The h Bar

1:36 AM

the footnotes begin >:D

6:31 AM

Helmholtz theorem states that in electrostatic conditions, the field is uniquely determined by its divergence (rho) and it's curl (0), and that sort of gives us the coulombs law, under certain assumptions like field goes off faster than 1/r and the potential integral is convergent. Now under these considerations, suppose I have an infinite sheet charge distribution

The coulomb integral is divergent, but we can still apply gauss law and some symmetry considerations to find the field. But what is happening here?

Relativisticcucumber

7:27 AM

it seems time reversal has a more relaxed requirement on inner products, namely $\vert \langle \tilde{\beta} \vert \tilde{\alpha} \rangle \vert = \vert \langle \beta \vert \alpha \rangle \vert$ so i am wondering why time reversal should be considered a symmetry if it allows for inner products to not be strictly conserved? isnt this against the canonical formalism of symmetries as unitary operators that do leave the inner products preserved?

Mr. Feynman

8:17 AM

Time reversal is not unitary

@SillyGoose I sometimes use too many footnotes and end up with half page of footnotes

Ryder Rude

10:02 AM

@Relativisticcucumber symmetries can be anti-unitary too. U shud look up Wigner's theorem

Kinematical symmetries are defined as transformations which leave measurement probabilities invariant. So this why the inner product can change, as long as the modulus of the inner product is unchanged.

Does geometric quantisation give u a deep understanding of quantum mechanics, or is it just a recipe to end up with usual quantum mechanics on hilbert space? @Slereah

To me, it looks like just a recipe to end up with usual QM. I hav no motivation for why the recipe is the way it is

Slereah

I mean it doesn't even work in the general case, so idk

But it does have plenty of interesting parts to it

Ryder Rude

Oh

Slereah

Like how the phase structure of QM is constructed simply as a generalization of the Poisson algebra

Ryder Rude

Why is it a generalisation?

Slereah

They both have the same algebra but a different global group

Ryder Rude

10:08 AM

Oh

I remember reading this on nlab

Yes, this sounds extremely interesting

@Slereah I was reading this 8 step recipe. But i have no motivation for the steps. Could the motivation be that this recipe is trying to get a different global group of the same algebra?

math.ucr.edu/home/baez/quantization.html . This is what i was reading. @Slereah

Slereah

The hermitian line bundle is what you'll get your wavefunctions from, the U(1) bundle is the phase of the wavefunction

the square integrable sections are because the wavefunction is square integrable

and the polarization is to relate the position and momentum roughly

Ryder Rude

Yes. It is an understandable recipe if we are anticipating usual quantum mechanics

Slereah

Well I'm afraid we are

If you change the bundles to something else you won't get the appropriate theory

Ryder Rude

But i was thinking, if we didnt know about usual QM, what would be the motivation to introduce complex line bundle and to look for the symplectic potential and to map functions to pre-hilbert operators using that formula? Are all of these steps trying to get a different global group of the same lie algebra? @Slereah

Slereah

You can obtain different theories if you use different bundles, but overall yes you're not gonna find a natural way to justify them

But that's the same as all of physics

There's no natural structure to any physical theory

We just use them because they match what we see

Ryder Rude

10:22 AM

nlab said that the circle group is our only other option to integrate the lie algebra. And circle group means complex numbers? @Slereah

But i dont completely underatand the nlab article completely

Slereah

There is certainly an action of circles on complex numbers

But you could use a line bundle of a different field, you could use an R principal bundle instead

Those lead to different theories

Ryder Rude

Oh

Slereah

you can check individually why those theories do not work

Ryder Rude

Yes. I have heard about quaternion QM

Slereah

there's also a real version of QM

and there's a "classical" version of wavefunctions

Ryder Rude

10:23 AM

Oh

@Slereah is this related to KvN mechanics?

KvN has classical wavefunctions

Slereah

Yes one of them is Koopman

one of them is also koopman van hove, IIRC

You can look at various variations on the theory and they lead to theories that don't work for various reasons

Ryder Rude

Oh. But KvN does work. It's just physically incorrect because it's Newtonian mechanics.

Slereah

I mean if by work you mean physically incorrect 🤔

Ryder Rude

Oh

I thought u meant mathematical issues by "not working" :P

So these theories r fine mathematically. They all r theories of probabilistic measurements

But complex numbers r the ones that work

Among many other arbitrary choices

Like different polarisation sometimes leads to unitarily inequaivalent theories

Loong

10:56 AM

@Slereah I am a little bit surprised that you didn't mention that Kaczynski died.

Slereah

I did, just not here

RIP

I tried looking at his thesis in his honor but it's all complex analyis and baire spaces

Loong

well, once again, he is "better known for other work"

Slereah

11:17 AM

Never do complex analysis kids

Ryder Rude

12:10 PM

Newton's achievement is truly remarkable. A universe completely determined by two initial values and a second order differential eqn. Such a simple but revolutionary thought.

This was the beginning of modeling in physics

It is so simple but so hard to come up with

Even a 6 year old could understand it. People would resort less to superstitions if this reductionist deterministic model of the universe is taught since an early age

naturallyInconsistent

Galileo actually already had Newton's 2nd Law

Ryder Rude

Oh

naturallyInconsistent

@RyderRude it already is. 15 yo formally, 10 yo informally, here. It does not have the effect you hope for

Slereah

Students fail to understand it properly

And a few physicists probably

Ryder Rude

@naturallyInconsistent 15 is too late. 10 is somewhat too. But i dont think anyone is teaching the intuitive idea of second order diff eqns to 10 year olds

Slereah

12:20 PM

I don't think it would be particularly that good

Ryder Rude

@Slereah a deterministic view of the universe would make sueprstitions go away

It should be universal knowledge

Slereah

It certainly wouldn't

Ryder Rude

Just like counting

Slereah

Not to mention it is very arguable that the universe is deterministic

Ryder Rude

Yes. It would be lying because of QM

Still, it would promote rational thinking to teach people that two initial conditions and a second order diff eqn describes the universe

I think it should be universal knowledge

But barely anyone knows about it

ACuriousMind

12:24 PM

you're about a decade late to be a New Atheist :P

Slereah

Or two centuries to be a logical positivist

or two thousands to be a stoic

Or twenty thousands to think that the sky gods have already traced your destiny

Ryder Rude

Lol

I would guess many many people even before Galielo had thought of diff eqns describing the universe

Silly Goose

do wigner symmetries preserve transition amplitudes or transition probabilities?

Ryder Rude

@SillyGoose they preserve probabilities becuz amplitude changes under anti unitary symmetry

Silly Goose

okay great

naturallyInconsistent

12:41 PM

@Slereah few??

@RyderRude Is this yet another poem about refrigerators and cars moment?

Ryder Rude

What is the reference? @naturallyInconsistent

naturallyInconsistent

@RyderRude there is nothing to reference. It is just a generic thing, that every possible subject of poems have already been made, unless it refers to a new invention. And differential equations were new inventions at the time

Ryder Rude

I'm sure many people had equivalent ideas to diff eqns

It is very hard to trace the first inventor of an idea

naturallyInconsistent

Some Indian mathematicians already arrived at calculus long before the Europeans had. And they write their maths in prose. Maybe they had a poem about 2nd order ODE

Ryder Rude

We think people suddenly come up with revolutionary theories, but the theory is always slowly discovered and refined throughout generations

@naturallyInconsistent oh

I'm sure even people in BC had these ideas

For e.g. i used to think Darwin literally turned the world around in one day

But those ideas had been around for thousands of years

Ideas only get slowly refined. Some people refine them more than others

There is no such person as an originator of an idea

naturallyInconsistent

12:48 PM

Discoveries are NOT so monolithic as to be categorised so cleanly. Hamilton's discovery of quaternions is not the kind of leap that could easily be repeated.

Curiously, Dirac was not unique in getting Dirac's equation, but the other guy got it in such a completely different form, that maybe it even took a while to establish that they are the same, and also that his route to discovery was nowhere near the stroke of genius that Dirac did, so that he felt too ashamed to publish. His version is actually practically useful in some field.

Ryder Rude

@naturallyInconsistent quaternions cud be one example where the originator of an idea is well defined

In most cases, there is no originator

naturallyInconsistent

And one example is enough to refute the absolutist way you framed that statement

Ryder Rude

For e.g., I'm sure no first person discovered fire

naturallyInconsistent

I mean, I fully agree with you that most discoveries could easily be rediscovered by someone else, and often are discovered by many at once too.

Ryder Rude

@naturallyInconsistent still, I wouldnt be surprised if some unknown people had thought of quaternions

Cantor's uncountable vs countable idea is very unique tho. I'm not sure about this one

But most likely, Cantor borrrowed from earlier work about infinities

Slereah

1:01 PM

Quaternions were an extensions of the theory of couplets which were based on complex numbers

Ryder Rude

Yes. I think u can come up with quaternions by making a complex number of complex numbers

But with a new imaginary unit

This is y these numbers occur in dimensions of powers of two

It also has some deep connection to spin in physics

Secret

So... lately my quantum mechanics had been going rusty so I restudy the whole thing using Susskind's theoretical minimum, and then I notice the following maths trivia

Slereah

You can make complex numbers of arbitrary dimensions

They will just fail to be division algebras

and that is indeed what Mr. Hamilton did originally

Ryder Rude

Yes! Hamilton was looking for a division algebra

Slereah

Since he just wanted a 3 d version of complex numbers

Ryder Rude

1:07 PM

This is what makes clifford algebra very special. They exist in any dimensions and they r division algebra always

Secret

a. The spin operator has an analogue to 3-vector direction (name the form $\sigma \cdot \hat{n}$) owing to how the basis of the state vectors are chosen (everything just alinear combination of spin up spin down state vectors), that allows them to as if split into 3 components for each spatial direction nicely as if it is a 3-vector
b. Postulate on why quantum mathematical formulation agree so well with experiment – The basis is chosen such that any significant experiment results just happens to pop up in the spectra of many Hermitian operators

naturallyInconsistent

@RyderRude That direction lies madness. There were so many people internationally trying it. Once quaternions were found, it became immediately obvious why complex numbers of complex numbers would fail.

Ryder Rude

@naturallyInconsistent it did not fail. It is a standard procedure to invent quaternions, octonions and sedenions today. I forgot the name of it

Something like "Ruelle construction"

Secret

Is is possible that a hilbert space formulation just happened among the possible theories, to match the best to the standard deviations obtained from experiments in heisenberg uncertainty principle?

ACuriousMind

@RyderRude Clifford algebras are not division algebras.

Ryder Rude

1:14 PM

@ACuriousMind but the geometric product is invertible becuz it has both dot and wedge

Slereah

you can look at this video for fun

Let's Invent the Triplex Numbers

►

ACuriousMind

@RyderRude I have no idea what you mean; it is a well-known theorem that the only division algebras over the reals are the reals, complex numbers, quaternions and octonions.

Physics Meta

0

Q: Reopening old closed questions

My question is motivated by this related post, which questions the practices of closing [homework-and-exercises] question. My own question is about older posts that remain closed and about the process for reopening them. My understanding is that recently closed posts have a time window for users ...

Secret

Ok tidying up some thoughts, I think lately I had been thinking about the notion of "there is no better theory according to the mathematics formulation" type of questions

We usually use occams razor to select good theories to test in experiments

but I wonder if some theories actually has a mathematical structure that ensures its optimality at least internally speaking, so that within the formulation, it rules out any better candidate theories

Ryder Rude

@Slereah i think Clifford algebra can subsume all of these algebras because Clifford allows for an arbitrary metric signature

@ACuriousMind i will have to look it up

@Slereah But there is also a weird algebra with i^2=0

Im not sure if Clifford algebra can subsume this one

ACuriousMind

1:19 PM

I think you're very confused about what an algebra is

an algebra over the reals is just a ring together with a scalar multiplication

Clifford algebras are a very particular kind of algebra

they are by no means exhaustive for the class of all real algebras

Ryder Rude

Yes. I'm not saying that they can subsume all algebras.

But they allow for arbitrary signatures, so they can subsume many algebras

But u r right. Not every multivector is invertible @ACuriousMind .

naturallyInconsistent

@RyderRude No, there is. It is used to define differentiation. And apparently it is great for automatic algebra systems.

Ryder Rude

@naturallyInconsistent how is it used to define differentiation? Is it related to the infinitesimal unit?

@ACuriousMind I still think every algebra has its own use. Trying to subsume things into Clifford feels very forced

And i dont think it even works

ACuriousMind

cf. en.wikipedia.org/wiki/Nonstandard_calculus

Ryder Rude

For e.g. the e1e2 multivector is slightly different from i

And you can even have a clifford algebra with complex numbers as Scalars. So Clifford algebra is not really clashing with complex numbers

@ACuriousMind this is similar to the algebra i mentioned. There is a "non-standard part"

But it's very different

I actually meant this one : en.m.wikipedia.org/wiki/Dual_number @ACuriousMind

e1e2 does rotate by 90 degrees, but we have to distinguish between left multiplication and right multiplication

With i, right multi is the same as left multi

So it is very forced to say that e1e2 is i. I hear many geometric algebra proponents say this

I think clifford algebra and other algebras can co-exist peacefully

Ryder Rude

1:54 PM

@naturallyInconsistent i think there is one use of these i^2=0 numbers in physics. They r used as Grassman numbers

Mr. Feynman

2:18 PM

The "question-answer" part of this is such a cool way to express physical ideas

Although I don't understand much :P

Balarka Sen

@ACuriousMind This is not really relevant to the discussion, but you might find this interesting: for a field $k$, consider the central simple algebras over $k$, i.e. finite-dimensional (not necessarily commutative) $k$-algebras with no two-sided ideals and center $k$. For a pair of CSA's $A_1, A_2$ over $k$, say $A_1 \sim A_2$ iff $M(n_1, A_1) \cong M(n_2, A_2)$.

The set of all CSA's over $k$ modded out by this equivalence forms a group, where the group operation is tensor product over $k$, called the Brauer group $\mathrm{Br}(k)$ of $k$.

If $k$ is not characteristic 2 etc, the $2$-torsion of $\mathrm{Br}(k)$ is generated by the Clifford algebras of nondegenerate quadratic forms over $k$.

Ryder Rude

@Mr.Feynman it has some crazy word salad for e=mc2

But sounds big if true

Slereah

2:50 PM

Just realized that the flowbox theorem is just one dimensional Frobenius

Ryder Rude

Another, other, other question: What are the constants of motions?

Math Answer: Let (M,ω) be a pre-symplectic manifold with an hamiltonian action of a Lie group G, then the moment map is constant on the characteristics of ω, that is the integral manifolds of the vector distribution x↦ker(ωx).

Is the above supposed to be Noether's theorem somehow?

I got it from Mr. Feynman's link

Balarka Sen

Yes, it is Noether's theorem

Ryder Rude

@BalarkaSen hi. What are the advantages of thinking in terms of deep math like above as opposed to pedestrian math like in the usual Noether's theorem?

I think this level of understanding is extremely cool

It must help in organising the concepts in full generality

Balarka Sen

I'm unsure what the pedestrian math way of thinking about Noether's theorem is. Typically in a first course in classical mechanics you see Noether from the POV of Lagrangian mechanics.

This is more of a Hamiltonian mechanics formulation.

Ryder Rude

I saw it in Hamiltonian mechanics, but it was using the Poisson bracket =0 thing

Balarka Sen

3:00 PM

Oh, then they're just completely equivalent.

Mr. Feynman

@RyderRude I mean, I don't even understand what that means

But I wish I could speak that language, which I'll call "the language of the gods" from now on

Ryder Rude

@BalarkaSen Can u please also explain the connection between e=mc2 and Poincaire group cohomology?

@Mr.Feynman same!

Balarka Sen

No, I don't know that one.

Charlie

The advantages of knowing the full mathematical formalism include that you can convert often hand-wavy physics language into an unambiguous rigorous framework. It eliminates the need to use intuition which is a useful guide but prone to error

Mr. Feynman

Fun fact, I found that link randomly while searching for help to understand Weinberg's ntoation without having to read it cover to cover

Balarka Sen

3:03 PM

Meh, I'm unimpressed by the Noether's theorem jargon. The moment map makes little to no sense to a mathematician if they don't think in terms of the actual physical meaning.

Charlie

But being able to switch back and forth between the two is really useful

Balarka Sen

I think math can be a useful organizing tool. But I'm of the Russian school and believe that that comes more from a place of pragmatism than a sacred belief in terminology.

Mr. Feynman

For most practical purposes it's useless to be able to cast Physics in a perfectly rigorous mathematical language, nor that can be of any help if you don't the Physics at the core, otherwise you'd only be a mathematician who enjoys the mathematical models of Physics

Balarka Sen

I think both practicing mathematician and physicists and their students and clan, largely speaking, lack pragmatism. That's a bad thing.

@Mr.Feynman Well, I'd argue it's also useless to cast mathematics in a perfectly rigorous mathematical language.

Mr. Feynman

On the other hand, once physicists have chosen the appropriate model to describe something, it is undoubtedly useful to understand it in a mathematically rigorous way to avoid getting confused between what is a general property of the mathematics we're using and what is in turn a physical feature of the universe

Balarka Sen

3:07 PM

It's a really bad look that when people outside the field of mathematics think of mathematics, they think of "language"

Even a lot of people inside the field of math believe that is true.

Mr. Feynman

Rigour is not just language though

Balarka Sen

Mathematics is neither about rigor nor about language. They're part of the culture of what a proof means, but mathematics is not about proving things either.

It's like saying physics is about experiments.

Mr. Feynman

I don't think that was implied anywhere above

Balarka Sen

I wasn't responding to anything particular, really

Slereah

The role of perfect rigor in physics is to form an esoteric caste of physicist that keep out the uninitiated

Charlie

3:12 PM

@BalarkaSen What would you say physics is about if not experiments (and some theory to make predictions)?

Balarka Sen

I don't have a one-word answer. If that were true, a chunk of modern physics (eg, string theory) would not be physics.

Charlie

But string theory isn't just being done for fun, it's being done with the intention that it one day be used to make experimental predictions that can be tested

Balarka Sen

I think string theorists would disagree with you on that

Ryder Rude

Balarka meant that physics is not solely about experiments @Charlie

Charlie

There are many string theorists I'm sure who enjoy the mathematical aspect of the theory, but string theory is still a physical theory

Ryder Rude

3:15 PM

But the most important tenet of physics is undoubtedly experiments

Charlie

Sure, but I don't think any person would claim that physics is entirely and uniquely about experiments and theory means nothing

Slereah

Physics is about having fun

Charlie

The reason you conduct the experiment is to gather data to compare to the predictions of the theory

Balarka Sen

I really don't think a theoretical physicist has experiments in mind when they do theoretical physics. Experiments is one component of a vast body of knowledge which has a consistent logic.

Slereah

I mean physics is like 2500 years old, and experiments weren't considered that important until about 500 years ago

So obviously it's not that important

WaveInPlace

3:17 PM

I don't think you can really compare pre and post scientific method like that, @Slereah. People thought about science very differently.

For one, they were wrong a lot more. :)

Ryder Rude

@BalarkaSen completely agree! Theoreticians just want to play around. Even if we are never able to test quantum gravity, it wouldnt stop theoreticians from having fun

Slereah

We still haven't even settled what science is supposed to be

Ryder Rude

Philosophy of ontology is also one of the goals of theoretical physicists

Slereah

I think it's mostly a patchwork of various things that are sort of related

WaveInPlace

I'm not sure there's one answer for what science is. There are millions of people doing research, and they all have their own motivations.

Charlie

3:19 PM

Theoretical physicists have less interest in theories that are not predictive though. String theory is complicated and has a lot of different branches to explore, but once one of them becomes a "dead end" in the sense that it simply isn't consistent with the real world, theoretical interest in it dwindles

Slereah

I've worked on many theories that are not predictive at all

Not even meant to!

Balarka Sen

"consistency" with the real world is not just something demonstrable or otherwise through experiments, is my point

Charlie

How does one demonstrate consistency with the real world of a prediction of a theory without an experiment?

Slereah

Most theoretical physics books don't even have a section on how to relate most of the math structure to the real world

It is crazy rare

Ryder Rude

I do physics only to get to know nature's ontology

Charlie

3:21 PM

That's implied in the notation, it's why they generally refer to it as spacetime and not a Lorentzian manifold

Balarka Sen

there's a chain of "epistemological breaks", which leads from some combinations of experiments and the foundations of existing theoretical underpinnings to the final conclusion.

Charlie

At least, once the theory is described

Ryder Rude

So I'm fine with a platonic mathematical description. But yes, it has to be consistent with what can be experimentally tested

Slereah

I have studied the problem and let me tell you boy it's not at all implied

I mean most of the time you have some vague idea, but 1) even then it's rarely straightforward 2) as theories become more complicated that's less and less true

Balarka Sen

eg, here's a simplistic example: no one can test string theory, but its a very natural conformally invariant field theory, and we know (a) field theories are extremely successful, (b) having the group of conformal automorphisms as the gauge group is extremely natural

so why not?

part of (a) and (b) lies in their experimental underpinnings

ACuriousMind

3:23 PM

@Charlie [citation needed]

Ryder Rude

@BalarkaSen We shud also note that at the moment string theory produces a result in conflict with tested observations, people would lose interest in string theory

ACuriousMind

people are still constructiing supersymmetric models even though we have zero evidence that supersymmetry is realized in nature

Slereah

One time some guy just studied vector theories of gravity even though he absolutely knew that they would not work

Ryder Rude

@BalarkaSen But that still doesnt mean that those people r doing string theory to predict experiments

ACuriousMind

@RyderRude [citation needed], cf. again supersymmetry

Ryder Rude

3:24 PM

@BalarkaSen So I overall agree. But consistency with experiments is still a criterion

Balarka Sen

@RyderRude the thing about string theory is it is very easy to fix it if it produces a result in conflict with tested observations

you just say the particles in LHC vanishes in one of the extra 11 complex dimensions

or youre just not using enough energy

Charlie

But there is still reason to believe supersymmetry may be found in experiment, if we later find that supersymmetry inherently conflicts with experiment at some point it would probably reduce the amount of research interest in it from a physics point of view

Ryder Rude

@BalarkaSen yes, but that still means that experiments r not disregarded. String theorists r interested in string theory only as long as it is consistent with observations. Observations r not disregarded in physics

ACuriousMind

also, "string theory" doesn't predict anything - it's like saying that "QFT" predicts something

predictions come from specific models, not theoretical frameworks

@RyderRude Many non-string theorists would disagree with this characterization

Ryder Rude

But then again, physics is very broad. Some people may find joy in constructing fictional physics universes. This narrow field of physics completely disregards experiments

There are physicists who construct ficitonal universes

And it is still physics because it is at least educational

Charlie

3:28 PM

@ACuriousMind I don't have a specific example, a better phrasing of that would be that presumably theoretical interest in it would dwindle. There is still value in trying to understand why it leads to a dead end but presumably focus shifts elsewhere

Ryder Rude

And it is analogous to real world physics

ACuriousMind

@Charlie I mean, what you're saying is how it's supposed to work

but I don't think the evidence works out in the case of string theory :P

WaveInPlace

Sunk costs are hard to get around.

If you've spent 20+ years on a theory, would you really abandon it?

Charlie

But surely it's tough to say that about string theory because it's predictions are out of experimental reach at the moment

ACuriousMind

@Charlie name one "prediction of string theory"

I can tell you how to produce essentially any (supersymmetric) particle content you want from string theory, just like you can construct QFTs with arbitrary particle contents

Charlie

3:31 PM

Like, presumably after GR was constructed there was increased interest in exploring manifolds with non-Lorentzian signature to see if they might also be useful in predicting experiment, but at a certain point the interest in them drops of from a physics standpoint as people recognised that they a bit of a dead end

Ryder Rude

@ACuriousMind Dont u think 95% of people wud stop doing string theory if it can no longer be saved to make it consistent with observations? Apparent lack of supersymmetry is still not in contradiction with observations

Balarka Sen

"exploring manifolds with non-Lorentzian signature" sounds like a math problem and not a physics problem

people do that

Charlie

@ACuriousMind I am totally talking from what I have garnered from the internet over the years but are there not predictions regarding black holes that come from models in ST?

@BalarkaSen I have no expectation that what I'm saying applies to mathematicians interest though, all bets are off then :p

ACuriousMind

@RyderRude Again, string theory is a framework, not a theory that makes specific predictions. If we observed something that is inconsistent with the Standard Model, we'd just say the SM is wrong, not QFT as a framework. You have the same situation with "string theory", I don't know what it would mean for "string theory" as a framework to be consistent with observations or not.

Slereah

@ACuriousMind I have tried all $10^{500}$ string theories and none of them work

ACuriousMind

3:36 PM

@Charlie I don't know any

Balarka Sen

how many calabi yau manifolds do we know currently?

its some huge finite number

prove the mirror symmetry by proving it for all of them

ACuriousMind

@Slereah see, but that number was mostly about CY compactifications that produce supersymmetric theories

Slereah

Alright let me try the other manifolds

...

nope

Still don't work

Ryder Rude

@ACuriousMind ok so the string theory framework can practically never go inconsistent with experiments. But then, this is the reason why string theory can forever be studied forever. My point is that, IF a theory cant be saved anymore, physicists wud throw it away. So this is still a basic criterion for doing physics

ACuriousMind

It seems to me you are projecting your idea of how physicists should work here

Balarka Sen

3:40 PM

im pretty sure you can make up totally dull unfalsifiable theories

"universe is a rumpelstiltskin with an action of the Poincare group"

there i did it

just because something is unfalsifiable doesn't make it physics

Ryder Rude

Then we shud not try to precisely define physics. This is what philosophers do

Balarka Sen

projecting what happens in math: if something is sufficiently interesting and makes all the right sounds, i.e. is consistent with understanding of mathematics (be it proofs, or intuition, or whatever you wish) in simpler examples, relates to other more well understood areas of mathematics -- then you call it a new mathematical theory

no one's trying to define physics. the argument was about whether physics is "experiments and prediction" set in stone

because i put forth the opinion, in analogy, that math is not "theorems and proofs" set in stone

Ryder Rude

It's not set in stone because i wud say a very narrow group of physicists are interested in fictional universes. And i wud still define that as physics

Balarka Sen

even ignoring fringe physics

the slogans in scare quotes are, IMO, a reductive way of looking at the two respective subjects

Slereah

I'm not very worried about what is or isn't physics really

Ryder Rude

3:47 PM

This reminds me of that meme about philosophers trying to stop doing philosophy and then categorising what is and isnt philosophy

This is also related to the "pile or not pile" paradox. Everyone agrees one grain of sand isnt a pile, while a lot of sand is a pile

But no one agrees about the transition point

The actual paradox is that a hard transition point cant be defined

Mr. Feynman

4:26 PM

@Slereah I mean, it's not like the QFT machinery would attract them even being unrigorous

Slereah

@Mr.Feynman I dunno, pop science has attracted a lot of people

If we kept everything as mysterious esoteric teachings we wouldn't have so many cranks

Pythagoras was right

Maybe we shouldn't eat beans

Mr. Feynman

4:46 PM

@Slereah but non rigorous physics is not pop science :P

Unless you didn't mean mathematically rigorous

Slereah

If you make the physics unreadable to pop science author you won't have any troubles

Mr. Feynman

What if the pop science author is Kip?

Or Feynman

Relativisticcucumber

merp merp merp

is merp physics ? i think so.

Mr. Feynman

Jigglypuff :(

Relativisticcucumber

why the sad

and another q -- i am reading about parity from sakurai and he presents the following argument where "the relation above" refers to the anticommutation relation between $\pi$ and $x$, and i am wondering why this conclusion is true? i see that these two eigenstates are eigenstates of the same operator with the same eigenvalue, but why cant the spectrum be degenerate?

@Mr.Feynman do you hate merps O.o

my anthem youtube.com/watch?v=QZ8RpW1PCgI

Relativisticcucumber

5:15 PM

@Mr.Feynman flees from merps. he fears their power.

as should we all

More Anonymous

@JohnRennie This video in unavailable :(

Mr. Feynman

5:41 PM

@Relativisticcucumber I hate a lot of things my dear

Relativisticcucumber

@Mr.Feynman what is smth u love not related to physics

or maths

Mr. Feynman

5:57 PM

@Relativisticcucumber myself

just kidding, I love reading manga and watching anime

Apart from that (or videogames some years ago), I don't think I have a stable hobby. I'm looking for another hobby, maybe drawing or learning a new language (but could that be considered a hobby). What's your hobby? @Relativisticcucumber

Relativisticcucumber

6:38 PM

hmmmmm

i really like to to run/work out and i also lately have enjoyed analyzing taylor swift's discography. let me show u a few plots ive been working on

Relativisticcucumber

6:54 PM

ok they are majorly lacking legends bc i accidentally deleted my powerpoint w all the info and titles BUT generally these are the main ones ive been working on:

so for the first one its a plot that shows all the albums, songs, and unique words to that song. so u select an album, then a song, then u can see all of the unique words. a unique word is defined as a word that only appears on that song in the album and does not fit into the category of "essential words" which is a list of words such as he, the, are, is, etc. the second one is a network of all songs and it shows which songs are the most connected, and they are color coated by album. [...]

[...] the connections are based on if the songs are connected above threshold level which is a parameter that i select. the last graph shows how interconnected the songs in each album are as a function of the same threshold from the larger network. i was examining how the connectivity of the albums changes across threshold. there are some kinks that i need to work out though.

oh no for some reason midnights has been left off of figure 1. another kink to work out.

Amit

7:39 PM

Do Taylor Swift songs form a Lie group?

@Relativisticcucumber Dynkin diagrams, lol

I like "anti hero" the version with the bleachers

Relativisticcucumber

YES

i love jack antonoff

Amit

mm let's hear that

oh, bleachers' singer?

thought it's a song name :)

Relativisticcucumber

yes and he co-produces a lot of taylor's songs

Amit

ahh, didn't know that

nice

Relativisticcucumber

omg a song jack antonoff -- i'd listen

Amit

7:44 PM

:D

Mr. Feynman

@Relativisticcucumber There are periods of the year when I feel like running, it's quite relaxing

@Relativisticcucumber lol this could become a paper :P

Relativisticcucumber

ill make a paper out of it for lols

stay tuned

Silly Goose

8:17 PM

:D @Relativisticcucumber

Slereah

8:36 PM

> Briefly: in classical mechanics, the Galilei group acts on the symplectic manifold of states of a free particle. But in quantum mechanics, we only have a projective representation of this group on the Hilbert space of states of the free particle. The cocycle is the particle’s mass.

Switching to a much more lowbrow way of talking: you can’t see the mass of a free classical particle by just watching its trajectory, since it goes along a straight line at constant velocity no matter what it’s mass is. But you can see the mass of a free quantum particle, because its wavefunction smears out fa…

I did wonder why one of the four fundamental length scale only involved the electron's de broglie's wavelength and not any force at all

Slereah

9:40 PM

Matter wave clock

A matter wave clock is a type of clock whose principle of operation makes use of the apparent wavelike properties of matter. Matter waves were first proposed by Louis de Broglie and are sometimes called de Broglie waves. They form a key aspect of wave–particle duality and experiments have since supported the idea. The wave associated with a particle of a given mass, such as an atom, has a defined frequency, and a change in the duration of one cycle from peak to peak that is sometimes called its Compton periodicity. Such a matter wave has the characteristics of a simple clock, in that it marks out...

Amit

It reminds me of a weird question I had about light clocks

If a room with a football, table and me holding a tennis ball in my hand start accelerating... to a certain speed $v$. It's rather clear "when" each object gains that same speed. The ball may roll backward to the wall and stop, my feet will be able to use friction to stand still, hence also imparting this speed to the tennis ball... table also likely will not move due to friction etc. But now suppose I have a laser in my pocket... or any light emitter.... need I finish the question? :)

If I shine the laser, at what point does it gain horizontal speed $v$? Clearly the whole device gained it, but what is happening internally to realize that is a bit mysterious to me somehow. I guess it must be just the speed that the electrons gained

Supposedly electrons will radiate so... yeah, maybe it's not that complicated?

bolbteppa

What Every Physicist Should Know About String Theory - ICTP Theoretical Physics Colloquium

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@MoreAnonymous See above

Looks similar to the one I linked to the other day (sound works)

Amit

Did they fix the sound?

bolbteppa

In the same YT list:

Unzicker annoys string theorists by asking about Witten's responsibility

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Amit

lol, this guy is an attention w***e

bolbteppa

9:56 PM

youtube.com/shorts/aUgKYHPszDg

What a god damn fool

It's all an anti-gravity conspiracy to brilliantly stagnate physics, this is from someone that (at least used to) be taken seriously

Amit

This is heavily edited so it's difficult to know. I sometimes think Weinstein's art form is to say 99.9% truth while emphasizing the 0.1% as a gateway and invitation to wild conspiracy theories lol

I mean sure so Ed's father was interested in Anti gravity, who cares. A lot of interesting work was done there, just relatively lately there was this interesting paper on warp drives...

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