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 xp

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.

en p e

Particle Physics:The Particle Menagerie

Bosons

Graviton…spin = 2mass = 0charge = 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 & EnergyEnergy 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 1646 - 1716

Thomas Young 1773 - 1829

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 mv2

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

• 1st Law: you can’t win

• 2nd Law: you can’t get out of the game

• 3rd Law: you can’t break even

Result: you may win some in the short term but in the long run

YOU LOSE!