The look-back time is
A) the time it takes for the light from an object to reach Earth.
B) numerically equal to the distance in light-years.
C) smaller for more distant objects.
D) all of the above.
E) a and b above.

Question

Quizplus · Accepted Answer

The look-back time is the time it takes for the light from an object to reach Earth, therefore option A is correct. It is also numerically equal to the distance in light-years, hence option B is also correct. As the speed of light is constant in the vacuum of space and the distance between Earth and the object determines the look-back time, the look-back time is smaller for more distant objects, making option C true. Therefore, options A, B, and C are correct, making option D correct as well. Thus, the best choice is E - a and b above.

The Look-Back Time Is