The h Bar

12:01 AM

@ChrisWhite yeah, I don't like that bit either

I don't mind the extra click as much as this though:

@DavidFullerton The site switcher take 5 seconds to load; it has an extra POST request attached to it. — Manishearth 1 hour ago

user54412

indeed - sometimes loading my multicollider takes quite a long time

ManishEarth

In other news, handling flags is fun sometimes

@ManishEarth and I having fun with the flags on @StackPhysics #stackexchange : http://t.co/UUvJzJmS0Z

Tweeted by Undo_SE on November 14, 2013 at 4:03 PM

ManishEarth

12:19 AM

@ChrisWhite there's a chance they'll keep it white on Physics, looking at Jeremy's comment

The plan is to use current HTML if it works, or redo the headers if it doesn't. Rest assured English will not look like that after the new bar goes in. — Jeremy Tunnell Oct 10 at 20:38

Also,

> Yes, the bar is black. Also give that a day or two to sink in.

I guess if we don't like them we can just poke them till they change it :P

user54412

@ManishEarth we won't be the only ones poking, I imagine - just look at Math.SE's colors

user54412

selected sites with color schemes not amenable to a black top bar: Christianity, Mi Yodeya, Mathematics, Mathematica, Physics, Programmers, TeX - LaTeX

user54412

12:45 AM

why do so many authors casually say "cutoff frequency" and leave it to the reader's imagination whether that's a low-frequency or a high-frequency cutoff?

Astrum

Christianity SE, that's..... interesting

sample from a "best answer": The clear and correct answer is simply: God's will. God ensured that it happened.

At least they don't pretend to be fact based.

tpg2114

@ChrisWhite It's not obvious from the context? That's the number 1 reason (lie) authors give for vague statements... :)

user54412

1:02 AM

@tpg2114 I wonder if I'll ever get to that point in my career, when I can just say things and it will be wrong for anyone to question me

tpg2114

@ChrisWhite Keep writing papers. Eventually sheer volume would probably put you there

David Z

2:05 AM

@Astrum I'm not really the best person to ask, having never used Schutz, but Carroll is more up to date with modern cosmology and GR info. For special relativity alone, though, it might be that Schutz is better. SR doesn't really change anymore.

Kazi arafat Ahmed

2:28 AM

How can I manually log in my account?
What would be the link?

"http://yahoo.com/"
what I would have to write next?

Anonymous

3:36 AM

@KaziarafatAhmed physics.stackexchange.com/users/login

Anonymous

3:59 AM

ChrisW, Toronto, Canada

131 1

Anonymous

Huh? What sort of a bounty did you give?

Anonymous

Oh, wait, no, different person, similar name, similar identicon.

Physics Meta

5:04 AM

0

Q: Banning homework: what to do with the tag if the policy is changed?

A recent proposal to change the homework policy gathered quite a bit of support, and a specific proposal for a new policy is currently being thrashed out. The new policy is basically just a rephrasing of the old one, effectively changing "you can ask homework questions, but only if they're about ...

discussion homework

David Z

6:30 AM

Our new book and resource recommendation policy is now in effect

7

15

Q: Are resource recommendations allowed?

What is the policy on asking for recommendations of books or resources on Physics Stack Exchange? What is a resource recommendation question? What sort of resource recommendation questions are allowed here? How should I answer a resource recommendation question? As a community member, how shoul...

discussion faq policy book

(finally)

ManishEarth

7:13 AM

@DavidZ This is the problem with sleeping. One misses things. I put up a feature-request to make sleep opt-in but they didn't listen!

Also, yay

TL;DR: "Ask recommendation questions, but we'll edit the heck out of your questions and delete all the answers." :P

@DavidZ Any reason why you didn't edit the banner on the answer there? I doubt that should stay (in the long run, at least)

David Z

Oh, yeah, I guess that could go. I overlooked it.

Astrum

7:39 AM

@DavidZ what a coincidence that ManishEarth posted that list of "good vs bad" resource questions =D

ManishEarth

@Astrum where?

I did?

oh those

Astrum

15

Q: Are resource recommendations allowed?

What is the policy on asking for recommendations of books or resources on Physics Stack Exchange? What is a resource recommendation question? What sort of resource recommendation questions are allowed here? How should I answer a resource recommendation question? As a community member, how shoul...

discussion faq policy book

yeah

ManishEarth

Why a coincidence?

Astrum

because I had asked david what he recommends for an intro to GR text

33

A: Getting started general relativity

I can only recommend textbooks because that's what I've used, but here are some suggestions: Gravity: An Introduction To General Relativity by James Hartle is reasonably good as an introduction, although in order to make the content accessible, he does skip over a lot of mathematical detail. Fo...

ManishEarth

Ah lol

Astrum

7:47 AM

guess I'll go with Schutz

ManishEarth

@DavidZ We probably need to deal with the old book questions soon. Delete all the answers not conforming to policy and preserve their content as a single CW list.

Keeps them clutter free. Though I'll meta post about this in the evening.

Astrum

I stumbled on this old post here on PSE

and I think the guy is wrong, e somehow he got best answer

6

Q: Integrating radial free fall in Newtonian gravity

I thought this would be a simple question, but I'm having trouble figuring it out. Not a homework assignment btw. I am a physics student and am just genuinely interested in physics problems involving math, which would be all of them. So lets say we drop an object from a height, $R+r$, it falls t...

homework newtonian-gravity kinematics acceleration integration

I checked it numerically, and the answer came out wrong

and I used a 10 sig figs

but it LOOKS right

ManishEarth

@Astrum units?

user54412

I don't know how an answer can be right or wrong - the OP never says what they want

Astrum

significant figures

user54412

7:53 AM

like, there actually isn't any question in there

ManishEarth

hmm true

Astrum

either way, the answer comes out wrong by 4.5 meters or so

when I tested it for 9.8 meters off the surface of the earth

so the t^2 would just be one, for 1 second

user54412

8:13 AM

@ManishEarth @DavidZ speaking of faq-ifying things, I think all the engineering faq needs is a couple pointers to good, on-topic engineering-inspired questions

ManishEarth

@ChrisWhite Agreed. Can't get on that right now though

Got a busy week ahead of me.

user54412

same here - i'll see if i have time though

ManishEarth

Any clue what this guy is trying to say? O.o

@Manishearth I'm not claiming anything, except in my first line which perhaps is misunderstood. Not sure how to word it but most people perceive time as a fixed line "action->reaction in chronological timely order". The grandfather paradox is based on that "action in the passed is reaction in the future". I claim there is not enough proof to support this and more research that proofs this wrong. What i am asking (in last line) is why do we look at time as a fixed line, and are there facts that i am wrong with that claim? The question might need rewording and explaining but not closure. — Menno Gouw 2 mins ago

user54412

philosophy gets such a bad rap because it's too easy to ask bad questions in it

user54412

and also because physicists and mathematicians are always telling people with bad questions "oh that's philosophy"

ManishEarth

8:27 AM

@ChrisWhite There really is only one question, and that can be subcategorized: "Why?". And usually it's a bad question :P

> the order-preserving foliations of timelike regions of spacetime

foliations? Gotta use that more.

user54412

@ManishEarth it's used all the time in GR in describing spacetime-filling families of nonintersecting 3-surfaces that are everywhere spacelike (and rarely anywhere else)

ManishEarth

ah

Akin to equipotential surfaces and the like? Makes sense.

user54412

except they shouldn't cross

ManishEarth

Nor should equipotential surfaces :P

user54412

@ManishEarth I'm pretty sure lines on contour maps join and diverge all the time, no?

ManishEarth

8:34 AM

Oh that way. I consider them the same line

..which in retrospect sounds silly

user54412

well, yeah, i guess they are - but they're topologically not lines where they have vertices

user54412

I remember chatting with Ed Witten about what makes string theory so appealing, and he boiled it down to eliminating those sorts of topological defects you see when point particles interact (think Feynman diagrams)

user54412

after all, when two strings merge, their worldsheet is everywhere a nice manifold

ManishEarth

@ChrisWhite But won't the same happen if the topology of the spacetime is abnormal? If we have a wormhole for example. Won't the ...er...equi-time surfaces have vertices?

@ChrisWhite Oh right, Ed Witten is in Princeton

For a moment there I was like "wow, you got in touch with Witten :D". Well, still awesome

@ChrisWhite ooh, that's a beautiful way of looking at it

user54412

@ManishEarth yeah well if you insist on throwing weird stuff into spacetime, yes, you will break things

ManishEarth

8:41 AM

hah

oh, by the way

in Teachers' Lounge, 51 mins ago, by ManishEarth

physics mods: I'm going to have exams next week; while I will be around I may not spend as much time on the site.

So I may be slow in replying on meta and chat.

Shouldn't matter much

user54412

@ManishEarth so now you'll be posting your exam questions on the main site, trying to get them answered before we ban all semblance of HW? I see how it is :P

ManishEarth

hahaha

I think I've only posted two sorta-homework-ish questions on the site

this and this

The former didn't arise out of homework, but was close enough.

ShuklaSannidhya

12:46 PM

Has anyone seen IUPAC's periodic table? Why is hydrogen in the first group?

Natanael

In http://arxiv.org/abs/hep-th/9705091 on page 3 the fotnote says "By deﬁning the ﬂuctuations in this way the expansion of the eﬀective action in powers of g
is an expansion in the number of loops" could someone explain how I can see this?

ManishEarth

1:25 PM

@ShuklaSannidhya It can be both in the first group and in the halogens. Some PTs put it greyed out over both.

But it usually is a positive ion so they keep it over the alkalis

Kazi arafat Ahmed

2:06 PM

"Energy is canonically conjugate with time" what does that mean?

Natanael

3:25 PM

@KaziarafatAhmed It means that energy is to time what momentum is to space. Momentum generates translations in space. The Hamiltonian (energy) generates translations in time.

Physics Meta

3:53 PM

0

Q: New book policy: What should we do about the old questions?

We have a new book/resource recommendation policy. However, it is of a form that it can only be applied to new questions. We have many old questions with answers that do not satisfy the policy, what should we do about them?

discussion book

user54412

4:16 PM

yay +101/-1 --- now the question is how to attract the public to more difficult questions on our site

Kazi arafat Ahmed

6:25 PM

I have several questions:
What does the canonical word mean?
What does the canonical conjugate variable mean?
Does it have to do anything with symmetry?
@Natanael

ManishEarth

People are voting for the wrong answer here :P

Natanael

6:40 PM

Do you know anything about Lagrangian and Hamiltonian formalism?
When going from the Lagrangian formalism to the Hamiltonian formalism one defines the canonical variables, I'm not sure where the words comes from but when defining for e.g. the momentum p one has to take the derivative of the Lagrangian L with respect to the time derivative of the coordinates, say dx/dt, according to p=(\partial p) /(\partial (dx/dt)). The words used are that p are conjugate to x.
There is a symmetry here also, which can be seen using Noether's theorem. Some results are:

Physics Meta

1

Q: Updating the *How to ask* FAQ

With all the current discussions about homework and changing site rules, I'd think we're missing something in the How to ask FAQ and I'd be interested to hear the members' views. It seems to me that the single most important thing about the question is that some effort has gone into writing it. ...

discussion

Kazi arafat Ahmed

I went through some wiki. It say the two variables are fourier transform duals. Measurement of one quantity leads to uncertainty to other variables. What does that mean. Can it be applied to classical mechanics?

@Natanael

Natanael

7:07 PM

@KaziarafatAhmed Yes that is also true. I'm not sure. I think that this can't be applied to classical theories as long as you don't talk about wave mechanics. The uncertainty relation here is that the better precision of measurement of one of the conjugate variables the more uncertain the other becomes. This is the core of quantum mechanics, see e.g. heisenberg's uncertainty principle.

Physics Meta

9:24 PM

2

Q: Dealing with level of resources in requests

One of the things that bother me the most about book* recommendation requests is the endless stream of similar requests that can spout around any specific topic, for all the different possible reader levels and prerequisites. "I'm an undergrad and I want to learn QM" says someone. "Me too, b...

discussion policy book

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