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12:00 AM
@ShaVuklia That is not my area of expertise, but from what I can tell you are on the right track :)
Actually..
Yeah not sure
Perhaps because each electron moving in one direction means a hole moving in the other direction?
 
yea, that's why it makes sense intuitively indeed
but it's technically not modelled that way, I think
rather, the effect of a positively charged electron moving in one way is the same as an electron moving in the opposite way
 
Yeah, that is what I was getting at I think
 
but you would somehow except this charge-dependence in the angular momentum operator, if that's the way to look at it
as a parameter
oh well, at least I can remember it, as it makes sense
 
Ok. Yeah the angular momentum should not depend on charge. That is why I just figured it might be how a hole is an absence of an electron (rather than thinking of their "opposite charge")
I see how what you were saying is different from what I was saying now
But like I said, this is not my area of expertise.
So this is just speculation
 
hm ye
 
12:31 AM
@AaronStevens Somewhat. I could learn more detailed information about it. But from what I do know black body has several definitions.
@AaronStevens But I always love to hear all points of view. So if there's some things you know, I'd love to hear them. :)
 
@ScientistSmithYT I don't know of more than the one main definition of black body, though I'm sure you can find it worded different ways.
 
I know that air when ionized with high enough voltages is the black body. But some other forms of evidence seem to say no.
@JMac Yes, the main two forms I know of are black body and black body radation. But the problem is that when I've looked at several definitions of them the definitions don't say what either really are. It's like the sources are telling me that a magnetic field is made of invisible photons. When really it isn't.
@JMac I wanted to thank you for your input. Not many people take questions like this as one that anyone can answer. So I'd like to take a moment and thank you for giving some information. It really helps. :)
 
@ScientistSmithYT To quote wikipedia "A black body or blackbody is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. " It's a hypothetical object that absorbs all the electromagnetic radiation that hits it (though it can still emit radiation).
 
If I ever ask a question anyone can help answer it. Even if it's just a little hint or a guess. Because that's where some answers are found. So if I ask a question it's everyones ballgame. :)
@JMac So a blackbody is a theoretical physical object that emits electromagnetic radation through the ionization of air via electricity.
So then that would mean the transfer is 100 percent efficient.
@JMac So we know the radation must be in the form of electromagnetic radiation. But what wavelength? And how do we measure it?
 
12:47 AM
@ScientistSmithYT Not really... The ionization of air doesn't have anything to do with the definition of a black body. What's important about a black body is that it absorbs all radiation that hits it. All objects radiate based on their temperature, and "black body radiation" is what you get when the object is not reflecting any of the radiation that hits it. It's extremely useful, because you can approximate the radiation from a large body as the blackbody radiation times an emissivity factor.
 
@JMac So for my example: Welding. Striking an electrical arc of hot plasma approximately 6,500 Degrees Fahrenheit. How would I measure the radiation off of the arc? Or how would I calculate it and the dose absorbed in human skin?
 
In principle, a black body emits radiation of all wavelengths. But not all of those wavelengths are emitted with equal intensity: the Planck distribution dictates that distribution.
In particular, there's a peak in the Planck distribution, i.e. a wavelength where the intensity is highest. But that wavelength turns out to be inversely proportional to temperature.
That means that one can infer the temperature of an object from its radiation spectrum. (so long as one can approximate it as an ideal black body)
This is known as Wien's displacement law. Wikipedia has a bunch of applications: en.wikipedia.org/wiki/Wien%27s_displacement_law
 
@ScientistSmithYT I don't know how it changes with temperature; but I just found in quick searching that one source claims the emissivity of an arc at ~25,000 °F is approximately 0.012, so quite a bit less than a real blackbody.
 
@Semiclassical Yeah I looked at those. And from what I understand the waves have a peak and the Planck Distribution formula calculates for the average radiation emision.
But I don't think I quite understand that entirely.
 
@ScientistSmithYT Honestly, the place I found the emissivity was a welding related paper. You might be able to find studies on the expected radiation from welding arcs. If you are curious about the safety I'm sure someone has done the math somewhere.
 
12:57 AM
@JMac Did it say 0.012 CPM?
@JMac Could you give me the link to the paper you looked at?
 
@ScientistSmithYT CPM? It's a dimensionless number that means it emits 1.2% of the net radiation that a true black body would emit. I already closed the random paper I found. Googling "emissivity of welding plasma" should find it.
 
@JMac Oh ok. CPM as in Counts Per Minute.
I found a few articles on it. But I have no clue how to convert the emisitivity to CPM. I looking to convert the emisitivity to radiation terms in CPM. So I could then determine what dose of radiation does what to the human body. Specifically the skin and finding a correlation between skin burn signs to the dose of radiation.
@JMac I've got to go for now. I have a meeting to attend, but I'll do some more looking into those articles. Then I'll come back and talk about what I've found and if it's right.
 
@ScientistSmithYT I don't think you would expect much ionizing radiation FYI.
 
1:16 AM
@EmilioPisanty Say congradulations from me. It's a big step.
I've only been in that place a fwe time, so I don't know if my advice is much good.
Try to relax and be yourself because you want a good cultural match nearly as much as you want oh-lord-a-job-any-job-at-all.
Do what research you can on the target department before you head out.
Come prepared for the teaching sample (if any).
I'm at a loss.
 
1:51 AM
@dmckee teaching sample seems to be rolled into the seminar
(which only adds to the pressure on that)
@dmckee yeah, I think that's the goal
@dmckee and thanks =)
 
 
4 hours later…
5:44 AM
@dmckee have you seen DavidZ around?
2
 
 
2 hours later…
7:30 AM
@frt132 hi :-)
@frt132 Did you want to ask about quantum field theory?
 
7:42 AM
@JohnRennie Hi! I was going to know more about those questions I asked about QFT, did some search but did not find obvious results.
 
@frt132 can I suggest an analogy? Bear in mind that like all analogies this one has limitations and shouldn't be taken too literally.
 
@JohnRennie Sorry, I want to know one thing, thank you! Why is Fourier transformation leading to the uncertainty principle? Is that because all matter are regarded to have particle-wave duality so they are treated as wave in this case which leads to the uncertainty principle
 
Wave-particle duality is a misleading concept and the world of physics would be better off if the phrase had never been coined.
 
Yes, I read somewhere probably it is a legacy of 18th century classic understanding
 
Quantum objects like electrons, protons, etc are neither waves nor particles. They are described by wave functions that can under the appropriate circumstances behave like waves or behave like particles.
But "behaves like" isn't the same as "is".
 
7:49 AM
Got it, the questions for QFT are really pressing for me, but I don't want to cost your time on the basics, I will watch all the PBS space time on the subject
and come back later : )
 
Quantum mechanics tells us how to describe a particle. It doesn't tell us what a particle "really is". Indeed most physicists would take the view that asking what a particle "really is" is a meaningless question best left to philosophers and other people with too much free time :-)
@frt132 if you want I can give you a simple analogy for how QFT works ...
 
Oh, yeah, sure
 
Consider a swimming pool that is still - no waves on its surface.
If you put your hand into the pool and waggle it then you can create a wave that travels across the pool.
The harder you waggle your hand the larger the amplitude of the wave.
But this is a quantum pool, and what you find is that you can't just create a wave of any amplitude. What you find is that is you waggle your hand to gently no wave is created.
Then as you waggle harder suddenly you find you've created a wave.
In QFT the wave is what we mean by a particle, so you've just created a particle.
 
but there's different magnitude of the wave in real life
 
If you waggle even harder the wave doesn't change until suddenly it doubles in amplitude. What just happened is you created a second particle so your wave now corresponds to two particles.
@frt132 in a real swimming pool the wave amplitude can be anything you want.
 
7:56 AM
> this is a quantum pool
 
But with a quantum field this is not the case. Well, not with massive quantum fields, but let's skp gently over this for now
The point is that when you try to transfer energy to a quantum field you'll find the energy gets transferred in quanta and each quantum creates one particle.
 
Cool
also the 'wave' doesn't have exact location?
 
@frt132 correct.
Though we can combine waves to create a wave that is localised. This is how we describe particle like interactions.
 
Since this is an invaluable opportunity, can I ask you something about some other thing?
I read in Stephen Hawking's Grand Design about an experiment. It was an experiment done by French doctors who perform open brain surgeries to remove tumors. They identify tumors in part by using electrodes to stimulate the patients' brain to see if the patients feel anything. And the patients actually reported to feel the subject feeling of 'intention' to move the hand etc when electrolly stimulated on the brain. I also read about drugs like DMT that make people 'see things'. etc.
 
Yes, you're welcome to ask. I'm in the chat room every day, so while debatably invaluable this is certainly not a unique opportunity :-)
@frt132 OK ... I must admin I'm not sure how physics comes into this ...
 
8:03 AM
There's more correlation I see about that, but It feels more and more to me that all the 'consciousness', be it attention, or ambition, or knowledge or logic or emotion etc are all from the somewhat deterministic and somewhat random evolution of everything. Does this aspect of 'determinism' somehow affect your philosophy about life?
 
I suspect most physicists take a pragmatic view. Since we will probably never know exactly how consciousness and the real world (whatever that is) are related we tend to ignore the question and just get on with studying what we can know. This is certainly my approach. I tend to get impatient with what I see as pointless debates.
 
Right, I am curious about this as I am having some difficulties with my own 'goal of life' thing, and thought that maybe knowing more about physics could help, thank you very much for the answer though.
 

 The Symposium

A Party Space for Philosophy.SE! Both philosophy and mundane c...
:-)
 
Thank you, honestly, I couldn't find much that might interest/inspire me there. Like Stephen Hawking said, phylosophy is kind of dead?
 
yeah, so is their chat room
 
8:12 AM
@frt132 speaking as one who is nearer the end of his life than the beginning, life rarely turns out as you expect or plan, so worrying about it is of limited use :-)
 
Will you consider cryogenics?
As a young adult, I guess I would definitely consider that : p, lol
 
Have myself frozen? Only if my descendants wanted to preserve me for future consumption, and I suspect I'd be a bit tough.
 
As for me, I kind of feel that I would want to regain consciousness someday to know more about the world in the future or the universe or the things we haven't discovered yet, even if the probability would be like 0.0001%. Probably the thought will change too though.
 
8:30 AM
everything changes
 
Plus ça change
 
thinking about a generalisation of ordinal numbers to linear order
Consider some ordinal number x, so big that x+1=x (once can envision that as x is so mind bogglingly big that the beginning of the queue is interpreted by the underlying model as an infinitely decreasing chain)
These are strange numbers that obeys the irreflexive relation x<x
 
 
2 hours later…
10:52 AM
Today's xkcd isn't great, but the alt text made me laugh
"Not actual size, except technically at one spot near the left."
 
 
4 hours later…
2:50 PM
Is anyone here?
 
"In mathematics, a Chevalley basis for a simple complex Lie algebra is a basis constructed by Claude Chevalley with the property that all structure constants are integers."
 
@Slereah too
 
Can only Mr. Chevalley do it or can I do it as well
 
you can do as well
 
2:55 PM
What are you people doing in your real life ?
 
@Knight Finding Complex life, the root of all negative problem
 
@AbhasKumarSinha have you completed your academics?
 
@Knight I guess no.
 
Are you in India or somewhere else?
 
@Knight India
 
2:58 PM
I heard so much about IITs in India, people mention it here so much
 
@Knight Yes
Where are you from?
If you are not Indian, don't overthink
 
US
 
@Knight oh okay, then what you have to do with IIT?
@Knight You can get seats too, but you'd have to appear JEE too.
 
Nothing hahah, people mention so much distress regarding it
 
@Knight They mention right
Insanely hard exam
World's top 5 hardest exam
and coachin? That's terrible, they lock you in a jail, in the name of IIT prep for 3 years, you know very less about outside world, you are not even allowed to walk out... :(
No phone, no TV, no internet
 
3:03 PM
So what they get finally?
 
@Knight IIT... You know the reputation of IITians across the globe?
 
No, I only heard about it from the Indians on this community
WOW @JMac is here
 
@Knight I'm surprised that you even know about it, it should not be popular in west... Yes, they are popular in India, ASEAN, Korean, chinese and those like countries...
 
@yuvrajsingh mentions about IIT in his profile
 
@Knight I M, currently studying in iit.
I passed the exam.
 
3:06 PM
@Knight Pride.... You know if you walk in India with IIT shirts, people will stare you like you are an celebrity
Even hotels offer discounts and banks offer loans for higher studies...
@yuvrajsingh bhai bhai bhai...
 
@AbhasKumarSinha This seems like a stereotype to me. Segregation, you know
 
Once you enter in Iit, it has it, s own problems.
 
@Knight Yes... ofcourse, I don't like that part...
@Knight You can read life experiences of Indian people here - quora.com/Is-the-IIT-tag-really-important to know more how important this is.
 
Is IIT only for engineering?
 
@Knight In India Engineering = billionare walking on streets.
 
3:10 PM
Means the same society pressure which I was mentioning yesterday
 
@Knight exactly...
@Knight see Traffic police left the riders just because they were IITians - qr.ae/TcX7r2
^He didn't charge penalty.
 
Do you people know about Harvard University?
 
Oh, I do not know that.
 
@AbhasKumarSinha Do they have to get their degrees in India for it to make them billionaires? The Indian students I went to school with definitely didn't give off the attitude that they were going to become rich with their degrees...
 
@Knight Don't care, if you know, engineering study in India at IIT > Harward
@JMac No you didn't get that probably
 
3:13 PM
@JMac Because it was not India
 
@Knight cop getting nervous because not behaving well with IIT students...
 
@Knight But they were getting engineering degrees. Based on Abhas' comment, that should make them billionaires when they go back to India, no?
 
Iit student are looking to get an seat in either MIT and Harvard.
 
@JMac He meant degree from IIT
 
@Knight But, one thing I can say about IIT - Best professors of the world for sure, no competition...
 
3:15 PM
Most of the good iit Ian's has this dream.
 
@JMac That was a metaphor....
 
I remember chitrang mrudia
 
@AbhasKumarSinha @AbhasKumarSinha No, you can't say that
 
@Knight I've seen a lot of rant and MIT Open Course videos on youtube, but one on NPTEL is way better, worst of worst professor is way better than the best.... You see yourself, I'm no one to just say like that.
 
3:19 PM
@AbhasKumarSinha You seem like you're incredibly biased towards IIT.
 
@yuvrajsingh I can say only one thing about your Chitrang Murdia that must be getting no hurdles from society and nothing else
 
@JMac Correction against IIT
 
@Knight @j Mac he was a born genius.
 
@yuvrajsingh How? I mean genius how?
 
@yuvrajsingh why? because he got Engineering Degrees?
 
3:20 PM
@AbhasKumarSinha You keep speaking as if their professors, education and status are like some sort of pinnacle. It seems like extreme bias.
 
I know in kota, among 5000 students, he was the one who beat teachers in the tough iit jee problem.
 
@JMac They actually are!
 
Got ALL India rank 1.
He was topper in IIT Bombay.
 
@yuvrajsingh I don't give a f**k
 
Really, bro I met, he is so cool,
 
3:22 PM
@yuvrajsingh I still don't give a damn
 
He enjoy life, and study. With passion
 
@AbhasKumarSinha ... Like I said. It seems like you are really biased. You can find people saying the same types of things about famous American engineering schools, like MIT for the obvious example.
 
@yuvrajsingh then it's good
@JMac Let them say, I don't have any problem....
 
@AbhasKumarSinha remember aman Bansal.
 
@yuvrajsingh yes, the king of STEM in India?
 
3:23 PM
@JMac Now can you understand my problem that I was mentioning yesterday. See these guys, how can you work without getting affected
 
@AbhasKumarSinha ... I'm not sure I understand. I'm pointing out what I see as a problematic viewpoint from you, that you have a strong bias towards IIT that may be misleading you.
 
@JMac Against
 
@Knight A good start is to try to critically examine your own biases...
 
@JMac I didn't get your humor
 
@JMac Do you know Prof. KL Seb?
 
3:26 PM
@AbhasKumarSinha That's total semantics, and I would still say you are biased towards it, because you seem to have an unshakable belief that it is some ultimate school.
 
@AbhasKumarSinha He doesn't mean anything like comparison, all he means that a good institute doesn't mean a whole good set of instructors
 
@AbhasKumarSinha Never heard of them.
 
@Knight IIT(s) - Good Professors, Crap system, crap institute, crap students...
@JMac oh okay, never mind...
 
@AbhasKumarSinha Yeah, professors can be good but best in world is kinda disrespect to people like Prof. Strang, Prof. Gross, Prof. Jerison, Prof. Sadoway and many others
 
@Knight Why? That's a useless point, if one is good, then why it's a disrespect for others?
 
3:30 PM
it's superlative
 
I meant - Professor Kizhakeyil Lukose Sebastian
^Indian professor, don't get confused...
Kizhakeyil Lukose Sebastian (K. L. Sebastian) is a professor of chemistry at the department of Inorganic and Physical Chemistry of Indian Institute of Technology, Palakkad, India. Prior to becoming a professor at IIT Palakkad, he was a professor of chemistry at the department of Inorganic and Physical Chemistry at Indian Institute of Science, Bangalore, for about 20 years. == Education == He did his Bachelor of Science (special degree) from the University of Kerala and his Master of Science from the University of Calicut. He stood first in the university when he completed his undergraduate and...
 
Where is @JMac ?
Why your Indian system always write stood first , gold medalist and all
 
@Knight Different things, for example. - high school isn't indian word, usually we use, senior schools...
 
@Knight Was that directed at me?
 
@JMac what?
What was directed at you?
 
3:34 PM
hahaha.... XD
 
2 mins ago, by Knight
Why your Indian system always write stood first , gold medalist and all
 
chill man....
 
@JMac are you Indian?
 
@AbhasKumarSinha Chill? I'm just wondering if he was asking me a question...
 
3:35 PM
@Knight No, Canadian. That's why I was a bit confused.
 
@JMac I thought that was directed to me...
 
@j Mac @Knight try jee advanced 2016 paper, how much you score?
 
@JMac So how it could be for you?
 
@yuvrajsingh 60(s) :(
 
You can automatically realize. Not you
@AbhasKumarSinha
 
3:36 PM
@yuvrajsingh ..?
 
@yuvrajsingh What it could tell me?
 
How difficult is for a student to get in iit.
 
@Knight You might have thought I was Indian... You just pinged me asking if I was there then followed up with that question not directed at anyone in particular, so I was asking if it was directed at me.
 
Where very single number can change your rank from thousand.
 
@JMac No, you were in misconception
 
3:38 PM
@yuvrajsingh this sucks actually...
 
@yuvrajsingh If I get 0 marks what could you say about me?
 
Nothing, iit exam, is for rejction not selection.
 
@Knight Which is exactly why I asked if the question was directed at me... I was just trying to figure out if you were asking me that question or not, because you asked where I was, then immediately after asked "Why your Indian system always write stood first , gold medalist and all". It seemed logical to assume it was directed at me.
 
@Knight You can still get admission to IIT using your 0 marks...
 
@JMac No, you are bullying me again (lol) I asked your location after that
 
3:40 PM
chill everyone chilll....
 
@AbhasKumarSinha What it will do to get an admission in IIT? Will it make sure that I would succeed in my dream of an elegant idea
 
@Knight Ofcourse...
 
@Knight You need to stop calling communication issues "bullying". It's actually pretty insulting to the people you are accusing of being bullies. You pinged me, then asked a question immediately after without pinging anyone else. Even though the question didn't really make sense to ask me, I had to clarify, because you made it seem like it was directed at me.
 
@JMac chill bola na
meh -_-
 
@JMac Your words are not light hearted
 
3:44 PM
@AbhasKumarSinha I get frustrated when people are unclear, then accuse the other party of bullying when they are just trying to clear things up and make the communication effective. It escalates the situation instead of clarifying it.
 
@JMac Reporter: How would you describe the tense situtation in the chat?
 
@JMac I too get frustarted when people ask for clarification even when they have understood the real thing
 
@Knight reporter: Are you willing to escalate the matter further?
 
Politician : No, all I want is people to be friendlu to each other
friendly*
 
I _didn't_ understand when I asked for clarification. You said "Where is @JMac ?
Why your Indian system always write stood first , gold medalist and all" To me, that looked like a question directed at me; but it didn't make much sense, so I asked you if it was directed at me. You treated as if it was obviously not; but pinging me then asking a question without directing it anywhere else makes it seem like a question for me.
 
3:46 PM
@Knight Greta: How dare you? :P
@JMac donald trumph: Let's make IIT Great again!
 
@JMac Okay, I said where are you because you left without any notif
 
@Knight I didn't leave... I just hadn't said anything in like... a minute. Either way, my point was just that pinging me, then immediately asking another question without directing it at someone else, makes me think the question might be directed at me, even if it doesn't make much sense to ask me. Just something to consider.
 
@JMac The way it was obvious to you, it was obvious to me too that I was asking it to @AbhasKumarSinha
 
@JMac Judge: Case Closed!
@Knight Mark Zuckerberg: I know everything, your privacy too!
 
@Knight It wasn't remotely obvious to me that you were asking Abhas. My first thought was that you were assuming I was from India. Nothing was "obvious" at all though, you pinged me then asked an ambiguously aimed question.
 
3:53 PM
@JMac So, what punishment you want to award me for that grave mistake?
 
@dmckee Quantum Mechanics: Why electrons move like waves?
@Knight Lottery winner
 
@Knight Nothing... I'd just appreciate it if you don't call me a bully for trying to clear it up and explain why I found it unclear. I'm trying to make communication clearer in the future.
 
Did you read that lol after bully? @JMac
 
I think you need to learn more about someone else (ie, become better friends) before insult (lol) works as intended
 
@Knight Yes; but it's also the second time in two days you've called someone else's actions "bullying lol" when it doesn't seem to be bullying at all. It just doesn't seem to help anything. The idea that people trying to clear things up are "bullying" is actually repeated often enough on this site that it gets frustrating.
 
4:00 PM
@JMac I'll write a book - how to bully someone like a pro on internet
 
@JMac It may be that you are frustrated with something else and making my thing an object to accuse of the cause of frustration
 
@JMac This actually all started with a joke which you didn't get.
@dmckee You didn't answer me.... :(
 
@Knight I'm frustrated with your use of bullying in inappropriate circumstances. Yes, it is amplified by other people using the word inappropriately; but I was addressing your specific choice to use bullying because it is the second day it has come up.
 
@JMac Can't you just imagine how hard are your words?
@JMac At least the society in which I live people talk like you when they hate you most
 
@Knight Can you point specifically to hard words by JMac?
 
4:04 PM
@Knight Do you know how insulting it is to be called a bully because you were just trying to understand what someone said, and then trying to help so that in the future the same thing doesn't happen again?
 
@AaronStevens NO i can't
 
@AbhasKumarSinha The phrase "move like a wave" is a bit a red flag for me (it sometimes signals a deep misunderstanding), so do you mind telling me what you mean by that?
 
@Knight Well then there you go
 
@AaronStevens Yeah, thank you
 
@dmckee I mean to ask, do they follow paths like waves?
 
4:06 PM
Nothing "follows a path like a wave". Even in classical waves nothing moves in a wiggly path.
 
@dmckee but they are continuous?
 
So the place to start is understanding motion in classical waves like ripples and waves on a string. Then understanding more abstract waves like light. Then applying that understanding to QM.
So, first question for the student: if you paint a red dot on a tight string and pluck the sting, how does the dot move?
 
$$ \dfrac{d}{dt} \dfrac{\partial}{\partial \dot q} i \hbar \dfrac{\partial \psi}{\partial t} = \dfrac d {dt} i \hbar \dfrac{\partial \psi}{\partial t} $$
 
Question (1b) if you float a cork on a pond and send some ripples past how does the cork move?
 
@dmckee oscillatory... But that's not what I meant, Do quantum objects move like energy propagated in water?
 
4:10 PM
You're jumping ahead. We'll talk about enegy flow (Poynting vector) in a while.
Which way does the dot of paint oscillate? Which way does the cork move?
 
yes
up and down...
This is what you wanted?
 
The paint moves perpendicular to the taunt string. The cork moves in a circle in a verticle plane lined up with the wave's direction of motion.
So we have established that things don't follow a sinusoidal path.
So ... what does the sinusoidal graph represent?
 
@JMac If everything is clear between us then can I leave now?
 
@Knight ... sure. I wasn't intending on keeping you here.
 
@dmckee $$f'(q) = a f(q)$$
^this...
 
4:17 PM
@dmckee, can you describe the wave which created by matter,
 
@JMac I hope by morrow's sunlight we both forget our heated arguments of today.
 
@yuvrajsingh ...? not true
 
Matter create wave, that, s what wave theory explain.
 
@AbhasKumarSinha But what does that mean? What is the physical meaning of $f$? (Aside, what is $q$ here?)
 
@dmckee sorry, it's a double derivative of f, is the general form of sinusoidal functions.
 
4:22 PM
@dmckee at least see my question once, when you get free
 
@JMac Should I conclude that you are not in mood of forgetting things as you have not replied to me?
 
@AbhasKumarSinha I recognize the math, but we're talking about physics. What does the math represent? And because this question is in the context of waves we need the argument to be of the form $ax \pm bt$ which adds to the behavior
 
@dmckee ok...
 
@yuvrajsingh At this point I have no idea what your question is? Are you asking about the underlying nature of "matter waves" from the old QM? Or about how mechanical waves get started?
 
Yes from your first part.
 
4:25 PM
Then this discussion with Abhas is relevant, though we haven't gotten to the point yet.
 
@Knight No... There just didn't seem to be much to reply to. FYI I'm less likely to forget if you keep pinging me and bringing it up.
 
@JMac Well, okay then let's not forget it.
 
@dmckee okay... next..?
 
@dmckee old QM
 
We're still working on the issue of where those sinusoidal graphs come from if no bit of matter moves along a path that wiggles? Why do people use those graphs for visualization and what do they have to do with the actual behavior of a wave?
And to answer that we need a definition of "wave". (A physics definition, not "a solution to a wave equation" which is very useful after you get the physical intuition but too abstract to be a starting place.)
Take a crack at it. Write down a proposed definition for "wave".
 
4:32 PM
every point of a curve behaving like a body of some mass and follows hooke's law
$$F = - kx$$
 
That, s sinosidally wave
 
@yuvrajsingh yes
 
Or harmonic wave.
 
@AbhasKumarSinha That's a reasonable starting point, but it has two issues for our purposes. (A) It only works for waves in matter (with bits of stuff bobbing back and forth). (B) It is satisfied even if all the oscilators are independent and there is not coordinated transmission of energy or information "along" the wave.
(A) will become an issue when we want to talk about light or QM.
 
@dmckee agree
then...
 
4:35 PM
(B) is more critical.
 
agree about (b)
(B) I mean
 
I use "a travelling disturbance" and an introductory definition.
 
@dmckee I understand
 
It has a couple of good points: (a) we haven't specified what is disturbed so it is nbot limited to matter, and (b) "travelling" enforces the spacial coupling requirement.
 
@dmckee nbot?
 
4:37 PM
And some bad points. it is very abstract and it's philosphocially troubling to talk about "standing waves" if your definition of "wave" requires that they are not standing.
@AbhasKumarSinha ::sigh:: "not".
 
The thing that makes it a wave is that something gets disturbed, then returns to its queiesent state. And that disturbance affects nearby stuff which also get disturbed so the effect move through space.
 
@dmckee Then it's $$ \dfrac{\partial^2 f}{\partial t^2} = v^2 \dfrac{\partial^2 f}{\partial x^2} $$
 
The sinusoidal graphs show a particular class of waves ("harmonic"), and they map the size of the distubance in space or time or both.
 
@dmckee true...
@dmckee yes
 
4:40 PM
Now generalize to E&M: Light is a wave in the electric and magnetic fields and it is the strength of the fields that gets disturbed. No physical thing is displaced, but there is still a disturbance and it moves.
Finally we come to QM.
 
@dmckee Maxwell's equations
 
The thing that is disturbed is the local probablity amplitude. (Here I am assuming the Schroedinger picture in the position representation.)
@AbhasKumarSinha Yeah. They are equations for the fields, and you end up with a wave equation that talks about fields.
 
@dmckee yes
 
So, the "wave" in quantum mechanics is a very abstract thing. Even more so than E&M waves, because the probability amplitude is not something you can do simple force experiments/demonstractions on the way you can with electric and magnetic fields.
 
@dmckee Use wave equation, assume de broglie's wavelength formula, then replace momentum in form of energy, if that is what you mean?
@dmckee understand that..
 
4:53 PM
@AbhasKumarSinha Are you asking how to arrive at Schroedinger's equation from a classical form? I addressed that a couple of times on the site: physics.stackexchange.com/a/290697/520 and physics.stackexchange.com/a/355499/520. You actually start from Hamiltonian mechanics and apply de Broglie assumptions.
 
@dmckee no, I wanted to know other possible interpretations... apart from von newman diarc axioms, hamilton Jacobi axioms, wave, line integral ones....
that assumption hurts me...
$$ \Psi(x,t) = e^{i(kx - \omega t)} \;, \tag{1}$$
 
 
1 hour later…
6:13 PM
physics.stackexchange.com/questions/519016/… I'm pretty sure people not reading OP carefully enough has now convinced OP that the science agrees with him, and that we can somehow get extra energy out of this system -_-
 
@Bob D thank you, that's exactly the acknowledgement that I was looking for. My thinking has been, why use your electric motor and battery to propel the larger vehicle, when you could propel the smaller vehicle. Then, you can harvest the energy from the smaller vehicle and do even better at moving much larger vehicles, than if you used the same electric motor and battery to propel them directly. I know it's difficult for people who have energy conservation on the mind, but it adds up. — James Montagne yesterday
harvest what energy?
 
Quantum dark orange-flavored anti-energy
Obviously.
 
@KyleKanos Yeah... exactly. I even tried to warn BobD because I recognized the OP from a similar question that turned into a legnthy chat session before. I could tell he basically asked a super unrealistic question, and because of people answering it without noticing that it was non-physical, it gave OP validation about things that sound very incorrect.
 
7:08 PM
Oh nice, I actually found the chat where I discussed this with them for much longer than I should have. chat.stackexchange.com/rooms/94165/… That's how where OP was trying to go with the question
 
@JMac Chats like that are so tiring
 
7:41 PM
@AaronStevens Yeah, that one was over several days IIRC so it wasn't so bad, but I was clearly getting frustrated by the end. He's so determined to have others validate that he's right... but like if he were, he might as well just go generate free energy and become mega-rich instead of trying to get people online to tell him it's correct.
 
@JMac Yeah I had a long convo one time about someone trying to argue how the speed of light isn't the same for all observers
And to make matters worse, someone else joined and started confirming what the other was saying by talking about weird, contrived doppler shift examples
Which didn't have anything to do with what was being discussed
 
@AaronStevens I could kinda tell his latest question was worded in such a way that people were going to answer it in a way that would "affirm" his idea. I don't know if he did that completely on purpose, but I saw where it was going and tried to stop it. Obviously that didn't work and he thanked the answerers for (kinda but not really) affirming his misconceptions
 
@JMac Yeah that happens sometimes. oh well
 
@AaronStevens Yeah oh well. I just don't like they he's clearly trying to use the site to affirm his own beliefs instead of understanding actual physics.
But he's not the first, and wont be the last :(
 
@JMac "I reject your reality and substitute my own."
2
 
7:49 PM
Assume good faith - and when you no longer do, disengage. Please also try to not disparage other users here - the line between factual criticism and personal attacks can be blurry, but I feel we're leaning a bit to close to the latter here.
2
 
 
3 hours later…
10:51 PM
1
Q: Should we test lowering the vote to close and reopen threshold?

tpg2114In early August, Stack Overflow (the company) announced an experiment to lower the number of votes required to close or to reopen a question to 3 votes on Stack Overflow (the website). The trial period was 30 days, and at the end (plus time for data crunching), the results and an in-depth analysi...

 
11:43 PM
@KyleKanos or anybody else who might know... any good recommendations for learning about transformations to arbitrary coordinate systems? I've been trying to transform the compressible, reacting Navier-Stokes equations (2D, steady) to coordinates attached to an arbitrary line through the flow
Doing it the... naive, computationalist way where I compute the transformation metrics and treat it like I would treat the grid leads to this huge, ugly mess of equations. But when I look for resources on the topic, everything either describes something simple, like conversion to polar coordinates, or they dive full on with the metric tensor and Christoffel symbol but don't explain how that works...
So I am trying to find a way to learn the best way to do this, that takes into account my poor engineering brain that is totally willing to treat differentials like fractions if I get my answer faster...
 
@tpg2114 numerically or analytically?
 
@KyleKanos Analytically. I'm trying to derive a theoretical model for the recirculation zone that forms behind a bluff-body flame holder.
So I can come up with a few different models for what the bounding line of the zone is, but I want to be able to know where that bounding line is. So I was trying to solve in the coordinate space of tangential and perpendicular to the dividing line and solve for the (x,y) coordinates where that happens
Given some models for the flow on either side of the bounding line, like potential flow or something, so I can get a velocity and pressure field
I suppose at some point I'll have to numerically solve the final equations
 
I guess over only ever done it when knowing the vector formalism (I.e., having nabla present) and just writing out the polar form instead of Cartesian
 
It isn't polar though, polar is the simple example everybody shows... but I need it for any arbitrary surface
 
11:58 PM
Yeah, not something that I've done :(
 

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