13
The birth moment of the Universe
When artists want to picture the start of a grand affair, they might identify the particular, briefest instant. The scale of what follows is something for the viewer to imagine, and is thus more mysterious, much greater and longer-lasting than the artist could show. Michelangelo did this in his painting of the Creation on the ceiling of the Sistine Chapel of the Apostolic Palace in Vatican City. He made the pivot on which the decoration turns the gentle moment in which the tips of God’s and Adam’s forefingers reach to touch, starting the history of humankind and putting in train the Christian story. The momentous birth of the Universe was likewise brief and very localized, but, in contrast to Michelangelo’s picture, very, very violent.
After birth, the life of the Universe became the subject matter of astronomy, identifiable in the large-scale and long-lasting history described in this book. The circumstances of the birth itself can be imagined, up to now at least, only as ideas enunciated through theoretical physics. According to these ideas, the Universe originated in the smallest imaginable time, only 10-32 of a second (10-32 is a number that can be expressed as a fraction by a numeral 1 divided by a number written as a 1 with 32 zeroes after it). The word ‘astronomical’ has, by metaphor, gained the secondary meaning of ‘enormous’, but this astronomical number must be one of the smallest in the whole of science, if not the smallest.
The Universe came into existence with an initial density and temperature that were unimaginably high. Under such compressed conditions, the Universe began united into one single system of forces and energies. This is the era in which its physics could only be described by the Grand Unified Theory, the one being sought by people like English theoretical physicist Stephen Hawking (1942–2018), rather than by the theories of general relativity and quantum mechanics separately. The four fundamental forces of nature – electromagnetism, weak nuclear force, strong nuclear force and gravitation – were unified into one fundamental force, expressed in many dimensions beyond the ones that we now perceive. The high density and temperature caused a tremendous pressure so the Universe began to expand and cool, and the forces separated. Gravitation separated from the others, followed by the separation of the strong nuclear force from electromagnetism and the weak nuclear force – this separation is why we now think of these forces as different one from the other. Time took on a different appearance from the three spatial dimensions. Some additional dimensions beyond the four that we now identify shrank and disappeared from view.
The Universe was expanding at about this time in a process termed ‘cosmic inflation’, a theory developed separately by American theoretical physicist Alan Guth (b. 1947) and Russian-American astrophysicist Andrei Linde (b. 1948). It started with a brief burst of exponentially rapid expansion, called inflation, which led to the more uniform growth that is happening today. During inflation, the Universe expanded by a huge factor – in that initial 10-32 seconds it doubled in size eighty times or more – that is, a factor of 1026.
The idea of inflation was the invention of Guth in 1979, which he almost stumbled over while tackling a problem of quantum mechanics and particle physics: namely, why there are no magnetic monopoles. Magnets always come as pairs of poles, a north and a south pole together, never as one or the other. The solution to this problem led him to the thought that, when it was dense and hot, the Universe once had monopoles in abundance but that they have all separated one from the other by a huge expansion of space. A short time later, Guth realized that this rapid inflation provided answers to two puzzling questions about the Big Bang: the ‘horizon’ problem and the ‘flatness’ problem.
The horizon problem is the following. The heat left over from the Big Bang is the so-called Cosmic Microwave Background radiation (CMB), which is almost completely uniform across the sky. Opposite parts of the sky, separated by many billions of light years, have never had a chance to interact with each other but nevertheless look the same. How could this be? No physical process could have acted to cause them to be equal.
The flatness problem is the question of why the content and speed of expansion of the Universe are so exactly balanced that it will just exactly expand for ever (see page 260). Inflation gives an answer: if there was some curvature at the outset of inflation, expansion will increase the radius of curvature and flatten the curvature. The Earth has a large radius of curvature, and it looks flat from where we stand on its surface, which is why the Flat Earth theory retained credibility for so long. Likewise, the Universe expanded to such a size that it is now flat.
These two problems were addressed by Guth in a paper entitled ‘Inflationary Universe: A Possible Solution to the Horizon and Flatness Problems’, published in 1981. Guth suggested that the Universe was originally in a state from which it decayed, expanding and liberating the energy that the Universe has today. The early phases of the expansion exposed different parts of the Universe to one another and that is how they all became the same; they retained their similarity as they separated. This solved the horizon problem. The expansion also ironed out any primordial curvature, making the Universe flat. This solved the flatness problem.
There were some theoretical difficulties with Guth’s version of inflation theory, which were addressed in 1982 by Linde. Linde was born to parents who were both physicists and grew up in Moscow. He married a physicist, Renata Kallosh, both of them moving to the United States in 1990 and becoming professors at Stanford University.
A third player in the inflation story was Russian astrophysicist Alexei Starobinsky (b. 1948), who was able to link some generalities of quantum physics with general relativity in describing how the Universe expanded. Starobinsky was able to predict from his model of inflation that the Big Bang would have generated gravitational waves. These gravitational waves would carry a picture of the conditions in the Big Bang as it was at this time, just as the CMB carries a picture of the Universe when it was 380,000 years old.
A gravitational wave detector known as the Laser Interferometer Space Antenna (eLISA – the prefix ‘e’ distinguishes the current design from a previous version) is being planned by ESA to detect these gravitational waves (as well as gravitational waves from binary stars and merging black holes). eLISA will orbit in space, so it does not have to cope with terrestrially generated motions like Earth tremors or the rumble of heavy traffic on an adjacent motorway, which confuse the operation of ground-based gravitational wave detectors but not one that operates in the peace of space (although it does have to cope with random impacts of material ejected by the Sun). Moreover, eLISA is being built to a gigantic scale, which makes it possible to detect low-frequency gravitational waves. This is a significant band in the gravitational wave spectrum that is thought to be radiated by close binary stars and supermassive binary black holes.
eLISA will consist of three spacecraft positioned at the corners of a triangle in space whose sides are 2.5 million kilometres (1.5 million miles) long, six times the Earth–Moon distance. The centre of the triangle will lie 50 million kilometres (31 million miles) from the Earth, following our planet in its orbit around the Sun. Each spacecraft will fly in a wavy orbit in such a way that the triangle rotates like a cartwheel about its centre and will carry two 46-millimetre (1.8-inch) cubes made of a gold-platinum alloy. The cubes are designed to float free inside a chamber (just as an astronaut floats free inside a space station) and are made of an alloy that is non-magnetic so the cubes do not respond to magnetic fields, with arrangements made to discharge any electrostatic charge that builds up so the cubes are immune to space weather and solar cosmic rays. The spacecraft will act as a shield to stop the solar wind from buffeting the cubes and disturbing their measurements of the much more subtle gravitational waves. The position of each cube is sensed and the spacecraft and its chamber are adjusted to maintain their position around the cube so that the cube is always in free-fall, able to respond solely to gravity. The separations of the cubes along the sides of the triangle will be measured by a laser interferometer system to an accuracy of 20 picometres (one-billionth of a millimetre – the diameter of an atom).
eLISA will detect gravitational waves as they pass through the solar system, causing the cubes to bob back and forth within their chambers. A test spacecraft launched in 2015, LISA Pathfinder, spectacularly proved that the technology proposed for eLISA works, so it is now being built and is scheduled for launch in the 2030s. It will become by far the largest scientific instrument ever made, almost on the scale of the solar system itself. It should be able to detect the Gravitational Wave Background from the inflationary period of the Big Bang. These gravitational waves are messengers from the Big Bang generated by random, independent events combining to create a cosmic gravitational wave background. The individual events are from dense volumes of Big Bang material that encounter each other or which oscillate. They produce random gravitational waves that make a continuous noise (much like radio ‘static’).
Cosmic inflation is a cosmological idea that, at first hearing, seems whacky. eLISA will tell us if cosmic inflation really means something. It will eventually show us what the start of everything was like, back in that first 10-32 of a second.
Quark-gluon plasma
When the temperature of the Big Bang material had reduced to some thousands of billions of degrees, the particles of which it was made had energies that are comparable to the highest energies reached in terrestrial particle accelerators, such as the Large Hadron Collider at the CERN laboratory in Geneva. The properties of fundamental particles established at places like CERN are properties that pertain to the earliest times in the Big Bang for which we have real evidence.
As described in Chapter 2, the Big Bang material right after cosmic inflation was made of a mixture of all the known fundamental particles, right down to the most fundamental particles currently known called quarks and gluons. These constituted the majority of particles at that time in a mixture known as a quark-gluon plasma. Quarks are the building blocks of protons and similar particles; gluons are the particles that carry the strong force that binds the quarks. The plasma also contained leptons, including electrons and muons and neutrinos, and the particles that carry the forces that act between these, including high-energy photons.
As the Universe aged to 1 millisecond, the plasma had cooled enough for triplets of quarks to bind together with gluons to make protons (two up-quarks and a down-quark) and neutrons (two downs and an up) and their antiparticles. Protons and neutrons are called baryons, so this is the time at which baryonic matter – our kind of matter – came into existence.
What about dark matter? Did it come into existence during inflation, before the hot Big Bang, or was it during the Big Bang itself, in parallel with baryonic matter? When cosmologists know what dark matter is, they might be in a better position to say.
The mixture included antiparticles as well as particles, produced in almost equal numbers. Antiparticles are complementary to particles. If a particle meets its antiparticle, they mutually annihilate – the particle falls into a metaphorical hole where it fits exactly. The result is empty space and energy, which radiates away. It is theoretically possible for antiparticle galaxies to exist that are indistinguishable from ordinary galaxies. They would contain anti-suns, anti-planets and alien anti-beings. It would be unsafe for us to shake hands if we encountered such a person – we would together result in mutually assured destruction.
The symmetry in the Big Bang between particles and antiparticles was not precise. For every billion antiquarks, there were a billion and one quarks, so when they all had touched and annihilated each other there was one quark left over, which is why the Universe consists of matter with no antimatter (except on a very local scale for a very short time after a very rare particle physics event of some energetic sort).
The Multiverse
In some versions of cosmological inflation developed by Linde, the Universe consists of separate pockets of exponentially large regions each with its own characteristic physics. The inhabitants of each pocket see themselves as living within an isolated region and think that it is the entire Universe, but there are unseen pockets all around. Such a system is called the Multiverse.
This concept provides an explanation for the anthropic principle, which tries to deal with the problem that the physics of the Universe seems fine-tuned in some ways so that it is possible for us to exist. The most startling example of the anthropic principle was discovered in 1952 by University of Cambridge astrophysicist Fred Hoyle (1915–2001) as a result of studying the ‘triple-alpha’ nuclear reaction as he searched for the reaction that powers red giant stars. Stars make carbon by combining two helium nuclei to make a beryllium nucleus and adding a third to make a carbon nucleus. Helium nuclei are also known as alpha particles, hence the term ‘triple-alpha’. The beryllium nucleus is unstable, so when triple-alpha was put forward as the process by which carbon was made in the Universe, it used to be thought that it would decay before the third alpha particle could combine with it. This would mean that carbon could not be made in stars, but this was evidently not so: carbon was not made in the Big Bang, it could be made only in stars, and it is the fourth-most common element in the Universe, made in abundance.
Hoyle realized that there must be a resonance (an enhanced interaction rate) in the second step of the triple-alpha process that helps the carbon to form before the beryllium disappears. In 1953, Hoyle travelled to the Kellogg Radiation Laboratory at Caltech to ask for help from researchers, including nuclear physicist William Fowler. He found it difficult to persuade the sceptical physicists to look for the resonance, but a relatively junior physicist, Ward Whaling, who had just moved to Caltech and was seeking a project, took up Hoyle’s suggestion and within a few months found the resonance. Fowler was so impressed by this result that he turned to investigate with Hoyle and the astronomers Margaret Burbidge and Geoffrey Burbidge how nuclear reactions in stars made all the elements (save hydrogen and helium). Fowler received the Nobel Prize in Physics in 1983 for this work.
The critical resonance that makes the manufacture of carbon in stars possible depends on a coincidence among energy levels in three separate nuclei: helium, beryllium and carbon. The coincidence is so precise that it looks as if the nuclear physics of the three nuclei has been arranged to make carbon abundantly. Since carbon is essential for life to exist, it seems the Universe has been made for our benefit. This is an anthropocentric (meaning ‘centred on humankind’) point of view, which in medieval times was thought to be literally true of the Universe as well as true metaphorically, with humankind the exclusive focus of God’s concern and the resources offered by Nature. Such views have lost much of their force since Copernicus revealed in 1543 that Earth is not the central focus of the orbits of the stars and planets (see page 37).
There are other scientific coincidences with an anthropic effect similar to triple-alpha that may have been organized by a powerful, beneficent being, who created the Universe for us. This is logically possible and is an argument that appeals to theologians because it provides a scientific context for the First Cause.
The First Cause is an argument for the existence of God, otherwise known as the cosmological argument. It originated in works by the Greek philosophers Aristotle and Plato, and in the West is associated mostly with the Italian Dominican friar and philosopher Saint Thomas Aquinas, who developed the Greek idea and discussed it in his theological writings. Aquinas argued that the Universe works as sequences of cause and effect: the Universe exists and someone or something must have caused this. The cause is God; the effect is the world. Aquinas inferred that there must have been a First Cause. Nothing caused the First Cause – and the First Cause is God.
The argument remains philosophically controversial and most physicists do not find the argument convincing. Everything else they study that seems to be fundamental appears, on closer examination, to have an explanation lying behind it. Physicists are human and fallible, so they do not apply this principle consistently: historically, they called the basic constituents of gases ‘atoms’ (see page 18) as the first causes of chemistry, before discovering the components of atomic structure like electrons and protons, which explained some of their otherwise inexplicable properties. Physicists repeated the same mistake when they began to talk about ‘fundamental’ particles, which have been discovered not to be fundamental at all, but are made up of quarks and gluons. The range of fundamental particles and the number of their properties has turned out to be enormous, with little in the way of elegant explanations. The Higgs boson elementary particle is one explanation that has been developed in order to explain why the fundamental particles have the otherwise inexplicable masses that they do. It lurks in the background as a ‘first cause’ of particle physics, although no doubt its property of ‘fundamental’ will be assailed.
It is always going to be possible in cosmology to ask the question ‘why?’, and an answer to the question ‘why did the Big Bang happen the way it did and create the Universe in the way it has been discovered to be?’ is that the Universe only seems to favour our existence because we would not be able to inspect the Universe if we were not here. This is a truism but it falls short as a satisfactory explanation of what seems to be a significant fact.
Somewhat more subtle is the Multiverse theory: it suggests that there are many universes (the Multiverse), each with a different set of physical constants and laws. Of the many universes, few have constants with the values required to make our life possible, and of course we live in one of these select few. According to this viewpoint, this is why there are such favourable coincidences – the Universe has to be this way, otherwise we would not be here to observe that this is what it is like.
The Multiverse can be linked to inflation. Andrei Linde’s theory of inflation proposes that, at the start of everything, quantum fluctuations cause tiny regions to expand rapidly and become isolated bubbles, one of which we inhabit as our Universe, living quarantined inside. This idea gives the possibility of the Multiverse a physical basis.
It is possible that there may be evidence on this topic in the image of the CMB. Inflation should impress a slight twisting pattern in the vibrations of the CMB’s radio waves called B-mode polarization. It is a subtle effect and even the most accurate currently available measurements of the CMB by the Planck satellite do not establish its existence. Equipment specifically designed to detect it has been set up in the Atacama Desert (the POLARBEAR experiment) and in Antarctica (the BICEP experiment), and elsewhere.
An intriguing direct hint that we live in a Multiverse is the existence of an anomalously large cold spot 10 degrees in size in the CMB in the constellation of Eridanus. Is it significant or is it a chance blob? Given the statistical properties of the size and temperature of the other smaller, less cold spots in the image, the probability that the Eridanus cold spot could come about by chance is 1 in 50. These odds mean that it is not impossible that it is a fluky result, but they are long odds and suggest that more study might be rewarding and find something interesting. What might that be?
A significant but speculative explanation for the cold spot is, perhaps, that it is a defect that was caused by one of Linde’s universes colliding with ours, like soap bubbles touching. This is a highly controversial explanation derived from a slightly less controversial theory, the Multiverse, and the unproven theory of cosmic inflation. The award of a Nobel Prize for the discovery of a second universe is probably not imminent.
The concept of the Multiverse might be attractive, yes, intriguing, yes – but it is speculative. However, the idea provides a possible escape route from the rather pessimistic conclusion of the last sentence of the previous chapter that our Universe ends in silent darkness. We can imagine another universe in the Multiverse that has the right physics, such that it is both open and populated with inhabitants. They might be able to be more upbeat about the far future of their universe than we are about ours.