[Farsight (OP)]

I've been doing a fair amount of research of original material, and the picture of general relativity that I get seems to be very different to what I was taught. For example, people tend to say the speed of light is constant, and Einstein said it. But it isn't true. Yes, he started with this as a postulate in 1905, but in 1911 he wrote On the Influence of Gravitation on the Propagation of Light, where we can see his ideas evolving as he talks about c = c₀ (1 + Φ/c²). Then in 1916 in section 22 of Relativity: The Special and General Theory he talks further:

"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)".

IMHO people tend to see the word velocity in the 1920 translation without seeing the context. Many skip over his reference to "one of the two fundamental assumptions", and don't see that he's talking about a serious issue with the SR postulate of the constant speed of light. Many do not realise that Einstein didn't speak English in 1916, and what he actually said was die Ausbreitungsgeschwindigkeit des Lichtes mit dem Orte variiert. This translates into the speed of light varies with the locality. He was saying the speed varies with position, hence the reference to that postulate. And what he also said, is that this causes the light to follow a curvilinear path like a car veers when the near-side wheels encounter mud at the side of the road.



People often react badly this. Einstein talking about the variable speed of light does not fit with the relativity they've been taught. They don't appreciate that relativity today is somehow different to Einstein's relativity. People think Einstein told us about curved spacetime, but when you read The Foundation of the General Theory of Relativity, incredibly, it's just not there. Yes, he talks about geometry and curvature and space-time, but he's giving the equations of motion, through space. He doesn't talk about "motion through spacetime" like people do these days. Surely everybody knows you can't move through spacetime, it's just the mathematical space where we plot our lines. There's other things that people aren't taught. Such as how Einstein was still derided by many theoreticians even in 1923. You can see a reference to this on page 53 of Graham Farmelo's Dirac biography The Strangest Man:

"At that time, Cunningham and Eddington were streets ahead of the majority of their Cambridge colleagues, who dismissed Einstein's work, ignored it, or denied its significance".

Many people don't know that despite the media accolades and public adulation, Einstein drifted out of the mainstream from 1927 when he fell out with Bohr and others over quantum mechanics. They don't know that General Relativity was a "cottage industry" until the sixties, when the Golden Age changed it significantly:

"The Golden Age of General Relativity is the period roughly from 1960 to 1975 during which the study of general relativity, which had previously been regarded as something of a curiosity, entered the mainstream of theoretical physics. During this period, many of the concepts and terms which continue to inspire the imagination of gravitation researchers (and members of the general public) were introduced, including black holes and 'gravitational singularity'. At the same time, in closely related development, the study of physical cosmology entered the mainstream and the Big Bang became well established... A number of simultaneous paradigm shifts characterize the Golden Age of general relativity. First and foremost, the Big Bang became the canonical cosmological model. Other paradigm shifts included a growing appreciation of the: Role of curvature in general relativity..."

Nor do most people know that in 1949 Einstein and Godel worked out that time is cofounded with motion through space, not with space. It's there in A World without Time: The Forgotten Legacy of Godel and Einstein by Palle Yourgrau. But perhaps the signal most important thing most people don't know, is that whilst aether is a taboo word which is most definitely out of the mainstream, Einstein's gave his Leyden address in 1920. And the title is Ether and the theory of relativity. There's Einstein, talking about space and calling it an aether: 

"Mach’s idea finds its full development in the ether of the general theory of relativity. According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-time, and are partly conditioned by the matter existing outside of the territory under consideration. This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that ‘empty space’ in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials g_μν), has, I think, finally disposed of the view that space is physically empty".

All in all it adds up to some huge differences, and some surprises. It seems that relativity has always been the Cinderella of modern physics, and despite his vast reputation, Einstein was hardly in the mainstream at all. Moreoever his understanding of gravity doesn't seem to be mainstream any more. What's especially surprising is how similar it is to the way Newton described it in Opticks:

Doth not this aethereal medium in passing out of water, glass, crystal, and other compact and dense bodies in empty spaces, grow denser and denser by degrees, and by that means refract the rays of light not in a point, but by bending them gradually in curve lines? ...Is not this medium much rarer within the dense bodies of the Sun, stars, planets and comets, than in the empty celestial space between them? And in passing from them to great distances, doth it not grow denser and denser perpetually, and thereby cause the gravity of those great bodies towards one another, and of their parts towards the bodies; every body endeavouring to go from the denser parts of the medium towards the rarer?" ^{queries 20 & 21}

The language is different, but the underlying concept is the same. The energy tied up as the matter of a planet "conditions" the surrounding space to create a non-constant g_μν along with a gradient in c which causes curvilinear motion. To many people this is unacceptable, because it isn't what they've been taught. It doesn't matter that it comes from Einstein and Newton and is supported by experimental evidence, they refuse to believe it.   



Show them two astronauts carrying parallel-mirror light clocks at different locations, and they will refuse to admit what the different readings on those light clock is telling them. They'll talk about coordinate speed and time dilation and spacetime curvature, anything to avoid what's in plain view: in a place where the gravitational potential is lower, the light goes slower.

Why is it that people seem unable to see what Einstein actually said, or the evidence that supports it?

[PhysBang]

I've been doing a fair amount of research of original material, and the picture of general relativity that I get seems to be very different to what I was taught.

Have you actually studied relativistic physics at the university level? Have you studied relativistic physics at the post-graduate level? Where and how were you "taught"?

For example, people tend to say the speed of light is constant, and Einstein said it. But it isn't true. Yes, he started with this as a postulate in 1905, but in 1911 he wrote On the Influence of Gravitation on the Propagation of Light, where we can see his ideas evolving as he talks about c = c₀ (1 + Φ/c²). Then in 1916 in section 22 of Relativity: The Special and General Theory he talks further:

"In the second place our result shows that, according to the general theory of relativity, the law of the constancy of the velocity of light in vacuo, which constitutes one of the two fundamental assumptions in the special theory of relativity and to which we have already frequently referred, cannot claim any unlimited validity. A curvature of rays of light can only take place when the velocity of propagation of light varies with position. Now we might think that as a consequence of this, the special theory of relativity and with it the whole theory of relativity would be laid in the dust. But in reality this is not the case. We can only conclude that the special theory of relativity cannot claim an unlimited domain of validity; its results hold only so long as we are able to disregard the influences of gravitational fields on the phenomena (e.g. of light)".

IMHO people tend to see the word velocity in the 1920 translation without seeing the context. Many skip over his reference to "one of the two fundamental assumptions", and don't see that he's talking about a serious issue with the SR postulate of the constant speed of light. Many do not realise that Einstein didn't speak English in 1916, and what he actually said was die Ausbreitungsgeschwindigkeit des Lichtes mit dem Orte variiert. This translates into the speed of light varies with the locality. He was saying the speed varies with position, hence the reference to that postulate. And what he also said, is that this causes the light to follow a curvilinear path like a car veers when the near-side wheels encounter mud at the side of the road.

I had thought that after being banned from yet another message board, you had finally given up on this misunderstanding of yours. You have previously claimed that you cannot do the detailed mathematics of general relativity and this is holding you back from actually following what this passage from Einstein actually means. Anyone who keeps reading beyond the passage you have cherry-picked here soon learns, if they can follow the mathematics in which the physics is written, that Einstein does not mean anything like what he said in 1911. He certainly does not mean anything like your mud and wheels example.

People often react badly this.

People react badly to your continued cherry-picking of two passages from Einstein, your choice to ignore any of the actual physics of Einstein, and your refusal to answer questions. This is what provokes a reaction to what you write.

People think Einstein told us about curved spacetime, but when you read The Foundation of the General Theory of Relativity, incredibly, it's just not there. Yes, he talks about geometry and curvature and space-time, but he's giving the equations of motion, through space.

No, he is not. You have admitted that you cannot do the mathematics of differential geometry. I suggest you take the time to learn this mathematics so that you can understand just how wrong you are here.

He doesn't talk about "motion through spacetime" like people do these days.

People do not do this. Please provide a specific reference from a credible source if you think otherwise.

But perhaps the signal most important thing most people don't know, is that whilst aether is a taboo word which is most definitely out of the mainstream, Einstein's gave his Leyden address in 1920. And the title is Ether and the theory of relativity. There's Einstein, talking about space and calling it an aether: 

"Mach’s idea finds its full development in the ether of the general theory of relativity. According to this theory the metrical qualities of the continuum of space-time differ in the environment of different points of space-time, and are partly conditioned by the matter existing outside of the territory under consideration. This space-time variability of the reciprocal relations of the standards of space and time, or, perhaps, the recognition of the fact that ‘empty space’ in its physical relation is neither homogeneous nor isotropic, compelling us to describe its state by ten functions (the gravitation potentials g_μν), has, I think, finally disposed of the view that space is physically empty".

As the author of the page that you link to to provide this quotation writes, "This address has been frequently misunderstood as positing that a return of the ether theory." That you entirely miss the point of the lecture is not something you should be proud of. Again, you should learn the actual mathematics so that you can understand what g_μν really means.

What's especially surprising is how similar it is to the way Newton described it in Opticks:

Doth not this aethereal medium in passing out of water, glass, crystal, and other compact and dense bodies in empty spaces, grow denser and denser by degrees, and by that means refract the rays of light not in a point, but by bending them gradually in curve lines? ...Is not this medium much rarer within the dense bodies of the Sun, stars, planets and comets, than in the empty celestial space between them? And in passing from them to great distances, doth it not grow denser and denser perpetually, and thereby cause the gravity of those great bodies towards one another, and of their parts towards the bodies; every body endeavouring to go from the denser parts of the medium towards the rarer?" ^{queries 20 & 21}

The language is different, but the underlying concept is the same. The energy tied up as the matter of a planet "conditions" the surrounding space to create a non-constant g_μν along with a gradient in c which causes curvilinear motion. To many people this is unacceptable, because it isn't what they've been taught. It doesn't matter that it comes from Einstein and Newton and is supported by experimental evidence, they refuse to believe it.   

One can always cherry-pick quotations from history that seem to look like modern physics. However, there is no relationship between the physics of the Opticks and the physics of GR. Additionally, the quotation that you have chosen comes from Newton's remarks on alchemy. If you unquestioningly support what Newton writes here, you seem to unquestioningly support all of Newton's alchemy.

Additionally, you can show no experimental evidence that demonstrates that there is a medium at work in generating the results of GR. If you can, please demonstrate with actual numbers and calculations. Since you admittedly cannot do the mathematics of GR, I cannot understand how you can believe your claims here.

Show them two astronauts carrying parallel-mirror light clocks at different locations, and they will refuse to admit what the different readings on those light clock is telling them.

Since this experiment has never been done, you cannot claim that this is experimental evidence.

Why is it that people seem unable to see what Einstein actually said, or the evidence that supports it?

Because they do not want to spend the time to learn the mathematics and physics involved. Thus they ignore the details of what Einstein produced and instead cherry pick out quotations that support their preconceptions.

[Farsight (OP)]

Physbang, you aren't countering the reportage I've given here. Instead you're attempting to deny it by dismissing what Einstein and Newton actually said as "cherry picking" and "alchemy". You're trying to support your own preconceptions, and without scientific evidence and carefully-contructed logical argument, your response is inadequate. Claiming that my mathematics or education is lacking or that I've been repeatedly banned doesn't make up for sincere discussion of this important matter. It's quite clear what Einstein said, and my astronauts example is fully supported by the GPS clock adjustment and the Shapiro time delay. The evidence is there, so please be aware that I started this thread as a spin-off to something that cropped up on a thread concerning gravity and work: http://www.thenakedscientists.com/forum/index.php?topic=27444.msg294032#msg294032.

All: see http://arxiv.org/abs/physics/0204044 for Einstein's Gravitational Field by Peter M Brown. It's a very interesting paper, well worth reading:
 
Abstract: There exists some confusion, as evidenced in the literature, regarding the nature of the gravitational field in Einstein's General Theory of Relativity. It is argued here the this confusion is a result of a change in interpretation of the gravitational field. Einstein identified the existence of gravity with the inertial motion of accelerating bodies (i.e. bodies in free-fall) whereas contemporary physicists identify the existence of gravity with space-time curvature (i.e. tidal forces). The interpretation of gravity as a curvature in space-time is an interpretation Einstein did not agree with.  

Peter M Brown posts here as Pmb, and knows his stuff. He and I don't always agree on the finer points, but we converse in a pleasant manner, and let's face it, if everybody agreed on everything, there wouldn't be much to talk about!

[PhysBang]

Claiming that my mathematics or education is lacking or that I've been repeatedly banned doesn't make up for sincere discussion of this important matter.

These claims are evidence that you are not interested in discussion and that you are perhaps incapable of such discussion. You continually misrepresent Einstein and when called on this, you become belligerent. It will happen here.

People have asked you before to do a direct demonstration that will show that you are correct: if you could perhaps run through the advance of the perihelion of Mercury or through the calculation of the rotation of any galaxy currently being used to detect dark matter, then you could easily show that your position is correct. You cannot do these direct demonstrations, unfortunately for your position.

It's quite clear what Einstein said, and my astronauts example is fully supported by the GPS clock adjustment and the Shapiro time delay.

Please show us the calculations involved in the GPS clock adjustment and Shapiro time delay and show us where they come up in your astronaut example. Please use specific values and calculations in your example.

All: see http://arxiv.org/abs/physics/0204044 for Einstein's Gravitational Field by Peter M Brown. It's a very interesting paper, well worth reading:

But there is probably something very wrong with this paper and the position of the author because the author has no published work in the field, despite the age of the paper. Can you find any evidence that is accepted by any group of peers in physics or in the philosophy of science?

Like always, you will fail to directly answer these questions because to take these questions seriously would reveal the horrible flaws in your position and the evidence for it.

[JimBob]

PhysBang, since you refuse to read your email or answer it, I must do this in public.

Personal attacks will not be allowed - period. PhysBang may not post for two weeks and another breach will result in a permanent ban. You did not heed the email sent and have refused to curb you ad-hominem post. You then may not have the privalage of posting to this site. If at the end of the two weeks you continue to make ad-hominem responses, the ban will be permanent.

JimBob, Moderator

[Farsight (OP)]

For the record, I'm very interested in discussion, and whilst the odd cross word sometimes escapes my lips, I'm not belligerent. I decline to give a mathematical demonstration of say the perihelion advance of Mercury because it's a diversion from the matter at hand. For GPS the relevant information is that the satellites employ atomic clocks, which count microwave pulses. Microwaves are electromagnetic radiation, essentially light. A quick check on GPS and general relativity then tells us "general relativity predicts that the atomic clocks at GPS orbital altitudes will tick more rapidly, by about 45.9 μs per day, because they have a higher gravitational potential than atomic clocks on Earth's surface". This will be reliable, and is clear scientific evidence that is fully in accord with Einstein's words and pmb's paper. Dismissing such evidence by claiming it isn't peer-reviewed sounds unreasonable, and besides, a quick search on arxiv on variable-speed of light yields a wealth of papers. I note one by Alexander Unzicker entitled The VSL Discussion: What Does Variable Speed of Light Mean and Should we be Allowed to Think About It?

[Ron Hughes]

I would ask one question of Phys, can he show us one cubic nanometer of space that does not contain radiation in the Universe? If the answer is no then it could be said that radiation is the aether of space.

[JimBob]

PhysBang has lost the privilege of answering for two weeks. If he choose, he can answer in a couple of weeks.

[Farsight (OP)]

Space is somewhat unique Ron. It's seemingly not there but it supports waves and fields, and it has this vacuum energy, so it isn't nothing. And because it has this energy, it has a mass equivalence of sorts. But the idea of motion cannot be applied to it, so it doesn't have mass like a cannonball. It isn't "matter" like the old luminiferous aether. I think of LIGO trying to detect gravity waves see http://www.ligo-la.caltech.edu/LLO/overviewsci.htm where you can read:

"If the two arms have identical lengths, then interference between the light beams returning to the beam splitter will direct all of the light back toward the laser. But if there is any difference between the lengths of the two arms, some light will travel to where it can be recorded by a photodetector".

Then I look at that Leyden address again and my attention is drawn to Weyl: 

"Of course it would be a great advance if we could succeed in comprehending the gravitational field and the electromagnetic field together as one unified conformation. Then for the first time the epoch of theoretical physics founded by Faraday and Maxwell would reach a satisfactory conclusion. The contrast between ether and matter would fade away, and, through the general theory of relativity, the whole of physics would become a complete system of thought, like geometry, kinematics, and the theory of gravitation. An exceedingly ingenious attempt in this direction has been made by the mathematician H. Weyl; but I do not believe that his theory will hold its ground in relation to reality".

..and I say to myself I should do more research here. See for example http://www.weylmann.com/conformal.pdf.

[Ron Hughes]

farsight, vacuum energy is a concept brought on by the invention of another hypothetical particle, the virtual particle, required to maintain the illusion that QM can explain the propagation of light.

[Farsight (OP)]

I'm afraid it isn't Ron. Einstein talked about the stress-energy of space long before virtual particles were proposed. And the Casimir effect demonstrates that there's a real phenomena there. It doesn't demonstrate that virtual particles are real particles, but it does demonstrate that vacuum energy is something real. For myself, I think there's a lot of merit in Evanescent modes are virtual photons, A. A. Stahlhofen et al 2006 Europhys. Lett. 76 189-195. See http://www.iop.org/EJ/abstract/0295-5075/76/2/189 

[Ron Hughes]

If all of space contains radiation, how would we know that fact does not somehow explain the observations. Until someone shows proof of virtual particles I will find it difficult to except them. You and I both think matter is a wave. We can point to the fact matter anti-matter annihilation's produce nothing but radiation but that test convinces no one that we're right. There is no spray of quarks or any other particles just radiation.

[Farsight (OP)]

I'm not asking you to accept virtual particles as real particles, Ron. Just that there's something real underlying say the attraction of an electron and a proton in a hydrogen atom. Quantum Electrodynamics is a good theory that employs virtual particles to come up with accurate preductions, but Feynman never said that these virtual particles are real particles. I think the best way to think of them, is like the "virtual pennies" that are added to your bank account when your employer pays in your salary. There are no actual pennies flying around. They're just accounting units for doing calculations.

Plenty of people, and I mean professional physicists, are coming to appreciate that particles like electrons and protons are wave configurations. Whilst it has rock-solid provenance going back to de Broglie and Schrödinger, it just hasn't been in the popular press yet. Give it time, and I'm sure it will be. It's amazing how long things can take to work their way through from journals into magazines and TV programs and text books, particularly when competing theories are involved.     

[Ron Hughes]

I do understand their use is a tool(something like a crutch)used as a mental aid in make some predictions about how energy is moved back and forth in the Universe. In my editorial thread I speak of molecular collisions and the squashing the respective fields. If the individual particles that make up the molecules are some sort of wave that can maintain itself for 10^30 years how does it affect the space around it to create it's infinite field? Did Einstein ever explain that field? It appears that questions along with answers only produce more questions.

[Farsight (OP)]

I'd say no, Einstein didn't explain it, but after everything I've learned I wouldn't be surprised if somebody pointed out some obscure paper he'd written and said here it is. Maybe http://en.wikipedia.org/wiki/Einstein%E2%80%93Cartan_theory goes some way towards it, wherein electron spin affects the surrounding space via something akin to frame-dragging.

[Ron Hughes]

I suspect frame dragging is also a function of time dilation.

[Farsight (OP)]

It isn't time dilation, Ron. It's more like a "twist":



If you moved through a region of twisted space, it would make you turn. Check out Gravitomagnetism and Gravity Probe B. Also see near the back of Minkowski's Space and Time where he emplys a wrench analogy:

"Then in the description of the field produced by the electron we see that the separation of the field into electric and magnetic force is a relative one with regard to the underlying time axis; the most perspicious way of describing the two forces together is on a certain analogy with the wrench in mechanics, though the analogy is not complete".

He's talking about a screw machanism. Check out On Physical Lines of Force and there's Maxwell talking about a screw mechanism too: http://en.wikipedia.org/w/index.php?title=File:On_Physical_Lines_of_Force.pdf&page=53. This is why we have the right hand rule. Imagine a stack of electrons in a wire. Their electric field is a "twist" field, so when a test particle moves down past them, or they move up past it, there's a rotation. It "turns". The thing to remember is that it's an electromagnetic field. It isn't an electric field that's separate from a magnetic field. There's only one field there, the electromagnetic field, and if you could see it, it would look something like a drill bit. A drill bit is twisted. Make a fist round a drill bit with your right hand, and push from the bottom. It turns. It's breathtakingly simple once it clicks.






Hi Good Elf!

[Good Elf]

Hi Farsight,

I agree entirely with your POV. I will add my two cents worth just to reiterate and reinforce some of the points you made. You have chosen a very interesting aspect of all physics. I notice that there is some controversy regarding Einstein's paradigm of "warped spacetime" in General Relativity. I realize the topic is moving on from there but I have only recently joined and this is my first post here so forgive me for touching base. Einstein treated gravity in a different way to electromagnetism. It "seemed very plausible" since electromagnetism relies on what appears to be underlying permanent charges which come in two varieties... nominally positive and negative while "mass", which plays the role of a "charge" in gravity, comes in only one form of "positive mass" and no "anti-mass" or anti-gravational mass... a purely hypothetical opposite pole to mass... something that would repel mess rather than attract it. I am not referring to anti-particles here but to something quite separate.

In the case of electromagnetic influence... it's influence is usually blocked by a couple of mils of opaque insulating material. This is because "force" superficially appears to have two ways to transmit itself. There is a local expression of forces (evanescent field) and a distant expression of forces (far field). The local expression of forces are in the near field and are associated with the notion of "virtual particles" in which the fluxes of "field lines" associated with the sources are not "detached from their sources" and the distant expression of forces and are associated with a propagating "force carrier or bosons"... in which the fields are dissociated from their sources and this leads to the bosons of the photon for electromagnetism and the graviton for "gravity". The propagated influence of photons are absorbed and converted to other forms of energy in "sinks". Gravitational influence is not so easily "dissipated" simply because there are no "sinks" for gravity only "sources"..

It is an interesting point to ponder that aside from the fact that light travels at the speed of light and is simultaneously affected by electrodynamics and also by gravity and "falls" identically like a projectile along the "surface of spacetime" and is a "limiting case of material projectiles" as V -> C. This suggests there really is not action at a distance dependent on the mutual mass between particles since such a theory would mean that if one of the two "attractive" objects was of zero rest mass there would be no "attraction" at all. It is possible to demonstrate very effectively that photons have zero rest mass. So... photons "fall" like a very light stone that is traveling infinitely close to the speed of light.

Gravity is deemed "symmetric" (unipolar) while electromagnetism is "anti-symmetric" (bipolar). We often discuss "forces" when we deal with these two different phenomena but the theory of forces cannot account for this alone since "forces" are actions at a distance while everything appears to point to an explanation due to the interaction between "particles" which depends on their mutual interactions. I would point out "a particle" is also a paradigm that might be hindering our ideas about "forces".

That "primary force" of gravity and the "primary force" of electromagnetism (charge and magnetism) do not appear to be primarily the result of the exchange of "force carriers" or due to continuous accelerations in the matter or charge sources. Einstein thought of gravity as a pseudo-force and is explained by his local theory of spacetime curvature.. his "General Theory of Gravatation" (ED: spacetime was a concept Minkowski invented not truly Einstein's own original idea but "near enough"). This was summed up by John A. Wheeler as "Matter tells space how to curve, and space tells matter how to move". Action at a distance for these "gross effects" is not required. A simplistic view of this concept is like a skateboard in a skateboard park.. the board moves according to it's velocity and the curvature directly under it's wheels at each instant in time and does not require the concept of a "distant source of force" attracting the skateboard be needed to explain it. That was another visual analogy so do not think too much about that simple notion.

Likewise gravity "appears" to not require distant forces to motivate the gross motion of planets of the rotation of galaxies... it gets it "moving orders" from the local curvature of spacetime. The complementary particle to the photon... the graviton would then play the same role as a photon in electromagnetism and would involve "real" gravitons but gravity... that we measure mass by using a set of scales... plays the same role as the electromagnetic forces we see in magnets electric motors and moving charges of various types... the mass "fluxes" (like the electromagnetic fluxes) remaining attached to the "sources" (whatever they are)and neither "primary force" requires propagating light or propagating gravitons. what I mean by this in the case of gravity curved spacetime explains the motion of celestial bodies while in electromagnetism charged particles (and magnetism) and their quasi-stationary fields explain the "forces" between charges. Each of these phenomena might appear to be separate and acting on different "manifolds" but a theory of combing these manifolds was Einstein's dream and is the base motivation for current String Theory today. The distant influence of both gravity and light due to carriers of force require the idea of accelerations in the sources generating these particles. There are some problems with all these theories.

I am not "undervaluing" the influence of light since almost everything in the universe we can sense is the effect of either quantum electrodynamics or of gravitation. The other forces (weak, strong forces) are not essential for the things we appreciate (may also be even detrimental) on a day to day basis and are involved with "nuclear radiations" of various kinds... so "light" and therefore photons in all their forms are very important to the way our world works... both real photons and virtual photons in all the forms of the motion of sources of the apparent permanent charge. Of course matter also plays a role in there as "mass" and as "matter waves" but this is not explained by QED.

Now returning to the core issue... Regarding the curvature of spacetime in the General Theory of Gravatation it might be "directly compared" with the property of optical diffraction in refractive materials. So instead of speaking about curved spacetime and Einstein had spoken in terms of a "gravitational refractive index" then this would effectively embed "matter" in an unseen medium whose property was to alter the speed of light rather than "warp some kind of unseen membrane" which we currently identify as "mass". The optical refractive index of a medium is a reflection of the speed of light through the medium and the speed of light in a vacuum.

Refraction is the change in direction of a wave due to a change in its speed. This is most commonly observed when a wave passes from one medium to another at an angle. Refraction of light is the most commonly observed phenomenon, but any type of wave can refract when it interacts with a medium, for example when sound waves pass from one medium into another or when water waves move into water of a different depth...

Wikipedia: Refraction [nofollow]

With gravity we cannot see any medium so we usually do not invoke a material medium to "conduct" gravity. None has ever been detected. Still... as a pure paradigm it "might be useful" to consider this property as if it did exist. This phenomenon exhibits "optically" as Einstein's Rings [nofollow] and we might like to consider spacetime curvature having a variable gravito-optical density reflecting and paralleling the idea of warping of a membrane. But are refractive index and a hypothetical gravito-optical density the same... No... But why not? That is a very interesting question.

We actually cannot verify the existence of either a "physical spacetime" or a vacuum refractive index altering material properties existing in the empty space around matter... That might be interpreted as a vacuum energy density in some way. This really is not a required part of the Einstein's Theory since all theories have their paradigms and they are taken up or discarded when required. What is important is we all realize that, while the paradigm assists us in visualizing the phenomena, it should not be thought of as the only way of understanding it and the future of science will change it's paradigms more often than some may want. The mathematical description of the theory should be attempting to describe this "mental picture" we have developed of these "forces" but do not be surprised when an experiment changes the results of some of the theory the paradigm is radically modified to account for these perceived conceptual anomalies.

As an additional point... There is very little differentiating "virtual" photons from "real" photons since photons can be created on demand and a sufficiently energetic process can produce these "real" photons from a source embedded in "virtual" photons... A radio transmitter is a source such as this... even the transitions in an atom can produce photons from virtual photons. On the other hand it is still to be shown experimentally that gravitons really exist to enable the analogy between the photon and electromagnetism and the graviton and gravity to be extended into an overall paradigm.

Cheers

[Ron Hughes]

Far, my understanding is that frame dragging occurs only if an object or particle is spinning. If the Earth had no rotation, an object placed anywhere on a sphere two hundred thousand kilometers from the Earth would experience the some magnitude and direction of acceleration as an object placed anywhere on that sphere.

Elf, Einstein spent the last thirty years of his life trying to unite electromagnetism and gravity. Some materials will block certain frequencies of the EM spectrum but no material, we know of, will block infrared. The best thermos bottle ever made, even with a complete vacuum, will have some infrared EM. There is no place in the Universe, man made or natural, where there is no radiation.

[Farsight (OP)]

There is a local expression of forces (evanescent field) and a distant expression of forces (far field). The local expression of forces are in the near field and are associated with the notion of "virtual particles" in which the fluxes of "field lines" associated with the sources are not "detached from their sources"

I couldn't agree more, Good Elf. Andrew Meulenberg told me about this maybe a year back, and others think this too, see http://www.iop.org/EJ/abstract/0295-5075/76/2/189. Apologies if I've mentioned it before, I'll send you a copy in case I haven't, and double apologies in case it was you who told me about it.

It is an interesting point to ponder that aside from the fact that light travels at the speed of light and is simultaneously affected by electrodynamics and also by gravity and "falls" identically like a projectile along the "surface of spacetime" and is a "limiting case of material projectiles" as V -> C. This suggests there really is not action at a distance dependent on the mutual mass between particles since such a theory would mean that if one of the two "attractive" objects was of zero rest mass there would be no "attraction" at all. It is possible to demonstrate very effectively that photons have zero rest mass. So... photons "fall" like a very light stone that is traveling infinitely close to the speed of light.

Not quite, Good Elf! Maybe you were keeping it simple, but see that squared-off circle representing a single electron? It's deflected half as much as light:

..←
↓....↑
..→

Gravity is deemed "symmetric" (unipolar) while electromagnetism is "anti-symmetric" (bipolar). We often discuss "forces" when we deal with these two different phenomena but the theory of forces cannot account for this alone since "forces" are actions at a distance while everything appears to point to an explanation due to the interaction between "particles" which depends on their mutual interactions. I would point out "a particle" is also a paradigm that might be hindering our ideas about "forces".

Excellent. People don't seem to understand what Newton was getting at when he said "so great an absurdity".  

That "primary force" of gravity and the "primary force" of electromagnetism (charge and magnetism) do not appear to be primarily the result of the exchange of "force carriers" or due to continuous accelerations in the matter or charge sources. Einstein thought of gravity as a pseudo-force and is explained by his local theory of spacetime curvature.. his "General Theory of Gravatation" (ED: spacetime was a concept Minkowski invented not truly Einstein's own original idea but "near enough").

It is so refreshing to hear somebody who actually knows the history, Good Elf.  

This was summed up by John A. Wheeler as "Matter tells space how to curve, and space tells matter how to move".

More's the pity that you and I know that a better way of saying it is "energy tells spacetime how to curve". Energy causes gravity, matter only causes gravity because of the energy content. If the space was curved, then regardless of velocity all balls thrown across a room would describe the same arc.

Action at a distance for these "gross effects" is not required. A simplistic view of this concept is like a skateboard in a skateboard park.. the board moves according to it's velocity and the curvature directly under it's wheels at each instant in time and does not require the concept of a "distant source of force" attracting the skateboard be needed to explain it. That was another visual analogy so do not think too much about that simple notion.

I like it, Good Elf. Here's a similar one I've used:

Imagine a swimming pool. Every morning you swim from one end to the other in a straight line. In the dead of night I truck in a load of gelatine powder and tip it all down the left hand side. This starts diffusing across the breadth of the pool, imparting a viscosity gradient from left to right. The next morning when you go for your swim, something's not right, and you find that you're veering to the left. If you could see your wake, you'd notice it was curved. That's your curved spacetime, because the pool is the space round a planet, the viscosity gradient is Einstein's non-constant gμν, and you're a photon. As to how the gradient attracts matter, consider a single electron. We can make an electron along with a positron from light, via pair production. Since the electron also has spin, think of it as light trapped in a circular path. So if you're swimming round and round in circles, whenever you're swimming up or down the pool you're veering left. Hence you find yourself working over to the left. That's why things fall down.

Likewise gravity "appears" to not require distant forces to motivate the gross motion of planets of the rotation of galaxies... it gets it "moving orders" from the local curvature of spacetime. The complementary particle to the photon... the graviton would then play the same role as a photon in electromagnetism and would involve "real" gravitons but gravity... that we measure mass by using a set of scales... plays the same role as the electromagnetic forces we see in magnets electric motors and moving charges of various types... the mass "fluxes" (like the electromagnetic fluxes) remaining attached to the "sources" (whatever they are)and neither "primary force" requires propagating light or propagating gravitons. what I mean by this in the case of gravity curved spacetime explains the motion of celestial bodies while in electromagnetism charged particles (and magnetism) and their quasi-stationary fields explain the "forces" between charges. Each of these phenomena might appear to be separate and acting on different "manifolds" but a theory of combing these manifolds was Einstein's dream and is the base motivation for current String Theory today. The distant influence of both gravity and light due to carriers of force require the idea of accelerations in the sources generating these particles. There are some problems with all these theories.

Yes, it's very sad. The virtual particles of QED morphed into real particles somewhere along the line. But Einstein's dream is not shattered, just overshadowed. You know that the electromagnetic field is curved space, don't you.  

I am not "undervaluing" the influence of light since almost everything in the universe we can sense is the effect of either quantum electrodynamics or of gravitation. The other forces (weak, strong forces) are not essential for the things we appreciate (may also be even detrimental) on a day to day basis and are involved with "nuclear radiations" of various kinds... so "light" and therefore photons in all their forms are very important to the way our world works... both real photons and virtual photons in all the forms of the motion of sources of the apparent permanent charge. Of course matter also plays a role in there as "mass" and as "matter waves" but this is not explained by QED.

I share your sentiment here. QED was always lacking an intuitive explanation of how it worked and what was the reality underlying the virtual particles. One has to understand the photon and the electron before one can make robust progress at the QCD level.

Now returning to the core issue... Regarding the curvature of spacetime in the General Theory of Gravatation it might be "directly compared" with the property of optical diffraction in refractive materials. So instead of speaking about curved spacetime and Einstein had spoken in terms of a "gravitational refractive index" then this would effectively embed "matter" in an unseen medium whose property was to alter the speed of light rather than "warp some kind of unseen membrane" which we currently identify as "mass". The optical refractive index of a medium is a reflection of the speed of light through the medium and the speed of light in a vacuum.

Music to my ears. The non-constant g_uv that causes curvilinear motion.

With gravity we cannot see any medium so we usually do not invoke a material medium to "conduct" gravity. None has ever been detected. Still... as a pure paradigm it "might be useful" to consider this property as if it did exist. This phenomenon exhibits "optically" as Einstein's Rings and we might like to consider spacetime curvature having a variable gravito-optical density reflecting and paralleling the idea of warping of a membrane. But are refractive index and a hypothetical gravito-optical density the same... No... But why not? That is a very interesting question.

It is that, Good Elf. Space is just so utterly unique. The best phrase I can come up with is energy density.

We actually cannot verify the existence of either a "physical spacetime" or a vacuum refractive index altering material properties existing in the empty space around matter... That might be interpreted as a vacuum energy density in some way. This really is not a required part of the Einstein's Theory since all theories have their paradigms and they are taken up or discarded when required. What is important is we all realize that, while the paradigm assists us in visualizing the phenomena, it should not be thought of as the only way of understanding it and the future of science will change it's paradigms more often than some may want. The mathematical description of the theory should be attempting to describe this "mental picture" we have developed of these "forces" but do not be surprised when an experiment changes the results of some of the theory the paradigm is radically modified to account for these perceived conceptual anomalies.

I agree 100%.

As an additional point... There is very little differentiating "virtual" photons from "real" photons since photons can be created on demand and a sufficiently energetic process can produce these "real" photons from a source embedded in "virtual" photons... A radio transmitter is a source such as this... even the transitions in an atom can produce photons from virtual photons.

I'd say the difference between real photons and virtual photons is the difference between a swell wave and a bow wave. One travels, the other stands.

On the other hand it is still to be shown experimentally that gravitons really exist to enable the analogy between the photon and electromagnetism and the graviton and gravity to be extended into an overall paradigm.

There are no gravitons, Good Elf. Because a photon traveling through space causes gravity, and it's the only "particle" there. Have you seen How Long is a Photon? by Drozdov and Stahlhofen? See http://arxiv.org/abs/0803.2596.

Nice talking to you.