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History of the universe - from the Big Bang to Civilisation
Peter Green macadv@netspace.net.au www.scienceissues.net
An attempt to sum up what we know - the state of common current knowledge about the universe
Bya = billions of years ago
(a billion is a thousand million)
Mya = millions of years ago
Kya = thousands of years agoPart 1. The Big Bang and the formation of the universe
Many accounts of the origin of the Universe say the universe began between 10 and 20 bya. Since 2003 the figure of 13.7 billion years has been generally adopted as the age of the universe.
This was established as a result of data, released in 2003, from the NASA satellite - the Wilkinson Microwave Anisotropy Probe (WMAP). This is the probe that took the photo of the early universe shown below.
The beginning of time and space
The Big Bang created space and time. Nothing existed before it. To ask 'what happened before it?' is meaningless. It is equally meaningless to ask 'where did it happen?'. It is, oddly enough, more sensible to say 'everything was created out of nothing'. To say 'there was nothing and then it exploded' is amusing, but the best current theory says 'there was nothing, then everything was created in one explosive moment - the Big Bang'.
Like the creation of life, discussed in part two (under construction), what started the universe is one of the great mysteries of life.
The most vocal opposition to the theory of the Big Bang comes from the creationists. They believe the Bible is literal - that God created the Earth several thousand years ago, starting with Adam and Eve in the Garden of Eden (thought to be somewhere in Mesopotamia, today Iraq). Several generations later, the whole world was flooded, and Noah sailed his ark for forty days and forty nights, with every species of animal aboard. They believe we are all descended from Adam and Eve, and so too we are all descended from Noah and his wife. On the other hand, the Bible, say scientists, did get some things right. One example is that, on the first page of the Bible, when God created the world, He said 'let there be light'. The Big Bang theory also posits the beginning of the world in light.
The Big Bang theory is quite recent. A century ago, it was assumed that the universe was static, infinite in space, and millions of years old. The solar system was believed to be the centre of the universe, and the universe was believed to extend no further than the Milky Way galaxy.
It was less than 100 years ago that the Big Bang theory was proposed and around 50 years ago that scientists demonstrated that galaxies existed outside our own. Shortly after that, the Big Bang theory was accepted by most scientists. The only serious scientific theory opposed to it was the Steady State theory. This is the supposition that the universe didn't start at a point in time, but that new matter was continually created in the galaxies, allowing the universe to expand indefinitely.
The most convincing proof of the Big Bang is that the universe is expanding, and that it isn't all homogenous - the most distant galaxies are markedly different from those closer. The universe had, it was realised, to expand from something smaller than what we see at present. And there is no scientific evidence that any new matter has been created since the beginning of the universe.
Astronomy is the science of the heavenly bodies. Almost all of modern astronomy has been developed with improvements in the telescope - from Galileo, who, in his observations of Venus and Jupiter, concluded that the Earth went around the Sun, to Edwin Hubble, who demonstrated convincingly that the universe is expanding. Hubble's importance is indicated by his name being given to the space telescope launched in 1990.
Understanding the universe was also made possible by the microscope (to better understand things like molecules).
The origins of the universe are usually put under the term cosmology , which means the science of the universe (from logos , to know). This includes how the universe is constructed, how it changes today, and how it evolved.
Before we begin our journey down the highway of time, we have to pack a few things. To understand the Big Bang, you need to something about nuclear fusion. To understand fusion, you have to know a little about nuclear physics. This requires some knowledge of the atom. To understand the atom, you have to understand atomic particles. And all this means you need to know about the four forces in nature.
Without some use of such scientific terms, the history of the first half of the universe could be stated in just over fifty words: The Big Bang started as a speck of energy, expanded quickly, and in the first second, the first matter was created. 200 million years later the first stars and galaxies were made from the first matter, and more matter was made in the largest stars. Recently it has been proposed that all of the galaxies formed within one billion years, including the Milky Way galaxy (our galaxy).
Notice we had to use the words 'energy' and 'matter'. This is the stuff of nuclear physics.
In the next three pages, we will introduce all of these scientific terms. This shouldn't hurt too much - just remember to take a deep breath every now and then for the next five minutes or so.
If you already know about the atom and nuclear fusion, or you don't want to know anything about them, then you can go on ahead, and we'll meet you at the 'First second - this account actually starts here'.
Nuclear physics sounds hard - like rocket science or brain surgery. But 'nuclear' means to do with the nucleus of the atom (explained below), and 'physics' - well, that's just the study of matter and energy. Deep breath.
Matter (or mass) is the physical stuff of the universe. The concept of weight is more familiar to us, but weight is a combination of mass (the physical stuff) and gravity. Matter is scientifically observable and it can collide with itself (s pace is that which is occupied by matter).
Energy is what causes matter to move and change.
A glass of hot water (the glass and the water are matter) contains more energy than a glass of cold water. If you let it stand, its energy will be lost as radiant heat. Radiant heat, like light, is a form of energy that exists independently of matter.
Energy, unlike matter, can pass through itself. One light ray, made of photons, can pass through another.
The word 'atom' means 'indivisible', and was used by the ancient Greeks to mean the basic, indivisible unit of nature. The idea that all matter was made of atoms wasn't generally accepted however until a century ago. Prior to that time, there were thought to be just four elements - earth, air, fire and water.
One hundred years ago, the atom was found to be 'not indivisible' - it was made of smaller particles. And instead of four elements, we now know there are over 100 elements (some of them created artificially). Earth, air, fire and water are made of different combinations of these elements
Atoms consist of the subatomic particles electrons, protons and neutrons. At the centre of all atoms is the nucleus (original meaning is 'little nut'), which consists of the heavyweight protons and neutrons. All nuclei consist of protons and neutrons, except for hydrogen, which has one proton, and no neutrons. Nuclear physics is built around the study of the nucleus .
Hydrogen (top left) is the lightest element. It has one proton in its nucleus (and one electron). Helium (top right) has two protons and two electrons The principal particles making up the atom (subatomic particles) are the protons, neutrons, and the electrons.
The nucleus lies at the centre of the atom and consists of protons and neutrons. Both protons and neutrons are made of quarks.
Small, light electrons (shown in the diagrams above) orbit the nucleus.
Early models of the atom, about a hundred years ago, showed electrons orbiting the nucleus in a similar way to planets orbiting the Sun (like the diagrams above). Quantum mechanics, about fifty years ago, found this was misleading. The electron, although it is a particle, is more like a beam of light (ie. both a particle and a wave) than a speck of dust. It moves not in perfect circles, but around the nucleus in the form of energy waves, in an area called a cloud.
Atoms consist of 99.9% space. To put the same thing another way, the nucleus is 2 000 times smaller than the size of the atom. If a hydrogen atom's nucleus were enlarged to the size of a marble, the atom's diameter would be around 0.5 mi (800 m).
This is one of the most remarkable things I discovered in preparing this history. We tend to imagine atoms as small hard things. This may be because the word atom originally meant 'indivisible', and it is very hard to split. Also, diamonds, one of the hardest substances in nature, is made of carbon atoms. But a better spatial analogy for atomic structure is foam. Think masses of bubbles, mostly space. But remember that (as a result of the various forces, explained below) this mass of bubbles is one of the hardest materials we know. The hardness comes not from their matter, but from the forces (explained below) which bind them together.
The scale of the atomic particles can be likened to that of the solar system. If the solar system was the size of atom, the Sun would be the size of a nucleus. Pluto, the furthest planet, would be the size of an electron. But there are significant differences:
1. Electrons orbit in a 'cloud', as we saw. They are not solid objects, but more like energy waves.
2. The electrons orbit at different and changing angles, whereas planets orbit in roughly the same plane.
3. Electrons are held to the nucleus by the electro-magnetic force (electrons are negative, protons are positive), whereas planets are held to the Sun by gravity.
Note also that we cannot draw atoms (or solar systems) to scale. Well, maybe we could if the sheet of paper was the size of a football field.
The closest we can come to seeing atoms is using microscopes that use electrons instead of light. In the image below, single atoms appear solid, because the electron clouds, mostly energy, appear as a solid mass.
Atoms (appearing as white spheres) in a silicon crystal, viewed through an electron microscope. Now that you have a deep understanding of nuclear physics, we will 'go through' some particle physics.
Protons and neutrons, in the nucleus, are made of quarks (the word quark, pronounced quork, was originally a nonsense word used by James Joyce).
N eutrons weigh a little more than the proton. In this account I will be focusing on protons and electrons.
Electrons and quarks are the smallest things we know of - they are elementary particles . What are they made of? There is a theory that both electrons and quarks are both made of strings. And that if an atom was enlarged to the size of the solar system, a single string would be about the size of a tree. Although noone has ever seen a quark or an electron, we have clear physical evidence of both. Strings, however, have only a theoretical existence. They help to explain aspects of the behaviour of quarks and electrons, but there is no evidence of their physical existence.
There are other subatomic particles, such as photons - what light is made from.
This periodic table of elements shows all the naturally occurring elements, from the lightest to the heaviest. The numbers shown are the atomic number - the number of protons (and electrons) in an atom of an element. All these elements were created in the first half billion years, in order of their atomic number. Hydrogen was the first element produced in the Big Bang. Hydrogen, having just one proton, is also the lightest element. Hydrogen and helium are the least dense of all the elements. This is why they are used in balloons and airships. And they are the primary components of stars, as well as Jupiter and the other giant planets in our solar system.
Hydrogen is the most common element in the universe, making up 75% of all matter.
Helium is the second lightest element, with two protons, and lithium, the third lightest, with three protons. Most of the universe is formed from hydrogen and helium (99% in fact!). Helium is very stable - it is the main one of a few elements called inert (they used to be called the 'noble gases') because they have little or no natural reaction with other elements. Like hydrogen, helium is transparent to the human eye.
Helium is named after 'Helios', a Greek sun-god. It was first discovered as an element of the Sun.
Scientists working on future energy sources hope that our entire economy can be based on solar-generated and nuclear-generated hydrogen.
What if there were a form of energy that could solve our air pollution problems, would eliminate our dependence on foreign oil, could solve our balance of payments woes, would eliminate oil spills, would create domestic jobs, and could be made from unlimited, renewable, and sustainable resources? Well, there is -- it's hydrogen!
Rick Smith, President, Hydrogen Energy Centre, 1997.Force is a push or a pull - it has some effect on matter. The two forces we are most familiar with are the electromagnetic force and gravity.
When electricity was first being explored, between 1600 and 1800, it was found to be the same as magnetism. Both electricity and magnetism are part of the same 'electro-magnetic' force. One example is a metal detector - it generates an electrical field. A piece of metal nearby will create a distortion in this electric field, because the detector generates a magnetic field in any material that can conduct electricity. These two, the electrical field and the magnetic field, are part of same electromagnetic force.
And something you already know - gravity is different from electromagnetism.
In addition to gravity and the electromagnetic force, scientists have discovered two other forces, both at the nuclear level.
The electromagnetic force is seen in all kinds of radiation. It is matter carrying an electrical charge. On Earth, it is much stronger than gravity at short distances. In the atom, the electromagnetic force holds electrons (which have a negative charge) in orbit around the nucleus of the atom, attracted to the protons (which have a positive charge).
Gravitation is a force that attracts anything with mass (such as the proton) to every other thing in the universe that has mass. It is very weak when the masses are small, but can become very large when the masses are great (such as a galaxy).
The strong nuclear force binds the protons and neutrons together in the nucleus. It is 100 million times stronger than the electrical attraction that binds the electrons. It is of very short range - it extends only across the nucleus.
The weak nuclear force is a feeble force that helps to explain radioactivity; ie. how some elementary particles break up, or decay, into other particles. The static heard on a Geiger counter is the breaking up, or radioactive decay of an element such as uranium.
The four forces of nature formed in the first part of the first second of the Big Bang, before atoms and before fusion.
What frustrates scientists is that they don't know how all of these four forces work together. They have separate theories for each force, and they know how a couple work together, but many scientists are seeking one theory which would explain all four. Such theories, still speculative, are called either the 'theory of everything', 'grand unified theory' or 'superstring theory' (related to string theory - that proposes that quarks and electrons are made of strings).
I omitted to mention that, in addition to understanding the atom and nuclear physics, we need to know how quantum physics fits in.
Physicists are currently attempting to reconcile Einstein's theory of relativity (and classical mechanics, including Newton's theory of gravity ) with the theory of quantum mechanics (which includes the other three of the four forces).
Newton described gravity when he saw an apple fall (actually, gravity was sort of understood to cause things like apples to fall. Newton was first to suggest that the same force kept the moon in place). Newtonian mechanics is unable to explain how electrons can orbit the nucleus of an atom, and remain stable.
Relativity, like gravity, explains the big stuff - comets and galaxies, for example. Especially where very large speeds are involved.
Quantum theory, on the other hand, describes small stuff - very very small stuff, like atoms, and what they're made of.
Relativity and Quantum theory are not just separate theories, they actually contradict each other in many ways.
Tying these theories together cannot be done in three dimensions, so scientists have proposed a fourth dimension. String theory goes even further - particles, they say, are made up of tiny strings and membranes, which exist in ten or more dimensions.
Stephen Hawking is one of the best known physicists, and one of his best known works is 'A Brief History of Time'. It is not really a history of time, but an attempt to build a theory that would unite the theory of relativity and quantum mechanics into what he calls a 'quantum theory of gravity'. The book contains about five pages on the history of the universe.
Hydrogen nuclei fused together in the Big Bang to make helium. Fusing hydrogen into helium is also what makes stars, like our Sun, shine. And it is what happens in a hydrogen bomb.
A hydrogen nucleus is one proton. A helium nucleus consists of two protons and two neutrons, so to make helium, we ultimately have to get four particles together in the one spot. This can't be done in one go. The helium nucleus is created in a sequence of three steps, adding a particle at a time.
Deuterium nucleus: The word 'proton' is related to the word 'first', and 'deuterium' related to 'second' Fusion sequence in the Big Bang. Deuterium formed after the first minute, and helium within three minutes. made from proton + neutron Tritium nucleus: One proton, two neutrons. 'Tritium' is related to the word 'third'. made from deuterium + neutron Helium nucleus: Two protons, two neutrons made from tritium + proton Tritium and deuterium (by the way) are isotopes of hydrogen (isotopes of an element have the same number of protons as the element). Tritium is produced naturally in the upper atmosphere, is radioactive, and is produced for special applications in hydrogen bombs and nuclear reactors. Deuterium is unstable, and is found in small amounts in water.
Fusion then is the combination of two nuclei to make a heavier element. All protons (ie. the nuclei of hydrogen) carry a positive charge, and so naturally they repel one another (like charges repel). To get two protons to fuse together, their electromagnetic repulsion must be overcome. The very light nuclei of hydrogen atoms carries a weak positive charge, thus there is less resistance to overcome. This can only be done with massive heat - the same temperature as the inside of the Sun.
In the Big Bang, the heat had to drop to this level for fusion to occur. For any fusion since then (eg. in stars or the hydrogen bomb) the heat has to rise to this level.
When the positively-charged nuclei came close enough together, the strong nuclear force (explained above - much more powerful than the electric force) made the nuclei stick together.
Making helium from hydrogen, in the three steps explained above, is not that simple. Another deep breath.
Deuterium (consisting of a proton and a neutron) has a specific mass (I forget what that mass is right now). But when you add a proton and a neutron together, the result has a bit more mass than that of deuterium. The bit left over is converted into a photon - a particle of light energy. And this, if you have been following, is VERY important. Mass is converted into energy! This fact is true of all three steps in the fusion process: the mass of the two lighter elements, when combined, is a bit heavier than the mass of the new (heavier) element. This results in energy being given off at each step. Some of the mass is converted to energy.
It took Einstein to realise this. Prior to Einstein, it was said that matter could neither be created or destroyed, but Einstein realised that matter can be 'destroyed', if it is converted to energy.
This is explained by the most famous formula in the world:
E=Mc 2
This means E nergy is equal to M ass multiplied by the speed of light ( c ) squared. In everyday words, a very small amount of matter contains a very large amount of energy. A coin, for example, when converted to energy, could provide enough electricity to light up Las Vegas for 24 hours.
Einstein's equation also explains the energy source for stars and nuclear bombs
When matter is converted to energy it can produce enormous amounts of heat and light. How is this different from everyday processes which produce heat and light?
When you heat ice, it turns to water. When you heat water, it boils, and turns to steam. These are physical changes , because there is no change to the chemical composition of the substance. Steam can condense into water, and water can be frozen back into ice.
Another process we are familiar with is chemical reactions. When you burn a piece of paper, it turns to ash. Chemical reactions, unlike physical reactions, cause permanent changes. Have you tried getting the ash back to paper? In addition, energy is given off in a chemical change. When we burn paper, we can feel the heat.
Cooking, burning, rusting or even an apple turning brown are chemical reactions. Signs of a reaction taking place could include bubbling, colour change, smoke (a convincing example is when it comes out of your computer), or change in smell (see previous example).
In a chemical change molecular bonds are made or broken. In a physical change, only the molecules' speed of movement changes.
In both physical and chemical changes there is no loss or gain in mass. But in nuclear reactions, there is a change of mass.
Nuclear, as mentioned, means 'of the nucleus'. Once the nucleus is fused or split, the atom changes its identity -a change of substance occurs.
The alchemists of the middle ages looked for a 'philosophers stone' that would make gold from base metals and heal the sick. This stone would be a perfectly balanced distribution of the four alchemical elements : earth , air , fire and water.
Today we can make gold from lead (a base metal) in a particle accelerator , but the amount produced is so small it is not worth it. Gold, by the way, has an atomic number of 79 (ie 79 protons), and lead an atomic number of 82. So just take three protons off the lead, and you have gold.
Fission is the production of energy by splitting massive nuclei (such as uranium, the heaviest naturally occurring element) into less massive nuclei - such helium and lead. It occurs naturally when uranium decays. In thousands of years, it would be converted to a different element.
Fission has much more energy efficiency than oil (but is still three to four times less than fusion energy).
Fusion of light nuclei can give more energy per kg material than fission - t he hydrogen bomb is thousands of times more powerful than an atomic bomb. In both fusion and fission there is a conversion of mass to energy (both work by E=MC 2 ).
Fission can give rise to a chain reaction, which can be either rapid (as in an atomic bomb) or controlled (as in a reactor).
A hydrogen bomb works by fusion, but it is triggered by an atom bomb, which provides the tremendous heat required to start the fusion of the hydrogen atoms.
This reaction liberates an amount of energy more than a million times greater than one gets from a typical chemical reaction, such as the explosion of dynamite.
The amount of energy obtained through nuclear power plants is millions of times the amount of energy contained in a similar mass of chemical fuel such as petrol.
This energy, when let out slowly, can be harnessed to generate electricity. When it is let out all at once, it can make a tremendous explosion in an atomic bomb. Inside the reactor of an atomic power plant, uranium atoms are split apart in a controlled chain reaction. This chain reaction gives off heat energy, which makes steam, which turns a turbine to generate electricity.
Intensive research is being carried out to develop nuclear fusion as a source of energy on earth. The major obstacle is how to heat hydrogen to 100 million degrees, and keep it going. This temperature melts any solid substance on earth, so it may be another 50 years before we have a solution. Fusion creates less radioactive material than fission, and its supply of fuel can last longer than the sun.
And that concludes our brief look at nuclear physics. You can now breathe a bit easier. It will stop hurting soon.
"In the beginning" the universe was a ball of intensely hot and dense energy. The temperature was 100 million trillion degrees Celsius.
Even though it was denser than anything we know, there was no matter. The radiation was in the form of light . This ball of solid light (also referred to as radiation, or energy) was made initially of the smallest atomic particles, quarks and electrons. In case you have forgotten, atoms have a nucleus made of protons and neutrons, and these are made of quarks. Electrons orbit the nucleus. The extreme heat and density, in the first split second, prevented the quarks combining to form protons and neutrons. The universe at its inception was the size of atomic nucleus.
The beginning of the universe is also referred to as a 'singularity', because the four forces in physics (the electromagnetic, gravity, the strong nuclear force and the weak nuclear force) were combined into one - a single 'super force'. Science has no way of explaining how this state of affairs could exist.
The four forces separated totally within the first part of the first second. The first to separate out was gravity, which added a touch of seriousness to the occasion.
The first second (first second!) of the Big Bang has been described as ' an infinitesimal realm of utter chaos'.
The universe in this first split second expanded faster than the speed of light - many thousands of times faster than the speed of light.
Light travels at 186 000 miles per second - that's five times around the Earth in one second. But the universe, travelling faster than the speed of light, in less than one second, grew to a size larger than our solar system (other estimates say it grew to the size of the Milky Way Galaxy).
It currently takes light about ten hours to cross the solar system. It takes 100 000 years to cross our galaxy. So even the more conservative estimate (ie. that took less than a second for the universe to get to the size of the solar system) is hard to grasp.
It is also difficult to grasp that the universe, when the size of the solar system, was a ball of energy as dense as water. If all that seems just too weird, take consolation in the fact that after the first second, the expansion rate of the observable universe slowed to what it is currently - about 90% of the speed of light (it is in fact, gradually speeding up). But when it ran at 300 times the speed of light, even though it was for a fraction of the first second, it had a dammed good head start.
So it takes a very small amount of matter to make energy. Equally, then, in the Big Bang, it took a lot of energy to create the first matter, which was, in very quick succession, fused, giving off energy again.
The universe started as a glowing 'plasma soup' of quarks and electrons. Before the end of the first second, the temperature dropped to billions of degrees, and these particles bound together to form protons and neutrons. The first matter was created .
The universe got less hot (some say it 'cooled down') rapidly, to 1000 billion degrees Celsius at the end of the first second. This is the temperature within a nuclear explosion.
The temperature, and the density, continued to drop as the universe expanded, and continue dropping, very slowly, today.
At one second old the universe was denser than matter. One year later, its density was less than water.
More happened in the first second of the universe than any other second in history. To say that in a more scientific way, more has been written about this first second than any other second in time. I promise I will not spend half a page on any other second in history.
As the temperature dropped, the quarks began to clump together to make protons and neutrons. A proton is also a hydrogen nucleus.
The creation of the first protons is part of a process called 'primordial nucleosynthesis' (primordial means early, nucleon means atomic nuclei, and synthesis means creation ). In other words 'early atomic nuclei creation'.
The first nuclei to form in the Big Bang were the lightest, because they have the lowest number of protons. Within the first three minutes, the nuclei of helium formed (as set out above, under 'Fusion'). In addition, a very small amount of lithium (the third element in the periodic table) was created.
At ten billion degrees, the universe was still too hot for electrons to join the atomic nuclei to form whole atoms. The universe was still a ball of light, but its density had dropped to that of air in the Earth's atmosphere.
Although matter now existed - in the form hydrogen nuclei (almost 75%) and helium nuclei (almost 25%) , the universe was 'radiation dominated' and would remain so for the next 300 000 years, when it became 'matter dominated' (and has remained so ever since).
At the end of three minutes, this first stage of nucleosynthesis stopped. No more atoms would be created for another 200 million years.
Noone knows what came before the Big Bang. The world wide web, like the universe, is an intriguing place. One site suggests the Big Bang came about as a result of 'positive meeting negative': the 'primal production of hydrogen and helium happened as a consequence of positive spiritual energies meeting negative spiritual energies triggering the Big Bang.'
The first atoms created in the Big Bang were nuclei without the electrons that, especially on Earth, normally spin around them. They were not whole atoms. As such, they formed a plasma (such 'bare' nuclei are also said to be 'ionised'). Electrons formed before nuclei in the first second of the Big Bang, but the heat kept them from being bound to the nuclei. The early universe for the first 300 000 years was a plasma.
There are four states of matter. When you heat a solid, it may become a liquid. If you heat the liquid, it may become a gas. What happens when you heat a gas? It becomes a plasma.
A plasma can be thought of as an electrically charged gas.
The ancient Greeks proposed that the world was made from earth, water, air and fire - not dissimilar from the solid, liquid, gas and plasma.
Plasma was named after blood plasma. It was first 'discovered' in work associated with medical science. It resembled something living by apparently forming cells, and by being complicated and unpredictable, compared to the other three states of matter.
Like Rudolph's nose, it usually glows. And it scatters light, which made light of the early universe foggy.
Although plasma rarely occurs on Earth's electrically neutral surface (neutral because the atmosphere is under a higher pressure than space) , 99% of visible matter in the universe is made of plasma.
We use plasma to light fluorescent and neon tubes. The stars, interstellar gas, Sun, auroras and fire are made of plasma. In thunderstorms, the air becomes charged, or ionised (ie. a plasma) and allows lightning to flow.
The universe ceased being a plasma 300 million years later, at recombination, when the electrons combined with the nuclei of hydrogen and helium, to form neutral atoms. This is the way most atoms stayed from then on. A plasma occurs, since then, when energy, strips electrons from atoms (as happens prior to a star beginning to fuse hydrogen).
Everything in the world, all the material that exists today, was created in the Big Bang. All the matter in the universe, every star and galaxy (every chair and every city), was packed into a tiny dot at the Big Bang. What has happened since is that the energy and matter that existed at the time of the Big Bang has been rearranged in a huge number of different ways to form atoms, molecules, planets, and people, as well as the material on which this is written (whether paper, or phosphors on a screen). One thing that all scientists understand, and that forms part of their everyday work, is that matter, like energy, cannot be created or destroyed. This holds true since the Big Bang. No matter or energy has been created since then. What we got instead was the formation of matter, in the first three minutes, from the energy.
How did the scientists dream up something as wacky as a Big Bang? One of the most easy to understand reasons for the Big Bang theory is that all the galaxies in the universe are moving apart at a rapid rate. This was discovered in 1928 by the Astronomer Edwin Hubble (after whom the recent space telescope is named). Hubble, by the way, in 1928, estimated the age of the universe to be two billion years - out by only about 11 billion years. The expansion of the universe is now one of the very few incontrovertible facts about the universe. And this has to mean that the universe was once much smaller.
The rate of expansion is 50 kilometres per second for each 3.26 million light years way from us (ie. the further away from Earth we go, the faster the expansion is). How fast is the "edge of the universe" is moving away from us? Some say the edge it is close to the speed of light (and speeding up!). With today's technology, we can't catch it.
The Big Bang says the universe started at a particular time (more accurately, time began with the Big Bang). Science holds, similarly, that it will have an end. This means that the universe is finite - that it has a beginning and an end. Some scientists believe that there are universes 'before' or 'outside' ours, and so while our universe may be finite, infinity could still exist.
The universe is expanding, so it seems inconsistent to say it is infinite in space. But most scientists say that the universe has no edge - it is finite but unbounded. They liken the universe to a sphere - if you head off in one direction, you end up where you started. The laws of physics, however, cannot prove whether the universe is finite or infinite, in space or time.
After the first three minutes, not much happened for the next half hour. As we travel down the highway of time, we see nothing but a hot red opaque fog. This is all we see for the next ten days, and again for the next fifty years. It does, however get less hot as we go. This fog lasts until 300 000 years after the Big Bang.
When the temperature dropped to 3000°, 300 000 years after the Big Bang, the previously separate nuclei and electrons came together to form whole atoms. Whole atoms are also called 'stable', or 'neutral' atoms, since separately, the atomic particles, in a plasma, carry an electric charge. The first hydrogen and helium atoms appeared. This 'coming together' was in fact 'combination' (of nuclei and electrons), but the term used today to describe the coming together of any separated nuclei and electrons is 'recombination' (in the sense of reunion), so the word recombination is used to describe what happened then.
At the same time, the universe had cooled sufficiently to allow a change from being opaque and radiation dominated (with a small amount of matter, in the form of the lightest atoms) to transparent and matter dominated (the radiation had decreased along with the heat and density). This radiation left behind a 'glow' or remnant heat, that was, in the last 30 years, detected as 'cosmic microwave background radiation', and was another factor (along with the expansion of the universe) which helped to prove that there was a Big Bang.
The universe when it was 300 000 years old - from NASA's orbiting Wilkinson Microwave Anisotropy Probe (WMAP) What is the oldest thing in the world that is still visible? The Andromeda galaxy is visible to the naked eye on Earth, and we see it as it was 2.5 mya. The photo above shows the heat of the universe (the 'cosmic microwave background radiation') at that time. The universe wasn't technicolour - the photo is artificially coloured. Red is used to indicate areas that are a millionth of a degree warmer than the blue bits.
The universe up to recombination had been almost perfectly smooth, but m atter and radiation had, since the outset, formed 'wrinkles'.
The domination of matter allowed those slight irregularities in the radiation to form into irregularities in matter. These developed into clumps, and a few million years later became the first galaxies. Although scientists have got most of the first three minutes worked out (apart from the first bit of the first second), they have no idea how the universe went from very smooth (prior to recombination) to very clumpy (like peanut butter).
In the first 300 000 years, the universe was clouded with light-absorbing hydrogen gas.
With the formation of stable atoms, photons ( the carriers of electromagnetism, which travel at the speed of light) were set free. The universe became transparent. Light was free to move about.
Radiation (also called light) and matter were now separate - they were 'decoupled' . This point in history is therefore also referred to as the 'decoupling' stage.
In this history of the universe, I began at the beginning and, in this first part, had intended generally to mark off historic events in terms of 'billions of years ago'. The Big Bang, as you will remember, happened 13.7 bya, and the Milky Way Galaxy was formed by 12.7 bya.
But for most of this first part (ie. 'The Big Bang and the formation of the universe'), I more often describe events in terms of how long after the Big Bang they occurred. The Milky Way Galaxy, for example, was formed within the first billion years after the Big Bang.
Also, I sought to provide a continuous account of events in order. There are seven billion years between the Big Bang and the formation of the Earth, but this period is divided into very unequal time frames, based on the physics of the creation of matter and of the stars, as shown in the table below.
Since Big Bang (definitely not to scale) Part of the first second Inflation (rapid expansion) Radiation era One to three minutes Primordial Nucleosynthesis 300 000 years Recombination (also called 'decoupling' - matter becomes dominant) Dark Ages Matter era 200 million years First stars & first galaxies Star formation and Stellar Nucleosynthesis 600 million Reionisation 9.1 billion (4.6 bya) Solar System forms (and Earth) 13.7 billion Today The major events of the history of the universe
The periods of time shown are for the most part impossible to comprehend. One way of getting a perspective on it is by considering similar time frames for 'recent' events on earth, as shown in the table below.
200 kya (thousand years ago)
Neanderthal man and Homo erectus .
More recent events, to put the formation of the universe (shown in the table above this) in context 200 mya
The first dinosaurs
500 mya
Complex life appears in the sea - tiny worms and centipedes.
4 bya
Earliest (single celled) life on earth.
The history of the universe - to scale.The horizontal line in the diagram immediately above represents the history of the universe. The thickness of the vertical line at the far right (ie. the vertical line under 'Today') represents 42 million years. It was about 42 mya when the first monkeys appeared.
A final point in this digression about timeframes. Scientific accounts of the universe show ages (and other large numbers) in forms such as 10 6 (or 10 -6 ) years. These numbers can also appear on web pages as 10 6 or 10-6.
I won't be using this scientific notation here. But for those of you who are unfamiliar with it, when you read more scientific texts, you can translate 10 6 to whole numbers by putting six (in this example) zeroes beside the number 10.
10 6 = 10 000 000 (10 million).
10 -6 = one millionth .One way to understand the universe is as a combination of the smallest particles (in this case, quarks and electrons), and how they combine to form atoms. Atoms are combined to make molecules, and molecules are combined into cells of living organisms (as we will see in the next part 'Formation of earth and life'). The build up from small to large, historically, gets seriously interrupted after the atoms of hydrogen and helium form. Planets and life can't form from these two atoms. It will take 200 million years for the next elements to form.
For the first 300 000 years, the universe was a sea of opaque light. It looked similar to what you would see if you put on a pair of swimming goggles and dived into the Sun. The intensely hot fog of the Big Bang was cooling down, and the 'light went out' to become the blackness of space.
Recombination, 300 000 years after the Big Bang (the coming together of electrons with nuclei to form the first whole atoms), marks the beginning of the Dark Ages. It may sound odd to say that the universe became transparent, and this marks the beginning of the cosmological Dark Ages. But as the temperature drops, the intense light and heat cooled to become transparent. Because there were no stars, the universe went dark.
We travel on our journey in total darkness, for many millions of years. If there are signposts, or side roads, we can't see them.
At around 200 million years after the Big Bang, we start to strain our eyes to catch a glimpse of the lighting of the first star.
Scientists are very confident of most of the series of events following the first fraction of a second after the Big Bang. There is a lot of information about the first three minutes of the universe, and about recombination, but scientists fall very quiet when asked about the next, equally significant events - how the first molecules, stars and galaxies formed. These three events happened almost at the same time - once molecules formed, stars became inevitable. And galaxies are whole bunches of stars.
Imagine you're in a jet, strapped in beside the pilot, and he puts the nose down, into a sharp dive, and holds the joystick forward, so that you continue the dive into a tight loop. You're upside down at the bottom of the loop, and continue around to right side up. This increases the 'G forces' - you are pushed against the straps holding you in. Now imagine the pilot, while you're still in the loop, undoing your straps, but you stay where you are! It must be dark matter, you both agree.
Dark matter is thought to be concentrated within and around stars and galaxies. It is thought that this same dark matter governs the formation of superclusters of galaxies, as they emerged from the almost perfectly smooth ball of energy that was the big bang.
Dark energy , on the other hand, is used to explain why the expansion of the universe is speeding up. Like dark matter, its presence is 'inferred'. Unlike dark matter, it is distributed diffusely in space.
Dark chocolate is the third equally mysterious force. It can give people more mass than they think they have, especially around the outside.
Our Sun is a star - one of millions of stars, in our local galaxy - called the Milky Way galaxy. The terms 'Milky Way' and 'Galaxy' both come from the Greek galaktos , meaning 'milk'.
Galaxies are not evenly spread throughout the visible universe. They tend to form clusters of galaxies. These clusters have been likened to a spider's web, or bubbles in a foam (there's that foam structure again - like the atoms). Galaxies are closer together at the intersection of the strands of the web, or the meeting of three or four bubbles.
The raw material for all of this stuff (ie. planets, stars and the biggest things, galaxies) was formed in the Big Bang.
So what came first - the first star or the first galaxy? This is a trick question. It's like asking what came first, a tree or a forest?
Flying down the road of time, from the Big Bang, we wouldn't see the formation of galaxies until 'we saw stars'. Early galaxy formation, like the early stages of star formation, would be invisible in the blackness of space. Galaxies and stars arose in those areas where the density of atoms was greater than average (as shown by the photo of the universe at 300 000 years, on the previous page) . What we would hope not to miss is a glowing cloud that would become the first star. This star, like the millions and billions that lit up continuously ever since, could only form within the massive areas of dense gas that defined the galaxies.
We will consider galaxy formation first - if only to understand the structure in which the first star could be born.
The ball of energy that was the early universe was extremely homogenous, but not perfectly homogenous. Minor differences in matter/energy/dark matter slowly led to the formation of giant clumps of hydrogen gas. These were regions with higher-than-average matter densities in the expanding universe. The small fluctuations in the density of matter in the early universe grew with time and eventually collapsed to form a 'self-gravitating object' - an object held together by gravity.
The atoms in these clumps began to move faster, forming a hot gas, and this led to the cloud of gas beginning to turn slowly, and form a disk.
On the largest scale, these dense turning clouds of gas (molecular hydrogen and helium) would become galaxies - clusters of millions of stars spinning around on themselves. The dominance of gravity, in conjunction with dark matter, results in galaxy formation.
On smaller scales, the hottest areas of the condensed gas within the protogalaxy cloud became stars. The details of this process - how the gas clouds fragmented into stars and galaxies - is still poorly understood.
Most galaxies (including the Milky Way) congregate in groups or large clusters which may contain up to thousands of galaxies. And some of these congregate into bigger groups - called superclusters. The space within the galaxies is not empty, but is filled with gas that varies from cold, to a temperature of many millions of degrees.
Most Eastern Bloc physicists believe in 'top down' theories of large-scale structure: superclusters and clusters collapsed into huge flat gaseous disks of ordinary matter. Within them, galaxies condense. Western cosmologists however theorise that the universe formed from the 'bottom up'. That star clusters formed first and then, drawn together by gravity, clustered into galaxies and superclusters.
The current evidence (according to Western cosmologists) is that bottom up theories are more successful than top down.
Molecules are formed from different atoms coming together in groups of two or more to share their electrons. In this way, one atom can form a chemical bond with other atoms.
The best known example is the atoms of hydrogen and oxygen, which can bond to form a molecule called H2O. A lot of these molecules together form water. Water is a compound - a substance composed of two or more different atoms chemically bonded to one another, and which has distinctly different properties from the atoms from which it is made.
Anything that we experience on Earth as solid, liquid or gas is made of molecules - there are no independent atoms. In solids, molecules are locked together to form a grid or lattice. In liquids, the molecular structure is similar, but the connections are elastic, or 'springy'. Only in a gas are molecules able to move independently of each other.
No one has ever seen or handled a single molecule.
In space, atoms can exist independently or as parts of small molecules.
There is very little written about the formation of the first molecules. Scientists don't know how they first formed.
Two hydrogen atoms, normally, are unlikely to make a hydrogen molecule without the close proximity of a third element, such as carbon or oxygen, but these elements didn't exist at that time. It seems that hydrogen atoms can, in unusual circumstances, form hydrogen molecules and that these formed into clouds of hydrogen gas, and so created the first star. It is less likely that the first stars formed from non-molecular hydrogen and helium atoms.
The universe had cooled and matter had become dominant. 200 million years after the Big Bang, s light variations in the density of the gas of the expanding universe became amplified. These regions, although more dense than the space around them, were less dense than a vacuum on earth. They became clouds (of hydrogen and helium atoms), light years across in size, and slowly collapsed, or condensed.
These great invisible clouds also began to rotate. Some became so compact that their core heated to millions of degrees under the pressure. The beginning of star formation is one of the great mysteries - scientists still don't know exactly how the gas compresses to create a star.
Hydrogen molecules are believed to have formed in the coldest and densest regions of massive gas clouds. The centre of one condensed cloud then got hotter and denser until, about 100 000 years after the cloud formed (and 200 million years after the Big Bang), it became a plasma (electrons were stripped from the hydrogen nuclei) and it began to glow. This glowing fog was the first protostar .
The star was made in the same way that stars are made today - from the condensation of a rotating cloud of gas. And this is the same process as that which created the galaxies and the solar system.
Most textbooks on the universe say that stars are formed from clouds of gas and dust. I once spent several hours with a bottle of gas, blowing it into some dust, and didn't get one star. Clouds, yes. I found out since I was missing two small ingredients - a temperature of over five million degrees, and a cloud of gas and dust that is at least one light year wide (quite a bit bigger than our solar system). And one more thing - it should be 99% gas (hydrogen and helium) and 1% dust (any other elements).
Just over 200 million years after the Big Bang, the compressed and heated hydrogen atoms began to be fused into helium and the first star began to shine. Four hydrogen nuclei were fused into one helium nucleus - repeating the process of helium creation in the Big Bang .
Nuclear fusion, as we saw, is the merging of the nuclei of light atoms to form heavier ones. Such fusion is accompanied by the release of energy, which makes the star shine.
The first stars were very hot, very bright, and massive (at least 300, or up to 1000, times the size of the Sun). Consequently they lived a relatively short life - three to ten million years. Smaller stars, like our Sun, live for many billions of years.
Fusing hydrogen to make helium is what happened in the first three minutes of the Big Bang. But the starting conditions were very different from that of a star. The Big Bang was massively dense and hot, and as the universe cooled , it reached a temperature where fusion could occur. Stars however start with a cloud of cold hydrogen. This cloud heats up as it compresses, until the temperature was high enough for fusion to occur (primordial nucleosynthesis).
In the massive heat at the start of the Big Bang, hydrogen was preceded by atomic particles, mainly the neutron, proton and electron. The fusion process began with a free neutron combining with a proton to make deuterium. But in the cloud of hydrogen 300 000 years later there were no free neutrons. The fusion process in the star begins with two protons fusing together (one proton is then converted to a neutron) to make deuterium. This is one of several ways of making helium, and is called the proton-proton chain.
The proton-proton process:
• 2 protons = deuterium
• Deuterium + 1 proton = helium 3
• 2 helium 3s = heliumThe first star made helium by combining protons (ie. hydrogen nuclei). Larger stars today make helium via a different process, starting with heavier elements (carbon, nitrogen and oxygen). Making helium is the first step in the process of 'stellar nucleosynthesis' - the making of new elements (including metals). It is not the making of new matter, but the conversion of one kind of matter into another, accompanied by a release of energy. This process continues today.
Where the Big Bang converted energy to matter, stars transform matter into energy.
The hydrogen nucleus has one proton (its atomic number is one). The helium nucleus has two protons and two neutrons - its atomic mass is therefore said to be four.
If you put four hydrogen atoms on one side of a pair of scales, and a helium atom on the other, you would see that the helium atom is a bit lighter (by less than 1 per cent). So when you combine the four hydrogen atoms, you have a bit left over.
The mass of Helium is in fact 3.97. So when hydrogen is fused to make helium, .03 of the mass is left over and converted to energy (explained by Einstein's formula E=Mc 2). As the star converts hydrogen into helium, it gets hotter.
The 'main sequence' of any star is the burning of hydrogen. This lasts for 90% of the star's life. The first stars were massive stars, and lasted as little as three million years - very short in terms of an average star's life.
As the hydrogen was fused to helium, the core filled with helium `ash'. The fusion continued in a 'shell' around the helium core. Towards the end of its main sequence, the star began to expand, and increased in brightness.
The helium core became compressed and hotter, until, at a temperature of 120 million degrees, it started to fuse, and the star created two brand new elements. First carbon, then combining carbon and helium, oxygen . A helium burning shell developed below the hydrogen burning shell. The star expanded and cooled.
The creation of carbon in the star indicated that the star was beginning to die. The creation of oxygen would, around 10 billion years later, allow us to live and breathe.
The star continued to expand, and became a red giant. This is what will happen to our Sun in five or six billion years - it will expand to engulf the Earth. If this causes you any sleepless nights, remember it is five or six billion years, not million .
Stars less than twice the size of the Sun may live longer, but 'die' after they reach the red giant stage, and contract to become a stable, dense (one ton per cubic centimetre) 'white dwarf' - the size of the Earth, but with the mass of the Sun.
Solar Mass Less than two Two to three More than three Types of star - the first star was 'more than three' solar masses. Lifespan in years 10 billion 15 million 3-10 million Heaviest element Oxygen Silicon Iron End of life Collapse Collapse - Supernova Result White Dwarf Neutron star Black Hole
In stars more than twice the size of the Sun, the carbon core contracts and heats up to burn carbon and oxygen into neon, sodium, magnesium, sulphur and silicon.
Stars between two and three times the size of the Sun stop making elements at silicon (see table above). They explode in a supernova (explained next), shrink first to a white dwarf, and continue shrinking to become a neutron star , denser than a white dwarf.
In stars more than three times the size of the Sun (this is the category our first star is in) the burning of elements continued, into calcium, chromium, copper and others until iron was formed. These elements, remember, were not solid, nor even liquid (like molten iron), but were a gas plasma at millions of degrees.
The fusion of these elements occurred in ever-shortening durations. Our massive star, in the last weeks of its life, resembled a colossal onion, with an iron core at three billion degrees, surrounded by concentric shells of hot, fusing material, including (from the inside out) silicon, magnesium, oxygen, carbon, helium, and an envelope of unburned hydrogen.
Iron is the most stable form of nuclear matter and resistant to fusion. T here is no energy to be gained by burning it to any heavier element.
Iron is the most abundant element in the total composition of the Earth (>35% of its total mass)
These new heavy elements became the raw material for second generation stars (see table below) that today are very common in distant galaxies. Population I stars, such as the Sun, and most stars in the spiral arms of the Milky Way galaxy, are the most recent, and have what's called a 'high' percentage of metal (2% in fact!). A lthough they burn hydrogen to make helium, the youngest stars are created through a different process, because space is 'enriched' (or 'polluted') with heavier elements than hydrogen and helium.
First generation Second generation Star generations & populations. Our Sun is a Population I star. Population III Population II Population I Hydrogen and Helium - oldest Low metal percentage High metal percentage - youngest For the first 200 million years, there was no metal. No Metallica, Led Zeppelin, Iron Maiden, or AC/DC. Maybe this is why most of it was called the Dark Ages.
Once our star could not produce any more elements, its heat dropped. It no longer generated the energy needed to hold its layers of 'ash' up against its own gravity, and so the core collapsed until it reached nuclear densities. The core, when it couldn't collapse any more, must have looked, to the rest of the star falling in on it, like a brick wall. The infalling elements, collapsing inwards at 15% of the speed of light, " bounced" off the solid core, and produced a supernova explosion flinging atoms of carbon, oxygen, silicon and other heavy elements (all called 'metals') far out into the space around it.
For several months, it burned brighter than a galaxy, and left behind a cloud of brightly coloured gas, called a 'nebula' - gas (hydrogen and helium) and 'dust' made of other, heavier elements.
Supernovae today occur about once every few years in a galaxy. A nova ( 'nova' is Latin for new - in this case a 'new star') is the bright flare up of a dying star without it being destroyed explosively, and is much more common than a supernova. As we have seen, supernovae are not new stars either, but when the first supernovae were recorded, thousands of years ago , they were the result of stars invisible to the naked eye, and so were assumed to be new. And it is not a 'big nova'. A nova is when a pair of stars, of different ages, rotate around each other. One eventually, because of gravity, sucks the other in, and there is an explosion.
As we saw, intermediate stars (between two and three times the mass of the Sun) become a neutron star . Protons and electrons are crushed together and combine to form neutrons - hence a neutron star. A teaspoon full will weigh about a billion tons.
A s they spin they emit a sweep of radiation similar to the rotating beam of light beam from a lighthouse, but usually much faster. The speed of rotation can be several seconds, or up to 1000 times a second. Before it was realised that they were neutron stars they were called pulsars .
Pulsars are formed by the neutron star's immense gravity pulling gas from its companion star, such that this gas is accelerated to a third of the speed of light or more and "detonates" when it strikes the neutron star surface releasing great quantities of energy including thousands of bursts of x-rays that rise from the surface in pods or columns many times each second.
Some neutron stars spew matter into space at nearly the speed of light.
When the iron core of our massive star reached a mass equal to the size of the Earth, it collapsed (like all stars larger than three times the mass of the Sun). The outer layers were violently expelled in the supernova explosion.
And with this massive explosion, all the elements heavier than iron were produced, as they fused with the hydrogen nuclei around what was the star.
This 'heavy element enriched' gas became the raw material for future generations of stars and planets, and ultimately for you and me. All life on Earth is carbon-based. The matter in our bodies is billions of years old. We are stardust (or nuclear waste).
The elements formed in the first massive stars seeded the universe, allowing the formation of rocky planets, including Earth, and life to begin.
A website states 'There are people walking around on planet Earth who originally came from deep space. They look and act like normal human beings but their origins lie way beyond the outer reaches of solar system'. This is a confusing reference to all of us. The people they describe, 'walking around', don't 'look and act like normal human beings', they are normal human beings.
Our massive star collapsed first to a neutron star, but its gravity continued to crush the neutrons, and it collapsed until its radius was so small (maybe forty kilometres) that it became a black hole.
A black hole is much denser than a neutron star: a black hole with the same mass as the Sun would be the size a small town , and one with the mass of the Earth would fit in the palm of your hand (that is, if you could hold it without being sucked into it). Matter is literally torn apart upon entering the Black Hole.
Its density is equal to that of a nucleus, and, like the first part of the first second of the Big Bang, is called a singularity.
A black hole, by the way, is not a hole, despite the name, but a small and unbelievably dense mass. It is called a hole because the small dense mass sucks all matter and light into it. No light can escape, so it appears black.
At the beginning of the explanation of the structure of the atom, I mentioned that atoms can be though of as foam - mostly space. But if you took away the electrons, and packed the remaining nuclei together, you'd have some seriously heavy stuff.
It is thought that there are black holes in the centre of most galaxies. These are supermassive black holes that have sucked in millions of stars close to it, and may have originated from the collision of galaxies, especially during the first billion years.
The word Quasar is an abbreviation of QUAsi Stellar ('star-like') Radio source . Originally quasars could only be detected by radio. They are smaller than our solar system, but emit 100 times more light than the Milky Way galaxy.
Quasars are the farthest points of detectable light, and as such they are the oldest things we can see through telescopes. They formed around one billion years after the Big Bang and are short lived - lasting for ten to 100 million years, but there is currently a debate about whether the first quasars formed at the same time as the first galaxies. It may be that quasars started as galaxies, then evolved into supermassive black holes.
Element number
of protonsCreated in Big Bang:
Hydrogen
Helium
Created in the first stars:
Carbon
Nitrogen
Oxygen
Neon
Sodium
Magnesium
Aluminum
Silicon
Phosphorus
Sulphur
Chlorine
Argon
Potassium
Calcium
Chromium
Manganese
Iron1
2
6
7
8
10
11
12
13
14
15
16
17
18
19
20
24
25
26
Created in Supernovae:
Cobalt
Nickel
Copper
Zinc
Silver
Tin
Platinum
Gold
Mercury
Lead
Uranium
27
28
29
30
47
50
78
79
80
82
92In following the life of the first star, we covered about three million years. In that time, thousands or millions of stars formed. The birth of stars and galaxies was extremely quick (in the expanse of billions of years between the Big Bang and today).
A billion years after the Big Bang, the universe was about a tenth of its current size and many galaxies had formed. But the galaxies were not a tenth of the size that they are today. They were about the same size as they are today, and so they were much closer together, and often combined into larger galaxies. The early universe was more active, with star formation and collisions much more frequent. Star birth decreased considerably after the first few billion years, to a slower, but steady, rate of star formation.
The main direction of this 'history of the universe' is chronological. But as we travel away from the Big Bang, we discover that we there have been two other, parallel, side roads. One is 'up' the table of elements. The lightest element, hydrogen, formed first, and progressively heavier elements formed millions of years later, first in stars, then in supernovae. All the naturally occurring elements, from hydrogen to uranium, from which our world is made, formed in less than 250 000 years.
The other parallel road we can see is from the smallest things in the universe (quarks, which make up protons, for example) to the seriously biggest (galaxy superclusters). In the first few hundred million years, hydrogen atoms were spread out in space, and began to get move together more in some places, and less in others. These places varied from billions of miles or kilometers wide, to thousands of light years wide. At one billion years the largest things in the universe - galaxy superclusters - had formed from the atoms moving together to form stars.
We continue our drive through space, the next eight billion years is relatively uneventful. We pass millions of stars and thousands of galaxies, and are looking forward to the birth of the solar system. To pass the time, we will explore space, galaxies and planets.
The universe consists overwhelmingly of vacuum. The vacuum of space is much more devoid of matter than a vacuum on Earth, because vacuums on Earth a far from empty. But even the 'empty vacuum' of space is not totally devoid of matter - as we have seen, there are hydrogen and helium atoms (a very dilute gas) floating around. And there are other elements, especially beween the stars, such as carbon molecules and water molecules which are key ingredients for life. These are the raw materials of life. There is also treasure - gold, silver and tiny diamonds!
Nor is space devoid of energy. The energy in space exists in the form of subatomic particles - electrons, quarks and photons. But they are fleeting - as soon as they come into existence, they are gone with no trace of their existence. These particles of matter spontaneously spring into existence and then annihilate one another (originally proposed by Heisenberg in his Uncertainty Principle).
