The h Bar

David Z

17:00

@Danu I think it is. A lot of people post answers in the comments as a way of avoiding downvotes. Plus, comments are temporary, and if you answer a question, that information should be permanent.

@JohnRennie like, in terms of who our target audience should be?

Secret

http://physics.stackexchange.com/questions/211021/higher-dimensional-manifolds-examples
>A very easy (huge!) class of examples arises as the parameter spaces of some kind of object (with arbitrarily many parameters to obtain arbitrarily high-dimensional manifolds). – Danu 8 mins ago

My first and (hence) most favourite example is S(U,V,N) used in thermodynamics

Since I can handle tesseracts and other simple 4D objects, I can visualise it

More recently, effort have been placed to visulise the space *as seen from newtonian spacetime*

John Rennie

For example, suppose I ask a question that basically says "I don't know how to do this can anyone help?". Isn't that essentially a homework question?

ACuriousMind

@JohnRennie Yes.

John Rennie

But don't almost all questions fall into this category?

Danu

@DavidZ Well, I guess you have a point about avoiding downvotes. That aside, my answer-in-comments do not go against the temporary nature of comments: I only do this on question that I think do not merit a "real" answer post (or at least not one from me), but where I feel I could be of some help regardless.

David Z

17:01

@JohnRennie I'd say so - at least, it's something that should be off topic, regardless of whether we decide to call it "homework"

@JohnRennie how loose are you being with the wording?

Danu

I don't think those comments constitute permanent value that should be preserved

hence, I'm fine with them being temporary.

David Z

Eh, if you say so.

John Rennie

Take for example:

26

Q: Identification of particles and anti-particles

The identification of an electron as a particle and the positron as an antiparticle is a matter of convention. We see lots of electrons around us so they become the normal particle and the rare and unusual positrons become the antiparticle. My question is, when you have made the choice of the el...

0celo7

Isn't the proton the most common form of antimatter

Or something like that

John Rennie

Isn't that a "I don't understand this, tell me about it" question

ACuriousMind

17:04

@JohnRennie The difference is the difference between asking for the result of a calculation/how to do a calculation and asking for the explanation of a concept, I'd say.

David Z

@Danu I do think it's worth remembering that part of what we do here is to avoid helping out with bad questions as a way of discouraging such questions from being posted. If you post answers to bad questions in comments, it's like feeding the squirrels: it encourages more of them. (Not saying that particular question was bad, just speaking in general)

@JohnRennie I don't think so

Oh, by the way, it's time for our chat session to officially be over! The discussion can keep going; see everyone in two weeks!

John Rennie

@DavidZ I don't see there's a sharp cutoff

Danu

@DavidZ I don't do it with question that I consider worthless

ACuriousMind

The lines will always be a bit blurry, I don't think that means we should stop drawing them altogether.

Danu

I do it with question that I either (1) sympathize with but consider off-topic (2) don't want to answer personally but think someone else should answer

@0celo7 lolwat?

John Rennie

17:06

@ACuriousMind I agree we close obvious homework questions, but I wonder if we're a bit too ready to VTC.

David Z

@Danu well, in those cases I'd say (1) you're encouraging off-topic questions, and (2) why wouldn't you post an actual answer?

0celo7

@Danu yeah I think JD said protons are antimatter

Danu

@DavidZ (1) Meh, I think the positive impact offsets the negative in this case (2) Just don't wanna sometimes :P

(mostly insecurity or lack of time)

John Rennie

@0celo7 no, no, let's not go there :-)

David Z

@Danu what positive impact?

Danu

17:07

@JohnRennie Lmao

0celo7

Especially not while DZ is here, good call

Danu

@DavidZ I sympathize when I think the question is not bad, so I'd like to help the OP out, as in the most recent case

ACuriousMind

@JohnRennie Well, I don't think the dilemma between being a bit lenient and letting some bad questions slip or being strict and closing some okay questions has an obvious solution

John Rennie

@ACuriousMind agreed. It's just something we need to keep in mind.

David Z

@Danu so then why vote to close as off topic?

I mean, we're talking about questions you think are off topic, right?

Danu

17:10

@DavidZ Because I think it's off-topic :P

David Z

And also, what's the positive impact on the site?

Danu

But only slightly

and it's a good question in general (that is, out of the PSE context)

John Rennie

@Danu In this case it is an interesting question.

Maybe it's off topic and maybe not, but it's interesting.

Danu

@DavidZ Making one of the contributors happy---I don't think the encouraging bad content aspect is as much of an issue as you seem to imply it is.

David Z

@Danu we might have to agree to disagree on that too

Danu

17:12

@DavidZ Yup.

John Rennie

Given that Danu thinks it's off topic (but still thinks it's interesting) adding a comment seems a plausible thing to do.

Danu

(I knew I wouldn't win you over)

David Z

Although we could try to find data about how often someone whose first question is off topic comes back and becomes a good contributor of on-topic questions

That would be useful toward resolving this issue

John Rennie

@DavidZ It's not really "bad content"

Danu

@DavidZ That'd not be precise enough

You'd have to factor in the fact that I thought the question was good enough to deserve some help

John Rennie

17:13

It's just slightly misplaced content

0celo7

I just had a random thought: Why do small people look so smug? They think they're sooo smart that they don't need to be tall?

Danu

which is really a quite selective criterion

David Z

@JohnRennie the distinction I concern myself with is "content we want on the site" vs. "content we don't want on the site"

Danu

@0celo7 So wrong on so many levels

John Rennie

@DavidZ I'd quite like to see an answer to that question on this site

Danu does really, but won't admit it :-)

0celo7

17:14

@Danu Well? What's the answer?

ACuriousMind

@0celo7 wat

David Z

@JohnRennie to what question?

John Rennie

0

Q: What happens if locally manifold is seen as an Euclidean space?

I have been trying to understand the definition of a manifold and I have found out that the most common definition (even around here on S.E.) is: A manifold is a space that has a complicated "topology" globally but "locally" can be considered as an Euclidean space. So, what is the advantage (if...

general-relativity differential-geometry topology

At least I think that's what kicked off this discussion

Danu

@JohnRennie lololol

0celo7

@ACuriousMind What confuses you about it? I thought of that while walking to class, it's certainly not polished rhetoric.

ACuriousMind

17:17

@0celo7 You say "small people are smug" as if that were an obvious and universally accepted fact.

0celo7

Well they're not smug.

Their height is

I mean they're not smug

ACuriousMind

That does not make any more sense to me.

Secret

Random afterthought
One thing the Spring school give me an impression is that:

There's really a lot in common between particle physics and chemistry
For example, the way people detect particles using the detectors is basically analytical chemistry in steroids (they fared out worse than us analytical chemist because in particle reactions, some of their characteristics (such as some quantum numbers) are not conserved thus you can have, analogously speaking, an oxygen molecule thrown into the mixture and get back a bunch of hydrogen radicals)

ACuriousMind

In fact, that makes even less sense to me :P

Secret

The most important thing is that, I now finally understand what a linewidth is conveying in my IR spectra

Danu

17:19

@0celo7 really?

0celo7

I take it that's not a normal thought

Danu

No, it's really not.

ACuriousMind

@0celo7 No, it isn't :D

0celo7

Ok then

Danu

It makes you sound rather smug and arrogant :P

0celo7

17:20

How am I smug and arrogant D:

In this case

I know you all have your side theories on me

John Rennie

Have to go ...

Danu

@0celo7 The remark is very inconsiderate towards a large (depending on your own height, I suppose) class of people.

@JohnRennie :(

ACuriousMind

@JohnRennie See you :)

0celo7

Bye

ACuriousMind

@Danu Well, they're not exactly large :P

Danu

17:21

It's always such a privilege to have John around

@ACuriousMind Hurr durr!

David Z

@JohnRennie oh right. I'm not wholly convinced that's off topic - at least, I don't plan to VTC/migrate myself

ACuriousMind

@Danu Sorry, that had to be said.

I agree with the actual content of your remark, though

Secret

As for cosmology, one of the $\frac{d ln()}{dln ()}$ equation that describe how electron get freeze out (the frezzing out event in the history of the universe) into hydrogen which result in photons to no longer scatter (hence the univers become transparent) has the same underlying principle as Le chatelier Principle in equlibrium chemistry

0celo7

Hmm

Maybe I'm an asshole, but I don't see how that makes me smug or arrogant

Danu

@0celo7 Spend some more time contemplating :)

(although I agree those words are not the most accurate characterization of that remark, they just fit the remark itself quite well...)

Secret

17:24

My professor explained that that might be because phys chem do statistics on non reletavistic particles, thus it is all descrbed by boltzmann distribution, whereas in particle physics, the particle are ultrarelativistic thus described by bose einstein or fermi dirac

But they otherwise obey the same equlibrium rules

0celo7

Diagnose me

For some reason the idea of short people makes me uneasy D:

Danu

@0celo7 How tall are you, anyways?

Secret

that if perturbed, the system will try to minimize the change by shifting the equlibrium

0celo7

6'2"

Secret

In the past cosmology is like alien language to me, now it is basically chemistry

mixed with GR

Danu

17:26

@0celo7 That's pretty average by Dutch standards :P

Maybe some people think you're small

And therefore look smug

(?!)

0celo7

I'm talking averages here

Danu

sound ridiculous to you yet? :P

user54412

@Danu That's just because you're not at the top of the leaderboard for making starred posts ;)

0celo7

@Danu no

Danu

@ChrisWhite Wait, there's a leaderboard?

Secret

17:27

I think I will going to enjoy particle physics in the comming years, given my passion on it, and an extra intuition gain by the unexpected simialiryt with chemistry

Danu

:: drools ::

0celo7

Of course it sounds ridiculous

Danu

@0celo7 Well, good

0celo7

This whole thing is ridiculous

user54412

@Danu Not an official one. But if we compile results and post a chat message, I bet it would be starred.

0celo7

17:27

But I had that thought

Danu

@ChrisWhite DO IT

0celo7

Wondered if anyone shares it

David Z

OK I have to be off, see y'all later

Secret

This cause me to be able to formulate a joke as follows:

For a chemist to imagine what particle collider experiments are like. Imagine you are doing your good ol' analytical chemsitry and trying to elucidate an unknown

except that the unknown is so alien that you can have things like "put 5 grams of oxygen into the reaction mixture, and then you get back hydrogens of the same total mass, plus a lot of energtic mess"

what's more, unlike in chemsitry, where simple rules casn guide you on what reactions are possible, you are completely blank and can only wonder what hapens inside the reacti…

0celo7

Bye

skill patrol

17:29

Later pal

ya'all come back now real soon

:-)

0celo7

So my ODE teacher had to derive Euler's formula because only two people in the class had seen it before

American education!

skill patrol

:O

user54412

Ok, any thoughts on the Nobel prize?

skill patrol

@0celo7 How many in the class and what type of class?

0celo7

I want one

@skillpatrol 21? Honors ODE, mostly smart freshmen I think.

user54412

17:32

Compare this to 2002, which was also given two two neutrino experiment people looking at oscillations of solar neutrinos (plus a third person for unrelated stuff)

0celo7

We were doing nth order linear equations with constant coeffs

skill patrol

Still only 2 :-/

Huy

Euler's formula? you mean $e^{ix} = ...$?

0celo7

Yah

Hey brah

Huy

2 including you?

0celo7

17:34

Yah

Me and the dude behind me

Huy

better than only you

0celo7

So I had a probably stupid thought about that

Why do you need the power series

Huy

which one?

0celo7

Just show that the modulus is 1 and then find the equation for the complex unit circle

Huy

for the sine and cosine?

0celo7

17:37

Yeah

My solution is simpler

Huy

well in our analysis class we defined the sine and cosine by the power series and then deduced all their properties through it

skill patrol

^

0celo7

Well I'm not in analysis

Huy

and in physics you need Taylor all the time, no?

user54412

@0celo7 You shouldn't use the power series to prove that formula. Unless you're real careful, you're doing unjustified things. You have to have strong enough convergence of all series involved.

0celo7

17:38

Yes

@ChrisWhite he mentioned that

But for the purposes of the class...

None of us have had any analysis

Huy

you should really ask the person who plans the class what the purpose of a certain thing for the class is

skill patrol

Good point^

0celo7

It does not make sense to do an analysis proof when the class has not had analysis

But you need that equation to solve certain ODEs

skill patrol

Intent is everything.

0celo7

The intent is to convince the class that he's not making it up

skill patrol

17:42

Do you rewrite your notes?

0celo7

No

Why?

skill patrol

Pro tip: start.

0celo7

Not in that class.

skill patrol

Profs like to put that stuff in tests.

Just to make sure you're listening to them.

0celo7

I take good notes

But the material is easy

skill patrol

17:48

You're still in the first month.

0celo7

We have midterms in like two weeks

skill patrol

Do you have two term tests? And then the final.

0celo7

Depends on the class

I think most classes will give a midterm but not weight it more than a normal test

skill patrol

Do they grade on the curve?

dmckee

@ChrisWhite Prove? Maybe not, but for the purposes of class it's a strong plausibility argument. Related: academia.stackexchange.com/questions/54833/…

0celo7

18:04

@skillpatrol I don't think so

dmckee

For those who may be slightly confused by the Nobel announcement for this year, I've got a couple of comments.

First this year's prize is a grab bag.

Second, the committee is parsing the achievements pretty closely.

obe

A japanese scientist won the nobel prize in physics, that is my excuse to watch anime right now.

dmckee

They had already given one in 2002 to Ray Davis for the discovery of cosmic neutrinos (meaning solar one and the unexpectly small number).

Slereah

he would probably tell you that anime is for children and shake his head in shame

0celo7

Exactly

Problem set

dmckee

18:11

@Slereah Depends on the anime. Or so I hear.

0celo7

I can't imagine @dmckee watching anime

Slereah

@dmckee : Well public perception of anime in japan, anyway

obe

@0celo7 We're both children though.

dmckee

@0celo7 It neither better nor worse than other passive entertainment. Some is for children, so is for people and some is evidently for adults.

Slereah

not too different from ther public perception of cartoons here

0celo7

18:13

I'm not a child

@dmckee I know...I just can't imagine you watching either kind

Finally they starred something positive

obe

I disagree, you're17 right?

dmckee

When my brain hurts. Or I'm too sick to do something productive. Or I've been stressed for so long I've simply stopped being productive. Then I consume passive entertainment.

Mind you there is a season of Dr. Who I haven't seen yet, so anime has to wait in line.

obe

My little brother is obsessed with Dr. Who.

ACuriousMind

Jul 30 at 21:27, by 0celo7

I'm not even an adult.

dmckee

@ACuriousMind ::chorltes:: Not fair using his own testimony against him.

0celo7

18:19

Not adult does not mean child...

Also that was in a legal context

ACM in real life: "You said the opposite thing 35 days and 3 hours ago."

obe

I like being a child though.

0celo7

He should have been a lawyer

obe

Children are cool.

ACuriousMind

@0celo7 First meaning of the Wiktionary page for 'child': "A person below the age of adulthood"

0celo7

Wiki is not proof

Why are you all out to get me

skill patrol

18:22

I'm on your side pal.

0celo7

Thank you

skill patrol

Stop bullying my pal you, you Internet thugs :P

0celo7

Indeed

if you can't do analysis, you get shunned

if you don't like long hair, you get shunned

if you think short people are smug, you get shunned

skill patrol

Raider nation has always been shunned.

0celo7

and god forbid you misspell Groethendiek

that's when the Bruti charge

must have spelled it correctly :)

does anyone know how to put a list of numbers separated by commas in to excel and have all numbers stacked in a column

ACuriousMind

18:55

@0celo7 No, you didn't :P

John Duffield

@0celo7 : You said To act like a crank. JD? That's an insult.

@Davd Z : moderation please.

Rainbolt

Can whomever is flagging old messages stop? What purpose does it serve?

Arthur Chaparyan

Really basic physics question, how can I calculate how much energy can be generated by a heavy object floating on top of water anchored to a generator as the water goes down?

TildalWave

@ArthurChaparyan how does a heavy object float on top of water?

Arthur Chaparyan

@TildalWave Like a yacht

ACuriousMind

19:09

@ArthurChaparyan How does the "generator" generate the energy?

Arthur Chaparyan

@ACuriousMind The pull of the heavy object doing work through some sort of spin

TildalWave

@ArthurChaparyan so some sort of buoyancy device?

Arthur Chaparyan

@TildalWave sort of yes

Rainbolt

The heavy object is pushing (as the water goes down, it sinks)

Arthur Chaparyan

@Rainbolt I was imagining something attached to the top of the boat, so that's where the pull would come

ACuriousMind

19:11

@ArthurChaparyan I'm not exactly sure what you mean, but I'd guess the available energy is just the potential energy of the object.

TildalWave

@ArthurChaparyan calculate displacement mass

Rainbolt

@ArthurChaparyan Oh, that works too

Arthur Chaparyan

Basically I want to see how much energy would be generated if I had a boat in a big pool attached to a rope or something that is attached to a generator, and as the water goes down it generates electricity

TildalWave

Anyway, has the neurotic flagging by whoever was doing that stopped? I thought to go do something more useful with my time, if that's OK with that person.

user54412

@dmckee Someone pointed out to me that every 4-5 years it goes to something related to astro (2006 was COBE, 2011 was dark energy).

John Duffield

19:14

@Danu : don't accept that quantum physics "surpasseth all human understanding". You can visualize it. Ask a question about superposition, and another one about neutrino oscillation, and I'll help you out. But not in chat, it's too restrictive.

TildalWave

@ArthurChaparyan That's technically gravitational potential energy storage device, it should help you google it, there's loads of papers on the subject online

user54412

Still, if it was to go to astro, I was half suspecting the first exoplanet discoverers. Apparently the internet betting pools were on the velocity profiles of M31.

Arthur Chaparyan

@TildalWave Thanks! I'll look it up!

John Duffield

@DavidZ : or we could discuss what really happens when neutrinos oscillate.

0celo7

19:27

@ACuriousMind Well that's his fault for having a name incompatible with the languages I speak.

@JohnDuffield I have been personally told by the moderators that asking questions on the main site based on your chat comments is forbidden. Read my lips. Forbidden. You'll have to answer in chat.

@JohnDuffield If you don't like that, you can make a meta post.

skill patrol

F O R B I D D E N

0celo7

I think asking questions based on your posts is considered shaming because most people would find the stuff you say embarrassing. (That is not the stated policy of the mod team.)

I do know @JohnRennie considered my electron question shaming.

And he left.

Oh boy do I want him to make a meta post!

skill patrol

:-)

NeuroFuzzy

19:50

this should be a duplicate of a bunch of questions on math.stackexchange.com i think physics.stackexchange.com/questions/211069/…

dmckee

Experimental evidence is a postulate. Who knew? physics.stackexchange.com/questions/211045/…

John Duffield

@JohnRennie : a new answer awaits.

ACuriousMind

@dmckee Ha! So we theorists can now also claim all of experimental physics as just following from axioms?

That's nice.

John Duffield

@David Z : since @0celo can repeatedly call me names without moderator intervention, I think I ought to allowed to return the compliment, don't you? Or does PSE moderation only apply to people who stand up to bullies?

Hippalectryon

Since when is 'he called me names so I'll call him names' something respectable ?? ... I have no clue what's going on here, but ...

John Duffield

20:04

It isn't respectable. But it is an issue.

skill patrol

Only if you take issue with it.

We are on the Internet here.

ACuriousMind

@Hippalectryon This whole scenario has not been characterized by a lot of reason from the beginning :P

John Duffield

So, anybody want to talk physics?

Huy

$F = \frac{dp}{dt}$!

skill patrol

Newtonian

:P

We want Einstein and The Evidence :D

Hippalectryon

20:08

The Evidence ?

skill patrol

Yes, THE Evidence does not lie :P

2

Huy

$G^{\mu \nu} = \kappa T^{\mu \nu}$!

or maybe $R^{\mu \nu} = \kappa(T^{\mu \nu} - \frac{1}{2} T g^{\mu \nu})$!

skill patrol

Much better^

Huy

or $-\square \gamma_{\mu \nu} - \eta_{\mu \nu} \gamma^{\alpha \beta}_{, \alpha \beta} + \gamma^\alpha_{\mu, \alpha \nu} + \gamma^\alpha_{\nu, \alpha \mu} = 2 \kappa T_{\mu \nu}$!

skill patrol

@JohnDuffield I will agree with you on the moderation applying to "people who stand up to bullies" idea.

ACuriousMind

20:17

@Huy No, $F = -\nabla V$!

Huy

:(

sorry physics is just remembering a bunch of formulas, no?

2

ACuriousMind

@Huy Shhh, we're not supposed to say that out loud.

Huy

you're not, but I can. :D

ACuriousMind

:(

David Z

@0celo7 pretty sure that's not what you were told

@JohnDuffield have you tried flagging?

skill patrol

20:19

Basically, let the mods stand up to the bullies @JohnDuffield because that's what they were elected to do, right Sir?

ACuriousMind

1 hour ago, by TildalWave

Anyway, has the neurotic flagging by whoever was doing that stopped? I thought to go do something more useful with my time, if that's OK with that person.

John Duffield

@DavidZ : yes, the insults stick around.

David Z

I have to look into this, then

John Duffield

Thanks. Meanwhile, let's talk physics. Who wants to talk about neutrinos?

Hippalectryon

I'm just a student >.> I don't know nearly as much about physics as other people here

Danu

20:22

@JohnDuffield No, thanks. I don't think I stand to learn much from that.

skill patrol

9 mins ago, by Huy

or $-\square \gamma_{\mu \nu} - \eta_{\mu \nu} \gamma^{\alpha \beta}_{, \alpha \beta} + \gamma^\alpha_{\mu, \alpha \nu} + \gamma^\alpha_{\nu, \alpha \mu} = 2 \kappa T_{\mu \nu}$!

John Duffield

Anybody ever heard of photon effective mass? Slow down a photon, and some of its E=hf energy is exhibited as "effective mass". Slow it down to an effective speed of zero by trapping it in a mirror box, and all of its E=hf energy is exhibited as effective mass. And it is indeed effective.

skill patrol

::makes popcorn::

John Duffield

So, anybody, if you could find a way to make a photon in space slow down just a little then speed up just a little, what would happen to its mass?

ArtOfCode

It explodes and destroys the Universe?

John Duffield

20:30

Anybody?

ArtOfCode

@JohnDuffield Do I take that to mean the Universe will live to see another day?

John Duffield

Anybody heard of the travelling breather?

Anybody got a washing line?

Danu

Look, it's an electron on a Dirac belt!!! Oh wait... it's not blue :( Guess it must be a positron!

John Duffield

Anybody ever twanged a washing line? Now what sort of wave might that produce?

And does anybody have a pair of pliers? And a washing line?

Hippalectryon

A washing line in Paris would be quite useless ._.

Danu

20:38

What do you guys think about this:

physics.stackexchange.com/review/suggested-edits/101075

I'm unsure what to do

Reject for not reflecting author's intent?

ArtOfCode

@Danu Aye, reject

user54412

@Danu I'm not really sure

Danu

@ChrisWhite I guess it's too extensive---should just be a separate post.

That being said, it is clearly with good intent.

user54412

I mean, the author didn't seem to actively intend to not put that equation in; it was just laziness of a sort.

user54412

The edit just adds info from the link into the answer, doesn't it?

0celo7

20:42

@DavidZ I must have misunderstood the part where I told to never again let chat disagreements spill over onto the main site again.

David Z

Yeah, sounds like you did.

0celo7

You mind clarifying?

David Z

It's fine to ask legitimate physics questions inspired by a comment somebody makes in chat

0celo7

My electron question was legitimate.

user54412

Does this proposal sound like a good idea: Let edits to posts (especially to new posts) be actionable only by the post owner for some amount of time (an hour?), and only put it into the queue if nothing was resolved. This would lead to fewer rollbacks and also fewer rejected edits that the post owner would have approved if given enough time.

David Z

20:45

@0celo7 If you mean the one that got locked a while ago, no it wasn't

Danu

Hey @0celo7

3

Q: How long can a particle survive inside of the horizon of a black hole?

By examining the causal structure of a Schwarzschild black hole, one can see that a particle in region II is unable to escape to $r=\infty$. Such diagrams do not show, however, how long a particle can survive inside of region II without hitting the singularity. Can a particle survive indefinit...

general-relativity black-holes event-horizon

0celo7

Yeah

Danu

Remember how we discussed that your answer here was, in fact, quite incorrect?

0celo7

I still need to fix that

Danu

I think you should either delete it or heavily rework it.

0celo7

20:49

Be my guest to fix it...

I started to

Danu

I think you should delete it if you don't wanna fix it :P

0celo7

But you have to derive the equations for accelerated motion in curved spacetime

Which is crazy

Danu

Yes, you can't do it

(I don't think it's tractable)

0celo7

I can

It is possible!

Danu

I didn't mean you but "a person"

0celo7

20:50

I have the references

Danu

@0celo7 Go ahead and do it then :P

0celo7

Ah

Danu

But don't leave it like that

you can temporarily delete it

0celo7

In one post, it is not possible, this is correct

Danu

while you work on it

@0celo7 Right

0celo7

20:50

Honestly, fixing that is a project

Danu

Then the answer must be deleted

Until you think you've corrected it, or at least figured out how to.

0celo7

I have the relevant journal articles in my stack

Done.

user54412

@Danu Really? It's a spherically symmetric spacetime with a diagonal metric. 1+1D GR is basically just a redshift factor in the right places.

0celo7

The paper that JR linked has the right answer

Hippalectryon

I have a very basic question on special relativity; Wheeler defines an intertial (free float) frame using '... every free test particle initially at rest with respect to that frame remains at rest, and every free test particle initially in motion with respect to that frame continues its motion without change in speed or direction'. I understand that if the only force we consider is Gravity, but if we add other forces on the test particles, their movement won't be the same anymore...

How do we take that into account ?

0celo7

20:52

But it assumes the equations for accelerated motion in curved spacetime

Danu

@ChrisWhite But obviously we have to allow for someone with a jet-pack

How are you going to make precise how long someone can go how fast ejecting what amount of mass etc etc?

0celo7

If I had a week, I'd try to tackle the problem analytically

user54412

@Danu accelerating radially -- making an ODE inhomogeneous doesn't really make it that much worse :p

Danu

@0celo7 Thanks

@ChrisWhite I'll be eagerly awaiting your answer :D

0celo7

guys

user54412

20:53

Thought you'd say that :/

0celo7

the paper in the comments has the answer

Danu

@0celo7 Good

0celo7

someone just needs to condense it

Danu

Amend it! :D

0celo7

no, because I don't quite understand how accelerated motion in GR works

I think I need to hunt down one more article from the 60s

Brynjolf Calls a Bank - Skyrim Prank Call

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user54412

20:56

@Hippalectryon "free particle" is understood here to have no other forces. If you want other forces, of course the particles will accelerate with respect to each other. Then instead of $m \ddot{a} = 0$ Newton's second law becomes $m \ddot{a} = F$.

Hippalectryon

@ChrisWhite But, is gravity the only force that influences whether the frame is free float or not ?

0celo7

>gravity in SR

this ain't 1907

user54412

@Hippalectryon No. You can define a frame however you want. Even with no gravity in the universe, you can have an accelerated frame.

Hippalectryon

@ChrisWhite Sorry, I was not clear enough. For instance if the gravitational fields undergo great variations in the frame, then it's not free float. What about, say, a greatly changing EM field ?

Danu

@ChrisWhite by the way, the paper @0celo7 mentioned that contains a solution to the problem works out the result numerically, so I guess it's not that easy to do analytically.

0celo7

20:59

indeed

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