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01:19
Anybody have some fun books/movies to recommend? Just got done with a shoulder surgery and i suddenly have a lot of downtime. bonus points if it's science related but doesnt have to be.
02:11
that is the playlist for 6 lectures by Feynman
 
3 hours later…
05:09
@JohnT. I found The Shape of Inner Space a great read.
3
 
5 hours later…
09:48
@JohnT. have you tried asking in Sci-Fi chat?
We don't bite (anymore...)
10:05
Try reading Geometry Of quantum Theory or Gravitation
Textbook by Charles W. Misner and Kip Thorne... It'll surely be a good pass time you won't forget rest of your life...
@JohnRennie Have you tried Charles W Misner? :P
Only thing I hate in Computer Science engineering is that, the more you read, the more newer things come out... you might have completed a textbook with 10 k citations and when you surf internet, there are 50 other textbooks with 10 k citations.
There's one with non linear programming, dynamic programming, integer programming, all, one better than other...
Even if I take my whole life, I'd barely touch the essence of Computer Science Engineering Mastery....
Hello everyone. If $\vec{b}$ is electric force and $S$ the cross-sectional area of a platinum wire, what is $\int_S \text{curl}\vec{b}\cdot dS$?
10:57
@RewCie John is recovering from shoulder surgery, and you're recommending MTW? That book's so heavy it can be dangerous for even a healthy person to lift it! ;)
11:15
Dirac's General Theory of Relativity is nice and light :P
But honestly, downtime? I'd go and watch Queen's Gambit or something
12:09
@JohnT. I enjoyed Three Roads to Quantum Gravity at secondary school
 
1 hour later…
13:18
Can I pick up quantum field theory after Shankar's Principles of QM, or would I need to study more QM?
Anyone else find the notation $|\Omega V\rangle$, $\langle \Omega V|$ confusing? This notation breaks the equal preference between bras and kets. Because of this notation, bras have to be understood in terms of the corresponding ket
Is there any reason why we've stuck with this notation?
What do you mean by equal preference between bras and kets?
It means that neither has any preference over the other
I explained in my post how kets get the preference
For instance, we're forces to think of <Omega V| as the bra corresponding to the ket |Omega V>|.
forced*
Yes I saw that, but I am still confused. Why do you say neither has any preference over the other?
Without that notation, neither has a preference.
With that notation $|a V> means a|V>
BUT <aV|$ means a^* <V|
So the notation works differently for both
13:33
It is a shorthand for inner products. You would have to do the same thing either way
By a^*, I mean conjugate of a
So you're saying it should be <Va|?
Yeah, I'd recommend you look at QFT :P
It introduces an arrow notation where the arrow indicates the direction an operator acts
I'm saying we should write the operators and the scalars only outside of the symbol, like a|V>
Ah ok
Yeah I actually tend to do that myself. I never liked cramming things into the bras and kets
13:35
@RyderRude but an operator acted on by a scalar is still an operator
(but yes, this isn't something I've seen anyone do in a long time)
I was wondering if the cramming thing has any advantages
I only find it asymmetric and confusing
@Mithrandir24601 So I don't need to study more QM after Shankar's book to move on to QFT?
For inner products it is the same thing. For scalar $a$ and functions $f$, and $g$, you would still have $(af,g)=a^*(f,g)$
@RyderRude I have no idea what's covered in Shankar or the level it's aimed at, so don't really know to be honest
I have read Shankar, but I never went onto QFT haha
13:39
So what did u do after Shankar
I continued with the rest of my studies :)
I've not taken part in a formal course. I'm studying myself. So I really want to know where to move on
I'd like to study QFT
If it is for self-study then I say go for it. If you feel like you are missing something then you can always go back
But Shankar's book says it's an year worth of material.
I study biophysics, which doesn't depend on any QFT for the most part (yet) haha
13:42
@RyderRude Rule of thumb - start reading a good textbook (e.g. Srednicki, which is legally available for free here) and if you find it too difficult, then that answers your question
And QFT is taught to post graduates
thanks
Bye. I'll talk later :)
@PM2Ring atleast there are couple of free pdf copies :P
14:26
@BioPhysicist @BioPhysicist I thought about that function inner product. We could interpret (af,g) as the function af of the bra-function space, multiplied by the function g of the ket-function space. To evaluate this, we would flip the order of these functions in the product. To do that, we convert the bra af to the corresponding ket a^* f, and g to the corresponding bra g. So, we get: (af,g)=(g,a^* f)^*=a^**(g,f)^*=a(f,g)
So in interpretation, we have (af,g)=a(f,g)
in this* interpretation
whether the inner product of a Hilbert space is linear in the first or the second component is a conventional choice
annoyingly, mathematicians usually make one choice and physicists the other :P
But if we define the inner product, not as the product of two vectors of the same space, but as simply the matrix multi of a bra with a ket, then we can have it linear in both components. The property (a,b)=(b,a)^* would become bra(a)ket(b)=(bra(b)ket(a))^*, where bras and kets would obey bra(a)=adjoint(ket(a))
by bra(a), i mean a vector <A|. Similarly for the ket
we can use the property bra(A)ket(B)=(bra(B)ket(A))^*, and the linearity in the second component, to prove the linearity in the first component
I proved it for the inner product of functions above
14:55
but that's not what an inner product is :P
An inner product takes two vectors from the same vector space and outputs a number
whatever you define via the application of a "bra" to a "ket" is not an inner product
You cannot define the inner product of $\lvert \psi\rangle$ and $\lvert \phi\rangle$ as $\langle \phi\vert \psi\rangle$, because the definition of the map from ket $\lvert \phi\rangle$ to bra $\langle \phi\rvert$ requires the inner product
Technically, you could say this is a different inner product. Maybe call it inner product upgrade l
lol
that is, without an inner product, there is no meaning in talking about the bra corresponding to a ket
latex equations dont load here. im having trouble reading your last reply
look in the right upper corner (room description) of the chat room, there's a link for how to activate MathJax in chat
15:01
Hello everyone. Any hints in showing that $\int_V \rho \vec{u}\cdot \nabla \vec{u}\,\text{d}V$ is a force if $\vec{u}$ is acceleration and $\rho$ is density?
@Tangoed if you figure out the units of that expression, it presumably has units of force
I'm not sure what exactly there is to show
Oh, so just working with units is enough
Thanks
well, I can't read the mind of whoever gave you the exercise, but that's what I would understand by that
@ACuriousMind Are you saying that we need the definition of the inner product to define what we mean by the bra corresponding to a ket?
@RyderRude yes
15:02
@ACuriousMind Haha it's part of a pset
But I simply define it as the transpose conjugate of a vector
or the adjoint
@RyderRude that is not a basis-independent definition
oh i'll about that lol
i'll try to come up with something
i'll think
trust me, it doesn't work
but i could learn by thinking :)
failures also help
15:05
given an inner product that's linear in the first argument, the bra corresponding to a ket $\lvert \psi\rangle$ is defined by $\langle \psi\vert \phi\rangle := (\lvert\phi\rangle,\lvert\psi\rangle)$
15:36
@ACuriousMind Yea, it's impossible. Even proving the existence of orhthonormal basis uses the definition of inner product. So a basis-independent definition is a must here
I spent half of my day thinking whether the inner product properties were implied by bra-kets or the other way around lol.
 
8 hours later…
23:31
Sometimes people try a bit too hard to come up with the oldest example of a concept in math
I'm not 100% sure that the Grassmann algebra was the birth of superspaces
What did mister Grassmann even use them for
Let's see
"Die Lineale Ausdehnungslehre – Ein neuer Zweig der Mathematik"
Hm, tough read
A more readable one
People were way into quaternions in the late 19th century

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