The h Bar - 2019-07-07

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M.N.Raia

03:29

Good morning/afternoon/night for everyone!

I would like to ask you, specially for the people here who deals with General Relativity/Differential Geometry, physical implications about Manifolds.
Well, the most intuitive notion about a manifold as a model of physical reality, is then the notion of the "space of all events". Or even, the Earth itself: localy the world a, priori, appears to be flat, but if you take a high orbital flight you will see a $S^{2}$ space.

But, concerning the mathematics of a manifold, well, We have some ingredients:

bolbteppa

03:45

@M.N.Raia A topological space is the minimum amount of information needed to set up approximations, which lets you then establish notions like limits of approximations and functions between spaces which preserve notions of approximating (continuity). Given how general this is one needs to restrict the notion of being able to approximate to spaces which end up being like $\mathbb{R}^n$.

bolbteppa

03:59

Abstractly things like second countability, being Hausdorff, and paracompact, are properties that spaces like $\mathbb{R}^n$ possess that an abstract topological manifold should possess to be in line with properties $\mathbb{R}^n$ possesses. Being Hausdorff means that a given point can be approximated by points near it that can be considered far away from some other point to some error, and vice versa for that point, which is something $\mathbb{R}^n$ possesses, and it ensures limits are unique.

Being second countable encapsulates the fact that in $\mathbb{R}^n$ we can work with open balls of rational radii in finding closer and closer approximations to a given point rather than needing to use an uncountable infinite set of balls to get closer and closer to some point.

Paracompactness is a weakening of compactness that ensures partitions of unity exist (in Hausdorff spaces), where partitions of unity are needed to prove things like Stokes' theorem since you need to integrating over unions of submanifolds.

2 hours later…

Captain Bohemian

05:33

I feel thankful for people who reply my emails, which always gratify me.

1 hour later…

Novalium Company

06:40

@dmckee and @JakeRose I read your messages very carefully and I'm thankful for the advice, but right now my mind and my gut are on another decision. Luckily the time to decide hasn't come yet. I'm keeping an open mind, but as of right now, age 17, I'm on the no college decision. In the next two years maybe it'll change, maybe it won't, whatever it is, I'll make sure to think it very carefully.

I suggest we end this discussion now and come back to it a few years later. Again, thanks for the advice.

skullpetrol

06:53

did you follow this advice @NovaliumCompany?

May 19 at 2:14, by skullpetrol

@NovaliumCompany sounds like you should talk to a career guidance counsellor.

skullpetrol

07:04

I meant that^ should be available at your school

Also here is an overview :-)

> The examples and perspective in this article deal primarily with the United Kingdom and do not represent a worldwide view of the subject.

Novalium Company

07:20

@skullpetrol I know what I want to do. As I said, I have multiple ideas, some risky some not

Avnish Kabaj

I had to chose my college like last month

If you're indecisive then just go with the one which let's you explore yourself and have more options later on

I had to chose between cs at IIITD and textile at IITD

Novalium Company

@AvnishKabaj I have decided. I'm just keeping an open mind.

Currently I am 99 percent on the side of no college. I doubt anything can change my mind. That 1 percent is what I call keeping an open mind.

I appriciate the attempts to change my mind but I'd suggest trying again 2 years later.

skullpetrol

at least go to a career councillor and listen pal @NovaliumCompany

who knows, you may get some more ideas :-)

Novalium Company

07:36

sorry but nope

skullpetrol

:(

Avnish Kabaj

08:25

@NovaliumCompany man go to a college meet new people

Crypton

09:20

What are the exchange particles in the electrostatic interactions?By exchange particles imean what exactly is causing the force between them(charges)?Im not finding a source to read!!

ACuriousMind

@Crypton It's just photons, cf. physics.stackexchange.com/q/142159/50583

Crypton

@ACuriousMind nice thank you:-)

skullpetrol

09:35

strange, JohnRennie hasn't been seen for 19 hours after this message?

in Problem Solving Strategies, yesterday, by John Rennie

I need to work now for around half an hour, but I'll be back after that.

:-/

John Rennie

09:53

@skullpetrol I did return, after about 40 minutes, but the chat room was quiet.

Novalium Company

@AvnishKabaj no

John Rennie

10:33

> And English-speakers, understanding that revenge was a dish best served cold, went on to impose ASCII on the world and destroy dozens and dozens of other languages' unique letters in the same way. All of which could have been avoided if Johannes Gutenberg had stuck to Unicode from the beginning.

from this answer

Loong

10:53

Heh. Actually, Gutenberg had a quite similar idea and made many ligatures, special characters and punctuation marks. He had about 290 different characters in his type case.

ASCII has only 95 printable characters.

Novalium Company

Now that I research even more, college really seems like the worst thing for me.

skullpetrol

@JohnRennie Welcome back Sir :-)

Slereah

@M.N.Raia hausdorff for having unique limits

Pracompact and second contable to have a metric

Also a lot of theorems are wrong if your spacetime isn't Hausdorff

Ie no partition of unity

No Stokes theorem

Novalium Company

I'm actually getting pissed off about how stupid college actually is. Everyone learning the same things, the same way at the same time... it's like they are being prepared to be robots and work in a factory. So many students not knowing what to do with their lives, relying on other people to make decisions for them and tell them what to do. It's so dull...

And in the end, they end up with a shitty degree that doesn't guarantee them a job, a big student loan, thousands of dollars spent... the easiest path to mediocrity.

Anyways, I've made my decision

Thanks to everyone for the advice anyways

ACuriousMind

@NovaliumCompany That's...not how it is at most universities, at all. You usually get at least some choice over which courses to take, and no one cares how you learn things. The end goal is not to end up with a job (unless the course is very specific to some vocation), but to gain scientific knowledge in your chosen field of study.

Novalium Company

11:10

None of you is successful in the sense that I value, so why would I listen to the advice of people who haven't achieved what I want to achieve. The people who I find successful are all against college.

@ACuriousMind Alright, thanks, but this doesn't change my opinion at all

ACuriousMind

If you don't want to go to college, that's fine, but your image of it is seriously distorted.

Novalium Company

@ACuriousMind I don't want to go to college and that's fine

ACuriousMind

@NovaliumCompany Why are you talking about this here in the first place, then? If you don't want to listen to anyone here, don't waste our time and go talk to people you actually want to listen to.

Novalium Company

My image of college is not distorted, I just see it from another angle

@ACuriousMind You are right. :p

@ACuriousMind That's the best advice I've heard so far in this chatroom.

John Rennie

@NovaliumCompany I suspect that most of us hereabouts regard our college days as the most enjoyable of our lives. I'm not saying you would too, but I am wondering why you are discussing the issue with us when you already know where we stand and why we stand there.

Novalium Company

11:16

@JohnRennie I agree. Sorry.

John Rennie

Lots of people I know didn't go to college. Some have ended up richer than me and some poorer, but overall most have enjoyed their life. There are no right and wrong choices, just different choices.

2

Novalium Company

@JohnRennie Agreed

Well, I'm sorry if I have wasted your time. I value your advices and respect your opinions. Thanks.

John Rennie

@PM2Ring well, I've had a go at answering it. Whether this has advanced the role of physics in the modern world is debatable :-)

Jake Rose

11:54

@NovaliumCompany “none of you are successful in the way I value” harsh comment dude

What is the way you value?

@NovaliumCompany in fairness, none of us know what you want to do. If you want to be a scientist then there’s very little leeway in going to university. It’s just where you have to go for that type of career.

In regards to our success. We are all pretty successful in different ways. But I’d assume most of us are successful in one of the more important things, which is doing what we love. Most of us live happy lives. I think if you don’t value that type of success you’re heading down a path you’re going to be consistently disappointed by

I’d also like to second @ACuriousMind in that your view is quite distorted

We’ve all been there, or are currently there. We undeniably have a better basis to make a judgment from.

my opinion of university has completely changed from when I was 18 to now

@NovaliumCompany @ACuriousMind has a point also. You keep coming into this chat room and telling us all how much you disagree with university (or your idea of it) and how stupid it is. But this is a room that is very pro university. We’ve tried to have quite open discussions but you don’t listen to anybody and don’t engage in the discussions. So what’s the point?

skullpetrol

12:25

> Gresham's Law of trolls: trolls are willing to use a forum with a lot of thoughtful people in it, but thoughtful people aren't willing to use a forum with a lot of trolls in it. Which means that once trolling takes hold, it tends to become the dominant culture.

3

source: a harvard CSc PhD

Avnish Kabaj

He wants attention yo

I remember a kid from my school who purposefully acted different and you know was gung ho about Steve jobs and made himself look like a genius when he wasn't

Justified his crappy marks by using that Einstein quote

Emilio Pisanty

@NovaliumCompany that's a remarkably insulting thing to say, given that nobody is forcing you to be here or interact with any of us. If the only things you're going to do here are to disregard and dismiss the things said here and insult the people who say them, why exactly are you here? (serious question, not for you to answer to me but for you to answer to yourself.)

@AvnishKabaj looks increasingly like that. There's a name for that (trolling) and a clear (if unpleasant) response to it. I hope it's not the case.

skullpetrol

Perhaps the minimum age limit should be raised for this site?

Jake Rose

12:57

@skullpetrol I don’t know if I agree. I was using this when I was 16 as I think a lot of other serious students do. I think we just have to me more strict when it comes to addressing repeat behaviour

Novalium Company

13:35

@JakeRose Why do you think I do not engage and I'm here to disagree and annoy. I value each and every one of your opinions. I read them carefully and think about them. I understand that you are physics guys and university is definitely required if you want to have a career in a science.

I'm really really sorry if I have insulted anyone.

@JakeRose I really respect scientists, physicists, engineers, mathematicions... but if I was to be guided by someone, it will be the entreprenourial type of successful person.

@JakeRose For me, college has more to take than to give.

I never came here to troll, only to learn and listen, but sorry, I cannot pretend to agree on something, when I actually don't

ACuriousMind

13:54

@NovaliumCompany If you thought "None of you is successful in the way that I value" could be anything but insulting, you need to choose your words rather more carefully.

Novalium Company

@ACuriousMind I now understand it is insulting, sorry. I would rephrase it to "If I was to be guided by someone, it would be really helpful if that person was entreprenourially successful."

alarge

14:29

@NovaliumCompany Even if your ambitions are entrepreneurial rather than scientific (indeed I guess you have chosen the wrong chatroom), college opens doors. Most importantly you'd be networking, and even if you say that the skills you'd learn in college would be close to useless, the piece of paper you get at the end is not worthless as other people do ascribe value to it. I guess the best example of a degree of that type (where extracurricular activity is particularly important) is an MBA.

user8718165

Hello people:-)

Novalium Company

@alarge Networking is one of the benefits I see in college but I see more negatives than positives.

bolbteppa

"None of you is successful in the way that I value" haha unbelievable

Novalium Company

@bolbteppa :P

Ryan Unger

@ACuriousMind what’s the acceptable time to label someone a troll on this site

For the purpose of telling other people to stop feeding it...

John Rennie

14:42

@bolbteppa Steady on chaps. I suspect that's just an imperfect grasp of English and wasn't meant to imply we're all failures. Just let it drop.

ACuriousMind

@RyanUnger $\infty$.

Novalium Company

@JohnRennie Thank you.

Ryan Unger

@ACuriousMind we’ll all be dead long before then!

John Rennie

@RyanUnger death solves all ones problems.

Novalium Company

Pff, how did I manage to turn my favourite chat forum against me. :(

alarge

14:44

@NovaliumCompany So what are the negatives and positives that you see, and what major would you be going for, anyway?

ACuriousMind

@RyanUnger I, for one, plan to live forever

Novalium Company

@alarge :P

Ryan Unger

@NovaliumCompany can you even describe what success is to you

Novalium Company

@RyanUnger I can't

Ryan Unger

🙄

vzn

14:46

@NovaliumCompany "Ive decided" vs "Im keeping an open mind" are mutually contradictory dont you think? for anyone with intellectual abilities think college is the way to go, but was not fully enthusiastic about it myself both before, during, after. 1/3 of adults are college educated, it puts you in a select, even elite group. but yes there is the issue of conformity & groupthink which you raise. & yes entrepreneurial success is sometimes much different than college mentality... sometimes much harder...

bolbteppa

It's your life, nobody said you had to go to college, it's up to you

Ryan Unger

@JohnRennie really? I don’t know a single person who didn’t go to college

Responding an earlier comment about rich people who didn’t go to college

Novalium Company

@bolbteppa Thank you. I'm here to get more opinions by different people.

Ryan Unger

@ACuriousMind there’s more to university than Science :P

bolbteppa

Consider a Young diagram with two horizontal boxes (labelled $i,j$ and one vertical box (labelled $k$), representing a tensor $T^{ijk}$ which is symmetric in $i$ and $k$, and anti-symmetric in $i$ and $k$. Based on this alone you're supposed to know that $T^{ijk}$ will satisfy $T^{ijk} + T^{jki} + T^{kij} = 0$ because 'it consists of tensors which are anti-symmetric in $i$ and $k$ which are not in the totally anti-symmetric representation', how does this generalize?

If you set $T^{ijk} = M^{ijk} + M^{jik} - M^{kji} - M^{jki}$ and then write that sum out it all goes to zero, kind of astounding something could be predicted just by knowing $T$ was anti-symmetric in $i$ and $k$ and symmetric in $i$ and $j$

John Rennie

14:49

@RyanUnger In IT it's quite common to skip college and go straight into a job. College IT degrees aren't that highly regarded in the UK. Experience is far more value.

Ryan Unger

Oh I take it back, I know Bernardo

He did that @JohnRennie

ACuriousMind

@RyanUnger Yes, but you could get the orgies elsewhere, too...

John Rennie

@RyanUnger And he's doing very well!

Ryan Unger

👀

ACM back to his old ways

Not a very PG13 comment!

ACuriousMind

I don't see what's not PG13 about it as long as I don't elaborate :P

vzn

14:51

lol maybe we should nickname him "NC-17"

Ryan Unger

@JohnRennie yeah but I’ve talked to him and he wants to finish college

I think if you actually value scientific knowledge, getting at least one degree is inevitable.

vzn

← fully endorses orgies as the best alternative to college :P

Ryan Unger

@ACuriousMind the concept of an orgie isn’t PG13...wtf would you be elaborating on

bolbteppa

Hmm I think it might be obvious actually

Novalium Company

Greece ia nice

John Rennie

14:54

He meant an orgy of COBOL coding.

vzn

ugh COBOL orgies are definitely the most twisted o_O

ACuriousMind

@JohnRennie COBOL definitely isn't PG13!

Ryan Unger

I’m staying in academia to never have to program again

John Rennie

@ACuriousMind it's likely to corrupt and deprave innocent young programmers? :-)

vzn

@JohnRennie Bernardo seems to be doing well but hes said hes having thoughts about long hours/ work life balance/ immigration status (not in here much anymore) ... :|

ACuriousMind

14:57

@JohnRennie Most definitely. One needs a fortified mind to look at it and not be taken by madness

Novalium Company

Last thing. Am I allowed to ask questions and participate in the chatroom?

ACuriousMind

I do COBOL so that others don't have to ;P

John Rennie

@NovaliumCompany yes, of course.

Novalium Company

@JohnRennie Thank you.

vzn

@NovaliumCompany theres a longrunning game that goes on in here called "hot indignation at the outsider + n00b" so to speak :P

John Rennie

14:59

No there isn't

Ryan Unger

I think you should have to pass a basic physics test to talk in here

>Derive the fine structure constant from first principles

vzn

May 18 at 17:03, by vzn

@RyanUnger (lol!) I would never want to be part of a group that would allow me to be a member --Groucho Marx

Ryan Unger

@vzn Princeton became much less prestigious in my mind after they gave me an offer :P

vzn

@RyanUnger lol exactly! am thinking less of princeton myself lately also :P j/k :P

Slereah

15:29

Hello gents

@RyanUnger a noble dream

Twas mine once

But alas it was not to be

Slereah

15:40

Is there something discussing elastic collisions in GR outside of sachs wu

Seems a rare topic

Ryan Unger

@Slereah sw does it?

Slereah

16:00

Briefly

p. 92

A few papers talk about it as toy models for interacting matter

But I can't really think of a good general thing on the topic

Ryan Unger

@ACuriousMind my goodness the 2016 deus ex requres 74 GB

JMac

@RyanUnger Modern AAA games seem to really not care that they are competing for space with a ton of other games

Ryan Unger

16:15

@JMac Hitman 2 is taking 126GB

GTA5 is taking 83

Skyrim (with mods) over 100

:(

ACuriousMind

@JMac They don't have to care since they no longer have to pay for physical media containing them.

JMac

I got hitman 1 with all the DLC for like $10 or something, installed it for later; but had to uninstall because it took up a ton of space and I didn't play it yet

Ryan Unger

I have a TB of SSD space but it's almost out

Hitman 1 and 2 are fantastic

Hitman 2 contains all of Hitman 1

hence the immense size

JMac

i have about 1.2 TB of SSD, but it's 3 SSD's i've just added onto my system over time, so managing the space is a bit annoying since I need to fit any new install onto one of the SSDs

Ryan Unger

the problem with hitman is that they store assets for each level separately...so you have the same tree stored 15 times

the idea is that one can just install levels separately but this is stupid

Sir Cumference

16:18

@vzn Has any movie ever been rated NC-17 in practice

Ryan Unger

Cannibal holocaust...

JMac

yeah, kinda weird they didn't try to optimize it or anything, but that was probably a lot of effort, and on ACMs point, it's not like they companies are paying for storage space anymore

Ryan Unger

I still have Apex Legends installed...do I need that

it was fun at first...

JMac

BR's are not my thing I've found out. Apex felt pretty generic as far as BR's go, I probably played like 3 games until I gave up

the whole pace of BR games is too... inconsistent for me. I find the looting aspects and fighting aspects contrast too much, and I get into a loot mindset or a shooting mindset; but can't put the two together well

Ryan Unger

I just want Halo to finally be released

JMac

16:23

I'm probably gonna give it a shot, haven't played much halo on PC but it's more my type of FPS. I know Reach is coming out soon, but I haven't heard anything about actual dates yet, just a lot of "MCC is coming out in 2019!" with sequential releases

Ryan Unger

I haven't played Halo in many years

JMac

last one I remember playing was halo 3

Ryan Unger

I don't have an xbone so I never played 5

But I played all the others a lot

Sir Cumference

16:49

@ACuriousMind To be fair, they do usually care how you learn the material :P Instead of just reading the textbook I am required to go to 9:00am lectures that I'll be too tired to pay attention to.

Attendance costs up to 10% of the grade in a lot of classes.

ACuriousMind

@SirCumference That's university-dependent - I've never had mandatory attendance for any lecture

vzn

@SirCumference its a real rating but the "kiss of death" for mainstream viewing, it tends to decrease the audience very substantially, so hollywood typically prefers to edit movies to take out the objectionable content. en.wikipedia.org/wiki/List_of_NC-17_rated_films

Sir Cumference

@ACuriousMind That sounds like a wonderland

It's almost every class at my uni

Ryan Unger

@SirCumference uh what

I know where you go

I don’t believe a good university like that would have attendance

Sir Cumference

@RyanUnger I don't believe a good one would either :P

Sometimes it'll be a small amount, e.g.

user image

Other times I get classes like this

user image

If you can, feel free to look up some of my physics syllabi. You'll see this trend a lot

Ryan Unger

17:18

@SirCumference pretty sure [redacted] is an excellent university

For math and medicine anyhow...

@SirCumference take home quizzes? The fuck?

Sir Cumference

@RyanUnger Well that was for a class known to be unusually easy :P

Ryan Unger

@SirCumference so this is for physics classes or also math?

Sir Cumference

@RyanUnger Math tends to not have that problem. Actually math classes tend to be better altogether

Nicer curve, etc

Ryan Unger

Ah well it’s the superior field of study

Sir Cumference

Tho I assume the curve is because the math major is far smaller than the other majors here

Ryan Unger

17:23

It’s a small department

Sir Cumference

Which also causes things like inconsistent course offerings

bolbteppa

Math would still be Euclidean geometry if it wasn't for physicists

Ryan Unger

And it would be better for it

bolbteppa

Math had nearly 2000 years of being Euclidean geometry until Newton applied math to the real world inventing calculus out of necessity and so the modern era, 400 years of physics-based math has got us to e.g. Langlands etc should be a lesson to math people not to neglect physics

ACuriousMind

That's a...peculiar reading of history

Ryan Unger

17:31

I avoid all math that has to do with physics

bolbteppa

pde's is physics-math

I don't see people doing discretized pde's over finite fields, for some reason it's using numbers that arise in physics :p

Ryan Unger

Any physics older than 50 years isn’t really physics

vzn

lol! and you were just complaining about trolling. ps QM is over 1 century old at this pt o_O :P

Sir Cumference

@vzn I'd totally go to an NC-17 movie just to say I've been to one

tarit goswami

17:57

Is a quantum computer a non-deterministic finite automata?

Ryan Unger

@ACuriousMind lmao the recap video at the beginning of mankind divided

I forgot how convoluted human revolution was

ACuriousMind

@taritgoswami The automata of conputer science do not really correspond to computers, they correspond to programs (e.g. parsers for regular languages are usually finite automata), so that question doesn't really make sense.

@RyanUnger human convolution

tarit goswami

@ACuriousMind Ok, can u give an example of a real use of non-deterministic FA?

ACuriousMind

@taritgoswami NDFAs are equivalent to DFAs, so there are no examples where a DFA would not also suffice.

vzn

@SirCumference lol newsflash, porn (rated X, more than NC-17) is widespread on the internet.

Ryan Unger

18:14

@ACuriousMind $\mathrm{human}*\mathrm{machine}$

Slereah

@ACuriousMind quite old proof really

Turing did a proof that a non-deterministic turing machine was equivalent to a deterministic one back then

Same proof works for all machines rly

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