The h Bar

Danu

00:06

Is this now closable?

2

Q: Theory that gets rid of gravitional wave

Is there any theory that gets rid of gravitational wave and still matches with all correct predictions made by standard physics theories? (e.g. General Relativity)

gravitational-waves

HDE 226868

Even more generally, should questions like this be updated with answers?

Danu

@HDE226868 I don't think so.

HDE 226868

@Danu Rationale?

My other suggestion was to close them.

Danu

@HDE226868 The question has a date on it.

It's still clear, and the answers given at the time are still accurate

In particular, they display the sentiment at the time, which is what the question was about.

One might migrate them to HSM now ;D

ACuriousMind

@Danu A question that is about the outlook of physics at one specific time is not really a good physics question, is it?

2

tabchas

00:13

Hey guys

skull petrol

Hi

Danu

@ACuriousMind You can VTC if you'd like.

HDE 226868

@Danu I read it as "Are the current detectors sensitive enough to have a good shot at detection gravitational waves?" The answer at this point in time looks to be a yes.

@ACuriousMind Don't forbid Lord Kelvin from making predictions!

@Danu We could steal some Higgs Boson questions that way. . . Although they're too old to migrate.

tabchas

New guy here, and have a question to pick your brain (freshman in Electrical engineering here). I have a silicone tube and I sealed one end using silicone and epoxy, and connected the other end to an air pressure sensor. How do I calculate the range of air pressures I can get varying different forces on the silicone tubing? Is it P = F/A?

Thanks in advance!

Danu

Sounds way too engineer-y for me ;)

skull petrol

00:19

Electrical Engineering

A place to talk with friends from the EE community about vacuu...

1

Sidarth

hallo

tabchas

@Danu @skullpetrol Hmm, isn't this more of a physics question? I'm trying to understand how compressed air in a tube works

Sidarth

@tabchas how have you sealed it

what does the sealed end look like now?

tabchas

@Sidarth I used silicone, kinked it, and put epoxy. But if its easier, we can just assume that I have a silicone pipe, perfectly sealed on one end, and connected to an air pressure sensor on the other

@Sidarth how would I go about finding how much air pressure the sensor sees?

I'm assuming the diameter of the tube is needed, as well as the length

but not sure how to put it all together

Sidarth

hmmm....

any specs on the sensor?

btw, is what you are doing a sensor for measuring air pressures in tyres or something?

@HDE226868....you work with planet hunters??.....is that someway related to zooniverse???

tabchas

00:37

@Sidarth here's the sensor: digikey.com/product-detail/en/MPX5010GP/MPX5010GP-ND/464055

well I just wanted to understand a bit about compressed air in tubing

Danu

3

Q: Should gravitational waves be discovered already?

Gravitational waves are not discovered directly (yet). But does this have any consequences? Should we suspect out theories are wrong or not yet? I found some data about gravitational waves suspected spectrum, like here, and wonder, where is it taken from? Where is the location of indirect measu...

general-relativity experimental-physics gravitational-waves

what do you guys think?

Sidarth

@tabchas "How do I calculate the range of air pressures I can get varying different forces on the silicone tubing? Is it P = F/A?" does this answer your question?" 1.45 PSI MAX"

@Danu what does he mean by "directly"?

tabchas

@Sidarth Well so what I am asking is given an air bladder of a certain shape and material, how do I calculate the air pressure inside the material (not using a sensor, but with math)? In this case, I'm looking at a silicone tube that has a diameter and length.

Sidarth

@tabchas the pressure inside the tube will be the same as that of the outside atmosphere. Since you have sealed the tube at one end and connected the sensor at the other end, you will still be measuring the same pressure. However, when you deform the tube afterwards, then maybe you can find the change in pressure because of the change in the volume of the tube.

I dont think pressure has to do anything with the shape and size of the bladder

Danu

@Qmechanic I'm about halfway through in terms of # of questions (but already in mid-November of last year time-wise!).

tabchas

00:55

@Sidarth Hmmmmm, ok that makes sense

Sidarth

@tabchas btw...what are you doing actually?

tabchas

@Sidarth so really all I need is a way to calculate the volume of air inside the given air bladder

Sidarth

volume=pi*r^2*h

;)

for this one...i.e.

tabchas

@Sidarth I'm doing an experiment to find how weight correlates to air pressure

Sidarth

weight of what?

tabchas

00:59

@Sidarth well its a side project and I wanted to see if I could weigh things accurately using air pressure.

nothing specific

just like if I put a 10lb weight on it, I wanted to see if I could correlate that to air pressure

Sidarth

@tabchas well....that is a fine idea! Its like we see the weights effect on the deformity of the bladder, which in turn changes the air pressure , by which we find the weight...

dmckee

@tabchas So...a pressure transducer has a strain-meter at it's heart. And a typical digital scale also has a strain meter at it's heart, but with less complicated mechanism attached. Your device will be cruder then necessary.

Sidarth

i think its a very nice idea.

dmckee

It's a fine idea for a hack, but it has it's limits. It would be bad engineering.

Sidarth

@dmckee I concur......but there is only experience gained in doing so

dmckee

01:01

Yep.

tabchas

@dmckee Curious, why is it bad engineering?

dmckee

Because a stain meter of similar precision used directly would give you a more accurate reading with fewer parts and fewer failure modes.

Sidarth

@tabchas maybe to him its like using Hammer tech rather than Stark Industries sophisticated bells and whistles...;)@dmckee

dmckee

On the other hand, if what you have is the pressure transducer then pushing it into service is just good field expedient improvisation.

tabchas

@Sidarth haha

dmckee

01:04

Both skills are useful.

Sidarth

@dmckee "The concept of temperature is rich in interpretations and levels of abstraction"

good one

this is fun planethunters.org/#/classify

tabchas

01:22

@Sidarth so I have my sensor all hooked up, but am getting some strange results. So ideally, once its sealed, its supposed to show a constant pressure right? But its slightly decreasing over time. Any thoughts/ideas?

Sidarth

@tabchas what is the time range for your measurement?

tabchas

@Sidarth not sure. as in I'm really just trying to find out the limitations of air pressure tech (list out problems I find, try to find solutions, etc.) So right now I'm just hooking it up and reading the sensor with no weight applied.

Since it is reducing gradually, this is a loss of air pressure that could be due to a leak?

Sidarth

a leak occurs only when you have pressurized air inside

wa\hat are the readings?

what*

i guess that you must be using an arduino or something to make something of the readings?

or have you plugged the sensor to your pc?

0celo7

@dmckee If you like parkour, I highly recommend Assassin's Creed II.

tabchas

yea its plugged into an arduino @Sidarth

readings are about 0.3psi

and its decreasing slightly over time

could it just be the sensor accuracy that's in question? Just trying to see if there is anything on the physics side that i'm not taking into account

the sensor is rated at +-5% (not the best sensor ofc)

dmckee

01:34

@tabchas Could be a leak. With that low a pressure difference it would run slow.

You can make up your own leak test solution with water, dish soap and a little glycerin. Your basic bubble blowing recipe.

Dab a little around all the seams and look for the little bubbles accumulating.

0celo7

How does one get glycerin?

Drug store?

dmckee

Yeah. As far as I know that's one thing you can still just go get.

HDE 226868

@Sidarth "Work with"? Not really. Volunteer to comb through light curves to see if there's a pattern, like most people? Yes. And yeah, it's a Zooniverse project.

It's been a while since I gave it more than a glance, though.

0celo7

Hmm, listening to early 2000s Gabber. This may or may not be HQ, I can't tell :D

@HDE226868 What?

Gabber is early hardcore (techno)

The producers were guys in their garages, I'm saying the original quality is probably so bad anyway that it doesn't matter that this isn't HQ.

@HDE226868 What??

HDE 226868

Ohhhhh. . . I thought you were referencing me. Never mind.

0celo7

01:48

I can't find this song anywhere but some dude's Soundcloud

and he doesn't have a download button

Sidarth

had to take my dog out for a walk...

hmm....i cant see the link....it says "(removed)" here

@0celo7

@HDE226868 yeah...i just went through it.......its quite nice..:)

0celo7

@HDE226868 If you delete your comments you need to get rid of mine as well.

@Sidarth what

Sidarth

@0celo7 the music you are talking abt...

0celo7

Oh, I never posted the link, @Sidarth

But if you're interested, soundcloud.com/gordies626/alpha-twins-smack-my-derb

Sidarth

:)

listening

0celo7

01:55

Sadly a lot of this early gabber/hardstlye is not on iTunes or Beatport

I wonder if I just sent the producers a tweet if they'd send me the HQ version

I COULD get the vinyl, but not much I can do with that

@Sidarth it's...a bit of an acquired taste

As @Danu, this old stuff is typical emo music

(I'm not an emo)

@HDE226868 are you any good at analysis

FenderLesPaul

02:22

@Danu there's only one person there doing gravity stuff

Raphael Bousso

so I don't want to risk it

all the others do pure string stuff

0celo7

@FenderLesPaul Ah!

My analysis prof gave a challenge problem

I got two parts, can't get the third

let $(z_n)=(x_1,y_1,x_2,y_2,\dotsc)$ for sequences $(x_n)$, $(y_n)$

then $(z_n)$ converges iff $(x_n),(y_n)$ converge and $\lim x_n=\lim y_n$

I don't really know how to go about this...

after this I think I can complete the proof

@FenderLesPaul $(\Rightarrow)$ is easy: all subsequences converge to the same limit, and by hypothesis, $(z_n)$ converges.

user54412

in my mind both directions work pretty much the same

0celo7

I can't get the other direction...

user54412

fwiw I always visualize these things by coloring the elements

0celo7

What

user54412

02:35

say, x_n is blue by default

user54412

but x_n is red if it is within epsilon of the limit

0celo7

what

user54412

the forward direction says "assume there is an N such that z_N and beyond are all colored red; then x_{N/2} and beyond are all colored red, and same for y"

0celo7

Ah!

Lemme write up the proof, I think I have it.

Let $\epsilon >0$. Since $\lim x_n=\lim y_n:=z$, $\exists N\in \mathbb{N}$ s.t. $\forall n\ge N$, $|x_n-z|<\epsilon$ and $|y_n-z|<\epsilon$. But $x_n=z_{2n-1}$ and $y_n=z_{2n}$. So we have...something, don't know how to actually write this thing :P

Maybe I need $N/2\in\mathbb{N}$?

When I put the two statements together I get $\forall n\ge 2N-1$, $|z_{n}-z|<\epsilon$

user54412

exactly

0celo7

02:43

something like that

user54412

just one pedantic point

0celo7

Ok, well I don't know what to do about the pedantic point :(

user54412

the first N that works for x will be different from the first M that works for y

0celo7

@ChrisWhite Pick the max.

user54412

yes

0celo7

02:44

We've done that a billion times, not going to argue it again.

user54412

whether or not one can take the max (over an infinite set) is one of those pesky failure points for more advanced analysis

0celo7

What

user54412

that's where compactness or Zorn or something come into play

0celo7

I know what Zorn is

But what does Zorn have to do with $\max\{N,M\}$?

user54412

nothing really

user54412

02:47

I'm saying in other types of problems you'll want to take the max over a much larger set than one of two elements

0celo7

Oh, ok

Ok, so should I pick the first $N$ to instead be...what?

The prof once took off points because I ended a proof with $<M\epsilon$, so he probably wants it to end with $N$ as well

user54412

no what you did was right

0celo7

@ChrisWhite I know it's right, but the prof likes neat proofs.

Is $2N-1$ the right choice there?

user54412

looks good

0celo7

@ChrisWhite Ok, so I just make that $N$ an $M$ and write $N:=2M-1$, then it's neat?

user54412

02:53

?

user54412

is M the max of the integers from x and y?

0celo7

@ChrisWhite The prof takes off points if the final line of the proof is anything other than $$\exists N\in\mathbb{N}s.t. \forall n\ge N, |x_n-x|<\epsilon$$

So I can't have $2N-1$

357

03:17

@0celo7 nakahara defines tensors by $T: \bigotimes^p V^* \bigotimes^q V \to R$ but shouldn't it be the cartesian product instead of tensor product?

0celo7

@357 How the heck did he define $\otimes$?

What page? I should have the PDF here somewhere...

357

page 80.

0celo7

Uh, my PDF does not seem to have page numbers.

What section?

357

2.2.5

0celo7

It's clearly a typo, he has it corrected in the line where he talks about $\omega$.

357

03:21

I see.

so it should be

0celo7

Yes.

357

[insert large cartesian product symbol here]

ok

0celo7

@ACuriousMind ::cocks eyebrow:: rd.springer.com/chapter/10.1007/978-1-4684-0721-1_17

Secret

@357 $$\Huge{\times}$$

0celo7

That's a bit large.

357

03:29

@Secret try \large?

Secret

$\large{\times}$

357

:D

$T: \large{\times}^p V^* \large{\times}^q V \to R$

seriously...

0celo7

put {} around the crosses

357

same thing.

user54412

to be pedantic one should prefer a package that provides a \bigtimes or equivalent

0celo7

03:30

Listen to ^

user54412

they're different classes of symbol, and have different kerning rules

357

pse doesn't have that package.

0celo7

@357 you're bad at this

357

bad at what

0celo7

$$T: {\large{\times}}^p V^* {\large{\times}}^q V \to R$$

But that's not correct, either.

The $p$ and $q$ need to be on top.

And the kerning is messed up.

@ChrisWhite Is there a command to make a new bigoperator?

They didn't even try...

357

03:36

what latex font is that

0celo7

The Secretary's Handwriting.

@ChrisWhite What is the most-cited document in GR

Is it Hawking-Ellis?

user54412

@0celo7 \mathop

user54412

@0celo7 a very quick and probably wrong search tells me it's Weinberg with just over 5000

357

@0celo7 If you use mathtools package \bigtimes is defined and it has p and q on top.

I wonder if the typo will be corrected in nakahara 3rd edition.

will find out in 3 weeks!!!

0celo7

@ChrisWhite Weinberg's text on GR?

Or a paper by Weinberg?

user54412

03:45

the textbook

0celo7

Wow!

How many does HE have?

user54412

3500

0celo7

Where are you finding this?

user54412

ADS

user54412

I never could figure out how to use inspire, but that probably tracks citations better

0celo7

03:47

@dmckee Tutorial pls

user54412

also, particle physicists are vastly more prolific than astronomers, so it's no wonder Weinberg gets so much

0celo7

@ChrisWhite Is Weinberg cited so much because he had really up-to-date info on cosmology in that book?

I mean, hell, even Wald cites him 12 years later.

@ChrisWhite Is it normal that a HEP researcher publishes a book in an unrelated field and gets a massive amount of citations?

Or is Weinberg just a boss?

Wald has 3500 citations.

Oh, MTW has 5600 @ChrisWhite

@ChrisWhite You've probably cited MTW?

user54412

I don't understand. Certainly Weinberg wasn't up-to-date for long, given how dark matter wasn't full accepted, the universe was thought to be non-flat, and dark energy wasn't dreamed of at the time.

0celo7

Weinberg is 1972.

When was DM accepted?

Do you not understand why he has so many citations?

Or why I think he has so many?

user54412

@0celo7 not yet but I probably will

user54412

03:54

why he has so many

user54412

Rubin's paper came out in 1980

0celo7

Rubin?

user54412

Vera Rubin, who made velocity curve measurements for galaxies

0celo7

Oh, oh.

user54412

of course velocity curves had been constructed years before that (in someone's thesis, but I forget the name), just no one paid attention

user54412

03:56

and Zwicky was convinced of DM in the 30s

0celo7

Just like no one paid attention to the derivation of the Higgs mass using the 4 color theorem.

@ChrisWhite Face it, Weinberg's just a boss.

Anything he writes gets citations :P

His QFT book only has 1000.

The hell?

user54412

are you using ADS?

0celo7

Yeah

user54412

it's complete for astrophysics, but they may not have grabbed all the particle physics papers

0celo7

adsabs.harvard.edu/cgi-bin/…

He's still being cited o.o

How is a 1972 book on GR and Cosmology being cited in the 21st century

user54412

04:01

well, here's the refereed citations -- see if you can make sense of what they are

0celo7

@ChrisWhite How do citations actually work

If I'm writing about, say, some spacetime topology thing

Do I have to cite the Raychaudhuri equation?

user54412

it's a grey area

user54412

you generally don't bother to cite things everyone in your intended audience would know

0celo7

It's such a ubiquitous equation in the field

Have you heard of it?

user54412

yes, I know some tidbits of GR ;)

0celo7

04:04

Exactly

Ok, this dude takes the proper distance function for a flat FLRW universe from Weinberg

"The rest frame e-p density near
the pulsar surface is believed to be n ≥ 10^11 cm^−3
(Gedalin et al. 1998), while in the MeV epoch of the
early Universe , it can be as high as n = 10^32 cm^−3
(Weinberg 1972)."

user54412

lol

user54412

not like Weinberg was the first to write that down

user54412

in practice, mass-citations correlate with ease of finding and using the reference -- everyone has certain standard books on hand, but who's ever even seen Raychaudhuri's paper?

user54412

also, I personally feel citing a book without giving a page or chapter number should be forbidden

2

0celo7

Thank you

(for details, see Hawking and Ellis (1973))$^*$

$^*$ Page number FCK YOU

@ChrisWhite Weinberg's book is like 650 pages, too

It's not like you can just flip to the right page...

user54412

04:10

How appropriate a HNQ:

user54412

9

Q: Should authors omit statements / citations of well known results in response to referee requests?

I am asking this question to get further perspective on an issue that has come up with a student (undergraduate, mathematics) I am mentoring. At last summer's REU he wrote (in particular!) a solo paper. I was not directly involved with the research, but I gave him some feedback on the writing b...

publications citations mathematics

0celo7

@ChrisWhite Every time you post something from Academia you're complaining about how terrible those people are

user54412

Pete Clark is pretty reasonable actually

0celo7

I'm just wondering because I've been thinking about my future thesis

I wonder how much background material I have to give or source

user54412

theses are more background than typical journal papers

0celo7

04:14

undergrad thesis

user54412

even more so

0celo7

Have you read ACM's

It's pretty ridiculous

@ChrisWhite Suppose I do it on twistors. Will I have to explain the inverse function theorem, basic manifold stuff?

user54412

presumably not

0celo7

But having to explain sheaf cohomology is a safe bet?

user54412

One does not simply use sheaf cohomology without background information.

0celo7

04:20

I have no clue what it is

It's probably the dual of sheaf homology

0celo7

04:33

Are there any books on twistors by mathematicians?

@ChrisWhite What is the plural of "ansatz"

user54412

ansätze apparently

skull petrol

Ansätze

user54412

also, what part of "Chris White" looks German to you?

skull petrol

It could be the "White" part if your first name were "Blonde" :P

0celo7

sigh...

@ChrisWhite I speak german fluently

I wanted to know your gut feeling

@ChrisWhite What part of "0celo7" looks German to you

user54412

04:46

in English it would have to be ansatzes, right?

0celo7

@ChrisWhite Ok, that's what I was wondering!

If we steal the word from the Germans, do we also steal the plural?

user54412

I vehemently say no

user54412

then you end up in this mess where everyone retroactively wants to declare data to be a plural of a countable noun

0celo7

because you can't pronounce it?

user54412

the whole point of stealing something is that you're not beholden to its former owner's whims about how to use it

0celo7

04:50

@ChrisWhite I guess if we don't bother capitalizing it, there's no reason we should keep their plural either

skull petrol

How about "rent to own"?

0celo7

what

skull petrol

We'll borrow it as is until we get used to it.

user54412

someone -- I think from academia.SE -- once tried to convince me capitalization was a font choice

0celo7

umm

Academia.SE sounds like a strange place.

skull petrol

04:53

It is.

user54412

like, you can choose between Palatino and Book Antiqua, and you could choose between using capitals or not

user54412

I guess in that person's view my keyboard is multi-font enabled and I change fonts every time I press the shift key

0celo7

@ChrisWhite indeed.

skull petrol

05:09

Mathematik f ‎(genitive Mathematik, no plural) (study)

Perhaps ansatz should not have a plural also

If you're gonna steal it you might as well customize it

0celo7

05:51

@ACuriousMind The spider.

skull petrol

Eeeww

0celo7

That's what she said

No, really, that's what all the girls said

skull petrol

-_-

0celo7

Oh come on

What now

skull petrol

Does your gf like football?

TanMath

05:57

hey @MarkMitchison

@DanielSank hello! I haven't heard back fro you for a long time... is there anything you want me to do relating to my project?

@0celo7 I have a question!

Slereah

09:04

Hello the physics

skull petrol

hi

Secret

10:20

http://journals.aps.org/prd/abstract/10.1103/PhysRevD.93.041501
I have skim read this paper
Nothing about the evolution of its gravitational field suggest the outcome that Sciencedaily claimed (the cloest thing I can think of this is the paper mentioned the exponential growth of the field is smaler than modelled previously)
https://www.sciencedaily.com/releases/2016/02/160211142227.htm
How on earth did Sciencedaily get the idea that the paper's result imply you will not be crushed when falling into a black hole?

Slereah

11:05

arxiv.org/abs/1601.05120

arxiv link for you poor people

innisfree

11:54

@ChrisWhite sure, that was just one idea about how to maximise impact of PSE during these moments. I'd prefer verified members of an experiment etc (perhaps with a hat on their avatar), like verified celebs on twitter

ACuriousMind

@innisfree Mhhh, although I can understand your reasons, that would contradict the idea that it's the answer, not the answerer that counts

@0celo7 Not pictured: The smell? :P

John Duffield

12:24

@Secret : I don't know. I find myself disagreeing with things like this: "At the center of a black hole, density and gravity are infinite and the laws of physics and space-time, as we know them, cease to exist." And things like this: "A singularity evolves inside every black hole (BH), as guaranteed under very plausible conditions by the Hawking-Penrose singularity theorems [1]".

Physics Meta

0

Q: Maximizing potential of PSE around major announcements in physics

I don't think I need to tell you that recently there was an historic discovery that captured the interest of the popular press and general public, as well, of course, as that of the broader scientific community. As a consequence, we saw many questions about LIGO (see the ligo tag); some simple, o...

discussion feature-request

user116211

12:44

@ACuriousMind: I'm now reading Reif's Statistical Physics of the Berkeley course; it points at the same problems I were going through last few days. The book is quite good.

Electrical Engineering

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