Gravity (Hijack from What other field affect light like gravitational fields?)

[madmac]

I didnt read Verlinde's full paper in your link https://arxiv.org/pdf/1001.0785.pdf  but it is hell to read -- at first glance it looks like a joke paper, silly salad (but i aint a scientist) -- but Verlinde is serious (gulp). Judging by the following snippets it seems to me that what Verlinde is saying is that gravitational force does not need a field, it is a function of location, & this function of location is in effect a field, & therefore a field is not needed. Here Verlinde has not only murdered any sensible definition of a field, he has sawed the field up into little bits & has dressed hizself in its old garments & then strolled out of the embassy. I have just noticed that a Killing vector figures prominently in his paper.

............The holographic principle has not been easy to extract from the laws of Newton and Einstein, and is deeply hidden within them. Conversely, starting from holography, we find that these well known laws come out directly and unavoidably. By reversing the logic that lead people from the laws of gravity to holography, we will obtain a much sharper and even simpler picture of what gravity is. For instance, it clarifies why gravity allows an action at a distance even when there in no mediating force field. The presented ideas are consistent with our knowledge of string theory, but if correct they should have important implications for this theory as well. In particular, the description of gravity as being due to the exchange of closed strings can no longer be valid. In fact, it appears that strings have to be emergent too.............

...........An entropic force is an effective macroscopic force that originates in a system with many degrees of freedom by the statistical tendency to increase its entropy. The force equation is expressed in terms of entropy differences, and is independent of the details of the microscopic dynamics. In particular, there is no fundamental field associated with an entropic force. Entropic forces occur typically in macroscopic systems such as in colloid or bio-physics. Big colloid molecules suspended in an thermal environment of smaller particles, for instance, experience entropic forces due to excluded volume effects. Osmosis is another phenomenon driven by an entropic force. Perhaps the best known example is the elasticity of a...................

..............Space emerges at a macroscopic level only after coarse graining. Hence, there will be a finite entropy associated with each matter configuration. This entropy measures the amount of microscopic information that is invisible to the macroscopic observer. In general, this amount will depend on the distribution of the matter. The information is being processed by the microscopic dynamics, which looks random from a macroscopic point of view. But to determine the force we don’t need the details of the information, nor the exact dynamics, only the amount of information given by the entropy, and the energy that is associated with it. If the entropy changes as a function of the location of the matter distribution, it will lead to an entropic force. Therefore, space can not just emerge by itself. It has to be endowed by a book keeping device that keeps track of the amount of information for a given energy distribution. It turns out, that in a non relativistic situation this device is provided by Newton’s potential Φ. And the resulting entropic force is called gravity................

 

Edited November 2, 2018 by madmac

[ernst39]

In the framework of the gravitoelectromagnetic description of gravity (GEM), the gravitational field plays an intermediary  role in the interaction between masses.  

 

In that context, the gravitational field is  considered as a constituent element of nature,  set up by a given distribution of - whether or not moving - masses and it is, just as the electromagnetic field, defined by two three-dimensional intertwined  vector fields:  the “g-field” E_g  and the “g-induction” B_g.    These vector fields each have a value defined at every point of space and time and are thus, relative to an inertial reference frame O,  regarded as functions of the space and time coordinates.  

 

Just as the electromagnetic field (E, B), the gravitational field (E_g, B_g) is mathematically defined by a set of four partial differential equations, the “GEM-equations” (or the “Maxwell-Heaviside equations”) that describe how E_g  and B_g vary in space due to their sources - the masses and the mass flows - and how they are intertwined. These equations nor their solutions indicate an existence of causal links between  E_g  and B_g . Therefore, we must conclude that a gravitational field is a dual entity always having a “field-” and an “induction-” component  simultaneously created by their common sources: time-variable masses  and mass flows. 

 

GEM is consistent with special relativity.  The GEM equations are analogue to Maxwell’s equations in EM and it is proved  that these are consistent with special  relativity.  Thus, the Maxwell-Heaviside equations are invariant under a Lorentz transformation.   So, the principle of relativity is valid in the context of GEM.  And, from the postulate of the gravitational action, it follows that the same is true for the principle of equivalence..

 

Certain concrete predictions made on the basis of the gravito-electromagnetic description of gravity are perfectly in line with the results of cosmological observations.

 

Let's still remark that:

 

1. by taking into account the kinematics of the gravitating objects, GEM is an extension of Newtonian gravity.

 

2.  the starting point of GEM differs fundamentally from the starting point of GRT, because in the context of GEM space and time don’t play an active role in the description of the gravitational phenomena and laws.  It are elements of the description of nature that do not participate in the physical processes.

 

 

https://en.wikipedia.org/wiki/Gravitoelectromagnetism

 

Edited November 8, 2018 by ernst39