Astronomy quiz question: Hubble's law

Astronomy 10 Quiz 12, Spring Semester 2008
Cuesta College, San Luis Obispo, CA

Astronomy 10 learning goal Q12.2

[3.0 points.] Which one of the following statements best describes Hubble's law?
(A) Distant galaxies recede faster than nearby galaxies.
(B) Spacetime becomes more flat over time.
(C) Expansion must be followed by an equal and opposite contraction.
(D) There are equal amounts of dark matter and dark energy in the universe.
(E) The distances to other galaxies are farther away than expected.

Correct answer: (A)

Hubble's law correlates the recession speeds (v) of galaxies to their distances (d) from the Earth, where:

v = H*d.

Response (B) is related to the flatness problem of the cosmic background radiation, which is solved by the inflationary era. Response (C) is a mangled (but apparently convincing) version of Newton's third law: "For every action there must be an equal and opposite reaction." Response (E) is evidence (from type Ia supernovae) that the expansion of the universe is relatively recent.

Student responses
Section 5166
(A) : 36 students
(B) : 1 student
(C) : 6 students
(D) : 4 students
(E) : 2 students

Universe expansion movie

Continued Consistent Expansion (*.mov, 3.7 MB)
Hubblesite.org

Astronomy 10 learning goal Q12.2

This movie is not just a zoom-in shot! Note that as the universe expands, the distances between galaxies increases, while the size of the galaxies remains constant (due to gravitational interactions). This can be illustrated during the movie by covering one of the galaxies with the mouse cursor, and showing that that the size of the galaxy does not change relative to the cursor.