Anyone know of any good intro to astrophysics texts? Due to my current college plan, I won't have time to do any astrophysics courses for the next 2 semester. I would like to learn it on my own for now. What is the best introductory astrophysics text?
Turns out the professor I took GR from got his PhD under Ed Witten. I knew the guy was smart but damn.
Yesterday I had the idea that, because a single layer perceptron finds a dividing line (geodesic) in the input space, perhaps several layers also draw geodesics but in curved space, which explains why they can classify non-linearly separable pattern sets. Turns out they sort of [URL="http://colah.github.io/posts/2014-03-NN-Manifolds-Topology/"]do[/URL].
FUcking mindblowing, so glad I did GR and got a notion of manifolds & curved space, it's everywhere.
I just skimmed that quickly but it looks really neat. I'll have to give it a full read tonight. I don't know anything about neural networks though.
Manifolds and data science, it's my all star marriage :v:
Number-41 really nice animations. Looks like neural networks are just "playing around" until things start to look separable/nice.
Thanks for the link.
[editline]10th February 2016[/editline]
[QUOTE=JohnnyMo1;49519124]Turns out the professor I took GR from got his PhD under Ed Witten. I knew the guy was smart but damn.[/QUOTE]
[url]https://en.wikipedia.org/wiki/Edward_Witten[/url] this guy?
[QUOTE=Fourier;49708016][url]https://en.wikipedia.org/wiki/Edward_Witten[/url] this guy?[/QUOTE]
Yep. If I could get a PhD under any living physicist it would probably be him, but based on his papers and taking his class my GR professor wouldn't exactly be settling. I think that's a good goal for me. His research seems extremely interesting. Often more math than physics.
Apparently the LIGO measurement is 5-sigma
:o
holy fuck
[QUOTE=JohnnyMo1;49710112]Yep. If I could get a PhD under any living physicist it would probably be him, but based on his papers and taking his class my GR professor wouldn't exactly be settling. I think that's a good goal for me. His research seems extremely interesting. Often more math than physics.[/QUOTE]
Can't you write to him and say you are interested in research? Does GR professor need to settle anyway? (what GR means btw?)
[QUOTE=Fourier;49711989]Can't you write to him and say you are interested in research? Does GR professor need to settle anyway? (what GR means btw?)[/QUOTE]
I've actually spoken to him about it previously, and it looks like as an undergrad I had a good head start on the classes my research program would have required if I had gone there. Trouble is I didn't get into the program out of undergrad so I'm in a different program now. I may try to reapply to that program as a PhD student or possibly transfer as a Master's, not sure yet.
I meant I wouldn't be settling, because his research seems excellent, so it would be like working under Witten. Also GR is general relativity.
Ugh, Zee's GR book "Einstein Gravity in a Nutshell" literally has a section that is unironically called "A tensor is something that transforms like a tensor." Fucking kill me. He then goes on to talk about how a lot of students have an unwarranted fear of trying to understand tensors. [I]You are the reason for that, Zee[/I].
Can't believe people legit think this is a good textbook.
Necrobump and a half
Have been enrolled into a "Quantum Computing Project" as part of my degree programme, and it's absolute hell. Absolutely no prior material, no reading provided ( apart from own investigation ) and we've to make some arbitrary programme in an arbitrary language that can, at the very least, do Grover's Algorithm.
I struggle like mad with Quantum Mech; I can't seem to get Dirac notation to click with me, and is proving incredibly detrimental right now trying to understand the core concepts behind quantum gates and quantum logic as almost every explanation relies on a working knowledge of bra-ket stuff. Does anyone know of any sort of "Dummies guide to Quantum Mechanics" books that could potentially help out? I really need something that the introduction is simple enough it almost comes across as patronising - any help would be massively appreciated.
also metallic hydrogen huh, that seems to be all the rage right now
Griffiths is definitely the gentlest book I've seen, though not the best overall. Lots of informal explanation in the first two chapters to develop your intuition.
Yeah I like Griffiths mostly because it's easy to pick up.
[QUOTE=Matthew0505;51797626]with constant offsets
[img]https://i.imgur.com/v6SzJGX.png[/img][/QUOTE]
Is there a benefit to using this over something like CodeCogs?
I think I'm finally starting to piece together this quantum computer nonsense, but i'm just realising how incredible the whole thing is. I'd never really questioned what quantum computing was apart from some "fancy science thing", so this blew my mind a bit. It's a really fascinating concept, the idea of it all being defined by probabilities rather than set data is just so mind-blowing. I'm still trying to piece together the notion of quantities defined in dirac notation can relate to states of binary numbers.
[media]https://youtu.be/76I8g94xGLs[/media]
[QUOTE=Matthew0505;51799607]I was too tired to bother setting up a proper TeX thing.[/QUOTE]
[url]http://www.texpaste.com/[/url] is pretty quick and easy, for the future.
i don't know much about physics but i had a thought bouncing around my head lately. it sort of comes down to free will is not exactly free will.
given the nature of atoms, it makes sense that over time the natural elements that exist, came to exist. over time and given the large size of the universe, it makes sense (though incredible to have occurred) that eventually complex life could form from bonds of these natural elements. intelligent life therefore could exist due to the tendency of change over time as seen with evolution.
however we can predict how things will behave due to the limited number of fundamental particles in the universe and if we had knowledge of all the particles in the entire universe you could predict everything, even human behaviour. which would mean that free will is not entirely free will but caused by interactions with photons and other matter between living organisms many systems, releasing chemicals etc. to achieve a reaction. and if that holds true then it would be possible to predict the reactions, however you would need to know everything about the particles that are involved in the interaction, and therefore there is no free will.
again this is just a thought from someone with no proper knowledge of physics.
[QUOTE=Pat.Lithium;51835632]free will and determinism[/QUOTE]
This is an interesting idea to think about, and you're certainly not the first. Determinism presents an interesting philosophical issue.
Worth reading: plato.stanford.edu/entries/epiphenomenalism
Something interesting to ponder secondarily to the scale of the universe is the scale that we as organisms operate at. Even a single celled organism is absolutely immense compared to some of the auto catalytic RNAs that exist. If you haven't seen the animation "The inner life of the cell" you should check it out.
thanks for the info. i knew that there had to be some philosophy that existed that ponders the actual freedom of free will. this is actually quite exciting for me because it would mean that one day when we have powerful enough computers we could potentially accurately simulate free will. is there a philosophy thread? i have more questions but they don't really fit into the realm of science (at least not at this point in history).
Can someone explain to me how to integrate with respect to a vector? I need to know this stuff for my physics class, but I have never been taught it before. I taught myself a bit of linear algebra with regards to vector notation, linear independence, span, bases, and the meaning of the unit vectors. However, I'm lost as to how to integrate with regards to a vector. Take this example that I just wrote:
[img]https://dl.dropboxusercontent.com/u/1439792/derivation.png[/img]
Suppose lambda, k, and r are all constants, and that r is the distance from the origin to the infinitely thin arc of evenly-distributed positive charge. If you wanted to integrate to calculate the electric field vector, how would you do that? Since the electric field created by an infinitesimal charge only acts on a given point in the direction of the radius between the point and the charge, I know you need to take into account the direction. That's why I included the unit vector. And I know that the integral, essentially an infinite sum, can allow you to calculate the total electric field by summing up the infinitesimal charges that make up the arc of evenly-distributed charge. And I know how to do a simple integral, which should be especially simple in this case since you are just integrating d(theta) between two values of theta. But I don't know what to do with the unit vector. Pardon if my formatting is odd or if the logic I applied in that picture doesn't work. I'm not really good at math and I never use latex.
[editline]22nd February 2017[/editline]
I just realized since electric field lines point away from positive charge by convention, that there may need to be a negative in those equations. Oh well
The r vector can be broken up into your unit i and j vectors representing your x and y components.
In this case it would be -cos i - sin j since the individual vectors are left and down respectively (assuming you take that to be the negative directions)
I got ((k*lambda) / r)(-i-j) for my solution
I think that's right
Yes but do you have to integrate those trig functions too? Or do they just hang out there?
[QUOTE=OrkO;51865964]Yes but do you have to integrate those trig functions too? Or do they just hang out there?[/QUOTE]
I would assume so, as you're still integrating [t]https://latex.codecogs.com/gif.latex?%5Cvec%7Br%7D%20%3D%20r%5Ccos%7B%5Ctheta%7D%5Chat%7Bi%7D%20+%20r%5Csin%7B%5Ctheta%7D%5Chat%7Bj%7D[/t] with respect to theta.
I'm a bit unsure on how you actually show it's in the [t]https://latex.codecogs.com/gif.latex?\hat{k}[/t] direction
[QUOTE=OrkO;51865964]Yes but do you have to integrate those trig functions too? Or do they just hang out there?[/QUOTE]
Yes, you must have two separate integrals, here is my solution:
[T]http://i.imgur.com/UEtGqgU.jpg[/T]
[QUOTE=Instant Mix;51867774]I would assume so, as you're still integrating [t]https://latex.codecogs.com/gif.latex?%5Cvec%7Br%7D%20%3D%20r%5Ccos%7B%5Ctheta%7D%5Chat%7Bi%7D%20+%20r%5Csin%7B%5Ctheta%7D%5Chat%7Bj%7D[/t] with respect to theta.
I'm a bit unsure on how you actually show it's in the [t]https://latex.codecogs.com/gif.latex?\hat{k}[/t] direction[/QUOTE]
if you're referring to the 'k' in his work that's Coulomb's constant, I mean I'm assuming we're working in the xy plane
[QUOTE=thefreemann;51872198]
if you're referring to the 'k' in his work that's Coulomb's constant, I mean I'm assuming we're working in the xy plane[/QUOTE]
I'm being an idiot, I was getting confused with B fields being in a perpendicular plane to [t]https://latex.codecogs.com/png.latex?%5Cdpi%7B120%7D%20%5Cvec%7Br%7D[/t] (ie. in the [t]https://latex.codecogs.com/png.latex?%5Cdpi%7B120%7D%20%5Cvec%7Bk%7D[/t] direction. Thought E fields did the same.
I'm surprised this hasn't gone into a discussion about 2 particle physicists debating all the SU groups, and whether the proton is stable, or it decays.
what is the biggest theory as to how the big bang actually occurred? wouldn't all that mass in a single point have an incredible amount of gravity and become a black hole?
[QUOTE=Pat.Lithium;51925467]what is the biggest theory as to how the big bang actually occurred? wouldn't all that mass in a single point have an incredible amount of gravity and become a black hole?[/QUOTE]
I definitely can't speak for certain, however I'm not aware there are any real concrete theories because the physics of the universe was radically different at the spawn of the universe than now, otherwise the theories of the universe expanding at a speed > C, which is implied by studying the CMB, wouldn't make any sense.
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