The h Bar

@JaimeGallego The question is: do they process data classically, or quantum-ly (I don't actually know if that's a word, but you hopefully get the gist :P )

Jaime Gallego

There's a small Chinese man inside each one with an abacus

Mithrandir24601

@JaimeGallego NOOOoooo..... There's nothing I can do... ::hides::

SBM

3:58 PM

oh

hello

vzn

@Mithrandir24601 hi did you do a masters thesis in math physics? what was it on? have you heard of this? physics.meta.stackexchange.com/questions/7783/…

Mithrandir24601

@vzn Yeah - it was on Weak Measurements. I'm now doing a project on things called (quantum) t-designs

Anonymous

4:13 PM

@Mithrandir24601 I've been reading about that torque question for sometime now. Most sources seem to agree that when asked for toque about a point we consider only real torques and not the pseudo torques. Pseudo torque are helpful tools when working in non-inertial frames. Anyhow, thanks for your help!

Slereah

cosmologyscience.com/cosblog/…

Oh my

SBM

ohh

Slereah

"But too many math advocates in charge of setting University physics curriculum currently refuse to let you study physical cosmology principles unless you have an enormous higher math background !"

This blog is raising some red flags

"Sadly, this gratuitous math barrier prevents millions of students from enjoying physics, astrophysics and cosmology. This makes the math requirement a de facto example of a Priesthood (even if unintentional or unconsciously)."

SBM

What?

vzn

@Mithrandir24601 is it online anywhere, can you share it? would you have any interest in the guest session? think youd be great! have been tracking weak measurement quite a bit myself in recent times, need to blog on it again in near future... what are quantum t designs? can you say what college youre at? vzn1.wordpress.com/2015/11/03/…

Mithrandir24601

4:25 PM

@blue Hmm - I've don't think I've ever explicitly heard the phrase 'pseudo torque' before. If what I said was somehow useful and not confusing, then I'm glad to help!

vzn

@Slereah wild stuff thx for sharing, you always find the really eccentric stuff. has a crank element, but think author unzicker has some valid points. have made a few roughly similar ones myself about particle physics. reminds me a lot of the 2 excellent book critiques of string theory from years back. (yikes still on my to-read pile!) amazon.com/Higgs-Fake-Particle-Physicists-Committee/dp/…

Mithrandir24601

@vzn I don't think it's online anywhere... Erm... If you want me to do one, I guess I could? t-designs are similar to (classical) probability moments, integrated over a Haar measure - say you're in SU(4) [I put this in as an example, only to realise it's irrelevant...], with matrix representation $U$, then the t-design is $$\int_U U^{\otimes t}\otimes \left( U^*\right)^{\otimes t} dU$$

(oh, I'm currently at Bristol)

Jaime Gallego

@Slereah If you scroll down a bit, they show the long Standard Model Lagrangian

Slereah

Well there's always problems with science, but from that review a lot of the arguments seem a bit weird

Like saying that the standard model doesn't talk about mass

Although that may be the blogger's opinion since he seems to be an even bigger crank

vzn

@Mithrandir24601 did you do a thesis defense? can you put your thesis online? even a google drive link would be great. we do regular mtgs tues mornings biweekly, have you ever been to one? can you make that time? its 1600Z. its prob best time for a session if you can make it. chat.stackexchange.com/rooms/info/71/the-h-bar?tab=schedule theres one on jun13th can you make that one?

@Slereah lol he gave the book 9.7/10, taking off 0.3 for "lack of smoking gun quantitative specificity"... ps have you ever heard of dyakonov? hes written similar semi hilarious takedowns of QM computing...

Mithrandir24601

4:40 PM

@vzn Nope :) I did, though, have to do one for my third year lit. review. I should be able to make it on Tuesday, but might be a little late

SBM

what does that rotated XOR symbol mean?

Slereah

@vzn I have not

GR is more my thing

There is a big GR crank

I forget his name

vzn

@Mithrandir24601 think of session as good practice for phd defense... :)

Slereah

he's the guy that always talks about the Eddington coordinates being a scam

vzn

@Slereah @#%& physics cranks everywhere... how about that dude that was criticizing JR specifically on youtube... gotta go dig up that link again lol

@Slereah reminds me of garrett lisi, have tracked him some...

Slereah

4:43 PM

A lot of cranks commit the mistake of thinking that physics should be some 100% philosophical absolute truth

Mithrandir24601

@vzn The one I had in third year was terrifying enough - my supervisor (head of the detector physics group) brought in one of their experts in quantum computing (which was what my lit. review was on)

Slereah

And unique in that

So if two theories can predict the same things, everything is obviously a ruse cruise

I mean I'm pretty sure there are alternative theories that predict what the LHC detection has, but that's not really ground for saying the Higgs boson was a big old scam

vzn

@Mithrandir24601 lol ok thought you were talking about an english class! so did you review multiple refs or 1 in particular? we are huge QM computing fans in this chat room in case you hadnt noticed...

@Slereah "ruse cruise" hadnt heard that one before

@Slereah my personal major qualm/ contention/ caveat with particle physics is that its gotten too reductionistic and think its pushing the limit of what can be achieved in that way. (had some of that debate here once but it mostly fell on deaf ears.) do enjoy hearing of iconoclasts/ contrarians because they often have grains or specks of truth in their criticisms... sometimes verging on much more... ie cruxes...

dmckee

@BernardoMeurer As @user314159 was saying a certain amount of letdown is perfectly normal: you were investing huge amounts of time in this and always knew what you were going to do each day—work on the project— right? Now that's gone.

Mithrandir24601

@vzn Haha! My bad :P Should have been clearer... I just did superconducting - my supervisor was a bit of a fan (as much as a physics prof. could be a 'fan') of Martinis Group (he certainty seemed to be thinking that they were on to something), so yeah, I referenced Daniel Sank a couple of times in that

Slereah

4:50 PM

fortunately I don't care that much about experimental physics so I don't have to care too much about the drama

Well, not that drama, anyway

vzn

@Mithrandir24601 martinis has many fans with good reason, he seems right on the brink of it... do worry he may have over promised some at this point... wonder if the whole field might encounter some resistance/ setbacks as has happened eg in past with other fields eg (multiple) "AI winters". note ofc DS did a guest speaker session, its in chat logs... vzn1.wordpress.com/2016/08/09/…

Mithrandir24601

@Slereah I remember being shown the graph (or one of the graphs, assuming there's more than one) that indicated the discovery of the Higgs, and there was definitely a noticeable bump, well outside of error bars, so... I'll believe my lecturers and the graphs over some random guy online... :P

Slereah

Well it's always hard to really make out a significant bump

Although there is a simple method to check

but you know, I have my secret technique

For any experimental result, i wait at least one year

If it hasn't been proven wrong by then, it's probably fine

Bernardo Meurer

@dmckee Yeah, I get that, my solution is I just started a new project :P

vzn

so @Slereah last heard you were doing css for $ or something like that?

Slereah

4:58 PM

I am

terribly dull

Been writing my GR book at the same time

vzn

yeah know the feeling. "life is what happens while youre making other plans" —john lennon. doing any javascript? we have tons of that at times... what kind of web site(s) anyway?

Slereah

Eventually we will do javascirpt, yes

All the web languages

Mithrandir24601

@vzn I wouldn't be surprised if he's over-promised a bit, but there's definitely progress being made - they've (IBM) almost doubled the number of qubits (that Google had) in the past year or so already, so if progress keeps coming at this rate... :D Also, D-Wave seem to be on the verge of doing something better/faster than classical computing alone as well, so it's all pretty promising

vzn

our company is talking about golang/ nosql dbs these days, a radical shift, we are thinking of migrating off websphere/db2 to more open source stuff, its a radical eyepopping paradigm shift in a previously very conservative environment...

Slereah

Trends come and go

They're basically all the same outside of libraries, really

vzn

5:02 PM

@Slereah know what you mean, lived thru dotcom era and the trends were like big waves at the time, not as big waves lately, but still some energy/ momentum there... one of my fave refs on that en.wikipedia.org/wiki/Hype_cycle

@Mithrandir24601 nice to hear someone say something positive about dwave, they have a lot of detractors (eg dislike aaronsons constant/ endless near-bullying of them), was sorry to see geordie rose leave! think he & company personality were nearly inseparable ("scrappy")

Mithrandir24601

@SBM Forgot about this, sorry - it's the tensor product - $U^{\otimes t}$ means $U$ tensor $U$ t times

Slereah

lol "rotated xor"

The deeper i go in GR the more weird shit I find

SBM

oh sorry I did not know about that

vzn

@Slereah whats your book about? have you looked into tenev/ horstemeyer yet? you will not be disappointed :P vzn1.wordpress.com/2016/11/07/…

dmckee

@BernardoMeurer It helps to be able to (a) do some small projects between big one and (b) actually get away fro the keyboard occasionally—go to the beach for a day or something.

Slereah

5:05 PM

@vzn It's about GR

Like

All of it

at least that's the intent

Bernardo Meurer

@dmckee The sun is a deadly lazer

Slereah

I don't think I'll manage to fill all chapters

I am currently at 43 chapters, though most of them are barebones

vzn

@BernardoMeurer what prj are you done with? cpu? think of it just as going on hiatus, not ending... :)

dmckee

@BernardoMeurer And? The beach has pretty girls. And kids building sand castles. And dogs playing fetch.

And maybe someone flying a really cool kite.

vzn

@dmckee ooh pretty girls in bikinis where are the pics? :P o_O

dmckee

5:07 PM

But you can go to the mountains, instead. Or the desert.

vzn

@Slereah are you gonna get into dark matter/ energy at all? anything on verlinde? :) ... have been meaning to read my excellent new dark matter book...

Bernardo Meurer

@vzn A humongous data processing C program for my programming course

48 pages of code in size 8 font :P

Slereah

@vzn Well it's more focused on the theoretical side

Although I do have a little experimental chapter

I probably won't delve too deep into cosmological observations

Mithrandir24601

@vzn I was once sceptical, then they managed to change my mind. Even Aaronson's starting to come round - scottaaronson.com/blog/?p=3192

vzn

@BernardoMeurer cool what does it process? heard about your cpu prj that sounded way cool, encourage you to put your writeups online! ps when do you wanna be the guest speaker? you have lots to talk about now :P

Bernardo Meurer

5:09 PM

@dmckee I go to the park mostly, but it kind of depends on having people to play chess with

@vzn Bike trips for the Boston city bike thingy

The CPU project is cool, but it had to be killed because it was eating all my time :P

Guest speaker of what? :P

Mithrandir24601

to clarify things a little - I believe that they're not there yet, but they will get to a point where they'll be able to do a very, very small set of problems better, but not massively better, than classical computers will be able to

Although maybe in a number of years, they might have really good [massively better] speedup - who knows?

vzn

@BernardoMeurer (sigh!) physics.meta.stackexchange.com/questions/7783/…

Bernardo Meurer

@vzn Ah! I thought you were talking about something else

I'd love to talk about my stuff on the AMA

vzn

@Mithrandir24601 everyone incl me is cautiously optimistic, just like with the fusion field :)

Bernardo Meurer

Bore everyone to death with running Linux on FPGAs and ARMv5 cores :)

SBM

5:15 PM

What?

vzn

@BernardoMeurer cool! hey there are a lot of CS geeks in here, strong overlap between physics/ CS these days, think everyone is welcome, the more the merrier. can you do 1600Z tues sometime? have you ever been in the biweekly mtgs?

Bernardo Meurer

What's 1600Z?

Have not been to meetings

Tuesdays are good

vzn

@Mithrandir24601 "aaronson starting to come around" is roughly akin to "aaronson not stating that its the work of the devil anymore"... the word grudging comes to mind...

@BernardoMeurer awesome have you seen the meta posts by guests? could you cook one up sometime? (let me figure out a date 1st) next one is jun13th 1600Z (time in GMT), possible for you?

Bernardo Meurer

::checks calendar::

vzn

@BernardoMeurer FPGAs are a very big deal these days, have you heard what MS was doing with them? industry leader... eg bing backend worth big $$$, good wired article on that, just cited it recently, you may find some stuff to like/ enjoy in here vzn1.wordpress.com/2017/05/19/…

Bernardo Meurer

5:20 PM

13/06/17 1600 UTC sounds good to me

It's after my analysis exam

I can cook up a Meta post, sure

vzn

@BernardoMeurer awesome! :) ok let me confirm the time with @DavidZ 1st before you write the meta post. DZ is BM special guest for Jun13th slot ok with you? @Mithrandir24601 we could introduce you also at that mtg for future session & you could watch if you like

Mithrandir24601

@vzn That's fine with me - I might be a tad late, but that's not exactly important :P

vzn

@Mithrandir24601 yeah ok thx lets have you do a session where you can commit to being on time, thats one of the few minor prerequisites :) ... we tend to alternate mtgs, so maybe you could do one in mid july? also encourage you to put stuff youve done online before then...

Mithrandir24601

@vzn It's generally going to be a minor issue that I'll never be around at exactly that time, as that would be the earliest time I'd usually leave the office at - I'd leave a little earlier, but I have an essay deadline soon after that (Quantum Communications between ground and Satellite!) So, yes, I could make it on time anytime in July

vzn

@BernardoMeurer hope you go into some history of how you found the hbar chat room & ppl youve met here, & your connections to/ interests in physics etc, ofc CS is fine, but try to keep audience angle in mind...

Bernardo Meurer

5:27 PM

Oh yeah, I definitely have a lot to talk about the h-bar

I owe a lot to this chat :P

vzn

@BernardoMeurer ok, you might look at Secrets meta post, he went into very large/ minute personal detail & yet got significant votes! :) think its great to have you here and have enjoyed reading/ watching your various exploits...

Bernardo Meurer

@vzn I just finished reading it :)

Hehe, thanks man!

vzn

@BernardoMeurer was interested in hardware design myself around your age, found an amazing simulator called "the visible computer", it was an obscure geek classic on 8080... came out mid 1980s or so ... did 6502 atari assembly language... spking of hardware design have you ever heard of babbage/ lovelace? vzn1.wordpress.com/2015/12/11/…

Bernardo Meurer

Right now I'm using this crappy architecture my school created called P3, because I need to know it inside and out for my exams

Pisses me off really

We should just learn 68000

vzn

@BernardoMeurer aha, coded C/ pascal in that long ago on macintosh...

@BernardoMeurer welcome to "jumping thru hoops"... its endless. the last hoop is "shuffling off this mortal coil"...

dmckee

5:40 PM

@BernardoMeurer You have to learn MIX to read Knuth, so your instructors are in good company.

The deal is that they want a concrete basis for discussion, and want it to be as simple as possible without being too simple.

Bernardo Meurer

@dmckee I file a complaint against the department that they used P3 and not MIX

dmckee

Most real architectures make trade-offs they don't care to deal with.

vzn

@dmckee lol which as far as langs go is even better than scheme :P (had that lang in my freshman engr CS class... aka abelson+sussman)

Bernardo Meurer

Well MMIX

dmckee

@BernardoMeurer ::chuckles::

Bernardo Meurer

5:41 PM

Apparently the course was taught with x86 before P3 though, and the students basically built toasters instead of CPUs

Emilio Pisanty

@dmckee The Art of Computer Programming was written for a fictional architecture?

figures

Bernardo Meurer

@EmilioPisanty Well, you don't want to write a book to some architecture that becomes old

dmckee

@vzn (Whining stop ('cuase (good (for the soul) (is lisp))));

Bernardo Meurer

So you just create an abstract one

Well not abstract, just not real

dmckee

@EmilioPisanty Yeah. It doesn't even know if it is binary or decimal. a byte can represent wither 0 through 99 or 0 through 255. Yikes!

Emilio Pisanty

5:42 PM

@BernardoMeurer so... obsolete by design from day one?

it does sidestep the problem, sure

vzn

@dmckee a friend told me once in my mid university years he met Knuth at a conference & then told him had no idea who he was talking about, have since figured it out some :P o_O

Bernardo Meurer

If I met Knuth I would cry

Emilio Pisanty

@BernardoMeurer chill

I did see a seminar by Kip Thorne yesterday, though

Mithrandir24601

@vzn Heh. I met a Fields medallist once, without realising it :P (I've since met him again and was actually aware that time)

Emilio Pisanty

he's every bit as good as his reputation suggests

fun fact: the mirror displacements in LIGO are not only ${\sim}10^{-4}$ times smaller than an atomic nucleus, they're also comparable with the de Broglie wavelength of the 40kg mirrors

vzn

5:47 PM

@EmilioPisanty he worked on interstellar with nolan so thats enough credentials for me :P wired.com/2014/10/astrophysics-interstellar-black-hole

Emilio Pisanty

@vzn oh, I know, I jumped on his Interstellar book as soon as it came out

vzn

@EmilioPisanty whats he up to these days anyway? was the seminar at your school?

Emilio Pisanty

@vzn dunno what he's up to, but yeah, he stopped by my institute to give a colloquium

vzn

@EmilioPisanty hey any interest in doing the special guest session this summer sometime? iirc we discussed it some and you said post-phd was possibility :) physics.meta.stackexchange.com/questions/7783/…

Emilio Pisanty

@vzn could be, sure

vzn

5:51 PM

@Mithrandir24601 which one? might as well name him! :P

dmckee

@EmilioPisanty OK. That's cool.

Mithrandir24601

@vzn Tim Gowers

dmckee

In fact, that's astounding!

Emilio Pisanty

@dmckee yeah, I know

apparently, shot noise in the laser and photon pressure on the mirrors are canonically conjugate variables

dmckee

@EmilioPisanty ::boggles::

How?

Emilio Pisanty

5:52 PM

so when they talk about using a squeezed vacuum, they can only shift noise around from one of those two to the other

vzn

@Mithrandir24601 ah he has a great blog, am a fan, like one of his papers a lot in particular where he considers automated thm proving, have cited him quite a bit over years... he also had automated thm proving experiment awhile back... :) where did you meet him? this reminds me of an old letterman segment called "brush with greatness" iirc lol

Emilio Pisanty

@dmckee not sure

dmckee

I feel like there should be a simple explanation, but I can't quite make it fit together.

Emilio Pisanty

and moreover the two variables shift in importance as a function of frequency

so they need to use a squeezed vacuum whose squeezing angle changes with frequency

way cool stuff

@dmckee he gave an explanation which sounded reasonable, simple, and coherent at the time

and which I can no longer recall

vzn

@EmilioPisanty ok maybe july or august work for you? ok with writing a meta post intro like the others? defn want to hear about your phd etc am sure thered be a ton of topics :)

Mithrandir24601

5:55 PM

@vzn Actually met him a couple of times in my undergrad - one of his sons was in the college choir

Emilio Pisanty

And actually, that's probably a good question to ask on main and get the gold badge

Mithrandir24601

(I wasn't in the choir, but was heavily involved in the chapel in other ways)

Emilio Pisanty

@vzn probably July is a better idea

Mithrandir24601

@vzn I could do mine in August, when I'll actually have a PhD topic/title, if you want?

vzn

@Mithrandir24601 its up to you, figure you can be after BM, july is open so far if you want to do it, if you prefer to hold thats ok, see the phd topic/ title nice but not crucial... ps youve met DS in here right?

@EmilioPisanty ok will get back with you on nailing down a date, have to clear/ coord it with DZ, typically the 1600Z tues mtg works best, hope you can make that std time slot, if not we can discuss it

Emilio Pisanty

6:01 PM

@vzn hmmmm. That's Tuesday 6pm DST in central Europe, right? probably doable, then

Mithrandir24601

@vzn I don't think I've spoken with him, but I've seen him around in general

vzn

@EmilioPisanty :) thx! you can try a mtg or two before then to see some of the crowd/ atmosphere if you like, cant remember seeing you in those mtgs before (havent been too consistent myself lately tho either)

Emilio Pisanty

@vzn I've seen several AMAs

vzn

@Mithrandir24601 say hi to him! tell him what youre working on! am surprised you 2 havent hit it off yet :P

Emilio Pisanty

I find the activity of the usual Tuesday meeting to vary wildly, though

vzn

6:03 PM

@EmilioPisanty yeah do recall that now, thx for joining, you were an early choice but played coy for awhile :) :P

Emilio Pisanty

@vzn If by "played coy" you mean I had a thesis to write, then yes =P

vzn

@EmilioPisanty lol exactly, and am sure your life is so much more stress free now :P o_O

Emilio Pisanty

@vzn rather

vzn

@EmilioPisanty looking at your long profile but am thinking you havent linked your phd in that yet? need to review it myself :)

Mithrandir24601

@vzn Wait.. Hang on - DS - AHH! I mis-read that as DZ :P Yeah, I've spoken to Daniel a few times now...

Emilio Pisanty

6:07 PM

@vzn my thesis is plenty easy to find

vzn

@Mithrandir24601 another fun blogger is terence tao, check him out if you havent, seems to be occasional cohort of gowers...

@Mithrandir24601 heather one of our guests got to visit his lab in person! have you met heather yet? see her in here occasionally... middle school science student

Mithrandir24601

@vzn Yeah, I've spoken with her as well. I'd love to see round Google's place, but England's a bit far. Although, I did get to see D-Wave's place :)

Emilio Pisanty

that said, thesis writing had a complicated relationship with this site

vzn

@EmilioPisanty lol ok just thought you might want it in your profile spiral.imperial.ac.uk/handle/10044/1/43538

Emilio Pisanty

@vzn should I update my profile? probably yes. Have I got the energy to think about it nowadays? sigh =|

yeah, there's a bunch of places I should put that link in

starting with github.com/episanty/PhD-Thesis

vzn

6:12 PM

@EmilioPisanty its otherwise impeccably maintained. ofc youre no stranger to SE involvement

@Mithrandir24601 thats super cool. excellent blog fodder & also great topic for the guest session. was GR still there? did you meet him? maybe write up some impressions sometime somewhere! have been tracking dwave for many years...

Emilio Pisanty

0

Q: In what sense are shot noise and photon pressure canonically-conjugate variables in the LIGO interferometer?

This week I saw a seminar by Kip Thorne and he mentioned that in the LIGO interferometer, the photon shot noise is actually canonically conjugate to the noise induced by photon pressure acting on the mirrors; he gave a good explanation during the talk but I can no longer remember the details. How...

vzn

gotta go run to outdoor music festival near mtns & pick up guitar hero for ipad for summer (now a steal at only $40!), nice talking with you all, it was fun, excited about getting new chat sessions on the horizon :)

Emilio Pisanty

@vzn have a good 'un

vzn

@EmilioPisanty thx you too maybe do another thesis and youll spike your PSE score again :) bye

Mithrandir24601

@vzn Nah, it was only a little over a month ago - we had to sign NDAs, although I don't think they told us a lot that's not available online anyway. We did see round the lab, but weren't allowed to take photos :/

Well, not strictly true - we were only allowed to take photos of the outside of the machines

Which are really just black boxes...

Balarka Sen

7:00 PM

@BernardoMeurer You will like this: youtube.com/watch?v=yX8yrOAjfKM

Mithrandir24601

@BalarkaSen At least it's not running on Vista :P

Emilio Pisanty

@BalarkaSen I'm pretty sure a characterization of the Matrix as 'malware' isn't far off the mark

Bernardo Meurer

@BalarkaSen I did enjoy that hehehe

Mithrandir24601

@EmilioPisanty "Laughter is the best medicine, unless you have a broken rib." has to be one of the best quotes I've seen on a Thesis yet

2

Emilio Pisanty

@Mithrandir24601 thanks

I can vouch for the strictly-no-laughing thing on broken ribs

Mithrandir24601

7:12 PM

@EmilioPisanty Ouch

Emilio Pisanty

also intimately connected with the tram tracks at Karl-Ziegler-Straße

Mithrandir24601

@EmilioPisanty Sounds... Painful

Emilio Pisanty

@Mithrandir24601 yes, yes it was

that was me, pretty much

user314159

cool tune...fly like an eagle

Mithrandir24601

7:33 PM

@EmilioPisanty Oof - Looks.. Painful as well

Emilio Pisanty

@Mithrandir24601 the fall itself was relatively painful but not all that far out of the ordinary.

It was the minutes and the weeks afterwards that really stood out.

Mithrandir24601

@EmilioPisanty Ah, OK, then - you just tripped really. Nothing to worry about :P

Emilio Pisanty

@Mithrandir24601 would've been, yes

I get knocked down but I get up again and all that crap

just got right back on my bike and cycled home

... at which point it became evident that All Was Not Well

Mithrandir24601

Ah, you're still here now :P

Emilio Pisanty

though the circumstances still required that I cycle home for a half-hour with that broken rib, not the most pleasant experience I've been through, all told

Mithrandir24601

7:38 PM

[read: that sounds quite nasty, but slightly amusing]

Emilio Pisanty

@Mithrandir24601 I find the whole thing quite hilarious

did at the time, too

John Doe

@EmilioPisanty Do you know why a probability function where you have no knowledge of the random variable which is positive is given as $P(\gamma) = \frac{c}{\gamma}$ where $c$ is a constant?

Emilio Pisanty

though I very quickly learned not to physically laugh at how things were going

Mithrandir24601

Oh, good - I don't have to feel bad about finding it amusing then :P

Emilio Pisanty

@JohnDoe context?

@Mithrandir24601 not at all

user314159

7:39 PM

Are you on pain killers?

Emilio Pisanty

@user314159 this was over a year ago

they put me on some pretty strong stuff at the time

user314159

oh

Emilio Pisanty

but it was done in about five-six weeks

John Doe

@EmilioPisanty In a set of notes I am reading through they are explaining Bayes Theorem, which is $P(x|y) = \frac{P(y|x)P(x)}{P(y)}$, they consider the case where you have no prior knowledge, hence you don't know anything about $P(x)$, but what function do you choose to represent this. They choose $$P(\gamma) = \frac{c}{\gamma}$$ giving the reason that it is invariant under scaling transformation. Do you see this invariance?

Mithrandir24601

@JohnDoe multiplying $\gamma$ by a constant leaves $\int P\left( \gamma \right) d\gamma$ unchanged?

Emilio Pisanty

7:44 PM

@JohnDoe well, that function has the property that $$\int_a^b P(\gamma)\mathrm d\gamma = \int_{r\,a}^{r\,b} P(\gamma)\mathrm d\gamma$$

i.e. what Mithrandir just said

Mithrandir24601

(i.e. It's a Haar measure under multiplication :P)

Emilio Pisanty

However, it should be obvious that it cannot be taken as a legitimate probability distribution over an unbounded interval

you need to keep it away from both zero and infinity

John Doe

@Mithrandir24601 Thanks

Mithrandir24601

@JohnDoe No problem - I've been spending the last 2/3 weeks thinking about things like this, so it's nice to know that something's been sinking in :)

John Doe

@EmilioPisanty Are your integration limits $rb$ and $ra$ just multiplying $a$ and $b$ by some $r$?

@Mithrandir24601 Are you well schooled in stats?

Emilio Pisanty

7:48 PM

@JohnDoe yes

Mithrandir24601

@JohnDoe Erm... Well... I've taken some courses in things like probability for my undergrad, so... Not really

(but I've done a little bit)

Emilio Pisanty

@JohnDoe as another view on your distribution, it's a bit easier to note that it is the uniform distribution over $\beta = \ln(\gamma)$

you can model it as firing darts on a log-log sheet of graph paper

John Doe

@EmilioPisanty uniform distribution over $\beta = \ln(\gamma)$ is it related to the usual uniform distribution?

Mithrandir24601

[small ramble:] It's just that the project I'm working on involves these things called Haar measures, and that probability distribution you gave is a Haar measure over the positive real numbers under multiplication. The entire point of the Haar measure is that doing whatever transformation [multiplication] doesn't change the value of the measure

(OK, I don't know if it's the 'entire point', but as far as I'm concerned, it is)

AmagicalFishy

8:06 PM

Do you guys know if Goldstein's classical mechanics book has a lot of exercises?

And, do you like Goldstein or Taylor more?

Mithrandir24601

@AmagicalFishy No idea and... No idea (never read either), sorry :/

AmagicalFishy

Ah, no worries. I'm in need of a good mechanics book and have whittled it down to these two

Emilio Pisanty

@JohnDoe exactly

that also has interesting connections with Benford's law, if you're looking for other perspectives

Sir Cumference

8:27 PM

Hate how astronomy SE has a "ufo" tag

Slereah

77

Q: Theorems with an extraordinary exception or a small number of sporadic exceptions

The Whitney graph isomorphism theorem gives an example of an extraordinary exception: a very general statement holds except for one very specific case. Another example is the classification theorem for finite simple groups: a very general statement holds except for very few (26) sporadic cases. ...

soft-question big-list

good thread

Sha Vuklia

8:48 PM

Guys, they say here that the tension of the string on each mass is approximately constant, because we consider a small $\Delta y$. I don't really see why though. I understand it has to do with the fact that for small $\Delta y$, the length of the string segments stay approximately constant, so there is no stretching of the (massless) string.

So I'm guessing, as long as we can consider a massless string that doesn't stretch (but simply stays taut), we always deal with the same tension, even if there al $N$ little masses (beads) on the string. Is there some additional explanation, just so that this becomes more intuitive for me? Maybe with some argument that the net force on something has to be zero?

Anonymous

9:03 PM

@ShaVuklia Are you asking why the tension is constant throughout in a massless rope ?

Anonymous

Actually there is some stretching occuring when waves are traversing along a string!

Anonymous

So this "so there is no stretching of the (massless) string" part is wrong.

Sha Vuklia

9:26 PM

but we can say it's approximately constant, right? because of a relatively small $\Delta y$ @blue

Anonymous

9:36 PM

@ShaVuklia Yeah, the tension is indeed constant throughout because the string is massless.

Anonymous

But that does not prevent the string from being stretched

Anonymous

I recommend this:youtube.com/watch?v=YAGGksKd7qA in case you are learning the derivation of the wave equation

Anonymous

(1:3) The Wave Equation: Motivation (Walter Lewin, MIT)

►

Anonymous

Umm, wait. I shouldn't say the string is massless.

Anonymous

You are right, the variation is small.

Anonymous

9:44 PM

PDE 8 | Wave equation: derivation

►

Anonymous

This is a more rigorous derivation^. They explicitly prove why you can assume T to be constant.

Emilio Pisanty

@ACuriousMind you gotta wonder, sometimes.... physics.stackexchange.com/a/335797/8563

ACuriousMind

@EmilioPisanty possibly the strangest thing I've deleted today - it was a slow day, though :P

Emilio Pisanty

@ACuriousMind you deleted weirder things this week?

goodness

I guess I should keep a closer eye on the Recently Deleted tab

also, what's with praising the handwriting when the only appropriate action was a Not An Answer flag?

ACuriousMind

I...guess they wanted the user to have a positive experience before the post was inevitably deleted? :P

Emilio Pisanty

9:57 PM

@ACuriousMind I guess so too

Sha Vuklia

@blue yea that's were my question came from originally. (from Walter)

oh and thanks, I'll watch the second video

Emilio Pisanty

@ACuriousMind I remain unable to understand that kind of soft-hearted do-gooder kinda attitude, at least when it's directed at someone with an obvious disregard for the site and its community

but oh well

Bernardo Meurer

10:29 PM

@ACuriousMind Are you around?

dmckee

11:50 PM

@EmilioPisanty Ah, yes. Shock suppressed pain, and the dawning certainty that something is not quite as it should be. For me it was a displaced fracture of the humorous; the rest of the arm should bob like that.

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