A short history of the universe

A short history of the universe

The variety of the universe is awesome as well as its size. In this short post we will take a tour of the universe from its inception in the weirdness of Planck time, through the almost instantaneous sprawl into a scale that ordinary human measurements of time simply will not suffice to describe. Space needs its own scale – the light year. And amidst that immensity there arose a great variety of forms from natures natural laser gun – the quasar – to her greatest mystery – the black hole – to her most spectacular flourish – the supernova – and in between, a plethora of extraordinary planets from ringed giants that dwarf Saturn to hot ocean planets of pure water, to planet pairs locked in a mutual dance as they traverse their own sun.

The very early universe

The universe, they say, in the beginning exploded out of a “singularity.” A singularity is an event which requires infinite terms in equations to describe it. In this case the curvature of space and time, as described using Einstein’s equations of relativity, become infinite. Theologians around the world have always associated God with infinity and eternity, and so without stepping beyond the domain of standard, accepted physics at all, it can immediately be seen that something suspiciously like God is implied at the very beginning.

Anyway, enough of that, in this one we will stick with physics.

Planck time

The first epoch of the universe, called “Planck time,” unfolded in a very short period of time, just 10-43 seconds. That is, a decimal point followed by 43 zeros, and then a one. At Planck time, the diameter of the universe is said to be a “Planck length.” A Planck length is the distance travelled in Planck time, which may be as small as 10-33 centimetres in diameter. The term “Planck” comes from the German physicist Max Planck, who gave the term his name.

Owing to the way that physicists have divided the phases of the universe, the shortest cosmic period, Planck time, is followed by the longest general cosmic period, a 4.5 billion year stretch culminating in the formation of galaxies. But this very long period can also be subdivided into numerous sections. Little is known about the very early universe, and what follows here are really just calibrated estimations, but estimations which represent the majority view. This account is known as the “standard model” because it is accepted by the vast majority of physicists.

Above: Max Planck (centre) who gave his name to Planck time, a mysterious 10-43 second stretch of time at the beginning of creation, in which the four “fundamental forces” (gravity, electromagnetism, and the weak and strong nuclear forces) had not yet separated.

The four forces

During Planck time physicists believe that the four fundamental forces which drive the dynamics of the physical universe—gravity, electromagnetism, and the strong and weak nuclear forces—did not show any differentiation. At 10-43 seconds gravity is thought to have separated from the other forces. By 10-36 seconds, the strong nuclear force separated off. The fracturing of the strong nuclear force may have triggered the hypothetical “inflationary epoch”—a period of very rapid expansion between 10-36 to 10-32 seconds. If indeed it occurred, during the inflationary epoch the universe would have expanded from Planck length to a diameter of about 20 centimetres across. This was by far the most rapid period of expansion in the history of the universe. Space expanded far faster than the speed of light. If there was no inflationary epoch—some consider there to be very strong evidence for inflation, others that it is no more than a speculation—then the universe was slightly larger at the end of Planck time, and expanded more slowly. The existence of the inflationary epoch is the only point of contention in the standard model of the big bang.

Electroweak epoch and pair production

The so called “electroweak epoch” in which the electromagnetic and weak nuclear force remained indistinguishable, stretched until 10-12 seconds after the big bang. At this point the universe was still high enough in energy for large numbers of particles to form. The universe was composed of a plasma made up of the elementary particles. Collisions between photons were creating particle and antiparticle pairs of all kinds. A little understood reaction called “baryogenesis” resulted in a slight imbalance of quarks and leptons over antiquarks and antileptons in the early universe. This meant that matter predominated over antimatter. If matter and antimatter had remained in balance then matter and antimatter would have cancelled each other out, and there would be no mass in the universe. But as there was a small imbalance, some matter was preserved, and this makes up the matter in our universe today.

Matter and antimatter interactions involving the process of pair production and pair annihilation were key to mass and energy transfer in the early universe. When gamma ray photons collide, a particle and an antiparticle pair are produced. This can take place if the relationship of energy and mass satisfies a certain condition, defined by Einstein’s famous formula E=Mc2. If this condition is not met then pair production won’t occur. Usually the particles and antiparticles which are created attract each other and recombine, meaning that matter and antimatter cancel each other out, and turn back into gamma rays. This is called “pair annihilation.” As space expanded the particle and antiparticle pairs began to be pulled too far apart to recombine. This was necessary for created matter to remain created.

 

 

 

 

 

 

Above: The process of pair production and annihilation in which particles and antiparticles are created and quickly cancel each other out. Eventually the expansion of the universe pulled existing particles too far from their antiparticle pairs to be destroyed, and this gave rise to the matter that exists in the universe today.

One millionth of a second to fifteen minutes

During the first one millionth of a second after the big bang, the universe expanded from a size smaller than the Planck length to around the size of our solar system today. The diameter of the solar system based on the average distance of Pluto from the sun is around 49 AU. One AU is the distance of the earth from the sun, around 150,000,000 kilometres. As the universe expanded, the gamma rays became “red shifted” meaning their waves lengths increased as space expanded and they lost energy, which would have produced a red appearance, to any observer present. This meant that they could no longer create more particle pairs. During this time larger particles were able to form, including protons, neutrons, electrons, and positrons. When the universe was 10-6 seconds old, the temperature fell below the threshold for proton and neutron formation. When the universe was about 1 second old the temperature fell below the threshold for electron and positron creation. By now the universe was around one thousand times the size of our solar system.

Between three minutes and fifteen minutes after the big bang the temperature was right for “nucleosynthesis—the combination of protons and neutrons to form atomic nuclei—hydrogen, helium and small numbers of lithium and beryllium. By fifteen minutes the temperature of the universe was no longer hot enough for nuclear synthesis, and this could only resume following the formation of stars. The universe continued to expand but at a much slower rate. By the fifteen minute mark the universe was around 1000 times the size of our solar system today.

Primordial fireball

Between fifteen minutes and 380,000 years the universe existed as a plasma known in cosmological circles as the “primordial fireball.” After 380,000 years the temperature fell below 3000 degrees kelvin, and conditions were right for the production of atoms. From around the 380,000 year mark clouds of gas formed and the processes forming the galaxies began. By the 200 million year mark the fabric of space was composed of immense clouds of gas, interspersed from each other by still larger vacuum expanses. These clouds condensed through gravitational attraction and eventually formed stars and galaxies.

Stars, galaxies and planets

The first generation of stars were called “population one” stars. They were much bigger than today’s stars. They were one hundred times larger than the sun, and collapsed in just a few millions or tens of millions of years to form the first supernovae. The population one stars filled the early universe with light. The conditions within the stars were right for nucleosynthesis and so the stars created atoms. The population one stars were capable of generating atoms up to approximately atomic number twenty six (iron). Supernovae are the primary nuclear reactors in space, they are the only places capable of violent enough reactions to create heavy elements.

The population one stars died as supernovae, streaking space with the heavier elements created in their melt down, which mingled with the unassimilated residue of the big bang and created fresh nebulae from which the process of star and galaxy formation began again. At the present time, we are at the third generation of stars, called population three stars. Population two stars represented an intermediate step, containing less metallic elements than today’s stars but more than population one stars. Galaxy formation happens in a similar way for any generation of star. Clouds of gas separate and condense into vast rotating clouds of dust called solar nebula. At the centre, under the influence of gravity, a hot rotating gaseous disk begins to spin, as the cloud of gas contracts into a “proto sun.”

 

 

 

 

 

Above: The universe has known three “generations” of stars. The first, population one stars, were much larger than today’s stars and burned out very rapidly, collapsing in gigantic supernovae.

When the temperature of a protosun exceeded several million degrees kelvin the protosun began to convert hydrogen into helium. Contraction of the gas cloud stopped and a true star was born. In the outer reaches of the solar nebula, differences in density mean that material begins to clump and resists being drawn towards the centre, which leads to the formation of planets. In the case of our own solar system these clumps gradually coalesced into approximately a billion asteroids called “planetesimals,” each up to a kilometre across, some composed of frozen carbon dioxide, water, methane and ammonia, and others of rock. Collisions of planetesimals produced a gradual accretion of materials and planetesimals grew into protoplanets of around the mass of the moon. Over a period of 100 million years the protoplanets continued to collide, gradually reducing in size to the planets in the solar system today. The collisions produced heat. In the outer solar system gas moved slower as it was at a lower temperature, and so it tended to accrue around the larger protoplanets, creating the Jovian planets: the “gas giants,” Jupiter and Saturn. A small number of planetesimals survived capture and persisted as the asteroids of the solar system while others were ejected from our solar system altogether as the pull of the gas giants altered their course by a critical angle.

The earth continued to be bombarded with asteroids during its very early history, around four billion years ago. A single 4000 kilogram planetesimal hitting the earth would generate as much heat as a one kiloton nuclear explosion. Some collisions were much larger. The moon is believed to have been generated by a very large collision between the earth and a protoplanet about the size of Mars, showering material into the earth’s atmosphere and forming a large ring around the earth which accreted relatively quickly (over perhaps 100,000 years) to form the moon. The energy released by collisions and the gravity compressing the earth meant it became very hot, exceeding 2000 degrees kelvin. A large proportion of the earth’s material melted. Early continents were destroyed and the planet’s surface was reduced to an ocean of magma 100 kilometres deep. The molten iron sank to the centre due to its greater density, and formed the earth’s iron core.

Galaxies range in size from dwarf galaxies containing merely thousands of stars, to far more massive entities. Abell 229, the largest known galaxy, is estimated to contain one hundred trillion stars. Larger galaxies will “cannibalise” smaller galaxies which drift close to them, absorbing their stars due to their greater gravity. Spiral galaxies are composed of great winding isthmuses, splayed out like arms around a central hub. The “barred spiral” has a flattened or bar-like centre that flattened archipelagos slowly twist around. Ring galaxies appear as halos of light circling a white centre, caused by a compact galaxy bursting through the middle of a less compact galaxy and scattering a great swathe of stars across space which then coalesce in a ring.

Active galaxies emit particle streams from a supernovae core with a supermassive black hole at its centre, surrounded by a quasar ejecting twin streams of particles across space at the speed of light. Elliptical galaxies show up as uniform white spheres in space camera images. Galaxies lock into loose interacting patterns known as “groups.” Our own galaxy, the Milky Way, is part of a group of thirty, and is orbited by smaller satellite galaxies. The Milky Way is currently in the process of cannibalising two dwarf galaxies.

Above: An x-ray image of a quasar (NASA/CXC/A.Siemiginowska)

Space is awash with complex hierarchical arrangements of stars set out like fractals. Groups of galaxies extend in numbers up to a few dozens, and are themselves contained within larger clusters containing up to several thousand galaxies. Galaxy clusters are set within supercluster groups of several hundreds or thousands of galaxies which gives space a streaked appearance. Between the clusters and superclusters lie voids and super voids – immense vacuums containing nothing but the occasional wandering galaxy that mathematics has destined to slip the gravitational pull of its supercluster, and wend its independent way across space.

Above. Protruding spindles of solar nebulae give birth to stars 7000 light years from the earth (photo: Martin Heigan.)

The stars range in size from dwarf, to giant, to bright giant, to supergiant, and in some rare cases to hypergiants. Dwarfs and giants have been found in every colour range, from red through yellow, to green and blue. The destiny of each star is determined by its size, and this determines its colour. Most stars start out in the yellow giant range. If a star is less than 0.4 solar masses (one solar mass is the mass of our sun) it will gradually loose heat and mass and fade to a red dwarf where it will burn out very slowly, eventually passing away to a white dwarf and then, on a much larger timescale, fading to a cold black dwarf.

No black dwarfs yet exist—the universe is not old enough—but they are an expected feature of its future. The majority of stars are red dwarfs. If the star exceeds 0.4 solar masses it will swell and become a giant—usually a red giant, sometimes a rarer and hotter blue giant—before shrinking to a dwarf. If it exceeds 2.25 solar masses it will collapse into a supernova, and quickly decay to a neutron star, a super dense core as small as ten kilometres across. Neutron stars rip the solar matter from other stars that are close to them, causing huge fire storms and the formation of pulsars. If the star is of a higher solar mass still, it will grow to bright giant size, supergiant size, and possibly hypergiant size. Most supergiants are red, there are also blue supergiants—extremely rare stars, and the hottest in the known universe.

Supernovae can burn so brightly that for a short time they can outshine the remainder of the stars in the galaxy. The most common means of supernova formation involves large stars – stars exceeding nine solar masses – which begin to collapse as their star material declines. This collapse progresses in a staggered, buffered manner as heavier and heavier nuclei are detonated. The final collapse of the heaviest nuclei produces a ten second burst of neutrinos, which constitutes the main output event, and can emit more energy than the rest of the galaxy combined. If it is over twenty solar masses the collapsing star will form a black hole. If over fifty solar masses it will form a black hole so powerful that none of the material emitted in the supernovae explosion will escape the event horizon and the entirety of the stellar mass of the star will disappear from the observable universe. At much higher masses—over 140 solar masses (the largest stars, the hypergiants, reach 300 solar masses)—hypernovae are produced that explode so violently that a large amount of material can still escape the black hole.

Above: Supernova can burn brightly enough to briefly outshine an entire galaxy.

It is a mistake to think that other solar systems contain planets overly like our own. Lets take a look. XO-4b, is a gas giant in the Lynx constellation. The year on XO-4b is only four earth days. TrES-4 b, the so called “balsa wood planet,” is so light it would float on our oceans. HR 8779 c is ten times the mass of Jupiter, close to becoming a brown dwarf star. It is one of three neighbouring planets in the HR 8779 solar system that is like this. HD 189733 b is surrounded by a cloud-like wreath of magnesium silicate—a chemical used on earth as talcum powder. Formalhaut b is a Jupiter sized planet with enormous flat arcing rings, twenty times the diameter of Saturn’s rings. GJ 1214 b is a hot ocean planet, 75% of its mass is in the ocean, and 25% in the solid rock core. Gliese 581 c is a much smaller and more temperate ocean planet, possibly completely frozen, possibly with a temperate earth like environment, sparking rumours in cosmological communities of the possibility of life. Moons as well as planets are believed to have oceans, either at the surface in the manner of Earth or subsurface oceans caught between a warm core and a hard outer mantle of ice. There is speculation that Jupiter’s sixth moon, Europa, contains such a warm sub-surface ocean.

Above: The enormous red rings of Formalhaut b, which span 20 times the diameter of Saturn’s rings.

Binary star pairs exist—two stars locked together by the pull of gravity in a dance. These include the “eclipsing binaries” that rotate as regularly as two golf balls glued to opposing sides of a spinning basketball. If one of these binary star pairs collide they will cause the distinctive crimson coloured “luminous red nova” explosion. A binary star pair may also be a cause of a supernova. As one star ages and swells its material is sucked towards the other in a complex spiralling pattern, which can envelope both stars. The additional mass of the accreted material can cause the younger star to collapse to a neutron star and create a supernova, blowing the remnants of the swirling cloud of gas, and the aging partner star itself, across the cosmos. More mathematically complex still than star pairs, multi-star systems involve complex dynamics of rotation around their common centre of gravity.

Beyond the observable universe

Our galaxy is currently thought to contain 100-400 million stars. The observable universe contains around 100 million galaxies. The amount of mass in the unobservable universe may exceed the amount of mass in the observable universe by an order of 1020! Alternatively the total amount of mass in the universe may be less than that in the observable universe, because some of the galaxies we can see may actually be duplicates of other galaxies, the light from which has circumnavigated the curved surface of space-time and reappeared in our visual panorama. The observable universe is greater than the distance that light has travelled since the big bang because we can observe the images of galaxies which are now much further away due to the expansion of space: the edge of the observable universe is about 46 billion light years away.

Dark matter and energy

We still do not know what most of the universe is made of. Conventional matter makes up less than five per cent of the total amount of mass which calculations show must be present in the universe. Twenty three per cent of the mass is composed of dark matter. Dark matter is probably cold, which is why it cannot be detected from emitted electromagnetic radiation. It is speculated that it is made up of “weakly interacting massive particles” (WIMPS for short). These particles share many of the properties of neutrinos, but they are much larger and much slower moving, and they do not become entwined with atomic nuclei to form atoms. Other potential sources of hidden matter include masses on the inside of black holes. More mysterious still, “dark energy” (different to dark matter) makes up the remaining 73% of mass in the observable universe. This dark energy, also known as vacuum energy, permeates the whole of space, and is thought to be responsible for the increasing expansion rate of the universe. There is also considerable speculation as to whether areas of antimatter exist that are avoiding detection. These antimatter areas are thought to consist of antiparticle pairs of each particle that was created through pair production. There should be as much antimatter as there is matter, but these areas have not yet been discovered.

Although it is not beyond the realms of possibility that new evidence could emerge which presents a significant challenge to big bang theory, what has been described so far is agreed upon by the majority of cosmologists. What is surprising is that the standard model of the big bang unavoidably implies the existence of a creator with all of the traditional characteristics of God. If we wind back the universe to the very beginning the realm in which science can operate completely breaks down. We arrive at a singularity, in which space and time reach infinite values. The conventional response of science has been to assume that the singularity cannot really exist, and to try to explain it away. As a result a range of theories exist which extend the standard cosmological model in numerous ways. We shall look at these another time. All that needs to be said for now is that none of them succeed in removing the apparent presence of a creative source which has all of the traditional characteristics of the creator God of Judaism, Christianity, and Islam.

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