3:00 PM
@JohnRennie It's a programming language
@ACuriousMind I did know that :-)
But it's a programming language I've never used.
Can we please not turn the chat into CS again
But I was really just making a pun on Scala/scalar, I have no idea whether Scala supports tensors
@EmilioPisanty But anyway, my point is that today Acuriousmind taught me a very important context on what $\hat p|\psi\rangle$ has no physical meaning really mean. I always though such expression you cannot find a physical object that you can measure in experiments, but I never though that you cannot even get e.g. momentum information from it
I felt like this is one of my major misconception of quantum I had for many years...
@Secret You can get information though
$\langle\psi|P|\psi\rangle$ has meaning
3:01 PM
@ACuriousMind now he tells me, after I've read the Wikipedia article on Scala and wondered where the tensors came in :-)
@JohnRennie Heh, I'm sorry
@0celoñe7 yeah, but I am talking about $\hat p|\psi\rangle$ by itself. Before today, I don't even know you canno even extract a spectrum of momenta from it
I thought the pun was sorta obvious
Apparently it understand the concepts of covariance and contravariance.
@Secret What did you think $P\psi$ even was?
3:02 PM
@Secret See, there we have a characteristic issue: Why did you think you would be able to extract it in the first place?
You often ask questions of this form - I thought X would do Y, why doesn't it? - when the answer very often just is that there is no reason at all to assume X has something to do with Y.
@Secret What you are looking for is an expansion of $\psi$ in eigenstates of $P$.
@0celoñe7 yes precisely, that's why I thought acting the momentum operator on some arbitrary quantum state should in principle be able to give me something about momentum distribution
@Secret If you measure many times, yes.
Repeat the experiment many times, I mean.
@0celoñe7 Measuring the operator $\neq$ acting with the operator!
@ACuriousMind No shit.
I wasn't saying he was right.
I'm saying what he wants is to measure.
3:05 PM
Yeah, but this is precisely what Secret seems very confused about so I think it's important to be clear about that
(I wasn't assuming you were confused about that difference)
My confusion: I know that measuring $\neq$ acting with the operator, but I know that acting an operator onto its eigenstate will give me an observable that I can measure when doing experiments. Now as 0celo have clarified for me, since I can wrote an expansion of $\psi$ in eigenstates of $P$, and each eigenstate when acted by the operator will give me eigenvalues which are the observables, then I always thought I can somehow get the distribution of the eigenvalues from this
@Secret See, the crux there is the "somehow". Unless you know how (or at least have reliable sources tell you it's possible), don't go around assuming that's true.
Naively, the coefficients of the expansion will tell you which eigenstate contribute more to the quantum state is question, so is it logical that the observable that corresponds to the eigenstate with a larger expansion coefficient should have a larger probability to be obtained in the measurement?
@Secret is the concept of an eigenprojector that foreign to you?
I know projection operators for a given eigenstate (since you can sum them all into the identity operator by completeness), is that what you call an eigenprojector?
3:17 PM
@Secret At this point, you're just saying that if you know the decomposition of a state into momentum eigenstates, you know how likely it is to measure that momentum. But that's just the Born rule, you don't need to act with the momentum operator on the state at all to get that.
@Secret yes. That one can act on states as much as you want.
hmm, I see... this also brought up another question. How do we know which observable is a given operator corresponds to mathematically if all we have is a given basis, and the operator wrote under this basis representation, and also some quantum states supplied for the operators to act on

That is, suppose I have self adjoint operators $A$ and $B$ where all its components under a given basis is known, acting on some known quanutm states, is there a way to tell what observables they are giving me?
I don't understand the question. In quantum mechanics, you don't take a bunch of operators and ask "what observable is this?". You start with a bunch of observables and make them operators.
Ah I see, it seems I think about quantum backwards. I always thought that you can not only make an observable into operators, but you can also do the reverse of figuring out what self adjoint operators correspond to what observable
Is this for real? What do the panel think?
0

I am 10 years old. Today my father explained to me how the rockets work, he told me Newtown's Third Law of motion worked here. I asked him why it works, he was silent... I have wasted over a week thinking about this problem, now I am giving up... Can anyone explain me, so that I can sleep..

3:27 PM
@EmilioPisanty @ACuriousMind ...actually, I think I had all my physics thinking backwards. In general, I have this fixated conception that you can not only use experiments to tell you what model to construct, but you also can start with you model and figuring out what physics it corresponds to by performing known checks, providing the maths obey some known properties that the physical things are supposed to obey
@JohnRennie Well given that the poster admits to being 10 years old we kind of have to act on that :-/
poor guy of age 10 has already started having sleepless nights
@DavidZ Aha! He broke the age rule.
@DavidZ On it.
Oh I already took care of it @ACuriousMind
At least I contacted the right people, I didn't delete the post or anything
Or in short, I thought the model contains all the information that can recover the physics of what each physical based mathematical object (e.g. self adjoint operators) will mean
Anonymous
3:30 PM
He/she could be told to ask his/her parent's SE account if they have one.
@Blue My understanding is that they will receive an email suggesting exactly that.
@DavidZ Uh...take a look at the user history, I sent the message ~40 secs before you. ;)
Anyway, the question itself is legit IMO. There are plenty of other laws and principles in physics where we do have a more fundamental explanation that would make a decent answer to "why does this work?" Even for this one you could tie it to conservation of momentum.
@DavidZ Well, some people would say it is conservation of momentum
So this in the context of quantum it will be like not only I have observables for position and electron spin and thus I can wrote them into operators in the model, I can mathematically distinguish whether I have a spin operator or a position operator by just doing the maths
3:31 PM
@ACuriousMind darn
Did you send the message before posting here?
Anonymous
@DavidZ Great :) I wouldn't exactly agree with totally preventing curious 10 year olds from getting SE's help in getting answer to a legitimate physics question.
Is this kid serious? 10 ?!
This is response for some of my old misconception on how on earth do we mathematically distinguish between an electron and a neutron wavefuncton, for example
@FreeMind Who knows, but SE acts as if they are serious
But I think I understood now, the latter is not always possible. I will keep that in mind when I think about physics, I rely on the model too much on telling me what the physics are
3:33 PM
@FreeMind Is that shocking? In India, parents are booking seats for IITJEE coaching even before the child is born.
@DavidZ I started typing it, then saw you had responded in here, too, and thought I'd tell you I'm "On it", not sure whether I hit send before or after that. Eh, I think the CMs are smart enough to figure out these two tickets are an accidental duplicate, nothing bad or irreversible has happened after all
@Yashas I find your second sentence much more shocking than a 10 year old asking a question on physics.SE :P
I am waiting for the day when IITJEE gets banned. This exam is inhuman. Causes deaths, depression and what not.
You know, life is more than rushing through textbooks and being proud of oneself to be a genius who has learned all incomplete models proposed in Physics and other sciences.
Anonymous
3:34 PM
@FreeMind 10 years. Approximately grade 5. Seems a good question for their age. I had my first physics class in Grade 6 but probably knew about Newton's laws when I was in grade 5.
@Blue Sure, and I don't think anybody in the organization (or associated with it, as mods are) disagrees with that. The only reason to act is that SE could get in severe legal trouble if they don't - it's not about the question on the site, really, it's about personal information stored behind the scenes. The user's email address and the like.
^that
We're not ageist, but the (American) law is!
@ACuriousMind yeah, no harm done here.
Anonymous
@DavidZ I get it. Thanks for replying. :)
@Blue Yeah, that's pretty good. I was generally commenting on even cases more extreme than that.
3:37 PM
@Blue And actually, all you have to do to be under 13 years old and on SE is just not tell anyone how old you are.
Anonymous
@ACuriousMind oh, well that too :P
SE is just legally obliged to act when someone does reveal their age, but otherwise I'm pretty sure they couldn't care less.
@ACuriousMind Yeah that's another way. I two years old and I still cannot figure out how to walk. Could somebody tell me about the relation Newton's law to process of walking? :)
@ACuriousMind That seems pretty dishonest.
2

I am trying to solve an-harmonic oscillator (with $x^4$ terms) and need theoretical data to compare with my numerical data. I have searched research papers on anharmonic oscillators and few spectroscopy books like Banwell's. Can anyone recommend books or papers with theoretical data on an-harmo...

how is that a homework question?
VTC reason is homework
3:46 PM
@0celoñe7 I think it's just pragmatic. No-one wants to discourage enthusiastic pre-teens but the US government says you're not allowed to store their personal data. The easy solution is for the pre-teens to conceal their age, in which case everyone is happy.
The same applies to Facebook and Amazon, but my niece and her friends had accounts on both well before they were 13.
@JohnRennie Me too :D My DOB on FB says that I am 117 years old :D
@JohnRennie Everyone except for the government.
And it teaches kids a bad lesson.
@JohnRennie don't feed the troll, Johnnie Rae
Cue another don't call other users trolls discussion ...
3:52 PM
@EmilioPisanty What?
@JohnRennie I don't think 0celo7 is a troll.
But I suspect that last message may not have been meant entirely seriously.
@JohnRennie cc @0celoñe7 As far as I can tell, the law only prohibits knowingly collecting personal information from children under 13. If you don't know the person is under 13, it's not illegal to hold their information.
@0celoñe7 is it a bad lesson to teach kids how to get round arbitrary government regulations? I would have thought it taught them valuable life skills :-)
ah, let me fix that
Anonymous
Does the US government mention 13 "earth years" ? It just says 13 years. 10 earth years is approximately 16 Venus years. :P
3:54 PM
@Blue I'd wager there is a part in the USC that explains "year."
@0celoñe7 I would have thought so, but it's not showing up in the obvious places
@DavidZ Hmm. And if they lie about it, it's fine?
@DavidZ Does the U.S. Code not have a giant "definitions" section?
@0celoñe7 well, if they lie to the operator, then the operator doesn't know that they're lying, do they?
@EmilioPisanty No, but it might make the children complicit or something.
@0celoñe7 Well, if a kid lies about being under 13, the site collecting their information isn't liable because they don't know the kid's true age. So it's okay for the site. I don't know if it's okay for the kid.
BTW is anything on the agenda for our chat session?
3:56 PM
I am recalling instances of children being charged with manufacturing child porn for naked selfies.
@0celoñe7 well, it would make the children liars
Do we still have a chat session with Jim having done the AMA today?
@0celoñe7 yes, those were interesting
@0celoñe7 Each individual piece of the law tends to make its own definitions.
There are some general definitions but not that many of them.
@JohnRennie Of course
as in, 30%+ of a school getting charged with that
3:57 PM
@0celoñe7 I thought children under some cutoff age are not held criminally responsible in the US?
I can't remember what that age is, but I think it's at least 13.
@JohnRennie I personally knew a 15 year old girl who got in serious trouble for that.
@JohnRennie There are some provisions for reduced sentences for people under 18 for certain crimes, but there's no blanket exemption from liability based on age AFAIK
@DavidZ How does Tag Synonyms for voting topic work?
@Yashas like it says on the tin
@JohnRennie I also knew a 17 year old who was charged as an adult for conspiring with ISIS or something insane like that.
3:59 PM
@Yashas Submit a suggestion and people vote on it... actually that'd be a good one to discuss in the session
In the US, the age of criminal responsibility is established by state law. Only 13 states have set minimum ages, which range from 6 to 12 years old. Most states rely on common law, which holds that from age 7 to age 14, children cannot be presumed to bear responsibility but can be held responsible.
@DavidZ @EmilioPisanty I was looking for the details. How many votes are required for a tag synonym request to be accepted?
Not many people have voted on answers in that topic
That's what we have to figure out
Enough to convince SE
Anyway, it's time to get started
Welcome all to our biweekly chat session!
Please hold unrelated discussion until after we have finished with the prepared topics
Here's the agenda for today's session:

1. Intro, welcome newcomers, site questions (5m)
2. Recent physics developments (10m)
3. Tag maintenance (?m)
4. Open discussion
@DavidZ : Concerning agenda, I would like to ask the community for permission to replace the word 'burnination' with 'blacklisting' in this 2013 meta post. The point is that the definition were probably not spelled out properly at the time.
Hello, my name is 0celoñe7
4:01 PM
@Qmechanic sure, that can be part of our tag maintenance discussion (and perhaps a meta post too)
I am 0celo7's Latino brother
For now, is anyone here new to the site, new to chat, or new to chat sessions?
@DavidZ See above
Anonymous
@0celoñe7 Welcome. Are you any different from your brother? :P
Anyway... moving on, what's new in the world of physics?
4:07 PM
If anyone has 90 minutes to spare I think this is good fun:
The talk gives a nice history of approaches to unification, and Arkani-Hamed is an entertaining speaker.
(though I understand not everyone is a fan :-)
If anyone has hours and hours to spare, this is amazing.
@JohnRennie Is it really only 90 minutes? :-P
At the end of the talk Akrkani-Hamed says "I meant this to take only 45 minutes" :-)
Haha, figures
@JohnRennie I once tried to explain quantum mechanics to my statistics teacher in high school
I had intended for it to take 45 minutes
It took way longer
4:09 PM
I was thinking it'd be fitting if the listed video length were only 45 minutes but it went on for longer
I saw him give a seminar once and although it was interesting, it went for fully double the allotted time
I suppose most people have seen the pictures of Jupiter's great red spot?
:-) There is a part II but it focusses on split supersymmetry and is less interesting to the non-susy phenomenologists amongst us.
1 message moved to Physics Meta
3 messages deleted
1 message deleted
OK, well, if there's nothing else, let's talk about tags. There have been some assorted proposals for curating or removing tags raised on meta over the past week or so.
@DavidZ there have
4:15 PM
6

As suggested by Natheniel in Redundant tags I, I'll make a single question and let people vote on the answers (containing redundant tags to burninate.).

This is the place to put tag removal requests, although as @Qmechanic suggested, perhaps we should change the wording to "blacklisting"
@DavidZ I disagree - I think it should explicitly call for both burnination and blacklisting
@JohnRennie : Nima Arkani-Hamed is indeed always a great speaker. I'm curious: Was this talk recommended to you on some website?
However, the key problem with that one is that there is no clear criterion for success
What conditions must an answer to that thread fulfil for the process to kick in?
@EmilioPisanty : That would work for me.
@EmilioPisanty As I understand it, the point is that blacklisting includes burnination, but personally I'm not opposed to listing both
4:17 PM
And, if there are no such conditions, what's the point of the thread?
@EmilioPisanty We have to figure that out.
And seriously, why is a single catchall thread needed?
Why can't individual tags be dealt with on separate threads as they get brought up?
that would enable much freer discussion on the pros and cons
I appreciate where that thread came from, via centralcharge's lengthy series of requests with lots of tags in them, but that's not where we are nowadays
That's another thing to discuss. Personally I'd be fine with saying that new requests for tag removal be made in separate threads, but the ones that are already on that thread we should handle as they are.
@EmilioPisanty : I guess it is on the Phys.SE mods discretion at some point contact to the SE team, if they deem the proposal has a realistic change of being adapted.
@DavidZ sure, that's fair enough
4:21 PM
@EmilioPisanty : because there is too many.
@Qmechanic Well, on the part of the SE team it's just pushing a button, after making sure that there is indeed a consensus
@Qmechanic too many burnination requests?
@Qmechanic I don't think there are too many these days. New requests come up quite rarely.
the last one was posted four years ago
@Yashas they don't draw attention because they come once in a blue moon nowadays
4:23 PM
@EmilioPisanty : I'm only interested in blacklisting. Burnination is alway implicitly implied for me.
If you're in this kind of regime, sure, take steps to rate-limit the thing. If you're in nothing-happens-for-four-years mode, though...
@Qmechanic Either way. Too many what?
@EmilioPisanty : Not actually now, but potentially too many in the future.
@Qmechanic Well, if it becomes an issue then, we can deal with it as it comes up
As it stands now, the implicit message is "Tag cleanup is impossible on this site"
I would like to think that that's not how mods see the issue
@Qmechanic yeah, precisely. So why are we worried that there'll be a flood of requests?
4:28 PM
@EmilioPisanty : Because it is hot now.
@EmilioPisanty I think Qmechanic is worried that once we get rid of one tag, people will suddenly "remember" that's an option and flood meta with new requests, while you see the inactivity in the past as evidence that that won't happen. Honestly, I can't tell who's more likely to be right.
@ACuriousMind well, as I said, if it becomes a problem then we can deal with it when it becomes a problem.
As it is, the message with dupe-closures like this one is: yeah, that's not happening.
FWIW it seems like Stack Overflow deals with this by individual request questions (example)
And that leads us to Shog9's recommended procedure for burnination requests, which does specify one tag per question - although it would be legitimate to argue that this is meant for SO and may not apply to other sites.
But I do think that procedure would make sense for us too.
@DavidZ that's on MSE. If it was meant for SO only, it'd be on MSO.
The mods haven't really discussed this, but fellow mods, @DavidZ ,@ACuriousMind, ..., would you agree to send a concrete request to the SE team, with a handful of obvious blacklist & burninate requests, first and foremost general-physics, to get the process started?
4:33 PM
> There are a lot of burninate-requests posted to various meta sites...
@EmilioPisanty Good point, though there are things that get posted to MSE and "in name" are meant to apply network-wide, but nevertheless were decided only by looking at SO.
@DavidZ Either way, the phrasing on that post makes it pretty explicit that it's meant to apply network-wide.
@Qmechanic I think the real issue is determining a standard at which a blacklisting request should be considered "accepted"
@Qmechanic Sure, but we need to establish meta consensus on these tags first regardless of how obvious they are. Currently I only see possibly the two top-voted suggestions on the collected thread qualifying for that
@ACuriousMind I'd include the third one, too
4:36 PM
@DavidZ It was migrated from MSO to MSE by Shog himself, I think that should tell us we don't need to argue it could theoretically be only meant for MSO ;)
at +7/+0
@DavidZ not anymore.
@DavidZ : it seems difficult to give clear-cut general criteria. It is much easier to discuss special actual tags.
@ACuriousMind cc @EmilioPisanty Ah yeah... what I meant and should have said is that sometimes things which are posted on MSE and meant to apply to all sites nevertheless don't make sense for sites other than SO, or for non-programming sites, or for some set of sites that may include ours. Though I do think this particular post does make sense for our site.
As far as the existing thread goes, the clear consensus is on and , and I think it's pretty clear that there is a strong onus to deal with them now that it's come up.
As far as the rest goes, it's not clear what constitutes consensus on that specific thread, but it does tend to be much easier to tell whether there is or is not consensus on a proposal when it's on a separate thread
i.e. positive score of $\gtrsim$ 5 on the question, no significant downvote component, no significant opposition on comments or answers
you know, the usual deal
4:41 PM
@EmilioPisanty Sounds reasonable to me.
How about we close Tag burninate requests for voting and add a message linking to the MSE faqs on burnination and blacklisting
@EmilioPisanty also sounds reasonable to me
and then future requests can be posted on their own meta threads tagged with success criteria as usual
@EmilioPisanty : There could be cases were an ignorant majority is oppressing a minority tag.
@Qmechanic Agreed. Then it's important to look at the content of any pushback in comments and answers.
4:44 PM
What I'd suggest is that once a tag removal request has community support, according the criteria proposed by Emilio or similar, then the mods manually review it and if we think there is no reason to override that request, then we forward it on to SE. This gives us an opportunity to "veto" the removal request if it looks like the "ignorant majority" situation is happening.
@DavidZ that sounds good to me
@DavidZ : Agree, but I don't think we should adapt a specific voting limit.
19

The procedure is as follows: First, burninate the tag, if there are currently questions tagged with it. If there aren't currently questions tagged with it, you probably don't need to blacklist it - but see Step #2. Once the tag is gone - no longer used on any questions - decide if it needs to ...

I think we have a rough consensus on future procedure?
Sounds like it
4:46 PM
OK, so, can I ask that we move on to the top scorers on the existing requests?
@Qmechanic Yeah, we do have a general idea of what constitutes "consensus" from other debates, and it tracks with what Emilio suggested except for the 5-vote minimum.
the first is , which is currently just short of wiped out
24

I think this question has its place here because I am sure some of you are "self-taught experts" and can guide me a little through this process. Considering that : I don't have any physics scholar background at all. I have a little math background but nothing too complicated like calculus I am...

locked, needs a mod to remove the tag
1

Does physics address the topic of consciousness? For instance, does physics say anything about how it might arise or what might be its qualitative properties? I'm wondering because it's interesting how certain combinations of particles are conscious (at least apparently) while others are not.

@EmilioPisanty We should look at
or, was that changed back? hm
could use some additional attention to the tags
1

Many physics papers now have dozens of authors per paper. Experimental physics may have multi-organizational and multi-country contributing staffs, but I'd guess that most of the names don't contribute a word or equation to a paper, yet they get individual authorship credit. My question is who de...

I would argue should be tagged physics-careers and then closed
and that's it for general-physics
@DavidZ : Yeah, the only plus tag is currently math-phys.
4:48 PM
Ok, good
@EmilioPisanty done
So all that's left is to handle those last two and request the blacklisting
@EmilioPisanty That one I just deleted so we don't have to worry about the tags on it
@EmilioPisanty not sure how best to handle that
@DavidZ that feels a bit extreme
shouldn't it remain but under historical lock?
Well but then we'd have to figure out appropriate tags to put on it
well, soft-question and physics-careers would do OK
and then it just lumps it into the next item in the agenda
4:51 PM
If it's off topic, and significantly so (which I think it is), we don't lose much of anything by deleting it
@EmilioPisanty both tags which I have very strong objections to :-/
@DavidZ well, the answers are valuable, I should think
and that's what historical lock is meant for anyways
@EmilioPisanty I don't agree with that
though I guess I shouldn't argue with the votes
Well, I undeleted it for now anyway
@DavidZ hear me out on physics-careers and I think you'll see the point
OK...
there's currently 39 questions with that tag, all closed
many of them upvoted and with multiple upvoted answers
originally on topic
but no longer so
which is precisely what historical lock was made for
so
put a historical lock on all of them
and then, if it is at all possible, blacklist the tag so it can't be added to new ones, but without removing it from the existing locked ones
that way we retain the existing archive of the site, with clear markers that similar questions will no longer be received (and a clear signpost to Academia where they probably will be), and so that the tag cannot come back.
4:56 PM
So @DavidZ , @ACuriousMind , ..., concretely, as a start, should we contact SE team to b&b and ?
@Qmechanic Sure
8

The Stack Exchange team has the ability to blacklist a tag even when the tag still exists. With the combination of Shog's new tag-specific popup messages, some tags which are blacklisted now have messages that accompany why they are blacklisted. The tag is still kept around for those questions wh...

this seems to be possible
so just lock all physics-careers before you blacklist