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00:00 - 17:0017:00 - 00:00

00:03
I GOT IT
I HAVE THE PROOF
@ACuriousMind please check it when you see this
00:16
I don't care that it's sloppy
I have convinced myself that it's true
 
4 hours later…
04:27
Hmm, if I understood your proof and figure correctly, it seems by having connected components ending on the boundary, it prevents the existence of a few points (x,y) to lie in the open subset of $\Gamma$ hence preventing such subsets to not be connected components themselves...
 
2 hours later…
06:24
why am I awake.
 
5 hours later…
11:23
hi guys, what are the reasons that $C\lvert\gamma\rangle=-\lvert\gamma\rangle$ and $C\lvert 0\rangle=\lvert 0\rangle$? I understand that their charge parity must be $\pm 1$ because both the vacuum and the photon are not charged, but why $+1$ for the vacuum and $-1$ for the photon?
Because the vacuum has no charge at all?
Also the vacuum is invariant under the Lorentz group
So it should be that $CPT \vert 0 \rangle = \vert 0 \rangle $
Which should be obvious enough that this is true also for $P$ and $T$
Apparently the stress energy tensor doesn't diverges for the vacuum of the Gödel metric
12:12
@Slereah do you know what the proof of the square lemma is
Step 1 : draw a square
Step 2 : ???
...
12:27
@0celo7 That appears to be some kind of correct argument
@ACuriousMind so you get the jist?
You know
I wonder if it would be possible, for a theory with a known classical solution, to transfer that solution to the wavefunctional
@0celo7 Well, I also think I got the jist from what Milnor wrote, so I'm not really the best judge here
@ACuriousMind :(
What jist
Can you easily transfer the solution to a PDE to the solution of a functional differential equation
12:34
He didn't write anything
@ACuriousMind I have a reasonably correct proof now but I still don't know what Milnor wrote
@ACuriousMind I'm not asking to whine or be annoying, I'm legitimately curious what jist you saw
because you got one half of the proof, yeah, but not the other
12:53
@0celo7 Uh...how do you think I'm able to explain that in any other words than the inadequate one we already tried?
@ChrisWhite I think there are such people, they just work at Google.
@ACuriousMind Because I now understand it?
user116211
13:21
4
A: What Do We Get From Having Higher Generations of Particles?

Luboš MotlDear Chad, I thought you were an atheist. Most atheists tend to realize that many things that exist in the Universe have no "purpose". The existence of the Universe has no "purpose" that may be scientifically demonstrated. Even if life could exist in a Universe with 1 generation of quarks and le...

user116211
Was the first line really necessary?
user116211
@yuggib: o/
\o
@Slereah in which sense?
If I have the solution for an equation like $$\frac{\partial}{\partial x} f(x) = a$$
Can I transfer that solution to an equation of the form $$\frac{\delta}{\delta \varphi(x)} f[\varphi(x)] = a$$
Obviously for more complex equations
what do you mean by "transfer"
13:27
Well are the solutions going to be of the same form
With some transformations can I use them as solutions
probably not
Unfortunate
for instance, the initial conditions are different
what did you want to do that for?
The Sine Gordon equation
what for
not in which model
13:29
To write out explicitely the Hilbert space
since apparently it's Complicated
?
it's called problem of quantization
It is possible to write out explicitely the wavefunctions of QFT states using functionals
But it is rarely done
For that reason, I suppose
the problem is to identify the measure in the space of wavefunctionals
Hm, true
the space of wavefunctionals is something like $L^2(\mathscr{S}'_{\mathbb{R}}(\mathbb{R}^d);d\mu)$
13:32
Since the Hilbert product is $$\int \mathcal D \varphi(x) \Psi[\varphi(x)] \Psi^*[\varphi(x)]$$
it is the measure $d\mu$ that gives "problems"
I guess you need to define it, as well
for the free case, it is a Gaussian measure
for the interacting case....a mess
So I hear
no explicit form
13:33
I try to read Jaffe once in a while but then my eyes kinda glaze over
it is obtained as a limit of something using the Feynman-Kac formula
I say let's all go back to Bohmian mechanics
Then there will be no Hilbert space
that does not solve any problem of course
Can't know until we try!
I'm not quite sure how the QFT of Bohm works
the point is that we are not so able to cope with the non-commutative probability theory given by the algebra of CCR/CAR observables set in infinite dimensional classical spaces
13:47
IIRC it still uses particles
No fields involved
@Slereah I think so?
Maybe with some integrals thrown in
I know Weinberg does it at least once
I don't have his book here
He does a Gaussian functional solution to something
@Slereah as long as you want to reproduce the results of non-commutative probability theory, there is not much hope of obtaining something simpler I am afraid
check chapter 9 of his first book
13:50
Do you happen to know what the measure for $\phi^4_2$ looks like, btw
I can never understand what Jaffe is on about
@ocelo7 : it is so that $F_{\mu\nu} \to \Omega^{2}(x)F_{\mu\nu}$. If I would know this explicit rule, I would not ask the question here. — Name YYY 2 mins ago
Sass!
Heyo
Isn't the reason that the EM field is conformal invariant just that the Maxwell equation doesn't use the metric at all
It's all differential forms bullshit
@Slereah It does use it (it's hidden in the Hodge star/index positions)
Oh yeah
@ACuriousMind Is a symmetry of an action a symmetry of the EL equations
13:59
$$\star d \star F = j$$
Or something
@0celo7 Not necessarily
@Slereah real men use $\mathrm d^\dagger$
@0celo7 See this question for more info.
I wonder if there's any calculations done for the QFT in CTC spacetimes by what's his name
F-algebra or whatever he calls it
@Danu Could you do this?
14:08
Let $d\mu_0(\varphi)$ be the Gaussian measure with mean zero and covariance $(-\Delta+m_0^2)^{-1}$ on $\mathscr{S}'(\mathbb{R}^2)$. Then denote $$V(h)=\lambda\int_{\mathbb{R}^2}:\varphi^2(x):h(x)dx\; ,$$
where $h$ is a space(time) cutoff. This defines a measure (essentially via the Feynman-Kac formula) $$d\mu_h(\varphi)=\frac{e^{-V(h)} d\mu_0(\varphi)}{\int_{\mathscr{S}'(\mathbb{R}^2)} e^{-V(h)} d\mu_0(\varphi)}$$
then the euclidean measure $d\mu$ is defined as $d\mu=\lim_{h\to 1}d\mu_h$
Errrr
#rekt
Isn't that already what I would have guessed
and the measure for the wavefunctionals is the one restricted to time zero fields
What did he prove with that?
That it existed?
14:09
@Slereah yep
Oh well
So much for that
and that the theory satisfies Osterwalder-Schrader i.e. Wightman axioms
By the way
Jonah J. Jameson and the Goombas have in the book something about the limit of the measure $d\mu_t$, of a path integral at time $[-t/2, t/2]$, with $t\to \infty$, is unique
Is that related to the fact that the vacuum expectation value is just a path integral with no boundary
14:55
@Slereah Well but the photon has not charge too. And still its eigenvalue is $-1$.
Is it though?
Shouldn't it be 1
Since it is a real field
C parity −1
Hm
Odd
The CPT argument makes sense, but only if you know that CPT is always conserved, right?
If you don't have a shitty theory, CPT is always conserved
I forget the exact theorem but basically for any reasonable Lorentz invariant theory, CPT is conserved
Yep but if you want to check if your photon theory violates CPT, you need to know the C parity of the photon. You cannot deduce the C parity from CPT, because then, CPT is trivially conserved.
Oh wait
15:00
@Slereah Why? -1 is just a phase change.
Yeah after checking that isn't a problem
What's the difference in proving a left or right group action? $g_1(g_2 * a) = (g_1g_2) * a$ is this only for right group actions?
@Bass The photon charge parity is deduced from observing that the current changes its sign under charge conjugation, so for the coupling term $A_\mu J^\mu$ to be invariant you need that $A_\mu$ also changes sign
This is then inherited by the modes of $A_\mu$, which create the photon states, and hence by the photon states
@Obliv What do you mean "proving a group action"? What you've written there is a left action, the right action would be written $(ag_2)g_1 = a(g_2g_1)$.
oh.. okay. Thanks @acuriousmind
@ACuriousMind I see. And the vacuum? Must it be $C\lvert 0\rangle=\lvert 0\rangle$ for a consistent theory, or is -1 also possible?
15:07
@Bass My argument above already presupposes an invariant vacuum - If both $A_\mu$ and the vacuum changed their sign, the photon states $A_\mu$ creates from the vacuum would not
I'm unsure whether it would be in principle possible to have the vacuum have parity -1, but I suspect not.
Oh of course. So $C\lvert 0\rangle=\lvert 0\rangle$ is just a postulate, and we could as well say that vacuum has -1 parity and the photon has 1? The current would still change its sign, since it's made up of two particles..
@ACuriousMind Ok I see.
thanks
I still don't know what $|0\rangle$ is
QFT is such bullshit
@0celo7 It's nothing :P
^that :D
You either get physics crap that makes zero sense and sounds silly or you get legit PhD level math
yeah keep joking
QFT being shit is why I didn't become a physicist
15:11
you don't have to learn qft to become a physicist lol
Yeah you do
Any interesting physics
interesting/grant worthy
@0celo7 It is the Lorentz invariant state
@Slereah I don't understand how the Lorentz group acts on states
Read Weinberg on it mb
Chapter 2 is all about Lorentz actions on states
I did read Weinberg
Weinberg explains fucking nothing
And Weinberg is unreadable
No one understand the cluster decomposition principle
15:14
It's pretty equation heavy
@Slereah A mathematician currently giving a course on the unitary representations of the Poincaré group has told me he has no idea what the fuck Weinberg is doing there :D
@ACuriousMind language
All QFT books are garbage honestly
What about Glim and Jaffe
It's all math
u should love it
And when you read "good" notes they don't bother explaining anything that's confusing in the garbage books
I'm bad at math @Slereah
Took me 4 days to figure something out that ACM got instantly
15:15
@acuriousmind when you connect a positive terminal to a negative terminal in a circuit, does the information travel instantaneously, so that electrons begin to flow from the positive to the negative terminal?
@Obliv If only there were a wonderful Q&A site on the internet where that question certainly has been asked and answered...
If only
@ACuriousMind not everyone has your search skills dammit
The vacuum state is just the lowest energy eigenstate of the Hamiltonian operator
at least for the usual theories
15:17
why does it have to have a lowest
@0celo7 Well, it appears Obliv had not much trouble finding a fitting question :P
@ACuriousMind I couldn't
Because if it's unbounded from below u get bad things
what's another word for enjoy
You can have theories which are not bounded from below, btw
15:20
cherish?
They have no vacuum state then
Or well they do I guess
But it is not the lowest energy
@ACuriousMind mmm, does one cherish company?
Does $\phi^3$ have a vacuum state?
I suspect it do
@0celo7 Mmmh...relish perhaps?
@Slereah $\phi=0$ probably
@ACuriousMind did you google "enjoy thesaurus"
15:22
@Slereah which theories don't have a vacuum state?
Well some theories don't have a lowest energy state
But I think they still have a vacuum state
Some even have several vacuas
example?
$\phi^3$
@Slereah does not have a vacuum?
Fermions with commuting field operators
It is unbounded from below
Still has a vacuum tho
15:24
@Slereah Ok, right.
But $\phi^3$?
I think it's the same
@Slereah That's not a theory, the spin-statistics theorem forbids that.
I know it's not bounded from below, but probably still a vacuum state
Not sure tho
$\phi$ being a scalar, right?
yes
@ACuriousMind Sure it's a theory, it's just a garbage theory :p
15:25
Why does $\phi^3$ not have a vacuum?
If you compute the stress energy tensor you have a term $\propto \phi^3$
@Slereah Well, but it's not a consistent QFT, so it's a garbage example for your claim "you can have theories"
which means you can make the energy arbitrarily negative
Isn't $\phi^3$ just the interaction term of a free scalar theory? And the free theory has always a vacuum, after all its Fock space is constructed from the vacuum.
As said
It probably has a vacuum
15:27
@Slereah Arbitrarily negative $\neq$ no vacuum.
As in, a state invariant under Lorentz transform
ok
@Bass What? The exponent is cubic, not squared
But this isn't the lowest energy state
I think any odd power of the field will also be like that?
Although IIRC it gets non-renormalizable pretty quick
Like $\phi^6$ or so in 4D
@ACuriousMind I mean, the full lagrangian is something like $\mathcal L = \mathcal L_{\mathrm{free}}+\mathcal L_{\mathrm{int}}$, and $\mathcal L_{\mathrm{int}}=\phi^3$. And in the free theory we just have $\phi^2$.
15:29
I feel like this should be closed, but I'm not sure exactly what the close reason should be ...
0
Q: Is running in a zigzag helpful in avoiding being shot by an arrow?

BCLCTwo people A and B start at a certain point. B runs away from A to another point. A shoots arrows at B. Is it helpful for A to run in a zigzag rather than in a constant direction? To be more precise: Suppose A starts and remains at $(0,-1)$, and B starts at $(0,0)$ and has to get to $(0,...

@Slereah $\phi^n$ with $n>4$ is non-renormalizable.
yeah sounds about right
where is Duffield
But $\phi^3$ is also garbage
So basically it's only $\phi^4$
and also maybe $\phi^4$ doesn't make sense either
Basically QFT is garbage
@Bass Yeah, so? That you can construct a free vacuum doesn't mean that there is an interacting vacuum.
15:31
So in $\phi^3$, there are operators acting on the vacuum that lower its energy?
Mod alert!
@ACuriousMind Oh I see. Didn't know that.
@Emrakul what brings you here
Doesn't $\phi^3$ have some sort of catastrophe with those tadpoles?
Raising operators are only for free theories!
@ACuriousMind Yeah
The vacuum can radiate
Hence why things go downhill pretty fast
15:32
@Bass Renormalizability may not be all that it's made out to be - if QFT is just an effective description at "low" energies (like in string theory), there's nothing inherently wrong with non-renormalizable QFTs
But then what is the real theory!
Aaaaah
Renormalizability becomes crucial when you want that the QFT is a valid description at all scales
@Slereah Well, that's what nobody knows (yet)!
(it's probably not)
Is there a not garbage theory, though
Like... LQG?
LQG sounds alright
It has an effective cutoff
@Slereah Sometimes I think that although QFT is probably not the last word, it's too good for its own sake concerning the accuracy of predictions - we don't really get any hints as to what the "real" theory is from experiments currently
Well obviously yes
15:35
Because they all just tend to agree with QFT
Which is good, but also kinda boring
But it would be nice to have a theory that makes sense
user61230
@0celo7 Physics! Poking around chat, honestly.
@ACuriousMind So, how does Fubini's theorem for $(n-1)$-dimensional vertical slices imply it for $(n-k)$-dimensional ones
I've heard it's by induction on $k$ but I don't get it
I have proved it in the $k=1$ case but I don't see what the induction step is
Prove it for (n-k-1), imho
@0celo7 Ugh, I don't want to do integration theory now
15:38
My favorite trick to make cutoffs for QFT is the QUANTUM FOAAAAM
@ACuriousMind not integration
I've seen papers about making cutoffs with just a very dense wormhole gas at Planck scales as a cutoff
sets of measure zero
@Slereah "just a very dense wormhole gas"...
I'm trying to complete the proof of Thm 7.9 @ACuriousMind
15:40
Yeah that is how it is described
That's not what I know as Fubini, and I like measure theory even less
@ACuriousMind This follows from the usual Fubini theorem according to Lee
It's the form of Fubini needed for Sard's theorem
this sucks
I guess I have to make a bunch of vertical slices $V^k_c$ or something
Then the induction step is that Fubini with $V_c^k$ implies Fubini for $V_c^{k+1}$??
a center of a group of matrices doesn't have to be a symmetric matrix, right?
user54412
@Chris White I really don't understand why people here behave like short minded . If you see other stackexchange sites like mathstackexchange ,there are many similar questions with huge reputation like question1, question 2 ,question 3 and many more — pandu 3 mins ago
user54412
15:47
People keep making this argument. Do they not realize the logical conclusion is that we should just become a porn site? After all, that would get the most traffic.
7
I would support physics porn
It's an election year, I support strippers. - 2 Chainz.
Actually I think that song was from 2008, so
It's an election year, I support strippers. - Titty Boy.
@0celo7 was listening to this youtube.com/watch?v=oiQiTCxSaHA probably in my top 5 albums i've heard
i wonder if you'd like it
@ChrisWhite They are not making the argument because they want anything (good or bad) for the site. They are making it because it would mean their own question doesn't get closed, which is all they see.
@ACuriousMind Hmm, I need help with this
Not from a measure theory PoV but induction
When I assume it's true for the $n-k$ dimensional slices do I get to assume that $A$ is measure zero?
does that come with it?
well that might be a stupid question
is this a trivial induction?
@ChrisWhite I used to attempt a reasoned argument. These days I smile sweetly and click the Close link.
16:09
Re this question:
0
Q: C-parity violation evidence

SebgrI know about the CP-violation experiments from the 60's and the P-violation from the 50's. But, is there a similar experiment which displays (perhaps historically in the same way as the experiements of Wu and Christensen) the violation of Charge conjugation alone?

Can you have just charge conjugation? Wouldn't that mean having the same particle(s) with opposite charges?
Charge conjugation is just the antiparticle?
@JohnRennie What do you mean? You can certainly apply just the charge conjugation to a process and ask whether that's a symmetry
@Slereah I thought the particle and anti-particle were related by CP ...
@dmckee You can let your fellow moderator @Qmechanic know he's a real hero for crushing the spirits of a 13 year old girl by suspending her account ... she really loved being on the site and doing research to answer questions. Did I vote up some of her answers? yes ... Where they good answers? yes ... Did she have 100s of rep points that were from other users? YES
Well it will be an antiparticle with different parity, jeez
It's like $C a_k \approx b_k$
Or something
There might be a sigma 2 in there
16:15
@Young oh?
which user is this
@Young Qmechanic wouldn't have done that alone, it would be a decision agreed amongst all the moderators.
Mod abuse is nothing new to this site
Heather
good job to all of them then
"voting irregularities"
Can someone translate this please?
My account was deleted entirely from physics
16:17
good lord
@Qmechanic @DavidZ @dmckee Good job inspiring the next generation ...
I say the next generation can take a hike!
@Young don't bother, they have no feelings.
@Slereah Um, I think charge conjugation doesn't change the parity
I dunno
I don't have my books here
16:20
That's the reason there is "C-violation" by the weak interaction - it sends the interacting lefthanded neutrinos to the inert lefthanded antineutrinos
Do they even exist
@Young "voting irregularities"? Perhaps you can explain what young Heather was up to and why suspending her for seven days is an excessively harsh punishment.
not all sets of measure zero satisfy the Fubini theorem, do they
certain hyperplanes don't
lines
@Young Since the site does not verify any information about its users, we cannot treat users that claim to be "13 year old girls" different from those claiming to be emeritus professors. And if the account was suspended for voting irregularities, there must be something in the database that looked to the mods as if someone was abusing the voting system.
We've had troubles with sockpuppets voting each other up in the past, so they tend to be rather harsh on such irregularities.
She was on the site a ton and answered 14 questions in 2 days, having a blast researching questions. I up-voted most of her posts, but she had 100s of other rep points
16:24
@Young that's not what we asked you
I'm a 13 year old emeritus professor
Well, I'm not a sockpuppet
@Young Proof?
You're guilty of that until proved otherwise in my book
Ok then I don't understand the quest @JohnRennie
@0celo7 Stop trolling.
16:25
I assume the irregularities were my votes
@ACuriousMind I'm not.
I'm trying to prove a theorem and it's not working
Maybe the theorem is wrong
@Young so you know nothing about the reasons for her suspension then? You're just making assumptions?
@Young I don't think anyone gets suspended for such "serial upvoting". Usually the votes are just reversed, and maybe the voting account suspended.
@JohnRennie I like how you instantly assume the mods are just.
16:26
@JohnRennie She showed me the email from @Qmechanic and it claimed she was using sockpuppets
and my account was deleted from physics
She has done nothing else
How is one supposed to prove that one is not a sockpuppet?
Ah...you're sitting at the same IP address, and if you never did anything but vote on questions where she posted, then that looks exactly as if she was using a sockpuppet to bolster the reputation.
@ACuriousMind well she did
yes we're in the same house
I posted my own questions and answers as well but wasn't nearly as active as she was
Ok, so the mods saw mutual upvoting from two accounts using the same IP address.
That looks very like someone using a sockpuppet.
Ok well she responded to @Qmechanic and explained and he said take it up with SE and she is
16:31
Hi @Young, Thanks for the feedback. I understand if you are upset, but venting it in the hbar chat room is not constructive. Instead, to resolve your Phys.SE account and/or complain about Phys.SE moderators contact the SE team directly.
@Qmechanic sure it was constructive I got your attention and now you know what a great job you did ... have fun in your high tower
@0celo7 I made no such assumption. Young says one thing, the mods don't say anything at all, so I have no way of knowing who is right or wrong. My point is simply that because a user unknown to me joins the chat and accuses the mods of foul play doesn't mean that user is right.
@Obliv: arrows don't travel in zigzag lines!
Well according to Zeno they don't travel at all!!!
Zeno was a smart man
@johnR I meant a random straight path
16:40
I echo what Qmechanic said. No more discussion on that issue here.
between the bounds of the zig-zag path. I.e if it oscillates between x = -1 and x = 1 then the arrow travels straight at some x in between
hmm, but if we take $V_c$ to be $A$
then the induction fails
and I have an explicit example for why
@Obliv well yes, if you fire the arrow in a random direction you have a non-zero chance of hitting the randomly moving target. Even so, if I were the target I wouldn't be running in a straight line.
If it's a long distance away, it's pretty much random and you might have a better chance running straight as you'll cover more distance to avoid further fire.
OK we'll try the experiment. I'll get my bow and you get your running shoes :-)
3
16:48
@JohnR If you've ever played Rust, h1z1 or any other survival game, at a distance the first shot is usually meant to calibrate your next shot. so, if they're not an amazing shot you can get away with running straight for the first shot I think.
actually no.. that's if they're running in a straight path that's not parallel to you. If they're running parallel to you then forget it.
@ACuriousMind I literally need help with the induction step, I don't even know what it means to use induction here
@ACuriousMind I don't want your help with the measure theory bits, I just don't even know what the induction step looks like
00:00 - 17:0017:00 - 00:00

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