The h Bar

1:11 AM

@dmckee I would argue that the force of a table actually requires work. The force ultimately depends on the pressure of the matter Earth is made of, and that matter is compressed by gravity. Without a upward force, the table wouldn't be able to maintain that force. — Madde Anerson 42 mins ago

... uh ... I thought we had agreed that the biological system was different and that was the whole point of the discussion.

Any way, I thought I was trying to help, but I don't think I'm up to trying any more. Someone else want to take a crack at it?

tpg2114

1:45 AM

I get the impression it's a classic case of trying to run before you can walk

And OP is jumping to really complicated systems without understanding the basic definitions... But how to convey the basic definitions (and explain why they are needed) is never easy. I will take a shot at it, Alfred Centauri appears to be also

@dmckee I just noticed we have one fewer diamond user -- when did that happen? I know he/she wasn't very active for awhile. Also, should that position be filled or is it just being left vacant for some reason?

Kyle Kanos

mbq's not been a mod for a while now. Going back to like October or something, IIRC

tpg2114

I just now noticed it, I don't think I ever saw an announcement/discussion/etc about it

Kyle Kanos

There wasn't any

tpg2114

That would be why I didn't notice it then

Kyle Kanos

I think he's a mod over at Stats, where he's put more of a focus

tpg2114

2:02 AM

If it's been that long, I'm guessing there isn't a desire to fill that position

Although the last conversation on the matter on Meta (which indicated the lack of activity by that mod) did have some talking about it being nice to have more moderators, not fewer

Kyle Kanos

I think it's entirely up to the current mods if they think they should get an extra 1 or 2

David Z

Yeah we keep thinking about adding another moderator or two sometime, but our moderation load has never been enough to make it seem urgent

tpg2114

I knew the discussion was about adding 1 more to the total, which is why I was surprised when an existing spot went unfilled

I guess "am surprised" is more appropriate since it's a new discovery... heh

dmckee

2:24 AM

@tpg2114 It was several months ago (most of a year?). Attending to Cross Validated was taking all of mbq's time so he asked to be formally removed as a moderator.

Moderator elections are held when the team feels more moderators would be useful. Apparently they think the current crew is doing an adequate job.

We seem to have a lot of work occasionally---in spurts---but the average is manageable.

tpg2114

That's fair

tpg2114

2:41 AM

If you haven't voted to close yet, OP acknowledges it is a duplicate:

0

Q: Nature of increased mass in the compressed spring

When a spring is compressed storing some energy, there must be an increase in the total mass of the spring. Even if the temperature of the spring would increase a little bit, it should be possible to cool it down to the initial temperature and still have some stored energy. Most probably this ene...

Kyle Kanos

Interesting...defaultfile in Fortran is a thing

tpg2114

Huh. Definitely never heard of that one

And it's been around since F77

Kyle Kanos

I was looking at a code that was sent to me and it had it in there

tpg2114

Fortran I/O really annoys me.

Streams FTW

None of this record crap

Kyle Kanos

I haven't worked enough with streams to think of it one way or another

tpg2114

2:48 AM

The whole record-based IO is just a huge pain

We ran into massive problems with it

For PLOT3D, we had too much data so it would overflow the record length and we couldn't write data out

So we had to split it out, instead of writing (DO K, (DO J, (DO I ...))) style we had to split it and loop over K explicitly and write the J,I data

But then we found that the variable size used for the record length is implementation-specific

Or rather, how it treats overflows is different

GNU just craps itself

Kyle Kanos

I've never worked with large enough datasets to have that issue

tpg2114

But Intel will happily do it by setting the record length to be -<size in bytes of a chunk> and then put more record lengths in the middle of the record

So a file we would generate with an Intel compiled code couldn't be read by a GNU compiled code

Or when I had to write a reader in C where I actually had to parse apart record lengths... It was all a huge pain

Kyle Kanos

But using access="stream" (is it?) fixed that?

tpg2114

We moved to HDF5 instead of dealing with Fortran I/O

Now we don't need to worry about endianness or record lengths or anything

Kyle Kanos

The AstroBEAR code uses HDF5 for IO

tpg2114

2:54 AM

We just say "Put the data in this array"

tpg2114

3:07 AM

I got semi-annoyed when I answered a question and the person left a comment (basically) doubting I was correct. Combustion is kind of what I do... but I also didn't pepper my answer with citations and math so I can't expect somebody to just trust me

vzn

3:38 AM

this recent question cited Cavalcanti at Sydney re QM interpretations. hadnt heard of him, looked him up, found some interesting stuff. they claim to have (new) experiments that can actually test the copenhagen interpretation re reality of wavefn. anyone else have any opinion? cited some links at the end of the "toy models of QM" chat room.

6

Q: "Reality" of EM waves vs. wavefunction of individual photons - why not treat the wave function as equally "Real"?

In thinking how to ask this question (somewhat) succinctly, I keep coming back to a Microwave Oven. A Microwave Oven has a grid of holes over the window specifically designed to be smaller in diameter than the wavelength of the microwaves it produces, yet larger than the wavelengths of the visib...

quantum-mechanics electromagnetism wavefunction quantum-interpretations

toy models of QM

Danu

8:03 AM

I think I am the only holder of a golden badge on History of Science and Mathematics at the moment :D

DanielSank

8:54 AM

@Danu Would you like a cookie in recognition of your achievement? I'd offer a medal but it seems you already have one...

infinitesimal

9:05 AM

Professor Hardy was wrong!

infinitesimal

12:47 PM

@ACuriousMind I would like to apologize to you and the rest of the room for MY pathetic outburst the other day.

alarge

@infinitesimal That was an interesting read, and it reminded me of Andrew Wiles (who also was too old to get the Fields medal).

ACuriousMind

@infinitesimal Very well. Forgiven and forgotten, as far as I am concerned.

alarge

You should read this if you're looking to read about the adventures of a physicist instead.

3

infinitesimal

@alarge I liked the part about nobody saying anything to him at Princeton for 10 days :O

ACuriousMind

@Danu Area 51 claims the site has only been in beta for 99 days, you cheater!

infinitesimal

12:53 PM

not 101?

ACuriousMind

For me, it says 99 in the upper left corner

Gowtham

@ACuriousMind same

infinitesimal

same

ACuriousMind

Probably just something to do with the caching of data, though

infinitesimal

@alarge Thanks :-)

Kyle Kanos

1:29 PM

@ACuriousMind Private beta probably counts

Gowtham

@alarge fun read .

vzn

4:00 PM

also, video on zhang by New Yorker, & more on zhang. he won a macarthur genius grant. (won by some physicists also?)

Mark Mitchison

@alarge What an idiot...

Poor chap, but still an idiot.

vzn

inf, re "hardy was wrong" which assertion are you referring to? this one? (see also Mathematics number theory chat room)

> “No mathematician should ever allow himself to forget that mathematics, more than any other art or science, is a young man’s game,” Hardy wrote. He also wrote, “I do not know of an instance of a major mathematical advance initiated by a man past fifty.”

$Mathematics$ Number theory

alarge

@MarkMitchison I agree. But I also think the article captures well the sort of "arrogance" that I have found is quite common among physicists, especially students of physics (related, obligatory xkcd).

But of course in his case this seemed very extreme.

Mark Mitchison

4:23 PM

@alarge What is worrying is that academia seems to accept such individuals within its working environment. Very few other industries I can think of are willing to elevate such people to the highest rank, who have failed to develop even the most basic skills required of people in everyday society.

I hope that this will soon be a thing of the past. The modern insistence on public outreach and wider professional skills courses during PhD training should prevent this from happening. Hopefully.

And I love that xkcd, by the way. It is just a perfect description of the typical physicist attitude. I am definitely guilty of the same arrogance.

alarge

On the other hand, I don't really like the streamlining of academia, and I think it can be a very productive environment to those "misfit geniuses".

Academia, to me, has become too much about grants, citations, and lab management. In many ways the most successful scientists are those who have managed to get a large lab and pump a lot of papers (some are like 50-100 people). At that point it doesn't really matter if you have novel ideas as long as you know enough to surround yourself with people who do.

Kyle Kanos

> People who are socially inept can nevertheless be the most creative people. It's very important that they can't be fired. This is the genius of tenure.

Idiot

alarge

@KyleKanos I do to some extent agree with this though. The point of tenure is supposed to be that you don't need to be concerned with incremental research and pumping papers out, but can rather concentrate on bigger things (like Zhang, from the other article).

Kyle Kanos

4:40 PM

The point of tenure is to ensure you can't be fired for no reason.

We should not at all protect idiots

Mark Mitchison

Frankly I question that people who are that inept deserve a job.

Let alone a respected job.

The idea that you have to be a reclusive weirdo to be really good at physics is a myth

And it's a really harmful myth.

alarge

I think that in terms of management academia is lagging behind the industry: There's a Taylorian need to create performance metrics from H-factors to impact factors and I think this is harmful.

Kyle Kanos

It's really the culture, not management.

alarge

This of course is not surprising, as many of the professors are really managers more than line researchers, yet have not read anything about management (I attribute a lot of this to the "I'm smart, I know better than the lib-art types", but this might be my own misconception; That said, doctors are also similarly suspicious of MBAs even when there's a wealth of evidence that MBA run hospitals tend to do better than those managed by doctors).

Kyle Kanos

The whole of faculty are committed to the idea of h-indices

The higher the h-index (relative to their subfield), the better researcher they are and the better the department becomes

alarge

4:46 PM

Right, what I meant that management (resource allocation) in academia is driven by h-factors and such (i.e. that's what the culture has become, not that it's due to a few individual managers)

Kyle Kanos

What does "resource allocation" mean here?

alarge

Well, grants, largely.

But this of course in the end translates as incremental research where you can push out a lot of papers and thus also cite a lot of people (and be cited).

Kyle Kanos

What type of grants? NSF grants? University grants? Something else?

I just don't see the connection you're trying to make

alarge

My point is that you give money to those researchers who are the best. One's performance is measured by some arbitrary yardstick, h-factor for one, which has become very gamed.

Kyle Kanos

But I see that as disconnected from tenure

(which is what we've been talking about?)

alarge

4:51 PM

This leads to a push in certain kind of research.

Whereas with a tenured system, in principle, you don't necessarily have this push, as you don't have to care what others think. In principle.

Now I do realize that in practice you do have to worry about grants, supercomputer times and so on. But to me the idea of tenure is to give a researcher money to do research and let them decide how to use it.

Kyle Kanos

That's not at all tenure though

Tenure means that the university cannot simply fire Professor A just because

They need to "go through motions" in order to do so

Case in point: Frampton. Got fired because he was convicted of smuggling drugs

A professor at my university, literally a month after receiving tenure, was fired for sexual harassment of a student.

Both cases, the Uni had to go through proper motions to fire the people

alarge

Well my idealized form of tenure, or the reason for its existence in my mind was to enable researchers to pursue what ever they wanted and not be worried about having to prove their performance every quarter.

Even in this idealized version, you should be fired for sexual harassment, say, though. But my point was that tenure in principle does enable you to pursue "big ideas".

Which is why I mentioned the system of grants/h-factors to contrast with tenure.

Kyle Kanos

Well that idealized version is more aligned with current practices and seems strangely disconnected from your previous comments

alarge

But of course it's all messy in real life.

Mark Mitchison

Wow only just read to the end of that article. So he actually did know he was smuggling drugs

Kyle Kanos

5:06 PM

But it was a joke

Mark Mitchison

Haha

The whole thing is totally incomprehensible

Kyle Kanos

It's a special blend of arrogance and idiocy.

vzn

5:23 PM

KK, reminds me of lewin...

alarge

@vzn Here's a more in-depth account

vzn

alarge thx for detail was looking for more than the minimal/ anodyne/ negligible info available previously.

zhang is an interesting case study re academic system. he left it for many years & developed his breakthrough completely independently of the system

did he get tenure anywhere? havent heard that. he got a prof/ teaching position. not exactly ideal for pure/ heavy research.

vzn

6:08 PM

re your comments on academia vs industry, mgt styles vs research etc... unf it appears there is a strong capitalistic pressure on both. & increasingly universities are moving/ increasingly structured more like corporations... :(

Sofia

8:22 PM

@infinitesimal God Almighty, when you say that Hardy was wrong, please mention which Hardy. There is another Hardy, i.e. Lucien Hardy, with which the QM has to do, and who placed under doubt the Bohm interpretation of QM.

David Z

50

Q: Why do most formulas in physics have rational exponents?

I mean why is $F=ma$? why not $m^{0.123}$, $a^{1.43}$ or some random non integers or irrational? I hope you understand that my doubt isn't limited just to force or energy or velocity etc., it also extends to area of a square, circle etc. and all other formulas. I think whole thing starts with d...

quantum-mechanics homework-and-exercises newtonian-mechanics quantum-field-theory classical-mechanics

Debating whether to revert the title edit, as pointed out in a comment

Kyle Kanos

Yeah, I think that probably should be changed back

Sofia

8:52 PM

Hi @KyleKanos ! I found a particularly good question. The question may be implemented, after some modifications, in some interesting experiment, but I don't have the right to change the OP's text. I flagged it for the attention of the monitors, and I suggest that it be discussed between experts. I don't know an equivalent experiment done until today.

Kyle Kanos

I'm assuming your modifications would be a rather drastic change?

Mark Mitchison

@DavidZ I agree that should be rolled back to the previous question. The current edit invalidates almost all the existing answers, many of which are good ones.

Sofia

@KyleKanos I don't have the right. My modifications would be a suggestion how to implement it practically, not with micro-cameras, as he/she says, which are still macroscopic objects, but with unstable particles, for instance. What I would be interested would be some broader discussion on the question, between people in our site which are experts.

Kyle Kanos

@Sofia I see. Well you can always formulate it into your own question. Or you could create a chat room for discussing it

To be fair though, that guys post makes very little sense to me

Sofia

@KyleKanos : I'll tell you what's the issue here. In whatever experiment I saw with interference between two beams obtained from splitting the parent beam, the nature of the particle on the two paths was the same. Assuming that the paths are of equal length, that no devices along the paths change the nature of the objects in a different way from one path to the other, I never saw such a thing that on one path the nature of the particle changes, and on the other one doesn't.

@KyleKanos : when we split a parent-beam, and we don't introduce some nature-changing device on the path so as to bring difference between the two wave-packets, they evolve in the same way. I never saw, for instance, that on one path the particle decay and on the other path it doesn't. And it is not clear why this identical behavior.

Kyle Kanos

9:08 PM

Do you have a link to the experiment?

Sofia

@KyleKanos with decaying particles, such a phenomenon could happen. But I never saw. You mean, a link to the question, don't you? Yes, of course, it's here

Kyle Kanos

Not to the question, the link to the experiment you are describing

Sofia

@KyleKanos : never was done such an experiment A.F.A. I. K.

Danu

@ACuriousMind I PASSSSSSSSED

Sofia

@KyleKanos : this is why I say that this is an idea.

Kyle Kanos

9:13 PM

I guess I now don't see why you need to split a beam. If you're sending a particle in a prepared state down a path, what is the difference between doing it 1000 times and splitting it once & testing

But I guess the answer to OPs question is, simply "yes"

Danu

@infinitesimal What was this? :P

Kyle Kanos

@Danu Don't worry about it

Sofia

@MarkMitchison : maybe my eyes saw more than he said, but I understood that he wanted to put a camera for telling us which way the particle took, which path.

Kyle Kanos

@Sofia Mark is talking about the post DavidZ put up

Sofia

@KyleKanos : I made a mistake, I meant to send the mail to you not to him. I am sorry.

Kyle Kanos

9:19 PM

Okay

I'm confused about that guy's post still.

Sofia

@KyleKanos : as I say, so I understood the OP's intention, but maybe I understood more than he meant. In any case, what I understood would be interesting for thinking of an experiment.

Kyle Kanos

It seems as if his question is, Can I send a pair of signals in different directions and determine 'what happened' along the two paths?

Sofia

@KyleKanos : in this way the post would be very interesting, and there are tools - not a micro-camera, it is still a macroscopic object, but, for instance, decaying atoms.

Kyle Kanos

@Sofia I imagine that we could tell that one of the particles interacted (somehow) based on the differences in the received signal, but telling what that interaction was and where it took place seems a bit far-fetched.

Sofia

@KyleKanos : I don't understand you. Just a minute - one of the two particle interacted ... based on difference in received signal - there is no signal from outside, the decay is due to internal dynamics of an unstable particle.

Kyle Kanos

9:26 PM

@Sofia You are talking about your experiment, I'm talking about the post

Having a decay wouldn't enable you to "play back" its environment, as OP wants

The particle would have to somehow interact with the environment to produce a difference that would allow you to say something about the path it took

Sofia

@KyleKanos - any interaction with the environment would introduce decoherence. One won't get anymore interference, if this is what he meant. So, I don't know why is it interesting, unless he wants to know which way the particle followed.

ACuriousMind

@Danu Congrats!

Physics Meta

0

Q: Site name should be named 'Theoretical Physics'

This is not necessarily a bad thing, but is a reality of the site, especially given that the unsuccessful Theoretical Physics.SE site content was also merged here a while ago. It is undeniable that there is a significant Theoretical Physics dominated member base of this site, and as such, more o...

discussion

tpg2114

@PhysicsMeta Oh PhysicsMeta, when will you have anything interesting to discuss in here...

ACuriousMind

9:47 PM

If PhysicsMeta starts actually discussing something, we will probably have an invasion of AI researchers in here shortly.

tpg2114

My statement stands... that would be pretty interesting :)

Danu

9:59 PM

@ACuriousMind Heh.

@ACuriousMind I'm just that powerful. Feel the force slowly overtaking you!

ACuriousMind

I, uh, don't want to feel your "force". :P

Danu

FEEL IT... INSIDE YOU

tpg2114

Yeah, nothing creepy there.

Danu

I did turn power-hungry mod about 100 days ago now ;)

bolbteppa

Hey guys, the Ward Identities are like differential equations for correlation functions right? How do they relate to Schrodinger's equation? I mean isn't the correlator of <1> the solution of Schrodinger's equation, are Ward Identities like some generalization?

tpg2114

10:08 PM

I'd love to help but almost every phrase in that sentence is over my head...

bolbteppa

Haha thanks dude

tpg2114

QM is not my thing

ACuriousMind

@bolbteppa The Ward identities state that the expectation value of a (classically) conserved current is still conserved up to "contact terms"

JamalS

Ooh, look what I found ^ :)

tpg2114

@JamalS I assume you are excited about finding the book right? And not just about finding a photo of the book?

Danu

10:12 PM

^hahaha

JamalS

No wonder it's nicknamed the 'bible.'

At least this one isn't a novel :) hehe

ACuriousMind

@bolbteppa: The Ward identities have no relation to the Schrödinger equation I know of - they are consequences of gauge theories that, among other things, ensure the decoupling of unphysical gauge boson polarisations from the physical S-matrix.

bolbteppa

Gravitation is awesome, I love the differential forms pictures :) But Landau is more fun

JamalS

It's a third hand copy from a friend who got it from an astrophysicist in the 1970s. It's intriguing reading his handwritten notes

bolbteppa

Well, if <ABC...> is the correlation of n functions and d<ABC...> = <dAB...> + <AdBC...> is it's variation you can multiply by 1 = dg/dg and take a derivative with respect to the metric, which makes you derive w.r.t. e^iS so you get the energy momentum tensor in this expectation right?

If you take d<1> you get \int <T>dg but ahh I don't see Schrodinger anywhere you're right

Mark Mitchison

10:22 PM

@bolbteppa I would also like to add: there is no "generalisation" of the Schroedinger equation in quantum mechanics. It is the most fundamental evolution equation there is according to the theory. Any evolution equation for a correlation function will always be a consequence of the Schroedinger equation, not the other way round.

bolbteppa

Yeah that's exactly what I was thinking, is there any theory on evolution equations for correlation functions and how they relate to Schrodinger? I'm studying CFT and they derive PDE's from the Ward Identities, I'm just thinking that the <1> (path integral) is the Green function solution to Schrodinger, but <AB...> I'm not sure about

Mark Mitchison

Well if you have a correlation function, that is an expectation value of some operator. Just write down the Heisenberg equation of motion for that operator and then take the expectation value.

But perhaps that is not the sort of thing you are looking for.

ACuriousMind

@bolbteppa CFTs are a very special kind of QFT. In two dimensions (which I assume you are looking at), the theory is almost entirely about representations of the Virasoro algebra. The path integral (or the Schrödinger equation for that matter) is not something that is necessary to consider in a CFT - they don't need a Lagrangian/Hamiltonian formulation to be a proper QFT.

bolbteppa

10:37 PM

Thanks, I'm learning about CFT's from an integrability perspective for a project, trying to look at Liouville c > 1 CFT's e.g. physics.stackexchange.com/questions/162369/… :)

I think it's awesome how that theory should be solvable and there's every reason to be able to solve it theoretically for any D, as Polyakov says, but if anybody does any approximations (e.g. Hatfield's book) it just justifies the D > 25

infinitesimal

11:00 PM

Sorry @Sofia :P

toy models of QM

Number theory

Transcript for

$Mathematics$ Number theory