Consider the following hypothetical observations, some of which are real and some of which are fictional. For each observation, your job is to answer this question: If the observation were real, would it provide evidence for or against the idea that the universe is expanding? Sort each observation into the appropriate bin as follows:

A) Place an observation in the "Supports the expanding universe" bin if it would provide evidence that the universe is expanding.

B) Place an observation in the "Contradicts the expanding universe" bin if it would provide evidence that would force us to reconsider the idea of an expanding universe.

C) Place an observation in the "Neither supports nor contradicts" bin if it does not allow us to distinguish between a universe that is expanding and a universe that is not expanding.

A) Irregular galaxies outside the Local Group are moving towards us.

B) All galaxies in the Coma Cluster of galaxies have redshifted spectra

C) Galaxy speeds are faster in Summer than in Winter

D) The Andromeda Galaxy, a member of our Local Group, is moving towards us

E) The measured rate of expansion is the same in all directions

F) Galaxies 200 million light-years away move away from us twice as fast as galaxies 100 million light-years away

G) Spiral Galaxies move away from us 10% faster than elliptical galaxies at the same distances

Explanation:

The universe is expanding and has been continuously expanding since its formation billions of years ago. Because the universe does not have a center, everything is moving away from everything else through space.

Some of the statements in this question prove this while others contradict the observation of our universe expanding.

However, the Andromeda galaxy moving towards us neither supports nor contradicts this observation. The Andromeda galaxy is in our local group, a group bound together by gravitational force.

Supports the expanding universe

B) All galaxies in the Coma Cluster of galaxies have reshifted spectra

E) The measured rate of expansion is the same in all directions

F) Galaxies 200 million light-years away move away from us twice as fast as galaxies 100 million light-years away

Contradicts the expanding universe

A) Irregular galaxies outside the Local Group are moving towards us.

C) Galaxy speeds are faster in Summer than in Winter

G) Spiral Galaxies move away from us 10% faster than elliptical galaxies at the same distances

Neither supports nor contradicts

D) The Andromeda Galaxy, a member of our Local Group, is moving towards us