The h Bar

cows

00:13

back home. Read this from Wikipedia "If a Minkowski spacetime contains a compact region Ω, and if the topology of Ω is of the form Ω ~ R × Σ, where Σ is a three-manifold of the nontrivial topology, whose boundary has topology of the form ∂Σ ~ S2, and if, furthermore, the hypersurfaces Σ are all spacelike, then the region Ω contains a quasipermanent intrauniverse wormhole."

Did not even flinch

I would have been trembling 7 years ago

Good times. Fun words!

At any rate going to just chill out and do my thing

signing off for a week or so to work on some very very very very simple baby trivial easy high school level stuff appropriate for somebody like me :)

Sir Cumference

01:44

@NovaliumCompany Someone else. He's been here for years but just came back from a one-year ban

vzn

02:06

@skullpetrol seems like youve been a stranger too, whatvya been up to anyway?

vzn

03:48

An experiment hints at quantum entanglement inside protons / ScienceNews

↑ more circumstantial evidence for spacetime fluid-fabric, from LHC o_O

@Secret ps so great at least 1 person here knows/ immerses in Ideas Mix™... maybe something )( to do with all your dream journaling :)

something else rather eyepopping for anyone/ everyone carrying crushing student loan debt... $40M gift from billionaire...

Graduating students left stunned as billionaire pledges to pay off ALL of their student loan debt during his commencement speech at Morehouse College in Atlanta / dailymail

2

Fil

04:06

I have an question regarding Stack overflow...

a question

Sir Cumference

@Fil Well stackoverflow is a different site, but you can ask

Fil

when I try to write a code in a code area, there is always a message push CTRL^K or do something, I forgot what... and I can not do anything to post my code no matter how I try

so I can not make any advance in Stack Overflow

John Rennie

@Fil ctrl-K just formats text with four spaces to the left of it. e.g.

Hmm, I can't get this to render here in the chat

But anyway, starting a line four spaces makes it render as code

This line isn't code

This line is code

There. That second line starts with four spaces and appears in code format.

ctrl-K just puts in the four spaces for you.

Fil

04:36

Yes but nothing happens when I separate code 4 times...

same message again

John Rennie

@Fil Try it here. Type a line starting with four spaces and see if it formats as code.

Fil

04:56

wait...

#include <iostream.h>

int main()

{

int i, j = 3;

John Rennie

That isn't working. It should look like:

#include <iostream.h>
int main()
{
  int i, j = 3;

Ah! :-)

Fil

theres more

there's

cout << "i = " << i << endl

       <<"j = " << j << endl;

return 0;

}

and is this c++ builder or what?

And every time I write this code this message appear and I can not post it

(I 've forgot a line of code but this doesn't really matter

)

Sid

05:12

Game of Thrones finally ends.. :(

skillpatrol

@vzn now that's a nice tax write off

Akash. B

07:38

@JohnRennie you know c programing too?

John Rennie

@Akash.B yes

Akash. B

Great

John Rennie

Most physicists know how to program because it's used so much in physics

Akash. B

I also know programing

Like to check whether palindrome, prime etc

John Rennie

In C?

Akash. B

07:41

We have an IT syllabus for studying

John Rennie

It's a very valuable skill to have. And I have to say I enjoy programming.

Akash. B

Sometimes it aches my head if I didn't get it

@JohnRennie how it is useful for physics?

John Rennie

@Akash.B yes, programming does that :-)

@Akash.B in most big experiments these days the data analysis is done using computers. LIGO and the LHC couldn't work without huge computer programs to analyse their data.

Akash. B

@JohnRennie okay

Slereah

morgen

Abhas Kumar Sinha

08:10

@Slereah Good Morning sir...

Slereah

I have yet to be knighted

A knave I am

a scoundrel

Abhas Kumar Sinha

@Slereah very deep sir, very poetic

MartianCactus

08:42

hey

So black holes are basically masses that are compressed so much that till a certain radius from them the gravitational force is enough to not even let light out right?

so I have 2 widely differing questions here

Slereah

very roughly yes

MartianCactus

1) Photons don't have mass then how can they be affected by gravity?

Slereah

In general relativity objects aren't affected because they have mass

MartianCactus

whether you consider wave nature or particle nature of light

Slereah

gravity just changes what a straight line looks like

MartianCactus

08:44

yeah, it curves space time right

John Rennie

10

Q: How can gravity affect light?

I understand that a black hole bends the fabric of space time to a point that no object can escape. I understand that light travels in a straight line along spacetime unless distorted by gravity. If spacetime is being curved by gravity then light should follow that bend in spacetime. In Newton...

MartianCactus

so general relativity doesn't use the formula for gravitational force..

ok, i didnt google that question sorry

but this next question i did google

2) People say black holes have infinite density. Is that really true?

density*

Slereah

Well

if you consider the simplest black hole

And take any volume around its center

The mass remains the same

MartianCactus

theres a popular saying that "if you compress earth into the size of a golf ball it will become a black hole". But a golf ball has volume and hence not infinite density?

Slereah

That's because, past a certain size, an object will become subject to gravitational forces so intense that it will not stop collapsing

If you compress the earth to the size of a golf ball, it will keep on collapsing

until that point of infinite density

MartianCactus

08:49

ahh alright

but what if all the elementary particles are literally touching each other?

i dont think it can go to a volume below that..

Slereah

Well if you want to consider quantum mechanics for the collapse

things are going to get a whole lot more complicated

This is all for classical general relativity

MartianCactus

oh

so it just keeps collapsing to a singularity?

then what about the black hole they photographed just now

Slereah

what about it

MartianCactus

they say its event horizon occupies as much of a cross section as a solar system

Slereah

Sure

MartianCactus

08:53

so the actual black hole is infinitely small?

Slereah

The event horizon isn't composed of matter though

MartianCactus

and only its event horizon is that big?

Slereah

Well real black holes are a whole lot more complicated than what we're discussing, but roughly this is true, yes

MartianCactus

so the volume of all black holes in the universe is equal and only their masses differ which causes the difference in the size of their event horizon

Slereah

Really the situation isn't that much different from classical gravity when you consider the case of a point mass

A point mass is infinitely dense

MartianCactus

08:55

yes

Slereah

but its gravitational effects are felt at a distance

MartianCactus

yeah..

Slereah

the event horizon is just a distance at which the behaviour changes

MartianCactus

so what i said is true?

Slereah

Yes, the mass and the volume/area/radius of the event horizon are related

MartianCactus

08:56

ahh

alright i get it

and regarding the "light escaping the black hole", im still not quite clear even after reading that answer

Slereah

I would suggest learning about GR in details before worrying too much about what happens in a black hole

otherwise it's not gonna be terribly easy

things get very weird

MartianCactus

oh ok

im almost about to start college

i will be taking computer science and engineering for bachelors

and do something astronomy related in masters

Slereah

Well, to repeat what was previously said here

2

Not gonna need a whole lot of GR for engineering!

MartianCactus

i actually wanna go into the field of space exploration but most scientists need to have an in depth knowledge of computers for efficiency so thats why im doing that in bachelors

do you think that the correct path?

Slereah

Depends what you mean by space exploration

Should probably ask an expert in whatever you want to do the correct path

MartianCactus

09:01

hmm ya probably

Slereah

although whatever path you take for space exploration, odds of requiring GR are low

MartianCactus

space exploration as in space travel

Slereah

not a whole lot of exploring black holes

MartianCactus

nah i still wanna study GR someday

any idea on if i can just do it from the internet myself?

Slereah

Well there's no lack of ressources certainly

But you'd need to be fairly motivated

Also depends what do you mean by GR

GR covers a lot of ground

I've been looking at GR stuff for over ten years and I still find weird stuff I've never heard of before

MartianCactus

09:03

oh

just the basics i guess

Slereah

Then sure

Basic GR isn't that complicated

MartianCactus

dont wanna become a full fledged theoritical physicist

although it would be cool

but i have interest in the practical side too

so i want a bit of both

which is why i think engineering would be nice

PM 2Ring

@MartianCactus Good question. However, classical GR is agnostic regarding the composition of matter. It doesn't know anything about fundamental particles, or even atoms. To properly address what happens to matter near the core of a black hole we need a theory of quantum gravity.

MartianCactus

oh so the theory of everything basically

yeah classical GR doesnt work when you consider quantum pphysics right

and vice versa

Slereah

Things get complicated

PM 2Ring

09:08

OTOH, we can't observe what goes on inside the event horizon, so even if we did have a quantum gravity theory, we wouldn't be able to directly verify its predictions about black hole cores.

Sometimes people use a combination of QM & GR to predict stuff, like Hawking radiation, but that doesn't have a solid theoretical basis, so Hawking radiation may turn out to be a fiction.

Ben Crowell wrote a great answer about black hole singularities in classical GR. My favourite line is: "A singularity in GR is like a piece that has been cut out of the manifold. It's not a point or point-set at all."

Slereah

Hawking radiation does seem to appear in... pretty much every version of quantum gravity I can think of

It is likely to be correct

PM 2Ring

@MartianCactus Most of the time, that's no big deal, since GR gives roughly the same predictions as Newtonian physics, unless the gravity is extreme, which normally requires big objects with huge mass. And QM is only needed to explain the behaviour of tiny structures. So most of the time, they don't overlap. But when they do overlap, they don't play nicely together.

Slereah

Well they're not that bad either

as long as the backreaction is small it works out okay

PM 2Ring

@Slereah Sure, but at this stage we don't have a solid foundation for it. And it will always be extremely difficult to observe, except for very small BHs.

Slereah

Semiclassical gravity is generally considered to be fine as long as $$\langle T_{\mu\nu}(p) T_{\rho\sigma}(q) \rangle \approx \langle T_{\mu\nu}(p)\rangle \langle T_{\rho\sigma}(q) \rangle$$

MartianCactus

09:23

semiclassical?

oh nvm

so GR is and update of classical mechanics

in a way

and quantum physics is a completely different subject in it

right?

PM 2Ring

@MartianCactus We can combine QM with SR, without problems. And GR says that if you zoom in close enough to a chunk of curved spacetime it looks flat, so you can use SR on it. That strategy is mostly fine, unless your chunk of spacetime is particularly gnarly.

@MartianCactus Yep. GR is considered a classical theory, because it doesn't have any quantum stuff.

MartianCactus

whats sr

John Rennie

@MartianCactus Special Relativity

MartianCactus

oh

idk the difference im sr and gr

PM 2Ring

@MartianCactus SR is relativity on flat spacetime, without gravity. The mathematics is pretty simple. GR tells us how to do relativity with gravity. The maths gets a bit tricky. ;)

Slereah

09:38

To be fair the math also gets tricky in SR

PM 2Ring

@Slereah Well, I guess it can get messy, eg doing a completely general Lorentz transformation. But basic SR requires nothing more than high school algebra, although a bit of calculus can be handy.

Slereah

You can do special relativity with manifolds

things can get messy for general coordinate transformations

For accelerated observers and rotating observers

Also doing frame transport and that kind of nonsense

Novalium Company

Can anyone recommend me an introduction book to economics? That's easy to understand with practical examples and basic terminology?

Slereah

Maybe not the best channel to ask for such a thing

if we understood economics odds are good we wouldn't have gone after a physics degree

7

Novalium Company

xD

you may not have understood economics but you did have the chance to learn it ;)

Novalium Company

10:11

I'm thinking of some sort of a mechanism to check if something underwater is alive. I thought of a laser first, but I don't think it'll work. What about some sort of a electric motor to send a stream of water and see if it'll move?

What about speaker underwater :D?

I'm building a costume to help me explore the sea during summer.

Also what are some good gloves for underwater that I can hook up electronics to them?

Captain Bohemian

I have only had small touch with economics when in junior high school, feeling it somewhat boring.

Novalium Company

10:28

What is the yellowish led thingy called here:

What should I say to the hardware owner if I want to buy only such yellow "flat" led?

(and not the bulb type of electronics led)

Slereah

12:21

Economics is a lot of stochastic calculus

I hope u enjoy Markov processes

skillpatrol

12:55

Intro to Economics: Crash Course Econ #1

►

@NovaliumCompany^

skillpatrol

13:41

\o @Semiclassical

Semiclassical

o/

skillpatrol

TIL Bob Dylan went to the university of Minnesota

Semiclassical

yeah

there's also a Fourth St which runs nearby to the university (like really nearby) which some people take to be the origin of "Positively 4th Street". (though I've seen it credibly argued that it's actually about 4th St in NYC)

skillpatrol

cool

SDFG

13:58

@skillpatrol always wanted to ask..are you the user of the IDs @skullpetrol and @skullpatrol too?

good going

okay you wanna keep the others guessing

:)

Secret

15:14

@SDFG He has dozen other alts

SDFG

hmm

Well, if that's common knowledge, I don't know why he removed his response :P

Secret

@vzn Actually I did idea mixing stuff since I go to primary school lol

@vzn I am confused by how you get this interpretidon. Reading the paper, all I see is entanglement. There's no discussion on how this is connected to the nature of spacetime?

vzn

15:32

@Secret "entanglement" is the big buzzword across different/ crosscutting physics fields/ compartments right now. a recent Swingle survey links entanglement to spacetime fabric, this is from the AdS/CFT crowd. physicists are starting to approach the spacetime fabric idea from multiple directions, slowly converging/ "triangulating" on spacetime fluid fabric. some of this is related to QM + GR unification ideas.

Secret

right

vzn

@Secret old zen expr: in the beginners mind (shoshin) there are many possibiilities, in the experts only a few...

Secret

newscientist.com/article/…

AI creativity is getting more interesting less so in how close AI can replicate creativity, but in helping humans to discover blind spots in their thinking patterns

vzn

@Secret here a key buzzword is curiosity...

Secret

Currently I have a personal investigation that basically trying to get curiosity itself on autopilot

There's a kind of table that lists out the 4 types of unknown we are aware of

(here shows where it is used in the national defense context in some public seminar)

Based on the various groups spanning from science to politics I have interacted with in the past 8 years, the following is what is known so far:

A recent philosophy discussion about 21st century existentialism lead to the suggestions that "compound unknowables" may exists, despite it is unknowable that it is unprovable

In addition, science discovery tend to convert unknown unknowns into knowns and known known and known unknowns tend to interconvert

While blind spots is well known for being an unknown known, Emilo's questions highlight that folklore and common sense is also an unknown known

And the discussion on the nature of creativity and freewill in philosophy, combined with AI creativity discussions, lead to the possibility that witnessing a creative act can convert an unknown known into a known by showing us what lies outside what we aware

Basically, the limit of creativity is

> We don't aware that X exists

thus if this barrier can be overcame, then transcending creativity may be possible

Ryan Unger

16:12

@ACuriousMind Actually there's a steam sale on thursday

did you play mankind divided?

I finally played HR and it was great

ACuriousMind

@RyanUnger Not yet, it renders everything with weird-looking stripes on my machine and I couldn't figure out why

Ryan Unger

@ACuriousMind did you upgrade your gpu from the 660?

ACuriousMind

The pitfalls of Linux gaming :P

Ryan Unger

oh dear god.

ACuriousMind

@RyanUnger No, I think the next time I "upgrade" I will replace the entire machine.

After the RAM upgrade killed the Windows installation for reasons I still don't understand I'm not doing that again :P

Ryan Unger

16:17

@ACuriousMind yeah wait for the R9 series to come out

@ACuriousMind oh I remember that

you must have hit a singularity or something

ACM's incompleteness theorem

user2723984

the other day @bolbteppa posted some notes about susy/sugra/AdS/CFT. I'm interested in the subject but at a first look I can't really gauge the level (pun intended). Do you reckon someone who's had one GR and one QFT course can work through them or am I a fool for even thinking about it?

Ryan Unger

it's probably better to learn something tried and true rather than speculative physics

such as nonlinear hyperbolic PDE

ACuriousMind

@user2723984 Depends on the kind of QFT course and your pain tolerance/willingness to go on wild goose chases for concepts you don't yet understand :P

Ryan Unger

@ACuriousMind so did you watch the shitshow yesterday

user2723984

@ACuriousMind we did QFT without the path integral formalism unfortunately. Standard intro stuff, mostly QED up to one loop renormalization

ACuriousMind

16:22

@RyanUnger I haven't watched the last two seasons of GoT, and judging from the internet's response at large, I don't regret that decision!

user2723984

@RyanUnger that sounds awful

Ryan Unger

@user2723984 QFT? I agree

ACuriousMind

@user2723984 I haven't looked at bolbteppa's notes, but the path integral formalism is likely something that would be of broader usefulness anyway

user2723984

@ACuriousMind you're probably right, I'll look into that first as if I understand correctly it has applications in other fields too. It's not that I want to work on HEP anyway, just wanted to take a peek as it sounds very interesting.

Sir Cumference

16:52

@Slereah Well this is a thing

Econophysics

Econophysics is an interdisciplinary research field, applying theories and methods originally developed by physicists in order to solve problems in economics, usually those including uncertainty or stochastic processes and nonlinear dynamics. Some of its application to the study of financial markets has also been termed statistical finance referring to its roots in statistical physics. Econophysics is closely related to social physics. == History == Physicists' interest in the social sciences is not new; Daniel Bernoulli, as an example, was the originator of utility-based preferences. One of the...

Novalium Company

17:40

I got banned in GTA 5 for cheating :P

I spent 60$ on the acc...

Kyle Kanos

Maybe you shouldn't have cheated?

6

Nick

18:07

What is the best citation for this concept? vixra.org/pdf/1905.0178v1.pdf

Semiclassical

The “vixra contains a lot of crap” concept?

Nick

yeah :D

Kyle Kanos

Or that E=md^2/t concept?

Nick

but also, E=mc^2 derived from E=wt, who dunnit first? I'm sure this is before Newton.

Though this equation is always attributed to Einstein who is after Newton.

Semiclassical

Except that energy is power * time

Work is just a form of energy

Same units.

Nick

18:14

oh right, wow, vixra is bad for health. Can I get a reference textbook again? I think I need to go back to school.

Semiclassical

At best, you’ve got P=Fv and therefore E = Pt = F(vt)=Fd = work done by that force

Kyle Kanos

That ought to be in any freshman physics text, e.g. Halliday & Walker

Nick

ah, I just remembered I used Halliday and Resnick for something. Solving Irodov. This was many years ago.

Nick

18:29

@Semiclassical thanks!

I'll just cite the text then.

ACuriousMind

21:28

@Slereah sounds to me like "if we understood how to summon demons we wouldn't have gone for magic theory"

Slereah

@ACuriousMind Krasnikov's book has a part about demons

ACuriousMind

GR = GeneRal demonology

Slereah

I like how he used little dragons and also a mystical rune to label that curve

Pretty sure Krasnikov is a wizard

ACuriousMind

Do not meddle in the affairs of mathematicians, for they are subtle and quick to anger

user2723984

Demons aren't rare in physics

ACuriousMind

21:38

@Slereah Eth is not a mystic rune

It's even the standard symbol for the voiced English "th"!

Slereah

Not really a standard physics symbol

But Krasnikov is insane

He even uses a thorn in his notation

danielunderwood

> demons of this kind are called jinns in [127]

...so I must know, what is [127]?

Slereah

Yes, it is quite a mystical book

@danielunderwood arxiv.org/abs/gr-qc/0007064

ACuriousMind

...also, what are efreets, marids and daos in this context?

Slereah

though apparently it first appeared here

thelifeofpsi.com/wp-content/uploads/2015/01/…

one thing I want to do for my site is a halloween post

It will be about jiins, demons, ghosts and phantoms

though so far physics doesn't have any witches or goblins

ACuriousMind

21:52

Time to invent your legacy: The Lereah goblin.

Slereah

The goblin singularity

Although I guess that before you introduce a silly notation, you need some creds

Can't make your first paper about the lich integral

Hm, what else is spooky in physics

there are skeleton diagrams

user2723984

22:27

@Slereah ghosts

Slereah

Already said ghosts

as they are the most well known of spooky phenomenon

user2723984

ah, missed it

what else is spooky in physics if not action at a distance

Slereah

22:41

not a very good Halloween costume

user2723984

requires some originality in the design for sure

Slereah

It's just me with a very long stick

user2723984

that's just regular action at a distance

Slereah

Someone's gonna get poked by the stick

user2723984

pokey action at a distance, just one letter to go for a brilliant if easily misunderstood costume

you could just wear a regular halloween costume and perform Bell experiments

danielunderwood

23:44

Get a giant letter S and dress it up like a ghost

then you'll have spooky action...then put it on the stick?

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