The h Bar - 2013-07-30

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7:10 AM

0

Q: LaTeX symbols for physics

I 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"

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

discussion questions answers community-wiki

@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:

user image

@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

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?

Explaining 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?

So, 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...

newtonian-mechanics friction determinism

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 homework 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?

Using 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

user image

2

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

in any event, there's a stackexchange for that

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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