« first day (2636 days earlier)   

12:52 AM
@BalarkaSen winner winner chicken dinner
 
 
4 hours later…
4:37 AM
@Slereah are superconformal field theory and conformal field theory on superspace the same?
 
5:22 AM
::laughs maniacally:: what if mass is negative hehehehe
 
 
1 hour later…
6:46 AM
Hello, everyone :-)
@JohnR: Are you around?
 
@0celo7 then u'll have to prove the negative mass theorem like the nerd u are
 
7:12 AM
@Kaumudi.H yes, sorry for the slow response - dealing with wayward servers.
@Kaumudi.H what's up?
 
Ah, right.
@JohnRennie Hangouts?
 
7:43 AM
Hi guys, today I encountered a very strange Heisenbug that behave kinda quantumly
So the bug (whose origin is still unknown) result in some files in a series of files in a concatenation to be placed in the wrong place, such as file number 3-5 is being replaced by the entry 1-7 and 6-2 being replaced by 2-4
Some tracing found that the original files of 3-5 actually contains content for 1-7 for unknown reasons (similarly for 6-2)
Now, here's the quantumly bit: When I correct those two faulty entries and rerun the concatenation code again, now file 1-7 disappears even though I never touched its original copy!
so to further this quantum joke, somehow files 1-7 and 3-5 became entangled with the observable of existence in an anticorrelated manner. Still trying to figure out why
(and yes you guessed it: 2-4 disappeared)
Ok, some further troubleshooting I can explain the disappearance of 1-7 and 2-4: They are created by a different geometry script. As a result their corresponding entries is missing the line of atomic numbers, therefore, the molecule software failed to read those molecules in due to being the wrong xyz file format
Still checking the reason for the 1st though
 
8:14 AM
@0celo7 The whole dlmf site is 3.07GB (not including the 4665 nonexistant files that the site claimed to have)
 
9:02 AM
user image
2
even the table of content is awful
 
9:31 AM
I think the answer misinterpret the question?
https://physics.stackexchange.com/questions/381390/photon-thought-experiment
 
"an element α ∈ πr+1(φ) can be killed by surgery"
Brutal
 
10:03 AM
@0celo7 yeaaaaah boi
 
@BalarkaSen is there a special name for gluing a manifold to itself
I can only find informations for gluing two different manifolds
 
can you be more specific
you can glue anything to anything
 
Take a manifold, take two shapes $S_1, S_2$, remove them $M \setminus (S_1 \cup S_2)$, get some diffeomorphism between the boundaries $h : \partial S_1 \to \partial S_2$
 
There's no name for this that I know.
 
is there a book that discusses the topic
 
10:11 AM
You're adding a tube at $\partial S_1 \sqcup \partial S_2$
 
p. much
Though not necessarily a tube
 
@Slereah I don't see why a book would discuss this specific construction
 
0
A: Can the mouths of a worm-hole be torus shaped?

SlereahA wormhole with a torus-shaped mouth is a perfectly well-defined spacetime, yes. Via the usual cut-and-paste construction method, you can do the following : Take a copy of $\Bbb R^{n-1}$, remove two non-intersecting tori $T_1, T_2$. This gives you the manifold with boundaries $$M = \Bbb R^{n-1}...

^because this
I seem to recall it is used in the classification of $2$-manifolds
which is just $S^2$ minus a bunch of disks and then identified
 
Not in any proof that I know of
It's just a convenient construction
 
yeah, just wanna check if it's a manifold indeed
 
10:17 AM
Depends on what you are gluing
 
I guess it's probably not too hard to adapt the 2 manifold proof
 
What you did is a manifold, for sure
Locally it's gluing a half-ball to another half-ball
 
"it’s a structure where the neighborhoods of points are locally homeomorphic to open spheres in some ℜn"
Oh no
Fraktur
 
10:36 AM
@Slereah How to shift to next line in gnuplot (without the current line being executed)? I need to write something like this:
plot "print_1012720" using 1:2 title "Flow 1", \
"print_1058167" using 1:2 title "Flow 2", \
"print_193548" using 1:2 title "Flow 3", \
"print_401125" using 1:2 title "Flow 4", \
"print_401275" using 1:2 title "Flow 5", \
"print_401276" using 1:2 title "Flow 6"
There should be some shortcut key I guess
 
I do not know
 
Oh, okay no probs
Oh it seems just typing the next command without the plot variable is enough
I don't need to do anything extra other than placing a `,\` at the end of each line
Phew
 
Is it true that a vector under a transformation of the metric does not change? Or how does a vector transform under $g_{\mu\nu} \rightarrow g_{\mu\nu} + \alpha h_{\mu\nu}$?
 
What do you mean by "a change of the metric"
 
Do you mean a change of coordinates?
 
10:45 AM
Do you mean that you're changing the metric itself or the coordinates
 
(obviously a change of coordinates isn't going to change the vector)
 
if you mean the former, then yes, the vector only depends on the coordinates
well, the vector doesn't change, but its components do
 
From the metric you give I wonder if you're considering gravitational waves. If so that is a real change and the vector will change.
 
wot
I think the issue is what do you mean by a vector
If you just mean a vector field without any further specification, then yes, it will not change
If you mean a physical vector field like the EM field, then it may
 
are invariant interval of spacetime still invariant among accelerating frames?
 
10:54 AM
What do you call an interval
Do you just mean $ds$
And are we in flat space
 
sorry for confusion, I mean in flat space, & when I say interval I mean $c^2dt^2-dx^2$
 
Then no, it is not invariant.
You will get another metric in an accelerating frame.
 
@Slereah I see. thanks for the help. It is a shame I did not study relativity in depth :/
 
The big book of special relativity with stuff on all topics is "Special relativity in general frames" by Gourgoulhon, if you're interested
he goes into accelerated frames
 
@Slereah Thanks, I have just bought the hard cover reprint of Gravitation by MTW, Not sure if it is good place to start learning these stuffs?
 
11:07 AM
@Shing MTW is quite a hard book.
Accelerated motion is dealt with in chapter 6, but there are easier approaches to it in other books.
Obviously the geometry of spacetime is the same whether you're accelerating or not, but using an accelerated frame involves a change of coordinates so you're writing the same metric in different coordinates. For constant acceleration the appropriate coordinates are the Rindler coordinates.
If you search the site for rindler metric I've mentioned them lots of times in answers
 
@JohnRennie thanks! is it a good place to learn tensor? I always have hard time calculating tensors.
 
11:27 AM
I have yet to find a clean way to superimpose all possible frame of references onto a single diagram
 
11:39 AM
hahahahahahahahahahahaha
:dies:
 
:-D
X_X
 

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