The h Bar

ACuriousMind

00:00

the only reason I talked about this for so long is because someone claimed we were being unfair to the poor grifter in this case

Ryder Rude

does anyone know of a semi technical philosophy podcast

ACuriousMind

just read a book

Ryder Rude

that's too technical :P but ok

qwerty

@ACuriousMind ok - none of us appear to be people with a platform so the first part is not something we have control over, was my point. and people with platforms who promote nonsense tend not to listen.

Ryder Rude

i will maybe try an audiobook for philosophy

i learn better while listening

Amit

00:03

Mar 26, 2023 at 12:44, by Ryder Rude

Wut is a comprehensive book for the modern theories on this stuff? I mean, their equivalent of QFT

@RyderRude I also replied with a title a bit later :P but I still can't say I read it (don't think I will any time soon)

Ryder Rude

@Amit u have read philosophy books, right?

Amit

none fully

I read a bit of biographies of philosophers, does it count? lol

Ryder Rude

it does. u r good with philosophy discussions

ACuriousMind

@qwerty Hm, I think we're mismatched about the context here: When I said the showrunners should show some integrity, this was in direct response to Ryder trying a "it's just a podcasts, they're all like that" excuse - which, yes, might be the case, but I reject the implication that therefore it's okay. I am under no illusion I'm convincing any of the podcasters with what I say here.

Amit

well so was Socrates, what did he read?? :D

But thanks I guess

Ryder Rude

00:07

i cant keep with with ur discussions with Slereah

qwerty

@ACuriousMind oh I see, fair enough!

Ryder Rude

but im more into consciousness philosophies

Allie

podcasts are the worst

Amit

So start from Descartes

He thought therefore he was

Why do I know this? No idea, not from a book. lol

Ryder Rude

i will read something more modern. decartes thinks dogs don't have soul

lol

Amit

00:09

Nah I think you need to understand how the old guys thought

Ryder Rude

it is not necessary. e.g. in physics, u rarely need to read the things from the old guys

Amit

Because in many ways every philosopher criticizes / supersedes/ directly refers to whoever came before him in the same area of thought

Yeah that's how it's different I believe

Ryder Rude

i tried reading his meditations once, iirc. didn't make much sense

Amit

I suppose it's because philosophy is in many ways "Dialectical"

So don't read him directly, read a book like the one I mentioned in that link, Russell's. He must have mentioned Descartes too

Oh dang now that I think about it, I lied. I read a book about Socrates

Ryder Rude

i currently believe that reading old people is just an idea philosophers push for the field to look more intellectual

lol

Amit

00:12

I really forgot

qwerty

@Amit wdym in this context?

Ryder Rude

@Amit i will try an audiobook this time

@Amit nice

Amit

@qwerty I mean that it is in the form of argument, counter-argument etc. So you need to know the argument the previous guy put forward to understand the context of the response, etc.

Ryder Rude

bye everyone

Amit

gnight!

Ryder Rude

00:15

goodnight :)

qwerty

@Amit that sounds quite exhausting... I don't think I would have the patience for that, it sounds like reading through a chat or social media comment chain argument.

probably one where you think they're all wrong

Amit

@qwerty I agree, OTOH without ever noticing it, how much of the history of Physics do we in fact pick up while learning Physics, even though Physics apparently should be much more neutral and detached from history? :P

Which I am just mentioning to say, once you get interested in a subject, I think it's kind of inevitable to become interested in its history, too

qwerty

@Amit I suppose we can build up arguments, build up our understanding of it from first principles without needing to wade through the history first. that's the difference I guess

it appears constructive rather than oscillatory arguments

Amit

Yes, because we have the luxury of nature being the final judge and jury of it all, history does take more of a back seat. Nonetheless, every kindergarten kid knows that there was a "Michelson Morley experiment" some time circa 1900 and that it was a big thing, etc. :P

Ok it was 1887, but hey it's still kindergarten

and whether Philosophy is "oscillatory" or more of some kind of a "linear" progression, etc. is up for interpretation...

Okay I have to go, good night

qwerty

good night!! :)

user430580

00:38

good night Amit!

Silly Goose

Schwartz and Weinberg just need to have a child (textbook)

Amusingly, the Haag paper cited on the wiki for Haag's theorem looks quite like Weinberg's sort of notation

bolbteppa

00:54

@RyderRude That Riet interview is very good so far

Silly Goose

Schwartz seems to present QFT as essentially finding nice formulas for $a^\dagger(-\infty) - a(\infty)$ and vice versa. Is this an accurate sort of understanding?

bolbteppa

Even if I knew nothing about physics, the honesty this guy has in the interview would sell me, 30 seconds of that Lisi nonsense drove me up the wall, even if I knew nothing I could tell he was BS'ing me.

@SillyGoose Absolutely not

Presumably you're trying to talk about the LSZ formula?

Silly Goose

yesh

bolbteppa

Well LSZ is one way to describe a scattering problem, you can describe the same problem in other ways, the scattering problem is the problem, the setting of incoming free particles and outgoing free particles is forced on us from multiple perspectives, we all want to just solve the Schrodinger equation and study the solution but we can't do it so simply

This guy is an absolute legend: 'if you actually look at the criticisms of string theory, so much of it is about being against curiosity'

Relativisticcucumber

02:09

im taking the laplacian of this lovely boy. and i end up making use of the fact that $\nabla^2(\frac{1}{r}) = -4\pi \delta(r)$. however, i tried to do this without ever simplifying any powers of $r$, for instance i dont allow $\frac{r}{r^2}=\frac{1}{r}$. however, i only get the correct answer if i allow for this type of thing. namely, i find that i achieve the right answer if directly in the potential i reduce the $r's$ in the second term to let them equal one. is this really acceptable??

i feel strongly that it is not

naturallyInconsistent

02:28

@DannyuNDos You are correct in this assessment. In fact, usually people read Griffiths as an intro to Sakurai or Ballentine, and then Shankar as a refinement on those two, that is not exactly needed, because those are already pretty good texts on their own.

@DannyuNDos And the flow I just talked about, is kinda something you might want to take into account before accepting advice from people who say illogical things like:

5 hours ago, by Ryder Rude

i haven't finished the latter two, but they're standard references

@DannyuNDos Goldstein is indeed a bit too much; there are easier introductory books on analytical mechanics, but it is probably still worth reading. Like, you can skip the lengthy discussion on Bertrand's theorem and everything after Hamilton-Jacobi because it will be redone somewhere else with better motivation and all. As for EM, there is also a Griffiths, you know?

Actually, whether you should use a book or not, also depends upon the level at which you are at. Like, if you absolutely require rigorous argumentation, then none of these are what you should be doing. Whereas if you find rigorous mathematics too dense to read, and instead is happy with physics kind of handwaviness all over the place, then you should follow the route just mentioned.

4 hours ago, by Ryder Rude

@Amit i think so... I've never heard of this theorem :p

4 hours ago, by Ryder Rude

this theorem is def not relevant in QM

Silly Goose

My personal opinion is that Griffiths QM is a horrid thing :)

naturallyInconsistent

@SillyGoose you need to be painfully aware that your own demand for rigour is nowhere near the normal experience of most people.

qwerty

I hate all texts to varying degrees: this is why I write notes :P

Silly Goose

i think my problem with it is more mundane than that: Griffiths takes very long to get into the proper formalism of QM. Griffiths might give someone the impression that the "wave function" is what a quantum state is.

naturallyInconsistent

@ACuriousMind But it is a strict prerequisite; one needs to have Coulomb potential and light waves to start talking about QM. Not needed to have a lot more than that, but still, sad state of affairs if someone does not have the basics.

Silly Goose

02:38

I think Sakurai is not so great either. But chapter 2 of Sakurai I think was quite a good read initially

naturallyInconsistent

@SillyGoose It is actually tolerable; one can be extremely productive in nanotechnology with an understanding not any better than wavefunction = quantum state, just augmented with spin half if necessary

qwerty

@SillyGoose !! my experience also. I learned QM in 2nd year undergrad from griffiths, did ok, then flunked 3 and 4th year because I didnt even understand basic postulates and formalism

Silly Goose

i can conceive it's okay in practice, but i feel it is a bit of a crime against quantum mechanics

The wave function approach deemphasizes the algebra (in the mathematical sense) underlying quantum mechanics, which to me is the whole organizational structure of QM

qwerty

@SillyGoose YES

Silly Goose

Compare Griffith's treatment of QHO to a treatment done entirely in bra-ket formalism, for instance.

Although it has been a long time since I read Griffiths

naturallyInconsistent

02:41

@DannyuNDos GR is always its own module, when it is taught at all, as you have heard from ACM. But SR is somewhat in a sad state. If you try to teach it in intro CM, the student has no link of it to anything else, and will be incredibly confused. If you try to teach it entirely in EM, then the student may not see how it links to anything outside of EM, which turns out to be quite dangerously bad. If you do it in advanced CM, some students wont get to see any, and that is worse.

Silly Goose

at some schools in the states i think SR is "covered" in the "modern physics" course

naturallyInconsistent

Yet, as the manga "Death Note" opens with, it is something that you can understand in just a few week's worth of reading, and so it does not really require a gigantic module of its own. As such, it tends to be parcelled up. Just like poor Poland was.

@qwerty You might be horrified to know that there are intro to QM that is so baby, that it is weaker than Griffiths. One is actually supposed to follow the full course of many books, not just judge based upon one single book.

Silly Goose

somewhere in the world is a beautifully woven mathematical physics curriculum

qwerty

@naturallyInconsistent to me, baby doesnt mean skip out on underlying concepts though?

thats what I meant the other day

when we were talking about what I wanted from a textbook, ideally.

I feel like that is possible, but it's not a priority for many writers. they sort of assume you'll pick it up or that you dont need it hashed out and spelled out

naturallyInconsistent

@SillyGoose This is obviously a bad state of affairs, but this is a legacy issue. The pioneers themselves were trained heavily on wave analysis and did not know any linear algebra. They understood Schrödinger's wave mechanics a tremendous amount better than Dirac's. This means that when they wrote the first texts, they heavily skewed towards waves.

Silly Goose

02:48

indeed...perhaps in 10 years we will have a nicer newer formulation of QM hehe

naturallyInconsistent

@qwerty Baby is so baby that it does not even have the postulates explained properly. No maths. Barely even showed Schrödinger's equation. But did talk about the experimental background leading up to quantum---done well, it is actually surprisingly better than the usual treatment.

@SillyGoose how?

@qwerty It is a pre-reg for you, and everybody also agrees that it is definitely helpful for understanding QM, but plenty of students get by without knowing any classical Hamiltonian mechanics before jumping into QM. Their understanding might be defective in parts, but the general functioning is demonstrably fine.

@qwerty Sadly, it has been intolerable for meow meow for years by now.

qwerty

@naturallyInconsistent in what way?

naturallyInconsistent

@qwerty The correct reply is not what you said; it is what ACM said. What you are saying, and what RR is saying, is a misunderstanding of free speech.

Silly Goose

@naturallyInconsistent oh i dont have a reason i just am expressing optimism

i don't think i have learned classical hamiltonian mechanics properly :P

sadge

naturallyInconsistent

@qwerty It is a very pop-sci advertisement machine for string theory and other bits of even fringer physics; which is inevitable because you can literally pick up that the person writing those articles don't understand the basics of what they are writing. It gets much more understandable why things are like that when you understand that the USA university physics Bachelor's, outside of the Ivy League level, is very woeful.

@SillyGoose At your level of "properly", you'd be needing the full structure of symplectic manifolds. A student following your route would be lucky to graduate BSc in a decade.

Silly Goose

03:01

@naturallyInconsistent LOL

qwerty

@naturallyInconsistent they may be cranks but if they are not promoting violence or hate speech or things that are going to actively harm people, I dont see what you want to be done about it?

Relativisticcucumber

@naturallyInconsistent thats what im saying

im trying to make a new household rule that there can be no qft discussions before the first cup of morning coffee

we are so far at zero days of respecting that rule. hoping to break new ground tomorrow

Silly Goose

@Relativisticcucumber i have been waking up and my first thoughts in the morning are about QFT XD

Relativisticcucumber

@SillyGoose oh boy dont i know it

qwerty

@naturallyInconsistent I probably dont read the articles you read I guess. the ones I read were by natalie wolchover about 5 or 6 years ago and I thought they were nice

naturallyInconsistent

03:04

@qwerty Problems that are ignored may sometimes solve themselves. However, the other possibility is that it would fester. Those of us who had foreseen that drumpf had a chance, had to stare in disbelief as the world ignored that a long-ignored problem had festered into an all-consuming black hole.

@qwerty I'm not asking you to personally do something. I'm asking you to note that there is an underlying assumption to that discussion at all, and it is that that is problematic and we should push back against that

Silly Goose

@naturallyInconsistent i made an attempt at symplectic mechanics a little bit ago if you recall hehe. i have left that behind

although i feel i finally have the state of mind to begin to understand some differential geometry hehehe

also what does QFT look like for anyons

qwerty

@naturallyInconsistent people can say BS, people say BS all the time. "pushing back" is only practical when you have some kind of IRL or personal relationship with the people involved

naturallyInconsistent

@qwerty yeah, an editorial team always will have better and worse reporters. Inevitable.

@SillyGoose I also kinda like a rigorous introduction to physics stuff. But it is definitely not for beginners.

@qwerty No, you can watch some youtube drama that actually caused goodness. For example, after hbomberguy covered some plagiarism problems, some people finally took notice and some channels finally went dead. Like, we all have small things we can do to push back, even if it is not always effective. Of course, if someone needs to take a break from pushing back, or simply finds a different way to contribute without pushing back, that is always accommodate-able.

qwerty

03:27

@naturallyInconsistent if you want to be an activist that is very noble but you need social influence such as hbomberguy had as a big youtuber

you can organise to multiply your influence

you can do this like form unions

but that is all A LOT

naturallyInconsistent

@Relativisticcucumber I'm lost as to what your issue is. It seems that you are already definitely using the product rule. All you needed is the notion that $r\,\delta(r)=0$ to reconcile $\frac1r\left(1+\frac{\alpha r}2\right)$ v.s. $\left(\frac1r+\frac\alpha2\right)$

@qwerty that's what the last statement is for. Participate, but you don't have to be the one at the forefront.

qwerty

@naturallyInconsistent how do you participate if there is no existing organised movement? it's easy to say these things.

there are lots of things which really harm, really hurt people. even in academia. people talk but there's no organisation, no real change. there's lip service.

naturallyInconsistent

That's part of what ACM said. You push back in small ways, e.g. don't click links on stuff that you know is noise. In fact, steer people away from them if we can.

qwerty

That's what I was saying.

in my comment you replied to.

naturallyInconsistent

03:43

@qwerty Academia is a sprawling mess that really require congressional action by now. It is manifestly having double standards with how they were ok with student protests about the Vietnam war back in the day, ok with all the critical thinking lip service promotion, but once you protest the ongoing war, suddenly they call the cops on the kids.

Silly Goose

the current state of the world is noise~~

qwerty

@SillyGoose apologies for disrupting your high-level QFT discussions :(

naturallyInconsistent

@qwerty but note that my replies do not include blissful ignorance. Only choosing how and where to contribute to the push back. Your comment was a bit more on the ignoring side; which you also said is because you cannot deal with the handwaviness.

Silly Goose

oh no no discussion was interrupted

naturallyInconsistent

miao miao~~

qwerty

03:46

I wish I could contribute... but it may be another 50 years before I slowly learn all the concepts

to an acceptable non-woeful level

naturallyInconsistent

Oh, you might find yourself much closer to understanding than you currently think.

Silly Goose

i've got to learn a lot of things before i get too old :P. a few people have said that they can no longer learn new math after a certain point in time

naturallyInconsistent

Apparently that is not true

Silly Goose

i hope it is not true

qwerty

@SillyGoose i'm curious what was the upper bound they gave?

Silly Goose

03:52

i have no upper bound, but my ug advisor is perhaps 40-50 and stated he could not learn algebraic geometry. but actually upon reflection i suspect that he was being more humble about his existing understanding of algebraic geometry...

because he mentioned things like Čech cohomology , which to my understanding belongs to the realm of AG

Incredible maths proof is so complex that almost no one can explain it lol

Ryder Rude

07:02

Proving background independence of STRING THEORY

►

there r two formulations of background independence : 1. Being able to define the action without a fixed metric (like in Einstein Hilbert action) 2. Defining the action using a fixed metric, but showing that changing the metric is equivalent to changing the matter/field content

string theory may have background independence in the second formulation, but it is being worked out

ACuriousMind

07:33

@Relativisticcucumber ...why would you not allow $\frac{r}{r^2} = \frac{1}{r}$? It's a true equality!

@SillyGoose It might depend on what one means by "learning" algebraic geometry. I learned algebraic geometry in the sense that I can do the math, I know what a scheme is and how to do homological algebra and spectral sequences etc. - but I never reached a level of "understanding" that some actual algebraic geometers seem to have so that pictures like this make sense to them.

Slereah

Those are spaghettis

qwerty

if you eat the spaghetti you will understand them

Slereah

07:49

A good perspective on algebraic geometry for physicists imo is this book

amazon.com/…

It takes a very physical perspective on spectra of manifolds

also here if you like free books : drhuang.com/science/mathematics/book/gtm/…

Ryder Rude

08:16

> I don’t like that for anything that disagrees with an experiment, they cook up an explanation – a fix-up to say “Well, it still might be true”. For example, the theory requires ten dimensions. Well, maybe there’s a way of wrapping up six of the dimensions. Yes, that’s possible mathematically, but why not seven? When they write their equation, the equation should decide how many of these things get wrapped up, not the desire to agree with experiment.

> In other words, there’s no reason whatsoever in superstring theory that it isn’t eight of the ten dimensions that get wrapped up and that the result is only two dimensions, which would be completely in disagreement with experience

This criticism of Feynman is just as relevant today, more concrete than any other criticism of String Theroy

qwerty

good ol' epicycles

ACuriousMind

it's a shallow criticism because general relativity doesn't tell you which spacetime we live in either and QFT doesn't tell you the world must be the Standard Model - string theory is a proposal for a framework like GR or QFT, not a single specific theory. The criticism is fair only insofar as proponents of string theory tend to oversell their case, e.g. the "no free parameters in the action!" gambit, and then you quietly re-introduce parameters through the choice of compacitification

"I don't like that for anything that disagrees with experiment, they cook up an explanation. For example, QFT can have arbitrarily many particle generations. Well, there's a way to just have three. Yes, that possible mathematically, but why not two or four? The QFT equation should decide how many particle generations there are, not the desire to agree with experiment."

- Feynman if born one generation earlier, presumably

Ryder Rude

@ACuriousMind i did think of that rebuttal. After all, every theory has the desire to fit to experiment. So what's new here? But there is something new here. The number of dimensions was part of the hypothesis of Newtonian mech or SR, but it is the prediction of string theory

When the prediction of a theory goes wrong, u try to fix the hypothesis, not the output itself. E.g. if QM were to predict wrong probabilities, people would patch the Hamiltonian, not the probabilities themselves.

But string theory doesn't try to patch what led to their prediction, but its prediction. This is the sign of ad-hoc

Slereah

All theories do that

Ryder Rude

if string theory tried to patch the action to get the correct number of dimensions, it would be good

Slereah

08:30

It is the ol' debate of accomodationism v. predictionism

Ryder Rude

but ofc it's somewhat philosophical what's an assumption and what's a prediction. but i see the number of dimensions as a prediction of the theory

similarly, to be able to explain new particles in QFT people would be patching up the Hamiltonian

ACuriousMind

Better criticism in this direction would press the string theorists on how they still don't have a compactification that actually produces the Standard Model, i.e. what we observe, without extra bits like superpartners. That at least would directly engage with the question of whether string theory can actually produce realistic predictions, instead of mistaking a theoretical framework for a concrete model

Ryder Rude

@Slereah i don't see something this ad-hoc in qft. Sure, they try to introduce new fields to accomodate for new particles. But that is still a non trivial process

Slereah

I mean have you seen the evolution of QFT

ACuriousMind

@RyderRude It's also a "non-trivial process" to do compactification in string theory. You don't just say "well, I guess the six extra dimensions are rolled up" and that's it.

Ryder Rude

08:33

e.g. just because u added a new field, it doesnt mean u get the right probabilities automatically

Slereah

As a relativisitic theory of QM to a theory with negative energy particles to second quantization to a divergent theory to a renormalized theory to a theory with gauge etc etc

Ryder Rude

@ACuriousMind I'm aware... they have specific manifolds for this

ACuriousMind

I'm not a big string theory supporter but I wish the people criticizing it would at least make the effort to understand enough about it so that their criticisms can be accurate and would not apply the same to QFT or GR in their nascent phases

Slereah

The nuclear interactions starting as a Yukawa potential + 4-fermion interaction to the strong and weak interaction to strong and electroweak

adding arbitrary neutrino oscillation terms

qwerty

plato.stanford.edu/entries/prediction-accommodation

learned new words today, cool

ACuriousMind

08:36

but instead the most prominent representants of both sides of this interminable debate seem to have as their principal goal to make their opponents look stupid or unscientific, it's extremely exhausting

Ryder Rude

i still don't think it the same criticism applies to other theories. Because string theory puts a big constraint on the number of dimensions, and then u have to patch it up (and there is no reason u wouldn't patch it to 2 instead of 4)

qft does not put a constraint on what particles are allowed, which u then patch up

Slereah

The dimensions aren't observable and therefore aren't a particularly interesting part for prediction

And QFT very much does put constraints on particles

Ryder Rude

there is a difference between simply choosing the dimensions to be 2 or 4 as a hypothesis, and getting the dimensions as 10 but reducing it to 4 arbitrarily

Slereah

Big constraints on particle spin, gauge groups and interaction types

Why

Ryder Rude

@Slereah yes, but we don't patch it

Slereah

08:38

Don't we

Ryder Rude

example?

Slereah

As I said the theory has evolved wildly through its history

I just said

Nobody thought about restrictions due to renormalization until the 60's

Or whatever restrictions coming from the Coleman-Mandula theorem

Ryder Rude

yes, I'm aware qft constrains things. constraints are actually a plus point of the theory, as they basically reduce arbitrariness

Slereah

You just don't typically hear about it because it's pretty rare for books to talk about the general theory of QFT, it's very focused on the standard model

If you read books, I mean

Ryder Rude

I'm aware of constraints on interaction terms..

constraints are a plus point. It would have been the greatest achievement of physics if the 10D constraint of ST actually matched what we had known all along

but constraints are a minus point when they disagree with experiments

and constraints are exactly why this criticism doesn't apply to qft or GR imo. They don't have the constraint that disagrees with experiment

ACuriousMind

08:43

you're just focusing on the dimension because that's what all the popular criticism does; the dimensionality is really the least of the technical problems with how to extract a Standard Model-like theory from string theory

if you choose a random compactification you get a random theory with a particle content that's not at all what you wanted, and the particle content of the uncompactified theory is also not right

and one may conceive of a "compactification" not only in terms of a silly "let's make dimensions small" idea, but also simply as choosing different conformal field theories on the world sheet - that they may be represented as a $\sigma$-model with a 10d target space with 6 compact dimensions is secondary

Ryder Rude

@ACuriousMind these other criticisms can be evaded, because theorists can always say "maybe we will work it out". i just think the prediction about dimensions gives us a simple test to put a credence on the validity of string theory

ACuriousMind

but...they also worked out the dimension thing, you can just have a bunch of the "extra" dimensions be compact, and it turns out this also then generates particle content more like what you want if you do it right

Ryder Rude

@ACuriousMind yes. There is this view that that the dimension is simply the internal degrees of freedom of the Conformal field theory

@ACuriousMind well

idk what to say now

ACuriousMind

it's ridiculous to insist that string theory somehow "predicts" 10 flat dimensions and that anything else is just an ad hoc "patch" by string theorists not wanting to admit defeat; yes, the target space has to be almost always 10 dimensional, but there is nothing priviledging any particular target space (with any number of compact dimensions), just like GR can be phrased initially as a theory about manifolds of arbitrary dimension!

again, we have to be careful that we're not deploying critical arguments against string theory that could equally well work against theories we accept

Ryder Rude

but i addressed this. GR does have arbitrary dimensions, but it does not have a constraint on the dimensions. If GR was a still untested theory witha 10D constraint, we would be justified in putting a low credence on it

in absence of tests, there is little to judge the theory except these "logical" tests of credence

Slereah

08:54

Why

Is there a reason a specific number of dimensions is less valid

Ryder Rude

yes! because we are in 4D

Slereah

How do you know

qwerty

read flatland

Ryder Rude

if a theory puts a constraint to something other than 4D, its credence reduces

@Slereah it is the status quo

Slereah

Well if the pope says so I guess

Ryder Rude

08:57

in the absence of experimental tests, we have to use these philosophical tests to put a credence

i will cook an analogy. I'm sure this philosophical test is a reasonable one

ACuriousMind

the point is that a perfectly valid way to interpret string theory is that it shows that you can have the appearance of 4 dimensions without "actually" having 4 dimensions, calling into question if we really "know" the world is 4d

Ryder Rude

the idea is this "if a theory puts a constraint on something that is different from what is known, its credence reduces. Because the constraint counts as a prediction"

if u agree with the above, u agree with the criticism. It all comes down to the above philosophy

ACuriousMind

unless you subscribe to a weird relativistic version of a Kantian a priori intuition for a 4d spacetime, there's no reason to reject theories that have "more" as long as they can explain the 4d-like observations we have

naturallyInconsistent

I feel like Feynman in Character of Physical Law is relevant to this discussion. Paraphrasing from memory: In Physics we always want to have the specific cases. We don't care about the extra generality that the mathematicians work out. So we ask them for results in 3D. The mathematicians just say, substitute 3 into n. But we don't want to have to do that substitution. We want the mathematicians to do that for us. But they don't work for us. They have their own lives and own work, and if you are

not paying for their work, you don't get to ask them to do anything.

Later, you discover relativity, and the physicists goes back to the mathematicians, and ask, when you were talking about general n dimensions...

Ryder Rude

@ACuriousMind yes, this philosophical argument is also using "status quos". I'm sure we can't know if spacetime is 4D, but we can use it as the default knowledge

these principles can be debated... but u know they are rational to some extent

naturallyInconsistent

09:05

@RyderRude Then at the point where speculations that the Sun is the centre of the universe as opposed to the Earth being at the centre of the universe was raging, the status quo would reject the new fledging hypotheses for failing to reproduce the precision at which the data then accrued would be able to "predict"

Slereah

You are confusing the model with the ontology

ACuriousMind

If we're apparently so in love with Feynman, here's a quote cautioning against exactly this fallacy of just trusting your intuitions: "Science is the art of not fooling yourself, and you are the easiest person to fool"

Ryder Rude

@naturallyInconsistent and the status quo would be right in doing so

one can't know everything all the time. one has to go by principles that probably work

Slereah

Bit of a weird way to do research

naturallyInconsistent

@ACuriousMind I think Penrose's argument that compactification is insufficient, because there ought to be consequences of the extra degrees of freedom, is much more nuanced than the standard dissing argument, at least enough to evade your current criticism of such criticisms?

Ryder Rude

09:08

@ACuriousMind i go by the principle that intuition is to be trusted in the absence of evidence that betrays it

naturallyInconsistent

@RyderRude i.e. you are in favour of geocentric epicycles than heliocentrism if you do that. Of course, you get to be like that, but know that you are not making your case look good.

Ryder Rude

only in the absence of experimental tests, can we use these philosophical arguments to put a low credence on string theory

in the presence of tests, these arguments are irrelevant

naturallyInconsistent

@RyderRude yes, the intuition that ancient aliens built the pyramids? Or what other intuitions are you going for, this time?

Ryder Rude

@naturallyInconsistent i have no idea how u get my philosophy to support this argument

ACuriousMind

@naturallyInconsistent Now that's at least a more technical line of reasoning: I think the typical counterargument by string theorists is the swampland - sure, the compactification d.o.f. allow for more freedom in the spacetime geometry than we are used to, but the other properties of string theory,

in particular that you don't really choose the action but it's fixed to be the one anomaly-free SCFT with that target space, so if we look at all the possible effective 4d QFTs that can result from string theory's compactifications it turns out that the space of those effective theories is smaller than the space of renormalizable theories QFT alone would admit.

that is, even if it looks much less restrictive and more arbitrary than QFT in Minkowski space, the effective result is actually more constrained

naturallyInconsistent

09:12

@RyderRude Well, the onus is upon you to elucidate a coherent position on the issue.

@ACuriousMind oh, that's pretty interesting; have you heard of a proof / argument that this is the case? Or is it an ad hoc shield?

qwerty

@naturallyInconsistent this is unfair to RR because we have plenty of evidence and intuition that humans built the pyramids :p

naturallyInconsistent

@qwerty oh, you are going to become RinR2.0? lol

qwerty

@naturallyInconsistent what??

naturallyInconsistent

no, no, it's a joke

dont worry about it

ACuriousMind

@naturallyInconsistent It's called the swampland argument - the metaphor is that we have an island of "nice" effective QFTs resulting from string theory surrounded by a "swamp" of other theories that would be admitted by non-stringy approaches - and it's originally due to Vafa, see arxiv.org/abs/hep-th/0509212

naturallyInconsistent

09:17

Wikipedia it is miao miao goes~

ACuriousMind

my view of this argument is that it's not complicated once you understand how the production of effective QFTs from string theory works: All the effective theories must be dimensional reductions of the unique 11d SUGRA theory + string effects from peculiarities of the compactification, and it's clear you can't get all possible QFTs from this since you can't "delete" stuff, e.g. you can't get theories with only scalars or theories without 4d gravitons from this

the thing one can argue about is how restrictive this actually is (since that depends on what exactly the "string effects" can add) and what exactly this implies

qwerty

are you a superstring?

no, i'm a frayed knot

Slereah

Also fundamentally who cares if a theory is real

naturallyInconsistent

I think this is rather nice comeback, using the "fine tuning" of gravity to argue that allowable low energy EFT of string theories to be smaller than that of building up from QFT. But we don't care about general QFTs. We care about QFTs from the neighbourhood of Standard Model. That's a totally different situation. But I suppose such an argument is still very unfair to proto-theories.

@Slereah there will always be people who care about reality of theories. Like meow. Really doubt if we can all be silenced.

ACuriousMind

09:35

@naturallyInconsistent Well, there's of course also a lot of papers on string phenomenology, i.e. specific compactifications, in search for SM-like theories; last I checked they were very close to producing "just" the MSSM + gravity.

now, how valuable that is, given that we haven't found supersymmetry, is another can of worms :P

Ryder Rude

i have an analogy. Imagine a new theory with no evidence was constrained by the fact that entropy must not increase. now, to save this theory, they say that entropy is, in fact, not increasing if we go detailed enough. or maybe there are extra dimensions whose entropy is simultaneously decreasing

what credence to u assign to this theory

ACuriousMind

you haven't presented a theory

Ryder Rude

it is a meta level philosophical argument

doesn't rely on the particular sturcture of the theory

ACuriousMind

if string theory was just two sentences someone typed in a chat like that that said maybe there are 6 extra dimensions but they're rolled up so that we can't see them, of course no one would believe in it

2

@RyderRude I agree, it's the time-honored philosophical tradition of building a strawman

Ryder Rude

But would u agree that, these constraints, by themselves, reduce ur credence of the theory, that other facts about the theory may increase?

ACuriousMind

09:39

I refuse to engage in a silly game of making a list of things that would make me like a theory or not; we judge ideas as a whole, not by checklist

naturallyInconsistent

09:51

@ACuriousMind I just have the mundane argument against all such speculations: Y'all are free to research this in your free time and using grant money that you successfully applied for. But you don't get to proclaim that you are "the only game in town" and other shit until you have one well-established experimental evidence that differs from the Standard Model. You only get to monopolise lecture time when you achieve that.

I'm actually ok with supremely heavy superpartners and whatnot. Just dont get to promote them until verified differences have appeared compared to SM. If a much simpler theory can do everything that you can do, then you don't have much to add to a conversation.

ACuriousMind

@naturallyInconsistent Yes, I've said at various times that I don't like the way string theory proponents often talk about it, either:

1 hour ago, by ACuriousMind

but instead the most prominent representants of both sides of this interminable debate seem to have as their principal goal to make their opponents look stupid or unscientific, it's extremely exhausting

Ryder Rude

@ACuriousMind by reproducing QFT, do they mean reproducing S-matrix of QFT, or can they recover the local algebra of operators?

one could say that the action of QFT is recoverable from S-matrix

but QFT is still a lot more structure. One still needs to define local operators, as measurements are local in qft

ACuriousMind

@RyderRude You told me yesterday you "were aware of" the Wightman reconstruction theorem. Why do you now appear to have forgotten it entirely?

Ryder Rude

10:06

@ACuriousMind i am still familiar with it.. but even if u get the action, how do u "derive", from a S-matrix, the fact that local measurements are done in QFT along with the Born rule for it?

S-matrix theories define the S-matrix to be the only observable

ACuriousMind

I have no idea what you're talking about, and it's either because you don't understand Wightman or because you don't understand how effective QFTs are obtained from string theory

naturallyInconsistent

"still familiar with it"

Ryder Rude

i am just asking, what structure of QFT do we get out of string theory in these proofs? is it the operator fields or the S-matrix?

ACuriousMind

@RyderRude why don't you read a string theory text and find out if you're interested?

Ryder Rude

@ACuriousMind my question is easily something an outsider to string theory would ask to decide if string theory is good

qwerty

10:11

dumb question - been a while since ive done EM - i dont fully understand why the form of the maxwell action, and maxwell's equations aren't exactly the same regardless of choice of units -- this appears to be a somewhat special case? somehow it feels somehow counter to general covariance though i know it's not.

Ryder Rude

it is a thing for outsiders to ask these questions

naturallyInconsistent

@qwerty which "aren't exactly the same regardless of choice of units" are you referring to? i.e. example pls

qwerty

@naturallyInconsistent erm just thinking about the maxwell action for example

give me a sec

naturallyInconsistent

and im specifically asking for one change that happens

ACuriousMind

@RyderRude apparently you had no issue wasting 1 hour of your and my time making entirely uninformed claims about string theory; I don't see why I should now spend even more time explaining its technical details to you, which invariably you will forget again soon. If you have so much time to waste making claims without knowing anything, you could just as well spend that time first educating yourself on the topics you want to talk about.

I'm not seeking converts to string theory, if you don't start believing in it unless I explain it to you, it's no loss for me at all

naturallyInconsistent

10:14

Actually, ACM, this is what I've been telling you; you keep feeding them; how can you expect that that attention-seeking behaviour would ever stop?

ACuriousMind

@qwerty Are you talking about cgs vs si units?

Ryder Rude

@ACuriousMind i know this....

i just mean that there is a lot of difference between recovering the mathematical structure and recovering the physical interpretation of the theory

qwerty

right the constants out the front of F_{mu nu} F^{mu nu} in the maxwell action change depending on if you use gaussian units compared to SI. apparently this doesnt happen for most other things and one book or pdf singled it out as weird but didnt give an intuitive explanation, can't find it now. was watching the lecture symmetry principles which was talking about coordinates and covariance and it jogged a distant memory

@ACuriousMind yeah

Ryder Rude

From the S-matrix, u may apply a mathematical recipe to get an operator field, but this doesn't somehow declare that the local observables are physically observable

ACuriousMind

@qwerty it's just because cgs doesn't have the Ampere, while SI does, so stuff looks differently

it's only weird if you come at this from a pure mechanics standpoint where SI and cgs are the same up to numerical factors, but the difference is that SI adds the Ampere for EM while cgs doesn't

that is, while current and charge cannot be expressed in terms of other base units in SI, they can be in cgs, see also Wiki

qwerty

10:21

yeah I remember this vaguely

it's "just" a phenomenon of historical convenience of making units match up when doing dimensional analysis, right?

naturallyInconsistent

@qwerty Maxwell's action is an action. Any Lagrangian density has to be in units of energy per volume. The constant in front is just the conversion factor between the units of E and B fields to that of energy per volume.

ACuriousMind

honestly as a quantum field theorist I always struggle with having more than one unit/dimension :P (QFT sets $\hbar = c = 1$ and retains only powers of mass as dimension, essentially)

qwerty

@ACuriousMind how naive ;P we should replace mass with units of the action

naturallyInconsistent

Miao miao actually uses a unit system that is much nicer than both SI and Gaußian. Made every constant disappear from Maxwell's equations, and then reducing even energy and momentum into reciprocal lengths. Finally, to pin down the length unit, the electron's Compton wavelength is just nice to be convenient for any SR calculation. This way, everything is naïvely dimension-less

qwerty

@ACuriousMind haha all my textbooks worked in natural units and I spent a solid week adding c's everywhere to my phd thesis at one point so everything would be ~consistent~ between chapters. its not that bad, you just need to add the c to the units of the metric rather than in the metric

@naturallyInconsistent right, so I misremembered that maxwell's eqns change, right?

twas just the action

@naturallyInconsistent what system is this

naturallyInconsistent

10:33

@qwerty mine own produce. It was a wonderful day when, after a decade of musing, it finally formed into a concrete thing.

qwerty

I never enjoyed electrodynamics because it always felt so... messy. and messy for "weird" reasons like often seeing the same things over but in different formulations and conventions.

i like consistency a lot

naturallyInconsistent

@qwerty When D P M H comes in, it gets way worse.

But miao miao's unit system, stopping just before we pick the electron's Compton wavelength, makes E and B fields each have units of reciprocal areas.

qwerty

Sep 20 at 13:46, by qwerty

@Claudio "Hobbits delighted in such things, if they were accurate; they liked to have books filled with things that they already knew, set out fair and square with no contradictions." - LoTR, Tolkien. I am a hobbit.

@naturallyInconsistent gosh we never even covered that in my degree

@naturallyInconsistent will you one day share your notes somewhere? :) im curious now

naturallyInconsistent

@qwerty Those are absolutely horrible. There are many things that students routinely hate, and D P M H regularly appear on that list. However, unlike most things in physics whereby the introduction thereof would vastly improve the understanding of something later in physics, the D P M H seems to be something we can just go and replace with a simpler way of doing things. As such, I don't see the point of doing them any more.

@qwerty It will take decades to write the textbooks that miao miao is authoring, sigh.

qwerty

@naturallyInconsistent im writing a lot of notes too... if i dont write them down things will leave my brain :(

naturallyInconsistent

10:44

@qwerty RobWords on YT was just pointing out to meow meow that quite a lot of stuff in Tolkien's works are just English runes; and very readable if you know how to read them.

qwerty

it will also take me decades. for example this ONE one-hour lecture has taken me all day to even make brief notes on. this is why I told you it will take me 50 years to understand qft.

naturallyInconsistent

Yes, I have some LaTeXified notes. But those take so much time to write. If only miao miao could just leave things handwritten.

qwerty

@naturallyInconsistent i type much faster than I handwrite these days, but I do all my calculations and manipulations in notebooks first

@naturallyInconsistent I watched that too! it was very nice :)

Ryder Rude

10:57

i just did some research on it physics.stackexchange.com/a/70987

reproducing QFT from string theory is getting a qft Lagrangian to reproduce a similar perturbation series

i would just like to say that the physical facts about qft are not recoverable from a S-matrix

e.g. if i gave u some information to construct some operators, it doesnt establish that those operators are observable

when we say that a theory reproduces another theory, the implication is that the physical facts are reproduced, not the mathematical entities

Mr. Feynman

12:49

Why is half of the starboard somebody roasting RR? Lmao

qwerty

> The mathematical property of general invariance of a system of differential equations is highly nontrivial, but it is not often emphasised, although many
textbooks report about the “invariance of general relativity under arbitrary diffeomorphisms”. In fact, it is often confused with the mathematical possibility of formulating a theory using tensors — a property with little physical relevance that we shall denote general covariance.6 For example, Einstein’s equations are generally invariant, while the wave equation is not; however, both theories admit a tensorial formulation, so they can b…

the lecture that cited this paper was using "general covariance" to mean a symmetry principle.... so they just did exactly what this paragraph rails against.

naturallyInconsistent

@Mr.Feynman testament of how much ill will is incurred when someone is noisy and playing loose with facts.

ACuriousMind

@qwerty Honestly the words "invariance" and "covariance" are used by so many people in so many different ways that using them without a lengthy elaboration of what exactly one means is just inviting confusion

"diffeomorphism invariance" and the confusion around it is something of a running gag in this chat, see e.g. this

qwerty

13:05

@ACuriousMind im guessing it's 8 decades of dispute and counting, huh?

Slereah

That it is

Just read [30 different papers] for the skinny on it

ACuriousMind

probably even longer, but yes, lots of historical baggage there and things that never got properly unentangled (such as people conflating constructions specific to GR with general differential-geometric techniques applicable to physics in general)

Slereah

@ACuriousMind Well the paper was written in 1993 : sites.pitt.edu/~jdnorton/papers/decades.pdf

So now it's 11 decades

qwerty

@ACuriousMind It's been over a year (granted, I parked this for a long time) that i've had this on my to-understand list physics.stackexchange.com/questions/763220/…

Slereah

plus of course general covariance in some sense has been a debate since uuuuuuuh

2000 years maybe?

Depending on what you count it as

qwerty

13:10

I suspect I need to first learn very elementary group theory, then finish off these symmetries lectures and then I might be able to tackle it

ACuriousMind

@qwerty ah yes, I have an unanswered question on observables in GR too :)

qwerty

@Slereah add it to my infinite pile! :D

@Slereah where did you get that number?? lol

ACuriousMind

Euclid, I'm guessing :P

Slereah

Nah more the debates on absolute and relative space

Although I'm not sure that goes back to ancient greece

I know it goes back to Copernicus at least

Also motion relativity is somewhat recent I think?

I know Burridan briefly talks about it

> A ship drawn swiftly in the river even against the flow of the river, after the drawing has ceased, cannot be stopped quickly, but continues to move for a long time. And yet a sailor on deck does not feel any air from behind pushing him. He feels only the air from the front resisting him

I do remember that Ptolemy talks about how the notion of "up" and "down" is relative though

He uses it to explain how things work on a spherical earth

Mr. Feynman

@naturallyInconsistent miao miao

Ryder Rude

13:26

@Mr.Feynman naturallyinconsistent stars any msg directed against me

@Slereah Lee Smolin says that spacetime is a relational entity in GR

because the metric can be almost recovered from something called a "causal structure", which describes how events are causally related

naturallyInconsistent

@Mr.Feynman miao miao ~~

qwerty

@ACuriousMind those were very interesting and I have now bookmarked them

adds to the pile

time to log off, ciao!

naturallyInconsistent

13:43

ciao~

@RyderRude those are 4, 3, and many 2s.

Slereah

According to the Schreib, the weirdness of superposition in QM is due to the fact that the dependent sum of a category becomes a literal sum in a quantum one

nickbros123

@naturallyInconsistent I tried to learn forms and stuff, but they were full of germs so I left it

Slereah

Something relating to pointed types although I'm not quite sure what is pointed here

Apparently if you pick the slice category of a topos and take its category of pointed objects, it becomes a compact monoidal category, ie a category type for QM, but this is for pointed objects and the smash product

How that translates to Hilbert spaces and tensor products he does not say

user430580

14:53

A year after almost failing his high school physics class, a boy told his older brother,
"You know, my physics teacher was right about the optical Doppler effect. You see those cars. The lights of the ones approaching us are white, but the lights of the ones moving away from us are red."

Transcript for