Wonders of the Universe - Brian Cox [27]
This might seem complicated, but the conclusion is simple and profound. The reddening of the distant galaxies tells us that the Universe is expanding. This means that the galaxies we see in the sky today must have been closer together in the past. If, in your mind’s eye, you keep winding back time and you watch the galaxies getting closer and closer together, then, at a time given by the inverse of the Hubble constant, you will find that they must have all been on top of each other. In other words, the Universe we see today must have been incredibly tiny. This all happened around fourteen billion years ago, and that event is what we call the Big Bang. So Hubble’s remarkable observation is direct evidence that the Universe began with a big bang around fourteen billion years ago. All this was deduced in the 1920s simply by capturing the light from Cepheid variable stars and distant galaxies.
The Big Bang is difficult to visualise; it is easy to think of it as a vast explosion that flung matter out into a pre-existing void – a giant empty box, if you like – but this is completely wrong. The currently accepted picture is that all of space came into existence at the Big Bang. In fact, in the spirit of Einstein we should more correctly say that all of spacetime came into existence at the Big Bang. This means that the Big Bang didn’t just happen out there somewhere in the Universe, it happened everywhere at once. So the Big Bang happened in the bit of space between you and this book; it happened inside your head, across the road, at every point in the Solar System and inside the most distant galaxies. In other words, it happened at every point in the Universe. All of space was there at the Big Bang, and all it has done is stretch ever since. This has the rather mind-bending consequence that if the Universe is infinite today, it was born infinite. Everywhere that is here now was there then, but just squashed a lot! Nobody said cosmology was easy. So when we look at the distant galaxies and we see them all flying away from us, this is not because they were flung out in some massive explosion at the beginning of time; it is because space itself is stretching, and it’s been stretching since the Big Bang.
The Hubble expansion is one piece of evidence for the Big Bang, but there is another, perhaps more remarkable, fingerprint of the Universe’s violent beginning, delivered to us by the most ancient light in the cosmos
THE BIRTH OF THE UNIVERSE
Every second, light from the beginning of time is raining down on Earth’s surface in a ceaseless torrent. Only a fraction of the light present in the Universe is visible to the naked eye, though; if we could see all of it, the sky would be ablaze with this primordial light both day and night. However, some of this hidden light is not quite a featureless glow; the long wavelength universal glow known as the Cosmic Microwave Background (CMB) in fact displays minute variations in its wavelength. The CMB carries with it an image of our universe as it was just after its birth, and this discovery has provided key evidence that the beginning really did start with the Big Bang.
It was at the Big Bang that all of spacetime came into existence. The stars and galaxies stretched away across an infinite universe and many are still to be found today. Space is stretching still; housing the old galaxies alongside numerous new star-forming regions, such as NGC 281 k.
NASA
VISIBLE LIGHT
Standing among the dunes of the Namib Desert you become aware of the sheer scale of the landscape. It is a landscape sculpted by the Sun and coloured by it at all times.
Stretching along the west coast of southern Africa is the Namib Desert. It is the oldest desert in the world; its landscape is a shifting sea of sand of over 77,700 square kilometres (30,000 square miles) which changes every minute, a consistently arid wilderness that has stubbornly avoided moisture for over fifty million years. This is a world sculpted by the Sun;