The h Bar

8:30 AM

@ACuriousMind Bad memories, I assume

let's call them nostalgic

8:49 AM

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

9:09 AM

"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."

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

Did you know that LEGO® has a Grothendieck topology

That paper spells Yoneda differently in the same page

Yoneda and ioneda

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

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

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

9:25 AM

@NiharKarve Ah, thanks

It's a bug then

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

4 hours later…

Ryan Unger

1:27 PM

@NiharKarve why?

1:39 PM

@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"

2:11 PM

@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."'

@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"

2:31 PM

@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

@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

2:47 PM

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

@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"

3:08 PM

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?

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

oh wait

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

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

right?

yup

3:20 PM

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

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

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

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

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

@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

3:23 PM

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

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

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

hmm

@fqq Lol

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

3:31 PM

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

what if it's a fun experiment

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

checkmate Noether-believing sheeple

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

3:55 PM

@satan29 You heard of chemtrails?

First Time Playing Morrowind

I'm a professional chemtrail manufacturer

Just working at the chemtrail factory

Ryan Unger

►

morrowind memes are incredible

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

TES3: Morrowind - Voice of Yagrum Bagarn (Official)

►

Physics Meta

Congratulations to ProfRob on reaching 100k!

4:02 PM

@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