That's all that causes the Universe's expansion: the total amount of energy that's in it. We know that our universe is expanding at an accelerating rate, but what causes this growth remains a mystery. But actually this is not the case. Einstein believed that the Universe was an infinitely large, all-encompassing blimp. Dark energy: The mysterious force causing the universe to expand. September 14, 2012. Dark Energy. It was previously thought the expansion of the universe will continue for a while, stop and than the universe will contract again like a ball thrown upwards towards the sky stops after some time and then fall down again. From here to infinity, as far as we can tell, dark energy will continue to dominate the Universe. Scientists believe that there is something called a Dark Energy that is increasing the expansion of the universe. It is generally believed that the expansion of the universe is the result of the initial "explosion" of the Big Bang -- the matter created then is still being propelled outwards in all directions. For … Imagine the beginning of the Universe, BOOM, like an explosion from a gun. Physicists believe that only 4 percent of the universe is made … And all the rest of the expansion is the Universe coasting outwards.