The h Bar

Her work isn't an area I know a lot about, but I know that using gravitational lensing to measure dark matter distribution is an important technique in astronomy these days.

Jack Rod

4:34 AM

Yes

@JohnRennie what are you doing now?

John Rennie

I was just researching Priyamvada Natarajan's books.

Jack Rod

Ooh

John Rennie

It looks as if her book Mapping the Heavens is rather low level. More of a history of the subject rather than about leading edge research.

Jack Rod

?????????????

John Rennie

This book

Jack Rod

4:38 AM

I am no one judge a book now because I do not have much idea about dark energy

@JohnRennie

John Rennie

I use to love reading popular science books, but the trouble is that the more you learn about a subject the less interesting the popular science books are. You start wanting books that are more detailed.

Jack Rod

Indeed

xcodeking

Similar to how one can write an integral in terms of a power series, is there a standard way to convert a power series to an integral?

Think of, say, the Fresnel integral but backwards

John Rennie

@xcodeking When you say write an integral as a power series isn't this just Taylor expanding the function you're trying to integrate, then doing a term by term integration on the power series?

xcodeking

Yes

Captain Bohemian

4:50 AM

@JingleBells Do you really think the value of everything one works out is decided by how much money it is paid? I never think money has its intrinsic value. When I was in undergraduate ethic course group discussion, an issue is like donating money to poor people to see a doctor, I just argued:" why not ask the doctor to be kind in not charging money from poor people?"

John Rennie

@xcodeking so the problem is simply how you can take a power series and write in a closed form.

And I think in general you can't i.e. there are only a small subset of power series that correspond to a function that can be written in a closed form.

Captain Bohemian

@JingleBells I don't understand the raising campaigns are everywhere for dementia, poor children lacking food. Just ask the doctors specializing in dementia and food manufacture to exempt from charging money from these poor people is a good solution, I think.

@JohnRennie or if these workers really like money so much, just ask the government to print more billnotes to those poor people.

John Rennie

In the UK everyone who has an income pays a small percentage of that income to support doctors who treat people for free i.e. we pay tax to fund the NHS. This seems an excellent thing to me.

Charities ask people to voluntarily give a little extra so the NHS can be supported even more, and I see nothing wrong with this.

Captain Bohemian

I think doctors are generally far wealthier than a lot of people, if they lack money from treating poor patients, they wouldn't have much economical problems.

our Chinese government is very strange in asking everyone to have compulsory health insurance whether one has adequate income or saving or not.

John Rennie

Doctors are well paid but not among the top earners - in the UK at least - and they work very hard for their money. I don't begrudge doctors their salaries. It isn't a job I would want to do. I certainly wouldn't ask them to treat people at their own expense.

Captain Bohemian

5:02 AM

when I was in my MSc school, the stipend I got was barely enough to pay for basic living and tuition, but the government charged me for the premium for the compulsory health insurance.

John Rennie

The reason governments require everyone to have health insurance is that it isn't considered humane to watch other people die just because they can't afford to be treated. Well, in most countries it isn't.

The UK doesn't use the health insurance model, but I believe it is quite widely used. I don't know how it works in China.

Captain Bohemian

@JohnRennie really? In my impression, doctors are one of the most wealthiest professions in this world. When I was a child, adults told me doctors are the most wealthy and admirable.

My aunt was a pediatrician and his home was very wealthy and even hired maid, who cooked very delicious dishes every meal.

John Rennie

I think top surgeons in the UK earn less than £100K/year though that's from memory and I would have to check to be sure of that. Most directors of big companies earn more than that.

Yes, I was correct

Jack Rod

@JohnRennie is it government medical college

?

John Rennie

But that's in the UK. I don't know how this compares to the rest of the world.

National Health Service

The National Health Service (NHS) is the umbrella term for the publicly-funded healthcare systems of the United Kingdom (UK). Since 1948 they have been funded out of general taxation. There are four systems, one for each of the four countries of the UK: The NHS in England, NHS Scotland, NHS Wales and Health and Social Care in Northern Ireland. They were established together in 1948 as one of the major social reforms following the Second World War. The founding principles were that services should be comprehensive, universal and free at the point of delivery—a health service based on clinical need...

One of the very few things of which the UK can be proud.

Jack Rod

5:11 AM

@JohnRennie In india if you can have a government medical college seat which is filled by a exam like Jee called neet

You get free education plus+you will called as resident doctor

With some pay

Around 30 thousand per month which 2000 US dollar

But in case you have not got a chance in medical college you will have to pay million of rupees for a year ,which is what a private college fees which so expensive that even upper middle class cannot afford

Captain Bohemian

in my observation, doctors are very wealthy and have a lot of free time unless they are research physicians and those medical professionals who are really heavily loaded by works and have very low salary are nurses.

Jack Rod

.

Captain Bohemian

doctors delegate most tedious care works to nurses, so they don't really have a lot of works, yet they have very high salary.

Jack Rod

@JohnRennie Do you feel that entrance exam in he college has nay benefit?

I feel if someone is good intrest let say in engineering then he have to show is basic science skill in 180 minutes

Which gives no significance of his knowledge about that particular which he is going

John Rennie

@JackRod the problem in India is that there are far more students wanting college places than there are places, and you need some way of filtering them. In a perfect world there would be a place for every student who wanted one.

Jack Rod

5:20 AM

@JohnRennie My objective is,Why exam is the only way to filter out not any other way?

John Rennie

The problem is that providing so many places is too expensive for any government to afford. In the UK there is a place for any student who wants one, but you gave to pay £9K/year for a university place.

@JackRod exams are an easy way to filter students ...

Jack Rod

Which is more than a middle class income in india

Captain Bohemian

there are too many universities here for too few students, so almost everyone here can go to university; the problem is whether one can afford to pay tuition and whether there are research fields one is interested in working in.

John Rennie

I guess you could use interviews, but these require lots of man hours to conduct and therefore cost a lot of money.

@CaptainBohemian tuition isn't free in China?

Captain Bohemian

@JohnRennie no, tuition is even required for doctoral studies.

Jack Rod

5:23 AM

@JohnRennie there are University for every student but point is many of them are useless because there aim to make education as business

John Rennie

@JackRod It's about ¼ of an average middle class salary in the UK.

Jack Rod

@JohnRennie rupees and euro have big difference

Captain Bohemian

but not many people like to pursue PhD here, so a lot of departments lack doctoral students.

Jack Rod

World's richest temple during Equinox | Architectural marvel of Sree Padmanabhaswamy Temple

►

Miracle of the engineering art please see it once

How ancient people measure time

@JohnRennie

Captain Bohemian

but we have international graduate student program providing high stipends compared to other PhD programs; this program attracts a lot of Indians to come here to study.

but international graduate student program only has application-oriented research fields, none of which interests me.

misk94555

5:31 AM

Folks, say I've got an optical grating. It will disperse light into the spectrum, and it will create several orders.
How is the total light energy distributed between the orders?
Say, the incoming light is white, if that simplifies things.

Jack Rod

@CaptainBohemian china offers medical course s to international Students?

Captain Bohemian

@JackRod I don't know as I have not paid attention to medical education for long.

Jack Rod

@CaptainBohemian oh

Captain Bohemian

I even don't quite know the educational system in medical department. Not until I went to see a doctor earlier this year did I found doctors are distinguished into generalists and specialists, and generalists seem to generally only have BSc but I still don't know whether specialists have MSc or PhD.

it differs greatly from physics department - physics graduate with only BSc can't almost find a job as a physicist.

sorry, in the above, I meant my uncle, Father's brother, not my aunt.

John Rennie

5:55 AM

@misk94555 there's a nice Hyperphysics article on this here

For a grating with infinitely thin slits the intensity is independent of the angle of diffraction. For real gratings with non-zero slit width the intensity falls in a sinc function.

Captain Bohemian

I think ants like jellies very much. Yesterday when I ate jellies, a lot of ants came around. Now I eat jellies again, and even more ants come around.

Captain Bohemian

7:31 AM

@JohnRennie the government here actually only imposes compulsory health insurance to people who are affiliated with most organizations who adequately pay them to work, because the organization extracts a small part of the salary to pay the premium of the health insurance even before it issues the salary to the worker. For people who are not affiliate with any organization, they can actually choose to have health insurance or not though the government stipulates everyone to have health insurance.

John Rennie

I Googled healthcare in China and I'm surprised to see most people use private healthcare. I would have guessed a notionally communist state would have something like an NHS.

Korra

Okay, so I read on research gate that it's not very well known what is the time required for an electron to make a transitions

I thought it would be a week established fact

Well*

One of the answer said it's around a femtosec

Is it true?

And why is it hard to determine this time period accurately?

Does anyone know?

Captain Bohemian

@JohnRennie The government may send a letter to your home if they find you don't have the national health insurance, but if you still don't insure, they send a follow-up letter again, and if you still don't insure, they send again, and again and again, until finally they stop probably because they forget or get tired. But if you don't have national health insurance, you need to pay on your own to see a doctor, so the government doesn't actually execute (compulsory) national health insurance.

People who are unaffiliated with any organization and don't pay to the health insurance on their own may still not afford to see a doctor.

I am not sure if all universities pay the premium of health insurance for graduate students now because the stipends of a lot of graduate students are very low and some of them are even not paid.

and national health insurance may not be useful for everyone because it doesn't cover all medical expenses one needs.

B. Brekke

7:56 AM

Often when we solve an equation we do a Fourier transform. Then we often end up with an equation for every $k$, and these equations are decoupled. Why are not the equations for distinct $k$'s coupled? Does the initial equation have to be linear or is it something else?

ACuriousMind

8:11 AM

@B.Brekke The Fourier transform turns differentiation into multiplication - if your initial PDE contains differentiation w.r.t. a variable $x$ but no multiplication, you can therefore reduce the number of different partial derivatives by one by Fourier transforming that variable

that's what we do e.g. in the wave equation - we Fourier transform the spatial parts so that the equation is essentially turned into an eigenvalue equation for the remaining time derivative

Superfast Jellyfish

9:43 AM

When people say that photon is an excitation of the field, do they necessarily mean that it is an excitation of a plane wave mode, ie an eigenstate of the Hamiltonian with eigenvalue $1\hbar\omega$? Or can it mean any mode, as long as it is an eigenstate of the number operator with eigenvalue 1?

John Rennie

@SuperfastJellyfish We normally think of a photon as being a momentum eigenstate. Yes?

Superfast Jellyfish

I guess yes.

John Rennie

In principle you can write the field as a sum of any states you want, but we would normally write it as a sum of momentum eigenstates because that's how we think of particles and we want our states to correspond to particles.

Superfast Jellyfish

so then, say Gaussian wavepackets can be viewed as a basis change?

John Rennie

A Gaussian wavepacket is a sum of plane waves i.e. Fourier transform it and you get the spectrum of momentum eigenstates that it is built up from.

Superfast Jellyfish

9:52 AM

Yes. If I make an analogous “wavepacket creation operator” by a linear combination of old creation operators, then operating that on the vacuum should look like a wavepacket that’s created. Right?

Slereah

There is a gaussian wavepacket basis, yes

Although it's not a perfect basis because there are "too many" of them

Not all of them are linearly independent

Superfast Jellyfish

10:08 AM

Ah right. Makes sense.

abhas_RewCie

10:46 AM

HAPPY ENGINEERS DAY EVERYONE

skullpatrol

11:03 AM

looks like Germany is heading in the right direction

ACuriousMind

11:43 AM

@skullpatrol now do one with additionally a) the proclaimed climate goals (e.g. Paris agreement, Kyoto protocol and predecessors) and b) the reductions necessary to meet various maximal increases in temperature

skullpatrol

I'll try, but I don't think Our World In Data is that flexible.

I could send them an email for such a request.

Faded Giant

@skullpatrol No. Germany is currently shutting down all of its nuclear power plants – including the best nuclear power plants in the world. Therefore, the CO2 curves will go up again.

ACuriousMind

@skullpatrol you don't need to, the former information is e.g. at eea.europa.eu//publications/trends-and-projections-in-europe-1 (note how it's barely on track for the 2020 goals and widely expected to miss the 2030 and 2050 goals

what I'm saying is all these "look how much we've done" emission reduction graphs are meaningless unless you place something on it that tells you how bad (or good) that still is compared to meaningful targets

skullpatrol

ok

@FadedGiant Why are they shutting them all?

Faded Giant

politics and ignorance

plus some post-Fukushima opportunism in order to get re-elected

skullpatrol

11:56 AM

re-election fever is everywhere

abhas_RewCie

skullpatrol

:O

abhas_RewCie

lmao

Has anyone watched 500 days of summer?

How many of you excited for #AppleEvent?

I'll be getting a new iPod this December (probably)

skullpatrol

no and no

abhas_RewCie

okay..

iPad I mean, not iPod...

Charlie

12:11 PM

I actually didn't realise they still made ipods

ah

abhas_RewCie

Should I get iPhone 12 too?

not, iPod, I meant iPad

lmao

ACuriousMind

@Charlie It's odd how the "MP3 player" was a pretty large phenomenon where everyone wanted one and now you don't see them anymore at all because everyone just uses their smartphone.

abhas_RewCie

How's apple watch? Has anyone tried that?

skullpatrol

nope

abhas_RewCie

I'm confused, should I buy iPad and Watch or IPhone and Watch...

Okay... I'll go for iPhone 12 and a Watch...

That's better...

Although, I've a Nokia PureView 9 (Android), but 2 SP shouldn't be a problem.

Call me crazy, but I'm a bigger Android fan than iOS.

skullpatrol

12:17 PM

iOS is a monopoly

abhas_RewCie

Nu, Android has larger market share.

skullpatrol

i'm talking about the apps

abhas_RewCie

okay....

But, android is cooler.

Developer Mode, ADB, SDK and CatBoot tools!

crazy features.

This guy lives in 3020: twitter.com/Michael1979/status/1305594875547656192?s=20

Charlie

feels like a lot of apple products are a money sink

I can't realistically see myself enjoying the novelty of having a computer in my watch for more than 24 hours :P

abhas_RewCie

They are. No one buys Apple products for their features, they are just brought for their Branding!

Charlie

12:23 PM

Buying something for the brand isn't something I understand, pretty much at all

Superfast Jellyfish

12:55 PM

@abhas_RewCie I like my iPad for its features

Superfast Jellyfish

1:32 PM

If we consider a quadratic Hamiltonian of two canonically conjugate variables, is it guaranteed that eigenstates when represented in one of the variables will be a Gaussian times an appropriate Hermite polynomial in that variable?

ACuriousMind

@SuperfastJellyfish by "a quadratic Hamiltonian", you mean essentially the Hamiltonian of the harmonic oscillator?

abhas_RewCie

Why good papers have less citations?

Superfast Jellyfish

2:01 PM

@ACuriousMind yes

ACuriousMind

@SuperfastJellyfish then the answer is yes - it's the same Hamiltonian after all, just with different variables in it which doesn't change anything about how you solve the TISE for it

abhas_RewCie

2:28 PM

How many of you don't have a sibling?

Jack Rod

do any body know about barber paradox?

abhas_RewCie

yes

Russell's Paradox

There's a barber in the city who does haircut for everyone who can't do themselves. So, will the Barber cut his hair himself? Yes and No.

Formally, $A = [ X:X \not \in X] \iff X \in X \iff X \not \in X$

@ACuriousMind Does Twitter takes data from SE too?

Jack Rod

you forget about clean shave city

abhas_RewCie

I'm afraid, that iPad ad just popped out of nowhere.

I prefer trimming over shaving.

ACuriousMind

@abhas_RewCie I don't understand the question. What sort of data? Why would it "take it from" SE?

abhas_RewCie

2:43 PM

@ACuriousMind like chats? Do they take user data from here. I recently talked about iPad here and I'm getting ads on Twitter...

ACuriousMind

@abhas_RewCie I don't think they're parsing what you type here into chats. I'm guessing you've looked at or at least searched for the iPad you want to get recently?

Also, the ads aren't "Twitter" - ad providers are typically separate entities from the platforms serving the ads, and will track you with various methods across all sites you visit where they can do so

abhas_RewCie

@ACuriousMind Never, not on Twitter... :\

Jack Rod

@abhas_RewCie co-incidence s.e have some norms

abhas_RewCie

Let me check...

Jack Rod

i hope they have

abhas_RewCie

2:45 PM

@ACuriousMind So, they are tracking me on SE too?

Jack Rod

it is serious now does S.E sells user data....?

ACuriousMind

@abhas_RewCie On the pages where you see ads, probably. The ad networks fingerprint your browser with various methods and can essentially track you across all sites where you've loaded an ad from that network

abhas_RewCie

Okay, few hours ago, I searched and compared prices of iPad on Phone on Flipcart, (my Phone and PC both have same accounts opened), so, probably, that's why they are showing up in my PC too....

Jack Rod

y

ACuriousMind

you should use ad blockers and anti-tracking features for your browser if you want to avoid seeing targeted advertisement like that

abhas_RewCie

2:48 PM

okay...

sounds creepy. Now a days, data on internet isn't safe... :(

ACuriousMind

"now a days"? Tracking isn't particularly new, ad providers have tried to do that for a while now

abhas_RewCie

Now a days because of tech wars across nations...

Some of them are being very aggressive, like on YT ads

ACuriousMind

and most data you enter on the internet isn't "safe", and never has been. The moment you send anything in plain text (or only weakly encrypted) over the net, it can be read by someone determined enough

abhas_RewCie

That's why, I just switched to Tor, over a VPN

ACuriousMind

"safe" always is relative to what sort of threat you're trying to defend against - small-time scammers? multinational corporations? state secret sercvices?

abhas_RewCie

2:54 PM

I'm safe against all

Just got this minute ago...

I still feel tracked :(

@ACuriousMind see^

ACuriousMind

and what should I see there?

John Rennie

@ACuriousMind as I recall you have studied ancient Greek. Is it known how the word mene (Moon) was pronounced?

abhas_RewCie

All the things I'm writing here is coming in my Twitter feed.

bruh :(

ACuriousMind

@JohnRennie the more common word for moon is selene, but yes, the classical pronounciation is pretty certain - the 'e' sounds like the 'e' in English RP 'bed', 'm' and 'n' are just like you'd expect.

the classical accent was likely a pitch accent, so you'd have to speak the first syllable with a rising tone

(note that not all Greek 'e' are like this long 'e' - this is $\eta$ in Greek, but we transcribe $\epsilon$ also with 'e')

...why are you trying to speak Greek? :D

abhas_RewCie

because greeks are smart.

John Rennie

3:02 PM

Someone used the word on the radio and pronounced it to rhyme with bean.

I had a someone is wrong on the Internet moment.

ACuriousMind

ah, perfectly reasonable

John Rennie

And considerable Googling later I couldn't find a definitive statement. Is the final "e" silent?

abhas_RewCie

hehehe

Jack Rod

@JohnRennie Greek word on the radio was the talk on science?

ACuriousMind

@JohnRennie no, it's not silent

it's a two-syllable word me-ne

John Rennie

3:05 PM

So it's men - ay ?

ACuriousMind

no, both 'e' are the same sound

John Rennie

men - eh ?

ACuriousMind

in classical Greek it's the 'e' sound from 'bed', in modern Greek it'd be a long 'i'

John Rennie

Thanks :-)

abhas_RewCie

haha :)

Y'all literally speaking over text, I like that.

John Rennie

3:06 PM

My guess is they pronounced it like meme, not realising that meme was a word made up by that notorious ancient Greek Richard Dawkins.

bolbteppa

I remember reading they really don't know for sure how ancient Greek or ancient Latin were actually pronounced

abhas_RewCie

@JohnRennie Do you have a B Tech?

degree

I mean...

John Rennie

No. BA then PhD.

abhas_RewCie

BA means arts?

ACuriousMind

@JohnRennie both meme and gene are Greek loanwords though - but there's no word 'gene' in Greek, it's closest relative is genea

John Rennie

3:09 PM

For some reason Cambridge awards Bachelor of Arts degrees even for science.

Black arts possibly.

abhas_RewCie

@JohnRennie I can smell that

ACuriousMind

@bolbteppa there's plenty of scholarly difference over the finer points for sure, and there were different periods (e.g. Old Latin, Classical Latin, Vulgar Latin) where pronunciation shifted

abhas_RewCie

@JohnRennie Is BA substitute for BSc or what?

@ACuriousMind Do you hold a B Tech degree?

John Rennie

BA and BSc are both degrees in the UK. So a BA in science from Cambridge is equivalent to a BSc from any sane university.

ACuriousMind

@abhas_RewCie I don't know what a BTech is, there are only BA and BSc here, so no.

abhas_RewCie

3:12 PM

BA is usually for Arts, my mother did in history. BSc is usually given for science..

ACuriousMind

but actually our understanding of Latin and Greek pronounciation is pretty comparatively good for both languages being dead because there's many texts of speakers of one Language transcribing words from the other in their alphabet

abhas_RewCie

@ACuriousMind So, there's BE there?

John Rennie

@ACuriousMind aha, from mimēma.

B Tech sounds more like an engineering qualification.

ACuriousMind

@abhas_RewCie some universities also award bachelors of engineering, but really no one cares

abhas_RewCie

@JohnRennie Bachelor in Technology

@ACuriousMind Why? Engineering is not popular there?

ACuriousMind

3:14 PM

@abhas_RewCie a bachelor's degree is a bachelor's degree in some specific field, no one cares "of what" it formally is. Some universities give out BAs in math, others BScs in math, for example

John Rennie

I'm currently studying for my BOF - I expect to qualify any day now.

ACuriousMind

what matters is that it's a math degree, not whether it's called BA or BSc

abhas_RewCie

@ACuriousMind BSc is drastically different from B Tech/BE

ACuriousMind

not here

you'll find universities awarding "BSc" in engineering fields with no problems

abhas_RewCie

Okay, so they teach you Technological Engg in BSc too?

ACuriousMind

3:15 PM

well, only if you study engineering

abhas_RewCie

@ACuriousMind Oh... That doesn't happens here...

That's why I was asking...

Today's Engineer day

So, any engineers here?

In Technological/Engineering Degree?

John Rennie

@FadedGiant is a nuclear engineer.

abhas_RewCie

Wow!

@FadedGiant has B Tech too?

Faded Giant

@JohnRennie I'am only paid like one. Actually, I am a chemist.

abhas_RewCie

@FadedGiant LMAO, hilarious reply!

IBM started working on 1000 Qubit QC.

I'm already getting Goosebumps...

Faded Giant

3:19 PM

@abhas_RewCie No, I don't have a bachelor's "degree". Why your sudden interest in this particular "not a real degree degree"?

abhas_RewCie

@FadedGiant you mean B Tech?

Faded Giant

I mean bachelor.

Jack Rod

@abhas_RewCie in 2022

what matter is the course which you study rather than what prefix you use BTech,Bsc

@JohnRennie will you see tomorrow session?

abhas_RewCie

Because, I'm soon going for a bachelor's degree.

completed my high school.

John Rennie

@JackRod The interview with Brian Greene and Priyamvada Natarajan?

Jack Rod

3:32 PM

yes

@abhas_RewCie who i am?

John Rennie

I probably won't watch it live as I'm usually making lunch around that time. I've bookmarked the link to watch later though.

abhas_RewCie

LESSON 1: DON'T UNDERESTIMATE PEOPLE Proof: twitter.com/abhas_rewcie/status/1303287156161433600?s=20

@JackRod Yuvraj Singh

I should too change my name...

This RewCie is boring.

NEW NAME: Azmuth

Jack Rod

@JohnRennie when I was a kid I use to watch science festival videos a lot.

and I saw brian Greene for the first time with his string theory and gr video.

though he is very rusty on gr

Azmuth

Someone tag me.... ;_; I got a new name ;___;

Jack Rod

@Azmuth hi

Azmuth

3:41 PM

yo bro :)

John Rennie

@JackRod I first heard of him when The Elegant Universe came out. I read it when it was released and I thought it was very good as popular science books go.

Charlie

Isn't Greene still an active string theory researcher? How could he be rusty on gr

Azmuth

Because time is relative.

Jack Rod

@Charlie rusty refer to the way he explains it'

Charlie

ah

that would make more sense

although I thought his target audience was essentially non-scientists

Jack Rod

3:50 PM

yes

this is also true

he addresses the public which is new about this theory

Azmuth

Y'all have seen Sean Carrol's Physicist explains dimensions at 5 different levels?

It's insane!

They start dissing each other at last!

@JackRod You are trending in India

at #17

Jack Rod

he is my role model,I am a big fan of him so my family

Azmuth

@JackRod I'm too a big fan of you.

Jack Rod

how much laptop service cost?

Azmuth

depends

Jack Rod

3:58 PM

like?

Azmuth

upto from 2k INR to 20k INR

Jack Rod

i have hp 2017 model

Azmuth

Why do you want servicing?

Jack Rod

my pc programms run slow

i can't

Azmuth

format your PC

why?

Jack Rod

4:03 PM

i working on assignment

Azmuth

do you have a recovery partition?

Jack Rod

yes

Azmuth

use it.

Jack Rod

already i am running two ops

one is linux and other is windows

Azmuth

oh, which one is slow?

Jack Rod

4:05 PM

windows

Azmuth

nothing wrong, windows is supposed to be slow

Jack Rod

still, i want some basic servicing

should i give at service centre or external?

Azmuth

not sure.

I never take my laptops for software servicing

Superfast Jellyfish

@JackRod if you have an HDD, you can try replacing it with an SSD. That’s how I revived my old laptop

bolbteppa

4:34 PM

The algebraic approach to spinors finally clicked I think. In four-dimensions for example, a Dirac spinor is a four-component column vector
\begin{align}
\begin{split}
\Psi(x) = \begin{bmatrix}
\Psi_1(x) \\ \Psi_2(x) \\ \Psi_3(x) \\ \Psi_4(x)
\end{bmatrix}
\end{split}
\end{align}
If we view this as the first column of a $4 \times 4$ matrix
\begin{align}
\begin{split}
\Psi(x) = \begin{bmatrix} \Psi_1(x) & 0 & 0 & 0 \\ \Psi_2(x) & 0 & 0 & 0 \\ \Psi_3(x) & 0 & 0 & 0 \\ \Psi_4(x) & 0 & 0 & 0
\end{bmatrix}

Furthermore, since any $4 \times 4$ matrix can be expressed as a linear combination of the $4 \times 4 = 16$ Clifford algebra basis elements $\{I,\gamma_{\mu},\sigma_{\mu \nu},\gamma_5,\gamma_5 \gamma_{\mu} \}$ we can equivalently define a spinor as a minimal left-ideal in the Clifford algebra generated by the $\gamma^{\mu}$'s.

Azmuth

@bolbteppa I just wanted to ask, what was wrong with Diarc's version of Schrodinger's equation? Why we needed String Theory?

bolbteppa

Trying to find a quantum theory of gravity where Dirac etc are proving too hard

Azmuth

What is quantum Theory of Gravity?

bolbteppa

Theory of gravity which respects quantum mechanics

Azmuth

You mean just setting $V(x) = Gm_1m_2/x^2$ wasn't working?

for the equations?

bolbteppa

4:42 PM

No, that doesn't even respect Einstein's relativity

Azmuth

means?

bolbteppa

Azmuth

No, I mean what should be the correct potential?

if it's not $V(x) = G m_1 m_2/x^2$

bolbteppa

Azmuth

@bolbteppa I guess that comes from approximation of Schwarzschild's solution of EFE? (I guess I've seen this equation in Raybov's Celestial Mechanics)

bolbteppa

4:53 PM

Yes, you need general relativity

Azmuth

Or perturbation of flat space time ... then something like that?

$\eta_{\mu\nu} + \alpha_{\mu\nu}= g_{\mu\nu}$

and then approximation...?

bolbteppa

Just schwarzschild

Schwarzschild geodesics

In general relativity, Schwarzschild geodesics describe the motion of particles of infinitesimal mass in the gravitational field of a central fixed mass M {\textstyle M} . Schwarzschild geodesics have been pivotal in the validation of Einstein's theory of general relativity. For example, they provide accurate predictions of the anomalous precession of the planets in the Solar System, and of the deflection of light by gravity. Schwarzschild geodesics pertain only to the motion of particles of infinitesimal mass m...

Jake Rose

8:30 PM

Anybody used/read Tony Zee's relativity book

worth a look?

bolbteppa

8:45 PM

Yes definitely

123

9:32 PM

Hello all and John Rennie. I have one question about vector (magnitude) in rotating 2D non-orthogonal coordinatie system could be different axes ratio.

I thought vector magnitude is independent of choice of coordinate system. But i have seen vector magnitude is changing when rotating orthogonal coordinate have different axes ratio let say 1:2.

Also in skew coordinate system any axes ratio change the magnitude of vector when rotating the coordinate system. Any reason and physical significance of changing vector magnitude in these cases. It should be independent of axes choosen.

Pls answer anyone knows the answer. Thanks

bolbteppa

A vector will have the same magnitude only for those linear transformations which preserve the value of the inner product $\mathbf{v} \cdot \mathbf{v}$, e.g. in 3D a rotation of the coordinate system will do this. In general a linear map can alter the value of the inner product. For example a map projecting a given vector onto a vector pointing along one of the coordinate axes will in general produce a vector having a different magnitude than the original vector, it's just a projection.

"Yang—Mills gauge theories are not consistent with the definition of spinors as minimal left ideals of Clifford algebras" yikes

123

9:52 PM

Thanks for the answer@bol

@bolbteppa. I understand it is the projection. It means vector is not independent of choice of coordinate system.

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