hello

@CaptainBohemian Pov is point of view

@StanShunpike thank you.

Hi

Isn't the automatic generator of user images a potential swastika generator? Not that I feel concerned, I was just surprised some users image was a bit dubious.

@CaptainBohemian yes the Msc/ Phd system worldwide varies and in many places leaves much to be desired to say the least. academia sometimes has large amts of $$$ sloshing around (ie/ eg increasingly more corporatized model) but sometimes not a lot of it goes into science/ edu. think its a shame that many highly motivated/ educated ppl cant continue in the field of their choice, theres been many discussions about this over the years in the room. do you have a Bsc?

@vzn Of course.

but I only took courses during my BSc because there were no professors in that school whose research interests me.

@CaptainBohemian what were they working on? what are you interested in? and PS are you ever going to explain how you chose your nickname? seems quite incongruous sometimes :P

hello

There's this thing called a 4-bar linkage system.

the research of my undergraduate school focuses on optical engineering, film manufacture, etc.

Working out the equation of motions for this system is pretty straightforward.

I want to work out the equations for a related system called an RSSR system

I am mainly interested in fundamental physics.

In the RSSR system, you have revolute-spherical-spherical-revolute joints

@Loong Was the container full of nuclear waste? I think the answer to this tells how really confident the guys were in their design.

this system becomes a 4-bar linkage system if you require the revolute joints to be coplanar

but otherwise it has different properties

I'm having trouble telling what tools I would need to analyze a complex system like this

@vzn My nickname came from my email automatically.

because in the 4-bar linkage case, it's much simpler

and you just need basic trigonometry

@CaptainBohemian there is some crossover of fundamental physics into QM optics. sometimes ya gotta be flexible...

@CaptainBohemian ??? your university assigned you the email id captain bohemian?

but this RSSR system is considerably more complex, and i'm not sure what tools to google for. i haven't found a lot of great info. i found one paper i thought looked interesting, but

citeseerx.ist.psu.edu/viewdoc/…

they have no lagrangians

and i don't see how they can be describing the dynamics of the system without them

@vzn well, my undergraduate school mainly focuses on research of those optical themes which have technological applications, not the fundamental theoretical aspect.

@StanShunpike you might be able to break it down into simulation vs analysis.

@vzn can you elaborate? i don't follow

@StanShunpike there is software focused on simulation of a dynamical system and software focused on analysis of dynamical systems. the problem you described earlier of detecting motor dynamics may be able to be solved without fully analyzing all the physics. ML is a type of analysis.

what software would be suitable for this?

like autocad?

@vzn no, I chose it when I was in my MSc school, which was indeed a wonderland wherein I understood the bright side of my personality.

@StanShunpike you mentioned sympy right? need to look into that...

@CaptainBohemian cool so do you have a Msc? physics? did you do a thesis?

@vzn well sympy seems like maple. and i don't think maple has like CAD abilities. wouldn't that be necessary in the absence of equations of motion to describe a system?

@vzn yes, and that thesis let me more deeply understand what my interests lie in.

@StanShunpike looking at what you want to do, actually my 1st idea is to try a game physics engine. know a lot of ppl using unity think it could do a lot for you without a lot of hassle. its used a lot in low-end (casual) games. it could be a basic "proof of concept" to build on with other stuff later.

that's a great idea

@CaptainBohemian cool whats your thesis title? was it done in China?

@vzn if I type the title here, everyone would know my identity.

@StanShunpike it would help if you 1st write up what the project is about without thinking about what software is applicable. personally highly recommend getting a blog, although maybe few students do that...

@CaptainBohemian nobody is much concerned about anyones identity, but you could just state the general idea/ area if you prefer

Hard to avoid revealing enough info to be identified once you start talking about research you’ve published, yeah

@vzn people close to your fields would be concerned.

@CaptainBohemian lol "concerned" about what? think some people overthink that on here, and makes little )( sense to me :P but its one of the features...

I don’t think it actually matters but I’m also reluctant to talk too much about unpublished research

Tho that’s more out of regard for my collaborators then anything

@Semiclassical think SE chat can have very beneficial aspects many deriving from candor, have witnessed it a lot 1sthand over the yrs, but to each his own vzn1.wordpress.com/chat

It depends on context. If it’s a purely mathematical aspect of a physics research problem, I’m happy to talk about it

@Semiclassical its possible your collaborators would have no issue but yeah, its part of the consideration...

But if it’s something being prepped for publication, and I’m working with others, my inclination is to default to privacy

(Once it’s on arxiv it’s another matter, of course)

there are some highly competitive areas of science where discretion is sometimes preferred/ held to but think they are more the exception... possibly another area would be general heading of "breakthrus"...

@Semiclassical is it a highly-obeyed convention to upload a paper to arXiv before publishing it in journal?

@CaptainBohemian nah, but it's a good way to get attention out

it also sometimes happens that certain material would make the published paper too long or unwieldy. in that case, you might put up a preprint that contains that extra stuff

In particular, I ca say loads of plain English without anyone (including my past and future selves) to understood a word

However

ideas of my collaborators are a different story

The longer we measure the energy, frequency, mass of something, the better we know it (uncertainty is low). This is the energy time uncertainty right?

If we measure one of those 3 features for a very short time, their uncertainty is high?

Is longer time of measurement assosiated with higher uncertainty in time (and therefore lower uncertainty in the energy, mass, frequency...)?

I dont understand why measuring something for a long time will result in high time uncertainty?

@NovaliumCompany Depending on your measurement process, it may be true that longer measurement corresponds to higher accuracy, but this is definitely not "energy-time uncertainty". Energy-time uncertainty is often misunderstood because it is different from the other types of quantum uncertanity as there is no time operator, cf. physics.stackexchange.com/a/53804/50583 for a correct presentation of what the energy and time in the energy-time uncertainty are.

I need an explanation without math.

Longer time to measure is equal to high uncertainty in time and vice versa?

No, the time in energy-time uncertainty has nothing to do with measurement time

If you read the answer you linked, you'll find an as-math-free-as-possible description of what $\Delta t$ is in energy-time uncertainty:

> It tells you the approximate amount of time it takes for the expectation value of an observable to change by a standard deviation provided the system is in a pure state.

Its so complicatedly written and I cant understand it.

Ahh... I think I'll go with the thats how the universe works answer.

The more accurately we know the energy of something, the...???

(the longer time it must have taken us to measure it?)

(the less we know how long we have been measuring it?)

@NovaliumCompany The more accurately we can know the energy of the system, the slower the system is changing.

The extreme case of this is an energy eigenstate: All energy eigenstates are stationary states: Energy uncertainty is zero, and the system is not changing in time at all.

Still dont understand it.

Delta t describes the change of energy...... wuuut

It describes the speed with which the properties of the system are changing.

High certainty in the energy would imply high uncertainty in what?

It doesn't work like that.

That's why I said energy-time uncertainty is different from other quantum uncertanties above - there is no single quantity whose uncertainty would correspond to what the $\Delta t$ is.

Alright how does it work then in the simplest terms possible explained with the simplest words possible?

I don't think I can do better than what I said above: The more accurately we can know the energy of the system, the slower the system is changing.

So if energy certainty is high, then we know that the system isnt or is changing very little?

yes

thats weird :D

The better we know the mass of something, the better we know that mass isnt or will change very little?

@NovaliumCompany Mass is not an operator in non-relativistic quantum mechanics, so there is no uncertainty for it.

@bolbteppa What can I do with Classical Statistical Mechanics which I can't do with Classical Mechanics? Can you give me some example for that?

@NovaliumCompany if you want to learn QM I suggest trying to do the maths. It’s not super complicated stuff for most intro courses..

@AbhasKumarSinha you can’t deal with many particle systems for one

@JakeRose Didn't get that?

@JakeRose What are the prerequisites for it?

@JakeRose I'm not interested in the mathematics. :)

(:)

-(:)-

[-(:)-]

(::)

@NovaliumCompany then you’re essentially not interested in physics. Without the foundations of mathematics you will misinterpret and not understand nearly anything in contemporary physics.

@AbhasKumarSinha well if you want to deal with many particle systems (for example hundreds of particles, which even then is a relatively small amount) you’d have to solve Newton’s laws which means solving HUGE matrix equations

its just simply too calculation heavy

so we use statistical mechanics

@JohnRennie you around?

what does it mean when people say “spin doesnt have a spatial wavefunction”?

@JakeRose do they say that? Spin isn't an object so it's hard to see why it would have any spatial component to it. Typically the wavefunction of some system would have a spatial component and a spin component.

@NovaliumCompany you made the argument that you’ll have to take the explanation “that’s just how the universe works” aka not understanding it. Yes the universe works that way but it doesn’t mean you can’t strive for a better understanding. For example the energy time uncertainty comes from Erhenfests theorem combined with the general uncertainty principle for quantum mechanical operators

wgat does spatial wavefunction mean?

just it can be written $\psi (x,y,z)$ ?

@JakeRose I've no idea. It seems a somewhat odd thing to say. I'd need to see some context.

How does one send pictures nowadays

@JakeRose are you on mobile or laptop?

I was on mobile

just swapped back to the full site

ignore my notes

but that’s the line anyway

I'm not sure to be honest. Spin is a property of a system, so it will be part of a wavefunction but I wouldn't say there is a wavefunction for spin.

In chemistry, depending on what approximation you are using, you can or cannot split the wavefunction into orbital and spin wvaefunctions

Even phd students in quantum seem confused by what he’s talking sbout

weird considering he was such a good elcturer

Spin is not a spatial property. The Hilbert space where spin states live in does not depend on the position of space

Eh... making such a distinction seems to create more confusion than it fixes.

The general rule for quantum states, which works for everything you'll find in chemistry, is to list all the states you'd allow classically, then let the quantum state be a superposition of any of them.

Naively, if you have a classical particle that can spin up or down, you describe it with 4 things: x, y, z, and whether the spin is up or down.

So at the quantum level the full wavefunction is a function that takes in numbers (x, y, z) and a boolean (up or down) and returns a number, the amplitude to be in that state.

Perhaps what the lecturer is getting at is that it's tempting to think that boolean (up, down) is really three numbers (L_x, L_y, L_z). But that doesn't work. Spin is classically more like a boolean than a tuple of reals.

In other words the wavefunction is \psi_i(x, y, z) where i is up or down, rather than \psi(x, y, z, L_x, L_y, L_z).

If I have these four equations

yeah, that spin behaves like a boolean is what makes it very very different from our classical intuition of angular momentum

and I’m trying to find r and t in terms of k and a

I have four equations right, so can eliminate four variables?

constants even

So am I right in saying that having 2 equations would allow me to write b in terms of c (or vice versa p) and a and k

then having four allows me to eliminate both b and c

and and r or t depending on which one I’m going for?

why Is it the more complicated maths I do the more the basic stuff goes down the drain

@JakeRose I understand the basic mathematics of QM so I dont know whats the problem here.

@JakeRose Have a nice day! :)

@NovaliumCompany do you? From the stuff you’ve said here recently it doesn’t feel like you have a good appreciation of them

im not tying to be rude

i just see the questions you ask a lot and I want to highlight my concerns of your learning

@JakeRose I understand what you are saying and you are probably right. I'm learning QM to some very basic level to which I can have a discussion on the topics. I don't want to dive deep into the complexity of the subject. I have no desire to become a physicist, just to widen my view on the world.

Roy Glauber in memoriam at Nature Photonics

by my group leader and Fritz Haake

Math is a wonderful subject and definetly widens your 'feel' of the subject.

(unfortunately paywalled - email me and I'm happy to send copies)

> Glauber married Cynthia Rich in 1960 and had two children Jeffrey and Valerie. Glauber and Rich divorced in 1975. Even though he suffered for a long time from that break-up, he was extremely happy that he was awarded custody of the children. Bringing up Jeffrey and Valerie as a single parent was a great achievement.

> Glauber said in his Nobel lecture, “I’m sure there is some number of papers I never got to write as a result, but raising those children and seeing them succeed was not an experience I would trade for the missing papers or any sort of recognition.”

@JakeRose I'm 16 y/o self-taught person from Bulgaria driven only and only by curiosity. If the mathematics of QM become interesring to me, I'll make sure to learn them :)

I hope this clears your concerns.

The mathematics of QM is actually pretty interesting in itself (functional analysis, linear algebra)

@NovaliumCompany as well as complex analysis, PDEs, abstract algebra, topology, group theory, and a wide range of interesting approximation schemes to make many problems tractable. whatever math you learn, it is likely to show up somewhere in playing around with QM

@dsm Alright, thanks.

@NovaliumCompany More importantly: the math is QM. The "stories" around it -- Schrödinger's cat and the like -- are just that: stories. Quantum mechanics is the math, and any attempt to describe it without the math is ultimately doomed.

Moreover, I strongly disagree with @Secret and @dsm's characterizations there. It is definitely possible to find places in QM where complex analysis, PDEs, abstract algebra, topology, group theory, and functional analysis play a role, from marginal to central. But they are not necessary to understand the mathematical core of QM.

The only thing you really need is linear algebra. Nothing more.

amazon.com/Q-Quantum-Terry-Rudolph-ebook/dp/B074DYJTKN

I strongly recommend this book

The first few chapters are available for free at qisforquantum.org

Six quantum pieces is also very good.

Neither requires a strong mathematical background - they are accessible at high-school level, and they'll teach you the crucial bits of the mathematical core that are really needed to firm the hand-wavy concepts into concrete manipulations.

@EmilioPisanty That's great! I might read one of the two books you recommended but I still don't understand what exactly I will gain by learning the math. I need a specific example please.

@NovaliumCompany To be fully blunt: without the math, everything is just fables. If you want to talk about quantum mechanics instead of quantum woo, you need to be conversant in the math.

hi @Qmechanic

Hi

@Qmechanic since you're here - if there's mod feedback regarding the comment thread here I'll be happy to hear it. I don't think I was past the line but I'm happy to be corrected if necessary.

I'm fairly annoyed at the (presumably) revenge downvote, particularly when it's likely that I'm the only one that's going to take the time to actually answer the question this person wanted answered, but ultimately that's on OP.

@EmilioPisanty So to better understand whether an idea about let's say quantum technology is possible and not just a "scam" and so on... I need to have idea about the equations, which will tell me everything I need to know? Such as not falling into the trap of zero-point energy technologies which magically extract the energy and so on...? We know that energy isn't extactable because the virtual particles pop in and annihilate so fast that we are literally unable to do anything useful with them?

@NovaliumCompany that's... not a great example, but yes, along those lines.

@NovaliumCompany If you actually understand the math you understand that "virtual particles" are not "popping in and out of existence" at all.

↑ that.

(i.e. that is why it's not a great example.)

This idea comes precisely from taking a Feynman diagram and trying to tell a story about it instead of seeing it as the mere representation of a specific integral in a perturbation series it is.

@ACuriousMind And how would the math tell me that? Give me the equation?

@NovaliumCompany It would allow you to correctly interpret the equations.

OK but what exactly is the piece of math that will tell me that they are not popping in and out of existance?

instead of relying the fables made by others, which leaves you liable to over-interpreting them in ways that depart from the parts where the fables coincide with the math.

What's the equation that will tell me that ""virtual particles" are not "popping in and out of existence" at all"?

@NovaliumCompany the role that Feynman diagrams play within perturbative expansions in quantum field theory.

@EmilioPisanty didn't say they are necessary to understand the core. I was adding to the 'interesting math' in QM.

does that sound like meaningless alphabet soup? yes, it probably does. And it will until you're conversant in the mathematical formalism.

but until you're able to understand it, then you'll be unable to understand just how much of the "particles popping in and out of existence" is a fable.

@NovaliumCompany The point is that there is nothing in the formalism corresponding to such an event of particles popping in and out of existence. To see that there is none, and to understand why claiming that Feynman diagrams shows such events is wrong, you need to understand the whole perturbative LSZ formalism of quantum field theory, not some single equation.

@dsm with all due respect, given the background of the conversation, your comment was pretty unconstructive.

@ACuriousMind LSZ formalism will tell you things that you can explain in words, right?

No, it won't.

I mean, I can try to tell you "in words" how we compute the integrals and do the expansions, but there's just no point to it

The purpose of the formalism is not to tell a story, it's to be the most accurate quantitative theory we have

@NovaliumCompany Taking the "virtual particles pop in and out of existence" claim at face value is analogous to watching Shrek without realizing that there are no ogres or dragons or talking animals in the real world, and thinking that it's a documentary.

You cannot claim to understand the theory if you do not understand, at least in principle, how it arrives at its quantitative predictions

Ok, tell me in words what happens if it's not virtual particles pop in and out of existance?

And, I mean, it's okay if you don't. Not everyone needs to be a quantum field theorist. There's no shame in not understanding it

My dream is to do something with neuroscience and neurotechnology, that's why I don't want to spend so much time trying to understand complex topics such as QM, but I want to have some idea of what's going on.

@NovaliumCompany As ACM said, there's nothing wrong with sticking to pop-sci treatments. Just be aware that a huge fraction is just fables - and, more importantly, be willing to acknowledge that there are parts that require a higher technical background to understand fully. It's perfectly OK to go "OK, it's not like that, and it takes a technical background to understand what it is like".

Your questions thus far are pretty far from that, though.

@ACuriousMind Does anyone really need to be a quantum field theorist? ;)

I read "How to teach Quantum Physics to your dog" and it gave me some idea of what's going on but with a few equations. Now I don't know if I've really learned anything...

@ZeroTheHero I know several quantum field theorists who have gone on to use their QFT background extremely effectively in extremely productive careers in quantum information and quantum simulators

dunno if you need to be a field theorist to do good work there but it certainly seems to help

no

wait

oh

@ZeroTheHero you meant actually work on QFT for keeps?

@ZeroTheHero Hey, don't ask me, I'm just a programmer pretending to be a physicist on the internet :P

@ACuriousMind You have all this knowledge... just go and do something useful for the world instead of being a slave to some boss.

@NovaliumCompany calling people "slaves" is.... not particularly nice

@EmilioPisanty I'm talking in terms of professional job. I'm sorry if I have offended anyone.

@ACuriousMind Sorry if I have offended you.

@NovaliumCompany The rule of thumb is: don't assume.

i.e. with assumptions like "you're a programmer therefore you must be unhappy with your job"

or "you're a programmer therefore your job is not useful for the world"

I get it, I'm sorry

cool

I'm still 16 so puberty kicks here and there.

I bet there's a QM mathematical model for puberty as well... because why not

@NovaliumCompany I'm not a slave and the software I help produce touches more lives than my physics ever would have. I like my job, even if the silly COBOL jokes may at times not make it look like it :P

@ACuriousMind I understand. You are absolutley right. I don't know what hit me...

@ACuriousMind out of interest, what sorts of people interact with the software you write?

you can't have all the "smart" people focus only on science, then everything else would go to hell

I mean, "I work for SAP" is a pretty broad descriptor

or is all of SAP literally writing software for enterprises to interact with their employees and customers?

Last thing before I go to bed: If my only introduction to QM is amazon.com/How-Teach-Quantum-Physics-Your/dp/1416572295 from a scale 1 to 10, how well do I know what's going on?

@EmilioPisanty Directly? Only other programmers. We basically develop the ABAP equivalent of static analysers like Coverity.

@ACuriousMind ABAP is the SAP brand of COBOL, right?

yup

::googles "Coverity"::

wait, hang on

you write code analyzers in COBOL?

or do you write static analyzers for code written in COBOL?

the latter sounds reasonable

the former sounds utterly horrifying

@NovaliumCompany it takes a fair bit of time to evaluate books like this. From a first brush, it doesn't look too misleading.

Both, we write code analysers in COBOL that analyse COBOL (with some help from the underlying compiler which is written in C). So it's the reasonable kind of horrifying ;)

@ACuriousMind nope, still horrifying

(Modern ABAP isn't really all too much like COBOL anymore, much like modern C++ doesn't have all too much in common with old C)

@EmilioPisanty The thing is, I don't know where and to what level of complexity I'll need QM in my life but it doens't matter because most of my curiosity has been satisfied. I'll probably read another QM book just to remind myself the material and to widen my view even more.

But as @JohnRennie says, if something is not interesting to you and you don't enjoy it, don't do it. I currently have no attraction to the complex mathematics behind QM so I'll stay in the pop-culture level knowledge :P

@NovaliumCompany so long as you're willing to listen when you're told that your understanding is incomplete and fully accept that your understanding is only partial, there's nothing wrong with that.

There's a well-written "progress report" by the Coverity inventors here in the "Communications of the ACM" (make of that name what you will :P) that reflects the general experience when you produce such analysers pretty well

You guys are much MUCH more advanced in QM than me, so I listen to your every advice, but I also listen to my goals as well and I want to spend my time. I absolutley understand that my understanding of QM is partial but I think for my needs and curiosity, it's enough for now.

I wanna again thank every single person in this chat room because you are all great! <3

@NovaliumCompany thus far in this conversation, you haven't shown much inclination to listen, I'm afraid to say.

@EmilioPisanty "I also listen to my goals as well and how I want to spend my time"

"accept that your understanding about field X is partial" needs to go beyond theory and into practice

@EmilioPisanty How would it go into practice?

My understanding of quantum physics is what Black Widow's understanding of it is in Endgame. (I hope that's not a spoiler)

@NovaliumCompany Basically, the conversation above is a series of repetitions of the theme "it's more complicated than that, and we cannot explain it without a full dive into the formalism" "please explain it without a full dive into the formalism".

it's perfectly OK to go "oh, OK, so it's more complicated"

I only want to point out that you never did that.

@EmilioPisanty I understand. You are right. I guess I just wanted the easy way - read simple book on QM and pretend you are a professor and have knowledge about the subject...

How much time does it take to learn that formalism and complex math anyways? (Through books and internet)

@NovaliumCompany That seems like how you wind up on the internet posting theories that don't make sense.

@NovaliumCompany the core basics? a few months, in good conditions.

All I need is the core basics.

The full thing, though -- frankly, I don't think it can be really achieved without dedicated university instruction through to the master's level.

@EmilioPisanty One of the 2 books you recommended will do the job?

@NovaliumCompany yes.

Or at least get you a fair bit of the way.

It depends on how much of the formalism you want to access.

Alrigh then. I will take a break from QM a bit (read something else) and I'll come back with new powers reading one of the books you recommended.

> unsoundness was controversial in the research community

yes, yes it was

@EmilioPisanty Alright. I think that's a wrap on the conversation?

@NovaliumCompany good to hear.

happy to discuss those books when you do get around to them.

@EmilioPisanty Sure thing. Thank you again, very much! And sorry if I've been annoying :p

@EmilioPisanty It is also unpopular with the users :P "What do you mean, this thing does't find every bug?"

@ACuriousMind I once got a friend (physics phd student) to believe that there's a flag for the C compiler that makes it take a somewhat longer time compiling but then guarantees that the program will never fall into an infinite loop

Ah, good old -fgullible

@ACuriousMind it was -turing on my machine, but I think that's outdated notation

@ACuriousMind @EmilioPisanty Full disclosure: currently wading through the literature on anyons, fusion rules and CFT...

I know one and a half of these three :)

@ZeroTheHero or, in other words, you had the natural reaction of anybody exposed to QFT?

@EmilioPisanty not "natural" no.

but when you have to read some of that stuff - you know follow the thread where some of the references take you - yes it can cause some reaction.

I just wish my last class in FT wasn't 25+ years old.

training wheels back on for sure.

and @EmilioPisanty agreed that it's one of these topics where somehow you find you never quite learned what you shoulda learned.

its been a while since I’ve read something that condescending

“Read a simple book and pretend you are the professor with knowledge on the subject...”

is he suggesting we don’t know about quantum mechanics?

@JakeRose I think you're misreading that

It's supposed to be his thought process, not someone else's

This guy...

I cant put into words

I.e. it's self-deprecation, not condescension

I don't think he's the first person to think they can easily understand things after taking a basic course. the fact that he's here discussing it and seems to recognize that thinking that way is bad is a good sign IMO.

^that

@NovaliumCompany an analogy to us trying to explain quantum mechanics without mathematics is flying a kite made of bricks.

You just can’t do it

@JMac I don’t think he’s recognising that it’s bad though. I just feel like no matter what any of us say to him he still thinks he doesn’t need the maths.

I’m stressed from revision maybe I’m too harsh.

Between the end of my lecture courses and exams I have precisely 8 days

With 2 exams on a Saturday no less

@JakeRose Depends on what he's trying to do. If he's just curious and wants to understand it a bit better than all the vague stuff you hear from pop-sci, he might not need the math. If he actually wants to participate in the cutting edge of the field he's gonna run into issues without the math, but it all depends on the end goal.

@JMac I’m mostly basing my annoyance of him asking us to explain something without maths when we told him the only way too explain it is with maths

but yeah, fair enough.

If he doesn’t want to then it’s his choice and gotta respect that

Math is just a really compact way of expressing ordinary words. In principle we could tell him everything "without math" but it would just take forever.