Wonders of the Universe

PICTURING THE PAST

On 30 June 2001, the Wilkinson Microwave Anisotropy Probe, known as WMAP, was launched from the Kennedy Space Center in Florida. This highly specialised telescope was built with a single purpose: to capture the faint glow of the CMB and create the earliest possible photograph of the Universe. After nine years of service, WMAP has recently been retired, but its photograph is still the object of frenzied research because it contains so much rich detail about the early Universe and its expansion and evolution ever since.

This much-studied image is probably the most important picture of the sky ever taken. It may not look like much; it doesn’t have the beauty of a spiral galaxy or nebula, but to a scientist it is the most beautiful picture ever taken because it contains a vast amount of information about the history of our Universe.

The raw image from WMAP shows the glow of our Milky Way Galaxy as it creates a hot bright band across the sky, but once this detail and other observational side-effects are removed, we are left with this simplified, but equally important and informative, picture below. This photograph of the night sky documents in extraordinary detail the structure of our universe at the time of recombination. Over the nine years in which WMAP was in service, the detail of this image has been repeatedly refined, which in turn reveals more and more detailed information encoded in the primordial light.

The WMAP data is presented as a temperature map of the sky. The wavelength of the detected light at any particular point corresponds to a temperature; shorter wavelengths are higher temperatures, longer wavelengths are lower ones. The red areas are hotter than the blue, but only by around 0.0002 degrees. The average temperature of the CMB is 2.725 degrees above absolute zero. On the Kelvin temperature scale, that’s 2.725 K, or -270.425 Celsius.

Despite being incredibly tiny, these temperature differences are of overwhelming importance because they tell us that in the very first moments of our universe’s life there were regions of space that were slightly denser than others. These virtually imperceptible differences might not seem much, but without them we would not exist. That’s because these little blips in the CMB are the seeds of the galaxies. The red spots in the CMB correspond to parts of the Universe that were on average around half a per cent denser than the surrounding areas at the time of recombination. As the whole Universe expanded, these areas would have expanded slightly more slowly than their surroundings because of their higher density – effectively, their increased gravity due to their higher density would have slowed the expansion, causing their density to increase further relative to the space around them. By the time the Universe was one-fifth of its present size, just over a billion years after the Big Bang, these regions would have been twice as dense as their surroundings. By this time the matter in these regions was dense enough and cool enough to begin to collapse under its own gravity, leading to the first star formation and the emergence of the cores of the galaxies, including our own Milky Way. This is the cosmic epoch we see in the most redshifted Hubble Space Telescope data – the formation of the first galaxies – and their seeds are the minute fluctuations visible in the Cosmic Microwave Background Radiation.

This detailed picture of the Universe in its infancy was pieced together from data collected over several years by the Wilkinson Microwave Anisotropy Probe (WMAP). The different colours reveal the 13.7-billion-year-old temperature fluctuations that correspond to the seeds from which the galaxies grew.

NASA

As the Universe expanded, the denser areas within it expanded more slowly than others because of their increased gravity. By the time these areas were twice as dense as their surroundings, the matter within them was sufficiently cool and dense to collapse under their own gravity and form the first stars and cores of new galaxies.

The rest, as they say, is history. Across the cosmos, countless suns began to switch on and the fill the Universe with light. For billions of years, generations of stars lived and died until, 9 billion years after it all began, in an unremarkable piece of space known as the Orion Spur off the Perseus Arm of a galaxy called the Milky Way, a star was born that became known as the Sun. This is the story of how our solar system has its ultimate origin in those dense areas of space that appeared in the first moments of our Universe’s life. But what is the origin of those tiny fluctuations in density that we see in the CMB?

This is perhaps the most remarkable piece of physics of all. The most popular current model for the very very early Universe is known as inflation. The idea is that around 10– 36 seconds after the Big Bang, the Universe went through an astonishingly rapid phase of expansion in which it increased in volume by a factor of around 10⁷⁸! In less scientific notation, that’s a million million million million million millionths of a second after the Big Bang, and an increase in volume by a factor of million billion billion billion billion billion billion billion billion billion. This was all over by 10^–32 seconds or so. Before inflation, the part of the Universe we now observe, all the hundreds of billions of galaxies in our night sky, would have been far, far smaller than a single subatomic particle. At these minute distance scales, quantum mechanics reigns supreme, and tiny quantum fluctuations before inflation would have been magnified by the rapid expansion to form the denser regions we observe in the Cosmic Microwave Background spectrum. If inflationary theory is correct, the CMB is therefore a window onto a time in the life of the Universe far earlier than 400,000 years after the Big Bang. We are seeing the imprint of events that happened in the truly mind-blowing first million million million million million millionths of a second after it all began. I find this the most astonishing idea in all of science. From a vantage point of 13.7 billion years, little beings like you and me scurrying around on the surface of a rock on the edge of one of the galaxies are able to understand the evolution of the Universe and speculate intelligently about the very beginning of time itself, just by decoding the messages carried to us across the cosmos on beams of light. The power of science is quite genuinely daunting, the richness of its stories unparalleled, the cosmos it reveals, beautiful beyond imagination.

There is one last twist to this story. Throughout our journey, light has been the messenger, carrying stories of far-flung places and the distant past to our shores. But there is evidence from one of the ancient sites on our home planet that light may have played a far more active role in our history than mere muse

The Burgess Shale is one of the most important and exciting fossil sites in the world, where a staggering amount of diverse animals are to be found, dating back over 500 million years.