The h Bar

Taking velocities to be small and keeping first order terms is equivalent to taking $c$ to be very, very large. I think. Don't bet your life on that.

If you're interested in relativistic fluids, see some of the later chapters in Landau's fluids book and any cosmology text for a wealth of applications.

user1667423

@0celo7 Sounds good, thank you for your help.

12:20 AM

@user1667423 Since we're only concerned with the terms with ratios $v/c$, it is easy to see that $\lim_{c\rightarrow\infty}\equiv\lim_{v\rightarrow0}$.

@user1667423 What Danu means by $p=\mathcal{O}(u)$ is that we take the pressure to be small enough so that a term $\propto pu\sim 0$ in this limit.

@0celo7 HE is $130?

@Icosahedron $99 IIRC.

I thought you already had a copy.

It was a gift remember.

Yeah, so?

I didn't think it would cost that much.

I bought HT.

(first print book in a while)

12:31 AM

You have to use well established acronyms.

hughston, todd.

can that be well established?

No.

The book itself isn't well established.

I believe it is, though in the uk only.

There are a lot of good GR classics that are not known.

Elementary General Relativity by Clarke, HT, and space-time and singularities by naber.

I think that last one is a less difficult version of HE, with less material.

The first one looks fairly advanced.

I'm borrowing the first one from the library and I bought HT.

I'll read them both, and do the exercises in Zee.

Though I'm not reading Zee.

12:38 AM

The first one is above you.

How far?

All I have is ToC, so I can't say for sure. It should be your second, maybe even third book.

You should learn other stuff in the mean time, to get some maturity.

I'm not familiar with the material in chapter 5.

I'm reading 5 books for that maturity.

It was going well except for zee.

I still don't understand how you don't like Zee when every other physics book has the same layout.

...sorry what is ToC?

12:42 AM

Table of Contents.

Should have been a "the" in that sentence.

I thought it was referring to a book.

Tomorrow I have to make the 9 hour drive to Tennessee.

Joy.

For your uni?

Yes, orientation.

Fly there.

Where did you find the ToC for Clarke?

I didn't borrow it yet, and I can't find the ToC.

12:56 AM

amazon.com/…

@Icosahedron Not made of money.

His other book "Elementary General Relativity"

Oh

It's out of print.

@Icosahedron Well that one there is something I'd read.

Though university libraries have it.

12:58 AM

IDk about that one then.

amazon.com/Analysis-Space-Time-Singularities-Cambridge-Lecture/…

On the level of HE.

I know that too.

Though his introductory book is out of print.

Once I finish all of the books I currently own (in about 2 or 3 years), my next book will be

amazon.com/Quantum-Field-Theory-Curved-Spacetime/dp/0521877873/…

I've already read that, it's elementary.

$3x + 5 = 7$

That equation came late and I was really concerned for a second.

I mean, aren't you already at that levle?

1:04 AM

Yes.

I have a crapload of other things to read in other subjects.

+ a little something called college

Argh, I also want to buy GSW.

No monies for all this

There is one other way...

I'm sure I could do that, but I like having the physical book.

We've been over this.

Do you learn better with a physical copy?

Maybe.

I have digital copies of all of my physical books on my iPad to use as references on the go.

All legit of course, Mr. FBI.

You forgot the equation?

1:10 AM

No.

You retarded or something?

For the latter I mean.

Nope.

Then it wasn't directed towards me?

No.

I vastly prefer hardbacks as well.

This paperback HE looks pretty ghetto.

It was imaginary then, like some kind of ghost in the $\hbar$.

Rebind it.

1:13 AM

No monies

It doesn't close properly.

Show me your rebound version.

Solution: Place Einstein on top of it when he's sleeping, for 3 hours.

He'd fuck that shit up with hair and claws.

I don't have an imaging device.

Otherwise I would post pictures of my cat beside my rebound HE.

Do you do most of your learning on the couch with a blanket?

Yes. I'm also sitting on a second blanket.

The blue one.

Maybe I'll stop by a book binder over the summer and see what they can do about HE and Straumann.

Normally they remove the softcover, trim the spine, and rebind it to a hardcover.

It is about $10-$50 to rebind a book.

Back to shankar, later.

1:29 AM

Up to $50?

Not worth it.

Just buy your books used if money is a concern.

@alarge A used out-of-print hardcover will be more expensive than the in-print softcover.

Depends, but often times yes, out-of-print versions do tend to be considerably more expensive.

But you can get the in-print softcover cheaper used than new. Sometimes the discount is quite large.

True, but I'm not willing to put my money on the table for a used product without being able to inspect it first.

I've bought probably 50 or so books used online. Only one had markings where there shouldn't have been any.

1:41 AM

Do they look like someone has read them, i.e. are there streaks from thumbing the pages?

I usually buy my books in "good" condition. Which is to say that they usually do look like someone's used them, but without any highlighting or other "abuse".

2:32 AM

@Danu My openings are fantastic. That particular time I was trying to mate him early with the bishop-queen pairing, but he moved the pawn instead of the knight. I usually open with d4,e3.

@Danu And I think the tactic was move the rook under the queen (losing it), then moving my knight to a4 and then taking his queen

4:56 AM

Can anyone explain renormalization to me (experimentalist) without reference to QFT and in a few sentences?

Danu

6:39 AM

@KyleKanos That was indeed the tactic :)

@DanielSank no. :P

I think you should read some book on stat mech... I've heard it's used there, nonrelativistically

@KyleKanos I like d4, not so much e3

@0celo7 @user1667423 the nonrelativistic limit is also about $p\ll \rho$

@DanielSank perhaps e.g. chapter 13 of Sachs, Sen & Sexton

...or Pathria & Beale, ch. 14

In stat mech, it is usually done to understand phase transitions AFAIK

also ocw.mit.edu/courses/physics/…

Q: How to keep a bucket of water from freezing by only natural means?

6:59 AM

10

Strange question. I am working on a fictional story where a person has to carry a bucket of water for hours during a blizzard. Is there any natural way to keep a bucket of water from turning to ice in below-freezing conditions like that? Assume there are no other materials available except what c...

19 upvotes on a comment that says this would be better at Worldbuilding, but zero flags, and zero votes to close. Seriously, people....

3

@DanielSank I don't truly understand it myself, to be honest

@Danu Awwww, really? Nothing's that complicated...

but from what I can tell, the gist is this: when you have a model for some system (e.g. a physical theory), the model ignores the fine details of the system's behavior, for some definition of "fine". Renormalization is a way of constructing the model so that it doesn't depend on that definition.

@DavidZ That is helpful. Thank you.

It would be awesome if there is a reasonably simple physical system in which this idea is useful.

There probably is, and I would love to come up with an explanation, but I'd have to actually understand renormalization first :-P

@DavidZ Right.

user54412

7:08 AM

@DanielSank What if this idea is only useful for poorly-defined theories, and any self-consistent, sensible theory will have no such need for it?

@ChrisWhite Then the example would be awesomer, because it would demonstrate that!

:)

I think this magic example exists, but my reasoning is mostly via unfounded association to something else.

9:15 AM

@Danu That was hidden in "$p$ is small" and not having said condition on $\rho$.

Danu

9:31 AM

@DavidZ Damn :P The problem is this issue that was raised earlier in meta: People cannot VTC to arbitrary sites (although I guess it cannot be nicely fixed)

Want me to flag it now?

9:54 AM

@DavidZ I can only do so much with 24 close votes per day :P

@ACuriousMind if you're using up your daily allotment of close votes I'll give you a pass :-P I can't imagine that every one of those 19 people - well, 18 who are not me (but also the comment author) is out of close votes though!

@Danu couldn't hurt

I definitely agree that the migration system is messed up, but even if people can't vote to migrate to a certain other site, they should still be voting to close as off topic

@DavidZ Unless I have a very busy real life day, I'm almost always out of close votes before the end of the day lately.

It's probably worth thinking about how to encourage more close voting from other 3k+ members

3

10:10 AM

I think we've talked about that here before, no one had a really good idea. There may be some people who are unaware of the review queue, but surely the close button is not something they could be unaware of, right?

Some people probably could be, but not so many

I suspect the problem is that people think closing and migrating are mutually exclusive, whereas one is supposed to be a prerequisite for the other

1:09 PM

@ACuriousMind Is it just me, or is appendix A in HE unintelligible?

At least, the notation is so bad it hurts.

His "derivation" of Newton's law hurts. "Now if $dt$ is constant"

I think that is usual for old texts

Ever read something from Newton? Pure gibberish :P

Proof writing has come a long way in the past 200 years.

@DavidZ More badges!!! :P

He uses $i$ as a proportionality constant and $a$ for the speed of light...

2:04 PM

@Waffle'sCrazyPeanut You can get 3 badges from the reviews: Custodian, Reviewer and Steward. What more could you get?

Do badges really encourage people that much?

Besides, if that's the motivation, once someone gets all the badges, they're done. It'd be nice to have a more lasting motivation.

Perhaps they could care about the site? :P

@DavidZ The gold ones do

But, somewhere along the way, I discovered I was actually enjoying doing the reviews in which I got the gold badges. So I keep doing it

And I also wanted to surpass Brandon in one queue (ended up passing him in another one or two)

@ACuriousMind haha :-P

That would be the best way

Lol...filling out an application and two questions are Estimate the number of hours you have spent programming for class and Estimate the number of hours you have spent programming outside the classroom

Low-ball estimates: 3k and 10k, at least

2:12 PM

I suspect the best focus might be on increasing the number of people who are doing reviews and casting close votes at all

@KyleKanos I believe that makes you officially an Expert

@DavidZ Possibly. Though some of that time is spent golfing...

(which isn't really useful in a professional setting)

I dunno, when I think about all the time I spent in college calculating the rotation frequencies of orbiting beer cans or the like, I have to imagine that's pretty much "physics golf", but it still counts

I think

@ACuriousMind @DavidZ I would review if I just remembered to. I just never think about it.

@0celo7 Do you see an orange box + white number at the top of the page?

(top of the main page, not chat)

Honestly, I almost never go through the review queues either. But I do scan down the front page looking for questions which look like they might be close-worthy. And I also have the mod flag queue...

2:25 PM

@KyleKanos No.

@0celo7 Okay.

I hardly go on the main site anyway.

I have plenty of my own questions to answer.

It appears on every question page, tag page, help center, etc. In case anyone's curious:

2:38 PM

@KyleKanos I'm not sure, but I think I filled out that exact same application a month ago

Data sciences course?

yessir

that's the one. Those questions made me laugh too

I still haven't heard back from The Bank, so I'm getting nervous and sending out apps where I can. This one was just another one of the lot.

likewise

I was told that one of the higher ups at The Bank would be forcing them to make a decision 'soon.'

That was 2 weeks ago :/

2:50 PM

41 mins ago, by David Z

Besides, if that's the motivation, once someone gets all the badges, they're done. It'd be nice to have a more lasting motivation.

So what, more badges?

Yeah, that could motivate some fellas (considering the gamification scheme of SE)

There is actually a member who hit 1001 reviews and then stopped :(

Hah! Exactly...

But I think he stopped on the site altogether too

2:53 PM

But, other than that, I don't see any idea to motivate people to VTC :/

what about candy? Delicious candy

T-shirts?

@KyleKanos I thought of swags. But, wouldn't that be too-much for a clearing VTCs? :D

Maybe

Q: Remove the flag notification in the top bar when I have done my job with it

Phew.. I've cleared some questions from the queue :)

Emilio Pisanty

3:28 PM

@DavidZ Yes, but that number has mostly lost its meaning as it's often not actionable and rarely represents the amount of reviews one can do.

e.g.

30

I have the moderator privileges on Code Review. Even though it's quite rare that flags appear over there, it is still quite annoying that once I have done my job with a flag and therefore cannot do anything else with it, the flag in the top bar remains there. Why do I have to keep seeing that fl...

feature-request flags top-bar

15

Q: Please dim the color of the review task counter when there are no actionable tasks

I am glad to notice that the massively annoying refusal of the 10k flag counter to disappear when I'm not needed has been appropriately dealt with via the extreme decapitation method of simply eliminating the 10k flag queue. As of a few days ago, the orange-ish counter on the top bar now links to...

feature-request review top-bar

22

Q: Modulate the review notification's color to reflect changes, or make it dismissible

Following another feature request that was completed yesterday (Notify users of possible reviews on toolbar), users of several sites have noticed a persistent notification in the top bar for flags that need reviewing. Previously this notification pertained only to suggested edits, but it now disp...

feature-request review design top-bar notification-bar

user54412

4:00 PM

@DavidZ As you have said many times before, being better suited for another site is in no way a contributing factor to being closed. That comment says nothing about whether or not the question is on-topic here.

7:08 PM

@DanielSank Probably the simplest example of renormalization, taught in any first course on stat mech, is the Kadanoff decimation procedure of the Ising model. It is useful near the phase transition points where the system under study becomes scale free and can be entirely described by some scaling exponents. Surprisingly, even systems that seem very different can sometimes belong to the same universality class when it comes to their phase phenomena.

@Danu You like g1-f3? Or something else?

9:55 PM

@ACuriousMind The reason why we have mandatory counseling is because a big part of the US News college rankings is "% of students who finish in 4 years".