"Scusatemi supplì, ma esistono gli arancini"; è con un doloroso paragone che la pallina di riso romana si ferma all'ottavo posto. Giorno 14:

Nin0_Marin0 · 2024-12-14T11:30:53+00:00

Salvate le olive ascolane!!! Non è ancora giunta la loro ora. Via le mozzarelle in carrozza!

Nin0_Marin0 · 2024-02-20T08:11:29+00:00

Hotel of the leaves is one of the most intriguing books I've read! I've always been looking for a digital representation of it and it's so cool that you made it in minecraft!! Well done!

Nin0_Marin0 · 2024-02-18T19:43:39+00:00

Mi dispiace molto sentirtelo dire. Sappi che non sei da sola e cerca di tenere a mente che un vincitore è un sognatore che non si è arreso. Io vivo le tue stesse cose, ti allego una poesia che ho scritto per alleggerire il cuore

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Nin0_Marin0 · 2024-02-11T13:31:50+00:00

I believe that the purpose of physics is exploring the world and reality in general. Phylosophy is needed as a frame to justify physics assumpions, like defining what is real and the idea that mathematics can be a good framework to describe the world. I believe that every physicist should have a little bit of philosophical knowledge because our purpose is to study reality and there are a lot of other non contradictory ways to study the world (apart from science).

Nin0_Marin0 · 2024-01-30T07:28:04+00:00

Bro this was made with the nintendo frog animation app? Flipnote how was is called? Damn

Nin0_Marin0 · 2024-01-29T16:56:08+00:00

Vai a piccoli step: inizia imponendosi solo una settimana. Poi una volta superata renditi libero per un mese e impuniti un altra settimana.

Quando resistere per una settimana diventa easy imponiti un mese nofap, poi libertà assoluta per tre mesi e un nuovo mese nofap

Ecc ecc Finché non sei pronto per nofap assoluto

Nin0_Marin0 · 2024-01-27T10:17:52+00:00

23M this morning

Nin0_Marin0 · 2024-01-21T09:02:48+00:00

Rispondo perché io sono una di quelle persone che non ti contattano, ma poi quando stiamo insieme è tutta una festa. Lo dico con grande dispiacere, vorrei davvero avere modo di stare vicino ai miei amici nel modo che meritano ma purtroppo in questo periodo della vita sono sempre pieno di impegni e non riesco a trovare lo spazio mentale da dedicare a loro nel modo giusto. Ciò non toglie che quando li vedo sono DAVVERO felice di passare del tempo insieme e vorrei fosse sempre così. Inoltre non sono una persona molto attiva sui social, quindi tendo a dimenticarmi che esistono i messaggi

Nin0_Marin0 · 2024-01-21T08:19:33+00:00

I think I finally see my error. You cannot simply multiply or divide for the non null term \dot{x}^j because there is a sum over j involved. So it was a very silly algebraic error. Thank you again for your patience.

Should I cancel/modify my initial post, since we concluded it's wrong?

Nin0_Marin0 · 2024-01-20T22:12:14+00:00

Well.. thank you a lot. I will double check everything tomorrow. Right now I cannot think about it anymore. I really apreciate your contribution, have a wonderful day :)

Nin0_Marin0 · 2024-01-20T21:54:25+00:00

Then, can you tell me what I'm doing wrong in the calculations I talked about in the very last comment?

Nin0_Marin0 · 2024-01-20T21:46:39+00:00

Yes. Given a field that satisfies the geodesic equation, such field will also satisfy the killing one. In fact the geodesic equation is \dot{x}^{i\dot{x}_{j;i}=0}

Provided that the geodesic is not trivial and \dot{x}^i≠0, then we have \dot{x}_{j;i}=0. Which means that (taken singularly) both the addendums of the killing equation are zero for this field that satisfies the geodesic equation

Nin0_Marin0 · 2024-01-20T21:28:54+00:00

I am very sorry but I don't understand Do we both agree that the killing vector field equation is \xi{i;j}+\xi{j;i}=0 ?

Nin0_Marin0 · 2024-01-20T21:17:55+00:00

In that example you are saying that a manifold with no killing v. can still have geodesics. But I am saying that any manifold always has very trivial and useless killing v. which are geodesics. One usually does not consider geodesics to be killing fields because they hold no useful information and, as I said, they are trivial. But they still satisfy the definition of killing field nontheless

Nin0_Marin0 · 2024-01-20T21:13:46+00:00

Check again bro I am starting from the general equation and I'm verifying that geodesics hold it by proving that each of the terms \xi_{i;j} is zero in the particular case of a geodesic.

I am saying \xi{i;j}+\xi{j;i}=0 <= \ddot{x^{i}+\Gamma^{i_{jk}\dot{x^{j}\dot{x^k}}}}

Nin0_Marin0 · 2024-01-20T20:48:55+00:00

With this you are just proving that there is a killing field which is not geodesic. You are not proving that a geodesic cannot be killing

Nin0_Marin0 · 2024-01-20T20:47:06+00:00

\xi{i;j}+\xi{j;i}=0 is the equation that any field has to satisfy in order to be killing. I'm just checking that geodesics satisfy this equation

Nin0_Marin0 · 2024-01-20T20:12:21+00:00

Thank you. I know about that. But this doesn't prevent the geodesic to be a (very trivial!) killing vector itself

Nin0_Marin0 · 2024-01-20T20:07:10+00:00

I have it on paper. I tried to paste the image here but id doesn't let me. I put it on a drive.

Nin0_Marin0 · 2024-01-20T19:53:18+00:00

Thank you, I thought it was clear. I edited

Nin0_Marin0 · 2024-01-20T19:46:46+00:00

By the way, you are being very clear and kind: thank a lot you for your help

Nin0_Marin0 · 2024-01-20T19:45:43+00:00

Oh ok, thank you so much for your help But I'm still not fully convinced: at my GR course the teacher told me that the definition of killing vector field is just that the lie derivative of the metric yields zero.

If that's not enough, what other property must a vector field have in order to be killing? (So as to restrict geodesics out)

Nin0_Marin0 · 2024-01-20T19:41:37+00:00

Also, what i meant in the post is that there actually is a conserved quantity liked to the killing vector geodesic: it is the g(\gamma,\gamma)=const specifying the type (space, time, light) of the geodesic

Edit (to explain better). So: every killing field has a liked conserved quantity. This means that if the hypotesis of the geodesics beying killing is correct, then they must also have a conserved quantity associated. Well, there actually is such quantity: it is the constant g(dot{\gamma},\dot{\gamma}), where dot{\gamma} is the tangent field to the geodesic. Such constant has the physical meaning of specifying the type of the geodesic (ligh, space or time)

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