This book introduces the basic concepts of particle cosmology and covers all the main aspects of the Big Bang Model (expansion of the Universe, Big Bang Nucleosynthesis, Cosmic Microwave Background, large scale structures) and the search for new physics (inflation, baryogenesis, dark matter, dark energy). It also includes the majority of recent discoveries, such as the precise determination of cosmological parameters using experiments like WMAP and Planck, the discovery of the Higgs boson at LHC, the non-discovery to date of supersymmetric particles, and the search for the imprint of gravitational waves on the CMB polarization by Planck and BICEP. This textbook is based on the authors’ courses on Cosmology, and aims at introducing Particle Cosmology to senior undergraduate and graduate students. It has been especially written to be accessible even for those students who do not have a strong background in General Relativity and quantum field theory. The content of this book is organized in an easy-to-use style and students will find it a helpful research guide. Cosimo Bambi is Professor at the Department of Physics of Fudan University. He received the PhD from Ferrara University (Italy) in 2007.
He was a postdoc at Wayne State University (Michigan), at IPMU at The University of Tokyo (Japan), in the group of Prof. Dvali at LMU Munich (Germany). He moved to Fudan University at the end of 2012 under the Thousand Young Talents Program. His research interests cover several areas in gravity, cosmology, and high energy astrophysics.
He has published over 80 research papers in refereed journals and 2 review papers.DOLGOV Alexandre Dmitrievich is a professor at Universita di Ferrara, Dipartimento di Fisica, Italy; ITEP, Moscow, Russia; and Novosibirsk State University, Novosibirsk, Russia. He got his PhD (Candidate of Science in Russia) in 1969. He won Lenin Komsomol Award in 1973, Landau-Weizmann Award for theoretical physics in1996, Pontecorvo Prize by JINR in 2009, Friedmann Prize by Russian Academy of sciences in 2011. His publications include more than 250 titles in English and Russian with an overall number of citations about 6500. Among them there are several review papers published in Reviews of Modern Physics, Physics Reports, Sov. Uspekhi, Surveys in High Energy Physics, and books 'Kosmologiya Rannei Vselennoi' ('Cosmology of the early Universe'), MGU Publishers, Moscow, 1988 and 'Basics of Modern Cosmology', Edition Frontier, Paris, 1990.2. Book Title Introduction to Particle Cosmology Book Subtitle The Standard Model of Cosmology and its Open Problems Authors.
Cosimo Bambi. Alexandre Dmitrievich Dolgov Series Title Copyright 2016 Publisher Springer-Verlag Berlin Heidelberg Copyright Holder Springer-Verlag Berlin Heidelberg eBook ISBN 978-3-662-48078-6 DOI 10.1007/978-3-662-48078-6 Hardcover ISBN 978-3-662-48077-9 Softcover ISBN 978-3-662-51587-7 Series ISSN 2198-7882 Edition Number 1 Number of Pages XI, 251 Number of Illustrations and Tables 9 b/w illustrations, 21 illustrations in colour Topics.
If we're going to start somewhere, we may as well start from the beginning. Let's rewind our clocks to what scientists believe is the earliest event in the history of our universe: the Big Bang. We'll see if we can wrap our heads around the beginning of time, and then we'll walk through some of the major events that have occurred in outer space since then. Most people have heard of the Big Bang since it is our best explanation for how the universe came to be the way we observe it to be today. The words 'Big Bang' are a bit misleading, because this event took place microscopically and may not have produced any sound.
Sound requires a medium, such as air, to travel through. But there was no medium around yet, so the event was probably silent. The name 'The Big Bang' actually came from an opponent of the Big Bang theory, Fred Hoyle, but it nevertheless stuck. So what was the Big Bang? Imagine everything in the universe condensed into one tiny point of matter and energy. This miniscule, dense object not only contained the energy and atoms of everything that will ever exist, it also contained both space and time themselves.
Scientists refer to this point as 'the Big Bang singularity'. It is a stretch of the imagination to try to picture this all-encompassing object, because our minds want to place it in some region of space at some particular instant in time. But space and time were born from this singularity with everything else in the universe. We cannot define the location of the singularity, for there was no space yet in which to place it.
We cannot speak of what happened before it came to be because there was no such thing as time yet. There was no concept of 'before'. Time began at the Big Bang, the beginning. For argument's sake, let's consider the possibility that the universe is infinitely old. If this were true, then an infinite number of events would have already occurred before we came into existence. Looking backward in time, we would see yesterday followed by the day before yesterday, and then the day before that, and then the day before that.
That means, if the universe were infinitely old, the present moment could never come to be. An infinite number of events would have to happen before it, which is impossible. Well, clearly, the present moment has been reached, as you are reading these words right now. Since the string of events in history was able to reach the present moment, then there had to be a beginning of time. The Big Bang is what set our universe's clock ticking. Keep in mind that I'm talking about space and time in our universe. Perhaps something unknown to us existed, and from that unknownness, our universe sprouted.
That very well may be the case, but we can't think of that unknownness in the same way that we think of space and time in our universe. Perhaps there was some other space and time outside of our space and time, or perhaps something very different from space and time existed and gave rise to the Big Bang. We really don't know. For our purposes here, we'll keep our discussion focused on space, time, matter, and energy in our universe.
Okay, so back to the Big Bang. The Big Bang theory cannot describe exactly what happened the instant that the Big Bang occurred, but it comes pretty darn close. Within the first super tiny fraction of a second (less than a trillionth of a trillionth of a trillionth of a second) the Big Bang singularity contained the same amount of matter and energy that we have today, but in a different form. Little is known about the state of matter this early in time.
We do know that the universe expanded incredibly quickly and cooled down in a period known as 'inflation'. The universe continues to expand today, but the expansion was much more rapid during inflation. At the end of this inflationary period, there were elementary particles, light, and energy. When I say 'elementary particles' I mean particles even smaller than atoms—particles that we can't break down into smaller pieces, as far as we know.
Additionally, some mysterious stuff that we call 'dark matter' may also have existed. We'll save a discussion of the elementary particles and dark matter for later chapters. All of these particles were moving at incredibly fast speeds in an incredibly hot environment. Some of the elementary particles came together to form protons and neutrons. Protons and neutrons are the particles that make up the nucleus of an atom. Different amounts of protons and neutrons will make up the nuclei of different atoms.
(Side note: the word 'nuclei' just means more than one nucleus.) The smallest nuclei are the nuclei of hydrogen and helium atoms. They only contain a few protons and neutrons. So, as the universe continued to expand and cool, protons and neutrons were able to combine to form the nuclei of helium atoms within the first 20 minutes. Meanwhile, electrons were still floating around freely.
It was not until about 379 000 years later that electrons began to orbit nuclei to form hydrogen and helium atoms—the first atoms of the universe (figure ). Figure 1.1. These are the common forms of hydrogen and helium atoms.
The purple circles represent protons, the yellow are neutrons, and the green are electrons. (Not drawn to scale.
Actually, you can assume all images will not be drawn to scale.) Download figure: Particles of light, called 'photons', continued to travel about on their own. These photons were traveling in the form of microwave radiation (we'll discuss the different forms that light can take in chapter ). They became what is known as 'the cosmic microwave background radiation'. This cosmic radiation is still detectable today.
In fact, it is one of the main pieces of evidence that supports the Big Bang theory for the history of the universe. Once hydrogen and helium atoms formed, the universe continued to expand and cool. By the time 200 million years had passed after the Big Bang, the temperature dropped significantly, and particles became less energetic. In dense regions the gravitational attraction of matter was able to bring hydrogen and helium atoms together into clumps.
These clumps of matter were distributed fairly uniformly throughout the universe. They were the beginning of galaxies like the Milky Way galaxy in which we live. Within the galaxies, matter in smaller dense regions continued to come together by gravitational attraction. The atoms became close enough together for nuclear fusion to take place. That's when nuclei of smaller atoms fused together into nuclei of larger atoms, releasing energy. These hot, energetic clumps of atoms were the first stars in the universe.
Inside the stars, hydrogen atoms continued to fuse into helium atoms, giving off light and heat in the process. Some of these stars fused all of their hydrogen into helium and then continued to fuse helium into heavier elements like carbon and oxygen.
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But in forming the heavier elements, not as much heat was given off. So pressure from the gravitational attraction inward began to overcome pressure from the thermonuclear heating pushing outward. In massive stars, this caused the core of the star to collapse. A massive star in this final stage implodes fantastically. The core collapses into a super dense object, and the exterior follows inward. Most of the star then bounces off of the dense core, flying out into the universe.
This explosion of a star is called a supernova. Supernovae release their heavier elements into the universe.
The heavier elements are then caught in the galaxies by gravitational attraction. Those elements form new bodies such as planets. Earth itself was made from elements that formed inside stars of the early universe. And about 8 billion years after the Big Bang, the Earth and several other planets in our Milky Way galaxy began orbiting the sun. Thus, our solar system was formed.
The elements which originated in stars caused life to form on Earth. The star that we orbit today (the sun) continues to provide the light and energy necessary for us to survive. So, quite literally, we owe our existence to the stars. And since the elements that make up our bodies came from stars, in a sense we are stardust.
While I have left out many of the details, this summary brings us up to speed with the birth and growth of the universe over the past 14 billion years or so. Figure summarizes these events. In the following chapters, we'll discuss how this amazing universe works, and we'll explore some of its most mysterious features. We'll unpack the forces that underlie all of nature. With an understanding of space, time, particles, and forces, we can get into Einstein's revolutionary theories of relativity as well as the mind-boggling nature of quantum mechanics.
We'll explore some interesting questions from a physical perspective, like whether it is possible to travel through time. And we'll discuss some of the most enlightening physical discoveries of today.