Assuming that a particle and its antiparticle have the gravitational charge of the opposite sign, the physical vacuum may be considered as a fluid of virtual gravitational dipoles. Following this hypothesis, we present the first indications that dark matter may not exist and that the phenomena for which it was invoked might be explained by the gravitational polarization of the quantum vacuum by the known baryonic matter.Let us start with a major unresolved problem. The measured galaxy rotation curves remain roughly constant at large radii. Faster than expected orbits, require a larger central force, which, in the framework of our theory of gravity, cannot be explained by the existing baryonic matter. The analogous problem persists also at the scale of clusters of galaxies.The favoured solution is to assume that our current theory of gravity is correct, but every galaxy resides in a halo of dark matter made of unknown non-baryonic particles (for a brief review on dark matter see for instance: Einasto, 2010). A full list of the proposed dark matter particles would be longer than this letter; let us mention only weekly interacting massive particles and axions. In spite of the significant efforts dark particles have never been detected. Let us note that in order to fit observational data for a galaxy, the radial mass density of dark matter in a halo should be nearly constantThe best developed alternative to particle dark matter is the Modified Newtonian Dynamics (MOND). It states that there is no dark matter and we witness a violation of the fundamental law of gravity (see brief review of Milgrom, 2010). 2In a recent series of papers (Blanchet 2007a(Blanchet , 2007b Blabchet and Tiec 2008, 2009) it was shown that, in spite of the fact that MOND phenomenology rejects the existence of dark matter, it can be considered as consequence of a particular form of dark matter. The key hypothesis is that dark matter is a dipolar fluid composed from gravitational dipoles (in analogy with electric dipole, a gravitational dipole is defined as a system composed of two particles, one with positive and one with negative gravitational charge). Hence, Blanchet and Tiec have introduced dipolar fluid as a new candidate for non-baryonic dark matter; the galaxy rotation curves can be considered as result of the gravitational polarization of the dipolar fluid by the gravitational field of baryonic matter.While the work of Blanchet and Tiec has attracted a significant attention, a very different idea concerning the gravitational polarization (Hajdukovic, 2007(Hajdukovic, , 2008 passed in silence. The key hypothesis advocated by Hajdukovic is the gravitational repulsion between matter and antimatter, i.e. particles and antiparticles have gravitational charge of opposite sign. Consequently the virtual particle-antiparticle pairs in the quantum vacuum should be considered as gravitational dipoles. Thus, the quantum vacuum may be considered as a dipolar fluid, what is much simpler and more elegant than the dipolar fluid composed from ...

Quantum vacuum and the matter immersed in it interact through electromagnetic, strong and weak interactions. However, we have zero knowledge of the gravitational properties of the quantum vacuum. As an illustration of the possible fundamental gravitational impact of the quantum vacuum, we study the gravitational field of an immersed point-like body. This is done under the working hypothesis, that quantum vacuum fluctuations are virtual gravitational dipoles (i.e. two gravitational charges of the same magnitude but opposite sign); coincidentally, this hypothesis makes quantum vacuum free of the cosmological constant problem. The major result is that a point-like body creates a halo of polarized quantum vacuum around itself, which acts as an additional source of gravity. There is a maximal magnitude ${g_{\rm qv\max}}$ of gravitational acceleration that can be caused by a polarized quantum vacuum; the small size of this magnitude (${g_{\rm qv\max}} < 6\ \times {10^{ - 11}}\,\mathrm{ m\,s}{^{-2}}$) is the reason why in some cases (for instance within the Solar system) the quantum vacuum can be neglected. Advanced experiments at CERN and forthcoming astronomical observations will reveal if this is true or not, but we point to already existing empirical evidence that seemingly supports this fascinating possibility.

Recently, the gravitational polarization of the quantum vacuum was proposed as alternative to the dark matter paradigm. In the present paper we consider four benchmark measurements: the universality of the central surface density of galaxy dark matter haloes, the cored dark matter haloes in dwarf spheroidal galaxies, the non-existence of dark disks in spiral galaxies and distribution of dark matter after collision of clusters of galaxies (the Bullet cluster is a famous example). Only some of these phenomena (but not all of them) can (in principle) be explained by the dark matter and the theories of modified gravity. However, we argue that the framework of the gravitational polarization of the quantum vacuum allows the understanding of the totality of these phenomena.Comment: Accepted for publication in Astrophysics and Space Scienc

Before the end of this decade, three competing experiments (ALPHA, AEGIS and GBAR) will discover if atoms of antihydrogen fall up or down. We wonder what the major changes in astrophysics and cosmology would be if it is experimentally confirmed that antimatter falls upwards. The key point is: If antiparticles have negative gravitational charge, the quantum vacuum, well established in the Standard Model of Particles and Fields, contains virtual gravitational dipoles. The main conclusions are: (1) the physical vacuum enriched with gravitational dipoles is compatible with a cyclic universe alternatively dominated by matter and antimatter, without initial singularity and without need for cosmic inflation; (2) the virtual dipoles might explain the phenomena usually attributed to dark matter and dark energy. While what we have presented is still far from a complete theory, hopefully it can stimulate a radically different and potentially important way of thinking.