The

**Penrose interpretation** is a prediction of Sir Roger Penrose (born 1931) about the relationship between

quantum mechanicsQuantum 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...

and

general relativityGeneral relativity or the general theory of relativity is the geometric theory of gravitation published by Albert Einstein in 1916. It is the current description of gravitation in modern physics...

. Penrose proposes that a

quantum state remains in superposition until the difference of space-time curvature attains a significant level. This idea is inspired by

quantum gravityQuantum gravity is the field of theoretical physics which attempts to develop scientific models that unify quantum mechanics with general relativity...

, because it uses both the physical constants

and

The gravitational constant, denoted G, is an empirical physical constant involved in the calculation of the gravitational attraction between objects with mass. It appears in Newton's law of universal gravitation and in Einstein's theory of general relativity. It is also known as the universal...

. It is an alternative to the

Copenhagen interpretationThe Copenhagen interpretation is one of the earliest and most commonly taught interpretations of quantum mechanics. It holds that quantum mechanics does not yield a description of an objective reality but deals only with probabilities of observing, or measuring, various aspects of energy quanta,...

, which posits that superposition fails when an observation is made, and the many worlds hypothesis, which states that alternative outcomes of a superposition are equally "real", while their mutual decoherence precludes subsequent observable interactions.

Penrose's idea is a type of

objective collapse theoryObjective collapse theories are an approach to the interpretational problems of quantum mechanics. They are realistic, indeterministic and reject hidden variables...

. For these theories, the wavefunction is a physical wave, which experiences wave function collapse as a physical process, with observers not having any special role. Penrose theorises that the wave function cannot be sustained in superposition beyond a certain energy difference between the quantum states. He gives an approximate value for this difference: a

Planck mass worth of matter, which he calls the "'one-graviton' level".

He then hypothesizes that this energy difference causes the wave function to collapse to a single state, with a probability based on its amplitude in the original wave function, a procedure derived from standard

quantum mechanicsQuantum 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...

. Penrose's "'one-graviton' level" criterion forms the basis of his prediction, providing an objective criteria for wave function collapse. Despite the difficulties of specifying this in a rigorous way, he mathematically described the

basis states involved in the Schrödinger–Newton equations.

## Physical consequences

Accepting that wavefunctions are physically real, Penrose believes that things can exist in more than one place at one time. In his opinion, a macroscopic system, like a human being, cannot exist in more than one place for a measurable time, as the corresponding energy difference is very large. A microscopic system, like an

electronThe electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...

, can exist in more than one location forever, unless the energy difference becomes large enough.

In Einstein's theory, any object that has massMass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

causes a warp in the structure of space and timeIn physics, spacetime is any mathematical model that combines space and time into a single continuum. Spacetime is usually interpreted with space as being three-dimensional and time playing the role of a fourth dimension that is of a different sort from the spatial dimensions...

around it. This warping produces the effect we experience as gravity. Penrose points out that tiny objects, such as dust specks, atoms and electrons, produce space-time warps as well. Ignoring these warps is where most physicists go awry. If a dust speck is in two locations at the same time, each one should create its own distortions in space-time, yielding two superposed gravitational fields. According to Penrose's theory, it takes energy to sustain these dual fields. The stability of a system depends on the amount of energy involved: the higher the energy required to sustain a system, the less stable it is. Over time, an unstable system tends to settle back to its simplest, lowest-energy state: in this case, one object in one location producing one gravitational field. If Penrose is right, gravity yanks objects back into a single location, without any need to invoke observers or parallel universes.

Penrose speculates that the transition between macroscopic and quantum states begins at the scale of dust particles (the mass of which is close to a

planck mass). Dust particles could exist in more than one location for as long as one second, a time that is easily measurable with standard equipment. He has proposed an

experimentAn experiment is a methodical procedure carried out with the goal of verifying, falsifying, or establishing the validity of a hypothesis. Experiments vary greatly in their goal and scale, but always rely on repeatable procedure and logical analysis of the results...

to test this theory, called FELIX (Free-orbit Experiment with Laser Interfometry X-Rays), in which an

X-ray laserA laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...

in space is directed toward a tiny mirror, and fissioned by a beam splitter from tens of thousands of miles away, with which the photons are directed toward other mirrors and reflected back. One photon will strike the tiny mirror moving en route to another mirror and move the tiny mirror back as it returns, and according to conventional quantum theories, the tiny mirror can exist in superposition for a significant period of time. This would prevent any photons from reaching the detector. If Penrose's hypothesis is correct, the mirror's superposition will collapse to one location in about a second, allowing half the photons to reach the detector.

However, because this experiment would be difficult to arrange, a table-top version using millions of reflections between two mirrors has been proposed instead.

## Response

David DeutschDavid Elieser Deutsch, FRS is an Israeli-British physicist at the University of Oxford. He is a non-stipendiary Visiting Professor in the Department of Atomic and Laser Physics at the Centre for Quantum Computation in the Clarendon Laboratory of the University of Oxford...

, from Oxford’s

Centre for Quantum ComputationThe Centre for Quantum Computation or CQC is an alliance of quantum information research groups at the University of Oxford. It was founded by Artur Ekert in 1998....

, endorses the many worlds theory. He dismisses Penrose's interpretation as "based more on aesthetics than science", as no experimental anomalies have been observed. However, Penrose has responded that if his prediction is true, no experiments have been performed at the particular 'one graviton' level where quantum theory becomes overwhelmed by macroscopic effects.

## See also

*The Emperor's New Mind*The Emperor's New Mind: Concerning Computers, Minds and The Laws of Physics is a 1989 book by mathematical physicist Sir Roger Penrose.Penrose presents the argument that human consciousness is non-algorithmic, and thus is not capable of being modeled by a conventional Turing machine-type of digital...

- Interpretations of Quantum Mechanics
- Orch-OR
Orch-OR is a theory of consciousness, which is the joint work of theoretical physicist Sir Roger Penrose and anesthesiologist Stuart Hameroff. Mainstream theories assume that consciousness emerges from the brain, and focus particularly on complex computation at synapses that allow communication...

*The Road to Reality*
*Shadows of the Mind*Shadows of the Mind: A Search for the Missing Science of Consciousness is a 1994 book by mathematical physicist Roger Penrose, and serves as a followup to his 1989 book The Emperor's New Mind: Concerning Computers, Minds and The Laws of Physics....

- Schrödinger-Newton equations
The Schrödinger–Newton equations are modifications of the Schrödinger equation and derived from Gauss' law for gravity, proposed by Roger Penrose in The Road to Reality, that mathematically describe the basis states involved in a gravitationally-induced wavefunction collapse scheme:\nabla^2 \Phi =...

## External links