Question about gravity
in [Physics]
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From: PD on 15 Mar 2010 14:57 On Mar 15, 1:43 pm, kenseto <kens...(a)erinet.com> wrote: > On Mar 15, 2:27 pm, PD <thedraperfam...(a)gmail.com> wrote: > > > > > On Mar 15, 1:25 pm, "kens...(a)erinet.com" <kens...(a)erinet.com> wrote: > > > > On Mar 15, 10:08 am, Huang <huangxienc...(a)yahoo.com> wrote: > > > > > On Mar 15, 9:04 am, kenseto <kens...(a)erinet.com> wrote: > > > > > > On Mar 15, 6:43 am, "Peter Webb" > > > > > > <webbfam...(a)DIESPAMDIEoptusnet.com.au> wrote: > > > > > > Not a whole lot to add to what Inertial in particular said. > > > > > > > In GR, gravity is a virtual force in a similar way to centrifugal force in > > > > > > Newton. In both cases its really an acceleration, and the force is just the > > > > > > product (literally) of this acceleration and the mass of the object. > > > > > > > Einstein in GR gave a geometric interpretation of what gravity is. This is > > > > > > very appealing, because it provides a mechanism for force at a distance. > > > > > > Wrong it provides no such physical mechanism. It merely assumes the > > > > > existence of a physical entity caLLED the fabric of spacetime for the > > > > > interacting object to follow. The problem with such assumption is: > > > > > What is the fabric of spacetime physically? This question is relevant > > > > > because SR/GR deny the existence of physical space. > > > > > > Ken Seto > > > > > What ? ".... SR/GR deny the existence of physical space......" > > > > > What the devil are you saying man ????? > > > > > The theory of relativity says that gravity IS deformation of space. > > > > How can this same theory deny the existence of space ??? Better visit > > > > your optometrist really, really soon. > > > > Sigh...How can you deform space when space is defined by Einstein as > > > "empty space".???? > > > Being empty means it has no matter in it. Having no matter in it does > > not mean that space cannot have physical properties. Physical > > properties are not limited to matter. > > Bullshit. fields are stresses in a solid medium occupying space > according to steven weinberg Solid medium? He said nothing about an electric field being a stress in a solid medium. Do you just make this stuff up as you go along? Physical properties are not limited to matter. You know that there is a permittivity of EMPTY SPACE? You know there is a permeability of EMPTY SPACE? You know there is an impedance of EMPTY SPACE? You know there is a gravitational potential in EMPTY SPACE?
From: "Juan R." González-Álvarez on 15 Mar 2010 15:01 dlzc wrote on Mon, 15 Mar 2010 11:11:30 -0700: > Dear "Juan R." González-Álvarez: > > On Mar 15, 8:03 am, "Juan R." González-Álvarez > <nowh...(a)canonicalscience.com> wrote: >> dlzc wrote on Mon, 15 Mar 2010 07:08:28 -0700: >> > On Mar 14, 11:42 pm, MicroTech <henry.ko.nor...(a)gmail.com> wrote: >> >> Can someone in this forum please help me sort out a confusing issue? >> >> > As usual, you have received some pearls and some jokers so far. >> >> > Let's just add that with "reasonable" simplifications, Einstein's >> > Relativity (gravity =/= force) reduces to Newton's gravitation >> > (gravity = force). >> >> Nope. >> >> First, recent research shows that GR does not reduces to NG, with >> textbooks claims about this being wrong. >> >> Second, even if we ignore this point the approx geodesic equation >> >> a = -@phi/@x >> >> obtained from GR cannot be interpreted as describing gravity as a >> force. Wald does beatiful remarks about this in his textbook in GR. > > Thank you for a very informative response. It will help the OP and > posterity. Not that I agree with you, depending on the simplifications > considered, but not important here. Hum, that part of my message was not addressed to the OP or to "posterity", it was addressed to your mistake that GR (where gravity is never a force), reduces to NG (where gravity is always a force). In the middle I found my copy of Wald, just to check that he analizes a = -@phi/@x in the page 77. Therein Wald explains how the Newtonian viewpoint and the general relativistic viewpoints are radically different and he explains why. That part of his work is correct, the part which is not correct is that his eq. 4.4.21 is not the correct Newtonian expression. This is all explained in some of the references you snipped. The part of my message directly addressing the OP question gave the relevant citations (now snipped by you): Field Theory of Gravitation: Desire and Reality 1999: arXiv:gr-qc/9912003v1. Baryshev, Yurij, V. See also the next analysis done in "From Gravitons to Gravity: Myths and Reality." http://www.worldscinet.com/ijmpd/17/1703n04/S0218271808012085.html And specially http://www.canonicalscience.org/publications/canonicalsciencereports/20092.html All those references explain in detail why textbooks in GR are wrong and why people as Hawking are wrong when do the claims quoted by the OP. The article by Padmanabhan reports some funny inconsistencies found in the classic textbook C. W. Misner, K. S. Thorne and J. A. Wheeler, Gravitation (W. H. Freeman, San Francisco, 1973). and then proves why the claims in this textbook are not right. -- http://www.canonicalscience.org/ BLOG: http://www.canonicalscience.org/publications/canonicalsciencetoday/canonicalsciencetoday.html
From: glird on 15 Mar 2010 15:32 On Mar 15, 2:42 am, MicroTech wrote: > >< Can someone in this forum please help me sort out a confusing issue? Many scientists (including Einstein) claim that gravity is not a force, but the effect of mass on the "fabric of space-time". Many other scientists refer to gravity as one of the four fundamental interactions (three, if one considers the unification of the weak and electromagnetic interactions, the "electroweak" force). > Our physicists are confused because they don't define, thus don't know, what their words mean. For examples, they don't define force or mass or gravity, etc. Once you know that "a force" is "a net pressure"; and that "a mass" is "a quantity of matter"; and that a gravitational FIELD is not a gravitational FORCE, the answers to your question can be understood. >< Adding to the confusion, some scientists use both concepts with no apparent difficulty: Stephen Hawking (in his "A Brief History Of Time") first says that gravity is not a force, but "simply" the effect of mass on the "spacetime fabric" (making it "curve"). However, later in the book, he refers to gravity as a fundamental force, carried by the graviton. So what is gravity, "really"? Does anybody really know? Or do we just know its effects? > I will explain it to you when I finish reading the rest of this message. [Along the way I will enclose my comments in brackets.] >< Is it an attractive force [yes] "mutually pulling" [no] the Earth towards the Sun (and vice versa), "causing" the Earth to "fall" towards the Sun? And due to the "forward motion" [yes] of the Earth, exactly matching the "gravitational pull [no]", it stays in orbit (just like any other satellite, man-made or not); OR Is it the mass of the Sun that "curves space-time" [yes], so no force is interacting with the Earth [not true], it is just moving in a "straight line" along a "curved spacetime" geodesic? [If "staight" means "curved', yes. In reality, no.] At my current level of understanding, gravity should be one or the other, and not both... > You just put your finger on the precise point of ignorance due to failure to define words such as "gravity". > References to published papers (accessible online) would be much appreciated! "The Nature of Matter and Energy", 1965, explains the mechanism of gravity. The explanation is updated -- but not changed insofar as it went -- in "What it all is and Why" (1989) and "The Theory of Reality" (1990) and The Anpheon (2010 and counting). Here, in a nutshell, are the answers to your questions: 1a. A "gravitational field" is a density gradient (grad d) that surrounds and accompanies the nucleus of any matter-unit. (A "matter- unit" is a self-maintaining pattern of matter and energy. The material of which it is formed travels with the pattern.} 1b. The "4-d space-time" invented by Minkowski in 1908 is a map of the grad d permeating space. The first three "dimensions" denote lines u,v,w in different directions than each other in a local portion of non-dimensional space, and the fourth dimension denotes the "time" it would take for a given event to happen at any given point u,v,w. The amount of non-co-ordinate time it would take for a given event to happen is a function (depends on) the density of the place where it happens. The shape of a u or v or w line is a map of the density per successive point in those 3-d directions. Accordingly, even though Minkowski's curved space-time isn't physically real, it DOES accurately map the density and rates of events in matter-filled space. Similarly, because the density is variable in all directions from any given point, and because a g-FIELD is an over-riding density gradient which is represented by the "curvature" of a local portion of the 4d space-time continuum, the result provides a way to accurately predict the path(s) of transient objects. 2. A "gravitational FORCE" is a net pressure. It does exist. But it is not a push or a pull exerted on an object by some external thing. It is a net force that arises INSIDE of any atomic body embedded in, thus permeated by, a g-field. (An atom is a matter-unit. It has a dense spinning nucleus surrounded by a series of clouds of matter each of which has a density gradient that decreases in intensity in the direction of the perimeter.) Now that you know what a g-field and a g-force ARE, you can easily understand the mechanism of gravity: 3a. When an atomic object (a body made of atoms) is embedded in a local g-field (grad d), its own internal grad d sums with that one. This causes a net gradient to exist in every atom in that object. (The "net gradient" is always denser in the direction of the nucleus which is the central cause of the g-field.) 3b. Inside of every atom there are a series of circulating wave systems. (They are called "subatomic particles".) Any such wave system will compress the matter in the +t direction (+t indicates the direction in which something is moving, and -t denotes where it had been a moment earlier). Because of a basic property of ALL matter, particulate or not, the compressed matter in the +t direction(s) will resist further compression increasingly more strongly as its density increases. It therefore presses back. 3c. Although a circulating wavicle (wave system in an atom) is moving in the +t direction for an infinitesimally small amount of time per given point, its speed (cFs, where c is the speed of light in a vacuum and Fs is the Fine Structure number) is so great and its circulatory path (2 pi r, where r is the length of the radius of its orbit) so small, that the total result (the "net force") will be enormously more than the weight (pressure) of the wavicle itself. 3d. Because the direction of the field-force is always toward the denser side, which is always toward the outside source of the g-field in which the atomic body is located, the net force (pressure is a force) that arises inside the responding object will be toward the center of the g-field. Accordingly, gravity (which is BOTH a g-field AND a g-force) is an "attractive force" (its direction is toward the source) and its density gradient(s) are accurately described by the metric of curved space-time. glird
From: mpc755 on 15 Mar 2010 16:43 On Mar 15, 3:40 pm, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > MicroTech wrote: > > Can someone in this forum please help me sort out a confusing issue? > > It's remarkable how simple questions like this generate a firestorm of responses > from people who know essentially nothing about the topic. Plus a few sensible > replies. > > It can be very difficult for people unfamiliar with the subject to distinguish > sense from nonsense. The only reliable way I know is that the fools and idiots > don't refer to textbooks, while the knowledgeable people often do. I recommend > you start with: > > Geroch, _General_Relativity_from_A_to_B_. A non-mathematical > introduction to the concepts of GR. > > > Many scientists (including Einstein) claim that gravity is not a > > force, but the effect of mass on the "fabric of spacetime". Many other > > scientists refer to gravity as one of the four fundamental > > interactions (three, if one considers the unification of the weak and > > electromagnetic interactions, the "electroweak" force). > > In General Relativity, gravitation is MODELED as being a geometrical effect > which is related to the mass and energy distributed in the universe. > > In other theories, such as Newtonian gravity, gravitation is modeled as a force. > > And one of the hot topics in theoretical physics for the past 2-3 decades has > been the quest to unify GR with quantum mechanics, which has generated the > notion of gravitons and guesses of how they might interact. At present there is > no complete and believable theory containing gravitons, however, and they remain > primarily a bunch of guesses. > > Note that discussing MODELS is quite different from claiming "gravity is > thus-and-so". It also describes our state of knowledge much more accurately. > > > So what is gravity, "really"? Does anybody really know? Or do we just > > know its effects? > > From the standpoint of the philosophy of science, it's rather clear that we > humans cannot "really know" how nature actually works. All we can do is make > models of the world we inhabit, and refine those models using experiments and > observations. > > At present, the best model we have of gravity that is generally accepted in the > physics community is General Relativity. But there are rather solid indications > that it is incomplete, and must be replaced by a better theory; unfortunately, > at present we don't know what that theory might look like, and seem to be > depressingly far from understanding even how to approach it. > > > Is it an attractive force "mutually pulling" the Earth towards the Sun > > (and vice versa), "causing" the Earth to "fall" towards the Sun? And > > due to the "forward motion" of the Earth, exactly matching the > > "gravitational pull", it stays in orbit (just like any other > > satellite, man-made or not); OR > > > Is it the mass of the Sun that "curves spacetime", so no force is > > interacting with the Earth, it is just moving in a "straight line" > > along a "curved spacetime" geodesic? > > This can be modeled either way. There are a number of measurements that imply GR > is considerably more accurate than Newtonian gravity. But don't think this > implies that your second description is "correct" just because GR models it that > way -- other "gravitational force" models can obtain equally-accurate agreement > with observations. > > > At my current level of understanding, gravity should be one or the > > other, and not both... > > That's rather naive. Nature does whatever it is that she does, and presumably > that is just one thing (likely corresponding to neither of these models). We > humans try to figure out what nature does, but there are inherent limitations on > our ability to figure such things out, and there are inherent limitations on our > ability to make observations and perform experiments. > > > References to published papers (accessible online) would be much > > appreciated! > > Much of what you might find via Google about this is at best useless, and all > too often downright wrong. I doubt that you're ready to tackle the research > literature. I suggest you start with Geroch's book mentioned above, and branch > out from there. > > Juan R. González-Álvarez wrote: > > First, recent research shows that GR does not reduces to NG, with textbooks claims > > about this being wrong. > > This depends on the meaning of "reduce". Certainly the physicist's sense of this > holds, in that the experiments that support NG do not refute GR, but rather > support it as well. As I have said before, you use an inappropriate meaning of > "reduces", and the textbook examples are just fine to suit their purpose. > > Tom Roberts Or you can realize aether is displaced by matter and the pressure associated with the aether displaced by massive objects is gravity.
From: BURT on 15 Mar 2010 16:52
On Mar 15, 1:43 pm, mpc755 <mpc...(a)gmail.com> wrote: > On Mar 15, 3:40 pm, Tom Roberts <tjrob...(a)sbcglobal.net> wrote: > > > > > > > MicroTech wrote: > > > Can someone in this forum please help me sort out a confusing issue? > > > It's remarkable how simple questions like this generate a firestorm of responses > > from people who know essentially nothing about the topic. Plus a few sensible > > replies. > > > It can be very difficult for people unfamiliar with the subject to distinguish > > sense from nonsense. The only reliable way I know is that the fools and idiots > > don't refer to textbooks, while the knowledgeable people often do. I recommend > > you start with: > > > Geroch, _General_Relativity_from_A_to_B_. A non-mathematical > > introduction to the concepts of GR. > > > > Many scientists (including Einstein) claim that gravity is not a > > > force, but the effect of mass on the "fabric of spacetime". Many other > > > scientists refer to gravity as one of the four fundamental > > > interactions (three, if one considers the unification of the weak and > > > electromagnetic interactions, the "electroweak" force). > > > In General Relativity, gravitation is MODELED as being a geometrical effect > > which is related to the mass and energy distributed in the universe. > > > In other theories, such as Newtonian gravity, gravitation is modeled as a force. > > > And one of the hot topics in theoretical physics for the past 2-3 decades has > > been the quest to unify GR with quantum mechanics, which has generated the > > notion of gravitons and guesses of how they might interact. At present there is > > no complete and believable theory containing gravitons, however, and they remain > > primarily a bunch of guesses. > > > Note that discussing MODELS is quite different from claiming "gravity is > > thus-and-so". It also describes our state of knowledge much more accurately. > > > > So what is gravity, "really"? Does anybody really know? Or do we just > > > know its effects? > > > From the standpoint of the philosophy of science, it's rather clear that we > > humans cannot "really know" how nature actually works. All we can do is make > > models of the world we inhabit, and refine those models using experiments and > > observations. > > > At present, the best model we have of gravity that is generally accepted in the > > physics community is General Relativity. But there are rather solid indications > > that it is incomplete, and must be replaced by a better theory; unfortunately, > > at present we don't know what that theory might look like, and seem to be > > depressingly far from understanding even how to approach it. > > > > Is it an attractive force "mutually pulling" the Earth towards the Sun > > > (and vice versa), "causing" the Earth to "fall" towards the Sun? And > > > due to the "forward motion" of the Earth, exactly matching the > > > "gravitational pull", it stays in orbit (just like any other > > > satellite, man-made or not); OR > > > > Is it the mass of the Sun that "curves spacetime", so no force is > > > interacting with the Earth, it is just moving in a "straight line" > > > along a "curved spacetime" geodesic? > > > This can be modeled either way. There are a number of measurements that imply GR > > is considerably more accurate than Newtonian gravity. But don't think this > > implies that your second description is "correct" just because GR models it that > > way -- other "gravitational force" models can obtain equally-accurate agreement > > with observations. > > > > At my current level of understanding, gravity should be one or the > > > other, and not both... > > > That's rather naive. Nature does whatever it is that she does, and presumably > > that is just one thing (likely corresponding to neither of these models). We > > humans try to figure out what nature does, but there are inherent limitations on > > our ability to figure such things out, and there are inherent limitations on our > > ability to make observations and perform experiments. > > > > References to published papers (accessible online) would be much > > > appreciated! > > > Much of what you might find via Google about this is at best useless, and all > > too often downright wrong. I doubt that you're ready to tackle the research > > literature. I suggest you start with Geroch's book mentioned above, and branch > > out from there. > > > Juan R. González-Álvarez wrote: > > > First, recent research shows that GR does not reduces to NG, with textbooks claims > > > about this being wrong. > > > This depends on the meaning of "reduce". Certainly the physicist's sense of this > > holds, in that the experiments that support NG do not refute GR, but rather > > support it as well. As I have said before, you use an inappropriate meaning of > > "reduces", and the textbook examples are just fine to suit their purpose. > > > Tom Roberts > > Or you can realize aether is displaced by matter and the pressure > associated with the aether displaced by massive objects is gravity.- Hide quoted text - > > - Show quoted text - You can share the flow of space or go against it while decelerating infreefall. When fall is resisted there is weight by a space speed timeless acceleration. There is timeless acceleration with an increase in flow of energy in time. A ball is pushed down the hill and has full weight. Mitch Raemsch |