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RewCie

05:04

Hi everyone

antimony

05:19

hi @RewCie

RewCie

05:37

@antimony hello there!

3 hours later…

Slereah

08:30

@ACuriousMind Bad memories, I assume

ACuriousMind

let's call them nostalgic

Slereah

08:49

The BRST people must be disappointed, because every time I read their actual names, I think "Who the hell is that"

Becchi-Rouet-Stora-Tyutin

I never remember their names

Slereah

09:09

"To define a very general notion of space, one needs a category of geometrical building blocks, which we call Legos. This must be equipped with a (subcanonical) Grothendieck topology τ."

Nihar Karve

I feel physical pain whenever someone says "LEGOs" instead of "LEGO"

Slereah

Did you know that LEGO® has a Grothendieck topology

That paper spells Yoneda differently in the same page

Yoneda and ioneda

Vincent Thacker

Anyone noticed that profile pictures on Meta seem to have changed?

Not the profile picture on the user's profile itself; I mean the picture as shown at the bottom-right of posts

Nihar Karve

@Slereah jeez man I hope you aren't using this as an intro to BV

@VincentThacker Yes: meta.stackexchange.com/q/367595

Vincent Thacker

09:25

@NiharKarve Ah, thanks

It's a bug then

Slereah

@NiharKarve I'm just trying to assemble my lego set

4 hours later…

Ryan Unger

13:27

@NiharKarve why?

Nihar Karve

13:39

@RyanUnger oh it's just that everyone learns that "Lego" is already in plural form

except in America, for some reason

so it just sounds really odd, like someone saying "sheeps"

ACuriousMind

14:11

@NiharKarve I don't think this is uniquely American, I've heard many Germans speak about 'Legos', too

it's also a pretty common phenomenon for irregular plurals (or other forms) to become regular over time, regardless of what is "correct"

doesn't matter whether lego is plural, it doesn't sound like plural to most

bolbteppa

twitter.com/lego_group/status/842115345280294912

Official verdict: 'Never, ever "legos."'

Nihar Karve

@ACuriousMind English-speaking world then. But I didn't say either was wrong (though legally, "Legos" is wrong), only that "Legos" sounds weird to me

For instance I agree that "maths" is an abomination, I don't hear anybody calling it "econs"

but often I write it out of habit

(sorry if this was unclear, my previous two comments were meant to indicate that I do not have a reflexive aversion to American English)

but don't get me started on "could care less"

ACuriousMind

14:31

@NiharKarve it admittedly sounded a bit to me as if you were implying no one except the "uneducated Americans" would ever think of not using the correct plural for lego :P

if that's not the case, all the better

Nihar Karve

@ACuriousMind yes, I can see the ambiguity there. I just meant that much of the English-speaking world learns to say "Lego" while Americans learn to say "Legos". But not as a right/wrong distinction.

fqq

14:47

@NiharKarve I strongly prefer maths, although I am not very confortable with the /θs/

Nihar Karve

@fqq apparently θ is a hard sound for many non-native learners of English to pick up

in an Indian accent it's tʰ instead, which is arguably easier to string together with "s"

satan 29

15:08

I was trying to see the connection between conservation laws using ordinary newtonian mechanics, and lagrangian mechanics

Consider a system of particles

then the lagrangian T-V will have T as a sum of terms containing $1/2 m \dot{x_{i}}^2$, and V as a sum of terms containing $V(|x_{i}-x{j}|$

now, its clear that this is invariant under the transformation $x_{i}=> x_{i} + x$

and so $\dfrac{\partial{L}}{\partial{\dot{x}}}$ will be conserved, i.e momentum

However, it seems to me that the lagrangian will be the same if an external force is applied?

so it appears that the lagrangian is invariant to spacial transforms under an external force too...which means the momentum is conserved even if theres an external force?

ACuriousMind

@satan29 how do you add this "external force" to the Lagrangian?

satan 29

oh wait

ACuriousMind

don't forget that it's potentials, not forces that enter into the Lagrangian, and the potential of a position-independent force is not position-independent itself

satan 29

there will be an extra sum of $V'(x_{i})$ terms

right?

ACuriousMind

yup

satan 29

15:20

thats the incorporation of the external force....and now its clear that the entire thing is NOT invariant under spatial transformations, hmm

Slereah

The classic example is Aristotelian gravity

All objects fall to the center of the earth

(or the universe)

A very clear prefered point

no translation invariance

satan 29

also about time translations

can you give me an example where the lagrangian is not invariant under time translations?

like...for space translations I had a very clear picture in mind

Slereah

The common example for that is to imagine that your experiment is acted upon by a machine

And you turn on your machine at time $t = t_0$

And you don't consider the machine as part of the system

satan 29

basically, as long as there is no "outside interaction", simply moving around the system does nothing

ACuriousMind

@satan29 well, the reason energy conservation is so universal is that it's hard to come up with examples that don't involve arbitrarily saying some stuff is not part of your system

Slereah

15:23

The common example is a forced harmonic oscillator

fqq

@NiharKarve yes in general it's not very natural to me but I'm fine with it, it only feels cumbersome in some combinations

I can always shift it to f and pretend I'm cockney

satan 29

@ACuriousMind hmm basically I dont quite know how to "inerpret" translations like $t=> t+ e$

ACuriousMind

@satan29 it means it doesn't matter whether you perform your experiment at 1 am or 1 pm

satan 29

hmm

Nihar Karve

@fqq Lol

"Oi fam, wagwan" "Nuffin, got an atilla at mafs"

Slereah

15:31

@ACuriousMind I'm not doing it at 1 AM you slavedriver

ACuriousMind

what if it's a fun experiment

Slereah

Dumb physicists thinking the time of the day doesn't matter

There's a big glowing ball in the sky during the day

seems pretty important

Nihar Karve

checkmate Noether-believing sheeple

satan 29

the sun doesn't really exist actually, the government is trying to fool us

Vincent Thacker

15:55

@satan29 You heard of chemtrails?

Slereah

I'm a professional chemtrail manufacturer

Just working at the chemtrail factory

Ryan Unger

First Time Playing Morrowind

►

morrowind memes are incredible

Vincent Thacker

@Slereah interesting; what do you guys put in them?

Slereah

TES3: Morrowind - Voice of Yagrum Bagarn (Official)

►

Physics Meta

Congratulations to ProfRob on reaching 100k!

Slereah

16:02

@VincentThacker The usual, mind control, poison, chemicals to turn people gay, high fructose corn syrup

Ryan Unger

classify manifolds?

certainly the dwarves have moved past (smooth?) manifolds

Slereah

Yagrum Bagarn is a big nerd

Physics Meta

16:27

Q: How to react to comments containing compliments, criticism, etc.?

On this site it says that comments should not contain compliments, criticism etc.. Now if I see such a comment is it better to add another comment making the user aware of the linked site, which would violate the conventions stated on the same site, or just to ignore it? I already tried to find a...