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HST and 'dark matter'
Guest_PhilCo126_*
post May 11 2007, 05:13 PM
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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.
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djellison
post Mar 11 2010, 05:47 PM
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Is it just me, or is this a catastrophically screwed up analogy?

"Fill a bucket with water, grab it by the handle and whirl it in an arc above your head. If you do it right, you will stay dry. A mysterious force seems to glue the water into the upside down bucket. Scientists are still unsure about where this force comes from"

Errr - F=MA and A=V^2 / R

Nothin mysterious about it.
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Mongo
post Mar 11 2010, 06:04 PM
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That was my first thought too, but how does the water 'know' that it is experiencing circular acceleration? The magnitude of the 'centrifugal' (or conversely, centripetal) force is easily calculated, but the reason it exists is apparently much harder to understand. Einstein never could. As the example stated, if the Earth were rotating in an otherwise empty universe, would it still be considered to be rotating? And would it still experience polar flattening as a result? If it does, how does it 'know' how quickly it is rotating (to generate that degree of flattening) with nothing to act as an external reference frame, and if it does not, why does the presence of some other random object(s) in the universe affect the shape of the earth, to a far larger degree than those caused by tidal effects? And is one other physical object in the universe enough to establish a reference frame, or is an entire universe equivalent to ours necessary? If so, why?

Inertia is very easy to handle mathematically, it's practically the first thing taught in high school physics, but its origin is apparently much more difficult to explain. It appears that this new theory of gravity by Verlinde has inertia fall out almost automatically, in terms of entropy gradients.
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stevesliva
post Mar 11 2010, 07:13 PM
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QUOTE (Mongo @ Mar 11 2010, 01:04 PM) *
Inertia is very easy to handle mathematically, it's practically the first thing taught in high school physics, but its origin is apparently much more difficult to explain. It appears that this new theory of gravity by Verlinde has inertia fall out almost automatically, in terms of entropy gradients.


Yes, but I don't understand why an balanced entropy gradients are so much more gee-whiz than balanced forces. Someone will be unsatisfied with not knowing the origin for the 2nd law of thermodynamics, right?

I understand the elegance of describing inertia in terms of entropy, but in my mind, it's just saying that this thing we think is fundamental is just like this other thing that is fundamental. It's still fundamental.

I would think that if some young einstein asked his physics teacher "why is there inertia?" the answer would be "it's fundamental." Upon reaching university, a physics professor might say, "actually, it can be expressed as a manifestation of entropy." At which point the young einstein says, "why is there entropy?" Does the physics professor say, "it's fundamental?" tongue.gif

Is the reason it's so gee-whiz because entropy is a fundamental property of everything, not just matter and energy, but also information? We're better linking in the concepts of data and uncertainty with matter and energy?
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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


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