The h Bar

6:00 AM

The big advantage of paper over technology is being able to draw things.

user228700

@JohnRennie At the end of the course? The semester?

It would really suck to be in Word when the lecturer starts drawing pictures on the whiteboard. Or even writing complicated equations.

John Rennie

^

Dawood ibn Kareem

Unless you're 0celot of course, who likes Word for some reason.

user228700

@DawoodibnKareem We're not allowed to use laptops during lectures so.

The Raiders of Las Vegas

6:01 AM

Wtf

John Rennie

@Kaumudi.H sometimes a course would last less than a semester, and sometimes more than a semester.

user228700

@JohnRennie Ah, hmm, I see.

John Rennie

But actually most lasted a semester, so yes I'd tidy up and file the notes at the end of the semester.

The Raiders of Las Vegas

Why no laptops?

user228700

I was wondering, actually, rather than the sort of books you used, the way you'd write things down etc. I realise that different people employ vastly different systems but still.

John Rennie

6:02 AM

Attempt to write a prefix and contents page so I could understand the notes when I went back to them at the end of the year.

Dawood ibn Kareem

I used my own shorthand so that nobody would ask to borrow my notes.

Avantgarde

Why laptops during lectures? For taking notes?

user228700

@JohnRennie Ah, OK.

John Rennie

If I'm honest I mostly just copied what the lecturer was writing on the board. Sometimes the notes passed through my eyes and out of my hand without ever passing through my brain. Particularly if it had been a late night.

The Raiders of Las Vegas

Are you allowed to record the lectures?

John Rennie

6:05 AM

@TheRaidersofLasVegas I suspect most lecturers wouldn't be keen on that

user228700

Thing is, I have a tendency to spend way too much time making sure that my notes look very nice. I'm sure that I'd miss half the lecture if I remained bend up about this, no?

Dawood ibn Kareem

@Kaumudi.H Yeah, don't do that.

user228700

@TheRaidersofLasVegas Again, I don't really know. I bet I could do it in secret using my phone or something but I've done this before, and it's not really effective at all.

John Rennie

My experience was that I had to scribble like fury to keep up, so I quickly gave up on trying to make the notes look nice.

Dawood ibn Kareem

@Kaumudi.H Yeah, don't do that either.

John Rennie

6:07 AM

I'd go back through the notes at the end of the day and tidy them up.

user228700

@DawoodibnKareem OK :-P

user228700

@JohnRennie Ah, I see.

Dawood ibn Kareem

You could get into real trouble if you record the lecturer without their permission, and somebody finds out.

Of course, you can always ask the lecturer on the first day if they mind being recorded. Most lecturers would say it's OK. But if they say no, then you have to respect that.

Avantgarde

I can hardly think of a prof who would say yes to that

Dawood ibn Kareem

46

Q: Why wouldn't a professor allow a student to record audio of his lecture?

I am a master’s student in a public university in the state of New York. I do not consider myself to be disabled in any form but I do find it difficult to concentrate in class. I lose focus too often and have difficulty recalling concepts taught during class. So I find resources such as recorded ...

John Rennie

6:08 AM

@Kaumudi.H I suspect you're worrying far too much. My experience was I got swept along and life was so busy I barely had time to think let alone worry.

Dawood ibn Kareem

@Avantgarde I would have been fine with it when I was a lecturer.

user228700

This is what my notes look like at the moment:

user228700

Dawood ibn Kareem

Those are FAR too beautiful.

The Raiders of Las Vegas

Have you heard of the "Yale method" of note taking?

John Rennie

6:14 AM

@Kaumudi.H but those are notes taken from a book.

Dawood ibn Kareem

And is that your big toe with the pink nail polish?

John Rennie

In the lectures you'll be straining to hear a mumbling lecturer and straining to read the drunken spider scrawl they laughingly call handwriting.

The Raiders of Las Vegas

^

user228700

@JohnRennie Well, yes :-/

John Rennie

Unless you have a secret note taking superpower the priority will be just getting all the information down, without worrying about it looking nice.

Dawood ibn Kareem

6:17 AM

You could get yourself into a group of three or four students, and take turns taking notes. That way, you can (most of the time) actually sit back and enjoy the lecture.

Avantgarde

Wow haha, collaborative action.

user228700

@DawoodibnKareem Yes :-/ I painted it to prevent myself from attacking my nail in times of stress. I'm quite insecure about it so shush, OK?

user228700

@TheRaidersofLasVegas No, I will Google it now.

The Raiders of Las Vegas

Cornell Notes

The Cornell Notes system (also Cornell note-taking system or Cornell method) is a note-taking system devised in the 1950s by Walter Pauk, an education professor at Cornell University. Pauk advocated its use in his best-selling book How to Study in College. == Overview of method == The Cornell method provides a systematic format for condensing and organizing notes. The student divides the paper into two columns: the note-taking column (usually on the right) is twice the size of the questions/key word column (on the left). The student should leave five to seven lines, or about two in (5 cm), at the...

user228700

@JohnRennie Right, right. Hmm, perhaps I should quit worrying about it so much.

John Rennie

6:19 AM

It's impossible to quit worrying. That's human nature :-)

The Raiders of Las Vegas

@Kaumudi.H Sorry, got the university name wrong :-/

Avantgarde

I did the Cornell way a few times. Rest, just copied everything

John Rennie

Don't worry about the future or worry that know that worrying
Is as effective as trying to solve an algebra equation
By chewing bubble gum
The real troubles in your life are apt to be things
That never crossed your worried mind
The kind that blindsides you at 4 p.m. on some idle Tuesday

user228700

@JohnRennie Will it be completely mental to attempt to do it using different colored pens?

user228700

@TheRaidersofLasVegas Oh, no problem :-) Thanks!

John Rennie

6:20 AM

@Kaumudi.H No, I used to use differently coloured pens. They are particularly useful for diagrams.

Dawood ibn Kareem

@Kaumudi.H That is generally considered to be a good idea.

Get yourself one of those multicoloured biro thingies.

user228700

@JohnRennie Ah, it's good :-) By you or..?

John Rennie

Baz Luhrmann - Everybody's Free To Wear Sunscreen

►

Dawood ibn Kareem

But don't suck the end, because you'll ruin it.

user228700

@DawoodibnKareem Ah, hmm, but I have a collection of pens already. Still, I s'pose it would be more efficient to use this one.

user228700

6:23 AM

@DawoodibnKareem OK, I wont :-P

Dawood ibn Kareem

Assuming it's comfortable in your hand.

John Rennie

You'll lose pens by the dozen - they run away to hide when you aren't looking. Personally I recommend cheap biros.

user228700

Wokay!

user228700

Thanks so much :-)

Dawood ibn Kareem

There are two types of people in the world. Those who are always losing pens, and those who are always accumulating pens. There seems to be no way to switch from being one to being the other.

5

The Raiders of Las Vegas

6:24 AM

How to take Cornell notes

►

John Rennie

@DawoodibnKareem You mean the net divergence of the pen field is zero??? :-)

Dawood ibn Kareem

LOL

user228700

I've started packing and my room's a veritbale mess!

Dawood ibn Kareem

Will one of your sisters take over your room?

user228700

No, no, this isn't my room, really. It's more of a common room.

Dawood ibn Kareem

6:27 AM

So the mess isn't really your problem.

user228700

Nah :-)

user228700

OH, and say, what sort of system did you use for revision?

Dawood ibn Kareem

Who me?

I can't really remember.

The Raiders of Las Vegas

There's a third type, namely those that don't know how to use a pen :P

user228700

You, John, anybody's who's willing to answer.

user228700

6:31 AM

@DawoodibnKareem Dang. OK.

The Raiders of Las Vegas

@Kaumudi.H What did you do in the past?

user228700

At school, I used to come back home and read the whole lesson if one was just started that day. Then, I'd do all the exercises/problems in advance. This was until 10th. After that, it all went to crap.

The Raiders of Las Vegas

Your pre-10th method is the ideal method imo

Stay ahead of the lectures

John Rennie

I think the most effective way to revise is to work through past exam papers.

user228700

@JohnRennie Ah, hmm, and how often would you do this?

John Rennie

6:37 AM

That always feels a bit rubbish because it feels as if you're learning how to pass the exam rather than learning the subject, but it works.

Avantgarde

Yeah well, as you said before, it depends on the person. But since you've done it before, it is a good idea to go through the lecture notes everyday. And a few problems. And yeah, exam papers like John says.

John Rennie

@Kaumudi.H Only before the exams, not routinely during the term.

I suspect you'll find it very different to revising for the entrance exams.

user228700

Ah, right, no, I'm asking about all the remaining days, during the term.

John Rennie

The individual courses tend to be more focussed then you get an exam on the course. So the work is harder but the area you have to revise is much smaller.

@Abcd have you tried asking in the JEE room?

Abcd

@JohnRennie Nobody's online in the JEE Room

user228700

6:39 AM

@JohnRennie Ah, hmm, right.

John Rennie

@Abcd you're welcome to ask in that room then ping me here.

Abcd

@JohnRennie I didn't get you. Should I post the question at both places?

John Rennie

@Abcd Post only in the JEE room, then if no-one is around post here saying please look at my question in the JEE room

The Raiders of Las Vegas

Ping John in the JEE room

Abcd

@JohnRennie Okay.

John Rennie

6:41 AM

→ 2 messages moved to JEE Preparation

Dawood ibn Kareem

@Kaumudi.H I'm not sure that I ever had time to revise, other than immediately before the exams.

The Raiders of Las Vegas

Yeah^, proper time management is a huge concern.

Dawood ibn Kareem

But doing the assignments tells you fairly quickly if there's stuff that you didn't grok first time around.

user228700

Hmm, I see.

user228700

@TheRaidersofLasVegas How do you mean?

John Rennie

6:50 AM

@Kaumudi.H I wouldn't worry too much about time management. Worry about finding enough time to eat and sleep :-)

user228700

Hmm. Apparently, I only have a forty five minute window to eat my meals.

John Rennie

It usually takes me 45 seconds :)

Dawood ibn Kareem

@JohnRennie Hey, if she's confined to her room from 6:45pm to 6:00am, I don't think it's going to be that hard.

John Rennie

If you take 45 minutes to eat a meal you're not hungry enough!!

The Raiders of Las Vegas

16 mins ago, by The Raiders of Las Vegas

Stay ahead of the lectures

They will go very fast.

John Rennie

6:52 AM

@DawoodibnKareem confined to the building, not to her room.

user228700

@JohnRennie No, no, I mean that I only have a certain window. If I miss it, I will have to go an empty stomach till the next window.

John Rennie

@Kaumudi.H is that likely?

I suppose you could always buy emergency supplies - bags of Maggi ...

user228700

:-) Haha, yes. I'm taking a kettle with me so I should be able to make Maggi from time to time.

user228700

@TheRaidersofLasVegas Ah, right.

John Rennie

@Kaumudi.H I'm going to try that meal with Maggi noodles again this weekend, but with a different sauce to accompany it.

The Raiders of Las Vegas

6:56 AM

May 13 '16 at 17:35, by DanielSank

I wasn't kidding at all. In college time management, and sleep management in particular, is a huge factor in success.

Research PhD

Rumplestillskin

Does any one know the procedure in tensor calculus when you multiply a christoffel symbol that is actually antisymmetric when you compare it with the lower indices of the Christoffel symbol? So the product is $\Gamma^j_{ik}*(u^i S^k) where the (u^i S^k) is not symmetric about it's indices?

Avantgarde

procedure for doing what?

user228700

@JohnRennie Oooh, nice! :-) Which sauce?

John Rennie

@Kaumudi.H haven't decided. I was wondering how they would go with something like butter chicken.

user228700

Ah. Unfortunately, I am not the right person to ask this :-/

John Rennie

7:07 AM

I could have a vegetarian sauce ...

Dahl with cream?

Make a mild dahl, then add some whole chickpeas and some cream and some chopped fresh chilli.

user228700

Truth be told, that doesn't sound very appetising even to me. On its own, I'm sure it would make for an excellent curry but I'm not sure how well it would work with maggi noodles.

John Rennie

Oh well, I'll just have to SLAUGHTER SOME CHICKENS then :-) Where did I put my axe?

user228700

:-) Didn't see any chickens in your garden!

The Raiders of Las Vegas

It's with your shotgun :P

John Rennie

@Kaumudi.H I've eaten them all

user228700

7:10 AM

Uff.

The Raiders of Las Vegas

Shotgun, axe, knife,...

John Rennie

Now you're making me sound like a psycho killer :-)

The Raiders of Las Vegas

:-)

John Rennie

For the record I don't own an axe or a shotgun.

The Raiders of Las Vegas

Psycho was a great thriller

Dawood ibn Kareem

7:12 AM

Is the blackbird still alive?

John Rennie

Yes, they're too bony to be worth eating :-)

The Raiders of Las Vegas

Buttered blackbird?

John Rennie

Although the Chester rush hour has now started and the traffic noise has drowned out the blackbird.

It'll quieten down again in an hour or so.

Dawood ibn Kareem

Dawood makes a mental note to keep John Rennie away from his pigeons.

The Raiders of Las Vegas

You have pigeons?

John Rennie

7:14 AM

We used to eat wood pigeons when I was a lad. We lived in the country and the pigeons were regarded as a pest because they eat crops. So hunting them was considered a public service.

But pigeon isn't very nice to eat.

Dawood ibn Kareem

Mine will not eat your crops.

John Rennie

Very tough and gamey.

Dawood ibn Kareem

They do quite like silver beet though.

Slereah

hey hey

The Raiders of Las Vegas

Yo yo

Slereah

7:16 AM

So there are black holes, white holes, red holes, blue holes

are there green holes

Dawood ibn Kareem

I'm just thinking about that episode of Blackadder when Rowan Atkinson gets into trouble for shooting Stephen Fry's favourite pigeon.

The Raiders of Las Vegas

You forgot grey holes.

Slereah

Which ones are grey holes

The Raiders of Las Vegas

Between black and white

John Rennie

I suppose strictly speaking all black holes are really grey due to Hawking radiation.

Slereah

7:17 AM

But that means that they are BLACKbody

John Rennie

Well, black bodies aren't black ...

The Sun is an excellent approximation to a black body.

Slereah

But it isn't grey, either!

The Raiders of Las Vegas

Gravitationally completely collapsed object.

Dawood ibn Kareem

@JohnRennie Are you sure that was a blackbird in your garden? Not something big and yellow?

John Rennie

@DawoodibnKareem :-)

Dawood ibn Kareem

7:19 AM

John Rennie

That would be a big meal :-)

Secret

Disambiguation (disambiguation)

Disambiguation is word-sense disambiguation, the process of identifying which meaning of a word is used in context. Disambiguation may also refer to: Sentence boundary disambiguation, the problem in natural language processing of deciding where sentences begin and end Memory disambiguation, a set of microprocessor execution techniques == Music == Ø (Disambiguation), a 2010 album by Underoath Disambiguation (Pandelis Karayorgis album), a 2002 album by Pandelis Karayorgis and Mat Maneri == See also == Ambiguity, an attribute of any concept, idea, statement or claim whose meaning, intentio...

The Raiders of Las Vegas

Q star

A Q-Star, also known as a gray hole, is hypothetical type of a compact, heavy neutron star with an exotic state of matter. The Q stands for a conserved particle number. A Q-Star may be mistaken for a stellar black hole. == Types of Q-stars == SUSY Q-ball B-ball, stable Q-balls with a large baryon number B. They may exist in neutron stars that have absorbed Q-ball(s). == See also == Black hole Stellar black hole Compact star Exotic star Preon star Quark star == References == == External links == Abstract, Are Q-stars a serious threat for stellar-mass black hole candidates?, Miller J...

Slereah

Let's invent more color holes

Green holes, yellow holes, cyan holes

The Raiders of Las Vegas

Rainbow holes

Slereah

7:27 AM

Can gravitational wells separate wavelengths

Or at least have redshifting depending on the distance, so that a light beam going near it appears rainbow

The Raiders of Las Vegas

Hmm,...

Slereah

If I have blue light beams at impact parameter $r_1, r_2, ...$, do they each have a different color

Secret

quora.com/…

may be good leads

John Rennie

In GR the bending of the light doesn't depend on wavelength - but you knew that ...

Dawood ibn Kareem

@JohnRennie So there are no rainbow holes? :-(

John Rennie

7:38 AM

@DawoodibnKareem there has long been a suggestion that spacetime might cause a very small dispersion due to quantum gravity effects. Attempts have been made to measure this but the effect has never been detected and anyway not all quantum gravity guys believe it exists.

Slereah

Is that the Lorentz violation effect

Dawood ibn Kareem

7:57 AM

@JohnRennie So does that mean that one day, Stephen Hawking is going to prove that all black holes come in rainbow stripes?

John Rennie

@Slereah It's the idea that spacetime interacts with light as if it was discrete (I'm being cautious with the terminology here!) and the propagation of light is affected by this. The effect is bigger for shorter wavelengths, hence the dispersion. But whether anyone really believes this I'm not sure.

@DawoodibnKareem you need to careful about ideas in quantum gravity. No-one has any idea of what is going on so there are lots of ideas that are interesting but basically pure speculation.

The Raiders of Las Vegas

8:10 AM

Have you studied any advanced molecular quantum chemistry @JohnRennie

John Rennie

Depends what you mean by advanced. I did a lot of quantum chemistry in my final year as an undergrad, but that was mainly computational rather than deep theory and I haven't worked in the area since.

The Raiders of Las Vegas

Yeah, I meant grad work.

John Rennie

I very nearly did my PhD on quantum chemistry but got lured away by solid state photochemistry instead.

Anyhow, what were you going to ask about?

The Raiders of Las Vegas

What lured you away?

I just wanted to know your speciality.

John Rennie

@TheRaidersofLasVegas I thought it would be more fun to do a more experimental PhD. And I think it was the right choice. I suspect I'd have got bored just doing theory.

I had a hugely enjoyable time playing with some biiiiiiiiiig toys! :-)

The Raiders of Las Vegas

8:15 AM

Cool.

John Rennie

I get the impression from the people here that not everyone enjoyed their PhD, but it was the best three years of my life.

It's been downhill since then :-)

The Raiders of Las Vegas

In what sense do you mean "downhill"?

Slereah

at a place lower than uphill

The Raiders of Las Vegas

As in coasting along easily?

Secret

I like theory because it explains things and I like the weirdness of the abstract, but I cannot do 100% theory else the ugly numbers of each datum will bore me out due to being intangible

It also explains why I do chemistry rather than physics, because (I think I have mentioned that many times already) physics experiments are less tangible than chemistry when it comes to touching and tossing around the experiment subject itself

> How often are you able to touch an electron and not get electrocuted?

Dawood ibn Kareem

8:25 AM

@TheRaidersofLasVegas He means his life has been getting worse and worse since that time.

He's not entirely serious. Hence the emoticon.

Dawood ibn Kareem

8:42 AM

Observation: Stack Overflow is full of muppets.

The Raiders of Las Vegas

Conclusion: ?

Dawood ibn Kareem

Manamana

Slereah

doo doo doo doo doo

Dawood ibn Kareem

Ah, so you use Stack Overflow too?

Secret

last night dream: Gist is the following:

Law has a paradoxical existence in this dream. According to the dream's script, she is a figment of my imagination even in the context of the dream. However for unknown reasons, she exists as a physical, fully autonomous individual. Nobody knows why she exists.

This paradoxical existence of her result in her response and mannerisms to be like as if many mutually incompatible scenarios superimposed on each other. For example:

1. She is a tacit girl, meaning that she and I knew to a certain extent what each other is up to without saying much (this is why there is't much dialogue of her in t…

My dreams are getting more and more weird

I think I either have spend too much time in cardinals, or quantum mechanics

The Raiders of Las Vegas

8:50 AM

en.wikipedia.org/wiki/Mah_N%C3%A0_Mah_N%C3%A0?wprov=sfsi1

Secret

NB: back in my grade 4, I had an imaginative friend, but by Grade 6 that is no longer necessary

The Raiders of Las Vegas

Did he have a name?

Secret

she: Kily C

she is based on a good friend of mine back in Grade 1-3 which have moved to another school

though all of this memory is no longer meaningful when I discovered in 2016 that it is all an act

The Raiders of Las Vegas

The act of friendship?

Secret

yes, pretending to care but she is not

(you can have betrayals in friendship level stuff you know...)

The Raiders of Las Vegas

8:57 AM

There's plenty of more fish in the sea pal.

Secret

I am not worried about her anymore, I now have some very good friends that I can trust for life

The Raiders of Las Vegas

Cool.

Secret

As for what happen in Grade 6? Well, teachers taught me the idea of the scientific method. I then took the belief of scientism, thinking science is all powerful. Acompanying with that is the attitude of truth seeking. Since an imaginative friend is fake, the idea becomes meaningless

My scientism then dies out by 2010, and becomes agnosticism

and this is why I have the mindset to understand esoterics and religon, and why pseudoscience is pseudoscience

ACuriousMind

9:25 AM

@0celoñe7 That's not a quantum mechanics question and I have no idea why the claim should be true to begin with.

Secret

how does one satisfy the Maxwell equations distributionally?

ACuriousMind

With a distribution. (I don't understand the question)

Secret

me neither, (it is a term used in 0celo's question) my naive guess will be somehow the classical field is described by a distribution rather than some continuous function, and that satisfy the maxwell equations

ACuriousMind

Yeah, precisely - you have a distribution instead of a function that satisfies the Maxwell equations. What's the question?

Secret

I see, in that case, I think the physics will be obtained by integrating this field of distribution over allspace

I guess that's the answer to the question. My question, if wrote in another way is "what is meant by "satisfy the maxwell equations ditributionally"?"

The Secrets of Feynman Diagrams | Space Time

►

In other news, currently watching this.

Slereah

9:39 AM

maybe read an actual book on the topic rather than watching meme videos

Secret

I do have a couple of books, but right now in this PhD I don't have time to read them fully. I plan to catch up somewhere hopefully in year 2

but as emilio and acuriousmind have found, I need to restart with QM first, cause my QM is still a mess

I think sakurai might have the ingredients I need to fill in funtional analyis like gaps such as stone's theorem and other things related to the framework of hilbert space

The major achievement in the latest discussion is that emilio and acuriousmind have discovered I actually thinking all of physics backwards and hence my foundation of thinking is all backwards. This explains why despite the effort I spent on physics and I actually has a physics degree, my physics still suck. Now, with that problem identified, hopefully I will know when not to overinterpret the maths

ACuriousMind

@Secret Honestly, what you lack is not mathematical sophistication so much as an understanding how quantum mechanics actually works, i.e. how to extract probabilities, measurement results or time evolutions from it. The mistakes you've made are not due to some lack of "functional analysis", but because e.g. instead of applying the Born rule you came up with some convoluted idea about applying operators, or talking about "ensembles" of Hamiltonians when that wasn't grounded in QM at all.

Secret

That is likely had something to do with my backward thinking that is recently identified by you guys (previously it was identified in maths by my linear algebra professor, causing all my proofs to unknowingly proving the converse instead). The problem that had always been plaguing me is I tend to overinterpret the maths, because of the strong belief that I can recover all the known physics from the mths framework in the model, side effects include weird ideas about operators that you mentioned

Elaboration on "recover all the known physics from the maths framework in the model":

ACuriousMind

See, all that is...pretty irrelevant for anyone but you. When other people discuss QM with you, they don't generally care what personal belief causes you to make mistakes. They care that you should correct these mistakes and do correct quantum mechanics in order to have a constructive conversation with you.

skullpatrol

> ::makes popcorn::

Secret

9:51 AM

That is true, and identify that the beliefs exists is the important first step. This si why I like to chat with other people, they can see personal beliefs of mine that is mostly unconscious when I do things and I otherwise don't aware of

So the point is, if I don't know what the personal beliefs that lead to my msitakes, it will be much harder to correct for them since we don't know why it occurs in the first place

ACuriousMind

@JohnRennie There is almost nothing that all quantum gravity guys believe exists ;) (I'm fairly sure not even "spacetime" counts)

skullpatrol

10:04 AM

Have you considered the source of your misconceptions being the meme videos where you're trying to learn rigorous arguments? @Secret

Secret

@skullpatrol pretty sure not for quantum mechanics, because having done a undergrad in QM, I did not watch meme videos on quantum mechanics. As for QFT, I knew well I don't have enough background, thus I kinda expect my questions will be kinda shaky, but I decided to push on anyway for (reasons), because I knew that when I get my QFT solid, I will know more details about those QFT questions I ask

and interestingly, despite my lack of background, my questions tend to made it through and after enough clarifications, somewhat understandable to the experts and me, and at some uncommon occassions, actually touched upon important points

Anonymous

@DawoodibnKareem There is a way to switch from the former to the latter. Just stop carrying pens with you. Borrow them from others and never return. ;) (Even if 90% of the people claim their pen back the other 10% is bound to forget that they ever lent you a pen) I had tried this experiment in school before XD

Secret

I am not terribly sure why I push on my questions, it might be my relative impatience (but then, there are questions of mine that I want to ask and decided to not ask because I don't have background to even formulate them), or it might be because my fear when I get expert on that subject, I will loss access to those worthy questions that only an amateur mindset can ask

skullpatrol

Sure, but it takes so much more wasted energy, no? @Secret

Dawood ibn Kareem

@Blue So you consciously decided to become a thief?

Anonymous

10:12 AM

@DawoodibnKareem Yes :P

Dawood ibn Kareem

I'm glad I'm not a priest.

Anonymous

I did it because I had lost dozens of pens before by lending them to people. It was my time for revenge :P

skullpatrol

Blue revenge?

Secret

@skullpatrol There are good questions that only a fresh, amateur has high probability to ask, this is one reason why a lot of professors found undergraduate teaching fruitful because of the good questions from the bright minds. Once we get used to a framework enough, we often lost the ability to question deeply abut the framework due to comformality (but see researchers on the foundations on the subjects for exceptions, though I don't normally expert I can be those lucky ones)

Anonymous

@DawoodibnKareem Nowadays (atleast in our country) priests are the greatest *****

Secret

10:16 AM

thus, even if energy is wasted, it might be worth the trouble

(especially googlign often let you understand just enough to formulate the question and communicate it to the askers)

skullpatrol

Don't forget lost time.

Secret

In this whole world, there is only one thing that can really get on my nerve:

> The hopelessness of unable to explain why something occurs

thus both my non dark and dark sides work synergistically towards my passion for science and knowledge in general, because, in a sense, the dark side has a common enemy

skullpatrol

"Why?" is a question that can be asked infinitely many times, pal.

Secret

There are ways to prevent it asking many times, we are a lot better than our ancesters on figuring out "why"

Mithrandir24601

@Secret it might be a better idea to learn QM before QFT

Secret

10:29 AM

48 mins ago, by Secret

but as emilio and acuriousmind have found, I need to restart with QM first, cause my QM is still a mess

I said that already

Mithrandir24601

Ah, fair enough - I missed that bit...

Secret

With them having identified what caused all my conceptual errors, I think it should now be easier to fix them

skullpatrol

Knowing is half the battle :P

Secret

Now since how maths and physics people have found my thinking is backwards, I am starting to worry whether my whole thinking of my life is also backwards...

skullpatrol

...that, my friend, is a philosophical question.

Secret

10:34 AM

well, if I am lucky, someone will found that out soon

No matter how self aware one is, there are delusions only the others can see

...

skullpatrol

Indeed, "delusions of grandeur" being the most common example.

Secret

I am so glad that I have not decided to end that QTF discussion a day ago when I realise I am to my limits on what I even vaguely know about QFT, had I did that and wrote the message something along the lines of "wait, I think I don't understand QFT enough to think about this question, I think I should left it later", Emilio and acuriousmind might need to take 5-10 more years to discover exactly why I don't know how quantum mechanics actually works

and thus identified that I had all my physics thinking backwards

skullpatrol

5-10 years is a lot of time and energy to spend

Secret

indeed indeed, and you can imagine the battles I have with my millions of pet theories

Almost every question I ask is actually a means to slay a pet theory, in order to get closer to the truth. The questions can be answered via a variety of means, asking others is just one of many

If asking others is the only way to answer a question, then h bar will become unusuable as my question generation rate will mean it will be flooded constantly

above all, I hate the unexplained with passion, thus when I ask questions, it is really doing cold blooded murder in a sense

skullpatrol

...interesting

Secret

10:48 AM

having said that, there's a catch, only unexplained things that caught my attention sufficiently will I demonstrate that cold blood, you cannot expect me to go rage when you just throw anything unexplained at me. This partially explains why I am inactive in main, the other reason is I don't answer if I don't 100% know the answer

and that I am lazy to check questions

Secret

10:58 AM

Hmm..., suppose we fix a spacetime coordinate, and then draw different vertices of a feymann diagram, then it is easy to see how it represents different process. Now to figure out how the interpretation go from electrons moving to position moving by positing the diagram such that the electron/positron line is aligning with the space axis (thus its trajectory will be spacelike in the diagram). This needs quite a bit of QFT

It is important to stress that feymann diagrams are covariant (or lorentz invariant?, I am never good with terminnologies...) thus if the axes are not fixed, it does not matter how the diagram is oriented, it will describe the same process

ACuriousMind

@Secret Feynman diagrams do not depict trajectories.

Secret

I don't know how you can describe the electron being drawn like a line, of course it cannot be trajectories, I think I need a better term for describing that its line to be aligning with the spacelike axes

ACuriousMind

A Feynman diagram also doesn't really have axes, even if people like to pretend they do

And it's not "the electron" being drawn, the lines really just represent certain integrals.

Stop trying to do whatever you're trying to do, and first learn the actual, technical meaning of a Feynman diagram before you proceed.

Secret

So this one diagram describes all 6 possible processes (electron positron annihlation, pair roduction, photon absorption emission) at the same time?

Ok, will do, leave it to later

ACuriousMind

I really don't understand how you can say "Oh, my QM is really weak, I should go back to that" and then ten minutes later start talking about QFT again.

If you want to talk about QFT, get some book or lecture notes on QFT and work through them. Then you have a chance to say something about Feynman diagrams that actually corresponds to what they mean instead of what all the popscience "explanations" claim they mean.

Secret

11:08 AM

because generating questions that might be worthwhile to revisit is my first priority (for fearing once I get expert, I will lose the ability to access these questions and the worldviews it can potentially offer (even though the noise level is high)). This is also why I don't tag people in these questions, because they are not urgent

back in my hounours, I have tried that once in reading QFT lecture notes, and then I get confused, but I think with better understanding and mindset now, I think I can get past that roadblock previously in the lecture notes

The first thing I need to do when I get back to quantum, is to figure out how to apply the born rule properly, and then figure out what operators are doing and how to correctly interpret the physics of expressions involving operators

skullpatrol

Don't forget about the value of a good textbook.

Secret

sakurai should be good enough

1010011010

Hi all

skullpatrol

Hi

1010011010

I have a seemingly trivial question but I can't find good material on it, it's about operator algebra

It's really simple (I think) so does anyone know a good book I can try for this?

It's stuff like the operators requires to derive T^2 = 1 etc., with T the time reversal operator

There is good material on tihs, but I don't understand all the steps

ACuriousMind

11:15 AM

Can you be a bit more explict what you mean by "operator algebra"?

1010011010

I suppose a good start would be the "allowed operations" I can use during the derivation of an expression like T^2 = 1, starting from T^2 = UK UK, with U some antiunitary operator and K complex conjugation

In that example, I for instance don't see why UKUK = U U^* K^2 (I'd say it's U U^* K, not squared)

Or the parity operator, showing that P e^{-ik\cdot r} = e^{ik\cdot r} P^{-1}, stuff like that

Is this called operator algebra? Maybe that's why I can't find good stuff on google for this kind of thing

ACuriousMind

I think that's more "quantum mechanics" than "operator algebra" (I mean it is technically part of what operator algebra entails, but you won't find anything useful for you by searching for that)

The problem in your first question is that complex conjugation is not even a linear operator, so writing it "K" and multiplying it to toher operators as if it were is a bit misleading.

Ah, but since $U$ is also antilinear that might not be a problem.

1010011010

:) As you can see, it would be nice to have some kind of reference material relating to this kind of stuff

ACuriousMind

Well, I think the reference material are simply books about quantum mechanics

Usually whatever you're reading should give you enough information about how these equalities you're confused about are derived - there are no special books that just teach you how to move operators around

1010011010

Shame. Would love to see a more in-depth discussion about it, also on a more formal level.

ACuriousMind

11:27 AM

For instance, the parity operator thing - it depends on how you defined $P$ what the correct way to show that is

If $k$ is just a number and $r$ is an operator and you know $[P,r]$, then you can get the result by expanding the exponential into its power series

More sophisticatedly, using a variant of the BCH formula

1010011010

$k$ the momentum vector in k-space, $r$ is generalized direction in real space afaik

Secret

(Actually, while midway through the video, he describe them as if there are axes, near the end of the video, he mentioned how mathematically all process that can be interpreted by a given feymann diagram are the same and that only the topology of the vertices matter. though he could have done better on the discussion about virtual particles and off shell particles, he only mentioned whether they correspond to physical particles is debatable as they are unmeasurable)

but he might should have mentioned about how they are terms in the perturbative expansion

but anyway, this and the little bit of S matrix stuff I learn in a lecture note I read back in my chemistry honours, is my current knowledge limit on QFT

no wonder why skullpatrol and slereah calls that meme

user685252

28 mins ago, by skullpatrol

Don't forget about the value of a good textbook.

Secret

I have many QFT and QM textbooks, I just have not read them yet because, chemistry

Secret

11:51 AM

2 hours ago, by skullpatrol

Don't forget lost time.

But yeah, time... how I wish I was a quantum particle so that each of my superpositiosn can read QM+QFT, one read abstract algebra, category theory, integrals etc., and one left behind to do computational chemistry and organometalics

and then all of them combine so I can know all 3 of them at once with the same amount of time spent as a graduate

[some rant]

that amount of effort I spent in preserving my friend circles and all our pasts such that there is never a past now matter how much the word have moved forward in time, because the past is being forcibly pulled to the present!!!

user685252

5 hours ago, by The Raiders of Las Vegas

May 13 '16 at 17:35, by DanielSank

I wasn't kidding at all. In college time management, and sleep management in particular, is a huge factor in success.

Secret

The fact I know how important the past memories are and the unforgivingness of the lost of youth mean that I go so far as to literally uproot it to the present day

(that's a metaphor of course, but close enough)

Time... and soon growing up itself, will soon have no say nor control of my and my group's life!