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On January 24 2012 23:39 Teoita wrote:Show nested quote +On January 24 2012 23:28 rei wrote:
WTF i want to see some of these shit storm, Give us and example so we can all feel stupid together. Solve Shroedinger's equation for a particle in an infinite well of potential, with a Dirac delta of potential that can be put anywhere in the box. H=p^2/2m+v(x)+g*delta(x-a), where v(x) = 0 for 0<x<a, infninity anywhere else. g is a constant.
You know, as an electrical engineer I actually understand that mostly. I'm not quite sure how to solve it. Isn't p = h*k in quantum theory? I know it's not classical momentum. I'm assuming that delta(x-a) is the dirac delta function at (x-a) which is nothing more than a sample of height 1 at point a. I'm not sure how that applies to quantum mechanics though, cause I've only seen it in signal processing.
On reading more of the thread.... it sounds like that's not the dirac delta function? I'm not sure what delta distribution is and if it's just the same thing.... oh lawdy lawd.
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I'm really sorry for saying this, but you just made me feel a whole lot better about my situation. I'm an economy student (and I know, it's just a made up science, but sadly it does use the same math as physics when you major in mathematical analysis) and we were always outraged why anyone would expect us to understand shit that only physics students will ever get. (We used to call them mad scientists, but on a physics blog that's not the best idea, is it? :D)
All our books on the more complex math were those of physics students', so when we tried to look anything up, it usually started with an example of heat transfering (I clearly remember this being on Fourier analysis) in a way that'd require another 3-4 hours to at least get an idea what it was all about.
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On January 25 2012 01:39 Mindor wrote:
I'm really sorry for saying this, but you just made me feel a whole lot better about my situation. I'm an economy student (and I know, it's just a made up science, but sadly it does use the same math as physics when you major in mathematical analysis) and we were always outraged why anyone would expect us to understand shit that only physics students will ever get. (We used to call them mad scientists, but on a physics blog that's not the best idea, is it? :D)
All our books on the more complex math were those of physics students', so when we tried to look anything up, it usually started with an example of heat transfering (I clearly remember this being on Fourier analysis) in a way that'd require another 3-4 hours to at least get an idea what it was all about.
Oh Fourier analysis is easy, as long as you're not doing the integrals by hand. It's just a transformation from time to frequency. I'm not sure why you'd ever use it for economics...
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Wow, it's interesting to me that you made it all the way to your third year in physics and your complaint in the QM class is how you need to use mathematics that you haven't learned yet. In my experience, that is almost always the case unless you're really far ahead in math. In almost every physics class I took we had to be comfortable doing mathematics that we formally didn't learn yet. It was only because I doubled as a math major that I formally learned the math (later on or at the same time).
This is not the usual complaint about physics majors in quantum mechanics. I think this is a good sign that you need to start reconsidering things if your issue in a high level physics class is the mathematics.
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Calgary25998 Posts
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United States22883 Posts
I wish you all of my luck for the year so you can get through it. 
I wasn't man enough upper level physics. I pussied out. :X
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I teach advanced Quantum Mechanics at University, if you have specific questions, shoot ahead.
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One day you're going to be 30, and be like....why the fuck did I take Quantum Mechanics?
You might cite the odd interested factoid, which is rockin' cool.
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On January 25 2012 02:05 Zorkmid wrote:
One day you're going to be 30, and be like....why the fuck did I take Quantum Mechanics?
You might cite the odd interested factoid, which is rockin' cool.
Yeah seriously OP, what are you trying to get out of a physics degree? I think the field is interesting but gl finding a job :/
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On January 25 2012 01:41 EternaLLegacy wrote:Show nested quote +On January 25 2012 01:39 Mindor wrote:
I'm really sorry for saying this, but you just made me feel a whole lot better about my situation. I'm an economy student (and I know, it's just a made up science, but sadly it does use the same math as physics when you major in mathematical analysis) and we were always outraged why anyone would expect us to understand shit that only physics students will ever get. (We used to call them mad scientists, but on a physics blog that's not the best idea, is it? :D)
All our books on the more complex math were those of physics students', so when we tried to look anything up, it usually started with an example of heat transfering (I clearly remember this being on Fourier analysis) in a way that'd require another 3-4 hours to at least get an idea what it was all about. Oh Fourier analysis is easy, as long as you're not doing the integrals by hand. It's just a transformation from time to frequency. I'm not sure why you'd ever use it for economics...
That's my point. We had an exam where we had to make the teacher explain us the physics behind the differential equation we were supposed to solve, because we couldn't understand the proposition. Now at least I can feel better that physicists weren't born with some astral knowledge and it's not as "self-explanatory" as we were lead to believe.
+ Show Spoiler +Fourier transform is used in statistics and probability theory, so it's not that far fetched. I'm pretty sure it had something to do with probability density functions (I'm horrible with names, I stopped remembering them at Pythagoras...I don't really get how logical people like mathematicists would call functions by a name that doesn't tell you what they do) and I'm sure that we used it in practice to create orthonormal bases for Hilbert spaces.
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So I'm a high school student considering taking physics in uni... stop scaring meeee
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On January 25 2012 02:11 IMoperator wrote:Show nested quote +On January 25 2012 02:05 Zorkmid wrote:
One day you're going to be 30, and be like....why the fuck did I take Quantum Mechanics?
You might cite the odd interested factoid, which is rockin' cool.
Yeah seriously OP, what are you trying to get out of a physics degree? I think the field is interesting but gl finding a job :/
I'm sorry, but I have to ask what kind of insight you have into the job market. A pyhsics degree is a great career move, at least where I come from. They're hired basically everywhere because they're trained problem solvers who are familiar with complicated math and often programming. Banks, insurances, stocks, logistics, you name it. Physicists and mathematicians can be found in almost every big company somewhere, trust me.
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On January 25 2012 02:20 Mindor wrote:Show nested quote +On January 25 2012 01:41 EternaLLegacy wrote:On January 25 2012 01:39 Mindor wrote:
I'm really sorry for saying this, but you just made me feel a whole lot better about my situation. I'm an economy student (and I know, it's just a made up science, but sadly it does use the same math as physics when you major in mathematical analysis) and we were always outraged why anyone would expect us to understand shit that only physics students will ever get. (We used to call them mad scientists, but on a physics blog that's not the best idea, is it? :D)
All our books on the more complex math were those of physics students', so when we tried to look anything up, it usually started with an example of heat transfering (I clearly remember this being on Fourier analysis) in a way that'd require another 3-4 hours to at least get an idea what it was all about. Oh Fourier analysis is easy, as long as you're not doing the integrals by hand. It's just a transformation from time to frequency. I'm not sure why you'd ever use it for economics... That's my point. We had an exam where we had to make the teacher explain us the physics behind the differential equation we were supposed to solve, because we couldn't understand the proposition. Now at least I can feel better that physicists weren't born with some astral knowledge and it's not as "self-explanatory" as we were lead to believe. + Show Spoiler +Fourier transform is used in statistics and probability theory, so it's not that far fetched. I'm pretty sure it had something to do with probability density functions (I'm horrible with names, I stopped remembering them at Pythagoras...I don't really get how logical people like mathematicists would call functions by a name that doesn't tell you what they do) and I'm sure that we used it in practice to create orthonormal bases for Hilbert spaces.
Honestly it sounds like physics departments just really suck at actually teaching anything. I'm taking a general relativity course and literally the first half the course is just pure math so we know how to solve everything in the physics later. And our department is pretty terrible overall (though this professor is great). Something tells me you guys picked poor schools for physics. Should've done engineering.
On January 25 2012 02:32 surfinbird1 wrote:Show nested quote +On January 25 2012 02:11 IMoperator wrote:On January 25 2012 02:05 Zorkmid wrote:
One day you're going to be 30, and be like....why the fuck did I take Quantum Mechanics?
You might cite the odd interested factoid, which is rockin' cool.
Yeah seriously OP, what are you trying to get out of a physics degree? I think the field is interesting but gl finding a job :/ I'm sorry, but I have to ask what kind of insight you have into the job market. A pyhsics degree is a great career move, at least where I come from. They're hired basically everywhere because they're trained problem solvers who are familiar with complicated math and often programming. Banks, insurances, stocks, logistics, you name it. Physicists and mathematicians can be found in almost every big company somewhere, trust me.
Physicists don't get jobs as physicists. You're better off with a math degree, and infinitely better off with an engineering degree. Maybe it's different across the pond, but here in the US nobody really does physics anymore because it's basically an engineering degree with no exposure to application. You only do it if you want to become an academic and go all the way to PhD.
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On January 25 2012 02:31 MutatedMiracle wrote:
So I'm a high school student considering taking physics in uni... stop scaring meeee
Physics is so much more than QP. Don't worry about it, the rest makes sense.
I've taken (and passed) Quantum Physics, Quantum Mechanics, Advanced Quantum Mechanics and Quantum Electronics courses but I've never had any use of it what so ever (didn't want to go for PhD). It's fun and a the math in AQM and QE is fun, when you practically have to learn new ways to integrate and calculate things by diagram rather than formulas.
You'll need a high threshold for "accepting" physics rather than being good at understanding it to pass any QP course. Accept the physics, learn the math, pass the test.
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I'm doing research in particle physics, and have been teaching more or less this stuff (a bit below your level though, only first half year of QM, 2:nd year of the education, with ordinary square wells in 1D, no dirac deltas etc). I agree that this part is the first time (in most physics educations) where you run into really abstract things, so it requires a new kind of mindset to handle.
Most of previous physics is more intuitive, things you easily can imagine and have some understanding of from the start. For example you have some understanding for what pressure of a gas is, or kinetic energy etc. But the phase of an electron wavefunction?  So it really puts your picture of physics to the test when you no longer deal just with quantities that have clear observable meanings.
Also it is essentially the first time you have to rely on more abstract mathematics. Are you doing this in a linear algebra formulation, or more of an integral formulation? ie, do the teachers refer to the electron state mainly as a vector or as a function? When I was teaching this, we used a book that was formulated in terms of functions and integrals, and barely mentioning the linear algebra, while I have always loved the beauty of the linear algebra formulation of quantum mechanics, although slightly more abstract.
Well, if you want some help with understanding these things, I may be able to give you a pointer or two, but it seems your intention is to just pass the exam. So good luck!
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Russian Federation1132 Posts
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Just dropping by to wish you luck!
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My High School teacher had a PhD in physics... why he taught high school he said, was because loved the way students in highschool treated physics with curiosity instead of in university where they all hated it and were miserable and he had his students dropping out even a month before they were done their degree. He taught the course at a higher level and when it came to grade 12 exams, even the students that had 40-50% in his class got 70+ on the final. He told me that I shouldn't go into physics unless I really wanted the feeling of blowing my brains out everyday. So im in Compsci now
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Ahaha, this brings me back to my quantum mechanics course(s) in uni aswell. I remember on the final for quantum mechanics A, we had 3 hours to do the exam, but when time was up, nobody was more than half done, so the prof gave us two more hours, but still nobody was done, we just called it and left. 
Switched to honors math, and it's been much of the same. bleh.
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Geez this is ironic, I was just about to get started on my getting-ahead reading :/
I'm getting a masters in Chemistry but I've recently been quite drawn to my Uni's Physics Department's Quantum Mechanics courses (instead of the "The Quantum Theory of Matter" likely pussy Chemistry course equivalent).
Linear Mathematics (Linear Algebra) and just about all of MIT's Physics courses, or simply online university Quantum Mechanics resources, have fun (:
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EPT
