/pg/ - Physics General

why does nobody respond to people here?

which uni?

Because people who discuss physics here are all larping.

If you're with a good prof it usually doesn't matter where you go. Of course you'd have to work harder to produce more work so that you get your reputation up.

>being this delusional

>almost no one posts here
it appears Veeky Forums is a math focused board

No. It's because op used /pg/ instead of the superior /PhG/

11 months till thesis hand it.
I'm holding on to my butt.

I recommend /pg/ ~ /physics/ general

WZW terms found in Graphene Landau levels: arxiv.org/abs/1411.5684.
Low energy Graphene is a Dirac semimetal with a big [math]SU(4)[/math] symmetry. The fact that it's possible to construct topological actions with it shows that TQFTs other than those arising from [math]SU(2)_k[/math] Chern-Simons can be realized in physical systems, and holds new possibilities for topological quantum computing. In fact I think Microsoft is big on using fermions on Graphene as topologically protected qubits recently.
What's the thesis on?

Solid State and molecular physics is fucking me up hard bros. I heavily underestimated the time I needed for to study and now I have 5 days until exam.

Have you tried to contact Ciprian Manolescu? I recently found out that he did his phd on TQFTs.

Is the no jobs for physicists meme true? Will I be working at a mcarnolds with a 4 year degree while I support myself through my masters?

This guys is doing what I wish I could do.

Yes. I got a physics degree, realised there was no future in it unless research, went and got a Renewable Energy MSc.

lmao im doing donkey dicks like fuck all
sometimes i feel like pursuing physics is suicide

Alright. I'm in the process of making up the ground I lost the past two years. I have 2 and a bit months before my 3rd year starts, so I'm getting a bit of a head start. (I need to average 80+% next year, which in bong terms, is insane). I think I might want to do too much - I want to make a decent way through the following books:
Steeb: Nonlinear Dynamics, Chaos, and Fractals - Problems and Solutions
Foot: Atomic Physics
Pressley: Elementary Differential Geometry
Steane: Relativity Made Relatively Easy
Simon: The Oxford Solid State Basics
Nielsen & Chuang: Quantum Computation & Quantum Information
Jammer: The Philosophy of Quantum Mechanics
Lange: intro to the Philosophy of Physics

as well as reading fiction, poetry, and writing two books.. tfw adhd-i. at least I have a diagnosis now.

You're all over the place. Just read the Landau-Lifshitz series.

>all over the place
Not really.. half of those are written by people who taught the very courses I'm taking. The rest I'm reading out of interest.
Oh and I'm doing Bartle & Sherbert's real analysis too. It's just difficult to know if my proofs are satisfactory.

can I get to a good PhD program from a shit tier bachelors? I'm at CUNY Hunter right now, 3.5 gpa from first year. getting an accelerated masters in physics and a bachelors in math- 3.7 gpa in physics (11 cr so far) and 4.0 in math (12 cr so far)

narrow your interests or you will be learning too much to learn much of anything at all

There's little chance of that. I'd feel like I was missing something. I'm just going to have to acquire the ability to focus for 10h straight every day... that'd be the dream.

that's certainly not the case now: act in response to reality, not in response to potentiality

Algebraic topology and homotopy/homology can be used to describe defects in disordered media: journals.aps.org/rmp/abstract/10.1103/RevModPhys.51.591.
Given the stablizing subgroup [math]H< G[/math] of the symmetry group that fixes the space of low energy states [math]R \subset \mathcal{H}[/math], the topological orders of the theory is characterized by [math]\pi_n(R/H)[/math], where [math]n=0[/math] characterizes a planar defect (e.g. domain walls), [math]n=1[/math] a line defect (e.g. cosmological strings) and [math]n=2[/math] a point defect (e.g. Dirac monopoles). This is also related to the Goldstone-Nambu theorem (where non-trivial topological orders can cause a massless zero mode to form) and the Mermin-Wagner theorem (where long range topological ordering cannot exist in a conformally invariant theory for dimensions larger than 2).

I know very little about physics.

Has state-of-the-art physics gotten harder to gather evidence for through experimentation over the years? Most of Einstein's ideas were checked within his lifetime but it seems like most things to do with string theory or supersymmetry are years away from experimental verification and unlikely to happen in the lifetimes of the physicists who contributed to the theory?

There's open problems in mathematics that are several thousands of years old like existence of odd perfect numbers, are there any 'very old' ideas in physics that are still stuck in the theoretical stage?

Started my first bit of QM and found it mixed. The math felt a touch tedious at times, but the physics was fantastic for the most part, learning how certain things defy every day notion of common sense.

>sound gay af

The theory of topological phase transitions developed by Kosterlitz and Thouless in the 1970's was only recognized by Nobel in 2016, and the gap between theoretical and experimental discoveries are only going to widen. The relatively recent idea of non-Abelian excitations might not even be experimentally verified in my lifetime.
Even without all the /x/-tier shit like string theory it still takes a very long time for experimentalists to catch up.

Going to begin with my Master thesis in material physics this October, very excited for it!
Topic will be to analyze the dynamics and local structure of amorphous silicon.
For the future I might continue on the same topic and go for the PhD or try to find a job in the semiconductor industry here in Germany e.g Globalfoundries.

The more I know, the closer to reality I am..

I do see what you mean, though. It's just a bit more difficult than that.

bra-ket is comfy af though

I doubt that some constants are actually constants.
They must have had different values at the time of the big bang and it's extreme conditions which certainly would change some aspects on the research of it.

The math is the best part. Read Sakurai or Ballentine to get an idea of the actual math behind QM, the math in Griffith (which is 9 times out of 10 what people like you are reading) is just computations.

Why not Cohen-tannoudji however it's spelled?

Too mainstream.

You can get jobs in consulting easily

What about Shankar?

Couldn't get into grad school because I'm a brainlet and got a low score on the pgre. Looking for a job now. Any advice for getting into grad school later in life? What would I do about letters of rec?

It's ok but not deep enough. If you're hardcore I recommend von Neumann.

I'm about to start my last year or my bachelors and aiming to work in quantum computing.

How's the field for anyone in it?

Expanding on this I've always wondered, are the physical constants in nature rational?

I get that we define our units and therefore change what these values are. Like the speed of light for example.

But if in math an irrational number stays irrational in all rational bases shouldn't certain physical constants as well?

And what would this mean of the universe?

Are you fucking for real? Changing units is not the same as changing number bases.

But if we define rational units it gives a system that is rational.

Or am I missing something?

Working on a PhD in High Energy Experimental, with focus on hardware. I never felt like physics had lost meaning until now. It has been almost a year and I haven't done any 'real' physics. I am working on design and construction of a large area, high efficiency (99.99%) detector for a potentially game-changing experiment, but it feels like nothing but grunt-work. I think I got spoiled doing software and simulation for the experiment, but I enjoy working with my hands. The only thing I really got going right now is building a cosmic ray test stand I designed, utilizing some large cathode strip chambers, for testing the detector components. I need to get readout electronics for the chambers, design the gas system, and get some trigger paddles up, and then I get to write some analysis software for it. Should be fun, more fun than tech-work all day.

I think I have unknowingly enrolled in an engineering degree, but I'm not sure yet.
At least I will have skills most other physicists wont; I'm looking at you LHC experiments.

hey guys I wanna start studying quantum mechanics by my own. Any good books to start with?

>dirac delta generalized function

That's the nature of your field. Loads of simulations, programming.

I think you can find a better place than Glovalfoundries.

I am learning about differential algebras, hopefully they have applications to Physics.

I started doing research in neuroimaging and I have a fairly strong physics and math background and is why I passed interview to get position as an undergrad.

However, I don't know much about coding and programming. I have to use MatLab.

I need to complete a project by Tuesday and I basically have to make these different shapes like a cone, pyramid in MatLab using linear algebra or something.

How do I do this? Any tips on going about on learning how to do this? Or just about MatLab in general?

Really confused and don't want to embarrass myself in front of my PI. Would be very grateful for any user's help

Are there more of these pictures

Anyone? :(

Not that I am aware of

Got any advice for my situation?

Unfortunately I'm not familiar with MatLab, we just use Mathematica and Python around here.

If you understand how to describe your object by a mathematical notation, be it in the form of a point cloud, a matrix notation or vectors, the rest follows naturally as Matlab was designed to manipulate matrices and visualise the results.

Is math all practice or just natural aptitude? I suppose someone who wasn't gifted for math can never reach the understanding of someone who is and has worked upon his natural talent.

>tl;dr math's pure natural aptitude after a certain point IMO

Simulations and programming I like.
Gluing scintillator together is getting old.

Math requires a natural aptitude of "the willingness to practice lots".

I'm just starting to take Algebra 1 in the next semesters. lol

Going into final year undergrad. Reading some QFT. Do you have any recommendation for undergrad thesis in QFT? (hopefully something better than φ4 or QED)

QCD is fun

>QFT
>Undergrad
These two things do not go together.
My recommendation is not to be a pretentious fuck and think "oh look at me, I'm doing QUANTUM FIELD THEORY!!!one!!"
[math]\phi^{4}[/math] theory is just really just cute examples to work through at this point. QED is replaced by Lattice-QCD, which is something only those with doctorates work on/program.
The only interesting thing you can do is look at running coupling constants with higher-order corrections. Good luck though, it is nothing but long and tedious calculations.

>These two things do not go together.

Not him but at my school you can do two semesters of QFT your senior year if you want.

Going from industry to academia is difficult, what you might want to do is try getting a job that will help you get your masters and then pivot to getting a PhD. You can also always apply to a masters program, get you GPA up and then apply to a different PhD program or try getting into the one at that uni. I would also stress that some masters programs accept both academic and professional letters of rec.

Shankar is a good book to self study from since it starts with the prerequisite linear algebra and doesn't really assume too much overhead
I think the word you're looking for is 'distribution'
mathworks.com/matlabcentral/newsreader/view_thread/171309?requestedDomain=www.mathworks.com
For the most part you know the functions that generate various objects and you use those to plot the objects.
What do you like about QFT? How much of a background do you have? What book are you using? Point is you're likely doing an exposition on QFT but need a subject matter but this depends on a lot of factors that should first consider before picking a topic, so what about QFT do you like?

Thanks for the book recommendation!

I think that's only the problem I am having. I really am not sure how to describe these. It's been a while since I've taken Linear Algebra and I think that's how I need to describe these shapes.

Could you or some user explain what I would need to do to describe a cone or cylinder for example?

>what you might want to do is try getting a job that will help you get your masters and then pivot to getting a PhD

Hmm, how would I go about pursuing a job like this? I'd imagine that I would have to state my desire for going back to school but how common is this for an employer to actually provide this opportunity. I appreciate the answer though. I've been depressed about it but I still love reading and learning about physics and mathematics, even if I'm out of school.

Currently using {Peskin and Schroeder}'s book. Mostly I like its mathematical elegance or better stated its mathematical can-be-made-elegant, and the fact that you can arrive to pretty much everything from "first principles". My background (relative to that) is 2 courses on QM, SpRel, GenRel, DiffGeom and pretty much all undergrad program

These were programs I've seen on the corporate side of things, so I don't know if you can do it for math/physics, but for what it's worth there's some info here.

gograd.org/financial-aid/companies-paying-for-grad-school/

What you might want to do is outlined here

academia.stackexchange.com/questions/23485/3-4-years-since-i-graduated-how-should-i-time-asking-for-recommendations

academia.stackexchange.com/questions/24592/email-to-a-professor-after-long-time-for-recommendation?rq=1

You might wanna try keeping in touch with some of the people you got letters of rec the first time around, or possibly try and find professionals that have some academic connections to write a letter for you. I think your best bet for grad school is first applying to a masters program (easier to get into) and then trying to go into a phd program from there (this is assuming your employer won't help with grad school).

So you're getting a proper background, that's good, (a great follow up is Zee's book), so is the formalism of QFT what you find attractive, it's power, or is there anything else? Any specific topic that has caught you eye yet (operator algebras, superconductivity, gauge theory)? The fact that you have a good background in GR and Diff Geo is also good.

I should also add that are you interested in QFT for physics purposes (particle physics and the like) or for more mathematical purposes (things like it's connection with Knot theory)?

For now it is only the formalism, I haven't seen it's power in action since I've just started reading.
If by operator algebras you mean the Lie algebras one usually sees in these courses, then it's fun but just that; fun. If you mean something more general like algebras of Banach space operators blah blah, then I don't know, haven't seen it. If that connects somehow to QFT, it might be a great thing (got any link on that?)
Superconductivity falls easily into gauge theories, doesn't it? Isn't it just abelian gauge symmetry breaking? Also from Stat Phys pov I find it quite uninteresting.
Gauge theories in general, yes, I find them quite interesting.
Forgot to mention courses on Stat Phys of particles, and Stat Phys of Fields (Landau GInzburg theory, mean field theory, a bit of Euclidean Path Integrals and a teeny tiny look at renormalization)
Probably I'm going for the physics purposes, falling for the quantum gravity meme, but if I get more mathematical connections later I might as well go for that

aï aï aï aï sorry, *its (instead of it's in the first line)

By operator algebras I meant things like C* and Von Neumann algebras, though if you prefer QFT to be nice and algebraic then this might be up your alley

princeton.edu/~hhalvors/aqft.pdf

Although gauge theory is quite general and superconductivity is a facet of it there are other aspects of super conductivity that are completely unknown (it's still a very open field), what I meant was that superconductivity at the level of BCS theory is pretty well understood and as such one could write a pretty good thesis on an overview of the subject. If you're doing statistical physics of fields then one thing you could do is try doing an exposition on the origins of AdS/CFT first coming from calculations by hawking of black hole entropy (also gives a nice way of getting into quantum gravity).

I assume you've done Feynman diagrams?
Check out the books by Strocchi and Fujiwara for info on non-perturbative methods in QFT.
>Superconductivity falls easily into gauge theories
No, I wouldn't say "easily"; there is no general procedure that maps second-quantized Hamiltonians into quantum field theories. The only one that's been rigorously formalized is the Haldane mapping which maps the universality class of Ising-type models into those of [math]\phi^4[/math] theories.
Superconductivity however can be described and characterized by category theory (arxiv.org/abs/1506.05805), which [math]is[/math] related to holonomies seen in gauge theories. The braiding matrices arising from the holonomies are also used to define Wilson loop variables a la string theory (or vice versa, see arxiv.org/abs/0707.1889).
If you're interested in QFT from the constructive/algebraic point of view Baez has a good book on it. Strocchi's book on symmetry breaking also delves into von Neumann algebras and how they're used to generalize Goldstone's and Neother's theorems via spontaneous symmetry breaking.

That superconductivity/category theory paper actually looks really nice. I know about Baez but Strocchi is new to me, thanks user.

You should unironically use LaTeX and Tikz.

>Peskin and Schroeder
It's a great intro book; other good ones are Bjorken and Drell, and Srednicki.
Don't read Zee btw it's shit.

Thanks, AQFT looks neat.
Will check out these books, thanks. Also the papers

why do you need the relative minus sign in first order bhabha scattering? i still don't understand this

Which part? They're all standard Feynman rules.
If you mean why they're all multiplied by [math]-i[/math] that's because the Wick rotation [math]t \rightarrow -i\tau[/math] gets rid of those prefactors. Sometimes you want to keep track of this prefactor which basically tells you that this is a relativistic QFT and not an Euclidean one.

I was talking about the minus sign between the s- and t-channel diagrams. Wouldn't the same wick rotation be applied in the case of bosons? Aa far as I can understand it this minus sign only applies to fermions, and it somehow has to do with the anticommutation relations of fermionic creation and annihilation operators.

>and it somehow has to do with the anticommutation relations of fermionic creation and annihilation operators.
This is correct. The s-channel and t-channel amplitudes are related by a particle permutation, which picks up a minus sign due to the fermionic particle statistics. If you look closely at the s-channel and t-channel diagrams you can see that they're the same graph up to a particle pair permutation. The way I understand it is via spin-statistics theorem, which you can find in Wightman's book on axiomatic QFT. This is basically the same situation as the case in regular QM where you have [math]\Psi(x_1,x_2) = -\Psi(x_2,x_1)[/math].

Ok ty. The spin-statistics theorem is also in PS i think.

No problem user.
>The spin-statistics theorem is also in PS i think.
I don't think it's proven there though. Wightman and Streater constructed an entire axiomatic framework for QFT that is strong enough to prove spin-statistics (but probably also too strong since it can also prove Haag's). Check it out if you're interested.

Since this is the closest thing to the math general I have to ask, what happened to the math general?

>physics
>close to math

I'm not set at Globalfoundries, it was just an example, Id rather prefer Intel.

Put an end to this madness. What is the answer here?

This cancerous avatarfag spammed it to shit and the janitor deleted it out of laziness. Please keep him contained in this thread.

>having a conversation is spamming
Beyond retarded.

Can anyone explain to me in layman's terms (I've not studied physics past high school) the particle-wave duality of light?

I understand that at different times light can display the properties of particles or waves, but is not really either - but can it be explained what it actually is? Do photons, and packets of photons, have a constantly oscillating electromagnetic profile, and is that why light is wave-like? Or do photons alter the electromagnetic property of the particles they pass through? If the latter, then how is it that electromagnetic radiation can occur through space? Sorry for the confusion, it's my first attempt to understand quantum theory.