What does science tell us about the origins of the universe? Did it all start with the Big Bang?  What was before the Big Bang? Where did matter come from?  How did the elements form? How were stars and galaxies made?

2.2: Cosmology Conclusions                                                                                          (Statement 8)

No philosophy or religion can explain the mystery of existence itself, and nor can science, but science currently explains:

●          How the universe evolved from a split second after the Big Bang about 14 billion years ago;

●          Why everywhere in the universe looks roughly the same to us, why space-time is so flat, what the fundamental forces are, perhaps even how the fundamental constants were set;

●          How matter was formed, how the elements formed, how stars and galaxies were formed;

●          And scientists are also exploring what might have happened before the Big Bang.

…more

2.2.1   Scientists are still trying to discover what really are the most fundamental things.  Some of their ideas are called string theory or super-symmetry, but so far we don’t know if any of these are true.  more (later) 

2.2.2   Scientists have discovered

            ●          4 fundamental forces: gravity, electromagnetism, weak and strong force;

            ●          24 kinds of fundamental particles: quarks, leptons, antiquarks & antileptons.

            The laws of physics that link these together involve about 20 fundamental constants, such as the speed of light. 

            The current description of these fundamentals is called the ‘Standard Model’.

            There is lots of evidence for this model, including experiments in synchrotrons and high energy particle accelerators such as those at CERN near Geneva.  more (later) 

2.2.3   Forces are carried by carrier particles.  The strong force is carried by gluons, the electromagnetic force is carried by photons, the weak force by W⁺, W^- and Z⁰ bosons, and gravity is carried by gravitons (though no-one has seen these yet).  Scientists expect to find a fifth fundamental force, whose carrier is the Higgs Boson, which deals with mass.  Scientists also suspect that a ‘scalar field’ carried by an ‘inflaton’ was involved in the first split second.  more (later)

2.2.4   The force, mass or charge came in discrete lumps, like tokens, called quanta, just like coins come with discrete values.  This is quantum theory, which we know is true.  When they collide particles can swap quanta of things like mass or change, or they can join together.  Particles can also split up into other particles.  Pairs of particles can appear out of nowhere, then disappear again.  They do all this following some rules but when they do it and which way they do it is pretty random.  This means we can’t totally predict what will happen in future.  more (later)

2.2.5   We frequently talk about these particles, the matter and anti matter and carrier particles, as though they are like bullets, small lumps.  But sometimes it is better to talk about them as though they are waves, a lot like water waves.  Perhaps we should call them wavicles, but most people don’t.  Instead, when they behave like bullets we call them particles, and at other times we call them waves.  Even when we talk about particles, often we can’t say exactly where they are, and we imagine they are more like a patchy cloud that collapses into a bullet only when it hits something it is going to react with.  more (later)

2.2.6   Quarks and leptons are called matter.  Antiquarks and antileptons are called antimatter.  Matter and antimatter particles are almost identical except one has a negative electric charge (eg an electron) and the other had a positive charge (eg a positron).  When some particles, such as electrons or photons, fly around on their own this is called radiation.  If an antimatter particle collides with a matter particle (eg if an electron hits a positron) they both turn into other particles (eg high energy photons, called radiation).  When high energy photons collide they can turn into matter and antimatter particles.  more (later)

2.2.7   Space-time – three dimensional space plus time - is curved.  This is part of the theory of relativity which we know is true.  This means that when we add together speeds and so forth the result is not a simple addition.  Compare this to the angles of a triangle, which add up to 180 degrees on a flat surface.  But the angles of a triangle drawn on a ball are sharper so they add up to less than 180 degrees.  The angles are wider in a triangle drawn on a saddle (which goes down at the sides but up in front and behind) so they add up to more than 180 degrees.  At high speeds the universe behaves like it is a 4 dimensional saddle.  Once it might have been a very steep saddle.  more (later)

2.2.8   Science does not explain what caused our universe to exist in the first place.  (Neither does any religion.) We do not know what existed prior to the Big Bang.  Each proposed explanation assumes something did actually exist before the Big Bang.  more (later)

            ● Perhaps it was just a massive random fluctuation, where matter appears out of nowhere then later disappears.

            ● Perhaps the universe is in a cycle of expansion and contraction, and this phase began after the last Big Crunch.

            ● Perhaps our universe began as a black hole in a bigger universe.

            ● Perhaps (according to string theory) 2 multidimensional membranes collided, 

            ● Perhaps there are many, perhaps billions of universes, so explaining what caused our universe to exist is part of an even bigger problem.

2.2.9   When we talk about age of the universe we really mean the time from the start of the Big Bang, about 14 billion years ago, even though we don’t know what happened before then.  more (later) 

2.2.10 The first split second, called the Plank era, lasted 10^-43 seconds, which is very, very quick.  Scientists don’t understand what happened in that first instant.  The whole universe was a very small, very hot, very dense, ball of energy or radiation.  We think of this as lots of different kinds of fundamental particles, carrying forces or mass or charges, rushing around at humungous speeds, crashing into each other, rapidly changing as they join together then split apart again.  We can think a higher temperature or high energy means the particles are moving or jiggling faster, so as they cool they slow down.  Scientists suspect all the forces were combined into one, because the particles had no mass.  more (later) 

2.2.11 At the end of the Plank era gravity worked separately from the other forces: gravitons passed between particles with mass, pulling them towards each other.  There were fundamental particles crashing into each other at very high speeds, perhaps joining together to make the heavy particles predicted by some theories such as monopoles and gravitinos.  more (later) 

2.2.12 The second instant – the inflation era – lasted for 10^-38 seconds, 100,000 times longer than the first, but still only a split second.  The universe at this time was probably patchy, with some regions different from others.  There was one region, which might have been quite small, where most of the energy came from a high-energy scalar field.  The “strong” force began to work separately.  This caused that region to expand enormously quickly, doubling in size about 100 times.  This is called inflation.  Gradually the scalar field became weaker, so the heavy particles could not be created any more.  Eventually the expansion slowed down and it took longer and longer for the universe to double in size.  more (later) 

            Imagine a balloon with some bumps and patches of dots on it that is blown up to millions of times its initial size.  In the end an area on the surface would be almost flat, even if the bumps were the same height, because they would be millions of times wider.  There would be very few of the original dots, and the whole area would look fairly uniform.  Small lines drawn on the balloon as it finished blowing up would become quite large.

2.2.13 The particles created in this region at the start of the expansion became so widely separated that now they are too rare to detect.  This region, which was now huge, was homogenous: almost the same everywhere we can see, because it all began from the same patch, even though there has not been enough time for the universe to mix, or no time for light to travel right across it.  However, very distant parts of the universe that we’ll never see might be different.  Space time in our region had become almost flat: when we add speeds simple addition is very close to the combined speed, at least for low speeds.  Small fluctuations that arose near the end of inflation got much larger, so there were some areas a tiny bit more dense than others.  more (later) 

2.2.14 At the end of inflation, most of the energy of the universe was contained in this scalar field, carried by ‘inflatons’.  These broke up into quarks and leptons and other particles.  The strong force, carried by gluons, began to work separately, holding together groups of 3 quarks (and 3 antiquarks), which are called protons and neutrons (and antiprotons and antineutrons).  Protons are positively charged, antiproton are negative, and neutrons are neutral.  more (later)

2.2.15 The third instant – the electroweak era – lasted for 10^-10 seconds, a billion billion times longer than the inflation period, but still less than a billionth of a second.  The electromagnetic and weak forces began to act as separate forces.

            The weak force, carried by W⁺, W^- and Z⁰ bosons, changes protons from protons to neutrons and back again.  For instance, one of the 3 quarks in a proton can change into another type of quark by emitting a W⁺ boson, turning the proton into a neutron, and the W⁺ boson turns into a positron and a neutrino.  We can still see such reactions today.  more (later) 

2.2.16 The fourth period – the first part of the particle era – lasted up to 10^-4 seconds, a million times longer than the previous one.  All 4 fundamental forces now worked separately.  The electromagnetic force, carried by photons, we see as electricity, magnetism, radio waves, microwaves, infrared, visible light, ultraviolet, X-rays and gamma radiation.  When high energy photons collide they can make pairs of particles and antiparticles.  Particles were as numerous as photons.  Eventually, as they slowed down, protons, antiprotons, neutrons, & antineutrons could no longer be created from two photons.  more (later) 

2.2.17 The fifth period – the second part of the particle era – lasted up to 10^-3 seconds (a thousandth of a second), about ten times longer than the fourth.  Most of the particles & antiparticles flying around crashed into each other turning into photons (gamma radiation).  About one in a billion particles could find no antiparticle, so most of the antimatter disappeared and what remained was mostly matter (and the photons).  Some antimatter is still being created now but it quickly bumps into some matter and they annihilate each other in a burst of light. Pairs of electrons (matter) and positrons (antimatter) are still being created from photons.  more (later)

2.2.18 The sixth period  – the era of nucleosynthesis - lasted up to 3 minutes, about 100,000 times longer than the fifth.  Initially protons and neutrons started joining together in groups of 2 or 3 (called nuclei) but the new nuclei were torn apart by the high temperatures.  The protons and neutrons initially were in about equal numbers.  As the universe cooled (to below 100 billion degrees) protons stopped converting to neutrons, but neutrons still converted to protons, so eventually protons outnumbered neutrons by about 5 to 1.  A proton on its own can be called a hydrogen ion.  A proton joined with a neutron is a form of hydrogen, an isotope, called deuterium.  Deuterium colliding with other particles made it easier to make larger nuclei.  A proton joined with 2 neutrons is an isotope of hydrogen called tritium.  Two protons joined with two neutrons is called helium.  If a helium nucleus fuses with a tritium nucleus we get lithium - three protons joined to 4 neutrons.  The protons make these nuclei positive.  An element is a bunch of atoms in which the nucleus has the same number of protons.  By the end of 3 minutes, the nuclear fusion into hydrogen, deuterium and lithium stopped, but as the universe cooled further (to below 10 billion degrees) these nuclei no longer break up and are stable.  more (later) 

2.2.19 The matter in the universe consisted of 75% (by mass) hydrogen nuclei (i.e. individual protons), 25% (by mass) helium nuclei (about 12 hydrogen nuclei for each helium), trace amounts of deuterium (about 1 for each 40,000 hydrogen atoms) and lithium nuclei. These proportions being found in reality is strong evidence that the big bang theory is correct.  We have no direct evidence for the accuracy of the big bang model before nucleosynthesis.  more (later)

2.2.20 The seventh period – the era of nuclei - lasted from 3 minutes to 380,000 years.  The universe was a hot “plasma” of mostly hydrogen and helium nuclei (which are positive) and (negative) electrons.  Photons bounced from particle to particle, not traveling very far, meaning the Universe was opaque.  more (later) 

2.2.21 When the universe was 380,000 yrs old, it had cooled to a temperature of 3,000 degrees.  By then the electromagnetic force was strong enough so that the negative electrons combined with the positive nuclei to form stable, neutral atoms of hydrogen (with one electron spinning around it) and helium (with 2 electrons spinning around it).  Later 2 hydrogen atoms would join together to form hydrogen molecules (H₂), which is hydrogen gas.  Helium atoms generally travel on their own.  This was called recombination, even though electrons and nuclei had not combined in a stable way before.  more (later)

2.2.22 The photons interact with any charged particles flying around but not so much with the neutral atoms.  Photons were free to stream across the universe, meaning the universe became transparent.  We can still detect these as the cosmic microwave background radiation, 14 billion years later.  more (later)

2.2.23 Each kind of atom has a fixed number of orbits the electron can occupy so it has a fixed amount of energy.  An electron in a higher energy orbit can suddenly jump to a lower energy orbit, and the energy lost is carried away in a photon.  Alternatively, if a photon hits an electron, it can disappear and its energy is absorbed by the electron in a higher energy orbit.  The amount of energy a photon carries is shown by its wavelength, which is like its colour.  So each kind of atom has its own unique pattern of colours, called a spectrum.  If there is light coming from it, we can tell what is in a gas from a long distance away, which is called spectroscopy.  more (later) 

2.2.24 The eighth period – the period of atoms – lasted from 380,000 years to about a billion years.  The universe was filled with atomic gas, but it was dark.  The small variations in density at the end of inflation meant that the gas was slightly clustered.  Higher density regions had slightly greater gravity, so they pulled in more gas and became even more dense.  The gas gradually formed clouds,  groups of clouds and very long strings of clouds,  which later became stars, galaxies, galaxy clusters, super clusters and “filaments”.  more (later) 

2.2.25 The gas clouds were condensed by gravity into balls. The hydrogen and deuterium became so tightly packed under high temperature and pressure that they fused together in a nuclear fusion reaction, generating heat (the particles move faster) and light (emitting photons) and making helium.  The heat stopped the stars from contracting more tightly.  more (later) 

2.2.26 As the hydrogen and helium and so on were used up the fusion reaction stopped.  The outer layers of the star could no longer resist gravity, which was pulling the star's outer matter inward toward the centre. 

            In big stars the gravity pulled the atoms so close together that 3 helium-4 atoms could fuse together to form carbon-12.  Carbon could fuse with ordinary hydrogen, deuterium and helium to form other heavier atoms.  These fusion reactions produce heat - fast particles – causing the stars to explode, turning into supernovae, spewing the light and heavy atoms into space. 

            Smaller stars shrank more slowly because their gravity was weaker.  Atoms from the middle of the star rose to the surface and were blown off into space. 

            Either way, heavy elements moved into the space between the stars, and some of these condensed to form small solid grains of dust.  more (later) 

2.2.27 The cycle of the birth and death of stars has occurred several times, with each successive generation of stars starting off with a greater quantity of heavy elements than the previous generation.  The later generation stars collapsed some of the heavier elements fused to make even heavier ones.  This formed al the heavier elements, such as oxygen, nitrogen, sulphur, phosphorous, silicon, iron, gold and lead.  If a nucleus had x number of (positive) protons it generally had x number of (negative) electrons orbiting around it, so the atom was neutral.  more (later) 

2.2.28 Even heavier elements formed, whose nuclei had more than 92 protons and over a hundreds neutrons, but these break apart fairly quickly, giving off protons and neutrons or changing protons into neutrons (or vice versa) and giving off electrons, positrons or photons.  more (later) 

2.2.29 All nuclei with more than 83 protons (such as Radium, Thorium, and Uranium) are unstable and eventually break up, but do so more slowly so some are still around.  Nuclei with more than 126 neutrons (like heavy isotopes of lead, mercury and gold) also break up slowly. Smaller atoms also decay slowly if they have lots of neutrons.  For instance carbon atoms with 6 protons but 8 neutrons (carbon-14) can randomly expel a positron, turning a neutron into a proton, changing the atom into nitrogen-14.  This happens to half the carbon-14 atoms about every 5740 years.  more (later)

2.2.30 The first galaxies – clusters of stars – came into existence about 1 billion years after the Big Bang.  We are still in the era of galaxies.  There are billions of galaxies, each typically with billions of stars.  more (later) 

2.2.31 We can see the universe is still expanding.    The further they are, the faster the stars are moving away from us.    more (later) 

            Imagine baking a cake mixed with raisins: as the cake – the universe – expands all the raisins – particles – move apart from each other, although the raisins don’t change in size.

            As stars move away from us the light (the photons) they emit has a longer wavelength, which is called the red shift.  Imagine rowing a boat, paddling at a fixed rate.  As the boat moves faster the waves the paddles make as they dip into the water are further apart.  How much further apart they are tells us how fast the boat is moving.

2.2.32 If the Big Bang theory was false and universe was infinite and filled with stars then the sky would not be black at night, because in every direction there would be many stars.  But the Universe did have a beginning, so the number of visible stars is limited, and because it is expanding, their light is red shifted out of the visible range, so night time is dark.  Daytime is light only because the Sun is so close.  more (later)

2.2.33 When some huge stars run out of fuel their huge gravity makes them shrink so that all the mass is in a very small ball.  For some, the gravity around the ball is so high that anything that gets close enough, even photons (particles of light), is sucked into the centre, so  these are called black holes.  For others, after the star explodes as a supernova, what is left is mostly neutrons, and some of these spin very quickly sending off an electromagnetic beam, like a lighthouse, so these are called pulsars (pulsing stars).  more (later) 

2.2.34 The galaxies are rotating faster than expected if we calculate using visible stars.  Scientists have proposed there is other “dark matter” in the universe to provide the additional mass so that their calculations are correct.  This would be atoms and other particles that are not emitting any radiation that we can detect, so we call it “dark” matter.  more (later)

2.2.35 The expansion of the universe seems to be accelerating.  Scientists have proposed that there is also “dark energy” that we otherwise cannot see causing the acceleration.  more (later)

2.2.36 After these processed worked through for 14 billion years to now, the universe is now composed of a very tiny percentage (0.03%) of heavy elements like carbon, oxygen and iron, ten times that of (0.3%) neutrinos, 0.5% stars, 4% free hydrogen and helium, 25% dark matter and 70% dark energy.  more (later)

2.2.37 If the average density of the universe now is less than a critical value – about five hydrogen atoms per cubic metre – then it is infinite (or “open”) and will keep expanding – the galaxies within the infinite space keep getting further apart.

            If the universe is more than that critical density then it is finite (or “closed”) and the expansion will stop.  A closed universe is a bit like the surface of a balloon: if you travel all the way in one direction you end up arriving back at the start.  more (later)