Preflight 2

Post your response on the course Compass site

Due Friday, Feb. 12, 12noon

Reading

Course Text

Peacock

Chapter 5.5

Peacock (1999) came out just as the evidence for cosmic acceleration and dark energy was just starting to appear. Thus there is some mention of the first evidence, but the discussion is fairly brief.

Articles

"The Cosmological Constant"
Living Rev. Relativity, 4, (2001), 1
Online article: at this URL; you can read it in HTML or download a version PDF

This is a comprehensive but very readable overview of both observational and theoretical issues surrounding the cosmological constant or dark energy. It's longish, but you won't need to read the whole thing unless you want to.

Questions

The questions are really meant to help guide your thinking as you read. You may find it helpful to look at the questions first and bear them in mind as you read.

Note: Since you brave souls taking the course have very different backgrounds and interests, the Preflights are an obvious place to try to introduce some flexibility to pursue your particular interests more. So this Preflight will focus on Dark Energy in general, and you'll read some about both observational and theoretical issues. But you'll also have an opportunity to go in more depth in whatever aspect pleases you.

1. Cosmic Acceleration/Dark Energy: Observational Evidence. Take a look at Carroll, Sections 1 and 3. The level of your reading can reflect your interest and background, and then adjust your answers accordingly.
   1. Summarize the main lines of observational evidence for cosmic acceleration? For dark energy? Which is the most direct? Which is the least direct? How many observations have to be wrong to make dark energy unnecessary?
   2. Discuss possible problems and/or uncertainties with some or all of the evidence from part (a). What efforts have been made to address these problems? How might future work (already planned, or dreamed of) address these issues?
2. Dark Energy: Cosmological Implications Take a look at Carroll, Section 2.
   1. What is the connection between cosmic acceleration and a cosmological constant/dark energy?
   2. Dark energy can be defined as any cosmogical component with equation of state parameter w < -1/3. Given this definition, how are dark energy and the cosmological constant related?
3. Dark Energy: (Un)physical Attempts at Explanation. Finally, take a look at Carroll, Section 4. If you don't have much of a particle physics background, at least look at the introdution and anthropic principle subsections. Answer the following in proportion to your reading (but at least attempt the first two questions).
   1. Why is a nonzero cosmological constant a surprise from a quantum point of view. What is the naive quantum prediction for the comological constant, and how wrong is it?
   2. What is the anthropic principle? People generally have strong reactions to antropic arguments. What is yours--do you find it useful or at least compelling?
   3. For the particle-physics inclined: how well does the (observed) cosmological constant fit into theories going beyond the Standard Model? If the cosmological constant (or dark energy) is indeed real, what is your best bet as to the explanation--i.e., what new physics do you think is likely to be involved?
4. What material did you find difficult, confusing, or unclear? What material would you like to know more about?


5. Other questions or comments?