Freethought & Rationalism Archive

Ted Hoffman · 10-01-2002, 02:20 AM

I need the help of someone with some knowledge of Physics, astronomy etc.
The conventional definition of gravity is "The invisible force between objects that makes objects attract each other."

Gravity has been said to be the curvature of space-time according to relativity. But it is said that this space-time model of GR lacks causality and "Le Sage-type models are our only current viable alternatives that at least respect the causality principle." says
<a href="http://www.metaresearch.org/publications/books/PushingG.asp" target="_blank">Says this review</a> which adds:

Quote:

. Here we learn the "bare essence" of Le Sage’s inspiration. The universe is filled with "ultra-mundane corpuscles" of very small size and very high speed that constantly impinge upon matter. On Earth, the apple falls from the tree, not because something from the Earth pulls it down, but because more corpuscles strike the apple from above than from below because the Earth absorbs and blocks some corpuscles from below. Two bodies in space likewise shadow one another from some corpuscle impacts, with the result that the corpuscles that do impact produce a net force on the outward-facing sides of the bodies, pushing them toward one another. From this mode of action, we see the origin of the title of this book: "pushing gravity".

Matthew Edwards discusses the brief revival of Le Sage’s model in the late 19th century, spearheaded by Lord Kelvin. The debates on this subject among Kelvin, Maxwell, and other contemporaries are classic science, with each side making telling arguments. But ultimately, the theory was swept away by the advance of Einstein’s general relativity in the early 20th century.
This reviewer’s own chapter provides the most complete exposition of how Le Sagian gravity produces all the features of Newtonian and Einstein gravitation, and several more features presently unrecognized by physics as well. The key to understanding the phenomena and answering objections is to recognize the need for two different media operating on vastly different scales, a "light-carrying medium" and a graviton medium. This chapter includes the modified Newtonian formulas needed to compute these effects, together with numerical estimates of the new constants in the formulas. These include a gravitational shielding coefficient, a graviton drag coefficient, and a finite-range parameter. The chapter proceeds to show how this picture fits into a broader cosmological and quantum physics context. For example, it leads to a natural mechanism for redshifting light as it travels, providing an alternative to an expanding universe. It also offers an alternative to the as-yet-undiscovered "dark matter", which need not exist after all. It eliminates the singularity when matter collapses to an ultra-dense state (i.e., no more "black holes" as such, although high-matter-density objects still exist). And it introduces enough heat energy to readily explode planets if anything were to interfere with the efficient flow of graviton-heated light-carrying medium from planetary interiors. A list of historical objections to Le Sage-type models and their resolutions is also presented.

Are there people here who are familiar with this "pushing gravity" model? I would like to know its weaknesses and I am expecially interested in it as far as planetary explosion mechanisms are concerned. But any critical comments would be appreciated.

[ October 01, 2002: Message edited by: Intensity ]

Secular Pinoy · 10-01-2002, 04:40 AM

This <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=57&t=000414&p=" target="_blank">thread</a> discusses the current understanding on gravity, though it did not delve in this pushing gravity hypothesis. It a good start, though.

Jesse · 10-01-2002, 05:37 AM

I don't know anything about "pushing gravity", but I was struck by this section of Van Flandern's review:

Quote:

Many of today�s physicists have not looked or even thought beyond the "curved space-time" explanation for gravitation. Those who have, realize that a curvature cannot be a cause of a motion unless a force acts. For example, in the classical "rubber sheet analogy", a small body on the side of a dent in a rubber sheet made by a large mass will not start rolling downhill unless there is already gravity under the rubber sheet to give meaning to "downhill" and provide a force. But that defeats the purpose of the analogy as an explanation for the cause of gravity.

Van Flandern is really badly misunderstanding the rubber sheet analogy here. Hasn't he ever heard of "geodesics", the central idea of general relativity? If you're an ant travelling along a curved surface, the shortest distance between two points may not be a "straight line" but rather some sort of curved path, and general relativity just says that mass curves spacetime and matter always travels on geodesics in this spacetime. In the rubber sheet analogy, it would work just as well if you treat gravity wells as bumps rather than depressions--either way, geodesics on this sheet will look the same.

Here's an interesting <a href="http://www.lns.cornell.edu/spr/1999-05/msg0016447.html" target="_blank">sci.physics.research post</a> suggesting the rubber sheet analogy should be abandoned because it tends to mislead laymen in just this way--still, one would expect more from Van Flandern if he claims to understand general relativity himself.

Ted Hoffman · 10-01-2002, 09:17 AM

Secular Pinoy: Thanks for the link.

Jesse: Hasn't he ever heard of "geodesics", the central idea of general relativity? If you're an ant travelling along a curved surface, the shortest distance between two points may not be a "straight line" but rather some sort of curved path, and general relativity just says that mass curves spacetime and matter always travels on geodesics in this spacetime.

Intensity This ant analogy can't be used to discredit Flandern's argument because an ant has energy which it uses to move against many other forces but Flanderns' argument addresses the case of an object (non-living): "...a small body on the side of a dent in a rubber sheet made by a large mass will not start rolling downhill unless there is already gravity under the rubber sheet to give meaning to "downhill" and provide a force. But that defeats the purpose of the analogy as an explanation for the cause of gravity". His argument, I beleive, is that the rubber-sheet analogy relies on the concept of gravity to have meaning so its a self referencing argument (why does the large mass make a dent on the sheet? Why can't the sheet curve upward for example?) In any case, your ant analogy is false because by definition "Objects which travel under the sole influence of gravity follow geodesics." An ant doesn't travel under the sole influence of gravity does it?. I have seen better analogies - like the person driving when he takes a corner on a bend and the centrifugal force pulls him/her away from his direction of movement, the centrifugal force there can represent a potential well and this is an analogy that does not rely on gravity.
The link you provided says "the rubber-sheet
analogy completely fails to convey the essential point that geodesics are *straight* in the *intrinsic* geometry of spacetime"

In what sense exactly is the curved path shorter than a straight one?

To expect that Van Flandern has a poor understanding of the rubber sheet analogy, or to wonder whether he has ever heard of geodesics requires quite a stretch of imagination. Either you have no idea who he is, or you are letting something else cloud how you assess whatever he wrote. I would also appreciate it if you desisted from such ad-hominems and instead focused on the argument itself, not the one making it.

[ October 01, 2002: Message edited by: Intensity ]

Ted Hoffman · 10-01-2002, 09:44 AM

Oh, Jesse and others, I have found a link that can give you a pretty good idea about push gravity theory <a href="http://www.magna.com.au/~prfbrown/news99_b.htm" target="_blank">An Overview of the Concept of Attenuation [Pushing] Gravity </a>

I have also found some refutations <a href="http://www.lns.cornell.edu/spr/2000-09/msg0027985.html" target="_blank">Gravity Push Refuted</a>

I haven't gone through them yet.

Jesse · 10-01-2002, 10:00 AM

Intensity:
This ant analogy can't be used to discredit Flandern's argument because because an ant has energy

Equally irrelevant. I just used the ant to illustrate the idea of a being stuck on the space with no sense of an "outside" and no ability to see the shape of the space from above--the idea is that this ant, trying to find the shortest path between two points, would have to follow a geodesic. The ant itself (or how it moves) is not important, all that's important is the idea that the shortest path between points is a geodesic. The idea that matter under the influence of gravity follows geodesics is simply an axiom of general relativity, it doesn't need a meta-explanation in terms of "forces" any more than "every action has an equal and opposite reaction" needs a meta-explanation in terms of miniature accountants who keep track of how much force was applied to their particle and calculate how much force must be applied back in order to balance the books. Every theory has axiomatic statements: "matter in the absence of non-gravitational forces always travels along geodesics" is one in general relativity.

edit: actually, a better comparison would be the fact that moving objects in classical physics travel in straight lines unless some outside force is acting on them. This corresponds rather closely to the notion that objects in general relativity travel along geodesics, especially since geodesics in flat spacetime are straight lines. Do you (or Van Flandern) think that travelling along geodesics needs a meta-explanation but travelling in straight lines does not? If so, why?

Intensity:
yet his argument addresses the case of an object (non-living): "...a small body on the side of a dent in a rubber sheet made by a large mass will not start rolling downhill unless there is already gravity under the rubber sheet to give meaning to "downhill" and provide a force. But that defeats the purpose of the analogy as an explanation for the cause of gravity". His argument, I beleive, is that the "curved space-time" relies on the concept of gravity to have meaning so its a self referencing argument (why does the large mass make a dent on the sheet? Why can't the sheet curve upward for example?)

As I said before, it wouldn't make any difference at all if you inverted the sheet so that dents became bumps--the shortest path between any two points would be exactly the same. This is exactly why I said Van Flandern had misunderstood the rubber sheet analogy.

Intensity:
In any case, your ant analogy is false because by definition "Objects which travel under the sole influence of gravity follow geodesics." An ant doesn't travel under the sole influence of gravity does it?

Uh, that's why it's an "analogy." You might as well say "the analogy is false because by definition 'mass bends spacetime' but a sheet of rubber is not spacetime is it?"

In an analogy, one thing represents another. In my analogy the correspondence is as follows:

curved rubber sheet = curved spacetime

ant trying to find shortest path between two points = object moving in the absence of non-gravitational forces

Intensity:
I have seen better analogies - like the person driving when he takes a corner on a bend and the centrifugal force pulls him/her away from his direction of movement, the angular momentum there can represent a potential well and this is an analogy that does not rely on gravity.

This analogy doesn't say anything about how gravity relates to curved spacetime, which is what we were discussing. And come to think of it, rather than an "analogy" it looks to me like a rather concrete illustration of the equivalence principle.

Intensity:
In what sense exactly is the curved path shorter than a straight one?

Shorter means shorter. Take a measuring tape and lay it along the geodesic and it will be shorter than any other path you could draw between the two points.

Consider airplane flights, which generally travel on the shortest path between two points, which on a sphere is a section of a "great circle" (a path whose center is the center of the sphere, like the equator or the lines of longitude). But if you project this path onto a Mercator map it will look like a curve rather than a straight line.

Intensity:
To expect that Van Flandern has a poor understanding of the rubber sheet analogy, or to wonder whether he has ever heard of geodesics requires quite a stretch of imagination. Either you have no idea who he is, or you are letting something else cloud how you assess whatever he wrote.

Yes, I know who he is--among other things he's a relativity-denier who argued that GPS sattelites don't use general relativity, but relativists who checked his claims said he had simply gotten the math wrong:

Quote:

More recently, astronomer Tom Van Flandern, who once worked for the U.S. Naval Observatory in Washington and who conducts eclipse expedition tours and runs a Web site with a newsletter that promotes interest in scientific ideas "outside of the mainstream of theories in Astronomy," claims to have discovered a dirty secret. Van Flandern was hired to do some consulting work for the physics department at the University of Maryland on the global positioning system (GPS), the ring of 24 satellites circling the Earth, which, among other convenient attributes, will be able to pinpoint precise locations for befuddled automobile drivers anywhere on the planet. According to him, the confusing "rigmarole" of relativity isn't needed to maintain the GPS, even though it clearly should be.

Van Flandern has argued that because of Einstein's theory of relativity, clock rates on GPS satellites should need to be adjusted continuously to keep them in sync with users on Earth. But they're not, he told the American Spectator (April 1999). The GPS programmers don't need relativity. "They have basically blown off Einstein," Van Flandern says.

Is this true? Could this be a real crack in the "temple" of Einstein's theory?

I asked Neil Ashby, a professor of physics who works at the University of Colorado and specializes in theoretical general relativity with practical applications. "I am acquainted with Tom Van Flandern and his view," he told me. "It is incorrect to claim that no relativistic corrections are used after launch. Actually because GPS satellites are in eccentric orbits, they suffer frequency variations due to their varying speeds and varying heights above the Earth's surface. Information is transmitted down to the receivers from each satellite, which enables receivers to make a relativistic correction which accounts for these effects."

He added: "Einstein has not been 'blown off.' On the contrary, a great deal of thought has gone into the problem and all of the known special and general relativistic effects have been accounted for if they are predicted to be big enough to be important."

Other gravitation specialists, such as Charles Misner at the University of Maryland, Lawrence Mead of the University of Southern Mississippi, Clifford Will of the University of Washington in St. Louis and Steve Carlip of the University of California at Davis, confirm that special and general relativity are built into the software for GPS.

But the most interesting aspect of Van Flandern's objections to relativity bears directly on Einstein himself and his professional integrity. According to Van Flandern, Einstein cheated.

Van Flandern told the American Spectator's Washington correspondent, Tom Bethell, that he had reason to believe Einstein manipulated his field equations for one of his most momentous predictions: the advance of the perihelion of Mercury, the point in orbit where a planet is closest to the sun. Astronomers have long observed that this point, like the oval end of an ellipse drawn with a spirograph, is itself subject to motion, and over the years revolves around the sun just like the planet itself. In the case of Mercury, this effect is pronounced. It was assumed to be due to gravity and the closeness of the planet to the sun, but Newtonian theory could never predict its advance accurately. It was a classic problem by the time Einstein came along, and his general theory of relativity solved it immediately.

Too brilliantly, for some.

According to the Spectator's account, Van Flandern "asked a colleague at the University of Maryland, who as a young man had overlapped with Einstein at Princeton's Institute for Advanced Study, how, in his opinion, Einstein had arrived at the correct multiplier. This man said it was his impression that, 'knowing the answer,' Einstein had 'jiggered the arguments until they came out with the right value.'"

Curious why the source for this remarkable claim was never named, I contacted Bethell, who told me he was not given permission to name the source. Van Flandern was even more mysterious: "There's a reason," he wrote, "why that person was not quoted by name." He then suggested I send him any queries, which he could forward to this source for consideration.

Instead, I went to the University of Maryland on the Web, where a search revealed five working physicists who got their doctorates from Princeton within the decade after Einstein's death.

One of them is Carroll Alley, who received his degree in 1962. When I called him to ask about the mysterious quote, he told me he had indeed hired Van Flandern to do some work in celestial mechanics. As for knowing Einstein personally, Alley recounted how he had had the pleasure of attending the last lecture given by the great physicist before his death in 1955.

When asked about the claim that Einstein manipulated his equations to get a correct prediction, Alley, acknowledging that he was indeed the mystery man quoted in Bethell's article, told me, "That was not an accurate quote."

What he did say was that Einstein knew that Mercury's observed perihelion was 43 arc seconds per century more than predicted by Newton's theory. "A lot of people say that he didn't know it, but he did," said Alley. This is no surprise to anyone familiar with the history of astronomy or the various biographies of Einstein written by Ronald Clark, Abraham Pais and Albrecht Flsing.

Indeed, the burning question at the time Einstein was working on general relativity was not what the perihelion figure was, but how to account for it without making special assumptions. This is a key point, because cranks offer all sorts of counter theories that rely on nothing but special assumptions.

In short, to say that Einstein knew what the correct prediction should be and that he "jiggered" his multipliers to get it are two very different statements, the latter of which Alley disavowed in our conversation.

I contacted Van Flandern for clarification about the quote he had given to the Spectator regarding Einstein's alleged tampering. "Basically," he answered, "the choice of coefficients of potential phi in the space-time metric is arbitrary. Einstein knew the unmodeled perihelion motion of Mercury, and therefore confined his attention to metrics that predicted this quantity correctly."

I asked Carlip whether this made any sense.

"No, it makes no sense at all. Van Flandern seems to have invented a free parameter where none exists. There is one free parameter, but it's just Newton's gravitational constant, G, and is fixed completely by the requirement that the theory reduce to Newtonian gravity in the weak-field, low-velocity limit. Once you've fixed that, everything else is completely determined." According to Carlip, "Van Flandern seems to be under the impression that there are a bunch of adjustable parameters in general relativity that can be fiddled with. This is certainly not true."

"As far as I can tell," he added, "Van Flandern simply doesn't understand the Einstein field equations."

Other physicists I queried also flatly reject the notion that Einstein ever fooled with his figures. "I doubt very much that Einstein had any problem calculating [the perihelion]," wrote Ted Jacobson, a gravitation specialist at the University of Maryland. Ashby agreed, as did Lee Smolin, a specialist in general relativity at the University of Pennsylvania and author of "The Life of the Cosmos": "I have also personally checked the calculations about the perihelion of Mercury, as have I'm sure thousands of other people."

Michel Janssen and John Stachel have been working on the Einstein Papers Project at Boston University, reviewing the letters and papers of Einstein for publication in a new series. Janssen in particular worked closely on a review of Einstein's Mercury paper, and he was not amused about the accusation of fudging.

"Not to put too fine a point on it," he said, "that is crap."

--from <a href="http://dir.salon.com/people/feature/2000/07/06/einstein/index.html?pn=3" target="_blank">this</a> salon.com article on relativity-deniers

Intensity:
I would also appreciate it if you desisted from such ad-hominems and instead focused on the argument itself, not the one making it.

Van Flandern's competence in understanding general relativity does have some relevance to assessing his views on alternative theories of gravity. In any case, saying that someone has misunderstood a scientific subject is not a personal attack and therefore does not qualify as an "ad-hominem" (it might be an ad hom if I was using this to say his views on 'pushing gravity' must be wrong, but I mainly just wanted to address his criticisms of general relativity).

[ October 02, 2002: Message edited by: Jesse ]

Jesse · 10-01-2002, 10:16 AM

You can find a bunch of newsgroup threads on the subject of "pushing gravity" <a href="http://groups.google.com/groups?q=%22le+sage%22+gravity&ie=ISO-8859-1&hl=en&btnG=Google+Search" target="_blank">here</a>. Unfortunately I didn't see any threads where the "pushing gravity" advocates actually offered detailed calculations of how their theory could duplicate experimentally-confirmed results from general relativity.

[ October 01, 2002: Message edited by: Jesse ]

atrahasis · 10-01-2002, 09:57 PM

Now, Space Time is not only warped it is twisted!
Thats according to Wei Cui of the Massachusetts Institute of Technology<a href="http://whyfiles.org/052einstein/frame_drag4.html" target="_blank">Here</a>

Ted Hoffman · 10-02-2002, 01:19 AM

Jesse, thanks a million for your response especially for the links to pages on push gravity and the paper on Van Flandern questioning Einsteins methodology.
But its clear from the info you have provided that Einstein knew the outcome:

Quote:

What he did say was that Einstein knew that Mercury's observed perihelion was 43 arc seconds per century more than predicted by Newton's theory

If he already knew it, it simply means he needed a way (formula) of arriving at it as Flandern says :

Quote:

"the choice of coefficients of potential phi in the space-time metric is arbitrary. Einstein knew the unmodeled perihelion motion of Mercury, and therefore confined his attention to metrics that predicted this quantity correctly."

I don't see the connection between being incompetent and thinking Einstein "confined his attention to metrics that predicted this quantity correctly".

When someone says something that doesn't go down well with mainstream ideas or challenges currently accepted paradigms, he is called incompetent and a crank. I think its very unfortunate.
But I guess its human nature. We simply have to live with it.
see <a href="http://groups.google.com/groups?q=the+speed+of+gravity+repeal+speed+limit&h l=en&lr=&ie=UTF-8&selm=8oafnc%248gr%241%40nntp9.atl.mindspring.net &rnum=1" target="_blank">this page</a> where he systematically and competently refutes all points his objectors make. Notable are the following statements he makes (this would be for Jesse who makes simplistic assesments of Flanderns works):

Quote:

...your objection to a new way to think about the problem seems to be "But we're accustomed to doing it this other way."
Do you have any objection more substantial than that?

Quote:

But you have merely recited the standard view for the past century without answering any of the experimental objections (gedanken and actual) to that interpretation that have now arisen. The problem here is not that I need to become familiar with the standard model. It is that I am all too familiar with it, and have raised a number of points to show that the
standard interpretation cannot explain experiments and causality at the same time. It is therefore logical to switch to another interpretation that can explain both. Perhaps the most important point of all in my new draft is that, even if the standard interpretation were still experimentally viable despite my conclusion that it is not, an alternate interpretation consistent with ftl propagation in forward time exists and is clearly experimentally viable.
That is more important than showing that this particular interpretation is "the right one" because, by merely showing that the universal speed limit doesn't need to exist anymore, we open up wonderful new avenues for physics to explore and to advance the understanding of nature.

And about the rubber sheet analogy and its violation of causality principle:

Quote:

I'm pointing out that this mathematical approach pays a terrible price in physics by violating the causality principle. Those equations may work, but call for instantaneous updating of distant fields to infinity, or the absence of regeneration in static fields, either of which makes the acceleration of bodies magical (i.e., without physical cause).
To use a loose analogy, you cite equations that describe the acceleration of bodies, but not the cause of that acceleration. But equations, however elegant, do not have the means to make physical bodies accelerate. Only interaction with a tangible entity can do that. If a "field" or "curved space-time" is the cause of the acceleration of a target body, then the field or curvature must consist of tangible entities that can act on matter.

Just think about the rubber sheet analogy, even as an analogy. If the target body sits on the side of a dent in the rubber sheet, why wouldn't it stay in place forever? What gives the target body a sense of which direction is "down" unless a tangible force (such as gravity under the sheet) comes along and gives it a push or pull in some preferred direction? Those are the
kinds of issues that equations alone cannot begin to answer. But enabling possible physics answers to such questions is what my paper is all about.

And as for your "unquestionable Einstein:

Quote:

bs: Einstein found and answered that in 1907 or thereabouts when he realised that his ideas about scalar gravity would not work.
tvf: But Dumbkoff [1908] shot down Einstein's answer, and was later awarded a Nobel Prize for his insight. :-)

Seriously, what good is a vague illusion to the preeminent physicist of the 20th century having answered my objection 93 years ago when neither you nor anybody else knows today what that answer is? I've seen Einstein's papers on this subject in the 1912-1916 period, a crucial period for the
formulation of GR, and he was citing standard Lienard-Wiechert retarded potentials with scalar retardation only in that time period. I seriously
doubt that he had any deeper insights that he never felt the need to mention again after 1907.

Incompetent indeed.

More importantly, I would appreciate it if someone here can pinpoint exactly which part of <a href="http://www.metaresearch.org/cosmology/gravity/speed_limit.asp" target="_blank">this paper</a> demonstrates that Flandern does not understand GR equations of motion. In the paper, he directly deals with Carlips objections as he demonstrates that ftl(faster than light) speeds are possible and violate no physical laws - his use of GR, LR and SR equations to support the idea necessitates only one with a proper grasp of such equations to be able to determine the validity of his arguments.
Any pysicist or astronomer who shows signs of backing up what he says might have his job on the line, or get labelled a crank him/herself so what we get from them should be expected. I talked earlier about the "collective madness" that grips scientists. Any new idea that challenges old paradigms is met with iron-clad resistance. Fortunately, me as a layman is not obliged to take sides - yet.

This is a guy who deals with objections from fellow scholars directly and he has a site that exposes his ideas to criticism, and he takes time to respond to silly questions from both experts and laymen alike. He doesn't strike me as a fruitcake.

So, anyone?

PS: I intend to write to Steve Carlip to get his specific objections to what Van Flandern argues (especially about weaknesses of rubber-sheet analogy violations of the causality principle and ftl speeds being possible) and I hope he wont resort to "but that violates the principles of GR", or "but physics textbooks say so" kind of arguments.

[ October 02, 2002: Message edited by: Intensity ]

Jesse · 10-02-2002, 03:49 AM

Intensity:
Jesse, thanks a million for your response especially for the links to pages on push gravity and the paper on Van Flandern questioning Einsteins methodology.
But its clear from the info you have provided that Einstein knew the outcome:

Quote:

What he did say was that Einstein knew that Mercury's observed perihelion was 43 arc seconds per century more than predicted by Newton's theory

Sure, just like Newton already knew the orbits of the planets that he later showed how to derive from his theory. The point is that before Newton there was no simple law that could be used to derive the observed outcome, and the same is true of Einstein and the perihelion of Mercury.

Intensity:
If he already knew it, it simply means he needed a way (formula) of arriving at it as Flandern says :

Quote:

"the choice of coefficients of potential phi in the space-time metric is arbitrary. Einstein knew the unmodeled perihelion motion of Mercury, and therefore confined his attention to metrics that predicted this quantity correctly."

But this is the part that Van Flandern got wrong, according to every single relativists who reviewed his claim. The only arbitrary coefficient in the space-time metric is the gravitational constant G, whose value has been known experimentally since Newton�s time. Thus, there is no way that Einstein could have fine-tuned the parameters to agree with the observed perihelion of Mercury. And the space-time metric itself can be derived uniquely from basic assumptions of general relativity like the equivalence principle and the idea that objects follow geodesics.

Intensity:
I don't see the connection between being incompetent and thinking Einstein "confined his attention to metrics that predicted this quantity correctly".

The connection is that he made bold claims about Einstein fudging his results which were based on a faulty understanding of the mathematics of general relativity, at least according to every relativist who reviewed his claim. Unless they are all wrong on this point and he is correct, I would say that makes him "incompetent" in the subject of general relativity.

Intensity:
When someone says something that doesn't go down well with mainstream ideas or challenges currently accepted paradigms, he is called incompetent and a crank. I think its very unfortunate.

Except that this is not an empirical issue which depends on your interpretation of the evidence, this is simply a mathematical question about the equations of general relativity. The space-time metric either has a free parameter or it doesn�t, there�s no possibility of a "paradigm shift" here (although certainly a paradigm shift could lead us to think the equations of general relativity are wrong, but that�s a totally different issue).

Likewise, the question of how GPS sattelites work is also not open to debate, his claims are either right or wrong. According to the people who actually know how their clocks are calibrated, he is wrong.

Intensity:
see this page where he systematically and competently refutes all points his objectors make.

How do you know he "systematically and competently refutes" all their objections if you yourself are not-well versed in this subject? For someone who claims to be open-mindedly going wherever the evidence takes him rather than simply cheerleading for Van Flandern, this is an odd claim.

In any case, none of his arguments on that page say anything about the issue of free parameters in the space-time metric, or about the workings of GPS sattelites, so I�m not sure why you think it�s relevant.

Quote:

But you have merely recited the standard view for the past century without answering any of the experimental objections (gedanken and actual) to that interpretation that have now arisen. The problem here is not that I need to become familiar with the standard model. It is that I am all too familiar with it, and have raised a number of points to show that the
standard interpretation cannot explain experiments and causality at the same time.

Unless all the relativists quoted simply don�t understand the mathematics of the space-time metric, apparently he is not so familiar with the standard model.

Quote:

I'm pointing out that this mathematical approach pays a terrible price in physics by violating the causality principle. Those equations may work, but call for instantaneous updating of distant fields to infinity, or the absence of regeneration in static fields, either of which makes the acceleration of bodies magical (i.e., without physical cause).

Another quote which I am fairly certain is inaccurate simply on mathematical grounds (again, this is not an empirical issue where there is room for debate). I have read a number of different statements by relativists on exactly this issue of the speed of gravitational influences in general relativity, and they all say that according to the mathematics of GR, such influences can travel no faster than the speed of light.

Quote:

To use a loose analogy, you cite equations that describe the acceleration of bodies, but not the cause of that acceleration. But equations, however elegant, do not have the means to make physical bodies accelerate. Only interaction with a tangible entity can do that. If a "field" or "curved space-time" is the cause of the acceleration of a target body, then the field or curvature must consist of tangible entities that can act on matter.

This is simply a philosophical claim, and I have already explained why I think this is nonsense. Every theory has axiomatic statements�why does the idea that objects travel along geodesics need a meta-explanation in terms of "interaction with a tangible entity?" Presumably he does not think that objects in classical physics moving in straight lines requires any such meta-explanation�why not? A geodesic is the closest equivalent of a straight line in a curved space. Likewise, why doesn�t "for every action there is an equal and opposite reaction" require some sort of meta-explanation to tell us why the reaction is equal as opposed to twice the magnitude or something? His claims here appear to be founded on nothing but his own intuitions.

Quote:

Just think about the rubber sheet analogy, even as an analogy. If the target body sits on the side of a dent in the rubber sheet, why wouldn't it stay in place forever? What gives the target body a sense of which direction is "down" unless a tangible force (such as gravity under the sheet) comes along and gives it a push or pull in some preferred direction? Those are the
kinds of issues that equations alone cannot begin to answer.

I don�t know how many times I can say that the issue of "down" and "up" is irrelevant to the rubber sheet analogy. All that is relevant is the fact that the shortest distance between two points on a curved sheet will not always be a straight line. You could replace the depressions by humps and it would still be a perfectly valid analogy. Van Flandern has simply taken the analogy too literally here, a common mistake among laymen but one which no competent relativist would make.

Intensity:
And as for your "unquestionable Einstein:

Gee Intensity, I don�t remember saying anything about Einstein being "unquestionable." Perhaps you could provide a quote where I even hinted at anything like that. Remember, the thing I am calling Van Flandern "incompetent" for is not that he thinks Einstein�s theory is wrong, but simply that he has failed to understand the theory on its own terms. It would be like if I claimed that the force of gravity is inversely proportional to the cube of the distance in Newtonian physics�regardless of how gravity works in real life, the fact is that the equations of Newtonian physics tell you the force is inversely proportional to the square of the distance.

Quote:

bs: Einstein found and answered that in 1907 or thereabouts when he realised that his ideas about scalar gravity would not work.
tvf: But Dumbkoff [1908] shot down Einstein's answer, and was later awarded a Nobel Prize for his insight. :-)

Unless I have misunderstood, this claim would appear to be in error. According to <a href="http://www.slac.stanford.edu/library/nobel/" target="_blank">this</a> page I can find no record of anyone named "Dumbkoff" receiving a Nobel Prize in physics.

Quote:

Seriously, what good is a vague illusion to the preeminent physicist of the 20th century having answered my objection 93 years ago when neither you nor anybody else knows today what that answer is? I've seen Einstein's papers on this subject in the 1912-1916 period, a crucial period for the
formulation of GR, and he was citing standard Lienard-Wiechert retarded potentials with scalar retardation only in that time period. I seriously
doubt that he had any deeper insights that he never felt the need to mention again after 1907.

Incompetent indeed.

Uh, do you actually understand the details of what Van Flandern was talking about here or are you just satisfied that no incompetent man could talk with such self-assurance?

Intensity:
More importantly, I would appreciate it if someone here can pinpoint exactly which part of this paper demonstrates that Flandern does not understand GR equations of motion. In the paper, he directly deals with Carlips objections as he demonstrates that ftl(faster than light) speeds are possible and violate no physical laws - his use of GR, LR and SR equations to support the idea necessitates only one with a proper grasp of such equations to be able to determine the validity of his arguments.

I�m not sufficiently familiar with the mathematics of GR to understand the issues involved in the speed-of-gravity calculations. Unless you are yourself, I wonder why you ask, since you presumably wouldn�t understand the answer. If you�re genuinely interested and not just trying to "challenge" relativists, you could take a look at <a href="http://math.ucr.edu/home/baez/PUB/debate" target="_blank">this</a> compilation of newsgroup posts in response to various Van Flandern claims about relativity.

Intensity:
Any pysicist or astronomer who shows signs of backing up what he says might have his job on the line, or get labelled a crank him/herself so what we get from them should be expected.

Not really, Intensity. Again, you might make such an argument if we were talking about empirical issues, but this is just math! If Van Flandern was right and a "physicist or astronomer" could see that his math was correct and that the mainstream had made some sort of mistake, I don�t see how anyone could criticize them for pointing out, specifically, what that mistake was. Seriously, do you think paradigm shifts apply to math too?

Intensity:
I talked earlier about the "collective madness" that grips scientists. Any new idea that challenges old paradigms is met with iron-clad resistance. Fortunately, me as a layman is not obliged to take sides - yet.

The more you make statements like "Incompetent indeed" (about a paragraph by Van Flandern which you probably didn�t understand and which had nothing to do with what I was accusing him of incompetence for) or claim that a paper by him "systematically and competently refutes all points his objectors make" (when, again, I doubt you understood many of the details of the issues being debated) the more I find your claims of impartiality difficult to swallow.

Intensity:
I intend to write to Steve Carlip to get his specific objections to what Van Flandern argues (especially about weaknesses of rubber-sheet analogy violations of the causality principle and ftl speeds being possible) and I hope he wont resort to "but that violates the principles of GR", or "but physics textbooks say so" kind of arguments.

Again, this is just a mathematical question of what the mathematics of GR does or does not predict, regardless of the empirical truth about how fast gravitational effects propogate in reality. As such "that violates the principles of GR" would be a perfectly valid response, provided he showed in detail how the equations lead to the conclusion that gravitational waves travel at light. But again, what would be the point of asking this question unless you already knew enough about the mathematics to be able to follow the proof?

One thing you could ask him, though, is whether it is important that the depressions point "down" in the rubber-sheet model, or whether it is only the shortest distance between points that is relevant. I am confident that he would verify my answer on this.

[ October 02, 2002: Message edited by: Jesse ]

10-01-2002, 09:17 AM	#4
Ted Hoffman Veteran Member Join Date: Feb 2001 Location: "" Posts: 3,863	Secular Pinoy: Thanks for the link. Jesse: Hasn't he ever heard of "geodesics", the central idea of general relativity? If you're an ant travelling along a curved surface, the shortest distance between two points may not be a "straight line" but rather some sort of curved path, and general relativity just says that mass curves spacetime and matter always travels on geodesics in this spacetime. Intensity This ant analogy can't be used to discredit Flandern's argument because an ant has energy which it uses to move against many other forces but Flanderns' argument addresses the case of an object (non-living): "...a small body on the side of a dent in a rubber sheet made by a large mass will not start rolling downhill unless there is already gravity under the rubber sheet to give meaning to "downhill" and provide a force. But that defeats the purpose of the analogy as an explanation for the cause of gravity". His argument, I beleive, is that the rubber-sheet analogy relies on the concept of gravity to have meaning so its a self referencing argument (why does the large mass make a dent on the sheet? Why can't the sheet curve upward for example?) In any case, your ant analogy is false because by definition "Objects which travel under the sole influence of gravity follow geodesics." An ant doesn't travel under the sole influence of gravity does it?. I have seen better analogies - like the person driving when he takes a corner on a bend and the centrifugal force pulls him/her away from his direction of movement, the centrifugal force there can represent a potential well and this is an analogy that does not rely on gravity. The link you provided says "the rubber-sheet analogy completely fails to convey the essential point that geodesics are straight in the intrinsic geometry of spacetime" In what sense exactly is the curved path shorter than a straight one? To expect that Van Flandern has a poor understanding of the rubber sheet analogy, or to wonder whether he has ever heard of geodesics requires quite a stretch of imagination. Either you have no idea who he is, or you are letting something else cloud how you assess whatever he wrote. I would also appreciate it if you desisted from such ad-hominems and instead focused on the argument itself, not the one making it. [ October 01, 2002: Message edited by: Intensity ]</p>

10-01-2002, 10:16 AM	#7
Jesse Moderator - Science Discussions Join Date: Feb 2001 Location: Providence, RI, USA Posts: 9,908	You can find a bunch of newsgroup threads on the subject of "pushing gravity" <a href="http://groups.google.com/groups?q=%22le+sage%22+gravity&ie=ISO-8859-1&hl=en&btnG=Google+Search" target="_blank">here</a>. Unfortunately I didn't see any threads where the "pushing gravity" advocates actually offered detailed calculations of how their theory could duplicate experimentally-confirmed results from general relativity. [ October 01, 2002: Message edited by: Jesse ]</p>

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10-01-2002, 04:40 AM	#2
Secular Pinoy Veteran Member Join Date: Feb 2001 Location: Quezon City, Philippines Posts: 1,994	This <a href="http://iidb.org/cgi-bin/ultimatebb.cgi?ubb=get_topic&f=57&t=000414&p=" target="_blank">thread</a> discusses the current understanding on gravity, though it did not delve in this pushing gravity hypothesis. It a good start, though.

10-01-2002, 09:44 AM	#5
Ted Hoffman Veteran Member Join Date: Feb 2001 Location: "" Posts: 3,863	Oh, Jesse and others, I have found a link that can give you a pretty good idea about push gravity theory <a href="http://www.magna.com.au/~prfbrown/news99_b.htm" target="_blank">An Overview of the Concept of Attenuation [Pushing] Gravity </a> I have also found some refutations <a href="http://www.lns.cornell.edu/spr/2000-09/msg0027985.html" target="_blank">Gravity Push Refuted</a> I haven't gone through them yet.

10-01-2002, 09:57 PM	#8
atrahasis Regular Member Join Date: Mar 2002 Location: South of Sahara Posts: 216	Now, Space Time is not only warped it is twisted! Thats according to Wei Cui of the Massachusetts Institute of Technology<a href="http://whyfiles.org/052einstein/frame_drag4.html" target="_blank">Here</a>

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