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4:00 PM
@JohnRennie also, when they do speak intelligible English, they're as likely as Englishmen to say 'taking the piss', if not more
 
Irish (Gaeilge), also referred to as Gaelic or Irish Gaelic, is a Goidelic language of the Indo-European language family originating in Ireland and historically spoken by the Irish people. Irish is spoken as a first language by a small minority of Irish people, and as a second language by a rather larger group of non-native speakers. Irish enjoys constitutional status as the national and first official language of the Republic of Ireland, and is an officially recognised minority language in Northern Ireland. It is also among the official languages of the European Union. The public body Foras na...
 
@BalarkaSen I just googled it and no shit, that definitely sounds disturbing.
 
> spoken as a first language by a small minority of Irish people
 
Right?
 
is that related to piss off?
 
4:01 PM
> A couple moves to an old house to find the man's brother and the wife's former lover who has turned into an ugly beast. He now bids the woman to bring him human sacrifices to help him be whole again.
Brr
 
@JohnRennie =P
 
@skillpatrol I don't think so ...
 
@skillpatrol (only) in that they both contain the word 'piss'
 
I see.
 
@Kaumudi.H videodrome?
 
4:02 PM
The most disturbing crap that I watched recently is a gameplay of "Layers of Fear". That game, Jesus Christ.
 
with Debbie Harry?
 
Nah, it's Hellraiser
 
I didn't watch the movie but I read the Clive Barker book. The first scene in the movie is that a man gets ripped apart by hooked chains when he unlocks a portal to some kind of hedonist heaven
 
Ah the Clive Barker story
 
4:03 PM
@Kaumudi.H Actually, that sounds like par for the course for a horror movie to me
Not that I like horror as such much, but it doesn't sound exceptionally disturbing
 
This:
Turns into this:
 
Why is the woman in the first picture stroking a ferret?
 
The Texas Chainsaw Massacre now that is horror...
 
@JohnRennie No. Clue.
 
4:06 PM
@JohnRennie Because it's plushy?
@Kaumudi.H I have to say, that looks...ridiculous :P
 
@ACuriousMind I don't like horror either but the messages in these movies are exceptionally great, and the ideas are fascinating
 
@ACuriousMind It's disturbing af in the game.
Layers of Fear is a psychological horror video game developed and published by Bloober Team for Linux, Microsoft Windows, OS X, PlayStation 4 and Xbox One, which released worldwide on 16 February 2016. In Layers of Fear, the player controls a psychologically disturbed painter trying to complete his magnum opus, as he navigates through a Victorian mansion, with disturbing secrets about the painter being discovered. The gameplay, presented in first person perspective, is heavily story driven and revolves mostly around puzzle-solving and exploration, as the game intensifies after each level while...
 
If you want something non-horror by Cronenberg I recommend "Naked Lunch". Great film, totally weird, absolutely like nothing else
 
plushy adjective - made of or resembling plush; soft to the touch.
A ferret?
 
Time to use the old noodle
 
4:08 PM
@BalarkaSen Movie buff, are we?
 
@EmilioPisanty I have to compute the Jordan measure of Cantor sets. Woo...
 
Cronenberg, totally weird. Really? :-)
 
@JohnRennie I dunno, the ferret in the picture looks plushy to me
 
me too
 
I mean it seems very much so that the field is the basis for the algebra
 
4:09 PM
@0celo7 hohohohohoho
 
On the other hand
No $\pi$
 
good practice, though
 
So I dunno
 
@Slereah You do realize that $[\phi(f),\phi(f')]$ is well-defined
 
@JohnRennie Thought u don't watch movies! :-|
 
4:09 PM
Or do you have first-hand experience stroking ferrets so you can say they aren't plushy?
 
outer measure should be easy, right?
 
@0celo7 Yes
 
@EmilioPisanty No, inner measure is trivially zero
Outer measure -- who knows
 
@ACuriousMind plush in the sense of rich?
 
I guess if there's only $\phi$ and no $\pi$ involved, that's probably well defined?
 
4:10 PM
I suspect the Jordan measure of the usual Cantor set is zero
 
But on the other hand
 
But something strange happens when you modify the parameter
 
@Kaumudi.H I actively try to get myself exposed to pieces of art. I wouldn't classify myself as a movie buff, but I have watched some, yes. I like visually stunning stuff
 
WHY IS $\pi$ NOT DEFINED
 
@ACuriousMind yes, ferrets were used for hunting when I were a lad. They are basically semi-domestiated weasels.
 
4:10 PM
The field momentum seems like a pretty important thing to leave out
 
I've handled ferrets many times.
And been bitten by them.
 
Aaaargh
 
the greeks defined it :P
 
@Slereah Yes, that's what I said at the time :-)
 
the Greeks are a meme civilization
 
4:12 PM
@Slereah If you don't have a Lagrangian you don't have a field momentum.
 
^ get rekt
 
@JohnRennie I see
 
Don't you need a field momentum to define...
the momentum
That sounds mildly important in a QFT
 
momentum of what?
 
I defer to your superior ferret experience, then
 
4:12 PM
the momentum depends on your field theory
 
The state
 
@JohnRennie hunting what?
 
@ACuriousMind google the bursting cancer scene (from Videodrome) if you've got the guts
 
My field theory is Klein Gordon
 
@skillpatrol Rabbits, rats, anything small.
 
4:13 PM
@Slereah not if you''ve got $a$ and $a^\dagger$.
 
But $a$ and $a^\dagger$ sound even worsely defined!
and if you have those you can define $\pi$ anyway
 
Also, if you demand that your space of states carry a unitary rep of the Poincaré group a priori, as I think most axioms do, you don't need to "define" the momentum at all.
 
maybe
 
It's already part of the given data
 
@Kaumudi.H I watched Videodrome because it had Debbie Harry in it :-)
 
4:15 PM
Well, at least I maybe know why it defines an algebra, at least
(maybe)
 
@EmilioPisanty For the Cantor set, you remove open middle thirds. So you're left with closed intervals of length $(2/3)^n$ in each step.
 
I suppose the field operator by itself suffice to define n-point correlation functions
 
So just pick $n$ large enough so that $(2/3)^n<\epsilon$.
 
Which seems to be what axiomatic QFT people love
 
What are we doing with Cantor sets
 
4:16 PM
@JohnRennie gentlemen prefer :-)
 
So the measure is zero for the usual cantor set. Now what happens if we modify it...
@BalarkaSen Jordan measure
 
Also i guess that they have derivatives of the operators defined
So you can define the momentum thusly
 
@rob Oh my god, Spanier just said the Carnegie hall thing...
 
It's just 0 right
 
4:18 PM
@BalarkaSen Yeah. But I just realized the problem is to compute $c([0,1]-C)$
 
@Slereah $\pi =\dfrac cd$ which pi are you talking?
 
The quantification of the canonical momentum
 
The outer measure is no larger than $1$.
Clearly :P
 
Sure
 
4:20 PM
Maybe I should not do this during a physics lecture. Bai
 
k see ya
 
rob
@0celo7 Good plan.
 
Hm
Maybe
 
@rob do you know why Chris White deleted his account?
 
Maybe that's why they include the propagator in the definition of the field
 
rob
4:28 PM
@skillpatrol I have untrustworthy second-hand information. I wasn't a mod at the time. I'd prefer not to speculate.
 
They can't use the momentum to define it and remain an algebra
 
@rob ok, thanks anyway.
 
Aha! It's an ermine not a ferret (though they are closely related).
 
Perhaps that's why there's no QFT axiom system from the lagrangian
Well outside of path integral ones
 
Nice work Sherlock :-)
 
4:31 PM
Then you run into weird distribution products
@ACuriousMind does this sound reasonable
 
there is some penis joke in this ^ answer
 
@AccidentalFourierTransform Only if you go looking for it :P
 
0
Q: Am I right here?

faheemahmed400In Maxwell's treatise he discusses addition law of current elements as follows: ]2 My interpretation of this is: At a distance sufficiently great w.r.t. the size of small sinuosites, a straight wire is equivalent to sinous wire. Am I right?

oh what a great title
YES YOU ARE RIGHT HERE, WITH US
@ACuriousMind is that yet another penis joke?
 
@AccidentalFourierTransform huh?
Quote please
 
> The deeper we go, the smaller it becomes
 
4:35 PM
is the lecture over?
 
My mind is very innocent, thank you
@skillpatrol no
@ACuriousMind oh, the reason I was telling you about the woman is because it reminded me of Miranda
Close-ups on jiggling...elements
 
@skillpatrol why the face?
 
you said your mind is very innocent
 
Alright, I think I've got at least a grip on why AQFT works
Phew
 
4:41 PM
@skillpatrol yes, it is
 
@Slereah but does it?
(sincere question)
 
Well
 
I was suspended the other day for talking about topology
 
I think it's probably a theory that's a bit
Small
 
Apparently there was an immoral double meaning
:(
 
4:42 PM
I'm guessing things become less nice when you try to use non-linear theories or define operators more complex than products of the field operator
 
@0celo7 Ah, is the camera placement similarly terrible? Miranda's fault was not only the fanservice as such, but also the infamous camera that managed to rarely show her face in conversation :P
 
apparently
 
@ACuriousMind The camera will be in the middle of her elements while they are jiggling.
Like, they will cover the lower part of the screen
 
Euclids Elements :P
 
...what kind of euphemism is "elements"? :P Anyway, I see.
 
4:43 PM
Hi Ramanujan
 
..hello, John Rennie
 
@ACuriousMind I'm a mathematician
And apparently balls is not allowed :P
Also it would be confusing...
 
@ John Rennie, so what about it?
 
@Ramanujan you know that Newton's first law tells us that if no force is applied an object moves in a straight line?
 
@JohnRennie or a geodesic if you're on a constraint surface
 
4:45 PM
@0celo7 ssh
 
'course I guess I have to show that the product of two field operators makes sense, but that sounds reasonably easy
 
Yeah.. I know the newton's laws of motion
 
0celo wants to do euclidean geometry using riemannian geometry
 
Again, not so trivial.
 
isn't it
 
4:46 PM
@Ramanujan Exactly the same is true in general relativity, but in GR the definition of a straight line is a bit weirder. The GR version of a straight line is called a geodesic.
 
Isn't it just the canonical metric on $R^n$
 
The fifth postulate requires some tricky calculus of variations
 
o that
Also are you aware
There are more than five postulates
 
nobody cares, @0celo7
 
Now, one could cheat and just do analytic geometry.
 
4:47 PM
@ John Rennie, isn't there any simple definition?
 
But coordinates are cheating
 
but @0celo7
 
@BalarkaSen that's fine, I don't do math for other people to care
 
can't you use a coordinate patch
Which, in flat $R^n$
Is the whole manifold
 
You can, but that's cheating.
 
4:48 PM
@Ramanujan the simple definition is that a geodesic is the line followed by an object that has no force acting on it i.e. whose proper acceleration is zero.
 
You need to use Jacobi fields and stuff
 
@Ramanujan The astronauts in the International Space Station are following a geodesic, which is why they are weightless i.e. they experience no force acting on them.
 
@ John Rennie, is it same as zero reaction force?
 
@0celo7 too bad
 
@Ramanujan I'm not sure what reaction force means.
 
4:51 PM
@ John Rennie, both the action and reaction force being equal and opposite
 
can anyone help me simplify these badboys? physics.stackexchange.com/questions/312340/…
 
@Ramanujan In geodesic motion there is no force acting on the astronaut at all. Not a reaction force and not any force.
@takashi Hmm, posting homework then drawing a moderator's attention to it isn't the greatest stragey ...
 
Oh oh. And @JohnRennie how much energy does the sun radiates in a second? Is it 27*10^23 or 2.7*10^23?
 
The solar luminosity, L☉, is a unit of radiant flux (power emitted in the form of photons) conventionally used by astronomers to measure the luminosity of stars. It is defined in terms of the Sun's output. One solar luminosity is 7026382800000000000♠3.828×1026 W. This does not include the solar neutrino luminosity, which would add 0.023 L☉. The Sun is a weakly variable star, and its luminosity therefore fluctuates. The major fluctuation is the eleven-year solar cycle (sunspot cycle) that causes a periodic variation of about ±0.1%. Other variations over the last 200–300 years are thought to be much...
 
@JohnRennie so what?
 
4:58 PM
@Ramanujan $3.828 \times 10^{26}$ W according to that article.
 
W stands for watt @JohnRennie
 
@Ramanujan Correct i.e. joules per second
 
@Qmechanic @dmckee @DavidZ @rob @ACuriousMind: chat.stackexchange.com/transcript/message/35457673#35457673
 
Ohh..
@JohnRennie, Are you a PhD holder?
 
5:00 PM
@DanielSank I gave up debating the homework policy in favour of hammering nails into my kneecaps because it was less painful and more productive.
10
 
@JohnRennie Well we're different people, aren't we?
 
are you? ARE YOU?
 
I value clarity and utility for new users a lot and the homework policy runs contrary to that. I will not give this up until the situation is improved.
 
@DanielSank yes, I'm now a person with perforated kneecaps.
 
5:01 PM
CHEMISTRY?
 
@JohnRennie What?
 
@YashasSamaga Physical chemistry!
 
yea, even worse.
 
just kidding :P
 
5:02 PM
But yes, you're correct, I am basically an imposter.
Gadzooks, I am unmasked!
 
What's a gadzook?
@JohnRennie Here's what happened with the homework policy as I see it:
 
Apparently JFK used the expression. Well, well, you live and learn.
 
i have a question mr @JohnRennie the phd holder. why do objects appear to get smaller when move away from them.
 
Gadzooks that is, not homework policy
 
5:05 PM
 
I have a question mr @JohnRennie the phd holder. Who is the handsome gentleman in your avatar?
 
@takashi Your eye/brain judges size by the angle subtended, and the angle subtended decreases as an object gets farther away. I'm sure there's a question on the site that discusses exactly this.
 
What have I started?!
 
5:06 PM
1) Many discussions were had in which folks talked about changing the spirit of the policy, i.e. they talked about what posts should and should not be considered on topic.
2) Zero progress was made.
3) I made a post suggesting changing the wording of the written rules to remove self-contradictions and improve clarity.
4) That post was upvoted.
5) Others decided this simple solution wasn't complicated enough and made a series of meta posts going back to asking what posts should and should not be on topic.
I'll note that in step #5, the associated meta posts didn't actually ask any questions! However, users still posted answers essentially giving their own thoughts on the homework policy, thus again steering us away from focused effort to actually improve anything.
 
i know that part. and i looked it up on the site but none of them answer why does the brain judge the size of an object by the angle subtended?
but seriously about my question which was classified as homework. those photos where visulizations for clarifying my question. how does wires without resistors affect the overall resistance of the circuit.
 
@takashi No idea. That's not a physics question, that's down to brain chemistry. Though my guess is that early humans who couldn't judge distance away got eat by sabre toothed tigers and failed to reproduce.
 
ok thanks for the help.
 
Because how else do you want to judge the distance
There isn't a lot of visual information you can use to judge a distance
You have to make some assumption about the shape and size of the object
 
@takashi wires are normally treated as having zero resitance so you can change their length without affecting the circuit.
 
5:11 PM
there are two eyes so that we can judge the depth
 
@DanielSank I'd be fine with implementing the changes outlined in your post immediately, except for the tag name. However, people might have voted on the general idea in the answer and not the specific wording therein. How about a new meta post about the specific wording of the new close reason, which we'll feature, and set a deadline by which the highest voted new wording will be implemented, barring unforeseen serious objections?
 
@YashasSamaga that only works for near objects.
Beyond a certain distance (that I can't remember) the parallax is too small to be detectable.
 
@JohnRennie ok that was what i was looking for. i am kind of new to this website so sorry if i caused any trouble.
i am just trying to get along
 
@JohnRennie, what is parallax angle?
 
We'd also need to draft a new FAQ post the close reason can link to, which strikes me as the more difficult issue
 
5:12 PM
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek word παράλλαξις (parallaxis), meaning "alternation". Due to foreshortening, nearby objects have a larger parallax than more distant objects when observed from different positions, so parallax can be used to determine distances. Astronomers use the principle of parallax to measure distances to the closer stars. Here, the term "parallax" is the semi-angle o...
Basically your left and right eye see objects from slightly different angles. The brain can detect this difference and uses it to determine the distance.
But for distant objects the difference in the angle between the left and right eye is very small, and the difference is too small for the brain to detect.
 
@ACuriousMind Very good. I will put this on my evening todo list.
Thanks.
 
ok i get a new one. are there any models which explain how wobbling plates work.
 
todo list updated.
 
and for very distant objects the angular distance is not the same as the luminosity distance, because of the FLRW shit
 
@ACuriousMind That will take work but I don't anticipate unusual difficulty.
@JohnRennie see that? Progress.
 
5:17 PM
@DanielSank The difficulty in question is: "Who's gonna do it?" ;P
 
Take the nails outta your knees.
@ACuriousMind How do you feel about a shared Google Drive document on which we and others can make comments and additions for a while before posting to meta?
 
@DanielSank good idea
 
@DanielSank there is a sandbox for that somewhere?
 
@DanielSank That's nice iff you actually have more than one or two people interested in contributing
 
5:18 PM
@AccidentalFourierTransform stackedit.io is a good place
writing a consistent set of docs on a homework policy is remarkably difficult
 
@ACuriousMind Build it and they will come.
 
@AccidentalFourierTransform If you mean the meta sandbox post, every edit still bumps it, so that's no good
 
and there's at least seven different pieces of text that need to be addressed
 
@EmilioPisanty Seven?!
No way.
 
@ACuriousMind so set up an open stackedit.io
 
5:20 PM
@EmilioPisanty Yes, I have nothing against that
 
@DanielSank I've reread your meta post and it seems fine to me.
 
@DanielSank sorry, six
 
I am reading about 3DOODLER. 3D pen.
 
everything listed on this thread.
 
@EmilioPisanty Only one of those looks 'hard' to me.
Useful link, thanks.
 
5:23 PM
@DanielSank it depends on how radical a change you want to make
 
remember he's got 8 arms :P
 
that proposal was a "ban homework but keep the tag" thing which was ridiculously hard to make consistent
 
@EmilioPisanty I'll look through it this evening
For my part, the goal is to produce something self-consistent.
 
See also additional thoughts here.
 
...and remove the word "homework" wherever possible.
 
5:25 PM
@DanielSank so what happens to the tag?
stays on as it is?
 
@EmilioPisanty I don't know.
 
what happens to its tag wiki and tag wiki excerpt?
 
I personally think that if it's easy to change a tag, we should change it.
@EmilioPisanty That's the same question asked three times.
 
because that's the main interface between your policy and some newbie coming in with a homework question
@DanielSank not really, because the three components (the tag's name, the tag wiki, and the excerpt) have different functions and come into play at different times
 
@EmilioPisanty I would say the main interface is the message that shows up when a question is closed. That, or a meta post I link to in a comment when I think a question is in danger of being closed.
I barely ever look at tags.
 
5:27 PM
@DanielSank that's way too late
 
You can't "change" a tag but you can make synonyms.
 
@EmilioPisanty Dude, if a new user shows up and posts a question, they're not reading tag wikis.
 
you want to communicate "this question is likely to be off topic" (if it's the case) before folks post those questions
 
The first time they're going to hear about the 'homework policy' is either after a closure or if someone comments a link.
 
I.e. we cannot get rid of homework or homework-and-exercises as a choosable tag, but we can make it so they are remapped to new-tag upon entering them.
 
5:28 PM
@DanielSank no, but the tag wiki excerpt does show up as a tooltip when they add the tag, see
 
@EmilioPisanty Yeah but that never happens, does it?
@EmilioPisanty Do new users add the tag?
 
@DanielSank Sometimes
 
Most tags are added by Qmechanic, yes?
@ACuriousMind Sometimes.
 
@DanielSank some of them might, and you want to take every opportunity you get
 
They also sometimes add mathematical-physics. It's really rather random what tags new users tend to put on questions, in my impression
 
5:29 PM
Anyway, yes we should fix the tag wiki. I'm not going to do it right now. I said I'd work on this in the evening.
That's ten hours from now.
 
@DanielSank no rush
 
@EmilioPisanty Agreed.
@ACuriousMind lol
 
just wanted to say: you want to think through all the parts of the system, where they come up and how they fit into the puzzle, and how they should change to reflect your policy
 
@EmilioPisanty ok let me make a list of things to update...
one sec
 
you don't want to be this guy:
hmmmm
 
5:31 PM
why not?
 
@DanielSank 'cause things break, and people get upset =P
 
you don't what to come off as "obnoxious"?
per foot note
 
main point is: the homework policy is a system that's more complicated, with more interacting parts, and with more interaction surfaces, than you initially think it is
 
@skillpatrol But I am obnoxious.
 
5:33 PM
@DanielSank close reason and close message are the same, I think
 
@EmilioPisanty Yeah, which is why I want to restrict to clarifying the policy's written word rather than debating the spirit of the thing.
@EmilioPisanty Can comment on Google docs ;-)
@EmilioPisanty Really?
 
'nnyways, I need to shoot off
@DanielSank I think so. check.
 
checking...
 
'bye y'all
 
5:36 PM
@EmilioPisanty yeah, same
 
5:55 PM
Is this on topic?
0
Q: Distance times Velocity

dashnickIs there a meaningful physical concept of $distance * velocity$? Came across something analogous in computer science and was wondering if there was any physical analogue.

 
6:20 PM
@BalarkaSen @EmilioPisanty One can show that the difference of two Jordan-measurable sets is measurable. Thus $[0,1]-C$ ($C$=Cantor set) is indeed Jordan-measurable.
And, since clearly $[0,1]-C$ and $C$ are disjoint, and $C$ has measure zero, then $[0,1]-C$ has measure one.
Now, proving that the difference is measurable is not hard, if one has the Lebesgue criterion for Jordan measurability: a set is Jordan measurable if and only if its boundary has zero Lebesgue measure.
Because then $\partial (A-B)\subset \partial A\cup \partial B$ has zero Lebesgue measure if $A$ and $B$ are Jordan-measurable.
 
"When an atom is accelerated, I believe the radiation emitted by the positive nucleus and negative electrons will have opposite signs at each point in the wave and so cancel essentially exactly."
o0
what did I read?
 
Now, one can use the contapositive to show that if $C_\delta$ is a non-Jordan-measurable Cantor set (fat Cantor set), then $[0,1]-C_\delta$ is not Jordan measurable.
 
6:45 PM
Obviously not
Since atoms have dipolar moments
 
is $$A^{\pm\pm'}=c_1\pm c_2\pm' c_3$$ a bad notation?
or is it clear enough?
anyone? :-(
I just had the worst beer ever
fucking disgusting
I was at the store, and I hat to pay with my credit card because I wasnt carrying any money
and the minimum price to pay with the cc was 5€
and I only had 4.30 in my basket
 
7:15 PM
@AccidentalFourierTransform what?
 
so I grabbed this mint flavoured beer
to give it a try
and at the first sip, I almost threw up
turns out, it was beer with rum
@0celo7 in some stores, you cannot pay with a credit card if the check is below a certain number
in this case, 5€
and I didnt have any cash
frigging rum
 
Well in that case you buy another thing
Like a candy bar or stick of gum
 
I bought this beer
 

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