The h Bar

3:11 PM

lol

reminds me I was on narcotic drugs for like 15 days I should get back to doing physics.

you're a junkie now

Get back on the drugs

smokeeeeeeeee

Do amphetamines, it is what Erdős recommends

they're only pills, and I have 30 left.

no use for them though.

3:13 PM

Sell them to me

I'd give them to you for free but I don't think I can ship them.

Cloth shoes: never again. They're getting stained :/

Bake them into a cake, then send the cake

I wonder if I can wash them

lol that works.

3:14 PM

Or don't bake them in but send us a cake, still

@Slereah why would you turn down free drugs

^

Free cake is breddy good

@ACuriousMind you ******* junkie

all of you

user116211

Why do you want to eat arbitrary pills @0celo7 o.O

3:16 PM

@MAFIA36790 I don't

I'm a law-abiding citizen

but seriously drugs are dangerous, I was on this really strong drug a day after surgery and I was becoming delusional and I thought the nurses were trying to kill me at night.

user116211

hmm.... also nice.

I was doing something

Oh the AMA quesitons

@3075 That sounds rather terrifying :/

yeah I could barely sleep.

3:17 PM

Maybe really just send a cake, then

It is highly possible no nonsense from me in future chat messages will ever beat that collosal nonsense that I posted a few hours ago

@Secret I don't think most of us read that.

I don't read anything over ~5 lines

Even then if it's 5 lines the first 2 better be damn good

I have not finished my sentence, lol :D

@ACuriousMind Did I tell you I worked Mr. Morton into my literature final essay

therefore whatever incoherent thing Acuriousmind et. al. encountered from me in the future, it should be a lot more comprehensible than anything that ever existed since the dawn of time

3:20 PM

...wat

@Secret ...do you always announce things like this or do we get special treatment

I think the last known appearance of Mr Morton was your midterm or something

@FrancescoS NO

@ACuriousMind I worked him into the final.

@0celo7 ??? He hasn't said anything

I have a tendency to immitate aperture science broadcasting systems

The prompt was to sit down a puritan minister and a transcendentalist and get them to agree on something

3:21 PM

@0celo7 sorry?

@ACuriousMind I didn't finish that thought

@FrancescoS This is a GR zone today, no QFT

and the full itallics give an impression I am talking to some covert party in the background

@ACuriousMind and while Morton is not a puritan minister, I worked him in anyway

Oh, you're just jealous I might answer other people's questions. Carry on, then :P

and the prof liked my essay so much he sent out an email about it

3:22 PM

@0celo7 Don't worry, let you talk about what you want; I don't care ;)

which brings into point of another of my tendency: I have a tendency to immitate spy agencies

@ACuriousMind implying you've helped me at all today

I like to think I've become more self-sufficient, but you're the judge of that

@0celo7 No, I did not imply that...

@ 0celo7

2 mins ago, by Secret

I have a tendency to immitate aperture science broadcasting systems

@Secret ???

@Secret honestly you might have some issue

you say really random stuff

user116211

3:24 PM

nods T__T

@ACuriousMind You implied I'm jealous for your attention

@ 0celo7 Well, as long I am not random when solving problems and responding to correct social context, it will be fine

My mind is an exploding mini big bang, quoting one of my professors

Is that the Australian term for ADHD

9 mins ago, by Secret

It is highly possible no nonsense from me in future chat messages will ever beat that collosal nonsense that I posted a few hours ago

The reaosn I said that is because you guys managed to sent the most flagship of my pet theories into a (temporary?) grave, thus anything that comes after will not be utter nonsense

@ACuriousMind Is Milnor's def of cobordism on page 42 equivalent to the standard one

3:28 PM

and this is indeed what is intended, since I have been frustrated for years how to shot it down

I am so glad I don't have quantum pet theories...

else I will be frown upon by the physicists

@ACuriousMind And do you know if $M$ is supposed to be compact here

@0celo7 I have no idea what the "standard one" is

@ACuriousMind what do you think cobordant means

I don't have an opinion on that, I never really needed the notion

@ACuriousMind But I thought TQFTs were functors on the category of cobordisms

3:33 PM

So?

implying you should know what a cobordism is

@0celo7 why do you think ACuriousMind should know everything?

@0celo7 I think that category is much narrower than what one calls in general a "cobordism".,

@FrancescoS induction

http://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1025&context=linguist_faculty_pubs
A prosodic theory of nonconcatenative morphology

Why do linguistics reminds so much of category theory. Is analysing languages a type of category...?

3:41 PM

Languages are a category.

Most things are categories

I see

ACM might disagree

Most things you care about are categories.

I think that's correct.

Q: Energy Conservation in Changing Potential Well

0

If you prepare a particle in a basis state, $|n\rangle$ of an infinite potential well of length $L$, the energy of that state will be $\langle E\rangle = E_n$, with zero variance. If you then instantly increase the width of the particle well by some method to $2L$, this state becomes a superposit...

quantum-mechanics energy-conservation wavefunction wavefunction-collapse

sounds like a time dependent perturbation theory on particle in a box will give us some insights

I am guessing that extra energy has to be supplied or taken away by whatever that expanded the well

Otherwise I cannot do this problem on top of my head, will deal with this later

4:00 PM

@Obliv I just don't respond on these occasions. While it's very tempting to make some cutting comment that never ends well.

@0celo7 It seems a bit harsh to close that. I don't know the answer, so while it may seem obvious to you it isn't obvious to everybody.

@JohnRennie It's not obvious.

That's the whole point

You'd have to write a book on it

The answer is in Wald

or at least a partial answer is in Wald

There are about 7 essential GR books and you get no love from me unless you've checked all of them

No love unless you perused the 3000 pages for the answer

user116211

^^^^ Note that

user54412

@JohnRennie cf my meta post ;)

@ACuriousMind How pretentious is writing $M^n\in\mathsf{ Ob(Man)}$

Is that even acceptable

@Slereah 3000?

MTW is 1200, right?

HE is 400, Straumann is 700, Wald is 400

4:08 PM

Well how many pages is HE + MTW + Wald + Straumann + whatever

Errr...

O'Neil

O'neil

BEE

Sachs-Wu

Penrose

Sachs-Wu has no answers

Just questions.

4:09 PM

you need questions before you can have answers

Carroll, I guess

Yeah

Zee, Weinberg

Duffield

For sure.

@ChrisWhite if the sufficient prior research requires reading 0celo7's seven essential GR books then I think we should be lenient :-)

@ChrisWhite which meta post?

4:10 PM

Springer has a spacetime handbook

I wonder if it's any good

can't get a mycopy of it

@0celo7 Unless you're specifically going for the category theoretic angle, I'd consider "Let M be a manifold" to be better in all respects.

so probably not.

amazon.com/dp/3642419917

@ACuriousMind Good point, although not even categorical geometers write Ob(Man)

Don't know about category theorists though

4:11 PM

I've seen Ob(Man) in AQFT

I usually see the Ob omitted, anyway

$300, must be good

Only noobs write Ob, just like only noobs put hats on their operators ;P

I still put hats on my operators and arrows on my vectors

Like a good boy

My list of GR books comes out to well over 4,000 pages

user116211

4:12 PM

@JohnRennie Now I could get what 7 denotes in 0celo7 ;|

SO GET OUT OF MY FACE UNLESS YOUVE CHECKED ALL OF THEM

Oh and Stephani

Stephani is p. important

4,700

Throw in that one book on twistors

5,100

And some math books

8,000

let's make it an even 10.000

Arnold for the action principle

Oh

Abramowitz and Stegun obviously.

Rudin

4:14 PM

My favorite GR book, of course

PDG handbook

amazon.com/Physics-Stargates-Parallel-Universes-Wormhole/dp/…

It has the best cover

PDG doesn't contain a lot of GR

a lil bit of cosmology but that's about it

We're probably at 15,000 pages

@JohnRennie unless you have checked all of these books, your question deserves to be closed.

Is it weird that I know how long books are

amazon.com/Making-Starships-Stargates-Interstellar-Transport/dp/…

Wait a moment

I know HE is 392 pages long

4:16 PM

Woodward

Give or take

Isn't that the crazy guy

I have lots of chapters memorized

I know the HE and Wald chapters by heart

when you read wormhole stuff, you have to remember the crazy guys

@0celo7 well it would keep the PSE nice and quiet :-)

4:18 PM

@JohnRennie well there's not a single good explanation of time dilation in those books

Well they are GR books

Not pleb SR

I don't even know SR

@0celo7 You need to come to me for that

@JohnRennie I might write a correct answer to that one day.

But I'm not very interested right now

SR is GR for Minkowski space

obviously

4:20 PM

@0celo7 Another correct answer?

@JohnRennie no the correct answer.

In terms of geometry

I'd have to think about it first

>thinking before answering

You're not gonna win internet points that way

Q: Relativity of temperature paradox

Was I wrong to close this? My reasoning was that reading the duplicate would teach the OP enough to answer their question. However I'm now wondering if that's fair.

0

The imagined scenario: Part A: From special relativity we know that velocity is a relative physical quantity, that is, it is dependent on the frame of reference of choice. This means that kinetic energy is also relative, but this does not undermine the law of conservation of energy as long as w...

special-relativity statistical-mechanics temperature kinetic-theory doppler-effect

@JohnRennie I think there is enough overlap to call it a duplicate - however, the answers to the other question don't seem particularly decided on what the actual answer is.

@ACuriousMind My PDE prof hatred linear operators :(

ODE prof didn't

>hatred

*hatted

@ACuriousMind coincidentally the PDE prof is an applied mathematician and the ODE prof is a geometer

Or maybe not coincidentally

4:40 PM

Does a geometer build triangles and such

for the triangle shop

He's the one who proved the Godel thing

@ACuriousMind The OP's doppler shift case seemed to align with Einstein and Planck, while the statistical mechanics approach of case b seemed to be aligned with Landsberg. Given that it is obviously a duplicate, but

@JohnRennie Dear Mr Rennie, thanks a lot for the linked post, I had not come across it yet. Regarding the duplicate mark, although there's overlap between the two posts, namely the discussion on whether temperature is relative or not, but my post is rather presenting a concrete scenario and asking questions about it, including how temperature is correctly defined in such circumstances. Moreover, I still don't see the bottom line, so am I to go with case a or b? or both are wrong? Would you mind reconsidering the duplicate mark? — user929304 24 mins ago

1) how to address to the OP politely but completely and explain why it is a duplicate in order to clarify things? and

2) It turns out the issue of temperature is still quite disputed, for temeprature to be defined in the most rigorous way, I am guessing we should always use the themodynamic beta defintion of $\frac{\partial S}{\partial E}$...?

the kernel of a group action is different from that of a homomorphism right

@JohnRennie if the question is a (not necessarily strict) subset of the other one, such that any reasonably complete answer to the other question would also cover this one, then you were right to close the question. Otherwise, you weren't. So I'd say.

@DavidZ I was kind of hoping for a yes/no answer :-)

4:52 PM

IMO the fact that reading the other question would teach the OP enough to answer their own question does not itself make the question a duplicate, although it is probably correlated with being a duplicate.

@DavidZ OK so the answer is no. I'll withdraw the close vote.

@Obliv ...what?

defined differently* @acuriousmind

There is no such thing as "kernel" of a group action. I'm not sure what you're talking about

@acuriousmind crazyproject.wordpress.com/2010/01/20/…

4:55 PM

@JohnRennie I didn't actually read the question, you know

@Obliv Yeah, unless you get me a better reference than a website called "crazyproject", I'm going to go ahead and say "kernel of a group action" is not a commonly used term.

@DavidZ Now he tells me! I've just reopened the question. Oh well, I'll leave it to the jury to decide. If I'm unsure about closing as a duplicate I guess the sensible course is not to close it.

the text by dummit & foote called it that

what do you call it

That there looks like...the intersection of all stabilizers. I guess it is actually the kernel of the map $G\to\mathrm{Aut}(X)$ that one can get from any group action.

@JohnRennie eh, I dunno, closing tends to prompt people to edit the questions to improve them so it's not the worst thing

5:01 PM

so why is it defined as $\{g \in G~|~ga = a$ for all $a \in A\}$ ? It doesn't define it in the text and I thought it would be defined as $\{(g,a)~|~g\in G~a\in A, ga = I_A\}$ It seemed like the right idea.. @acuriousmind

eh you don't have to answer that I'll just take it for what it is actually

@Obliv 1. $ga=I_A$ doesn't make any sense, as $A$ is just a set. 2. What do you mean "why" is it defined like that? It's defined like that because that's what corresponds to the kernel of the group homomorphism $G\to \mathrm{Aut}(A)$.

@acuriousmind you said $ga$ is the image of an element of $G\times A$ so I thought it made sense in my mind.

...what is $I_A$ supposed to be?

identity in the target set $A$

$G\times A \to A$ no?

Sets don't have identities.

5:05 PM

One thing (as a user in PSE in the long past) that often annoys me is when people close questions, they seldom respond why and how it is a duplicate.

It is true that closing a question will prompt the OP to edit their questions, but for some questions, some clarifications might be needed to point them in the correct direction on what need to be edited

And the trouble is, not all of us are as 24/7 as the h barers and some of the users don't even bother to explain the closure

Having said that, I have no idea ho can this be resolved, given that we cannot really control individuals

so the kernel doesn't really exist, except to a homomorphism that is precisely the group action? @acuriousmind

@Obliv what?

okay nevermind

If anyone visits my school note that the best toilet on campus is on the 5th floor of the Chemical engineering building

Clean and they have good toilet paper

are you living in the maths department, given that you are quite mathematical oriented?

(too lazy to dig the chat log for your education background again)

5:19 PM

@Secret no

I live in engineering buildings because I am an engineer

i see

what subfield of engineering have you studied?

Nothing yet, I'm in my first year

I see

And I'm not "math-oriented"

I don't even know what a set is

Literally, I don't know what the definition is.

ok

speaking of engineering, I have a couple uni friends who studied chemical engineering, electrical engineering and renewable energy engineering (such as photovotalics)

They are often very helpful in remind me how to relate my research chemistry to the engineering disciplines

I however, know very little about it, other than chemical engineers always need to deal with a lot of differential equations, and circuit diagram like interfaces in order to ensure the right amount of chemicals were added into the reactor

5:33 PM

Sets are a primitive notion

They are not really defined

Only operations on sets are defined

Q: What are the largest numbers in physics?

6:12 PM

He's off again!

-1

In mathematics there are some big numbers such as the busy beaver numbers which are large but have a short description. I was wondering if we allow physical definitions of numbers we can make some bigger ones. So how big is this number (very approximately), assuming we live in a spatially infinit...

physical-constants statistics

The largest number and cDonalds Theorem - Look Around You

►

6:49 PM

So anyway, what is the largest number in physics

1 (number of universes)

Something more???

Where is your number curiousone, i am waiting. nothing? then dont open your mouth — Loffen 35 mins ago

YES

GET REKT

@0celo7 you don't study math, neither sets nor linear algebra, you don't study physics like SR, yet you study Sobolev spaces in general relativity books, & Sard's theorem in differential topology books, touche

@bolbteppa dude I understand linear algebra

That was a year ago

I am thinking hard of how to formulate my question on Math Overflow

I don't want to sound like a yahoo

I must think like a mathematician

:p

6:55 PM

What topology are you working with

Are all your operators bounded?

What function space

What is BB(BB(99))

What bornologies are you using?

Topology is $\Bbb R^2$ minus two disks (or squares), identified with [some function i'll write down]

Function space is like

Schwartz

That's pretty broad

That's usually the function space for scalar fields

What's the metric?

6:57 PM

Metric of the original space is flat space metric

I'm not sure if Schwartz space is well defined for weird topologies

I know it's not generally defined for some spacetimes

Q: The best Question Grand reopening - Gather

Weak topology is defined as the topology that makes all functions continuous, so people just say weak topology

Physics Meta

0

my question Large numbers in physics was closed. Two users gave a "reason". The first one didnt make any sense at all. And the second one I have adjusted my question to take care of. So now could we reopen? If not, can I get a reason? I dont get what people have agaisnt my question. I get at fir...

discussion

Locally you have a past, a present, a future and a lot of "side-ways". Globally you have a past, a present, a future and a lot of "side-ways". Why do you think that will change? As for time-like curves... I would stay away from that. Absolutely nothing prevents theories from having unphysical solutions and that's what these are. — CuriousOne 29 mins ago

smashes head

so what is a manifold, anyway

CuriousOne is the Karl Pilkington of physics

I am a manifold

Of manifold ancestry

"the best question grand reopening"...is this a troll?

7:00 PM

I've removed some comments that were off topic and/or inappropriate, and their replies. — David Z ♦ 2 hours ago

Abuse!

We call that "moderation".

@ACuriousMind Maybe we should perform moderation in moderation.

@0celo7 No it isn't. Loffen is being a twit.

@JohnRennie That's offensive, please remove it.

@0celo7 Busy beaver number. There's a nice description of them here

7:06 PM

computation theory has a lot of big numbers

twit is not an offensive word. Swap the i for an a though ...

Although as an ultra finitist, I don't really believe in numbers superior to 53

@Slereah 53 is a bit high

I haven't seen 53 in the night sky

@ACuriousMind Do you have access to Guillemin-Pollack

what number appears in the sky?

69 B)

what is an equivalence relation, anyway

7:14 PM

It's a relation

That has the properties of an equivalence

I think it's like

Symmetry

lol, apparently bordism is a thing

Reflectivity

the third one

so a cobordism is the dual of a bordism

Errr... transitivity

@Slereah transitivity

7:15 PM

yeah that one

@ACuriousMind Don't you think cobordism is such a nice word?

usually with the semantic that "eh I guess that's the same object"

> A central insight connecting algebraic topology with mathematical physics is that a strong monoidal functor on a category of cobordisms with values in something like the category Vect (with its standard tensor product of modules) may be thought of as a formalized incarnation of what in physics is called a topological quantum field theory

wipes brow

Too much algebra 4 me

I just wanted a nice notation for "M and N are cobordant"

7:18 PM

$$M \mathfrak{Cobord} N$$

List of cohomology theories

time to prove that cobordism is an equivalence relation

oh boy

This is a list of some of the ordinary and generalized (or extraordinary) homology and cohomology theories in algebraic topology that are defined on the categories of CW complexes or spectra. For other sorts of homology theories see the links at the end of this article. == Notation == S = π = S0 is the sphere spectrum. Sn is the spectrum of the n-dimensional sphere SnY = Sn∧Y is the nth suspension of a spectrum Y. [X,Y] is the abelian group of morphisms from the spectrum X to the spectrum Y, given (roughly) as homotopy classes of maps. [X,Y]n = [SnX,Y] [X,Y]* is the graded abelian group given as...

@ACuriousMind A list for you

is it a noob move to write $(N\times[0,\epsilon))\cup (N'\times(1-\epsilon])$

instead of $N\times[0,\epsilon)\cup N'\times(1-\epsilon]$

7:50 PM

oh wow $\mathfrak{v}$ is a v

Yeah fraktur is kind of shit

how do I do piecewise functions in TeX

13

Q: piecewise function

So this is a piecewise defined function I have that I need to talk about: f(a,b) = \left\{ \begin{array}{lr} \text{open} & : \text{RMSD}_\text{s-open}\ge6, \text{RMSD}_\text{closed}\ge6\\ \text{closed} & : \text{RMSD}_\text{closed}\le2 \\ \text{semiopen} & : \text{RM...

math-mode

Do autistic people usually insult other people? I don't remember if they do

If they don't loffen is a pretty obvious troll. (since he claimed he was autistic in one of his comments)

Oh I'm pretty misinformed. It appears autism is related to more aggressive behavior.

I am mild asperger, which nowadays is classified as part of the autism spectrum, and I don't recall myself insulting other people, for example

in fact, autism people are best known for their tendency to ignore anything irrelevant to their goal, and I found insulting other people a terribly inefficient thing in terms of getting my answers

8:15 PM

So this is why they make up reasons and vote to close? I have autsim I wouldnt understand, it just doesnt make sense to me — Loffen 1 hour ago

haha the best defense

The spectrum covers a lot of ground and there is a lot of variation in exact symptoms even among people at comparable points (areas?) on it. I don't claim to be an expert, but I think that some behavior that could be classified as 'persistent' or 'focused' if you were being clinical can come across as aggressive or even hostile to people not used to it.

Oh gosh please don't ban me

I'm so sorry

Not that I care for the purposes of PSE moderation. Be nice applies even if you don't get it.

@Slereah Your thing is in 19 hours

So I'll be busy during it

Lucky!

I probably should prepare something

8:27 PM

In a dijets analysis (for example at LHC), one studies the contributions to $pp\rightarrow jet + jet$ coming from the $uu,du,dd$ valence-quarks initial states because $u\bar{u}$ or $uc$ initial and final states in the Standard Model are highly suppressed. My questions are:

1) How does one reconstruct that the dijets come from these initial states?
2) The SM says processes with $u\bar{u}$ or $uc$ initial states and $u\bar{u}$ or $uc$ final states are suppressed. Why can't we take these processes into account if we suppose it exists another model?

>:(((((((((

For example, look at this paper arxiv.org/abs/1201.6510 at page 4, beginning section 3

@FrancescoS I'm not sure we have any regular familiar with these sorts of calculations. @dmckee might be your best bet.

@FrancescoS if you've figured out e.g. physics.stackexchange.com/questions/229259/…, you might want to write an answer so future students of the book can find an answer if they get stuck there too

I never did collider physics. I did go to a collider summer school one year, but that was circa 15 years ago.

8:34 PM

@dmckee and you can't remember?

Reconstruct goes the usual way. First generate a clustering analysis to define tracks as either in or out of the jet. Add up the energy (from the calorimeter) and momentum of the tracks that are ruled in and construct a four-vector. Try out all possible combinations of pairings between jets until you know which combination(s) gives reasonable physics and go with those; perhaps assigning a weighting to them.

Both the cluster identification and the combinatorial problem are hard to get exactly right, but good 'mostly right' methods exist.

@dmckee so, can you understand from which interactions the jets come from?

I don't recall anything about the hows and whys of jet flavor surpression.

@FrancescoS You certainly get the mass of the state that gave rise to the jet, which gives you some information but is not always definitive. The rest I don't recall.

@dmckee ok, thanks you very much