HOW DO WE KNOW THAT THE UNIVERSE IS A ‘COSMIC LATTE’ COLOUR?
When we go outside and look at the night sky, it looks black in between the stars. But that’s because we cannot see the millions of faint galaxies that are spread throughout the universe – our eyes cannot detect enough of this light. Instead we can use a telescope and analyse the light from millions of galaxies, spreading out each galaxy’s light into a spectrum, like a rainbow. If we then average the light from these galaxies, we can create a digital spectrum that represents the light emitted in our universe. Comparing this cosmic spectrum with the spectrum of a white light, the universe’s colour is beige, or as one of our readers called it, cosmic latte. This idea was taken further by Katie Paterson’s studio in the UK. For their art project, I calculated the colour of the universe over time from the
Big Bang and even estimated what it would be like in the far future. From this, the art studio created a colour wheel called the ‘Cosmic Spectrum’. The universe started out extremely hot, with a blue colour, cooling to orange as the universe expanded. And then the first stars formed in young galaxies, becoming blue again. Now it’s the beigeyellow colour, and in the far, far future, trillions of years from now, it will be red again as most of the light could be from red dwarf stars.
brief period of inflation that moved parts of the universe apart faster than the speed of light. The picture that the CMB provides is one of the baby universe – it’s almost like we’re looking back to when time and space first shuddered into existence.
Penzias and Wilson were awarded the Nobel Prize for their discovery, but there was still much to learn about the CMB – we wanted a map. Stepping up to the challenge, a fleet of missions have since come and gone, the very first being the NASA-owned
Cosmic Background Explorer (COBE) probe, which began snapping pictures of the CMB as soon as it was launched in 1989. Offering four years of service,
COBE produced the very first map of hot and cold spots within the CMB, brought about by the early universe’s gravitational field that would later form the seeds of gigantic clusters of galaxies that stretch for hundreds of millions of light years across the universe. COBE’s lead scientist, George Smoot, also won the Nobel Prize, but hot on the heels of COBE came the Wilkinson Microwave Anisotropy Probe (WMAP). It boasted an improved resolution and got to work mapping the entire sky, logging the differences in temperature of the CMB down to 25 millionths of a degree.
What WMAP also uncovered told astronomers about the shape of the universe; they figured that since the boldest and brightest bursts in the map were a mere one degree across, we must be living in a flat universe. By 2010 WMAP had sniffed out its last microwave, producing over nine years of information. WMAP had laid down some important foundations, making the mission a huge breakthrough. Meanwhile, as WMAP was put into retirement, a new space observatory was waiting in the wings, ready and willing to build on our knowledge
“It’s almost like we’re looking back to when time and space first shuddered into existence”
of the early universe thus far – the European Space Agency’s (ESA) Planck. Operating in a range of microwave and infrared frequencies, the spacecraft promised an even higher level of accuracy, putting its instruments into overdrive in an attempt to lock down any answers given away by the deepest recesses of the universe. And Planck gave as good as it got from the universe, imaging the CMB in unprecedented detail. It might have ended its mission in October 2013, but we are now the proud owners of a more accurate picture of an almost perfect universe, as well as a more prominent point in time when the event began.
The truth of the matter is that this microwave background isn’t the only feature of the universe that’s telling us how it began – there’s more enticing evidence, and
we’re making sure we’re taking advantage of it. These extra telltale signs are ripples in space-time called gravitational waves. These elusive oscillations represent one of the jigsaw pieces of Einstein’s theory of relativity. Gravitational waves can be created by all kinds of massive objects, but some were also believed to have formed in the Big Bang and could still be rippling through the universe today. The problem is that it’s not easy to directly detect them, but their evasive behaviour means that the universe also has difficulty influencing them under its will. This is good news for us, as they’re the only known form of information that’s able to reach us undistorted from the instant of the Big Bang. The trick is catching them, because you need very sensitive detectors indeed.
Not put off by their shyness, scientists have been intent on pinning these waves down. Unlike the common electromagnetic radiation that we’re used to, gravitational waves, which are the result of massive events such as the merging of supermassive black holes, like to work their way through all types of matter – whether it be gas or dust. Attempts to grab gravitational waves by the tail, which include the likes of a large-scale experiment called the Laser Interferometer
Gravitational-Wave Observatory (LIGO), haven’t gone unnoticed, but the events are still quite rare. We need something better, and while ‘advanced LIGO’ has been in the works since 2008, the ESA has been thinking outside Earth’s atmosphere and straight into the thick of space.
The plan is to build a mission that has the ability to deal with such a slippery character. Scientists think they might have that pegged with the help of a planned mission, the Laser Interferometer Space Antenna (LISA) – a large-scale space mission that will not only better detect this phenomenon, but will be able to survey the entire universe directly with these waves, unpacking the secrets locked in the formation of galaxies, how stars evolve as well as the early universe.
And that’s not all… planned for launch in 2037, the people behind the craft proudly proclaim that it will also be able to tell us more about the structure and nature of space-time. There will also be the opportunity for uncovering more about black holes, as well as other unknown objects. Before it begins to achieve its incredible goals, an advanced scout, namely LISA Pathfinder, was launched in
2015, paving the way for LISA in an attempt to test the complex art of gravitationalwave detection.
As we understand from the reams of data brought about by the teamwork of missions and theories, we think we’ve put together a pretty robust photo album – or timeline – from the universe’s birth all the way through to its 13.8-billion-year-old self. Shortly after its sudden appearance, there was nothing except for a plasma soup. The universe was incredibly hot, with particles of both matter and antimatter – the opposite of matter – rushing apart in all kinds of directions. Then it began to cool, producing equal amounts of matter and antimatter, which swiftly annihilated each other.
Luckily for us, and for some reason that nobody currently understands, there was extra matter left over. As the universe began to peter out, cooling further, particles – the building blocks of matter – began to take shape. The first stars formed around
400 million years after the Big Bang, followed by the first galaxies – the oldest galaxies we’ve seen so far are a whopping 13.7 billion years old.
As much as we are sure the Big Bang happened, the universe can still throw a spanner or two in the works by presenting
a few things that we are still trying to figure out. Where did the universe come from? We don’t know. Why did it appear in the first place? We really can’t be too sure. And there’s more. The fact that there was more matter than antimatter in the early universe along with why a mysterious repulsive form of energy, known as dark energy, is causing the expansion of the universe to accelerate rather than slow down as had been expected are questions leaving scientists scratching their heads. What we do know is that the Big Bang was not an ‘explosion’ into anything – the Big Bang happened everywhere, which is why everywhere is filled with the CMB. And we also know that the ultimate destiny of the universe depends on who wins the great cosmic battle over the fate of the cosmos. Will gravity tug the universe back or will dark energy keep it expanding forever?