Lecture.3

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Lecture # 3 Origin of the Universe
ORIGIN OF THE UNIVERSE • The Big Bang scenario for the beginning of the Universe • The Singularity • The Earliest Time in the History of our Universe • The Planck Epoch • Grand Unification Epoch • Inflation • Different times in the early history of the Universe • The time the Universe was 10 seconds old • Origin of Mass
Using powerful telescopes today, we find that the Universe is “ aging ” and evolving from a point 13.8 billion years ago. Extrapolating the present observations back in time, astronomers concluded that the Universe started from a dense and hot state, called the Big Bang. By observing the most distant galaxies, one could see what the Universe was like about 1 billion year after the Big Bang. Galaxies beyond that are too faint to be seen as yet
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THE BIG BANG • The Universe is becoming cooler and less dense as it expands. • This means that the Universe started from a point of extreme density and heat. • During the hot phase of the history of the Universe, the photons could transfer themselves to matter and vice-versa • The early Universe was filled with photons, matter, anti-matter, converting from one type to the other
Seeing back into the cosmos alma sirtf galex
Evidence for the Big Bang • Expansion of the Universe and the fact that the velocities of galaxies increase proportional to their distances from us • Presence of the Cosmic Microwave Background (CMB) radiation • Light element abundance- the fact that the abundance of light elements (hydrogen and helium) from the Big Bang model agrees with the measured abundance
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“It is far better to grasp the universe as it really is than to persist in delusion, however satisfying and reassuring.” “We are the representatives of the cosmos; we are an example of what hydrogen atoms can do, given 15 billion years of cosmic evolution.” Carl Sagan
HISTORY OF THE UNIVERSE • The Big Bang theory explains how the Universe grew from intense heat and extreme density to what we see today- with galaxies and clusters of galaxies. • In the following slides we go through the history of the Universe by dividing it into different eras and time intervals • We use known laws of physics and present observations to push our knowledge of the Universe back in time
Singularity Right at the time of the Big Bang, the density of the Universe was infinite – all the mass in the Universe was concentrated in a very small volume. At that time, there were no distinction between space and time. This is called singularity . Given the concentration of matter and hence, the huge gravity produced, and the small volume the matter was concentrated, quantum properties of matter become important. To explain the Universe at this very early times, needs a marriage of the theory of the very small (quantum theory) and the theory of gravity (General Relativity)- Quantum theory for Gravity. We have no information about the Universe at that time.
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The Planck Epoch 0 < t < 10 -43 sec • This is the earliest epoch in the history of the Universe – the Planck time. • To study the Universe before this time requires the theory of Quantum Gravity. After this time, one could apply present laws of physics to study the state and the evolution of the Universe. • At the Planck time, the size of the Universe was a Planck length – 1.6 x 10 -35 meters • All the forces in the Universe at this time were united in one grand force. • Energy fluctuations generate a rapidly changing gravitational field which, would wrap the space and time
A Timeline of the Universe
“I have not failed. I've just found 10,000 ways that won't work.” Thomas Eddison
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FORCES IN NATURE ü There are a total of four forces in nature: Gravity, Electromagnetism, Weak and Strong ü Gravity holds planets and stars together and is effective at large distances ü Electromagnetism is much stronger than gravity and depends on the electric charge of a particle instead of its mass ü The strong and weak forces operate over extremely short distances of the atomic size. The strong force binds atom nucleus together. The weak force is responsible for nuclear reactions- fission and fusion
ERA OF THE GRAND UNIFIED THEORIES (GUT) 10 -43 < t 10 -36 sec ü At high temperatures of the early Universe (10 27 K), the four forces were united into one Grand Force ü Gravity was separated from the other three forces at the end of the Planck era when the temperature of the Universe reduced. ü The Grand Unification was ended when the strong force was separated from the electromagnetic and weak forces (electroweak) at a temperature of 10 27 K and at 10 -36 seconds after the Big Bang ü Under very high temperature and energy, electromagnetic and weak forces form a single force, electroweak. ü This is the force which dominated the Universe during the Planck era. Therefore, the 10 -43 seconds after the Big Bang was the time which gravity was separated from other forces ü These forces were mediated by virtual particles (lecture # 2). To generate these condition to see these particles today, needs huge amount of energy.
Unification of Forces
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Creating conditions at a time soon after the Big Bang- Accelerators
“I've missed more than 9000 shots in my career. I've lost almost 300 games. 26 times, I've been trusted to take the game winning shot and missed. I've failed over and over and over again in my life. And that is why I succeed.” Michael Jordan
The Epoch of Inflation • Modern technology allows us to test theories back to a time 10 -33 seconds after the Big Bang. • Physics as we know it ceases to function at 10 -43 seconds after the BB, called the Plank Time. • Using particle colliders, scientists have uncovered a number of clues about what happened in the early universe, after the Plank time. • The early universe underwent a period of very rapid expansion. • By 10 -33 seconds, the universe expanded from the size of a proton to the size of a basketball. • This expansion is called inflation. Insert figure 81.5
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Problems Solved by Inflation The rapid acceleration generated during the inflation offers an explanation of how the Big Bang might have been launched. Horizon Problem: why Microwave Background Radiation is uniform throughout the Universe? The regions outside each others cosmic horizon are disconnected and hence, there is no reason they should have the same temperature. In the inflation scenario, our present Universe once had a size a fraction of a proton. Therefore, at the beginning, the light travelled many millions of times across what became our observable Universe. This allowed the temperature to even out and become uniform across the Universe. Flatness Problem: Observations show that the Universe has zero curvature- being almost precisely flat. The inflation removes any curvature the space may have had by inflating the Universe so rapidly, it flattens the Space.
Inflationary Universe • Inflationary scenario proposes a phase of accelerated expansion for the Universe at about 10 -35 sec after the Big Bang. • During the inflation, the size of the Universe increased by 10 26 times and its temperature dropped by a factor of 10 5 during a very short time. • After the inflation the rate of the expansion reduced and the Universe continued to expand to the present time. • Because of the inflation the parts of the Universe that were in contact with each other before the inflation were expanded away after that, solving the horizon problem. Also, any structure at the early Universe was smoothed away after the inflation, solving the flatness problem.
Distribution of the Temperature in the Cosmic Background Radiation
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The Flatness Problem solved by rapid expansion of the Universe
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Likely Cause of the Inflation The inflation is likely caused by a negative vacuum energy density or positive vacuum pressure as a result of the separation of strong force from other forces. This left the Universe with much more energy than it could have and hence, a rapid outward force, producing a large number of particles in a very short time. The inflation era lasted from 10 -36 seconds after the Big Bang to sometime between 10 -33 and 10 -32 seconds. Following the inflationary period, the Universe continues to expand but at a less accelerated rate
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“Everything you'll ever need to know is within you; the secrets of the universe are imprinted on the cells of your body.” Dan Millman
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THE ELECTROWEAK ERA 10 -32 < t < 10 -12 sec ü The name comes from the unification of electromagnetism and weak forces ü At 10 -32 sec after the Big Bang, the potential energy that had driven the inflation was released, reheating the Universe. ü This energy is responsible for the creation of many particles including Gluon+Quark mix that filled the Universe at the time. ü The temperature of the Universe at this epoch was 10 15 K, enough to unify electromagnetism and weak forces. At this point W and Z particles and Higgs bosons were mediating the forces. The age of the Universe was 10 -10 sec. ü Once the Universe further expanded and cooled, production of W and Z particles were halted with those remaining particles decayed ü At this point the particles did not yet have mass. ü After this time, the four forces became distinct as they have been ever since.
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History of the Universe
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“Only two things are infinite, the universe and human stupidity, and I'm not sure about the former.” Albert Einstein
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Quark + Gluon Epoch 10 -12 < t < 10 -6 sec • At 10 -12 sec, the four forces in the Universe were separated • The temperature of the Universe was still high enough to forbid quarks combining to form protons and neutrons • This epoch came to an end at 10 -6 sec when the energy in the Universe fell below what was needed to bind protons and neutrons • Quarks came together when the Universe was 10 -6 sec old and hence, seized to be found as free particles.
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A Timeline of the Universe
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“Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality.” Nikola Tesla
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Proton+Neutron (HADRON) Epoch 10 -6 < t < 1 sec • At this epoch, the Quark+Gluon soup dominated the Universe. As the Universe expanded, the distance between quarks increased- so did the elastic force between them due to the gluons. • When the distance between two quarks reached 10 -15 meters, the gluon force between them broke, producing two new quarks- one at each end of the break. • As the Universe expanded, its energy reduced to a level that was no longer enough to break the gluon bond between the quarks. The temperature at this point was 10 10 K. • Each quark at this point was tied to its neighbor, generating hadrons and anti-hadrons. The temperature of the Universe was still high enough to continuously generate hadrons and anti-hadrons • As the temperature became cooler, their production stopped and the existing hadron/anti-hadron collided, leaving a small fraction of the hadrons at 1 sec after the Big Bang. The protons and neutrons were created at this epoch
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Lepton Epoch 1 < t < 10 sec • At the end of the hadron epoch, the energy density of the Universe became lower that could no longer produce hadrons. Instead, the remaining energy created lighter particles- leptons (electrons, neutrinos) and anti-leptons (anti-electron (positron) and anti-neutrino). • Electrons and positrons collide and produce photons. In turn, photons collide and produce electron-positron pairs. • When the temperature drops to 10 10 K, photons could no longer produce electron-positron pairs while they continue to collide • The remaining electron and positrons were then attracted to protons to produce atoms.
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“Two roads diverged in a wood and I - I took the one less traveled by, and that has made all the difference.” Robert Frost
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Radiation, Matter and Antimatter • In the first second of the early universe, matter did not really exist; rather, everything was radiation or energy . Cosmologists call this time period the early universe . • When energy is converted into matter, antimatter is formed as well. • For a proton-antiproton pair to form, the temperature must be more than 10 13 K. • Matter and antimatter annihilate on contact, releasing energy. • There must have been an asymmetry in the amount of matter and antimatter formed in order for there to be a predominance of ordinary matter today.
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Origin of Particles
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The Origin of Mass • Every particle passes through a field called “Higgs” field that is present in the entire Universe. • The Higgs fields are associated with a particle called Higgs bosons that it uses to interact with other particles • Particles interact with the Higgs field via the exchange of Higgs bosons. This gives particles their mass. Stronger they interact, more massive they are. Particles that do not interact with the Higgs field, are massless and move with the speed of light. • According to the law of conservation of energy, mass is not created but given to particles via its interaction with Higgs particles. When the mass is given to a particle, its speed is slowed down.
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History of the Universe
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“Philosophy is written in this grand book, the universe, which stands continually open to our gaze. But the book cannot be understood unless one first learns to comprehend the language and read the letters in which it is composed.” Galileo Galilei
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