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2:26 AM
whoop whoop
 
3:24 AM
,000,000 the second, third, fourth,...stars on this message are worth a million each.
7
 
vzn
4:21 AM
in Computer Science, Dec 23 '16 at 2:06, by vzn
> People stumble over the truth from time to time, but most get up and go on as if nothing had happened. —Churchill
 
 
3 hours later…
7:04 AM
@SirCumference dying a slow death
 
:'(
perhaps, @loong we should think of it as a rebirth?
when faced with the thought of death...
 
 
1 hour later…
8:18 AM
morning
 
8:33 AM
You know I wish books would offer like a representative picture of the equations therein
Just a small sample of the equations and you get a pretty good feel of what kind of book this is going to be
 
I am looking for a book on PDE that has this kind of feel :
Because I am encountering this kind of stuff a lot lately and I probably need to learn it
something something PDE something something Sobolev space
Maybe I should do an Official Classification of Equation Feelings
 
the approach discribed by Paul Halmos to reading a math textbook is official enough for me
> Don’t just read it; fight it! Ask your own questions, look for your own examples, discover your own proofs. Is the hypothesis necessary? Is the converse true? What happens in the classical special case? What about the degenerate cases? Where does the proof use the hypothesis?
 
I want to fight it
I want to KILL IT
 
that is how you pwn it
 
Wow, originally recorded 1958 :O
 
Here's something recorded an even longer time ago!
 
thanks for sharing
 
9:15 AM
I have asked a US friend to try for an interlibrary loan for that thesis
I'll get the bloody thing
If I have to steal it myself
 
Hi guys
This comes from the Feynman Lectures, but I do not get the sentence in red
Why the negative?
 
@Slereah a) Evans: 'Partial Differential Equations'; b) Taylor 'Partial Differential Equations' 3 volumes.
 
I'll start with the one that's not 3 volumes, I believe
I'm running out of shelf space as it is
 
9:30 AM
I don't know exactly what those norms mean but they look very similar to the usual PDE stuff in those books
 
Typical Lp norms I think?
 
What does the $L_t^p L_x^r$ thing mean, it's like a norm on a normed space or something
 
That it's $L^r$ integrable in space and $L^p$ integrable in time?
 
Yeah maybe it means $L_t^q$ on the $\mathbb{R}$ factor in $\mathbb{R} \times \mathbb{R}^d$ and $L_x^r$ on $\mathbb{R}^d$
Probably in the Fourier section of one of those books
 
it is the art of ~estimates~
Which is what I'm hoping to do
because I want to check if all of physics is a sham
just in case
estimates is what you're supposed to do when you say "it's small" but that nobody does
for all I know those $\mathcal{O}(\varepsilon^2)$ perturbations are about $10^{30} \text{m}$
 
9:47 AM
This kind of math in physics is a sham
 
I mean I know it exists
There's plenty of estimates shenanigans in GR
And that's kind of what Ryan does
But they are scary papers
Hence why I must investigate this first
It seems the book you recommended follows the "Put some absolutely indispensible theorems in the appendix" philosophy
 
Yeah, but they are standard recommended books for this kind of stuff, I think the 3 volume one proves more of those things, this stuff was just too hard and too unmotivated for me
 
Although this isn't quite as bad as Straumann's "Put everything about differential geometry in the appendix"
Who needs differential geometry for GR!
One thing I do not approve of : multi-index notation
Would it kill you to write two index instead of one
It's not like you're gonna do an order 32 PDE
Even order 3 rarely appears
Order 9 PDE
The horror
 
10:17 AM
@Shootforthemoon Any ideas?
 
so weird thought:
If all abstract things exists and is experimentally accessible, then what distinguish between physics and metaphysics?
 
Abstract : existing in thought or as an idea but not having a physical reality
 
If they are experimentally accessible, i.e. with objective measurements, then there's no difference and the metaphysics would be still physics
 
I see
 
It's generally not terribly interesting to take two vague but opposite labels and blurring them
in philosophy circles that u enjoy this is called a language game
aka wanking
 
10:31 AM
I can't find a univocal definition of electric potential difference and a good source with all the concepts explained: voltage, voltage drop, voltage rise, signs, etc. Is there a reference or a book you advise?
 
@Shootforthemoon Do you want to it for electric circuits or for classical electromagnetism?
 
@Knight Both of them actually
 
@Shootforthemoon Do you know multivariable calculus?
 
@Knight yes, a little bit
We faced the topic, not so in detail, but still the general part and the main concepts
 
11:01 AM
See if it’s your first introduction to Electromagnetism then go for University Physics by Sears and Zamskey, if you have already learnt the basics of EM then go for Introduction to Electrodyanmics by Griffiths and Feynman Lectures on Physics Volume 2 .
@Shootforthemoon
 
Thanks very much @Knight
 
@Shootforthemoon You're always welcome.
 
12:10 PM
@JakeRose yeah, I figured that out
 
My niece has just received an offer of a place at Girton college Cambridge!
I'm getting all nostalgic now :-)
 
12:33 PM
@JohnRennie Congratulations to your niece. She must have inherited your traits.
 
@Knight not really, she's applied to do a degree in archaeology not physics.
 
1:02 PM
@JohnRennie Means she is gonna hypothesise about what happened in past?
 
1:57 PM
that's a...useful way to remember it
 
Mr. Astro Nomer
 
he's got some top tier physics memes
 
2:13 PM
Wow! I've never seen a comment with 4,000,000 stars until now :P
 
2:24 PM
* 4,000,000
 
He should have used 000,000
 
true
00,000,000,000,000,000,000,000
 
@JohnRennie Aww... Congrats! Making me nostalgic for that day - we had a school open day the next morning (I got the call in the evening), so I have a wonderful memory of sitting in orchestra when one of my friends asked if I got an offer. The conductor (who was also my form tutor, music teacher and knows my parents) overheard. Much fun :D
 
an Avagadro's number of consecutive zeros
 
Also, if this holds up, wow:
 
2:43 PM
165 pages :-/
 
2:54 PM
@Mithrandir24601 is there anyway to put the rss feed from that blog in the classical channel room?
 
@APerspicaciouslyCuriousMind It's already there
in The Classical Channel, 22 hours ago, by Scott Aaronson
posted on January 14, 2020 by Scott

Here’s the paper, which weighs in at 165 pages. The authors are Zhengfeng Ji, Anand Natarajan, my former postdoc Thomas Vidick, John Wright (who will be joining the CS faculty at UT Austin this fall), and my wife’s former student Henry Yuen. Rather than pretending that I can provide intelligent commentary on this opus in […]

 
okay, thanks :-)
I should check that room more often.
kinda quiet in there
+
I'm not into comics, that much
which is all I see when I do go in there
 
3:09 PM
What people in business mean by saying "your target market"? I mean, is there a list online where I can choose one?
 
@NovaliumCompany It basically means - which group (s) of people are you going to try to sell this to. Marketing to men between the ages of 13-18 is a lot different than marketing to women between 40-55 for example. I'm sure you could find a lot more ways to divide it. You could also target groups based on hobbies, for example.
 
A target is what you aim at.
 
Yeah, got it. So I "make it up"? There isn't like an official website where you choose from?
 
Got it
@APerspicaciouslyCuriousMind Your name is suprisingly familiar
 
@NovaliumCompany You can probably find some good lists around. I doubt there is anything official; but I bet there are plenty of marketing textbooks that actually do have categories, like age group demographics and stuff.
 
Gotya, thx
 
Your objective is to reach a certain market of buyers.
 
Like marketing to 5-18 year old men probably doesn't make much sense, since a 5 year old and 18 year old typically have very different interests, so taking an age range from someone who actually studied marketing is probably a good idea.
 
If anyone wants to learn Marketing and Analytics, I'll teach him, contact me.
 
3:23 PM
Is the Minkowski metric invariant under a transform of scale?
 
@NovaliumCompany A website, or other external agent, cannot tell you who you are targeting. Just think, who is your business, product, etc. for? That is your target market
For example, if I was a diaper company, my target market would be "people who have babies"
The target market is just whoever you think would want to buy your product, engage in your services, etc.
 
@AaronStevens Are there different diapers for boy and girls.../ I don't remember anything about it.
 
@AbhasKumarSinha I don't believe so. Except for, perhaps, different patterns that tend to be associated with boys/girls I suppose
 
@AaronStevens Okay...
 
@AbhasKumarSinha How do you doing?
 
3:31 PM
@Knight Grea... you..
 
@AbhasKumarSinha I’m good
 
@Knight Doing wat.../
 
@AbhasKumarSinha I have just watched the movie Heat
 
@Knight Is it cold in states/
5G data in India for 1.3 USD
/perGB
 
Actually we have got Wi-fi here in US
 
3:36 PM
@Knight Wifi is free in India, for most of the public spots, but very less people use it for security issues.
 
@Knight Presumably India does too... But people do still pay for data on their phones.
 
@JMac Have you watched Heat?
 
@Knight No.
 
Very old movie... It's 2 decades almost now.
 
YOU should watch it
It’s old but a great movie
 
3:43 PM
The only old movies of hollywood I've enjoyed is MIB, Jurassic Park, Titanic and Spy Kids with my father.
There are other ones too, dun remember them, very old days.
 
All those movies doesn’t convey any strong idea.
 
@Knight A 1 year old kid won't understand anything whatever kind of movie that is, whatever, spending childhood time with father is one of the time, irrespective of movie.
 
@AbhasKumarSinha now you are big so please watch some good movies
 
@Knight I'm big now, that's why I lack time.
 
@AbhasKumarSinha Make some time
 
3:49 PM
@Knight no time to make time.
 
Everyone has got 24 hours only in a day
 
I'm getting old and grey, a lot of schoolwork....
@Knight To be precise, career is more important.
 
@AbhasKumarSinha What you doing these days?
 
@Knight Carrier, exams, practicals, lack of sleep for many days, half dead.
 
@AbhasKumarSinha What exams?
 
3:52 PM
@Knight Preboards.
 
@AbhasKumarSinha Do you know driving?
 
@Knight No time, I go to school by walking, cycling to more distances, all the shops and commodities are nearby, never needed.
 
@AbhasKumarSinha Do you know 🏊‍♀️ swimming?
 
@Knight Yes.
 
@AbhasKumarSinha Can you save me during drowning?
 
3:59 PM
@Knight no, I never took life saving/rescue courses. I only know to swim in controlled environment and some calm rivers, not more than that.
 
@AbhasKumarSinha Why?
 
@Knight Swimming is a sport, not a way to become a superhero.
 
@AbhasKumarSinha Just imagine that your friend is drowning and you could save him to become a hero in your sweetheart’s heart
 
@Knight I can rescue without swimming.
 
4:15 PM
1
Q: What is the "recipe" to do General Relativity?

B. W.All, The recipe for classical mechanics for one particle: come up with expressions for all forces, solve F = ma to arrive at position as a function of time. The recipe for quantum mechanics: come up with an expression for the potential energy, solve Schroedinger's equation to arrive at the ...

salt and pepper is enough....
I just now fell in love with Fluid Mechanics...
 
4:45 PM
-9
Q: PLS HELP WITH QUESTION EXPLANATION

cute girls CAN SOMEONE PLS HELP ME WITH PART C !!! Why are they using the equation v=at

OP seems to be a young student (somewhere around 13 or 14 years) beacuse the question he is asking is of very elementary level (I think Physics starts from there only) . And his frustration for not being able to solve that problem shows that he needs care and not the downvotes.
 
@Knight Down votes are not personal, nor are they a discouragement from learning physics. Down votes are solely for the purpose of this site. It is not a good question for this site, so the down votes make sense
It is not the job of this site to help others with physics homework
 
@AaronStevens I know
And I agree too
@AaronStevens You know I got the movie that I was searching for. It’s name is American Gangster
 
@Knight Oh, that's good
 
5:00 PM
@AaronStevens You know how to drive a moto-bike?
 
@Knight I have never done that, but I would assume it is not too lard to learn
 
@Knight we will answer if they ask in a chat room, just not on the main site.
 
What is the best thing you saw today?
I saw this:
 
@AbhasKumarSinha my lunch
 
@JohnRennie Sir he didn’t got that much reputation, those downvoted destroyed him.
 
5:03 PM
@JohnRennie What was it?
 
Carrot with coriander!
 
@JohnRennie seems Pulao....
Cool...
I'm coming... XD
 
@AbhasKumarSinha a risotto really, but it's basically the same as a pulao
 
@Knight I think they started with 1 rep, so they didn't lose any rep actually
 
@JohnRennie Oh okay..
Ama start learning Karv Maga and Shaolin Kung Fu from Today....
 
5:08 PM
@AbhasKumarSinha lots of countries have meals that are basically stuff cooked with rice.
 
Does anyone here like ice-cream?
 
@JohnRennie We have alot of meals basically cooked with rice...
 
@Knight Additionally, they have been given the appropriate resources to learn how to ask better questions that are on topic for this site. Up votes give much more rep than down votes take away. If they want to use this site and ask good questions, then they have the ability to do so. No one has been destroyed here :)
 
@Knight Go outside with a cone, you'll get some
 
@AaronStevens I agree
@AbhasKumarSinha I think cone will be safe but not my body
 
5:10 PM
Does anyone here knows Wing Chun Kung fu....
@Knight So take another cone for your body.
 
@Knight doesn't everyone like ice cream?
 
@JohnRennie Or at least some form of frozen dessert?
Custard, gelato, etc.
 
208
A: Why does ice cream get harder when colder?

John RennieA couple of decades ago I was peripherally involved with some research on the properties of ice cream being done by the company Walls in the UK. The work was on relating the consistency of the ice cream to the microstructure, so it was quite closely related to your question. Anyhow, ice cream ha...

The company I used to work for makes ice cream :-)
 
@AaronStevens Love Custard.
@JohnRennie Gimme Ice Cream too...XD :)
 
@JohnRennie For example sugar poisons the surface of the ice crystals and changes their morphology
Poisons?
 
5:15 PM
@AaronStevens Physics...
 
@AaronStevens inthe context of crystal growth a poison is a compound that adheres to the surface and prevents crystal growth on that surface.
 
@JohnRennie Do you know how to make ice creams of small ball shape/
 
Make a large chunk of icecream and scoop out a ball shape :-)
 
@JohnRennie smaller ball, about 0.5 cm diameter.
Hey Google seems down here.
 
Use a small scoop :-)
 
5:19 PM
@JohnRennie Interesting. I have never heard of that before. I guess it is similar to "doping" for those who are not familiar with semiconductors
 
@JohnRennie Using liquid nitrogen and dropping small drops of cream... This was secret recipe by some brand, now revealed.
 
@AaronStevens I think you get so used to your discipline that you forget not everyone is a colloid scientist :-)
 
What is the market of keyboards and mice?
Input technology?
 
@NovaliumCompany everyone who uses computers.
 
... what?
I'm asking for the name of the market.
 
5:22 PM
@NovaliumCompany is there any name to any market/
@NovaliumCompany pheripherals.
 
Just... thanks. :-)
 
@JohnRennie A similar thing happens in the biology lab we collaborate with that works with fruit flies. In order to do genetic crossing, you have to make sure you know which types of flies are mating with which other types of flies, so you know the possible outcomes of their offspring.
The issue is that the female flies store sperm from previous mates, so if you want to be as careful as possible you only want to use virgin female flies. Therefore, you often hear talk of "collecting virgins" in the lab :)
 
@AaronStevens Mating flies? I guess there are a lot of more important jobs too hahah XD
 
@AbhasKumarSinha a lot of discoveries about human genetics started with fruit fly experiments.
 
@JohnRennie Oh okay...
 
5:26 PM
@JohnRennie Nobel prize on circadian rhythm was given to fruit fly researchers
Fruit flies are a really good model organism to use in studying biology
 
@AaronStevens After Cockroaches.
 
@AbhasKumarSinha Not really? haha
 
@AaronStevens Okay, then after diosaurs.
 
Fruit flies had destroyed the fruit export market of Thailand. So "mating flies" can be an important topic, not just as a model.
 
Welp, I'm under 18, can I watch mating flies...?
XD kol hahahaha...
Bye everyone
Good Knight
 
5:43 PM
1
Q: Can anyone explain the REAL reason why $CO_2$ increases global temperatures (not the simplistic greenhouse analogy provided for public consumption)?

Hip89The greenhouse effect analogy of global warming is that atmospheric carbon dioxide $CO_2$ absorbs some of the infrared radiation emitted by the Earth, and redirects a portion of that radiation back down to the Earth's surface, thereby heating the surface more than it would have done if that radia...

Is this on topic for this site?
 
@AaronStevens What’s your weight?
 
@Knight huh?
 
@JohnRennie Sir seeing your food I can hypothesie that you are a thin man, am I right?
 
@Knight 66kg
178cm tall, so my BMI is actually about normal.
I need to go. I have a book to finish for a book club meeting at the weekend. See everyone tomorrow.
 
6:00 PM
@YuvrajSingh... I’m good with whatever I’m now. Okay?
@JohnRennie Have a good book sir.
 
6 messages deleted
Be kind to each other, folks.
 
@ACuriousMind I’m sorry sir. I will manage to be kind to everyone.
 
@ACuriousMind i don't think my message was rude in anyway though I would like to say sorry if anyone felt so.
 
@JohanLiebert It was just collateral damage because I didn't want to leave it there without its context. No worries.
 
Hi
 
6:13 PM
Hi
 
What happens if you take a lightcone rotated by -45 degrees
 
@Ultradark What happens to what?
 
What happens to the metric if you take a lightcone rotated by -45 degrees and exponentiate all coordinate pairs in the light cone, $L$, $(x,y)\in L$ such that the new points are $(e^x,e^y)\in L.$ Is the metric still equivalent to the Minkowski metric?
 
@Ultradark exponentiation is bi-Lipschitz so I'd imagine your metric is strongly equivalent
 
I know that the Minkowski metric is $ds^2=c^2dt^2-dx^2$ (but I think I would need to transform the metric because I rotated the lightcone.) and then I would have to again change the metric due to the exponentiation process. finally, I think I would have to verify whether the metrics are indeed the same
@SirCumference okay, thanks I'll look into that
 
6:25 PM
Then again I ought to review analysis so my word isn't worth much
 
6:40 PM
Hey guys! I was looking into thin-shells in GR, where the spacetime is flat inside while Schwarzschild outside. Do you know any paper(s) in which they derive the matching conditions and evaluate the Einstein action on the solution?
 
 
1 hour later…
@Loong So basically... SE are running the company to the ground; but showing emotion when people talk about their displeasure with them will likely make them worse. Fun.
 
So the beatings will continue until morale improves.
3
 
8:59 PM
I'm trying to understand the components of a gravitational slingshot, and I don't understand some aspects of the assist.
If anyone can answer my question, that would be great.
0
Q: Gravitational Slingshot

DarkRunnerIf a spacecraft slingshots around a planet P (with escape velocity V) at an angle $\theta$, I understand that the resulting velocity is $${ v }_{ 2 }=({ v }_{ 1 }+2u)\sqrt { 1-\frac { 4u{ v }_{ 1 }(1-cos(\theta )) }{ ({ v }_{ 1 }+2u)^{ 2 } } } .$$ However, this equation does not involve the mas...

 
9:17 PM
@SirCumference Sorry to ping, but could you please take a look at my question?
 
to quote our resident mod:
2 days ago, by ACuriousMind
In general, please don't ping people with your questions unless you have reason to believe they will be interested in answering them.
 
Sorry; I'm just anxious for an answer to my question, as I've scoured the internet, but haven't found a suitable solution (including in Physics Stack Exchange) anywhere
 
9:48 PM
If anyone can take a look at my question, that would be great
0
Q: Gravitational Slingshot

DarkRunnerIf a spacecraft slingshots around a planet P (with escape velocity V) at an angle $\theta$, I understand that the resulting velocity is $${ v }_{ 2 }=({ v }_{ 1 }+2u)\sqrt { 1-\frac { 4u{ v }_{ 1 }(1-cos(\theta )) }{ ({ v }_{ 1 }+2u)^{ 2 } } } .$$ However, this equation does not involve the mas...

@Semiclassical Should I take my question to AstronomySE? Seems like I'm getting no feedback here
 

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