The Universe is rapidly expanding. This seemed as though it was impossible decades ago but it is now accepted as scientific fact. There is a force pushing the universe towards an unknown infinity but scientists do not quite understand the exact properties of this force pushing galaxies apart. This energy, or dark matter as it is often called, accounts for over 68% of the total energy in the observable universe but we really don't understand it.
Furthermore, it's unclear why it is that there is precisely the amount of dark matter present in the universe to allow matter to form, rather than be pulled away from itself in a vast empty space.