The h Bar

heather

3:01 PM

@BernardMeurer, there's several keyservers offered, which one is best?

Bernard Meurer

Doesn't matter :)

Pick the one that's easiest to type

Also, I hadn't exported my privatekey, that was just my key ID

v. good

heather

hkp://keys.gnupg.net

Bernard Meurer

What's your key ID?

Qmechanic

@ACuriousMind and reviewers: Could one argue to keep it open because of the physics word space-time in the question formulation, cf. this meta discussion?

Bernard Meurer

@heather

heather

3:08 PM

@Qmechanic, should i put the word spacetime in all my math questions here then?

or any physics related word?

Bernard Meurer

Also, which server is that, idk it

Export to hkp://pool.sks-keyservers.net

heather

@BernardMeurer, id: 4D6B346C

that isn't a option

that key server

ACuriousMind

@Qmechanic I guess one could argue that but the physics question would be why do we use a manifold to model spacetime, not what is a manifold. The answers touch on the former but most seem to interpret the question to be mainly about the latter, which is purely mathematical no matter how you look at it.

Bernard Meurer

@heather I hate Ubuntu

@heather I find nothing containing that ID

@heather Settings Configure > Key Servers

Add that keyserver

heather

okay one moment

there's no settings>configure>key servers, there's settings>configure shortcuts, settings>configure toolbars, and settings>configure kgpg

Bernard Meurer

3:15 PM

Configure kgpg > Keyservers

heather

okay

Bernard Meurer

Let me know once you have exported to hkp://pool.sks-keyservers.net

heather

exported

Bernard Meurer

Got it!

Do you have a browser on the Linux side?

heather

a bad browser, but yes

Bernard Meurer

3:19 PM

You can get my key by clicking on Key Server Dialog

And searching for my name

"Bernardo Meurer"

@heather Install Firefox?

sudo apt-get install firefox

ACuriousMind

lol, do all your account names contain "nerd", @heather?

Bernard Meurer

@ACuriousMind I have that theory too, lol

She'll regret it when she's older and needs a work email :P

heather

@ACuriousMind, a lot of them, yeah =P

@BernardMeurer, found you

lemme install firefox

Bernard Meurer

:)

heather

do I "import"?

Bernard Meurer

3:23 PM

Yeah

heather

k

Bernard Meurer

Go on File > Editor

Write me a message!

Click encrypt and select me

heather

it says no key imported =(

Bernard Meurer

Do I show up on your key list?

heather

no, i'll try to import again

got it to import

Bernard Meurer

3:27 PM

:)

heather

now you're not showing up when I click encrypt

=/

Xasel

hey anybody here expert in fluid dynamice

and strong gravity stuff

can he//she kindly share their expertise here:

0

Q: Behaviour of Fluids under strong gravitational field

We were being given intro to fluid dynamics at our school So the thing that sparked me up is $ g$ in expression of: Static pressure of fluid Bernoulli Principle I am curious how fluids(especially liquids) will behave when they are near or at strong gravitational fields and when they approach...

Bernard Meurer

@heather Right click my key

and click sign

heather

okay

which sign? "sign key" "sign user ID" "sign and mail user id"

Bernard Meurer

User ID

and Key

In any order

ACuriousMind

3:31 PM

@BernardMeurer Don't you want to explain what signing is first? :P

Bernard Meurer

@ACuriousMind Nah, you can do it :P

heather

okay

I'm chatting from the linux side of my computer now

yay firefox!

ACuriousMind

Well, signing another user's key means that you have, in some way, verified the user is who they pretend to be.

Bernard Meurer

:)

ACuriousMind

Conventionally, I would only sign the key of someone I have met in person.

Bernard Meurer

3:33 PM

@heather What ACM is saying is important

ACuriousMind

The idea here is that of a "web of trust" - if people I trust have signed another user's key, I will be reasonably sure they are who they say they are even if I have never met them.

heather

okay...

well, i trust the bernard meurer is bernard meurer

which is kind of sad, because this online stuff is the stuff you're decidedly not supposed to do

but i do trust him

so

ACuriousMind

Well, his key was generated today and doesn't have any signatures. That's suspicious ;)

heather

suspicious?

how so?

oh...well. um.

Bernard Meurer

Because I could be a russian spy

that killed the real me

ACuriousMind

3:36 PM

I'm kidding. But generally I would be suspicious if the key someone sent me was just generated, unless I just walked them through how to do it

heather

a bit late for that. 0_o

Bernard Meurer

and created a new keypair pretending to me me

so we can talk and I can steal our valuable info

heather

right

so, i've signed you

ACuriousMind

In this case we have, however, witnessed the reason why the key is fresh :D

heather

and i've written a message, i've clicked encrypt, clicked you, and now it says "begin pgp message" in the text editor

so now what?

Xasel

3:37 PM

I guess this will be added to list unanswered question of mine:physics.stackexchange.com/questions/298052/…

heather

wait a bit @Xasel, if someone wants to/can answer it they will

Bernard Meurer

@heather See if you received an email

heather

in my gmail (open on the chrome side) i'm not getting an email

Bernard Meurer

Wait, then

Open it on the linux side

SO

heather

see...well...did i tell you that my chromebook has, um, issues with that?

Bernard Meurer

3:39 PM

I have to go have lunch

heather

enjoy your lunch!

Bernard Meurer

Get cracking to decrypt that

There is a signature, telling you I actually wrote that message

and a message, just for you

@ACuriousMind Help her plox

I gotta go

brb

heather

bye

I got it decrypted!

=D

@BernardMeurer, ^

John Rennie

@heather @BernardMeurer all good fun, but why wouldn't you just use gmail?

heather

(::shrugs::) because I'm a spy at heart

=P

John Rennie

3:50 PM

There is an undeniable entertainment factor in getting these things working, but the novelty has a tendency to wear off after a bit :-)

ACuriousMind

@JohnRennie The paranoid might say that the gmail encryption is symmetric TLS (right?), so using additional asymmetric RSA protects you against a wider variety of attacks?

John Rennie

and if you're an international terrorist you may worry about such things.

heather

oh, I'm sure @JohnRennie

but still

why not?

Bernard Meurer

4:27 PM

Okay, I'm back!

@JohnRennie To teach her about GPG :)

@heather

heather

@BernardMeurer, okay, decrypted, let me send you a message...

John Rennie

Too broad? Too little effort?

0

Q: Specific heat fermi gas bose gas in 2d

How can I find the specific heat of a T = 0K fermi gas and bose gas in 2d?

quantum-mechanics statistical-mechanics

heather

4:42 PM

@BernardMeurer, ^

ACuriousMind

Hey you kids know you can send those messages via email, right? :P

heather

=P

teenager @ACuriousMind ;)

ACuriousMind

I'm also a bit worried about the "v1" there

heather

what about it?

ACuriousMind

The current stable version of GnuPG is 2.0.30

heather

4:44 PM

oh...

how do I update?

Bernard Meurer

5

Q: Can't upgrade GNUPG?

I'm trying to upgrade my 1.4.14 GNUPG to 2.0.26 version and the repository has 1.4.14 version... I tryied removing it and building the lastest version from the official GNUPG website downloading its source code (2.0.26), but I can't do it! it is always 1.4.14! and gpg generates this key: -----B...

gnupg

meh, GPG 1 is still fine

@ACuriousMind What'd your Key ID

ACuriousMind

@JohnRennie No effort, homework-like.

Bernard Meurer

Lemme add you

GPG IS THE NEW FACEBOOK

heather

@BernardMeurer, your message isn't decrypting

ACuriousMind

@BernardMeurer 2D700203, but my point was that these messages are rather cluttering the chat and are of no interest to anyone but the two of you.

Bernard Meurer

4:47 PM

@ACuriousMind Are you on any keyserver

@ACuriousMind Okay, okay, we'll stop :P

Got you

heather

@BernardMeurer, nice, Make is the best!

Bernard Meurer

gmx.de? REALLY?

ACuriousMind

@BernardMeurer Should be on sks and mit at least

Bernard Meurer

Yeah, it's on sks

heather

sks?

Bernard Meurer

4:49 PM

It's the keyserver you got my keys from

ACuriousMind

@BernardMeurer At the time I made that, the 1 GB storage they offered was really good.

heather

oh, okay

Bernard Meurer

@ACuriousMind I forget that you're old :P

heather

Hmm, I found one person, but I don't know if it's right

ACuriousMind

@BernardMeurer Yeah, I think I have had that address for about 10 years now

heather

4:51 PM

well, okay, gmx.de is there, so that makes sense

ACuriousMind

Might be a little less, I don't remember

heather

it's weird associating a real name with you

Bernard Meurer

@heather If he has a viking name it's ACM

heather

yup, viking name

ACuriousMind

lol

heather

4:51 PM

many umlauts

ACuriousMind

my real name is not a secret

Bernard Meurer

@ACuriousMind Okay Martin

or should I say...

JOHN DUFFIELD

heather

er...that's not a viking name

whoa, that just got weird

gmx.de, i've never heard of that before

Bernard Meurer

I literally broke my entire encryption today

heather

because you shared your private key earlier?

Bernard Meurer

4:55 PM

I hadn't

but I freaked out and thought I had

so I deleted it

and revoked the key

ACuriousMind

Was it the fingerprint?

Bernard Meurer

Ye

But then everything was bound to it

heather

so you were freaking out and it was your public key all the time?

Bernard Meurer

and now I gotta unfuckup everything

Ye

heather

lol

Bernard Meurer

4:56 PM

I gotta start drinking less

heather

(::shakes head in sympathy::)

anyone want to help with a python infinite loop that shouldn't be happening?

Bernard Meurer

Now I'm anxious about drinking too much. I'm going to have a beer to relax

John Rennie

Purely out of idle curiousity, how do I look up a key id like the one ACM posted? Is there an equivalent of DNS for GPG keys?

Bernard Meurer

@JohnRennie Uhum, lemme get you a link

@JohnRennie sks-keyservers.net/i

It doesn't work too well

John Rennie

@BernardMeurer that doesn' find anything when I enter ACM's key ...

Bernard Meurer

5:00 PM

IIRC there are some really good windows GPG clients

Yeah here it's not working either

John Rennie

Not that I'm stalking him - I have no other ID to test with :-)

Bernard Meurer

but it works on GPG

E421C74191EA186C

Try mine

heather

mine's back in the transcript a bit

(my ID)

4D6B346C <-here it is

how do you know how many people have your id?

John Rennie

gives "no results"

Bernard Meurer

Yeah, idk what's up

heather

5:03 PM

eh, I do exist, I reassure you

::shrugs::

Bernard Meurer

@JohnRennie get WinGPG

SIGN ME PLZ

ACuriousMind

The website doesn't work for me, either, but Thunderbird's enigmail extracted the keys without problem

Bernard Meurer

Same here, kmail works fine

John Rennie

OK WinGPG is running, but I see no way to input key ids ...

Bernard Meurer

import keys

John Rennie

5:08 PM

It appears to offer only import of .asc files

Bernard Meurer

Bah, I was sure it was WinGPG the name of the good one

I'm on a roll today

Put that in a text file

and import it :P

John Rennie

Too late. It has been uninstalled.

My patience for things that don't work is severely limited these days.

Bernard Meurer

Well, there IS a good client for windows

I just seem to have the name wrong :)

John Rennie

google.co.uk/…

2

Bernard Meurer

GPG4Win!

Thanks Google!

heather

5:15 PM

@JohnRennie, "that bernard can't remember" =P

John Rennie

OK let's try that again ...

It worked :-)

Bernard Meurer

:D

John Rennie

The trouble is that having satisfied myself that it works i actually have no reason to use it :-)

Bernard Meurer

Lol, let's exchange illegal material

Jordan Evans

I having trouble asking a question on this site without it sounding off topic. I don't want to clutter the site with more attempts to ask off topic questions. Is this a chat room a place to get advice on getting my question ready or at least find out if it's appropriate for this forum?

Slereah

5:21 PM

Sure why not

John Rennie

@JordanEvans Hi Jordan, yes here is the ideal place to ask.

Jordan Evans

@JohnRennie exellent

I'm looking the data that will give me a number will tell me how much technology has subsidized the average person's life in modern society compared to hunter gather days or agrarian.

That question was off topic, so I need help with it.

Slereah

I don't really think you can really rephrase it in a way that's relevant to physics

you might want the sociology people or something

Bernard Meurer

Yeah @Slereah is right

Slereah

or history

Bernard Meurer

5:27 PM

Worldbuilding maybe

ACuriousMind

@JordanEvans What sort of "number" are you looking for? Life expectancy? Child mortality?

John Rennie

@JordanEvans I don't understand what that means.

Jordan Evans

I was assuming because one would be measuring energy/work it would make it appropriate for here.

John Rennie

What does subsidy mean in this context?

Jordan Evans

@JohnRennie For example, once we had to pick our crops, now we have machines do the picking. Energy and technology has subsidized our lives. I'm guessing the work we once used to do can be quantified. That amount is the subsidization.

Slereah

5:31 PM

it is really a question that would be more at home on the history SE, I think

John Rennie

I thnk you mean how much has technology improved productivity ...

Hi @Copernic

Jordan Evans

@JohnRennie That is good way to say it.

Bernard Meurer

@JohnRennie How can "leichester" be lester?

John Rennie

@JordanEvans in that case about 99%, possibly 99.9%, of current productivity levels are due to technological developments since our hunter gatherer days.

@BernardMeurer that's the way it is. Logic doesn't apply to these things.

Bernard Meurer

What the hell

Jordan Evans

5:33 PM

@JohnRennie Okay, so what's a good way to ask that for this site or is really not appropriate for this site?

ACuriousMind

@JordanEvans Work, as measured by the physical unit "Joules", is a rather poor measure of "productivity" or progress. How difficult, time-consuming and relevant a task is is almost completely unrelated to how much physical work you have to do to complete it.

Slereah

Not appropriate

John Rennie

I don't think it's appropriate here. Sorry.

ACuriousMind

Your question is not about physics, it's about economics and sociology

heather

is there an economics/sociology se?

Slereah

5:35 PM

Yes

John Rennie

Since @Copernic is here, this is a potentially interesting question:

1

Q: Does earth rotate in a shorter time at 0m than at 5000m?

We know rotation period of earth (stellar day) is 86164.098 903 691 seconds of mean solar time. At 0m time is supposed to be more dilated than at 5000m because of gravitational time dilation. Then hypothetically we count less nanoseconds at 0m relative to 5000m of altitude. Then assuming this ...

general-relativity time relativity earth time-dilation

heather

well then, @JordanEvans, try the chat room on economics/sociology/whatever se

John Rennie

Does a very rotating rigid body develop internal stresses due to time dilation within it?

Jordan Evans

Thanks, I see.

ACuriousMind

There are no rigid bodies in relativity

John Rennie

5:37 PM

@ACuriousMind one where in the steady state the shear is everywhere zero

ACuriousMind

And yes, I'm pretty sure a body will be ripped apart by internal stresses before you will noticably detect "time dilation"

Jordan Evans

The shoulders of giants, the great subsidy.

John Rennie

@ACuriousMind I don't mean a Ehrenfest disk type rotation, I mean rotation like the earth is rotating.

ACuriousMind

@JohnRennie Where's the difference, except for the Ehrenfest disk rotating much faster?

John Rennie

Since the gravitational time dilation varies from the core to the surface does that effectively mean the angular velocity changes with depth.

Copernic

5:39 PM

1

Q: Does earth rotate in a shorter time at 0m than at 5000m?

We know rotation period of earth (stellar day) is 86164.098 903 691 seconds of mean solar time. At 0m time is supposed to be more dilated than at 5000m because of gravitational time dilation. Then hypothetically we count less nanoseconds at 0m relative to 5000m of altitude. Then assuming this ...

general-relativity time relativity earth time-dilation

John Rennie

Assuming the velocity of rotation is small enough for special relativistic effects to be negligable.

ACuriousMind

@JohnRennie Well, that depends in what frame you define "angular velocity", no?

Copernic

You said "Everything (except c of course) is faster in a dilated frame. That's how time dilation works." Twin paradox doesn't work that sense.

John Rennie

@Copernic the twin paradox works in exactly that sense:

39

Q: What is the proper way to explain the twin paradox?

The paradox in the twin paradox is that the situation appears symmetrical so each twin should think the other has aged less, which is of course impossible. There are a thousand explanations out there for why this doesn't happen, but they all end up saying something vague like it's because one tw...

special-relativity time reference-frames relativity

And see also:

41

Q: What is time dilation really?

Please will someone explain what time dilation really is and how it occurs. There are lots of questions and answers going into how to calculate time dilation, but none that give an intuitive feel for how it happens.

relativity time-dilation

heather

-2

Q: Can Tachyons at Rest be able to Resist the Gravitation Pull of a Black Hole?

I'm new here, but recently I have been looking around for things on tachyons and black holes. I understand that because, theoretically, tachyons can travel faster than the speed of light, they would be able to escape a black hole due to them possessing a speed faster than a black hole's escape ve...

black-holes tachyon

is this really off-topic? it seems on-topic to me...

ACuriousMind

5:43 PM

@heather It's unclear what it's asking. Tachyons are not expected to have "positive mass" and they can't be "at rest".

John Rennie

@heather for that question to make sense you have to define the equations of motion for your hypothetical tachyon.

As it stands the question is unanswerable.

I VTC'd as non-mainstream.

Copernic

"Everything (except c of course) is faster in a dilated frame. That's how time dilation works."

Even human cell life cycle, right? Then you are telling me that both twins have the same apparence, but one is older than the other one.

John Rennie

@Copernic I'm telling you that you need to read the articles I linked to understand what time dilation is and how it works.

heather

@ACuriousMind, @JohnRennie, that makes sense, thank you.

Copernic

I read it! Thx

John Rennie

5:45 PM

The twin paradox is probably the single worst understood physical situation in all of science.

ACuriousMind

@JohnRennie The twin paradox is probably the single worst ~~understood~~ explained physical situation in all of science.

John Rennie

@heather If you're intrested I can recommend an excellent book on tachyons, FTL travel, etc. I know, I know, yet more interestign books :-)

@ACuriousMind not now it isn't (John says smugly :-)

heather

@JohnRennie, I'd be glad to read it =) I love exploring breaking the laws of physics

Copernic

"Everything (except c of course) is faster in a dilated frame. That's how time dilation works." I am sorry, but I disagree.

ACuriousMind

@JohnRennie I'm rather sure the professionals understand it perfectly fine. They're just, for some unfathomable reason, fond of acting as if it's all a big mystery.

Same as with the virtual particles/quantum fluctuations schtick - they know better, they just act as if they didn't for reasons I don't understand :P

John Rennie

5:49 PM

@heather amazon.com/Time-Travel-Warp-Drives-Scientific/dp/022604548X

It's a really well written book. Enough maths to be interesting without so much maths it's impenetrable.

@Copernic An observer chooses a coordinate set, and one of the coordinates is $t$. All observers do this. Everything is then measured using the coordinate time $t$.

heather

ooh...what level of maths are in there? @JohnRennie

John Rennie

Time dilation happens becauise a different observer will in general be using a different set of coordinates, and the two $t$ axes will not match up.

That means different observers assign apcetime events to different values of $t$.

But with a single observer's cooordinates $t$ is just a time axis as we (think) we all understand.

@heather You would have no problems with it.

The level of maths is around A level as taught in the UK, i.e. ages 17 to 18, but you're easily up to that level already.

heather

@JohnRennie, okay, I will most certainly add that to my list, it looks incredibly interesting!

John Rennie

If you wanted an ebook then erm, cough, a friend of a friend might have a copy.

Just to decide if you want the hardback of course :-)

heather

gotcha...i think i'll just purchase it; i prefer physical books =) thanks for the offer though!

John Rennie

5:55 PM

@Copernic the point is that an observer at some distance $r$ from the centre of the Earth chooses a time coordinate and in that coordinate system the angular velocity of the Earth has some constant (i.e. independent of depth) value.

An observer at a different height $r'$ does the same and because their $t'$ axis doesn't match the other observer's $t$ axis they measure a different, but still constant, angular velocity.

But I think there is some interest in calculating the four acceleration for corotating points inside the Earth to see what the value of $a^\phi$ is and whether it varies with depth.

Emilio Pisanty

@JohnRennie I found this today, it feels strangely relevant

Bullshit

Bullshit (also bullcrap in the US) is a common English expletive which may be shortened to the euphemism bull or the initialism BS. In British English, "bollocks" is a comparable expletive. It is mostly a slang profanity term meaning "nonsense", especially as a rebuke in response to communication or actions viewed as deceptive, misleading, disingenuous, unfair or false. As with many expletives, the term can be used as an interjection, or as many other parts of speech, and can carry a wide variety of meanings. A person who communicates nonsense on a given subject may be referred to as a "bullshit...

i.e. specifically the last section:

John Rennie

@EmilioPisanty relevant to what? Our resident GR expert? :-)

Emilio Pisanty

> Bullshit asymmetry principle
> Publicly formulated the first time on January 2013 by Alberto Brandolini, an Italian programmer, the Bullshit Asymmetry Principle (also known as Brandolini's law) states that:
> > The amount of energy needed to refute bullshit is an order of magnitude bigger than to produce it.

5

John Rennie

@Copernic NB Emilio doesn't mean you, he's referring to someone else :-)

Copernic

And you are saying me that the observer in a dilated frame wil measure a quicker velocity than the other one. That is absolutely nonsense.

John Rennie

5:59 PM

@Copernic It isn't nonsense, it's what happens.

heather

@EmilioPisanty, so true.

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