The h Bar

12:01 AM

@barrycarter : no, make it the Earth's orbit round the Sun. The Earth goes round the Sun ten times, and you can count those orbits from afar. And if you could see some regular clock, you would see that it was synchronised with those orbits.

barrycarter

@JohnDuffield OK, but I'm going to ignore the Earth's small acceleration around the Sun. OK, but after I accelerate, only about 1.8 seconds has passed on Earth's clock, right?

John Duffield

@barrycarter : After you accelerate to 0.8c in 1 second according to your clock, the Earth's clock would read circa 1.2 seconds. Sorry, I got something back to front in my answer. I'll fix it.

barrycarter

@JohnDuffield OK, but essentially no time at all. Now, as I travel towards Earth at 0.8c, Earth's clock ticks off less time than my clock because of time dilation, correct?

John Duffield

@barrycarter : not correct. Your clock ticks off less time than Earth clocks because of the time dilation. Your clock ticks off 6 years while Earth clocks tick off 10 years.

barrycarter

@JohnDuffield OK, but special relativity says time in other reference frames is dilated.

@JohnDuffield Everyone else's clock moves slower than mine (if we're both at constant velocities and not accelerating)

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

12:13 AM

Hello

barrycarter

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ Greetings

John Duffield

@barrycarter : it doesn't actually say that. Who told you it does? Remember you could watch the Earth orbit the Sun ten times as you approached. And then if you could see some smaller clock on Earth, you would see it keeping pace with the Earth's orbit. It would tick out a year each time the Earth went round the Sun.

0celo7

hi

barrycarter

@JohnDuffield Time dilation is a fundamental principle of relativity, but note: en.wikipedia.org/wiki/… says "In special relativity (or, hypothetically far from all gravitational mass), clocks that are moving with respect to an inertial system of observation are measured to be running more slowly. This effect is described precisely by the Lorentz transformation."

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

@0celo7 Greetings

0celo7

12:22 AM

argh

why are books so vague

barrycarter

@0celo7 Why do you think "books are so vague"?

0celo7

trying to prove a consistent choice of light cone allows one to find an everywhere future pointing vector

not going well for me

barrycarter

@0celo7 Why do you say that?

0celo7

the books that have the proof either have (a) typos or (b) make claims I can't verify

barrycarter

@0celo7 Is it because have the proof either have a typos or b make claims you cannot verify that you came to me?

0celo7

12:25 AM

what?

ACuriousMind

lol, did you just turn into a chatbot, @barrycarter?

barrycarter

@0celo7 Can you elaborate on that?

ACuriousMind

You sound eerily like ELIZA.

barrycarter

@ACuriousMind I was wondering how long it would take to figure that out.

John Duffield

@barrycarter : there's no problem with time dilation. It takes you ten Earth years to get home whilst six years tick by on your clock. You and your clocks are time dilated. The problem is that somebody's been telling you Twins-Paradox porkies. As you approach the Earth, you count 10 orbits, not 3.6.

barrycarter

12:26 AM

@ACuriousMind That's literally what I was doing.

0celo7

@ACuriousMind what?

ACuriousMind

@barrycarter It would've taken 0celo7 a bit longer, I think :P

barrycarter

@JohnDuffield Yes, but if my clocks are time dilated compared to earth, aren't earth's clocks time dilated compared to me by relativity?

0celo7

I have no clue what you're talking about

barrycarter

@0celo7 I was feeding your statements into ELIZA, an old time "automatic chat" program.

@JohnDuffield Porkies? Seriously? Are you Glaswegian or something?

0celo7

12:27 AM

@barrycarter Huh?

barrycarter

@0celo7 Porkies = porkie pies = lies. Rhyming slang.

@0celo7 en.wikipedia.org/wiki/ELIZA

0celo7

what the HELL is this proof

this makes zero sense, maybe JD is right

barrycarter

@JohnDuffield The problem is: since I'm moving 0.8 c wrt to Earth and Earth is moving 0.8 c wrt to me, we both must experience the same effects on each other.

@JohnDuffield I don't call that the twin paradox, but, whatever you call it, it's a consequence of relativity.

John Duffield

@barrycarter : no. There's a symmetry in the Twins Paradox when you and I pass each other in featureless space and we can't say who's moving. But when you're heading towards the Earth it isn't the same. A year is the time it takes the Earth to orbit the Sun. And you see ten orbits as you approach. It's that simple.

barrycarter

@JohnDuffield So you're saying that I'm moving and the Earth isn't moving (except for its orbit around the Sun)? So my clock is slower on an absolute level?

John Duffield

12:38 AM

@barrycarter : yes. You're the one who took the 8-light-year trip and accelerated rapidly to 0.8c. You're the one who can measure the CMBR dipole anisotropy which demonstrates your motion with respect to the universe. You're moving, you're time dilated, and when we meet up you've got fewer grey hairs than me.

OK, I've got to go I'm afraid.

barrycarter

@JohnDuffield OK, it still sounds like you're claiming there is a preferred rest frame for relativity, which isn't what that answer said.

@JohnDuffield Awww.... next time we meet, let's forget about the Earth/Sun and do the same experiment with two rocks in featureless space.

Another way to think about it: suppose I'd been moving at 0.8c all along and never accelerated at all.

GPhys

@FenderLesPaul to what extent do I go to thank my rec letter writers? formally in person after I decide, letters? Do you know the norm

well, the first obviously

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

Sacrifice a goat? :D

barrycarter

Grad students are cheaper

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

My apologies to all the goat lovers in the room.

barrycarter

12:51 AM

"goat lovers" is perhaps not the best term to use here

In fact goat lovers will often sacrifice goats so the goats can't talk afterwards.

ACuriousMind

If the goats could talk beforehand, you've got a completely different problem.

John Duffield

@barrycarter : I didn't use the phrase preferred frame. There's a difference between that and the CMBR rest frame of the universe. Anyway, I really must go. Meanwhile remember this: special relativity is simpler than you think. Those rocks in featureless space are simple too. Imagine they rotate once a minute, and that this rotation serves as a de-facto clock. Meanwhile don't be suckered into believing in mystic woo by people who peddle it for a living, and don't want it made simple.

OK, I really must go now. Bye.

barrycarter

@JohnDuffield We can continue this later.

@JohnDuffield But with rocks in space, you have no idea if you're going towards them or they are coming towards you.

@ACuriousMind Goat hookers do it for grass?

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

Grass, ass, or gas. Nobody rides for free.

ACuriousMind

^my thoughts exactly.

barrycarter

12:57 AM

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ Grass for ass, then gas.

la la la nothing to see here

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

lol

ACuriousMind

You have to be careful which of those accounts you ping :P

barrycarter

Whoa, that was a typo

Oh, he's not even in this room, how did he end up on autocomplete?

ACuriousMind

I'm like 97% sure that they're the same user, though, so it's fine

@barrycarter autocomplete works for every user that's been in the room in the last 2 days

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

Raider nation is strong on all accounts.

barrycarter

1:00 AM

@ACuriousMind That is pretty cool.

ACuriousMind

@HDE226868: Worldbuliding deals in nightmare fuel now? ;O

barrycarter

Anyone else willing to explain special relativity to me?

HDE 226868

1:21 AM

@ACuriousMind Maybe I'm less likely to be traumatized by anything I read because I finished Brave New World over the weekend, and thus have already collected a lot of nightmare fuel, but yes, apparently.

That's a case where if I see the question on the Newest section of the front page, I simple pass it by unless a flag comes up.

vzn

Two defining features of quantum mechanics (nonlocality/ contextuality) never appear together / physorg

↑ lets see that derived from the axioms of current QM. if it cant be, then QM is incomplete! o_O

an even more radical idea: circumstantial evidence for local hidden variables...

0celo7

1:41 AM

This is the most nontrivial trivial theorem

0celo7

1:59 AM

A minimal amount of research about the thing you ask about would have shown you that there are many different vacuum solutions (different metrics with the same stress-energy). And another minimal amount of thought would tell you that it cannot happen that two different stress-energies produce the same metric. — ACuriousMind 2 hours ago

> And another minimal amount of thought would tell you that it cannot happen that two different stress-energies produce the same metric.

@ACuriousMind Really?

That's not trivial at all.

You have to prove that two metrics which have the same Einstein tensor are isometric.

I don't know how to do that.

In fact, that's likely not even true. You have to specify boundary conditions to get the metric from the Einstein tensor.

It's not uniquely determined by the Einstein tensor, so I don't see how one Einstein tensor can give a unique metric.

Hmm, you might want to disregard all of that, I misread the comment.

:)

JM97

4:06 AM

Could anyone please answer this question physics.stackexchange.com/questions/227121/…

0celo7

@ACuriousMind I just got a response from a prof 12 days late...

Quill

I just got an invation to join here, wat

Ferrybig

7:56 AM

Can someone rollback/delete this question

David Z

@Ferrybig wrong place to ask. Just flag it for mod attention.

user507974

8:08 AM

howdy gents

David Z

hi

user507974

@vzn how would that hold up to the bell inequality then

@DavidZ how goes your day

looks like a lot of the usuals arent online today

Slereah

Hello

David Z

I think this is a relatively quiet time

it's the middle of the night in the US

user507974

@Slereah that picture still gets me every time

@DavidZ true, prime time for ACM tho i would think

so how advanced is everyone here?

physics wise

Slereah

8:12 AM

I'm all about the legal business

Bass

9:37 AM

@ACuriousMind I see. Do you have a specific topic in mind which you need approved? Any plans for doing a PhD?

yuggib

@user507974 advanced compared to what?

ACuriousMind

10:11 AM

@Bass The topic is likely to be "quantum gauge theory" in one form or another, but there's a "definition" phase before I actually start writing anything during which that will become clearer. PhD plans are not more than "Yes, please" currently ;)

Slereah

10:25 AM

Lucky man

My PhD was mostly "no thanks"

ACuriousMind

You might have misunderstood me. I meant "Yes, please" is my answer to "Do you want a PhD?" :P

Slereah

I did not

Nobody told me "Do you want a PhD" :(

user116211

11:42 AM

Current is vector?

user116211

It's the surface integral of current density; that gives it a sense of direction.

user116211

But is current scalar?

user116211

Scalar quantity is a quantity, which is invariant under rotations. Current is not invariant under rotations. Also, the physical quantities can include pseudotensors (including pseudoscalars), and even things like sum of tensor and pseudotensor - such quantities are definitely not among those you listed. — Ruslan Oct 30 '14 at 16:15

user116211

In fact, it may appear scalar, depending how you define differential cross-section vector $d\vec A$ in definition of current $I=\int\vec Jd\vec A$. If you define it so that it changes direction under parity inversion, then $I$ is pseudoscalar. Otherwise, it's scalar. Or I may be wrong, and $d\vec A$ has some unambiguous definition. — Ruslan Oct 30 '14 at 18:02

user116211

Can anyone tell me whether current is actually pseudoscalar or scalar?

Slereah

12:07 PM

To check if a quantity is a scalar or a pseudoscalar, perform a parity inversion on the system

And see whether or not the quantity remains the same

user116211

@Slereah Let me google what parity inversion is.

Slereah

It is the operation $x \rightarrow -x$

user116211

@Slereah thanks.

user116211

like time-reversal.

user116211

@yuggib: o/

user116211

12:12 PM

I remember your time-reversal explanation with Abelian group.

David Z

12:22 PM

Something worth remembering: parity inversion flips one dimension of the space, not all dimensions

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

How's life?

yuggib

@user36790 \o

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

(^_^)/

user116211

@DavidZ $y$ will remain same?

David Z

12:38 PM

Yep, if you flip $x$, then $y$ remains the same

If you assume rotational invariance (which we always do), it doesn't actually matter which direction you flip

user116211

@DavidZ got the point; thanks.

David Z

Fun fact: the reason for this is that in even-dimension spaces (2D, 4D, etc.), flipping all dimensions is equivalent to a rotation

ACuriousMind

12:51 PM

Sigh...why do silly questions about "uncertainty" always go hot?

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

I feel ripped-off, I up dated my mini to iOS 9.3 and didn't get the "night shift" option :(

ACuriousMind

(that's a rhetorical question)

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

"We" know ;)

user116211

@ACuriousMind You can't do anything of that...... the misconception will go forever for non-physicists and you will be there to save them and we will be there to upvote you :)

user116211

Oh.....

user116211

12:52 PM

Damn.

user116211

I'm ignored by ACM.

user116211

::cries::

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

Why?

What's he got to do with it?

user116211

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ check the last few days chat.... you'd get it.

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

Link?

user116211

12:55 PM

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ wait....

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

...waiting

user116211

Don't want to remember....

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

reading...

user116211

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ Don't ping me with that again :(

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

You used to have different picture of a dog on your avatar, right?

user116211

1:01 PM

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ still there.

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

I see.

Wow, that got ugly fast :-/

user116211

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ hmmmm......

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

"wipe the floor with you..." That would get anybody's blood pressure up.

Definitely an instigating remark.

Live and learn.

user116211

Hope one day ACM will lift the ban ;/

user116211

Fingers crossed.....

user116211

1:14 PM

Waiting for that one day :|

David Z

Well, when someone doesn't want to listen to you, probably the best response is to not bother with them. Just try to post stuff that makes them miss out ;-)

i.e. good stuff

If someone chooses to ignore you when you are posting good content, it's their loss

and trust me, you can't please everyone

user116211

@DavidZ That's why I like you.... thanks.

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

Just say you're sorry and won't do it again and I'll star it...the rest is up to him @user36790

user116211

@DavidZ I'll learn; would increase my knowledge..... wow! I'm really feeling good. Thanks!

user116211

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ I've done it immediately then.... check that.

user116211

1:18 PM

BTW,

user116211

> To err is human.

user116211

@DavidZ: _/_

user116211

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ And I can't repeatedly say sorry to someone; I apologised once. That's it. I can't do it multiple times. I've not committed a sin.

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

Then let it go.

user116211

@Sᴋᴜʟʟᴘᴇᴛʀᴏʟ: Thanks, nevertheless.

Sᴋᴜʟʟ ᴘᴇᴛʀᴏʟ

1:28 PM

Thanks for the context.

David Z

2:55 PM

I believe our chat session is still in an hour, right? Time changes always mess me up a bit.

ACuriousMind

@DavidZ Yes

yuggib

let's do a chat session with no general relativity for once, since it is way too much discussed in this chat nowadays

0celo7

There's never GR in the chat sessions

I'm always in analysis lecture

yuggib

there's always GR in this chat

0celo7

That's not a bad thing!

yuggib

3:00 PM

I think that $\geq 70\%$ of the physics-related posts on this chat are GR-related

0celo7

I would say the GR that we talk about isn't physics

yuggib

Jan 20 at 14:21, by yuggib

geometry is boring

0celo7

I'm actually completely disinterested in the physics of GR

yuggib

Mar 1 at 15:24, by yuggib

as I said before, geometry is boring

David Z

We can talk about the homework policy

yuggib

3:02 PM

disallow homework-type questions completely

David Z

I had wanted to work up something new to discuss for that but I've been way too busy (and sick for a while, too)

@yuggib I wouldn't mind, but I think a lot of other people would disagree

ACuriousMind

@yuggib That's...kinda how it is already, isn't it?

yuggib

@ACuriousMind no, there's the show sufficient research effort, explain a concept, blah blah

ACuriousMind

At least, the questions "allowed" under the current policy I don't mind. The issue is not the policy, it's that it is inconsistently enforced.

David Z

and I think the main issue is determining what counts as homework. Or really, what criteria do we want to use to disallow questions, which should cover homework-like questions.

yuggib

3:03 PM

I think that disallowing them completely would be a far better deterrent

Terry Bollinger

or physics?

David Z

@ACuriousMind since it's been too long since we talked about this, can you remind me of the details of how it's inconsistently enforced?

yuggib

@TerryBollinger $\text{physics}\setminus\text{general relativity}$

0celo7

Screw you

vzn

@user507974 thx for asking. bells thm has very subtle loopholes which even "pro physicists" are not so aware of. bells thm focuses on "nonlocality" and there are other similar constructions for "contextuality".

0celo7

3:05 PM

If I was smart enough to do PDE I would do PDE!

ACuriousMind

@DavidZ Simply by not enough people voting to close HW questions, and too many people upvoting blatant homework questions.

yuggib

@0celo7 you're not the only one talking about GR a lot

0celo7

@yuggib Apparently the school has a proxy service so one can access Springer, etc. when off campus.

Terry Bollinger

clearly I am walking in late on, ah, discussions e.g. on GR?

yuggib

@0celo7 ah

nice

David Z

3:06 PM

@ACuriousMind ah, right. Agreed.

Terry Bollinger

Ah well, have a nice day all...

0celo7

Who talks about GR besides me and @Slereah

And @ACuriousMind, much to his chagrin

ACuriousMind

@DavidZ Closing a HW question after it has gotten three upvotes and two answers is not the deterrent closing is meant to be, and it shows. There are several users who've been here long enough to know that such questions are disallowed, and yet they keep asking them because they get what they want, even if the question gets closed.

David Z

Indeed. So the question is, how to do better?

We can complain all we want about the situation you're talking about, but it only helps if it generates ideas for improvement.

(not the question to you, specifically, just the question that we all need to think about)

vzn

suggest hw policy be a meta issue/ post. theres probably already a voted policy right?

ACuriousMind

3:10 PM

@DavidZ I don't know. I can't do anything to make other people enforce a policy, and I can't make them care about the site.

David Z

@vzn There is. We're trying to change it because it's not working.

vzn

@DavidZ so how about a meta post explaining why its not working and needs to be revised. ps nearly exactly same problem over on Computer Science where it shows up in chat/ meta & there is continued disagreement over it even by mods...

ACuriousMind

and I think I'm saying it's not the specific policy that's not working, it's that too large a fraction of our userbase simply doesn't care about policies.

David Z

@ACuriousMind right, but there are quite a few things mods can do, and there are quite a few more things that the high-rep regulars can do if enough of us agree on it.

@ACuriousMind yeah, that's worth keeping in mind.

vzn

@ACuriousMind that sounds like a (larger) "quality control" & "user conformance" issue.

David Z

3:11 PM

Maybe we can do something about that.

@vzn Well, the chat discussions are part of the process.

ACuriousMind

@DavidZ What do you have in mind?

@vzn Yes. That is also an issue. I know that at least some high-rep regulars feel the quality is getting worse.

David Z

@ACuriousMind For example, we could send warnings to users who repeatedly post homework-like questions, regardless of whether those questions get upvoted/downvoted/closed/answered. Maybe even issue suspensions. I'm not sure we should be doing that, but it is an option.

vzn

@DavidZ lol have a book on psychology called "talking is not enough" :|

@ACuriousMind that likely could/ can be quantified with actual statistics... anecdotally think its a common feeling among SE regulars/ high rep users...

ACuriousMind

@vzn No. Because the low-quality content gets upvoted, which is the problem.

vzn

@ACuriousMind ok but surely not by much? that is indeed sometimes a problem on larger sites. a problem that many smaller ones might "like to have".

ACuriousMind

3:15 PM

There's no statistic for "the average quality of an upvoted post on this site is lower than it was a year ago"

yuggib

@ACuriousMind It is getting worse...it's a (sad) fact

vzn

@ACuriousMind agreed. voting is the main quality control mechanism.

one datapoint: SE had those intermittent "site reviews". do they show up here? its a (small) attempt at independent measurement outside of voting.

0celo7

@yuggib you think this hw policy talk is better than GR?

vzn

@0celo7 and you think GR talk is better than GDP? :P

David Z

@vzn I don't think they do that anymore, at least not for graduated sites. We could do our own.

yuggib

3:17 PM

@0celo7 not sure...they are almost equivalently boring ;-P

0celo7

@vzn No, GDP trumps everything.

vzn

@yuggib so then what is not boring? anything? seems everything is boring to jaded chat regulars :P

0celo7

@yuggib Maybe I'll do some geometric PDEs next summer

ACuriousMind

@DavidZ Yeah, that...doesn't seem to conform to the idea of community moderation at all.

0celo7

My advisor's work is in Ricci flow and related topics

Slereah

3:19 PM

yuggib

@vzn I said that geometry is boring (for me), and site policy discussion has never been entertaining

Slereah

>looks it up

>Dynamic mirror Casimir effect

My sides

yuggib

necessary maybe, but not entertaining

David Z

For our next chat session (hopefully) I'll put something on meta that will make this less boring.

yuggib

@0celo7 that's already better ;-)

David Z

3:19 PM

No need to worry about it too much at the moment

yuggib

then when you get rid of that word "geometry", it's perfect :-D

David Z

There is also this ongoing saga of the 750 GeV bump we could talk about

0celo7

@yuggib why all the geometry hate

Geometry is so intuitive

yuggib

@0celo7 I do not hate it, we are just indifferent to each other

vzn

@yuggib so whats the (constructive) alternative to geometry then? ofc you know anything you say will be shot down :P (ps like discrete math more myself sometimes)

0celo7

3:21 PM

@Slereah well, is it wrong?

Slereah

Not a clue

couldn't find the paper about it

The paper they linked is not Aisha Mustafa's paper

I know that it's not a new effect

0celo7

Knowing what the Casimir effect is at age 19 is pretty impressive

Slereah

Birrell and Davies had it a while ago

I know that Eric Davis that crazy man included it in his interstellar propulsion report a while back

yuggib

@vzn without choice there are disasters in all math (including geometry)

0celo7

What

Slereah

3:22 PM

And i know that the dynamic Casimir effect is basically diddly squat in terms of thrust

yuggib

but as far as I know the constructivist theory by Bishop is one of the most appreciated

vzn

@yuggib what? axiom of choice?

Slereah

Also all those news articles all reference the same source

OnIslam.net

yuggib

@vzn yep

Slereah

Which makes me suspiscious

vzn

3:24 PM

there is a lot of stuff about new propulsion systems lately... heard about "ion drive" from a researcher last summer talk... apparently very controversial...

0celo7

Actually you need Zorn for a GR proof

Don't remember which one

Slereah

There's always stuff about new propulsion systems

Hype about Alcubierre goes back to the 90's

yuggib

@0celo7 yeah, you need Zorn or the geometric Hahn-Banach a lot in geometry

vzn

@yuggib certainly very much "sympathize" with constructivism as a computer scientist & am still waiting for someone else (expert) to make more of a connection...

0celo7

@yuggib I've never needed that

I don't do geometry in infinite dimensional spaces

yuggib

3:27 PM

@0celo7 you can encounter geometric hahn-banach in finite dim spaces as well, I am pretty sure

0celo7

When

I've never even heard of it

yuggib

@vzn I don't know how to connect directly constructivism and computer science, but apparently there is some lingering (and sometimes reviving) interest in mathematicians towards a constructive approach

vzn

@yuggib did you mention your phd thesis in here before? what is it?

@yuggib have noticed myself constructivism seems to be very close to something like "there exists an algorithm X such that..."

yuggib

Hahn–Banach theorem

In mathematics, the Hahn–Banach Theorem is a central tool in functional analysis. It allows the extension of bounded linear functionals defined on a subspace of some vector space to the whole space, and it also shows that there are "enough" continuous linear functionals defined on every normed vector space to make the study of the dual space "interesting". Another version of Hahn–Banach theorem is known as Hahn–Banach separation theorem or the separating hyperplane theorem, and has numerous uses in convex geometry. It is named for Hans Hahn and Stefan Banach who proved this theorem independently...

FenderLesPaul

@GPhys I don't think there's any canonical protocol

I got them simple gifts

yuggib

3:30 PM

@vzn my phd thesis is quite disconnected from what we're talking about... ;-P

vzn

@yuggib all math is connected (if X then Y). :P whats the title?

yuggib

@vzn yeah, the spirit is more or less that you should reduce everything to natural numbers and "counting"

@vzn classical limit of the nelson model? or something like that

it has been (sadly) a long time

357

hi

ACuriousMind

Hey @357, long time no see!

vzn

@yuggib oh thought you had math phd? its physics? arxiv.org/abs/1205.4367

0celo7

3:32 PM

@357 Thought you were dead!

yuggib

@vzn math phys is mathematics, and not physics ;-)

FenderLesPaul

@yuggib preach

357

you could have messaged me on skype to find out. what if I really was dead?

0celo7

@FenderLesPaul I'm going to work out 8.1.1 in Wald tomorrow with my advisor, there's a typo in it

2

Will send you the results

The correct proof is in BEE, but it's too damn vague

FenderLesPaul

@0celo7 Which one is BEE?

0celo7

3:34 PM

Global Lorentzian geometry

FenderLesPaul

Ah ok

@0celo7 And awesome, thanks!

0celo7

A different proof method is given in O'Neil

But I don't understand it either

vzn

@yuggib what year?

357

I left for only a few weeks and you guys all have weird profile images.

FenderLesPaul

I have the same one

:)

yuggib

3:37 PM

@vzn 2012

almost four years

0celo7

Why does that have two stars

Did I say something stupid

@357 Uh, I wouldn't talk to you anymore

vzn

@yuggib lol ok coders feel the same way about code

357

@0celo7 :(

yuggib

@vzn I don't know, but I have the impression that a four-year-old code is ancient :-D

0celo7

I should get a new profile pic

Suggestions?

357

3:42 PM

some weird shape.

0celo7

No

357

what does your current profile pic depict?

0celo7

A young lady playing an oboe

357

that's kind of random.

0celo7

That's what you think.

vzn

3:46 PM

@yuggib so are you working now on math, or physics, or math-physics? research?

0celo7

Some boring math stuff

Who knows

vzn

@0celo7 seems strange/ near contradictory youre interested in GR but not gravity waves :|

0celo7

That's physics

Pretty boring

ACuriousMind

Wow, chat finally managed to notify me of the chat session before it has started

The last few times it very helpfully informed me about it starting "10 minutes ago" or something like that

David Z

Yeah, the notifications of chat events seem quite neglected

vzn

3:58 PM

@0celo7 am now thinking maybe mistook/ misjudged/ misinterpreted/ prejudged some of your 0celo7ian philosophy. maybe it is not so much "nihilism" as "boringism"... with a few subtle differences :|

0celo7

I am in no way a nihilist

vzn

@0celo7 lol you admitted to some )( awhile back

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