title: Quantum decoherence

text: As a consequence, the system behaves as a classical statistical ensemble of the different elements rather than as a single coherent quantum superposition of them. From the perspective of each ensemble member's measuring device, the system appears to have irreversibly collapsed onto a state with a precise value for the measured attributes, relative to that element. And this provided one explains how the Born rule coefficients effectively act as probabilities as per the measurement postulate, constitutes a solution to the quantum measurement problem.


title: Quantum decoherence

text: where the formula_4s form an einselected basis ("environmentally induced selected eigenbasis"), and let the environment initially be in the state formula_5. The vector basis of the combination of the system and the environment consists of the tensor products of the basis vectors of the two subsystems. Thus, before any interaction between the two subsystems, the joint state can be written as


title: Quantum decoherence

text: where formula_7 is shorthand for the tensor product formula_8. There are two extremes in the way the system can interact with its environment: either (1) the system loses its distinct identity and merges with the environment (e.g. photons in a cold, dark cavity get converted into molecular excitations within the cavity walls), or (2) the system is not disturbed at all, even though the environment is disturbed (e.g. the idealized non-disturbing measurement). In general, an interaction is a mixture of these two extremes that we examine.


title: Quantum decoherence

text: If the environment absorbs the system, each element of the total system's basis interacts with the environment such that


title: Quantum decoherence

text: The unitarity of time evolution demands that the total state basis remains orthonormal, i.e. the scalar or inner products of the basis vectors must vanish, since formula_13:


title: Quantum decoherence

text: This orthonormality of the environment states is the defining characteristic required for einselection.


title: Quantum decoherence

text: In an idealised measurement, the system disturbs the environment, but is itself undisturbed by the environment.


title: Quantum decoherence

text: where formula_20 was used. "Additionally", decoherence requires, by virtue of the large number of hidden degrees of freedom in the environment, that


title: Quantum decoherence

text: As before, this is the defining characteristic for decoherence to become einselection. The approximation becomes more exact as the number of environmental degrees of freedom affected increases.


title: Quantum decoherence

text: Note that if the system basis formula_4 were not an einselected basis, then the last condition is trivial, since the disturbed environment is not a function of formula_23, and we have the trivial disturbed environment basis formula_24. This would correspond to the system basis being degenerate with respect to the environmentally defined measurement observable. For a complex environmental interaction (which would be expected for a typical macroscale interaction) a non-einselected basis would be hard to define.


title: Quantum decoherence

text: The utility of decoherence lies in its application to the analysis of probabilities, before and after environmental interaction, and in particular to the vanishing of quantum interference terms after decoherence has occurred. If we ask what is the probability of observing the system making a transition from formula_2 to formula_26 "before" formula_2 has interacted with its environment, then application of the Born probability rule states that the transition probability is the squared modulus of the scalar product of the two states:


title: Quantum decoherence

text: The above expansion of the transition probability has terms that involve formula_32; these can be thought of as representing "interference" between the different basis elements or quantum alternatives. This is a purely quantum effect and represents the non-additivity of the probabilities of quantum alternatives.


title: Quantum decoherence

text: To calculate the probability of observing the system making a quantum leap from formula_2 to formula_26 "after" formula_2 has interacted with its environment, then application of the Born probability rule states that we must sum over all the relevant possible states formula_36 of the environment "before" squaring the modulus:


title: Quantum decoherence

text: The internal summation vanishes when we apply the decoherence/einselection condition formula_38, and the formula simplifies to


title: Quantum decoherence

text: If we compare this with the formula we derived before the environment introduced decoherence, we can see that the effect of decoherence has been to move the summation sign formula_40 from inside of the modulus sign to outside. As a result, all the cross- or quantum interference-terms


title: Quantum decoherence

text: have vanished from the transition-probability calculation. The decoherence has irreversibly converted quantum behaviour (additive probability amplitudes) to classical behaviour (additive probabilities).


title: Quantum decoherence

text: In terms of density matrices, the loss of interference effects corresponds to the diagonalization of the "environmentally traced-over" density matrix.


title: Quantum decoherence

text: The effect of decoherence on density matrices is essentially the decay or rapid vanishing of the off-diagonal elements of the partial trace of the joint system's density matrix, i.e. the trace, with respect to "any" environmental basis, of the density matrix of the combined system "and" its environment. The decoherence irreversibly converts the "averaged" or "environmentally traced-over" density matrix from a pure state to a reduced mixture; it is this that gives the "appearance" of wave-function collapse. Again, this is called "environmentally induced superselection", or einselection. The advantage of taking the partial trace is that this procedure is indifferent to the environmental basis chosen.


title: Quantum decoherence

text: Then if the transition happens before any interaction takes place between the system and the environment, the environment subsystem has no part and can be traced out, leaving the reduced density matrix for the system:


title: Quantum decoherence

text: Now the case when transition takes place after the interaction of the system with the environment. The combined density matrix will be


title: Quantum decoherence

text: To get the reduced density matrix of the system, we trace out the environment and employ the decoherence/einselection condition and see that the off-diagonal terms vanish (a result obtained by Erich Joos and H. D. Zeh in 1985):


title: Quantum decoherence

text: The density-matrix approach has been combined with the Bohmian approach to yield a "reduced-trajectory approach", taking into account the system reduced density matrix and the influence of the environment.


title: Quantum decoherence

text: Consider a system "S" and environment (bath) "B", which are closed and can be treated quantum-mechanically. Let formula_54 and formula_55 be the system's and bath's Hilbert spaces respectively. Then the Hamiltonian for the combined system is


title: Quantum decoherence

text: where formula_57 are the system and bath Hamiltonians respectively, formula_58 is the interaction Hamiltonian between the system and bath, and formula_59 are the identity operators on the system and bath Hilbert spaces respectively. The time-evolution of the density operator of this closed system is unitary and, as such, is given by


title: Quantum decoherence

text: where the unitary operator is formula_61. If the system and bath are not entangled initially, then we can write formula_62. Therefore, the evolution of the system becomes


title: Quantum decoherence

text: where formula_65 is the operator acting on the combined system–bath Hilbert space, and formula_66 are the operators that act on the system and bath respectively. This coupling of the system and bath is the cause of decoherence in the system alone. To see this, a partial trace is performed over the bath to give a description of the system alone:


title: Quantum decoherence

text: formula_68 is called the "reduced density matrix" and gives information about the system only. If the bath is written in terms of its set of orthogonal basis kets, that is, if it has been initially diagonalized, then formula_69. Computing the partial trace with respect to this (computational) basis gives


title: Quantum decoherence

text: where formula_71 are defined as the "Kraus operators" and are represented as (the index formula_72 combines indices formula_73 and formula_74):


title: Quantum decoherence

text: This is known as the "operator-sum representation" (OSR). A condition on the Kraus operators can be obtained by using the fact that formula_76; this then gives


title: Quantum decoherence

text: This restriction determines whether decoherence will occur or not in the OSR. In particular, when there is more than one term present in the sum for formula_68, then the dynamics of the system will be non-unitary, and hence decoherence will take place.


title: Quantum decoherence

text: A more general consideration for the existence of decoherence in a quantum system is given by the "master equation", which determines how the density matrix of the "system alone" evolves in time (see also the Belavkin equation for the evolution under continuous measurement). This uses the Schrödinger picture, where evolution of the "state" (represented by its density matrix) is considered. The master equation is


title: Quantum decoherence

text: where formula_80 is the system Hamiltonian formula_81 along with a (possible) unitary contribution formula_82 from the bath, and formula_83 is the "Lindblad decohering term". The Lindblad decohering term is represented as


title: Quantum decoherence

text: The formula_85 are basis operators for the "M"-dimensional space of bounded operators that act on the system Hilbert space formula_54 and are the "error generators". The matrix elements formula_87 represent the elements of a positive semi-definite Hermitian matrix; they characterize the decohering processes and, as such, are called the "noise parameters". The semigroup approach is particularly nice, because it distinguishes between the unitary and decohering (non-unitary) processes, which is not the case with the OSR. In particular, the non-unitary dynamics are represented by formula_83, whereas the unitary dynamics of the state are represented by the usual Heisenberg commutator. Note that when formula_89, the dynamical evolution of the system is unitary. The conditions for the evolution of the system density matrix to be described by the master equation are:


title: Quantum decoherence

text: Decoherence can be modelled as a non-unitary process by which a system couples with its environment (although the combined system plus environment evolves in a unitary fashion). Thus the dynamics of the system alone, treated in isolation, are non-unitary and, as such, are represented by irreversible transformations acting on the system's Hilbert space formula_90. Since the system's dynamics are represented by irreversible representations, then any information present in the quantum system can be lost to the environment or heat bath. Alternatively, the decay of quantum information caused by the coupling of the system to the environment is referred to as decoherence. Thus decoherence is the process by which information of a quantum system is altered by the system's interaction with its environment (which form a closed system), hence creating an entanglement between the system and heat bath (environment). As such, since the system is entangled with its environment in some unknown way, a description of the system by itself cannot be made without also referring to the environment (i.e. without also describing the state of the environment).


title: Quantum decoherence

text: Consider a system of "N" qubits that is coupled to a bath symmetrically. Suppose this system of "N" qubits undergoes a rotation around the formula_91 formula_92 eigenstates of formula_93. Then under such a rotation, a random phase formula_26 will be created between the eigenstates formula_95, formula_96 of formula_93. Thus these basis qubits formula_95 and formula_96 will transform in the following way:


title: Quantum decoherence

text: Since any qubit in this space can be expressed in terms of the basis qubits, then all such qubits will be transformed under this rotation. Consider the formula_74th qubit in a pure state formula_103 where formula_104. Before application of the rotation this state is:


title: Quantum decoherence

text: This state will decohere, since it is not ‘encoded’ with (dependent upon) the dephasing factor formula_106. This can be seen by examining the density matrix averaged over the random phase formula_26:


title: Quantum decoherence

text: where formula_109 is a probability measure of the random phase, formula_26. Although not entirely necessary, let us assume for simplicity that this is given by the Gaussian distribution, "i.e." formula_111, where formula_112 represents the spread of the random phase. Then the density matrix computed as above is


title: Quantum decoherence

text: Observe that the off-diagonal elements—the coherence terms—decay as the spread of the random phase, formula_112, increases over time (which is a realistic expectation). Thus the density matrices for each qubit of the system become indistinguishable over time. This means that no measurement can distinguish between the qubits, thus creating decoherence between the various qubit states. In particular, this dephasing process causes the qubits to collapse to one of the pure states in formula_115. This is why this type of decoherence process is called collective dephasing, because the "mutual" phases between "all" qubits of the "N"-qubit system are destroyed.


title: Quantum decoherence

text: Depolarizing is a non-unitary transformation on a quantum system which maps pure states to mixed states. This is a non-unitary process, because any transformation that reverses this process will map states out of their respective Hilbert space thus not preserving positivity (i.e. the original probabilities are mapped to negative probabilities, which is not allowed). The 2-dimensional case of such a transformation would consist of mapping pure states on the surface of the Bloch sphere to mixed states within the Bloch sphere. This would contract the Bloch sphere by some finite amount and the reverse process would expand the Bloch sphere, which cannot happen.


title: Quantum decoherence

text: Dissipation is a decohering process by which the populations of quantum states are changed due to entanglement with a bath. An example of this would be a quantum system that can exchange its energy with a bath through the interaction Hamiltonian. If the system is not in its ground state and the bath is at a temperature lower than that of the system's, then the system will give off energy to the bath, and thus higher-energy eigenstates of the system Hamiltonian will decohere to the ground state after cooling and, as such, will all be non-degenerate. Since the states are no longer degenerate, they are not distinguishable, and thus this process is irreversible (non-unitary).


title: Quantum decoherence

text: Decoherence represents an extremely fast process for macroscopic objects, since these are interacting with many microscopic objects, with an enormous number of degrees of freedom, in their natural environment. The process is needed if we are to understand why we tend not to observe quantum behaviour in everyday macroscopic objects and why we do see classical fields emerge from the properties of the interaction between matter and radiation for large amounts of matter. The time taken for off-diagonal components of the density matrix to effectively vanish is called the decoherence time. It is typically extremely short for everyday, macroscale processes. A modern basis-independent definition of the decoherence time relies on the short-time behavior of the fidelity between the initial and the time-dependent state


title: Quantum decoherence

text: We assume for the moment that the system in question consists of a subsystem "A" being studied and the "environment" formula_116, and the total Hilbert space is the tensor product of a Hilbert space formula_117 describing "A" and a Hilbert space formula_118 describing formula_116, that is,


title: Quantum decoherence

text: This is a reasonably good approximation in the case where "A" and formula_116 are relatively independent (e.g. there is nothing like parts of "A" mixing with parts of formula_116 or conversely). The point is, the interaction with the environment is for all practical purposes unavoidable (e.g. even a single excited atom in a vacuum would emit a photon, which would then go off). Let's say this interaction is described by a unitary transformation "U" acting upon formula_123. Assume that the initial state of the environment is formula_124, and the initial state of "A" is the superposition state


title: Quantum decoherence

text: where formula_126 and formula_127 are orthogonal, and there is no entanglement initially. Also, choose an orthonormal basis formula_128 for formula_117. (This could be a "continuously indexed basis" or a mixture of continuous and discrete indexes, in which case we would have to use a rigged Hilbert space and be more careful about what we mean by orthonormal, but that's an inessential detail for expository purposes.) Then, we can expand


title: Quantum decoherence

text: respectively. One thing to realize is that the environment contains a huge number of degrees of freedom, a good number of them interacting with each other all the time. This makes the following assumption reasonable in a handwaving way, which can be shown to be true in some simple toy models. Assume that there exists a basis for formula_118 such that formula_135 and formula_136 are all approximately orthogonal to a good degree if "i" ≠ "j" and the same thing for formula_137 and formula_138 and also for formula_135 and formula_138 for any "i" and "j" (the decoherence property).


title: Quantum decoherence

text: This often turns out to be true (as a reasonable conjecture) in the position basis because how "A" interacts with the environment would often depend critically upon the position of the objects in "A". Then, if we take the partial trace over the environment, we would find the density state is approximately described by


title: Quantum decoherence

text: that is, we have a diagonal mixed state, there is no constructive or destructive interference, and the "probabilities" add up classically. The time it takes for "U"("t") (the unitary operator as a function of time) to display the decoherence property is called the decoherence time.


title: Quantum decoherence

text: The decoherence rate depends on a number of factors, including temperature or uncertainty in position, and many experiments have tried to measure it depending on the external environment.


title: Quantum decoherence

text: The process of a quantum superposition gradually obliterated by decoherence was quantitatively measured for the first time by Serge Haroche and his co-workers at the École Normale Supérieure in Paris in 1996. Their approach involved sending individual rubidium atoms, each in a superposition of two states, through a microwave-filled cavity. The two quantum states both cause shifts in the phase of the microwave field, but by different amounts, so that the field itself is also put into a superposition of two states. Due to photon scattering on cavity-mirror imperfection, the cavity field loses phase coherence to the environment.


title: Quantum decoherence

text: Haroche and his colleagues measured the resulting decoherence via correlations between the states of pairs of atoms sent through the cavity with various time delays between the atoms.


title: Quantum decoherence

text: In July 2011, researchers from University of British Columbia and University of California, Santa Barbara were able to reduce environmental decoherence rate "to levels far below the threshold necessary for quantum information processing" by applying high magnetic fields in their experiment.


title: Quantum decoherence

text: In August 2020 scientists reported that ionizing radiation from environmental radioactive materials and cosmic rays may substantially limit the coherence times of qubits if they aren't shielded adequately which may be critical for realizing fault-tolerant superconducting quantum computers in the future.


title: Quantum decoherence

text: Criticism of the adequacy of decoherence theory to solve the measurement problem has been expressed by Anthony Leggett.


title: Quantum decoherence

text: Before an understanding of decoherence was developed, the Copenhagen interpretation of quantum mechanics treated wave-function collapse as a fundamental, "a priori" process. Decoherence as a possible "explanatory mechanism" for the "appearance" of wave function collapse was first developed by David Bohm in 1952, who applied it to Louis DeBroglie's pilot-wave theory, producing Bohmian mechanics, the first successful hidden-variables interpretation of quantum mechanics. Decoherence was then used by Hugh Everett in 1957 to form the core of his many-worlds interpretation. However, decoherence was largely ignored for many years (with the exception of Zeh's work), and not until the 1980s did decoherent-based explanations of the appearance of wave-function collapse become popular, with the greater acceptance of the use of reduced density matrices. The range of decoherent interpretations have subsequently been extended around the idea, such as consistent histories. Some versions of the Copenhagen interpretation have been modified to include decoherence.


title: Quantum decoherence

text: Decoherence does not claim to provide a mechanism for some actual wave-function collapse; rather it puts forth a reasonable framework for the appearance of wave-function collapse. The quantum nature of the system is simply "leaked" into the environment so that a total superposition of the wave function still exists, but exists – at least for all practical purposes — beyond the realm of measurement. Of course, by definition, the claim that a merged but unmeasurable wave function still exists cannot be proven experimentally. Decoherence is needed to understand why a quantum system begins to obey classical probability rules after interacting with its environment (due to the suppression of the interference terms when applying Born's probability rules to the system).


title: Kevin Maxwell

text: Kevin Francis Herbert Maxwell (born 1959) is a British businessman. In the 1990s, Maxwell was acquitted of charges relating to financial crimes connected with the business practices of his father, publishing tycoon Robert Maxwell. Formerly disqualified from being a company director, he has been declared bankrupt twice. He is co-founder of the thinktank Combating Jihadist Terrorism.


title: Kevin Maxwell

text: Kevin Maxwell (born 1959) is the eighth child of Elisabeth (née Meynard), a French-born Holocaust scholar, and Robert Maxwell, a Czechoslovak-born British publishing tycoon. His father was Jewish and his mother was a French Protestant of Huguenot descent. Kevin is one of nine siblings (two of whom died in childhood). These include his older siblings Christine Maxwell, Isabel Maxwell, and Ian Maxwell along with his younger sister Ghislaine Maxwell. The family resided at Headington Hill Hall from 1960, where the offices of Robert Maxwell’s Pergamon Press were also located.


title: Kevin Maxwell

text: Maxwell, along with his brother Ian, joined the family publishing business. He spent most of his working life before 1991 employed by his father, including a spell as chairman of Oxford United F.C. Robert Maxwell was known for his domineering disposition and this included behaviour towards his children. Editor Mike Molloy, who had worked for Robert Maxwell at the "Daily Mirror" and "The European", described a conversation he had with Kevin on a flight to Moscow, where Kevin detailed his discontent in working too much with no time left for seeing his family.


title: Kevin Maxwell

text: Maxwell was serving as Chairman of Maxwell Communications Corporation and at Macmillan Inc. at the time of his father's death in 1991. Robert Maxwell was found floating in the sea near the Canary Islands in proximity to his yacht "Lady Ghislaine" in November 1991. After his father died, it quickly emerged that there were severe financial troubles with the Maxwell empire that Kevin and Ian Maxwell were connected, in particular with the pension funds for thousands of Mirror Group employees. Following his father’s death, and the collapse of the Mirror Group media empire, Kevin Maxwell became the biggest personal bankrupt in UK history with debts of £406.5 million in 1992. He was later tried and, in 1996, was acquitted of fraud charges arising from his role in his father's companies.


title: Kevin Maxwell

text: British courts determined that Coopers & Lybrand made gross errors during their 1990s audit of the Maxwell group of companies and fined Coopers & Lybrand a record 3.3 million pounds.


title: Kevin Maxwell

text: The bankruptcy was lifted three years later, and he co-founded media company Telemonde, which later failed. He entered into a further arrangement over debts he accrued subsequently. After his discharge from bankruptcy in 2005, Maxwell went into the property industry where he has been involved in establishing large property deals, including the sale of Earls Court Exhibition Centre and Olympia, and the purchase of Stables Market in Camden Town.


title: Kevin Maxwell

text: On 8 July 2011, as a result of an Insolvency Service investigation into the collapse of Syncro, a Manchester-based construction company, Maxwell was disqualified from being a company director for eight years.


title: Kevin Maxwell

text: Maxwell announced, in September 2018, that he and his brother Ian had founded a UK think tank called Combating Jihadist Terrorism (CoJit) with the aim of better understanding terrorism and its causes.


title: Kevin Maxwell

text: Maxwell met Pandora Warnford-Davis while both were attending Oxford. They married in 1984 and have seven children together. The family lived in the Elizabethan Moulsford Manor, near Didcot in Oxfordshire in 2005. The couple separated in 2007, and later divorced.


title: Volkswagen Type 2 (T3)

text: The Volkswagen Type 2 (T3) was the third generation of the Volkswagen Transporter and was marketed under various nameplates worldwide – including the Transporter or Caravelle in Europe, T25 in the UK, Microbus in South Africa, and Vanagon in North and South America.


title: Volkswagen Type 2 (T3)

text: It was larger, heavier, and more angular in its styling than its predecessor, the T2 but shared the same rear-engine, cab-over design. It was produced in a rear wheel drive version as well as a 4WD version marketed as "Syncro."


title: Volkswagen Type 2 (T3)

text: The T3 was manufactured in Hannover, Germany from 1979 until 1991. Production of the Syncro (mostly for official use, like postal service or German army) continued until 1992 at Puch in Graz, Austria, where all 4WDs were built. A limited number of 2WD models were also produced at the Graz factory after German production had come to an end. South African production of the T3 continued, for that market only, until 2002.


title: Volkswagen Type 2 (T3)

text: Following the Type 2 T2, the Type 2 T3 initially featured air-cooled engines; later years had water-cooled engines. Versions produced in South Africa from 1990 until 2002 featured an Audi five-cylinder engine.


title: Volkswagen Type 2 (T3)

text: Volkswagen marketed the Westfalia camper variant throughout the T3 production, with features including a raised roof (either pop-up or fixed), refrigerator, sink, and stove.


title: Volkswagen Type 2 (T3)

text: basic steel or chrome-plated steel bumpers with plastic end-caps. Air-cooled models (1979 to mid-1983) lack the lower grill above the radiator of the water-cooled models, except on models with factory air conditioning. Production of the Syncro four-wheel drive model began in late 1984, with the world premiere taking place at the Brussels Commercial Vehicle Show in January 1985. The original Syncros came equipped with the gasoline 1.9 with and a "4+G" gearbox, with the G being a low gear for offroad use ("Gelände" in German).


title: Volkswagen Type 2 (T3)

text: 1986 model year models received revisions including a rev counter/tachometer, more fabric choices, redesigned air conditioning, enlarged water-cooled engine with a more advanced engine management system, and redesigned transmissions. Exterior changes included rectangular headlights (on selected models), and different paint options. Alloy wheels and larger fiberglass bumpers with trim along the rocker panels were optional (standard on Hannover and Wolfsburg Edition vans). For 1990 and 1991 model years, a "Carat" trim level was available which included all available options except the Westfalia conversion and Syncro.


title: Volkswagen Type 2 (T3)

text: Some 1979 through 1981 models received 6 welded-in metal slats covering the engine ventilation passages behind the rear windows. All later models had black plastic 16-slat covers that slotted in at the top and screwed down at the bottom.


title: Volkswagen Type 2 (T3)

text: During the 1980s, the U.S. Army and Air Force in Germany used T3s as administrative (non-tactical) vehicles. In military use, the vehicle's nomenclature was "Light Truck, Commercial".


title: Volkswagen Type 2 (T3)

text: Porsche created a version called B32 in a limited edition. The van, based on the luxurious Carat model, was equipped with the 3.2 liter Carrera engine and was originally developed to support Porsche's testing activities in Algeria. Ten of these were built, with some sold by Porsche to special customers, even having a Porsche VIN. Porsche themselves also used the Porsche-engined bus to transport staff rapidly. Top speed was around , although Porsche only claimed to ensure that the numbers could be replicated with nine people in the car and with the air conditioning on full.


title: Volkswagen Type 2 (T3)

text: There was one other six-cylinder engine used in the VW Transporter: the Oettinger WBX6. The development of this engine was originally contracted to Oettinger by Volkswagen; it was derived from the regular four-cylinder Wasserboxer and meant for projected use in the T3. When VW abandoned the project, Oettinger bought the rights to the design and put it on the market. As such the six-cylinder shares many parts with the four-cylinder Wasserboxer. The WBX6 was originally only available with a three-speed automatic transmission, incorporating many Audi 100 parts to accommodate the higher power and torque.


title: Volkswagen Type 2 (T3)

text: With the internal combustion engine and transaxle mounted very low in the back, the T3 had much larger disc brakes in the front, and drums in the rear. Axle weight is very nearly equal upon both the front and back ends of the vehicle. Unlike the T2 before it, the T3 was available with amenities such as power steering, air conditioning, power door locks, electrically controlled and heated mirrors, lighted vanity mirrors, and a light above the glove box (some of which were standard equipment in later (non-commercial vehicle) models).


title: Volkswagen Type 2 (T3)

text: The automatic was a standard hydraulic three-speed unit, the same 090/010 unit as used in Audis of the era. These featured a cast aluminum alloy case for the transmission section and a cast iron case for the final drive section.


title: Volkswagen Type 2 (T3)

text: The 091 manual transmission was a four-speed unit, featuring a lightweight aluminum alloy case; from 1983 a 5-speed transmission was available as an option on certain models; a 5-speed was fitted as standard on Syncro four-wheel-drive models.


title: Volkswagen Type 2 (T3)

text: The oil filler tube for the engine is located behind the flip-down license plate door, as is the oil dipstick and the power steering fluid reservoir (when fitted) on Petrol models. Diesel models have the reservoir in the front right corner of the engine bay. Early models had a twist-on/off non-locking gas cap right on the outside just under and behind the passenger side door. A locking cap was standard on later models. 4 Wheel Drive (Syncro) models have the fuel tank in the rear above the transmission so the filler is on the right-side rear corner. The spare tyre lies in a tray under the very front of the van (as the engine is in the back), just below the radiator.


title: Volkswagen Type 2 (T3)

text: Because of the engine placement, a T3 has nearly equal 50/50 weight distribution fore and aft. The early air-cooled engines were somewhat expensive to produce and had some reliability problems. Volkswagen originally meant to replace them with the Golf's inline-four engine but the cost of re-engineering both car and engine made them opt for updating the flat-four instead. An overhead-cam design was mooted but rejected as a willingness to rev was considered to be of less importance than low-end flexibility and low cost. The new 1.9 L "Wasserboxer" (for a water-cooled boxer) was also originally considered for use in certain other Volkswagens such as the Gol, which still relied on the old air-cooled flat-four at that time.


title: Volkswagen Type 2 (T3)

text: The U.S version 1.9 liter and up water-cooled gasoline engines experienced significant and repeated problems with cylinder head surface erosion and coolant leaks. 2.1 L engines suffered the same, mostly due to not having the antifreeze changed often enough, and the use of phosphated coolant, which caused corrosion in the cooling system.


title: Volkswagen Type 2 (T3)

text: There were four general petrol engine variants between 1979 and 1991, with several sub-models. All were overhead-valve push-rod horizontally opposed four-cylinder engines. Available engine options differed between regions. Aftermarket VW specialist Oettinger also offered the WBX6, a six-cylinder version.


title: Volkswagen Type 2 (T3)

text: The Wasserboxer featured an aluminum case, cylinder heads, and pistons, and a forged steel crankshaft. The Wasserboxer, as with all VW boxer engines has a gear-driven camshaft. It also featured Heron, or "bowl-in-piston" type combustion chambers where the combustion takes place within the piston bowl area, and not just in the cylinder head as would be the case with flat top pistons. The switch to water-cooled boxer engines was made mid-year in 1983. T2 transporters or 'bay window' vans, produced in Brazil until 2013, were switched to inline-four-cylinder water-cooled engines and a front-mounted radiator in 2005.


title: Volkswagen Type 2 (T3)

text: In contrast to the standard flat-four gasoline engines, all diesel engine options were of an inline-four configuration. The turbodiesel arrived in January 1985.


title: Volkswagen Type 2 (T3)

text: In the U.S., the T3 was sold as the Vanagon, which is a portmanteau of van and station wagon. The name Vanagon was coined by Volkswagen to highlight their claim that the T3 had the room of a van, but drove like a station wagon. U.S. Vanagon model variations included the Vanagon, featuring vinyl seats and a spartan interior; the Vanagon L with optional cloth seats, more upscale interior panels, and an optional dashboard blower; the Vanagon GL with more equipment like a padded steering wheel and front armrests; and the Westfalia pop-top camper Vanagons, which came in two versions. A Camper version known as the "Campmobile" with integrated kitchen, complete with refrigerator (which ran on propane, 110 V or 12 V), a two-burner stove, and stainless steel sink with onboard water supply. A fold-down rear bench seat converted to a bed and the pop-top included a fold-out bed; these models could sleep four adults. A 'Weekender ' version that lacked the refrigerator, propane stove, and sink of the full 'camper' versions offered an optional removable cabinet with a 12 volt cooler and self-contained sink. In 1984, the Wolfsburg edition was configured with a rear bench seat and two forward-facing middle seats. Under the bench seat, which folded down to make full-size bed, was a storage compartment and a rear heater.


title: Volkswagen Type 2 (T3)

text: Wolfsburg Edition "Weekender" models featured two rear-facing seats behind the front seats in place of a centre bench seat and a table that could fold up from the sidewall – or fold down when not in use. Multivan models featured Wolfsburg Edition trim and an interior with rear-facing seats, the same fold up table, a pop-top with an upper bed, and cabinet behind the rear seat on the driver's side. Wolfsburg Edition and camper van vehicles were outfitted for Volkswagen by the Westfalia factory.


title: Volkswagen Type 2 (T3)

text: Syncro models were manufactured in limited numbers from 1984 through 1992, with the four-wheel-drive system added by Steyr-Daimler-Puch Works in Graz, Austria, with a short wheelbase and 48/52 front/rear weight distribution. The majority of the Syncro production run used the same 14 inch wheels as the RWD version. A limited number of 16" Syncro versions were also produced. The main differences between the 2 models was 16" wheels with 205R16 tires, larger front brakes 280mm discs instead of 254mm disc that was on the 14" Syncro but they shared the same calipers and brake pads. The 16" Syncro had larger rear brakes taken from the VW LT and fender flares which hid the area where VW trimmed the arches to give more room for larger tires.


title: Volkswagen Type 2 (T3)

text: Model years 1980 through 1985 featured round sealed beam headlights. Subsequent models for North American and European markets featured round sealed beam headlights or smaller square headlights, with the primary lights outboard and high beams inboard. Later models from South Africa returned to round headlight housings for both the primary headlights and high-beams. This is known to VW enthusiasts as the "South African look," and swapping the square headlights to round headlights is a popular conversion by van owners with non-South African vehicles.


title: Volkswagen Type 2 (T3)

text: The T3 was replaced by the T4 (Eurovan) in the U.S. market in 1993 (1992 saw no Volkswagen vans imported to the U.S. market, aside from custom campers sold by companies other than Volkswagen).


title: Volkswagen Type 2 (T3)

text: Top-of-the-line Wolfsburg Edition Westfalia Campers, which had all options, were at the top of the price range. In addition to the camper models, a Carat trim level was available for 1990 and 1991 model years. This model included all options available for the Transporter configuration.


title: Volkswagen Type 2 (T3)

text: Production of the T3 continued in South Africa until June 2002, when, due to the economies of scale, Volkswagen SA were obliged to discontinue production after parts supply started to become an issue. The South African T3s post-1991 had a face-lift which included modified front door sheet metal, bigger side windows behind the B pillars, and different rear grilles in the D pillars. The bodyshell is a true RHD design lacking the unused door track cover on the offside and LHD wiper arm mount points as found on earlier models (which were originally designed as an adaptation of a LHD twin-sliding door bodyshell). On models with 5-cylinder engines, the boot floor was raised to accommodate the taller engine and has small storage areas either side of the engine hatch. Internal changes include a fully padded dashboard featuring a smaller glove box and updated vacuum-powered ventilation controls operated by round knobs rather than slide levers, while the fuse box was also relocated to the right-hand side of the steering column. At the front of the vehicle, twin headlamps in both round and rectangular configurations were fitted along with a full width lower grille incorporating the indicator lenses, which were changed from amber to smoked lenses from 1999 onwards. This grille and headlight combination was not found anywhere else in the world. These later South African T3s became known as Big Window T3s due to their larger side windows.


title: Volkswagen Type 2 (T3)

text: In January 1991 the 2.1 Wasserboxer engines were replaced with five-cylinder Audi engines in the "Microbus" and "Caravelle", while a VW 1.8 inline-four cylinder engine was used in the "Kombi" and "Van" models. A 2.1 Wasserboxer Syncro Big Window model was also added, in Microbus or Caravelle trim. 89 Big Window Syncros were sold in 1992; the big-window body was used in the Syncro from 1990 and in 1991, mixed in the "German" small-window body, so exact numbers of Big Window Syncros are unknown, although 89 were sold in 1992. The Syncro model was discontinued in 1992. There were also 4 or 5 factory-built 5 cyl 2.5i Syncros, with K-Jetronic fuel injection, 16" rear trailing arms and brakes and 15" wheels. One was in a small window body, 3 are known to survive (1 small window, and 2 Big Window Syncros). The five-cylinder T3s came out initially with a 2.5-litre K-Jetronic fuel-injected engine in 1991, but this was replaced in March 1995 with a 2.6-litre with an improved fuel injection system and two styles of 15" alloy wheels as standard (Rhein or Starburst) along with larger ventilated front disc brakes. The automatic option for the 2.5 was dropped, leaving only the five-speed manual. A slightly lower spec 2.3 five-cylinder fuel-injected model was introduced four months after the 2.6, but was equipped with a 4-speed transmission and modified wrap-around steel bumpers.


title: Volkswagen Type 2 (T3)

text: There was also a basic bus, with an inline-4 inclined 1.8 carburetor engine. The 1.8 carb motor was a Golf-derived motor, fitted into the bus like an inline-4 diesel in a T3. Called the "Volksie bus", it was a basic bus, with steel 15" rims, single round headlights, steel wrap-around bumpers, and with no aircon or PAS.


title: Volkswagen Type 2 (T3)

text: Near the end of production, a top of the range Caravelle 2.6i known as the "Exclusiv" incorporated two rear-facing seats in place of the centre bench seat, a fridge and a folding table in the back of the vehicle and Carat 2 alloy wheels. A Microbus 2.6i with similar features, but with Rhein alloy wheels were known as the "Activ". The last T3 off the production line in Uitenhage on Friday 16 June 2002 was a gold-coloured Microbus 2.6i which Volkswagen SA retained for their AutoPavilion, Place of Cars and Legends, which first opened its doors in 2004. The vehicle was later written off in a transporter roll-over accident in November 2006, after returning from a display in Cape Town.


title: Volkswagen Type 2 (T3)

text: In 1994, the Swedish insurance company, Folksam tested a Vanagon T3 in a head-on collision with a Volvo 700 series wagon (estate). The crash test was full-frontal (50/50) at 31 mph (58 Km/H). The result was that the driver of the Volvo would have received a head injury criterion (HIC) of 3868. An HIC of 1000 is considered deadly. The Vanagon driver would receive a HIC of only 155. Furthermore, the "chest impact" for the Volvo driver was 65. A chest impact of 60 is considered deadly. The Vanagon driver's impact was only 30.


title: Volkswagen Type 2 (T3)

text: Furthermore, the German engineering testing laboratory for the insurance industry Allianz Zentrum für Technik (AZT) performed tests on 4 June 1984 in Japan. The results were published in the September 1984 ADAC Motorwelt journal. The Vanagon/Caravelle with subjected to crash tests into a fixed 40% barrier at 35 Km/H, which corresponds to a head-on collision at 50-55 Km/H. According to AZT, this test is said to be representative of 90% of all accidents. A series of these crash tests were performed, which compared the T3 to similar vans manufactured by Nissan, Isuzu, Mitsubishi, and two vans from Toyota. The written results stated, "The Volkswagen Transporter type 2 affords excellent passenger safety". "The legs were not endangered. And the legroom was only slightly restricted." All doors opened easily. With regard to repair of the vehicles after the crash tests, the five Japanese vehicles were declared a "total loss" or "write-offs". Regarding the Vanagon, the report states "It would be possible to fully repair the VW type 2 at reasonable cost".


title: Volkswagen Type 2 (T3)

text: Crash tests were also conducted using US market vehicles by Californian firms Calspan and NTS on behalf of the NHTSA. Three full-frontal tests at speeds of 29.5-34.9mph (47.7-56.2kph) with a fixed barrier were conducted between 1980 and 1988. While all three tests showed minor passenger compartment intrusion, the resultant HIC for the driver of the Vanagon ranged between 1313 and 1905. The passenger dummy fared better receiving a HIC between 831 and 1060.


title: Volkswagen Type 2 (T3)

text: In a 47 mph (75 Km/H) crash between the front of a Volkswagen LT31 (structurally the same as a T3) and rear of a stationary full-size Chevrolet Impala, the rear of the Impala was completely destroyed with the rear trunk being pushed up to just behind the driver's seat. Yet, the VW remained "operational" (drivable) and "the doors could be opened relatively easily" And "the deformation of the interior was negligible", as declared by the testing agency.


title: Volkswagen Type 2 (T3)

text: In an "overturn" test of "a fully equipped VW (Type 2 T3) Westfalia customized camping vehicle" traveling 'sideways' at a speed of 31 mph (50 Km/h) on a specially designed 'sled' that 'launched' the vehicle causing two complete rollovers, the report found that "the roof remained fully intact and the doors remained closed". The report went on to say, "If passengers wear seatbelts, the danger of injury in this kind of accident is relatively low". In another rollover test, the T3 was rolled down a 32ft high (10 M) hill. This is equivalent to a 3-story building. This resulted in the van flipping over 4 1/2 times. It was reported, "the shape of the body and the roof remained intact."


title: Volkswagen Type 2 (T3)

text: These vans were made with a "forward deformation zone" consisting of four "side members" below and in front of the passenger compartment making a four-pronged forked frame with a "deformation element" which is mounted in front of this making it extremely effective at absorbing impact. The front cab has extensive protection by means of four vertical struts that connect an impact-absorbing box section cross-member. Additionally, there is another box framed horizontal strut on the inside of the vehicle that attaches to the door frames. And another yet goes through the sides of the doors to help protect passengers from lateral impact. The steering wheel has two energy-absorbing buckle points, with a detachable steering column that prevents the steering wheel from being pushed into the cabin. And the spare tire, which is mounted on the underside in the front of the vehicle, is also used to absorb shock.


title: Volkswagen Type 2 (T3)

text: The T3 has a large cult following, especially the Westfalia camper version, and many owners have had the VW engines replaced, due to their reputation of being underpowered and unreliable, particularly the Wasserboxer.Subaru EJ engines are one of the most popular engines to install for increased power, as the EJs flat-4 design is similar in size and configuration to the original VW pushrod engines. Other conversions have included Porsche 911 engines, VW Rabbit diesel engines, Golf/Jetta petrol engines and Ford Zetec engines. Five-cylinder Audi engines were used in South Africa on higher-trim vans after the Wasserboxer engine was discontinued in 1991, until the T3 was discontinued in 2002.


title: Intellivision

text: The Intellivision is a home video game console released by Mattel Electronics in 1979. The name is a portmanteau of "intelligent television". Development began in 1977, the same year as the launch of its main competitor, the Atari 2600. In 1984, Mattel sold its video game assets to a former Mattel Electronics executive and investors, eventually becoming INTV Corporation. Game development ran from 1978 to 1990 when the Intellivision was discontinued. From 1980 to 1983, more than 3 million consoles were sold.


title: Intellivision

text: In 2009, IGN ranked the Intellivision No. 14 of the greatest video game consoles of all time. It remained Mattel's only video game console until the HyperScan in 2006.


title: Intellivision

text: The Intellivision was developed at Mattel in Hawthorne, California along with the Mattel Electronics line of handheld electronic games. Mattel's Design and Development group began investigating a home video game system in 1977. It was to have rich graphics and long lasting gameplay to distinguish itself from its competitors. Mattel identified a new but expensive chipset from National Semiconductor and negotiated better pricing for a simpler design. Its consultant, APh Technological Consulting, suggested a General Instrument chipset, listed as the Gimini programmable set in the GI 1977 catalog. The GI chipset lacked reprogrammable graphics and Mattel worked with GI to implement changes. GI published an updated chipset in its 1978 catalog. After having chosen National in August 1977, Mattel waited for two months before ultimately choosing the proposed GI chipset in late 1977. A team at Mattel, headed by David Chandler, began engineering the hardware, including the hand controllers. In 1978, David Rolfe of APh developed the onboard executive control software named Exec, and with a group of Caltech summer student employees programmed the first games. Graphics were designed by a group of artists at Mattel led by Dave James.


title: Intellivision

text: The Intellivision was introduced at the 1979 Las Vegas CES in January as a modular home computer with the Master Component priced at and a soon-to-follow Keyboard Component also at . At Chicago CES in June, prices were revised to for each component. A shortage of key chips from manufacturer General Instrument resulted in a limited number of Intellivision Master Components produced that year. In Fall 1979, Sylvania marketed its own branded Intellivision at in its GTE stores at Philadelphia, Baltimore, and Washington, D.C. On December 3, Mattel delivered consoles to the Gottschalks department store chain headquartered in Fresno, California with a suggested list price of . The Intellivision was also listed in the nationally distributed JCPenney Christmas 1979 catalog along with seven cartridges. It was in stores nationwide by mid-1980 with the pack-in game "Las Vegas Poker & Blackjack", and a library of ten cartridges. Mattel Electronics became a subsidiary in 1981.


title: Intellivision

text: Though the Intellivision is not the first system to have challenged Warner Communications's Atari, it is the first to have posed a serious threat to the market leader. A series of advertisements starring George Plimpton use side-by-side game comparisons to demonstrate the superior graphics and sound of Intellivision over the Atari 2600. One slogan calls Intellivision "the closest thing to the real thing". One example compares golf games where the other console's games have a blip sound and cruder graphics, while the Intellivision features a realistic swing sound and striking of the ball, and a more 3D look. There is an advertisement comparing to the Atari 2600, with the slogan "I didn't know". In its first year, Mattel sold out its initial 175,000 production run of Intellivision Master Components. In 1981, more than one million Intellivision consoles were sold, five times as many as in 1980.


title: Intellivision

text: The Intellivision Master Component was branded and distributed by various companies. Before Mattel shifted manufacturing to Hong Kong, Mattel Intellivision consoles were manufactured by GTE Sylvania. "GTE Sylvania" Intellivision consoles were produced along with Mattel's, differing only by the brand name. The Sears Super Video Arcade, manufactured by Mattel in Hong Kong, has a restyled beige top cover and detachable controllers. Its default title screen lacks the "Mattel Electronics" captioning. In 1982, Radio Shack marketed the Tandyvision One, similar to the original console but with the gold plates replaced with more wood trim. In Japan, Intellivision consoles were branded by Bandai in 1982, and in Brazil there were Digimed and Digiplay consoles manufactured by Sharp in 1983.


title: Intellivision

text: Inside every Intellivision console is 4K of ROM containing the Exec software. It provides two benefits: reusable code that can effectively make a 4K cartridge an 8K game, and a software framework for new programmers to develop games more easily and quickly. It also allows other programmers to more easily review and continue another's project. Under the supervision of David Rolfe at APh, and with graphics from Mattel artist Dave James, APh was able to quickly create the Intellivision launch game library using mostly summer students. The drawback is that to be flexible and handle many different types of games, the Exec runs less efficiently than a dedicated program. Intellivision games that leverage the Exec run at a 20 Hz frame rate instead of the 60 Hz frame rate for which the Intellivision was designed. Using the Exec framework is optional, but almost all Intellivision games released by Mattel Electronics use it, and thus run at 20 Hz. The limited ROM space in the early years of Intellivision game releases also means there is no space for a computer player, so many early multiplayer games require two human players.


title: Intellivision

text: Initially, all Intellivision games were programmed by an outside firm, APh Technological Consulting, with 19 cartridges produced before Christmas 1980. Once the Intellivision project became successful, software development was brought in-house. Mattel formed its own software development group and began hiring programmers. The original five members of that Intellivision team were Mike Minkoff, Rick Levine, John Sohl, Don Daglow, and manager Gabriel Baum. Levine and Minkoff, a long-time Mattel Toys veteran, both transferred from the hand-held Mattel game engineering team. During 1981, Mattel hired programmers as fast as possible. Early in 1982 Mattel Electronics relocated from Mattel headquarters to an unused industrial building. Offices were renovated as new staff moved in. To keep these programmers from being hired away by rival Atari, their identities and work location was kept a closely guarded secret. In public, the programmers were referred to collectively as the Blue Sky Rangers.


title: Intellivision

text: Most of the early games are based on traditional real-world concepts such as sports, with an emphasis on realism and depth of play within the technology of the time. The Intellivision was not marketed as a toy; as such, games such as "Sea Battle" and "B-17 Bomber" are not made in the pick-up-and-play format like arcade games. Reading the instructions is often a prerequisite. Every cartridge produced by Mattel Electronics includes two plastic controller overlays to help navigate the 12-button keypad, although not every game uses it. Game series, or networks, are "Major League Sports", "Action", "Strategy", "Gaming", "Children's Learning", and later "Space Action" and "Arcade". The network concept was dropped in 1983, as was the convenient gate-fold style box for storing the cartridge, instructions, and overlays.


title: Intellivision

text: Starting in 1981 programmers looking for credit and royalties on sales began leaving both APh and Mattel Electronics to create Intellivision cartridges for third-party publishers. They helped form Imagic in 1981, and in 1982 others joined Activision and Atari. Cheshire Engineering was formed by a few senior APh programmers including David Rolfe, author of the Exec, and Tom Loughry, creator of one of the most popular Intellivision games "". Cheshire created Intellivision games for Activision. Third-party developers Activision, Imagic, and Coleco started producing Intellivision cartridges in 1982, and Atari, Parker Brothers, Sega, and Interphase followed in 1983. The third-party developers, not having legal access to Exec knowledge, often bypassed the Exec framework to create smooth 30 Hz and 60 Hz Intellivision games such as "The Dreadnaught Factor". Cheaper ROM prices also allowed for progressively larger games as 8K, 12K, and 16K cartridges became common. The first Mattel Electronics Intellivision game to run at 60 Hz is "Masters of the Universe" in 1983. Marketing dubbed the term "Super Graphics" on the game's packaging and marketing.


title: Intellivision

text: Mattel Electronics had a competitive advantage in its team of experienced and talented programmers. As competitors often depended on licensing well known trademarks to sell video games, Mattel focused on original ideas. Don Daglow was a key early programmer at Mattel and became director of Intellivision game development. Daglow created "Utopia", a precursor to the sim genre and, with Eddie Dombrower, the ground breaking sports simulation "World Series Major League Baseball". Daglow was also involved with the popular Intellivision games "Tron Deadly Discs" and "Shark! Shark!". After Mattel Electronics closed in 1984, its programmers continued to make significant contributions to the videogame industry. Don Daglow and Eddie Dombrower went on to Electronic Arts to create "Earl Weaver Baseball", and Don Daglow founded Stormfront Studios. Bill Fisher, Steve Roney, and Mike Breen founded Quicksilver Software, and David Warhol founded Realtime Associates.


title: Intellivision

text: The Intellivision was designed as a modular home computer, so from the beginning, its packaging, promotional materials, and television commercials, promised the addition of a forthcoming accessory called the Keyboard Component. The Master Component was packaged as a stand-alone video game system to which the Keyboard Component could be added, providing the computer keyboard and tape drive. Not meant to be a hobbyist or business computer, the Intellivision home computer was meant to run pre-programmed software and bring "data flow" (Videotex) into the home.


title: Intellivision

text: The Keyboard Component adds an 8-bit 6502 processor, making the Intellivision a dual-processor computer. It has 16K 10-bit shared RAM that can load and execute both Intellivision CP1610 and 6502 program code from tape, which is a large amount as typical contemporary cartridges are 4K. The cassettes have two tracks of digital data and two tracks of analog audio, completely controlled by the computer. Two tracks are read-only for the software, and two tracks are for user data. The tape drive is block addressed with high speed indexing. A high resolution 40x24 monochrome text display can overlay regular Intellivision graphics. There is a microphone port and two expansion ports for peripherals and RAM. The Microsoft BASIC programming cartridge uses one of these ports. Expanded memory cartridges support 1000 pages of each. A third pass-through cartridge port is for regular Intellivision cartridges. It uses the Intellivision's power supply. A 40-column thermal printer was available, and a telephone modem was planned along with voice synthesis and voice recognition.


title: Intellivision

text: David Rolfe of APh wrote a control program for the Keyboard Component called PicSe (Picture Sequencer) specifically for the development of multimedia applications. PicSe synchronizes the graphics and analog audio while concurrently saving or loading tape data. Productivity software for home finances, personal improvement, and self education were planned. Subject experts were consulted and their voices recorded and used in the software.


title: Intellivision

text: Three applications using the PicSe system were released on cassette tape: "Conversational French", "Jack Lalanne's Physical Conditioning", and "Spelling Challenge".


title: Intellivision

text: Programs written in BASIC do not have access to Intellivision graphics and were sold at a lower price. Five BASIC applications were released on tape: "Family Budgeting", "Geography Challenge", and "Crosswords I, II, and III".


title: Intellivision

text: The Keyboard Component was an ambitious piece of engineering for its time, and it was repeatedly delayed as engineers tried to reduce manufacturing costs. In August 1979, a breadboard form of the Component was successfully entered into the Sears Market Research Program. In December 1979, Mattel had production design working units but decided on a significant internal design change to consolidate circuit boards. In September 1980, it was test marketed in Fresno, California but without software, except for the BASIC programming cartridge. In the late 1981, design changes were finally implemented and the Keyboard Component was released at in Seattle and New Orleans only. Customers who complained in writing could buy a Keyboard Component directly from Mattel. The printer, a rebadged Alphacom Sprinter 40, was only available by mail order.


title: Intellivision

text: The keyboard component's repeated delays became so notorious around Mattel headquarters that comedian Jay Leno, when performing at Mattel's 1981 Christmas party, got his biggest response of the evening with the line: "You know what the three big lies are, don't you? 'The check is in the mail', 'I'll still respect you in the morning', and 'The keyboard will be out in spring.'"


title: Intellivision

text: Complaints from consumers who had chosen to buy the Intellivision specifically on the promise of a "coming soon" personal-computer upgrade, eventually caught the attention of the Federal Trade Commission (FTC), who started investigating Mattel Electronics for fraud and false advertising. In mid-1982, the FTC ordered Mattel to pay a monthly fine (said to be ) until the promised computer upgrade was in full retail distribution. To end the ongoing fines, the Keyboard Component was officially canceled in August 1982 and the Entertainment Computer System (ECS) module offered in its place. Part of Mattel's settlement with the FTC involved offering to buy back all of the existing Keyboard Components from customers. Mattel provided a full refund, but customers without a receipt received for the Keyboard Component, for the BASIC cartridge, and for each cassette software. Any customer who opted to keep the products was required to sign a waiver with the understanding that no more software would be written for the system and absolving Mattel of any future responsibility for technical support. They were also compensated with worth of Mattel Electronics products.


title: Intellivision

text: Though approximately 4,000 Keyboard Components were manufactured, it is not clear how many of them were sold and they are rare. Many of the units were dismantled for parts. Others were used by Mattel Electronics programmers as part of their development system. A Keyboard Component could be interfaced with an Intellivision development system in place of the hand-built Magus board RAM cartridge. Data transfer to the Keyboard Component RAM is done serially and is slower than the Magus board parallel interface.


title: Intellivision

text: In mid-1981, Mattel's upper management was becoming concerned that the keyboard component division would never be able to produce a sellable product. As a result, Mattel Electronics set up a competing internal engineering team whose stated mission was to produce an inexpensive add-on called the "Basic Development System", or BDS, to be sold as an educational device to introduce kids to the concepts of computer programming.


title: Intellivision

text: The rival BDS engineering group, who had to keep the project's real purpose a secret among themselves, fearing that if David Chandler, the head of the keyboard component team, found out about it he would use his influence to end the project, eventually came up with a much less expensive alternative. Originally dubbed the "Lucky", from LUCKI: Low User-Cost Keyboard Interface, it lacked many of the sophisticated features envisioned for the original keyboard component. Gone, for example, was the 16K (8MB max) of RAM, the secondary CPU, and high resolution text; instead, the ECS offered a mere 2KB RAM expansion, a built-in BASIC that was marginally functional, plus a much-simplified cassette and printer interface.


title: Intellivision

text: Ultimately, this fulfilled the original promises of turning the Intellivision into a computer, making it possible to write programs and store them to tape, and interfacing with a printer well enough to allow Mattel to claim that they had delivered the promised computer upgrade and stop the FTC's mounting fines. It even offered, via an additional sound chip (AY-3-8917) inside the ECS module and an optional 49-key music synthesizer keyboard, the possibility of turning the Intellivision into a multi-voice synthesizer which could be used to play or learn music.


title: Intellivision

text: In the fall of 1982, the LUCKI, now renamed the Entertainment Computer System (ECS), was presented at the annual sales meeting, officially ending the ill-fated keyboard component project. A new advertising campaign was aired in time for the 1982 Christmas season, and the ECS itself was shown to the public at the January 1983 Consumer Electronics Show (CES) in Las Vegas. A few months later, the ECS hit the market, and the FTC agreed to drop the $10K per month fines.


title: Intellivision

text: By the time the ECS made its retail debut as the Intellivision Computer Module, an internal shake-up at the top levels of Mattel Electronics' management had caused the company's focus to shift away from hardware add-ons in favor of software, and the ECS received very little in terms of furthering the marketing push. Further hardware developments, including a planned Program Expander that would have added another 16K of RAM and a more intricate, fully featured Extended-BASIC to the system, were halted. In the end, six games were released for the ECS; a few more were completed but not released.


title: Intellivision

text: The ECS also offered four player game-play with the optional addition of two extra hand controllers. Four player games were in development when Mattel Electronics closed in 1984. "World Cup Soccer" was later completed and released in 1985 by Dextel in Europe and then INTV Corporation in North America. The documentation does not mention it but when the ECS Computer Adapter is used, "World Cup Soccer" can be played with one to four players, or two players cooperatively against the computer.


title: Intellivision

text: In 1982 Mattel introduced the Intellivoice Voice Synthesis Module, a speech synthesizer for compatible cartridges. The Intellivoice is novel in two respects: human sounding male and female voices with distinct accents, and the speech-supporting games were designed with speech being an integral part of the game-play.


title: Intellivision

text: Like the Intellivision chipset, the Intellivoice chipset was developed by General Instrument. The SP0256-012 orator chip has 2KB ROM inside, and is used to store the speech for numerical digits, some common words, and the phrase "Mattel Electronics presents". Speech can also be processed from the Intellivoice's SP650 buffer chip, stored and loaded from cartridge memory. That buffer chip has its own I/O and the Intellivoice has a 30-pin expansion port under a removable top plate. Mattel Electronics planned to use that connector for wireless hand controllers.


title: Intellivision

text: Mattel Electronics built a state of the art voice processing lab to produce the phrases used in Intellivoice games. However, the amount of speech that could be compressed into an 8K or 12K cartridge and still leave room for a game was limited. Intellivoice cartridges "Space Spartans" and "B-17 Bomber" did sell about 300,000 copies each, priced a few dollars more than regular Intellivision cartridges. However, at $79 the Intellivoice did not sell as well as Mattel expected, and Intellivoices were later offered free with the purchase of a Master Component. In August 1983 the Intellivoice system was quietly phased out. A children's title called "Magic Carousel", and foreign language versions of "Space Spartans" were completed but shelved. Additional games "Woody Woodpecker" and "Space Shuttle" went unfinished with the voice recordings unused.


title: Intellivision

text: A fifth game, "Intellivision World Series Major League Baseball", developed as part of the Entertainment Computer System series, also supports the Intellivoice if both the ECS and Intellivoice are connected concurrently. Unlike the Intellivoice-specific games, however, "World Series Major League Baseball" is also playable without the Intellivoice module (but not without the ECS).


title: Intellivision

text: In the spring of 1983, Mattel introduced the "Intellivision II", a cheaper, more compact redesign of the original, that was designed to be less expensive to manufacture and service, with updated styling. It also had longer controller cords. The Intellivision II was initially released without a pack-in game but was later packaged with BurgerTime in the United States and Lock'N'Chase in Canada. In 1984 the Digiplay Intellivision II was introduced in Brazil. Brazil was the only country outside North America to have the redesigned Intellivision II.


title: Intellivision

text: Using an external AC Adapter (16.2VAC), consolidating some ICs, and taking advantage of relaxed FCC emission standards, the Intellivision II has a significantly smaller footprint than the original. The controllers, now detachable, have a different feel, with plastic rather than rubber side buttons and a flat membrane keypad. Users of the original Intellivision missed the ability to find keypad buttons by the tactile feel of the original controller bubble keypad.


title: Intellivision

text: One functional difference was the addition of a video input to the cartridge port, added specifically to support the System Changer, an accessory also released in 1983 by Mattel that played Atari 2600 cartridges through the Intellivision. The Intellivision hand controllers could be used to play Atari 2600 games. The System Changer also had two controller ports compatible with Atari joysticks. The original Intellivision required a hardware modification, a service provided by Mattel, to work with the "System Changer". Otherwise the Intellivision II was promoted to be compatible with the original.


title: Intellivision

text: It was discovered that a few Coleco Intellivision games did not work on the Intellivision II. Mattel secretly changed the Exec internal ROM program in an attempt to lock out third party games. A few of Coleco's early games were affected but the 3rd party developers quickly figured out how to get around it. Mattel's own "Electric Company Word Fun", however, will not run on the Intellivision II due to this change. In an unrelated issue but also due to Exec changes, Super Pro Football experiences a minor glitch where the quarterback does not appear until after the ball is hiked. There were also some minor changes to the sound chip (AY-3-8914A/AY-3-8916) affecting sound effects in some games. Programmers at Mattel discovered the audio differences and avoided the problem in future games.


title: Intellivision

text: As early as 1981 Dave Chandler's group began designing what would have been Mattel's next generation console, codenamed "Decade" and now referred to as the "Intellivision IV". It would have been based on the 32-bit MC68000 processor and a 16-bit custom designed advanced graphic interface chip. Specifications called for dual display support, 240x192 bitmap resolution, 16 programmable 12-bit colors (4096 colors), antialiasing, 40x24 tiled graphics modes, four colors per tile (16 with shading), text layer and independent scrolling, 16 multicolored 16x16 sprites per scan-line, 32 level hardware sprite scaling. Line interrupts for reprogramming sprite and color registers would allow for many more sprites and colors on screen at the same time. It was intended as a machine that could lead Mattel Electronics into the 1990s, however on August 4, 1983, most hardware people at Mattel Electronics were laid off.


title: Intellivision

text: In 1982, with new machines introduced by competitors, Mattel marketing wanted to bring an upgraded system to market sooner. The "Intellivision III" was to be an upgraded but backward-compatible system, based on a similar CP1610 processor and with an improved graphics STIC chip producing double the resolution with more sprites and colors. The Intellivision III never proceeded past the prototype stage; a new EXEC was written for it, but no games. It was cancelled in mid-1983. A Mattel document titled "Target Specification Intellivision III" has the following.


title: Intellivision

text: According to the company's 1982 Form 10-K, Mattel had almost 20% of the domestic video-game market. Mattel Electronics provided 25% of revenue and 50% of operating income in fiscal 1982. Although the Atari 2600 had more third-party development, "Creative Computing Video & Arcade Games" reported after visiting the summer 1982 Consumer Electronics Show that "the momentum is tremendous". Activision and Imagic began releasing games for the Intellivision, as did hardware rival Coleco. Mattel created "M Network" branded games for Atari's system. The company's advertisement budget increased to over for the year. In its October 1982 stockholders' report Mattel announced that "Electronics" had, so far that year, posted a nearly profit on nearly sales; a threefold increase over October 1981.


title: Intellivision

text: However, the same report predicted a loss for the upcoming quarter. Hiring still continued, as did the company's optimism that the investment in software and hardware development would pay off. The "M Network" brand expanded to personal computers. An office in Taiwan was opened to handle Apple II programming. The original five-person Mattel game development team had grown to 110 people under new vice president Baum, while Daglow led Intellivision development and top engineer Minkoff directed all work on all other platforms. In February 1983, Mattel Electronics opened an office in the south of France to provide European input to Intellivision games and develop games for the ColecoVision. At its peak Mattel Electronics employed 1800 people.


title: Intellivision

text: Amid the flurry of new hardware and software development, there was trouble for the Intellivision. New game systems (ColecoVision and Atari 5200) introduced in 1982 took advantage of falling RAM prices to offer graphics closer to arcade quality. In 1983, the price of home computers, particularly the Commodore 64, came down drastically to compete with video game system sales. The market became flooded with hardware and software, and retailers were ill-equipped to cope. In spring 1983, hiring at Mattel Electronics came to a halt.


title: Intellivision

text: At the June 1983 Consumer Electronics Show in Chicago, Mattel Electronics had the opportunity to show off all their new products. The response was underwhelming. Several people in top management positions were replaced due to massive losses. On July 12, 1983, Mattel Electronics President Josh Denham was replaced with outsider Mack Morris. Morris brought in former Mattel Electronics president and marketing director Jeff Rochlis as a consultant and all projects were under review. The Intellivision III was cancelled and then all new hardware development was stopped when 660 jobs were cut on August 4. The price of the Intellivision II (which launched at earlier that year) was lowered to , and Mattel Electronics was to be a software company. However, by October 1983, Electronics' losses were over for the year and one third of the programming staff were laid off. Another third were gone by November, and on January 20, 1984 the remaining programming staff were laid-off. The Taiwan and French offices continued a little while longer due to contract and legal obligations. On February 4, 1984, Mattel sold the Intellivision business for . In 1983, 750,000 Intellivision Master Components were sold, more than three million units from 1980 to 1983.


title: Intellivision

text: Former Mattel Electronics Senior Vice President of Marketing, Terrence Valeski, understood that although losses were huge, the demand for video games increased in 1983. Valeski found investors and purchased the rights to Intellivision, the games, and inventory from Mattel. A new company, Intellivision Inc, was formed and by the end of 1984 Valeski bought out the other investors and changed the name to INTV Corporation. They continued to supply the large toy stores and sold games through direct mail order. At first they sold the existing inventory of games and Intellivision II systems. When the inventory of games sold out they produced more, but without the Mattel name or unnecessary licenses on the printed materials. To lower costs, the boxes, instructions, and overlays were produced at lower quality compared to Mattel.


title: Intellivision

text: In France, the Mattel Electronics office found investors and became Nice Ideas in April 1984. They continued to work on Intellivision, Colecovision, and other computer games. They produced Intellivision "World Cup Soccer" and "Championship Tennis", both released in 1985 by European publisher Dextel.


title: Intellivision

text: In 1985, INTV Corporation introduced the "INTV System III", also branded as the "Intellivision Super Pro System", using the same design as the original Intellivision model but in black and silver. That same year INTV Corp introduced two new games that were completed at Mattel but not released: "Thunder Castle" and "World Championship Baseball". With their early success INTV Corp decided to produce new games and in 1986 introduced "Super Pro Football", an update of Mattel "NFL Football". INTV Corp continued a relationship that Mattel had with Data East and produced all new cartridges such as "Commando" in 1987 and "Body Slam Wrestling" in 1988. Also in 1987, INTV Corp released "Dig Dug", purchased from Atari where the game was completed but not released in 1984. They also got into producing next generation games with the production of "Monster Truck Rally" for Nintendo Entertainment System (NES) in 1991, also released as "Stadium Mud Buggies" for Intellivision in 1989.


title: Intellivision

text: Licensing agreements with Nintendo and Sega required INTV Corporation to discontinue the Intellivision in 1990. INTV Corporation did publish 21 new Intellivision cartridges bringing the Intellivision library to a total of 124 cartridges plus one compilation cartridge.


title: Intellivision

text: In 1989, INTV Corp and World Book Encyclopedia entered into an agreement to manufacture an educational video game system called Tutorvision. It is a modified Intellivision, the case molded in light beige with gold and blue trim. The Exec ROM expanded, system RAM increased to 1.75K, and graphics RAM increased to 2KB. That is enough graphics RAM to define unique graphic tiles for the entire screen.


title: Intellivision

text: Games were designed by World Book, "J. Hakansson Associates", and programmed by Realtime Associates. Sixteen games were in production, plus one Canadian variation. However, the cartridges and the Tutorvision were never released; instead World Book and INTV Corporation sued each other. In 1990, INTV Corporation filed for bankruptcy protection and closed in 1991.


title: Intellivision

text: An unknown number of later Intellivision SuperPro systems have Tutorvision hardware inside. A subset of these units contain the full Tutorvision EXEC and can play Tutorvision games.


title: Intellivision

text: Intellivision games became readily available again when Keith Robinson and Stephen Roney, both former Intellivision programmers at Mattel Electronics, obtained exclusive rights to the Intellivision and games in 1997. That year they formed a new company, Intellivision Productions, and made "Intellivision for PC Volume 1" available as a free download. Intellivision games could be played on a modern computer for the first time. That download includes three Intellivision games and an MS-DOS Intellivision emulator that plays original game code. It was followed by "Volume 2" and another three games including "Deep Pockets Super Pro Pool & Billiards"; a game completed in 1990 but never released until this download in 1997. In 2000 the "Intellipack 3" download was available with another four Intellivision games and emulators for Windows or Macintosh.


title: Intellivision

text: Intellivision Productions released "Intellivision Lives!" and "Intellivision Rocks" on compact disc in 1998 and 2001. These compilation CDs play the original game code through emulators for MS-DOS, Windows, and Macintosh computers. Together they have over 100 Intellivision games including never before released "King of the Mountain, Takeover, Robot Rubble", "League of Light", and others. Intellivision Rocks includes Intellivision games made by Activision and Imagic. Some games could not be included due to licensing, others simply used different titles to avoid trademarked names. The CDs are also a resource for development history, box art, hidden features, programmer biographies, video interviews, and original commercials.


title: Intellivision

text: Also in 1997 Intellivision Productions announced they would sell development tools allowing customers to program their own Intellivision games. They were to provide documentation, PC compatible cross-assemblers, and the "Magus II" PC Intellivision cartridge interface. Unfortunately, the project was cancelled but they did provide copies of "Your Friend the EXEC", the programmers guide to the Intellivision Executive control software. By 2000 Intellivision hobbyists ultimately created their own development tools, including Intellivision memory cartridges.


title: Intellivision

text: In 2005 Intellivision Productions announced that new Intellivision cartridges were to be produced. "Deep Pockets and Illusions will be the first two releases in a series of new cartridges for the Intellivision. The printed circuit boards, the cartridge casings, the boxes are all being custom manufactured for this special series." "Illusions" was completed at Mattel Electronics' French office in 1983 but never released. "Deep Pockets Super Pro Pool & Billiards" was programmed for INTV Corporation in 1990 and only released as a ROM file in 1998. However, no cartridges were produced. Previously, in 2000, Intellivision Productions did release new cartridges for the Atari 2600 and Colecovision. "Sea Battle" and "Swordfight" were Atari 2600 games created by Mattel Electronics in the early 1980s but not previously released. "Steamroller" (Colecovision) was developed for Activision in 1984 and not previously released.


title: Intellivision

text: Also in 1999, Activision released "A Collection of Intellivision Classic Games" for PlayStation. Also known as "Intellivision Classics", it has 30 emulated Intellivision games as well as video interviews of some of the original programmers. All of the games were licensed from Intellivision Productions and none of the Activision or Imagic Intellivision games were included. In 2003, Crave Entertainment released a PlayStation 2 version of Intellivision Lives! and then Xbox and GameCube version in 2004. In 2010, Virtual Play Games released Intellivision Lives! for the Nintendo DS including one never before released game, "Blow Out". In 2008 Microsoft made Intellivision Lives! an available download on the Xbox Live Marketplace as an Xbox Original and playable on the Xbox 360.


title: Intellivision

text: In 2003, the Intellivision 25 and Intellivision 15 direct-to-TV systems were released by Techno Source Ltd. These are an all-in-one single controller design that plugs directly into a television. One includes 25 games the other ten. These Intellivision games were not emulated but rewritten for the native processor (NES-based hardware) and adapted to a contemporary controller. As such they look and play differently than Intellivision. In 2005 they were updated for two-player play as the Intellivision X2 with 15 games. They were commercially very successful altogether selling about 4 million units by end of 2006.


title: Intellivision

text: Several licensed Intellivision games became available to Windows computers through the GameTap subscription gaming service in 2005 including "Astrosmash, Buzz Bombers, Hover Force, Night Stalker, Pinball, Shark! Shark!, Skiing and Snafu". Installation of the GameTap Player software was required to access the emulator and games. The VH1 Online Arcade made nine Intellivision games available in 2007. Using a Shockwave emulator these Intellivision games could be played directly through a web browser with Shockwave Player. In 2010, VH1 Classic and MTV Networks released 6 Intellivision games to iOS. Intellivision games were first adapted to mobile phones and published by THQ Wireless in 2001. On March 24, 2010, Microsoft launched the Game Room service for Xbox Live and Games for Windows Live. This service includes support for Intellivision games and allows players to compete for high scores via online leaderboards. At the 2011 Consumer Electronics Show, Microsoft announced a version of Game Room for Windows Phone, promising a catalog of 44 Intellivision games. AtGames and its Direct2Drive digital store has Windows compatible Intellivision compilations available for download purchase.


title: Intellivision

text: The number of Intellivision games that can be played effectively with contemporary game controllers is limited. On October 1, 2014, AtGames Digital Media, Inc., under license from Intellivision Productions, Inc., released the Intellivision Flashback classic game console. It is a miniature sized Intellivision console with two original sized Intellivision controllers. While adapters have been available to interface original Intellivision controllers to personal computers, the Intellivision Flashback includes two new Intellivision controllers identical in layout and function to the originals. It comes with 60 (61 at Dollar General) emulated Intellivision games built into ROM and a sample set of plastic overlays for 10 games. The Advanced Dungeons & Dragons games were included as "Crown of Kings" and "Minotaur". As with many of the other Intellivision compilations, no games requiring third party licensing were included.


title: Intellivision

text: In May 2018, Tommy Tallarico announced that he acquired the rights to the Intellivision brand and games with plans to launch a new home video game console. A new company, "Intellivision Entertainment", was formed with Tallarico serving as president. "Intellivision Productions" has been renamed "Blue Sky Rangers Inc." and their video game intellectual property has been transferred to "Intellivision Entertainment". At the Portland Retro Gaming Expo, in October 2018, the Intellivision Amico was officially revealed.


title: Intellivision

text: Ken Uston published "Ken Uston's Guide to Buying and Beating the Home Video Games" in 1982 as a guide to potential buyers of console systems/cartridges, as well as a brief strategy guide to numerous cartridge games then in existence. He described Intellivision as "the most mechanically reliable of the systems… The controller (used during "many hours of experimentation") worked with perfect consistency. The unit never had overheating problems, nor were loose wires or other connections encountered." However, Uston rated the controls and control system as "below average" and the worst of the consoles he tested (including Atari 2600, Magnavox Odyssey², Astrovision, and Fairchild Channel F).


title: Intellivision

text: Jeff Rovin lists "Intellivision" as one of the seven major suppliers of videogames in 1982, and mentions it as "the unchallenged king of graphics", however stating that the controllers can be "difficult to operate", the fact that if a controller breaks the entire unit must be shipped off for repairs (since they did not detach at first), and that the overlays "are sometimes so stubborn as to tempt one's patience" .


title: Intellivision

text: A 1996 article in "Next Generation" said the Intellivision "had greater graphics power than the dominant Atari 2600. It was slower than the 2600 and had less software available, but it was known for its superior sports titles." A year later, "Electronic Gaming Monthly" assessed the Intellivision in an overview of older gaming consoles, remarking that the controllers "were as comfortable as they were practical. The unique disk-shaped directional pad provided unprecedented control for the time, and the numeric keypad opened up new options previously unavailable in console gaming." They praised the breadth of the software library but said there was a lack of genuinely stand-out games.


title: Intellivision

text: "Intellivision, Super Video Arcade, Tandyvision One, Intellivision II, INTV System III, Super Pro System"


title: Intellivision

text: The directional pad was called a "control disc" and marketed as having the "functionality of both a joystick and a paddle". The controller was ranked the fourth worst video game controller by IGN editor Craig Harris.


title: Gravitational lens

text: A gravitational lens is a distribution of matter (such as a cluster of galaxies) between a distant light source and an observer that is capable of bending the light from the source as the light travels toward the observer. This effect is known as gravitational lensing, and the amount of bending is one of the predictions of Albert Einstein's general theory of relativity. Treating light as corpuscles travelling at the speed of light, Newtonian physics also predicts the bending of light, but only half of that predicted by general relativity.


title: Gravitational lens

text: Although Einstein made unpublished calculations on the subject in 1912, Orest Khvolson (1924) and Frantisek Link (1936) are generally credited with being the first to discuss the effect in print. However, this effect is more commonly associated with Einstein, who published an article on the subject in 1936.


title: Gravitational lens

text: Fritz Zwicky posited in 1937 that the effect could allow galaxy clusters to act as gravitational lenses. It was not until 1979 that this effect was confirmed by observation of the Twin QSO SBS 0957+561.


title: Gravitational lens

text: Unlike an optical lens, a point-like gravitational lens produces a maximum deflection of light that passes closest to its center, and a minimum deflection of light that travels furthest from its center. Consequently, a gravitational lens has no single focal point, but a focal line. The term "lens" in the context of gravitational light deflection was first used by O.J. Lodge, who remarked that it is "not permissible to say that the solar gravitational field acts like a lens, for it has no focal length". If the (light) source, the massive lensing object, and the observer lie in a straight line, the original light source will appear as a ring around the massive lensing object (provided the lens has circular symmetry). If there is any misalignment, the observer will see an arc segment instead.


title: Gravitational lens

text: This phenomenon was first mentioned in 1924 by the St. Petersburg physicist Orest Khvolson, and quantified by Albert Einstein in 1936. It is usually referred to in the literature as an Einstein ring, since Khvolson did not concern himself with the flux or radius of the ring image. More commonly, where the lensing mass is complex (such as a galaxy group or cluster) and does not cause a spherical distortion of spacetime, the source will resemble partial arcs scattered around the lens. The observer may then see multiple distorted images of the same source; the number and shape of these depending upon the relative positions of the source, lens, and observer, and the shape of the gravitational well of the lensing object.


title: Gravitational lens

text: Gravitational lenses act equally on all kinds of electromagnetic radiation, not just visible light, and also in non-electromagnetic radiation, like gravitational waves. Weak lensing effects are being studied for the cosmic microwave background as well as galaxy surveys. Strong lenses have been observed in radio and x-ray regimes as well. If a strong lens produces multiple images, there will be a relative time delay between two paths: that is, in one image the lensed object will be observed before the other image.


title: Gravitational lens

text: Henry Cavendish in 1784 (in an unpublished manuscript) and Johann Georg von Soldner in 1801 (published in 1804) had pointed out that Newtonian gravity predicts that starlight will bend around a massive object as had already been supposed by Isaac Newton in 1704 in his "Queries" No.1 in his book "Opticks". The same value as Soldner's was calculated by Einstein in 1911 based on the equivalence principle alone. However, Einstein noted in 1915, in the process of completing general relativity, that his (and thus Soldner's) 1911-result is only half of the correct value. Einstein became the first to calculate the correct value for light bending.


title: Gravitational lens

text: The first observation of light deflection was performed by noting the change in position of stars as they passed near the Sun on the celestial sphere. The observations were performed in 1919 by Arthur Eddington, Frank Watson Dyson, and their collaborators during the total solar eclipse on May 29. The solar eclipse allowed the stars near the Sun to be observed. Observations were made simultaneously in the cities of Sobral, Ceará, Brazil and in São Tomé and Príncipe on the west coast of Africa. The observations demonstrated that the light from stars passing close to the Sun was slightly bent, so that stars appeared slightly out of position.


title: Gravitational lens

text: The result was considered spectacular news and made the front page of most major newspapers. It made Einstein and his theory of general relativity world-famous. When asked by his assistant what his reaction would have been if general relativity had not been confirmed by Eddington and Dyson in 1919, Einstein said "Then I would feel sorry for the dear Lord. The theory is correct anyway." In 1912, Einstein had speculated that an observer could see multiple images of a single light source, if the light were deflected around a mass. This effect would make the mass act as a kind of gravitational lens. However, as he only considered the effect of deflection around a single star, he seemed to conclude that the phenomenon was unlikely to be observed for the foreseeable future since the necessary alignments between stars and observer would be highly improbable. Several other physicists speculated about gravitational lensing as well, but all reached the same conclusion that it would be nearly impossible to observe.


title: Gravitational lens

text: Although Einstein made unpublished calculations on the subject, the first discussion of the gravitational lens in print was by Khvolson, in a short article discussing the "halo effect" of gravitation when the source, lens, and observer are in near-perfect alignment, now referred to as the Einstein ring.


title: Gravitational lens

text: In 1936, after some urging by Rudi W. Mandl, Einstein reluctantly published the short article "Lens-Like Action of a Star By the Deviation of Light In the Gravitational Field" in the journal "Science".


title: Gravitational lens

text: In 1937, Fritz Zwicky first considered the case where the newly discovered galaxies (which were called 'nebulae' at the time) could act as both source and lens, and that, because of the mass and sizes involved, the effect was much more likely to be observed.


title: Gravitational lens

text: In 1963 Yu. G. Klimov, S. Liebes, and Sjur Refsdal recognized independently that quasars are an ideal light source for the gravitational lens effect.


title: Gravitational lens

text: It was not until 1979 that the first gravitational lens would be discovered. It became known as the "Twin QSO" since it initially looked like two identical quasistellar objects. (It is officially named SBS 0957+561.) This gravitational lens was discovered by Dennis Walsh, Bob Carswell, and Ray Weymann using the Kitt Peak National Observatory 2.1 meter telescope.


title: Gravitational lens

text: In the 1980s, astronomers realized that the combination of CCD imagers and computers would allow the brightness of millions of stars to be measured each night. In a dense field, such as the galactic center or the Magellanic clouds, many microlensing events per year could potentially be found. This led to efforts such as Optical Gravitational Lensing Experiment, or OGLE, that have characterized hundreds of such events, including those of OGLE-2016-BLG-1190Lb and OGLE-2016-BLG-1195Lb.


title: Gravitational lens

text: In general relativity, light follows the curvature of spacetime, hence when light passes around a massive object, it is bent. This means that the light from an object on the other side will be bent towards an observer's eye, just like an ordinary lens. In general relativity the speed of light depends on the gravitational potential (i.e. the metric) and this bending can be viewed as a consequence of the light traveling along a gradient in light speed. Light rays are the boundary between the future, the spacelike, and the past regions. The gravitational attraction can be viewed as the motion of undisturbed objects in a background curved "geometry" or alternatively as the response of objects to a "force" in a flat geometry. The angle of deflection is:


title: Gravitational lens

text: toward the mass "M" at a distance "r" from the affected radiation, where "G" is the universal constant of gravitation and "c" is the speed of light in a vacuum.


title: Gravitational lens

text: Since the Schwarzschild radius formula_2 is defined as formula_3 and escape velocity formula_4 is defined as formula_5, this can also be expressed in simple form as