The
magnetosphere shields the surface of the Earth from the charged particles of the
solar wind. It is compressed on the day (Sun) side due to the force of the arriving particles, and extended on the night side. (Image not to scale.) Wikepedia.
It was formerly thought that gravitational forces acting on earth were much different than forces acting elsewhere in the larger realm of solar system and universe.
Newton, established for the first time, that it - the universal realms of the large and small - is all connected by a singular, commonly acting, unidentified invisible force. That is the gist of Newton's proven discovery - the proven extrapolation of the same force that causes relatively miniscule apples to fall, also causing the orbiting of the relatively enormous planets.
('The thump of a great apple in the stillness of a crisp October morn. Motivated only by the mere necessity of perfect ripeness.' - Hawthorne.)
Newton, finally acknowledged the conditional existence of gravity; only because his own newly invented calculus confirmed that, indeed the same force that motivationally generates falling apples, does likewise generate and sustain the orbits of planets. Yet, as we are about to be reminded, Newton took great care to point out that he did not know or purport to know the identity of gravity, and that his mathematical address to gravity is not concerned with or dependent upon its causal identity, or, its direction...
Newton’s thoughts on ‘the occult (pre ‘Field Physics' recognized) force (Maxwell’s Electromagnetic Field, omnidirectionally projecting <in the pattern of a spider-web> at light speed out of all material entities)’:
“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.
“And this is one reason why I desired that you would not ascribe inanimate 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 for 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.” - Isaac Newton, On Gravity.
As we shall see, the popular term 'Newtonian concept of attraction (a pulling force)', as applied to gravity, was never unconditionally endorsed by Newton. The concept of gravity as 'a pulling force of attraction' remains a speculative though understandably popular term, coined by Newton's beneficiaries. All of this is to say that the conceptualization of gravity as any sort of pulling force of attraction was not Newton's resolute conceptual or by any means exclusive definition of gravity. Allow the derivation of this last statement to be further qualified:
I wish to cite at this time what is to say the least, a most interesting alternative concept concerning the identity of (what Newton was always careful to call 'universal') gravity. An otherwise completely ignored statement which might even be correctly categorized as 'obscure', or 'inconsequential'. Were it not for the fact that this statement is made by Sir Isaac Newton. And, were it not for the fact that this statement is included in the very (3 page, non-mathematical) Preface to The PRINCIPIA MATHEMATICA.
From the beginning of the 1st to the end of the 2nd page of Newton's three page Preface to The PRINCIPIA MATHEMATICA, Newton is discussing the motions of falling objects and orbiting planets. By way of his applied mathematical descriptions of the effects of the force of gravity. At this time, Newton offers the following statement about what causes the gravitationally induced motions of planets & apples, quote:
“For I am induced by many reasons to suspect that they may all depend on 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."
That quote and its extraction will henceforth be referred to here, as THE GRAVITATIONAL ALTERNATIVE. Not my gravitational alternative; Newton's Gravitational Alternative to be exact. I repeat the quote (of particles and systems-of-particles: of matter), 'are either mutually impelled towards each other and cohere in regular figures (orbits; juxtapositions), or, are mutually repelled and recede from each other .'
It implies directly and categorically, that gravity may in fact be the opposite of the universally considered impelling or 'pulling force of attraction'; that is to say, Isaac Newton and his formal definitions, directly and resolutely suggest that gravity may in fact be a repelling or pushing force.
It is difficult to over dramatize the very existence of this statement, its author, and especially its contextual implications. It categorically allows that everything Newton mathematically confirms and describes in The PRINCIPIA MATHEMATICA - from orbiting planets, falling apples, aquatic, terrestrial, and atmospheric tides - all the large and small phenomena of gravity - is caused by one of two kinds of forces: the conventionally considered impelling or pulling force of attraction, or, its exact opposite, a repelling/ pushing force. That is fact #1.
Fact #1 evokes at least one question: Allowing possible advantage in Newton's Gravitational Alternative that gravity may in fact be a repelling (pushing) force rather than an impelling (pulling) force, how might any such advantage be experienced and applied?
That question and its derivation might still be deemed obscure and inconsequential, if its direct unequivocal answer did not exist, most profoundly, at the heart-foundation of the latest and most advanced generalized theory of gravity in the history of Physical Science. That being Albert Einstein's GENERAL THEORY OF RELATIVITY.
In the first quarter of this century, Albert Einstein, in observing the already well known inversely proportional equivalence of gravitational and inertial mass values (which will be explained, shortly), described this equivalence as: 'an astonishing coincidence', and then applied the cause of his astonishment to the monumental task of formulating an unprecedented theoretical generalization concerning the identity of gravity. That, being none other than the General Principle Of Relativity; which principle is quite literally the foundation upon which rests Einstein's entire General Theory of Relativity. The most advanced statement about gravity, to date.
The General Principle is also misnomered as the 'Equivalence Hypothesis', or, more appropriately, 'The Principle Of Equivalence', which states:
'There is no way to distinguish the effects produced by the inertial force of acceleration (a pushing/repelling force) from the effects produced by gravitational force (assumed to be a 'pulling/impelling force: identity unknown').
Quotation excerpted from Total Field Theory @ http://forums.delphiforums.com/EinsteinGroupie