The h Bar

paracetamol

07:00

._.

2

I live in the southern rocky mountains of Canada. I was in bed the other night when I saw a small scurrying shadow out of the corner of my eye. The source of the shadow was a small spider (95% sure it was a barn funnel weaver), approx 2cm in diameter. I killed the spider. Interestingly, what in...

arachnology

^ Wow :O

I'll send this over to The Periodic Table :3

user228700

If I am allowed to divert your attention from moths for just a bit, @JohnR: I've found out just now that my family is moving out of Chennai after I move out to college this fall :'-(

John Rennie

Oh wow! Where are you going? Somewhere nice?

paracetamol

Hmm?

user228700

@JohnRennie We don't know yet. No place is as nice as Chennai :'-( It's...home.

John Rennie

@paracetamol it was a xenomorph spider! :-)

paracetamol

07:03

@JohnRennie Um...I just popped over at The Periodic Table...and yeah, it's a "nice" place...I guess...

user228700

^ @JohnR: para has put me on ignore.

John Rennie

@Kaumudi.H I wouldn't be too hasty to judge. I've moved several times - Sudan 9 years, Somerset 10 years, Cambridge 6 years and now Chester for 31 years. Each time it's initially a wrench, but you quickly come to love your new home.

@Kaumudi.H his loss

paracetamol

You know, if you answer the moth question you'll get 25 rep soon :3

@JohnRennie Someone died?

Shakes head

user228700

@JohnRennie Ah, yes, I see. But I've lived here for 18 years now :'-(

Anonymous

@Kaumudi.H How does it matter? Your college will be in another city anyway, won't it?

paracetamol

07:07

@JohnRennie Sometimes I wonder if I really have to go for the quasidetailed description of stuff they drive into our brains at Bio class when I have you :3

user228700

@blue Yes, but I won't have a home to come back to.

paracetamol

> Couldn't have been bigger than an inch. Took the picture at night. Has characteristic orange stripes across wings and dorsal thorax. A pair of black dots present on either wing; one pair located on the distal region of the wings and another (less conspicuous) pair located on the proximal region of the wings (laterally over thorax). No immediate/visible response when I shone a flashlight at it (eventually moved the torch up to the antennae, still no reaction).

John Rennie

@Kaumudi.H I sympathise - I'm just saying that few things are as bad as you think they're going to be (few things that don't involve red hot knitting needles anyway).

Anonymous

@Kaumudi.H Will you sell away your Chennai house or what? You could visit during holidays...

user228700

@JohnRennie Yes, I suppose. I will have to wait and see.

user228700

07:09

Hmm, you've mentioned red hot knitting needles a few times now. Did u ever have an unfortunate incident with them? :-P

user228700

@blue I live in a rented apartment. We do have a house of our own in the outskirts of Chennai but emphasis on: outskirts.

Anonymous

@Kaumudi.H I see :/

Anonymous

I've always been moving since childhood

Anonymous

So I'm not attached to any place as such

user228700

Ah, well, that's just as bad, I'd guess...

John Rennie

07:11

@Kaumudi.H it was a silly jokes from my childhood. But that's OK because I have a silly sense of humour :-)

paracetamol

1

A: What moth is this?

That is a red striped tiger moth. An initial search hasn't found a picture I'm sure is redistributable, so I've linked a Google image search instead. The number of spots on the wing seem variable. The pictures show examples with four and six spots as well as two spots.

user228700

@JohnRennie :-) Wokay.

Balarka Sen

@0celouvsky every Riemann surface.

any 2-manifold admits a complex structure

oriented closed

paracetamol

Danke Herr @JohnR

Anonymous

@Kaumudi.H Um, I can call almost every major Indian city as my city =P Each one is good in its own way :)

Always Confused

07:15

@paracetamol Thank you for sharing.

user228700

@blue That's a bit...strange but good for you! :-)

paracetamol

@Always Bitte ;)

@blue Hullo o/

Yeah... I un-ignored you ._.

Don't ask why ಠ_ಠ

Balarka Sen

i am not sure if i connected to the city i am living in for the last 5 years

Anonymous

@paracetamol I knew, you can't live without me ;)

paracetamol

Don't get too complacent there buddy -_-

John Rennie

07:19

@Kaumudi.H I think you'll be surprised at how engrossing university is. You're surrounded by hundreds, if not thousands, of other people all around your age and all with roughly the same interests.

Once you get over the initial feeling of dislocation (everyone gets this!) it is intoxicating!

user228700

From here, that sounds more anxiety-inducing than comforting but I hope it's great :-)

Balarka Sen

Here's a description of a city I like: "Unreal City, / Under the brown fog of a winter dawn, / A crowd flowed over London Bridge, so many, / I had not thought death had undone so many. / Sighs, short and infrequent, were exhaled, / And each man fixed his eyes before his feet."

paracetamol

@JohnR You wanted "harder"? Here ye go mate!

0

Q: Moth that resembles a leaf. What species is this?

Location: Urban area near the Western Ghats, Kerala, South India Date: Sometime in September, 2016 Climatic Conditions: Humid, frequent rains. Brief description: Head isn't prominent from the dorsal view. Wings outstretched even when at rest. Antennae largely concealed under the fore wings...

species-identification entomology

John Rennie

@Kaumudi.H The first few weeks are scary because you're on your own - the safety net that your parents have always provided isn't there. I'm not saying this to try and scare you - it happens to everyone so what I'm saying is don't worry if your initial reaction is I want to go home!

paracetamol

Oh, hullo @Kau o/

:/

@JohnR I really want to see you try and get this 3:)

Smug expression

user228700

07:24

@JohnRennie Hmm. Well, I s'pose some of the anxiety comes from all of the new people aaah but I hope I can find my niche.

John Rennie

@Kaumudi.H you'd be surprised how easy it is to hide in a crowd if that's really what you want to do.

You don't have to jump in at the deep end.

user228700

Hide? What dyou mean?

paracetamol

Oh crap...

@Always Know this moth?

John Rennie

@paracetamol: does the Biology SE encourage that sort of species identification question? It seems a bit routine.

paracetamol

@JohnRennie Apparently, yeah ._.

Just following the crowd, just following the crowd :3

@JohnRennie biology.stackexchange.com/questions/tagged/…

John Rennie

07:30

@paracetamol I think it's this one though that doesn't help as it just describes it as an unidentified moth.

paracetamol

Tickles @Kau

@JohnRennie Whoa, you're good! But...you still couldn't identify it BWAHAHAHAH! (...and neither can I ._.)

John Rennie

@paracetamol it looks a bit like Micronia aculeata but doesn't have the spots.

paracetamol

^Apart from that and the colour issue...I'd say you've pretty much nailed it :O

I admire your tenacity :O

Secretly envious of @JohnR

Sighs

It looks like @Kau has indeed forsaken me :'(

How brutal...

John Rennie

@paracetamol she thinks you have her on ignore ...

paracetamol

^ I do...more like I did 3:)

In the end, I suppose un-ignoring her wouldn't do me any harm :3

Especially if she's into giraffe sex :D

1 hour ago, by Kaumudi. H

Yes, @JohnR: The vlogbrothers occasionally make videos about giraffe sex as well :-P

John Rennie

07:39

You started it with the animal high jinks!

paracetamol

Smiles to self

user228700

@JohnRennie Well, he did put me on ignore. While I haven't put him on ignore, I have decided to ignore him anyway. How the heck am I to respond to "tickes @Kau" after all the jabs?

paracetamol

@JohnRennie Hey! It's called innate curiosity ;)

John Rennie

@Kaumudi.H He also says Tickle John so I doubt it's personal :-)

user228700

@JohnRennie He tickles everybody but still.

paracetamol

07:40

@Kaumudi.H Well, you could laugh for once ^_^

John Rennie

I suspect it just means ping John i.e. a way of attracting someone's attention.

Balarka Sen

i stand by that this is utter childishness

paracetamol

yesterday, by paracresol

tickles @JohnR

4 hours ago, by paracetamol

Tickles @0celo

Tickles @Balarka

Balarka Sen

shove off pal

user228700

@paracetamol I'm afraid that your weird sense of humor doesn't bring even a smile to my face.

paracetamol

07:41

^ Tickles @Kau some more

John Rennie

@paracetamol: just be cautious about bugging any specific person. The moderators are ever watchful.

paracetamol

Geez, live a little lady :P @JohnR Point there ._.

Anonymous

I wonder if you tickle people in real life to attract attention :D @paracetamol

user228700

@paracetamol You learn to be more thoughtful!

John Rennie

@paracetamol If someone tells you to stop bugging them then you stop - no ifs, no buts.

user228700

07:43

^ Exactly.

paracetamol

@blue No... voice modulation suffices ._.

@JohnRennie Roger that!

user228700

I have had this conversation way too many times for my liking so I will now go back to ignoring you, thank you very much.

paracetamol

in The Periodic Table, Jan 6 at 11:27, by Kaumudi. H

x'D Aha! Exactly!

@Kaumudi.H Bows

@JohnR The colour still bugs me though :(

Pun intended

John Rennie

@paracetamol The trouble is that while there are relatively few species of birds there are frakking millions of moths.

paracetamol

[Unrelated: Just confirming: You don't bear me any ill-will because I tickled you, do you?]

@JohnRennie True that ;D

How about we do spiders next?

Hopes @Kau is arachnophobic

user228700

07:47

Sigh. It did happen:

user228700

yesterday, by Kaumudi. H

@paracresol :-( Please don't ruin The h Bar for me.

paracetamol

Rolls eyes

Slereah

"non-Hausdorff manifolds may have any cardinality from $\mathfrak c$ upwards"

Physics Meta

0

Q: A way to mark questions as non-duplicates?

I'm new to SE but practically every day I come across constructive, thought-out questions that are very quickly marked as duplicates -- while a simple comparison with the alleged duplicate shows very clearly that they are asking a quite different thing. Often, the two questions are about the sa...

discussion questions tags duplicates

Slereah

Fairly big

John Rennie

07:50

@paracetamol From now on, until you are advised otherwise you don't ping or otherwise reference Kaumudi, even indirectly. This is a final warning.

paracetamol

@JohnR Also, I've got pictures of my neighbour's kittens but I couldn't care less about identifying them...guess the only reason I took those pictures in the first place was because they were kittens! :3

@JohnRennie Deal

Balarka Sen

@Slereah Hm. I thought you get an upper bound by 2nd countability.

Slereah

Manifolds aren't required to be second countable, though

It's only recommended

Balarka Sen

My manifolds certainly are!

Slereah

Well yes but I'm sure they're also Hausdorff

user228700

07:52

@JohnRennie Thank you _/\_

Balarka Sen

But yeah if you don't assume second countability things will become bad

Slereah

I think the complete feather is probably really fucked up cardinality-wise

Balarka Sen

Ya

It's probably 2^c

Slereah

Hm

Apparently there are non-hausdorff manifolds used for twistor spaces

iopscience.iop.org/article/10.1088/0951-7715/1/1/004

Balarka Sen

my favorite non Hausdorff manifolds are leaf space of foliations

Slereah

07:58

well it's the only one commonly used for anything

Balarka Sen

It brings a pretty interesting question actually. Can every non Hausdorff 2nd countable manifold appear as leaf space of foliations?

I certainly don't know an example.

paracetamol

Incredible! Someone's actually beaten you to it @JohnR!

1

A: Moth that resembles a leaf. What species is this?

Not a Moth, it's a Geometrid emerald butterfly. http://www.fnanaturesearch.org/images/stories/ns/marked/M/7002.jpg

Slereah

I think the easiest way to have an arbitrary sized non-Hausdorff manifold is like

Take the line with $\aleph_n$ origins

It's probably fairly simple to define, though not very secound countable

Balarka Sen

Yeah

Good idea. That's probably exactly it.

John Rennie

@paracetamol I'm not convinced. Your moth/butterfly doesn't have the hairs on the edges of its wings, and the shape of the wings is different.

The trouble is that there are so many species of butterfly/moths that there will be many species that look almost the same as yours.

paracetamol

08:04

@JohnRennie Well, it comes pretty close ._.

John Rennie

Close, but no cigar

paracetamol

So I guess that remains my accepted answer... unless you come up with a better one ;)

I'm hinting

0

Q: Intriguing marks on the abdomen. What spider is this?

Location: Urban area near the Western Ghats, Kerala, South India. Date: Sometime in the summer, 2016

species-identification arachnology

Try that^

@JohnR I decided to chuck the description for that one... since I have you! A devoted bird/insect watcher cum Goggle user!

Slereah

What i would like to know, though

Do non-Hausdorff manifolds always contain a Hausdorff submanifold

Balarka Sen

A point is a Hausdorff submanifold.

Slereah

Of the same dimension

AND THAT ISN'T THE EMPTY SET

I'm seeing you coming a mile away

Balarka Sen

08:09

lol

Well, a manifold means there's an nbhd around any point homeomorphic to R^k. That R^k is a Hausdorff subfold

(Sorry :P)

Slereah

True enough, I suppose!

John Rennie

@paracetamol too easy

Slereah

"Any homeomorphism of the line with a double origin must either fix both origins $0$ and $0^*$ or interchange them."

paracetamol

Laughs

I applaud you @JohnR :D

Slereah

"The complete feather does, however, exhibit a homogeneous non-Hausdorff 1-manifold"

That bloody feather

paracetamol

08:13

Go on, be a good physicist and write up that answer :3

By the way... what keywords did you use? O_o

Slereah

maths.ed.ac.uk/~jmf/CV/Seminars/EDGE2012.pdf

that's an odd title

Balarka Sen

@Slereah Not surprising, because you have a lot of "origins"

Any point is modeled on a tripod

Slereah

Hm

Apparently there are two symbols used in the literature to imply that two points are branching points

Either

or

what to use

John Rennie

@paracetamol this

Balarka Sen

pYq

Slereah

08:20

I guess it is more evocative

It's actually \Ydown in some Latex package

John Rennie

@paracetamol I guessed that the patterns in the web would be the most distinctive feature. Incidentally your question appears to have been deleted ...

paracetamol

@JohnRennie Yeah I deleted it... apparently the species was too obvious (to everyone but me)

Slereah

Apparently xYy is symmetric and reflexive, but not transitive

“Non-Hausdorff spaces, often regarded as a technical nuisance, sometimes produce a global disaster.”

Good quote

Balarka Sen

i concur

paracetamol

Anyways, I'm off @JohnR. Cheerio! o/

Slereah

08:27

“Kelley’s book set the cat among the pigeons in 1955 by daring to omit the Hausdorff condition from many of its definitions.”

I get the impression that mathematicians don't like non-Hausdorff manifolds too much

John Rennie

@paracetamol Bye

Secret

08:41

0

Q: Are neutrinos diffused or defracted by the moon?

We all know that neutrinos pass directly through things, even big things such as the earth. However it is also known that neutrinos interact with matter as a result of the Z boson or neutral current. This results in small amounts of momentum transfer and people have looked at whether this is me...

neutrinos diffusion moon weak-interaction

(I have a comment after reading this question, but I am unable to express that in words)

Perhaps the closest thing I had in mind is captured by the following two words: "But... why?"

user228700

@JohnR: What's for lunch? :-)

John Rennie

@Kaumudi.H I haven't decided, but I might just have some fruit. The week I spent at my Mum's has not been without its effect on my waistline.

user228700

Ah, I see. OK :-)

John Rennie

What I usually do is eat very sparingly for a couple of weeks and that sheds the surplus fat. Then I can go back to eating like a pig again.

Yesterday was a very healthy, and very tasty, vegetable pilau.

user228700

Ah. That sounds like a good plan :-)

Secret

08:49

I tend to eat like a horse. I eat a lot of salad (and sometimes I am too lazy to get dressing that I decided to just shove the vege into my mouth without thinking

John Rennie

Salad (without dressing) has astonishingly few calories. You literally can't eat enough of it to keep you alive.

Unless, like a horse, you spend your entire waking hours eating :-)

Secret

Well, a few piece of lean chicken breast and some bread (no butter) or rice makes a long way

I do eat steak though, but I tend to choose those that are not too fat nor too dry

John Rennie

But splashing on dressings containing oil and sugar rather spoils the benefits :-)

Secret

balsamic vinegar is usually quite healthy. It does not have that much additives compared to other types of dressing (except compared to plain white vinegar of course)

John Rennie

09:10

2

Well it made me chuckle :-)

Secret

Q: Did you hear oxygen went on a date with potassium?
A: It went OK.

and then Boom!

---
Think of your favorite 90's band, then pick a card

"Um, ok"

What band did you think of?

"Ace of Base"

Now look at your card

"Holy sh--"

atband.com

Found nothing about "Ace of Thymine" though

O wait a minute, I missed the joke: Ace of Base (Thymine)

Secret

I don't understand this one:

Q: How can you spot a chemist in the bathroom?
A: They wash their hands before they use the toilet.

paracetamol

09:26

@JohnR Mind a question on orbital angular momentum? 0:)

John Rennie

@paracetamol Yes?

paracetamol

Going by the equation given in the diagram...wouldn't the orbital angular momentum of an s-electron be zero (since l =0)?

Baffled look

John Rennie

Correct, the orbital angular momentum of an $s$ electron is indeed zero.

paracetamol

O_o

John Rennie

Are you about to ask how that can be if the electron orbits the nucleus?

paracetamol

09:29

After studying the Bohr Model for the past 4 years.... ^Yeah ...

Slereah

why would you study the Bohr model for four years

it's fairly wrong

paracetamol

@Slereah Grade 9 to Grade 12 ;)

Slereah

I'm fairly annoyed

paracetamol

It was a part of my syllabus ._.

Slereah

Ther's two papers

one paper was written after the other, and he knows of it

And they use different terminology for the same things

and they're basically the only two papers talking of it

John Rennie

09:32

@paracetamol electrons, like all quantum objects don't have a position. The electron is described by a wavefunction and this is an extended object.

Slereah

So I can't go with what notation is most common

John Rennie

So an electron is not a point particle orbiting the nucleus.

paracetamol

@JohnRennie Go on

Wait...

Slereah

you can define positions in the path integral formalism

paracetamol

@JohnRennie Alright, but then what on earth does an electron even do in an s orbital?

It's not like it's perfectly still there ._.

Patiently waits for John's explanation

Slereah

09:34

in QM it's best not to worry about what something does in between measurements

otherwise you run into issues

paracetamol

^ True that ;)

John Rennie

Any quantum system is described by its wavefunction. To extract a physical property you operate on that wavefunction with the appropriate operator.

Secret

I just treat all quantum particles as clouds that interfere with each other

paracetamol

@JohnRennie Yeah, that's pretty plain sailing so far...

Slereah

I mean you can perform arbitrarily many measurements in between

if you do, you'll find that particles don't really have a well defined trajectory

They just appear here and there

with no clear pattern

paracetamol

09:35

@Slereah Why does this make make think of Zeno's paradox? :3

Slereah

It's really not related

John Rennie

The expectation (i.e. average) value of the position is given by the position operator, which is just $\mathbf r$. We get $$<r> = <\psi|\hat{r}|\psi>$$

And if you evaluate that for an electron ina hydrogen atom it comes out as zero, which is unsurprising as the spherical symmetry tells us that on average the electron will be at the position of the hydrogen atom.

paracetamol

Vaguely follows

John Rennie

The point is that many of the properties we naturally think of for macroscopic objects, like position and velocity, don't have precise values for quantum objects.

paracetamol

^ Right...

John Rennie

09:39

If you ask what is the position of an electron that is a meaningless question.

You can ask what is the probability I will find the electron here?

Where here means some region of space.

paracetamol

Mmm

John Rennie

Anyhow where we came in is that the angular momentum is a property of the wavefunction and shouldn't be taken to mean there is a point mass whizzing around the nucleus.

4

Q: How can one describe electron motion around hydrogen atom?

I remember from introductory Quantum Mechanics, that hydrogen atom is one of those systems that we can solve without too much ( embarrassing ) approximations. After a number of postulates, QM succeeds at giving right numbers about energy levels, which is very good news. We got rid of the orbit ...

quantum-mechanics atoms electrons hydrogen

And there are literally dozens of other questions that are similar.

Gerold Broser

@JohnRennie You mentioned on Sun that you had to go to work on Mon. Is Easter Monday not a holiday in the UK?

John Rennie

@GeroldBroser I'm a contractor not an employee so I work the hours that suit me.

Gerold Broser

@JohnRennie me 2 :)

@JohnRennie I see. Same here.

@JohnRennie Otherwise I certainly wouldn't be allowed to hang around here frequntly. :)

Secret

09:48

0

Q: Why must the Einstein tensor be linear in the Riemann curvature tensor?

In the classic book by Misner, Wheeler and Thorne, they justify the form of the Einstein tensor, G, by the fact that it is the unique tensor which satisfies 1) G vanishes when spacetime is flat 2) G is a function of the Riemann curvature tensor and metric only 3) G is linear in the Riemann cur...

general-relativity

linear as in propottional or wrt each component...?

John Rennie

My main task is to check that there are no dead servers, and if I find any try to revive them or if that fails alert the engineers. This has to be completed before the engineers get in at 8 a.m. Otherwise my time is my own.

I didn't have to work on the holiday, but putting in an hour or so is worth it to make my life easier on Tuesday morning.

Slereah

why must we suffer so

I'm trying to install the glossaries package but it just won't work

I'm monkeying around with the package manager but it won't intall

Gerold Broser

@JohnRennie Probably you didn't see this ~3.5hrs ago: "@JohnRennie "The aim of physics is to explain observations." – Isn't that different with theoretical physics?"

John Rennie

@GeroldBroser Broadly speaking physicists try to construct mathematical models that can then be used to make predictions about how physical systems will behave. Then we test thsoe predicitions by experiment.

Gerold Broser

@JohnRennie "Broadly" means in theory, right? ;)

John Rennie

09:54

So for example Newton constructed a mathematical model for gravity, now known as Newton's Law of Gravity, and found that it did indeed describe the motion of the planets - well almost, Einstein added a few extra details :-)

What the theoreticians do is construct new mathematical models. For example string theory is exactly this sort of mathematical model.

The trouble is that all the simple mathematical models were constructed long ago, and therefore any new models are scary complicated.

Gerold Broser

There was this physicist of whom has been said that he was so theoretical that whenever he was in town all experiments failed instantly. Was this Leibniz?

John Rennie

If you take string theory as an example, it isn't really a theory since we don't fully understand the mathematics involved in the modelling. So the theoreticians have lots of scope for studying the mathematics of string theory. This may seem rather abstract, but at the end of the day the aim is to construct the model.

@GeroldBroser that has been said of lots of theoreticians :-)

Slereah

Newton didn't understand the mathematics of calculus terribly well, either

John Rennie

Pauli effect

The Pauli effect is a term referring to the supposed tendency of technical equipment to encounter critical failure in the presence of theoretical physicists, allegedly due to their extreme inability to handle them. The term was coined after mysterious anecdotal stories involving Austrian theoretical physicist Wolfgang Pauli, describing numerous instances in which demonstrations involving equipment suffered technical problems only when he was present. The Pauli effect is not related with the Pauli exclusion principle, which is a bona fide physical phenomenon named after Pauli. However the Pauli...

Slereah

Calculus was a bit touch and go until the 19th century

File `glossary-hypernav.sty' not found. \@gls@loadlist

I put it in by hand dammit >:|

John Rennie

10:00

I suspect that many theoreticians just love what they do and they aren't too fussed whether it eventually ends up being used to make experimentally testable predictions. However their work needs to be seen in a broader context as supporting work for a model that will eventually be experimentally testable.

Gerold Broser

@JohnRennie "all the simple mathematical models were constructed long ago" – Reminds me a bit of... who was it who said in the early 20th century: "the science of physics is at its end, there's nothing more to discover"

Slereah

It has finally compiled, but I don't think it's working, still

Gerold Broser

@JohnRennie sounds like famous last words.

John Rennie

@GeroldBroser that isn't what I said. Using your words it would be: there's nothing more that is simple to discover.

Gerold Broser

@JohnRennie It was Kepler who did the great work regarding the planets, wasn't he?

John Rennie

10:03

And indeed the new discoveries that revolutionised 19th century physics were relativity and quantum mechanics, neither of which could be reasonably described as simple :-)

Gerold Broser

@JohnRennie Sure Newton was very important, too.

@JohnRennie SRT isn't that hard, I think.

Slereah

@GeroldBroser Obviously you've never read a SR book on epistemology

It's fairly hard to describe the epistemology of GR

You have to define the whole congruence and simultaneity at distant points sort of thing

John Rennie

@GeroldBroser to really understand special relativity you need to understand that it's just GR in the zero mass limit. That is, SR is a geometric theory and you work with it using differential geometry.

Generations of students have been taught the Lorentz transformations and gone away thinking they understand SR when they don't.

Gerold Broser

@JohnRennie You're right. I didn't...yet. Can you suggest one? Preferably with a German edition.

Slereah

the best special relativity book is Gourgoulhon

relativite.obspm.fr/sperel

John Rennie

10:07

@Slereah not a beginners book though.

Gerold Broser

@Slereah I'm sorry, usually I don't make fun of other people's names, but this name sounds like directly jumping out of Lord of the Rings. ;)

John Rennie

@GeroldBroser I don't know of a really good undergrad level book on SR. I suspect there would be little point in a book teaching the geometric approach to SR because it's almost as much work as learning GR, so you just learn GR instead and you get an understanding of SR for free.

Slereah

Well this is the beginner SR book I used

I don't think it exists anymore

Gerold Broser

@JohnRennie I didn't mean about SR, but about what you mentioned: SR in the context of science theory.

John Rennie

@GeroldBroser I'm not sure what you're asking there. SR in the context of science theory?

Slereah

10:11

Well if you want the epistemology bit, try Reichenbach

Basically the problem of special relativity (although that's also a problem of classical physics) is that you have to define very precisely what experiments mean

Gerold Broser

@JohnRennie You said: "Obviously you've never read a SR book on epistemology" and dict.cc translates this (also) as Wissenschaftstheorie 'science theory'.

Slereah

That was me :p

Gerold Broser

OOPS! silly...blind me

Slereah

What it means in SR for something to be of a certain length, or a process to take a certain time, has a specific meaning

John Rennie

@GeroldBroser you are confusing me with someone who gives a damn about the philosophy of science :-)

Slereah

10:14

plz

Gerold Broser

@Slereah Perhaps your face is too small for me on your pic ;)

John Rennie

Epistemology

Epistemology (/ᵻˌpɪstᵻˈmɒlədʒi/; from Greek ἐπιστήμη, epistēmē, meaning 'knowledge', and λόγος, logos, meaning 'logical discourse') is the branch of philosophy concerned with the theory of knowledge. Epistemology studies the nature of knowledge, justification, and the rationality of belief. Much of the debate in epistemology centers on four areas: (1) the philosophical analysis of the nature of knowledge and how it relates to such concepts as truth, belief, and justification, (2) various problems of skepticism, (3) the sources and scope of knowledge and justified belief, and (4) the criteria for...

Epistemology is the theory of knowledge i.e. what it means to know something.

Slereah

Gerold Broser

@JohnRennie :) If you come to Vienna once again I owe you a dinner...promised...boy scout's honour!

Slereah

Here it is in all its glory

Gerold Broser

10:16

LOOOL! Thank you Slereah...very much! Now I know...

John Rennie

@GeroldBroser thanks, though I have no immediate plans to go there :-)

@Slereah That looks awfully like Tony Blair ...

Slereah

it is very much not

Gerold Broser

@JohnRennie I'm not going to leave.

John Rennie

If I lived in Vienna I wouldn't want to leave either :-)

Gerold Broser

@JohnRennie But Johnson is worse, isn't he?

John Rennie

10:19

Politicians are an inevitable evil - inevitable in the sense that homo sapiens is a political beast. But that doesn't mean I have any great respect for its practitioners, nor any great interest in discussing it.

Gerold Broser

Ouch...don't write this in a public chat...the research funds!

...though I agree 99 %.

@Slereah, you dont' know how much I honored you at this very moment.

Slereah

I hope nothing sexual is involved

Gerold Broser

ROFL

where are you...

...from. I love this sense of humor.

"love" not in a sexual sense, yes!

Slereah

France

Gerold Broser

but no, something rather trivial

Bon jour, mon ami!

I just created a new bookmark folder in my browser and your G. book link is the first to take its virginity.

Dam... "G-point" and "virginity"...how to get out of this story now!?

ping Am I disconnected or are you?

Slereah

10:30

I'm around

Gerold Broser

afk 10

Slereah

@JohnRennie You may not care about epistemology now but try remembering when you first learned GR and tried to learn what the instantaneous length of an object was :p

It's not a trivial thing

"How smooth are the ten functions $g_{ij}$? In physics we usually lay such questions aside until they are forced on us, and we would be inclined to accept extreme smoothness."

That's when you know a book is written by a physicist

Also he calls the line element the magnitude of an infinitesimal vector

yikes

John Rennie

This is where the mathematically inclined tell us it's a tensor product, and most of us decide we don't care :-)

Balarka Sen

Tensor makes me tensor.

Slereah

Synge is actually a fairly good treatment of GR for a book written in the 50's

Usually really old GR books are fairly poor because it was before a lot of the theory was built

He even uses tetrads

With the form $\lambda^i_{(a)}$

John Rennie

10:47

@BalarkaSen The Demolished Man?

Slereah

Synge has a whole chapter on the "world function"

I have literally never seen that used outside of Visser's papers

Xasel

hello everybody1

John Rennie

Hi

Xasel

Does anybody know how to mathematically prove/derive that direction of electric field is tangent to the lines of electric field force envisioned by Faraday(I suspect some vector calculus black magic going here) @JohnRennie: Hello sir, long time no meet how ware you ?

John Rennie

@Xasel that's the way the field lines are defined isn't it? Unless Faraday had some other deinition.

Slereah

10:58

yeah by definition the trajectories of a vector field have the vector field as tangents

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