Astronomy quiz question: observing the early universe

Astronomy 210 Quiz 6, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

[4.0 points.] What makes it possible to observe the very early universe, just after the start of the big bang?
(A) Dark energy.
(B) Curvature of space-time in the universe.
(C) Doppler effect.
(D) Finite speed of light.

Section 70160
(A) : 0 students
(B) : 6 students
(C) : 5 students
(D) : 10 students

Correct answer: (C)

The finite speed of light means that it takes time for light from distant objects to reach the Earth. Thus looking at an object a given number of light years away means that it appears as it did that same number of years in the past. This is used to great advantage when observing extremely distant objects nearly as far out in light years as the universe is old.

Apparently students successfully discriminated against the dark energy distractor.

"Difficulty level": 65% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.40