Today the Astrophysics community has banned this idea on the grounds of Einstein's theory General Relativity (GR), and it is hardly ever mentioned in modern textbooks any more. This is astonishing considering the fact that GR was presented in 1915, more than a dozen years before the advent of antimatter. A similar relation holds true for Friedmann's models (1922) which are the basis of today's 'Standard Model' of the Cosmos. In addition they violate nature's probably most fundamental CPT symmetry. This symmetry continues to be tested carefully which no unique consensus as of today. However, the Astropysics community seems to be more inclined to wait for the discovery of such a violation than to allow putting to question whether GR is able to handle antimatter correctly.

Many of the difficulties in a fundamental understanding of features of the 'Standard Model' would conceivably disappear if we went back to this old idea, such that I started to ask the heretical question, whether there might not be a generalization or modification of GR that was compatible with MAR.

There is a vast literature on Cosmology of which I only mention the very concise and well readable books by Andrew Liddle in which the basic questions are clearly exposed.

In the following I list a chronologically ordered sequence of short essays on the topic, which have to be considered as reports of work in progress. They are purposely left unchanged despite of the fact that they occasionally contain statements that turned out to be incorrect later on.

- Evidence for Matter-Antimatter Repulsion, a list of the most conspicuous problems that would find a straightforward explanation with MAR.
- Bipolar Gravity, a first step towards a modification of GR. These are purely static considerations.
- Lattice Model of the Universe, a regular model which exemplifies that MAR generates a contribution to the dark matter problem. However, the effect was grossly overestimated at the time.
- Poster presented at the Annual Meeting of the
Swiss Physical Society, 15.-17. June 2011 in Lausanne

Review and further progress (radiation pressure, neutrinos as possible Dark Matter candidates) - Physics with Negative Masses (http://viXra.org/abs/1303.0100) is a proposal to have negative gravitational masses in physics as the consequence of the requirement that the time-translation operator must have an unbounded spectrum. This route was taken after it became clear that General Relativity is unable to accommodate negative masses, since positive- and negative-curvature situations can never be equivalent.
- "Black Hole"-type objects (http://viXra.org/abs/1311.0120) obtain a new aspect in negative-mass Physics. They just represent a further level in the sequence of late-stage states of stars, after the various dwarf types and the neutron stars. Their expected high temperatures could lead to antimatter generation, which may show up in emitted slow positrons and electrons, giving rise to the galactic 511keV gamma-ray emission. Furthermore, they may provide a simple explanation for Black-Hole jets.
- A Remark on Relativistic Quantum Mechanics (http://viXra.org/abs/1407.0124) in which it is shown, that negative masses are a consequence of the two-valuedness of the representations of the Lorentz-group in Hilbert space. This elaborates on an earlier statement that the worrying negative-energy solutions of the Dirac equation are actually negative-mass solutions.
- What's Wrong with General Relativity? (http://viXra.org/abs/1502.0067) A simple argument is presented, which questions the consistency and, hence, validity of the theory of General Relativity. This theory allows exclusively for non-negative masses and so is the main obstacle to accepting any proposal of a gravitation-theory with negative masses.
- Static Fields as Mass-Currents and Mercury'sperihelion shift (http://viXra.org/abs/1505.0078) The quantum-field nature of static classical fields is explored. They appear as stationary mass-flows and, thus, should exhibit retardation effects. This aspect revalidates an early calculation of Mercury's perihelion shift.
- What's Wrong with General Relativity? (2) (http://viXra.org/abs/1506.0038) Arguments are advanced that question whether dynamic corrections (retardation effects) will not substantially modify the result of General Relativity for the perihelion shift of Mercury and, thus, destroy the good agreement with the experiment.
- Lattice model of a MAR-Cosmos.
The model is defined on a 3-dimensional periodic lattice and illustrates
the separation of matter and antimatter.
The initial state is a randomly-distributed density of both species on the
lattice sites, without any intended implication for the actual Cosmos!
An illustration is given by the following two videos:

Dotted representation, in which matter and antimatter are represented by yellow and cyan dots (in either assignment). A frame in white shows the unit cell of the model.

Contours in stereo, where contours are shown which contain 50% of the total mass of matter and antimatter. For a stereo impression the left-hand picture has to be watched with the right-hand eye and vice versa.

- On Generations in Elementary Particle Physics (http://viXra.org/abs/1609.0214). This is a spin-off from a consideration of representations of the Lorentz Group.
- On Gravitational Waves and Black Holes (http://viXra.org/abs/1710.0252). This short note questions whether the observed gavitational waves can be attributed unambiguously to the merger of black holes.
- What's Wrong with the Weak Interaction? (http://viXra.org/abs/1805.0521). Further studies of the representations of the Lorentz Group revealed the full structure of leptons, the light elementary particles. It also transpired that anti-particles are related to particles by improper Lorentz transformations, such as parity or time reversal. There seems to be no need for a fundamental 'Weak Force'.
- On Quantum Field Theory and Gravitation
(http://viXra.org/abs/1911.0010). Quantum fields are considered as
representations of the Lorentz group, the symmetry group of space-time.
There are two propagation mechanisms.
- Spin propagation is specific for the various spin-carrying field types, but does not affect the scalar field.
- Density propagation originates in the density property of fields and it's dependence on Lorentz contraction. This propagation affects all fields alike and is the only propagation mode for the scalar field. Thus, we conclude that density propagation is the action of gravity, and that the scalar field is the gravitational field.

- On the Polarization of Gravitational Waves (http://viXra.org/abs/2001.0398). The type of waves proposed by General Relativity (GR) violate translation invariance within phase planes of a planar wave. This opens the questions whether GR allows for gravitational waves at all, and thus, whether it has any physical significance.