# [Mesa-users] epoch-dependent G

Marco Pereira ny2292000 at gmail.com
Tue Oct 4 23:45:42 UTC 2022

```The hydrogen density would also be around 10 times higher.

On Tue, Oct 4, 2022 at 7:01 PM Marco Pereira <ny2292000 at gmail.com> wrote:

> Dear Francis and Mesa-Users,
>
> In the past, it seems that epoch-dependent G investigated only small
> variations.
> Article a) tried to test a variable G but did so while trying to keep G
> constant.  They didn't explore my option.
> Article b) just proposed that the Sun was more massive but lost mass
> through solar winds (a diet).
> So, what I am proposing is distinct and hasn't been done yet, as far as I
> can tell.
>
> a) Can a variable gravitational constant resolve the Faint Young Sun
> Varun Sahni, Yuri Shtanov
> https://arxiv.org/abs/1405.4369
>
>
> *b) Assessing the massive young Sun hypothesis to solve the warm young
> Earth puzzleDavid A. Minton, Renu Malhotra*
> https://arxiv.org/abs/astro-ph/0612321
>
> #######################################################
> I would like to investigate large variations of G.
>
> I want to calculate G to be inversely proportional to the 4D radius of the
> Universe (inverse of the epoch).  This means that G would be 1.5 the
> current G0.  That would work if the Sun started as 46% of the current Sun
> mass and accreted 9% every billion years.
> Of course, the whole galaxy would also have a radius that was 0.46 the
> current radius. Angular momentum conservation would have the sun rotating
> twice as fast around the galaxy. The hydrogen density would also be around
> 300% higher.
>
> So, I would like to increase the rate at which hydrogen is accreted into
> the sun, have a variable derivative for G, and start with a smaller mass.
>
> So, that is what I would like to try. This is the back-of-envelope
> calculation. We all know that the sun loses mass through solar wind.  The
> sun should gain mass from falling hydrogen.
> [image: image.png]
>
> I will dig deeper into your suggestions. If anyone wants to help me do the
> calculation, I would be more than grateful.
>
> Cheers,
>
> Marco Pereira
>
>
> On Tue, Oct 4, 2022 at 5:00 PM Francis Timmes <fxt44 at mac.com> wrote:
>
>> hi marco,
>>
>> the topic of variable G arises every now and then. one example is
>>
>> https://lists.mesastar.org/pipermail/mesa-users/2022-February/013504.html
>>
>> and
>>
>>
>> https://docs.mesastar.org/en/release-r22.05.1/using_mesa/extending_mesa.html#using-the-other-hooks
>>
>> https://docs.mesastar.org/en/release-r22.05.1/
>>
>> seem relevant.
>>
>> fxt
>>
>>
>>
>>
>>
>>
>> > On Oct 4, 2022, at 12:56 PM, Marco Pereira via Mesa-users <
>> mesa-users at lists.mesastar.org> wrote:
>> >
>> > Hi,
>> >
>> > I installed MESA-r22.05.1 and its SDK.  I finally was able to install
>> the program and create the Dox folder using doxygen.
>> > So, I am ready to try to understand the program.  That said, what I
>> want to do might be quite localized.
>> > I want to add into the integration step the knowledge of the value of G
>> (Newton's Gravitational Constant) at that time.
>> >
>> > Any guidance would be much appreciated.  Also, what I have (oxygen HTML
>> files) doesn't see to be documented enough for me to understand the program
>> with just that.
>> >
>> > Where can I find broader information on what each module and each file
>> does?
>> >
>> > That said, my thirst for knowledge might not be relevant if the
>> epoch-dependent G can be surgically added.
>> >
>> >
>> > Marco
>> > _______________________________________________
>> > mesa-users at lists.mesastar.org
>> > https://lists.mesastar.org/mailman/listinfo/mesa-users
>> >
>>
>>
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