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7:10 AM
0
Q: LaTeX symbols for physics

EvaristeI realised that a bunch of LaTeX symbols actually cannot be used in stackexchange, for example $$\right)$$ gives me nothing... Is there a way around this?

 
user54412
7:32 AM
astro-ph theme of the day: the 3rd stage of grief (bargaining) - try whatever statistical prestidigitation you can to find Earth-like planets in Kepler data, knowing all the while that there will never be enough data to validate your conclusions
 
user54412
also
 
user54412
Public Service Announcement: If you are a pseudo-scientist submitting to hep-th or hep-ph or gr-qc, please refrain from cross-posting to astro-ph when you don't even understand the basics of the astrophysical systems you think back your pet theory
 
user54412
</rant>
 
8:11 AM
Public Service Announcement: If you are a scientist making a ranty Public Service Announcement, _please_ do not do so in the h bar when Manish is around. Only Manish is allowed to rant here. :P
</rant>
ArXiv doesn't have comments, right?
(You probably could make cross posting deadly by assembling a group of astro-ph patrollers)
And, I'm off
 
 
3 hours later…
11:21 AM
This chat room always seems to hold the oddest tidbits of conversation, im not sure if thats because of the people in here or if thats just because thats the way physicists think though :P
 
 
2 hours later…
1:41 PM
@ChrisWhite @ManishEarth
Public Service Announcement: Please don't rant around when Crazy Buddy isn't is alive...
</rant> :)
 
@CrazyBuddy
Public Service Announcement: Due to the sudden influx of PSA's we have introduced a new threshold of only one PSA a day from tomorrow onwards :P
</rant>
 
@RhysW Duh... I should've added there: "Workplace fellas shouldn't step inside h-bar" Because we're busy (but, don't have a job) whereas you're almost free all-time (with a job) :P
 
@CrazyBuddy hey im not all free time! im just effective at managing it so that it appears i have a lot of free time without impacting my work :P
 
@RhysW Whaa..? I doubt that :)
 
@CrazyBuddy One can achieve a lot with the amounts of caffeine i have in my system xD
 
1:51 PM
Hmm... I just received an email from SE for my James question :)
 
2:09 PM
0
Q: Create CW posts "Awarded at 10 rep"

Dimension10On the privileges page, it's written that CW "posts" can be created by anyone with > 10 rep. Shouldn't it be changed to "answers"? . . .

 
@RhysW Both I would say. The avid chatters aren't physicists anyway, just physicists-in-training (mostly)
 
@RhysW I'd add up that these avid-chatters are quite icky & itchy phys.-freshmen
(I meant physics and not psycho...) :D
 
@CrazyBuddy Not really
Both of us are sophomores
And Chris/tpg are grad students
 
@ManishEarth I know...
But, they aren't avid (we're) I am... :D
 
3:10 PM
Physics chat session within a few minutes people...
I'll catch up at approx. 10 mins after it has started (gtg to dinner)
 
Dinner - nice idea. Reading physics chat during that even better.
 
3:48 PM
What..? No people around..?
Welcome to Physics Chat Session everyone :)
 
I'm here
I'm posting a question
A homework question
OK, not really, but it arose from homework :P
 
@ManishEarth: Ohh... yeah... I'll flag it... oops,.. -_-
 
Comes from an assignment which I already submitted the solutions for :P
 
@ManishEarth Searching for different kinds of solutions..? :)
 
No, I don't like my solution much :P
 
3:55 PM
ahh...
 
The problem is solved, it's just that my resolution of an apparent paradox (which wasn't really asked for in the first place) isn't as nice as I'd like it to be
@CrazyBuddy Here:
 
@ManishEarth I think I've seen that... Did you post it here already..?
 
yes
but at that time the assignment was still active
And while I doubt the prof would mind, I didn't want to "get homework help" :P
 
@ManishEarth What? I hate HWs... :)
@ManishEarth: To be true, I've already begun to hate "engineering" :/
Nowadays, I don't like calculating, finding numbers kinda stuff...
 
So, it's officially chat session time
 
4:01 PM
Yay
 
Yeah... just now...
 
Who're here..? only 4? o.O
 
Anyone have something to talk about?
 
Hmm
 
grads do the discussion... undergrads just watch with popcorn (atleast me) :D
 
4:03 PM
Well, if I could finish up that question of mine, we could discuss it :P I have a situation where Newton's laws seem to be nondeterministic.
 
user54412
@ManishEarth you know, there are situations where they sorta are ;)
 
Yeah, I was going to say I think I've heard of that
 
> Wanted dead or alive (or both): Werner Heisenberg. For the murder of Isaac Newton. We suggest you bring a lack of knowledge of his momentum as he is highly elusive without it.
 
user54412
this is the sort of thing I only know because of my philosophy studies - they don't teach you the problems with classical physics so much in physics courses
 
@ChrisWhite Especially the nonlinear ones
And yeah, complicated situations too
Especially stuff like gyroscopic motion
 
user54412
4:06 PM
the classic example is a ball rolling up a symmetrical hill in just such a way that it comes to a complete stop, in finite time, at the top
 
You think you know how to solve any newtonian system handed to you, and then you realize you don't. A hundred times.
@ChrisWhite hmm
 
user54412
time reversibility tells you if you place the ball at the top it should then spontaneously role down
 
@ChrisWhite $e^{-x^2}$?
 
user54412
but then you realize time translation invariance says there is no particular moment when it should start rolling more than any other moment
 
oh right
wow
 
user54412
4:08 PM
and symmetry says you shouldn't be able to predict which way the ball rolls down
 
interesting
 
user54412
I forget the functional form
 
@ChrisWhite $e^{-x^2}$ has all derivatives zero at x=0, but it still takes off and attains nonzero values later.
 
user54412
but it shows the problem with $C^\infty$ solutions to differential equations that are not analytic
 
@ChrisWhite Isn't this analogous to mexican hat?
 
4:10 PM
@ChrisWhite Ugh... So you people are basically saying that a cup with cool water - you can't predict whether ice was dissolved in dry water, or the cup was taken from the fridge and placed out..! ??? o.O
(Irreversibility and invariance) -_-
 
user54412
@ManishEarth You know I've never actually used the mexican hat potential - i'm not even sure what it does
 
user54412
Is that the site logo?
 
@ChrisWhite Makes the universe work :P
yeah that
 
user54412
I feel like I should know this :P
 
Spontaneous symmetry breaking is a mode of realization of symmetry breaking in a physical system, where the underlying laws are invariant under a symmetry transformation, but the system as a whole changes under such transformations, in contrast to explicit symmetry breaking. It is a spontaneous process by which a system in a symmetrical state ends up in an asymmetrical state. It thus describes systems where the equations of motion or the Lagrangian obey certain symmetries, but the lowest energy solutions do not exhibit that symmetry. Ponder the bottom of an empty wine bottle, a symmetri...
ping @DavidZ
 
4:12 PM
Way ahead of you
25
A: How does the Higgs mechanism work?

David ZExplaining the Higgs mechanism properly is a fair bit beyond the level of the Feynman lectures, but here's an attempt. Spontaneous symmetry breaking In order to understand the Higgs mechanism in detail, you need to know about two concepts that are involved in quantum field theory. The first is ...

 
user54412
there are mexican hat functions in signal processing - but I don't think those are the same...
 
Oh great
@ChrisWhite nope
@DavidZ -1 diagram not mexican enough
 
@ChrisWhite Similar function, completely different use
 
user54412
@ManishEarth You want awesome diagram skillz? I recently stumbled on this old answer
 
lol
 
4:15 PM
lol
Paint ftw
 
user54412
it's a circuit... and it's a fish!!!!
 
Why desn't any answer there mention electroplaques?
RHW explains this beautifully. But the diagrams aren't so great :P
0
Q: Why is this classical system seemingly non-deterministic?

ManishearthSo, I was solving this problem1 and I realized that the system given seems to be non-deterministic when analysed with classical laws. The situation is thus: A rope is wrapped for an angle of $\theta_0$ around a fixed pole (the circle in the diagram). One end is fixed to a wall, and the other e...

Posted
Homework question in disguise. Downvote away :P
 
user54412
electroplaque - that sounds like something my dentist might tell me I have, in a very grave voice
 
lol
in The DMZ, 19 mins ago, by CodesInChaos
But my particle physics prof managed to used the index μ with three different meanings in a single expression
in The DMZ, 19 mins ago, by CodesInChaos
Once identifying a muon, two occurrences of one implicitly summed four-index(thanks to Einstein's sum convention) and once as another four-index that's not summed over
 
@ManishEarth I guess technically it should have the tag? Although when you write a question properly it shouldn't really matter
 
4:27 PM
@DavidZ Sure, add it :P IMO an on topic HW question is indistinguishable from a normal question when the "this is HW" part is excised.
I wasn't sure, so I didn't add it.
 
@ManishEarth true
I personally don't care too much
 
@DavidZ: BTW, I was explaining one of your answers today... :P
41
A: Don't heavier objects actually fall faster because they exert their own gravity?

David ZUsing your definition of "falling," heavier objects do fall faster, and here's one way to justify it: consider the situation in the frame of reference of the center of mass of the two-body system (CM of the Earth and whatever you're dropping on it, for example). Each object exerts a force on the ...

(during a chat in facebook)
 
Oh, yeah, that one comes up a lot
 
There are at least a couple other answers on the site deriving the same thing by different methods
 
4:35 PM
@CrazyBuddy interesting
@DavidZ hmm, really? First time I'm hearing of any of these
(I know the concept, just didn't know that such a question existed here)
 
@ManishEarth it might have been before you joined, I'm not sure
 
hmm, maybe, though I've browsed through many of the older posts
 
@ManishEarth @DavidZ: First, I made others believe that all objects fall at the same rate... Then, I confused them that it's just an approximation :P
 
@CrazyBuddy That's like all of physics
 
Indeed
 
4:37 PM
Yeah... That got almost everyone (in my lecture) confused..!
I said physics is made of complete approximations & idealistic objects.. :D
that it's never true :P
@DavidZ Really? I didn't find any of those... Maybe, I'd have to scan other users (other than you, John & Chris)
 
You can probably look at the linked questions from that one I answered
 
user54412
@ManishEarth so i've been pondering your question, and I'm just wondering - why does \mu enter into these inequalities?
 
Finally, can you get an idea on how it settled..?
 
@ChrisWhite Because no slipping.
 
user54412
like, wouldn't the same static situation hold if the string were frictionless
 
4:41 PM
But yeah, it's confusing
@ChrisWhite Yeah, that's another issue
 
@DavidZ: I suggested them to imagine a ball & another planet (say Mars) falling towards Earth (:P) instead of classic stone & feather Galileo's example...
 
@ChrisWhite if you take no friction you get a deterministic answer --> $T_1=T_0$
But with friction you get a range
Of course, one can assume that friction will minimize itself, but that seems a bit arbitrary to me
 
user54412
hmmm, or does that angle not have to be symmetric about vertical? in which case you need two angles to specify the problem?
 
@ChrisWhite It's symmetric in the given situation. Assume. (I'll edit that in).
But not necessary unless you want to consider a string with mass
 
user54412
so i'm still waiting for suggestions for an avatar that's not a green square
 
user54412
4:50 PM
how can i turn this into a contest with rewards?
 
@ChrisWhite bounty!
:P
 
@ChrisWhite white square? :-P
 
user54412
lol
 
I guess that's pretty much the end of the chat session... slow day today
 
user54412
and @RhysW didn't even ask anything about wormholes
 
5:00 PM
lol
 
@DavidZ Yeah... Did we have sped-up session ever..? o.O
 
What do you mean?
 
Every session is sleepy or drunken..!
 
??
 
Never mind..! -_-
 
5:22 PM
@ChrisWhite huh wormholes?!
where!
 
le wild layman appears :P
 
how come pictures are square when lens's are circular?
:P
 
There's an SE for that :P
 
@ManishEarth haha :P
 
But that's just because screens are square
 
5:24 PM
i did actually have a wormhole question earlier, forgotten what it was now though
 
Does anyone know if an iPhone 4S movie has a constant frame-rate?
 
user54412
@Gugg I just asked siri on my 4S...
 
And?
 
user54412
she referred to google, which referred to some forum, which seems to indicate frame rate slows down in darker conditions
 
OK, that's unfortunate. Which brings me to the following question: How do I measure the speed of a thrown baseball without fancy stuff (other than a non-JB iPhone)?
 
user54412
5:37 PM
looks like this is forced by software, not hardware - i see several suggestions for how to fix this with jailbraking
 
user54412
or possibly by using (buying? expensive?) FiLMic Pro
 
user54412
 
user54412
@Gugg have both a ruler and a clock in the video?
 
I only have a kitchen clock.
 
@ChrisWhite hehe, getting creative now xD
 
5:43 PM
Today the adidas Snapshot app was released, but it only does soccer balls.
 
cant you make it look like one? :P
 
I'd have to make it look as big as a soccer ball...
 
closer to the camera?
how do they determine the size? do they know how far from the camera it is? :P
 
No, you input one of three size options.
Then it determines the distance itself, I guess.
 
cant you lie to it? :P
 
5:48 PM
And then divide by the factor between a soccer ball and baseball diameter? Hmm
 
yeah
figure out how far it woul dneed to be to be misinterpreted as a soccer ball at a different distance :P
 
But I think it needs the ball to be steady to begin with.
I'd like to throw the ball, not kick it.
 
ah
 
So, perhaps instead of a clock I could balance another ball on my head, which will dislodge and follow a nice parabola and then from that calculate the time in each frame. Can somebody do better (easier) than that?
 
use smething more reliable than an iphone? :P
 
5:59 PM
Did nobody measure the speed of baseballs before film and radar?
 
the ones i saw were big net type things that guessed the speed from the impact
you stood a set distance away from the measurer
 
Suppose I swept a clay infield, throw the ball and measure the distance between two bounces, would that provide enough information? Probably not, but how about three bounces then?
 
user54412
I would bet three bounces could get a decent answer with calibration - I wouldn't want to try to predict a priori how much energy will be transferred amongst spin, linear motion, and the ground upon impact
 
6:30 PM
Back, to the iPhone then. Suppose I take a picture, could I count on the ball being blurred along some length and then use the "picture time" (what is that called?) to work it out? Or won't the ball be visible at all?
 
user54412
7:02 PM
@Gugg In principle that should work, but there is probably some anti-blur technology at work inside the phone
 
user54412
a feature bug of sub-prosumer cameras is that they all do an enormous amount of post-processing on the images that cannot be turned off
 
user54412
for example, if you look at digital pictures from the 90s, when CCD's were relatively new technology, you'll see lots of graininess, and part of that is cosmic rays hitting the chip
 
user54412
that can't be stopped, but now images are filtered to remove spurious "noise" - which is why many cameras have a hard time taking pictures of stars
 
user54412
I wouldn't be surprised if there is some sort of unsharp masking being done before the data is even saved
 
7:41 PM
@ChrisWhite Many thanks.
Next up: soup!
Why is gazpacho a soup and a smoothy not a soup?
 
I really ought to change the room topic to reflect the real topic (Anything but physics. Unless it's Monday) :P
Actually it's more of Physics+Programming+Rants+WhateverCatchesGuggsFancy :p
 
Sounds OK to me. :)
So, no cooks? Doesn't matter. Does dusk really have a different light than dawn?
 
8:07 PM
I'm so very hungry
Question: since basically every paper that is published (unless it's just reaffirming something old) is on the 'cutting edge' of science, a little, how do editors judge whether it's real or just garbage? Not like, fake data, but just a bad concept or execution?
 
user54412
8:36 PM
@YungHummmma that would also be good to ask on the chat associated with Academia
 
user54412
I short answer I suppose is editors rely on reviews from people also at the cutting edge, people who should have some idea what results to expect
 
user54412
and certainly there are bad concepts that get published, and probably there are good ideas that get rejected - it's pretty imperfect
 
11:37 PM
@YungHummmma Most people work on a reasonably compact set of problems and they know and are known to many of the others working on the same problems, so the preconditions for a reputation are in place and, in fact, reputation plays a big part in it. Newcomers to the subfield will be subject to special scrutiny, and had better make it clear that they understand what has gone before.
 

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