Cosmic Quest

The Curious Country | December 2013




Scientists are revealing the origins and structure of the universe, black holes, dark energy and dark matter, writes Wilson da Silva.



IT’S THE ULTIMATE question: where did we come from? How did we get here? These are overwhelming questions which have been asked as long as there have been people.


Today, scientists working in this field, known as cosmology, are finally answering them. And Australians are at the forefront of both finding the answers and developing the astonishingly complex technology needed.

When the 20th century began, the Milky Way galaxy – the bright swathe of stars easily seen at night – was thought to be our entire universe.​

Only in the 20th century has cosmology improved on what the Ancient Greeks knew. Since Galileo’s time 400 years ago, people have known that some ‘stars’ – those that wandered the night sky – were actually planets, that they were much closer to us and, like our Earth, they orbited the Sun. 


A century later, Isaac Newton developed a powerful explanation for their movements based on how falling objects behave. These laws of motion and universal gravitation apply not only to falling apples, but to how planets move in the sky. The laws came to dominate our understanding of the physical universe for the next 300 years.


When the 20th century began, the Milky Way galaxy – the bright swathe of stars easily seen at night – was thought to be our entire universe. But as more powerful telescopes were built, astronomers were astounded to discover that the universe was more immense than anyone had imagined. It took until the late 1920s to fully accept that the Milky Way was just one of many ‘island universes’, or galaxies. For thousands of years, scientists had believed the universe was static and unchanging. But suddenly, there was a lot more universe than anyone expected. 


And then it got really strange. 



IN A SCIENTIFIC PAPER published in 1905 Albert Einstein proposed his theory of special relativity, the now famous E=mc2. In it, he expanded Newton’s laws of motion so that they applied to objects moving at high speed and explained why light was unaffected by these laws: why it was that, if a car travels at 80 kilometres per hour, its headlight beams do not travel at the speed of light plus 80 km/h.

Einstein's 1905 paper on special relativity

He postulated that the speed of light is the same for all observers and set the speed of light in vacuum – 299,792,458 metres per second –  as a universal constant; the maximum speed at which all energy, matter and information in the universe can travel.


Later, in a 1916 paper, Einstein postulated the general theory of relativity, which applied his earlier idea to larger bodies governed by Newton’s laws of universal gravitation. In Newton’s model, gravity is the result of an ‘unknown force’ produced by immense objects which act on the mass of other objects. 


Einstein suggested gravity actually arose as a property of space and time: the greater the mass of an object – such as a moon or a sun – the more it distorted, or bent, the fabric of space. And because relativity links mass with energy, and energy with momentum, the curvature of space-time – the gravitational effect – was directly related to the energy and momentum of whatever matter and radiation was present. 


It sounded bizarre, but the theory neatly accounted for several strange effects unexplained by Newton’s law such as anomalies in the orbits of Mercury and other planets. If true, it would also mean the universe is not static and unchanging, something Einstein himself worried about. 


But he didn’t need to worry. American astronomer Edwin Hubble astounded the world in a 1929 paper showing conclusively that the further away astronomical objects are, the faster they appear to be travelling away from us. The only possible explanation was that the universe was expanding and, hence, changing – just as Einstein predicted.

Over the next 50 years, countless observations by astronomers have confirmed this seemingly fantastical notion.

In the far future galaxies would spread farther apart, while in the distant past the universe must have been smaller and denser, eventually congregating at one single, unimaginably hot and impossibly compressed point. Did time itself have a beginning?


This is the origin of Big Bang theory. Over the next 50 years, countless observations by astronomers have confirmed this seemingly fantastical notion. Parallel advances in the physics of the small – the atoms and the subatomic particles that constitute all things – helped build a solid framework of evidence around this view of how the cosmos arose.


After the initial expansion, about 13.7 billion years ago, the universe cooled sufficiently to allow the superheated energy to condense into various subatomic particles, eventually forming protons, neutrons and electrons. From this morass came the simple elements of hydrogen, helium and lithium. Gigantic clouds of these elements coalesced as gravity took hold, forming stars which ignited with heat and light, eventually forming galaxies as the stars clumped toward each other. 


The Cosmic Background Explorer (COBE) satellite mapped the 'smoothness' of the cosmic background radiation

Inside stars, clouds of gas – compressed by the titanic crush of gas columns above them – created all the heavier elements: carbon, iron, silicon, lead and so on. Some of the stars eventually died in cataclysmic explosions known as supernovae, expelling heavier elements inside them into space where gravity again brought them together, forming planets and moons. Even the ‘echo of the Big Bang’ was discovered in 1965 – a cosmic background radiation permeating all space, created by the raging oceans of white-hot energy at the dawn of time.



FROM THE 1960s onwards,  astronomers tried to answer the question: would the universe continue to expand forever or collapse back in a Big Crunch? 


They didn’t get far. Observations began to indicate that there wasn’t even enough visible matter in the universe to account for gravitational forces they could see acting within galaxies and between them. One of the first to recognise this was Ken Freeman, an Australian astrophysicist whose 1970 paper on how spiral galaxies rotate was the start of the paradigm shift that came to be known as ‘dark matter’. 

“There must be additional matter which is undetected ... its mass must be at least as large as the mass of the detected galaxies.”

“There must be in these galaxies additional matter which is undetected … its mass must be at least as large as the mass of the detected galaxies, and its distribution must be quite different from the exponential distribution which holds for the optical galaxy.” The paper is now one of the most cited single-author papers in astrophysics. 


Suddenly, a big portion of the stuff making up the universe was understood as a strange kind of matter that doesn’t emit light or interact with normal matter in any except via gravity. Evidence for dark matter has since repeatedly turned up in astronomical observations: in the lumpiness of the cosmic background radiation or the velocity dispersion patterns of galaxy clusters, for instance. 


Physicists have proposed a number of particles responsible for dark matter. One group is known collectively as weakly interacting massive particles (or WIMPs), another is a new light neutral particle, the axion. Several projects to detect them directly are underway – mostly in deep underground laboratories that reduce the background effect from cosmic rays – in places like old iron and nickel mines the U.S. and Canada and a mountainside in Italy.

Astronomers were again stunned in 1998 when two international teams – one led by Australian astrophysicist Brian Schmidt – announced that the expansion of the universe was accelerating.

As if that wasn’t enough, astronomers were again stunned in 1998 when two international teams – one led by Australian astrophysicist Brian Schmidt – announced that the expansion of the universe was accelerating, rather than slowing as had been expected. This was a surprise as the defining feature of gravity is that it slows moving objects over the time: hence, the universe’s expansion should be slowing in the billions of years since the Big Bang.


Einstein’s general theory of relativity allows gravity to push as well as pull, but most physicists had thought this purely theoretical. Not anymore. 


How it does this and what does it, is a complete mystery. One explanation is that this ‘dark energy’ is a property of space, that empty space itself possesses energy. Because this energy is a property of space itself, it wouldn’t be diluted as space expands. As more space is created by the expansion of the universe, more dark energy is created, causing the universe to expand faster and faster. 


What cosmologists now know is that 68 per cent of the universe is made up of dark energy, and 27 per cent is dark matter. The rest – everything on Earth, all ‘normal’ matter – makes up less than 5 per cent.


It’s amazing to think how far cosmology has come in a century and how much more is known today than anyone living in 99 per cent of human history. Understanding just 5 per cent of the physical universe over the last four centuries has already brought us astonishing advances in technology and living standards. Whatever the explanation for the puzzling 95 per cent that remains, it will surely lead to important new insights that will be equally as beneficial. 


INFOBOX

WIFI FROM SPACE


Another surprising repercussion of Einstein’s theories was that a stellar object might grow massive enough that even the speed of light was not fast enough to escape its gravitational pull – theoretical objects dubbed ‘black holes’.


But they would be devilishly difficult to find. In 1974, physicist Stephen Hawking suggested that under certain circumstances, small black holes might ‘evaporate’ and leak radio signals as they vanished. These signals would be weak, buried in background cosmic noise and probably ‘smeared’.


In 1983, hoping to be the first to detect an evaporating black hole, CSIRO physicist and engineer John O’Sullivan and his colleagues came up with a mathematical tool to detect the tiny, smeared signals against a background of intergalactic distortion. 


They didn’t find them. But the technique they developed, he realised, could allow data sent wirelessly over many different frequencies to be recombined at the receiver.


And so, WiFi was born.

Wilson da Silva is a  science journalist in Sydney, and the co-founder and former editor-in-chief of the Australian science magazine COSMOS . This essay originally appeared in the book, The Curious Country.

© 2019-20 Wilson da Silva. All rights reserved.