Cuesta College, San Luis Obispo, CA
[20 points.] An astronomy question on an online discussion board[*] was asked and answered:
sai: We know that [the] big bang created everything we know today, but if it formed the universe where did the big bang take place?!Discuss why this answer is correct, and how you know this. Explain using observations and evidence related to the Hubble law.
Dude: Right where [you] are standing.
Solution and grading rubric:
- p = 20/20:
Correct. Understands that (a) Hubble's law is that the recession velocity of galaxies is proportional to distance (greater redshift of absorption lines for distant galaxies compared to nearby galaxies), corresponding to the expansion of space between galaxies, and (b) extrapolating time backwards means that the distance between everything was zero, thus any location can be said to be where the big bang took place (or may instead argue for no unique center of expansion for expanding-space-between-galaxies universe).
- r = 16/20:
Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of the two points (a)-(b) is correct, other is problematic.
- t = 12/20:
Contains right ideas, but discussion is unclear/incomplete or contains major errors. Only one of the two points (a)-(b) correct, other is missing, or both are problematic.
- v = 8/20:
Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion based on evidence of the earlier stages in the history of the universe, with little or no substantive discussion of Hubble's law, such as everything was created by the big bang, therefore everything can be said to be where the big bang took place.
- 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:
Exam code: midterm02s3Ar
p: 4 students
r: 11 students
t: 9 students
v: 7 students
x: 3 students
y: 0 students
z: 0 students
Exam code: midterm02n1cT
p: 7 students
r: 7 students
t: 7 students
v: 4 students
x: 2 students
y: 1 student
z: 0 students
A sample "p" response (from student 1027):
A sample "v" response (from student 1177):
Another sample "v" response (from student 8436), still showing the astronomy love: