5:00 PM
The other 2 are still suspended, thus they might have violated some rules
But diracpaul's is weird, his profile is nonexistent, as if someone deleted it

who is Diracpaul

I remember it was a user that a lot of people including mods chatted about 3-4 days back in chat. He is often praised for his answers

Did he make a fuss over something

I have no idea
he was mentioend
not present in chat

fussing is a good way to get banned when you are a good user
Trying to get mods to change their policies is risky business

5:02 PM
true

MODS THAT ARE ALL GREAT AND THAT I APPROVE OF
Hey there's an exotic matter tag
Energy conditions are my favorite things

I have one question involving exotic matter $_{\text{because my scifi needs it...}}$ It has been answered by someone pointed out something I overlooked, but I never get the time to revise it with a stronger condition yet to ask deeper
It is possible once I get the coordinate system to align properly, the forces will add in a way that cancels in the way expected for physics
and I might be able to answer my question in the process

Compared with MSE, my PSE questions are quite compact (laymane sense) and tidy

which one is the exotic matter one

5:13 PM
The still WIP one

Rigid body?
It's not really exotic matter related

oops I mislabelled
the one benath it
actually
The question in its current state is quite satisfactory because the answers ties to the question nicely

Well if you are too liberal with negative energy in your theory there is indeed quite a risk of VACUUM COLLAPSE D:
If there is no minimum energy, fields just drop down infinitely, emitting an infinite amount of energy
In existing negative energy states this isn't much of a problem though

yup, this has been hinted in the comments in "Is is possible to have a ghost mode that is also tachyonic?"

Well, define "possible"
It has been talked about, certainly
Ghost fields were somewhat of a popular topic in the 90's because they were a candidate for accelerated expansion

5:18 PM
are they commonly employed to model the inflation period or dark energy at those times?

Not really, no
As far as I know currently inflation is mostly thought to be from symmetry breaking
(false vacuums contribute to the cosmological constant, from what I recall)

I see
Btw That ghost field question has been answered, and I suspect it is more voted due to its close ties with theroetical physics or contemporary research focuses
My most highly voted question of my 11 ones is the magnetic monopole one, because despite of 50 years of no signal, it remains as a very hot topic

Well topological defects are a common feature of QFT
That has never been observed
it is somewhat frustrating

and that 50 years of no results is what caused me to be prompted to ask in the opposite direction

Well, they are not guaranteed to exist, even in QFT
They depend on initial conditions
and they can't form, since they are linked to topological charge
(although you can have very similar structures forming)

5:26 PM
I think I have read about them (such as the GUT monopoles) that they are postulated to form by phase transitions as the universe cools down after the big bang, which then the expansion then diluted their distributions

They are also not 0-1-2 dimensional structures, despite what is said in pop science
They are indeed built around a string, point or surface, but it's not a discontinuity either

GUT monopoles are like an onion
Dirac monopoles are connected by a dirac string

Of interest if you need them for sci fi things, though
There's a paper about the Casimir effect generated by a domain wall
It is quite interesting
It's a nice addition because doing QFT for the real Casimir effect is quite complicated since it's around a periodic structure
But a domain wall, that is pure QFT you can do by hand

Speaking about casmir effect, I think one of the most frequently mention topic about it is photon generation from the vacuum between after you somehow mess with the plates (detaisl forgot) and also the repulsive casmir effect whcih is of great interest to nanotech because it gives another way to manipulate the nanocomponents

Do you mean the oscillating mirror

5:32 PM
I think so, I vaguely remember it is something oscillating

popsci likes to report that phenomenon as "making light out of nothing"

You can generate particles with an oscillating boundary, yes
It's an old QFT in curved spacetime result

I am still MILES away from understanding the details, however

5:36 PM
^ will be answered in next post

O btw this is what I read when I was grade 11, and later year 1:
http://arxiv.org/abs/1105.5587

and that is precisely how I know slightly more about monopoles before I do uni physics

Well if you need weird spacetime things, feel free to ask me :p
It is my favorite topic

I have not decided the story yet, but I kinda have the setting set
and the most important of these is (and the reason why I have bee nreserarching about time travel for 3 years):

Time travel for civillain that is as common as travelling in airplanes, and it works by back to the future style (because I hate fate!)
It is a massive project, driven purely by my interest and desire to jot down the ideas I came up since grade 4

http://secretuniverse.wikia.com/wiki/Secret_Wiki

Back to the Future is indeed best

another important topic is negative mass, which is used to make wormholes
In fact, my negative mass article is one of the highly visited articles there, there's even one instance where Richard Hammond left behind a comment to refer me to it for ideas
but attempt to connect with him had so far received no response, probably because Iscrew up in writing that email and make it sounds more like an advertisement campaign
The scifi is the primary reason I end up reading a lot of monopole articles, and arguably the first time I read journal articles (which at that time it is way over my head thus I can only pick bits I understand at that time)

I'm not too fond of magnetic monopoles because the math is kind of horrid
domain walls are much easier to grasp

5:45 PM
I feel kind of silly... I'm struggling to prove basic Lie algebra stuff in smooth manifold language.

The progress in the worldbuilding of the scifi wiki was hindered mainly because I am still working on a back to the future type time travel that is comparable to general relativity concepts, which involve a lot of cross checking to ensure the maths behave the way expected for general relativity
which explains why there isn't much there, except articles which are products of some of my emotional tantrums

Like, if I work with "the representation of a Lie algebra" all the proofs become trivial. If I work with "a left invariant vector field on a smooth manifold with Lie group structure" I waste hours.

GR time machines tend to not work out too well
I did send a mail to Visser about a loophole I am wondering about, but still no answer!

and GR as far I know, are not very compatible with back to the future sytle time travel (also knwon as type 3 time travel)

well there's no "leaking" of causality
In any physics thing
it's just a plot device

5:48 PM
GR makes good "everything set to stone, i.e. type 1" time travel, though
Just CTCs is sufficient to do the job

you can look up branching spacetime for the other kind
But there isn't much

are they related to evett's many worlds interpretation, in that the branching spacetimes don't interact with each other and are branched because of soem events?

kinda
there isn't much work done on them
Basically spacetime has branching points at events where it can split into several copies

I think I have considered something similar before in my time travel model, but maybe my maths is not refined enough to join the dots

It is not nice math.

5:54 PM
my language teacher pulled me out of class today and told me I need to work harder because I'm way too behind
feels like high school :p

Back in 2010, I used to be a big fan of many world interpretation (and its lax version in popsci, which allow the copies to interact (hence the term parallel universe)),

but then somewhere in 2012, I found that the interpretation has some issues (such as energy conservation given so many universes are produced every second and (forgot hierachial or something problem).

Its lax version suffer even more. From analysing more than 30 works of time travel in novels, games, and other media, I found that it is simply WAY TOO MAELABLE and hence PRACTICALLY UNFALSIFIABLE to be useful in prediction

The MWI is an interpretation of QM

@FenderLesPaul that's what you get for being a bum

@Slereah yayyy point set general relativity!

5:56 PM
It's not really made to have testable predictions

@NeuroFuzzy don't you have Hawking-Ellis

Also as far as I know it has no problem with energy conservation

@0celo7 Yeah but at least THAT'S hausdorff

There's one non-Hausdorff manifold in HE
The Taub NUT spacetime

@0celo7 I think she knows I don't give a shit about the class but for some reason gives me good grades every semester
I know absolutely nothing about the language :p

5:58 PM
I like how he calls them Y-manifolds

are you in an inappropriate relationship with her

Because Y is a branching :p

IT IS A FLUX CAPACITATOR

the only thing I've been in a relationship with is insomnia cookies
still can't gain weight though

5:59 PM
^^lol

hey it isn't funny :(
I've been trying to gain weight for 4 years
literally haven't gained a pound

No I am responding two post up, i.e. Sleareah

Chocolate bars are the secret

I can't I'm allergic to chocolate

Lard then

6:01 PM
but I don't want to make that bump noise by tagging sleareah
hence the two "^"

@Secret Oh.
@Secret good idea!
@Secret Now I won't have to inflict that bump noise on people again.

no one is allergic to chocolate
also what on earth are insomnia cookies

^^It only works if the post are not far away

@Slereah huh, I didn't know that.

otherwise who would like to read somehting like $\text{^}^{88888888888\dots}$

6:04 PM
Non-Hausdorff spacetimes aren't used that much, though
They are not particularly useful

wtf when are they ever used?

@0celo7 nice profile pic

They are sometimes proposed as an alternative QM interpretation model
Where each branch corresponds to a quantum measurement or whatever
But I have never seen an actual formulation proposed

@StanShunpike it stands for Timmy Turner

@StanShunpike thank you

6:05 PM
that's really sounding like Evett's

Usually it's just like "Here's the topology of the space, now use your imagination"

@FenderLesPaul cmon, lol. Thats a vols logo

> PROHIBITED ITEMS
Weapons ~ Alcoholic beverages ~ Cans, bottles, coolers ~ Radios without headsets ~ Open umbrellas ~ Video cameras
Stadium seats with arms ~ Large bags or parcels, including backpacks and large purses ~ Artificial noisemakers
that's no fun

Weapons ~ Alcoholic beverages ~ Cans, bottles, coolers ~ Video cameras < sounds like the week end I'm planning

Every phone has a video camera
Wtf

6:07 PM
Explosives and booze

@yuggib a "mathematical convenience", that's a nice way of phrasing it.

tomorrow at 1800 this campus will be going nuts
@FenderLesPaul GR talk, don't be a bum

tfw you left shankar on the public transit.

tfw your roommate turns off the light and you're still in the room
seriously

time to look in lost and found...

6:12 PM
he leaves the bathroom light on but now I'm in the dark
@obe wasting time...

i'll look later.
i have a pdf.

@0celo7 ok
I'm only a bum when it comes to general education classes :p
because I give zero fucks about them

are you at home
where are you
when will this happen

no I'm in my office
sometime tonight?

you need to work in the office
you are a bum

6:14 PM
nuhuh
cries

What is the T for 0celo7?

Timmy Turner

@Secret There is a process for having your account deleted, which is what happened in this case. The user was not subject to any moderation activities. As far as we know he was simply frustrated that the site wasn't what he wanted it to be.

Temujin
The university was founded by Genghis Khan

@dmckee I see, thanks
@Slereah One of the most unaddressed plot point in back to the future style time travel stories is that how does spacetime look to an outsider, that is, how will history be look like to people who are not the one who initiate the change (since on TV, the change often took place when we saw the characters making a change). Another question that is poorly addressed is that why the change took place only at the moment when the change is made (see examples in Looper, Primer, and of course back the the future , there are a couple other examples also)

6:19 PM
The most unaddressed point is HOW DOES BIFF GET BACK TO 2015 IN BACK TO THE FUTURE 2

Using the De Lorean?

But why did he not come back to the alternate timeline he created's future

@obe home game tomorrow

@0celo7 I was sleeping and that message at 100 vol. scared me.

Speaking of Genghis Khan
Did u know

6:22 PM
What game is a home game?

In the 13th century, the most powerful christian in the world wasn't the pope
It was a Mongolian priest

what is wrong with {world - Americans}

Yahballaha III

^x8 that I am not sure, I have not conpletely finished the analysis on Back to the Future

it's a god damn football game played in the home stadium

6:23 PM
Ruler of the church of the East

We don't have that in canada. I think.

what's football?

Because most of the population was in that region back then

you mean handegg?

Really I'm not sure any time travel movie ever really did anything that didn't fuck up the plot
Books can do okay but movies are usually meh
Even Primer is kind of fucky

6:25 PM
Primer is as far I know the only time travel story that explores gradual bckground time travel

One thing that annoys me in time travel movies and such is that usually
Time travel is ALL AT ONCE
There's no gradual development of the technology
It's all "We have time travel now"

what is handegg

We can send people through
@0celo7 : American football

no, american football is american football

Soem stories have establish the time machine's timeline though, such as how some scientist made a time machine, and then the plots starts from that
a lot of them nowadays that are not type 3 tend to follow wormhole like time travel schemes
that is

6:27 PM
Have you read the end of eternity
Quite fucky but a fun story

not yet
I have not read The Time Machine yet also, though I have analyse the novel of The Time Traveler's Wife

Is talking about Lie groups in terms of smooth manifolds and not using matrix representations, all that useful?

Time travel is kind of a weird concept
Because it's one of the rare fictional concept that is very recent
the idea of travelling to the past didn't exist before the 19th century

@Secret The time machine is a great book.

@NeuroFuzzy : Define useful

6:29 PM
I have a copy of that, I just need to squeeze itme from my chem honours to read it

It is certainly done a lot

Hehehe I'm unable to define "useful"

you know math people
They hate representations of mathematical objects

My currently WIP model that I plan to use in my scifi is kinda simialr to the ADM formalism, in that instead of having a static spacetime manifold (as how GR works) the whole thing is dynamic, evolves with the proper time of the observer

To comply with relativity princple (and because it evovles with proper time), the manifold itself depends on the observer (basically extending length contration and time dilation to the global structure of the manifold)

What I need to iron out is that whether the maths are actually compatible. I suspect the tensro covariance suggested by Acuriousmind migh

@NeuroFuzzy useful means it makes money

6:34 PM
Dude what happened to you?
Were you always like this?

Be carefum
ADM formalism outright forbids time travel!

Above comments showed I really have not read enough stuff. Anyway this is a LONG personal project, thus I just need to take my time to get the basics right
"One cannot understand time travel without mastering both GR (and its variants) and quantum mechanics"

Pretty much
You need a foliation to do ADM correctly
Slice up the spacetime into nice spaces at points in time
Which you can't do if you have causality shenanigans

@ACuriousMind I feel like you had a post containing a more accurate & eloquent version of the rant I posted here:
1

Your observation is correct! The issue is one that is regrettably rather commonly left unexplained in physics texts: A single coordinate system on a manifold does not define the spacetime. Often, the coordinates useful for computations in physics do not even cover the entire space, i.e. they are ...

Any idea what I'm talking about?

Ah, the Skeksis coordinates

6:45 PM
What a way to get 100+ upvotes!
Also, I'm loving the new "cite" feature! Though I suspect it won't be used all too much.

@Danu This is why I am a mathematican more than a physicist, because I like to work globally whenever possible and then zoom into the special cases using assumptions

@Secret Yes? :P
@Secret Hah, thanks for complimenting my accuracy, I guess? :P

I first learnt about terms like chart, atlas, pullback in sean caroll's lecture notes
one thing I like abotu topology is that it is quite visual

@Secret That's not topology, though :P

a lot of concepts can be illustrated with pictures with annotations

oops, I mean differential geometry

6:49 PM
Carroll's book is where I, too, first heard these words.
However, it didn't teach me much. I needed a more extensive treatment.

well topology is somewhat visual too, usually

This is my 600th consecutive day online on Physics Stack Exchange!

On 9/11

^^cool

Who can beat that? I think it's longer than @ACuriousMind has even been a member!
@ChrisWhite Maybe?

6:52 PM
visited 430 days, 77 consecutive
Damn

I think I've missed only a single day, discounting the first 30 days after becoming a member

I want to post more but that would require being at home more :p
Can't write long ass post at work

@Danu congrats

@Slereah For the past two days, I've really been in the mood for making some posts :)

My favorite posts to answer are the one where everyone says "No!"
And I am like "OF COURSE"
And I whip out some weirdo paper

6:58 PM
@Slereah Yes, we know you like CTC's :P

I DO
It's too bad that I know enough about them to know they are probably impossible :p
They have that weird cycle of papers where some guy says "MAYBE CTC POSSIBLE"
And someone else replies "CTC TOTALLY IMPOSSIBLE"
And then back again
Currently the chronology protection thing seems pretty hard to break though
That plus the whole "Any time machine in the future of a Cauchy surface can also develop into another metric in the future"
(although those Cauchy developments have singularities in them, so pick your poison)
Though singularities are probably easier to get rid of with QG than CTCs
(I can talk about CTCs for hours but I will feel less insane if someone answers :p)

7:16 PM
@Slereah You killed the h bar.

Someday I should make a big folder of CTC papers and put it online
THE WORLD MUST KNOW

user54412
7:54 PM
@Danu My best streak was 566 days, from 2012-07-30 (about when I joined) to 2014-02-15. Then SE was down for enough hours I couldn't log in :(

user54412
Feb 17 '14 at 1:04, by Chris White
nooooooooooo - the network was down, thus ending my 560+ day streak

user54412
I was never diligent enough since, and so I miss about 1% of days.

@Danu I owe it all to the HNQ. It's certainly not my best answer, after all.

user54412
@dmckee I upvoted that before it was popular to do so ;)

It's not a bad answer or anything. It, just very popsci: pithy, accessible and short.

8:04 PM
That is the most valuable answer
"What happens if I bike on the moon" is gonna net you more points than "analytic and algebraic topology of locally Euclidean metrization of infinitely differentiable Riemannian manifold"

user54412
While there might be a correlation between votes and difficulty level, I'm pretty sure there isn't much of one between votes and intrinsic quality.

user54412
I think it's just that most answers aren't intrinsically awesome (or else we would redefine "awesome") -- mine certainly aren't -- so the HNQ effect is more likely to land on less awesome Q&As.

It's pretty hard to gauge answer quality, though

user54412
Of course we only have two data points trying to counter a widely held anecdotal feeling.

8:22 PM
@Slereah CTCs are a lie
man
Hobson's GR book is terrible

They are still quite interesting

I was just kidding lol

Hello

I am pretty annoyed when someone answers "X is a theoretical construction, you shouldn't ask questions about it!"

I agree. Everything should be questioned. Questioning either reminds you how cool something is because it is true or you find a hole in it and it turns out to be wrong.

8:35 PM

3 hours later…
11:08 PM
@ChrisWhite muahahaha, I reign supreme! (601, baby!)

11:33 PM
For all y'all popcorn munchers out there:
Check out the fight between Alfred Centauri & Gottlieb:
Michael A. Gottleib, if you aren't pulling our legs, and if you have any sense of self-esteem, you should delete this adolescent nonsense and hope that it is soon forgotten. - "I intend to remove myself (for a second time) from the Physics Stack Exchange, only this time permanently, which would be a loss for you" - Check your premises... — Alfred Centauri 23 hours ago
Me-owww!
@JohnDuffield Now that's a hilarious thought.

11:45 PM
I volunteer to be a moderator too
@skillpatrol there's literally hordes of Oklahoma fans patrolling the streets
and I have to do laundry tomorrow, I need my white clothes

I am dying from anxiety.
Idk what to do.

@obe From what?

Preparing for QFT.

@Danu eh

@FenderLesPaul

11:55 PM
that Gottlieb guy has always been a prick

high on his own position

tomorrow will be absolutely nuts

what's tomorrow?

over 100,000 people on campus D:
it's gonna be insane

11:56 PM
wtf why?

@obe you should practice shutting off the part of your brain that worries ^^

football
why do you think I changed my avatar

first home game of the season

11:57 PM
right that's a thing

@NeuroFuzzy Though 0celo7 said that I'm screwed as an understatement.

@obe that's also the reason you have TODO lists/schedules: You can plan out, the day before, "I'll just work on these problems", and then when the time comes and you're anxious because you're not doing something else, you shut that part of your brain off and say "it's on the todo list, past me knows better than present me."

@NeuroFuzzy I'll listen to this advice, thanks.

Man if people could shut off the part of their brain that worries
life would be quite something