The h Bar

So your matrix has (cos theta, sin theta) in the first column, and up to a sign it has (sin theta, cos theta) in the second. You can nail down the sign by requiring the determinant to be 1.

0celo7

Ah!

WillO

2:12 AM

That gives you a one-one correspondence between the parameter theta (which varies over the circle) and SO(2)

0celo7

Let me check that.

@WillO My solution is to compute the dimension of $\mathrm{SO}(2)$ using the definition and submersion theory, then appeal to the classification of 1-manifolds

and use that it's compact

the only 1-dim compact connected manifold is the circle

WillO

Oh my lord!

0celo7

@WillO I've been doing too much topology :P

WillO

Intuitively, it should be clear (I hope) that you can rotate the plane by moving the point (0,1) to any other point on the circle, dragging the rest of the plane along with it --- and that's the only way to rotate the plane.

bolbteppa

lol

0celo7

2:15 AM

@WillO Yes, of course.

WillO

So rotations correspond 1-1 to points on the circle. Okay, I'm glad to see the "of course"!

0celo7

Actually, there's a neat proof of this in Zee using Lie algebra

Although I think he first claims it's "obvious" and writes down the matrix directly?

WillO

Your proof is like proving that the cube root of 2 is irrational by appealing to Fermat's Last Theorem

0celo7

Well my proof gives a smooth bijection.

A diffeomorphism actually

bolbteppa

What is your definition of $SO(2)$ in your submersion proof

WillO

2:18 AM

So does mine, as long as you believe that the sin and cos functions are smooth.

0celo7

@bolbteppa Subgroup of $\mathrm{GL}(2,\Bbb R)$ with determinant $1$ and orthogonal

@WillO hmm

WillO

Ocelo: That's SL(2), not SO(2)

0celo7

@WillO wait, what

@WillO typo.

WillO

the def you just gave bolbeteppa --- it's SL2

ah.

okay . and orthogonal.

you can edit your past remarks?

0celo7

Yes

WillO

2:20 AM

Sure enough --- I see that you can

0celo7

Hit the up arrow on your keyboard

WillO

So I can say something idiotic, have you tell me it's idiotic, then go back and change it to something very smart, and leave you looking like the idiot for anyone who comes along later.

0celo7

@WillO ohhh

@WillO There are edit histories with timestamps

dmckee

@0celo7 Uhm ... it's one of the few actually useful groups that is pretty easy to bluff your way through intuitively?

0celo7

@dmckee bah, intuition

bolbteppa

2:24 AM

If you want to get from $SO(2)$ to the cos, sin matrix you can follow what Zee does in his group book and go from $R^tR = I$ to the lie algebra $R = I + \omega$, explicitly construct the anti-symmetric matrix $\omega$ then exponentiate back to the lie group to get the matrix, or you can do baby trigonometry

0celo7

I recall that being an extremely hard trig problem, actually.

I had to google it eventually

there's a trick

bolbteppa

No, if you just draw a picture of rotated axes you get it immediately

WillO

Once you've got R^TR=!, you've got a^2+b^2=1 for the first row, so you've already got a=cos theta, b=sin theta

bolbteppa

That too

WillO

So if you've got as far as R^tR=I, the lie algebra is an insane detour (unless you're trying to illustrate a technique you plan to use in other contexts)

bolbteppa

2:28 AM

Two parameters in the first column, then the second column is orthogonal so you have the same two parameters in that column, then unit determinant restricts free parameters to one

This is why you have to read Landau:
"In the limit of small velocities, the particle must be described, as in the non-relativistic theory, by a single two-component spinor: on taking the limit $\vec{p} \rightarrow 0$ we find $\zeta = \eta$, so that the two spinors which form the bispinor are equal. This, however, reveals a defect of the spinor form of Dirac's equation: in the limit, all four components of $\psi$ are non-zero, although only two of them are really independent. A more convenient representation is one in which two of it's components are zero in the limit."

WillO

2:46 AM

@0celo7: Have you made any progress with your RIcci question?

0celo7

Typing up the solution now

WillO

oh! congratulations.

0celo7

My prof solved it

WillO

You might be ahead of me on this, but I hope you'll post that solution so that others don't get sucked into spending time on it.

0celo7

Well, I am typing it

But I haven't asked him if I can

It's really his work

You need a really specific theorem on flows, actually

WillO

2:57 AM

At the very least, you should edit your posts to let me know you've got a solution.

Secret

If SO(2) is a circle, what shape is SO(3)?

0celo7

Sphere with antipodal points identified

@WillO

That do Carmo result is the key.

Secret

I.e. Real projective plane?

0celo7

@Secret Yes.

For the proof...eh, it's in Hatcher?

WillO

It's not hard to see. You can identify the unit three-sphere with the unit quaternions.

0celo7

3:06 AM

@WillO well, what should I do

I don't want to take credit for this result

WillO

0celo7: I think the main thing is to let people know they can stop working on it. If I were you, I would post what you've just typed up as a solution, with a clear statement up front that you got the main idea from your professor (I don't think you need his permission for this, though others might disagree). If you're not comfortable doing that, you should (in my opinion) at least edit the post to say at the top that you now have a solution and hope to have permission to post it shortly.

0celo7

Aight, I posted it

WillO

Thank you.

0celo7

Ok, now what

Algebraic topology I guess

WillO

Did you delete the MO post? I don't see it.

0celo7

3:13 AM

Yeah

No use keeping it

Ulthran

Hi

WillO

Huh. I also don't see it under "Recently Deleted". Maybe it takes a little while to show up there?

0celo7

dunno

WillO

anyway, thanks.

Itachí Uchiha

8:12 AM

Can I single moving charge create magnetic field?

Slereah

Yes.

Itachí Uchiha

web.hep.uiuc.edu/home/g-gollin/relativity/…

but this explanation need a group of charged particles inside the wire

for example,if there is a moving charged particle and there is another stationary(relative to 1st particle) charged particle.Will we find magnetism working there?

David Z

8:43 AM

There will be a magnetic field, you just need a different sort of physical reasoning to justify it.

3

A: Magnetic field of a moving point charge

Remember that superposition holds for the electric and magnetic fields. That is, you can calculate them individually and then add their fields together to get the field at any point. For the moving charge, $q_1$, the magnetic field is 0 in its frame but boosting to the co-moving frame, we have $...

for example. A search for magnetic field point charge brings up several other resources.

Itachí Uchiha

8:57 AM

@DavidZ,Thank you very much.

Yashas Samaga

9:24 AM

I am so disturbed by the Quantum Eraser experiment...

Itachí Uchiha

10:01 AM

Is D(electric flux density)=integral of E.dA/integral of dA

David Z

10:29 AM

@ItachíUchiha If it's the $\vec{D}$ I think you're talking about, no. The equation is something like $\vec{D} = \vec{E}/\sigma$ (that may not be quite right, but it's something simple like that). $\vec{D}$ is the "effective" electric field in a medium; the $\sigma$ accounts for the ability of the medium to partially cancel out or enhance the "base" electric field $\vec{E}$.

ACuriousMind

10:40 AM

@WillO Only >10k users can see deleted posts.

Secret

@acuriousmind A tiny question. In index notation, am I allowed to pull out the derivatives, or that the nocommutativity of derivatives in general is not taken account by the index notation?

Is this legal
$[v_b\partial_cu_a+u_a\partial_cv_b]\epsilon_{abc}=\partial_c[u_av_b]\epsilon_{abc}?$

sorry for the numerous typos...

ACuriousMind

What "non-commutativity"? But yes, applying the product rule is of course legal.

Secret

Clarification: By noncummutativity, I mean something like $\partial_i Aj \neq A_j\partial_i$

Ok

FrancescoS

Hi guys. Isn't this differential cross section symmetric under the exchange 1 <-> 2 ?

ACuriousMind

It appears to be, yes

FrancescoS

10:51 AM

So, I don't understand why it is written [1 <-> 2]

Secret

@FrancescoS What is the physics described by the differential cross section formula above. It strongly reminds of electromagnetism for some reason?

FrancescoS

@Secret it is q qbar -> e+ e-

ACuriousMind

@FrancescoS What? The [1<->2] means that you should have both the $q_k(x_1)\bar{q}_k(x_2)$ and a $q_k(x_2)\bar{q}_k(x_1)$ term. If you only had the term first that's explicitly written there, it would not be symmetric

Secret

Ok, that's an annihilation process. In that case it is beyond my knowledge scope. But aren't fermions antisymmetric under exchange?

Ok

FrancescoS

@ACuriousMind but I can change variables x_1 -> x_2 in the second piece and I get again the first piece, not?

ACuriousMind

11:01 AM

@FrancescoS $q(1)\bar{q}(2)$ would not be symmetric. $q(1)\bar{q}(2) + q(2)\bar{q}(1)$ is. I'm not sure what your problem is, sorry

Secret

Hmm, I recognise q is a quark, but I am not very sure what q(particle no.) suppose mean, its wavefunction...?

FrancescoS

It is just a function, there are no anti-commuting rules

ACuriousMind

@FrancescoS But still, if you take just $q(1)\bar{q}(2)$ and switch the numbers, you get $q(2)\bar{q}(1)$ which is not the same.

FrancescoS

@ACuriousMind $\int dx_1 dx_2 q_k(2)\bar{q}_k(1) = \int dx_2 dx_1 q_k(1)\bar{q}_k(2)$ under the changing of variables $1<->2$, not?

ACuriousMind

$q$ and $\bar{q}$ are different objects, after all

FrancescoS

11:05 AM

@ACuriousMind Yes, but you have an integral, and you can change name to the variables

ACuriousMind

@FrancescoS No equal sign!

FrancescoS

Why?

ACuriousMind

Ohhhhhh

You're right

If you only need the whole integral to be symmetric, then you don't need the second term

FrancescoS

this is what I mean… and I don't understand why there is written that exchanging 1<->2

ACuriousMind

I guess they wanted a manifestly symmetric integrand

I wouldn't worry about it

FrancescoS

11:14 AM

boh.. ok

there should be a 1/2 factor.. it seems you are counting twice the same thing

ACuriousMind

Eh, who cares about numerical prefactors ;)

Secret

Well, I do lol, by always lumping them into one big constant called spiral @

Secret

11:30 AM

@Acuriousimind Q3. After I found your answer on PSE to Q2 on 1:1 correspondance on hamiltonian to potentials (which is false because there exists isopsectral potentials). I am trying to model this scenario in the Quantum Moves game. However I am not sure how to model it because I cannot use perturbation theory because the potential will be changing quicker than the time dependence of the wavefunction.

Do I simply use some kind of born oppenhenier approximation and assume the wavefunction does not get changed by the potential well being translated quickly to the right side in order to compl…

Itachí Uchiha

Then,does Maxwells 1st equation mean that the rate of change effective electric field is equal to electric charge density.

Sanya

Maxwell's 1st equation as in \nabla \vec{D} = \rho/\varepsilon @ItachíUchiha ?

Itachí Uchiha

@Sanya Yes

Secret

wait maxwell 1st qeustion (Gauss law) is $\nabla \cdot \vec{D}=\frac{\rho}{\varepsilon}$ not $\nabla \vec{D}=\frac{\rho}{\varepsilon}$

Sanya

hmm, I find it hard to interpret a rate of change (i.e., temporal) of \vec{D} into that - I'd rather say that a temporal change of the charge density \rho induces a change of the spatial gradients of the \vec{D} field

Secret

11:41 AM

So it means the flux of electric field in an infitesimal volume is equal to the charge density divided by episilon

ACuriousMind

@Secret I have no idea what you're talking about

Sanya

@Secret with $\nabla \vec{a}$ I mean $ \partial_i a_i$, I thought that was standard usage, sorry

ACuriousMind

@Secret ...the dot was pretty much implied.

Secret

@Sanya O sorry, I did n't realise that convention, because I am too used to seeing gradient of vectors i.e. $\partial_iv_j$

Sanya

ah ok, yeah, I see the problem with my notation @Secret

something like $\nabla \vec{a} = \sum_j \partial_j a_i \vec{e}_i$?

Itachí Uchiha

11:45 AM

Alright.Thanks everyone.

ACuriousMind

Having to do that operation on a vector is rather rare, since it is not one of the two "natural" differentations on vectors

Secret

well, $\nabla\vec{v}$ is pretty much the jacobian matrix of $\vec{v}(x,y,z)$

@Sanya and yes, you will get a 2nd order tensor as a result

Itachí Uchiha

what is the difference between B and H?

Secret

whether you have subtracted away the field due to bound currents or not

H is field caused by free currents, while B is caused by both free and bound currents in a magnitised object

Sanya

@Secret no, the jacobian would be $\nabla \vec{v} = \partial_i v_j \vec{e}_j \otimes \vec{e}_i$, what I wrote above would be a new vector again - but well, doesn't really matter, what I meant has become clear and I understand why it is a bad notation :D

Secret

11:50 AM

ok

Itachí Uchiha

umm..what are bound currents?

Sanya

en.wikipedia.org/wiki/… they are basically the response of the matter to the applied field

Secret

They are currents due to the magnitisation of the material, If you have a bunch of magnetic dipoles in the material it can be distributed evenly or unevenly

Each magnetic dipole can be dscribed by a current loop due to ampere law.

Now similar to green's theorem, current loops can be added up and thus all the interior loops will be cancelled, leaving behind an overall surface current $\vec{K}$ loop that described the overall dipole moment due to all these dipole moments. If your magnetisation is not even, such as there are places where the dipoles are concentrated (the divergence is non ze…

(Please supplement me if there are any mistakes)

Sanya

you should rewrite the wiki page

0celo7

12:30 PM

@ACuriousMind Do you know anything about the Euler class of a sphere bundle?

Secret

@acuriousmind @JohnRennie (This is basically a state transition problem thus you might also be able to help)
http://i.stack.imgur.com/Abyq3.png
Let me elaborate. So the scenario is that there's a 1D potential well with a parabolic shape, and then inside there's an atom described by a probability distribution that is bimodal. The task is to move your potential well and adjust its depth in a way so that this bimodal wavefuntion become unimodal. Once you start moving the well, the probability distribution will start to slosh back and forth like a liquid

0celo7

@ACuriousMind Huh? Covariant differentiation is totally natural

The only things more natural are childbirth and pooping

and the natural numbers

Oh, but is it a natural transformation in the bundle functor sense

ACuriousMind

@Secret ...you would need to implement whatever algorithm the game uses to understand how the game works, obviously.

@0celo7 no

0celo7

@ACuriousMind Hmm, I'm surprised

Seems like something you'd need for gauge theory.

Qmechanic

@DavidZ : I didn't notice your comment before now. First of all, the question seems off-topic, so I'm not sure it is worth finding the optimal tags.

@EmilioPisanty : A question which asks whether an translation into English exists can be on-topic, but it seems off-topic/too localized to ask for a translation into any other language.

Secret

12:42 PM

@ACuriousMind
I always thought I can somehow approximate the scenario since that's what we physicists do all the time in modelling a scenario by making simplification

For that one, my naive intuition was suggesting that analogous to how when you have a bowl of sloshing liquid when you jut the bowl to the left while the liquid is sloshed to the right, then you get a bowl of liquid that is more stationary because the movement of the bowl counters the direction the liquid is sloshing to.

however because this is quantum, I suspect I would need to do the maths to check whether the naive intuit…

Secret

1:49 PM

@Acuriousmind EDIT: Ok I found the algorithm data from the nature article http://www.nature.com/nature/journal/v532/n7598/full/nature17620.html. The potential in dimensionless units is a gaussian potential $V_{tweezer}=\mathcal{A}exp(-\frac{2.0 (x-x_0)^2}{w_0^2})$ where $w_0$ is the waist and $\mathcal{A}$ is the depth. The time dependent schroedinger equation is then solved using the split step method (by treating the nonlinear and linear part of it as independent, solve them separately in the frequency domain and then fourier transform them back into the time domain)

Secret

@Secret This is wrong, reading the article will tell you that this is actually the tunneling solution, and that the reason why same energy levels will result in a faster drain is because there is tunneling resonance. Anything else that follow after this point requires reading tunnel resoance first before judging

David Z

@Qmechanic if it's irredeemably off topic, it doesn't matter for this question, but I do think we should be clear on the issue for the future. My understanding was that resource-recommendation was the only tag to receive the banner and wikification.

Qmechanic

2:26 PM

@DavidZ : To be honest, it seems more fair to treat spec.ref. and res.recom. in the same way, i.e. make both CWs, but actually I think your understanding is what was decided in the past. Did we write this down somewhere?

David Z

2:44 PM

I'm not sure. I guess we should go back and look at the meta post where we determined the banner for recommendation questions. My understanding was that that discussion only applied to resource recommendations, not specific references, and the wording of the banner was written with that in mind.

I don't really mind wikifying it quite so much - granted, I would prefer to have specific-reference questions not be CW, but my reasons are mostly the same as why I would prefer not to wikify resource recommendations either. The issue that I think needs to be clarified is whether we put the post notice on specific-reference questions.

18

Q: Are resource recommendations allowed?

What is the policy on asking for recommendations of books or resources on Physics Stack Exchange? What is a resource recommendation question? What sort of resource recommendation questions are allowed here? How should I answer a resource recommendation question? As a community member, how shoul...

John Duffield

3:15 PM

@DavidZ : it certainly is. And so ironic!

@DavidZ : you're not wrong about that!

@JohnRennie : Sabine Hossenfelder doesn't know the difference between virtual particles and vacuum fluctuations.

John Duffield

3:41 PM

@ItachíUchiha : no. The electron has an electromagnetic field. When you start moving relative to it, you do not create a magnetic field for it. You just see its electromagnetic field a little differently, that'll all.

Quiet today. Whistle whistle:

Is there anybody there?

John Duffield

4:19 PM

No. OK I gotta go. Bye.

user54412

4:35 PM

@DanielSank I found the article I was thinking about: link.springer.com/article/10.1007/s00041-012-9221-x Let me know if you can't get access. Anyway, page 2 has both parts of the sampling theorem as I know it, and presumably one of those 5 references proves it in a satisfactory way.

user54412

In particular, it's interesting that the convergence on reconstructing the fourier transform is slightly weaker than for the function itself.

Bernard Meurer

@ChrisWhite Can you explain the fourier transform to me using only emoticons?

user54412

@BernardMeurer o.O >.V <.< :/

user54412

Now the question is whether I was explaining it, or explaining that I can't.

Bernard Meurer

I have no clue what i just read

peterh

4:55 PM

@JohnDuffield How you got 17 downs for the same post? If they are coming from the same person, it is very hardcore sockpuppetry.

Secret

@BernardMeurer : T = :e : -i (: F)

Bernard Meurer

@Secret You should write an entire paper like this

You're very good at it

Secret

well considered the fact that mind basically broken and warped into a mush due to 5 years exposure to time travel theory

Bernard Meurer

@Secret Can you explain time travel with emojis?

Secret

: ) -> : O & :X -> : ?

Translation: 2 types: CTC and branching timelines

rest is unknown

Bernard Meurer

5:05 PM

This should really be a thing

Secret

I need someone to anchor that neutrino wtf slereah on h bar for more than milliseconds. Even ICECUBE have problem catching him and he is CRUCIAL for the tiem travel theory development

peterh

VLQ + unclear

Bernard Meurer

I'm calling Pearson

Physics Meta

0

Q: Déjà-vu answer, or a blatant case of reposting a deleted post?

There's something strange going on with this answer. I seem to recall reading exactly the same answer written by the same users some days ago. It received some comments about the aether theory, and got negative rep. Nevertheless, the current answer is dated some minutes ago. I don't think that t...

discussion answers

David Z

5:23 PM

@BernardMeurer |:=~

Secret

O wow, that's even better

delta become a sine wave

bonus point that the emoticon seen as a whole, reminds of uncle jack

David Z

I'm tweeting that

Secret

A chat with my friend on quantum mechanics. He is said by my friends as very classical minded

blue is me

I love quantum mechanics because it challenge everything we knew about intuition,
and with craziness, came possibilities of exploring a larger reality

I am starting to wonder whether I will find a classical mechanics book harder to understand and more abstract, lol

DanielSank

@Secret anti intuition? I dunno about that...

Secret

5:38 PM

that's kinda a more chinese-english way of saying "against our intuition"

not sure if anti intuition is a proper word

DanielSank

Physicists ought to consider carefully whether it's a good idea to perpetuate the slogan that"quantum mechanics is weird".

2

I think not.

Secret

For me, I will say to a layman. "Quantum is weird, but there are 3 gist that explain most of the weirdness (and then tell them the 3 gists)"

ACuriousMind

It's only weird if people insist on classical mechanics being "intuitive". Which it becomes to many only after years of education in the first place :P

5

Secret

I actually learn quantum before knowing what a lagrangian is back in our undegrad course

ACuriousMind

Our intution is much more a matter of training and getting-used-to than we tend to admit

Secret

5:41 PM

and just recently because of reading vol 2 of susskind book first, I am actually more used to quantum.

vzn

@Secret after quite a bit of effort cant get any of my associates/ peers to read Tenev/ Horstemeyer (yet) despite lobbying/ cajoling... :( how/ when did you find that paper anyway? ps thx for posting your meta announcement so quickly, was a bit surprised, guess you are highly motivated! and darn, forgot to mention it at end of last mtg, should have, an oversight, but 1st time so far the next talk date was lined up/ nailed down in time...

Secret

@vzn I just google "spacetime youngs modulus" because I am wondering whether someone had ever tried to define that before

vzn

@Secret how recently did you find it? it is fairly new... wish there was some discussion/ reaction somewhere in cyberspace, could locate any... also found you musing about stress-energy tensor awhile back in transcript etc

Secret

Acuriousmind, btw you saw that ping I told you about me digging into the quantum move article thingy? I will try to calculate that later

@vzn You, JD, ACM and many others was aruging about the material science model of spacetime, which arose my itnerest as JR previosuly said you cannot define a young modulus

ACuriousMind

@Secret I saw it, but as usual I can make little rhyme or reason out of what you're trying to do. Not that that has ever stopped you.

vzn

5:47 PM

@Secret didnt see him say that but think hes (JR) flat out wrong as the paper & prob some other (scattered?) refs lay out, although agree its very novel/ unorthodox/ contrarian/ subversive etc (all my favorite stuff aka BREAKTHRU!) =D

Secret

@vzn I think I wrote clearer than my old messages for that one, perhaps since you and JR are somewhat more align to my thought process, you two might be able to translate to ACM?

Also remeber that we don't know the existence of that paper when we said about young modulus not defined for spacetime, JR does not need t be blamed for that

@ACM
But anyway, the question now evolve into a simpler one.

So basically after all that searching, I figure that the initial state is the 1st excited eigenstate of the gaussian potential, and the sloashing around is a superposition of some eigenstate of th…

vzn

anyway Tenev/ Horstemeyer original date was mar22 & am sorry missed it on that day! :(

@Secret ACM is apparently giving me cold shoulder at moment, nothing unusual about that, also DS is ignoring the paper so far, 0celo7, etc, seems quite phenomenal here in a physics room they wont even say a single word... maybe @Slereah can "break the ice" :( o_O ... was musing would like to have a study group session on the paper, what do you think?!

Secret

Uh for slereah. ICECUBE have trouble detecting even a speck of him for ages.
What happening to his time dilation, he is like a muon decaying in just picoseconds and does not persist for a moment in h bar

vzn

@Secret maybe hes ("finally") getting some work done at his (new) job :P he said it was on datamining, cool stuff surely

DanielSank

@ACuriousMind well, I would venture that fundamental statistical nature of the world is surprising whether or not you've been subjected to classical mechanics books.

But still, I guess it not useful to tell people that QM is weird.

Secret

5:57 PM

@ACuriousMind Ok the question boils down to this. The potential they are using is the gaussian well

The initial state is the 1st excited state wavefunction. During the mouseclicking which changed the well's depth and width, the wavefunction evolves into a superposition of eigenstates (in a way such that the probability distribution obtained is similar as if the original wavefunction get sloshed around in the well)

After moving the potential sharply to the right, the wavefunction take the shape that is identical to the ground state wavefunction.

@vzn btw does my above (the blcok of text just above this line) of my original paragraph sound comprehensible to you on what I am trying to do?

vzn

@Secret dont know what you are referring to, its vague, prev chat box? what?

ACuriousMind

@DanielSank People have no trouble believing in magic even in the absence of or even contrary to evidence, why should we have trouble believing in statistics with overwhelming evidence? I'm not convinced there is such a thing as a universal human "intution" regarding physics, at least not one that prefers determinism over probabilism

vzn

@ACuriousMind almost a philosophical statement from someone who hates interpretations... coincidentally am digging up a (famous) quote by feynman that was ringing in my ears lately, am sure everyone here will like, esp whoever starred dmckees recent quote wrt it (quite a few), its quite similar...

Aug 9 at 20:07, by dmckee

A lot of what goes on in these discussions is epistemology. Peolpe what to know what the quantum world "really is". Well, so do I, but I've had to come to terms with the lack of cog-wheels in there.

↑ reminiscent of copenhagen interpretation...

Secret

My interpretation of quantum mechanics is basically "shut up and calculate" but with the mathematical entity treated as a real thing I can touch with my hands

vzn

> I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possibly avoid it, ‘but how can it be like that?’ because you will get ‘down the drain,’ into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that. —Feynman

Secret

6:09 PM

I like visualisation, but it is the abstraction that tells me what is the gist to be visualised

dmckee

@DanielSank I agree that "weird" isn't a useful word, and I avoid it like the plague in class. Both Einsteinian relativity and quantum mechanics are different from the world we think we live in, but the rules are just as comprehensible as the rules for classical mechanics with Galilean relativity.

vzn

one might say, that in a sense, after decades forced with no alternative, throwing up hands in air in some desperation/ despair/ futility, physicists have given up on "physics"... :( o_O

dmckee

I make that the focus of my teaching. Learn what the rules are and how to apply them. Live with the slightly more involved mathematics. Then practice.

Physics Guy

@Ocelo7 Hey, could you please give a link to your homepage about GR and differential geometry ?

DanielSank

@ACuriousMind interesting point about magic, yet I am unconvinced. I know no physicist who believes in magic (shall we agree to leave religion out of this?).

Physics Guy

6:12 PM

Yes.

Secret

Fun fact: magic used to be religion until the catholic church outlaw/supress them all

DanielSank

@dmckee you da man.

vzn

@DanielSank what kind of magic? or was it unspecified

Secret

@dmckee I am similar, except I do an extra step in order to make them readable by genral popualtion: Explain as many of the maths in visual or interactive form so that they can get their hands dirty and know what the physics really felt like without much fear of maths

-without loss of much rigor

part of the fun of abstract algebra is the rules are so alien to our experience that you might as well say you went into a different universe

but once you get used ti them you will appreiciate the inhabitants of this alien space

ACuriousMind

@DanielSank Well, no physicist believes in magic because we all get it beaten out of us in the course of the education - but since we learn classical physics first, this just instills a belief in determinism and classical measurement in most. Since quantum mechanics and relativity are then usually taught through "paradoxes" like twins or double-slit, a firm conviction about quantum mechanics and relativity is never imposed - we're told it is okay to find them strange.

vzn

6:16 PM

@PhysicsGuy (he is shy/ evasive at times & almost never cites it, was having trouble myself & dug it up & finally bookmarked it) ... this one? einsteinandtheevidence.wordpress.com

Physics Guy

Yeah, thanks.

Secret

If Johnrennie is on, I 'd love to tell him about my experience on one of the newscientist talk I joined today

vzn

← remembering a scene in 5th grade when 2 cute girls asked if I believed in magic, and said yes after some hesitation, and they turned their backs giggling/ laughing o_O

ACuriousMind

But I really think it's not a statement about human nature that makes us prefer determinism, it's a statement about our current culture.

vzn

@Secret "joined a talk"?

Secret

6:20 PM

@vzn https://www.eventbrite.co.uk/e/meet-your-microbes-the-surprising-world-inside-you-tickets-26156141724
This

ACM: susskind joked about in his book that he said there's once a guy who think all quanttum, and then he did not survive being eaten

vzn

@ACuriousMind there are some very simple classical experiments that can reproduce the infamous double slit (which even feynman was enamored with as the embodiment/ central/ epitome mystery of physics), they are not recorded/ remarked on much & are very buried, think classical physics has yet many more surprises up its sleeve... eg re Tenev/ Horstemeyer ;)

Secret

Imagine if macroscopic quantum is the norm rather than the minority, perhaps we will have find classical mech weird

Physics Guy

@Secret Interesting thought.

We would find it "too easy".

vzn

@Secret you attended in person? near england? thought you were in australia? eventbrite.co.uk/e/…

Secret

The event took place in my uni

and there will be a quanutm one on october

eventbrite.co.uk/e/…

vzn

6:30 PM

(oh thats weird the urls for subpages dont seem to work quite right)

Secret

As a side note, I think acurioudmind might understood me better, if we ever met face to face one day. In my experience, no one in my uni ever confused about my questions probably because most of my explaantions go to body language

Th only instance they will be confused is when they spot me using a worng concept

which I will quickly amend the question with the corrected concepts

vzn

are those events in different places in the world? you say one took place at your university, in australia? which one?

Secret

UNSW, the event name is called Meet Your Microbes

vzn

@Secret oops sorry there is a South Wales near britain. guess yours is New South Wales. ← still learning geography

ok this one? sounds cool! not cheap but all day. hope to hear about it. (you really should try blogging!) eventbrite.co.uk/e/…

Secret

The highlights are:
1. Your microbiome composition controls the nervous system of the digestive tract (enteric nervous system) which in turn communicate with the central nervous system

2. Your microbimoe also regulate the repair of the digestive tract, utilisation of fat, medicine utlisation, allery and disease prevention

actually, I am most incomprehensible in text format communication

My entire research group get thoroughly confused by my 1st draft of my thesis and my co supervisor basically has the same response as acuriousmind in keep saying "what?" after reading each line

Bass

6:40 PM

Zee writes: The statement that $Q_\alpha$ transforms as a Weyl spinor means $[J_{\mu\nu}, Q_\alpha] = −i{(\sigma_{\mu\nu})_\alpha}^\beta Q_\beta$, where $J_{\mu\nu}$ denotes the generators of the Lorentz group.

Why is that so?

Secret

My supervisor, while can comprehend my thesis (probably because we has some similarpersonality traits that cause him to be able to align with my thinking) said he noticed a quirk about my writing

Imagine a paragraph with no fullstops in sight, for example

Bass

@ACuriousMind The basics of classical mechanics are certainly easier to teach/learn than those of GR or QM, don't you think? So those people probably mean "easier" by "more intuitive".

Secret

I then became the confused one on why the need to add fullstops every now and then and he explains the logic of most people:

It appears that when people are interrupted when reading a sentence, they start from the last fullstop. But for me I can restart where I last left off in the middle of a sentence. I did not aware of this until he pointed it out for me, learned quite a bit on how most people thinkg of things

So the point of adding fullstops more frewuently is to avoid long sentence, which are mostly invisble to me due to the way I read

vzn

does anyone know why CuriousMind and ACuriousMind have nearly the same name? mere coincidence? some kind of joke/ rivalry? (think the latter seems a misnomer sometimes) :P

@Secret ok thought you were done with your thesis, are you talking about undergrad thesis, still writing it?

Secret

7:05 PM

@vzn I already done the thesis, I am just talkign abotu hsitory

peterh

@Secret All of the biblical religions outlaw it, it is very strictly forbidden in the Old Testament.

ACuriousMind

@Bass GR certainly. With SR and basic QM I'm not so sure

Remove the "teaching by paradox" and teach them axiomatically like Newtonian mechanics from the beginning, and I think especially SR loses a lot of what is called "unintuitive"

Secret

yeah, once the worldline concept sinks in, all the paradox disappears

Bass

@ACuriousMind Sounds good. I still think CM is more intuitive than SR, GR and QM. All those theories reduce to classical mechanics in the low energy / "macroscopic" / first order / whatever limit. We as humans experience the classical limit only. It seems quite natural that most people find it more intuitive. Took us more than 200 years to find out there's more.

2

@ACuriousMind A hint on this?

ACuriousMind

7:27 PM

@Bass $Q_\alpha$ is a supercharge? Anyway, the r.h.s. is precisely how the generators of angular momentum act on a Weyl spinor.

I'm not sure what more there is to say

Bass

@ACuriousMind Yes. A Weyl spinor transforms like $\psi^\alpha\mapsto -\frac{i}{2}\omega_{\mu\nu}{(J^{\mu\nu})^\alpha}_\beta\psi^\beta$ where $J^{\mu\nu}$ is the matrix of the $(\frac 12,0)$ representation, right?

ACuriousMind

yep

Bass

So how does one go from that to Zee's remark about the supercharge? (does it matter if $Q_\alpha$ is a supercharge or some other Weyl spinor?)

ACuriousMind

Well that $[J,Q] = \text{Weyl spinor transformation}$ is the definition of what it means to have a Weyl supercharge

From where to where do you exactly think there is a step missing?

Bass

Can't I think of $\psi^\alpha\mapsto -\frac{i}{2}\omega_{\mu\nu}{(J^{\mu\nu})^\alpha}_\beta\psi^\beta$ as the definition of what it means that $\psi$ is a Weyl spinor?

ACuriousMind

7:38 PM

Yes

And Zee's equation says taht the commutator of the Weyl supercharge with the angular momentum is exactly the transformation of that charge under that angular momentum as a Weyl spinor

Bass

I don't see how $\psi^\alpha\mapsto -\frac{i}{2}\omega_{\mu\nu}{(J^{\mu\nu})^\alpha}_\beta\psi^\beta$ leads to $[J_{\mu\nu}, Q_\alpha] = −i{(\sigma_{\mu\nu})_\alpha}^\beta Q_\beta$.

(sorry for mixing $\psi$ and $Q$)

ACuriousMind

Well, it doesn't lead to it. The l.h.s. is defined by the r.h.s.

OH, wait

You do realize that $\sigma$ is just the notation for $J$ in the $(1/2,0)$ rep, right?

Bass

Huh..? One moment..

Bass

7:53 PM

I see. On the l.h.s. he means $J^{\mu\nu}$ in the sense of "the generic angular momentum", which, when applied on $Q_\alpha$, turns out to be $\sigma_{\mu\nu}$, which means $Q_\alpha$ is a Weyl spinor. Right?

ACuriousMind

@Bass yep :)

Bass

@ACuriousMind Cool :) thank you!

Which bands at Wacken did you like most?

ACuriousMind

@Bass Most definitely: Arch Enemy! Sub Dub Micromachine and Ektomorf were some surprising smaller bandsI didn't know before. The oldies Saxon and Twisted Sister did a great show, too. Unfortunately I don't remember all too much from Blind Guardian due to a bit too much Met ;P

vzn

8:16 PM

2 hours ago, by vzn

> I am going to tell you what nature behaves like. If you will simply admit that maybe she does behave like this, you will find her a delightful, entrancing thing. Do not keep saying to yourself, if you can possibly avoid it, ‘but how can it be like that?’ because you will get ‘down the drain,’ into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that. —Feynman

← going down the drain since young,
widely thought a blind alley,
eventually to escape like nobody yet has,
& will never stop asking how it can be like that,
am starting to see the light,
halleluja!

0celo7

@ACuriousMind wtf

What is Met

And all of those other things you said

ACuriousMind

@0celo7 honey wine

0celo7

Oh, Meade?

ACuriousMind

All those other things are bands :P

DanielSank

8:47 PM

@ChrisWhite thanks

@ACuriousMind Meade is delicious.

ACuriousMind

Yes, yes it is :)

Bass

@ACuriousMind I see :) Arch Enemy's too fast for my taste, I'm more into the doom or stoner stuff. Ektomorf sounds cool, need to check out their work.