From The Big Bang to Galaxies

[STUDENT SOLUTIONS TO THESE PROBLEMS]
TOPICS   |  PARTICLES
 

If you have REDSHIFT software select 'Guided Tours' and then 'From Big Bang to Galaxies'. This is a simple look at the role of elementary particles , radiation and forces in the accepted model of the evolving universe.This animation and the book 'The First Three Minutes' by Stephen Weinberg should be sufficient for you to carry out the exercises presented here.
 
 

Q1) Assuming the validity of a 'Universal time' , how long ago did the expansion of the universe begin ?
 
 

Q2) After what length of time did the first elementary particles form ? What were they ? What force would have been dominant here ?
 
 

Q3) As the temperature fell, which matter particles were created after 0.1ms ? What process is this an example of : p + p -> 2g ?

Q4) A useful 'rule of thumb' from statistical mechanics is that characteristic photon energies are given by E = kT where k is Boltzmann's constant and T is the absolute temperature.There is a 'Threshold Temperature' for each type of material particle which must be reached before particles of this type may be created out of pure radiant energy.
 
 

(i) Show that Boltzmann's constant is 8.617 x10-5 eVK-1

(ii) Show that the rest energy of an electron (or positron) is 0.5113 MeV . Now show that the 'Threshold Temperature' at which an e+ / e- pair could be produced from two photons is about 6 x 109 K ( 6 Billion degrees)

(iii) Using data from the data page , verify that the threshold temperatures for the elementary particles in this table are correct:(Source S.Weinberg -The First Three Minutes)
.




(iv) Comment on the relevance of these simple calculations on the population of the very early universe.


Q5)If the universe in the first few minutes was really composed of equal numbers of particles and antiparticles, what would have happened as the universe cooled below say 1 billion degrees ? Has this happened ? So what can you conclude ?

Q6) Comment fully on the graph below which refers to the 'Radiation Dominated Era' of the universe.
 


Q7) At 0.1 milliseconds why is the universe energy dominated ?
 
 

Q8) After 3 minutes what elements formed ? How ?
 


Q9)As the universe continued to expand for 300,000 years, what did the temperature fall to ? What process could now occur ? What fundamental force has now become important ?
 
 

Q10) What caused the first 'structure ' in the early universe ? Which satellite detected the traces of this in the early 1990's ? In what region of the EM spectrum does this lie ? What temperature has the ' Universal Background' cooled to ? Sketch a ' Black-Bodyradiation curve' for this.
 
 

Q11) After how long did galaxies start to form ?
What fundamental force has now become important ?
 
 

Q12) What happened to allow elements heavier than helium to form ? What process must operate ?
 
 

Q13) What happens if matter and antimatter meet ? Suggest why some people think that some galaxies could be made of antimatter . (See also Q5)

Hopefully from running the REDSHIFT animated software and answering these questions you will now see how intimately the study of elementary particles and cosmology are connected. By developing theories of how elementary particles behave, testing their consequences with very high energy particle accelerators and the study of cosmic 'rays', physicists strive to understand the history of the universe.The very high energy events pictured below have been recreated in the 1980s in particle accelerators but prior to this could only have occurred in the early stages of the universe.
 



BACK TO THE TOP