The h Bar - 2021-03-23

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3:24 AM

@ACuriousMind mathematicians have the prejudice of requiring you to know whether doing X makes sense before doing so. physicists just do it and see if stuff still makes sense after :P

2 hours later…

Bohemian relativist

5:18 AM

is the formula $(T^a_G)_{bc}=if^{bac}$, where $T^a_G$ is the adjoint representation matrix of the group G and $f^{bac}$ is the structure constant for the group G, provable or a definition?

5:31 AM

How to seach for a group for a given telegram link

try the search box

5:42 AM

@Semiclassical sometimes if it doesn't; we may need to reexamine our senses

5:54 AM

user image

I am getting stuck up with this...

It is a telegram group which I intend to join

@user85795

don't know, sorry

6:36 AM

@RajorshiKoyal Try to join by mobile phone.

Luckily, unlike in our previous study, we have no reason to believe Evangeline the Adulterator gained access to our stored doses.

6:53 AM

ok

2 hours later…

9:09 AM

Who has the toughest exams? China vs. India

@Slereah I think George was present for most of my lab courses :P

9:29 AM

reminds me of that article on p-hacking

putanumonit.com/2016/12/18/multiplicitous

once in a while I read about like psychology studies and it makes me glad I do physics

Sometimes they will just believe in garbage for a few decades : en.wikipedia.org/wiki/Priming_(psychology)

There's an xkcd for that, too

putanumonit.com/2018/09/07/the-scent-of-bad-psychology

also good

"But if a study was p-hacked, if the researchers kept juggling different hypotheses, including and excluding outliers, and tweaking the measurements, then it is almost guaranteed to land in the 0.045-0.05 range because that’s where the hacking will stop and the champagne will pop."

Mithrandir24601

10:13 AM

No-one's talking about the new evidence of physics beyond the standard model today?

The problem is that experiment repeatedly fails to uncover any evidence for BSM physics.

That damps down even the more enthusiastic speculators.

They've all moved to cosmology where the experimental evidence is less constraining :-)

Mithrandir24601

@JohnRennie No, this is actual experimental evidence

@Mithrandir24601 citation?

Mithrandir24601

@JohnRennie inspirehep.net/literature/1852846

3.1σ signals have come and gone before.

Mithrandir24601

10:17 AM

@JohnRennie Hence 'evidence', not 'proof' :P

"3.1 standard deviations" - meh

I'm pretty certain I've already heard about the lepton universality results. They've been in various blogs.

I'd have to check it's the same authors.

I feel like we get a 3 sigma signal that then disappears about once a year

Mithrandir24601

To be clear, yes, this is a result of about 3 sigma, which is 'evidence', not 'proof', but other results have also been suggesting this for a couple of years now

First reported a year ago

Mithrandir24601

10:20 AM

> with a statistical significance of about 1 standard deviation

@Mithrandir24601 I'm not saying it's bunk but I see little reason to get excited about it prematurely - if this is real, we can just wait until enough evidence has accumulated to be sure this isn't a fluke.

Yes, the figures have firmed up since then, but only to 3.1σ, which is interesting but not exciting.

Mithrandir24601

@ACuriousMind Gahh, this is a physics chatroom, physics is exciting!

Yes, I know this isn't proof, but that doesn't make it 'not interesting to talk about in a physics chatroom'

well, you did get us talking about it! :P

Mithrandir24601

:D

10:25 AM

I guess the problem of my lack of excitement is that I don't know a good implication of this breaking of universality. Is this just "hm, there's probably a very very weak additional interaction", or could there be more interesting changes to the Standard Model implied by this?

More importantly, my C++ is giving me an error that I don't understand ...

Or rather, I understand what it's telling me but what it's telling me makes no sense.

Mithrandir24601

@ACuriousMind If I'm not mistaken, it's pointing in the direction of Z' Boson. Again

Apr 13 '18 at 22:20, by Mithrandir24601

@G.Bergeron It is? Last I heard (just a couple of months ago) there's a distinct possibility of a discovery of a Z' boson. Of course, they only had it at the 3.[something] sigma level, so not a discovery, but a strong indication, alongside a few other things also pointing in the 'same direction'

I mean, sure, the additional interaction likely needs a gauge boson

Mithrandir24601

I mean, aside from that, I'm not sure

I'm not a particle physicist, although coincidentally enough, I have a subsection in my thesis about simulating B mesons, which I'm writing today XD

(It's about simulating B mesons because that's what the local particle physics prof told me was interesting in the particle physics world as of a couple of years ago)

11:10 AM

@Mithrandir24601 physics is exciting, but after a few years it's hard to get excited about this sort of thing again

seeing people write ten/hundreds of papers about what turn out to be statistical fluctuations...

"There are in this world optimists who feel that any symbol that starts
off with an integral sign must necessarily denote something that will
have every property that they would like an integral to possess. This
of course is quite annoying to us rigorous mathematicians; what is
even more annoying is that by doing so they often come up with the
right answer."
https://projecteuclid.org/euclid.bams/1183525452

2

11:33 AM

@Mithrandir24601 that story has just made the BBC Radio 6 news :-)

Mithrandir24601

@JohnRennie Yeah, I know, we got an email about it from said local partical physics prof :P

bbc.co.uk/news/science-environment-56491033

Oh, minor alteration - I believe the results have been accepted for publication in Nature Physics

11:50 AM

The same measurement was made with a 2.6 σ significance in 2014

> Additional Higgs bosons, or a new, heavy version of the Z boson, could alter the relative rate of electron and muon production and be detected in this way.

12:11 PM

@PM2Ring sorry for the reply. I was on vacation until today. I don't think I got the point across of what I was saying. Perhaps it'd be easier if I just typed up a paper and published it or something. Reichenbach's epsilon essentially just says that no non-local experiment can measure the unidirectional speed of light. I agree. So I figured I'd design a local one

3 hours later…

3:11 PM

This question seems very interesting but seems to have been way to hard for anyone to answer so far. Perhaps it should have been asked at Physics.SE instead, does anyone here know anything about this topic?

11

Q: Why does the Wolff algorithm slow down in a 4-body Ising model?

In the paper that introduced "Self-learning MC" (an ML-inspired MC technique, as I understand) the authors consider a many-body Ising model as an example to show the efficiency of their algorithm. The model looks like this: \begin{equation} H= -J \sum_{\langle i,j\rangle} S_i S_j - K \sum_{ijkl\i...

ising-model monte-carlo solid-state-physics k-local-hamiltonians

3:59 PM

@ACuriousMind I notice we get a lot of MathOverflow questions in the Ticker feed here. Would it be reasonable to also add tags such as this one: mattermodeling.stackexchange.com/questions/tagged/… ?

@NikeDattani The watched tags in the feed from other sites are currently for sites whose main topics aren't usually associated with physics (MO, Worldbuilding, Chemistry, etc...). Matter Modeling looks to me much more like e.g. Astronomy or Quantum Computing - most of the questions could reasonably argued to be about physics.

@ACuriousMind I see. Half the questions are about modeling chemistry though and the solid-state-physics tag only has 20 questions. Also, the majority of the ticker feeds come from Physics.SE right?

yeah, I'm not sure how many people really look at the ticker, tbh. Once upon a time it was only questions from physics.SE, and then we added some tags from other sites where we wouldn't necessarily expect to look for physics questions

since then this list has remained unchanged

I think my point is that solid-state-physics seems a rather arbitrary choice to add the feed - 3 of the 4 tags on the question you just posted seem to me as if they would contain physics questions exclusively

but when we get to the point where were adding dozens of tags from another site, it's probably easier for everyone to just go to that site and look at the questions directly

4:16 PM

It sure is interesting. Not knowing much about it I would guess Wolff's algorithm deals with two-point correlations better than with four-point ones. "it's not that different" is a bit of a stretch.
Do we know how well the algorithm performs in the plaquette-only ($J=0$) model?

Hello. Is there a way to ask if entanglement is behind some astrophysical phenomena without getting the question closed? This is not a joke. I repeat. Not a drill.

Presumably if your question is about mainstream physics and can clearly be answered then sure @Exocytosis

Mainstream physics yes, not inventing anything. I am just affraid QM not being gravity oriented, this might end up in a disaster (question closed).

Like I suppose I cannot ask if entanglement is connected to gravitational phenomena, or can I?

@ACuriousMind I'd say solid-state-physics contains physics questions exclusively, whereas Ising Model and k-local-hamiltonians have a lot of overlap with chemistry, quantum computing, computer science, operations research, etc.

Kitaev's "k-local Hamiltonian problem" was devised for studying QMA completeness, which is a branch of computational complexity theory and quantum computing.

I mentioned "operations research" because what we call Ising model is what OR people call "QUBO": quadratic binary optimization (spin up = 1, spin down = 0).

I wrote a question about this connection between Ising model and QUBO:

24

Q: Where/when did the fields of Operations Research and Materials Modeling begin to cross-pollinate?

Operations Research is a field of mathematics in which optimal or near-optimal solutions are sought for complicated problems. In the modeling of materials, we often optimize Ising models, in which the discrete variables on $\{-1,1\}$ or $\{0,1\}$ represent spin-up particles ($\,\uparrow\,$) and s...

condensed-matter model-hamiltonians optimization ising-model history

But I asked to have it closed because it seemed to be too hard for anyone to answer. It could be re-opened if someone here might be able to write some answer though!

I put a 300 point "long-term bounty" on it via the site's Meta. So if someone answers I'll put the bounty on. No point putting the bounty on before that though.

4:35 PM

@Exocytosis You'd have to explain why you think entanglement has anything to do with the phenomenon in question, and whether or not the question is closed or not will depend on that explanation. Just asking "Is entanglement connected to X?", or asking it with a poor motivation, will likely earn you downvotes and/or close votes as unclear what you're asking.

@Exocytosis As long as you cite reasonable papers of the "it from qubit" side of things I don't see why not?

@NikeDattani why would you close a question for being too hard to answer? do you mean it's too broad in the sense that it would require a textbook rather than an answer?

@fqq I'm not sure about how it performs for the plaquette-only model, I'm curious to see what OP says about that! And that's a good suggestion about 2-point correlations being dealt with better than 4-point correlations, in fact you might have hit the nail perfectly on the head there?

@NikeDattani @ACuriousMind You know, at three questions a day, I wouldn't object to having the ticker show all of the Matter Modeling questions for a little while. There's a lot of overlap between MM and Physics, and visibility here might help MM succeed.

2

The OP wrote something about the algorithm being based on machine learning, and if the ML model was only "trained" using 2-point correlations, it might not work on 4-point correlations. You might have a good idea there.

4:38 PM

@rob Ah, I didn't look at the volume here. 3q/day sound good to me.

Thanks @rob!

ACuriousMind has made a change to the feeds posted into this room

@NikeDattani You're welcome!

That should work, but I'm not 100% certain I did the right thing because it didn't turn the feed url into a description

@ACuriousMind You raise a good question. One thing I can say is that the site only entered public Beta in May 2020 and that question was closed 2 months later in July 2020. We had a tiny number of users compared to now, so the chances of the question getting answered was very low, and it was maybe just occupying space in the "unanswered queue" which was distracting users from the more answer-able questions. Does that make sense at all? I know it's probably not the most satisfactory answer!

4:43 PM

The ML algorithm performs well, it's Wolff's algorithm (flipping clusters instead of spins) that gets slow. Still, clusters are built on links and not on plaquettes, maybe that's the point.
Actually, having a look at the paper, the ML algorithm seems to only learn two-point correlations (with different ranges) and still work well

@NikeDattani Eh, over time most sites collect questions in the unanswered queue that are very specific, very hard to answer or some combination of both. Closure is for questions you don't want on the site, but since a mod closed it I guess your site has a different attitude there.

@ACuriousMind It was also closed only 2 months after the site entered Public Beta, so the site's "attitude" was still not fully crystallized. There wasn't much discussion on Meta, for example.

I'm okay with my question being closed in that case though. There's a comment indicating that I'll put a 300 point bounty on it for anyone that answers, so if someone does want to answer, it can be re-opened. Maybe it could be re-opened earlier (for example now!) but I'd rather give other people's unanswered questions attention than my own.

@NikeDattani But that's an additional hurdle a potential answerer has to jump through! The idea is that the threshold to participation on SE is low - if you have a question or know the answer to a question, you can just type it in, you often don't even need to explicitly create an account beforehand. In your case, a passerby has to actively contact a mod to reopen the question, which someone who isn't a long-term user of the site is unlikely to do

@fqq You seem to have quite a grasp of what's going on in the Wolff's algorithm paper! It's been one of the longest standing unanswered questions on MMSE, so you'd probably get the necromancer badge if you do manage to answer it.

@ACuriousMind You raise a good point. In fact someone who finds the question while surfing the web, may not even have enough rep to flag a post or to write a comment!

I'll definitely think about it, but at the moment I don't have a clear enough idea to answer it

4:55 PM

@fqq We may have to wait for the OP to answer your comment first!

@ACuriousMind It seems the ticker feed for MMSE worked! There was 5 questions this time, but that's only because this was the first feed. From now on I think it will only be about 3 questions/day as Rob had mentioned.

yeah, the first instance of a feed always posts everything still "visible" in the feed, which is tolerable for tickers but really annoying for feeds posted as messages

you'll create a feed and then some random time later the bot just dumps 5-10 oneboxing links into the room

Yea that can be very annoying.

For a room like this which is so active.

5:19 PM

@fqq hah, that's a great line

6:08 PM

0

Q: Should I re-ask a question that was recently closed by editing it and removing meta-comments?

I recently asked this question: https://physics.stackexchange.com/questions/622976/is-there-such-a-concept-as-opposite-colors This question was closed and I was directed to this meta thread by a comment: https://physics.meta.stackexchange.com/questions/13449/reopening-a-question-after-fixing-issu...

2 hours later…

7:45 PM

Say I post a question and get some answers which don't satisfy me but some other question's answers do (which i didn't notice before)..Is there anything I can do to accept that other question's answer in some way? The other question's answer answers my question...

I don't want to delete my question :) I can mark it as a duplicate..

@ACuriousMind you are the answerer

@ManasDogra If your question is a duplicate, you should mark it as such. You can't accept answers to a different question or anything like that. If your question is not a duplicate and the other answer just more or less "accidentally" also answers your question, you could for instance post an answer to your own question (perhaps as community wiki) citing the relevant parts of the other answer

@ACuriousMind Okay i will write an answer as community wiki after sometime and acknowledge you. Thank you.

@ACuriousMind Is it okay if I discuss some points of that answer(related to my question) with you tomorrow?

sure

8:11 PM

@ACuriousMind you can be 100% certain now.

it takes awhile

1 hour later…

9:30 PM

0

Q: Question appearing blurred (less visible). Any explanation?

Please, find a screenshot of my PhysSE homepage. Is there any explanation why that question would appear semi-visible?

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