Please give me some clues about the calculations for a non-rotating black hole

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Homework Help Overview

The discussion revolves around calculations related to non-rotating black holes, specifically focusing on dimensional consistency in equations involving parameters such as ##p## and ##q##. Participants are examining the formulation of expressions and their implications in the context of general relativity.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants are questioning the dimensional consistency of certain expressions, particularly the argument of the logarithmic function. There is a suggestion that the expression might need to be reformulated for clarity. Some participants express uncertainty about the definitions of variables involved, which affects their ability to verify calculations.

Discussion Status

There appears to be a productive exchange regarding dimensional analysis, with some participants gaining insights from the comments made. References to external resources, such as Sean Carroll's notes on Kruskal coordinates, have been introduced to aid understanding, although no consensus has been reached on the specific formulations discussed.

Contextual Notes

Participants note the lack of clear definitions for certain variables, which complicates the verification of their calculations. The discussion also highlights the importance of dimensional consistency in the context of the equations being analyzed.

park
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Homework Statement
non-rotating black holes
Relevant Equations
Kruskal coordinates
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The right-hand side doesn't look dimensionally consistent to me. Could it be that the argument of the ##ln## function should be something like ##|r/r^* - 1|## instead of ##|r - r^*|##?

It's a bit hard to check your work since you haven't indicated how ##p## and ##q## are defined.
 
oops! my mistake! p and q is defined ...
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i finally got a clue with your comment about dimensions!
For consistency of dimension, i think r-r* of (8.13) should be r/r*-1
 
park said:
i finally got a clue with your comment about dimensions!
For consistency of dimension, i think r-r* of (8.13) should be r/r*-1
Yes, things seem to work out better with the r/r*-1 form.

I'm not very familiar with Kruskal coordinates. Sean Carroll's notes on GR are freely available on the internet.
https://www.preposterousuniverse.com/grnotes/

He discusses Kruskal coordinates in this chapter:
https://preposterousuniverse.com/wp-content/uploads/grnotes-seven.pdf
The relevant material starts around page 182. Note equation (7.74) on page 186. I think his ##\tilde u## and ##\tilde v## are similar to your ##p## and ##q##, and his ##u'## and ##v'## are essentially your ##p'## and ##q'##. (But I believe Carroll is missing an overall negative sign in his expressions for ##v'## in (7.75) and (7.76). He corrects this in his published textbook.).
 

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