A little direction regarding dark energy.

[Slimchandi]

I am writing a 2nd year essay for my Physics degree, and have chosen dark energy as my topic. I've been reading papers and material for around a week now, and would like some reassurance that I am heading in the right direction and have made no major blunders or omissions. Here's the general structure of my essay ATM.

• Hubble's observations of red shifts
• Study of early universe requires old bright objects (discard Cepheids, SN 1a use)
• Recent study shows excessive red shift in far SN, accelerating expansion.
• CMB evidence discredits excessive warping of space to fill critial energy density. Universe is essentially flat.
• Requires antigravitational effect, re Einstein's original equation cosmological constant.
• Show negative pressure with classical thermodynamics (vacuum energy associated with space)
• Friedmann equation governs expansion, define w factor (p/rho) as important to nature of dark matter
• Describe various theories with w values (Cos constant, quintessence, phantom energy(?)).
• Evaluate evidence for each, sum up

The title of my essay is to critically analyse the evidence and compare theories. Do i have things in roughly the right order, am I missing anything crucial. I haven't officially covered any of this material yet in classes, so a formal knowledge is not necessarily required to be shown in the essay.

 

[hellfire]

This structure makes sense to me. Either in point 6. or in 8. you could mention the fact that the QFT vacuum produces a negative pressure that is completely discordant with the cosmological observations ("old cosmological constant problem"). In point 7. I would mention the so called "new cosmological constant problem": why does the acceleration of expansion take place in the present universe and not earlier or later. This reference gives a nice overview.

 

[ohwilleke]

I would think that it would be easier to start with the Friedman equations (summarily stating the assumptions behind it and that it flows from GR) and then showing how you need to fill in the blanks, then show how various blanks have been filled in. This first, makes the model dependencies clear, and second, gives the other points more context.

 

[Slimchandi]

ohwilleke: Thanks for the input. Because I haven't done any formal study of GR and the Friedmann equations I decided not to use them on a formal basis. From knowing nothing about cosmology a week ago, I think I've done reasonably ok!

hellfire: Thanks for the reference, I'm fairly sure I have come across it before but I've read a lot of papers over the last few days, might have just skimmed it. The old problem is now in the essay, and as I have to critically analyse evidence (!) the new problem will be an interesting addition.

I've found Carroll's papers to be a really good introduction on this subject, hope others find this useful.

 

[Nereid]

If you can somehow mention that none of the other observational evidence for the concordance model (esp large scale structure) is inconsistent with DE, that would help - i.e. it's a complete package, not just a curiosity, added as an ad hoc patch.