HST and 'dark matter' Options

[Guest_PhilCo126_*]

ASA Updates Plans for Hubble 'Ring Of Dark Matter' Briefing

GREENBELT, Md. - NASA will hold a media teleconference at 1 p.m. EDT on May 15 to discuss the strongest evidence to date that dark matter exists. This evidence was found in a ghostly ring of dark matter in the cluster CL0024+17, discovered using NASA's Hubble Space Telescope. The ring is the first detection of dark matter with a unique structure different from the distribution of both the galaxies and the hot gas in the cluster. The discovery will be featured in the June 20 issue of the Astrophysical Journal.

[Mongo]

Just to give a taste of how (some) physicists are viewing this idea, here are some extracts from some of the involved papers:

Part 1 of 2

Notes Concerning "On the Origin of Gravity and the Laws of Newton" by E. Verlinde -- Jarmo Mäkelä

If the idea of gravity as an emergent effect, rather than as a fundamental force turns out to be correct, we may currently be in a somewhat similar position as were the founders of quantum mechanics and atomic physics about 100 years ago. Instead of attempting to understand the microstructure of matter, however, we should, in this time, attempt to understand the microstructure of spacetime itself.

The Coulomb Force as an Entropic Force -- Tower Wang

If one accepts the holographic principle as well as our generalizations and reinterpretations, then the Coulomb's law, the Poisson's equation and the Maxwell's equations can be derived smoothly. Our attempt can be regarded as a new way to unify the electromagnetic force with gravity, from the entropic origin.

Gravity from the Entropy of Light -- Alessandro Pesci:

This suggests a deeper description of what we have discussed. Indeed, holography can be stated to mean that the allowed number of elementary bits of information in layers per unit bit of thickness, at given sum of the energy per bit and pressure, is limited (by an actual value). To the extent that concepts like bit of information, energy associated with a bit and pressure of a collection of bits can be regarded as primeval and, as such, meaningful even in absence of space, holography is pre-existing to space. In this perspective, when space is introduced as the information on ‘where’ information is, the energy in the bit should spread to keep unchanged the elementary amount of information for the bit, and this would be quantum mechanics. When expressed in terms of this space of information, holography would then become the metric theory which describes gravity.

Newtonian Gravity in Loop Quantum Gravity -- Lee Smolin

The idea that the unification of quantum theory with gravity is essentially thermodynamic has been on the table since the discovery of the laws of black hole thermodynamics and Bekenstein’s discovery of black hole entropy. The discoveries of the Unruh temperature and Hawking radiation strengthened the reason for hoping for a deep relationship between gravity, quantum physics and thermodynamics.

Very early in this history, Bekenstein hypothesized that the entropy of any isolated system is bounded by its area. In 1994 ’t Hooft extended this to the bold conjecture that the degrees of freedom needed to describe an isolated system in nature can be considered to live on a two-surface surrounding the region, with the number of degrees of freedom finite and proportional to the area in Planck units. He called this the holographic principle and since then we have come to call any application of the relationship between area and entropy as “holographic.” As developed by Susskind and then Maldacena and many others this led, in the context of string theory and supersymmetric quantum gauge theory, to the AdS/CFT correspondence.

The furthest realization of this idea to date, in the context of gravitational theory, is the discovery by Jacobson that the Einstein equations can be derived from the laws of thermodynamics, assuming only that Bekenstein’s proportionality between area and entropy is universal. This idea has been studied also by Padmanabhan and others, but there has remained the feeling that there was a further discovery, just over the horizon.

In a remarkable paper, Erik Verlinde has provided the next step, which is a non-relativistic analogue of Jacobson’s argument, in which he derives Newton’s law of gravity from thermodynamics plus the relationship between area and entropy. A different argument to the same conclusion has also been provided by Padmanabhan.