Hi, Can someone provide me some self reading material for Condensed matter theory? I've done QFT previously for which I could happily read Peskin supplemented with David Tong. Can you please suggest some references along those lines? Thanks
@skullpatrol The second one was in my MSc and covered considerably less than my first and (I felt) didn't do it in any particularly great way, so distinctly average. The third was pretty decent - I liked the way he did things and was essentially a more mathematically detailed version of the first :)
2. A weird particle or state that is made of a superposition of a torus region with clockwise momentum and anticlockwise momentum, resulting in one that has no momentum along the major circumference of the torus but still nonzero momentum in directions that are not pointing along the torus
As will be elaborated with some annotated pictures later, the particle like state mentioned in 2 seemed to behave like a gravitational analogue of anapoles
where imagine a region of spacetime that got simutaneously frame dragged in the clockwise and anticlockwise direction
Since gravity does not obey superposition, I am not even sure if the result of having two opposite directions of frame dragging will cancel each other out
The dream also mentioned of some GR simulator that can simulate any type of spacetime
Same thought as you, however I think the major challenge of such simulator is the computational cost. GR calculations with its highly nonlinear nature, might be more costy than a computation of a protein.
However I can see some ways approaching it. Recall how Slereah was building some kind of spaceitme database, that could be the first step. Next, one might be looking for machine learning techniques to help on the simulation by using the classifications of spacetimes as machines are known to perform very well on sign problems as a recent paper has shown
Since GR equations are ultimately a system of 10 nonlinear PDEs, it might be possible the solution strategy has some relation with the class of spacetime that is under consideration, thus that might help heavily reduce the parameters need to consider to simulate them
I once asked how hard it would be to do a GR sim of something with just discrete symmetry (cubical) and two people said it would be a very hard PhD thesis
I just mean this: The EFE is a tensor equation relating a set of symmetric 4 × 4 tensors. Each tensor has 10 independent components. The four Bianchi identities reduce the number of independent equations from 10 to 6, leaving the metric with four gauge fixing degrees of freedom, which correspond to the freedom to choose a coordinate system.
@ooolb Even if that is really possible (I always can talk about things in a non joking perspective), the issue is that 1) Unlike other people, I cannot incubate my dreams for a certain topic due to Mechanism 1 (consicous desires have reduced probability of appearing in dreams), and 2) For 6 years, my dream still yet to show any sign of revisiting the exact same idea, and there are no known instance of either sequel dreams nor recurrence dreams
@0celo7 I felt this aspect can be helped by machine learning. You can train a neural network with some PDEs of a known class with some known constraints, and let it figure out the best solution for some new PDE after say training it on 1000 different PDEs
Actually that makes me wonder, are the space of all coordinate choices more than all possible moves of Go?
isomorphic = one to one and onto mapping? All coordinate transformations are diffeomorphisms of the manifold...as such...they are also isomorphisms...and so...1?
I am trying to find a good way to sort the gauges in equivalence class that are easily manageable but so far I can only think of the class of gauges related by linear or affine transformations
The following is what the warp drive saw in the dream look like. Red denote regions where the spacetime is expanding and blue denote the region where the spacetime is contracting
and, don't ask me why it has those weird portals or tube like geometries, it is simply what it looks like in the dream
though given the original alcuberrie drive can actually host CTCs, it may be not that far fetched
enumaris: From what I understood from the dream, the warp drive showed here may be some variation of the alcuberrie metric with a global topology that has 4 holes in it whereas the original alcuberrie drive, if I recall, don't have holes
orbit stabilizer: h bar is my home chat, because this is the first SE chat I joined. Maths chat is the 2nd one I joined, followed by periodic table, biosphere, factory floor and many others
also another interesting thing is that Dream Johnrennie has a remark about the flat spacetime bubble in the middle:
He said that the bubble of that radius [of the order of a starship] cannot be stable with spherical geometry
As for the real Johnrennie, I am not sure what he will say, but from what I knew, I don't recall anything controlling the size of the flat spacetime region of any warp drive metrics
Btw, since gravity is nonlinear, do we expect if we have a region where spacetime is frame dragged in the clockwise direction being superimposed on a spacetime that is frame dragged in the anticlockwise direction will result in a spacetime with no frame drag? (one possible physical scenario that I can envision such can occur may be when two massive rotating objects with opposite angular velocity are on the course of merging)
Gravitational waves would in principle be diffracted just like light waves or electrons, but in practice they interact so weakly with matter that it's hard to see what you could make the slits from.
Well. I'm a begginer in the study of General Relativity ok? My knowledge about the subject is based on books like Schutz, Hartle,Carroll and introductory papers. About quantum mechanics I have a poor knowledge yet.
So, what I meant about "Gravitational Double slit experiment" is: There's and gravitational analogue of the Double slit experiment, for gravitational waves?
Hmm, I am thinking of an array of LIGOs as the detector, and thus the slits can show up as the relative amount of the arms get stretched comparing one LIGO device to another...
but I guess the major challenge is how to find a single graviton source, if any
@JackClerk the double slits experiment is just interference of two coherent sources, where we get the two sources from a single light beam using the two slits. But gravitational waves interact so weakly with matter that it's hard to see how we could screen a gravitational wave to get two coherent GW sources.
But if we could figure out a way to do it then yes GWs would interfere just like light wave.
Thank you @Secret and @JohnRennie . But for conclude the discussion, I want to put a "silly picture" here: Imagine a huge double slit plate in space close to a strong source of gravitational waves. Then like water waves, and light, we will see the pattern?
How will the nonlinear nature of gravitational waves play a role in Jack Clerk's scenario, Johnrennie, I suspect the interference will be a lot more complicated than its optical counterpart?
@JackClerk gravitational waves produce tidal forces on any matter they pass through. As you move from a maximum to a minimum those tidal forces would become zero.
So, if the source (like a Black Hole binary) are sufficent away, then in the regions of destructive interference, space-time would have a flat geometry and then with we put a spherical object in this region the metric will become schwarzschild-like.
if**
Pardon, I just spend some naive-phylosophy time here with these discussions**
Note that even when the GW intensity is non-zero spacetime is still flat on average i.e. the effect of the GW is to produce oscillations around a flat mean.
The situation was even more dire for Calculus and I managed!
This is a neat strategy I have found-revision becomes more bearable when I have The h Bar open on the side.
In all honesty, I actually prefer exam season! At all other times-as I have observed in this semester, at least-there is nothing exciting to do. This system of tortuous panic, followed by a reward is obviously very satisfying.
My opinion is that I need you kaumudi to decrease the probabilty of h bar having software system infrastructure conversations, which confuse me like hell and is why I take refugee in the maths chat a few weeks ago
(Not that I have questions to ask or anything; like I said, it is a little relieving to be with friends while I am panicked. I think it is possible to gauge how much of a social recluse I am from this, because I spend some of my free time hanging out with you lot, even though I am literally inside a hostel teeming with hundreds of my peers)
@Kaumudi.H meh. Puzzling is rather quiet these days and i don't really hang out much on Physics.SE. plus, I have got a bit of work to complete and some questions to write.
Well it has its pros and cons. Python, like matlab, can vectorise many operations and has some really simple API, but being to used to it will make you unable to deal with things under the hood
I don;t have enough R experience to comment about R, though
I found python easy to use mainly because my way of thinking and coding is like a matrix and array: I read much faster when things are presented vertically
One thing I don't like about C and C++ is all those semicolons syntax, but otherwise it is fine and you can write something as complicated as a game from it
in fact, a lot of python libraries are ultimately C++ codes really
that's true. though back in high school ,regardless of code, our teacher taught us to always indent your code to allow easy reading and troubleshooting. We are also taught the 4 spacebar indentation convention
this is better than indenting by tabs because tabs can be unpredictable at times, especially in python where it relies on tab to understand what you are saying
@JohnRennie I wish I can just tab because I am also lazy, but sometimes tab insert 4 spaces while other times it inserts 5-6 spaces, thus screwing up a block of if then conditions in my code, which is why I had no choice
I currently automate almost everything from job submission to data extraction, and later on, with the help of the machine learning group in my uni, we might be able to automate a GUI library search thingy
I can do all tasks related to my work without leaving the text editor (of course, such text editor is emacs). The only inconvenience is that some websites don't render in a optimal way (but most of the work-related ones do)
I have a quick question. If the displacement of a particle executing S.H.M is given by $x=a\cos \omega t+b\sin \omega t$, then how are we to find its amplitude?
Hi to all. Does anyone know where I could write matlab code online(for free)? Apparently another one of my institutions great inspirations is to have a matlab-oriented computational physics course without having matlab on the universities pcs. Thanks.
@Kaumudi.H Hacky way: 1st thing is that $\psi\left(x, y, z, t\right) = \psi\left(x, y, t\right)$, so no propagation in $z$-direction. Now, in '$1$ unit' of time, it travels $\frac{\sqrt{3}}{2}$ units in the $y$-direction and $\frac{1}{2}$ units in the $x$-direction. Use this to form a triangle and you'll get the answer with simple trig :)
@Kaumudi.H Ah, it was okayish. It was mostly memory based. Each small question was of 10-15 marks. No idea what they expect me to write for questions like "Describe acoustic and optic phonons" for 15 marks!! I only wrote two small paragraphs...meh. I don't like this subject much :P (physical electronics). Hope to do better in the upcoming tests so that there isn't a huge effect on the gpa.
@Blue Seriously, testing how much someone's remembered about a subject has exactly no bearing on how good they are at that subject! ::glares at examiners::
You're just testing how good their memory is! What use is that!!
@Blue Ok, thanks. I found a way by connecting to the servers of the university( the program isn't installed on the pcs on the computer room, but if I connect to the server of the university- which means running remotely another environment, i found an older version of matlab). But thanks again.
@user685252 No; I am saying that it has no bearing on how good you actually are at the subject - it has no bearing on how good you are at applying knowledge; it doesn't test problem solving skills; it doesn't take into account that, if I'm sitting in the office having forgotten the difference between different types of matrix decomposition or something, I can just search the internet (or a textbook), so it doesn't say how good someone is at research in that subject;
it doesn't test how good you are at deriving anything - someone can write down a definition without any understanding, while someone who can derive it, but has forgotten it probably won't have time in an exam situation. In short, testing memory is not the same as testing understanding
If you really want to test someone's understanding, give them a few problems in that area that they've never seen before and give them a reasonable amount of time to do it, with access to textbooks etc.
