The h Bar - 2022-11-28

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2:32 AM

@Tanner-reinstateLGBTpeople Related: en.wikipedia.org/wiki/Vortex_theory_of_the_atom "Lord Kelvin first conjectured that atoms might be vortices in the aether that pervades space."

4 hours later…

6:32 AM

Hi All..

Hello @JohnRennie Sir

Hi :-)

@JohnRennie Sir yesterday you were discussing about PE. The example of earth and me.

Let's move to the problem solving room

@JohnRennie Aye Sir..

2 hours later…

8:35 AM

Greg Egan is releasing a new novel in Feb 2023, set in a universe with 8 generations of (virtually) stable leptons. There's an excerpt & info about the physics & chemistry on his site. gregegan.net/SCALE/SCALE.html

> In the novel Scale, however, the premise is that there are eight leptons, with masses that are all powers of two times the mass of the lightest one [...] What’s more, they all have lifetimes much longer than the current age of the universe.

Sounds exctiing

The good thing about Greg Egan's books is that although he knows a lot about physics he doesn't let it dominate his books. Too many hard SF writers (Hannu Rajaniemi I'm looking at you) let it dominate to the point where the story ceases to be entertaining.

8:51 AM

I read Incandescence by him a long time ago, liked it and I keep meaning to read something else of his but somehow I haven't actually come around to it

Too many books too little life ...

Apparently the golden ratio is related to projective geometry

although looking at things, it's basically impossible to search for anything related to the golden ratio

Egan has a bunch of short stories online: gregegan.net/BIBLIOGRAPHY/Online.html

The results are 99% insane people

ACM, you might enjoy Riding The Crocodile, which is kind of a prequel to Incandescence.

9:00 AM

I know of Egan yes

user image

The average google result for things relating to the golden ratio

There's a lot of good stuff in the Fibonacci Quarterly. fq.math.ca

I don't know why crazy people love the golden ratio so much, it doesn't seem that exciting

Also Cut The Knot. cut-the-knot.org/arithmetic/algebra/FibonacciGCD.shtml & cut-the-knot.org/do_you_know/GoldenRatio.shtml

You can understand basic properties of the Golden Ratio without knowing much mathematics. OTOH, if you're mathematically naive, you may feel like you've discovered some deep & profound Secret Of The Universe just because you've understood some fairly basic mathematical fact. I call it the Sacred Geometry fallacy. Yes, triangles are cool. That doesn't imply that God is some kind of triangular structure. ;)

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sagecell.sagemath.org/…

9:16 AM

When I read about it the golden ratio doesn't feel that much more amazing than say, $\sqrt{2}$

But nobody is exclaiming that some A4 sheet of paper is divine

The continued fractions of $\phi$ and $\sqrt2$ are very similar. In fact, sometimes $1+\sqrt2$ is known as the silver ratio. en.wikipedia.org/wiki/Silver_ratio

Who gets the bronze ratio?

The metallic means (also ratios or constants) of the successive natural numbers are the continued fractions: n + 1 n +...

Even less cool

The continued fraction of $\phi$ has the slowest convergence, so in that sense, it's the most irrational number. And because the numerators & denominators in its convergents grow so slowly it has lots of good rational approximations. So things that are kinda close to the golden ratio can easily be mistaken for it. That is, lots of things that people think are connected to the golden ratio may not be, they're just coincidentally close to it. :)

In the 1920s, plastic was the new wonder material. But the connotations of the term "plastic number" haven't aged well.

In mathematics, the plastic number ρ (also known as the plastic constant, the plastic ratio, the minimal Pisot number, the platin number, Siegel's number or, in French, le nombre radiant) is a mathematical constant which is the unique real solution of the cubic equation x 3 = x + 1. {\displaystyle x^{3}=x+1.} It has the exact value ρ = 9 +...

9:37 AM

My body obeys the exact proportion of the aluminium number 😔

Snub icosidodecadodecahedron

In geometry, the snub icosidodecadodecahedron is a nonconvex uniform polyhedron, indexed as U46. It has 104 faces (80 triangles, 12 pentagons, and 12 pentagrams), 180 edges, and 60 vertices. As the name indicates, it belongs to the family of snub polyhedra. The circumradius of the snub icosidodecadodecahedron with unit edge length is 1 2 2 ρ − 1 ρ...

the hell is this garbage shape

It's related to en.wikipedia.org/wiki/Compound_of_five_cubes

From gregegan.net/SCIENCE/Origami/Origami.html

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9:55 AM

that origami isn't optimized at all

doesn't resemble an animal at all

10:18 AM

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Can anyone help how to solve this problem ? I tried relativistic kinetic energy formula $KE = ( \gamma - 1) m_0 c^2$ . Can I relativistically write $E=Pt$ ? I think it should not be $E= \gamma t \cdot P$ , because we are observing particle with particular velocity.. whereas the power of light given is also in my own frame.. is my reasoning correct ?

Correct answer is given 1st option (bolden the answer) but using relaticistic expressions I am not able to get any answer ? $\gamma m_0 c^2 = Pt $ So, $ \gamma = \frac{Pt}{m_0 c^2} $ .. this way I get $ (\gamma - 1) m_0 c^2 = \left (\frac{Pt}{m_0 c^2} - 1 \right) m_0 c^2 $... is it fine or wrong approach ?

1 hour later…

11:40 AM

Would you say that renormalisation, in general, is a process of guessing a higher energy Lagrangian given a lower energy Lagrangian? We make this guess by postulating additional terms added to the lower energy Lagrangian, with constants that absorb the perturbation divergences

But I don't think this fully captures renormalisation. e.g. in QED, renormalisation is simply the process of making the coupling dependent on the energy scale to absorb the perturbation divergences. There is no change to the Lagrangian here, no additional constants introduced

The lower energy lagrangian is related to our "higher energy Lagrangian guess" by the method of functionally integrating out the high energy modes

12:01 PM

@RyderRude No, renormalization goes the other way: You start from a high-energy/small-distance-scale theory and go to a low-energy/large-distance-scale

it sometimes looks different because we can run this process backwards by asking "what kind of high-energy theory would give this low-energy one if renormalized?", but strictly speaking this backwards running is not part of the renormalization group

@RyderRude the lack of "new terms" in QED is related to the concept of (ir)relevant operators

you only need to write down the relevant ones to determine the renormalization flow

Oh, so renormalisation loses information. One could say that the "guessing the high energy Lagrangian" process is the thing we do to arrive at a high energy theory

I'm having a hard time connecting the "integrate out high modes renormalisation" with the "make $e$ dependent on $\lambda$, $\lambda \rightarrow \infty$ renormalisation.

@ACuriousMind

@RyderRude the connection is the notion of the effective action: Your "mode renormalization" gives you some effective action at scale $\lambda$ like $S[\phi](\lambda) = g_2(\lambda)\phi^2 + g_4(\lambda)\phi^4 + g_6(\lambda)\phi^6$ etc. So knowing the effective action at each $\lambda$ also gives you a running coupling

@RyderRude only if you throw away the irrelevant operators

12:17 PM

Oh, that makes sense :P. Renormalisation is a function of $\lambda$

What are irrelevnat operators?

The terms that get deleted?

@RyderRude the ones you would call "non-renormalizable"

we call them "irrelevant" because you can show that their running couplings always decrease as the scale $\lambda$ decreases, so it's not really worth it to pick them up

They are only relevant in higher energies?

These are the terms we guess, right?

and since generally our Lagrangians already consist of all renormalizable terms we could manage to write down with our symmetry and field content, this is the reason the "non-Wilsonian" renormalization gets away with not introducing additional terms

We guessing UV complete theory from low energu theory

I really wouldn't call it guessing

you can, in principle, run the renormalization group equations backwards, you just need to reformulate the problem so that that makes formal sense

12:20 PM

There is a systematic way to calculate the information loss from renormalisation?

again, there is only "information loss" if you've decided to throw away the irrelevant operators

You mean that there are only finitely many mathematical terms that can takw part in the Lagrangian of QFT

Assuming symmetries and renormalizablility and stuff

@ACuriousMind yeah, there is no reason to throw them away other than calculational convenience

@RyderRude yes - the higher-order terms are always irrelevant/non-renormalizable

Otherwise, all the information is still there in the integrated lagrangian

Why do we call them non-renormaizable? I think "negligible" is the right word

Non renormalizable makes my brain go at non-curable divergences

well these two are equivalent

the terms that become irrelevant in the IR are exactly the ones producing the infinite UV divergences in the non-Wilsonian approach

12:27 PM

That's surprising

i.e. the power-counting non-renormalizable terms are the irrelevant terms

So how do the divergences of these terms get cured? By introducing even more terms at even higher energies?

@RyderRude No, it isn't: For the inherent Wilsonian cutoff $\lambda_0$ the irrelevant terms go to zero as the scale $\lambda$ becomes much smaller than $\lambda_0$. The power-counting approach essentially wants to have a well-defined theory at $\lambda_0 = \infty$, and that means all scales are "much smaller" than the cutoff. So for a theory that is UV-complete you don't have any of the non-renormalizable terms in the UV completion to begin with.

all this isn't simple because there are so many different ways to talk about renormalization but I promise it's all pretty consistent in the end ;)

Yeah, I only half-understand this right now. I'll pick up a book.

12:55 PM

I realize I didn't argue this very well: The handwaving (but consistent) reason there are no irrelevant terms in the UV completion is because their coupling constants would have to be infinite to still be relevant at finite scales. This is why their divergences are incurable in the power-counting approach: If they were finite you can't see them at the finite renormalization scale at all!

3 hours later…

3:50 PM

Why is handwaving so satisfying when one does it but so frustrating when others do?

@Feynman_00 Because when I handwave something, I'm clearly just skipping over things that are irrelevant to the argument. When others handwave something, they omit the essential steps ;)

2 hours later…

6:07 PM

I don't handwave, I only present elegant and intuitive reasoning

Only other people can handwave

1 hour later…

7:07 PM

I have a very simple question that is driving me slightly nuts

If you have a ball rolling on a flat treadmill, from experiment I know you can have a stationary condition where the ball is rolling at the same speed as the treadmill, and thus is stationary relative to the treadmill

Thinking a little harder about this, I consider the net force and come to the conclusion that the ball must move backwards. But it doesn't? Is this a balance of the force from the treadmill and some fictional force?

Two degrees later and this is driving me nuts

ohhhhhh

no slip condition means 0 friction force pushing the ball....

This paper "Something is wrong in the state of QED" by Oliver Consa - arxiv.org/abs/2110.02078 - put forward some serious accusations against QED. The claims are so bold that I naturally thought some people probably already debunked this or reduced the weight of the claim. However, I couldn't find any such attempt on the internet, and especially nothing on PhysicsSE. Any thoughts about this?

intuitively I'm still expecting some energy to be lost, and that to be put back into the system by the movement of the treadmill

@Earman I haven't touched QFT/QCD in a long time, and my understanding was only basic at the time. But this paper doesn't seem to do anything but throw around accusations and not really mathematically justify much of its criticism

Knowing people who work in this field, I think it's widely accepted that QCD/QFT is a fundamentally philosophically challenging theory due to renormalizaiton, but it is still an extremely valid theory for it's explanations of many other things other than the fine structure constant

Oliver Consa seems to have a hatred of QED and related theories but all of his criticisms only hit at the pop sci level from what I can see online

7:27 PM

physicsdetective.com/something-is-rotten-in-the-state-of-qed - this is a related article about the paper.

His latest blog post on his website: "Overhyped physicists: Richard Feynman"

It seems some of the stuff he brings up is worthy of talking about, but it also seems he has a disliking for the current state of physics without the requisite h-index/publications to be considered a field expert

@JakeRose Yes, you are right that he didn't mathematically justify any of his claims. But why does he need to do that! His claims are not mathematical. He is revisiting history mostly.

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Q: Should useful duplicates be obviously linked from their nominal original question?

There has been much discussion in the past on both Physics and other Metas about How to deal with answers to duplicate questions, especially when the duplicate questions or its answers are useful. It is possible to merge questions, but this can be challenging. Duplicate questions are closed with ...

discussion duplicates

@SillyGoose britneyspears.ac/lasers.htm

3

7:52 PM

@JakeRose Let us ignore his 'hatred' or such name-calling and solely focus on the accusations he raised. It just feels bad that throughout college life you heard that qed is the most successful theory in physics, g-factor precision is out of world etc. and suddenly you see somebody, who himself is a physicist and not just a philosopher/layman, raises these accusations.

> who himself is a physicist [citation needed]

also that's not how it works, I'm sure you can find physicists saying random stuff about any physical theory

Even Penrose has said some pretty random stuff about "consciousness."

8:09 PM

BTW it looks like the department in the affiliation has not existed for some years

@ACuriousMind So even you handwave? :P

1 hour later…

9:34 PM

@Earman the first lines in most QFT courses I’ve been to have been “this is right, but it’s got to be wrong!”. The physics community understands the issues with renormalisation (otherwise they’d be pretty bad at their job!) but the theory agrees with experiment in large ways that shouldn’t be ignored

Which I think is what he’s trying to say? He’s afaik not bringing up anything novel that anybody in the field doesn’t already know (though I’ve not fact checked much of what he said given jus non-peer reviewed publication, lack of academic history or just general bad vibes)

It seems that he is about as much a physicist as I am :p

Can someone help me understand this s3-us-west-2.amazonaws.com/courses-images-archive-read-only/… I don't get how these rays interact with each other on the screen

like they're not touching, and they don't even end up on the same point

I guess it'd make more sense if they drew new wavefronts once these get near the screen

like if these arrows just represent wave fronts, drawing a new wave from each point emanating in all directions and interfering at a point on the screen then it'd be more visually clear I feel

10:10 PM

imgur.com/a/rf1uk71 is the wording in this problem correct anyone know

pretty sure they meant to say velocity but i'm not positive

10:26 PM

@Earman It is not worth anyone's time to debunk some random person's misinterpretations of modern physics. It is trivial for anyone who understands QFT to see that QED is not just the g-factor and that if renormalization would be a "problem" of the kind alluded to here this would extend to the whole of the Standard Model as well - but the SM is certainly supported by more than the measurement of the g-factor.

Don't be blinded by all the historical details: This is a common crank tactic - overloading the debate with historical specifics and exact quotes from physicists at the early point in the development of a theory in order to disguise that they actually have no technical argument and don't really understand what they're talking about

3

@ACuriousMind Would this imgur.com/a/rf1uk71 make sense to you and if you were then asked in another part to find the speed in the y direction from earth

if I take the notation $u^{'}_x $ to mean the velocity in the x direction what information would I have about the y..

the exercise certainly wasn't proofread :P

"Then an object fired", question mark at the end of an imperative ("Derive...?")

and no the exercise doesn't make sense to me because it suddenly uses a coordinate system it never defined

I feel like I have to make a very big leap of faith to assume what it's asking

it's garbage, get a better source of exercises :P

assuming it wants me to write the relativistic velocity derived from the lorentz transformation equations

yeah it's a part of a pamphlet of home made questions from my non-native physics professor lol

to go along with class notes

non-native english speaking*

10:35 PM

oh, if this isn't even published it can always just be a typo/oversight

I really would just ask the person the exercise is from what they meant instead of engaging in lengthy exegesis

10:59 PM

oh since time dilates the y-component velocity also changes

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Nov '2228

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