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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, 06:25 PM
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So it'snot a question about a bucket at all, it's just asking WHY F=MA
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Greg Hullender
post Mar 11 2010, 10:25 PM
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QUOTE (djellison @ Mar 11 2010, 10:25 AM) *
So it'snot a question about a bucket at all, it's just asking WHY F=MA

This has been a question for a long time. I remember my Physics professor at Caltech making a point of it when I was a freshman back in 1977.

When I was a kid, protons and neutrons were thought to be fundamenal particles, although there was a bewildering array of other, short-lived subatomic particles. It was exciting to witness the discoveries that replaced all that with the much more elegant system of quarks and leptons, and it's even exciting to think we may be witnessing another major refinement.

It'll be nice when someone has worked out an easier way to explain it to the educated layman. Meanwhile, I'm still waiting for someone to explain how they plan to test this hypothesis.

--Greg
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Marz
post Mar 11 2010, 10:56 PM
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QUOTE (Greg Hullender @ Mar 11 2010, 04:25 PM) *
This has been a question for a long time.


lol - who would've thought a spinning bucket is at the heart of modern physics?

I think the essence of the Bucket is to understand what aspects of gravity are mathematical abstractions or a natural phenomenon. From Greene's layman book "Fabric of the Cosmos" Chp 2, The Universe and the Bucket:

"If velocity is something that only makes sense by comparisons ... how is it that changes in velocity are somehow different, and don't also require comparisons to give them meaning? ... Could it be that there is some implicit or hidden comparison that is actually at work every time we refer to our experiences of accelerated motion? This is a central question .... it touches on the deepest issues surrounding the meaning of space and time."

Meanwhile... I'll have to decide what feels less silly:

Dark Matter (and perhaps Dark Energy) or holographic screens. Planetary geology is so lovingly concrete in comparison.
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Mongo
post Mar 12 2010, 12:27 AM
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QUOTE (Marz @ Mar 11 2010, 11:56 PM) *
Meanwhile... I'll have to decide what feels less silly:

Dark Matter (and perhaps Dark Energy) or holographic screens. Planetary geology is so lovingly concrete in comparison.


The term 'holographic screen' is perhaps a little unfortunate. We are not talking about some special movie screen on which to watch Avatar in glorious 3D! It is simply a way of describing the information associated with any volume of spacetime as being encoded on the surface boundary of that volume (when observed from outside that volume), hence the term 'screen', and since there is always more information contained in that screen than can be observed from outside, it is also 'holographic'. The term was originally applied to the event horizens of black holes, where it made perfect sense to refer to a 'screen' which screened the interior from outside observation, but it was found that the concept could be extended to any (continuous) 2D surface that fully enclosed some volume of spacetime.

In the case of this theory, they are taking the holographic screens to be the smallest possible, each one surrounding a single point of spacetime, which leads to gravity by means of thermodynamic arguments. At the other end of the scale, by taking a holographic screen that encompasses the entire 'universal horizon' of this universe, it is possible to generate a force that matches that of so-called 'dark energy', which is the cause for the cosmological acceleration at very large distance scales.
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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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