Dark energy (IMAGE) Royal Astronomical Society Caption This graphic offers a glimpse of the history of the Universe, as we currently understand it. The cosmos began expanding with the Big Bang but then around 10 billion years later it strangely began to accelerate thanks to a theoretical phenomenon termed dark energy. Credit NASA Usage Restrictions No restrictions. License Public Domain Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.