The h Bar

user228700

10:00 AM

Heck, I bet we all pronounce even pronunciation differently.

John Rennie

People confuse it with pronounciation, which is the act of convertng words to pronouns.

user228700

What? I didn't even know that...

John Rennie

That ... might not be 100% true

Anonymous

@Kaumudi.H Wait, what? It is differently taught in different schools. Some schools teach American English and some teach British English (only in terms of spellings). However, most people here use an accent that is typical to just India. How did you conclude that whole of India uses "British English"?

user228700

@JohnRennie -_- Thanks.

ACuriousMind

10:04 AM

@DawoodibnKareem Oh. Hmmm. I think that's an overly narrow definition of "accent", in particular since the phonemes might actually change (e.g. in certain regions of South Germany, there are people who make no difference between a voiceless and a voiced 's' (which are distinct phonemes in standard German) - the two phonemes have collapsed into one)

user228700

@Blue Well, of course we have an accent! I was referring to the pronunciation of most words and also that when some people use grammar incorrectly, it's shoved under the rug of "Indian English" but that's generally frowned upon by most people who take English seriously like journalists and English teachers etc.

ACuriousMind

@Kaumudi.H lol, he's (almost surely) joking :P

Dawood ibn Kareem

Phonemes are defined by the existence of minimal pairs. In those South German regions, I would argue that /s/ and /z/ are still distinct phonemes, even if they're pronounced identically.

John Rennie

@Kaumudi.H for reasons that make no sense to anyone pronounce is the verb but pronunciation is the noun.

ACuriousMind

@DawoodibnKareem How can there be a minimal pair for two "phonemes" that the speakers pronounce identically? (i.e. all the "minimal pairs" are actually homophones)

user228700

10:07 AM

@Blue: For example, to use the word doubt in place of question was established to be OK under the terms of Indian English but no one would recommend you do that if you're writing something important.

Dawood ibn Kareem

So at what point in the development of a linguistic variety do you stop calling them minimal pairs and start calling them homophones?

ACuriousMind

@DawoodibnKareem When a speaker of said linguistic variety perceives no difference between the two spoken words

user228700

And also crap like "She didn't come only". The only in this sentence is used for emphasis; it would a paraphrasing of "She didn't even come!" That too is "Indian English".

Dawood ibn Kareem

@Kaumudi.H Yes, it is. And who is any American or Briton to label it as "incorrect"?

Anonymous

@Kaumudi.H Ok, some people pronounce words differently to what it is supposed to be in either British English or American English. That can be accepted as a genuine mistake. My point is that that it is wrong to say "whole of India uses British English".

Dawood ibn Kareem

10:10 AM

@ACuriousMind I see your point. I think I'm poorly equipped to argue this. Part of the issue is that I don't think I have any such "merged phonemes" in my own speech.

user228700

@DawoodibnKareem It's only incorrect in that a majority of the English speaking population of the world wouldn't understand it.

Dawood ibn Kareem

@Kaumudi.H I think you'll find that a billion or so Indians are the majority of the English speaking world.

Anonymous

@Kaumudi.H Again you are generalizing. How can you say "no one" would recommend? I have used the word "doubt" in that way in several of my essays at school. None of the teachers batted an eyelid.

user228700

@Blue I was certainly exaggerating when I said "The whole of India", yes.

Dawood ibn Kareem

@Kaumudi.H So in what parts of India do they speak non-British English, in your view?

user228700

10:13 AM

@Blue And that's only because it's accepted among Indians to do this. If you're publishing something to be read by a much wider audience, it would confuse a lot of people as it did 0celo, who was the one who told me about it an lengthy conversation we had many many months ago.

Anonymous

@DawoodibnKareem It depends on the school. I was taught both versions of English (spellings) at my school.

ACuriousMind

@DawoodibnKareem Alright - the example I gave actually comes up pretty regularly, because the German words for the number sex ("sechs") and sex ("sex") (as in "having sex with someone") only differ in the voicedness of the initial 's'. For people who don't perceive the sounds as different, these words are homophones, and they tend to speak all 's'-sounds as voiceless. Which means that when they count to "six", people from other regions hear them saying "sex" and not "six".

Dawood ibn Kareem

@Blue The distinction between British English and American English encompasses far more than just spelling.

user228700

@Blue Did some of your teachers really pronounce aluminium like aluminum?

Anonymous

@DawoodibnKareem I know. We were free to choose any one.

Dawood ibn Kareem

10:15 AM

@ACuriousMind But presumably people from that area are themselves aware of whether they're saying sechs or sex, right?

ACuriousMind

@DawoodibnKareem Well, they know what they mean, but the words are true homophones - they can only tell from context (or from the written form, of course).

Dawood ibn Kareem

My first wife would have argued that I pronounce had and head identically, when speaking English. She was wrong, of course, and for me these are not homophones at all.

Anonymous

@Kaumudi.H Most of them would pronounce it like Aalu-mininum

user228700

I think that in this conversation, there is a fundamental miscommunication as to exactly what the difference is between types of English. We're all (Me, Blue & Dawood) talking past each other.

Dawood ibn Kareem

@ACuriousMind Thinking about it, in my speech (when speaking English), bear and bare are homophones. But they're not homophones for all speakers of English. So I guess you're right. But I still believe that variations of pronunciation is a wider category than variations of accent. I have just failed to express myself adequately regarding what the difference is.

Indian English

Indian English is any of the forms of English characteristic of India. English is a lingua franca of India. == English proficiency == Though English is one of the two official languages of the Union Government of India, only a few hundred thousand Indians have English as their first language. According to 2001 Census, English is known to 12.6% Indians in the 2001 census. An analysis of the 2001 Census of India, concluded that approximately 86 million Indians reported English as their second language, and another 39 million reported it as their third language. No data was available whether these...

ACuriousMind

10:21 AM

@Kaumudi.H Well, "type" is a bit too unspecific. I and Dawood were mainly talking about pronunciation while you and Blue seem to also have drifted into differences in grammar or the meaning of certain words (such as "only" or "doubt")

Dawood ibn Kareem

Also, people outside South Asia don't understand the Indian English words for large numbers.

Indians often don't seem to realise this.

Anonymous

lakhs, crores :P

Anonymous

haha

Anonymous

Even we have to spend some time calculating when foreigners mention million or billion :P

Dawood ibn Kareem

If somebody offered me a lakh rupees, I wouldn't know whether to leave it lying in the gutter, or buy myself a palace.

Anonymous

10:24 AM

@DawoodibnKareem Try to memorize it: 1 lakh has 5 0's while 1 crore has 7 0's. :D

Dawood ibn Kareem

I'm not going to try to memorise it. I have no use whatsoever for that particular piece of information.

Unless you're about to offer me a lakh rupees. Then I'll try to figure it out.

Anonymous

Then don't complain when someone mentions figures in lakhs or crores and take some time to convert them.

Dawood ibn Kareem

I'm not complaining. Just commenting that Indians often don't realise that nobody else knows what they're talking about when they use these terms.

That definitely makes "lakh" and "crore" features of Indian English.

Mostafa

Does anybody know what English is this?: youtube.com/watch?v=5mQ5GoXQuWU

Dawood ibn Kareem

Sounds to me like some Caribbean variety, but I couldn't be sure.

Anonymous

10:28 AM

@DawoodibnKareem I haven't seen any foreigner realize that many Indians have trouble understanding when they mention figures in million or billion. People just need to have some mutual understanding and patience while conversing.

Anonymous

Yes, I agree with your point.

Dawood ibn Kareem

@Mostafa No, I'm wrong. The performers are Nigerian.

Mostafa

@DawoodibnKareem I've tried a lot and could barely understand %50 of it

Dawood ibn Kareem

OK, hint - "collabo" means sex.

Mostafa

lol

Dawood ibn Kareem

10:31 AM

But yes, it's very hard to understand.

ACuriousMind

I think that might qualify as a different language instead of a variety of English, much like Dutch qualifies as a different language from German although there are mutually intellegible varieties of Dutch and German near the border.

Anonymous

I was learning some Spanish basics last week from a Youtube video series. I could hardly understand that instructor's English. Guess every country has their own version of English that is derived from British/American English.

ACuriousMind

@DawoodibnKareem That at least explains the top comment :P

Dawood ibn Kareem

@Blue Well of course. That's how languages evolve.

parvin

hello. i have a question which is off topic!
has any one used a chat room in SE with the title "mathematics"?

I was there about 2 days ago and now it's vanished :/

Anonymous

10:35 AM

BTW did American English and British English originate separately or one was derived from the other?

John Rennie

@parvin This one

Dawood ibn Kareem

@Blue You do understand that USA was formed out of a bunch of (mostly) British colonies, right?

Mostafa

I specifically have no idea of this part: "I get your password and you know say I don code.......me I don code"

parvin

@Blue there is a room for linguistics in which guys know so much about language roots and origins, check there

Anonymous

@DawoodibnKareem Yeah I thought so too

Anonymous

10:36 AM

@parvin Sure

parvin

@JohnRennie why couldn't i find it?! it must have been internet connection issue..thank you!

ACuriousMind

@Blue Languages that truly originate separately from one another (in the sense that we don't know any historical relation between them) tend to be much much more different.

Dawood ibn Kareem

@Mostafa Yeah, I don't know what that means.

Secret

Hmm, I thought I just saw johnrennie's wavefunction tunneled into the maths chat room momentarily

Anonymous

@ACuriousMind I get that. I should rather have asked: which one came first? :P

John Rennie

10:39 AM

@Secret It did, but luckily I came to my senses quickly :-)

Secret

lol

Dawood ibn Kareem

@ACuriousMind I thought the general consensus among linguists were that there are no languages that originated separately - in other words, there was just one "original language" from which all other languages have evolved. Except of course for the created languages like Esperanto and Klingon.

ACuriousMind

@DawoodibnKareem It's a popular hypothesis, but we really don't have enough evidence to conclude there's a single ur-language.

Dawood ibn Kareem

@Blue Neither came first. They both evolved from earlier English.

ACuriousMind

E.g. there are plenty of language isolates where we have no idea where they came from

Anonymous

10:41 AM

@DawoodibnKareem Probably

ACuriousMind

One of them in the "middle" of Europe - no one really knows what the Basque language's deal is

All other European languages are well-known to be related, just that one is completely different

Dawood ibn Kareem

@ACuriousMind But are there any serious linguists who believe that Basque originated separately from everything else?

Anonymous

I will be surprised if someone says that English and Sanskrit originated from one "original language" :D

Anonymous

Hard to believe

ACuriousMind

@DawoodibnKareem I am genuinely not sure what linguists believe about this

Dawood ibn Kareem

10:43 AM

@Blue Absolutely. They both evolved from Proto-Indo-European.

Anonymous

wow

Dawood ibn Kareem

But, of course, Proto-Indo-European is probably not "the original language". It, in turn, would have evolved from something earlier.

ACuriousMind

@Blue That's actually relatively well-established

Anonymous

We learn something new everyday :'). Hehe.

Secret

So, yesterday, we gone semi philosophical and discussed about:

in Mathematics, 18 hours ago, by Ted Shifrin

Do we have a physical model of $\aleph_1$?

Semi and I then give spacetime and temperature as examples

Dawood ibn Kareem

10:49 AM

Hang on, we don't even know whether $\aleph_1$ is the same cardinality as $\Bbb R$. How could we possibly have a physical model for it?

Secret

Ah I forgot, we assumed continuum hypothesis in our discussion

Dawood ibn Kareem

Oh, well that makes it much less interesting.

Anonymous

@Kaumudi.H It seems that there have been discussions on only and doubt on English Stack Exchange before. As of now if one writes "only" that way in school it will surely be considered incorrect. But, I'm sure that in a few decades that will start being widely accepted.

user84215

I think there are many real quantities in physics

Secret

What I am more interested recently is, however:

in Mathematics, 18 hours ago, by Secret

I wish one day we humans will discover something physical that has size $\aleph_2$ that would be really awesome

Dawood ibn Kareem

10:52 AM

@Blue You may find that some schools are less prescriptive than others in this regard.

Secret

(NB I know so little about cofinality that I dared not to touch cardinals beyond continuum hypothesis until I have a solid background of it)

Anonymous

@DawoodibnKareem Maybe. My school surely wouldn't have allowed that usage of "only" and discard it as SMS/Twitter/Facebook lingo :P

Dawood ibn Kareem

@Secret I'm trying to imagine how something of size $\aleph_2$ could possibly fit in the known universe. But I might be looking at it the wrong way.

Secret

Well, an infinite set does not need to be unbounded. It is, however, not very clear how to get beyond the continuum since reals are already complete. We do have ordinals, though, but they are very different from the reals

user84215

Physicist have not discovered anything that has size $\aleph_1$ yet.

Secret

11:01 AM

One possible way to think about this problem is what kind of physical entity require us to index it with the power set of reals for example

user84215

Discovering something having infinite size is meaningless in physics.

ACuriousMind

@Secret What do you even mean by "size" there? "Size" is not a formal notion in physics.

user84215

magnitude

ACuriousMind

At least not in any way that assigning an infinite cardinality to it would make sense.

Secret

I am thinking more about how the naturals are discrete, while the reals are a continuum, thus some not necessary well ordered set with cardinality $\aleph_2$ may correspond to something "more continuum" (I don't really know what that means, as the reals are already complete, and thus there are really no gaps so anything extra has to be infintesimals or something). If I just interpret a physical thing with $\alphe$ as magnitude,
then we are going to blow up to infinity and the universe may not allow that

ACuriousMind

11:10 AM

@Secret How are the reals "something physical" we "discovered"?

user84215

My statement is false?

Secret

We don't discover the reals, but we do use continuous variables like temperature alot

in Mathematics, 19 hours ago, by Semiclassical

Temperature is genuinely a continuous variable; there's no fundamental unit of it. However, temperature rests on a statistical description of the system, and so is not a fundamental aspect of the universe.

and while we do treat spacetime as a continuum too, it is quite possible it is something discrete in order to have quantum gravity, thus temperature and related parameters are really the few things that can exists as a continuum

John Rennie

@aminliverpool I think your statement is meaningless.

ACuriousMind

@Secret Then we already have variables that are of greater "size" than the reals - fields. The set of all real functions of real numbers is of greater cardinality than the reals.

John Rennie

Physicists describe the universe using mathematical models.

Dawood ibn Kareem

11:13 AM

@Secret Sorry, I refuse to buy into discrete space time. If we had it, we'd have to throw away all sorts of symmetry properties to do with rotation.

John Rennie

If we use a model of something as the manifold $R^n$ then it's cardinality is that of $R^n$.

It's tempting to ask if that's really true, but then you'd have to decide what you meant by real, and no-one has managed that yet.

ACuriousMind

@Secret I think you are once again chasing some statements that sound fancy but don't actually mean anything physically interesting.

Secret

@ACuriousMind Wow, I have not thought of that. I knew one good example of a $\aleph_2$ set is $\Bbb{R}^{\Bbb{R}}$ (the other being the power set of reals) and I have been pondering how on earth can we put the space of functions (as functions are mathematical constructs) into the physical universe, I never considered fields, but it seems to be a nice example

@ACuriousMind How is temperature not a valid physical example. While I do know it is not fundamental, there really isn't a notion of smallest unit of temperature as far I know?

Meanwhile:

in Mathematics, 19 hours ago, by Secret

whether we can have some fundamental aspect of the universe that has size $\aleph_1$, I am not sure, but my bets put on time

user84215

In physics observable quantities are regarded as continuous ones to use mathematical tools to formulate them.

John Rennie

Wow, only 3 items in my review queue. That has to be a record. Has someone been assassinating the homework posters again?

@aminliverpool yes, that tends to be convenient.

ACuriousMind

11:20 AM

@Secret Of course temperature is a valid example of a real-valued quantity. And "there is no notion of a smallest unit of temperature" is a physically meaningful observation. That we model temperature by real numbers and that the real numbers have a certain cardinality is not.

Anonymous

@JohnRennie In this java code (line 71) how is it valid to create an object of Student class in Solution class without even extending/inheriting the Student class it? Any idea?

ACuriousMind

A rational-valued quantity would also have no smallest unit - this observation is really not about cardinality.

user84215

So we cannot conclude that they are real quantities.

user84215

I mean real numbers

John Rennie

@aminliverpool no-one is claiming they are.

Dawood ibn Kareem

11:21 AM

@Blue What makes you think you need inheritance in order to instantiate an object?

John Rennie

@aminliverpool It is just convenient to assume they are.

Secret

Well, I am just curious on whether our physical world actually did allow something that models the alephs, indeed, other than as a piece of trivia, it is not very interested to the community at large

Anonymous

@DawoodibnKareem Because it doesn't make much logical sense otherwise. We are creating an object of class which is no way related to the current class

Dawood ibn Kareem

@Mostafa and I believe you'll find "go" means "will" here too.

Secret

But in my own opinion, I still find it nice to know that we do have physical examples of infinity, in some sense

Dawood ibn Kareem

11:23 AM

@Blue Of course it makes logical sense. You're creating a Student object. There's no need to extend anything. The Student class is already perfectly adequate as a description of Student objects.

John Rennie

@Blue I don't understand the problem. One of the methods in one class is instantiating an object of an unrelated class. What's the problem?

Secret

So, (most people might disagree with me that it is interesting), but my point is, this discussion does told me infinity does physically exists, in some form in our physical universe

user84215

So we cannot discover something having infinite size.

Dawood ibn Kareem

@Blue The ClassLoader loads the Solution class first and starts running main. When it reaches new Student( ... ), it loads the Student class. Because Student extends Person, it then loads the Person class. Once all three classes are loaded, we can make Student objects.

John Rennie

doing so would take an infinite time ...
You could prove something was finite in a finite time, but how would you prove it wasn't finite?

Anonymous

11:26 AM

@DawoodibnKareem The ClassLoader loads the Solution class first because it contains the main method? Or some other reason?

user84215

discovering=observing

Secret

aren't there physical process that blows up in finite time, I do recall some of these (I forgot the name, though)

John Rennie

@aminliverpool yes

Dawood ibn Kareem

@Blue When you run your program, you specify on the java command line which class to start with.

Anonymous

@DawoodibnKareem In BlueJ I usually execute the main method. So yeah, makes sense now. Thanks!

Secret

11:27 AM

(ok nvm, it is literally called Finite Time Blowup processes)

ACuriousMind

@Secret The rationals are also infinite. You are constantly changing what you are talking about. Also, the physical existence of mathematical concepts is itself a concept of dubious meaning. You are conflating physics - describing the world by mathematical models - with the ontological position that these models are "real", whatever that means.

user84215

What is the question exactly?

Dawood ibn Kareem

When you do that, BlueJ starts a new process that looks like
**java solution**
maybe with some other command line options in there. In terms of what happens next, it's really no different from running from the command line. There needs to be a function with the signature
**public static void main(String[] args)**
inside the class that you specify on the command line - that is, the class that you tell BlueJ to run.

ACuriousMind

It's a classic example of a map/territory fallacy - just because I used crayons to draw a picture of you, it doesn't follow you consist of crayons.

John Rennie

@aminliverpool Presumably:

25 mins ago, by aminliverpool

Discovering something having infinite size is meaningless in physics.

Dawood ibn Kareem

11:30 AM

Not infinite size! Just something that can be measured with a continuum.

Anonymous

@DawoodibnKareem Yes. Gotcha!

Secret

Yeah, my focus is the continuum, that's why I ignored the countably infinite rather unawarely

Dawood ibn Kareem

I use a real number to express my height. There are infinitely many real numbers. It does not follow that my height is infinite.

user84215

anyone has any problem with my statement ?

Secret

But Acuriousmind point still holds. I do have a problem of conflating relational existence with physical existence,
I am guiilty of this, just because this had the side effect of actually making abstract concepts more "tangible" and easier to think about

ACuriousMind

11:32 AM

Now, I'm not saying it's completely wrong to claim that the "reals" "exist", but this requires to you assume that the models of physics are the same as the reality they describe. This becomes somewhat troubling when you consider the models are subject to change as new science happens.

Anonymous

@JohnRennie Got it now :)

Secret

right, in that case, it is equally valid to have height, temperarture etc. to be wrote in terms of rationals, that will eliminate the need for a continuum

Dawood ibn Kareem

@Secret Please don't limit me to using rational numbers to express my height.

Secret

I won't, I really like all those cardinal numbers because thy do weird things

Dawood ibn Kareem

I may well be $\sqrt{33490}$cm.

ACuriousMind

11:35 AM

@DawoodibnKareem Are you $\pi$ meters tall? :P

Secret

I like anything that is weird

user84215

real numbers, infinity, ... are only mathematical ideals.

Dawood ibn Kareem

@ACuriousMind No, but when I was younger, I was $\pi/2$ metres tall.

ACuriousMind

Nice application of intermediate value ;)

Secret

But yeah, I think I need to be more careful not to get trapped by the map/territory fallacy

(though that will mean I need to develop a mindset on working with concepts without need to be able to "feel" it, whatever that means...)

Dawood ibn Kareem

11:37 AM

@ACuriousMind My parents always believed I was rather irrational as a teenager.

ACuriousMind

Hehe. Since the rationals are of measure zero, I guess all teenagers are irrational almost always...

Secret

Indeed Indeed

Dawood ibn Kareem

I'd go further than that. I'd say that all humans are irrational right now.

Secret

Wondering how many of them are transcendental

ACuriousMind

@DawoodibnKareem Even when they do math?

Dawood ibn Kareem

11:39 AM

@ACuriousMind I edited my comment. I realised it was false.

ACuriousMind

Very...rational of you.

Dawood ibn Kareem

You see why I don't buy into quantised space time?

Secret

hmm?

Anonymous

@DawoodibnKareem One more question. I know that an abstract class is one which cannot be instantiated but can be sub-classed. But, what is the benefit of using an abstract class then if I could manage with a normal class ?

Secret

@DawoodibnKareem I mean, why don't you?

user84215

11:43 AM

then what are in the gaps?

Dawood ibn Kareem

Well, you have Student and Person, right? Suppose you also had Professor and TeachingAssistant and Janitor. If every Person is a Student or a Professor or a TeachingAssistant or a Janitor, then maybe you'd never instantiate Person directly. Declaring Person as abstract communicates that as the intended use of the Person class.

Remember that writing code isn't just about telling the computer what to do. It's also about telling other people who look at your code what you intended to do.

ACuriousMind

@aminliverpool What gaps?

Dawood ibn Kareem

@Secret OK, how do I get from being 1000000000000000000000000000 distance-units tall to being 1000000000000000000000000001 distance-units tall?

ACuriousMind

@DawoodibnKareem wear high heels

user84215

if we consider spacetime discrete

Dawood ibn Kareem

11:46 AM

LOL!

Secret

well, if the unit is of planck length, then easy, 1m will overshot many many planck length

Anonymous

@DawoodibnKareem Oh, okay!

ACuriousMind

@aminliverpool From the intrinsic view of spacetime, it would have "gaps" no more than continuous spacetime has an "outside".

Dawood ibn Kareem

@Secret OK, so same question. How do I get from your "many many" to many many + 1?

How long does it take me, and how tall am I while it's happening?

Assuming I don't grow upwards at the speed of light, of course, otherwise the answer would be one Planck time, or something ridiculous like that.

Secret

1/planck's legnth is a finite but increadibly huge number. It is trival to add one more planck length.

If I understood about quantized spacetime correctly, at the smallest scale, and assuming quantum stuff not prominant so we can talk abotu tracjectories, then motion will look like 8 bit games it just hop from one unit to another

i.e. instead of seeing ----------->, you see - - - - - - -> instead. This is perfectly fine since in the discrete topology, such motion is still continous anyway

(and don't forget, I am weird enough to consider about modelling discontinous worldlines, so...)

Dawood ibn Kareem

11:50 AM

I get what you're trying to say, but I still reject it. I just like my space continuous.

Secret

It's ok, I don't have strong preference for or against spacetime being continuous

as either choice is going to increase diversity and keep me from being bored anyway...

Dawood ibn Kareem

OK, here's another example. If I travel 1000 Planck lengths north, then 1000 Planck lengths east, how far away from my starting point am I? If the answer is 1414 Plank lengths, then what happened to the extra 0.213....?

Secret

Assuing the units are equares, then the correct metric has to be the manhattan distance, so you cannot get surds

Dawood ibn Kareem

Please, don't Manhattan this! As I said earlier, that throws away all the rotational symmetry we've come to know and love.

Extending your argument would imply that if I travel 1000 miles north and 1000 miles east, I'd be 2000 miles away from my starting point. Which I'm plainly not.

Secret

Experiment will inform us what spacetime truly is, whether it is fundamental, or a bunch of calabi yaus, or just a network of entanglement, or something more exotic. I am not worried, as long it is what the epxeriments told me, I am happy

Anonymous

11:54 AM

@DawoodibnKareem Here, in line 52 which class's display() method is being invoked? According to me Book book = new MyBook(title, author, price); creates an object of MyBook class but it is treated as Book class's object. So the display method should invoke the abstract Book class's display() method which is an empty method. However, according to the output it seems that the subclass's method display() has been invoked.

Anonymous

Could you explain where is my logic wrong?

Dawood ibn Kareem

It's MyBook's display method that gets called. That's what polymorphism is all about.

The method is chosen according to the class of the object that was created; not the type of the variable that you referenced it with.

Secret

@DawoodibnKareem If spacetime is really discrete and we are considering things where this chunkiness is important, we probably cannot think in terms of the continuum anymore, thus yes, rotational symmetry might had to be broken. If it does not, then we need some other group to play the role of rotation as we know it

Dawood ibn Kareem

I wish to keep rotational symmetry. I quite like rotational symmetry.

It's nice and symmetrical, in a rotational kind of way.

Anonymous

@DawoodibnKareem The class of the object book is Book or MyBook ? I'm finding the statement Book book = new MyBook(title, author, price) a bit confusing

Secret

11:57 AM

But remember, models are nice, but they are not necessary the reality, experiment told us what the reality is (and I am quite truth seeking, modulo that conflation that acuriousind and many others spot in my thinking)

Dawood ibn Kareem

The class of that object is MyBook.

Anonymous

@DawoodibnKareem But then why don't they just write MyBook book=new MyBook(...) ?

Dawood ibn Kareem

But you can reference it with a variable of type MyBook, or a variable of type Book, or a variable of type Object. It doesn't matter which.

Secret

ultimately, all models has to test against experiment, only experiment has the final say on the reality (or something sufficiently close to it)

Anonymous

@DawoodibnKareem Okay, I didn't know that

Dawood ibn Kareem

11:58 AM

@Blue OK, that question appears on Stack Overflow. Along with many duplicates, because people keep asking it. I'll try to find it for you.

603

Q: What does it mean to "program to an interface"?

I have seen this mentioned a few times and I am not clear on what it means. When and why would you do this? I know what interfaces do, but the fact I am not clear on this makes me think I am missing out on using them correctly. Is it just so if you were to do: IInterface classRef = new Objec...

Secret

Though, I have to say, I really like this one:

Anonymous

@DawoodibnKareem Reading it, thanks

Secret

47 mins ago, by ACuriousMind

@Secret Then we already have variables that are of greater "size" than the reals - fields. The set of all real functions of real numbers is of greater cardinality than the reals.

I have spent ages trying to find a nice example where $\Bbb{R}^{\Bbb{R}}$ is used and this nailed it

Dawood ibn Kareem

How about trajectories?

The number of paths from where I am now to where I'll be in 5 minutes is $\aleph_2$, right?

Secret

well, the problem of that is you can only have a finite number of trajectories realised at any one time in a region

so, in a sense, you cannot have all $\aleph_2$ at once

Dawood ibn Kareem

12:02 PM

(assuming the continuum hypothesis as usual, of course)

So? Neither can I have all $\aleph_1$ temperatures at once, but we can still speak of $\aleph_1$ possible temperatures.

Secret

Ah, valid point

Anonymous

14

Q: Is it possible to call subclasses' methods on a superclass object?

Animal is a superclass of Dog and Dog has a method called bark public void bark() { System.out.println("woof"); } Consider the following: Animal a = new Dog(); if (a instanceof Dog){ a.bark(); } What will happen? the assignment isn't allowed the call to bark is allowed and "woof"...

java inheritance subclass superclass

Secret

right, then in that case both trajectories and fields should work as $\aleph_2$ models

Anonymous

The answers to this question seem to contradictory.

Anonymous

Animal a = new Dog()

Dawood ibn Kareem

12:04 PM

I find trajectories slightly easier to visualise than fields. But maybe that's just me.

Anonymous

They say that a is an object of Animal class rather than Dog class so when we call a.bark() it won't work

Dawood ibn Kareem

No, a is a reference of type Animal. It refers to an object of class Dog.

Secret

I tend to picture scalar fields as a region with different color gradients which represent the magnitude and phase, and vector field as being blown and move around in all directions as you move through it, and tensor field is like at each point, you are being squished in all directions

My next challenge is to visualise quantum fields, because they are weird

Dawood ibn Kareem

It's important to remember that all variables in Java are either primitives or references.

Secret

and as usual, I like weird things

Dawood ibn Kareem

12:07 PM

The compiler won't let you write a.bark(), because it's possible for a to refer to a Cat, which presumably can't bark.

Anonymous

@DawoodibnKareem Ok. But then why wouldn't a.bark() work if in my program book.display() works and invokes the subclass method even though book is an "object" of MyBook but a reference of type Book ?

Dawood ibn Kareem

Because you've declared display() as an abstract method in the Book class. Which means that every Book needs to be able to run display().

If you try to make a non-abstract subclass of Book that doesn't have a display() method, you'll get a compile error.

Anonymous

@DawoodibnKareem So you mean that in my program the abstract class's display() (which is empty) will be invoked rather than the subclass's display()?

Dawood ibn Kareem

Whereas, there's no abstract method bark() in the Animal class, so it's possible to have a subclass of Animal that doesn't include bark().

@Blue No, it's not invoked. Abstract methods are never invoked.

All they do is tell the compiler that it's OK to call display() on any object whose class is a subclass of Book.

Anonymous

@DawoodibnKareem Aha! That I guess is a typical property of abstract classes and abstract methods which I didn't know earlier. I think I understood it now

Anonymous

12:13 PM

"Abstract methods are never invoked." Need to remember this!

Dawood ibn Kareem

OK. But this is important. When you write a subclass of an abstract class, you must EITHER make the subclass abstract too, OR override all the abstract methods.

The compiler will force you to do this.

But what it's basically doing is stopping you from having an object, with a method that doesn't have any implementation.

Like if MyBook didn't have its own display() method, then the JVM wouldn't know what to do when it gets to book.display().

So the compiler stops you from getting into that situation.

Anonymous

@DawoodibnKareem Makes sense. I'm able to connect the dots now. Your explanation was very helpful :)

Dawood ibn Kareem

OK, no problem.

Secret

NB, I wonder next time when I discuss something, I should rewrite my post at least 3 times, cause it seems I made too many omissions and typos, to the point of accidentally confusing people

Barking Cat - woofing cat

►

RE: Starred

Anonymous

12:50 PM

Why does my avatar stay on the active people's list even when I close the window? Is this a bug? Or intentional?

Secret

O btw, I think I am stupid. I forgot the cantor set is an example of a $\aleph_1$ set that has gaps

ACuriousMind

@Blue Unless you click on "leave", your avatar will only drop out after a periodically running script detects you have been inactinve in chat for a while.

Secret

so even my premise that $\aleph_0$ = has gaps, and $\aleph_1$ = has no gaps is also wrong

Anonymous

@ACuriousMind Hmm, so should we complain in the mother meta about this? Or has it been already discusses before? Also I'd like the feature which shows who is typing.

Secret

which means the question is really not physically interesting even if in the highly unlikely case that map=territory, because we cannot really distinguish between the cardinals $\aleph_0$ and $\aleph_n$ based on whether something has gaps, and we must use bijective maps to compare between them

ACuriousMind

12:53 PM

@Blue You can of course complain, but I don't think it's a bug - it's intended to work that way.

Secret

NB gaps may be formalise as follows: finite valued infima and suprema of any sequence of elements in a set that is not located within the set

Anonymous

@ACuriousMind Okay. Yeah, maybe. But it should be worth making a meta post about this.

Anonymous

I'll perhaps write one if I get time

ACuriousMind

@Blue Note this should go to Meta Stack Exchange, not to our physics meta.

Anonymous

@ACuriousMind Yup, I know that. Thanks for reminding

0celoñe7

12:59 PM

@JohnRennie it works

Naveen Balaji

Hey guys! Today my friend showed me a video in which Kip talks about the depiction of the spherical wormhole in Interstellar. I have read the paper on worm holes by Kip titled, 'wormholes in spacetime' a long time ago but don't recollect the mention of a spherical appearance. Do anyone of you know a paper which might discuss this?

Anonymous

@NaveenBalaji Maybe this ? I didn't read it though

0celoñe7

@NaveenBalaji you're on a first name basis with him?

bolbteppa

1:23 PM

Anybody understand the proof that $sp(4)$ is isomorphic to $so(2,3)$?

Naveen Balaji

@Blue Thanks man, that's the one.

bolbteppa

In a sense it is just comparing lie algebras, but the crazy thing is that it starts bringing in charge conjugation, going between $so(2,4)$ and $so(2,3)$, and constructs the symplectic matric and matrices satisfying the symplectic condition from gamma matrices, but how that shows the isomorphism I am at a loss...

Naveen Balaji

@0celoñe7 Nah. Even if I did know him or saw him I wouldn't do what your friend did in a conference with Gerard 't Hooft.

0celoñe7

@NaveenBalaji My friend?

Naveen Balaji

you were 0celousky right? Or else this is not a thing to be talking to the wrong dude.

0celoñe7

1:32 PM

yeah, but I have no idea what you're talking about

Naveen Balaji

I pretty sure you meant this to be a joke, but I must say it was crazily convincing.

You told me that your friend had a pic of Gerard's butt crack, and you went on to describe the ass's geometry. Don't believe me? Go check (although I don't remember the exact date)

0celoñe7

@NaveenBalaji I have no recollection of that

Naveen Balaji

1:47 PM

Then, lets just drop this

0celoñe7

I can't find it

what are you on about?

Secret

quick cantor set question. Is the following sequence 0.2,0.22,0.222,0.2222,0.22222,... converges to 1?

John Rennie

@0celoñe7 what does?