Constructor theory is a proposal for a new mode of explanation in fundamental

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...

in the language of

ergodic theory Ergodic theory (Greek: ' "work", ' "way") is a branch of mathematics that studies statistical properties of deterministic dynamical systems; it is the study of ergodicity. In this context, statistical properties means properties which are expres ...

, developed by

physicists A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate caus ...

David Deutsch David Elieser Deutsch ( ; born 18 May 1953) is a British physicist at the University of Oxford. He is a Visiting Professor in the Department of Atomic and Laser Physics at the Centre for Quantum Computation (CQC) in the Clarendon Laboratory of ...

and

Chiara Marletto Chiara Marletto is a Theoretical physics, theoretical physicist at Wolfson College, Oxford, Wolfson College, Oxford. She is a pioneer in the field of constructor theory, a generalization of the quantum theory of information. Life Marletto gr ...

, at the

University of Oxford , mottoeng = The Lord is my light , established = , endowment = £6.1 billion (including colleges) (2019) , budget = £2.145 billion (2019–20) , chancellor ...

, since 2012. Constructor theory expresses physical laws exclusively in terms of which physical transformations, or ''tasks'', are possible versus which are impossible, and why. By allowing such

counterfactual Counterfactual conditionals (also ''subjunctive'' or ''X-marked'') are conditional sentences which discuss what would have been true under different circumstances, e.g. "If Peter believed in ghosts, he would be afraid to be here." Counterfactual ...

statements into fundamental physics, it allows new physical laws to be expressed, such as the constructor theory of information.

Overview

The fundamental elements of the theory are tasks: the abstract specifications of transformations as input–output pairs of attributes. A task is ''impossible'' if there is a law of physics that forbids its being performed with arbitrarily high accuracy, and ''possible'' otherwise. When it is possible, a ''constructor'' for it can be built, again with arbitrary accuracy and reliability. A constructor is an entity that can cause the task to occur while retaining the ability to cause it again. Examples of constructors include a

heat engine In thermodynamics and engineering, a heat engine is a system that converts heat to mechanical energy, which can then be used to do mechanical work. It does this by bringing a working substance from a higher state temperature to a lower state ...

(a thermodynamic constructor), a

catalyst Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...

(a chemical constructor) or a computer program controlling an automated factory (an example of a programmable constructor). The theory was developed by physicists

and

. It draws together ideas from diverse areas, including

thermodynamics Thermodynamics is a branch of physics that deals with heat, work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by the four laws of the ...

statistical mechanics In physics, statistical mechanics is a mathematical framework that applies statistical methods and probability theory to large assemblies of microscopic entities. It does not assume or postulate any natural laws, but explains the macroscopic be ...

information theory Information theory is the scientific study of the quantification (science), quantification, computer data storage, storage, and telecommunication, communication of information. The field was originally established by the works of Harry Nyquist a ...

, and

quantum computation Quantum computing is a type of computation whose operations can harness the phenomena of quantum mechanics, such as superposition, interference, and entanglement. Devices that perform quantum computations are known as quantum computers. Though ...

. Quantum mechanics and all other physical theories are claimed to be ''subsidiary'' theories, and quantum information becomes a special case of '' superinformation''. Chiara Marletto's ''constructor theory of life'' builds on constructor theory.

Motivations

According to Deutsch, current theories of physics, based on

quantum mechanics Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...

, do not adequately explain why some transformations between states of being are possible and some are not. For example, a drop of dye can dissolve in water, but

shows that the reverse transformation, of the dye clumping back together, is effectively impossible. We do not know at a quantum level why this should be so. Constructor theory provides an explanatory framework built on the transformations themselves, rather than the components. Information has the property that a given statement might have said something else, and one of these alternatives would not be true. The untrue alternative is said to be "

". Conventional physical theories do not model such counterfactuals. However, the link between information and such physical ideas as the

entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...

in a thermodynamic system is so strong that they are sometimes identified. For example, the area of a

black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

event horizon In astrophysics, an event horizon is a boundary beyond which events cannot affect an observer. Wolfgang Rindler coined the term in the 1950s. In 1784, John Michell proposed that gravity can be strong enough in the vicinity of massive compact obj ...

is a measure both of the hole's entropy and of the information that it contains, as per the

Bekenstein bound In physics, the Bekenstein bound (named after Jacob Bekenstein) is an upper limit on the thermodynamic entropy ''S'', or Shannon entropy ''H'', that can be contained within a given finite region of space which has a finite amount of energy—or co ...

. Constructor theory is an attempt to bridge this gap, providing a physical model that can express counterfactuals, thus allowing the laws of information and computation to be viewed as laws of physics.

Outline

In constructor theory, a transformation or change is described as a ''task''. A ''constructor'' is a physical entity that is able to carry out a given task repeatedly. A task is only possible if a constructor capable of carrying it out exists, otherwise it is impossible. To work with constructor theory, everything is expressed in terms of tasks. The properties of information are then expressed as relationships between possible and impossible tasks. Counterfactuals are thus fundamental statements, and the properties of information may be described by physical laws. If a system has a set of attributes, then the set of permutations of these attributes is seen as a set of tasks. A ''computation medium'' is a system whose attributes permute to always produce a possible task. The set of permutations, and hence of tasks, is a ''computation set''. If it is possible to copy the attributes in the computation set, the computation medium is also an ''information medium''. Information, or a given task, does not rely on a specific constructor. Any suitable constructor will serve. This ability of information to be carried on different physical systems or media is described as ''interoperability'' and arises as the principle that the combination of two information media is also an information medium. Media capable of carrying out quantum computations are called ''superinformation media'' and are characterised by specific properties. Broadly, certain copying tasks on their states are impossible tasks. This is claimed to give rise to all the known differences between quantum and classical information.

References

Bibliography

* * Marletto, Chiara (2021). The Science of Can and Can't. Penguin. ISBN 9780525521921.

External links

* *
Deeper Than Quantum Mechanics—David Deutsch’s New Theory of Reality
Mediums.com'
''The Physics arXiv Blog''
28 May 2014. * Kehoe, J.;
To What Extent Do We See with Mathematics?
. ''Scientific American'' Guest blog. 2013. *
Formulating Science in Terms of Possible and Impossible Tasks
. ''edge.org''. 12 June 2014. * {{Cite news , date=21 May 2014 , title=Reconstructing physics: The universe is information , work=NewScientist.com , type=Two leading quantum physicists say information is key to understanding the universe. Their constructor theory puts it centre stage , url=https://www.newscientist.com//article/mg22229700.200-reconstructing-physics-the-universe-is-information Fringe physics

Overview

Motivations

Outline

See also

References

Bibliography

External links