The h Bar

Bass

15:00

Oh, you get another algebra by defining $M_+=M_1+iM_2$?

ACuriousMind

The name "compact" comes from the fact that a Lie group is compact if and only if the Killing form is definite, so the compact real form integrates to a compact Lie group

@Bass Yes. Note Qmechanic's careful phrasing "one-to-one correspondence" instead of just saying that it is $\mathfrak{su}(2)$, which would be wrong.

Bass

@ACuriousMind OK I see. So the "sign problem" is still open?

ramsay

if $\frac{dy}{dx} $ is not a fraction why do we take it as a fraction in physics?

ACuriousMind

@Bass I believe it's a problem of differing conventions. I think now my first version of the commutation relations that you corrected might have been the correct one after all

John Rennie

@DanielSank if your food is too bland add fat (butter), salt or chilli, or preferably all three. That works every time for me :-).

Bass

15:05

@ACuriousMind But (1) it's different from the Wiki article about Witt's algebra, and (2) it says that $[M_+,M_-]=-2M_3$ in my notation.

ACuriousMind

Because for the current version of the commutation relations, $L_0 L_{-1}\lvert l\rangle = (L_{-1} L_0 + [L_0,L_{-1}])\lvert l\rangle = (lL_{-1} + L_{-1})\lvert l \rangle$, so $L_{-1}$ raises the eigenvalue of $L_0$.

I chose the differing convention on purpose so that $L_{-n}$ would lower stuff, but I might not have thought it through

user116211

@HariPrasad quite good.... I dared to answer Physics first ;P

ACuriousMind

I think my $L_0$ is $-L_z$.

Hm, no

Bass

Well, feel free to revert my edit. There may be differing conventions involved, but as I said, I tried to redefine the operators with minus signs and $i$'s, but it just does not fit. Would be great if you find the time to update the answer, but if not, no problem. They're just bloody signs after all :)

ACuriousMind

@Bass: There is a geometric reason the -1,0,1 part of the Witt algebra has to be $\mathfrak{sl}(2,\mathbb{C})$, because if you look at the conformal transformations these three generate, they are precisely the Möbius transformations

I cannot, however, see currently where exactly the problem in what's written in that answer lies

Bass

15:30

Hmm, I think it might fit if we define the ladders as $M_\pm=i(M_1\mp iM_2) = iM_1\pm M_2$, then $[M_+,M_-]=2M_3$ and $[M_3,M_-]=M_-$ and $[M_+,M_3]=M_+$.

ACuriousMind

@Bass: Ha! With the current commutation relations, the solution is $L_1 = -L_+$ and $L_{-1} = -L_-$. This gives $[L_+,L_-] = 2 L_z = 2 L_0 = [L_1,L_{-1}] = [-L_1,-L_{-1}]$ and $[L_0,L_\pm] = \pm L_\pm = \mp L_{\pm 1} = [L_0,L_{\pm 1}]$.

Wait

I hate signs. -.-

Bass

@ACuriousMind So $L_+=L_1+iL_2$?

ACuriousMind

@Bass Forget about $L_1,L_2,L_3$. The problem is purely about matching the $\mathfrak{sl}(2,\mathbb{C})$ algebra $L_+,L_-,L_z$ to my truncated Witt algebra $L_1,L_0,L_{-1}$. I'm not changing the definition of anything.

Bass

@ACuriousMind Well I don't know the definition of $\mathfrak{sl}(2,\mathbb C)$, except the one you get from the $L_i$. And I think you cannot get that right except if you define it as $L_\pm=iL_1\pm L_2$ instead of $L_\pm=L_1\pm iL_2$.

But I'm curious if you find another solution. Gotta go now. Thanks for your help!

user116211

15:53

@DanielSank: Session is about to begin....

David Z

Here's the tentative agenda as I have it:

1. Intro, welcome newcomers, introduce room owners, take policy questions (10m)
2. Recent physics developments (10m)
3. Homework policy replacement (10m)
4. Open discussion

any additions?

...time travel (-10m)...

John Rennie

@DavidZ closed timelike curves 10m, 20m, 30m, 40m ...

David Z

:-P

John Rennie

or I suppose that should really be:
closed timelike curves 10m, 10m, 10m, 10m ...

David Z

I think I found our open discussion topic of the day, lol

OK, anyway. Let's get started. Welcome to the chat session, everyone!

ramsay

16:01

how to link a site in comments

David Z

Here's the agenda for the hour:

1. Intro, welcome newcomers, introduce room owners, take policy questions (10m)
2. Recent physics developments (10m)
3. Homework policy replacement (10m)
4. Open discussion

Please keep the room clear of other discussions until the open discussion period.

First item of business: who's here?

Anyone new to chat, new to chat sessions, and/or new to the site?

:29118378 oh well I was just going to say the same :-P

user116211

@DavidZ ::waiting for 10 min::

David Z

Well, anyway. One thing to mention first, so that everyone knows, we have two new room owners: @JohnRennie and @ChrisWhite (who isn't here maybe)

4

John Rennie

:: takes a bow ::

2

David Z

:: holds up APPLAUSE sign ::

ArtOfCode

16:05

Cheers for stepping up, guys :)

Looking forward to working with you, 'cos no doubt I'll need to...

user116211

::congratulating John and Chris::

David Z

This was discussed on meta in this question, pinned on the sidebar. Basically, room owners are here to help defuse arguments, but also to help with things like pinning messages and clearing stars, providing access to people without enough rep, etc.

ArtOfCode

@DavidZ no can do on the last one... mod-only, last time I checked

David Z

@ArtOfCode oh really? OK, never mind. I thought I read that room owners could do it (and I remember being surprised to learn that)

ArtOfCode

@DavidZ Mods can definitely do it, room owners do have access controls but I don't think they can permit sub-20 rep users.

David Z

16:08

Well, they're here to do whatever they can do, at any rate.

Access restrictions are not relevant here.

ArtOfCode

aye aye

David Z

I suppose nobody has policy questions? If so we'll move on to recent physics developments.

ArtOfCode

The most effective room owner is basically a moderator - here to mediate and arbitrate when it's needed.

David Z

What's happened in physics in the past couple weeks?

ArtOfCode

bbc.co.uk/news/science-environment-36068599

Gravitational wave mission passes "sanity check"; BBC 2016-04-18

David Z

16:11

"GOAT" :-P

John Rennie

Isn't there an eLISA test flight in space at the moment?

I had an idea they've launched a mission with a pared down version of the position detector to check how well it performs.

David Z

I think I may have heard about that.

John Rennie

LISA Pathfinder

David Z

What's the relationship between GOAT and (e)LISA?

yuggib

(e)LISA is secretly a GOAT

AccidentalFourierTransform

16:14

John Rennie

I think eLISA is the mission i.e. the kit that will be floating around at the Legrange point, while GOAT is a committee set up to advise on strategy

cosmos.esa.int/web/goat

David Z

Ahh, that makes sense

Too many things needing acronyms

ArtOfCode

LISA = Laser Interferometer Space Antenna, i.e. the stuff they use to measure gravitational waves

David Z

Here's another interesting one: the WOW signal could be comets

John Rennie

it's a bit surprising there haven't been more detections at LIGO given how quickly they nabbed the first GW. Does anyone know what's going on there?

David Z

16:17

@JohnRennie I thought they were just going through their analysis pipeline on other events, but there have been a few more. That's just a rumor though. I don't have any official information.

John Rennie

>That's just a rumor though
Rumours? Do say more :-)

Martin

I guess they might not just announce each result separately now. And maybe they do even more checking - they can take their time now.

David Z

That's literally all I remember

It does make sense that they would kind of push through the first analysis at the expense of the others, to get a solid result out ASAP

That WOW signal thing has a Gofundme proposal, by the way

Martin

From the quantum computing side, if anybody is interested in policy making, there is an attempt to get 1bn € from the European Union qurope.eu/manifesto - not too new, but I came accross it on several channels recently.

David Z

(we can run a bit over time since the schedule is relatively empty today)

@Martin interesting, what for?

John Rennie

16:22

@Martin Just as long as they can get it through before 23rd June! :-)

Martin

@JohnRennie: It'll not all fall apart directly...

@DavidZ: Basically to get money and have a better coordination for research towards quantum technologies, in particular quantum networks, simulators and computers.

David Z

Cool, cool...

OK, maybe we move on to the homework policy replacement for now.

15

Q: Replacing the homework policy 1: what existing questions should be on/off topic?

TL;DR: post examples of current questions which are edge cases for the new policy, look through the list, and vote answers UP if you think they should be ON TOPIC vote answers DOWN if you think they should be OFF TOPIC When we last left the ongoing examination of our homework po...

All I really wanted to say about this was to remind everyone to go through and examine the links posted as answers, and vote on them accordingly.

If anyone has questions about interpretation, or anything, this is the time to ask them.

My plan is to give people a few more days to submit and vote, then start drafting a new policy later this week.

John Rennie

There seems to be a theme emerging that not enough effort is the thing that annoys most people.

Will there be a discussion at some point to weigh up the various factots involved?

David Z

@JohnRennie Yeah, I agree. But I'm trying to figure out things like, is it just not enough effort, or not enough effort in combination with being a simple question, or being a yes/no question, or so on?

@JohnRennie We could have that discussion now, if you want

John Rennie

Do you think you are getting enough feedback, based on the answers already present?

David Z

16:32

I think more is still better, but yes, the response has been pretty good, in terms of quantity

John Rennie

I'm not sure how use a discussion now would be as we seem fairly quiet at the moment. Unless anyone else wants to discuss it now?

David Z

I haven't looked that closely at the responses yet, but my preliminary impression is that people are voting on some basis other than simply whether questions show effort or not.

But this will become more clear after I take a closer look at the responses and do some analysis.

I think at the next chat session we'll have more to discus.

user116211

@DavidZ Yes, and they would get more time....

David Z

Yeah :-P Not that we have anything competing with it today, really...

user116211

@DavidZ: hmmm...newbies are coming now ;(

David Z

16:40

Anyway. Unless there's something in particular anyone would like to talk about with respect to the replacement policy, I'll just remind everyone to go read the answers and vote accordingly.

Then we can move on to open discussion.

@MAFIA36790 (welcome all!)

user116211

:)

user116211

@DavidZ Can anything be discussed? (sorry, I'm new to it ;P)

David Z

Yes, that's what "open discussion" means (though I suppose we would give priority to people who wanted to continue topics from earlier in the chat session)

John Rennie

I have a suggestion for a canonical Q/A, if it won't raise too many groans, but this time it's one I can't write myself.

yuggib

what is your opinion about mathematical rigour in physics departments (both at the research and teaching level)? It is my opinion (and a quite common opinion in the countries I have been to) that rigour in physics is declining, and is now almost exclusively found in mathematics departments

user116211

16:42

@DavidZ: Have you noticed there are two Physics Chat Session ends... ?

John Doe

Hi all

user116211

@DanielSank :))

yuggib

@JohnRennie i.e.?

DanielSank

@MAFIA36790 hi

David Z

@MAFIA36790 Yep, I know, it's because the event scheduling system is stupid

John Rennie

16:44

@yuggib we get questions over and over about vacuum fluctuations, but I've never seen a really good answer.

user116211

John Rennie

There is a suitable question here:

11

Q: Are vacuum fluctuations really happening all the time?

In popular physics articles and even some physics classes I've been to, the vacuum of space is described as being constantly full of quantum fluctuations. Supposedly, all sorts of particle-antiparticle pairs at all scales are constantly appearing and disappearing. We end up with a mental image ...

quantum-field-theory vacuum

ACuriousMind

@yuggib I have no idea about "declining" but rigour is often treated as something annoying rather than a goal in itself, in my experience

John Rennie

But I don't think it has any really thorough answers.

DanielSank

@DavidZ I would like to discuss this issue but the chat sessions are usually when I'm asleep

AccidentalFourierTransform

16:45

why have our ears not evolved to hear "gravitational waves"?

yuggib

@ACuriousMind by rigour I mean treating mathematical subjects with the proper mathematical precision

John Rennie

In an ideal world there would be a comprehensive answer that we could bookmark then direct people to every time the question comes up

user116211

@AccidentalFourierTransform good one.

Martin

@yuggib: I know a few mathematical physicists who complain that there are hardly any good mathematical physicists left on the physics side, so maybe you are right. On the other hand, at least in quantum information (since moslty people like to deal with finite dimensional stuff) rigour is still upholding on the physics side, too...

John Rennie

I'm being drowned out by rigour - bloody mathematicians :-)

David Z

16:46

@DanielSank I mean, you can do it now... or some other time when you are here, it just wouldn't be part of a chat session

DanielSank

Ok. I'll ping you this evening. But you're on China time, yes?

yuggib

@Martin yeah that's a common complaint...and limiting to finite dimensional systems is more a severe restriction than a preservation of mathematical precision in my opinion :-P

David Z

Yep

It's currently almost 1 AM local time

DanielSank

#globalnetworkproblems

ACuriousMind

@JohnRennie I think there is no "good answer". I have never seen anyone make precise what they mean by "vacuum fluctuations". It's a term that exists solely in handwaves and pop-sci.

yuggib

16:49

@JohnRennie But this type of paper used to be common and appreciated in physics, at least 60 years ago

ACuriousMind

Or rather, the few technical things I've seen called "vaccum fluctuations" don't merit all the fuzz

John Rennie

Arnold Neumaier's article here seems as good a description as I've read, but would want fleshing out for the less technical site members:

mat.univie.ac.at/~neum/physfaq/topics/vacfluc

yuggib

@JohnRennie @ACuriousMind I would probably rather make a canonical answer explaining what Feynman diagrams and perturbative calculations are, and especially are not

John Rennie

The point is that years of popular science programmes have left people with the impression that the vacuum is full of pairs of particles appearing and disappearing.

Everytime someone posts a question based on this misconception we say it's not like that but never go further than this.

Martin

@yuggib: There might be two problems at hand. First of all, during the first half of the 20th century, physics was rather dominated by Germany, the second by the USA From my experience, the level of mathematics required for a German physics degree usually exceeds the level required for an American one.

ACuriousMind

16:54

@JohnRennie But...he's taking as granted that "vacuum fluctuation" means "non-zero standard deviation". The question you linked specifically asks about the idea of particle-antiparticle pairs popping into existence. The two things are entirely unrelated, the latter comes from a too literal reading of Feynman diagrams, not from what Neumaier talks about.

I mean, he just says "it doesn't mean particles popping into existence", but the misconception itself and its origin aren't addressed there

Jiminion

@JohnRennie Then what is it like?

John Rennie

@Jiminion I kind of know, but not well enough to write a really good answer on it. You'd need someone better versed in QFT than me to do it justice.

yuggib

@Martin maybe; nevertheless it seems a common trend across countries (even the ones like France that have a very strong tradition in mathematics)

Martin

@yuggib: Yes, my claim would be that the strongest influence everyone.

John Rennie

@ACuriousMind but wouldn't that paper be a good starting point?

yuggib

16:57

@Martin I don't know about that; local trends are rather diehard

David Z

I wish I had time to do this one... but I don't (and I'm probably not the best person for it anyway)

Jiminion

@JohnRennie It can be frustrating to try to pick up this stuff because every "answer" tends to involve another set of terms and concepts that you'd never heard of before. :) (like Feymann and his magnets.)

ACuriousMind

@JohnRennie Well, but...it's really not like that. Like, not at all. It isn't a simple misconception about a particular part of the theory, it's simply not at all how quantum field theory works. I cannot think of an explanation I could possibly give that is not essentially a precise introduction to QFT, and that's definitely too long for an answer

Jiminion

@ACuriousMind What's a good intro. QFT book?

John Rennie

@ACuriousMind Damn. I can see I'm going to have to learn QFT :-)

ACuriousMind

16:59

@Jiminion No idea, never read one. I learned it in a course with these notes

David Z

@Jiminion Most people use Peskin and Schroeder these days

Jiminion

I think many things can be explained easily if sufficient time and effort is made to develop the teaching materials.

Woit has QM notes available as well.

Martin

@yuggib: Maybe, maybe not. On the other hand, maybe the hurdles become too high? I mean, your paper comes from a time where operator theory had barely developed yet and since it came out of physics, physicists kept up with it. Today, you have to go through Reed & Simon to understand the full rigour of mathematical physics...

DanielSank

@ACuriousMind you can measure vacuum fluctuations in a resistor.

John Rennie

@Jiminion that's simply not true. Some things require exorbitant sweating from the student, no matter how well taught they are.

QFT is notorious for this. The reason we don't all understand QFT is because it's bloody hard!

ACuriousMind

17:02

@DanielSank So...what do you mean by that?

Jiminion

@JohnRennie So string theory will always take 10 years of hard math crunching to understand? I'm not so sure. (Sometimes I think that isn't learning so much as indoctrination.)

John Rennie

@Jiminion basically yes. well, you say 10 years, but I suspect I could study it for the remainder of my natural life without making much headway :-)

David Z

Oh, and that's it for the chat session. Feel free to keep talking, and remember to vote on those answers. See everyone for the next one in two weeks!

DanielSank

@ACuriousMind if you cool a resistor to millikelvin temperature and then measure is voltage you find fluctuations in said voltage which exceed that predicted by the thermal prediction.

John Rennie

@Jiminion the problem is that you have to master a lot of maths to understand something like string theory. That's layers and layers of maths, and you have to thoroughly understand each layer before starting on the next one.

ACuriousMind

17:05

@DanielSank Okay. So, for you, "vacuum fluctuation" means what Neumaier is talking about, that the standard deviation of some observable isn't zero in the vacuum state

DanielSank

There's a term in the spectral density of voltage fluctuations which is basically hbar omega / 2.

@ACuriousMind more or less.

It also refers to nonzero amplitude for particles, but I think these are actually the same thing

Jiminion

@JohnRennie And if after 10 years, you think its bollocks, then you are stuck. You've wasted all that time.

yuggib

@Martin yeah, but there are still so many physics-related questions without a satisfactory mathematical answer

and it seems to me that people now do not even know

DanielSank

Back in a bit

John Rennie

@Jiminion but you had fun along the way, and most of us do physics mainly because it's fun

Martin

17:11

@yuggib: That is probably true. One problem here could be that only a very limited number of topics is really known in a given community at a given time. It always seems to me that so much knowledge is just burried now that was available maybe 30 years ago.

Jiminion

@JohnRennie I thought most grad students did Physics for post-docs and then assist. Prof. and then tenured Prof.

Martin

When mathematicians and physicists don't really talk to each other anymore, both sides will lose sight of interesting problems relevant to their field, but at its periphery from the current point of interest.

John Rennie

@Jiminion that describes what they do, not why they do it. The why they do it is because it's fun.

Trust me, no-one studies theoretical physics for the sex, drugs and money.

6

yuggib

@Martin That is indeed true, and I make often use in my research of extremely old papers where there are results that people nowadays ignore.

Jiminion

Does QFT assume continuous space? (seems to...)

yuggib

17:18

@Jiminion why?

there is plenty of QFT on a lattice

it's much easier

... well maybe not so much easier, but easier

Martin

@yuggib: Yes. The problem is often to find these results - and it gets worse the less mathematics you know. I always dream of a mathematics search engine where I can just enter what assumptions I want to make and how the result should look like and they will search it...

yuggib

@Martin :-D

that would leave a lot of people without topics I am afraid

DanielSank

@JohnRennie money, no. Sex and drugs...

John Rennie

... no. :-)

Martin

@yuggib: you mean, because they don't have to reinvent the wheel anymore? Maybe, but then they could do more interesting stuff instead - and by "they" I wouldn't necessarily exclude myself...

user54412

17:24

@ArtOfCode The interface seems to say I can permit it, and I think I've seen it done by non-mod owners.

yuggib

@Martin more or less yes, and also because many results are just a $\varepsilon$-modification of existing ones, that if someone really scans in the literature may even be included in some previous work

but I agree that it would be a very useful tool

user54412

@DavidZ A nice expensive x-ray satellite blew up shortly after launch... or were you looking for good news?

Martin

@yuggib: Ah, yes, of course - very true... The question is, whether current technology and advances in machine learning could not provide such a machine in the near future. I always wanted to discuss this with somebody maybe at Google or Wolfram...

John Rennie

@ChrisWhite I'd also concluded that the room access controls seem to give me the option of adding any user, though I haven't tried it on a low rep account. Maybe we should set up a test account to try it.

user54412

@JohnRennie Maybe you should just abandon that account and start over at 1 rep. Level the playing field and all ;)

user54412

17:33

@DanielSank The Hungarian in me will fight your turmeric with home-grown paprika.

Hari Prasad

@ChrisWhite organic?

user54412

I don't know what that means really. My paprika isn't made of nanobots, if that's what you're asking.

Jiminion

@Martin If such a machine was developed at Wolfram, it would be "a new branch of science". :)

2

Hari Prasad

@ChrisWhite Organic means not using chemicals i.e growing paprika using natural substances

ArtOfCode

@ChrisWhite shrug I couldn't back last year when I was a non-mod RO, but it might have changed.

user54412

17:37

@HariPrasad All chemicals are natural :)

user54412

Besides, "unnatural" things like the Haber process are the only reason the Earth can feed billions of people.

Hari Prasad

@ChrisWhite I didn't mean to say about chemicals from Andromeda. :D

DanielSank

17:52

@ChrisWhite Hmmm. I think turmeric wins.

hubot

Hello!

vzn

@Martin very interested in "automated thm proving" & have collected a lot of material on that subj, looking to push boundaries etc... so far AI has not had much affect on mathematics but maybe we are right on the cusp of a chg there... the recent AlphaGo breakthru is reason for optimism

hubot

I'm actually working on C++

I'm going to work on Java and C#

soon

I had lower secondary exams

vzn

@JohnRennie @DavidZ have heard you mention admitting sub-20 rep users into chat, but does this happen much? maybe you could describe a scenario/ example. how would they request it? on their Q/A? can they comment on their own posts? etc

yuggib

@Martin Ask @DanielSank ;-)

Hari Prasad

17:54

@hubot Are you a StackExchange bot?

hubot

No, I'm not bot

vzn

quite a lively chat session today! sorry missed it :(

yuggib

@hubot saying you're not a bot is the first evidence you are :-P

John Rennie

@vzn occasionally I see an answer from a new user that isn't really answerable because it's too confused or too broad, but it's an interesting topic and I think I'd like to discuss it with them in the chat. However the new user will have a very low rep and that bars them from the chat.

In such circumstances I would consider adding them to the room if they want to continue the discussion.

Martin

@vzn: I believe that automated theorem proving in realms where humans excel is quite some time away - but I consider a search engine a step into this direction, yes.

vzn

17:57

@JohnRennie ok. but anecdotally it seems uncommon that new users are willing to enter chat. do like to invite users into chat myself (CS areas/ chat rooms) & occasionally run into the sub-20 rep problem. think its a great idea to try to bring in the "energetic" ones.

John Rennie

@vzn I agree it's not likely to happen very often, but it's nice to have the option.

Martin

@yuggib: Yes, but I guess it's the wrong branch of Google. Search or the alphaGo people would be better suited - although his boss does give talks about "Quantum Machine Learning" and that is an active area of research (not sure what to think about it though).

vzn

@Martin thx for that ref (re "EU QM manifesto") it looks neat/ significant! reminds me of the markram $1B (EU) initiative for brain research which unf is controversial/ challenged/ criticized etc. ... presumably the QM initiative will have much more consensus.

re math vs physics topic... there is some shearing going on. some physics theories have gotten ("grown") extremely abstract and have broken away from physics + "verification"...

Obliv

@BernardMeurer hey do you know much about functional programming?

vzn

@Martin Gowers has a neat paper on this & has done some research in the area, recommend looking at it. he describes a "sci fi" like scenario in one paper. but presumably decades away unless there is some unexpected breakthru. (but AlphaGo was an unexpected breakthru.) =D

Martin

18:03

@vzn: Yes, the EU brain research flagship is indeed a precursor of this.

vzn

@Martin do you know if the $1B brain grant was finalized? had not heard much more on that. actually agree with some of the criticisms of it having problematic aspects. are you in US or EU?

Martin

@vzn: Yes, I think it was. I'm in the EU by the way.

vzn

@Martin which country? US here

Martin

Germany

@vzn

vzn

australia seems to have good state/govt-sponsored crypto initiatives also, now bearing some fruit.

skimming the QM manifesto. re recent comment AI + QM field, it says leading to "new paradigms in machine learning and artificial intelligence." (p7)

Martin

18:08

I think so. I'm interested to see how it goes in the future. The Quantum Manifesto at least is backed (as one of the authors) by one of the leading scientists in QI and certain branches of Condensed Matter and he is very well connected in general, so there might be a good chance.

vzn

...p7 reference to "disruptive technology". has some of the flavor of silicon-valley-speak...

Martin

@vzn: Yes, I believe it says so. Quantum machine learning, etc. is a hot topic at the moment. I've seen talks titled "Quantum AI" and so on, but usually, they don't have anything new just yet. The technology is not nearly developed yet.

Hari Prasad

@0celo7 you are back!

Martin

There are many buzzwords in there. That's not uncommon to get grants, though, is it...

I wish it were different, though.

vzn

@Martin havent heard much about QM + ML + AI myself yet despite tracking all these fields very closely, but wouldnt rule it out either...

@Martin certainly (already) many top endorsers, which one are you referring to?

Slereah

18:14

There's nothing specific of AI in quantum computing

vzn

anyway the proposal is great and would expect other countries to definitely notice it hopefully at some point, hopefully US also. reminds me somewhat of sputnik, which was quite legendary in spurring our country.

Slereah

A quantum computer is equivalent to a classical Turing machine

Martin

@vzn: No, I mean Cirac, who is one of the authors of the proposal according to the main site.

Hari Prasad

@Slereah How come that's possible?

vzn

agreed most of this is more in a speculative realm, but generally ML+AI increasingly requires big data, and "big cpu", and QM computers are aimed at that, and there may be more specific areas of benefits eg simultaneous/ concurrent search of large search spaces, database related improvements, etc

Slereah

18:16

@HariPrasad Just do a computer algorithm that does the calculation for every possible combination of states after measurements

Martin

Yes, I do see where QC could be interesting, but the experimenters have to catch up first...

Slereah

It is slower but equivalent

Hari Prasad

@Slereah No! Both have different purposes and build.

Slereah

Well yes, but my point is that any algorithm made in one can be made on the other

Of course computation speed is different

vzn

@Martin btw who "gives talks about QM ML"?

ACuriousMind

18:19

@Slereah Neither a classical nor a quantum computer is equivalent to a Turing machine, strictly speaking (the tape isn't infinite) :P

vzn

@HariPrasad QC is still mostly in the scifi realm...

Hari Prasad

@Slereah Its not just the computation speed. Both are made for different purposes and by different architecture(both software and hardware). But you can use a quantum computer as a Turing machine and not the other way.

Slereah

@ACuriousMind Well I didn't say that I was talking about a physical quantum computer :p

Hari Prasad

@vzn NOt really

Slereah

@HariPrasad Doesn't matter

Mathematically speaking they both have the same class of algorithms

Hari Prasad

18:21

@Slereah Unless you can play Call of Duty on a Quantum computer. :D

Martin

@vzn: Hartmut Neven from Google for instance. Probably Seth Lloyd. The guys in the references here: en.wikipedia.org/wiki/Quantum_machine_learning

Slereah

Sure you can

Hari Prasad

@Slereah lol yeah

Slereah

I mean not currently obviously

Since current existing ones have like 1000 bits

But a theoretical quantum computer, fine

Hari Prasad

@Slereah There is not much theoretical use of quantum computers. What we need is a real one.

vzn

18:23

@Slereah dwave? their ("adiabatic") qubits are much different than "std" qubits... and also nobody is anywhere near their qubit count. (google/ martinis lab, other world leader, measures about ~5 max so far... hi DS!)

Slereah

Not a clue

Hari Prasad

@vzn Yes because, there are different ways to make physical qubits

Slereah

5 or 1000 doesn't matter too much to play DOOM on it, really

vzn

@Martin, reminds me, do you ever read aaronson? a usually fun blog... he has some very "colorful" QM/QC presentations/ powerpoints

Hari Prasad

@Slereah Doom will struggle to run since there is not such environment there.

Slereah

18:26

I have read a paper on quantum programming language

It was

QUANTUM C

Basically it's just C with some extra bitwise operations

Hari Prasad

@vzn scottaaronson.com

vzn

proposal p15. QC "Based on quantum bits that can be zero and one at the same time..." lol aaronson mentioned that as a faux pas in his latest blog scottaaronson.com/blog/?p=2694

Hari Prasad

@Slereah Sam, Is it still snowing in your area?

Slereah

It's april

So no

Hari Prasad

wow almost 4 people left the chatroom at the same time!

Bernard Meurer

18:41

@Obliv Hey

@Obliv github.com/bemeurer/euler-function

And no, I barely know anything about functional, why?

Obliv

my earbuds are on like full volume and you actually blew out my eardrums. thanks

Hari Prasad

@JohnDuffield Do you think firewalls actually exist?

Martin

@vzn: Yes, I do read his blog. It's mostly very nice - I agree.

John Duffield

@skillpatrol : what sudden change? There's always been bullies dishing abuse. They just have more ways to do it these days. By the way, looking at what vzn was saying, here's an example. I hate that sort of stuff.

Hari Prasad

@BernardMeurer Not bad!

Obliv

18:45

@BernardMeurer for whatever reason my textbook is actually asking me to write a computer program finding the g.c.d of two integers and the linear combination $ax + by = (a,b)$. The solutionbook I referred to used haskell which is a functional programming language. It seemed unfair how easy it was for him when I have to use java ;_;

I'm thinking of just skipping this exercise for now :x

John Duffield

@HariPrasad : yes, but not the way they're usually described. See this answer.

Hari Prasad

@JohnDuffield hum... I don't read such long answers. It hurts. So can you please explain me in short?

Bernard Meurer

@Obliv Do you have to write a GCD algo? Those are a pain in the butt

John Duffield

@HariPrasad : sorry, no. Ask David Z why not.

Bernard Meurer

@Obliv stackoverflow.com/questions/4009198/…

As long as you don't need binary GCD

user54412

18:57

@BernardMeurer only in arbitrary precision :p

Bernard Meurer

@ChrisWhite Everything is horrible in arbitrary precision, that's what's so great about it!

:D

I have the precision fever

if it breaks on 2000 decimal places it's not worth a dime

Bernard Meurer

19:11

@ChrisWhite Did you ever implement Baillie-PSW?

kevin Tah N.

@vzn I am in fact interested in mathematics research. What sort of topics are you working on?

@barrycarter your game idea is quite interesting. I have developed an adventure game, with some character running around jumping fighting etc. I am trying to put some game AI in it and then a few other things. I might also modify the game physics etc. I am writing this game in C#. I will take a look at your game today.

Obliv

19:32

@BernardMeurer Wait, why is it a pain in the butt? Isn't it just the euclidean algorithm done recursively?

Bernard Meurer

@Obliv Because arbitrary precision

Obliv

oh. I'm a common plebian in programming so I don't have to worry about that :p

Bernard Meurer

It's more fun when you have to rewrite everything ::cries blood::

Obliv

lolol

Yeah I imagine it gets significantly more complicated when you account for precision..

hey btw @BernardMeurer whats the difference between rem and mod? Don't they both return remainders

Bernard Meurer

rem is integer remainder, satisfying: (x quot y)*y + (x rem y) == x

mod is integer modulus, satisfying: (x div y)*y + (x mod y) == x

rem(5, -3) = 2
mod(5, -3) = -1
rem(-5, 3) = -2
mod(-5, 3) = 1

vzn

20:05

@Martin more qm cpu news from reddit re australia

Quantum computing closer as RMIT drives towards first quantum data bus / escience news

Obliv

nvm

Bernard Meurer

@Obliv Did you get it?

Obliv

the rem vs mod thing?

@BernardMeurer what does x quot y return as opposed to x div y?

Bernard Meurer

@Obliv stackoverflow.com/questions/8111120/…

Obliv

20:21

oh wait.. I didn't know that was a haskell-specific question. For some reason i just assumed it would be something in other languages..

DanielSank

@Martin Yo.

Bernard Meurer

@Obliv Some have those operators, some don't

Obliv

oh ok

Bernard Meurer

Hey Dan

DanielSank

20:35

@BernardMeurer sup?

Bernard Meurer

Not much, trying to buy some pecan pralines; you?

DanielSank

@BernardMeurer Weirdly, I drank a praline soda yesterday.

It was good, but too sweet.

Bernard Meurer

Praline soda? Not on my wildest dreams I thought that'd be a thing

I'm addicted to pecan pralines, and apparently so is my soon-to-be lady

DanielSank

@BernardMeurer Rule 43 applies to soda.

Bernard Meurer

Rule 43?

DanielSank

20:39

Use the internet, grasshopper.

Bernard Meurer

Ah, I see

This one?

DanielSank

That's the one.

Bernard Meurer

Hmm, I might try it; it looks tasty

Oh, and I think I'll be going to UCSD

Unless GA Tech accepts me from their waitlist (unlikely)

knzhou

20:52

I need the running of the strong coupling constant for a computational task -- the PDG just lists it at one energy scale, and I don't want to integrate the beta function by hand.

Is there a standard reference for this?

Bernard Meurer

I didn't understand what you need

@Obliv

FenderLesPaul

21:58

@ChrisWhite yeah they did that with the theory floor in the physics building too

except they have blackboards and offices

but the blackboards are all in an open space

and it's really loud because everyone is out there

idk why they thought that would be a good idea

Bernard Meurer

23:18

@FenderLesPaul Why people use blackboards and not whiteboards?

ACuriousMind

Physicists tend to be old-fashioned and like blackboards more

Bernard Meurer

The chalk hurts me eyes

Does that mean I can never be a physicist? :O

barrycarter

23:54

@kevinTahN. Thanks. Contact me via google chat [email protected] - - I'm trying to avoid this chat since it's a major timesuck :\

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