IPB

Welcome Guest ( Log In | Register )

HST and 'dark matter'
Guest_PhilCo126_*
post May 11 2007, 05:13 PM
Post #1





Guests






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.
Go to the top of the page
 
+Quote Post
 
Start new topic
Replies
Mongo
post Mar 11 2010, 03:36 AM
Post #2


Member
***

Group: Members
Posts: 723
Joined: 13-June 04
Member No.: 82



Sorry to resurrect this long-dead thread, but a paper just appeared on ARXIV that bears on the possible physics behind MOND.

As background, in recent months a new theory of gravity has received a lot of attention. A Dutch physicist named Erik Verlinde appears to have made the crucial connections that allow for a physical explanation of gravity (both Newtonian and relativistic) as well as related concepts like Newtonian mechanics, inertia and indeed space and time itself. This is a bold claim, but top physicists like Lee Smolin, George Smoot and Gerard 't Hooft have jumped on board in recent weeks. This is no crackpot idea.

On the Origin of Gravity and the Laws of Newton -- Erik Verlinde

QUOTE
Starting from first principles and general assumptions Newton's law of gravitation is shown to arise naturally and unavoidably in a theory in which space is emergent through a holographic scenario. Gravity is explained as an entropic force caused by changes in the information associated with the positions of material bodies. A relativistic generalization of the presented arguments directly leads to the Einstein equations. When space is emergent even Newton's law of inertia needs to be explained. The equivalence principle leads us to conclude that it is actually this law of inertia whose origin is entropic.


What Verlinde found is that gravity can be explained as an entropic force -- a pseudo-force that results from the universal tendency to maximize entropy (the Second Law of Thermodynamics). Other examples of entropic forces include osmosis, and the 'force' causing large polypeptide molecules suspended in a fluid to curl up into a roughly spherical shape, instead of stretching out in a linear fashion. (This is NOT due to intra-molecular bonding forces, but instead is due to the fact that there are many more internal degrees of freedom in a spherical configuration than in a linear one, and hence a 'random walk' between states, driven by random collisions with the fluid molecules, will almost inevitably result in a spherical configuration.)

In Verlinde's theory, the most fundamental quality is information, which is stored in what are called 'holographic screens' that separate and define every point in space-time. These holographic screens are not new, they have become an indispensable concept in black hole physics over the past decade or so. They have the effect of 'smearing' information over a large area, rather than having it concentrated at a single point -- resulting in quantum mechanics. The amount of information associated with matter and its location is measured in terms of entropy. Changes in entropy associated with changes in location result in an entropic force, which when the math is done exactly matches gravity, both Newtonian and relativistic. The theory also automatically generates an additional force that exactly matches the effects of so-called 'dark energy' which had been recently postulated in order to explain the observed changes in the Hubble constant at extreme distances. In this theory it is a consequence of information being stored at the 'universal horizon', covering every point in the universe. Additionally, it provides an easy and natural explanation of inertia, which had always been a big puzzle.

Over the past two months a great many additional people have written papers, filling in and extending the theory. So far, it has been found to accurately describe both Newtonian and relativistic gravity, Newtonian mechanics including inertia, the early period of cosmological inflation, the current cosmological acceleration commonly ascribed to 'dark energy', and much of electrodynamics (!) including the Coulomb law, the Poisson equation and indeed all the Maxwell equations -- raising the possibility that electromagnetism is also a non-fundamental entropic force, with the photon perhaps being akin to the phonon (soliton) as a derived 'particle'. The newest such result concerns MOND:

Entropic corrections to Newton's law -- Leonardo Modesto, Andrew Randono

QUOTE
It has been known for some time that there is a deep connection between thermodynamics and gravity, with perhaps the most dramatic implication that the Einstein equations can be viewed as a thermodynamic equation of state. Recently Verlinde has proposed a model for gravity with a simple statistical mechanical interpretation that is applicable in the non-relativistic regime. After critically analyzing the construction, we present a strong consistency check of the model. Specifically, we consider two well-motivated corrections to the area-entropy relation, the log correction and the volume correction, and follow Verlinde's construction to derive corrections to Newton's law of gravitation. We show that the deviations from Newton's law stemming from the log correction have the same form as the lowest order quantum effects of perturbative quantum gravity, and the deviations stemming from the volume correction have the same form as some modified Newtonian gravity models designed to explain the anomalous galactic rotation curves.

[...]

Let us now focus on the corrections to Newton's laws stemming from the volume correction to the area-entropy relation. We notice here that the form of the potential is of the same functional form as the correction to the Newtonian potential posited by Modified Newtonian Dynamics (MOND) in order to model the anomalously flat galactic rotation curves.


Of course this does not prove that some form of MOND is correct, but it does raise the likelyhood a good deal, in my opinion.

p.s. -- if anybody wants to see links to other papers regarding aspects of this theory of gravity, please let me know on this thread and I will post links to the more important papers.
Go to the top of the page
 
+Quote Post

Posts in this topic
- PhilCo126   HST and 'dark matter'   May 11 2007, 05:13 PM
- - Littlebit   A dark matter ring? How/why would DM be corraled i...   May 11 2007, 05:35 PM
- - Mongo   Colour me sceptical on this one -- which should be...   May 11 2007, 11:04 PM
- - Tman   From the Hubble site http://hubblesite.org/newscen...   May 17 2007, 07:53 AM
- - Mongo   The wedding ring of MOND and non-exotic dark matte...   Jun 12 2007, 01:41 AM
- - nprev   I'm with you, man. Dark matter has always been...   Jun 12 2007, 03:46 AM
|- - dvandorn   QUOTE (nprev @ Jun 11 2007, 10:46 PM) ......   Jun 12 2007, 04:22 AM
- - Mongo   Using globular clusters to test gravity in the wea...   Jul 18 2007, 01:11 PM
- - nprev   MOND + neutrino mass is looking more and more plau...   Jul 18 2007, 02:40 PM
- - Mongo   Sorry to resurrect this long-dead thread, but a pa...   Mar 11 2010, 03:36 AM
- - Explorer1   So in layman's terms, this is a potential ...   Mar 11 2010, 04:46 AM
|- - Greg Hullender   QUOTE (Explorer1 @ Mar 10 2010, 08:46 PM)...   Mar 11 2010, 05:00 AM
- - Mongo   Just to give a taste of how (some) physicists are ...   Mar 11 2010, 05:42 AM
- - Mongo   Part 2 of 2 Modified gravity emerging from thermo...   Mar 11 2010, 05:46 AM
- - nprev   There's definitely a deterministic flavor to t...   Mar 11 2010, 05:47 AM
- - stevesliva   I find it interesting that physicists have been co...   Mar 11 2010, 05:08 PM
- - Mongo   From Inertia Theory -- Paul Davies: QUOTE Fill a ...   Mar 11 2010, 05:37 PM
- - djellison   Is it just me, or is this a catastrophically screw...   Mar 11 2010, 05:47 PM
|- - Mongo   That was my first thought too, but how does the wa...   Mar 11 2010, 06:04 PM
|- - stevesliva   QUOTE (Mongo @ Mar 11 2010, 01:04 PM) Ine...   Mar 11 2010, 07:13 PM
- - djellison   So it'snot a question about a bucket at all, i...   Mar 11 2010, 06:25 PM
|- - centsworth_II   QUOTE (djellison @ Mar 11 2010, 01:25 PM)...   Mar 11 2010, 06:46 PM
|- - Greg Hullender   QUOTE (djellison @ Mar 11 2010, 10:25 AM)...   Mar 11 2010, 10:25 PM
|- - Marz   QUOTE (Greg Hullender @ Mar 11 2010, 04:2...   Mar 11 2010, 10:56 PM
|- - Mongo   QUOTE (Marz @ Mar 11 2010, 11:56 PM) Mean...   Mar 12 2010, 12:27 AM
|- - AndyG   QUOTE (Marz @ Mar 11 2010, 10:56 PM) lol ...   Mar 12 2010, 11:05 AM
- - Shaka   If Earth were in an otherwise empty Universe, why ...   Mar 11 2010, 06:47 PM
- - Mongo   The following is just my own understanding of what...   Mar 11 2010, 07:30 PM
- - monty python   I'm really loving this thread, but for some re...   Mar 12 2010, 06:58 AM
- - SteveM   I've noticed that none of the arXiv papers are...   Apr 4 2010, 02:13 PM
- - Floyd   Mongo "As the example stated, if the Earth we...   Apr 4 2010, 03:38 PM
- - Greg Hullender   That begs the question, Floyd. --Greg   Apr 4 2010, 04:23 PM
- - stevesliva   The NY Times covers Verlinde, and does the newspap...   Jul 13 2010, 12:46 AM
|- - AndyG   QUOTE (stevesliva @ Jul 13 2010, 01:46 AM...   Jul 13 2010, 12:08 PM
- - nprev   No, it's not. But I liked the cartoon.   Jul 13 2010, 01:54 AM
- - Hungry4info   If I'm not mistaken, "order", in ref...   Jul 13 2010, 01:41 PM
|- - Juramike   Entropy would be maximum for an evenly diffused bu...   Jul 13 2010, 01:55 PM
- - Greg Hullender   Mike: if any of the separated atoms/particles can ...   Jul 13 2010, 02:17 PM
|- - Juramike   Full inline quote removed - Mike, you should know ...   Jul 13 2010, 03:05 PM
- - Greg Hullender   Which means the maximum entropy ought to be when a...   Jul 13 2010, 08:04 PM
- - stevesliva   Experiments would seem to indicate gravity is not ...   Aug 24 2011, 10:57 PM
- - nprev   Actually, seems that interpretation of the theorie...   Aug 25 2011, 12:18 AM
- - Mongo   This paper just came out on arXiv, in response to ...   Sep 14 2011, 12:56 AM
- - Mongo   No surprise at all to me. Maybe now the Dark Matt...   Apr 19 2012, 10:37 PM
- - Mongo   Dark Matter gone missing in many places: a crisis ...   Apr 20 2012, 03:51 PM
- - Mongo   Beating an increasingly dead horse here: Vast Str...   Apr 25 2012, 09:26 PM
- - stevesliva   Does make you wonder if "dark matter" wi...   Apr 26 2012, 02:33 AM
- - Mongo   The Bullet Cluster as Evidence against Dark Matter...   Jan 27 2017, 08:31 PM
- - Gerald   I'd think, the vast majority of astrophysicist...   Jan 28 2017, 03:44 AM
- - fredk   I agree with Gerald. I'm familiar with the bl...   Jan 28 2017, 06:24 AM


Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 28th March 2024 - 06:10 PM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member.