Announcements Exam 2 is next time (March 4). Will cover Chapters 1 – 3 and Chapter 4 through page 98 (up to but not including Waves) of Foundations of Modern Cosmology. Sample Questions are posted Project topics are due before spring break (March 6). Decide on a topic and come talk to me about it. The topic can be anything of current cosmological interest. A two or three sentence “abstract” will be due next time (worth 5% of the project grade).

The Universe according to Quantum Mechanics You can’t tell precisely where anything is. You can’t tell precisely how fast anything is moving. Particles act like waves. Waves act like particles. Particles can pass through “solid walls” A very non-deterministic universe completely contrary to Newton’s mechanical universe

According to the Bohr model you cannot tell where the electron is, only what its energy is. Heisenberg's Uncertainty Principle says

The Bohr Energy Level Diagram Electron energy is quantized

When an electron changes energy level it radiates or absorbs a photon of light

Ionization If an incoming photon has enough energy it can completely knock the electron out of the atom

Isotopes have the same atomic number but different mass number

Radioactive Decay by Alpha Particle emission

Radioactive decay by Beta particle emission

Nuclear Fission splits large nuclei

Nuclear fusion combines small nuclei

What are protons and neutrons made of? If they can decay into something else, they must be made of something smaller.

Particle Physics: The Particle Menagerie

Bosons Graviton…spin = 2 mass = 0 charge = 0

Fermions

The fundamental particles combine to make baryons

Mesons are made of two quarks

The Four Fundamental Forces: The Strong Nuclear Force The best thing we have to describe the strong nuclear force is called quantum chromodynamics or QCD

The Electromagnetic Force

The Weak Nuclear Force Alpha Decay Beta Decay

The Gravitational Force which best describes gravity is Einstein’s General Relativity. We will go into GR in much more detail later Newton’s Universal Gravitation works well for most situations but the theory

Work & Energy Energy is a relatively new concepts. Gottfried Leibniz first proposed something similar to kinetic energy in the late 1600’s. Thomas Young was the first to use “energy” in the modern sense in 1807 Gottfried Leibniz Thomas Young

Physical Work: the application of a force over a distance

Potential Energy: the ability to do work Each of the four fundamental forces has a potential energy associated with it. The one we see the most is gravitational potential energy. The electromagnetic potential is the foundation of chemistry (and circuits). Nuclear potential is important in the interiors of stars and the early universe.

Kinetic Energy: energy of motion Anything that moves and has mass has kinetic energy: ½ mv 2

Conservation of Energy Energy can never be created or destroyed. Only its form can be changed

Thermodynamics

The Zeroth Law of Thermodynamics Thermodynamic Equilibrium means there is no net heat flow from one object to another

First Law of Thermodynamics Basically a statement of the Conservation of Energy

Second Law of Thermodynamics Any system which moves heat from a cool temperature to a warmer temperature must have some energy input. Any system which does work by removing heat from a heat source must exhaust some heat

Third Law of Thermodynamics You can’t get there from here! It is impossible to achieve a temperature of absolute zero

The Laws of Thermodynamics Zeroth Law: there is a game called thermodynamics and you’re in it 1 st Law: you can’t win 2 nd Law: you can’t get out of the game 3 rd Law: you can’t break even Result: you may win some in the short term but in the long run YOU LOSE!