About the Universe

Everything in the Universe rotates. The Earth spins on its axis. The whole planet orbits around our parent star, the Sun. The Sun rotates around the centre of the Milky Way, along with the billions of other stars in the Galaxy. Studying how fast stars at the very edge move reveals the mass of the whole galaxy. The faster the Galaxy rotates, the more mass there is inside it. There is also stuff out there that we just can't see - and so it's called 'dark matter'. If this dark matter wasn't there, galaxies would fly apart as they spun round. Imagine looking at a tower block at night. Although you can only see lights coming from some of the rooms, that doesn't mean that there aren't any more rooms in the tower. Just like these unlit rooms, dark matter can't be seen, because it doesn't shine. Finding it will help to answer one of the most fundamental questions in astronomy - what is the fate of the Universe.

The fate of the Universe is basically a battle fought between the inward pull of gravity and the outward push of expansion. So astronomers are trying to calculate the strength of these forces. The amount of gravity the Universe has to wield against this expansive onslaught depends on how much stuff there is out there in space. Anything with a mass has its own gravity. Even you yourself have a gravitational force that attracts everything else around you, including other people. The bigger you are, the stronger this force is, and so, the Earth, being the most massive thing around, completely overwhelms the tiny forces that we personally possess. So to calculate the fate of the Universe, we must weigh it to find its density.
Also, in about 4 billion years the Sun will expand and engulf our planet Earth. Also around the same time, our nearest galactic neighbour, Andromeda, will start to crash into our own galaxy, the Milky Way.

Life on Earth must escape into space if it is to survive.