Question

Listed following are four models for the long-term expansion (and possible contraction) of the universe. Rank the models from left to right based on their predictions for the average distance between galaxies five billion years from now, from smallest to largest.

Answer 1

Smallest distance to largest distance:

1. recollapsing universe

4. critical universe

3. coasting universe

2. accelerating universe

Step-by-step explanation:

At a certain point in time, the average distance between galaxies depends on the rate of expansion: the quicker the expansion, the greater the distance.

Furthermore, the recollapsing universe has the smallest average distance among galaxies, as its rate of expansion by nature is decreasing enough so that the expansion will stop altogether eventually.

The critical universe has the closest expansion rate followed by the coasting universe.

In an accelerating universe, the rate of expansion grows greater with time, and that's why this model suggests the future largest distance between galaxies.