The h Bar - 2015-11-18 (page 4 of 4)

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5:03 PM

Wow, hardcore $\cong$ pop now.

Ok, let me put it in these terms: if the gravitational wave is travelling along the z-axis, imagine that the wave is confined inside a gaussian beam shape, and that the wave is polarized along the x-axis. So points near the beam placed along the x-axis at opposing sides of the beam, will be able to send messages back and forth with less delay that a light ray would be able to, if the wave was not present — diffeomorphism 26 mins ago

@ACuriousMind I think he's making the ol' assumption: if there's a wave there must be something waving.

@0celo7 Yep, probably right (although that is not OP, it is another user which I can rarely understand :P)

Holy crap Hellsystem's Devil Face is 3 years old...

Where has the time gone!?

Alexander Bollbach

i am no physicist nor mathematician but i had a confusion about discrete vs continuous laws of nature.

are you a physician?

Ask the question, we'll answer if we can/think it's interesting

Alexander Bollbach

what is the difference between the two? is continuous just an ideal concept that there are no discrete points because if u plug stuff into a formula don't u ultimately have to represent it in some discrete form?

i get discrete because it is objectively representable, like states 1,2,3 etc.. but how can continuous be actually represented

5:09 PM

Why can't we have nice music like this anymore

@AlexanderBollbach I'm...not sure what you by discrete or continuous.

Can you please give an example?

@AlexanderBollbach I'm not quite sure what you're asking. What is a "discrete law of nature", and what do you mean by "discrete form"?

Alexander Bollbach

isn't discrete and continuous like basic concepts in physics and math?

quantized or analog

@AlexanderBollbach I know what discrete and continuous means. I don't know what a "discrete law of nature" or "discrete form" is.

@AlexanderBollbach Are you asking about quantum vs. classical?

Alexander Bollbach

not exactly

5:12 PM

And not everything quantum must be "discrete".

Alexander Bollbach

i mean maybe those are examples of discrete vs continuous

i guess i just don't get the concept of continuous as applied in math or on paper

It would really help if you can give us an example what you're thinking about

Alexander Bollbach

i don't have any examples in mind

Continuous means that the preimage of an open set is open...

:P

Alexander Bollbach

i could produce some if the concepts themselves aren't enough to go on

yeah i don't know about sets that much

5:13 PM

@AlexanderBollbach Neither of us have heard of these concepts before.

Alexander Bollbach

what

thats insane

Perhaps.

Alexander Bollbach

i read these words literallt everyday just reading lay person physics stuff

@0celo7 Not in "discrete" vs. "continuous", that usually is $\mathbb{Z}$ vs $\mathbb{R}$.

@ACuriousMind I know

I was being cheeky

5:14 PM

@0celo7 How was he supposed to tell?

1 min ago, by 0celo7

:P

You're bad at this.

@AlexanderBollbach Then give us examples.

@0celo7 I would also use that if what I said is correct, but may come across as a bit brusque

@ACuriousMind Fair enough.

@AlexanderBollbach Let's just say that I can grab a random book from my shelf and it will not mention "discrete laws of nature" or "continuous --".

@AlexanderBollbach Okay if you hear "discrete" vs. "continuous", it's the difference between the integer numbers and the real numbers - in the first, you can "step forward" by adding 1, there's a well-defined notion of a successor of a number. In the second, that doesn't work, the reals are infinitely divisible, between two real numbers is always another, so there is no "step size".

What about the rationals, though :p

5:22 PM

I was just waiting for someone to say that :P

@Slereah interested in qm computing? :D

What about them?

@0celo7 They're also infinitely divisible, but usually not seen as "continuous" (for one, because they have a bijection to the integers, for another, because they have the discrete topology as a subset of the reals)

@ACuriousMind Hmm

Ich sehe kein issue

I'm half serious about that

I'm not sure what the issue is

"Are the rationals continuous"?

No, because they're not complete

5:26 PM

@0celo7 The issue is mainly that it is not really defined what it means to say of a set/space to be "continuous", one just uses "continuous" in an informal way to mean the "opposite" of discrete (but not really the formal negation).

Alexander Bollbach

continuous to me represents the idea that a dimension/space/value or whatever isn't quantized.

@ACuriousMind Ah

@AlexanderBollbach Define quantized

@AlexanderBollbach Well...that's not formally defined either, what is a discrete (or "quantized", but I'd reserve that word for actual quantum phenomena) dimension supposed to be? Spaces can be "discrete", but calling every non-discrete space continuous seems a bit weak. Values could be either discrete or continuous in the sense that they either lie in the integers (or an image of the integers) or in the reals.

Alexander Bollbach

well i am a musician so i know the concept of quantization through the process of shifting over any music element in time, the x axis, by some amount to place it on some "discrete" value

at regular intervals

Completeness of the real numbers

Intuitively, completeness implies that there are not any “gaps” (in Dedekind's terminology) or “missing points” in the real number line. This contrasts with the rational numbers, whose corresponding number line has a “gap” at each irrational value. In the decimal number system, completeness is equivalent to the statement that any infinite string of decimal digits is actually a decimal representation for some real number. Depending on the construction of the real numbers used, completeness may take the form of an axiom (the completeness axiom), or may be a theorem proven from the construction. There...

Alexander Bollbach

5:31 PM

quantize a rhythmic pattern to 1/16 notes would involve taking all the values that happened with precision to the micro second and "snapping" them to values (1.16 notes at 120bpm tempo) that are note precise to microseconds but perhaps milliseconds

@ACuriousMind I found out that my topology class covers AoC, cardinality, etc.

And analysis 1 next semester does logic.

@AlexanderBollbach That may be the musician's concept of quantization, but I don't see any direct connection to the physicist's idea of quantization, which, by the way, is not the same as discretization.

discretizing is what you do when you want to feed your theory into a computer, quantizing is what you do when you want to get quantum physics from classical physics.

@ACuriousMind there actually is an amazing/ extraordinary connection between "discretizing vs quantizing" that hasnt been widely uncovered/ appreciated yet...

@ACuriousMind So quantum computers are discrete quantized things

@vzn What do you mean?

5:39 PM

@ACuriousMind its a long story...

have blogged about it somewhat

@vzn If it is "amazing" and "extraordinary", surely there are papers about it?

@ACuriousMind maybe on viXra

@ACuriousMind there are many amazing & extraordinary papers yet to be written, agreed? :)

@vzn For things not yet written, one should suspend judgement until one reads them, agreed?

yes there are bazillions of papers touching on it, dancing around it...

@ACuriousMind & so we are right back where we started eh? :)

0celo7 how many papers have you published? :P ...

5:44 PM

@0celo7 weird subdivision of subjects...we will talk about forcing and models of ZF soon so :-P

0celo7 something for you to ponder outside of physics

Rationals aren't complete because there are rational sequences that do not converge to rationals

@Slereah Thank you for that random fact :P

Yo @Danu :-)

It was not random you numbskull :V

5:49 PM

@Slereah for any topology?

@Slereah You also forgot to add Cauchy in there :P

The sequence $1,2,3,4,\dots$ converges to no rational, but also to no real, and yet the reals are complete.

What's a Cauchy numbskull

@Slereah you are allowed to give us the finger that time...

but it's funny to be mathematically pedantic

that it is

in physics you have handwaving, not pedantry

6:03 PM

right

hand waving is to physics as pedantry is to math :P

6:14 PM

"This doesn't converge? Let's say it does."

guess and check

Hmm...I cannot flag as NAA and flag for mod attention? Damn.

I would choose the latter.

Problem is, I have already done the former because it is NAA

But I'd also like to notify the mods in particular...

@ACuriousMind Flag once! :)

You can link it to the chat and argue what's wrong with it.

6:20 PM

^

I have a reason not to post it in chat.

And had I known I can only use one flag, I'd have chosen the mod flag, yes.

Ah, thanks @Qmechanic

live and learn :P

@ACuriousMind : What did I do?

@Qmechanic You deleted the post in question.

@ACuriousMind : OK I think I know which.

6:30 PM

@Qmechanic I thought it was a bit extreme

also @ACuriousMind

physics.stackexchange.com/posts/219240/revisions

What's so terrible about it?

Okay, I didn't want to chat about it because:

11 hours ago, by DanielSank

@user36790 Would you mind not talking about that user any more?

but now we have to

@EmilioPisanty There's a user going around that is convinced that dmckee, DanielSank, ja72 and a host of other users are really just sockpuppets of DanielSank

And this is another of their accounts - the deleted post is just the passive-aggressive version of their belief that "DanielSank doesn't know any physics".

The same account has other already deleted answers which are more...explicit about this

@ACuriousMind How can facts be passive-aggressive?

@Slereah Did you retake the Castle?

What "sea monster" should I expect?

Should I bring the Fat Man?

user image

@0celo7 What? The high praise there is rather obviously ironic if you see the post in context with the other posts of the user

Wait...you can't even see the deleted post, what are you talking about?

@ACuriousMind Oh, OK, fair enough.

@ACuriousMind Also fair enough.

@EmilioPisanty : I guess I'm not allowed to talk about it, so let me just say that this is the N'th post caused by the same person using multiple accounts that I had to delete in the last couple of days, and hence, the gloves are off.

6:39 PM

@Qmechanic Sure, now that there's more context that's pretty OK.

Bare knuckle UFC?

Could have had a slightly clearer message, I guess. "to keep the site clean" looks weird to any 10k'er that happens to wander in. (Yeah, I know, there's loads of us.) "For moderation reasons", maybe?

Not that it really matters.

What does your @EmilioPisanty avatar represent?

@skillpatrol Good question. Figure 11(c) of arxiv.org/abs/1507.00011 .

Closest-approach times of an electron that's been tunnel ionized by a strong laser field.

Nice :-)

6:46 PM

I took the castle yeah

And their funky dynamics as a function of the asymptotic momentum. For any given momentum there's multiple roots of r(t)·v(t)=0, and if you move the asymptotic momentum around they play musical chairs. If you do a closed loop in momentum space the roots can end up swapping chairs.

It's a giant giant crab

user image

user image

Neat graphs

@Danu Yeah, those took something like three days all told

Supplementary info took a week

episanty.github.io/Slalom-in-complex-time

@MarkMitchison still around?

7:45 PM

@ChrisWhite any luck on the job hunt so far?

8:19 PM

How much longer are we without John's company?

It's hard being without a friend...

The suspension period ends in 2 days.

Perhaps, he may not come back...

Hi @TanMath :-)

@skillpatrol hello!

hey @MarkMitchison!

@EmilioPisanty looks like.. I talked to him about a week ago.. looks like he last talked 2 days ago... you guys in the same university?

@TanMath Yeah

Just wondering if he was still logged on, was all.

@skillpatrol I hope he comes back

I enjoy the game we play

I know you do ;-)

@EmilioPisanty he left this comment 6 hours ago.

I tend to agree with him...

8:44 PM

@yuggib "Analysis 1" is code for "set theory"

I take a different analysis class that uses Rudin and does analysis

9:16 PM

@0celo7 why?

10:02 PM

Rudin is the standard undergrad textbook in the U.S. @yuggib

"The Classic"

@skullpetrol the why was for the set theory thing

why do st in an analysis course (apart from the very basics if needed)

Oops, sorry :-/

Perhaps they do st to prepare students for further courses?

Would that^ be considered "pedantry"? @yuggib

maybe... :-P

:-D

1 hour later…

11:29 PM

Hell...no one ever curated those res. rec. answers after the policy was established.

There are so many highly upvoted answers which just say "read this book, it's good"

Why were people so adamant about letting res. rec. stay on topic when most answers those questions get are just devoid of any actual content?

11:44 PM

@ACuriousMind I beg to differ

Case in point:

36

A: What is a good introductory book on quantum mechanics?

Introduction to Quantum Mechanics by David Griffiths, any day! Just pick up this book once and try reading it. Since you have no prior background, this is the book to start with. The most voted up answer right now has referenced books that are pretty rigorous and dense in content. Griffiths is no...

38 upvotes for "Go read Griffiths".

google.co.uk/…

45 results for explicitly curated questions

Oh, you meant to differ with no one curating!

plus many more where there was little need for a dump answer

(that google link doesn't work for me, but I see what you mean)

11:48 PM

for sure there's many that still need a thorough going over

but that doesn't mean that we didn't do many of them

Maybe I have just bad luck stumbling upon those where that hasn't happened yet

Maybe, maybe not

If it's just answers with some commentary where you disagree with the upvotes, then there's not all that much to be done about it, really

but if it's just answers with no commentary then by all means give them the treatment

@EmilioPisanty The problem I have is that the commentary is often of a completely anecdotal nature ("I like it","It's good for X") instead of being the semi-objective commentary demanded in the policy (say why specifically you like it, what sets it apart, what topic does it cover)

That one's a hard one to fix, and I feel we do an OK job within the circumstances.

The answer you reference does give (I feel) more than just "I like it", it gives a pretty good description of the level of the book

But I agree with your comment

Which is why I feel [books] questions should always be CW

@EmilioPisanty Well, I agree with that, and it seems currently that's the majority view although +11/-2 is a little less voting activity than I'd have liked.

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