Upon the basic assumption that the universe's physical space consists in an undetectable continuous and incompressible fluid, it is found that the propagation, through such a medium, of transverse waves - like gravitational standing waves or electromagnetic waves - entails loss in the wave frequency and propagation speed as the distance from the waves' source increases. It is a conclusion that derives from the hypothesis that the fluid cosmic space (which is here dubbed "the plenum" and thought of as destitute of mass) is kept cohesive by its own kinetic viscosity , in place of an impossible dynamic viscosity. Thus, the hypothesis leads to question the postulated constancy of the speed of light.

Against the conservative attitude of the academic world, a massive number of clues indicate that our universe consists substantially in an undetectable fundamental essence, which is commonly referred to as ?ether?. The need for the ?ether? was finally and openly admitted even by Einstein; whereas quantum physics lingers still on fuzzy concepts like ?zero/ground energy level? or similar ones, with no capacity of re-founding physics from the bottom up. The basic problem is now to try hypotheses on what the ether is and which properties are inherent in it.

This paper draws materials also from a book of mine, to try suggestions for a different approach to physics. The space of our universe is here addressed as it were a finite physical?though undetectable?fluid continuum (not consisting of component particles), here dubbed the ?plenum?, which is surrounded (and partly permeated) by a boundless space of ?true vacuum? (the void). In the void no physical event occurs. All material elements and detectable phenomena are effects of kinematical states of the ?plenum?. Allowing for such a basic assumption, the principal issue addressed here regards gravity and gravitation. Instead of ?mutual attraction between masses?, gravitation is here viewed and described as one particular effect associated with vortexes of plenum that establish gravitational fields. Also the formation of mass and the aggregation of matter components are viewed as states of plenum around nuclei of void, which ?enters? the physical space through tears and openings caused by motions and/or turbulence of the plenum. The analysis leads to the formulation of tentative gravity and gravitational equations, though a complete solution to them requires further research.

At variance with a largely shared opinion, both the foundation and the logical structure of Special Relativity (SR) have substantially been laid by Hendrik Lorentz and by Henri Poincar?, not by Albert Einstein. Yet, the mathematical generalization of SR comes from Hermann Minkowski, who in 1907 proposed the spacetime reference frame in its current notation, though the first mathematical formulation and use of a spacetime reference frame was clearly made by Poincar? in June 1905. (?Spacetime? is also referred to as ?chronotope?).

In this paper, which forms a "Special Appendix" to the book "Vacuum, Vortices and Gravitation" (fully and freely readable online at www.mario-ludovico.com), questionable points of Einstein's special relativity are given evidence. In particular, the well-known mass-energy equivalence equation is discussed in the light of Lorentz's theoretical analysis concerning the motion of a material body with respect to the ether. It is in fact remarked that the mass-energy equivalence equation is not an achievement of Einstein's special relativity. That equation is intrinsically inherent in the Lorentz's definition of "transverse mass", when the body's relative speed with respect to the ether is nil.

Perhaps, in a view to attaining - by his own - the "equivalence" relationship between mass and energy previously and differently formulated by Poincar?, Einstein published in September 1905 a very short paper, in which - starting from his precedent paper on special relativity - he "proves" the equation E = mc²  through the introduction of an unexpected simplification-approximation of the Lorentz's factor  1/(1-v²/ c²)^1/2 , which Einsteins equals to 1+v²/2c² cutting the relevant series at the second order term. Should one consider such a formal expedient as logically acceptable and appliable to all special relativity equations, the theory would  take (particularly from the experimental standpoint) a "physical" significance remarkably different from that conventionally celebrated.

Accounting for the possible existence of the "ether" (or "plenum" in the author's terminology) the same mass-energy equivalence can be  obtained analytically, with no use of relativistic paradigms. It is also observed that the introduction of Minkowski's "chronotope" has actually involved the mass-energy equivalence as an axiom proper to the spacetime paradigm.

From the APPENDIX to the book "Vacuum, Vortices and Gravitation"

Hubble's Law is currently formulated as follows: V_r = HR , where V_r is the galaxies' mutual recession speed, R the varying mutual distance, and H is a constant of proportionality known as Hubble Constant.

Used in this form, Hubble's Law - along with some analytical implications of Einstein's field equations - has led most astrophysicists and cosmologists to assume that the universe is expanding, and that the expansion had to start from a unique point of almost infinite concentration/density of mass/energy, i.e., from a place in which the ?mutual distance? between any kind of matter components (if any) was R_o ≈ 0 Then, according to most cosmologists, something like a huge explosion (the ?big bang?) can explain the initial tremendous force that caused the
expansion of the universe. (According to Russian mathematician Alexander Friedmann (1888-1925), Einstein's chronotope is possible of both
expansion and contraction).

Other supporters of the big-bang theory do now incline to think of the ?big-bang? not as of an explosion, but only as of the beginning of the universe's expansion, though I cannot grasp what they mean for ?big-bang? or any other ?more appropriate? dubbing of the event. In any case, big-bang theories adopt General Relativity as their basic reference paradigm.

Belgian astronomer George Lema?tre (1894-1966) was the first theorist of the universe's expansion, this viewed as originating from a ?primeval super-atom?. Lema?tre availed himself of General Relativity and of Hubble's statistics concerning the observed correlation between distance and mutual recession speed of galaxies. Subsequently, Dutch astronomer Willem De Sitter (1872-1934) did also theorize the expansion of the universe, adopting both Hubble's observational data and (sic!) Einstein's arbitrary ?cosmological constant? that a repented Einstein had later to label as his ?greatest blunder?.

Through recent decades the theoretical framework of big-bang theories developed and underwent several changes with a number of ad-hoc adjustments, because of astronomic observations incompatible with theoretical statements and predictions. The sequence of the adjustments had even led theorists of the universe's expansion to the need for considering Hubble coefficient H no more as a ?constant? but as a cosmological parameter that varies with time.

This essay of mine is based on my intent to avoid any reference to both Newtonian and Einsteinian cosmological models. As to me, Hubble constant is only the coefficient of a statistical linear correlation between two sets of observed data, i.e., between mutual distances and recession speeds of galaxies. I have no intention to attach any other significance to Hubble's statistical correlation, so that constant H, as a ?statistical coefficient?, shall be considered as a modifiable constant only upon more accurate and unbiased astronomical observations, which inevitably imply refinements in the identification of the most appropriate value for H. If the sequence of future observations corroborates the linearity of Hubble's correlation, this statistical law should be accepted as an experimental law, from which one can draw logical deductions as well as observational predictions. Therefore, I deem it improper and I reject all efforts to bend Hubble's law to the needs of abstract and questionable cosmological theories. What follows is a way to analyze Hubble's law with the only purpose of giving its simple logical implications the due evidence, with no need for either relativistic or other kind of cosmological reference and interpretation.

Upon this basis, it's easy to prove that, when t = 0 (i.e., at the supposed beginning of the universe's expansion), not only could not R_o be nil, but also that the initial distance between galaxies under formation had to be several million light-years. Moreover, a logical implication of Hubble's law predicts that the galaxies' recession acceleration too (i.e., a_r = H V_r = H² R) increases with the recession speed and distance, as observed and confirmed during recent years. Which is also an observational confirmation of the reliability of Hubble's law in the form it was originally formulated.

Additional notes, in a close connection with the text of the relative book , regard the formation of shape and dynamics of galaxies as due to the rise of vortices of physical space (i.e., vortices of "plenum", the Universe's basic and undetectable fluid continuum) around "cores" of nothingness.