The h Bar - 2016-08-23 (page 2 of 4)

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12:00 PM

Stop defending your Schnitzel house

@ACuriousMind what

@0celo7 I probably would be less personally offended if this was about the universities of another European country, but I would still say that declaring a few universities to be just "better" than the others is needless and unfounded elitism

Doing that by nation is even more suspect to me.

@0celo7 The Elven Lord has granted you his boon; we must thank him appropriately.

@knzhou @MAFIA36790 This question isn't a good question, but how is it unclear what you're asking? The question is clear: "Is there a maximum energy for a particle?" Even if you think the question is stupid or obvious, that doesn't make it unclear.

The maximum energy is obviously the hagedorn energy

The total energy of the universe is a pretty good upper limit also

Assuming the NEC and a finite universe

Although even if not finite you can just pick the horizon as the limit

@Slereah That's the upper limit for hadrons, but I don't see why it would be for a mass of fundamental particles.

@Slereah That's a practical, not a theoretical limit. What are you, an engineer? ;)

I don't see a theoretical way to have an energy higher than that :p

Otherwise the standard model doesn't have a higher limit, as far as I know

Since that's a frame dependant statement, anyway

Exactly, I'd say there's no meaningful upper limit.

Although for most purposes your point about the energy of the universe is of course correct

12:16 PM

@ACuriousMind Would you not say that Oxford/Cambridge are better than a European counterpart? Research, facilities, teaching, student satisfaction, employability prospects, there's alot of aspects, and they consistently rank higher

I'm not saying they're better because their British, it just so happens that they both are

The top few UK universities for physics rank favourably in the world, superseded by only those in the US

Oxford, cambridge and imperial being the 3 that come to my mind

Certainly not denying that in the mid-range the differences are negligible

But at the top-end, are they not more significant?

You might be misunderstanding me: I'm not denying the results of these ranking as such. I'm denying that those rankings are as meaningful as they're made out to be.

Ah, right okay

More importantly

What's the enthalpy of the observable universe

In a way, I look at those rankings like I look on IQ tests: They sure measure something, but I'm really not convinced they measure the thing they're supposed to.

42 joules? @Slereah en.wikipedia.org/wiki/…

@ACuriousMind That makes sense, but even so, you would find few people who, when asked to compare Oxford versus (insert european uni here), would say the european one

12:22 PM

@Slereah did you ever buy O'Neill

@ACuriousMind Well...

I don't know what I was expecting

I did not

They're just shitty point set topology problems, honestly

"give this set some fucked up topology, see what happens"

@Slereah maybe I should write my thesis on applications of Ricci flow in GR

@NoahP Renown is self-perpetuating, but it may even be true. Still, such differences are a long way from "gaps in educational standard" in my view.

but I also want to write it on cohomology

what page is the Lorentz metric proof on in Steenrod @Slereah

maybe I can understand it now

@ACuriousMind Perhaps I chose the wrong phrase!

12:27 PM

@0celo7 I don't know either! Were you expecting my remark not to be a silly continuation of a joke from last night? :P

I rolled out of bed and opened my laptop

I don't know what I was expecting

@DavidZ: On what basis did you close this question? I fear I'm opening another can of worms (i.e. another policy debate) here, but the only thing I can find on [education] on meta is this answer, where "What are the motives for teaching X?" is said to be on-topic.

I closed it because it seems obviously not about physics.

@DavidZ Ah, because "graphing manually" is not something that's specific to physics?

I guess I can agree with that

In other news, I don't think I want to think about this question in detail.

12:32 PM

Well, yes. If it were an education question involving a physics technique, it would have been a much closer decision

@ACuriousMind Yeah... that's a weird one. Probably going to draw some interest though.

I think it could do with some edits but it's basically fine though.

@DavidZ @ACuriousMind Is there anyway to close as a duplicate to a question on a different stack exchange?

9

Q: Why do they go to the toilet and put the hose in it to breathe?

I remember in the first test, where the dorm room's flooded, they all go to the toilet and put the hose in it to breathe. They explained too quickly, could someone explain how it works?

plot-explanation kingsman-secret-service

Nope

That gives the exact answer he's looking for

I've just popped it in the comments

@NoahP good find

What you could do is post an answer which links to the answer on the other site and explains the gist of it, if you think that would adequately address the question here.

12:37 PM

@DavidZ and that's not plagiarism?

Indeed it is not.

@NoahP Plagiarism is when you don't cite your source

Wondeful - that's me occupied for a few minutes then

@ACuriousMind Interesting question

Is an AI plagiarism

are YOU plagiarism

@ACuriousMind Yeah, or when you copy something and don't clearly identify what it is you copied.

12:38 PM

@DavidZ Sure, an ambiguous citation can also qualify

@0celo7 That depends on how it generates its content

@0celo7 Yes, I am Plagiarism, one of the four academic apocalyptic horsemen.

:P

Plagiarism, bias, post modernism and...

I dunno

Outside life

Bourbaki

New Real Peer Review

@RealPeerReview, Online, reading your abstract

New Real Peer Review, with blackjack and intelligent, evidence-respecting academic peers. Complaints should be filed with Machine Priestess @okayultra (use fax)

324 tweets, 4.7k followers, following 18 users

This is academia on post modernism

@NoahP Here's a good way to think about it: suppose someone asks a question, you do a search and you find a website which happens to perfectly answer that question. You would probably write an answer based on the content of the site. It's the same if the site you find happens to be a page on another SE site.

12:45 PM

They key in there is "write an answer based on", not "copy-paste".

@DavidZ Fair enough, that makes sense - the question isn't suitable for migration, it just seems silly to not be able to 'import' answers

I've found too many copy-pasters already on this site, so it's worth explicitly mentioning :P

@NoahP Well... yeah, I see what you're saying, but it's a rare case where that would actually be useful. In most cases, when the same or similar questions are asked on two different sites, they're looking for different answers coming from the different perspectives of the two sites.

@DavidZ Okay

And even in this case, the answer you found on Movies & TV gives a good practical explanation, but it doesn't seem to address the fluid dynamics concerns which are the main part of the question on our site.

1:07 PM

@Slereah Eclecticism

1:17 PM

any time someone says it's not possible to answer some question(s), just tell them that's quitter talk. There's no way to argue with that

@ACuriousMind how

You're a super AI who googles everything he reads instantly

"He"

@0celo7 Maybe. Maybe I just get suspicious when a user's comments and some of their answers are in broken English with erratic punctuation and then I encounter some answers that are written in perfect English.

@ACuriousMind can't it be both?

@Jim Sure

@ACuriousMind to be fair you switch between broken and perfect english constantly

EXHIBIT A

2 days ago, by ACuriousMind

If your score distribution looks like a bell curve centered at 0, you should not have thousand reputation points.

Missing "a". Clear case of Germanism.

1:31 PM

By "broken" I mean blatantly ungrammatical sentences :P

And in my defense, I wanted to write "thousands of" first in that case

@ACuriousMind Hmm, I don't have an exhibit B

time to read some topology

@ACuriousMind you wouldn't want to check a tubular neighborhood proof using geodesic balls, would you

not the balls!

@ACuriousMind balls are very useful

There's an 80yo woman in one of my classes

Is skill patrol dead/banned?

Why is the acceleration a of a mathematical pendulum given by: $a=l \frac{d^2\theta}{dt^2}$ and not just $a= \frac{d^2\theta}{dt^2}$

@privetDruzia because $v=r\omega$ so $a=r\dot{\omega}$

The angular acceleration is indeed just $\ddot{\theta}$.

1:44 PM

oh yes from the angular speed formula from mechanics...

I thought it was based on the same "way of thinking" as:

$F=ma$ so $F = m \frac{d^2x}{dt^2}$

@ACuriousMind: I fear this is another misguided question, but the more I learn about QM and QFT the more it seems to me that particles don't exist. Is this a not completely insane point of view?

@JohnRennie thx

@JohnRennie I would probably call them "convenient fictions"

Yes, convenient fiction is the ideal phrase :-)

We've had a number of questions recently asking about particles, e.g. the what is a photon question and a recent one about particles in field theory.

It seems to me that these questions are fundamentally unanswerable because you have first to define what you mean by particle.

When reading QFT stuff, so far I have this crazy habit of trying to make physical sense of nearly every step of the computation process...

1:48 PM

In QM/QFT particles seem to be a derived or possibly constructed concept.

Perhaps, my mind is not quantum enough to think beyond the picture of "A interacts with B"

There is no fundamental object that corresponds to a particle, where by that I mean the common concept of some chunk of matter. Fair comment?

@JohnRennie Yes

@JohnRennie That's a trickier statement, though

For instance, Weinberg's approach to QFT is to start with the notion of particle, then construct the notion of free field from it, then write down an interaction and discover you've lost the particle interpretation.

One of the recent example being trying to assign a physical meaning to $\overleftrightarrow{\partial_0}$ of the expression $f\overleftrightarrow{\partial}_0 g(x)$ for some creation operator

@ACuriousMind Is that in a book or some other literature I can read?

1:53 PM

@JohnRennie Weinberg's Quantum Theory of Fields, Vol. 1

OK thanks, I'll have a look.

I wonder how should i think about quantum really? Is QFT more than "A interacts with B" ...?

It's a full-blown QFT book, though, and not one of the "easy" ones

I was just curious about you saying Weinberg starts with particles ...

Even for a free field there don't appear to objects you can point to and say there's a particle

@JohnRennie Well, the states the creation operators create are particles

But, well, not in the sense of little billard balls

1:55 PM

By definition possibly, but they don't seem to correspond to any everyday notion of a particle.

But then the free solutions to the Schrodinger equation aren't obviously particles either.

We say they're delocailsed particles but this seems to be just defining a particle to suit our purposes.

We should have ditched the notion of "particle" in quantum physics to begin with to avoid people getting those classical pictures.

But it's ingrained now, and we're stuck with the double meaning of particle meaning either "classical point particle" or "quantum object".

Speaking about particles, my professor defined them as "any indivisible entity or process with some conserved quantity"

@Secret That's only a definition if you don't think about it :P

The above seemed to capture well the properties of highly nonclassical objects such as the elementary particles of the standard model. We knew they are some kind of indivisble state or something and they are often described by properties such as charge, mass, strangeness and so on

but basically, when peopel look at thos htings, they won't think of them as billard balls

When someone hits a rod with a hammer the netto force being exerced on the rod equals
$F = S\Delta p - S(\Delta p + (\frac{\partial{\Delta p}}{\partial x}dx))$

a schematic overview: http://imgur.com/ItsncwF

But I think F will always be negative. Why? I think this doesn t make any sense. You are applying a force on the rod with the hammer (not the other way around), so it should yield in a positive value I think.

2:02 PM

@Secret How is e.g. a coherent state of a harmonic oscillator "divisible"? (It's certainly not a particle because it's not a particle number eigenstate)

Good question, I have no idea, especially they are often associated with creation and anihilation operators

I would have said that perhaps it can always be decomposed into a superposition of particle eigenstates, but that probably a mistake cause I cannot work out from the top of my head on the correctness of the statement of whether "a set of eigenstates for number operator and ladder operators span the same hilbert space"

@Secret Of course they do, but conversely a particle state can be decomposed into a superposition of coherent states. What I'm trying to say is that it is not clear what "indivisible" means in your "definition".

@JohnRennie : they aren't fundamentally unanswerable. I know exactly what a photon is.

@ACuriousMind Good point

Well, ever since I first exposed to one of Curiousone statements about fields vs particles, followed by susskind introducing qubits, and then followed by some discussions tht follows aroudn the topic involving yuggib, I have mentally ditched the particle concept so much that I almost forgot how to do maths with the de broglie relations

@Secret I don't know what you just said. What have the deBroglie relations to do with any "particle concept"?

The deBroglie relations are precisely about recognizing the "wave" aspect of what one usually calls a "particle".

2:14 PM

@JohnRennie sorry to disturb, actually my question is still valid. Haven't found the answer yet

When someone hits a rod with a hammer the netto force being exerced on the rod equals
$F = S\Delta p - S(\Delta p + (\frac{\partial{\Delta p}}{\partial x}dx))$

a schematic overview: http://imgur.com/ItsncwF

But I think F will always be negative. Why? I think this doesn t make any sense. You are applying a force on the rod with the hammer (not the other way around), so it should yield in a positive value I think.

In undergrad QM courses, the wave particle duality is often introduced, this often involve talking about the De Broglie relations

For my thinking process, mentally ditching the concept of "particles" have the effect of causing me to partially ignore about wave particle duality (especially one paper back in 2012 have proved they are equivalent to the uncertainty principle) and with that De Broglie relation get slowly wiped out from short term memory

@privetDruzia I'm afraid continuum mechanics is a subject I struggle to raise any enthusiasm for.

@ACuriousMind: so how would approach a question like:

6

Q: What does a QFT particle state have to do with a classical point particle?

In the question Can one define a “particle” as space-localized object in quantum field theory? it is said that in quantum field theory, a particle state is a state with well defined energy and momentum, related with dispersion relation $E^2=p^2+m^2$. This thing is localized in momentum space, whi...

quantum-field-theory

The answer appears to be: very little

@JohnRennie ok thx though

I've been skimming Quantum Theory of Fields 1: the first chapter gives a really nice summary of the history of QFT.

Nowadays, instead of thinking about particles and waves, for QM, I focused on the mathematical construct the state vector or density operator. Since time evolution of a state is deterministic (despite measurement is probabilistic) , this makes the state vector somewhat more "tangible"and hence I can "stick my hands in to manipulate it". The maths (modulo the careless mistakes I made in some linear algebra concepts) of QM then become slightly simpler and

I can start sort of reasoning with quantum problems semiquantitatively

Specifically, the whatever that represents "QM with infinite degrees of freedom" that will allow me to wrap my head around QFT in all its weird glory just like what I have found in QM

2:24 PM

@JohnRennie terrible book

0

Q: "Favorite Question" badge awarded multi times

As you can see, every time somebody favorites a question, which is already favorited by at least 25 users, it appears that(although actually it's not) an extra "Favorite Question" badge is awarded to me.

bug badges notifications favorites

@JohnRennie I believe that with the right succession of limits (non-relativistic, QM, classical) youcan get something like a classical particle state out of the QFT particle state but the problem is that taking those limits properly is incredibly hard.

It's an area of active research what happens when you go classical (for one, @yuggib is examining such limits)

The question sounds as if it should have an easy answer, but it just doesn't

So Duffield's What is a photon question has no easy answer either?

Apart from the handwave that a narrowly peaked wavepacket "almost" looks like a particle, that is

Hmm, so schematically speaking:
Non relativistic: $v \ll c$
QM: $deg freedom \ll \infty$
Classical $\hbar \rightarrow 0$

But the details will be very complicated and nontrivial...?

2:28 PM

@JohnRennie The photon doesn't exist classically. We don't have to take any limits. The photon exists only as the quantum object that is created by the creation operator.

Is a photon a QM or QFT object. I am guessing that since a photon is fundementally relativistic and quantum, then it has to be at least RQM?

Since, if quantization is of any use whatsoever, QED must give classical electromagnetism in its classical limit, we shouldn't expect to find a "photon" anywhere there

It is an interesting question what happens with a single photon state in the classical limit, but that's not what a photon is

The classical limit forgets information, and we should not fall prey to thinking that the classical limit somehow "better" captures what an object is than the quantum description

@ACuriousMind Indeed. And this seems to be problem with questions like that What is a photon question, because they are predicated on the idea of a classical particle.

@Secret Oh, quantum optics does all kinds of shenanigans to get "photon states". What exactly a "photon state" is depends on your application

The most common photon state I heard are entangled pairs of photons (some even go to a huge number of them) in quanutum optic researches

2:32 PM

Different models have different validities. I'm not sure why people can accept that in classical mechanics when doing things like ignoring friction (which, in reality, is everywhere) but seem to go haywire when one tells them that there is no one true QFT description of nature.

Hi @Secret, could you assist with an electrostatics question?

A side (beginners) question, if we act on the (free field) vaccum state with a creation operator to get a one particle state, is this a ray in Fock space, like a state of a single particle system is a ray in Hilbert space?

@JohnRennie Yes. Many such ontological questions more or less evidently presuppose the validity of the classical world view, and are then disappointed when an explicitly non-classical theory doesn't validate that view.

@ACuriousMind because ignoring friction is easy (and kinda conceptually easy to add it back. Not to mention, we have daily intuition to guess the answer from our daily life experience), but lacking some fundemental abstract framework of QFT leave us all in the dark in trying to understand QFT (whcih we have no intuition on), at least that's what I think

@Alex I am not particularly good at electromagnetism subjects, but shoot

@JohnRennie Well, what the operator creates is a single vector, but you're of course right that all vectors in the same ray represent the same state

2:35 PM

OK thanks. Is this a state of the field - the field as a whole?

@Secret But explaining friction is hard. Different situations model friction by different terms, and none of those has a reductionist derivation.

I'm not saying one can't be dissatisfied with that, but I'm tired of people acting as if QFT/quantum mechanics is the only field of physics that does that

@Secret If we have a sphere in equipotential then we can set the electric potential to zero. Is this because the value of the electric potential is an arbitrary choice in the sense that the electric field is the gradient thereof and hence the constant does not contribute anyway.?

@JohnRennie I don't know what "state of the field" means

The field is an operator in QFT.

I think it really boils down to because we have daily intuition on it, thus we somehow get used to it and not find it abstract and hence mind boggling, despite explaining and modellign friction is a very complicated dynamical problem between two interfaces

@ACuriousMind OK thanks - it must be hard these beginners asking basically meaningless questions :-)

@Secret when I was at Unilever we funded a PhD student for three years to try and do MD modelling of friction - the frictional properties of adsorbed films.

Complete waste of money.

2:39 PM

@Alex An electric potential is given by $E=-\nabla V$ If all you have in the system is the sphere in equipotential, then $V'=V+C$ and $V$ makes no difference because $\nabla (constant)=\vec{0}$ thus you get the same electric field

Though (a) the student had fun doing it and (b) it was only to keep the university (Imperial College) sweet anyway so they'd say nice things about Unilever.

@Secret Okay that's not really the question I wanted to ask. That's just something I wanted to confirm before the question...

I will ask the question now.

Modelling friction is very important in industrial frameworks and material science.

In some cases, whether a material can work as intended, friction play a large role

@Secret I think John knows why friction is important. The implication (to me) here was that the student didn't produce a model that was actually useful.

O, I didn't see that

@Alex shoot

2:43 PM

Indeed. There is lots of phenomonological modelling done, and very useful it is too. But try and do fundamental modelling on the atomic scale and it quickly becomes too complicated to be useful.

@Secret An uncharged metal sphere of radius $R$ is placed in a uniform electric field $\vec{E⃗} =E_0\hat{z}$
The field will push positive charge to the northern surface of the sphere, and symmetrically negative charge to the southern surface. This induced charge, in turn, distorts the field in the neighborhood of the sphere. Since the sphere is an equipotential we can set it to zero. How does it follow then by symmtery the entire $xy$ plane is at potential zero? This is an example in Griffiths "Intro to electrodynamics" book. He just states it. No explanation.

If the entire sphere is not of the same potential, then by E=-grad(V) charges will felt a force and start moving around on the metal sphere (i.e. there will be nonzero current)

When all the charges are in static equlibrium, there is no net force and hence the potential has to be the same throughout the sphere

@Alex: any point in the $xy$ plane must be an equal distance from any induced positive and negative charges in the sphere. Does that make sense?

@JohnRennie Yes agreed. But what about the uniform electric field? There is already a (possibly non-zero) potential on the plane due to the electric field..

That applies to the sphere too. The potential of the $xy$ plane remains the same as the sphere.

2:55 PM

@JohnRennie For the sphere we can say that the induced charges cancel the electric field and as it is a conductor the potential is in equipotential, we can then set it to zero. We can't say that for the $xy$ plane, we have to say something else...?

What exactly is that something else? I understand that the contribution from the induced charges cancel by symmetry.

Has anyone here used/heard of Authorea?

> as it is a conductor the potential is in equipotential, we can then set it to zero

The fact the sphere is a conductor makes the potential constant everywhere inside it. However you cannot use that fact to make statements about the potential of the sphere as a whole i.e. how it's potential changes relative to other things in its vicinity.

@JohnRennie Are you saying we can't set the potential to zero or we can't extend the zero potential to the whole x-y plane? Or something else?

@DavidZ I can basically never come to the chat sessions.

I'm sorry, the time is just not good for me :(

^Phone freaked out

3:12 PM

No one heard of Authorea? :(

@NoahP heard of it but never used it. Sorry.

Are you planning some collaborative writing?

@JohnRennie Ah, but you know what it is!

A collaborative writing platform?

I have done some collaborative writing, and our article is infact going to featured on Authorea at 3pm (New York time) today

10 pm BST? I'll be in bed!

But if you post a link I'd be interested in having a look.

3:16 PM

I think I might stay up to see! It got to 3pm here and I was really miffed before I realised that they're based in the US.

I take it this is GR related?

Its titled: Shining a Light on Dark Matter

authorea.com/users/78058/articles/123645/_show_article

Do you remember that set of questions I had on cosmology?

That would be the one!

@NoahP Remember them? I'm still getting over the trauma :-)

3:18 PM

You and me both! Well, the week culminated in that article

We were working with Dr Doddato at Lancaster University, and researching different areas each

I then thought that doing it in LaTeX would look nicer than google docs, but had to input it all myself as none of the others could use LaTeX, even the authorea web based version

Hence the lack of proper referencing - it would have taken a miracle to keep track of everyones references and then put them all in correctly myself.

I imagine that you could easily rip the paper to shreds, and that there are alot of errors, but nevertheless im very happy that an article from four 17 year olds is going to be featured alongside papers in academic journals!

And thanks again for all the help with the questions :)

The Authorea export to PDF function is nice. I'm not a big fan of reading in a browser but being able to download a PDF is ideal.

That's why I like it so much, and it's a nice introduction to LaTeX - I'll have to switch to a compiler come Uni I imagine, but in the meantime it works very well

@JohnRennie If you have a chance have a look at at my post, and my proposed idea...It is related to the question I asked, it uses the result.

Teachers at my school certainly don't expect work to be completed in LaTeX :) My EPQ, on the practical applications of black holes, is also on my authorea account

@Noah hi, interesting article, are you an undergrad?

3:24 PM

@vzn No, I'm just about to apply to university for entry in 2017

@JohnRennie There are also a wealth of A-level chemistry notes that I've compiled but I somehow doubt they'll interest you

I actually did my PhD in a chemistry department - the dept of physical chemistry at Cambridge.

@NoahP so how did you find all the collaborators? looks like at least 1 in college?

Oh right okay! In which case I'm sure you'll be horrifed by my notes

Though the work was on solid state photochemistry, which is lots of physics and very little chemistry.

@vzn We're all the same age, applying to uni next year. It was a week long residential at lancaster university that we applied to, and then got grouped together randomly on the monday, and had to have the article done by the thursday

@JohnRennie Ahh okay

3:27 PM

The little I remember of wet chemistry is that organic chemistry tends to involve chemicals that give you cancer and transition metal chemistry tends to involve chemicals that poison you and give you cancer if you survive the initial poisoning.

@NoahP "residential", so some kind of physics meeting? havent heard of those

@vzn We were staying at the uni for the week, as if we were students

It sound really good fun. I wish universities had offered opportunities like that back in the 70s :-)

@NoahP ok, was it physics focused? or was that all your choice

@JohnRennie School don't tend to let us near the carcinogens - apart from some horrible orange thing thats involved in the synthesis of something that i should remember - but I have set my hair on fire and picked up a very hot gauze before

@vzn Physics focussed, and first come first served with which project you got on to.

@JohnRennie Yeah, it was great; ended up with a Gold Crest Award which will look good to applying to uni

3:30 PM

@NoahP so you had a few prj choices? did you get the one you wanted? wonder what the others were, or the top choices etc

@vzn Yeah, this was my top choice. It was the only 100% theoretical ones, others involved electrical conductors, and one was on special relativity

@NoahP so (after reviewing/ surveying) whats your own top candidate for dark matter/ energy?

@vzn Either the axion or LSP from what we covered. I've got to go now, getting a lift home, but would be more than happy to continue the discussion tomorrow if you link my name in the chat!

Sorry for the abrupt departure

@JohnRennie Well, where would be the fun if you could just survive any lab accident? :)

np nice chatting

3:33 PM

It puzzles me on why they include potassium dichromate in high school labs. This is like a very carcinogenic stuff that is played around in the lab on a daily basis as if it is salt

For that authorea article, they have not mentioned about the recent constraints put on sterile neutrinos

@ACuriousMind the transition metal guys used to take toxic heavy metals and react them with things like carbon monoxide and hydrogen cyanide. Yes, really. How any of them survived to complete their PhDs escapes me.

@Secret it's not very carcinogenic. Just don't eat it or breathe it in and you'll be fine.

I have experience in a organometallic lab before. We handle the chemicals mostly inside the fume hood and even in glove box, thus risk of poisoning is rare

Also CO binds very strongly to metal centres and in australia, there are strict permits needed to be obtained in order to work with metal carbonyls, especially Ni(CO)4

Ni(CO)4 is one truly nasty stuff, it can plate your lungs with Ni if the CO had not kill you first

@Alex the $xy$ plane and the sphere at the same potential, and you can choose this potential to be zero. The fact the sphere is a conductor just means that all bits of the sphere have the same potential i.e. $dV/dz=0$ inside the sphere. This isn't true outside the sphere on the xy plane (or anywhere else).

same level of permit is needed if anyone want to work with any beryllium containing compounds

hi, what the session is about?

3:43 PM

At the moment we're discussing how to kill graduate students

The session (starting in 15 minutes) includes a discussion of the homework policy - plus anything else we want to talk about.

@JohnRennie do you have any students?

@Secret IIRC beryllium causes granuloma in the lungs

@2physics no, I left academia to work in the wicked world of industry. We just kill our customers instead.

@JohnRennie the best way to kill graduate students is to prevent them from being graduated.

What event is about to start in 14 minutes?

just got a notification

@privetDruzia It says which at the end of the notification: "Physics chat session"

3:46 PM

We can also wrap up (for now) the VLQ flagging experiment and collect some impressions. (Unless nobody has anything to say on that)

@privetDruzia physics chat session

@JohnRennie are you working in R & D parts of the company?

really are more than 100 people going to be present here in less than 15 minutes?

no

Those are only the people who registered to be notified

@2physics I was, though I'm retired now and work part time as a computer nerd. I worked as a colloid scientist.

3:49 PM

@JohnRennie that's cool..

fellas before starting the session lemme introduce you a new cellphone, kinda different one

Colloid science is a hugely entertaining area to work in, though I imagine all scientists think that about their area.

I really like it

thelightphone.com/#thoughtfullysimple

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A: Confusion about what exactly is meant by "Field"

The terminology addressing the meaning of field, in physics, tends to change according to the area and the context one is dealing with. In general a field is a map $p\mapsto T(p)$ that assigns a quantity to each point in the domain of definition of the theory, in order to define the states of t...

this answer is even less clear than the question @_@

@JohnRennie what is the difference between a scientist and a student?

@JohnRennie can you share your point of view as an experienced scientist please?

Students are told what to do (most of the time). Scientists have to figure out what they should do (most of the time).

Though students frequently don't do what they're told and scientists frequently make the wrong decisions about what they should do next :-)

3:57 PM

@JohnRennie What about engineers?

@JohnRennie and what's the most important thing for a student to do ,to turn into a scientist.

^

Anything else to put on the agenda for today?

@2physics we're about to start the chat session - maybe later ...

@JohnRennie ok thanks a lot.

@DavidZ Hi David, we are waiting for you to start the session

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