River Model and Reviews

Recent readings include:
The river model of black holes. By Andrew Hamilton and Jason Lisle.
They review how one can rewrite the Schwartzchild metric to represent a river of space flowing through a "flat" background. The points of the paper are: it is a good model to explain black holes to non-expert and it can be generalized to include rotating/charged black holes.

In this model space is basically flowing into the black hole like a river. At the event horizon it flows at the speed of light, the photons are like fishes which cant swim faster than c. (There's even a picture fishes swimming upstream.)

Unrecognized terms\phrases included.

• Kerr-Newman geometry does not admit conformally flat slices
  
• ADM formalism
  
• tetrad
  
• Doran-Cartesian coordinates
  
• Jacobi Identity
• vierbein
  

The Kerr metric and the ADM formalism I was able to remind myself about from past GR studies. Still not exactly sure what the difference between a tetrad and a coordinate system is. Googling Doran-Cartesian coordinates gets only this paper back again. According to the references Doran was one of the first river type metric for a black hole guy. I looked up the Jacobi identity but already forgot. Vierbein in context appears to be some kind of transform, between the normal metric and the Doran-Cartesian(?) river metric. It is also German for four legs/legged.

Comments: I cant resist wondering where the space is going? Is it being dissipated inside the black hole? Is it just building up? Is it just taking the analogy too far?

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Also read.

• Quantum fields and "Big Rip" expansion singularities. Bill Hiscock and Hector Calderon
  Saw Hector's talk, had to read the paper.
  
• From COBE to WMAP: A Decade of Data Under Scrutiny. Louise M. Ord
  Reading lots of reviews.
  
• Does Chaotic Mixing Facilitate Omega Cornish et. al.
  Shortest abstract ever.
• Spontaneous Inflation and the Origin of the Arrow of Time Sean Carroll and Jennifer Chen
  Still reading but Apparently though they might not have needed the Cauchy surface.
  

Journalistic Integrity

The integrity I refer to titlisticly refers not to some kind of honesty in reporting but instead in reporting at all. Thus the sense of my use is more like the kind integrity you would like a bridge to have. I have always feared online journaling. I percieved it as some sort of academic community service which was a very grown up thing to do. It turns out that not only is this manifestly a forgone conclusion (somewhere out there is a blog by a gentleman from the persective of his "naughty hand") but the format turns out to be perfect to record my academic pursuits.

I am a graduate student studying physics. I read lots papers and spend my free time trying to sort out the parts that I dont recognize. Thus this format is perfect for recording this journey. Also, I have heard that journaling improves one's writing ability.

For example I tend to wander onto other subjects. Sure this is an ecceptable style, but only for the right crowd and only if you can work it.
So today is Christmas Eve 2004 V1.0.
We are making our second family oriented this year, this time to balmy Chicago in two days time (yes on christmas). Thus "Christmas One: The Getting of Presents and Relaxing at Home" will be followed closely by "Christmas Two: Aloft to Chicago (via Western Delta Hub - SLC)".

Cosmology Book

I finished Scott Dodelson's "Modern Cosmology" the other day. By finished I of course mean switched from reading the text to reading bold words, headings, figures and final equations.

It is a detailed look at the physics of the standard post big-bang model. Early universe physics appears to be rife with perturbation theory.
eg Let there be some first order scalar or tensor perturbations. What do they do to the stuff? (stuff includes matter, dark matter, and photons)
OR
Let there be some perturbation in the stuff. What does that do to the curvature?
I actually read half of the book, very nearly word for word. Doing this I did learn a couple of things including that scalar and tensor perturbations are completely independent.

The most important lesson I take away from this is that "Cosmology" really is a word without meaning. Or really is that it has a different meaning for everyone.

What I wanted to learn, but didn't was how CMB anisotropies "prove" the existence of Dark Matter. All I found was that if you suppose some non-interacting substance you get lots of smaller perturbations because they can't coalesce via your everyday radiation processes. This is what we see in the angular size spectrum of the CMB, lots more small clumps than matter would make. My naive perspective is that if gravity works differently at large scales a similar situation would arise.
My greatest challenge in becoming a good theorist will be to avoid ad-hoc or lay-sounding "theories". I must learn enough to know what can and cant reasonably be proposed. For example, I don't know enough about current ideas in quantum gravity to avoid thinking that maybe the gravity quanta have a decay lifetime, so that if there are large distances between the attractors the quanta could decay into somethings that interact differently. This would explain the sharp diversion point from Newtonian physics in the rotational curves of many spiral galaxies.