Wonders of the Universe - Brian Cox [23]
There are about 100 of these galaxies in the image, and they are among the most distant objects we have ever seen. Some of these faint red blobs are well over twelve billion light years away, which means that when their light reaches us it has been travelling for almost the entire 13.75-billion-year history of the Universe. The most distant galaxy in the Deep Field, identified in October 2010, is over thirteen billion light years away – so we see it as it was 600,000 years after the beginning of the Universe itself.
It is hard to grasp these vast expanses of space and time. So, consider that the image of this ancient galaxy was created by a handful of photons of light; when they began their journey, released from hot, primordial stars, there was no Earth, no Sun, and only an embryonic and chaotic mass of young stars and dust that would one day evolve into the Milky Way. When these little particles of light had completed almost two-thirds of their journey to Hubble’s cameras, a swirling cloud of interstellar dust collapsed to form our solar system. They were almost here when the first complex life on Earth arose and within a cosmic heartbeat of their final destination when the species that built the Hubble first appeared.
The story hidden within the Hubble Ultra Deep Field image is ancient and detailed, but how can we infer so much from a photograph? The answer lies in our interpretation of the colours of those distant, irregular galaxies
ALL THE COLOURS OF THE RAINBOW
The breathtaking Victoria Falls are one of the most famous and beautiful natural wonders on our planet. Fuelled by the mighty Zambezi River, the falls lie on the border between Zambia and Zimbabwe in southern Africa. The falls were named by David Livingstone in 1855, the first European to see them. He later wrote: ‘No one can imagine the beauty of the view from anything witnessed in England. It had never been seen before by European eyes; but scenes so lovely must have been gazed upon by angels in their flight.’ That’s about right from where I stood. There are few better places on Earth from which you can experience the visceral power of flowing water, but there is an ethereal feature of the falls that is just as enchanting and far more instructive for our purposes, because it holds the key to interpreting the Hubble Deep Field Image.
Hovering in the skies above the falls are magnificent rainbows, a permanent feature in the Zambian skies when the Sun shines through the mist. Rainbows are natural phenomena that have enchanted humans for thousands of years; to see one is to marvel at a simple but beautiful property of light and, as is often the case in nature, they are made more beautiful when you understand the science behind them.
Scientists have attempted to understand rainbows since the time of Aristotle, trying to explain how white light is apparently transformed into colour. Our old friend Ibn al-Haytham was one of the first to attempt to explain the physical basis of a rainbow in the tenth century. He described them as being produced by the ‘light from the Sun as it is reflected by a cloud before reaching the eye’. This isn’t too far from the truth. The basis of our modern understanding was delivered by Isaac Newton, who observed that white light is split into its component colours when passed through a glass prism. He correctly surmised that white light is made up of light of all colours, mixed together. The physics behind the production of a rainbow is essentially the same as that of the prism. Light from the Sun is a mixture of all colours, and water droplets in the sky act like tiny prisms, splitting up the sunlight again. But why the characteristic