Cosmology Lecture 10

The paragraph discusses the comprehensive theory of elementary particles, which includes numerous parameters ranging from 25 to 150. These parameters encompass various fundamental quantities such as the masses of quarks and electrons, coupling constants, and the electric charge of particles. The theory also enumerates the different particles and their mathematical relationships, with some particles being more closely related than others. The speaker highlights the importance of understanding these parameters to explain phenomena from nuclear physics to chemistry, given infinite computing power.

This section delves into the fundamental constants of physics, such as the speed of light, Planck's constant, and Newton's constant. These constants are universal and apply to all forms of matter and energy. The speaker explains the concept of Planck units, which are derived from these constants, allowing for the creation of a system of units based on fundamental physical quantities. The paragraph also touches on the significance of these constants in understanding the deep and universal laws of physics.

The speaker performs dimensional analysis to determine the units of various physical quantities, including the speed of light, Planck's constant, and Newton's constant. By combining these constants, a fundamental unit of length, time, and mass can be derived, leading to the concept of the Planck length. The Planck length is calculated to be extremely small at 10^-35 meters, indicating a fundamental scale at which the laws of physics operate.

Building on the concept of the Planck length, the speaker calculates the Planck time, which is the time it takes light to traverse the Planck length. This leads to a discussion about the early universe and how the microwave background radiation observed today is a remnant from a time when the universe transitioned from being opaque to transparent. The paragraph connects these fundamental units of time and length to the observable universe and its formation.

The speaker introduces the concept of the Planck mass, which is derived from the Planck length and time. By using the mass-energy equivalence principle (E=mc^2), the Planck mass is calculated, and its significance is discussed in terms of the energy that would be released if it were fully converted into energy. This energy is likened to the energy content of a tank of gasoline, providing a relatable comparison for the听众.

This paragraph explores the vastness of the universe and the scale at which the Large Hadron Collider (LHC) operates compared to the Planck scale. The speaker emphasizes the vast difference in scales and the unknowns that exist between them. It highlights the complexity of particles studied at the LHC and the many parameters needed to describe them within the standard model of particle physics.

The speaker discusses the Higgs boson, its mass, and the fine-tuning required within the standard model to explain its observed properties. Supersymmetry is mentioned as a potential explanation for the Higgs boson's mass, although it is noted that the simplest supersymmetric models tend to predict a mass that is lighter than what is observed. The paragraph touches on the challenges in understanding why the Higgs boson has the mass it does and the implications for physics beyond the standard model.

The speaker describes the WMAP, which created a map of the cosmic microwave background radiation. This map shows the temperature fluctuations in the early universe, which are believed to be the seeds of the large-scale structures like galaxies and clusters of galaxies. The paragraph explains the importance of these fluctuations in understanding the formation and evolution of the universe.

The paragraph discusses the theory that the observed fluctuations in the cosmic microwave background radiation originated from quantum fluctuations in the early universe. The speaker explains the concept of a damped harmonic oscillator and how it relates to the scalar field in the expanding universe. The quantum fluctuations are proposed to have been stretched across the sky, leading to the structure we observe today.

The speaker uses the example of a damped harmonic oscillator with a time-dependent restoring force to illustrate the behavior of the inflaton field during cosmic inflation. As the universe expands, the restoring force diminishes, causing the field to oscillate and eventually settle at a non-zero value. This process is connected to the quantum fluctuations that lead to the observed anisotropies in the cosmic microwave background radiation.

This paragraph focuses on the concept of the horizon size during inflation and how it relates to the freezing of waves. As the universe expands, waves with different wavelengths freeze at different times, depending on when they reach the horizon size. The speaker explains that shorter wavelengths freeze later, leading to a complex pattern of frozen waves that contribute to the structure of the universe.

The speaker describes the end of inflation as the universe transitions from exponential expansion to a slower rate. The energy density of the universe dilutes, and the field values at different points in space begin to deviate due to quantum fluctuations. This leads to the formation of 'blobs' or regions with higher energy density, which are the seeds for the formation of large-scale structures like galaxies. The paragraph connects the quantum fluctuations during inflation to the observed structure in the universe.

The final paragraph addresses the concept of cosmic variance, which refers to the fact that we can only observe one instance of the large-scale structure of the universe. The speaker cautions against drawing strong conclusions from a single observation and emphasizes the importance of scientific literature over sensationalized press reports. The uniqueness of our universe is highlighted, as we cannot repeat the experiment of observing the universe's formation and evolution.