# Coordinate and proper time, null geodesic

• I
PeterDonis
Mentor
2019 Award
We can't "help you with all of these questions"; that would require a full course in relativity, and that's way beyond PF's ability to provide.

You have already received a number of responses that indicate, first, that at least one item in the full question (item e) doesn't make sense as stated, and second, that you appear to lack important background knowledge that is crucial for understanding the question you're trying to answer (let alone actually answering it). Those are not problems that can be solved by you continuing to ask questions here. You need to provide more information, such as what I've already asked: what textbook is this problem from, and what chapter/section/problem is it? That might at least help with the first issue (that item e in the question doesn't make sense as stated). The only way to help with the second issue (your background knowledge) is for you to put in the work to learn the basic concepts involved in the question (such as what I suggested, Killing vectors), which, as I said, is beyond the scope of what PF can provide.

We can't "help you with all of these questions"; that would require a full course in relativity, and that's way beyond PF's ability to provide.

You have already received a number of responses that indicate, first, that at least one item in the full question (item e) doesn't make sense as stated, and second, that you appear to lack important background knowledge that is crucial for understanding the question you're trying to answer (let alone actually answering it). Those are not problems that can be solved by you continuing to ask questions here. You need to provide more information, such as what I've already asked: what textbook is this problem from, and what chapter/section/problem is it? That might at least help with the first issue (that item e in the question doesn't make sense as stated). The only way to help with the second issue (your background knowledge) is for you to put in the work to learn the basic concepts involved in the question (such as what I suggested, Killing vectors), which, as I said, is beyond the scope of what PF can provide.
DOESNT CHANGE my intial question. i repeat i do not want the answer to all of these questions.
have i missed something? XDXD

DOESNT CHANGE my intial question. i repeat i do not want the answer to all of these questions.
have i missed something? XDXD
ii know what a killing vector field is and at no point have i asked for info on it !!!. my question was solely the confusion of e which others agreed is confusing, yet you're not telling them to increase their background knowledge, you even said its confusing yourself.
genuinely lost with this thread. XD

PeterDonis
Mentor
2019 Award
i do not want the answer to all of these questions.
It's hard to tell that when you explicitly say this:

It should be clear from this discussion that nobody else has understood what question you actually want the answer to. We can't read your mind, and the fact that it's perfectly clear to you what question you want the answer to does not mean you've successfully communicated that to anyone else.

my question was solely the confusion of e which others agreed is confusing
Yes, we all agree part e is confusing. But that doesn't help us to understand what your actual question is. If your actual question was the only statement in your OP that was phrased as a question, then it's already been answered:

Your first post only has one question in it: "Can I confirm these ideas are correct?" That has been answered: no, they are not exactly correct.
In other words, no, your proposed method of solution in the OP is not correct. Is that all you wanted to know?

I've also pointed out repeatedly now that it would help to resolve the confusion about part (e) if you would give us more context: what textbook is this question from, what chapter/section/page? So are you going to provide that information or not? If not, we can just close this thread as it's going nowhere.

It's hard to tell that when you explicitly say this:

It should be clear from this discussion that nobody else has understood what question you actually want the answer to. We can't read your mind, and the fact that it's perfectly clear to you what question you want the answer to does not mean you've successfully communicated that to anyone else.

Yes, we all agree part e is confusing. But that doesn't help us to understand what your actual question is. If your actual question was the only statement in your OP that was phrased as a question, then it's already been answered:

In other words, no, your proposed method of solution in the OP is not correct. Is that all you wanted to know?

I've also pointed out repeatedly now that it would help to resolve the confusion about part (e) if you would give us more context: what textbook is this question from, what chapter/section/page? So are you going to provide that information or not? If not, we can just close this thread as it's going nowhere.
Does anyone really post on a forum expecting a yes or no answer ? No you expect discussion? Or what the hell are you going to learn ?

Context... Erm as said above, that's he reason I posted the entire question. The question comes from an exam paper from my university in the UK...

stevendaryl
Staff Emeritus
Does anyone really post on a forum expecting a yes or no answer ? No you expect discussion? Or what the hell are you going to learn ?
Well, if you posted to generate discussion, that's fine. There was quite a bit of discussion about the topic, so you should be happy. But then you complained that nobody answered your question, which makes it sound like you had a specific question you wanted an answer to. Nobody knows what that question is.

You're unsatisfied with the answers you have been given, but nobody knows why, and you can't tell them.

Well, if you posted to generate discussion, that's fine. There was quite a bit of discussion about the topic, so you should be happy. But then you complained that nobody answered your question, which makes it sound like you had a specific question you wanted an answer to. Nobody knows what that question is.

You're unsatisfied with the answers you have been given, but nobody knows why, and you can't tell them.
i complained because people went astray and decided to state their general knowledge, not consise with what I had questioned, and then someone complained about me not having the background knowledge of such posts, when I hadnt asked for it !!

Mister T
Gold Member
and then someone complained about me not having the background knowledge of such posts, when I hadnt asked for it !!
When a question is asked a back-and-forth discussion almost always follows. Sometimes the discussion goes over my head and I have to just gean what I can from it and try to learn more about it if I'm interested. Education, formal or otherwise, is much more than learning how to answer questions. It involves understanding.

When a question is asked a back-and-forth discussion almost always follows. Sometimes the discussion goes over my head and I have to just gean what I can from it and try to learn more about it if I'm interested. Education, formal or otherwise, is much more than learning how to answer questions. It involves understanding.
yes, fair enough if you had pointed towards that, but at no point did ii point towards killing vector fields. what followed was someone merrily tapping away at their keyboard banging on about killing vector fields, and then a post asking ME where is my background knowledge !

stevendaryl
Staff Emeritus
i complained because people went astray
There is no way that the discussion can "go astray" if there isn't a specific question to answer. So it seems to me that either you ask a specific question (and then you can complain if nobody answers it) or you can spark a general discussion, and then let it go where it will. There is no basis for complaint in the latter case.

There is no way that the discussion can "go astray" if there isn't a specific question to answer. So it seems to me that either you ask a specific question (and then you can complain if nobody answers it) or you can spark a general discussion, and then let it go where it will. There is no basis for complaint in the latter case.
erm nah. i dont think the world revolves around me. rather, if you think a discussion may be useful by taking a de-tour, you should mildly talk about the subject, or introduce it, and ask whether that person has the background knowledge for it or not, before ASSUMING they DO NOT, writing an essay about ut and getting your knickers in a twist about the fact that they don't

stevendaryl
Staff Emeritus
erm nah. i dont think the world revolves around me.
Your complaints seem to suggest otherwise. You're upset that people didn't spend more time figuring out what you want from this discussion and complying with it.

Your complaints seem to suggest otherwise. You're upset that people didn't spend more time figuring out what you want from this discussion and complying with it.
u really want me to repeat myself?
no i am not.
the fact that it was complained why dont i have some desired background knowledge, when i asked nothing about it, and it was immediately assumed i did not have it.
i think you've got that, you just dont like loosing arguements.

stevendaryl
Staff Emeritus
u really want me to repeat myself?
No. I told you what I want. I either want you to ask a specific question, or else let the discussion go where it will, without complaining.

Nobody has any idea what you want out of this discussion.

No. I told you what I want. I either want you to ask a specific question, or else let the discussion go where it will, without complaining.

Nobody has any idea what you want out of this discussion.
i believe they do about 6 posts ago, you can't let it go since felt the need to reply to my clarificaiton posts which i was asked for.

martinbn
The question comes from an exam paper from my university in the UK...
Presumably from a module on general relativity. What was, if there was one, the recommended text(s)?

stevendaryl
Staff Emeritus
i believe they do about 6 posts ago, you can't let it go since felt the need to reply to my clarificaiton posts which i was asked for.
Okay. I'm dropping this discussion. Maybe we could take vote: Does anybody know what the question is?

Last edited:
PeterDonis
Mentor
2019 Award
i believe they do about 6 posts ago
Oh, you mean your questions are all resolved now? Good, then we can stop the pointless wrangling about who understands what. Thread closed.