Astronomy midterm question: no-center universe expansion

Astronomy 210 Midterm 2, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

[20 points.] Discuss why the expansion for the universe has no center, using observations and evidence related to the Hubble law in your explanation.

Solution and grading rubric:

• p = 20/20:
  Correct. Argument involves redshifts (and thus recession velocities) being proportional to distances (i.e., Hubble's law), and how this implies that there is no unique center, any other galaxy would observe a similar Hubble's law. May also invoke no-edge, no-center argument of an non-finite universe.
  
• r = 16/20:
  Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.
  
• t = 12/20:
  Contains right ideas, but discussion is unclear/incomplete or contains major errors.
• v = 8/20:
  Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.
  
• x = 4/20:
  Implementation/application of ideas, but credit given for effort rather than merit.
  
• y = 2/20:
  Irrelevant discussion/effectively blank.
  
• z = 0/20:
  Blank.
  

Grading distribution:
Section 70160
p: 23 students
r: 3 students
t: 2 students
v: 2 students
x: 0 students
y: 0 students
z: 0 students

A sample "p" response, discussing Hubble's law (from student 1225):

Another "p" response, discussing "Cosmic Haterade" (from student 7120):