In numerous previous publications, a fundamental theory was advanced to explain the baffling cosmic observation associated with conjectured dark energy and the surprising measured accelerated rather than decelerating expansion of the universe [1] -[4] . Exact calculations based on particle-wave duality in highly mathematical set theoretical formulation led to an ordinary measurable energy density of E(O) = mc²/22 where m is the mass and c is the speed of light, i.e. only 1/22 of Einstein’s famous energy density [4]. This was a remarkable result and in full agreement with the latest and most accurate cosmic measurements and supernova analysis which incidentally led to the award of several Nobel Prizes in Physics on two different occasions [1] [4] . For dark energy the density found was which amounts to exactly showing with absolute clarity that Einstein’s density, lacking the quantum component, is blind to any distinction between ordinary energy and dark energy [1] -[4] . Thus apart of the quantitative resolution of this major problem, a fundamental conclusion was reached elevating Einstein’s relativity formula E = mc² to a quantum relativity equation

where E(O) is the ordinary energy of a quantum pre-particle in a five-dimensional Kaluza-Klein space time and E(D) is the negative dark energy of the quantum pre-wave in the same Kaluza-Klein space-time [1] -[4] . Seen in this way we begin to understand why ordinary positive energy can be detected and measured while the negative dark energy could not, at least not directly nor using any conventional method [3] [4] . The reason for this failure is as simple as it is unexpected and is anchored in the deep logic of set theory [4] . In set theoretical terms, a quantum particle is a physical materialization of the zero set [3] [4] . The quantum wave on the other hand is the physical materialization of the empty set [3] [4] . Since “measurement” interferes with the empty set and causes it to become non-empty, the empty quantum “wave” set transmutes instantly to a zero quantum “particle” set at measurement [3] [4] . This is what we call wave collapse and that is why the negative dark energy of the wave cannot be measured in the ordinary way unless wave non-demolition measurements could be developed in the future [1] -[4] .

The preceding set theoretical explanation, although mathematically and logically accessible and in some sense even intuitive, cannot be called physically obvious. For instance it is true that we have a clear picture of a particle with a wave as its cobordism, i.e. as its surface. Never the less particles and surfaces although inseparable, cannot be dealt with experimentally except via the contra-intuitive perspective of wave-particle duality [3] [4] . All the same it would be more than desirable to have a conjugate more down to earth and conventional physical picture to go hand in hand with the fundamental set theoretical interpretation just outlined [1] -[4] .

In the present work we think that we have at long last found a parallel physical interpretation to our set theoretical picture which is in a one to one correspondence with the zero set-empty set particle-wave duality [3] [4] , [7] -[9] . This we explain after a very short introduction to the role played by relativistic hydrodynamics in cosmic dark energy research [10] .

To sum up we could look upon dark energy which is the negative energy of the quantum wave surface of the quantum particle core [8] as being analogous to the physically and classically real capillary surface energy which cannot always be easily measured due to spontaneous jump into the lower energy level of the core [5] -[7] . Here we are speaking of higher and lower in absolute terms and are of course disregarding the sign convention. We conclude by noting the immense importance of relativistic hydrodynamical models in physics and astrophysics [10] as well as the similarity between dark energy and the imperfection sensitivity of the buckling of thin elastic shell structures [7] .

I am in more than one sense indebted to our teacher the late Prof. Dr. Dr. Theodor Lehmann who initiated my serious interest in Einstein’s relativity although we were in a purely applied civil engineering mechanics department at the then Technical High School of Hannover, West Germany in the sixties of the last century. I am also indebted to Prof. J.M.T. Thompson (FRS) for introducing me to the book of H. Dingle “Science At The Crossroads” refuting special relativity though for the wrong reasons as it became obvious here. The discussion with Prof. Thompson also took place in a civil engineering department in University College, London, UK in 1969 with a stability research group which was established by Lord Henry Chilver.