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00:00 - 14:0014:00 - 22:00

2:00 PM
@HDE226868 hah
 
user116211
> Please correct me if I am wrong.
 
@slereah are you around
 
user54412
Then internet: proof that a large fraction of the population is mentally unhinged.
 
But is the sample representative :P
 
user116211
2:04 PM
@ChrisWhite There are people in internet who still thinks relativity is a conspiracy.
 
I think quantum field theory is a conspiracy.
 
user116211
@0celo7 Digging the Amazon shows Anthony Zee's book on QFT is quite famous among the buyers.
 
@0celo7 yeah, QFT was developed by the man
 
But most physics is a cult anyway
 
user116211
Hey @yuggib.
 
user116211
2:18 PM
Got the second volume of Courant and Hilbert from the library; the whole book is on PDEs. The book contains Courant's work on finite element method. But there is no exercise ;/
 
user116211
But the book is in good condition ;)
 
@MAFIA36790 I see. Anyways, it is more a piece of history than an interesting reference nowadays
 
@yuggib No, by Jews.
And I guarantee the average QFTist has not done any of the "experiments" that "verify" it, either.
 
user116211
@yuggib hmm. Yes, the book is not covered even in additional reference in the course. But it would be interesting to read his works and Hilbert's lecture notes.
 
I am
 
2:29 PM
@JohnRennie You went to Cambridge though didn't you?
 
@slereah I was wondering 1) what are you currently working on , and 2) what kind of math do you have to know for it (i'm assuming GR but anything else?)?
Recently been interested in the ideas of CTC's and time in general and I think you're an expert on that right?
 
Trying to show that some spacetimes with compactly constructed chronological horizons have no closed causal geodesics
 
user116211
@BernardMeurer He had lots of adventures (there);P
 
@Slereah Do you even know how to do that
You don't know any topology
 
I can't seem to figure out what that means @slereah guess I have to learn diff geo :\ I have an idea of a geodesic but not a causal geodesic anyway. Nor do i have any idea what a chronological horizon is..
 
2:42 PM
What is a geodesic @Obliv
 
well from what I gather from the wiki page it seems straightforward. It's a generalization of straight lines in curved spaces. In this context the curved space is the space-time we use in GR? @0celo7
 
What is a straight line though
 
a path between two points that makes no turns? (i guess in curved space the curvature is something unavoidable?)
 
@BernardMeurer yes, I did my first degree at Peterhouse and my PhD at Jesus.
 
@JohnRennie What
 
user116211
2:47 PM
@JohnRennie Jesus?
 
@JohnRennie Would you happen to know where I can get an oxygen sensor
parts per million in air
 
@0celo7 it's just calculus
 
@Slereah basic algebra and calculus
 
Peterhouse is a constituent college of the University of Cambridge, England. It is the oldest college of the university, having been founded in 1284 by Hugo de Balsham, Bishop of Ely and granted its charter by King Edward I. Today, Peterhouse has 226 undergraduates, 86 full-time graduate students and 45 fellows. The modern name of Peterhouse does not include the word "college". Despite being one of the smallest colleges, it has one of the highest overall endowments, more than £250 million, including property in central London such as the Albany apartment complex in Piccadilly. Peterhouse is widely...
 
Well not basic
It's a fancy calculus
But no need to involve topology
 
2:48 PM
How does it have a 250 million endowment with like 350 people
 
wow...
if that isn't high class then I don't know what is
 
Just gotta solve some bounds of the geodesic equation
 
Jesus College is a constituent college of the University of Cambridge, England. The college's full name is The College of the Blessed Virgin Mary, Saint John the Evangelist and the glorious Virgin Saint Radegund, near Cambridge. Its common name comes from the name of its chapel, Jesus Chapel. Jesus College was established between 1496 and 1516 on the site of the twelfth-century Benedictine nunnery of St Mary and St Radegund by John Alcock, then Bishop of Ely. The cockerel is a symbol of Jesus College, after the surname of its founder. Three members of Jesus College have received a Nobel Prize....
 
I bet they had some killer food there @johnR
 
> The College of the Blessed Virgin Mary, Saint John the Evangelist and the glorious Virgin Saint Radegund
Catholic school in England?
Why didn't they burn it down
 
2:49 PM
The formal banquets were very good, though the regular food they served to undergrads wasn't that great
 
Formal banquets?
 
lol 'formal banquets'.. if only they had those in schools here :P
 
@Obliv a geodesic is something that satisfies the geodesic equation
 
user54412
I was actually surprised to see lots of Catholic churches in Oxford. Or at least that's what their signs said.
 
@0celo7 geodesic equations are those that model the path of a particle in a curved space-time? (that's a guess)
 
2:52 PM
You had to wear your gown to the formal banquets, though not the silly hat
 
user54412
also, by the late middle ages that town must have had a church for every 30 residents
 
@Obliv A free particle, yes
Still not sure how non-free particles work
 
what do you mean by 'free'? Can the model distinguish this?
 
free as in not being acted on by a force
 
@0celo7 that happens a lot. Read any history of hanging.
 
2:53 PM
but this is true in Newtonian physics as well
 
@JohnRennie See, that's an awesome school
 
if you constrain a particle to a curved surface the particle will move as a geodesic wrt. the isometric embedding metric
 
@0celo7 why does a force change anything? If the motion is a 'straight line' then regardless of the velocity/acceleration isn't the important thing being modeled the path?
i should probably stop asking questions with no knowledge of the math formalism
 
something moves differently if there's a force acting on it vs. not
$F=ma$ vs. $0=ma$
 
@Obliv remember that a geodesic is a trajectory in spacetime not just in space.
 
2:56 PM
oh right.. but I thought @0celo7 was talking about curved spaces only and not spacetime
 
@JohnRennie you know lots about cohomology, right?
 
If you take the same path in space but move at a different speed along it that is a different trajectory in 4D spacetime
 
@JohnRennie I was saying geodesics show up in Newtonian physics too
 
@0celo7 what I know about cohomolgy would fit in a fly's arse and still leave room for my brain.
 
@Slereah ?
 
2:59 PM
I liked the snarky comment you left for me over the weekend @0celo7 just for you, I won't ask any algebra questions to ACM this week ;)
 
Nice
@HDE226868 Out of curiosity, why no flag?
 
user116211
@JohnRennie gotcha
 
@JohnRennie got a few floz LN2 left over ;)
 
@0celo7 Dip your finger in it and keep it submerged for 10 seconds
 
3:17 PM
@BernardMeurer it wouldn't do any permanent harm, it would just hurt.
It takes a lot longer than 10 secs to freeeze a finger.
 
@JohnRennie I don't want to harm my friend, I just want him to feel pain :)
 
@BernardMeurer liquid nitrogen burns are very, very painful!!
 
@JohnRennie Perfect!
 
I could have sworn I just saw a notification appear for a new question about grapes in microwaves, but I can't see the question. Was it on a different SE?
Aha!
0
Q: Grapes In Microwave Clarification

Simon MitchellI am considering attempting an experiment in which one puts two, almost severed, halves of a grape in a microwave with a glass over it. To my knowledge so far, the grape halves act as focal point for the radiation and the microwaves will burn the small part of grape skin that isn't severed, provi...

 
@JohnRennie Can we have a [grapes] tag?
 
3:29 PM
@JohnRennie Hmm
 
@0celo7 remember the banana?
DON'T anyone star that!! :-)
Predictable as ever :-)
 
Dang it
You got me
 
@JohnRennie what?
oh, yes
would the skin not all die though
that would be pretty horrible
 
3:47 PM
@JohnRennie OP wants to put their grapes inside the microwave?
Sounds like a bad idea to me.
Also of concern are the reports by commentators that they've also put their grapes inside their ovens.
 
@EmilioPisanty I've done it plenty of times
It's totally safe
apart from the third degree burns of course
 
@0celo7 many of us have dipped our appendages in liquid nitrogen for a second or two and suffered no harm. Obviously at some point it will start killing the tissue though exactly how long is safe I don't know.
@EmilioPisanty Have you never done the experiment?
 
@JohnRennie He doesn't like to live dangerously like us
@JohnRennie Is it safe te remove the microwave generator from a microwave-oven and strapping it onto my own system?
I want to overdrive it
 
user116211
@bernard When i hear grapes stuff in microwave oven, I link it with you. So, I'm naming those Bernard's Grapes Experiment.
 
@MAFIA36790 :O I feel honored!
 
3:57 PM
@BernardMeurer Perfectly safe, only give me plenty of warning so I can make sure I'm nowhere in the vicinity. It's probably also warning the local burns unit in advance.
 
@JohnRennie Where in the UK do you live again? :p
And hey, my experiments have only caught fire 3 times
 
Damn, I think that info is in my Facebook profile. Quick, how do you edit it?
 
user116211
@3750: You changed your DP!
 
I used to get the big capacitors out of old TV sets, connect them up in series and charge them to 400V (rectified UK mains). When you short them it creates a humungous arc.
 
@JohnRennie HA I KNOW IT NOW
@JohnRennie Blowing up caps is pretty cool
 
user116211
4:00 PM
@JohnRennie You crazy nerd ;))
 
invert the polarity at 300V of a 100V rated cap
it's AMAZING
Specially when you order 2k farad or larger badly made caps from China
 
We used to, erm, borrow magnesium powder from the school chemistry lab and use the arc to set it off. That's a biiiiiiiiig flare.
 
@JohnRennie I've been working on an arc speaker for a while
 
It's been done. There's a YouTube video somewhere.
 
but I haven't found a satisfactory way to generate sound from the controlled arc without massive noise caused my how hard it is to control the arc
Yeah, but they all have noise, I want a nicer solution :v
RUN LINUX ON AN ARC
HA
 
4:10 PM
@JohnRennie I like my grapes safely away from fire, thank you.
 
I wonder if it works for tomatoes ...
 
@JohnRennie That's probably a much easier experiment for testing size dependence than finding tomato-shaped grapes.
 
Plums? aubergines? I'd say there's a PhD thesis worth of research there.
If Bernard manages to stay out of hospital perhaps he could tune the microwave frequency as well.
 
@JohnRennie what does nitric acid do to stainless steel
 
Does twitter get oneboxed here?
#DaeshRevendique LA MORT DE STANNIS BARATHEON KING OF WESTEROS AND OF THE FIRST MEN. KING OF THE ANDALS LORD OF LIGHT
 
4:15 PM
Twitter gets oneboxed. Why doesn't arXiv?
Am I the only one who reads arXiv as arcksiv?
 
@0celo7 I think conc nitric will etch it, but only quite slowly. Dilute nitric e.g. nital will have little effect.
 
@0celo7 that would be arξiv, not arχiv
 
Apparently it rusts it
@DavidZ lol
αρξιv
 
user116211
It's chi
 
@0celo7 someone in mathchat is asking for your opinion on a physics matter. Seeing as you're "basically a physicist" maybe you can help him
 
4:20 PM
@JohnRennie I could probably control the microwave
 
Link?
 

 Mathematics

Associated with Math.SE; for both general discussion & math qu...
 
I'm not a physicist 👿👿👿
 
are you that lazy
 
On mobile
 
4:20 PM
I guess if maybe i could dump the ROM on mine and take a look at the assembly behind it
 
oh
 
it's probably not that difficult
 
Don't know how to switch rooms in mobile
 
change url from /rooms/71 to /rooms/36
and get rid of the /the-h-bar
 
IIRC there's a dropdown menu at the top
for rooms you're in already
 
4:24 PM
@DavidZ Could you ask if they intend to get the chat on the actual mobile app?
 
@BernardMeurer I could, but I bet it's already been brought up on Meta Stack Exchange
and I suspect the answer is no (but don't take my word for it)
 
@DavidZ thanks!
So no they won't do it apparently
I've grown to really dislike the stack exchange developers :/
 
Well, do keep in mind that they're busy
And if you ask me, the new mobile interface for chat is pretty good.
 
@DavidZ It's unusable over here
 
Good night!
 
user116211
4:27 PM
There are lots of good plans/proposals rotting in Meta SE yet to be implemented; they are really busy.
 
@BernardMeurer you'd better not be saying that if you're using it now ;-)
 
@DavidZ I'm not?
I'm on my desktop
I literally cannot chat on my phone (iPhone 5) because, I'm sorry, but as far as I can see the mobile interface is crap
 
Why?
I mean, what goes wrong when you try to chat on the phone?
 
user116211
And for my mobile, there is no app T__T
 
back when the new mobile interface cam along it just would bug and freeze or jump all over the place
now it just defaults to the desktop interface on mobile which is unusable
and also, had SE open sourced their app the community could be working on this
 
4:31 PM
Ah, well that's entirely different from my experience
I would advise making sure there's a bug report describing this behavior on Meta Stack Exchange
 
@DavidZ I don't report bugs in closed source projects, but thanks for the reference :)
 
Depending on how badly you want to use it, you could try a different browser
@BernardMeurer well in that case your right to complain is somewhat tainted
 
@DavidZ both iOS Chrome & Safari just take me to the desktop version
@DavidZ Which is why my original complaint wasn't that the web mobile chat is bad, but rather that there is no chat built in on the app
and, tbh, it all boils down to it being proprietary, closed source software
which is ridiculous for such a community-driven website
I mean, keeping the site closed source is necessary, obvious and super understandable, I'm not Stallman, but the App?
 
@BernardMeurer Yeah, and my response (well, not that I really care, but this is what you'd likely hear from SE as well) is that there is no need for a chat interface built into the app because there is a perfectly functional (as far as the devs are concerned) mobile web interface
 
@DavidZ Which is what happens when the users can't actively contribute to the things they use :)
 
4:36 PM
It's also what happens when the users don't file bug reports.
 
@DavidZ Why would I file a bug report and literally do their job for them (that of debugging) when their source is closed?
Closed source on non-critical code is a bloody cancer
you should open source everything that you can without damaging your business model
SE doesn't do that
 
Hi there!
I was hoping to chat about some quantum mechanics stuff. Anyone around?
 
@BernardMeurer Filing a bug report is not debugging. It's making the devs aware that the bug exists. I claim that it's not their job to discover every bug. Yes, they should do some testing to identify and fix as many bugs as they can, but it would take them thousands of years to go through all the different configurations that people actually use.
 
@DavidZ They wouldn't have to if they were committed to their community members and open sourced the app
 
user116211
@Jade196 Just jot down your query; any interested one would reply sooner or later if they want.
 
4:42 PM
They don't have to test all configurations even with a closed-source app. Open sourcing has nothing to do with it. People can still file bug reports without seeing the source code.
 
@Jade196 I'm pretty certain there's already a question on the site about why the wave function has to be complex ...
 
user116211
@JohnRennie yep.
 
I'll do a search and check for that.
Although I think I read it, and they just sad it couldn't be real.
I'm not talking about real wave functions.
I'm talking about all other sorts of abstract algebras.
 
user116211
42
Q: About the complex nature of the wave function?

yayu1. Why is the wave function complex? I've collected some layman explanations but they are incomplete and unsatisfactory. However in the book by Merzbacher in the initial few pages he provides an explanation that I need some help with: that the de Broglie wavelength and the wavelength of an elast...

 
@DavidZ They can, but then again, why not just let the users who can fix their own issues?
 
4:43 PM
Thank you for the link! I'll check it out.
I'm looking at it, and it's the same old same old. Just saying about how the wave functions wouldn't make sense if they were real.
 
@BernardMeurer any number of reasons. To know why exactly they chose not to open-source chat, you'd have to ask them. (the SE people)
 
I'm not advocating for the quaternions, persay, but they are an extension of the complex numbers.
They have similar properties. Why not have quaternion wave functions?
 
user116211
there was Ron's answer discussing that; I didn't find that question, though ;/
 
@DavidZ On the SE meta?
 
Sure, if you want.
 
4:46 PM
Or is there anyone specific I could ask?
 
It may have already been posted.
I suppose you could also use the "contact us" link in the site footer to send an email to the team. But I think meta would be more likely to get a response.
 
user116211
@Jade196: You can ask new question if you are not satisfied with the current one or you think they are not answering your query.
 
I could give that a try, yes.
But if I might ask you a question:
 
@DavidZ Ha, so basically because the app has a bunch of bad practices
 
What do you think about the fact that only the amplitude of the wave function matters?
 
user116211
4:48 PM
@Jade196 not me
 
That there is a degeneracy in it s.t. the phase doesn't matter.
Not you?
 
Not so much do my homework for me as do my project for me!
-2
Q: Please explain this project to me

EventhorizonI've been struggling with this project for a few months now and I frankly can't break out of my way of thinking. Will you please explain what the author expects of me? Project

 
user116211
@JohnRennie Don't know why people think we would go to the link to get the question.
 
Well, it's actually a reasonable thing to think if someone isn't used to our insistence on all the relevant information being in the question
People generally don't realize that following links takes effort or that it's a thing that a person might not do.
 
5:04 PM
So, you guys know how in the standard model U(1) is the symmetry group for E&M and SU(2) and SU(3) are the symmetry groups for the weak and strong forces?
Well, from each of those symmetries comes a force and conserved currents (a la Noether's theorem).
That is, from each of these symmetries comes a force and particles associated with it.
So, if there is a U(1) symmetry in the wave function, shouldn't there be a force and conserved currents that go along with it, too?
 
The symmetries you refer to are local gauge symmetries of the Lagrangian. Requiring the Lagrangian to respect the symmetry requires the force carrying particles to be added.
Homework? Insufficient effort? Both?
0
Q: Alpha Particle moving through a magnetic field

lianameereHow would I find the acceleration of an alpha particle moving through a magnetic field given the force of the magnetic field, the charge, the initial velocity and the strength of the magnetic field.

 
I could see that being homework-like
 
So here's a question
Say I wanted to buy a replica of the IPK for my coffee table.
Can I get one online?
 
Yes, that is how the standard model works. Those symmetries on the Lagrangian necessitates the forces and particles related to them.
Shouldn't a symmetry in the probability space have some sort of similar constraint forces or conserved currents?
All Lagrangians (not just that of physics) have this property of constraint forces.
An inherent symmetry in the wave functions is a constraint on them...
 
5:29 PM
↑ a PR team with a little bit too much very-very-late-night time on their hands?
 
 
3 hours later…
8:18 PM
http://physics.stackexchange.com/questions/116595/why-is-the-application-of-probability-in-qm-fundamentally-different-from-applica/116609#116609

I have finished reading all the answers here, in particular the noncommuntative probability answer

If I understood this correctly, it seems events in classical logic and quantum logic are governed by very different mathematical objects (pretty much the same mentioned in Susskind's book also: Set vs Hilbert spaces of operators)

Since quantum phenomenon demonstrate superposition, they can be modelled by vector spaces (thus states and projectors ca
In contrast, classical probability is governed by sets. There is no "richer structure" (for lack of a better term) in transforming the set in any notrivial way when a proposition is applied or asked. Therefore when we ask for a proposition e.g. P and Q, we are effectively have a set, we then fliter out the bits that are in P, and then after that, fliter those that are in Q.

Because nothing is being changed in the set (other than elements being selected out by the propositions), it is easy to see that P and Q must euqla to Q and P, hence classical probability is commutative
I am tempted to think that the structure where quantum probabilities live in are kinda like set with some extra properties (e.g. linearity and superposition) and this is what allow the resulting probabilities to become noncommutative.

One can also think of this in an opposite direction (since quantum is more fundamental). As pointed out by the answer, if the operators P and Q are orthogonal, then PQ and QP maps any state vector to their kernal. Therefore, perhaps, the classical set and classical logic is a result of the hilbert space being so (I don't know what is the correct term) that ca
Howver, I am guessing that it is safer to just consider the two type of logic to be different, given that I am still a beginner in understanding all of this
 
@Acuriousmind @yuggib @vzn @NeuroFuzzy (Danielsank is currently too busy, thus not tag)
https://ncatlab.org/nlab/show/Gleason's+theorem
http://physics.stackexchange.com/questions/116595/why-is-the-application-of-probability-in-qm-fundamentally-different-from-applica/116609#116609

(The question below does not require reading the long wall of text before it)
The answer and nlab also mentioned about the counterexample of Gleason theorem in 2D

$$P=\frac{1}{2}(I+\sum_{i=1}^3 n_i\sigma_i)$$
What is the physical meaning of this hermitian projector. (If I understood what it implies correctly) why
 
8:53 PM
@Secret Sorry, my set-theoretical/deep knowledge of rigorous classical probability and therefore rigorous quantum probability is laughable.
@Secret It's a projection onto the spin vector pointing up along the $\hat{n}$ axis.
@Secret You can see this by using my favorite identity, (1) en.wikipedia.org/wiki/…
Or not, actually, sorry*
you can see it by applying it to the +1 eigenvector of $\vec{n} \cdot \vec{\sigma}$, $\uparrow_n$, which gives you $\frac{1}{2}(|\uparrow_n\rangle+|\uparrow_n\rangle)$
And then apply $P$ to the -1 eigenvector of $\vec{n} \cdot \vec{\sigma}$, $\downarrow_n$, which gives you $\frac{1}{2}(|\uparrow_n\rangle-|\uparrow_n\rangle)=0$
 
why is that your favorite identity
you hipster
what's wrong with $\mathrm e^{\mathrm i\pi}=-1$?
 
@0celo7 too complex.
Or, um... too real?
 
gross
 
9:11 PM
@0celo7 Too Euly
I find its derivation a bit circular
 
9:23 PM
Stop
 
The difference between my example and yours is exponential
 
what is wrong with you
 
Procrastination :(
 
@0celo7 No flag on what?
 
9:40 PM
@HDE226868 your avatar
 
@0celo7 What do you mean?
 
@HDE226868 you changed your avatar for other atrocities in France.
 
@0celo7 Ah. Well, I hadn't thought about it, but considering some other recent tragedies, it felt too Western-centric.
 
Did you come up with that on your own or did I make an impression when I pointed that out?
 
On my own.
 
9:47 PM
Hmm.
 
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