Cosmology 2
The Particle Physics Connection

Elementary Particles . . . a very brief look

• To understand many of the modern ideas of the origin of the Universe, we must briefly examine
  
  
  
  
  
• This completes our look at the structure of matter that we began when we talked about the atom and then, later, the nucleus. (We will look briefly at the molecule in our final lecture.)
  
  
• Although not complete, physicist today believe that everything in the Universe is composed of two types of particles which interact through four fundamental forces; this has become known as:
  
  
  
  

  Elementary Particles Quarks (6 flavors): Leptons (6 flavors):

  Composite Particles

  
  
  
• Four Forces govern the interactions among the elementary particles:
  
  

  The Strong Nuclear Force binds quarks of different color charge together to form protons & neutrons binds protons and neutrons together to form nuclei strong (set strength = _____), but short range quantum carrier: gluons	The Electromagnetic Force binds electrons & nuclei together to form atoms binds atoms together to form molecules strength = _____; infinite range quantum carrier: photon
  The Weak Nuclear Force responsible for radioactive decay (turns one quark into another) affects all particles with flavor strength = _____; short range quantum carrier: W and Z bosons	The Gravitational Force attractive force for all matter and energy strength = _____; infinite range quantum carrier: graviton (?)

  
  
  
• For a more complete summary of the Standard Model, visit the Contemporary Physics Education Project page at http://particleadventure.org/particleadventure/frameless/chart.html
  
  
• Unification of the Four Forces:
  
  
  
  
  
  
  
  
  • Gravity
    
    
    
  • Strong Nuclear
    
    
    
  • Weak Nuclear
    
    
    
  • Electromagnetic
  
  
  
  
  
  
  
• Where in the Universe would such high temperatures exist?
  
  
  

Milestones in the Big Bang

• After the Big Bang, the Universe expanded and cooled. As the temperature dropped, several important milestones were reached according to how we understand elementary particles and the four forces:
  
  
  
  
  
  
  
  
  
  
  
• What is the significance of the Planck Time?
  
  
  
  
  
  
• What is Cosmological Inflation?
  
  
  
  
  
  
  
  
• What problems does it solve?
  
  
  
  
  
  
  
  
  
• What problems does it present?
  
  
  
  
  
  
  
  
  

Evidence for and Predictions of The Big Bang Model

1. The Expansion of the Universe:
   
   
   
   
   
2. The Cosmic Abundance of Deuterium and Helium:
   
   
   • Prediction:
     
     A few minutes after the Big Bang, the Universe had cooled to
     
     
     
     
     
     But,
     
     
     
     
     
     All that could be made was:
     
     
     
     
     
     
   • Observation:
     
     What do we observe in the Universe today?
     
     
     
     
     
     
3. Cosmic Background Radiation
   
   
   • Prediction:
     
     After about one million years after the Big Bang,
     
     
     
     
     
     Now, photons,
     
     
     
     
     
     Today, these photons are still here, but, due to the expansion of the Universe,
     
     
     
     
     
     
   • Observations:
     
     
     
     
     
     

The Fate of the Universe

• What is the fate of the entire Universe? Will it continue to expand forever? Or will the expansion slow down, stop, and reverse in a backwards big bang . . . or "Big Crunch"?
  
  
• The only thing that we know of that will stop the expansion is
  
  
  
  
  
  
• What determines if gravity is strong enough to stop the expansion?
  
  
  
  
  
  
• The amount of mass in the Universe is given by the average density of matter. The average density of matter required to stop the expansion is known as:
  
  
  
  
  
  
• Calculations show that the fate of the Universe is determined by the average density of matter; this also determines the overall geometry of the Universe (which is another way of saying the same thing):
  
  
  
  
  
  
  
• Can we measure the density of matter in the Universe?
  
  
  
  
  
  
• But what about Dark Matter?
  
  
  
  
  
  
• But what about Inflation?
  
  
  
  
  
  
• What about the newly observed acceleration of the expansion?
  
  
  
  
• Conclusions: