Nathalie Lees © HarperCollins
TIMELINE OF THE UNIVERSE: THE BIG BANG TO THE PRESENT
The history of the Universe can be split into several phases, according to the physical conditions that existed at the time. Things happened quickly in the first fractions of a second, when the Universe was filled with an intensely hot soup of energy and exotic particles. From this emerged the first protons and neutrons which were later to form the nuclei of the first atoms – mostly hydrogen and helium. After the emission of the cosmic microwave background, around 400,000 years after the Big Bang, the pace of events became more sedate. According to current understanding, the Universe will continue to expand forever, eventually fading into darkness in the unimaginably distant future.
Nathalie Lees © HarperCollins
The construction of all the chemical elements in the Universe can be illustrated with the most basic demonstration – so simple, it’s child’s play. To understand how the structure has emerged, all you need is a pot of bubble mixture. Blow one bubble and you have returned to the beginning of time, when all that existed in the Universe was the proton.
There’s a mystery at the heart of science for which, as yet, we have no explanation, and that is that this universe is simple. Underlying all of the astonishing complexity appears to be a magnificent simplicity, and nowhere is that simplicity more obvious than in the construction of the elements.
MATTER BY NUMBERS
Throughout human history the discovery and use of specific chemical elements has been intricately linked with the rise of civilisation. It is believed that copper was first mined and crafted by humans 11,000 years ago, and the specific characteristics of this metal ushered in a new age of technology and the transition from stone tools and weapons to metal ones. Four thousand years later it happened again but with iron which, even today, when mixed with carbon to form the alloy steel is the exoskeleton of industrial civilisation.
These two elements played a role in our history because of their particular physical characteristics. Copper was almost certainly the first metal to be used by humans; as it is such an unreactive chemical that it is one of the few metals that occurs naturally in its pure state. It is also very soft and malleable and so relatively easy to work into tools and weapons. When combined with another metallic element – tin – copper forms the alloy bronze; when combined with zinc it forms brass. Iron is, perhaps surprisingly, the most abundant element on Earth, and the fourth-most abundant element in the rocks of Earth’s crust. Although more difficult to extract and work with than bronze, iron is an excellent material for weapons manufacture as it is harder and lasts longer than bronze.
These two metals have had a profound influence on human history and sit just a couple of spaces apart in the periodic table. Iron (Fe) is element number 26 and copper (Cu) is at 29. The first humans to use these metals would, of course, have had no idea of the reason for the physical similarities and differences between the two elements. So what is the fundamental difference between them? The answer is remarkably simple. As described earlier, the atoms of each element are composed of three building blocks: protons, neutrons and electrons. We do not need to consider the quarks inside the protons and neutrons, because at the temperatures we encounter on Earth they stay locked away. So when discussing Earthly chemistry, we can ignore them.
THE SIX LIGHTEST ELEMENTS IN NATURE: HYDROGEN TO CARBON In each element the number of protons (p) in its nucleus is the same as the number of orbiting electrons, but the number of neutrons (n), which have no electric charge, can vary.
We have already encountered the first four elements; one of these, hydrogen, has an atomic nucleus consisting of a single proton. The proton has a positive electric charge, which allows it to trap an electron in orbit around it to form a hydrogen atom. The electron carries a negative electric charge, equal and opposite to that of the proton. This means that hydrogen atoms are electrically neutral. The reason why the electron has exactly the equal and opposite charge of the proton is not known. This is even more surprising when you look at the quarks that build up the proton. The proton is made up of three quarks – two up quarks and one down quark. The up quark has an electric charge of +2/3, and the down quark has a charge of -1/3. The electron has a charge of -1. So it is only when they are combined to form a proton that everything balances out properly. The neutron consists of two down quarks and an up, which means that it has no electric charge at all. This cannot be a coincidence, and it is one of the great challenges for twenty-first-century physics to explain it.
Chemical elements differ because of varying numbers of protons in their atomic nucleus, but the number of neutrons makes no difference to their chemical properties. Chemistry is down to the way the electrons behave that orbit around the nucleus, and the number of electrons is equal to the number of protons. As we know, the hydrogen atom consists of one proton and one electron, but there is another form of hydrogen called deuterium. Deuterium has a neutron attached to the proton inside its nucleus, but this doesn’t change its chemical properties as there is still only one electron. Technically speaking, deuterium and hydrogen are two different isotopes of the same element. Helium atoms always have two protons and two electrons; it also has forms with one and two neutrons, known as helium-3 and helium-4 respectively. Next comes lithium, with three protons, three electrons and either three or four neutrons, sometimes more. Carbon has six protons and varying numbers of neutrons, and so on. The rule is that each successive element has one more proton in its nucleus, and at least one more neutron, although the number of neutrons varies. The neutrons help the nucleus to stick together; which is bound tightly by the strong nuclear force, and neutrons add to this, even though they have no electric charge. Electric charge is a bad thing for the nucleus; because the protons are positively charged, they repel each other and try to blow the nucleus apart. The neutrons don’t suffer from this problem, which is one of the reasons why heavier nuclei tend to have more neutrons than protons.
So the construction of chemical elements is simple. If you want to turn iron into copper, add three protons and a handful of neutrons to its nucleus. That’s all there is to it. This is easier said than done, of course, yet nature can do it because when the Universe was only a few minutes old the first four chemical elements existed. The building blocks were present, but the heavier elements were assembled later
THE MOST POWERFUL EXPLOSION ON EARTH
The now iconic image of a hydrogen bomb explosion. This mushroom cloud was produced by the detonation of XX-33 Romeo on 26 March 1954; it was the third-largest test ever detonated by the USA.
US DEPARTMENT OF ENERGY / SCIENCE PHOTO LIBRARY
Years before the Manhattan project designed and delivered the most destructive weapon used in anger in the history of warfare, two of the greatest physicists of the age had already lost interest in the idea. Edward Teller and Enrico Fermi were friends and colleagues who would both go on to be members of the Manhattan team, but in 1941, before any type of nuclear bomb had been assembled, their minds were already wandering beyond the bomb that would later be dropped on Hiroshima and Nagasaki with devastating effect.
The Hiroshima and Nagasaki bombs were fission bombs, which work by splitting the nuclei of very heavy elements (uranium in the case of the Hiroshima bomb and plutonium for the Nagasaki bomb), into lighter elements such as strontium and caesium. This is the assembly of the elements in reverse. Each time a nucleus of uranium or plutonium splits, neutrons are released which trigger the splitting of other nuclei. In this way a nuclear chain reaction ensues. Each time a heavy nucleus splits, a large amount of energy is liberated – this ‘nuclear binding energy’ is stored in the strong nuclear force field that sticks the protons and neutrons together inside the nucleus.
However, even in the very early stages of the Manhattan project, years before the idea of a fission bomb was a physical reality, Enrico Fermi postulated that there was the very real possibility of creating a far more powerful type of bomb
. Edward Teller became obsessed with his friend’s idea and spent the next decade designing and building a device that would create the most powerful explosions ever made on Earth. It earned Teller the title ‘father of the hydrogen bomb’.
On 1 November 1952, the fruits of Fermi’s conversation with Teller were realised. Ivy Mike was the codename given to the first successful testing of a hydrogen bomb on Enewetak, an atoll in the Pacific Ocean. The explosion was estimated to be 450 times more powerful than the bomb dropped on Nagasaki, producing a fireball over five kilometres (three miles) wide, a crater two kilometres (one mile) wide and wiping the tiny atoll off the map. Teller had collaborated with another Manhattan scientist, Stanislaw Ulam, to design the bomb, but he wasn’t present for the explosion. Instead he sat watching a seismometer thousands of miles away in his office in Berkeley, California. The explosion was so powerful that he was able to clearly see the shockwave from the comfort of his office. ‘It’s a boy!’, he cryptically told his colleagues to inform them of the success.
The Ivy Mike test was the first man-made nuclear fusion reaction. Nuclear fusion is the direct opposite of fission; it is the process by which two atomic nuclei are fused to form a single heavier element. The hydrogen bomb reproduces the process that occurred in the first seconds of the evolution of the Universe – the assembly of hydrogen into helium.
The Teller–Ulam design for the hydrogen bomb that exploded on Enewetak is the basic design employed by all five of the major nuclear weapon states today. Although the fusion element of the design is only part of its explosive power, combined with the other stages contained within the bomb it creates destruction on an unparalleled scale.
Here are two completely different ways of creating new elements and releasing vast amounts of energy. The first, fission, involves taking a heavy element and splitting it. The second, fusion, involves taking lighter elements and sticking them together. But how can both these processes result in energy being released? Isn’t there a contradiction here? There isn’t, of course, because this is how nature works. It’s all down to the delicate balance between the electric repulsion of the protons in the nucleus and the power of the strong nuclear force to stick the protons and neutrons together. Since there are two competing forces, one trying to blow the nucleus apart and one trying to glue it together, you might think there must be some kind of balancing point – an ideal mixture of protons and neutrons that is perfectly poised between attraction and repulsion. There are in fact two elements that are very close to the mixture of optimal stability, and these are iron and nickel. Elements lighter than these can be made more stable, releasing energy in the process, by fusing them together. Elements heavier than these can be made more stable, releasing energy in the process, by breaking them apart.
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Look up into a clear blue sky and you are bathing in the energy of nuclear explosions on an unimaginable scale.
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To be completely accurate, we should mention that there are other factors than just the balance between the electromagnetic and nuclear forces that feed into the stability of the elements. These are to do with the shape of the nucleus itself and that the balance between protons and neutrons is favoured for quantum mechanical reasons. (If you are interested, google ‘Semi-empirical mass formula’ and enjoy!)
Here on Earth, fusion may seem the ultimate human technological achievement but actually it’s the most natural thing in the world. It didn’t only happen at the Big Bang; it’s a process that can be found occurring across the Universe as we speak. In fact, it illuminates the whole Universe and happens all the time millions of miles above our heads.
Fusion is the process that powers every star in the heavens, including our sun. Look up into a clear blue sky and you are bathing in the energy of nuclear explosions on an unimaginable scale. Deep in the Sun’s core, 800,000 kilometres (500,000 miles) below the surface (where temperatures reach fifteen million degrees Celsius), the Sun is busy fusing hydrogen into helium at a furious rate. In just one second the Sun converts 600 million tonnes of hydrogen into helium, releasing as much energy as the human race will use in the next million years. This is the energy that makes the stars shine and fills the Solar System with heat and light.
The shining Sun is one of the most natural demonstrations of the effect of fusion. It, and all the other stars in the heavens, are powered by the fusing of hydrogen and helium.
It is the process of turning hydrogen into helium that creates the energy that allows all life on Earth to exist, but for all its power the Sun only converts hydrogen, the simplest element, into helium, the next simplest. This process is repeated across the night sky; every star in the Universe began its life fuelled by hydrogen and powered by this reaction.
So the assembly of the second-simplest element, helium, is well understood. We know the stars can do it, we know it happened in the very early Universe, and we can even do it ourselves on Earth. But this doesn’t help to explain the origin of the other ninety-two naturally occurring elements. Clearly, somewhere in the Universe there must be a plentiful source of the other elements because they are everywhere, our whole planet is made from them. We are made of billions and billions of atoms; from magnesium, to zinc, to iron and, of course, the one atom that life is more dependent on than any other – carbon. Every human being on the planet is made from about a billion billion billion carbon atoms. That’s an unimaginable number of carbon atoms that simply didn’t exist in the early moments of the Universe. Where did they come from? The answer must be nuclear fusion, and the natural place to look is within the stars themselves
FROM BIG BANG TO SUNSHINE: THE FIRST STARS
The first stars formed around 100 million years after the Big Bang. The rate at which they burned their hydrogen fuel essentially depends on their mass. The more massive the star, the brighter it shines and the shorter its lifetime. The key to understanding how the heavier elements came into being lies in what happens to stars when they have exhausted their hydrogen fuel. For the most massive known stars, this may take only a few million years. For stars like our sun, it may take ten billion years – but the Universe has been around for plenty of time to allow generations of stars to live and die.
The brightly shining constellation of Orion is clearly visible as it sets in the night sky.
© Tony Hallas/Science Faction/Corbis
RED GIANT
As a star exhausts its hydrogen stores you might expect it to slowly flicker away, but for stars like our sun, the opposite happens. Having spent millions or billions of years with the core as its beating heart, a star that is running out of hydrogen in fact swells up to potentially hundreds of times its original size. Such stars are known as red giants.
One of the closest red giants to Earth is the star Alpha Orionis, better known as Betelgeuse, the ninth-brightest star in our night sky and one of our nearest neighbours in cosmic terms, a mere 500 light years away. Betelgeuse has long been familiar to stargazers, notable for its brightness and reddish tinge that is clearly visible to the naked eye. Sir John Herschel studied the star intensely in the nineteenth century, recording the dramatic variations in its brightness. However, it was only when three astronomers from the Mount Wilson Observatory in California tried to measure its diameter that we realised this was no ordinary star. Albert Michelson, Francis Pease and John Anderson used a specially designed telescope to measure the scale of this red star using a technique known as interferometry. By measuring the angular diameter (the apparent size of an object from our position on Earth), they came up with a number that, although it’s been refined since, revealed something profound: Betelgeuse is a true giant in every sense. This star is about twenty times the mass of our sun but its size is rather more impressive. If you put Betelgeuse at the centre of our solar system it would dwarf our sun. In fact, Betelgeuse would extend past the Earth’s orbit, encompassing everything out to Jupiter. Current estimates suggest it is around 800 million kilometres (500 million miles) in diameter; a vast,
ethereal wonder that would fill our solar system with a single wispy star.
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Betelgeuse is a vast wonder that would fill our solar system with a single wispy star.
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Due to its immense size and relative proximity, we can study Betelgeuse in incredible detail. In 1996, the Hubble Space Telescope took a picture of Betelgeuse that was the first direct image of another star to reveal its disc and surface features. We’ve even imaged sunspots on its surface and been able to study its atmosphere in ever-increasing detail. However, it’s not the surface of the red giant that holds the clue to where the heavy elements are made; to understand that, we need to journey deep into its dying heart
NASA
These images of Betelgeuse are based on pictures taken by the Very Large Telescope at the European Southern Observatory, in Chile, and show gas plumes bursting from the star’s surface into space.
Betelgeuse is the ninth-brightest star in our galaxy and one of our nearest neighbours. It can be seen from Earth with the naked eye – easily identifiable in the night sky for its brightness and reddish tinge.
STAR DEATH
When making a television documentary, you are always looking for visual ways to tell complex stories. While filming Wonders of the Universe, we journeyed all over the world in search of analogies and backdrops, but for me the most successful of all was an abandoned prison in the heart of Rio de Janeiro, Brazil.
Wonders of the Universe Page 11