The h Bar

@WilliamBulmer ah, yeah I noticed earlier. Well, welcome!

As you've noticed, this is kind of an informal "gathering place".

Hm, note to self: these 5 minutes can also be a chance for the regulars who are around to introduce themselves.

Anyway, let's move on to recent physics developments. What's happened recently in the world of physics that we should be aware of?

The magical disappearing 750GeV resonance!

Of course ;-)

Has anyone been through the ICHEP talks?

4:07 PM

That probably overshadowed everything else at ICHEP

21 hours ago, by vzn

The Search for a New Type of Neutrino Turns Up Empty / wired

did they actually announce it? I missed that...

Ah yes, I saw that earlier - good catch. No sterile neutrinos eh?

@JohnRennie "easy come easy go..."

I mean the disappearance? So far I only heard rumours...

4:08 PM

Yeah, it was officially announced

@Martin of the 750GeV resonance? If so yes it's official.

Shame really

Aug 5 at 20:05, by GPhys

ATLAS result: https://twitter.com/Resonaances/status/761575139234443264

among other places

wondering. they will probably not publish a paper on the null result will they? (750GeV)

Thanks - I was away over the weekend, so that's probably it. That means that a lot of preprints are obsolete...

@Martin yes, about 500 of them :-)

4:10 PM

@JohnRennie: yeah, I had a similar number in mind.

@vzn I'm sure they will publish a paper giving their (null) results for searches in that mass range

@JohnRennie the Twitter feed is a decent source. There's a lot of information there.

Does anybody know whether anything else has turned up? Or are we in a particle physics desert?

@JohnRennie saw an interesting one (announcement pg that is) on promoting physics in the media, wish it was recorded and/ or transcript

@Martin I haven't been through the ICHEP talks in any details, but it does look a bit bleak at the moment.

Hmm. I recall seeing a paper many years ago that argued, I thought pretty well, that a fourth fermion generation was very unlikely. That presumably would have applied as much to neutrinos as to the electron generations.

Looking is always good though!

4:13 PM

The sterile neutrino isn't a member of a fourth lepton generation though ...

@TerryBollinger Well, apart from the fourth generation, I think a lot of people are still quietly hoping for some supersymmetry to turn up

@Martin there is nothing else. Everyone's hoping for some sort of discovery soon, but nothing seems particularly likely.

Ah! I only just now read that article. I didn't realize it was a sterile neutrino under discussion.

A surprise sure would be nice...

So basically, it doesn't look too good for many supersymmetric models...

I hear there's a good chance of a discovery in dark matter research soon

4:14 PM

Ah yes, Xenon got a null result too.

@JohnRennie ichep2016.org/media_lunch (some tiein to our speaker sessions)

@DavidZ: That's interesting. Any positive result?

@DavidZ really? what?

No, not yet. You would have heard about it.

Dark matter and dark energy... I mean, it's not like there aren't some great mysteries out there!

4:15 PM

What dark matter expt is looking good at the moment?

From what I've heard, DM detector technology is advanced enough that it should see some sign of something in the next decade or so, if any of the reasonable theories are correct

Rumours or hope?

Okay, so "hope" it is...

With the null result from Xenon I thought things were looking rather bleak

Yeah, pretty much - there is no specific prediction as with accelerator physics

Though I believe they going ahead with son of Xenon

Q: Should history of physics questions be on topic?

4:16 PM

@JohnRennie someone needs to come up with more creative names

Anyway, time to move on to the history policy discussion.

23

When we last visited the issue of history questions, the dedicated History of Science and Mathematics Stack Exchange was in its early stages. At that time, we decided against closing questions for being historical, but with the implication that it may make sense to revisit that decision someday. ...

I'm not really sure how much there is to discuss about this

but I did want to run it by chat before officially making that an FAQ post

Any thoughts?

29 votes to 0 seems fairly conclusive

(sorry a bit late to the discussion) Are they any popular non SUSY particle candidates that the searches hope to find soon?

@Secret we'll come back to that after the session

ok

@DavidZ Well, I already voiced my concerns about the subjective aspect of the policy in the top voted answer a while back

4:19 PM

@ACuriousMind yeah, I remember from the last time we discussed this

I think the votes suggest that most people don't find that a significant concern.

I doubt that one can make a policy that's unambiguous and objective in all cases, so I think the top answer is nice.

In particular that one cannot really determine whether those "why was X discovered before Y" questions are "about physics" because the answer could always just be "well, just historical accident"

Though a minor contamination of the site with off topic history questions is less painful than the torrent of alleged physics questions that are inappropriate we already live with.

@ACuriousMind If I understand correctly, the policy proposed by Emilio would render such questions on topic. (Which I agree with)

Most questions would be on topic under that policy, which is good, I think.

4:24 PM

It would be good to have a short summary to put at the top of the answer, for people who don't care to read through it. Should we just use the one from the end, or can we do better?

Emilio's summary is pretty good. I would just put it at the beginning as an abstract.

If I understood correctly, PSE aims on helping visitors on the conceptual aspects of physics, and history questions that motivate the modern physics model developments will greatly aid in the process. It also help make explaining some of the concepts in the abstract models less abstract by having experiments that suggest why it is this concept in this model we are using

@Secret well... I suppose so, but we do not in general make questions on topic just because they help people understand the conceptual aspects of physics.

also am I missing the point in asking whether it is necessary to draw a line on some time period where "modern understanding of physics" is defined?

I felt if this is used as a migration or close reason, one might need to define that clearly to avoid ambigurity

or maybe not, I am not sure...

It's necessary to define the boundary of our scope. Whether we use time periods to do that or not is (or, was) up for discussion.

There were proposals to do so, but we decided against them.

4:31 PM

make sense

@Secret: modern understanding of physics means "today". Everything that is really important as to how we understand the theory is therefore on topic. I'd be inclusionary if it's ambiguous.

Q: Received rep twice for the same edit

Anyway, the allocated 15 minutes are up, so let's call this discussion finalized. I'll convert that post to an FAQ soon, and move the summary to the top.

Physics Meta

1

I suggested one edit to a post, but when it was approved I received rep for it twice. I know there's some sort of autmated rep cleanup done regularly (nightly?), but I'm not sure if this is a known issue covered by that or not.

bug editing suggested-edits

Q: Flagging low quality answers: an experiment

Now let's move on to the VLQ flag experiment

14

Abstract: We are experimenting with expanding the scope of the very low quality (VLQ) flag. For two weeks, August 8-21, moderators will not decline any VLQ flags. We will allow these flags will sit in the queue as long as needed for the community to deal with them. We ask you, the community, t...

discussion featured flagging review non-mainstream-physics

@PhysicsMeta perfect timing, lol :-P

Anyway, our purpose here is (1) to make sure everyone knows this experiment is happening, so you can use VLQ flags a little differently from the way that is normally recommended

and (2) to get preliminary feedback on whether this alternate usage pattern seems to be helping

We've only been doing this a couple days so there may not be much feedback to be had yet

but does anyone have thoughts?

user54412

I'm still very worried about this.

4:35 PM

I haven't been doing much reviewing recently so I'm not in a great position to comment. However I haven't noticed the VLQ queue getting bigger.

@ChrisWhite you mean about allowing answers to be deleted for wrongness?

user54412

Yes. Emilio's entire post is based on the premise that this needs to happen, and we're going to figure out the best way to do so.

@JohnRennie that's what I've noticed as well. At the moment, there are zero VLQ flags in the mod queue, for what that's worth.

user54412

It's been craftily phrased to lock down any objection, by calling the whole thing an experiment.

find this hard to follow. is VLQ going on more with Q or As?

user54412

4:37 PM

Moreover, where does this end?

@vzn mostly answers I think

user54412

I mean, in the new regime being proposed, every last one of JD's answers, old and new, will be quickly deleted by 5 high rep users.

user54412

This might be a good thing some will argue, but it doesn't stop there.

@ChrisWhite I'm not sure that's true.

@ChrisWhite well, just because it's an experiment doesn't mean it's immune to objections

4:38 PM

does "mod decline VLQ flag" mean it doesnt go in a community review queue?

After all those answers can already be deleted if the high rep users choose to do so, and they haven't been.

@vzn AFAIK when a mod declines a VLQ flag, that removes it from the review queue.

@ChrisWhite was suspecting myself this was a disguised/ veiled anti JD effort... have seen other stuff on this in chat eg data explorer queries with him at top of list :\

user54412

@DavidZ The experiment is asking how to best accomplish a regime change -- that's the kind of experiment that should not be approved without first deciding that such a change was going to happen.

The core of Emilio's post is that we should be able to use a VLQ flag to draw attention to poor quality answers.

4:40 PM

@JohnRennie: not really. I mean, I've reviewed a fair share of VLQ posts and I've often wanted to hit the "delete" button but didn't because that's not what it was for. Now, in principle I can.

user54412

@JohnRennie Well, because I personally choose not to abuse my moderation powers like that.

@JohnRennie that is a fair point, but one could also argue that the high-rep users haven't yet had a way to coordinate voting on such answers. (Which is not actually true, people have chat, though it hasn't been used in that way)

The point is to get those answers appearing in the VLQ review page.

user54412

But we're talking about making this a highly censored site.

@ChrisWhite that does not seem to be true to me at all

4:40 PM

What the reviewers then choose to do with them is another matter.

The experiment is not about deleting answers, it is about using VLQ flags to draw attention to them.

I think the "drawing attention" is fine (meaning: still don't delete but downvote). We don't literally censor then, but only make sure that more people see a bad answer and hopefully downvote.

user54412

@JohnRennie That's just fundamentally untrue:

user54412

> when reviewing low-quality posts, choose to delete such "harmfully incorrect" posts

[Please filter away the emotions when reading this] I personally get annoyed when I go on PSE and see answers that use the wrong physics. It is quite misleading to visitors for some topic that it may be not easy to figure whether their answer is based on sensible and well established and might be mislead by wrong concepts

For example, there are couple of graduates and researchers using PSE to guide them the correct way to think about a physical problem, and the wrong answers (especially those which are not obvious in the wrongness for those unexperienced in the field) to be misleaded

2

@Martin Precisely

4:42 PM

@JohnRennie But...what are you going to click in the VLQ queue? The experiment says to delete "harmfully wrong" answers.

That's not "drawing attention", it's deleting.

it sounds like the main issue is mod(s) are previously doing a lot of "decline VLQ" but the post doesnt seem to say how much...?

@JohnRennie: Yes, but as Chris White points out, that's not what the experiment says it's about.

Maybe that should/could be changed.

@Secret deleted posts are still viewable by anyone with 10k rep, and moderators

(for the record)

user54412

Let's not mince words. Emilio was sore after a single rejected flag, and he designed this whole "experiment" to bypass the safeguards against non-elected members having too much discretionary power when it comes to permanently removing content.

@vzn we could collect some statistics on that, at some point

user54412

4:44 PM

What hypothesis are we even testing?

3

can understand it would be annoying to mods if they are repeatedly declining VLQ on the same posts...?

ok, in that case, I think VLQ is a good suggestion, especially to address the lack of an analogue to "closed questions" for physically incorrect answers

@ChrisWhite "non elected vs elected"? sounds like the two factions just need to work it out

user54412

Another question: Can anyone indicate a post they would downvote but not vote to delete under this proposed paradigm?

The abstract has been added to Emilio's question since I last read it, and having just read it I have to concede I'm a bit uneasy with the emphasis on deletion.

4:46 PM

@ChrisWhite In my understanding, the hypothesis is that the site will be better off if we allow a certain class of answers, the "harmfully wrong" answers, to be deleted by community action

The control is our standard policy of never deleting an answer because of its incorrectness, no matter how wrong it is

@JohnRennie FWIW the abstract was my addition.

@ChrisWhite "indicate a post they would downvote"? why not just downvote it? this stuff is sure hard to follow

The VLQ is important to me as a way of reviewing, and I would like to see it used better.

I don't have time to go through every answer, and if other members spot an answer they think should be reviewed then the VLQ queue is a good way to do it.

From my experience, soemtimes the downvote is not enough to draw attention to a bad answer that is not obvously wrong (you need around -5 votes to get someone to be aware it is a bad answer)

VLQ for reviewng and drawinf attention = good, deleting, = too dangerous unless necessary

@DavidZ How was it disallowed before? If five people recommend deletion in the VLQ queue, the post gets deleted. Or did the mods monitor all VLQ deletions for whether they were appropriate?

@ChrisWhite here's one

4:48 PM

So I think flagging for VLQ is an effective way to organise reviews.

user54412

@JohnRennie But would we be having this conversation if the queue didn't exist at all? Would we be pushing to turn 10k users' downvotes to delete votes out of the blue?

@DavidZ there was some related discussion in chat. thought someone was suggesting SE policy is that heavily downvoted answers serve as a "signal" of what to avoid, and deleting them does not provide that signal any more...

@ChrisWhite I could, but then agian, my downvote finger is rather trigger-happy :P

@ACuriousMind it was against policy. If enough people vote to delete from the queue, the answer gets deleted anyway, but that's going against the policy. There was no outside enforcement of that policy; it was up to the community to use deletion responsibly.

@ChrisWhite but I have no way of looking at what other 10K users have downvoted.

Well, no easy way. The VLQ queue is an easy way for me to look at what other users think are poor quality answers.

user54412

4:51 PM

@DavidZ But if the whole point is to make this site less offputting to professionals, wouldn't that have to go to? It's certainly not doing any good, even though it isn't 100% wrong.

@ChrisWhite well, if you want to make that argument, you'd be supporting Emilio's point that answers which are wrong, to a certain level, should be deleted.

user54412

Anyway, my point is that maybe we really do want to move in the direction of quality at the cost of censorship. But we should only do so after serious consideration of the endpoint we desire, rather than just focusing on momentary impulses like "I really don't like this content"

@DavidZ wonder if youre almost being too impartial here. think you can express your own opinion on it, cant even figure out what it is yet...

@DavidZ Yeah, and I think that's the underlying issue: Most people flag and review using their own notion of "very low quality", not the actual policy (which, as I said in my meta post, would make the VLQ flag obsolete because you can flag everything that's VLQ under the policy as something else).

OK, here's another example. This one may not be incorrect, really, but I don't believe it's useful.

4:54 PM

@ACuriousMind ding ding ding ding

So now we're trying to solve two different issues - inconsistent VLQ behaviour and a lot of crap answers - with this one "experiment".

@ACuriousMind yeah, exactly. So one consequence of this experiment is bringing the policy on VLQ flag handling more in line with how people are actually using it.

I agree almost entirely with everything @ACuriousMind is saying right now.

@ACuriousMind especially the "ambiguriously crap" ones, like what david Z linked that might look useful at first glance...

and some answers that use models that are a little bit off the mainstream but cannot be easily tell from unexperienced askers

I agree with ACuriousMind, too. I've been wanting to bring it up on meta a couple of times but then forgot it (mostly, when I see an answer that is just a completely idiotic personal theory that I really don't want to delete but can't because it does technically qualify as an answer).

4:56 PM

The problem is that consistent behaviour of a queue can't use personal notions of "this answer is really crap", so we're sliding down the slippery slope @ChrisWhite is warning about because the objective criteria are things like "wrong" and "non-mainstream" which cover far more than what any given user sees as "crap".

This is very useful feedback.

though I'm not yet sure what to make of it all

Can we separate the two issues of (1) using VLQ flags and (2) deleting answers? Is that a useful step forward?

@Martin Yes, that kind of answer, as some answerers have very sophisticated pet theories that are nto easy to tell apart from the one consistent with experiments

@JohnRennie But what do you want to do with VLQ flagged posts, then?

@JohnRennie sounds good

4:57 PM

@ACuriousMind it sounds like the existing VLQ policy is not being followed & then wonder if any change in it would be followed either... also is it a communication problem or are people intentionally not following the policy etc

@ACuriousMind: I completely agree. What I could see though is an "alert queue" to consider down voting in the sense of John Rennie's ideas.

So a queue more like the first post and last answer queues?

@ACuriousMind I'd like to see what other users have flagged as VLQ so I can decide what to do. That might be just to downvote or it might be to add a comment, or maybe a new answer of my own. Or, yes, it might be to vote to delete.

@JohnRennie well... in the long term, no, not without major changes to the system. The way the SE system is designed, flags put things in front of the moderators. They may go through a review queue first, but review queues are only meant to reduce the burden on the mods. And the only thing mods can do with a low-quality answer is delete it. (Or do nothing)

I've tried to consistently vote "Looks OK" when the question at least tries to give an answer to the question at hand, is formatted such that it is at least legible and has more than a couple of words.

4:59 PM

@Martin some sites have a separate room to deal with problematic posts using group effort... although this room already does serve that nearly routinely...

user54412

@JohnRennie I think that is useful. For (1) the main options seem to be (a) mis-use the tool, (b) re-tool the tool, or (c) ignore the tool. For (2) the options seem to be (a) delete or (b) don't delete. These are rather orthogonal issues.

is david z saying we currently have no data (i.e. no VLQ flags) on the queue yet?

@vzn: Maybe I should look here more routinely.

@Martin that's how it's supposed to work, according to the policy (except during this experiment)

I guess my aim would be to have 1(b).

5:00 PM

@JohnRennie Hmm, well, that satisfies your curiosity of what others think is VLQ, but how does it improve the site?

@Secret we do have some data. There have been VLQ flags that have appeared in the queue and then been handled, presumably by community action.

I mean, there is already a publicly visible signal that you think a post isn't useful, it's a downvote.

4

@Martin am saying only that people "routinely" talk about questionable stuff in here but theres lots of other noise that the editorial attn is buried/ sandwiched in...

@ACuriousMind It helps me reduce the impact of poor answers by downvoting, commenting, adding my own answer or maybe deleting. Without the queue I would probably never see the answer.

@vzn I think we could stand to use the chat for that purpose more often.

5:01 PM

@DavidZ: Yes, I know, I read and reread the policy a few times, because it sometimes leaves a sore feeling to click on "looks ok" if the content is garbage...

@ACuriousMind I have seen many -2 vote answers that oscillates between 0 and -3 over time. I am not sure if that's an issue

@Martin Yeah, there have been complaints on Meta Stack Exchange about the naming of that button.

@Secret that's a different issue, I think

@DavidZ there are different issues, ie are there multiple ppl that really intensely (ie sustainably!) wanna play "janitor"? if so maybe its sustainable in another room & they dont have to watch all the other misc chat in here

@JohnRennie Are you aware that the 10k tools let you see the lowest-voted answers in a certain time period?

user54412

@Martin That's why I often clicked "skip," as unhelpful as that is for clearing the queue.

5:03 PM

@Secret How does that relate to what I said?

(cont. response to JR) I.e. you can monitor what people think is low quality without flags, just look at what's most downvoted.

And oh, just like that our chat session is over!

@ChrisWhite: I often do that, too - but as you say, it doesn't really help.

Everyone remember DanielSank's AMA is this Friday, outside the normal chat schedule

To those who want to/have to leave, see you in two weeks! Meanwhile, we can keep discussing this experiment here.

@ACuriousMind That there are posts that are not useful, but does not get a downvote large enough t warn people it is not useful. I have seen a couple when browsing PSE casually

@ACuriousMind I don't see how that helps. Suppose you downvote an answer so it's now at -1. I'm not going to see that answer in any report of lowest score answers. However if you VLQ it I will see it in the review queue.

5:04 PM

@Secret Yes, that's because people don't downvote enough. This is a third issue I complained about about a year ago

@DavidZ Daniel Sank, Phd/ Google quantum computing lab, stackexchange physics guest speaker Aug 12 2016 (announcement/ history, just wrote up)

@JohnRennie Go look at the "lowest voted answers" of today

I see a bunch of zero score answers there.

I just read part of the chat log and I would like to make an observation:
The biggest problem with the meta post about the VLQ flag experiment is that nobody could tell what the hell it was trying to say.

So you're pretty much guaranteed to see every answer with negative score in there.

user54412

@ACuriousMind Clearly you're not doing your job then ;)

5:06 PM

@DanielSank to be fair David added an abstract that made it clearer.

I think he did that since we discussed the issue.

@DanielSank TL;DR!

@vzn huh, nice. I didn't realize you were writing about this stuff externally.

@JohnRennie That doesn't help at all.

That "abstract" is a retroactive summary stating the result of what should have been a discussion.

@ACuriousMind Hmm, OK, I'll take a look. Do you have a link?

@DavidZ =D thx (plz star it everyone!) write occasionally about SE/ physics (have physics category on blog). the date chg pushed up my schedule (might have written more, but maybe its better shorter!)

5:08 PM

@ACuriousMind You know what the problem there is, I almost never down-vote because of the -1 rep.

@ChrisWhite I'm four votes away from having 10k total downvotes and I have more downvotes than the Community user. I think I'm doing pretty well at being the Grinch ;P

I think I would need to get more up-votes for my good content before I'd be comfortable down-voting as much as I really ought to be.

@ACuriousMind I wish we could all be as good a Grinch as you.

@DanielSank so do I

@ACuriousMind ~~2nd~~ 3rd ACM as premiere grinch :P

@vzn you know it pings me every time you edit your message

5:09 PM

I originally responded to Emilio's meta post by saying that really we all need to up-vote more so people feel ok down-voting.

@DavidZ really? oops! thats @#%& lame/ bug ouch

But then I figured that was off topic and deleted it.

@DavidZ since the chat session is over, can I ask you that non SUSY question?

@Secret sure

@JohnRennie ?!? who are you quoting?

5:11 PM

ACK, wait a second, someone please get rid of the time on the AMA pinned post.

We're all in different time zones, posting a time is confusing.

oh lol, that's the chat message time stamp.

I'm a moron.

@JohnRennie if it's talking about such people, it's not offensive, not to the standard we use for flagging here.

Carry on.

@DanielSank lol beg to differ :P

If it's implying that someone in the conversation is such a person, then yes, it's offensive.

@david Z any non SUSY candidates that the cosmology and particle phsyics community that are particularly excited to spot signs of given that we might be in a particle desert?

Comic Database: Steve Hughes... Offended?

5:12 PM

@DavidZ It's only offensive if you care.

►

@DanielSank You've got 11.5k rep, what do you need more for?

@JohnRennie Here, look under "stats". You can also access that page by clicking on "review" and then clicking on "tools" in the upper left corner.

@Secret the leading candidate is probably WIMPs. Dark matter particles. But there are many, many conflicting predictions about what the properties of real WIMPs might be.

@Secret wow used that term "desert" myself lately, thought it was poetic but ofc guess others have used it, it would be amusing to trace etymology

@vzn yeah, it's very common

@ACuriousMind I want those Google site analytics.

user54412

5:14 PM

@ACuriousMind The power of Google is withheld until 25k

user54412

^^

@DanielSank nah, there's a difference between being offensive and actually offending (a specific) someone.

Wait, I have access to Google site analytics?

@DavidZ Well ok, but I needed to post Steve Hughes.

@ACuriousMind :D

@DanielSank Fair enough ;-)

5:15 PM

I am more excited to see if some bump in the future that suggest something none of us modelled before, i.e. non dark matter non SUSY. But from what I recall from what johnrennie said, it seems BSM particles are unlikely until we get to the GeV (or is it TeV?) scale

@Secret Oh of course, everyone is hoping to see something unanticipated. It just seems unlikely that the LHC is going to make that discovery.

(it's TeV)

(we're already at GeV scale)

@DavidZ aka in economics "diminishing marginal returns"....

But lets say suppose we are in the (highly unlikely) worst case scenario, that after getting to TeV and we still get a particle desert, then what should we do?

@Secret Build a bigger accelerator :-P There are plans for 100 TeV colliders in the works. If those don't find anything... well, I don't know. We have problems.

Hmmm, why would we get a sizable number of referrals from 0.0.0.0???

5:19 PM

@ACuriousMind is this the answer you are talking about regarding 1:1 correspondence hamiltonian and potential: physics.stackexchange.com/questions/13480/…

@Secret: do indirect eperiments. There are atomic physics experiments that can say something about scales at which SUSY will occur soon. I think indirect experiments in condensed matter might at least give interesting pointers in the not too far future.

@Martin Looks like a job for the spectroscopists also

@DavidZ when you have a hammer everything looks like a nail ... also reminds me of the story of the drunk looking for his keys under the lamppost.... :\

@Secret: They can try of course. I was just intrigued to recently see experiments where they used diatomic molecules to test SUSY scales, so I guess it's not the end.

@ACuriousMind hm, I'm not sure. I think it's some quirk of how SE processes the records, since that doesn't show up in the moderator analytics tool (which is a little different). You could ask on Meta Stack Exchange.

5:25 PM

@DanielSank (dude...) permeability of space is a real thing, you know that right? en.wikipedia.org/wiki/Permeability_(electromagnetism)

If things are quiet now, I'm going to head off... let's keep thinking about this VLQ experiment

@DavidZ lets flag the VLQ post VLQ :P (& thx again to DS for pointing the "elephant in the room" and/or naked emperor, was afraid myself)

Herr_Mitesch

5:51 PM

Did anyone look at my question about the Poincare group acting on spacetime yet? It's pretty basic, I'd be glad for every help!

physics.stackexchange.com/questions/273298/… this is it

@ChrisWhite : "Let's not mince words. Emilio was sore after a single rejected flag, and he designed this whole "experiment" to bypass the safeguards against non-elected members having too much discretionary power when it comes to permanently removing content." Well said that man.

@vzn Of course.

@ACuriousMind Still around?

@JohnRennie : because it's true.

6:08 PM

@DanielSank are you aware of "classical" ("non EM") analogies of c = 1/√(ε0μ0), have you heard a discusssion anywhere?

Holy, cow! But I loathe the Hot Network Questions sidebar. May it die, rot, and disappear!

@dmckee Good. Gooooood. Release your anger.

Feel the power of the dark side of the force.

It screws up the quality signally function of post scores.

@vzn First of all, "classical" does not mean "not E&M".

Second, sure, you have such analogies in acoustic waves.

@DanielSank am aware of that (hence "scare quotes")

6:09 PM

There simply isn't a way to fix that.

@dmckee Wat?

@DanielSank think its likely in all kinds of waves even non acoustic

@vzn Yes, the wave equation itself makes impedance meaningful.

You have two conjugate variables in the wave equation.

@DanielSank Posts that appear in the HNQ are seen and judged by an audience that is (a) larger than the usual audience on the site the question lives on and (b) consists of different people with a different notion of quality.

The ratio of their amplitudes is what we electrical folks call "impedance".

@dmckee True dat.

Duder, go drink some lemonade.

6:12 PM

So the meaning of scores on those questions is completely different from the meaning of scores on other posts on the same site.

Lemonade is delicious and will wash away your sorrows.

@DanielSank also think maybe the lorenz eqns show up in other contexts outside of special relativity...? thought they might be in gases (am trying to remember stuff maybe glimpsed in a fluid dynamics class textbook ~25yr ago)

@dmckee True dat.

@dmckee the hot post sidebar is why I almost got 100 votes on this.

@vzn What are lorenz equations?

@DanielSank in special relativity "time/space dilation" something like that

sorry ~~lorenz~~ lorentz found it en.wikipedia.org/wiki/Lorentz_transformation

And so we get high scored on questions like physics.stackexchange.com/questions/270289/…. Which is the kind of question a rank beginner might ask, but consists of nothing but a string of misconception.

It needs answering, but it is not a good question.

6:16 PM

@ACuriousMind Is $H^0_{dR}(\Bbb N)=\prod \Bbb R$ or $\bigoplus\Bbb R$?

It would have to be the first

We're not taking the compact cohomology

@DanielSank At least you wrote a lengthy answer! I got a gold badge for one sentence

@0celo7 The former.

@DanielSank That is at least a subtle question and a detailed answer full of physics.

But then we could have $a:=(1,1,\dotsc)\in\Bbb R^\omega:=\prod\Bbb R$, right?

So what is $a\otimes a\in\Bbb R^\omega\otimes\Bbb R^\omega$

Would it not be an "infinite" matrix with diagonal $(1,1,\dotsc)$?

@0celo7 No, it would be a matrix filled with 1s

@ACuriousMind Good answer though.

6:22 PM

@ACuriousMind I'm stupid, yes.

What about $(1,1,\dotsc)\otimes(1,0,0,\dotsc)$?

@0celo7 One row or one column of 1s, all other entries 0 (depending on how you write matrices)

Generally, $v\otimes v$ has rank $\leq 1$, we had that yesterday already

Since the tensor product admits only finite sums of simple tensors, it can't contain any matrix of infinite rank.

@JohnDuffield the big question is whether anything "new" can be derived/ calculated/ measured etc from the insight....?

@vzn : it's new to some people. See this.

@ACuriousMind ...that's highly nontrivial

@ACuriousMind oh

@ACuriousMind Well now you know something new about Künneth

@ACuriousMind Is the "th" in there pronounced in the German way

@dmckee Yeah but the point is that it has like ten times more votes than other similarly good answers I've written because it wound up on the hot posts list.

@ChrisWhite I want to star this more.

6:31 PM

@0celo7 ...probably?

@ACuriousMind Are you willing to hear about homological algebra

oh wait, I'm not allowed to ask about asking

oh no

@ACuriousMind Suppose we have a double differential complex $K=\bigoplus K^{p,q}$

Let $p$ go horizontally and let $q$ go vertically, like this:

by summing over diagonals, we get another complex with vector spaces $K^n=\bigoplus_{p+q=n}K^{p,q}$

@ACuriousMind Make sense?

Yes

Let $\delta$ be the horizontal chain map on each row and let $d$ be the vertical chain map on each column

Now, let $L$ be another double complex with the same chain maps

Define $D=\delta+(-1)^pd$, which is a chain map on the $K^n$s defined earlier

Let $f:K\to L$ be a double complex homomorphism, i.e. it commutes with chain maps and preserves degrees

Still makes sense?

Yes

The claim to prove is that if $f$ descends to an isomorphism $f^*:H_d(K)\to H_d(L)$, then $f^*:H_D(K)\to H_D(L)$ is also an isomorphism.

where $H_m$ is the cohomology functor of the chain map $m$

I have a proof of this in the case where $H_\delta(K)=H_\delta(L)=0$, i.e. the rows are exact.

Do you want to see it?

6:40 PM

Tell me what your question is first

Is it true when the rows are not exact

In the text, the rows are exact.

But the exercise makes it seem more general

@JohnRennie Isnt a glueball massive because of the Yang-Mills- mass gap ? I think I read a paper where they defined the mass of a glueball via Lattice gauge theory.

@ACuriousMind In the row-exact case the strategy is to take a $D$-cohomology class, represent it with a $D$-cocycle, then reduce it to its $q$-top component, which is actually a $d$-cocycle, so it represents a $d$-cohomology class.

I think that basically shows that $H_D(K)\cong H_d(K)$, which should be true

but from there it's obvious

I'm wondering about the general case

Is that still Ricci-Flow ?

No

@ACuriousMind Doesn't want to hear about Ricci flow

6:48 PM

Whats then ?

Homological algebra

Thats good. You told me that you wanted to start with algebraic topology

Thats it.

@PhysicsGuy : polite cough. Note that glueballs are hypothetical. And that gluons in ordinary hadrons are virtual. And that virtual particles only exist in the mathematics of the model.

@JohnDuffield That cant be easily said. I once heard a debate which took hours, the question was, whether virtual particles are real or not.

I think John is right, virtual particles are not real. Although what does "real" mean...

6:59 PM

John, we all know that you trot out that "only exist in the math" line every chance you get, but the math still gives better prediction than you every have.

@PhysicsGuy : there is an underlying reality in that virtual particles are field quanta. The field is real. But virtual particles aren't short-lived real particles that pop in and out of existence.

@0celo7 Here's my attempt at a counterexample: Take $K$ as the complex that has $K^{0,0}\to K^{0,1}$ and $K^{0,0}\to K^{1,0}$ as isomorphisms and zero everywhere else, and $L$ as the same complex except the map between $K^{0,0}$ and $K^{1,0}$ is the zero map. Take the complex morphism as the one that's the identity on all objects except $K^{1,0}$, where it's the zero map. Although $H_D(K)$ and $H_D(L)$ are isomorphic, I think the induced morphism sends $H_D(K)$ to zero in $H_D(L)$.

@JohnDuffield how do you explain vacuum energy, then ?

John like to say a lot of things about "underlying reality" but he means "the way I believe it to be".