The h Bar - 2015-05-05

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4:45 AM

@AlfredCentauri here's an example question that I would be on the fence about downvoting: physics.stackexchange.com/q/181144/66165

According to @ACuriousMind 's criteria, I would think this would be worth of downvoting because the information being sought can be found in many textbooks and may not even really be a physics problem but more math.

Yet I personally wouldn't downvote because I have been in such situations and genuinely trying to learn and have gotten stuck. But it seems tricky and I agree with @ACuriousMind that downvotes are meant to convey information about the quality of the question, which is think this one is kinda low.

5:01 AM

@StanShunpike so electrodynamics class sucks.

15 pages of lienard wiechert stuff.

Not getting better I take it?

No. I hate Griffiths with a passion now. :D

I can understand that. I prefer Jackson.

What's the worst thing about Griffiths?

I would imagine that would be worse than this in terms of "do 15 pages of calculus"

It's really not Griffiths that's the problem actually. It's much harder to do 15 pages of the work when you don't think it will even be graded fairly.

I know exactly what you mean! Grading is so arbitrary. My econ class TA skims the problem sets and grades basically based on a set of criteria so that he can do it without actually reading the pset. Needless to say, I am not taking his word I did the problems correctly.

I once took a lab component to a chem course and the teacher said "we just don't give good grades on the first assignment" and I sorta looked at her incredulously and thought "what's the point then?"

5:09 AM

Sheesh, yeah. Silliness.

Anyways I'm going to talk to the professor after I do well on the first midterm (which I will hopefully!)

Is he a good prof? Does he do the grading or is it TAs?

Oh it's a separate grader, not the prof or the TA, who goes down and compares word-for-word with the solutions manual. I think he doesn't like my work because it doesn't match the solutions manual. And everyone else's does...

doesn't match it word-for-word*

Yeah, I hate grading like that. Reciting information isn't thinking its regurgitating

And there are many ways to solve some problems

Are your psets out of Griffiths or do they make them up from scratch?

Oh, if there's a solutions manual then its from the book obviously

5:42 AM

Yep, from the book.

8 hours later…

1:23 PM

@ACuriousMind Damn you! you convinced me that entropy would never be a Noether charge!

There goes my Nobel prize

@NeuroFuzzy Griffiths is awesome

1:36 PM

Oh jk the paper by Wald was from 93 :P

2:27 PM

ahh, we have a chat session coming up, don't we...

2:45 PM

Yeah...

Such a lively session

@Danu I think I just cited a post by Lubos saying that :P

And that entropy of a black hole is a Noether charge doesn't mean that this works for other systems

@Danu Huh? The session starts only in one hour, doesn't it?

@ACuriousMind Then my notification thing is wrong

@ACuriousMind Yeah, obviously it hinges on the somewhat observer-independent nature of a black hole

@Danu The schedule confirms that it's not happening yet

...Mongolian Death Worm? :D

3:05 PM

@ACuriousMind Very nice

3:43 PM

I'm going to go home, hopefully the internet lets me back into the chat session

What is tat 'event' starting in10 minutes ?

@Ramanewbie A physics chat session; I'm not sure what's on the agenda for today.

@Ramanewbie Our bi-weekly chat session

@What must I do ?

@Ramanewbie If there's anything you want to chat about then this is your opportunity

If there isn't then you don't need to do anything

3:53 PM

@Ramanewbie We often go off-topic though, but that's when it gets really interesting.

Not that you could not also chat about it at any other time, but chat session is where more people than usual are here

ok

Although there appear to be only five of us active at the moment. That's including David who's currently in a superposition.

I think Danu will be coming.

Incidentally @ACuriousMind I agree completely with your post about downvoting.

And I see eleven other people do as well

3:58 PM

@JohnRennie Well, I'm not really contradicting your OP, either. I don't deny that some questions may be unfairly downvoted (and I've no idea whether that has become more or less frequent).

That meta post has become a bit...unfocused, judging from the answers.

@ACuriousMind I suspect my post touched a nerve for some people.

Hence the 28 upvotes, which I don't think it deserves.

So, you guys have a physics chat session in a physics chat room?

@JohnRennie Yeah, downvoting is always kind of a hot issue (just look at all the debate on mother meta). It's just that some are talking about the actual question you linked, some are discussing downvoting duplicates a bit more generally, and others seem to think that we generally downvote too much. It's mainly the latter crowd I wanted to address.

@yilduz Yes, though how much chatting actually gets done depends on who's around ...

@yilduz Well, do you want us to have a biology chat session here? ;)

4:02 PM

:P

So what do you talk about all the rest of the time, then?

Sex, drugs and rock and roll of course

4

In other words, everyday life for physicists :-)

Makes perfect sense.

Hmmm...I have missed the rock and roll, I think

I've missed all of them except the rock and roll.

Well... does aspirin count? :)

I don't even like taking that.

4:06 PM

It's my last resort when I have a headache - I don't usually take it either.

I only take it if I've got a particularly bad hangover :P

Howdy

But I fondly recall cooking it in a chemistry lab

I was stuck in a time loop for a while

Can you do much that's interesting with aspirin?

4:07 PM

I crystallized acetylsalicylic acid (aspirin).

@JohnRennie Not really, I guess

^

With codeine, available at your local supermarket, you can hydrolyse off a couple of ether groups.

To make heroin :-)

Oops, no, that makes morphine not heroin.

You have to add back a couple of groups to make heroin, but the details escape me now.

@DavidZ What kind of time loop?

@JohnRennie You're not going to go Breaking Bad someday, are you? ;)

@Icosahedron ez-pz

4:12 PM

A couple of years before I started my degree at Cambridge, a couple of postdocs were caught making LSD at the chemistry labs :-)

Actually, I do have a physics question to ask:

2

Q: Quantum mechanical monopole

Recently in physics news, scientists have experimentally discovered the so-called quantum mechanical monopole. It seems that a quantum mechanical monopole is different from a magnetic monopole. So my question is what exactly is a quantum mechanical monopole and what are the differences between th...

quantum-mechanics magnetic-monopoles

I was going to answer this, but realised I didn't know enough about the subject for a good answer.

@JohnRennie I think Emilio does a good job.

@ACuriousMind actually infinite browser redirect loop

@ACuriousMind I don't think Emilio's answer address the question of how vorticity in a BEC models defects in quantum field condensate.

So, not that much to do with time really

If you take the Higgs field as an example, symmetry breaking produces a condensate, and this condensate has an angle in the complex plane.

4:16 PM

@JohnRennie Perhaps I'm blind, but where does a quantum field condensate play a role here?

Isn't that what the Higgs field does?

It settles to a non-zero lowest energy value.

Yes, I replied to your "how vorticity in a BEC models defects in quantum field condensate."

acquiring non-zero VEV is indeed what one calls a condensate in QFT

But I don't see what it has to do with the synthetic monopoles

Right, but the idea of monopoles is that if the condensate nucleates at different places you can end up with a mismatch of the angles and a point defect that looks like a monopole

This really applies to the GUT breaking

I've never heard of it happening with electroweak breaking

But isn't the basic principle the same?

So how does the BEC described in the Nature article model monopole formation by a quantum field condensate?

I think Bose-Einstein condensation is quite different from the "condensation" that happens in QFT/symmetry breaking, but I could be wrong

Ugh, sorry folks, my internet connection is completely b0rked (technical term) so I have to peace out

Happy chatting

4:21 PM

Quite different indeed, but from the article about the paper (I don't have access to the paper itself) the vorticity in the BEC is proposed as a model for monopole formation in a condensate.

@JohnRennie Ah! I think you are talking about Polyakov monopoles from GUT breaking, which are not Dirac monopoles

@ACuriousMind Yes, but isn't the point of the paper to model a Polyakov monopole?

@JohnRennie Both papers I see linked in the article (nature.com/nature/journal/v505/n7485/full/nature12954.html and journals.aps.org/prl/abstract/10.1103/PhysRevLett.103.030401) are about Dirac monopoles

Ah, OK, I reread the artice and it specifically talks about Dirac monopoles ...

It was the line in the article "Researchers have in fact suggested that the Big Bang should have forged magnetic monopoles as elementary particles" that made me think of Polyakov monopoles.

Just as well i didn't attempt an answer then :-)

That line is indeed a misleading, as you are right, the "Big Bang monopoles" are supposed to be Polyakov. I guess trying to connect research to the Big Bang is just too fancy to resist ;)

4:34 PM

Say you know a person who hasn't done any real math in ~10 years, and that person wanted to go to school and study physics. What would you suggest be that person's first step?

@yilduz That depends. What qualifications does the person have? How much maths did they learn?

Not much. A first level calculus class in 2005. As for qualifications, nothing really in the way of math and physics.

Been working in IT for a while, educated in IT security.

To suceed at a physics degree you have to really want to do it. This especially applies to someone past the first flush of youth, because learning new stuff gets harder as you get older.

Your friend should try reading up on physics and maths to see how interested they are.

It's not my friend. It's me. :P

Actually trying to answer questions on this site is not a bad start, but stick to the basic questions!

I don't want to put you off, but getting a physics degree won't do wonders for your salary.

4:40 PM

I know.

The reason for doing it is because you really want to.

Exactly.

And if you really want to, don't wait to go to university. Start learning about physics in your spare time.

Pursuing a physics degree vs continuing in IT security will greatly reduce my salary in the long run.

If you try, and find it too hard or not interesting enough then you'll probably struggle with a formal physics course.

4:42 PM

Do you know of any good resources for that?

@yilduz MIT Open Courseware, Yale Open Courseware, Perimeter Institute.

Should I try something at Coursera or a similar site?

1

Q: Beginners Textbooks in physics

Hello I am fifteen and I already know everything that my school has been teaching me so I have been going ahead. I have already been studying mathematics far past where I am at school, but I am very interested in physics. I want to learn everything up to advanced topics such as super-string the...

resource-recommendations

3

Q: Beginner Physics Resources?

I'm interested in learning physics. I do realize that the subject is large and that it would be easier if I had a specific area of interest. However, I do not. I suppose I want to learn about the fundamentals of it all; the axioms that combine all physics fields. Or, in other words, a high school...

education resource-recommendations

Ah, right. I forgot where I was for a minute. :P

Those questions got closed, but there are still some useful answers to them.

4:44 PM

Thank you, both.

As it happened I started as a physicist (well, physical chemist) then went into IT. Now I'm retired from IT and getting interested in Physics again :-)

Oh nice!

What did you do in IT?

Network management

Which basically means a bit of everything, from setting up servers to configuring Cisco routers.

All good fun, but things change so quickly these days it's hard to keep up.

Very nice. Did the two subjects help you to better understand each other at all?

Yes, it moves very quickly.

@yilduz No :-)

4:47 PM

Oh well. :P

I suppose studying any form of science tends to make you methodical, and that helps when dealing with complex networks.

But the maths involved in network management is pretty trivial.

Well then, the guys at my last job should have studied science.

Everything there was just chaotic.

Terry Bollinger

5:47 PM

Alas, I was on the road and missed today's chat. But here's an easy topology question for anyone bored: Is there any way to saw straight through a wooden cube one time to create a perfect hexagonal face? If yes, how? Bonus question: What is the equivalent shape formed by slicing a tesseract in the same fashion? (Must go now, will check back later.)

6:26 PM

0

Q: How does the lagrangian derived if it has dependence on coordinate additional to field itself and derivative of itself?

In book "QFT" By Lewis H. Ryder , page83~85 .i don't understand why he introduce so much variation,and it confuse me though.i am wondering what is the difference between total variation and variation of field,thanks.

quantum-field-theory lagrangian-formalism action

This question (v1) seems to ask about calculus of variation in field theory. Is it unclear what you're asking / too broad?

1 hour later…

7:49 PM

@Qmechanic I think it is.

@JamalS Nope.

@JohnRennie Oh yeah, about the downvoting thing.

I'd like to talk about that

@Danu What are your thoughts on it?

I'm tired now

But maybe tomorrow or something

2 hours later…

10:11 PM

@0celo7 I think.

Though how did you integrate $\sqrt{2t - t^3}$?

You do know I'm obligated to report that...

You signed a thingie.

report what

You can, under no circumstances, talk about the test.

:<

...did you not listen to the proctor?

They have a 15 minute speech about this, before and after the exam.

10:14 PM

I don't remember that.

Though the thing is that I did not have a graphing calculator so I couldn't integrate that.

You signed that you understand.

Wow.

:/

Cats

I don't remember.

1 hour later…

11:44 PM

hi

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