t'Hooft has suggested that the holographic conjecture (based on Bekenstein bound) implies that a 5-D spacetime can be viewed as 4-D spacetime with the fabric of space as the fifth dimension. Bekenstein says (http://eskesthai.blogspot.com/2004/11/information-in-holographic-universe.html):
'Superstring theory rules in the 5-D spacetime, but a so-called conformal field theory of point particles operates on the 4-D hologram. A black hole in the 5-D spacetime is equivalent to hot radiation on the hologram--for example, the hole and the radiation have the same entropy even though the physical origin of the entropy is completely different for each case.'
Can the spacetime fabric as the fifth dimension be treated by causality? Can the mechanism of gravity be extended from LeSage gravity (see 5 star book by Edwards on LeSage: http://www.amazon.com/exec/obidos/tg/detail/-/0968368972/103-7201186-4953411?v=glance).
Basically, in Newton's time there was a suggestion of an 'aether' in which pressure shielding causes gravity. The clearest and most brief description is by Richard P. Feynman in his 1965 published BBC lectures 'The Character of Physical Law'. Feynman has a diagram showing an object being pushed towards another which is shadowing it from space pressure.
However, as Feynman said in 1965, the theory was pretty useless as it couldn't predict gravity. I have an issue with this. Edwards (book cited above) is against the big bang model, but my objective is unify causal LeSage gravity with the big ideas of physics, including the big bang; see http://nigelcook0.tripod.com/ or http://members.lycos.co.uk/nigelbryancook/
Since Peter Woit won't allow me to post anything positive on his blog, I've put my views here: http://eskesthai.blogspot.com/2005/07/history-of-gravity-and-equivalence.html
In general relativity, the gravitational potential is proportional to energy density and pressure contributions. For non-relativistic matter the pressure is negligible, so only the energy density matters. But where you get to relativistic speeds, pressure is important.
Before summarising the gravity mechanism I came up with, here is my stringy treatment of the fabric of spacetime inspired by t'Hooft:
1. Holography is the encoding of information from a larger number of dimensions into fewer dimensions, eg a 3-D image on a 2-D photo.
2. Gravitation is modelled in GR as distortions in 4-D spacetime.
3. Gravitation can therefore be seen as a 4-D distortion when the underlying reality is a 5-D spacetime.
Kaluza in 1919 introduced the 5th dimension into GR, obtaining Maxwell's electromagnetism. However, like string theory now, it was a non-predictive speculation. A theory should explain something or predict something, not merely demonstrate that various sets of equations can be associated by arbitrary, artificial assumptions of the number of dimensions.
t'Hooft has suggested that the holographic conjecture (based on Bekenstein bound) implies that a 5-D spacetime can be viewed as 4-D spacetime with the fabric of space as the fifth dimension. Bekenstein says ( http://eskesthai.blogspot.com/2004/11/information-in-holographic-universe.html ):'Superstring theory rules in the 5-D spacetime, but a so-called conformal field theory of point particles operates on the 4-D hologram. A black hole in the 5-D spacetime is equivalent to hot radiation on the hologram--for example, the hole and the radiation have the same entropy even though the physical origin of the entropy is completely different for each case.'The spacetime fabric as the fifth dimension appears real to us, and therefore we can treat it by the laws of causality for a perfect fluid.
In the standard model, the Higgs boson is postulated to cause inertial mass, which by Einstein’s equivalence principle is also gravitational mass. Recently, Quantoken pointed out on Lubos' blog that the usual approach to quantum gravity, invoking gravitons as a mediator by analogy to the photon mediator in QED, may contradict Einstein's equivalence principle. The graviton involved in gravity would also have to occur in all accelerations. This naturally leads to a pressure type approach to quantum gravity.
LeSage around 1748 first came up with a prediction based on a pressure shielding mechanism for gravity which had begun in Newton's time, and LeSage used it to predict that - since gravity depends on the matter inside the earth and not just the surface area - the atom muct be mainly 'empty'. This was verified eventually by x-rays and radioactivity.
If there is a pressure in space masses will be pushed together by mutual shielding. The contraction effect in general relativity compresses the earth’s radius by 1.5 mm; by the same pressure effect for inertial mass in motion, you get the FitzGerald contraction in the direction of motion (the drag on moving objects is simply the increase in mass that occurs as speed rises). The gravitational contraction is radial only, not affecting the circumference, so there a difference between the true radius and that calculated by Euclidean geometry. Thus curved space using non-Euclidean geometry, or you can seek the physical basis of the pressure in the surrounding universe. I authored a paper: 'Solution to a Problem with General Relativity', CERN Document Server paper preprint EXT-2004-007. This was published in the April 2003 issue of 'Electronics World' (click on my name).
Pressures can result from the big bang. The recession varies from 0 to c with distance while corresponding times vary from 15,000 million years towards zero, so the matter of the universe has an effective outward acceleration of c divided by the age of the universe. This acceleration, a = c/t, is small, about 10^-10 ms^-2. But by Newton's 2rd law, the actual outward force, when properly allowing for the varying effective density of the observed universe as a function of spacetime, is large and by Newton's 3rd law it has an equal and opposite reaction, inward Higgs field pressure. The shielding of this pressure numerically predicts gravity quite well. To model both forces as pressure effects, you need find you need two pressures: virtual radiation pressure for charge and Higgs field for mass.
Photon radiation: this causes electromagnetic force in a similar way but is much stronger because in addition to the big bang effect, the potential adds up between similar charges like cells in a battery or displacement current between capacitor plates. The charges are randomly distributed so any straight line summation will encounter similar numbers of both charges and cancel out completely. The correct summation is a zig-zag so the effective sum is the square root of the number of charges in the universe times the gravity force: this predicts the strength of Coulomb's law quite accurately. Similar charges exchange extra energy and recoil apart, while opposite charges partly shield one another and are pushed together by a very slightly similar force due to the surrounding expanding universe.
If you have a big bang with speeds increasing in spacetime
v = dR/dt = RH,
(where H is Hubble constant) that means acceleration of
a = dv/dt = [d(RH)] / [dR / (RH)] = RH^2,
so there is outward force (by F = ma), due to the big bang universe around my apple, which means by Newton's 3rd law that there equal and opposite reaction of higgs bosons (inward force divided by area is the Higg’s field pressure).
This inward force is carried by the fabric of space around matter, so the inward pressure (force / area) goes as the inverse-square law, causing gravitation since the earth below the apple partially shields the pressure from the downward direction. The correct force of gravity turns out to be
F = mMG/r^2,
G = (3/4) H^2 / (pi x density x e cubed)
= 6.7 x 10^-11,
which is a factor of half e cubed = 10 times off the value that the critical density suggests. Put another way, this mechanism proves the cause of gravity while correcting the formula for the 'critical density' by the factor half e-cube, so the dark matter problem disappears and there is a direct comparison possible between the measured force of gravity and the big bang expansion and density data. The result is correct to within 2% for experimental data, which is fortuitous due to the error bars on the data, but it is a useful test. (http://nigelcook0.tripod.com/)