# The Quantum to Classical Transition Information physics claims there is only one world, the quantum world, and that the _appearance_ of a "quantum to classical transition" occurs for any large macroscopic object that contains a large number of atoms. For large enough systems, independent quantum events are "averaged over." The uncertainty in position and momentum of the object (_Δv Δx > h / m_) becomes less than observational accuracy as _m_ gets large and _h / m_ goes to zero. Note that macroscopic objects are quantum objects. But the uncertainty in their position and momentum is not detectable by our measuring instruments. The classical laws of motion appear to apply perfectly to macroscopic objects, because quantum effects can be neglected. Bohr called the discontinuous (and indeterministic) "quantum jumps" in his model for the atom the "quantum postulate." [Niels Bohr](https://www.informationphilosopher.com/solutions/scientists/bohr/) correctly insisted that classical physics plays an essential role in quantum mechanics. His Correspondence Principle allowed him to recover some important physical constants by assuming that the discontinuous quantum jumps for low quantum numbers (low "orbits" in his old quantum theory model) _converged_ in the limit of large quantum numbers to the continuous radiation emission and absorption of classical electromagnetic theory. We know that in macroscopic bodies with enormous numbers of quantum particles, quantum effects are averaged over. So that although the uncertainty in position and momentum of a large body still obeys Heisenberg's [indeterminacy principle](https://www.informationphilosopher.com/freedom/indeterminacy.html), the uncertainty is for all practical purposes unmeasurable and the body can be treated classically. We can say that the quantum description of matter also _converges_ to a classical description in the limit of large numbers of quantum particles. We call this ["adequate" or _statistical_ determinism](https://www.informationphilosopher.com/freedom/adequate_determinism.html). It is the apparent determinism we find behind Newton's laws of motion for macroscopic objects. The statistics of averaging over many independent quantum events then produces the "quantum to classical transition" for the same reason as the "law of large numbers" results in the "central limit theorem" in probability theory. Both Bohr and Heisenberg suggested that just as relativistic effects can be ignored when the velocity is small compared to the velocity of light (_v / c_ → 0), so quantum effects might be ignorable when Planck's quantum of action _h_ → 0. But this is quite wrong, because _h_ is a constant that never goes to zero. In the information interpretation, it is always a quantum world. The correct conditions needed for ignoring quantum indeterminacy are when the _mass_ of the macroscopic "classical" object is large. Noting that the momentum _p_ is the product of mass and velocity _mv_, Heisenberg's [indeterminacy](https://www.informationphilosopher.com/freedom/indeterminacy.html) principle, _Δp Δx > h_, can be rewritten as _Δv Δx > h / m_. It is thus not when _h_ is small, but when _h / m_ is small enough, that errors in the position and momentum of macroscopic objects become smaller that can be measured. The quantum to classical transition is then when _h / m_ becomes small. A similar limit can be seen by analogy with optics. When the wavelength of light is large compared to the dimensions of the system, wave optics must be used and diffraction effects become important. On the other hand, when the wavelength of light is small compared to the apertures in the optical system, geometrical optics is applicable (ray tracing). Similarly, classical mechanics is applicable when the de Broglie wavelength _λ = h / p_ is small compared to the dimensions of the experimental measurement apparatus. Once again, the quantum to classical transition is when _h / p_ = _h / mv_ becomes small. Note that the macromolecules of biology are large enough to stabilize their information structures. DNA has been replicating its essential information for billions of years, resisting equilibrium and keeping its entropy very low despite the second law of thermodynamics The [creation](https://www.informationphilosopher.com/introduction/creation/) of [irreversible](https://www.informationphilosopher.com/problems/reversibility/) new information also marks the transition between the quantum world and the "[adequately deterministic](https://www.informationphilosopher.com/freedom/adequate_determinism.html)" classical world, because the information structure itself must be large enough (and stable enough) to be seen. The typical measurement apparatus is macroscopic, so the quantum of action _h_ becomes small compared to the mass _m_ and _h / m_ approaches zero. ## Decoherence Theory and the Quantum to Classical Transition Decoherence theorists say that the quantum-to-classical transition occurs because of interactions with the environment, for example ever-present thermal photons. The cosmic microwave background is a constant source of low-energy photons. Without specifying the mechanics of the interaction between the photons and the quantum system being described, the decoherence theorists say that the photons cause the "selection" of preferred pointer positions, for example, the eigenvalues of the combined target quantum system and the measurement apparatus. They call this "einselection," a word coined from "environmentally induced superselection." Decoherence theorists say einselection explains the appearance of wave function collapse (they deny actual collapses) and the emergence of classical descriptions of reality from quantum descriptions. Information physics agrees that classicality is an emergent property, but it is not induced in open quantum systems by their environments. Macroscopic quantum objects, with _h / m_ so small that the uncertainty _Δp Δx > h_ is undetectable, appear classical in both open and closed environments. Unlike information physics, which identifies exactly how radiation interactions with matter (the emission, absorption, and scattering of photons) erase path information about correlations between the molecules of a gas, thus proving Boltzmann's H-Theorem and his assumption of "molecular chaos," decoherence arguments about environmental photons are merely "hand waving." Decoherence theorists also say that our failure to see quantum superpositions in the macroscopic world _is_ the [measurement problem](https://www.informationphilosopher.com/problems/measurement/). The [information interpretation](https://www.informationphilosopher.com/introduction/physics/interpretation/) of quantum mechanics explains clearly why quantum superpositions like [Schrödinger's Cat](https://www.informationphilosopher.com/solutions/experiments/schrodingerscat) are not seen in the macroscopic world. Stable new information structures in the dying cat reduce the quantum _possibilities_ (and their potential interference effects) to a classical _actuality_. Just before opening the box, quantum mechanics provides the two possibilities of "live" and "dead" cat, with calculable probabilities. Upon opening the box and finding a dead cat, an autopsy will reveal that the time of death was recorded and in some sense "observed." A human experimenter is not needed to [collapse the wave function](https://www.informationphilosopher.com/solutions/experiments/wave-function_collapse/). The macroscopic cat is its own measuring apparatus and observer. Not only do objects appear to be "classical" when they are large enough, the classical laws of motion, with their implicit [determinism](https://www.informationphilosopher.com/freedom/determinism.html) and strict [causality](https://www.informationphilosopher.com/freedom/causality.html), [emerge](https://www.informationphilosopher.com/knowledge/emergence.html) when microscopic events can be ignored, but this determinism is fundamentally [statistical](https://www.informationphilosopher.com/freedom/adequate_determinism.html). Information philosophy interprets the wave function _ψ_ as a "possibilities" function. With this simple change in terminology, the mysterious process of a wave function "collapsing" becomes a much more intuitive discussion of _ψ_ exploring [possibilities](https://www.informationphilosopher.com/freedom/possibilities.html) (with mathematically calculable [probabilities](https://www.informationphilosopher.com/freedom/probability.html)), followed by a single _actuality_, at which time alternative probabilities go to zero ("collapse") instantaneously. Information physics is standard quantum physics. It accepts the Schrödinger [_equation of motion_](https://www.informationphilosopher.com/introduction/physics/interpretations/#equation), the [_principle of superposition_](https://www.informationphilosopher.com/introduction/physics/interpretations/#principle), the [_axiom of measurement_](https://www.informationphilosopher.com/introduction/physics/interpretations/#axiom) (now including the actual information "bits" measured), and - most important - the [_projection postulate_](https://www.informationphilosopher.com/introduction/physics/interpretations/#postulate) of standard quantum mechanics (the "collapse" that so many [interpretations](https://www.informationphilosopher.com/introduction/physics/interpretations/) deny). But the conscious observer of the Copenhagen Interpretation is not required for a projection, for the [wave-function to "collapse"](https://www.informationphilosopher.com/solutions/experiments/wave-function_collapse/), for one of the [possibilities](https://www.informationphilosopher.com/freedom/possibilities.html) to become an _actuality_. What it does require is an _interaction_ between systems that creates [irreversible](https://www.informationphilosopher.com/problems/reversibility/) and observable, but not necessarily observed, _[information](https://www.informationphilosopher.com/introduction/information/)_. Among the founders of quantum mechanics, almost everyone agreed that _irreversibility_ was a key requirement for a measurement. Irreversibility introduces thermodynamics into a proper formulation of quantum mechanics, and this is what the information interpretation does. Information is _not_ a conserved quantity like energy and mass, despite the view of many mathematical physicists, who generally accept [determinism](https://www.informationphilosopher.com/freedom/determinism.htnl). The universe began in a state of equilibrium with minimal information, and information is being [created every day](https://www.informationphilosopher.com/introduction/creation/), despite the second law of thermodynamics Classical interactions between large macroscopic bodies do not generate new information. Newton's laws of motion imply that the information in any configuration of bodies, motions, and force is enough to know all past and future configurations. _Classical mechanics conserves information_. In the absence of interactions, an isolated quantum system evolves according to the unitary [Schrödinger](https://www.informationphilosopher.com/solutions/scientists/schrodinger/) _equation of motion_. Just like classical systems, the [deterministic](https://www.informationphilosopher.com/freedom/determinism.htnl) Schrödinger equation conserves information. Unlike classical systems however, when there is an interaction between quantum systems, the two systems become _entangled_ and there may be a change of state in either or both systems. This change of state may create new information. If that information is instantly destroyed, as in most interactions, it may never be observed macroscopically. If, on the other hand, the information is stabilized for some length of time, it may be seen by an observer and considered to be a "[measurement](https://www.informationphilosopher.com/problems/measurement/)." But it need not be seen by anyone to become new information in the universe. The universe is its own observer! Compare [Schrödinger's Cat](https://www.informationphilosopher.com/solutions/experiments/schrodinger_cat/) as its own observer. For the information (negative entropy) to be stabilized, the second law of thermodynamics requires that an amount of positive entropy greater than the negative entropy must be transferred away from the new information structure. Note that despite the Heisenberg principle, quantum mechanical measurements are not always uncertain. When a system is measured (prepared) in an eigenstate, a subsequent measurement (Pauli's measurement of the first kind) will find it in the same state with _perfect certainty_. What then are the possibilities for new quantum states? The transformation theory of [Dirac](https://www.informationphilosopher.com/solutions/scientists/dirac/) and [Jordan](https://www.informationphilosopher.com/solutions/scientists/jordan/) lets us represent _ψ_ in a set of basis functions for which the combination of quantum systems (one may be a measurement apparatus) has eigenvalues (_the axiom of measurement_). We represent _ψ_ as in a linear combination (_the principle of superposition_) of those "possible" eigenfunctions. Quantum mechanics lets us calculate the probabilities of each of those "possibilities." Interaction with the measurement apparatus (or indeed interaction with any other system) may select out (_the projection postulate_) one of those possibilities as an actuality. But for this event to be an "observable" (a [John Bell](https://www.informationphilosopher.com/solutions/scientists/bell/) "beable"), [information](https://www.informationphilosopher.com/introduction/information/) must be created _and_ positive entropy must be transferred away from the new information structure, in accordance with our two-stage [information creation process](https://www.informationphilosopher.com/introduction/creation/). All [_interpretations_ of quantum mechanics](https://www.informationphilosopher.com/introduction/physics/interpretations) predict the same experimental results. [Information physics](https://www.informationphilosopher.com/introduction/physics/) is no exception, because the experimental data from quantum experiments is the most accurate in the history of science. Where interpretations differ is in the picture (the visualization) they provide of what is "really" going on in the microscopic world - the so-called "quantum reality." The "orthodox" Copenhagen interpretation of [Neils Bohr](https://www.informationphilosopher.com/solutions/scientists/bohr/) and [Werner Heisenberg](https://www.informationphilosopher.com/solutions/scientists/heisenberg/) discourages such attempts to understand the nature of the "quantum world," because they say that all our experience is derived from the "classical world" and should be described in ordinary language. This is why Bohr and Heisenberg insisted on the path and the "[cut](https://www.informationphilosopher.com/introduction/physics/heisenberg_cut.html)" between the quantum event and the mind of an observer. The information interpretation encourages visualization. Schrödinger called it _Anschaulichkeit_. He and [Einstein](https://www.informationphilosopher.com/solutions/scientists/einstein/) were right that we should be able to picture quantum reality. But that demands that we accept the _reality of quantum [possibilities](https://www.informationphilosopher.com/freedom/possibilities.html)_ and discontinuous random "quantum jumps," something many modern interpretations do not do. (See our visualization of the [two-slit experiment](https://www.informationphilosopher.com/solutions/experiments/two-slit_experiment/), our [EPR experiment](https://www.informationphilosopher.com/solutions/experiments/EPR/) visualizations, and [Dirac's three polarizers](https://www.informationphilosopher.com/solutions/experiments/dirac_3-polarizers/) to visualize the superposition of states and the projection or "collapse" of a wave function.) Related to the [Heisenberg Cut](https://www.informationphilosopher.com/introduction/physics/heisenberg_cut.html), but really quite different. ## Three Examples of a "Classical" Apparatus - the Photographic Plate, a CCD, the cloud chamber. A macroscopic object with a vast number of quantum-scale systems prepared in "metastable" states. ## The Decoherence Explanation Schlosshauer agrees there is only one world - the quantum world. But there is no universal wave function, which is a construction to prevent any new information being created and establish determinism.