Wonders of the Universe - Brian Cox [29]
Forget state-of-the-art kit, all you need to use to detect hidden forms of light is a simple radio. As you tune, it you will pick up information encoded in a wave of light.
Only a fraction of light is visible in the Universe. This infrared image shows the massive scale of the Universe and demonstrates how the electromagnetic spectrum extends to wavelengths that are too long for our eyes to detect. Here we can see hundreds of thousands of stars at the core of the Milky Way Galaxy, but so many are still hidden from our view.
NASA
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