The h Bar

7:40 AM

morning

7:52 AM

Last night dream there's a philosophical content:

"What distinguish you from your doppelgängers in other timelines"

"It is the decisions you made every single second that you believed to be right, that make you stood out against your counterparts"

That seemed to suggest you and your timeline counterparts can be easily told apart by the memories they have, i.e. history

Ba'lroc Demos

8:23 AM

Thanks. Now I understand

8:34 AM

The April Fool is cute but they really didn't go all in

it really just feels like a modern site with some old paint

the design is still way too modern

8:45 AM

@vzn New paper on why some theories of quantum gravity fail

Physics is now full of swampland's, marshes, pelicans, zoo's...

John Rennie

@bolbteppa disturbingly plausible :-)

The spontaneously/weakly broken $\mathbb{Z}_2$ Marshymmetry might link it to the standard model

9:00 AM

That reminds me of Greg Egan's short story about strange attractors, Unstable Orbits in the Space of Lies

@Secret You may enjoy Greg Egan's short story The Infinite Assassin.

I like the clockwork rocket

it is a weird experience for me to read a book and thinking

"Wait a moment, this universe doesn't make sense, because the Cauchy problem would be ill defined!"

and then a few pages later he addresses that

'You know you're a relativist when...' :p

Well I mean it's literally a book on spacetime signatures :p

Honestly I didn't care about the plot that much

I'm more YES MORE SIGNATURES PLEASE

Sylvester's Law of Inertia is the Gandalf of the plot I'd say

honestly he could have made that into a paper

9:13 AM

@bolbteppa I think this can actually be made serious. Theories that seemed to have all the nice things, but otherwise does not fit are so common that perhaps checking if there is a pattern that governs them could be useful

who knows, maybe it will shed more light on how to find theories that work

:) I've read most of Egan's stories, but I still haven't gotten round to reading the Orthogonal and Dichronauts series, although I have looked at the related articles on his Web site. Although I love his diamond-hard approach to scifi, I feel that sometimes all the science exposition can make reading his stuff more like hard work than entertainment. ;) OTOH, I did enjoy all the GR in Incandescence.

@Slereah Check out his site, there's heaps of material about that, for both Orthogonal & Dichronauts. There's even an app where you can play with Dichronauts geometry. There might be an app for Orthogonal too, I can't remember.

FWIW, I was introduced to Greg Egan's work in the early days, when he was working as a programmer for a medical research institute. One of my old school friends was a biochemist at that institute.

@Secret but is there a fractal pattern in there

No I mean the general idea, not the exact paper

In fact, I don't even know what it means if a theory landscape has a fractal boundary

Hmm...

I bet if Greg Egan teamed up with his buddy John Baez to write a text book, it'd sell like hotcakes. Especially if they got Randall Munroe (xkcd) to do the illustrations.

If given a theory landscape, the dry lands and the marshlands form a boundary that is the shape of a fractal, it means there exists two theories that is basically identical except for one or two parameters or concepts, and that alone will determine whether you end up in marshland on dry land

The existence of even one such fractal boundary means theories that can describe our universe are in a sense, "very fine tuned" because one parameter differ by even just a infintesimal amount, and then you end up no longer describing reality (or rather in this case, not a form of string theory)

I don't think physical matter have that level of resolution to do that, though I do not rule out you can get something as complicated as the British coastline

9:31 AM

@Secret That's not really relevant though. If the parameters are real (or complex), rather than integer or rational, then the parameter space can contain a fractal.

right

@PM2Ring I am aware

p-adic parameter spaces link us to Fermat's Last Theorem also

What was Fermat's first theorem anyway

Q: Opposite of Fermat's Last Theorem?

14

So Wiles' proof showed that no three positive integers $a$, $b$, and $c$ can solve the equation $a^n+b^n=c^n$ for any integer value of $n$ greater than $2$. Now what about the opposite? What does this mean for any $a$ greater than $2$, and $x$, $y$ and $z$ are positive integers in the equation $...

soft-question

9:41 AM

forum.bodybuilding.com/showthread.php?t=124113961&page=1

ack it's starting to get interesting, and then it got cut off

But wow, that the rate of shifting worldlines can form a gradient, never thought of that kind of time travel dynamic before

The assassin is one stable invariant, which probably explains why regardless of where he shifts, it does not matter. His fate is literally wrote into the worldplane itself

I think the finite version of this story of Egan may help me to better refine my scifi, because a similar scenario like that short story can happen since my settings has back to the future style time travel that is used by any pedestrians in a daily life basis

Think time travel as common as public transport if you want to imagine what that means

Also I am predicting in a few days, the time travel within my dreams may start to go crazy, as it is now made aware of this whirlpool dynamics

and no doubt my dreams will start to be inspired by that idea

filmshortage.com/dailyshortpicks/axiomatic

movie version of Axiomatic

10:19 AM

Egan had taken a class on Second Order Temporal Dynamics

Qmechanic

@bolbteppa : Some april fools' day papers on the arXiv: Superfluous Physics & The Marshland Conjecture :D

@PM2Ring I think the assassin should took some S himself so that if he got trapped in a set of measure zero by the dreamer, he can at least map himself out of it and escape

One needs to be a whirlpool in order to stop a whirlpool

But then, perhaps that may not be enough ,as the dreamer can anticipate that, take some S herself so she effectively spread herself all over the world, and then anticipate the assassin taking S to do the same, thus predict where the spread out assassin under S will be, and coordinate those sets of assassins so that they trapped in a higher order cantor set made of the flows themselves

I guess who can win really boils down to, just who can control a higher order of transitions, and correctly coordinate all their lower order counterparts to ensure one or the other get trapped into a cantor set dynamic

I personally fell for the superset of supernumary rainbows and supermultiplets

10:35 AM

> Just as supersaturation is more solute in less spatial
volume than expected, by Lorentz invariance dissolution can also happen in less time than expected, as observed in
the endochronic, or superluminal, dissolution of resublimated thiotimoline

I like that one

Because thiotimoline is an important component of my scifi. Trying to understand just how this fictional material works is one reason I spent a lot of time studying time travel

Other than that, that article seemed to stick the prefix "super" on pretty much anything

which kinda reflects my sentiment about hidden sector theories somewhat, because people are basically inventing a whole class of duplicate particles in order to hope that one such duplicate will describe dark matter

@Secret Perhaps, but then the assassin is also causing damage to the multiverse structure. And you have the danger that the assassin may go rogue. Out-of-universe, my impression is that Egan wanted to explore the dynamic of whirlpool vs the stability imposed by the assassin.

His novel Quarantine also explores the theme of people controlling Many Worlds time streams. And several of his stories feature people with AI brains that cannot create multiple worlds when they make decisions. See greg-egan.fandom.com/wiki/Qusp

11:06 AM

Egan really took the question of the philosophy of self to a whole new level with his multi-worldline stories

12:33 PM

"In Dirac (1945) he proposed a concrete infinite-dimensional representation space whose elements were called expansors as a generalization of tensors. These ideas were incorporated by Harish–Chandra and expanded with expinors as an infinite-dimensional generalization of spinors in his 1947 paper."

1:00 PM

@bolbteppa The horror

What is it even for, Hilbert manifolds?

Q: Can a spinor be defined as any quantity which transforms linearly under Lorentz transformations?

No idea

13

Recently I’ve come across a few papers from China (e.g. Xiang-Yao Wu et al., arXiv:1212.4028v1 14 Dec 2012) that make the following statement: ...any quantity which transforms linearly under Lorentz transformations is a spinor. It’s my understanding that e.g. a 4-momentum vector also transf...

special-relativity representation-theory spinors

GodotMisogi

1:17 PM

reddit.com/r/dataisbeautiful is on fire today

hey guys, would anyone explain a bit to me why $\left< n_\omega-1 | \ n_\omega+1 \right> = 0$, where the ket is for $n$ photons of frequency $\omega$

I am reading Schwartz's QFT, and get a bit confused

knzhou

1:32 PM

@Shing Do you understand why that is for a single harmonic oscillator?

@knzhou yeah, because those are eigenvectors for a single harmonic oscillator?

@Shing Lemme see

\begin{eqnarray}
\langle n - 1 | n + 1 \rangle &=& 0 \\
&=& \langle n | a^\dagger a^\dagger | n \rangle
\end{eqnarray}

Hm

Doesn't really help I suppose

knzhou

@Shing If you understand it for a single harmonic oscillator, then why is this case different?

The photon field is a collection of harmonic oscillators, and here we're focusing on a single one.

1:48 PM

@knzhou um... I don't quite understand why we can use $\left| n \right>$ for photons in the first place.

is that the very postulate he made for the whole thing?

@Shing Fourier decomposition

2:40 PM

@Slereah thanks... let me think over it

Q: Should history of physics questions be on topic?

3:05 PM

@Slereah You can delay Fourier decomposition by keeping your Fouriers in the refrigerator. ;)

4

Dvij Mankad

3:49 PM

Why is this a PSE question rather than an HSM question? physics.stackexchange.com/questions/59221/…

I am asking because it is highly upvoted and I cannot see any close-votes :/

user351417

4:05 PM

@DvijMankad Perhaps it was made before the HSM site picked up?

user351417

The canonical history post on physics meta is from 2016. That question is from 2013.

user351417

27

When we last visited the issue of history questions, the dedicated History of Science and Mathematics Stack Exchange was in its early stages. At that time, we decided against closing questions for being historical, but with the implication that it may make sense to revisit that decision someday. ...

discussion faq scope

jech.bmj.com/content/60/1/6

user351417

@DvijMankad The close votes would have aged away if they'd been cast soon after the question was asked, but the upvotes must have accumulated over a long period of time.. And it got bumped by an answer today, so maybe it'll get migrated away..

A: Is it ok to upload joke papers to arXiv?

@Chair It's too old to migrate.

I guess it got bumped due to physics.stackexchange.com/questions/469869/… hitting the HNQ

Sir Cumference

4:27 PM

117

There is a long tradition of posting joke papers to arXiv on or around April Fool's Day, especially in astro-ph - see the list below. The fact that all these papers were approved for arXiv offers some evidence (though not proof) that joke papers are okay. It's probably best to limit joke papers ...

Waiting for the latest update lol

improbable.com

lol

Is this related to ig nobel

4:49 PM

@SirCumference The upside of JD's return to Physics from suspension is that he'll spend less time on Astronomy. ;)

ACuriousMind

@PM2Ring Friendly reminder: Let's not discuss suspended users in chat where they cannot respond. Just let sleeping dogs lie ;)

@ACuriousMind Rightio. (But he's no longer suspended).

ACuriousMind

@PM2Ring The chat account is suspended for 302 days and the physics.SE account until April 18th. What am I missing?

5:05 PM

@ACuriousMind Oh, ok. I thought I saw a fresh post from him on Physics a day or 2 ago. Maybe I was dreaming...

Yeah, it was on Astronomy. Sorry for the confusion. Please feel free to delete my posts on this matter.

ACuriousMind

no worries

when I dream of SE it's usually of things like 1000 flags in the mod queue :P

I dream of new OPs on stackoverflow actually posting a MCVE...

Danu

5:40 PM

@bolbteppa I think you're wrong. Line bundles have nothing to do with quantum physics per se.

But honestly I don't really want to debate this with you, so let's just agree to disagree. I'm happy with the discussion I had with the others before.

@Danu fair enough, it's still wrong to pretend we can derive QM results like the Dirac quantization condition from classical physics

6:55 PM

Yay! I just hit the rep cap. I've only done that a few times, so it still has some novelty value for me. :)

7:53 PM

Vote for emojis on today's xkcd

Anonymous

I wonder...will that onebox here?

Anonymous

Oh, LOL!

Anonymous

@PM2Ring I love this. :D

You get that boring version via the mobile site m.xkcd.com/2131

Should I have mentioned that it's highly addictive? :D

Anonymous

...it is!

Anonymous

8:00 PM