03:00 - 21:0021:00 - 00:00

3:15 AM
@DanielSank It's been ages since I coded a kernel driver, and that was just updates to support a updated piece of hardware. Never had to debug at that level of detail.

3:33 AM
finally got the right estimate for Appendix A
very nice

2 hours later…
6:54 AM
I need to figure out how coujterfactual infomation actually works

7:30 AM
Was in Irvine for 3 days. Did an interview with Verizon (Software). Let's see what happens now. I probably enjoyed myself too much on the white board lolz
In the meantime will be going hardcore on math all night today and tomorrow morning.

7:51 AM
lolz. It's been a while since I heard this youtube.com/watch?v=fV8vB1BB2qc
^^^^ I've grown now

I've got a hunch that the acceleration of a wormhole is related to the shape tensor of the embedding

8:14 AM
Feeling awesome!!!!
Going to read math all night. Just need to get my stuff ready
will be going hardore on the whiteboard, and on collab edit
Tonight I will be an algebraist!!!!!!

Nerd

lol

@DrSatan1 You're in luck. There happens to be a spare photon here at the moment. It's just reflecting off my face right now, but you're welcome to use it.

8:47 AM
Bitcoin is $6k :) 9:37 AM Oh no now it's$1!

9:51 AM
Man there's nothing out there for timelike hypersurfaces
It's all spacelike and null hypersurfaces

10:01 AM
@lılostafa schadenfreude is just so enjoyable :-)

1 hour later…
11:08 AM
@DawoodibnKareem Man I waited too long. You need to tell me when the photon is there and hopefully I can catch it if im quick enough over here

11:34 AM
weirdness level is returning to normal. Resetting to default interaction mode

12:05 PM
B.W.T Kibble & F. H. Berkshire classical mechanics
H. Goldstein
R.D. Gregory, Classical Mechanics, Cambridge University Press, 2006
these are 3 books
do you suggest any of it?

I only have Goldstein thus I cannot comment

Anonymous
@ManolisLyviakis Goldstein is very thorough. But, hard.

12:29 PM
@Blue

Anonymous
@ManolisLyviakis I don't know

so goldsteins is hard?
i got a copy of it in my library
and im having a course on classical mechanics

Anonymous
@ManolisLyviakis By hard I implied it takes time to go through. It's not impenetrable

lagrangian systems etc

Anonymous
If you're taking a course Goldstein would be a very useful reference (It's a graduate level textbook)

Anonymous
12:38 PM
But I'm not sure you'd like to use it as a primary textbook

Review Newtonian mechanics-Lagrange equations and principle of conservation-Hamilton principle
thats our material for the semester
pretty much
euler-lagrange eq ..
seems like the first two chapters of goldstein XD

Anonymous
That sounds pretty elementary. I don't know any classical mechanics which covers only that much or primarily that much. But there are some very good video lectures on those particular topics.

Anonymous
@ManolisLyviakis Yup

ok can you point me to those lectures?

Anonymous
@ManolisLyviakis This and this‌​. You'll find the second playlist relevant from Lecture 43 onwards. The first playlist builds on the basics and is one of my favorites.

Anonymous
12:51 PM
The video quality of the first playlist is unfortunately restricted to 240p.

ok really thanks
the first one think will do it

The question of whether we "see" the light or the object illuminated by the light was conclusively answered by Feynman. — Emilio Pisanty 22 hours ago
We physicists still have a rather antagonistic attitude to philosophers
While we cannot said anything on whether the object still exists if we cannot detect it (cause that is metaphysics), we can get quite close to an explanation in the form of how the object's existence is technically inferred from the information carried from it after something else interacts with it
In the case in question, we can say that we saw the light bouncing off the object, and the information it carries allow us to infer the object is there
Ah. I'd say it's both, then. We can definitely see light independent of a specific object it's reflecting off of, but light also allows us to see objects by the light bouncing off of them. Either way, both definitions give the same section of the light spectrum. — Chris 2 days ago
I'd say Cherenkov radiation is a good example. It's created by a charged particle, but you aren't really seeing the particle (if nothing else, it's much too small). It's really just semantics, though. — Chris 2 days ago
chris gives a nice answer though
Emilo: Having said the above, the conversation gets a little bit .... strange currently in the philosophy chat room as the user just happened to raised about it
so I will say what I said above may not be entirely correct

1:07 PM
@Secret I can tell you my (personal) reaction

fair enough
philosophy can be tricky, especially when the philosopher who discussed to topic put too much spiritual sounding stuff into it, which will make the discussion fully outside of physics and thus irrelevant to physics, as that feymann lecture implies
In fact, when I first looked at that question, I will have the same reaction as chri's first comment
since our notion of "visible" is the one based on biology

in The Symposium, 11 mins ago, by Zane Scheepers
Air is not visible. If air was visible we would be blinded by a thick fog. Likewise, light is invisible, if light was visible, we would be blinded by a 'thick multi-coloured fog'
exactly the same kind of pointless question settled by Feynman

@BalarkaSen help
I'm going crazy

1:28 PM
Do all time-orientable spacetimes admit a foliation by timelike curves?
The time-orientation defined a timelike vector field $X$, which defines some $1$D subspace of the tangent bundle, and since $[aX, bX] = 0 \in W$, the Frobenius theorem should always be true, no?

if you have a nowhere zero vector field I'm inclined to believe the integral curves foliate the space

Good
Any idea when timelike geodesics foliate it?

No idea
If you want to learn about geodesics, there is Berger's book
or Besse, whatever

Any good book on timelike hyperspaces btw?
I'm having trouble finding much theorems on them

wot

1:36 PM
All GR books are all about spacelike hyperspaces and null hyperspaces
No love for the timelike hyperspaces

do you mean hypersurfaces

Oh yeah
sry

no clue, sorry

Maybe I should look up stuff on branes
Timelike hypersurfaces are just $(n-1)$ branes
I'm trying to define accelerations for wormholes and it's not too trivial
I think I can do it via the shape function of the embedding or something
I'd like to foliate by geodesics since the acceleration of a curve in the embedded manifold is gonna be a function of both the intrinsic and extrinsic acceleration, so it would be nice to have a way to only have the extrinsic acceleration

1:56 PM
Glad our philosopher in question is thinking more of the cognitive science point of view of vision
hence once the terms are clarified, the answers drops out
But yeah, there is an insane amount of machinery and translation needed to get the terms right
in The Symposium, 6 mins ago, by Secret
When one asks a philsophical question that is based on physics, one need to be able to translate the philosophical terms to their physics counterpart. We cannot assume either party will understand the language of the other side without guidance

"a nonsingular, differentiable flow φt : M → M acting on a differentiable manifold M is called geodesible if there exists a Riemannian metric on M such that the orbits of φt are geodesics of this metric."
That's the stuff
I need me some geodesibleation
"On the other hand, product manifolds N × R are trivial examples of manifolds foliated by geodesics with an orthogonal integrable distribution."
Yessss
That's good

2:14 PM
@0celo7 what did you need help with

@BalarkaSen math room

2:32 PM
Jesus
the close queue
Géométrie globale des feuilletages totalement géodésiques
Man am I glad to be French sometimes
If all the math papers were in Dutch it would be quite difficult
"Dans cet article, nous nous sommes intéressés aux feuilletages totalement géodésiques lisses de codimension 1 des variétés lorentziennes"
Nice B)

2:50 PM
@BernardoMeurer @Phase @loocsieulb @CooperCape @ACuriousMind false alarm, I'm not jewish

3:09 PM
@Secret ask the super-genius philosopher to take a 50W flashlight, hold it pointing at their eye at a 1cm range, and turn it on, and decide whether light is indeed invisible

That's rude, but a very effective advice
meanwhile my suggestion is like this:
in The Symposium, 2 hours ago, by Secret
Take a piece of live retina section which is connected to an ammeter, shine some light onto it, you will see the needle of the ammeter deflect
in The Symposium, 2 hours ago, by Secret
Therefore light is perceived as bright because it stimulate our neurons to give the electrical signals

Anonymous
3:41 PM
@0celo7 I was expecting that...

@Blue I actually have trace amounts of Indian
@Blue also wtf

Anonymous
@0celo7 I'd say "everyone has". But I'm now curious as to how

Anonymous
@0celo7 What?

@Blue why won't you let me be jewish

Anonymous
@0celo7 You're misinterpreting me

3:46 PM
@Blue don't know, family history doesn't go back that far
also these are my brother's results, and we have different mothers. Still waiting for mine

Anonymous
Heh

so maybe I do have some Jew in me from my mother
but probably not

Anonymous
Reminds me that I look way different from all my family members (in terms of body features). I sometimes wonder whether I'm adopted :P

(We are all Africans)

Anonymous
@bolbteppa That is....true (In a convoluted sense)

I am sure I have some white nationalist blood in me
Makes me feel very superior

yeah baby
maga

Chat session coming up?

apparently

My question is why isn't anyone researching the 700'th power of the Ricci tensor's 547'th covariant derivative on a Kahler manifold

3:53 PM
Hm
Most of the papers on geodesic foliations are foliation of codimension 1
If a manifold has a geodesic foliation of codimension 1, does it also have a geodesic foliation of dimension 1
(it would help)

Cool... do we have anything in particular to discuss today?

28

In order to make the Sandbox easier to use, a new Sandbox question will be posted when the old one becomes too full. This Sandbox is currently active. You can check here for the full list of past and present Question Sandboxes. What is the Sandbox? This "Sandbox" is a place where Worldbuildin...

Hmm, I wonder if such thing will clog our system if used in PSE

Twistors are also timelike hypersurfaces, I don't know how twistors are so general if this is what they are tbh

@Secret I dunno, we could always try it

anyway, I need to sleep now thus unfortunately, I cannot join this session

Anonymous
4:00 PM
Does anyone here have experience with scikit learn ?

I don't know shit bout twistors

OK, we might as well call this chat session officially started. Welcome everybody! I don't know that we have anything in particular to discuss today so I don't think we need to set an agenda

I found some theorem for foliation by geodesics in the Riemannian case
Hopefully it generalizes nicely to the Lorentzian case

But if anyone is new to chat, new to chat sessions, or new to Physics SE and wants to make introductions and/or ask questions, this is a perfect time :)

@0celo7 Sweet, now I have no yids on the list of those I know.
My mind is at rest

4:14 PM
Rather quiet today

Falcon heavy first demonstration launch in 2 hours (18:30 UTC)
putting Elon Musk's Tesla in a heliocentric orbit
And they're going to recover all three boosters too. Two on land and one on a droneship

Oh yeah, I heard about that. Is there a link for video?

As Musk said, it will be a 'great rocket launch or the best fireworks display' :)
a lot of websites have claimed they'll live stream the event

I'll have to look around for it then

@DavidZ Oh SpaceX youtube channel itself:

4:24 PM
if I have time to watch

Oh nice
thanks

@Secret : FWIW, Phys.SE has a sandbox physics.meta.stackexchange.com/q/389/2451

@lılostafa unfortunately without taking along a teapot
or maybe they did put one in the trunk and didn't tell anyone?

^might b what I want

4:28 PM
that adds a whole new dimension to the debate

Oh, that reminds me (for some reason) that I stumbled across a published paper which discovered that a particular kind of radio burst could have been caused by opening a microwave oven
(and we even have a question about it)

5:13 PM
@Slereah looks like a crackpot paper.

does it
It does look like it's written in Words
Nothing too shocking about the content so far tho
Thinking about it, the foliation of a globally hyperbolic manifold by timelike geodesics might just be a geodesic flow problem

@JohnRennie Would you be available right now? I have some doubt regarding optics.
@Blue Are you available right now?

Hi all. Here's a random & tangental question, sorry: Does anyone know Dirac's 1964 Lectures on Quantum Mechanics well? That's where he showed that flat space is hugely easier to reconcile with QM in general and Hamiltons in particular than is the curved space of GR.

Anonymous
@Tanuj Depends on the question...

5:28 PM
that it is

@Blue Suppose there is a plane mirror kept on the inclined plane and an object is falling downwards from some height up on the incline. My question is, does the velocity of image equals the velocity of object at all instants?

@0celo7 I found a paper that literally gives a book cover in the bibliography

@Slereah wot

He gives the cover of BEE as an example of a spacetime such that $p \ll q$ but there's no timelike geodesic from $p$ to $q$

@TerryBollinger space is fluid :)

Anonymous
5:31 PM
@Tanuj For such cases, the common technique is to divide the velocity of object into two perpendicular components (along incline and perpendicular to incline) and then analyze those two separately.

@DavidZ needs some leadership maybe :)
@Blue curious, what are you gonna do with it?

@vzn that's JD's line

@Blue that's fine but won't the magnitude of the image velocity also be equal to object velocity? Since cos^2 theta + sin^2 theta = 1?

or was it spacetime is not a fluid
I miss John Duffield
2
when is he due to return?
wonder if he even cares any more

@0celo7 lol and thats your proof its wrong? :P
@0celo7 he wrote an entire book on amazon, was surprised to see that... yes ofc he cares... few others do though :P

5:36 PM
@vzn it's a pretty good proof
@vzn I mean cares about PSE
I probably wouldn't come back after a year

@0celo7 argument by ("non") authority

Anonymous
@Tanuj W.r.t object, the velocity of perpendicular to incline component of image, is twice the velocity of perpendicular to incline component of object

@0celo7 he was only banned in chat wasnt he? did think the yr long suspension was quite unusual...

Anonymous
@vzn I was thinking of contributing to their source. Was facing some issues, but nevermind. It's okay now

@Blue cool what area

5:39 PM
I once drank a spacetime
Only 3 weeks until he's unbanned

@Slereah maybe we should take bets on how long it takes him to get banned again o_O :P (or whether he even shows up...)

Anonymous
@vzn ML algos mostly

If you give me moderator powers it could be 0s

@Blue interesting... youre a physics major right? what are you doing with ML? is it physics related? etc

Anonymous
@vzn ECE major XD

5:45 PM
@Slereah honestly am gonna say, think some of his physics ideas are valid (have even bookmarked quite a few of his chat quotes!), but he does seem to have a "EQ" problem ("emotional intelligence," lively past discussion topic in here)
@Blue not typically ML field(s)

Anonymous
@vzn Well, we do have ML and AI courses in our 3rd year syllabus. I'm learning it as it seems quite interesting with a broad range of applications in computational physics. BTW, I think ECE here is equivalent to the Electrical and Computer Engineering streams you guys have in the US.

@0celo7 if I have a globally hyperbolic spacetime and a timelike vector field on the Cauchy surface, does the geodesic flow of those vectors cover the whole spacetime

@Blue so are they optional? yes ML is spreading everywhere even into atypical fields now. would be interesting to see the syllabuses if they are online :) ps think kaumudi is doing something like ECE also maybe, or was it software engr? yes ML showing up more in physics these days also, luv it :)

Or does there exist such a vector field, anyway

(...is bernardo studying CE? something close)

Anonymous
5:55 PM
@vzn Uh, yeah. Iirc there's a choice given between subjects like Electron Devices, Mobile Networks, ML/AI. Also some more probably. Semiconductor devices are boring af so you know which ones I'll choose :P

@vzn Let me point out that remarks about betting on users getting suspended again are rather inappropriate - when a suspension runs out, the users are welcome to return and shouldn't be hassled about their past suspensions unless they misbehave again.

@Blue thats really cool youre choosing ML even if given option not to! doubt same could be said of some other academics around here :P

@Slereah "Spacetime" would make a nice cocktail name, wouldn't it? :P

@ACuriousMind ok, duly noted, joking. would like to see JD figure out how to not get suspended much like eg 0celo7 managed to eventually :P actually have some ideas to seriously discuss with him and its great to hear there will be no prejudice in here against that :)

@vzn Really? You reply to me saying you shouldn't hassle users about their past suspensions by alluding to another user's suspension history?

5:58 PM
"Each two causally related points can be joined by a causal geodesic which maximizes time-separation."
ahah!
This could be it

@ACuriousMind uh, time/ cue for me to leave again? everything said by me is now wrong? :(

@ACuriousMind For relaxing times, make it Suntory Space time?

Well, now the trick is proving that timelike geodesic never cross for the foliation

@vzn Must have missed some context for interpreting "space is fluid". Ah well, it was worth a try...

@Loong Lost in Poincaré translations?

6:01 PM
:-D

@TerryBollinger it was ½ a joke. :) have lots of refs for anyone interested in fluid dynamics which is supposedly part of physics. but it seems many serious/ hardcore physicists have no taste for it, or "even less"... :(
@ACuriousMind even better than sex on the beach™ maybe slereah can come up with the ingredients/ recipe :P

Does the bundle reduction of foliations mean that if there's a $k$-foliation, there's also some dual $n-k$-foliation

6:22 PM
Ah, apparently the geodesic foliation on $M$ is done by taking the geodesic flow on $T^*M$ (which is indeed a foliation) and then projecting it on $M$
If there's no intersections it gives you the foliation
Apparently there is indeed a geodesic foliation for globally hyperbolic spacetimes, tho I don't get the proof 100%
It's a lot of geodesic flow and bundle stuff
"The geodesics define a foliation that is transverse to and complementary to the one defined by S, and is referred to as the Caratheodory complete figure"

-1

According to current ideas about String Theory, is that the standard model is but one vacuum in millions of the theory. It strikes me that to find the correct vacuum and search through all the possibilities is something that a neural network would be very good at. We might not be able to solve ...

Primarily opinion-based?

@Qmechanic I wouldn't say it's a good question, but the question of whether or not anyone has used genetic algorithms for this doesn't seem opinion-based to me.

frankly, I think @ACuriousMind's comment should be an answer
i.e. we don't have an algorithmic way to evaluate vacua
...aaaaand, somebody's gone and upvoted even that rubbish pile of a question

@EmilioPisanty That's actually not completely true - many aspects of the algebraic geometry involved, at least in a subset of cases, can be carried out by algorithms, so I'm not sure we can say that we have no algorithmic way to evaluate vacua in general

@ACuriousMind are the algorithms we have now sufficient to determine whether those vacua are a good description of reality?

6:34 PM
@EmilioPisanty At least in the cases I'm thinking of, you could conceivably get from the data determining the manifold to the low-energy spectrum of particles, which you could then compare with the Standard Model, so kinda yes?
Then again, that entirely misses the point - almost no one doubts that there is a vacuum that corresponds to the Standard Model in that huge landscape.

@ACuriousMind but we don't know for sure that there is one?

@EmilioPisanty Not with all the bells and whistles necessary for the full Standard Model, at least to my knowledge. But the manifold necessary for that is likely not "nice" enough to be amenable to the algorithms I have in mind, either

@ACuriousMind so, what you're saying is that the answer to OP's question is likely no but for nontrivial ways?

In isolation, we know of ways to generate all the parts of the Standard Model - gauge groups, fermions, etc.

Well there's that paper with the manifold that generates most of the SM

6:40 PM
@EmilioPisanty I'm saying the question of whether or not algorithms can examine vacua that are "interesting" is subtle and depends on your definition of "interesting". But the question as posed - whether or not anyone has used AI/genetic algorithms for that - is just bad because it's not evident what possible improvement that would have over classical algorithms in this case.

Because neural networks are good at this kind of stuff. — zooby 20 mins ago
"because neural networks are magical fairy dust that makes everything dandy"
bejeesus, that woo-ful of emptiness gets two upvotes?

@EmilioPisanty Welcome to physics.SE :P

Neural networks are only as good as your training set, and also they're very ressource intensive
I mean the human brain is a neural network
We have many of it and still no string theory solution!

booo

6:49 PM
ahhh

Classic

Will the neural network try out the $10^{500}$ vacua of string theory

0

Take electric field lines as example. In EM textbooks it is stated that The tangent of a field line gives the direction of the electric field The density of field lines is proportional to the field strength at that point My understanding is that field lines are not rigorous mathemat...

duplicate?

7:12 PM
Fuck
I messed up and started talking about hermitian scalar fields in my calculusnof variations class
I have a physicist reputation now

RIP
Career's over
Now you'll have to be an engineer

56

First things first, the background for this meta thread is the following issue reported by Enrico Gregorio (egreg) at the beginning of the year (January 11, 2017): Double backslashes disappear from code Since then, a lot of users (from high ranked to newbies) have devoted a significant part...

oh wow
that is one huge clusterfuck

7:36 PM
@Slereah whycant i Be a physicist
Damn autocorrect

you don't believe in physics

@Slereah GR

7:54 PM
ah, dammit
@Qmechanic, here I was thinking I was gonna unilaterally undo your dupeclose
0

Take electric field lines as example. In EM textbooks it is stated that The tangent of a field line gives the direction of the electric field The density of field lines is proportional to the field strength at that point My understanding is that field lines are not rigorous mathemat...

I was halfway through my answer when you closed it
it is now finished
but my dupehammer reopening got blunted by your sneaky tag edit
can I bother you with reopening it?
I don't think it's a duplicate
or, if it is, it is far enough that it should go to the queue

@EmilioPisanty Is your answer suitable for posting on the earlier instance as well?

@dmckee no, it is tailored to this specific one
the earlier instance has a lengthy answer by me

Well, I suppose means you can be fairly clear about why you think it is not a duplicate (I haven't looked at this case yet, and have to go to class).

@dmckee second instance asks specifically about whether one needs to start or stop streamlines halfway through a diagram

@dmckee when are you starting your industry job?

7:59 PM
and whether that does or doesn't scupper the validity of the entire notion

@0celo7 That fell through at the last minute. I'm still looking.

Shame. Good luck

that's covered incidentally by my earlier answer but it can use some closer examination

@Blue got time for some doubt clarification?

(Lol)

Anonymous
8:01 PM

I'll post it in the problem solving strategies

> some sort of superb owl event
lolz

@EmilioPisanty reddit.com/r/superbowl

@0celo7 double lolz

8:16 PM
@EmilioPisanty : I don't insist, but this question about field lines has been asked N times before, cf. e.g. the linked questions.

@Qmechanic sure
but very few touch on the creation / annihilation angle

Anonymous
@0celo7 I forgot to ask. What is PA?

@Blue Peano arithmetic

@EmilioPisanty : Ok, I'll reopen, but be prepared that duplicates lurk en mass.

Anonymous
In mathematical logic, the Peano axioms, also known as the Dedekind–Peano axioms or the Peano postulates, are a set of axioms for the natural numbers presented by the 19th century Italian mathematician Giuseppe Peano. These axioms have been used nearly unchanged in a number of metamathematical investigations, including research into fundamental questions of whether number theory is consistent and complete. The need to formalize arithmetic was not well appreciated until the work of Hermann Grassmann, who showed in the 1860s that many facts in arithmetic could be derived from more basic facts about...

Anonymous
8:21 PM
Interesting. I haven't heard of it before

@Qmechanic thx

Anonymous
I should learn mathematical logic properly someday...

I'm OK with this going to the queue, of course
^ it's live
fifteen minutes to go

@Blue The level of pureness makes me feel like I'm loosing something important in my brain. I mean, c'mon: "For every natural number x, x = x." Well done! You've defined the '=' sign!

Anonymous
@Mithrandir24601 Such documentation will surely helpful for the alien civilizations who might discover us in the future and wish to compare math textbooks. :P

8:35 PM
@Slereah I'm going to offer to do a class on Noether's theorem

@Mithrandir24601 Yes, defining the $=$ sign is precisely the point there

I kind of thought the professor butchered it

Are you gonna use the jet bundle

god no
I don't even know why one would need jets
What results do you get?

@ACuriousMind but why can't they just go "Definition: '=' is a symbol s.t. $x = x\, \forall x$"?

8:37 PM
@0celo7 euler-lagrange equation

(OK, to be fair, they've updated things nowadays)

And I think you can get Noether too
But with much tears

@Mithrandir24601 I'm not sure I understand your problem - they want to define the properties of the relation $=$, and state (perhaps a bit wordily) that it is a reflexive symmetric transitive relation.

You can define $=$

@ACuriousMind y u $the =? 8:39 PM @EmilioPisanty It felt natural bizarre @Slereah Yeah, it's an important symbol, I get that, but it feels really pedantic (I'm just ranting, really) Anonymous @Mithrandir24601 BTW hehe. It's "losing" not "loosing"! Now we know which important thing you've lost in your brain ;) (I make that same spelling error quite often) @Mithrandir24601 If you don't like pedantry you really shouldn't read about formal logic :D 4 @Blue ... I do believe you're right :P @ACuriousMind ::incoherent grumbling:: 8:41 PM It's basically "Pedantry: The profession"$x = y\$ is sometimes defined as $$x \in A \leftrightarrow y \in A$$

three minutes

You can check that the properties of equality are verified from this
$$A = B \leftrightarrow \forall x (x \in A \leftrightarrow x \in B)$$
Basically two sets are equal if they have the same elements

15 seconds!!!

Wow. Huge success
Also 2.2m people watching live on YouTube!

8:53 PM
What the... just happened

Incredible synchronized landing!

03:00 - 21:0021:00 - 00:00