The h Bar

3:36 AM

Has anyone else seen Sabine Hossenfelder's physics videos on youtube? Is she a crank? Is she an active researcher? They're showing up in my youtube feed, but I can't tell how much creedence to give her.

John Rennie

4:34 AM

@Dave I think she has left physics now, but she was a respected physicist work in the general area of quantum gravity.

Just recently she has attracted a certain amount of notoriety for her comments on a possible future new collider, but as is so often the case the situation has become rather over dramatised.

Slereah

7:16 AM

morning

Scientist Smith YT

@EmilioPisanty Well then there should be one like that. Because that would change a lot if no one thought of that frame of reference before. It would almost be dumb to not think of that frame of reference if you ask me.

@EmilioPisanty But lets say that doesn't exist for a moment. How would we explain different point of references from different objects? In this case the light is the object.

Slereah

0

Q: Notion of Present

Can't I sync all watches in spacetime and call this time slice the present? In Carlo Rovelli's book he tried to explain that the notion of the present is local only, which I could not follow.

I want to answer the question but the more I write the less sure I am that GR makes sense :V

Bloody synchronization

Gonna have to revise my original ideas for synchronization because it turns out the horismos isn't that trustworthy

Emilio Pisanty

7:34 AM

@ScientistSmithYT light is not an object

@ScientistSmithYT "physics would be simpler if it was simpler"? Yes. But wishing that nature were different won't get you anywhere.

Slereah

@EmilioPisanty I motion that we redesign the universe so it looks like this

One dimensional universe I can deal with

Emilio Pisanty

The relativistic formulas that relate different frames of reference (the Lorentz transformations) become singular when you try to have one of the frames move at the speed of light with respect to an existing inertial frame

It's described in extreme detail in Wikipedia, every textbook on special relativity, and a myriad questions on this site, so I'm not going to - this is the point where it shifts over to being your job to look it up

Slereah

Hm

Emilio Pisanty

@Slereah I'm pretty skeptical of that sketch. "my" view of lineland? The square's?

Slereah

Yes

Emilio Pisanty

7:43 AM

So it's not really a sketch, then, is it?

Slereah

Don't question the line

Emilio Pisanty

It's more of a walk-through model

@Slereah I'm not questioning the line, I'm questioning the plane

This is what the square looking at lineland would look like to the sphere

From outside the plane

Slereah

I think I need to prove $$p_1 , p_2 \in \gamma \wedge p_1 \ll p_2 \wedge p_1 \in N^-(q) \wedge p_2 \in N^+(q) \to \exists p_1', p_2', p_1 \ll p_1' \wedge p_2' \ll p_2 \wedge p_1' \in H^-(q) \wedge p_2' \in H^+(q) \wedge t(p_1, p_2) \geq t(p_1', p_2')$$

Easy peasy

Emilio Pisanty

But I'm skeptical that the square himself would reconstruct that model

=P

Slereah

It would help

in other words I need to show that while a null geodesic may not be on the horismos, but there is such a null geodesic which can be differentiated experimentally

And hopefully differentiated in finite time

I think that's reasonable, but I never trust a reasonable theorem

Also this would work fine for the ideal case where the observer just blasts the spacetime all the time with light rays and massive particles in every direction

But I'm not sure that will help for the realistic case with just sporadic sprays of photons

I mean obviously that theorem is wrong, but it may be correct in a globally hyperbolic spacetime

Yeah I think that is correct

$q \neq \gamma$ so since $\gamma$ has points in both $J^+(q)$ and $J^-(q)$, which are disconnected if $q$ is removed, it intersects the horismos in such a way

Scientist Smith YT

8:07 AM

@EmilioPisanty Well do we classify it as a person, place, thing or idea?

@EmilioPisanty But I'm probably going to move on from that topic and wait a while before I ask my next question.

@Slereah I've been there and done that. :) That's usually when I just stop... Fall asleep ... Then continue where I left off. I end up figuring it out soon after.

@Slereah Didn't work, I was trying to quote a text in a message you sent, but I still have yet to figure that out.

@PM2Ring I just saw your message in my inbox. And the link to the SE Q&A. I'll read that tomorrow. Well... (Its already the next day here so today, but after I get some sleep) thanks :)

Emilio Pisanty

8:34 AM

@ScientistSmithYT I wish you good luck in understanding physics under a worldview that allows only for those five categories.

PM 2Ring

@Dave Yes, according to Wikipedia, Sabine is still active in physics: "she is a Research Fellow at the Frankfurt Institute for Advanced Studieswhere she leads the Analog Systems for Gravity Duals group". She's been turning up in my YouTube feed too, but I haven't watched any of her clips yet, although I have read a few of her blog posts.

Sabine has ruffled a few feathers in the last year or so, for suggesting that there are better things to do with physics research money than building a bigger accelerator than the LHC. Also, her book Lost in Math: How Beauty Leads Physics Astray upset a few people. ;)

@EmilioPisanty Congratulations on getting the Optics gold badge!

Slereah

8:51 AM

Alrighty

I think I have a Proof

Phew

I think if you consider the shortest light trip between an observer and a point, you obtain the horismos trip

NOW

Can you perform a global synchronization from such data???

Dun dun dun

PM 2Ring

@Slereah Ben's answer looks ok to me. On a related note, see physics.stackexchange.com/q/503978/123208

Slereah

It is fine

But synchronization in GR is such an awful problem

I mean it's entirely fine if you assume a normal neighbourhood

But otherwise

Not so good

I mean really, what I'm basically doing is just GR trigonometry

Every light synchronization is just a triangle with one timelike side and two null sides

I know there's some papers on SR trigonometry but I'm not sure that is the case for GR

PM 2Ring

Triangulating the universe is hard. It's hard enough just triangulating the Earth's surface, but surveyors generally don't have to worry about the curvature being dynamic.

Slereah

Well I'm assuming some fairly generous hypothesis

1) global hyperbolicity

2) every point of spacetime has an observer going through it

3) every observer just shoots light beams and massive particles in every directions constantly

4) those beams contain every possible information from the observer

Basically this

Also if things get too tough I may also assume trivial topology because heck

But the one thing I will not assume is LOCAL NEIGHBOURHOOD

Because that is easy mode and also it's been done already

PM 2Ring

9:18 AM

There's a good reason that it's a GR slogan that simultaneity is local. Easy mode is (relatively) easy, hard mode is impossible. ;)

Slereah

Well global simultaneity is fine in GR if you assume global hyperbolicity

BUT

the hard part is getting it exclusively from measurements

Also I think "A spacetime constantly filled at all time with EM radiation from infinitely many sources containing infinitely much encoded data" probably stretches the definition of "test field" a bit

But I'll allow it

I mean assuming a foliation, it's trivial to find a simultaneity scheme, but then that's assuming you know the foliation in advance

PM 2Ring

But even if you succeed in building your synchronized network purely from measurements, it's still of limited value: over sufficiently large distances you still have the Andromeda paradox.

Slereah

Since it's basically $$t = t_1 + \varepsilon(x) (t_2 - t_1)$$

@PM2Ring Well I do make for some fairly generous hypothesis

The next step ideally would be "What subset of the metric phase space is given from a finite set of measurements?"

And perhaps even "How much deviation can you get from predictions given a set of measurements?"

Emilio Pisanty

@PM2Ring thanks =)

It's been a long time coming

It's nice to have gold tag badge that @JohnRennie doesn't have

Slereah

ie if you guess from the set of measurements that the initial data is $g_3(0, x)$, $\alpha(0, x)$ and $\beta(0, x)$, up to some uncertainty due to the measurement

Emilio Pisanty

9:25 AM

It's a super exclusive club, that

Slereah

How much uncertainty do you get at $t + T$

I have no idea if that can even be done, really

PM 2Ring

@EmilioPisanty :) Physics.SE needs all the hammer-wielders it can get.

Slereah

Even assuming very generous conditions, I think the subset of $\Gamma(SM)$ (space of all metrics) that fit a measurement is pretty large

Emilio Pisanty

@PM2Ring honestly, there's not that much movement on that tag. There'll be cases where the hammer is useful, but not all that many

Slereah

You could add arbitrarily much very high frequency variations and you'd still end up with the same measurements up to uncertainty

Although I think you can cut that down a bit with some restrictions on the total variation of the metric

PM 2Ring

9:33 AM

@EmilioPisanty True, and many optics questions (apart from blatant homework) seem to be of reasonable quality, so they're less likely to be closed for other reasons.

Swapnil Das

Can anyone help me out?

Slereah

Optics isn't as mysterious to the layman

Nobody wonders about the mystic mysteries of the lens

PM 2Ring

@Slereah And let's not forget about uncertainty due to HUP... or maybe we shouldn't worry about that until we get a quantum gravity theory. :)

Slereah

Well

I guess there was that

what-if.xkcd.com/145

@PM2Ring This doesn't matter all that much rly

Because it's not fundamentally different from instrument uncertainty

Swapnil Das

Slereah

9:36 AM

Also like

I haven't worked out everything, but just using a clock or rod in GR is fundamentally uncertain

Because the metric itself influences the mechanism

The metric is going to change the frequency of atomic clocks or the interatomic length of a rod

@SwapnilDas First hint : take a bigger picture because some of us are old people

Swapnil Das

@Slereah You have the zoom button on the right top corner :P

PM 2Ring

@Slereah True, but with HUP things get wobbly on a large enough scale, even in a flat Minkowski spacetime.

Slereah

@SwapnilDas Zooming an image doesn't increase the resolution!

@PM2Ring Sure, but the point is that I don't assume anything about the metric

Well

That's a lie

I assume that the variations of the metric are small enough that the uncertainty of our measuring apparatus is bounded to some known quantity

I don't think you can actually do GR with zero assumptions about the metric

@EmilioPisanty please explain

Swapnil Das

@Slereah Oh, I thought the words were clear.

Slereah

it is very blurry

Swapnil Das

9:44 AM

Yup ok I'm trying to magnify and repost,

It's a problem on gyroscopic motion.

PM 2Ring

@SwapnilDas It's a bit blurry on my phone, but it's readable. Unfortunately, I don't know how to solve your problem. My knowledge of gyroscopic stuff isn't as good as I would like

Swapnil Das

@PM2Ring Nvm thanks.

@Slereah Any improvment? :P

PM 2Ring

Sadly, the xkcd forums are still offline. It's been a couple of weeks now. :( forums.xkcd.com/index.php

@SwapnilDas Much better!

Swapnil Das

Oh.

Slereah

Know what's cool tho

You can make ultrastatic spacetimes into optical systems

Since it's basically the same Lagrangian

The metric just corresponds to some anisotropic medium

Though I'm not sure you can simulate every metrics with anisotropic media

PM 2Ring

10:03 AM

Yeah. The first time I heard about that sort of thing was an optical version of the Poincaré disc representation of the hyperbolic plane.

Slereah

10:44 AM

Let's build a glass hyperbolic plane

Slereah

11:07 AM

Hm

I think the global time function is just gonna be constructed from local data

Just find the synchronization in an infinitesimal neighbourhood

The foliation is the surface everywhere tangent to the distribution defined by these local synchronization

That might be the Marzke-Wheeler coordinates, rly, but who can tell since that paper is so vague

Slereah

11:34 AM

"Our academic system is descended from Akademos, a pagan grove near Athens, sacred to the goddess of wisdom. Members claimed ownership of all knowledge, by which they meant stuff they made up by their own powers of reasoning. Practical knowledge was left for tradesmen and servants.
So when you talk about “hard science” you are talking about the output from this bunch of pagan worshippers making up stuff in their own heads and calling it science, while insulting and rejecting people who work by observations and tests, as required by the scientific method. "

John Rennie

@EmilioPisanty :-)

tpg2114

I'm going to momentarily hijack chat for "personal" reasons -- if anybody knows US Citizens with an MS or PhD in Aerospace/Mechanical engineering or related fields (either graduated or soon-to-graduate) and experience with computational fluids, I am looking to hire people on my computational propulsion team. Pass the word, ping me here if needed and I can send out descriptions

3

Okay, back to regularly-scheduled programming

ACuriousMind

11:51 AM

@Slereah that's not quite right - Akademos was a hero, the Grove was called academeia (sacred to Akademos) , and Plato happened to build his school there, which in time came to be called academeia, too

Swapnil Das

@JohnRennie Could you help me with the above question?

Slereah

12:12 PM

@ACuriousMind Is the devil worshiping part of modern academia right though?

Slereah

12:29 PM

ACuriousMind

1:21 PM

@Slereah I swore to Baphomet I wouldn't tell.

Ryan Unger

1:43 PM

Of course ACM is a devil worshiper

Ryan Unger

2:00 PM

@Slereah where is this from

Slereah

@RyanUnger Opening statement of my thesis

Nah it's from quora.com/…

Sir Cumference

Morning

bolbteppa

2:31 PM

@vzn the pagan comment above may explain everything re establishment

Ryan Unger

It’s well known that academia is full of pagans

Emilio Pisanty

2:59 PM

@Slereah I would tell you to ask a full thread on main, but I'm no longer ambulance-chasing optics threads

vzn

3:22 PM

@bolbteppa not following. slereahs quote? where did it come from? not sure it is accurate history...

@tpg2114 very cool it would be great if you could post more info :)

bolbteppa

> So when you talk about “hard science” you are talking about the output from this bunch of pagan worshippers making up stuff in their own heads and calling it science, while insulting and rejecting people who work by observations and tests, as required by the scientific method. "

vzn

@bolbteppa the (greek) origins of science were (maybe surprisingly for some) "nonempirical". science is a very long ~2M historical thread. science started out roughly in philosophy + logic.

White Prime

3:38 PM

If gravity is merely the curvature of space, then how can it crush matter so tightly as in the case of neutron stars and black holes?

Ryan Unger

Why not

White Prime

Wow, Ryan, mate.

Awful response, bro.

Secret

Nonexistence has at least 6 types, Hinduism have forgot at least 3

White Prime

Also, a crazy thing is this: A bloke once asked that, if gravity is merely the curving of space, what actually makes planets continue moving. And on Physics SE the most answers said that the reason they move is......TIME. As if time was an accelerant, or something.

Ryan Unger

Maybe learn some basic physics

White Prime

3:45 PM

Dismiss the extra 'the'.

Ryan Unger

Do you even know what the Einstein equations are

White Prime

No, Ryan. In not a galaxy brain like you, mate.

I'm

Secret

ncehk2019.github.io/nce-live/?visibleCount=16

4 months of protest, and CCP does not even blink an eye

Ryan Unger

Then get a galaxy brain by learning some math...

Secret

Sometimes I am wondering whether protests actually do anything at all

Ryan Unger

3:48 PM

Don’t ask questions about physics without knowing the math

Secret

Governments all over the world are insanely complacent

White Prime

I hate math, Ryan. Bloody hate it a lot. Also, I'm crap at it.

I think it's clear that gravity is not merely the curving of space.

Gravity is a genuine force.

Ryan Unger

If you hate math then you hate physics

We can’t answer your question without math

White Prime

It's physical reality that interests me.

Ryan Unger

Well “force” is not a part of physical reality, it’s a part of how we understand the universe, which is math.

White Prime

4:00 PM

Not elaborate, indecipherable equations.

Secret

No maths can answer the questions of political instability

Nor why is humans so [data expunged]

White Prime

Secret, what protests are those pics showing?

Secret

Hong Kong anti extradition bill

White Prime

The world is indeed in a miserable state. And no, it's not Donald Trump's fault.

Ryan Unger

They’re decipherable if you put in a tiny amount of effort

Secret

4:08 PM

who's fault?

@WhitePrime so many people point fingers to prominent people, but I felt like there is something much bigger and more wrong about this world than it can be pointed to any person nor group

White Prime

Well, I view myself as reasonably intelligent. But when you guys are writing your long equations etc, I have absolutely no idea what they mean.

Secret, I can agree with that.

Secret

Something gone really wrong in this world, but it is not a human nor a group

I have no idea what that is

White Prime

Secret, obviously there's a lot that could be talked about when it comes to politics. But in short, the main problem that caused all the mess is the political class ignoring the will of the people.

Secret

indeed

Ryan Unger

4:29 PM

You only don’t know what they mean because you haven’t tried to understand them

White Prime

Ryan, that's true to be honest.

Slereah

4:46 PM

@RyanUnger !

i need your powers

Are there any known conditions for the maximal size of the convex normal neighbourhood

ie conditions relating the curvature tensor to the furthest you can go from the central point, for instance

vzn

@WhitePrime have some )( sympathy for your complaints. there are some new directions going on in physics, dynamic + some verging on radical, that may address them to some degree...

@Secret also some agreement but is it somehow worse than its ever been? could easily argue otherwise... which reminds me...

Sep 27 at 4:38, by John Rennie

On the seventh day God rested, and the Devil snuck in and created the Navier-Stokes equations.

Sep 27 at 4:37, by John Rennie

Fluid dynamics was invented by the Devil to stop physicists feeling too smug.

← devils advocate™ (in contrast to Dr Toothpaste lol!) o: o_O :P

Emilio Pisanty

This reads like: "we can't tell you on what legal grounds we think this is OK because it actually very well might not be, but if we told you that we would outright admit to culpability, which our legal department obviously considers undesirable. Please sue us if you'd like to know more, as that's the only time we can actually go into this." The answer would be improved by being a less glaring legal void. — Jeroen Mostert yesterday

damn

he said exactly what I wanted to say, but better ¬¬

vzn

5:36 PM

what the @#%& is going on with SE licensing chg? dont understand the raging flamewar at all...?!? :o o_O

rob

5:46 PM

@vzn Content submitted to SE is submitted under a certain set of terms. SE has announced that they are unilaterally and retroactively changing those terms (to something similar). However, the original agreement doesn't seem to give SE the right to make that change on old content; the right to re-negotiate the content license belongs to the creator, not to the licensee.

Sir Cumference

@WhitePrime What do you mean force

"Force" is defined mathematically

@WhitePrime Also it doesn't take a "galaxy brain" to learn Newton's first law...

Novalium Company

I view myself as substantially commonly unreasonably intelligent.

Now some annoyingly philosophical dude will say "I have no idea what you mean by intelligence blq blq"

Although, he'll be right

vzn

@rob afaict from the post cited by EP the new terms are very similar to the old terms, its just upgrading a version of CC license. supposedly "improved". have seen someone assert there was something illegal going on. have never seen such an epic flamewar on SE in ~1 decade... and have seen some really epic ones... o_O

879

Q: Firing mods and forced relicensing: is Stack Exchange still interested in cooperating with the community?

The last weeks and days have seen some erratic behaviour by Stack Exchange Inc., such as likely illegal changes to the content license and the firing of an upstanding community moderator with no explanation except copy-pasted responses (leaving many to believe it was for no good reason). It wou...

discussion support moderators community

Slereah

6:01 PM

0

Q: Bounds on the size of the normal neighbourhood

One of the most important feature of general relativity is the existence of the convex normal neighbourhood, a neighbourhood $U$ on which the exponential map is a diffeomorphism between $\exp^{-1}(U)$ and $U$. A lot of the so-called "locally Minkowski" arguments are based on this fact. But as fa...

general-relativity topology

Plz halp

rob

@vzn Similar, but not the same. There are a lot of interesting and subtle issues associated with Creative Commons-type licenses.

PM 2Ring

The consensus seems to be that the CC-BY-SA 4.0 licence is better than 3.0, but people are upset that SE changed the licence without asking us, and the licence terms clearly state that they must ask our permission.

Sir Cumference

@Slereah I'd suggest asking on the Math chat too about mathematical physics questions

DanielSank

Hi, everybody.

Does anyone here use Stack Exchange's email notification system?

I have been trying to use it, but it seems to not send mail.

...which is annoying.

Sir Cumference

6:20 PM

TIL SE has an email notification system

@DanielSank So it seems I was signed up for mail thus far, but never got any

Guess it's something you could bring up on meta

DanielSank

@SirCumference ~sigh~

Sir Cumference

@NovaliumCompany bro are you ok

Novalium Company

@SirCumference nope

Sir Cumference

you might want to tone it down with the posts

Novalium Company

:(

k

Sir Cumference

6:31 PM

i'm not a mod but a wall of random words might be seen as spam

Novalium Company

i hope I made some dudes laugh

at least

sir cumference u laughed?

:((((

(I'm not drunk don't worry, just really bored)

vzn

@rob still dont understand much )( at all... but it seems apparently a kind of near-religion among some with all the associated (ir) rational fervor... stallman + the word jihad come to mind... o_O

Scientist Smith YT

6:46 PM

@DanielSank I use the email notification system.

Loong

→ 27 messages moved to Trash

Although I am surprised that you know Hesburger.

Novalium Company

@Loong We have Hesburger in Bulgaria and it's yummy and cheap. McDonald's has become so goddamn expensive.

Loong

I see.

Novalium Company

@Loong u call no sugar coke with manually added sugar trash? ;(

Loong

I often call it Horseburger. ;-)

Scientist Smith YT

6:55 PM

@EmilioPisanty I don't know if what you said was sarcasm or not. If you could clear that up for me then I will be able to respond appropriately. I don't want to asume you're being sarcastic when you might possibly not be. And what 5 categories? I'm probably thinking of something else, so that's why I ask.

Novalium Company

@Loong Let's open up a chain called McDonarnolds.

Emilio Pisanty

@ScientistSmithYT Your response to "light is not an object" was

11 hours ago, by Scientist Smith YT

@EmilioPisanty Well do we classify it as a person, place, thing or idea?

which implies that you're working on a framework where any concept must be classified as object, person, place, thing or idea.

Leaving aside the aggressive and snarky tone of the comment I just quoted, I was simply pointing out that this viewpoint simply does not work in physics.

Scientist Smith YT

@Anyone Who Wants To Answer: How would our world operate if we knew what made up a magnetic field from any source creating a magnetic field? Like say we find (years from now, or longer) that a magnetic field was made of say neutrons and not photons, or protons. What could that be used for and how could we use it?

@EmilioPisanty Oh, ok. Got it. I didn't mean for the comment to be snarky or aggressive. Just know that I never mean to be harmful when I comment. It's either me saying what I know, don't know, or propose a comment in a statement form. Sorry if it came across that way.

Emilio Pisanty

If you were looking for a constructive conversation about physics, you took the diametrically opposite course of action. You were provided (here) with a concise description of the issues. You chose to respond with aggression.

Slereah

@ScientistSmithYT The only decent thing I can think of reading this is Feynman's argument on why the gravitational field has to be made from gravitons

He does a lengthy analysis of why the gravitational field must be a spin 2 massless field

The same kind of analysis holds for electromagnetism being a spin 1 massless field

Emilio Pisanty

7:02 PM

At this stage I don't see much point in any further engagement.

Slereah

He does actually do an analysis of what would happen if a force was mediated by fermions

Scientist Smith YT

@EmilioPisanty Alright.

@Slereah I'm trying to find a good question to ask, but can't find the right wording. Gravitational field? I'm confused...

Slereah

Well that's a different force, but the arguments are roughly similar

Emilio Pisanty

@vzn Regarding "have seen someone assert there was something illegal going on", I don't think that there's any real room doubt that the change is illegal. You can argue about whether the change is harmful and whether the illegality matters or not, but if SE has actual, valid arguments as to why the change is not a copyright violation, they have yet to provide them, despite continued and explicit requests that they do so.

Slereah

If the magnetic force is to be conveyed by a quantum field, then it has to be massless, because its field intensity decays as $1/r^2$

It can't be of even spin, because like repels like

Emilio Pisanty

7:10 PM

And yes, I agree, the current meltdown over on MSE is something to behold.

Slereah

it must be of odd spin because of this

But due to causality arguments, it can't be of spin $> 3/2$

Therefore it must be a massless particle of spin 1

Emilio Pisanty

@Slereah or -1

Slereah

@EmilioPisanty $\hat{S}$ not $\hat{S}_z$

you bum

Scientist Smith YT

@Slereah oh, ok. I just found out what fermions are. It seems that fermions are the same as quarks.

Slereah

Well

quarks are fermions

but not vice versa

Scientist Smith YT

7:12 PM

Huh? Why aren't fermions the same as quarks?

Slereah

I would say probably don't worry of what particles the electromagnetic field is made until you've learned the basics though

Emilio Pisanty

@Slereah only if you stick to boring vanilla old QM

Scientist Smith YT

I've learned some basics, but I do study in separate fields which seems to skip certain parts.

Emilio Pisanty

I'm using FQM (Fancy QM), where total spin can be negative

=P

@ScientistSmithYT not all fermions are quarks

Slereah

You know one thing I should try to work out someday is like

Emilio Pisanty

7:14 PM

leptons (including electrons and neutrinos) are also fermions but they're not quarks

Slereah

Continuous spin representations

They're almost never discussed

quite possibly the most horrible quantum field

Scientist Smith YT

@Slereah Oh, ok

Emilio Pisanty

it is also possible for a composite particle to be a fermion

@Slereah reference?

Scientist Smith YT

What do the "$" mean on the formula you gave "$1/r^2$" and what does "r" mean in this case... Radius?

Slereah

@EmilioPisanty it's part of the whole Wigner classification

Scientist Smith YT

7:19 PM

@Slereah I've just never been told what the signs mean in the chat and I've never asked until now. In different places different signs are used to mean different things.

Slereah

@ScientistSmithYT Those are for mathjax

See :

30

A: Any chance of MathJax in chat?

As a workaround while this request is pending, there exist several client-side workarounds that can be used to enable LaTeX rendering in chat, including: ChatJax, a set of bookmarklets by robjohn to enable dynamic MathJax support in chat. Commonly used in the Mathematics chat room. An altern...

Scientist Smith YT

I'll take a look

I don't see where it says what the signs mean.

@Slereah My guess is that the "$" sign is to quote the formula used. Am I correct?

Slereah

When you have mathjax active, anything between two dollar signs will display as a proper formula

Scientist Smith YT

Ok

I am assuming that "r" in the formula means radius. Am I correct to assume that?

Slereah

Yes.

This is just from the usual EM laws

Coulomb and Biot-Savart

Scientist Smith YT

7:39 PM

Ok

Sorry for the delayed response, had some stuff to take care of.

Slereah

8:21 PM

arxiv.org/pdf/math/0612860.pdf

Apparently this is the answer to my question

Slereah

9:01 PM

Oh gooood

Now there's WHEELER UNIVERSES

Yet another weird spacetime I've never heard of

bolbteppa

Possibility of continuous spin comes up in massless case in the Wigner method since the little group is the Euclidean $ISO(D-2)$

Slereah

Oh wait that's just a type of FRW metric

Man that's a whole other pan of GR I've never seen before

YET AGAIN

GR is a neverending hole

danielunderwood

9:16 PM

you might even call it a black hole

I'm afraid you've already crossed the event horizon

bolbteppa

How can a theory which says nothing can come back from across an event horizon describe what's across an event horizon - checkmate relativists

danielunderwood

Because those event horizons are inside this event horizon...it's just event horizons all the way down

> Quantization "puts hats" on the momenta and field variables

that's an interesting take on quantization

bolbteppa

Unified theory: get rid of the hats in the world and we're done

Slereah

Well no, the unified theory puts hats on everything

DanielSank

@ScientistSmithYT How do you interact with it? Do you subscribe to tags or did you set up a filter?

Slereah

9:22 PM

$$\overset{🎩}{\pi}$$

bolbteppa

Hatting gravity seems to make things stringy

Slereah

Nah

Hatting gravity gives you canonical QG

String theory is its own thang

bolbteppa

Inconsistent canonical QG

Polyakov: "That was the great event of my life before university. I tried to read many popular books. And I took some freshman courses in physics, and I never really understood them and they didn't engage me. At some point, I bought a second-hand copy of Landau and Lifshitz's Mechanics and that was just a revelation. I still think it's a great book."

Slereah

My thesis advisor was a russian dude

so he made me get L&L

Sir Cumference

@Slereah Pi bar is better

$$\pi\hspace{-0.3em}\overline{}:=\frac{\pi}{2 \pi}$$

2

bolbteppa

9:33 PM

Good advice

The big tragedy is the QED book is based off his class notes, he probably would have written a crazy book directly

@WhitePrime you should learn the math by picking up an intro collegel level physics book and pick it up as you go, you'll always be waving your hands talking about relativity without the math

Slereah

Also if you like wankery read some epistemology

Read some Karl Popper or something

bolbteppa

Or some Wittgenstein

Slereah

if you want some GR wankery read Reichenbach

Or Earman or Malament

bolbteppa

Tractatus Logico-Philosophicus

The Tractatus Logico-Philosophicus (widely abbreviated and cited as TLP) (Latin for Logical Philosophical Treatise or Treatise on Logic and Philosophy) is the only book-length philosophical work by the Austrian philosopher Ludwig Wittgenstein that was published during his lifetime. The project had a broad goal: to identify the relationship between language and reality and to define the limits of science. It is recognized by philosophers as a significant philosophical work of the twentieth century. G. E. Moore originally suggested the work's Latin title as homage to the Tractatus Theologico-Politicus...

> The project had a broad goal: to identify the relationship between language and reality and to define the limits of science

Slereah

If there's anything I learned doing GR is that whatever weird idea I had on the topic, usually someone had already done it, usually 50 years ago

If you don't know a lot about a topic and you have a thought about it, odds are good people have been having those thoughts before

bolbteppa

9:39 PM

If we didn't need the math very few people would put the time in to learning it

Slereah

the truth is that physicists don't actually like weird theories

They spent decades trying to prove GR wrong

there's no lack of counterarguments that were tried

Sir Cumference

@WhitePrime Every definition in math either represents a concept or solves a problem. Nothing is introduced because it'd be funny to do so.

To this end, mathematics can be made very intuitive by knowing what each definition is supposed to represent

bolbteppa

Except in category theory and on nlab

Sir Cumference

@bolbteppa I think you're exaggerating :P

Slereah

Have you ever read nlab

bolbteppa

9:42 PM

You clearly haven't seen functor string theory

Sir Cumference

I mean i know category theory has a rep for being, well, abstract nonsense. but c'mon

Slereah

Sir Cumference

i don't have a background in category theory so i can't judge that :P

Slereah

Well for a start they use "natural number objects"

Which are ABSTRACTION OF INTEGERS

bolbteppa

ncatlab.org/nlab/show/ambient+category

> An ambient category C is just a category from which internal structures take their objects and structure morphisms.

> If $\overline{C}$ has extra structure, like being (semi-)abelian or a site, then one can do extra things; this is made precise through the concept of doctrine.

> More generally an ambient category could be seen as a ‘universe of discourse’, as when C is a topos; see foundations.

Sir Cumference

9:47 PM

@Slereah you make it sound like this is a deadly sin

@bolbteppa mathematics in any subject i haven't studied will look like nonsense to me

this doesn't make category theory stand out lol

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