Penrose interpretation

ThePenrose interpretationis a speculation byRoger Penroseabout the relationship betweenquantum mechanicsandgeneral relativity.Penrose proposes that aquantum stateremains insuperpositionuntil the difference ofspace-time curvatureattains a significant level.

Overview

Penrose's idea is inspired byquantum gravitybecause it uses both the physical constants$\hbar$and$G$.It is an alternative to theCopenhagen interpretationwhich posits that superposition fails when an observation is made (but that it is non-objective in nature), and themany-worlds interpretation,which states that alternative outcomes of a superposition are equally "real," while their mutualdecoherenceprecludes subsequent observable interactions.

Penrose's idea is a type ofobjective collapse theory.For these theories, thewavefunctionis a physical wave, which experienceswave function collapseas 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: aPlanck massworth 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 standardquantum mechanics.Penrose's "'one-graviton' level" criterion forms the basis of his prediction, providing an objective criterion for wave function collapse.Despite the difficulties of specifying this in a rigorous way, he proposes that thebasis statesinto which the collapse takes place are mathematically described by the stationary solutions of theSchrödinger–Newton equation. Recent theoretical work indicates an increasingly deep inter-relation between quantum mechanics and gravitation.

Physical consequences

Accepting that wavefunctions are physically real, Penrose believes that matter 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 anelectron,can exist in more than one location significantly longer (thousands of years), until its space-time curvature separation reaches collapse threshold.

InEinstein's theory, any object that hasmasscauses a warp in the structure ofspace and timearound 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 aPlanck mass). He has proposed anexperimentto test this theory, called FELIX (free-orbit experiment with laser interferometry X-rays), in which anX-ray laserin space is directed toward a tiny mirror and fissioned by abeam splitterfrom 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 while moving 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 that uses optical cavities to trap the photons long enough for achieving the desired delay has been proposed instead.

See also

• Diósi–Penrose model
• Interpretations of quantum mechanics
• Orchestrated objective reduction
• Gravitational decoherence
• Schrödinger–Newton equation
• Stochastic quantum mechanics

Relevant books by Roger Penrose

• The Emperor's New Mind
• The Road to Reality
• Shadows of the Mind

External links

• Molecules – Quantum Interpretations
• QM – the Penrose Interpretation(Internet Archive)
• Roger Penrose discusses his experiment on the BBC (25 minutes in)
• "Tim Folger's 2005Discoverarticle "(PDF).(1.08 MB)