Quantum darwinism
Encyclopedia
Quantum Darwinism is a theory explaining the emergence of the classical world
from the quantum world
as due to a process of Darwinian
natural selection
; where the many possible quantum states are selected against in favor of a stable pointer state. It is proposed by Wojciech Zurek and a group of collaborators including Ollivier, Poulin, Paz and Blume-Kohout. The development of the theory is due to the integration of a number of Zurek’s research topics pursued over the course of twenty-five years including: pointer states, einselection
and decoherence.
A study in 2010 has provided preliminary supporting evidence of quantum Darwinism with scars of a quantum dot
"becoming a family of mother-daughter states" indicating they could "stabilize into multiple pointer states."
, the main interpretational challenge for quantum theory. The measurement problem arises because the quantum state vector, the source of all knowledge concerning quantum systems, evolves according to the Schrödinger equation
into a linear superposition of different states, predicting paradoxical situations such as “Schrödinger's cat
”; situations never experienced in our classical world. Quantum theory has traditionally treated this problem as being resolved by a non-unitary
transformation of the state vector at the time of measurement into a definite state. It provides an extremely accurate means of predicting the value of the definite state that will be measured in the form of a probability for each possible measurement value. The physical nature of the transition from the quantum superposition of states to the definite classical state measured is not explained by the traditional theory but is usually assumed as an axiom and was at the basis of the debate between Bohr
and Einstein concerning the completeness of quantum theory.
Quantum Darwinism explains the transition of quantum systems from the vast potentiality of superposed states to the greatly reduced set of pointer states as a selection process, einselection
, imposed on the quantum system through its continuous interactions with the environment. All quantum interactions, including measurements, but much more typically interactions with the environment such as with the sea of photons in which all quantum systems are immersed, lead to decoherence
or the manifestation of the quantum system in a particular basis dictated by the nature of the interaction in which the quantum system is involved. In the case of interactions with its environment Zurek and his collaborators have shown that a preferred basis into which a quantum system will decohere is the pointer basis underlying predictable classical states. It is in this sense that the pointer states of classical reality are selected from quantum reality and exist in the macroscopic realm in a state able to undergo further evolution.
As a quantum system’s interactions with its environment results in the recording of many redundant copies of information regarding its pointer states, this information is available to numerous observers able to achieve consensual agreement concerning their information of the quantum state. This aspect of einselection, called by Zurek ‘Environment as a Witness’, results in the potential for objective knowledge.
, Darwinian processes are not confined to biology but are any following the simple Darwinian algorithm:
Quantum Darwinism appears to conform to this algorithm and thus is aptly named:
From this view quantum Darwinism provides a Darwinian explanation at the basis of our reality, explaining the unfolding or evolution of our classical macroscopic world. It is perhaps surprising that this same mechanism operating at the emergence of classical reality from quantum reality is also seen by scientific theories to be operating at the emergence of biology from chemistry and at the emergence of culture from biology.
Classical physics
What "classical physics" refers to depends on the context. When discussing special relativity, it refers to the Newtonian physics which preceded relativity, i.e. the branches of physics based on principles developed before the rise of relativity and quantum mechanics...
from the quantum world
Quantum mechanics
Quantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
as due to a process of Darwinian
Charles Darwin
Charles Robert Darwin FRS was an English naturalist. He established that all species of life have descended over time from common ancestry, and proposed the scientific theory that this branching pattern of evolution resulted from a process that he called natural selection.He published his theory...
natural selection
Natural selection
Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....
; where the many possible quantum states are selected against in favor of a stable pointer state. It is proposed by Wojciech Zurek and a group of collaborators including Ollivier, Poulin, Paz and Blume-Kohout. The development of the theory is due to the integration of a number of Zurek’s research topics pursued over the course of twenty-five years including: pointer states, einselection
Einselection
Einselection is short for environment - induced superselection, a nickname coined by Wojciech H. Zurek. Classicality is an emergent property induced in open quantum systems by their environments...
and decoherence.
A study in 2010 has provided preliminary supporting evidence of quantum Darwinism with scars of a quantum dot
Quantum dot
A quantum dot is a portion of matter whose excitons are confined in all three spatial dimensions. Consequently, such materials have electronic properties intermediate between those of bulk semiconductors and those of discrete molecules. They were discovered at the beginning of the 1980s by Alexei...
"becoming a family of mother-daughter states" indicating they could "stabilize into multiple pointer states."
Implications
Along with Zurek’s related theory of envariance, quantum Darwinism explains how the classical world emerges from the quantum world and proposes to answer the quantum measurement problemMeasurement problem
The measurement problem in quantum mechanics is the unresolved problem of how wavefunction collapse occurs. The inability to observe this process directly has given rise to different interpretations of quantum mechanics, and poses a key set of questions that each interpretation must answer...
, the main interpretational challenge for quantum theory. The measurement problem arises because the quantum state vector, the source of all knowledge concerning quantum systems, evolves according to the Schrödinger equation
Schrödinger equation
The Schrödinger equation was formulated in 1926 by Austrian physicist Erwin Schrödinger. Used in physics , it is an equation that describes how the quantum state of a physical system changes in time....
into a linear superposition of different states, predicting paradoxical situations such as “Schrödinger's cat
Schrödinger's cat
Schrödinger's cat is a thought experiment, usually described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects. The scenario presents a cat that might be...
”; situations never experienced in our classical world. Quantum theory has traditionally treated this problem as being resolved by a non-unitary
Unitarity (physics)
In quantum physics, unitarity is a restriction on the allowed evolution of quantum systems that insures the sum of probabilities of all possible outcomes of any event is always 1....
transformation of the state vector at the time of measurement into a definite state. It provides an extremely accurate means of predicting the value of the definite state that will be measured in the form of a probability for each possible measurement value. The physical nature of the transition from the quantum superposition of states to the definite classical state measured is not explained by the traditional theory but is usually assumed as an axiom and was at the basis of the debate between Bohr
Bohr
Bohr may refer to:People:* Niels Bohr , Danish atomic physicist, Nobel Prize in physics 1922* Aage Bohr , Danish nuclear physicist, Nobel Prize in physics 1975, son of Niels Bohr...
and Einstein concerning the completeness of quantum theory.
Quantum Darwinism explains the transition of quantum systems from the vast potentiality of superposed states to the greatly reduced set of pointer states as a selection process, einselection
Einselection
Einselection is short for environment - induced superselection, a nickname coined by Wojciech H. Zurek. Classicality is an emergent property induced in open quantum systems by their environments...
, imposed on the quantum system through its continuous interactions with the environment. All quantum interactions, including measurements, but much more typically interactions with the environment such as with the sea of photons in which all quantum systems are immersed, lead to decoherence
Quantum decoherence
In quantum mechanics, quantum decoherence is the loss of coherence or ordering of the phase angles between the components of a system in a quantum superposition. A consequence of this dephasing leads to classical or probabilistically additive behavior...
or the manifestation of the quantum system in a particular basis dictated by the nature of the interaction in which the quantum system is involved. In the case of interactions with its environment Zurek and his collaborators have shown that a preferred basis into which a quantum system will decohere is the pointer basis underlying predictable classical states. It is in this sense that the pointer states of classical reality are selected from quantum reality and exist in the macroscopic realm in a state able to undergo further evolution.
As a quantum system’s interactions with its environment results in the recording of many redundant copies of information regarding its pointer states, this information is available to numerous observers able to achieve consensual agreement concerning their information of the quantum state. This aspect of einselection, called by Zurek ‘Environment as a Witness’, results in the potential for objective knowledge.
Darwinian significance
Perhaps of equal significance to the light this theory shines on quantum explanations is its identification of a Darwinian process operating as the selective mechanism establishing our classical reality. As numerous researchers have made clear any system employing a Darwinian process will evolve. As argued by the thesis of Universal DarwinismUniversal darwinism
Universal Darwinism refers to a variety of approaches that extend the theory of Darwinism beyond its original domain of biological evolution on Earth...
, Darwinian processes are not confined to biology but are any following the simple Darwinian algorithm:
- Reproduction/Heredity; the ability to make copies and thereby produce descendants.
- Selection; A process that preferentially selects one trait over another trait, leading to one trait being more numerous after sufficient generations.
- Variation; differences in heritable traits that affect "Fitness” or the ability to survive and reproduce leading to differential survival.
Quantum Darwinism appears to conform to this algorithm and thus is aptly named:
- Numerous copies are made of pointer states
- Pointer states evolve in a continuous, predictable manner, that is descendants inherit many of their traits from ancestor states.
- Successive interactions between pointer states and their environment reveal them to evolve and those states to survive which conform to the predictions of classical physics within the macroscopic world.
From this view quantum Darwinism provides a Darwinian explanation at the basis of our reality, explaining the unfolding or evolution of our classical macroscopic world. It is perhaps surprising that this same mechanism operating at the emergence of classical reality from quantum reality is also seen by scientific theories to be operating at the emergence of biology from chemistry and at the emergence of culture from biology.