“If we pick up a stone and then let it go, why does it fall to the ground?” The usual answer to this question is: “Because it is attracted by the earth.” Modern physics formulates the answer rather differently for the following reason. As a result of the more careful study of electromagnetic phenomena, we have come to regard action at a distance as a process impossible without the intervention of some intermediary medium. If, for instance, a magnet attracts a piece of iron, we cannot be content to regard this as meaning that the magnet acts directly on the iron through the intermediate empty space, but we are constrained to imagine—after the manner of Faraday—that the magnet always calls into being something physically real in the space around it, that something being what we call a “magnetic field.” In its turn this magnetic field operates on the piece of iron, so that the latter strives to move towards the magnet. We shall not discuss here the justification for this incidental conception, which is indeed a somewhat arbitrary one. We shall only mention that with its aid electromagnetic phenomena can be theoretically represented much more satisfactorily than without it, and this applies particularly to the transmission of electromagnetic waves. The effects of gravitation also are regarded in an analogous manner. |
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The action of the earth on the stone takes place indirectly. The earth produces in its surroundings a gravitational field, which acts on the stone and produces its motion of fall. As we know from experience, the intensity of the action on a body diminishes according to a quite definite law, as we proceed farther and farther away from the earth.
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>> Einstein said also that the gravity-effect of that gravitational field is caused by curved space-time, perfectly acceptable, but he does not explain the exact reasons or mechanisms as to how this spacetime-curvage functions, originates.
The mechanisms, the causes are not explained, he only says "The earth produces in its surroundings a gravitational field." That is further unelaborated, and therefore leaves a gap for others to fill this aerea in with theories.
Hence a theory like Le Sage's is picked up in the nineties and later elaborated on.
Such a theory may not be correct , but similar theories could further elaborate Einsteins gravity,
they don't always have to contradict it, they can be complemantary.
Also i refer to the idea of gravitons being the force-particles carrying the gravity effect, thus being responsible for Einstein's curved spacetime gravity, being responsable for the gravity field.
> Ref. : Scientific American , october 1999 :
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Is gravity a particle or a wave? Einstein described gravity as warped space-time, but there is also the theory that gravity is carried by hypothetical particles called gravitons. Is this a situation like the wave- particle duality of light, in which it is more convenient to think one way sometimes and another at other times?
Bradley Carroll, a professor of physics at Weber State University in Ogden, Utah, responds:
"According to modern physics field theories, each of the four basic interactions (a better term than 'force') is mediated by a type of particle:
"The strong (nuclear) interaction is carried by gluons. (This is the interaction that holds together the particles in the nuclei of atoms.)
"The electromagnetic interaction is carried by photons. (This is the interaction responsible for all electrical and magnetic phenomena.)
"The weak (nuclear) interaction is carried by weak bosons. (This is the interaction that governs certain radioactive decays, such as beta decay.)
"The gravitational interaction is carried by gravitons. (This, of course, is the interaction that gives rise to the familiar pull of gravity.)
"Although the graviton has yet to be observed, some of its hypothesized properties are known. It is a massless particle having no electrical charge. Its spin (a property of subatomic particles that is not directly analogous to the rotation of a macroscopic object like a top) is twice that of the other field particles listed above; in technical terms, its spin is 2 hbar instead of 1 hbar, where hbar is Planck's constant divided by 2 pi.
"Two masses attract each other gravitationally because they are constantly exchanging virtual gravitons, just as two electrically charged particles are drawn together--or repelled apart--by the exchange of virtual photons. (A 'virtual particle' is one that cannot be directly detected.) This exchange happens at all times. Gravitational waves, in contrast, can arise when an object undergoes an acceleration. Asymmetric supernova explosions or collisions between neutron stars are the kinds of events that could produce powerful blasts of gravitational waves. Gravitational waves have been indirectly detected in certain binary neutron star systems, in which the energy carried off by those waves causes observable changes in the stars' orbits.
"Virtual gravitons pass between two objects even when there are no gravitational waves present (for instance, when the masses are at rest), so it really isn't correct to say that gravity is a wave.
"An analogy with an electrically charged particle might help clarify the situation. When a charged particle is at rest, it is surrounded by a static electric field (no waves). If another charged particle encounters this field, it experiences a force. The quantum view would describe this in terms of an exchange of virtual photons by the two particles. On the other hand, if a charged particle is accelerated, its electric field is ' shaken' to produce an electromagnetic (light) wave that spreads out from the particle. In this case, the energy and momentum of the light wave are carried by real, detectable photons.
"In a similar manner, when a massive particle is at rest, it is surrounded by a static gravitational field (a static curvature of spacetime, no waves) . If another massive particle encounters this field, it experiences a force that can be described in quantum terms as an exchange of virtual gravitons by the two masses. On the other hand, if a massive particle is accelerated, its gravitational field is 'shaken' to produce a gravitational wave that spreads out through spacetime from the particle. The energy and momentum of that gravitational wave are carried by real gravitons."
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