What's so wrong about gravitational force acting at a distance? Well, try to imagine swinging an object in orbital motion without a string connecting it to the central point. Gravity as described in today's physics is just that; a pulling force acting at a distance even through vacuum, with no mediation of any material or known force field. If one calculates the attraction between the Earth and the moon, one would realize that if this force field had to be replaced by a weightless steel cable, it would require the cable to be about 800 km in diameter in order to withstand the strain. Between the Earth and sun, the cable would have to be nearly as large in diameter as the Earth; and the attraction between the components of double stars is millions of times greater than between the Earth and sun. This imaginary pulling action gives the false impression that the masses are the sources of such yet unknown, mysterious force field, we call the gravitational field. This also leads anyone to search for the force generating mechanism within the mass itself. Today, we are used to the term Earth's Gravity, but what if Earth's gravity is not generated by Earth itself? Einstein also showed that matter distorts space-time, and that space-time exists independently from matter. Since the force acts upon the surrounding space of matter, including all elements within the matter itself, then such a space-time model is indicative of a force field gradient, which in mechanical terms would generate a pressure difference. If space is made up of energy, then this means that such energy is being somehow distorted at the mass location. Note that even though Einstein proposed this space time bending by the presence of mass, it did not help much with our physical understanding of gravity. Using Einstein's classical ball on a rubber membrane analogy, modern physics seems happy enough to show that gravity is a curvature of space, even though the cause for stretching down the rubber membrane is unknown. In such an analogy, it would be gravity itself that deforms the elastic sheet by the ballís weight, but what deforms space by a bodyís mass? It's gravity! If so, then gravity cannot be caused by the curvature of space, because the curvature
would be caused by gravity. And as it should be clear enough for all you clever readers, this is a clear example of a circular definition, a useless analogy which explains absolutely nothing. It sounds good only as long as one does not try to understand its significance.
This reminds me of a statement by J.L.Synge in the following passage:
..... Thought is difficult and painful. The difficulties and pain are due to confusion. From time to time, with enormous intellectual effect, someone creates a little order - a small spot of light in the dark sea of confusion. At first we are all dazzled by the light because we are used to living in the darkness. But when we regain our senses and examine the light we find it comes from a farthing candle - the candle of common sense. To change the metaphor, the sages chase their own tails through the ages. A little child says 'Gentlemen, you are chasing your own tails.' The sages gradually lose their angular momentum, and, glancing over their shoulders, see what they are pursuing. But most of them cannot believe what they see, and the tail chasing does not die out until a generation has passed.....
This leads us to a very fundamental question: What mechanism is generating such pressure difference and distorting this space time or energy balance?
What did Newton think about gravity
Note that Newton never stated that gravity is necessarily an attractive force. In fact we find that both the concept of gravitational 'pull' and that of being an inherent property of matter are specifically denied by Newton himself to whom the concept is most often erroneously ascribed. For we find that about fourteen years after his culminating work in gravity, this topic is addressed by Newton in four letters he sent to Doctor Bentley. In his second letter, dated January 17, 1692-3, he says in reply to one from Bentley : You sometimes speak of gravity as essential and inherent to matter. Pray do not ascribe that notion to me, for the cause of gravity is what I do not pretend to know, and therefore would take more time to consider of it. In his third letter, dated February 25,1692-3, he expresses himself somewhat less guardedly : It is inconceivable that inanimate brute matter should, without the mediation of something else which is not material, operate upon and affect other matter, without mutual contact, as it must do if gravitation in the sense of Epicurus be essential and inherent in it. And this is one reason why I desired you would not ascribe 'innate gravity' to me. That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance, through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another,is to me so great an absurdity, that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it. Gravity must be caused by an agent acting constantly according to certain laws; but whether this agent be material or immaterial, I have left to the consideration of my readers. And again, in the conclusion of the third book of his Principia, Newton remarks : Hitherto I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypothesis ; for whatever is not deduced from the phenomena is to be called an hypothesis...As soon as one frees himself from the innate force concept, it becomes obvious that the most obvious way for an external agent to move two bodies towards each other is for it to PUSH them towards each other.
"and we derive from the celestial phenomena the forces of gravity with which bodies tend to the sun and the several planets. Then from these forces, by other propositions which are also mathematical, we deduce the motions of the planets, the comets, the moon, and the sea. I wish we could derive the rest of the phenomena of nature by the same kind of reasoning from mechanical principles; for I am induced by many reasons to suspect that they may all depend upon certain forces by which the particles of bodies, by some causes hitherto unknown, are either mutually impelled towards each other, and cohere in regular figures, or are repelled and recede from each other; which forces being unknown, philosophers have hitherto attempted the search of nature in vain; but I hope the principles here laid down will afford some light either to this or some truer method of philosophy."
Even more specifically, in Query 31 he affirms the following:"How these attractions may be performed I do not here consider. What I call attraction may be caused by impulse, or by some other means unknown to me. I use that word here to signify only in general any force by which bodies tend toward one another, whatsoever be the cause."
On page 2 of Principia, Newton wrote that gravity can be either an impelled or attractive force as follows, "A centripetal force is that by which bodies are drawn or impelled, or in any way tend, towards a point as to a center. Of this sort is gravity."
Searching in his early notebooks under the heading "Quaestiones" Newton speculates that gravity is caused by the descent of rays which strike all bodies and pushes them down. "Whither ye rays of gravity may be stopped by reflecting or refracting ..."
He went as far as proposing a series of very interesting experiments of which nobody seems to have ever cared of conducting in a professional manner: Try whether the weight of a body may be altered by heat or cold, by dilatation or condensation, beating , powdering, transfering to several places or several heights or placing a hot or heavy body over it or underneath it or by magnetism whether leade or its dust spread abroad, whether a plate flat ways or edge ways isn't heaviest, whether the rays of gravity may be stopped by refecting or refracting them, if so a perpetual motion may be made one of these two ways... The gravity of bodies is as their solidity, because all bodies descend equal spaces in equal times, consideration being had to the resistance of the air.
Photons and the consequences of its neglected rest mass
Before going into greater detail on gravity's real mechanism, it is very important to discuss a property of the photon which is of fundamental importance to the understanding of gravity. We find that Max Planck, the originator of light quanta resisted Einstein's point particle nature of light. In his recorded remarks which took place during 1909 in an audience at Einstein's talk we find him arguing Einstein's hypothesis of atomistic light quanta propagation through space. "If Einstein were correct, how could one account for interference when the length over which one detected interference was many thousands of wavelengths? How could a quantum of light interfere with itself over such great distances if it were a point object? Instead of quantized electromagnetic fields, one should attempt to transfer the whole problem of the quantum theory to the area of interaction between matter and radiation energy". That is, only the exchange of energy at the point of interaction between the source/target matter and the classical electromagnetic field is quantized. The exchange takes place in units of Planck's constant times the frequency, but the fields remain continuous and classical. Quantization can be considered like one trying to measure a time varying analogue signal with an analogue to digital converter, or with a digital voltmeter, the quanta is equivalent to the least significant digit, but that doesn't mean that the signal is varying in steps. So we have quantized or analogue to digital process interactions taking place between continuous electromagnetic fields and matter. This approach to quantum theory handles very well all of the problems of quantum optics including Einstein's photoelectric effect, without the requirement of the actual matter-like photon flying around. Note that the quite misleading term photon was not introduced by Planck, but by a chemist, Gilbert Lewis in 1926. Einstein himself was unclear about physical nature of the light 'wave' in 1905, this he admitted on 12 December 1951 in his letter to his friend M. Besso, in which he wrote: "All these fifty years of conscious brooding have brought me no nearer to the answer to the question: What are light quanta?" The concept of flying photons is totally redundant and remains unproven. Electromagnetic energy does not need any special particle to propagate in space. The same Einstein tells us that nothing, can be accelerated to the speed of light, except of course EM waves. Although I still make the use of the term photon in describing EMRP gravity theory, it is important that one understands, that matter-like photons do not fly from source to target, in fact no photon has ever been detected during its alleged travel. We never experience a photon, but only its effect at source and target. Propagation is a property of electromagnetic radiation, and photons are the quantized effect of momentum and electromagnetic energy released at the interface between either source matter or target matter and the electromagnetic wave. The quantum behaviour arises from the fact that matter is a standing wave structure, a De Broglie standing wave whose same existence depends on having an integer number of waves. In real life, the transmission of EM waves arises when such a standing wave steps down its number of nodes, and releases the difference as a travelling wave to the environment. The reverse occurs at the reciever side. We see light at the source and at the target matter, but we never see light travelling its path. Literally speaking, photons are only what and where you experience their effect. I believe that as Willis E. Lamb stated, the word photon should be stricken from the dictionary since there is no need for it. The photon is an effect and not a thing. To describe the entity that is travelling from source to target, it is enough that we use the simple term wave. If the rest mass of the photon were non-zero, the theory of quantum electrodynamics would be "in trouble" primarily through loss of gauge invariance, which would make it non-renormalisable; also, charge conservation would no longer be absolutely guaranteed, as it is if photons have zero rest mass. But regardless of what any theory might predict, it is still necessary to check this prediction by doing an experiment.
It is almost certainly impossible to do any experiment that would establish the photon rest mass to be exactly zero. The best we can hope to do is place limits on it. A non-zero rest mass would introduce a small damping factor in the inverse square Coulomb law of electrostatic forces. That means the electrostatic force would be weaker over very large distances.
Likewise, the behavior of static magnetic fields would be modified. An upper limit to the photon mass can be inferred through satellite measurements of planetary magnetic fields. The Charge Composition Explorer spacecraft was used to derive an upper limit of 6 ◊ 10-16 eV (1.06E-51kg) with high certainty. This was slightly improved in 1998 by Roderic Lakes in a laboratory experiment that looked for anomalous forces on a Cavendish balance. The new limit is 6E-17 eV (1.1E-52kg).