Is dark energy just an illusion? The truth is that no one really knows -- More is unknown about dark energy than is known. Many researchers claim to “know” how much dark energy there is due to its apparent affect on the expansion of the Universe. But other than that, it is a complete mystery. If it exists at all, then roughly 68 percent of the Universe should be composed of this mysterious dark energy, with the equally mysterious dark matter making up about 27 percent. The rest -- everything on Earth, everything ever observed in the Universe with all of our instruments, all normal matter -- would add up to less than 5 percent of the Universe. The thing that is needed to decide between dark energy possibilities – be it a property of space, a new dynamic fluid, or a new theory of gravity -- is more and better data. Researchers at the Scuola Internazionale Superiore di Studi Avanzati (SISSA) in Trieste, Italy, have been working on this problem and now have the first simulation of neutron star mergers that reproduce a dark energy-like behavior on cosmological scales. So far, their findings that dark energy is just an illusion are consistent with data acquired by the LIGO and Virgo interferometers during recently captured binary neutron star collisions and may be further tested and supported by next-generation gravitational interferometers, such as the Einstein telescope in Europe and Cosmic Explorer in USA.