If it existed a particle that had such properties that it both pushed away other particles of the same kind and it pushed away ordinary matter ,could this then explain dark matter and dark energy ? If the big voids of the universe was filled with such a particle, the net force of the particles in the universe would be outwards ,so the expansion would accelerate. If particles of this type surrounded a galaxy,they would push the edges of that galaxy inwards, so that the stars far from the center of that galaxy would increase their speed ,and it has been observed that the stars in a galaxy have a greater velocity than expected. In a cluster of galaxy this type of particle could push the galaxies together, allowing them to have a greater velocity than expected without escaping from the cluster,and this greater than expected speed has been observed. This particle could also explain the big voids in the universe,it would be a natural consequence of the particles properties.