The future of the Universe
For many years, scientists have tried to work out the density of the Universe. The answer to this would give them an idea of whether the Universe is going to expand forever, or if the gravitational attraction between all objects will eventually slow to a stop, attracting everything back together in a 'Big Crunch'.
Dark energy
Since 1998, astronomical observations of supernovaThe large explosion at the end of a large star鈥檚 life, which distributes much of the elements formed in the star across space. have suggested that distant galaxyA cluster of billions of stars, held together by gravity. are moving away increasingly faster. The expansion of the Universe appears to be accelerating. Scientists do not entirely understand how this could happen, but they have come up with an idea called dark energyAn unknown form of energy, put forward as a solution to the problem of why the expansion of the Universe is accelerating..
The nature of dark energy is still a complete mystery, but it is thought to cause the Universe to expand faster all the time. Astronomers have calculated that to make the Universe accelerate as observed, dark energy must account for 68 per cent of the Universe.
Dark matter
Another recently discovered anomaly is that galaxies seem to rotate too quickly for the mass of their stars. This suggests that there is mass in the Universe that is invisible to the instruments used by scientists. Scientists only know it is there because it has gravity that affects objects nearby. This unknown material has been called dark matterAn unidentified form of matter that accounts for galaxies rotating faster than their visible mass should cause.. Astronomers have calculated that 27 per cent of the Universe must be made of this dark matter.