Homework 2: The "Hubble tension"
This homework must be submitted on paper;
you may write out your work on paper,
or type it into some word processor and then print it.
Either way, staple together all pages and write your name
legibly at the top of each page.
This assignment looks at the history of the Hubble constant
(H0),
which relates the distance between objects in the universe
and the velocity with which they move away from each other.
You've seen Hubble's original paper describing his discovery
of the relationship in 1929.
Since then, there have been several phases in which
different astronomers have, um, disagreed about the value
of H0.
Please locate a recent paper describing this history,
and scan portions of it to answer the following questions.
We'll go over the paper, and the controversy,
in our next class meeting.
- Find a recent paper, published in 2026,
by authors Cai and Wang, which features the phrase
"Hubble tension" in its title.
- In what journal was this published?
- What are the volume number and page number for this paper
in that journal?
- Read the "Introduction" section of the paper
(you can skip the long paragraph starting with
"Hubble resolutions" -- it's mostly a long list
of references) and answer the following questions.
- How many "Hubble tension" controversies have there been
over the years?
- One of these fights was settled by measurements made by the
Hubble Space Telescope. What were the extreme values
of H0 in question at that time?
- How did those extreme values compare to the value determined
by Hubble himself in 1929?
- What are the extreme values in the most recent "Hubble tension?"
- Figure 1 shows several techniques used by astronomers to
measure the "Early Universe" value of the Hubble constant.
- Pick two abbreviations shown in color on the figure.
Write out the full names of the techniques
for which they stand.
- Figure 2 shows several techniques used by astronomers to
measure the "Late Universe" value of the Hubble constant.
- Pick two abbreviations shown in color on the figure.
Write out the full names of the techniques
for which they stand.