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vzn
2:32 AM
@MoreAnonymous hey, so whaddya think?
 
 
2 hours later…
4:39 AM
@vzn Well personally I dislike Bohmian mechanics .... (Not that Im too familiar with it)... Honestly I dont use an interpretation and just plough through math ....
 
 
2 hours later…
6:18 AM
@MoreAnonymous Some cosmologists, especially in older works, use the term "ur-stuff" to refer to the primordial or fundamental "substance" of the universe, before creation started. The name comes from the city of Ur.
 
 
1 hour later…
7:33 AM
morning
apparently the question "Why don't physicists go fuck themselves?" was deleted
Quite sad
I was curious to see the answer
@SirCumference obviously not
Look in front of you
Odds are good that there are objects in some places
and not in others
Very poor homogeneity
 
0
Q: Penalty time for obscene posts?

G. SmithI’ve noticed that obscene, offensive posts get deleted fairly quickly, perhaps automatically based on the large negative downvote they get. But I have not noticed offenders quickly being given penalty time. Does this happen more slowly via moderators? Is there a mechanism for moderators to be awa...

 
7:52 AM
At first I read "rude or abusive" as "nude or abusive"
 
Another option exists in universes with sufficiently small closed spacelike curves, although I suspect that such topologies aren't conducive to life. ;)
 
@PM2Ring wormholes
@RyanUnger Does the Gâteaux derivative ever actually depend on the function you're adding?
I notice that they tend to put it in the arguments
Like \begin{equation}
\frac{\delta F[\phi]}{\delta \phi} [f] = \lim_{\varepsilon \to 0} \frac{F[\phi + \varepsilon f] - F[\phi]}{\varepsilon}
\end{equation}
I assume it may be if $F$ is discontinuous
Or has one of those weird directionality
Not holomorphic or whatever
 
8:10 AM
@PM2Ring no wasnt aware of that
also anyone good at quantum mechanics?
 
Shoot
 
I could summarise the idea
or I could show u the actual post
which one would u prefer
?
 
just show the post I suppose
 
0
Q: Is this analysis contradictory with the $2$'nd measurment?

More AnonymousIntroduction There are $2$ systems $1$ and $2$. Let the Hamiltonian of system $1$ be $H_1$ and let it be in an energy eigenstate: $$ \hat H_1|E_m \rangle = E_m |E_m \rangle $$ Now, a measurement is done (forcing the system to a momentum eigenstate): $$ \hat p |p_j \rangle = p_j |p_j \rangle$$...

I think it's weird idea ... and im not aware of the literature on this kind of idea ...
 
@MoreAnonymous That's a very long question! It needs a TL;DR summary at the top.
 
8:20 AM
U mean like a summary? Something like this suffice: "The below idea is about making a system 2 which induces a measurment on system 1 and 1+2 obeys unitary evolution"?
To be honest the calculations were laborious ..
"The below idea is about making a statement on system 2 which induces a measurement on system 1 and 1+2 obeys unitary evolution"?
*
Also on a side note is there any way I can scroll up to a paticular stared comment?
Particularly this one: " I've said this before, and I sure as hell will say it again. You leaving academics is a serious loss for us"
 
9:00 AM
@Slereah I can see it now:
In seriousness I'm wondering if it'll be good enough to accurately get the observable universe's radius :P
 
@SirCumference on the scale of the observable universe the FLRW metric is believed to be a good approximation.
There have been various attempts to study the evolution of the universe including the departures from homogeneity but I don't think they have come to much.
 
@JohnRennie Yeah but getting the observable universe's radius requires knowledge of the scale factor over time. I'm wondering if the FLRW still works as a good approximation in the early universe (inflation period)
 
I mean the thing to remember is
The FLRW metric is spherically symmetric
and axially symmetric
So if you study the universe assuming either symmetry
 
The FLRW metric is a better approximation as the time gets earlier because the universe gets more homogeneous as you go back in time.
 
it will work
It will be a lot more complicated of course
and you may find out in the end that it is also homogeneous
But it's a fine program to study, just in case
 
9:07 AM
The CMB shows the universe at the time of recombination was homogeneous to about one part in 100,000.
(i.e. the density variations were around 0.001%.)
 
I always got confused when I thought about the 2nd law of thermodynamics and inflation
 
The tricky part of course is
Does approximate homogeneity of matter imply approximate homogeneity of the metric
It is a very tricky thing to prove
(Spoiler : it's not actually true unless you qualify it somewhat)
 
@Slereah "Homogeneity of the metric"?
 
Existence of Killing vectors etc
The Ehlers–Geren–Sachs theorem, published in 1968 by Jürgen Ehlers, P. Geren and Rainer K. Sachs, shows that if, in a given universe, all freely falling observers measure the cosmic background radiation to have exactly the same properties in all directions (that is, they measure the background radiation to be isotropic), then that universe is an isotropic and homogeneous FLRW spacetime, if the one uses a kinetic picture and the collision term vanishes, i.e. in the so-called Vlasov case or if there is a so-called detailed balance. This result was later extended to the full Boltzmann case by ...
This theorem except with approximate homogeneity
 
 
3 hours later…
12:28 PM
@Slereah I don’t get the question
 
The Gâteaux derivative is usually defined wrt to the function you add
But at least as far as I know in Lagrangian mechanics, the precise form of this doesn't matter
But does it matter in the general case
I mean I guess probably, since it only doesn't matter since we factor it out and always have $\delta S = 0$
But since I haven't done a whole lot of other cases it is hard to be sure
 
1:02 PM
I s'ppose it is a ~directional derivative~ in the end
In the space of functions
 
@Slereah gateaux is literally the directional derivative
for a function you have $$\lim_{t\to 0}\frac{f(x+tv)-f(x)}{t}=\partial_if(x)v^i$$
same thing for Gateaux
but there's some tricky parts, like it doesn't always have to be linear in $v$
 
Yeah I suppose it is
I mean it's basically what it is for the variation already
 
@Slereah for Lagrangian mechanics you usually have that the Frechet derivative is zero
 
Except in the continuum limit
 
which is much stronger
but the way physicists define things is via the Gateaux
and then they don't prove anything
again, check Melvyn Berger's book
 
1:06 PM
Yeah they basically just write $+ \delta \phi$ and then pretend it all works as usual with infinitesimal things
Which it mostly does, I suppose
I accidentally type Melvin Berger, who is a person who wrote the book "How Do Flies Walk Upside Down?: Questions and Answers About Insects"
I assume it's not that one
 
probably not
nonlinearity in functional analysis
I got it for $10 on Amazon, wise decision
printing quality was so good back in the day
 
it varies
Math was a bit hit and miss in the pre-Latex days
 
the font is nice too
but I'm saying the actual paper and binding
it's a very sturdy book
 
yeah I've had bad experiences with some books
Kleinert's book on path integral is a crime
It's a soft cover book of almost 2000 pages
Berger talks about QFT and write the scalar field operator as $\zeta$
The horror
 
1:45 PM
@Slereah this guy will tell you anything you need to know
 
I'll give it a look, thx
"Chain differentials with an application to themathematical fear operator"
What is
the fear operator
I am scared to look
 
is that in Berger?
 
Hi all
Simple and rookie question
Switching off time dependence in some arbitrary model
One has the density operator and the correlation function
 
It is not
 
The expressions seem somewhat similar, for example the density operator at the origin appears to be related by switching off space dependence in the expression for the correlation function
Is this the right way to link the two?
I'd like to use algebraic bethe ansatz to get a fraction of two form factors repeating the Slavnov calculation mostly
It's annoying because the references for the density operator point to something that does not mention the density operator explicitly, nor does it calculate it (it's a generalisation of the information shown in the reference)
But anyway I doubt that context contributes in any way to the answer
 
2:26 PM
Hopefully after reading this book mb I can read De Witt's paper on path integral
Since it's all Banach space shenanigans
 
2:44 PM
@Slereah we’ve been talking about Banach spaces for like 4 years now
How have you not just sat down with a book and done all of the exercises
 
Lack of motivation lately rly
can't focus that much
 
3:29 PM
Hi to all. Are there any symmetries of the SM that are deduced from other principles rather than stated by phenomenology?
Are there symmetries who's existence could be shown as equivalent to some other principle of the theory?
 
3:41 PM
I mean all the symmetries stem from experimental evidence
You can narrow down what symmetries are allowed using some broad principles
But in the end there's no deep reasons why it's some symmetry group rather than some other
 
Electrons act as small magnets and when many of them are aligned their magnetic fields add up together to produce a powerful magnet.
Can this be done macroscopically? I mean by stacking multiple magnets with opposite poles together can we get a stronger magnet?Please tell me.
 
@ConstantineBlack It's not really clear what it means for a symmetry to be "deduced" rather than "phenomenological". Since every continuous global symmetry corresponds to a conserved quantity, you can always argue that such a symmetry is "phenomenological" and just put in because we observe the corresponding quantity to be conserved.
Conversely, local (=gauge) symmetries are arguably never "phenomenological", since they are just redundancies in our particular choice of dynamical variables.
 
@Slereah I agree- and epistemologically it's logical . This is the way the SM is constructed. I was wondering if anyone tried to show that the existence of some symmetries could be based on another principle.
@ACuriousMind I agree. From the perspective you put it, I could rephrase like this: has anyone tried to show that some quantities should be conserved in order for a principle to hold.
Maybe what I wrote sounds a bit platonistic?
 
@ConstantineBlack I'm not quite sure what you mean, but famously, CP symmetry would predict that matter and antimatter are produced in equal measure, meaning that the observed imbalance ("non-conservation of amount of matter minus amount of anti-matter") requires (slightly) CP violating terms. Is that what you're looking for?
 
@RyanUnger despite the 4 years I bet you can't answer my question
33
Q: Hahn-Banach From Systems of Linear Equations

bolbteppaIn this paper1 on the history of functional analysis, the author mentions the following example of an infinite system of linear equations in an infinite number of variables $c_i = A_{ij} x_j$: \begin{align*} \begin{array}{ccccccccc} 1 & = & x_1 & + & x_2 & + & x_3 & + & \dots \\ 1 & = & & &...

 
4:12 PM
@ACuriousMind Thank you; It's very interesting how sometimes just a few lines of conversation clear up the mind. Just for clarity, from your point of view, would you say that symmetry is the best possible principle we have for interpreting the world or maybe other representations could also hint to new physics(maybe an understanding of the universe as an information processing unit or the purely algebraic approach from Furey)?
My thinking was on a epistemological basis; what if the hard-coding of symmetries could be approached from another- maybe more ontological- point of view. Your CP-vio
In the sci-fi scenario that all possible universes are possible, what would define in each universe the values of the interactions and it's symmetries? Would it be pure luck- an ensemble of all possible universes all likely possible?
 
@ConstantineBlack In the framework of standard QFT, this is unanswerable. There is a gigantic landscape of possible QFTs, and nothing "above" it to choose a particular one. The Standard Model is the QFT that fits best to our observations, and the theoretical framework provides no way to reason about why it isn't any other QFT.
 
Well there are some limitations on symmetry groups within QFT
Coleman-Mandula theorem and all that
 
When you ask about "all possible universes", you first need a theory that defines the ensemble of "all possible universes". For instance, while neither QFT nor string theory (ST) provide a way to assign probabilities to particular theories describing a universe, we know that at least in the low-energy limit where it is approximated by a QFT, ST allows for much less universes than QFT (those QFTs who cannot be obtained from an ST being known as the "swampland").
 
Also isn't there a restriction in QFT wrt the gauge groups?
I seem to recall some property
Which basically limited them to SU(n), SO(n) and some exceptional groups
It's in Peskin Schroeder somewhere
let's see
 
@Slereah Sure, there are "impossible QFTs", i.e. the parameter space for the values of coupling constants and symmetry groups is not wholly unconstrained. But in the end there is nothing in our observations that tells us "whatever the universe is, it must be described by a canonical QFT". We simply observe that one particular QFT, the Standard Model, fits the observations exceptionally well
 
4:23 PM
Well sure
But then the field is wide open
For all we know, 3 days from now, all of physics might be described by microscopic cats
 
Turtles all the way down heathen
 
I think the standard theory is usually little gnomes
 
There is no possible observation that could tell us whether the universe has "parameters" that are "tuneable". We could add arbitrary axioms to what we consider a "possible QFT" until we arrive at an axiomatization whose sole possible instance is the Standard Model
 
Correct
 
And then we could claim "hey, we have a parameterless model that exactly predicts the universe, truly we have understood the universe, and there is no other possible one"
but it would just be cheap smoke and mirrors
 
4:26 PM
Yet...
 
Given any set of observations you can always cook up an arbitrary number of different models for them
More of less complex, 'course
and we do have heuristics for the ones that seem to have predictive power
Tiny cats don't seem to cut it
Not even Schrödinger ones
Even most of the "big principles" of physics are only there just because we've never observed them violated
but that doesn't mean much
 
Well, every time you think you observe a violation of "the principle of least action", we just tell you that you got the action wrong ;)
 
I apply the principle of least action right now
 
Sitting in front of a computer and not moving? :P
 
Pretty much
 
4:30 PM
Unfortunately I don't have but the slightest idea of string theory. Aren't there problems with the swampland and de Sitter spacetimes?
@Slereah The history is a bit of racist against dogs; why none has ever consider that quantum dogs could make it ? The whole phenomenology think is a big discussion which may have it's roots in a more philosophical or epistemological basis.
@ACuriousMind But it seems to be a bit of tuned, no?
 
Man can you imagine if physics obeyed the principle of most action
Things would certainly be more intense
@ConstantineBlack cats are for physics
 
@Slereah actually, it does both, since it's actually the principle of extremal action :P
 
Dogs are for psychology
cf Pavlov
 
@ACuriousMind Is there any case where it is the most action?
 
4:31 PM
I think there is at least one question on the site about that but it minimizes my action not to search for it now ;)
@ConstantineBlack How does it "seem" so?
 
@Slereah wouldn't the new action 1/S where S is ur action ... So from minima u get a maxima
("principle of mist action")
 
Weinberg.
 
*most
 
We don't know what other universes, if at all, are truly "possible". We're extrapolating from a sample size of exactly one!
If I showed you a single dog and asked you to chart the space of all possible dogs from just looking at it, how good do you think you would do?
 
And of course
$$P(A | A) = 1$$
The universe had 100% of chance of existing as it is
Also "If things were different the universe would be different" is, while interesting, not a particularly deep observation
Anthropic principle never phased me much
Now on the other hand
If it turned out that the universe was finely tuned for life not to exist
then it would be another matter
I would be much more shocked
 
4:36 PM
@Slereah Given that you would almost certainly almost instantly die if you were transported to a random position in the universe, it is arguably almost tuned for life to not exist :P
 
@ACuriousMind You don't know really
 
Doesn't the 2'nd law of thermodynamics insist we're the lucky lottery winners to exist in a time period where life is possile
*possible
 
Maybe beyond the observable universe is nothing but comfy sofas
 
(the correct response to that is that in an infinite universe the notion of "uniformly random position" is incoherent :P)
@MoreAnonymous As opposed to the poor bastards who exist in the time periods where life is impossible, you mean?
 
@ACuriousMind Poor guy
It must suck really
I believe in America they just call it the midwest
 
4:39 PM
Define dog :)
I agree with you. But you could think of the fact that you and me both exist because of a "fine-tuning" of biological-genetic forces shaped by evolution and thermodynamic rules. On the same analogy, the existence of this one- and only this one- universe raises the question of a how(maybe even more than a why). Maybe we can track- not all possible dogs- but how these dogs came to be?
 
you know the anthropic people always talk about physical laws but not so much about boundary conditions
Which are also fairly important
 
@ConstantineBlack Well, this one universe - the only one we know of - probably started at the big bang. And apart from a very very tiny timespan in the beginning when quantum gravity effects might have dominated, we understand pretty much all of the "how" after that.
 
Also they always consider fairly minor modifications of physical laws
and not wild and crazy variations
 
@Slereah Isn't that a debate in cosmology? Whether the start is tuned with some very specific boundary conditions or it came from one of the zillion of inflation models?
@ACuriousMind You don't find the analogy valid?
 
Asking the probability of the universe being as it is implies that there is an alternative
 
4:50 PM
@ConstantineBlack The analogy is valid up until the point where we arrive at the fertilized dog zygote (the analogy of the big bang). For a dog, we can ask "What came before the zygote?". For the big bang, this question does not make sense, as there is nothing that could be called "before".
 
There is always the alternative of nothing.
 
Yes, but "nothing came before the big bang" is not really correct either. It's that the statement "X came before the big bang" does not make sense for any value of X.
 
@ConstantineBlack is there
 
Big bang came from nothing.
 
I'm not aware of that in any theory
 
4:54 PM
@ConstantineBlack I think there is a difference between "There was nothing before the big bang" and "There is no 'before the big bang'". Silly analogy: If you wanted to express that the sky has no taste, you would not say "the sky tastes of nothing", since that would imply that it in principle can have taste, but just tastes like nothing in particular.
 
I mean the sky does have a taste
Especially in China
 
Similarity, "Before the big bang there was nothing" implies, to me at least, that it is meaningful to imagine that there was something, but that there just isn't anything.
To me, it is important to realize the difference between a question not making any sense, and there being no answer
 
not even wrong and all that
 
It's an asymmetry :)
Don't you always need zeros and infinities?
@ACuriousMind Sorry, I didn't get it. I don't say before the big bang. Nothingness is the complete absence of anything, since no time exists to define a presence, an interaction.
I am not sure to what you are referring.
 
I'm advocating for being explicit and saying "Asking for anything prior to the big bang does not make sense in our current model" instead of something like "Before the big bang there was nothing" that could be misinterpreted (as the question making sense and the answer just being "nothing").
 
5:02 PM
It was me
i was before the big bang
Before me the void, after me the flood
 
Halo-like flood?
 
5:14 PM
@ACuriousMind Look, I think we are in agreement- even if admittedly I hold not even half your knowledge. About nothingness, it's your choice to accept if it is a valid alternative or not; regarding the borders defined by our current model, yes, maybe the thing is all about semantics. But the model has been conceived to describe and maybe explain why there is something and not nothing. This is not invalid, it is as I see it a sudden realization that comes for all existence.
Now, about the how: we can trace the genetic evolution of dogs, of all the ancestors back to the first ancestor. In the
*And I think it is valid to do string theory, not the opposite.
In reverse, maybe it is a paradox that the existence of "a" phenomenology is as absurd as it is logical.
 
@ConstantineBlack 1. I'm afraid I'm not sure what you're asking here, but "the model has been conceived to describe and maybe explain why there is something and not nothing." is a not a view of physics I share. Physics is conceived to describe and predict (and post-dict, in the case of the genesis of the eaarly universe) the world from as little input as possible
(and is it not amazing how rich the structures the Standard Model predicts are with just a handful of parameters?). It does not answer "why" these predictions should be true.
 
Does anyone know a little bit of Lua?
 
2. I never said that string theory is "valid" (nor that it is "invalid"), so I'm not quite sure what you're after here, either
 
There is that string.gsub() that replaces string in string. But for some reason is bugged for me.
 
More likely it is behaving as intended but you disagree with the intention ;) (I do not know Lua)
 
5:23 PM
I have this string "quest1|||quest2|||quest3|||" and I'm replacing "quest1|||" with "", but for some reason the output is "2|||3|||".
But instead of |||, I use ***
 
Am I giving the impression I am after something?
You wrote that my questions are invalid, but string theory is neither valid nor invalid?
And so we are at a fundamental disagreement: are you a theoretician that does mathematical physics not to understand the only thing that is (and why it is, or how it is, or why it isn't) but to predict and describe? Doesn't any theoretical pursuit hold an ontological or ontic view of the question it asks and of the object it studies?
 
@NovaliumCompany If this function expects a regular expression as input to identify the substring, then you need to escape the * to match the actual asterisk character instead of "any character"
 
Should I try using |||?
 
You give a definition of physics, but that is not it's origin. Physics may hold a different methodology from how the theologicians in middle ages asked questions, or the ancient greeks, or Heidegger or the aztecs, but the origin is still the same push or urge to understand the first questions about existence. You completely disagre?
 
@ConstantineBlack Indeed I largely reject any claims about ontology. The map is not the territory, and physical theories are maps of reality - they describe how reality behaves, not "what it really is" (if this is even a phrase that makes sense) nor why. I do not claim that all or even most physicists share this view.
I do (or rather, did) mathematical physics because I find beauty in modelling the world with the elegant structures of abstract mathematics. It is an astounding achievement that minds so small as ours can even comprehend accurate models of a universe so vast and varied, but I consider it hybris to think that physics is anything more than that - models.
@NovaliumCompany Better learn how to write regexes ;)
| is also a special regex character (alternative/or) in most, if not all, flavors
 
5:36 PM
What ACM said. The aims of modern physics aren't as profound as the medieval theologians, philosophers, etc. It just tries to build models that accurately map the physical world, and then tries to fully understand those models & their implications. And it tests the accuracy of those models by seeing how well they fit existing data, and new data produced by experiment.
 
OMG OMG OMG
it works
I replace the *** with |||
YAAAY
 
@NovaliumCompany Apparently, a full explanation of the pattern syntax accepted by Lua's gsub (which is not standard regex) is lua.org/pil/20.2.html
 
Oh man
Have you ever read papers from physicists who are really into ontology
 
All ontologies are models in that they are interpretations and nothing more. You want materialism, marxism, heidegerism, all ontologies (and the absence of them ) are representaions. Your claim here is also ontological, in the sense that no one is able to know something about pure things. And I couldn't agree more. That is not different in many respects to phenomenology in philosophy.
But also, your claim goes to an ethical level about hybris: this is also( and even more) a very subjective proposition and has nothing to do with anything.
 
It is mildly awkward
 
5:38 PM
@Slereah Only the first pages of them ;)
 
Isn't that right, TIPLER
 
@ACuriousMind "magic characters" * is one of them. That explains the problemnow.
 
The answer to "What was before the Big Bang?" is buried in a secret vault 5 km south of the South Pole.
 
there was a duck
 
@PM2Ring They are exactly as profound. Physics tries to describe everything from t=0 to t=inf. We are different in that we always(almost) try to speak about thinks that make sense, not souls or pure entities. We analyze absurdities(black holes) or we accept that no absurdities exist since black holes are real; we ask constantly for the nature of time. The method is different(for me better) but the origin is not. And this is not an ethical matter as I put it. Ethics are irrelevant.
Anyway, it seems that this doesn't lead somewhere. Unless someone has an argument to offer, I'll say ciao. @ACuriousMind May I ask a last- completely irrelevant- question?
 
5:50 PM
But physics doesn't try to describe reality directly. It makes partial models, and tries to describe those models. It doesn't claim that the models are true, merely useful.
 
sure (I think this conversation veered off-track somewhere and never got back on, so I'm happy to let it rest ;) )
 
BTW, Current BB theory doesn't try to describe t=0, only t>0
@ConstantineBlack Fair enough.
 
@PM2Ring This is all everyone did- ever. They just claimed differently(and who knows, maybe they were correct? The analysis must work on the methodology and the goals- pre -suppositions ). It would take a lot of space to analyze this, so let's leave it for some other day. Anyway, I agree with ACM, and since I appreciate his person and respect his thoughts, we should let it.
@ACuriousMind Tell me, is there any chance you know professor Berges at Heidelberg?
 
I took a course by him once, but we don't really know each other personally
 
Oh, OK then.
Thanks again for the (nice?? ;) ) conversation. Be well. I go to chat-nothingness.
Maybe I find something to eat there. Good night ;)
 
6:00 PM
Why doesn't python include multiline comments
Who thought excluding them was a good idea
 
@SirCumference You're eleven years late ;P
What do you need multi-line comments that are not docstrings for, anyway?
@Slereah I just now realize - that would be a cat-astrophy for physics!
 
6:17 PM
@ACuriousMind The bold text on this has scared me away from it
 
There's a couple of new badges on SO. stackoverflow.blog/2019/06/18/… And a couple have been retired.
 
@PM2Ring Not only on SO, this is SE-wide
 
Oh if you're asking what I'd need commented blocks for, well just keeping code handy so I know where it goes if I want to reimplement it
 
@SirCumference Can't you just pull it from the git history if you need it back?
 
Instead I need to keep it in an "if False" statement
 
6:18 PM
@ACuriousMind Oh, cool.
 
Code that is not used does not belong in your code, commented, behind an "if false:" or otherwise :P
 
@ACuriousMind Yeah but this is simpler and lets me test both the new and old code quicker
If e.g. I want to compare them several times, it's much simpler to just have the code on standby
 
@SirCumference Doesn't your editor let you comment & uncomment a block of lines? I just use KDE's kate, nothing fancy, but even it can do that.
 
@PM2Ring Vim and Jupyter don't do that afaik
@ACuriousMind Not in the finished product of course. But in testing and optimizing, or figuring out what's causing a specific error
It's often helpful to comment out a bunch of code so I can narrow in on the problem
 
Yeah, but in testing/prototyping I agree with PM2Ring that I'd expect any modern IDE to be able to (un)comment any number of lines as single comments.
 
6:23 PM
Oh crap Jupyter can do that
Neat
Well if only vim could too :/
 
I don't really know vim, but I'm willing to bet that "add a character in front of every marked line" is only a keystroke away - you just need to know which key ;)
 
It's still strange that python, unlike almost every language, doesn't naturally support multiline comments. Even JS does
 
Kate's not even an IDE, just an editor with a few extra things, like syntax highlighting and code folding. Ok, it has a builtin terminal, but I rarely use it. I prefer to run stuff in konsole.
 
Maybe it's bad practice or something, but I make use of them a lot to swap out code quickly, when finding a problem or optimizing
 
@SirCumference Well, if you happen to put """ and """ around your block, it will effectively comment it out
 
6:26 PM
Obviously the commented code would get removed in the end though
 
Which is how I treat blocking off chunks of python while debugging
 
@SirCumference Python is a rather opinionated language on many issues, so if Guido doesn't like the notion of multi-line comments, then there are not multiline comments ;P
 
@tpg2114 Yeah but this states in bold letters "Do not use triple quotes"
 
@SirCumference I'm pretty sure that Guido did it on purpose, but I can't think why, ATM. ;)
 
If that's just a convention then I don't care, but if it'll actually cause problems I ought to avoid it
 
6:27 PM
Iirc, it's also explicitly intended to be parsed by as simple a parser as possible, and multiline comments - and the escape syntax they would also necessitate - would make it rather needlessly more complex
 
@SirCumference I wouldn't publish code with it done like that. But if I'm just trying to figure stuff out, I'll do what I need to do and clean it up once I know the problem.
PEP 8 is what "finished" code should follow, for some definition of finished
In languages like Fortran that also don't have multiline comments, I'll drop a IF(.FALSE.) THEN // END IF block around stuff I want to comment out
Python whitespace makes that an annoying proposition though
 
"finished code" = "code I now hate so much I will only look at it if it causes a nuclear apocalypse"
 
In which case I probably don't care about the wall-of-comments anyway, and can just nuke it from orbit ;)
 
@tpg2114 Yeah I've been using "if False" blocks. Though it can be hard to tell which code is meant to be "commented" at a quick glance since they won't change color with this method.
Also seems needlessly more complex then just a native multiline comment
 
I haven't found myself really cursing the lack of multi-line comments though. If I need that many comments to explain my code when it's finished, I probably have made my code way too complex
For debugging, sure. But then the triple quotes works well enough
 
6:32 PM
@tpg2114 Oh I wouldn't use multiline comments in my finished code :P Just for keeping code on standby so I know where it goes if I wanna reimplement it
But if triple quotes won't cause any issues then that works for me
 
It won't break anything for sure. It might ruffle some PEP 8 purists, but eh.
 
if you're not using it in productive code, no purist will ever see it
 
Guido has actually approved the use of triple-quoted blocks as comments.
OTOH, they waste time being parsed. So I prefer to use a block of # comments.
 
If you're running on a potato that cares about the parsing time of triple-quoted strings, you probably shouldn't be running Python in the first place ;P
3
 
Fair point. But I do have a slow old computer. :D
And I started coding on a machine with a clock speed measured in kilohertz, so I learned very early not to waste time (or RAM), if I can avoid it. I am a bit more relaxed about stuff like that these days, but it's hard to eradicate those old patterns completely.
Bur another reason to prefer blocks of # comments is that they can easily be nested, unlike triple quotes.
 
6:46 PM
@ACuriousMind Don't knock my Russet co-processor
 
Heh ;)
 
@bolbteppa I don’t know any linear algebra
I can’t answer that question
 
@PM2Ring I regularly despair at code with giant single god methods that do everything because "method calls are expensive" :P
 
@ACuriousMind Well, Python function calls are expensive. But that's no excuse for stupid design. :) It just means you should avoid calls if you can write equally readable clean code that doesn't need a bunch of calls. Eg, a list or generator comprehension that calculates some expression on each item is invariably better than a map that calculates the expression in a lambda.
 
7:01 PM
yeah, I agree
 
A few hours ago on SO, I saw (in an answer) someone trying to sort a list named L like this: L = sorted(L, key=lambda X: X)
Sure, it works. But it's stupid!
 
7:31 PM
^ I'm trying to guess how you come to that point.
Either uncomprehended-cut-n-paste or planning-for-something-much-more-clever-that-you-never-actually-do are the only things that come to mind.
 
@dmckee By googling "how to sort a list" and landing on a page that explains sorted but not .sort()
If you learn a language by randomly googling how to do stuff, bad google fu can lead you astray very quickly
 
@ACuriousMind You also need to not understand that there has to be a better way or you would keep looking.
Otherwise hours of painful trial and error, desperate debugging and pulled hair can save you another ten minutes with your browser.
I google-fu my way through programming tasks in unfamiliar languages from time to time.
 
@dmckee You don't need a good way to do something to deliver your code and get paid. Just any way.
 
They are remarkable for the number of browser tabs they generate.
 
One thing I realized very quickly after starting to work on code analysis is that a large number of programmers simply do not care about any quality of their code beyond it "working". It can be a slow, unreadable mess that is impossible to debug or explain, but if it does what it is supposed to and you can sell to the end user that it really does need half a minute to fetch a single piece of data, then it's as good as it's going to get
 
7:44 PM
Uhg. I don't claim to write great code, much less the best possible code.
But I do strive for code that is aware of the existence of maintenance, and expects some other poor blighter (like my future self) to have to understand what it is doing and why..
 
Just today, I had someone complain to me that one of our checks got smarter and now realized that an error that was being "handled" by an empty if statement really wasn't. They had introduced empty if statements all over their code to get rid of the notification that they didn't handle an error and now were infuriated that that didn't trick the check anymore!
 
^ And they blame you. Of course. Ouch.
 
"This code has worked for years like this, we don't need to handle error situations. Please fix the bug in your check."
 
The code has been dangerously wrong for ten year. Luckily you got away with it. Don't you think you should change that before that luck turns?
 
Needless to say, there is a straightforward way to disable these notifications for specific situations where the programmer is really sure they don't need to handle it. But it would be "too much effort" (direct quote) to replace the empty if statements by the proper disabling of the notification
 
7:50 PM
I mean, if they really mean to discard error conditions then you just explicitly discard them, right? That's a secretarial task that you do on some day when you are too brain-burned for really thinking.
Or am I presuming that there are days when they do real thinking.
 
I feel it's not the thinking that is lacking, it's the caring
 
On a related note,
in Python on Stack Overflow Chat, Apr 9 at 15:09, by PM 2Ring
"Why do I need the spaces? It works without them." "Because you're writing so that humans have an easy time reading it. If you want to make it easy for the machine to read, write in assembler."
And of course
in Python on Stack Overflow Chat, Dec 3 '18 at 5:53, by Wayne Werner
> Always write code as if the person maintaining your code is a homicidal psychopath that knows where you sleep.
 
@PM2Ring I have a feeling that 1000 lines of "HEEEEEELP I'M BEING MURDERED" won't pass code review.
 
8:31 PM
Groovy! I just got another Lifejacket. For this: math.stackexchange.com/a/1250949/207316 Gotta love the HNQ effect. :)
 
there's a single lifeboat and no lifejackets on physics.SE
Motion to rename that boat badge to "Noah's ark" here
 
Interesting. I guess that means a physics.SE question with a couple of downvotes is truly bad, and is unlikely to be rescued by a great answer. Or something. :)
 
I think that's accurate. Questions that really get downvoted below -1 are usually a) far off the beaten path b) incomprehensible c) lazy homework d) rants
 
Does someone want to hammer this FTL causality question? physics.stackexchange.com/questions/486806/…
 
I think the only questions that get a couple of downvotes but stay open and end up with net positive score are usually HNQs, but them going HNQ usually means they get those downvotes only after getting heavily upvoted, thus not qualifying for the life* badges
 
8:50 PM
0
Q: Two questions in one

Alex DoeI know as a general rule it's good to keep questions simple if possible. I also think they can differ from case to case. Can someone please suggest whether to split this question into two? Or leave it together as question 1 may help provide context to question 2? Thank you

 
@ACuriousMind Ok. That maths question that I got Lifejacket on got a downvote & closed for lack of effort. The OP edited it with their attempt, it got reopened, I answered it, and it eventually went HNQ.
 
@PM2Ring Yeah, couldn't happen here, because just adding shown effort does not make a question any more on-topic.
We're arguably stricter than math.SE, which makes it more difficult to turn questions around from bad to acceptable
Whether that is good or bad is left to the reader to decide (I think it's good :P)
 
9:10 PM
0
Q: Should it be mandatory that close votes be accompanied by comments?

Alex DoeI have read the help page various times to get help with asking questions. While that helped, I still sometimes find my questions downvoted or voted to close. That is without explanation. That leaves me guessing and editing without knowing what exactly needs to be edited. Maybe I am not the only ...

 
9:45 PM
6
Q: infinitely many linear equations in infinitely many variables

M.G.Let $(a_{mn})_{m,n\in\mathbb{N}}$ and $(b_m)$ be sequences of complex numbers.We say that $(a_{mn})$ and $(b_m)$ constitute an infinite system of linear equations in infinitely many variables if we seek a sequence $(x_n)$ of complex numbers such that $\forall m\in\mathbb{N}:$ $\sum_{n=1}^{\infty}...

 
 
2 hours later…
11:21 PM
@PM2Ring it's crazy that these people seem to always have bizarre capitalization patterns
 
@danielunderwood He'd probably use multiple fonts & colours too, if he knew how. I guess that's what he's used to seeing on the parts of the Net he usually inhabits.
 
Oh man, could you imagine if SE allowed you to do custom HTML formatting?
 
Well, it'd let us spot the loonies even faster. :)
 

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