The h Bar

Slereah

12:02

Reichenbach's book is pretty neat

lots of top of the line thinking about spacetime and whatnot

but you can tell it was written in the 50's

before the big GR revolution

there are things he does not think of

Swapnil Das

Is mathematical physics a branch of theoretical physics?

Slereah

not quite

Swapnil Das

Or is it kinda independent?

@Slereah Oh.

Slereah

You can do mathematical physics on non-theoretical physics things

Swapnil Das

I see, like?

Slereah

12:05

Well, you know

Just practical physics sort of things?

Fluid mechanics

Thermodynamics

Electromagnetism

Swapnil Das

Yup.

Btw, another question.

Why are graduate theorists in their early years given experimental training?

Slereah

Are they?

Swapnil Das

Yup.

Slereah

also by "early years", do you mean before or after they graduate

Swapnil Das

1st year or so.

Slereah

12:08

well in their first year they do not know if they will be theorists

Swapnil Das

Well, graduates do MS, right?

Slereah

it is considered a good idea to have a well rounded physical education in the early years

and only then specialize

Swapnil Das

@Slereah Do you think that's good, personally?

ACuriousMind

@SwapnilDas That's a strange question, because at least for me that's not true - all my experimental training was during my bachelor's/undergraduate studies.

Slereah

I do not think

I only feel

Swapnil Das

12:10

@ACuriousMind So lucky you are!

@Slereah Oh, fine.

I liked the Cambridge system of deep specialization.

Yashas

@SwapnilDas High school physics practicals is strictly not equal to experimental physics

I am not sure what your definition of experimental physics is

ACuriousMind

@Slereah Perfectly acclimatized to the political world of 2017, then :P

Swapnil Das

From where does HS practical come from?

Slereah

rimshot

Yashas

@SwapnilDas You said ACM was lucky because he did not have to study experimental physics.

Swapnil Das

12:12

Yes. So?

Should I suicide? :P

ACuriousMind

I had to study it! Just...not during my master's.

Yashas

@SwapnilDas ?

I thought you had an impression that experimental physics sucks.

Swapnil Das

I have.

Yashas

The high schools courses in India are designed to kill the love for science and math.

Swapnil Das

(But only for me, personally).

Not only India, all others.

ACuriousMind

12:14

And I actually think it was good that I had to. Specialization is all well and good, but you need to know what you're missing by specializing in another field and every physicist should have a rudimentary knowledge of all field, be they "experimental" or "theoretical".

Yashas

To test for a chemical A, the teacher tells "put X, shake, put Y, boil, put Z, you will get a color which confirms". The teacher does not tell you what actually happens.

The high school courses suck.

Swapnil Das

Lol you're circulating things to no where now.

Yashas

and so do the high school exams

user228700

@JohnRennie It's certainly not the same as pialu and both taste very different from the other.

Slereah

Rudimentary knowledge of electromagnetics, mechanics, thermodynamics, chemistry, biology, sociology, gender studies, african american studies, fine arts, dance, hospitality, spot welding and juggling

the basic fields

Yashas

12:15

Biriyani is more hot than pilau I think.

Swapnil Das

I am in the opinion that those who are theory inclined should be taught higher mathematics or so, and their experimental burden should be halved.

ACuriousMind

@Slereah If you show me this marvelous university where you can study juggling, I'm in ;)

Slereah

@ACuriousMind Clown college?

Swapnil Das

You mean IIT?

Slereah

The sad truth is that most theoretical physics people do not find jobs

It is a good idea to have skills to fall back on

ACuriousMind

12:17

@Slereah Well, of course you also need to be able to study the rest from your list there

Slereah

I'm sure clown college has a robust curriculum

user228700

@Yashas Yep. Several people are also of the opinion that pilau is vegetarian whereas vegetarian briyani is a crime of some sort. I haven't had "proper" biriyani (with meat) so I can hardly comment on this.

Swapnil Das

@Slereah Why so?

Slereah

@SwapnilDas because theoretical physics is poorly funded

Swapnil Das

I see.

ACuriousMind

12:18

@SwapnilDas Many of those who are "theory-inclined" tend to realize at some point that while they might have been good at math they don't actually want to do actual theory. Of those who started studying with me saying they want to be theorists there are roughly 10% left actually doing theory.

Swapnil Das

@ACuriousMind Lol, why so?

ACuriousMind

This is before you add in the scarcity of theoretical funding that Slereah mentioned

Slereah

Theory sounds good until you actually have to do the math :p

ACuriousMind

@SwapnilDas Because when you get out of school and into university, you have basically no idea what you're getting into :P

Swapnil Das

@Slereah True.

@ACuriousMind Did you have?

Yashas

12:20

@SwapnilDas Don't ignore high school practicals; you will get screwed International Olympiad Selection Camps. Both theoretical and practical skills are checked.

Slereah

Balarka Sen

are we still talking about education and pedagogy

Slereah

Your average theory paper

Yashas

It is a very bad trend in the Indian education system. Nobody takes practicals seriously.

ACuriousMind

@SwapnilDas I thought I did, but I didn't. I was just lucky that I actually found I enjoyed theory.

Balarka Sen

12:20

we should talk about sound and vision instead

ACuriousMind

@Yashas The "international olympiad selection camps" are your argument for why one shouldn't ignore experimental training???

Swapnil Das

@Yashas My dear brother, I am not against High School practicals. Keep calm and go to bathroom.

ACuriousMind

I...don't know what to say

Swapnil Das

@ACuriousMind Oh please control yourself :P

Balarka Sen

chillax

Swapnil Das

12:22

lol.

Balarka Sen

if you don't know what to say don't say anything. easily done

ACuriousMind

@BalarkaSen Sound and vision of what?

Yashas

@ACuriousMind I did not mean to say that take experimental training for the sake of IPhO. I just pointed out becaz Swapnil is interested in taking the olympiads.

Balarka Sen

@ACuriousMind Of sound and vision!

David bowie-Sound and vision

►

Swapnil Das

For god's sake, when did I tell that I'm against experimentation? :P

Yashas

12:23

10 mins ago, by Swapnil Das

I have.

Slereah

Apparently Newton used the phrase "parts cannot be sensually perceived"

Very sensual

Swapnil Das

Experimental Physics is equal to HS practicals? Now you're making me angry.

Yashas

14 mins ago, by Yashas

@SwapnilDas High school physics practicals is strictly not equal to experimental physics

I just picked the wrong context.

Swapnil Das

He bhagwan (Oh god)

Yashas

I assumed that you were just another victim of the education system. So I made an attempt to put the blame on the education system and change your opinion of experimental physics.

Swapnil Das

12:26

No your assumption is wrong. I got 20/20 in Maths FA4 LOL

Yashas

20/20 is nothing special

Swapnil Das

Satire intended.

Yashas

3/4 of the class gets 20/20 in FA

Did you take NSEJS?

Swapnil Das

Here it is around 3.5/4 :P

No.

Yashas

20/20 is not an indication that the person likes what he does.

Swapnil Das

12:27

Cool down, man.

Yashas

Those who get 99% in 12th boards don't even get a rank in JEE Advanced.

Swapnil Das

Cool down.

ACuriousMind

@BalarkaSen Heh. I'm afraid I can't contribute much to that discussion :P

Swapnil Das

Anyone here interested in watching Nat Geo's Genius?

Balarka Sen

@Yashas But... that's not an indication that the person does not like what he does, either.

Yashas

12:29

Yes.

Balarka Sen

So I am not sure how that second sentence is even remotely related with the first.

Swapnil Das

Huh what?

Oh fine.

54

Q: Linear sigma models and integrable systems

I'm a mathematician who recently became very interested in questions related to mathematical physics but somehow, I already have difficulties in penetrating the literature... I'd highly appreciate any help with the following question: My aim is to relate a certain (equivariant) linear sigma mode...

Yashas

@BalarkaSen JEE Advanced tests for concepts and it is much more difficult than high school exams. Usually, the students who qualify for International Olympiads take the top JEE ranks. Anyone can get full in high school exams by mugging up but those students get caught in the competitive exams. In other words, high If you have 100% in high school exams, no good college takes you unless you have a good rank in a competitive exam. school marks have no value in India.

Swapnil Das

Unsolved problem in PSE?

Yashas

@BalarkaSen In other words, the high school exams are too bad at filtering out the student who loves the subjects and understands the concept from those who mug things up.

Swapnil Das

12:33

Thus proved.

Balarka Sen

@Yashas I have nothing whatsoever to agree or disagree with that wall of text about getting good ranks in competitive exams. How does qualifying or not qualifyinng in competitive exams have anything whatsoever to do with loving or not loving the subject? :P

I probably can't do half the problems in JEE. I certainly love math!

Slereah

Hey, the timelike cylinder!

I wonder if that's the first appearance of the timelike cylinder

Swapnil Das

@BalarkaSen Half of the math problems?

Slereah

sounds like a question for HSMSE!

Balarka Sen

Indeed.

Yashas

12:36

@BalarkaSen Getting a good marks in a JEE subject section requires a good understanding of the subject. It takes years to perfect them. Someone who does not enjoy studying it cannot do well. It is going to be hell if the person forces himself to study just because he wants a good rank. And that wasn't the point I wanted to make; I wanted to tell that school marks have no relationship with how much the person loves the subject. I used JEE marks as an evidence for my claim.

Swapnil Das

You're joking.

ACuriousMind

@Slereah Which version? The angular or the length coordinate timelike?

Balarka Sen

@Yashas There's some funny illogic going on here. "Someone who does not enjoy studying it cannot do well". That means "A person does good in JEE" $\implies$ "A person enjoys the subject". But surely it doesn't mean the implication in the other direction, right?

Yashas

@BalarkaSen Nope. It doesn't mean in the other direction.

Swapnil Das

Sheldon cooper was a prof. at the University of Heidelberg :P @ACuriousMind

Slereah

12:40

@ACuriousMind this one

ACuriousMind

@BalarkaSen I don't know whether "illogic" is a word, but I'm definitely stealing that.

Balarka Sen

@ACuriousMind :P Yeah, I think it is an actual word.

Swapnil Das

google.co.in/#q=illogic

ACuriousMind

@Slereah which one?

Slereah

Bloody hell it's not uploadîg :V

dropbox.com/s/blyfiivjy63m69n/timelike%20cylinder.png?dl=0

Can't seem to upload it to SE's imgur

The book is from 1957

Balarka Sen

12:46

@Yashas So we conclude this is not a measure of whether or not a person enjoys the subject, as your measure is "not getting good rank in JEE" and not "getting good rank in JEE".

Slereah

That's the earliest appearance of the timelike cylinder I can think of

although it's possible that it has been used before

Balarka Sen

Hence, we come back to the earlier question of why that sentence is relevant to the previous one.

By a logic-troll :)

ACuriousMind

@Slereah ah, I see

I bet SE has blocked images depicting weird spacetimes from their imgur :P

Slereah

Reichenbach isn't big on bibliography so basically nothing has a source

He probably thinks since he's a philosopher everything is obvious

Anonymous

@BalarkaSen I agree with you there.

Yashas

12:47

@BalarkaSen Uh no. JEE Advanced is too hard; it is impossible to mug things up and score well. The JEE Advanced effectively filters out those who have good conceptual understanding from those who don't. The students who prepare for JEE are very dedicated and hardworking. They generally love what they do. BUt it is true that not all (in fact, the majority) of those who are int he top 1% in high school exams don't do well in JEE.

JEE tests concepts; high school exams don't. Someone who isn't interested in the subject won't really bother to think deeper and understand the subject.

For most of them, the goal is to secure 100. My school rank was 51/169. There were 30 students with CGPA 10.0, mine was just 9.6. However, not a single person from my batch other than me has cleared KVPY.

The point I wanted to make was do not use high school marks.

Anonymous

@Yashas I think balarka's point is $a \implies b$ but $b\not\implies a$. Not everyone who likes maths does well in competitive exams.

Balarka Sen

@Yashas Look, dude. We just concluded "A person enjoy subject" does not imply "A person does good in JEE". Hence, a person can enjoy the subjects and not get a good rank in JEE. So "don't even get a rank in JEE Advanced." has nothing to do with enjoying or not enjoying the subjects.

This is basic mathematical logic.

Yashas

I really don't know what to say but every Indian is going to understand what I meant.

High school marks is not a measure of how much a person likes the subject was the main assertion.

Balarka Sen

I am just saying whatever you are saying is logically flawed :)

Anonymous

@Yashas That is right.

Anonymous

12:53

But not your second conclusion.

Yashas

JEE Advanced requires understanding concepts and applying them. Those who don't understand the subject don't stand a chance in JEE.

When I said those who score 99%+ in high school exams don't even get a rank in JEE, I meant they are too bad at the subjects but still scored 99% becaz the exams allow a person who can mug score good.

ACuriousMind

@Yashas Neither are any other marks. People can enjoy subjects without being good at them at all. Your claim is that only people who enjoy a subject will score well in its JEE (and I have no way of assessing the veracity of that claim), but even if that is true, it does not imply that people who don't score well don't enjoy the subject, which is what you seem to be saying.

Yashas

@ACuriousMind That wasn't my claim at all. It was misinterpreted.

As JEE demands conceptual clarity, I used it as an evidence to back my claim up for the high school marks case.

Anonymous

@Yashas Now, that is wrong. People who scored 99 percent in high school may not have prepared for competitive exams! That's why they do badly in JEE. That doesn't mean they are not interested in maths.

Yashas

@blue I am explicitly referring to the students who mug up to score 99%.

Who don't bother to understand; whose goal is to get 100/100 and nothing else.

ACuriousMind

12:56

@Yashas If you didn't want to say that high JEE scores imply that you enjoy a subject, then I have honestly no idea what you actually wanted to say.

Anonymous

@Yashas Right. You should have mentioned that here. :-)

Yashas

I did mention that several times @blue

Balarka Sen

If it was misinterpreted it was because it was written in a logically unparsable way. Hence why you're getting logic-trolled right now.

But I am gonna back off from this now :P

Fawad

In some coaching centered they only teach tricks to solve problems with conceptual understanding of that subject :/

Anonymous

@Yashas lol...they are trolling you...didn't you get it? =P

Yashas

12:57

9 mins ago, by Yashas

@BalarkaSen Uh no. JEE Advanced is too hard; it is impossible to mug things up and score well. The JEE Advanced effectively filters out those who have good conceptual understanding from those who don't. The students who prepare for JEE are very dedicated and hardworking. They generally love what they do. BUt it is true that not all (in fact, the majority) of those who are int he top 1% in high school exams don't do well in JEE.

"it is impossible to mug things up and score well. "

that was the point

0celouvsky

Oh my god

Yashas

but the same person can score 99% in high school exams

Fawad

@0celouvsky hey, for Christians god=Jesus?

0celouvsky

For Catholics, yes

I don't know about other denominations

Balarka Sen

@0celouvsky repulsed from seeing mathematical logic?

0celouvsky

12:59

@BalarkaSen I don't see any logic

ACuriousMind

@Fawad That's a major point of contention among the different Christian denominations

Balarka Sen

why are you exclaiming then

Yashas

@ACuriousMind Do you think someone who does not love physics can top physics in a graduate course? I was trying to make a similar argument in my previous replies. If a person does not like the subject and does not bother to understand the concepts, it is too difficult for him to secure a good rank.

Anonymous

@BalarkaSen He is calling god for help =P

Fawad

@ACuriousMind I see ,thank for replying.

Slereah

13:00

I wonder if there's a modern day epistemology book on GR

A good one, that is

ACuriousMind

Debates about the exact status of the trinity (god/"father", Jesus, holy spirit) have led to several schisms and rather ugly incidents over the course of the last two thousand years

Anonymous

I thought Santa Claus is considered a god....

Slereah

The Holy Trinity | Music Videos | Axis of Awesome

►

Yashas

Is Santa Claus real?

Slereah

I think I may have to do the bibliography by hand because JabRef doesn't seem to work too fine

Yashas

13:02

I mean, is it in the Bible?

Slereah

Santa Clause comes from Saint Nicholas

Anonymous

@Yashas He used to put chocolates in my stockings till I was 10 years =D

Slereah

Who is not in the bible

although he is a saint of the Catholic church

0celouvsky

@Slereah malament

Slereah

Hey Malament

Fawad

13:03

@blue say your parents you missed Santa Claus :D

Slereah

I know him from his QFT theorem

Anonymous

@Fawad I should. Really ;)

Slereah

is it "Topics in the Foundations of General Relativity and Newtonian Gravitation Theory "

socsci.uci.edu/~dmalamen/bio/GR.pdf

Fawad

@Slereah what's your age?

Slereah

I am 13

4

old enough for SE!

Anonymous

13:06

@Slereah On which planet?

Fawad

@blue or "in which base?"

Balarka Sen

@0celo That's a planet?

Slereah

That book isn't very epistemology oriented but it seems like a fine GR book

Anonymous

@BalarkaSen laughfactory.com/jokes/yo-momma-jokes

Balarka Sen

I know those jokes. I was making a meta-joke.

Anonymous

13:09

Those jokes are cringeworthy.

Balarka Sen

A planet called "yo momma" would be amusing.

0celouvsky

@blue take that back

ACuriousMind

@BalarkaSen New life goal: Become an astronomer, discover a planet, then name it?

Slereah

it even has a section on Gödel's spacetime

Let's see if it actually has the proof for it

0celouvsky

Proof for what?

Slereah

13:10

u know the one

0celouvsky

the one my advisor came up with?

Slereah

well, the one Hawking Ellis tries to say

it's one of those books that uses the pound symbol for the Lie derivative

0celouvsky

> Show that the tensor product makes $K(X)$ into a commutative ring with unit $\Bbb C_X$.

No

I refuse

Slereah

Also he uses sh for sinh

0celouvsky

@ACuriousMind What is the universal property for abelian semigroups?

Slereah

13:14

"They are closed curves, characterized by constant values for t, r, and z. We shall call them (or their images) Gödel circles."

The old Gödel circle

0celouvsky

$A$ is an Abelian semigroup, $B$ is the group "$A+(-A)$", and $G$ is some other group

$\phi:A\to B$ is the embedding

and $h:A\to G$ is a semigroup homomorphism

apparently it follows that $h'$ is unique

Slereah

"Other interesting features of Gödel spacetime are closely related to the existence of closed timelike curves. So, for example, a slice (in any relativistic spacetime) is a spacelike hypersurface that, as a subset of the background manifold, is closed. We can think of it as a candidate for a “global simultaneity slice.”
It turns out that there are no slices in Gödel spacetime. More generally, given any relativistic spacetime, if it is temporally orientable and simply connected and has smooth closed timelike curves through every point, then it does not admit any slices (Hawking and Ellis [30…

Damn it

0celouvsky

hahahaahahhahaahahah

Slereah

oh well

I'm saving it

0celouvsky

Why are you so upset?

Slereah

13:17

it's a nice enough book

0celouvsky

My advisor gave you the proof!

Slereah

well, you know

A whole chapter on Gödel's spacetime

You'd expect an explicit proof

Also the proof isn't quite the same

I'm still not quite sure what the HE proof is about

0celouvsky

@ACuriousMind c'mon, it's algebra

ACuriousMind

@0celouvsky From looking at the diagram, it appears you want a universal property not for a semigroup but for the completion of a semigroup (also called the Grothendieck group)

0celouvsky

@ACuriousMind Well yes

I'm looking at the Grothendieck ring of vector bundles

This book just doesn't call it that so my terminology is confused

ACuriousMind

13:21

So...what is your question to me? You have already written down the univ. property.

0celouvsky

How do I prove it?

ACuriousMind

Prove what?

0celouvsky

...the universal property

ACuriousMind

What's your definition of the completion/Grothendieck group, then?

0celouvsky

@ACuriousMind $B=A\times A/\sim$ where $(a_1,a_2)\sim (a_1',a_2')\Leftrightarrow \exists a,a'\in A: (a_1\oplus a,a_2\oplus a)=(a_1'\oplus a',a_2'\oplus a')$.

ACuriousMind

13:23

Do you take $A\times A$ and then quotient by a relation analogous to how the field of fractions of a ring is constructed?

Ah, yes.

0celouvsky

brb

Slereah

You know I find it a bit odd that basically from Gödel's paper until the 60's there was so little efforts on CTCs

Isn't it an interesting result?

0celouvsky

it's unphysical

physicists only care about measurable things @Slereah

Slereah

That makes it even more interesting

A theory that gives you an unphysical result is a theory in need of investigation

ACuriousMind

@0celouvsky So with that construction, $\phi$ is the map $x\mapsto (x,0)$. Let some $h : A\to G$ be given, and $h',h'' : B\to G$ such that the triangle commutes. Then $h'(\phi(x)) = h''(\phi(x))$, i.e. $h'(x,0) = h''(x,0)$ but since $h',h''$ are group homomorphisms you also have $-h'(0,x) = -h''(0,x)$ and $h'(x,y) = h'(x,0) + h'(0,y) = h''(x,0) + h''(0,y) = h''(x,y)$, so $h'=h''$, i.e. $h'$ is unique.

Slereah

13:32

Hm

Weyl wrote a book about causality in 32

and he was the one to write about CTCs in 22

ACuriousMind

Is there anything Weyl didn't meddle in?

That guy was prolific

Slereah

he was

I'm not sure what that book is about

Doesn't seem to be online

it's not too expensive, though

20 bucks

Ramanujan

Hello @yashas

Yashas

hi

Slereah

Oh wait

I think there was a Thing with Gödel for a while

Someone looked at the Gödel metric, found out that the geodesics were not CTCs and everyone did a sigh of relief

Ramanujan

13:38

Q. A block of weight 1N is moving with acceleration of 1m/s^2. Find the force on the block.

@yashas

Slereah

Without thinking that non-geodesic curves could be a problem

although that was in 61

Yashas

@Ramanujan Ask in JEE room before people equate your 10th grade high school questions to JEE>

Slereah

what did people do in between

Hm

Anonymous

@Yashas 10 th grade is not even high school

Anonymous

lol

0celouvsky

13:40

@ACuriousMind Uh, how do I get $h',h''$?

Slereah

Apparently there's a weird variation of the Schwarzschild metric with CTCs???

Yashas

@blue 9th, 10th, 11th, 12th grade is high school

Kyle Kanos

I'm voting to close this question because it appears to have been abandoned by its author and it has no answers. — sammy gerbil 23 hours ago

0celouvsky

How do I know that one can even factor $h$ through $B$?

Kyle Kanos

What the heck is that kind of close reason is that?

Anonymous

13:40

@Yashas Really? we call it middle school... (I think it's different for cbse)

0celouvsky

@KyleKanos three people agreed

Simply Beautiful Art

(not meaning to intervene, but here is my bump funk function which I recently made: googology.wikia.com/wiki/User_blog:Simply_Beautiful_Art/…)

Slereah

"In the so called 'elliptic interpretation' of this metric (first considered, but rejected, by Szekeres, but suggested since then by a number of authors) these two points are identified. The resultant manifold admits closed timelike world lines (penetrating into the region inside the Schwarzschild radius), and numerous authors have suggested that the existence of such lines implies the possibility of causal anomalies."

Whaaaat

This is literally the first time I hear of this

Kyle Kanos

Abandonded questions is not a reason to close a question. Suppose someone has an answer for it, but the problem is that they can't actually answer it because someone decided to close it for no real reason

Slereah

What the hell is that solution

0celouvsky

13:43

@KyleKanos I VTC'd

Simply Beautiful Art

@KyleKanos Happens all the time sadly

0celouvsky

@ACuriousMind Can one just "formally" apply $h$ to the first factor of $\phi(a)=(a,0)$?

Kyle Kanos

@0celouvsky Not in the review physics.stackexchange.com/review/close/171459

0celouvsky

@KyleKanos I was kidding but that snark is making me consider it

ACuriousMind

@KyleKanos Uh, please be nice even in instances like this where the close reason is completely off-target. In any case, I completed that review with a leave open decision.

Kyle Kanos

13:44

@SimplyBeautifulArt It shouldn't. And if it is happening, then it needs to be brought to attention of the community because it's wrong

0celouvsky

I don't even understand the purpose

Kyle Kanos

@ACuriousMind Fair enough; feel free to delete that if you want

And thanks for completing the review

0celouvsky

what does closing year old questions do

Simply Beautiful Art

@KyleKanos The best one should do is reopen, if appropriate, or find links to give to OP through comments.

Kyle Kanos

@0celouvsky Possibility of being roomba'd so that answered % stats increase?

ACuriousMind

13:45

@0celouvsky That's basically what $h = h'\circ \phi$ says $h'$ is doing.

Simply Beautiful Art

Not all answerable questions should remain open. Not all unanswerable questions should be closed. Just do the best of what you think is right.

Kyle Kanos

@SimplyBeautifulArt But the issue is voting to close them because they are unanswered...

Not unanswerable, just unanswered

Simply Beautiful Art

Oh, yeah, that's definitely not the right reason to close

If anything, the community user should be the only user who closes and deletes questions for lack of attention/being unanswered, and only after long periods of time

Slereah

Kruskal's 1960 paper includes the term "wormhole" already

neat

ACuriousMind

@SimplyBeautifulArt Closed questions with negative score are deleted by Community after some time

Slereah

13:49

ACuriousMind

But non-closed questions simply shouldn't be closed because they are old

2

If they are on-topic, they don't become suddenly off-topic just by aging, barring exceptional shifts in site policy in the interim

Simply Beautiful Art

@ACuriousMind I know, which is why I said that.

ACuriousMind

Ah, I wasn't certain if you were describing the status quo or saying how it should be, disregard that, then.

John Rennie

@Slereah It has never been clear to me how it can be argued that the two ends of the wormhole are in the same part of the spacetime i.e. there is a path between them that does not go through the wormhole.

0celouvsky

what

Slereah

13:54

@JohnRennie purely from the metric, nothing indicates it, no

Oh man

This sounds like something that would have been proven wrong or something later on

But I still have to check

unless he's talking only about the Kerr metric, but the paper seems to not cover those

"A hypothetical observer whose history is given by (10) lives and relives the same set of experiences endlessly, and might be described as a "Flying Dutchman"."

In this weird Schwarzschild metric sending something in the singularity will make it bounce back or something

I don't need more weird spacetime damn it

I'm too close to bedtime for this

I think it might be Schwartzschild with some weird identification

One of the paper I'm looking for isn't available online and is also in hungarian

tough

0celouvsky

14:23

What is the metric

Slereah

$$ds^2 = 2 du dz + (\frac{z^2}{2mr}) du^2 + r^2 d\Omega$$

It becomes Schwarzschild under the coordinate change $$r = 2m + \frac{uz}{4m}$$ $$t = r - 2m \ln(u/2z)$$

you may note that $r = 0$ has two solutions

I think this is the old wormhole trick sort of thing

Instead of having the coordinate $r$ defined on $\Bbb R^+$, have another coordinate defined on $\Bbb R$

Oh wait, there's a section on the identifications of the spacetime

journals.aps.org/pr/abstract/10.1103/PhysRev.143.1016

the paper btw

yeah apparently the whole CTC business only works under the interpretation that $(u, z, \theta, \phi)$ and $(-u, -z, \theta, \phi)$ are identified

Apparently it's not causal or time oriented

What the hell was Israel even thinking

That's like the least helpful Schwartzschild metric

I'm not even quite sure what that would look like in Schwarzschild coordinates

Switching $u,z$ with $-u,-z$ doesn't seem to change diddly in Schw. coordinates

Oh my god there's a ton of 60's papers on the topic

Help me

the ride never ends

I think it might correspond to twisting the region II and identifying it with region IV

Simply Beautiful Art

14:49

I like pretty graphs

Slereah

15:09

Is there even a rigorous atlas of the Schwarzschild spacetime in Schwarzchild coordinates

there's an exterior solution, there's an interior solution, but there's no overlap of those patches

Slereah

15:22

Damn

apparently Reichenbach came up with the timelike cylinder in 1928

He invented CTCs D:

Well, the first explicit example

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