The h Bar

1:40 AM

@BalarkaSen I talked to my advisor about Hsu's work, and he said that there's a well-known classical correspondence between solutions of certain PDE and Brownian motion. So it's conceivable that Brownian motion on a manifold can give you analytic information about the manifold. Furthermore, we know that the path space can give significant topological information about the manifold (think Morse theory). So it's not too crazy to imagine that Brownian motion can probe the path space, and ...

... you get topological information from it. The real surprise is that the program works out, because the details are very hard.

He doesn't think it's "worth it" because you have to develop so much machinery.

DanielSank

3:43 AM

What kind of answer does this admit?

Secret

[Random, dream inspired] Can we have a gas mixture that spontaneously compress itself until some equilibrium is reached? It seems unlikely given that increase in pressure usually proportional to decrease in entropy

John Rennie

6:49 AM

@Mystic Done

Secret

7:54 AM

1

A: Implications of achieving absolute zero

Real, true, honest-to-God absolute zero would destroy modern physics. With zero temperature comes zero velocity of the particles involved, and hence zero momentum. If the particles are contained an a known volume (which seems to be implied in the question), then the Heisenburg Uncertainty princip...

@HDE226868 are you saying such heat sink will be one where objects can transfer heat to it but can never raise its temperature, thus the equlibrium of the combined system will be at absolute zero instead of some temperature in between?

Jaime Gallego

@Secret A star's plasma collapses gravitationally when the core's thermonuclear reactions halt. If certain conditions are met, it will stay in equilibrium and won't eject mass.

Secret

Ah nice

BenRW

9:21 AM

Hi, I'm looking to understand why one of my questions is considered "not mainstream physics". As I'm a software engineer rather than physicist, I am starting from the assumption that the moderated who tagged it as such is correct — but at the same time, I don't know why they are, so I can't fix the question: physics.stackexchange.com/questions/316161/…

DanielSank

Op amp feedback has decided that op amps don't do anything.

@BenRW I've been around here for a while and i don't really understand what that tag is for.

John Rennie

Hi Ben. Extending GR to allow complex tensors isn't going to correspond to anything real, so it's just having fun with mathematics. I would guess that's why your question has been closed.

DanielSank

I disagree with that closure. It was modhammered and I think Qmechanic was in error.

John Rennie

The idea has been mentioned on the site before. Try searching for complex relativity or some variant of that.

DanielSank

@JohnRennie A lot of the mathy questions on the site are "just having fun with mathematics".

The question wasn't closed for being fun with math. It was closed because a single user had the power to close it and acted too quickly, IMHO.

John Rennie

9:28 AM

Yes, I wouldn't have closed the question myself. But equally I don't find myself outraged that it was closed.

DanielSank

I'm not outraged, but I'm annoyed.

This site isn't a zero sum game. We didn't gain anything by that question being closed.

The closure is obviously inconsistent with other activities on this site, i.e. other mathy questions are not closed.

Voted to reopen.

BenRW

"complex relativity" — that's a great keyword. Thanks!

(My knowledge is not enough to have known that's the right way to look for the idea)

I was slightly annoyed by the lack of detail in the reason, but "it's maths, go to math.stackexchange.com" isn't a problem for me. :)

(Well, perhaps my own quote there isn't right, but I get the sentiment is the point)

user228700

9:50 AM

@JohnR: Morning :-)

John Rennie

Hi :-)

user228700

How's it going?

John Rennie

I'm currently sat in my brothers kitchen in London.

In a bit we're going off to a butterfly centre to look at butterflies.

user228700

Ah, with family. OK, enjoy yourself :-)

John Rennie

Not that I'm that fussed about butterflies, but my niece and a friend want to go.

user228700

9:51 AM

Did u give ur niece that drive?

John Rennie

Yes. And a new battery for her laptop.

user228700

Cool :-) I also used to have two excellent uncles but they both changed quite a bit after marriage.

John Rennie

In return she spent several hours (it felt like hours) forcing me to watch her favourite YouTube videos :-)

user228700

@JohnRennie Haha, OK :-) It sounds nice anyway.

user228700

Were the videos Science-y videos? I'm a bit intrigued as to what she showed u :-P

John Rennie

9:54 AM

It's always nice visiting family. Well, for a short time it is :-)

user228700

@JohnRennie I can vouch for the second part of ur sentence :-P

John Rennie

@Kaumudi.H TED talks by James Veitch about spam e-mail. They were funny :-)

user228700

Omg yes, they really are x'D

John Rennie

Then videos of cats doing silly things. That wasn't so entertaining.

user228700

Lolol, OK x'D

user228700

9:56 AM

Have fun at the butterfly centre, then :-) We don't have one of those over here.

John Rennie

I plan to spend my time observing the wildlife - that's my niece and her friend :-)

user228700

:-)

user228700

Are u going to have a fancy lunch today, BTW?

John Rennie

My brother is a very good cook so I assume he'll be organising something

user228700

Oh, cool!

user228700

9:59 AM

Ah, it's only 10 AM over there.

John Rennie

Last night he made a pasta with a meat sauce. A simple meal but absolutely delicios.

user228700

I can't imagine what that would've tasted like but I'll take ur word for it :-)

John Rennie

My brother's family tend not to have a large lunch like me. Instead they have a dinner around 8 p.m.

user228700

Ah, ur brother's family is "normal" :-)

John Rennie

10:12 AM

Describing them as normal might be going too far :-)

user228700

Hehe.

user228700

I'm frustrated that ur comment about girlies liking soppy songs has garnered three stars >.<

John Rennie

Bing!

user228700

What? Nice! :-D Thank you.

John Rennie

To be fair, the girly girl stereotype exists for a reason.

That doesn't mean all women fall into that category.

user228700

10:21 AM

Well, yes, most stereotypes do exist for a reason but it's not particularly applicable to all women.

John Rennie

Agreed

user228700

And it's unfair that some people over here starred it, especially because most of them tend to assume the gender of new users over here ;-)

user228700

If neurology finds out that an affinity for subjects such as Physics does indeed have something to do with gender, gals like me and Heather-of all girls-would certainly not count as "girly" :-)

John Rennie

It was intended to be a throwaway comment, but attracted more attention that I expected or wanted. Sometimes that happens.

It's dangerously easy to drop in comments that maybe one wouldn't have posted had one been thinking about it.

user228700

Right. I understand.

John Rennie

10:26 AM

Someone on the SF Stack Exchange has asked about a short story they remember reading years ago, and I remember the story very clearly but cannot remember the title or author. That's soooooooooooooo frustrating!

user228700

Dyou know what's even more frustrating? I read three SF books that belong to a series but can't remember a single word from the title.

John Rennie

Didn't we talk about this a while back?

user228700

Nope, not this one.

John Rennie

What were they about? Can you remember anything that might jog my memory like character names?

user228700

Hmm, alright, so this is going to sound more vague than anything u've heard before but I'll give it a go--I think the story revolves around 4-5 children who have magical powers to control the elements (fire, water, earth)

user228700

10:31 AM

And no, no names or anything, all I can remember is this ^

John Rennie

There's a series about children being held captive in a boarding school like organisation. It turns out they are the children of gods and are being held hostage. The children have various god style powers.

user228700

Hmm, OK..? What is the name of this book/series?

John Rennie

Ah, now you're asking ...

user228700

Huh?

John Rennie

Children of Chaos? Something like that.

user228700

10:34 AM

Sigh, I don't think it's possible for me to even connect the dots if given the name of the book now. I only remember that it was gripping and beautiful. I borrowed them from the library so I may be able to check with them to find out which book series this was but again, this was like, 6 years ago and besides, I don't think my library maintains those kind of records.

John Rennie

Orphans of Chaos!

Orphans of Chaos

Orphans of Chaos is a 2005 science fiction, fantasy novel by John C. Wright. It is the first volume of the Orphans of Chaos trilogy that continues with the novels Fugitives of Chaos (2006) and Titans of Chaos (2007). == Plot synopsis == Five orphans - Victor, Amelia, Vanity, Colin, and Quentin (see Names and identities below)- who have spent their lives in a luxurious but strict and secretive British boarding school (Saint Dymphna's School and College for Destitute Children) begin to discover that they are different from the other children that they so rarely see. Unlike the village children, the...

user228700

::Googling images of cover of book::--I remember the cover :-P

John Rennie

Bing! :-)

user228700

What? No, I meant that I remember the cover of the book I have in mind but I'm googling to check if they match.

John Rennie

Ah - damn :-)

user228700

10:38 AM

Never mind >.< This isn't it but I don't care so much anyway. I've read a few books I have no recollection of. There was another creepy af book about a household which had a well in the garden, in which were seen faces of babies...and then those babies were born to their mums or something.

user228700

I used to be pretty sure that it's called "Faces in the well" or something but nope, that's another book.

user228700

OMG!!!

user228700

amazon.in/Faces-Water-Ranjit-Lal/dp/014333106X

user228700

Riiight, spoiler alert but those three girls were killed.

user228700

But YES, omg, I found the book!! :-D

John Rennie

10:41 AM

Cool :-) A comment on female infanticide?

user228700

Yep.

John Rennie

If you can remember anything about that book series let me know and I'll have a grub through the junkyard I laughingly refer to as my memory.

user228700

x'D I don't think there's anything I'm going to remember. This was 6-7 years ago and I've read a lot of books in these past years, even though it's nothing compared to how much u read.

user228700

Well, no, not in the immediately past years, I've read only like, 10 books in the past three years but before that.

user228700

I'm starving and there's nothing to eat :'-(

John Rennie

10:48 AM

You're starving? I have to wait until 8p.m. for the main meal. I could e dead by then! My emaciated corpse left slumped over my laptop!

user228700

There's always coffee and biscuits and money to buy whatever refreshments they allow at that butterfly centre, no?!

John Rennie

I could nibble a few butterflies I suppose.

Birds eat them, so they must have some nutritional value.

user228700

Am I psychopath or does that imagery sound beautiful not nasty for some reason? :-P

John Rennie

You're a psychopath :-)

user228700

:-P U have money, man!! I'm broke.

John Rennie

10:51 AM

Butterfly's bodies are kind of squishy and disgusting.

user228700

Yeah, I've killed a couple in my childhood after attempting to catch 'em.

user228700

Their colors sort of bleed into ur fingers.

John Rennie

I bet your immediate reaction wasn't "mm that looks tasty" :-)

user228700

What? NO, I don't wanna eat BUTTERFLIES!! I was only saying that using the words "nibbling" and "butterflies" together made sense and was kinda beautiful :-P

John Rennie

Ah, OK, in that case I retract the psychopath comment.

user228700

10:53 AM

Thanks very much :-P Can't believe u thought I wanna eat butterflies.

John Rennie

You're not a psychopath, just weird :-)

user228700

Says the man who buys two laptops a month :-P

John Rennie

When did I ever claim to be a normal, well adjusted person? I'm a physicist for heaven's sake!

user228700

:-P

user228700

OK, turns out that I'm not that broke, I have like Rs. 120 in my purse. I might as well go buy something, my kitchen is empty.

John Rennie

10:55 AM

Enough for a butterfly sandwich?

user228700

Have fun at the butterfly centre! :-)

John Rennie

Thanks. Enjoy whatever lunch turns out to be ...

user228700

@JohnRennie Great, this is a thing now -_-

user228700

@JohnRennie I've already had lunch. It's 4:30 PM here.

John Rennie

Ah, OK, afternoon tea then.

user228700

10:56 AM

Evening tea :-) Byebye!

John Rennie

Bye

peterh

11

Q: Why were well-known, valid solutions of the GR "off-topic" or "non-mainstream"? (suggestion)

I've found multiple times the closing of questions about the topic of general relativity/solutions of the einstein field equations. Examples are here and here. These judgement was: "not mainstream". High reputated physicists on the list seem to agree with my opinion (see for example John Rennie'...

discussion

0

Q: Complex valued spacetime curvature

I've just been reading about tachyons and tachyonic fields, and although they probably don't exist/are wildly unstable, I'm curious: What does imaginary mass do to spacetime curvature? Does ‘complex valued curvature’ even have a single plausible meaning the way real-valued curvature does?

general-relativity spacetime curvature tachyon

Dear Community, may I ask a correction?

The second post is now closed.

Mostafa

11:21 AM

The depressing story of India's sand mining

4

@YashasSamaga Almost cried by reading this :(

ACuriousMind

@JohnRennie @DanielSank @BenRW I believe this question was not closed for being "fun with mathematics" but for the exact non-mainstream reason stated: "complex-valued curvature" is not a mainstream concept, neither in physics nor in mathematics. Pseudo-Riemannian geometry simply does not allow one to speak of such a thing

The part about the tachyon is perfectly on-topic, if suitably rephrased: Asking what effects on curvature a (classical) tachyon would have is certainly a mainstream question about general relativity, although clearly hypothetical.

2

peterh

@ACuriousMind What if also the coordinates of the spacetime can be complex ones? It would essentially double the dimensions, and it would make the definition of the Gauss-curveture tricky, but it doesn't seem unimaginable to me.

@ACuriousMind The question was closed, because GR calculations have very often a said or unsaid sci-fi/worldbuilding/magic direction, at it leaded to the appearance of a closebutton-clicking reflex. But sometimes it is not okay, in my opinion this question is one of them, I think simply explaining what you wrote here would be an acceptable answer.

ACuriousMind

11:37 AM

@peterh General relativity has no reason to look at complex manifolds. And curvature in the pseudo-Riemannian sense would still be real-valued. Complex geometry has other objects that can be complex-valued, but pseudo-Riemannian geometry does not care whether the manifold has a complex structure or not.

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