The h Bar

5:15 AM

@JohnRennie suppose you use SI units ($m$,$kg$,$s$) and don't know anything about natural units. And I use the natural units ($\hbar=c=1$)

can you find the relation between my unit for mass and yours(which is $kg$)?

@JohnRennie taking this into account: "It is interesting to note that with the help of the [above constants] it is possible to introduce units [...] which [...] remain meaningful for all times and also for extraterrestrial and non-human cultures, and therefore can be understood as 'natural units'." by planck

@yuggib hi. can you help about that question?

@JohnRennie oh woke you up sorry :D:D

It was just coincidence. I start work around 6 a.m. and I usually check the chat around then.

ok thankgoodness

@2physics which question?

the one above

Anyhow, the simple answer is that I don't know. I would have to get out a pen and paper and work out what the mass unit is in natural units. To be honest I'm struggling to raise the enthusiasm for that.

5:29 AM

@2physics it is a very boring calculation

@2physics Google, Google, the unit of mass is the Planck mass

I should have known that. Oh well, it is six a.m.

you know, I'm following a video course and I don't understand it that when we use natural units how can we define the unit for mass, or why we use eV and some questions like this

alright thank you

5:49 AM

Using eV is just for convenience. It's a convenient unit for particle physics - using kg would mean lots of multiplying by ten to the minus large number.

@yuggib I'm not talking about calculating numbers, I'm talking about finding units. I mean for example c=1[Lp]/[Tp] = a(whatever we measure in SI units) m/sec and $\hbar$=1[Mp][Lp]^2 /[Tp] = b(whatever we measure in SI units for $\hbar$) kg m^2/sec and then we cant find any relation between masses units of these two systems using these two eqs

but if we also take the gravitational constant $G=1$ into account, then we have three eqs and three unknowns and we can find the mass unit also. but in particle physics we just consider $\hbar=c=1$ and I don't understand how this conversion can be made between two systems

Particle physics also assumes $G=1$. It's just that we don't often need to mention it because $G$ is so rarely relevant.

A: How fast can the Earth spin and support life?

6:22 AM

Somebody upvoted this??????

1

The massive dinosaurs existed because surface gravity around the globe at that time was not uniform. Surface gravity on Pangea was lower than it is today and higher antipodal to Pangea. The reason this happened is that the Earth's core elements moved off-center and away from Pangea. The Gravity T...

@JohnRennie okay it was my answer thankyouuu

7:03 AM

@0celo7 I would guess NO.

Hi, everybody.

I submitted the report for the paper I was reviewing. I'm freeeeeeeeeeeee.

Congrats.

11:15 AM

I am back

with my old self

11:26 AM

Much less...spiky

exactly :-)

11:39 AM

they probably changed something at gravatar, everybody got spikier

anyways I am reading nonstandard analysis

it is rather interesting what you can do with it; however it seems more a pedagogical/curiosity tool than something radically "new" (apart from the fact it was done in the sixties)

11:52 AM

@yuggib Well, it can't really do something "new" because it was meant to be a replacement of standard analysis, right?

@ACuriousMind not exactly, it was meant to give a richer environment on which you can do more things

however, it proves theorems well within ZFC so in that sense it can't provide anything new

and the environment is at times too rich: given any unbounded hypernatural $N$ (i.e. a "natural" that is bigger then all standard naturals), there are uncountably many unbounded hypernaturals both bigger and smaller than $N$

NeuroFuzzy

12:22 PM

@ChrisWhite if you're out there and don't mind random pings, I'd love to get your input on how to pragmatically couple point particles to an electromagnetic field in (for example) a simulation! physics.stackexchange.com/questions/278328/…

@yuggib I think nonstandard analysis suffers when it comes to reproducing some theorems in integration, however I am not sure how reliable my memory is

12:54 PM

@Secret nonstandard analysis is not a substitute for standard analysis...it's just a richer environment where more things make sense

1:21 PM

@yuggib i want to be too rich

1:48 PM

@0celo7 then you should start thinking about a career in finance/management

@yuggib I'm going to marry rich.

2:45 PM

@yuggib Have you heard anything about Li's Geometric Analysis text?

@EmilioPisanty contact me because of the willard article

3:05 PM

@Sanya How do you mean?

@EmilioPisanty sorry, bad english ... "for" instead of "because of"; anyway, I'd need an adress I can send it to or sth

@0celo7 nope...

3:27 PM

@Sanya I'm pretty easy to find online ;-). imperial.ac.uk/collegedirectory/index.asp?PeopleID=325066

It is impossible to play any games when it disconnects you every 10 minutes

4:04 PM

There is a traveling Matisse exhibit in OKC for another couple of weeks. Worth it if you can get there easily. But you have to buy ticket for a fixed time slot, so do some reaserch before jumping in the car.

4:31 PM

Hi, everybody

what is the scientist role in peer review issue you are thinking about?

@Secret Well, I think it's complicated with conflicting incentives.

I was hoping other people could comment on their experiences.

Well, my only data is from the chemistry sector. Various academics have been talking about the pros and cons of open access, but they also ramble about how some editors went through a pay to open access style which is not very healthy

@Secret What do you mean, some editors went through a pay to open access style?

You mean you can pay the journal to open access your paper?

There are some peer reviewed journals which allow the authors to make their paper open access, but it requires paying a certain sum of money, around 50 AUD if I recall

pubs.acs.org/page/4authors/authorchoice/index.html

For example

4:42 PM

50 AUD is not much compared to the cost of publishing a paper.

They also talked about the issues of using researchgate (most don't favor or found no need to use it), and also how high impacts journals tend to get more cites, thus becoming higher in impact and so on in a positive feedback loop

and also how funding tend to bias on any journal article that made its way to Nature

At least for chemsitry, they wonder whether the impact factor is a good measure of the quality of the review process

Yes, these are all important questions.

5:25 PM

@DanielSank Yeah, that's a thing.

Not usually 50 AUD though

journals.aps.org/authors/…

US$1800 for Physical Review A-E, $2900 for Phys Rev Lett

iopscience.iop.org/journal/0953-4075/page/…

£1700/$2700/€1950 for J Phys B

5:42 PM

@EmilioPisanty I have a problem with that.

Research is largely publicly funded.

The results ought to be public.

But even aside from that entire issue, I am struggling with the role of the individual scientist as a reviewer.

@DanielSank Yeah, but publication isn't free either.

APS has a very nice website which does help get research done faster, and it takes money and other resources to maintain a stable server.

I'm not saying those are necessarily services that we as a community should be buying (like e.g. paying illustrators at Nature to re-do scientists' hand-drawn horribilia into prettier stuff), but there's definitely nonzero value being provided by the publisher.

As to whether the price is right, then that's a separate argument. Probably on the side of "they're charging too much", if you ask me, but it's not an easy area to go into.

6:06 PM

@JohnRennie I thought he requires a little help. And his question is interesting/useful on the elementary level. I absolutely didn't have any intent to annoy you with it. If I had known it, I hadn't done it. Btw, I voted your posts more times up, as many times more reputation you have.

6:26 PM

@peterh "he requires help" is not a reason to upvote an answer. "The answer is good" is a reason to upvote an answer. Please stop breaking windows on the site: if you upvote bad content, more bad content will follow.

5

@EmilioPisanty "And his question is interesting/useful on the elementary level"

@peterh That's a reason for upvoting questions. This is an answer we're talking about.

@EmilioPisanty What about compensation votes? For example: if your opinion is mainly neutral about the usability of a question, althoug is highly up- or downvoted. You think it doesn't deserve it. What do you think, is it okay to vote into a direction with the intent to make the voting count of the question more near to the value you estimate?

@DanielSank Also I don't have any possibility to know, who votes me up/down, or who gives me stars on the chat. The stars don't have any significant effect to my behaviour, although I am happy if I get one.

user54412

@NeuroFuzzy That's an interesting question, but alas I don't have any good answer. I don't do particles myself, and the only particle codes I know about assume no self force. Moreover, they generally smooth out particles for numerical purposes, and this turns out to be a good thing because the "particles" in the code are actually meta-particles representing many point charges.

6:57 PM

@peterh Do you really think "Meh. This posts is nothing special in my opinion, but let me vote on it anyway" is a good idea?

Vote what you think about the post, not what you think about its score.

3

You don't know what the other voters were thinking, and they may have a good reason for voting the way they did that you just don't see at the moment.

I have bare basic doubt in quantum mechanics, can i ask ?

@dmckee I didn't say it that it would be a good idea. I asked him, what he thinks about this.

@A---B Yeah :-)

@dmckee +1 :-)

@peterh Thanks for allowing me. So some months back in chemistry class they told me that Rutherford's atomic model is broken because, Maxwell's laws says that moving electron will lose energy and thus will spiral and smash into the nucleus. So to overcame this problem we have energy levels in quantum mechanical model. So my doubt is where does this energy come from ? how does shells have their energy ?

Q: Why don't electrons crash into the nuclei they "orbit"?

7:21 PM

81

I'm having trouble understanding the simple "planetary" model of the atom that I'm being taught in my basic chemistry course. In particular, I can't see how a negatively charged electron can stay in "orbit" around a positively charged nucleus. Even if the electron actually orbits the nucleus...

quantum-mechanics electrons atoms models

Physics Meta

7:33 PM

1

Q: Questions with an ulterior motive

There are a lot of questions posted which ask about what mainstream physics says about something, but imply that the OP has a completely different opinion. For example: Let's get back to the Ether. What is it?. The OP has some theory about the ether, as shown in their answers on other questions...

discussion

7:50 PM

@A---B Are you literally asking "how come the Bohr orbitals have a fixed energy level?". That's one of the axioms of Bohr, so it doesn't make much to ask to prove an axiom. I think the answer in the greatest level of generality is that the energy levels are quantized because they correspond to eigenvalues of the Schroedinger equation of the system (I think this only works for one-atomic systems). Take this as a grain of salt, I am not a physicist.

The axiom does contradict much of our knowledge of classical physics, agreed. But it explains phenomenons which classical physics cannot (spectral lines, e.g.).

Typo: one-*electronic systems.

@BalarkaSen so you say that energy is just there ever since an atom is created ?

@BalarkaSen apart from the fact that Schrödinger QM is of course also an approximation, the answer that the energy levels appear as eigenvalues of the schrödinger hamiltonian is completely correct

@A---B What do you mean, "just there"?

@Sanya Thanks for verifying.

Are you also bothered that the planets "just" have the energy to keep them on their orbits?

7:54 PM

@A---B and which energy

My personal intuition of quantization is that "eigenvalues come in integers; 2.41-many or 3/2-many eigenvalues is nonsense". Good to know that's not a bad intuition :P

I mean the energy in shells of an atom ?

@A---B each shell that is occupied has an electron having that energy - each unoccupied shell does not have any energy as there is nothing "supporting" that energy

@A---B Take a hydrogen atom. The one and only electron is spinning the one and only orbital and thus have a specific kinetic energy in the Bohr model. But since the hydrogen atom is stable, the orbital which contains the electron must have energy = negative the energy of the electron which is spinning: this is conversation of energy.

If the orbital didn't have an energy, the total amount of energy couldn't be 0.

@BalarkaSen Uh, what?

8:02 PM

I suppose I said something nonsense; what, specifically?

"The orbital" is a synonym for "solution to the Schrödinger equation", i.e. it's a possible state for an electron. It has no existence apart from being such a state.

2

It's not that the electron and the orbital balance each other

I agree; but since OP's asking about the Bohr model specifically, I don't think he'd know what the Schrodinger equation would mean.

@A---B Uhm, ACMs post is a good answer.

Maybe, but your "the orbital has the energy of the energy of the electron" doesn't make much sense to be

If I edit a post out of the VtC review, does it get out from the VtC queue?

8:07 PM

@BalarkaSen well, in the Bohr modell there are orbits, i.e. circular paths around the atom core, that are - for some yet unknown reason - only stable in certain radii around the core and to each radius there corresponds an energy IF an electron is rotating the atom with that radius - can we put it like that if we do not want QM?

@ACuriousMind Hm, it's not clear to me why not. But I believe you.

@Sanya Sounds good to me.

I am not a physics person, I should duck out of this conversation :P

@BalarkaSen I think the moment "we" (physicists) stop talking to "other people" about what "we" are doing, we would be doing a big mistake - so I quite disagree with you :>

@ACuriousMind Oh, ok, so you're defining an orbital to essentially be a state for the electron which is in it, and defining the energy of the orbital to be energy of the electron which is in it.

Yes, that is what I take those words to mean

@BalarkaSen This isn't so even in a classical model: the energy of the system is $T+U$ where $T$ is the kinetic energy of the system and $U$ is the (negative in the usual gauge) potential of the system.

Q: If a 3k+ user edits a post out of the VtC review, does it get out of the review queue?

8:13 PM

@ACuriousMind That makes sense. Should have thought of that.

Physics Meta

0

Somewhere I've heard a rumor that a post gets out of the review queue if a 3k+ user edits it as part of the review. It may be an unintended side-effect, or a non-trivial interpretation of the spirit of the review votes from the software development side of the SE engine. What happens if a 3k+ us...

discussion

@dmckee Hm, true.

In a non-relativistic quantum context you can identify $-\frac{\hbar^2}{2m}\nabla^2$ as the kinetic energy opperator, but the orbital is not an eigenfunction of that opperator (though in the hydrogen atom the separated angular parts of the wavefunction are, that's the spherical harmonic part of the solution).

@Sanya Heh, there's always the fear of not understanding what the person next to me says. I know the "ideas" behind "classical" quantum mechanics, but never really read it thoroughly from a book or something (although I definitely want to at some point), partially because most QM books I have seen (not a lot) is essentially a lot of mathematics, giving less physical motivation.

@ACuriousMind I quoted BBS on my E&M discussion board.

8:20 PM

If we are talking about physics.stackexchange.com/questions/278010/…, then I have led the discussion into a blind alley, and I mean to address the core question at some point.

Also I have to admit that the mathematics in those books are "physics people mathematics", hence most of the time not rigorous. That sort of repels me, since I am a mathematical person.

@BalarkaSen I feel you. I am taking QM and it's not agreeing with me

@BalarkaSen you might want to try Ballentine for the mathematical part, I think that is not thaaaat awful in terms of mathematical correctness (it is still a physics book); as for the physics part ... well, I have no clue ... Maybe even the Feynman lectures? And well, about that part of not understanding ... that's basically the other persons job to make sure that you can understand - that's my take on it

@0celo7 You're hopeless, as mathematical logic does not agree with you either. Sorry.

@Sanya Fair enough. I think that's been recommended to me before too, I'll note it down somewhere.

@BalarkaSen One of the professors at our university does mathematical physics-style quantum optics and he recommended it in his lecture ... But it might not be enough for a mathematician, dunno. If you want a real math take on classical QM, I have heard the original von Neumann book is supposedly quite decent, but I've never read it

8:30 PM

@BalarkaSen Huh?

I talked to my topology professor, who said the empty hypothesis thing is a convention, not a logical necessity.

So once again, I was correct.

(I have yet to be incorrect.)

@EmilioPisanty Do you mean this question in your meta comment?

I think Ballentine is frowned upon. He calls velocity a fundamental observable and momentum derived.

@0celo7 "The fundamental physical variables, such as linear and angular momentum, ..." (L. Ballentine, QM, chapter 3) - I'm not sure about that

@Sanya I'm not going to pull it out now.

Working on a project.

@0celo7 You apparently do not agree with proof by contradiction.

8:39 PM

He says weird things in chapter 3 is all I know.

@BalarkaSen I don't doubt the logical consistency.

I think it's not very satisfying and I always prefer a direct proof.

@0celo7 I will be indebted to you if at some point later when you're done with the project, you'll find the time to hint me at somewhere I can look those weird things up; until then I'll also give it a more thorough read then I've done just now

@ACuriousMind Thrawn. Thrawn could be your next wonderful avatar.

@ACuriousMind Indeed I do.

That is a brilliant find.

Ah, I see now that @DavidZ deleted it. For the record, I would rather it stayed up. It provides a very valuable record of how that theory actually looks when challenged. If it just provokes too much animosity then I feel a historical lock would be better.

9:02 PM

Why is at a flat universe will slow it's expansion, a closed one will slow and collapse and an open one will expand forever?

@SpaceOtter It could be a good question, although its survival rate I would estimate below 50%.

Bugger. I've been put off asking questions by their low survival rate

@SpaceOtter Afaik the current measurements say it is flat and accelerated expands.

@SpaceOtter what is the usual time you spent on trying to solve a question before you ask it on pse?

Ya I know. WMAP cleared that up for us. @peterh

@Sanya At first too little. But now, I keep trying till I do

I ask chat if I don't know where to start looking just to get a refrence

9:07 PM

:)

sorry, gotta go

@SpaceOtter Thus, our universe if flat, and its expansion doesn't slow. Although it slowed until around 4-5 billion years ago.

Any one with a refrence

Are we absolutely certain it's flat? I thought WMAP found a minuscule curvature

Ya so where do I look to work out why we made that prediction (decelerating expansion) in the first place

@SpaceOtter It found flat universe below (small) measurement precision. What is not really an answer, because it could be anything.

@SpaceOtter The acceleration of the expansion is known, there is positive result from the 1a supernovas.

mmhmm. So I'm trying to work out why it's generally accepted that we live in a flat universe when that would suggest our expansion to slow down.

@SpaceOtter Btw, accelerating expansion has already happened once.

9:14 PM

At the beginning... yes I know

@SpaceOtter And let be light.

We've all seen the lambda CDM model diagram @peterh

Well, light, also photons, were created only after the end of the electroweak era

Who here is good with Matlab?

What does this have to do with a flat universe and expansion? I think you've lost me @peterh

9:19 PM

@SpaceOtter Your question was: "Why is at a flat universe will slow it's expansion,". It is not true. Here is a flat universe, accelerating its expansion.

@Sanya give me 5 hours

@peterh Pretty much what @dmckee said.

@SpaceOtter Maybe you could ask this also on the Astronomy SE, there is would have a better chance for survival, but lower chance to get useful answer.

ok @peterh My question should have been. Why is it we think a flat universe should slow it's expansion?

Astronomy SE is far too slow atm.

Hah!

9:22 PM

@EmilioPisanty I suspect first you read somehow only the first some words of this, then you read but you have somehow forgotten this, finally ignored this.

Google answered my matlab question

@SpaceOtter I'm not sure I understand your question. It's not the shape of the universe that controls expansion, but the ratios of dark energy to ordinary matter and energy desnity.

@peterh no, I'm aware of all of that.

I stand by what I said.

@EmilioPisanty Then I can't interpret this.

@EmilioPisanty Maybe something is still unclear?

@ACuriousMind Wrong.

9:27 PM

@ACuriousMind I was watching this lecture and he says "a flat universe will slow it's expansion, an open one will expand forever, and a closed one will slow and crunch" So I wondered why he said that when I knew that the accelerated expansion was due to Lambda

It's the shape of yo momma behind.

I'm assuming smart ppls like you know what lambda is

I should just ask the question

cosmological constant

Or rather keep searching the internet. Any recommended resources.

@SpaceOtter Yes, although I consider it bad style to refer to physical quantities by their variable symbol :P

9:29 PM

@0celo7 Ya, CDM

@ACuriousMind Really? Even in a lecture?

I didn't have effort to type "Cold dark matter and dark energy"

@SpaceOtter I wouldn't overexamine a statement made in a public lecture. Unless you can find another reference that back up this claim, I'd suspect he misspoke.

@0celo7 If you're not talking about a formula, yes.

A formula?

So it's perfectly scientifically ok for a flat universe to have accelerated expansion? I doubt he would get that mixed up he said it's the reason he got into cosmology

9:32 PM

@0celo7 Of course you can say "Lambda" if you're talking about a Lambda in a formula. Just don't substitute "Lambda" for cosmological constant in a normal sentence.

Should I just post the question

I thought our universe is flat and has accelerated expansion.

@ACuriousMind Oh, I disagree.

well... Probably flat

@SpaceOtter Sure, but I would urge you to find a better reference than a YouTube video. The link can rot and make your question non-sensical. That's the second reason I advised you to find another reference to back that statement up

WMAP wasn't perfect despite lot's of awards

9:34 PM

But it's perfecly possible for the universe to be flat and acceleratedly expand, if you just have enough dark energy

(I find cosmology really boring and will continue to work on homework)

@ACuriousMind Yes that's why i'm asking for refrences in chat. Unless you don't have any in which case i'll be gone

@SpaceOtter My point is that the statement as such is untrue - so you can't back it up

sigh you were doing so well

@ArtOfCode don't ban me please

9:35 PM

@0celo7 ::gasp::

@ArtOfCode We're having a discussion about cosmology, what's the problem?

what did I even do?

@0celo7 nah, it's not you this time :)

@ArtOfCode ok good.

I've been a good boy.

@ACuriousMind Alright thanks mate

9:35 PM

@ACuriousMind the problem's about an hour back, but someone flagged it

Oh, I see the flag now

lol

@EmilioPisanty Btw, what about this and this?

Oh, it was you flagging then @John. Yeah, I'd worked that much out.

What did Chris say?

9:37 PM

Night folks

something he shouldn't have done, especially for a room owner

oooooo

Wow!

Remind me never to piss off @ArtOfCode

He be playin no games!

@0celo7 you've done that enough to know how many games I don't play :)

@ArtOfCode Name one time I've pissed you off.

lol

9:39 PM

@ACuriousMind I'll slap you.

@0celo7 I'm just puzzled that you think you never pissed off any of the people that banned you :P

@ACuriousMind Huh? They were doing their jobs. I see no reason for them to be pissed.

@0celo7 months ago now, but you certainly did

I also consider all my bans in gross violation of the Geneva Convention, but that's for another time.

@ArtOfCode Huh, I really have no clue what I did.

Tbh, I just remember being banned and some mod telling me I did something I had no recollection of.

For some reason that has stopped.

that probably would have been me, I seem to remember banning you quite a number of times :)

9:41 PM

@0celo7 Ah...I don't want to have this conversation, let's just let it rest

@ArtOfCode I don't remember that.

@0celo7 either you stopped doing things you shouldn't have been, or people stopped flagging 'em... either way I'm happy

@0celo7 I do, I'm looking at your suspension history :P

@ArtOfCode Can you give some examples?

@0celo7 They collect a file from the next potential targets. All of the cages are reviewed by the CMs, they are needed to defend the decisions.

@peterh What?

9:43 PM

@0celo7 I'm seeing a lot of name-calling in there

@ACuriousMind Yes.... of course talking about unpersons is always unpleasant

@ArtOfCode Whom was I calling names?

um... just about everyone who was a regular at the time :)

Impossible, why would I call e.g. @ACuriousMind names?

Or @Slereah, etc.

That doesn't make much sense.

@0celo7 Mods can see even the deleted comments, but even they can't easily search in them. If a cage happens, the CMs automatically check this in the background. This is why the mod could show from your comments and earlier messages what you have long forgot.

9:45 PM

@0celo7 Oh yeah, baby, call me names.

wat

@ACuriousMind The fuck?

John Duffield

Does anybody know where this Poynting vector depiction comes from? It's from this question.

@ACuriousMind Sorry, I'm not attracted to you.

@JohnDuffield Did you reverse Google Image it?

John Duffield

No, I answered the question a while back, and now I'm writing a piece where I talk about the Poynting vector. I've got a fair few references, and was hoping this picture was from some authoritative/trusted website or textbook.

9:47 PM

@ACuriousMind I think it's weird that you want to have a sexual relationship with your duckling.

Incest is not cool.

@0celo7 lol

I have no idea what the duck etiquette on this matter is

quack

But I do remember that ducks are frequently necrophiliac, so their moral standards seem to not be very high to begin with