The h Bar

Yuvraj Singh...

06:56

@PM2Ring thanks:-)

user434058

07:52

Hi

skullpatrol

08:19

hello

user434058

09:02

Sup

skullpatrol

chillin, you?

user434058

Listenin'

user434058

09:36

I got a -2 because a user was removed. How can user removal result in loss of 2 rep?

Loong

You lose reputation for suggested edits.

user434058

@Loong But do questions get deleted if a user is removed, no, right?

Guru Vishnu

The question you edited was deleted.

user434058

@GuruVishnu But in those cases I don't even get a notice. This was specifically mentioned as user removal. I suppose some questions are also deleted if a user deletes themselves...

Guru Vishnu

Maybe 1 upvote and 4 downvotes got removed along with the deleted user?

Yuvraj Singh...

09:45

@ACuriousMind do you know, why @manishEarth left the site?

user434058

@GuruVishnu That seems probable :)

Loong

50

A: Update on the Manish situation

Oh, wow, I hadn't realized this was going on :) I first just wish to apologise to the community, both Chem.SE and Physics.SE, for my lack of activity. I'll shortly explain what happened, but I also just feel bad for causing this conflict, and think I could have handled this better. Sorry about t...

Physics Meta

10:07

0

Q: What is different between 'Physics' and 'Physics Meta'?

I'm recently join stock exchange. So I am not used to this system(also I'm foreigner; Korean). I join this group because I want to get a physics information. but there are two choice that physics and physic meta. What should I choose? (I'm sorry to my English writing skill, I'm practicing now)

support

Yuvraj Singh...

@Loong recent 207 days ago?

Why the community has not accept his resignation till now?

user434058

@YuvrajSingh... He's no longer a mod...

PM 2Ring

820

Q: What does "user was removed" mean and why did my reputation change because of it?

Message appearing when a user was removed. It seems I lost 1765 reputation points on Stack Overflow yesterday. The reason given in my history is "removed", with the description of "User was removed (learn more)". I don't understand what that means. What caused this? Return to FAQ index

support faq reputation reputation-history

user434058

10:22

@PM2Ring Thanks! Now the "-2" makes sense :)

user434058

$$\mathfrak{\Huge{\color{blue}{BYE}}}$$

PM 2Ring

Also see meta.stackexchange.com/a/7238/334566 which mentions that posts over 60 days old are generally protected from rep loss due to user removal / deletion. But I must confess I'm not totally clear on all the details, the rules are a bit complicated. ;)

FWIW, a year or so ago a prolific Physics member deleted their account (so they could focus on their exams). Several people got hit with rep losses >100. They didn't mind too much, since they were members with lots of rep.

user434058

@PM2Ring May I know who?

PM 2Ring

On Stack Overflow, it's not unusual to lose rep from deleted accounts. SO tends to attract a lot of sock-puppets and voting rings. Apart from the site powers that high rep brings, in the programming world, SO rep is a bit of a status symbol. So some people try to cheat the system in order to accumulate rep that they don't deserve.

Voting rings & sock-puppetry happens to an extent on all sites on the network. It's more of an issue on SO because of its huge number of members, and the huge rate that questions & answers get posted there, so it's a bit easier for the bad guys to hide in the crowd.

@FakeMod You can read about it in the transcripts of this room. ;) It wouldn't be appropriate for me to name names.

user434058

@PM2Ring Links ;)

user434058

10:34

?

PM 2Ring

@FakeMod Nope. ;)

user434058

@PM2Ring Time range??

PM 2Ring

Prolific posters like John Rennie tend to get hit with rep loss when voting rings are broken. The ring voters tend to randomly upvote existing good questions & answers in the attempt to disguise their voting patterns. It'd be kinda obvious if they only upvoted each other's posts.

user434058

user434058

Me right now... LOL

user434058

10:39

Mar 19 '18 at 16:30, by diobuc eulb

@Secret im deleting my account, do you have a discord or other thing i can add you on?

user434058

This?

user434058

@PM2Ring

user434058

👍

Slereah

11:05

"All this time, however, category theory was consistently seen by much of the mathematical community as ridiculously abstract."

user434058

0

Q: Confusion regarding the time derivative term in Lagrange's equation

I am solving a pendulum attached to a cart problem. Without going into unnecessary details, the generalised coordinates are chosen to be $x$ and $\theta$. The kinetic energy of the system contains a term (which contains) $\dot x\dot \theta cos\theta$. Now when evaluating $\frac{d}{dt}(\frac{\part...

classical-mechanics lagrangian-formalism

user434058

Should I flag this as a duplicate of the question suggested by QMechanic?

user434058

@Slereah Who's that guy in your profile picture?

Slereah

It's the cover of one of Spivak's book

user434058

@Slereah oh, alright.

PM 2Ring

11:31

@FakeMod Don't bother wasting a flag on it, I just voted to close it as a dupe of the target proposed by Qm. The 1st dupe flag sends the question to the Close vote review queue, but a close vote does that too (if it hasn't already been sent there). But dupe flags are also helpful to the close voters, since the proposed dupe (or dupes) appear in the close voting dialog.

user434058

11:48

@PM2Ring I don't think I am ever going to run out of flags (at least that's what I hope :)) since I get 34 flags a day.

user434058

But as you have already VTCed, I would not flag it redundantly.

Slereah

"The study of sets is the study of things in bins."

PM 2Ring

Rubbish!

user434058

@PM2Ring See that question, the OP has edited it and it no longer looks like a dupe.

Secret

Schrödinger functional

In mathematical physics, some approaches to quantum field theory are more popular than others. For historical reasons, the Schrödinger representation is less favoured than Fock space methods. In the early days of quantum field theory, maintaining symmetries such as Lorentz invariance, displaying them manifestly, and proving renormalisation were of paramount importance. The Schrödinger representation is not manifestly Lorentz invariant and its renormalisability was only shown as recently as the 1980s by Kurt Symanzik (1981). Within the Schrödinger representation, the Schrödinger wavefunctional...

Currently reading baez's category page

and when that knowledge of categories crossed with the little bit I am familiar with first and second quantisation (because we chemists do use these in many body solid state chemistry), I am starting to wonder,

whether the highly nonlinear interaction regime between two relativistic quantum fields lack a known mathematical formulation, may have to do with the notion $\Psi[\phi] = \langle \phi | \Psi[]\rangle$ becomes invalid, that is, it is impossible to separate out the components in an interacting relativistic QFT state because the nolinearlity screw up the notion of eigenoperators

user434058

12:07

physics.stackexchange.com/questions/tagged/random-walk

user434058

What does random-walk mean?

ACuriousMind

Have you tried googling "random walk physics"? :P

user434058

@ACuriousMind Oh! I see. I first thought that it might be some sort of pseudo-tag...

Secret

https://en.wikipedia.org/wiki/Multicategory
https://en.wikipedia.org/wiki/Operad
Ok these are so cool and answer my question of "why not more than 2"

math.ucr.edu/home/baez/categories.html

This is a very nice intro to category theory and it helps to consolidate some of my learning of said subject back when Mathien in maths chat wrote a blog series on category theory

as well clarify some of my intutions back when I read Mclane

PM 2Ring

Ok. I've retracted by duplicate close vote. — PM 2Ring 21 secs ago

@FakeMod The topic of random walks came up briefly a few days ago:

2 days ago, by PM 2Ring

@JingleBells Also see https://en.wikipedia.org/wiki/Random_walk

user434058

12:26

@PM2Ring Hmmm... I see.

PM 2Ring

An important thing in random walk theory is that if the space is 1 or 2 dimensional, then the walk is very likely to cross over itself, but in 3 dimensions & greater crossovers are much less likely.

Slereah

The probability is 1 and 0 respectively, even

user434058

14:01

user434058

Ah, finally a PALINDROME!!! This is probably the best thing that could happen to one's rep and badges...

3

user434058

I have seen everything, $\mathscr{\color{red}{BYE}}$!!!

Yuvraj Singh...

15:55

@JohnRennie hi:-)

John Rennie

@YuvrajSingh... hi :-)

Yuvraj Singh...

@JohnRennie actually today I was looking Einstein energy mass equation!I am surprised that till now this equation holds for every particle am I right?

John Rennie

Yes, and in fact it is even broader than that.

Yuvraj Singh...

Broader in the sense?

John Rennie

In GR the geometry of spacetime is related to an object called the stress energy tensor, and one part of that is the energy density i.e. energy per unit volume.

In this tensor mass and energy are treated as identical except that mass gets multiplied by $c^2$.

So mass and energy both curve spacetime in the same way.

Yuvraj Singh...

16:01

It create a impression inside me, if I say mass and energy are both same thing and universe fundamentals are based on mass

If new theory is discover it's fundamental should be based on mass and energy

And every particle will follow $$E=mc^2$$

@JohnRennie

John Rennie

I think any new theory would have to be compatible with relativity because relativity has so much experimental evidence.

Yuvraj Singh...

Yes

I will consider relativity as biggest discovery of century!

@JohnRennie

Slereah

@ACuriousMind Is there a point in having the fancy higher order geometry in classical mechanics?

Or is that something that is only relevant in QFT

I suppose that in classical mechanics, the choice of bundle is set, and there's no need to have it be flexible?

ACuriousMind

@Slereah In principle, you have instantons (and hence importance of the bundle choice) in classical mechanics as well. But $U(1)$ instantons are boring and don't really require the full machinery and classical non-Abelian theories where it would matter (other than for the purpose of quantizing them) are pretty rare.

Slereah

I don't mind that it's not realistic, just that it's there

Do initial conditions set the bundle?

I know that classical magnetic monopoles are directly related to the bundle's class

and they are conserved

Also assuming the spacetime globally hyperbolic, I would guess that the fiber bundle over the Cauchy surface is the same for all time?

B. Brekke

17:29

What does it mean physically that a fermion propagator has a negative sign?

Jordan Lawson

18:56

Hi

I wanted to know if three non equal vectors could add upto zero if they don't lie in a plane.

It's not mentioned if they are free vector s, can we translate them?

user434058

@JordanLawson No.

user434058

@JordanLawson Mostly they would be free vectors. Sometimes the "free-ness" is implicit.

Charlie

@JordanLawson See also en.wikipedia.org/wiki/Linear_independence

user434058

Yo @Charlie wassup?

Charlie

Hello sir

FakeMod I never asked you the same question back, where in education are you?

and/or research

user434058

19:11

@Charlie what, don't call me sir...

Charlie

Sirn't

2

user434058

@Charlie That's better :D

user434058

@Charlie oops I misunderstood that message. I am a 16 year old high schooler who would be in a college/University in the next 6 months.

user434058

@Charlie Seems like you're busy, are you?

Charlie

Ah ok

In general or right now?

user434058

19:15

@Charlie nvm, i just thought that coz you stopped responding :)

Charlie

No I'm just doing stuff in the background

user434058

Same here :)

user434058

@Charlie What are you currently learning?

user434058

I mean in your Physics course...

user434058

Hi

user434058

19:24

¿WƆ∀ lloɹʇ I op ʍoH

user434058

Hi @tpg2114

user434058

:)

user434058

Hi @CaptainBohemian

user434058

:)

Captain Bohemian

@FakeMod what's up?

Jordan Lawson

19:33

Thanks, guys

user434058

@CaptainBohemian nm. I sometimes see you here. I haven't seen you on the main site. However that has nothing to do why I pinged you ;P I just wanted to chat...

user434058

@JordanLawson Anytime.

Captain Bohemian

@FakeMod It's like this is the first time I see you.

user434058

@CaptainBohemian hehe, but yeah lately I am quite active. BTW, i see you're interested in gravitation and geometric physics, if you don't mind, then are you a researcher, or a student, or an enthusiast?

Captain Bohemian

@FakeMod I am a research student.

user434058

19:40

@CaptainBohemian oh, nice. That means you are learning and researching at the same time, right?

user434058

Anyways, I need some sleep now (that's why I was sounding so dumb), so good night :)

user434058

Bye

Charlie

I'm basically sitting third year undergrad @FakeMod

JingleBells

20:03

ew university

Amirhossein Taebi

Hi

is there any body?

Charlie

Yes? @amir

Amirhossein Taebi

I am confused about future of my physics studying

Charlie

What's your question? I won't necessarily know the answer but someone else might when they see it

Amirhossein Taebi

20:18

Often,I try to learn deep and perfect all the theories and problems not just memorizing them

but in other hand I have lack of the time and I lose my grades

Charlie

Are you in school? University?

Amirhossein Taebi

I am second year of uni

and grades are important for applying

but some people just memorize everything for the exam and get best grades

peterh - Reinstate Monica

Wow, I've got again 2 ups to my old posts. I think I will lose them again, with an "user removed" entry in my rep history

It would be so nice to know, what is in the background.

I am searching for new users with many ups in the SEDE

Charlie

If you're finding you don't have time you are either spending too much time doing a sub optimal revision strategy or aren't making enough time to study, there isn't really a magic formula

Learn the content from your lectures and then do as many practice problems as you can.

Captain Bohemian

lack of time is often a problem.

Sir Cumference

20:35

@AmirhosseinTaebi I was pretty much the same way in freshman/sophomore year

For starters, if you're planning to pursue physics, then the physics classes is what grad schools care about. Other classes are not as important

So if you're spending a sizable amount of time on others, try shifting it more toward the physics ones

Amirhossein Taebi

my goal is applying in great universities and grades are important

this term we have classical mechanics,statistics,mathematics of physics and modern physics(krane)

Sir Cumference

At least in the US, Physics GPA holds considerably more weight than total GPA

Slereah

22:47

@ACuriousMind Steenrod says that most tensor bundles are vector bundles, what the hell is a tensor bundle that isn't a vector bundle?

Infinite dimensional rep of the linear group?

Physics Meta

23:45

2

Q: Good answers to duplicate questions

I had a decent answer that received upvotes to a question that was later deleted as a duplicate. Where does the energy go when I short a capacitor? Since the answer was well received I thought it would be good to post it to the original question. I had assumed that this was the desired behavio...

discussion answers duplicates

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