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4:23 AM
There you have it. We're all wrong and only Duffield is right.

4:44 AM
@JohnRennie I don't think this is an approved comment...

You're right, I should step away from the keyboard.

He has a +1...not from me

From safesphere, who is firmly in the Duffield camp.
What burned me this time is we had a new site member, Alessandro, asking an interesting question and up pops Duffield. From Alessandro's comments you can see he didn't initially realise what sort of person he was dealing with.
What sort of impression does that give of our site to new members?

@JohnRennie that's the issue
we're not allowed to call people cranks when, please, we all know there are some on this site

5:06 AM
@JohnRennie you must not say his accursed name!

@Slereah :-)

hM
chapter 9 of Glimglam seems to have formulas for the Gaussian measure
although no examples
Also chapter 6 has some
Ah yes, and he does specify that $C = (-\Delta + m^2)^{-1}$

1 hour later…
6:26 AM
@Slereah this is the glim and jaffar book?
I probably know enough to read it finally
long book

6:42 AM
The very same
But kind of the same issues as other math texts
It's hard to find any actual calculations in it
Also the whole $\langle f, Cf\rangle seems to be itself a functional integral 7:06 AM You do have the relation $$d\gamma \approx e^{-\frac{1}{2} \langle \phi, C^{-1} \phi \rangle} \mathcal{D}\phi$$ Which makes me think that the inner product probably can be expressed as an integral possibly a stochastic one but people don't really seem to say how to compute that part closest I can find is 7:49 AM I probably need to read Glimglam and the Jaffman from the start hard to pick up the notation otherwise 8:46 AM The UK weather has returned to normal for the British summer: 9:08 AM smashing @JohnRennie Ever used path integrals in your field I wonder I know it's used in polymer science path integral over the various bendy shapes of polymers The furthest I got with polymer thermodynamics was the Flory-Huggins model. Polymer solution thermodynamics is like solid state in that it's far too complex to do from first principles so you end up using effective theories. $$Z = \int \mathcal{D}🦷 e^{-S[🦷, \dot{🦷}]}$$ 9:25 AM @JohnRennie Top Welsh names on that map Welsh comes from a completely different language group to the Romance and Germanic languages and it's very different to English. With most European languages an English speaker can recognise a few words here and there, but Welsh is completely incomprehensible. I am aware, yes We have our own celtic people in France too As a result Welsh town names not only look odd to English speakers but the pronunciation is very different too. with their own funny words Hey it's our friend @JohnDuffield Aha, yes, Breton. I had a vague memory that it shared a root with one of the continental languages but I couldn't remember which. 9:32 AM "About 400 other languages: Polish, Berber languages, East Asian languages, Catalan, Franco-Provençal, Basque, West Flemish, etc., as well as those who gave no response" Apparently the language census of France includes people who don't speak any languages I guess they asked a few babies Must have been an awkward interview I hear Welsh being spoken a lot in Chester. We're near enough to the border that lots of people from Wales come into Chester to shop. I like the language, or at least I like the way it sounds. Apparently Breton's the only still living Celtic language outside of old blighty anciently spoken as far as Turkey, tho Although Galatian, the Turkish one, doesn't have a lot of attested words mostly names Irish is still spoken, though I don't think it's as widely spoken in Ireland as Welsh is in Wales. Would I get in trouble for saying Ireland is part of great britain S I N N F E I N I'm a little uneasy about the subject as lots of people got killed as a result of the troubles, and courtesy of Brexit there's a danger the old wounds could be reopened again. 9:41 AM Just split great britain Give independence back to Cornwall If I were a Scot I'd be voting for independence right now. From a purely financial point of view it would be logical for Northern Ireland to unite with Ireland, but there are historical reasons why that won't happen at leat until the current generation have died off. Bit of an exaggeration I don't think anyone has been for Normandy independence in quite a while @JohnRennie fwiw an Irish PhD student at the same group where I studied had done her degree in Irish 9:44 AM Or Savoy I'm guessing you have a few weirdoes @EmilioPisanty Irish physics? Enough that she struggled a bit with thesis-grade written English @Slereah physics in the Irish language @EmilioPisanty I'm a bit surprised at that since English, or rather American English, has become the de facto standard scientific language. Doing your PhD in Irish feels a bit like making a point. There was that guy who wrote a latin math paper in 2008 @JohnRennie I will be in Liverpool on August 17 and 18, would be great to meet up I think I'm around ... @JohnRennie she did undergrad in Irish, then her PhD in English in London @EmilioPisanty dammit, I'm away that weekend. There's a scifi meeting I'm going to. Are you back on Monday? I've got some schedule freedom Yes, I'll be around on Monday. But getting to Chester and back will take a couple of hours once you've included waiting for trains and getting to and from the station. It's not a trip you could fit into your unch hour. Is there a conference in Liverpool? @JohnRennie Fantasticon? 10:16 AM hi all, I would like to mark this glorious moment in time in which I have exactly 1000 rep in both physics and math SE all things balanced Maybe I should downvote you For EVIL at least upvote if you want to be just mildly evil but why would you want to ruin such beauty don't you like symmetry? The evil Evil is compelling but what about round numbers they're compelling too 11:15 AM There's no movie about round numbers It's 101 dalmatians 11:40 AM 0 There's a common saying in the domain of the study of classical relativistic strings, that in the limit of a very short string, the action reduces to that of a point particle (there is for instance a sketch of a proof in Barbashov). I've been trying to show it. Consider the Nambu-Goto string act... 11:51 AM 12:02 PM for obvious reasons @Loong Exactly 12:20 PM @Slereah what do you mean by the FToC bit 0 Dark energy as expressed by the cosmological constant is, as the name implies, a constant of space. Therefore, in a cup of coffee, we get, for some static observer$t$, and a spacelike hypersurface$\Sigma$on which we do the actual volume integration, \begin{eqnarray} E &=& \int_☕ T_{\mu\nu} t... there u go @bolbteppa Exactly what I wrote afterward? @Slereah Well, there you go. First time I've seen emojis used in math also. The future is here. As an exercize show the energy associated with the coffee cup for an observer running in a hurry coffee cup in hand \begin{eqnarray} \lim_{h \to 0} \frac{\int_0^h f(x) dx}{h} &=& \lim_{h \to 0} \frac{F(h) - F(0)}{h}\\ &=& f(0) \end{eqnarray} @Slereah °˖✧◝(⁰▿⁰)◜✧˖° 12:33 PM Oh no the votes are coming in This better not be my new record answer :-D I don't know why people are trying to get it closed it's a perfectly well formed question I like how you start with a static observer and a spacelike hypersurface for the integration, and in the end the answer is "the energy per volume multiplied by the volume" @Slereah why wouldn't it be a constant and indeed a constant$< \infty$? @user2723984 Well might as well do it properly 12:40 PM However, the upvotes are just for \int_☕ Although I skipped the part where I consider a globally hyperbolic neighbourhood of the cup just in case the universe admits no Cauchy surface @Slereah you should totally include that, I think OP is interested in the minutiae @bolbteppa Well, why would it? I mean "why not" isn't a super rigorous proof hmpf, I forgot to edit the d I like that it states why the assumptions are valid, the exercise left for the reader and yes that integral, of course 12:41 PM If you use Neumann boundary conditions it's$\approx \sqrt{0/0}$I mean if you do the problem properly, the answer would be much more complicated Since the integral would depend on the observer and gravitational field and the shape of the cup but since "an average cup of coffee" is already filled with coffee, the obvious answer is 0 @bolbteppa guess it would be easier if I tried to see what it looks like on shell, but that is cheating a bit @user2723984 Well there is always dark energy in the cup even if filled No, you can't fit any dark energy in it because it's already full of coffee. I certainly don't drink dark energy in the morning. I fill my cup to the brink just to avoid that Sending$L(\tau)$to zero is sending$\sigma_2(\tau) \to \sigma_1(\tau)$which gives the limit in the FToC when you include the denominator part as you wrote it, it's only a function of time through the limits of integration but we sent them to zero before we do the$\tau$integral so the whole thing becomes a constant, the only issue could be that you divide by zero in the square root but 2.3 of Goto shows it can't be zero Hm Lemme see 12:48 PM @Slereah I wouldn't say it's well-formed. It shows no prior research, and why is it obvious that the units need to be Joules? Hm You're right $$\frac{-\det g}{g_{00}}$$ is always gonna be different from zero hm How do you get 2.5 of Goto 12:49 PM and finite @bolbteppa ancient japanese secret @bolbteppa you can give that answer if u want get some internet points begins to wax on, wax off This is another secret way to see NG as obvious ahh wait How can that quantity be$> 0$with Neumann boundary conditions Since it's literally$\partial_a X^\mu = 0g_{00}$would have to be$0$on the boundaries and same with$\det(g)$I guess we can show that both are not outside the boundaries and then, by continuity, their division is also that at the boundaries Neumann is$\partial_{\sigma} X^{\mu} = 0$right yeah Not$\partial_{\tau} X^{\mu} = 0$12:57 PM Well I mean By the by It also implies that Wait I forget Is Neumann for the spacelike or timelike direction or both Oh right, only the spacelike direction I think Hm Should probably be fine, but I'd better check by hand later You can tell I'm slightly taking the piss for that coffee answer because I use the Riemann measure$d\mu[g]$Which I have absolutely no good reason to in an answer like that @user2723984 at least so far, as far as we know, no one has been killed by dark energy, so y'know, it can only make you stranger @Mithrandir24601 Just wait until the big rip We'll see who gets killed @Mithrandir24601 Death by dark matter (some high energy physicists have too much free time) I think 2.5 is saying from$dx^{\mu} = \frac{\partial x^{\mu} }{\partial \sigma} d \sigma + \frac{\partial x^{\mu}}{\partial \tau} d \tau$if we choose$d \tau$so that$d x^{\mu}$is orthogonal to$v^{\mu} = \frac{\partial x^{\mu}}{\partial s_{\tau}} = \frac{1}{\sqrt{g_{00}}} \frac{\partial x^{\mu}}{\partial \tau}$then since$dx^{\mu} - (dx^{\nu},v^{\nu}) v^{\mu}$is the remainder of$dx^{\mu}$after we subtract off the component pointing in the$v^{\mu}$direction we can interpret it as leading to a 'pure' distance, and from Wait I just realized$g(t,t)$is Lorentz invariant in Minkowski space So even a boosted observer would measure the same energy although not if we used say the Schwarzschild metric 1:13 PM @JohnRennie yeah, I read the Science article, so that's why I felt so able to make such a bold claim @Mithrandir24601 :-) Some slight differences @JohnRennie Someone from my University is on that paper @Slereah If only the vertical axis was labeled @AaronStevens I think it's a fun paper, though I doubt it has made a great contribution to science :-) @AaronStevens fake internet points 1:23 PM From$d x_{\perp}^{\mu} = [\frac{\partial x^{\mu}}{\partial \sigma} - \frac{1}{g_{00}} g_{01} \frac{\partial x^{\mu}}{\partial \tau}] d \sigmawe then have \begin{align} dl &= \sqrt{dx_{\perp}^{\mu} dx_{\perp \mu}} \\ &= \sqrt{[\frac{\partial x^{\mu}}{\partial \sigma} - \frac{1}{g_{00}} g_{01} \frac{\partial x^{\mu}}{\partial \tau}] d \sigma [\frac{\partial x_{\mu}}{\partial \sigma} - \frac{1}{g_{00}} g_{01} \frac{\partial x_{\mu}}{\partial \tau}] d \sigma} \\ &= \sqrt{\frac{\partial x^{\mu}}{\partial \sigma} [\frac{\partial x_{\mu}}{\partial \sigma} - \frac{1}{g_{00}} g_{01} \frac{\pa @JohnRennie I suppose that is what the arxiv is for :) @Slereah wait, we can't redeem these points for prizes? @JohnRennie there's a whole report on the dangers of the LHC it's quite fun @AaronStevens I think you get a free hat if you break a certain number @JohnRennie got it @AaronStevens I plan to monetise mine. Pay me in BitCoin and I'll award your answer a bounty. All the ways the LHC will kill us Actually I'm really, really tempted to award a bounty to Sam's dark energy answer :-) 1:26 PM really elaborate answers to dumb questions is always fun @JohnRennie "A bounty has been put on this question because I need to pay rent" @AaronStevens Once you hit 100k, then yes. Yes you can :) @Slereah I'm fairly sure I read it when it was published. I don't think it's a great publication because it's impossible to make a safety assessment when we have no knowledge of the physics involved. The only useful point is that cosmic rays have been generating high energy collisions for the whole lifetime of the Earth and it hasn't been destroyed yet. But it's not a hat. The hat is reserved for mods :P @JohnRennie are we sure the earth was never destroyed 1:28 PM @Slereah I'm fairly confident it hasn't been destroyed yet in this universe. I mean, I haven't been out since this morning I can't check if the earth is still there I'm looking out of the window at it, and it's wet but still present. I don't know why you guys care so much. You're all just illusions being generated by the vat my brain is in. @JMac I'd like to quote Conan of Cimmeria on this “I know this: if life is illusion, then I am no less an illusion, and being thus, the illusion is real to me. I live, I burn with life, I love, I slay, and am content.” Obviously it's a completely facetious comment. You can't prove that you're not a brain in a vat; but obviously acting under that assumption brings you nothing of value; especially given that there's no real way to escape that possibility. 1:33 PM Perfect music for vat thinking @JMac says you I've seen that film! Creepers? yes Fiend Without a Face is a 1958 independently made British black-and-white science fiction-horror film drama from Amalgamated Productions. It was produced by John Croydon and Richard Gordon, directed by Arthur Crabtree, and stars Marshall Thompson, Kynaston Reeves, Michael Balfour and Kim Parker. The film was released in the UK by Eros Films; in the US it was released in June, 1958 by MGM as a double feature with The Haunted Strangler.Fiend Without a Face tells the story of mysterious deaths at the hands of a mentally created invisible life form that feeds on atomic power and then steals human brains... oh right Creepers is the one on the spine That feeds on your fear 1:42 PM I saw Fiend Without a Face when I was about nine and it really scared me. I'm ashamed to say, but the one thing that scared me as a kid was the Simpson's Frankenstein parody @JohnRennie heh. We had thunderstorms forecast for the entire day and they've been continuously downgrading it to light showers @Mithrandir24601 same here. We've had some hefty showers but no lighting. Disappointing really. @JohnRennie there was a very heavy downpour at some early part of the morning (like 4-5 am) but nothing worth mentioning since 2:15 PM 43 Basic Premise Can a microbiology professor require students to run laps on the track during class for a grade, even if the class usually has no physical component to it? Background As part of my role as a university professor, my college requires that I advise a number of undergraduate studen... Words fail me :-) @JohnRennie what a strange situation @JohnRennie I've been reading that too now. I just don't understand how someone could ever come to the conclusion "this is a good idea". I quickly did the math. If they are taking two classes a week in the 14 week and 7 week programs, if you factor in the running they are getting 10% less class time, while spending 20% more time at school; it makes no sense as far as education goes 3:17 PM You can’t compute the energy to ten decimal places from a volume that you have estimated to only two decimal places. — G. Smith 27 secs ago oh no We're going to have fights over this dumb question now 4:09 PM @Slereah well why did you write so many decimal places @RyanUnger Too lazy to work out So now I have to make an edit for the uncertainty also I should probably try to work out the energy in the Schwarzdschild metric, for fun 4:29 PM I very dull question (which I cannot find the answer in Google, but I'm sure it exists): Why are ultraviolet rays harmful (from the Sun... so on) and not x-rays? Maybe for the photon to do damage it has to be a specific frequency so it hits the cells, not below, nor above? afaik x-rays are harmful too, the Sun just doesn't emit much radiation of that frequency @NovaliumCompany Why do you think X-rays are not harmful? Hint: They actually are. @NovaliumCompany the Sun doesn't emit enough X-rays to be dangerous to us. Solar radiation in space is dangerous, but mostly due to charged particles not X-ray. This is an interesting question. Can the Penrose process occur with a rotating white hole? I think SE is having some problems Just when I clicked to submit an answer probably too many downvotes on meta.stackoverflow funnily enough, I was about to ask if anyone is having such issues with Overleaf at the moment @Loong what happened this time IsItUp has no problems with it, but when I try to reach it myself it doesn't respond seems to be working again now tho 4:57 PM works for me though I also seem to be getting doubled messages when I type in here...weird how will they fix the issue without looking on stack overflow 5:08 PM You know i should make a blog post on my site against significant digits I am morally opposed to significant digits I am morally opposed to significant digits Uncertainty is fine, but significant digits are made up sounds legit go do it I feel like significant figures "ought" to be a shorthand convention for uncertainty, e.g. the uncertainty in 0.25 is no more than 0.005 But I'm not at all sure that's consistent with how sig figs are actually used when I had labs in undergrad every single instructor had their own rule for significant digits that they thought God given, it was not rare to lose points on a report because we followed the convention of the previous instructor with the current one lol that's why I hated being a stickler about such things i mean, when it came to lab reports I was pretty picky about certain things. for instance, if you've got a figure, it ought to have a captioned label with citation in the text if your result was 0.2501±0.005, you write it as 0.250±005 and you lose point for the useless 0, you write it as 0.25±0.005 and you lose points for the missing digit solution: write 0.251±0.005 even if it isn't what you got lol 5:19 PM oof, lol and to others yet even 0.251±0.005 is wrong because the digit 5 in 0.251 is uncertain in this case, but 0.257±0.005 is right never understood if there's really a rule @user2723984 There is: the GUM. @Loong wtf is this real yes everybody was picky about figures, labels, legends and stuff like that but that I can understand because at least it's clear 2 @user2723984 yeah, exactly. it goes to the lab report as an written argument for how you're interpreting your data 5:25 PM All this has nothing on my grade 11 "advanced" math teacher and her rounding rules. Because on the first day we agreed as a class that "0.5 rounds up to 1" (as compared to round 0.5 to the nearest even number as another system), she would round 0.45 up to 1, because 0.45 rounds up to 0.5 which rounds up to one. People got marked wrong for rounding that down I'm a little sympathetic, tho, in that magazine/newspaper articles will frequently have figures/charts which just float off doing their own thing @Semiclassical However, JCGM 100 and ISO/IEC Guide 98-3 are identical in this case. @Slereah are you really defending your 8 sig figs on your answer so one does need to make clear to them that, in scientific writing, your figures need to be relevant and properly cited in the text @RyanUnger unfortunately yes. SE is a madhouse. 5:27 PM @Loong sure. the issue is whether instructors actually stick with that in practice agreed @Loong if anybody had mentioned the existence of guidelines I would surely have followed them, problem is that the instructors weren't aware of them in the first place similar problem in typography. They prefer to invent their own rules instead of checking whether there is a standard. especially with sig figs, I feel that they are taught quite early in basic math classes in middle school/high school and so people stick with whatever rule their crazy middle school teacher made up I don't think I really had a good grasp on sig figs until 4th year university when I took a course called "Measurement" and of course I've forgotten much of the useful stuff I learned in that course 5:39 PM Significant digits are not like significant They are more for tidying up results It gives you a nice cut off for the decimals with minimal loss of certainty but it's not strictly necessary @Loong who is in the wrong here @RyanUnger minus 647 votes, so it has never been so clear what the users think: meta.stackoverflow.com/q/387546/4064062 And SE usually says that it's the meta communities fault. So decide yourself. ;-) @Loong I mean, the posts are calling the SE team cry babies that seems to be the case am I missing something? or has all of the really bad stuff been deleted @Slereah I would argue that it's not just for tidiness sake. It's so that the numbers you present are a good representation of the results that you've gotten, instead of showing relics of calculation which don't reflect the actual abilities of your measurements @RyanUnger At least they are highly unprofessional. However, SE could announce what they want; the meta community would always hate it. Since April 2018 they have one PR/meta debacle about every two months. So there is not much trust and respect left. 5:52 PM @JMac The uncertainty gives you that it gives you precisely the boundaries of the measurement If you cut off the decimals, you add some uncertainty @Slereah And with 0.012463612 +/- 0.05 you're obviously misrepresenting the information pretty badly. Significant figures are still an important part of the presentation and how it is interpreted @Loong Meta is a mess right now @Loong what happened in april 2018? Jay Hanlon on April 26, 2018 Let’s start with the painful truth: Too many people experience Stack Overflow¹ as a hostile or elitist place, especially newer coders, women, people of color, and others in marginalized groups. Our employees and community have cared about this for a long time, but we’ve struggled to talk about it publicly or to sufficiently prioritize it in recent years. And results matter more than intentions. Now, that’s not because most Stack Overflow contributors are hostile jerks. The majority of them are generous and kind. Sure, a few are… just generous, I guess? But our active users regularly express thei … after someone complaining on Twitter Ah yes Women of color being conspired against on an anonymous online forum 6:08 PM So the impression was, the community can discuss on meta what they want and nothing happens. But if one random outsider posts something on Twitter, all hell breaks loose. I remember this post @Loong Yes; the issue with IPS was like the stupidest thing ever @JMac IPS? @JMac that was later, in October; but you are right, it was exactly the same fiasco again -229 Thanks for your input here and elsewhere on Meta. Please see the results of this discussion on the update post: Updating the Hot Network Questions List - now with a bit more network and a little less "hotness"! Some things happened yesterday that caused a need for us to (quickly) remove a sit... @RyanUnger Interpersonal skills. Two questions in HNQ from IPS were beside each other, and someone on twitter was offended by some coincidence. They decided that "programmers" shouldn't be subject to that stuff when browsing; and for some reason that prompted SE to remove the whole stack from HNQ instead of explaining to the user how little sense their complaint made 6:12 PM there's much more drama than you would expect on this site Loongs link has the stupid details uh what were the titles I don't think that post says it, does it? @RyanUnger meta.stackexchange.com/a/316976/369105 One of the answers shares it to show how messed up the policy is lmao I've always said SE policy is crap blah Can't find the uncertainty of the cosmological constant 6:21 PM @Slereah wot really just say it's +/- 1; don't even put units, leave that up to the reader to determine you mean the\pm$number? Yes$\Lambda$isn't commonly used in cosmology It's usually more the dark energy density$\Omega_\Lambda$does Weinberg report it Lemme see 6:23 PM I really should read this book I bought it years ago Nope It's a book from 1972 there's one from 2008 dude Back then they didn't really believe in a cosmological constant for the real universe he just says$\Omega_\Lambda\approx 0.7$6:37 PM Numbers have become nothing but coefficients to me PDG does have the uncertainty$\Omega_\Lambda = 0.73(3)$1 hour later… 7:58 PM -3 this question is for the people out there who are willing to think and not just jump to answer this question base on some text book teaching from a hundred years ago that dose not apply to today's knowledge. I created a gas/air from a magnet rotating between copper coils into a enclosed cylinde... @Loong The language of this kind of stuff always says a lot. They often use phrases like "Anyone willing to actually put any thought behind it" or "If you actually just thought for a second". It's like they somehow are completely uninformed that the textbook teaching is in use because of all the significant thought put into it. They really want people who are willing to think their way; which doesn't necessarily actually include critical thinking. Even gas is refusing to think that way. "the coolen gas/air in will no longer wants to stay on the ground." As opposed to normal gases that happily stay on the ground. He's probably breathing SF6 normally. 8:25 PM Hm Trying to think about how to integrate functions on non-Hausdorff manifolds It will require some finesse because the usual definition requires a partition of unity I guess I can work backward from what it should be Like$\int f\$ on the splitting real line should be $$\int_{-\infty}^0 f + 2 \int_0^\infty f$$
Hm
Is there something similar to the partition of unity but slightly weaker that would work on a non-Hausdorff manifold

Hallo, does anyone know why when averaging power signals, the SNR increases as N^(1/4)?

Maybe I can just define the integral on the H-submanifolds and identify where things are identified

8:40 PM
@Gyromagnetic Handwaving guess: a root-N effect from counting statistics, squared because power goes like the square of the amplitude.

8:57 PM
@Slereah what are you on about

@RyanUnger Exactly what I said

@Slereah why are you thinking about non-Hausdorff manifolds

I am a non-Hausdorff manifold

Integration on function spaces requires integrating on non-hausdorff manifolds?

It doest not
I am not very good at focusing

9:02 PM
hmm

9:26 PM
Is Galois theory related to Erlangen program?

The GR muse
She appears to me and tells me to compute curvature tensors

9:44 PM
ughhh...I need to figure out why a digital neuromorphic chip would be more computationally efficient than a standard CPU/GPU...
it seems that the analog case is clear

10:08 PM
hmmm

10:49 PM
@ACuriousMind @bolbteppa are there any classical solution of Polyakov on a non trivial cobordism
Like one string to two strings
Seems tricky to compute because of all the cobordism misery

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