The h Bar

Slereah

21:13

for some reason I get a lot more points when I ask QFT questions than GR

ACuriousMind

@Slereah lol, you asked a QFT question that appears to bash QFT. You're channeling a frustration that many have with it here

Slereah

Everyone wants QFT to make sense

ACuriousMind

Yeah. Silly people, expecting the world to make sense.

Slereah

I should find an actual proof that free and interacting theories aren't unitarily equivalent

0celouvskyopoulo7

I have gotten ZERO done today

Slereah

21:19

"they are not required to be" isn't as strong a statement as I'd like

0celouvskyopoulo7

shameful

ACuriousMind

@0celouvskyopoulo7 So tomorrow you'll get ONE done?

Slereah

Try proving a basic math thing before going to bed

ACuriousMind

@Slereah Isn't the thing about the $U$ in the interaction picture diverging basically that proof?

Physics Meta

0

Q: Which reasons make you vote negatively a question?

Recently I asked a question about classic mechanics, particularly, about central forces. (My question ) Why do you think that some people vote down? I appreciate your opinion and suggestions about how to ask questions.

Slereah

21:22

I guess?

ACuriousMind

I mean, if there were a unitary equivalence, it would have to be the "interaction picture time evolution". If you can show that's not well-defined, that'd mean there's no unitary equivalence. Of course one would have to look at that a bit more carefully

Slereah

Well I dunno, it could be a more complicated thing?

Like maybe $U = e^{itH} S$ for some operator $S$

Like maybe $\phi(x,0) = S \phi^0(x,0) S^\dagger$

I dunno

or is that also trivially wrong

@0celouvskyopoulo7 try proving that two opposite angles are equal

0celouvskyopoulo7

Wot

Slereah

First theorem of Hadamard's elementary geometry

That way u will have done a thing today

0celouvskyopoulo7

What's an opposite angle?

@Slereah Well I had an exam

And am supposed to be studying for one tomorrow

but meh

so what if I fail

ACuriousMind

21:27

@Slereah How are the time evolutions gonna be the same if $S$ is not the standard interaction picture. I mean, your $S$ needs to leave all expectation values unchanged

Slereah

The opposite angles are $AOB$ and $A'OB'$

0celouvskyopoulo7

@Slereah I have no idea. How does one prove it?

Slereah

Lemme see

Haven't read that book in a while, I forgot the axioms

(they're the Hilbert axioms)

GPhys

@0celouvskyopoulo7 okay they gave me time to do the 3 weeks of QM II homework I missed while I was sick and dying

also I lost so much weight while I was sick my pants don't fit anymore

also finals are next week so this is possible

Q____Q

Slereah

Let's see, an angle is defined by two lines (or three points), two angles are equal if by some transport they can be made to coincide, so $BAC = B'A'C'$ if we can transport $A'B'$ on $AB$ and $A'C'$ on $AC$ or vice versa

Hm

The proof of the theorem is just to flip the figure which, while true, isn't a very good axiomatic proof

0celouvskyopoulo7

21:31

@GPhys dude

what is wrong wtih you

I had my QM final yesterday, I think I survived

GPhys

@0celouvskyopoulo7 well, I almost died

I had pneumonia, among other things

ACuriousMind

@GPhys Well, you don't need your pants because you're not going to leave the house while doing all that stuff, so that's something ;) (tell me if you don't appreciate gallows humor)

GPhys

I couldn't really stand up without passing out and couldn't think straight at worst with painful productive coughing

but don't worry, I got better just in time to do three weeks of work 5 days before finals

Slereah

Let's see if Hilbert's book on geometry is better for axiomatic proofs

0celouvskyopoulo7

@Slereah are the motions $O(2)$ or $SO(2)$

+ R2

I can't into semidirect product latex

Slereah

21:33

$\textrm O(2)$

0celouvskyopoulo7

so a flip is allowed

idk

Slereah

yes

0celouvskyopoulo7

screw geometry

I am pure analysis now

I mean algebra

Slereah

though proving it from Hilbert's axioms would be tough

0celouvskyopoulo7

@ACuriousMind what do I do to algebra

ACuriousMind

21:35

I'm not actually an algebraist, I just like to pretend ;P

Slereah

solve $x + 2 = 3$

0celouvskyopoulo7

$x=1$.

@ACuriousMind Well my only two choices are to become an algebraist or an ergodic theorist

Slereah

Learn the algebra of asymptotic numbers and build QFT on them

0celouvskyopoulo7

No QFT

Slereah

I wonder what are the most obscure topics on PSE

Let's see if there's any geophysics questions

physics.stackexchange.com/questions/tagged/geophysics

a bunch, even

physics.stackexchange.com/questions/tagged/metrology

ACuriousMind

21:47

@Slereah Our resident metrologist has a good profile text about metrology :P

Slereah

Can we ask him what is the best measuring tape

not a lot of meteorology questions

I have a book of geophysics

IIRC my great uncle gave it to me

He's a crystallographer or something

v. into rocks

ACuriousMind

I was into rocks and crystals for a while. I still have a collection somewhere

0celouvskyopoulo7

You're a strange robot

Slereah

two books on geophysics, even

and a big ass crystallography book

very snore

0celouvskyopoulo7

Your face is a snore

ACuriousMind

22:01

@0celouvskyopoulo7 I never claimed otherwise :)

0celouvskyopoulo7

22:13

@BernardoMeurer

Migos - Slippery feat. Gucci Mane [Official Video]

►

Bernardo Meurer

@0celouvskyopoulo7 Stop

@ACuriousMind @dmckee He is harassing me

0celouvskyopoulo7

Quavo has his shirt on in the pool

dmckee

@BernardoMeurer But the really crucial question is do you pronounce it ha-Rass or Hair-us?

Bernardo Meurer

@dmckee The former

dmckee

Then you can't be an old fashioned southern gentleman. Which might be a good thing.

ACuriousMind

22:22

@BernardoMeurer How, exactly? (I mean I don't see why he posted that, and I don't find it particularly tasteful, but I don't see what's harassing about it)

0celouvskyopoulo7

@ACuriousMind Since when can Germans see music on YouTube?

Slereah

is there a fancy name for the linear part of a quasilinear PDE?

0celouvskyopoulo7

what's a quasilinear PDE?

ACuriousMind

Mar 24 at 1:58, by ACuriousMind

@0celo7 The GEMA actually settled their beef with YouTube a few months ago, many of what was blocked is now accessible without proxies

Slereah

The PDE is linear in the derivatives of the function

For a second order PDE, $$\alpha(x, f) f'' + \beta(x,f) f' + \gamma(x, f) f= \delta(x,f)$$

Bernardo Meurer

22:25

@ACuriousMind He knows I hate Quavo

And he keeps posting Quavo every day

And it triggers me

to see Quavo

or to think of Quavo

JUST WRITING QUAVO I GET ANGRY

FUCK QUAVO

0celouvskyopoulo7

I can't help it that Migos is releasing videos

Slereah

Most gauge theories are quasilinear, I think

ACuriousMind

I...have no idea who or what Quavo is and I'm not sure I want to know.

0celouvskyopoulo7

@ACuriousMind the first rapper in the video

With the nice teeth

Bernardo Meurer

@ACuriousMind QUAVO IS SHIT

ACuriousMind

22:27

Language, please.

Bernardo Meurer

Tell him to stop posting Quavo

It really triggers me

I can't deal with Quavo

0celouvskyopoulo7

Can we please not insult people.

Be Nice applies to everyone.

Bernardo Meurer

Quavo isn't a person

Slereah

"We restrict our exposition to first order quasilinear partial differential equations (FO-QPDE)"

ACuriousMind

@0celouvskyopoulo7 To be honest, several things in that video are pretty borderline with respect to Be Nice, so it'd be in your interest not to push that angle.

Slereah

22:29

useful acronym

Secret

22:56

Hey guys, (using Copenhagen interpretation), how do we know experimentally that the time evolution of a state is deterministic (even if the measurement outcome isn't) since we can only know what state we have prepared after measuring 1000+ copies of it?

ACuriousMind

@Secret Because there's no room for ambiguity in multiplying the state with the time evolution operator.

The "experimentally" there is a bit difficult - if you assume that the evolution of the probabilities is not deterministic, then...I have trouble seeing how you get any useful theory of nature at all

0celouvskyopoulo7

@ACuriousMind What?

Secret

Another question is about state preparation. According to non cloning theorem, we cannot clone an arbitrary unknown state. Suppose in a quantum computing experiment I need to prepare a superposition of spin up and down state. Based on what we have discussed so far, repeated measurement of copies is needed to determine it is indeed the superposition state we want. But measurement always project the state into eigenstates, thus how can we know which state we are preparing before measurement told

us which state we have prepared without destroying it?

More simply, we can prepare any state if we know how to do so. But how do we know without measuring it, which is needed to know what state is being prepared?

(Sorry uf my wording is about confusing, I need to think about how to phrase it better)

ACuriousMind

@Secret We're assuming that the same "procedure" yields the same state every time. Whether that's a valid assumption depends on the specific experimental procedure you're looking at - you might get a mixed state, i.e. an ensemble of different states when iterating the procedure, not a pure state.

Secret

Ah I see, so that's why I keep seeing quantum computing people are concerned about the fidelity etc. of their algorithms

0celouvskyopoulo7

23:46

@ACuriousMind Look, you may not like the video but I don't see what's not nice about it.

Slereah

I have a great idea to test Bohmian mechanics

Step 1 : take all matter in the universe, stack it to the left

Step 2 : send an electron to the right

The pilot wave will not be homogeneous in the universe and there will be a distinct change

Physics Meta

0

Q: Unclear What You're Asking

I recently posted a question closely related to (but not identical to) this one. I promise not to continue posting variants. That said: I have just voted to close this question as "unclear what you're asking", because it's entirely unclear what the OP is asking. However, in casting that vo...

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