Talk:Gravity/Archive 2

message: I added a missing section about physics of conservation of energy. IMHO it might be interesting to lay people becuase of the lack of gravitational forces accelerating free falling objects while kinetic energy of those objects is increasing. It often puzzles lay people since the physics of the automatic conservation of energy that math of general relativity assures through the vanishing divergence of T_{\mu\nu} isn't obvious. So I showed the physics of this phenomenon. 
There is also at the end of first section a new part about the true meaning of Newton's Law that makes Newton, for his refusal to interpret his equation as action at distance, the fortuitious discoverer of geodesic motion in spacetime (in this case in Euclidean spatial hypersurface) with Einstein showing how to transfer this law in a covariant form into pseudo Riemannian geometry or into any other suitable geometry. 
If there is a NPOV concern about this piece, IMO it should be reformulated rather than deleted. Jim  19:15, 28 Jul 2004 (UTC)
replies: text: Jim, your work could be in the physics course in the wikibooks, would that be acceptable to you? One of us could take steps to move it there. Ancheta Wis 11:05, 10 May 2005 (UTC)
thread_title:  Additions to Einstein's gravity section

message: "Attractive force" (non existent in gravitation) has been replaced by "interaction" that seems good enough a term to fit gravitation. 
The same in the previous section. Jim  18:41, 1 Aug 2004 (UTC)
thread_title:  Comparison with electromagnetic force 

message: "It often puzzles students of Einstein's gravity that without any force acting at distance the kinetic energy of a free falling objects changes. The puzzling question is "where this kinetic energy is coming form where the object is moving down or going to when the object is moving up"? The old "gravitational field" of the "attractive force" that was considered to be a repository of this "gravitational energy" in Newton's gravity isn't any good any more since now, if "attractive force" is zero, so is the "gravitational field". We need to identify another repository for this energy.
As we know the total energy of an object is E = mc2, where m is so called "relativistic mass", and c is speed of light. When object falls "down" its kinetic energy goes up. Energy has mass and so m goes up. However c2 drops down by the same amount since falling object gets into space where time is running slower (recall time dilation) and so the speed of light, as observed by the same observer who is seeing the increasing kinetic energy, is slower as well (that's why speed of light is not constant in gravitational field). If both m and c2 change in opposite direction by the same amount the product, the total energy of the object stays the same for a free falling object. That's how the conservatoin of energy works in Einstein's gravity.
There is one important result of Einstein's gravity: to keep the change of c2 the same as change of m there must be a relative increase in amount of space (space curvature) equal the relative time dilation. It might be said that the nature has to curve the space by the same amount as time gets dilated because of nature's inability to create energy from nothing."
:First of all, energy is only conserved in general relativity if spacetime possesses a timelike Killing vector field. Second of all, "relativistic mass" and "nonconstant speed on light" are outdated noncovariant concepts. Phys 14:11, 12 Aug 2004 (UTC)
replies: text: So? (Do you suggest that they should be reinstated as valid concepts? Jim  14:30, 19 Aug 2004 (UTC)
thread_title:  noncovariant explanation 

message: The sentence 
:So for the majority of cases in the universe, and certainly for almost all cases in our solar system except two already specified as #3 and #4 at the beginning, we may treat the space as flat, as ordinary Euclidean space 
is missing the referents and really should refer to the cases by name, as in, for example
:#3 (Precession of perihelion of Mercury) and #4 (deflection of light rays by a gravitational field) 
When the intervening header markup was inserted, the reference to "#3 and #4" became ambiguous. If this is not what is meant, please add the prose to help the reader. Ancheta Wis 00:27, 18 Oct 2004 (UTC)
replies: text: Thanks for the sugesstion. I modified the text accrodingly and I dropped also the numbers since they might become outdated if someone added to the list a line or two in front of those numbers without necessarily updating the rest of the page. I changed the suggested "by a gravitational field" to "in vicinity of the sun" to avoid the ambiguity of "gravitational field" meaning different things in Newtonian and Einsteinian theories. Jim  19:42, 3 Nov 2004 (UTC)
thread_title: A little disambiguation is in order

message: Does whoever wrote this section realize how large the planck mass is?  I am not disagreeing with their mathematics at this point.  What I would like them to realise is that the implication of the gravity not being transmited by a particle of less than the planck mass is that only large assemblies of particles can create a gravitational field while smaller particles can just react to a field that is already there. 
Consider the though experiment of taking a particle that is less than the planck mass and collapseing it into a black hole. If you do this you get a Schwarzschild radius that is less than the planck lenth. What do you get? --Hfarmer 16:32, 11 Feb 2005 (UTC)
replies: text: See Mach's principle and equivalence principle . That is indeed the implication; that the totality of the fixed stars, and other large assemblages form our conception of gravitation. Ancheta Wis 18:10, 11 Feb 2005 (UTC)

text: (William M. Connolley 18:38, 10 Mar 2005 (UTC)

text: This strikes me as original research. Do you have any published references so we are able to get a grip on its current "notability" in the sciences? Awolf002 18:26, 24 Mar 2005 (UTC)

text: (William M. Connolley 22:11, 24 Mar 2005 (UTC)

text: I do not believe we can accept the argument that "this belongs to the public" means it needs to be in WP. I only see some re-arranged equations that supposedly support your notion how gravity works, which is original research as far as I can tell. I object to having the "re-written" text in this article. Awolf002 15:33, 4 Apr 2005 (UTC)

text: Here is the WP policy about Original Research. What you should avoid is to interpret your re-schaled equations in a way that you just discovered or invented. WP strives to be a secondary source of knowledge, not a primary one. Hope this clarifies my point: If you are searching for a "bullhorn" to announce your ideas, WP is not it. Awolf002 17:31, 7 Apr 2005 (UTC)

text: Sorry. I reverted your changes again, since you still just seem to insert your own conclusions about a rewritten equation. There is no information in the rescaled force equation besides what you infer, and I do not find any primary sources for this. Awolf002 23:09, 12 Apr 2005 (UTC)
thread_title: Newton's law and Planck units

message: Please '12.152.104.82', stop adding that link! It gives a FILE NOT FOUND error. Awolf002 14:10, 13 Apr 2005 (UTC)
thread_title:  External link 

message: I am not impressed with the GR part of this page, but am not in a good position to edit it.
First, the tendency of object to move towards a massive object in GR is due to geodesic deviation, (which I hope to write on soon).  The change in time dilation, while closely associated with gravitaional potential, is not fundamentally the reason for gravitation.
Even if time dilation were known, noone would have known what to make of it or why it was associated with gravitation.  The reason for the illusion of gravity is because gravity does exist in accelerated frames of reference as a D'Almbertian force:  Since you are being accelerated, all objects in inertial motion must fall with respect to you.  The result is what is perceived as a gravitational field.
Also, gravitational potential is nothing more than the difference in kinetic energy that an object would have as a result of its being accelerated with respect to the observer between two positions.  (Yes.  That is the Newtonian definition.  Some things just don't change even in relativity.) There is no need to invoke changes in the speed of light, especially since such changes are in apparent contradiction to the constancy of the speed of light in SR.  (Yes.  I know that this is a real effect as perceived by an observer in accelerated frames even in SR.  However, it is an effect of gravitation instead of a cause and presenting it in this context will cause confusion).
--EMS 03:10, 27 Apr 2005 (UTC)
replies: text: EMS, what would you think about a move of some of the material which you object to, to another article, simply reducing the prose to two sentences about the effect of curvature, etc. Then another sentence which leads to Einstein-Cartan theory which makes clear that an affine theory, not a metric theory, provides a better description of gravitation. In other words, there is a lot more down the road for this subject and GR may well be only a stage in the development of this subject. Might you have a suggestion for the name of the page which could hold the material? Ancheta Wis 10:14, 27 Apr 2005 (UTC)
thread_title:  GR mistakes 

message: Inertia is a rockbottom concept in physics. I use the expression 'manifestation of inertia' to express a dynamic process. When two objects are moving towards each other a force is required to reduce their relative speed to zero, and the necessity to exert a force in order to change velocity is called inertia. With inertia, the acceleration is proportional to the exerted force. Without inertia, objects would be instantly accelerated to lightspeed.
When an electric car designed to regain energy on decellerating is switched to braking then the manifestation of inertia is driving the generators, recharging the batteries. So the manifestation of inertia is doing work. Alternatively, you can do the accounting by stating that the batteries are doing negative work in the process of being recharged.
The way I like to do the accounting is to state that the manifestation of inertia is doing work. (It doesn't really matter, as long as you make sure that you keep track of conservation of energy.) One can also state this in the form that manifestation of inertia is involved in conversion of potential energy to kinetic energy and vice versa.
I think the expression 'inertial force' is an oxymoron because there is one thing that manifestation of inertia cannot do: accelerate an object with respect to the inertial frame of reference. Manifestation of inertia arises in response to a force being exerted. When the force stops, the manifestation of inertia stops immediately too.
Inertia and manifestation of inertia have unique properties, and I think this justifies giving them a name of their own. 
The name 'fictitious force' is horrendous, I hate that expression so bad I can taste it. <BR>
--Cleon Teunissen | Talk 11:17, 28 Apr 2005 (UTC)
thread_title:  manifestation of inertia 

message: Please, do not add this link until you have shown us that this is not original research and can have its own description under "Alternative theories". Otherwise, it will always be removed. Awolf002 22:54, 8 Jun 2005 (UTC)
replies: text: If a viewpoint is held by an extremely small (or vastly limited) minority, it doesn't belong in Wikipedia (except perhaps in some ancillary article) regardless of whether it's true or not; and regardless of whether you can prove it or not.
Aetherometry (which I have never heard of before) most definitely qualifies as being held by a such a minority, assuming that is it not original research (which is even worse).
In addition, it is also noted that the primary focus of this page is Newton's theory of gravity.  As aetherometry is not Newtonian gravity, the link is inappropriate and misleading.  It should not be here, even if aetherometry is true. --EMS | Talk 02:54, 9 Jun 2005 (UTC)

text: Sometimes Wikipedia changes too fast.  Between the time that I saw the NPOV note and compared the most recent versions, the link got re-inserted.  So I assumed that the perpetrator was trying to justify his/her actions using the NPOV.  So I rescind my NPOV remarks, but still refuse to admit this link. --EMS | Talk 03:09, 9 Jun 2005 (UTC)
thread_title:  aetherometry.com link