Fix scaling in Kerr-Newman electrodynamics part

[ritzvik]

🐞 Problem
Currently, for correct calculation of trajectory in Kerr-Newman space-time, q(charge on test particle) or Q(charge on massive body) needs to be multiplied by 11604461683.91822052001953125 for correct calculation. It is not known from where this factor arises.

🎯 Goal

• Find out the reason for this problem
• Fix it.

💡 Possible solutions

• The code is written with reference from https://en.wikipedia.org/wiki/Kerr%E2%80%93Newman_metric
• These might also help
  • https://arxiv.org/pdf/gr-qc/0409025.pdf
  • https://arxiv.org/abs/gr-qc/0409025

📋 Steps to solve the problem

• Comment below about what you've started working on.
• Add, commit, push your changes
• Submit a pull request and add this in comments - Addresses #144>
• Ask for a review in comments section of pull request
• Celebrate your contribution to this project 🎉

[PSY27]

i want to work on this

[ritzvik]

I won’t recommend that you work on this. This requires deep theoretical knowledge. Regards, Ritwik

…

On 02-Feb-2020, at 3:00 PM, SAI SRAVAN MEDICHERLA ***@***.***> wrote:  i want to work on this — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or unsubscribe.

[ritzvik]

Find some easy ones please :) Or try if you want it badly. Regards, Ritwik

…

On 02-Feb-2020, at 3:00 PM, SAI SRAVAN MEDICHERLA ***@***.***> wrote:  i want to work on this — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or unsubscribe.

[JeS24]

@ritzvik @shreyasbapat Please check my derivation for the scale factor. I am unable to get the extra 1e-7 multiplicative term. I do believe, there's some problem with the way units are being modified in test_kerrnewman.py, but I can't put my finger on it.

Issue144ScaleFactorDerivJeS24.pdf

[ritzvik]

@JeS24 , the dimension analysis you did is really appreciable, and I mean it. I also saw that in Force = kg.m.s^-2, m got ignored during substitution of values. If you can please explain, otherwise, it's fine because it was, anyway, a wild goose chase. The method is not very convincing, but it does point to something.

[JeS24]

I also saw that in Force = kg.m.s^-2, m got ignored during substitution of values.

@ritzvik If you are referring to my derivation, then it's because, we want to get a conversion factor between SI and Geometric units. In geometric units, all physical quantities are related to or identified with powers of length, (in m), like powers of GeV (Energy) are used, in particle physics. In particle physics, energy equivalents are the preferred units. In GR, length equivalents make more sense, due to the space - time unifying nature (geometrical nature) of GR , which is also the reason behind the name, "geometric" units.

As for the factor, I was unable to get the exponential - 1e-7. This is missing and I don't think, the derivation has any such multiplicative factor.

[ritzvik]

I guessed geometric units were the reason, still needed to clarify. The presence of the rogue factor 1e-7 is duly noted.

[JeS24]

Using Charge per unit Mass (q) here, instead of charge, Q, is probably where the factor comes from. Although, this should be moot now, after #512 . Tests are needed regardless. There seems to be an implementation issue in the geodesic equations for KerrNewman, We need to check the equations once, before proceeding. I am skipping this test for now in #512.