How do astronomers look back in time?
The further light has to travel across the universe before it reaches the earth, the longer it takes to get here. That may sound obvious but it is very useful for astronomers. It means that when they look at objects in the furthest reaches of the universe, the light which is captured by the telescope and camera has taken most of the age of the universe to reach the earth. In other words they are also looking back in time to how the universe was shortly after it formed. However, it is not as easy as it sounds. On its way across the universe the light becomes stretched (because the universe is expanding) so that when it reaches the earth it is at much longer wavelengths than it was when it was originally emitted. This is known as ‘red-shift’. The light from the star-forming galaxies in this study has been stretched so much that it has been shifted from the far-infrared waveband, accessible only from space, to the submillimetre waveband. Submillimetre radiation is emitted in the region of
