THE BEGINNING AND THE END OF EVERYTHING Dedicated to the memory of Professor Stephen W. Hawking (1942–2018) CONTENTS Timeline Introduction 1: Our Place in the Universe 2: The Theory Within the Theory 3: The Expanding Cosmos 4: Two Smoking Barrels 5: Most of Our Universe is Missing 6: A Quantum Interlude 7: Into Darkness 8: The Even Bigger Bang 9: The Birth of Galaxies 10: From Out of Nowhere 11: Worlds in Parallel 12: Crunch Time 13: The Long Dark Eternity 14: Into the Unknown Acknowledgements Index TIMELINE Time = 0: Big Bang The universe is brought into existence in a state of infinite density and temperature. Where just a split second earlier there was nothing, now mass, energy, space and time all spontaneously come into existence. No one knows what caused the Big Bang, or what existed before it. Time = one 10-million-billion-billion-billion-billionth of a second: Planck era The temperature is still 100,000 billion billion billion degrees. Space and time exist as hazy, indistinguishable entities, governed by the laws of quantum physics. Time = one hundred-thousand-billion-billion-billionth of a second: inflation The universe undergoes a rapid cosmic growth spurt, increasing in size exponentially fast, solving various cosmological problems and creating the seeds from which large-scale structures in the universe such as galaxies and clusters later grow. Time = one millionth of a second: Quark era The universe is a sea of quarks, the tiny particles that make up protons and neutrons. Time = 1 second: Hadron era As the temperature drops below around 1,000 billion degrees, quarks condense into protons and neutrons (known collectively as hadrons), the basic building blocks of atoms. Time = 10–1,000 seconds: synthesis of light atomic nuclei The temperature falls to a billion degrees, allowing protons and neutrons to stick together and begin forming the light chemical elements – hydrogen, helium and a small quantity of lithium. Time < 380,000 years: Radiation era Although atomic nuclei exists at this time, the universe is still awash with fiercely hot radiation that rips apart any atoms attempting to form. Time = 380,000 years: recombination The temperature drops down to around 3,700 degrees C, allowing electrons to finally combine with protons to create the first atoms. The universe is now dominated by matter rather than radiation. Time = 380,000–180 million years: Dark Ages The universe is dominated by matter, but none of it has formed stars or galaxies or anything else luminous. Time = 180 million–1 billion years: cosmic dawn The first stars begin to shine – an event known as the cosmic dawn, which brings the universe’s Dark Ages to an end. Time = 1 billion–10 billion years: structure formation Galaxies, clusters and superclusters all begin to take shape from around 1 billion years after the Big Bang. Galaxies gather into clusters, and clusters gather into superclusters. Time = 9.2 billion years: birth of the solar system A cloud of hydrogen, helium and a few heavier elements circling around the Milky Way galaxy begin to collapse under its own gravity. The core of the cloud becomes a hot, young star, while around it a disc of material condenses and fragments into a mix of rocky, gaseous and icy bodies. This is the birth of our solar system. Time = 13.8 billion years: present day Today, the universe is in the stelliferous era – the age of the stars. Astronomers expect the stelliferous era to last until the universe is 100,000 billion years old, after which the formation of new stars will cease. By this time the sun will be long dead. Time > 100,000 billion years: far future Beyond 100,000 billion years, the behaviour of the universe is a largely unknown quantity. Although there are a number of theoretical possibilities for how the universe might continue to evolve – and how it will ultimately end its days.
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