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Black Holes

Black holes and the big bang were strange features of Einstein's Universe.

Light travels in straight lines. But the straight lines in Einstein's Universe appear curved when viewed in three dimensions. In General Relativity, light is bent by the presence of mass in exactly the same way that matter is, because gravity is a result of the very geometry of the Universe.

The more massive an object is, the more it bends space-time, and the harder it is to escape the pull of its gravity. It is possible for a super-dense object to have so much mass that nothing can escape from it, not even the fastest thing in the Universe - light. This is known as a Black Hole.

Astronomers now believe that Black Holes exist throughout the Universe, and have located a number of potential candidates. It is thought that a super-massive black hole exists at the centre of our own Milky Way galaxy.

Black Holes are not the only strange thing predicted by General Relativity. Einstein's original equations suggested that space-time cannot remain constant - it must always be either expanding or contracting. Not even Einstein could believe this strange result so he changed his equations. However, in the 1920's Edwin Hubble observed that the space between the galaxies is, indeed, expanding.

The consequences of the theory of Relativity seem bizarre. However the changes to the way we measure space and time that are predicted by this theory have been directly observed on Earth. In fact they are observed everyday - without them the global network of Global Positioning Satellites would not work.

GPS satellites send signals from orbit down to the surface of Earth and back again. To function correctly, the time taken by signals, and the positions of those signals, need to be measured precisely. These measurements would not be precise enough if Newton's equations were used - GPS satellites need to use the strange theory of General Relativity.

Visualisation of a black hole
magnifyVisualisation of a black hole

Galaxy cluster
magnifyGalaxy cluster

GPS satellite
magnifyGPS satellite
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