problems become exactly solvable. Supersymmetry is also a feature of most versions of string theory, though it may exist in nature even if string theory is incorrect.
The Minimal Supersymmetric Standard Model is one of the best studied candidates for physics beyond the Standard Model. Theories of gravity that are also invariant under supersymmetry are known as supergravity theories.
The Minimal Supersymmetric Standard Model (MSSM)
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An example of a flavor changing neutral current process in MSSM. A strange quark emits a bino, turning into a sdown-type quark, which then emits a Z boson and reabsorbs the bino, turning into a down quark. If the MSSM squark masses are flavor violating, such a process can occur.
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The Minimal Supersymmetric Standard Model (MSSM) is the minimal extension to the Standard Model that realizes N=1 supersymmetry, although non-minimal extensions do exist. Supersymmetry pairs bosons with fermions; therefore every Standard Model particle has a partner that has yet to be discovered. If these supersymmetric partners exist, it is likely that they will be observed at the Large Hadron Collider, which began operations in 2009. If the superparticles are found, it is analogous to discovering antimatter [1] and depending on the details of what is found, it could provide evidence for grand unification and might even in principle provide hints as to whether string theory describes nature.
The MSSM was originally proposed in 1981 to stabilize the weak scale, solving the hierarchy problem.[2] The Higgs boson mass of the Standard Model is unstable to quantum corrections and the theory predicts that weak scale should be much weaker than what is observed to be. In the MSSM, the Higgs boson has a fermionic superpartner, the Higgsino, that has the same mass as it would if supersymmetry were an exact symmetry. Because fermion masses are radiatively stable, the Higgs mass inherits this stability. However, in MSSM there is a need for more than one Higgs field, as described below.
The only unambiguous way to claim discovery of supersymmetry is to produce superparticles in the laboratory. Because superparticles are expected to be 100 to 1000 times heavier than the proton, it requires a huge amount of energy to make these particles that can only be achieved at particle accelerators. The Tevatron was actively looking for evidence of the production of supersymmetric particles before it was shut down on 30 September, 2011. Most physicists believe that supersymmetry must be discovered at the LHC if it is responsible for stabilizing the weak scale. There are five classes of particle that superpartners of the Standard Model fall into: squarks, gluinos, charginos, neutralinos, and sleptons. These superparticles have their interactions and subsequent decays described by the MSSM and each has characteristic signatures.
The MSSM imposes R-parity to explain the stability of the proton. It adds supersymmetry breaking by introducing explicit soft supersymmetry breaking operators into the Lagrangian that is communicated to it by some unknown (and unspecified) dynamics. This means that there are 120 new parameters in the MSSM. Most of these parameters lead to unnacceptable phenomenology such as large flavor changing neutral currents or large electric dipole moments for the neutron and electron. To avoid these problems, the MSSM takes all of the soft supersymmetry breaking to be diagonal in flavor space and for all of the new CP violating phases to vanish.
