## Friday, December 10, 2010

### The Penrose interpretation

..........is a prediction of Sir Roger Penrose about the mass scale at which standard quantum mechanics will fail. This idea is inspired by quantum gravity, because it uses both the physical constants $\scriptstyle \hbar$ and $\scriptstyle G$.
Penrose's idea is a variant of objective collapse theory. In these theories the wavefunction is a physical wave, which undergoes wave function collapse as a random process, with observers playing no special role. Penrose suggests that the threshold for wave function collapse is when superpositions involve at least a Planck mass worth of matter. He then hypothesizes that some fundamental gravitational event occurs, causing the wavefunction to choose one branch of reality over another. Despite the difficulties in specifying this in a rigorous way, he mathematically described the basis states involved in the Schrödinger–Newton equations.
Accepting that wavefunctions are physically real, Penrose believes that things can exist in more than one place at one time. In his view, a macroscopic system, like a human being, cannot exist in more than one position because it has a significant gravitational field. A microscopic system, like an electron, has an insignificant gravitational field, and can exist in more than one location almost indefinitely.
In Einstein's theory, any object that has mass causes a warp in the structure of space and time 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.[1]
Penrose speculates that the transition between macroscopic and quantum begins on the scale of dust particles (whose mass is the planck mass). Dust particles could exist in more than one location for as long as one second, and this is much longer than the time a larger object could be in a superposition. He has proposed an experiment to test this theory, called FELIX (Free-orbit Experiment with Laser Interfometry X-Rays), in which an X-ray laser in space is directed toward a tiny mirror, and fissioned by a beam splitter from 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 Penrose's approach, that the tiny mirror exists in two locations at one time. If gravity affects the mirror, it will be unable to exist in two locations at once because gravity holds it in place. [2]

However, because this experiment would be difficult to set up, a table-top version has been proposed instead.[3]