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00:07

0

Q: Is it a fact not an assumption in mainstream physics that the speed of light is invariant?

In my answer, I explained an experiment’s result without an assumption of the invariance of the speed of light. Then, the post was deleted because of mainstream physics policy. It surprised me because I did not use any non-mainstream theory (that is prohibited in that policy). I just did not use ...

Abhas Kumar Sinha

03:30

@FakeMod lol

@Kyubey No, I'm 17, in final year high school

Polt Twist, there was a billionare talking to you all!

Knight

@PhysicsMeta I can understand your frustration.

@FakeMod I know you spent 7 minutes on editing, it is a hard task to do on mobile , it hurts the eyes too. But do you think that @BenCrowell who has given so many good answers before and already have 73,000 reputations would do something only for +2 reputations.

@FakeMod Ben Crowell’s intention was not to make your edit unseen .

But if you want to ask me personally I would say that there was no good reason for your edit to be rejected, you edit really made the better.

JMac

03:54

@Knight physics.meta.stackexchange.com/questions/12622/… See my comment. I would argue that the edit actually did damage to the post by changing the equation; and without that it still wasn't necessarily that useful.

@Knight Also, users above 2000 reputation with the edit privilege actually don't get any reputation by editing other posts. So they are doing it with the sole intention of making the post better in almost every case.

Abhas Kumar Sinha

@Knight klol

@JMac Why eigenvalues of $ S$ are $s(s+1)$?

Physics Meta

04:14

0

Q: About molecules tag

I recently asked a question related to atomic and molecular physics and noticed that there is a tag of "atomic physics" but not for "molecular physics". To some extent, I think that the latter is replaced by the tag "molecules", but the question is, why "molecular physics" is not used as a tag in...

discussion tags

Abhas Kumar Sinha

@PhysicsMeta Stop it, you are spamming.

Abhas Kumar Sinha

04:34

@AaronStevens Hello sir

34 mins ago, by Abhas Kumar Sinha

@JMac Why eigenvalues of $ S$ are $s(s+1)$?

^

Knight

@JMac Yes. That’s the point. And why would someone not want the user to get +2. There must be some other reasons for Ben Crowell to do that

Abhas Kumar Sinha

@Knight he has got omnitrix

Knight

@AbhasKumarSinha Who has got what?

Abhas Kumar Sinha

@Knight Ben got Omnitrix

Knight

What is omnitrix?

Abhas Kumar Sinha

04:43

@Knight google it

JMac

@Knight He saw a way to improve the post and edited it. There was no way for Ben to know that the other user was working on an edit at the same time. FakeMod suggested his edit after Ben already submitted his.

And in this case the user should not have gotten +2 in my opinion, because the edit did nothing really necessary, and changed an equation that the OP had written.

Knight

@JMac Yes. But what I believe is that you can’t logically console a man who is hurt, reasoning disguised in sweet words would certainly do better.

Abhas Kumar Sinha

@EmilioPisanty please see this:

45 mins ago, by Abhas Kumar Sinha

@JMac Why eigenvalues of $ S$ are $s(s+1)$?

Knight

@AbhasKumarSinha He, Emilio, is not here

Abhas Kumar Sinha

@Knight ik

JMac

04:47

@Knight But saying they should get points when they shouldn't doesn't help. Just because the user may be hurt by the experience, it doesn't mean that we should just let them believe that the edit would have stood on it's own when it had actual issues that should be avoided in the future.

@AbhasKumarSinha You need to stop pinging people with questions like that. I'm quite sure you've been told not to do that in the past...

Abhas Kumar Sinha

@JMac okay...

Knight

@JMac Yes. So what you propose?

@AbhasKumarSinha It is knight over here?

Abhas Kumar Sinha

@Knight day

Plot Twist, you were all talking to a billionare

JMac

@Knight I don't really need to "propose" anything. My point is that even if Ben's edit didn't automatically reject that edit, it still should have been (in my opinion) rejected in the review because it changed an equation when it should not have. So it makes the whole situation a bit moot.

Knight

@JMac I agree. But can we just a little less rude to @FakeMod?

@AbhasKumarSinha when and how?

JMac

04:56

@Knight You seem to have a habit of calling me stating my opinion clearly as "rude" and I find it very strange. What about it is rude? Me pointing out issues when I see them is not an act of rudeness.

Knight

@JMac My apologies if I my words were seemed as exclusively for you. I tried to say that people in comment are responding to his anger, anger shouldn’t be responded with reproach

@AbhasKumarSinha Sir Facearea is here? Just talk to him

JMac

@Knight For one thing, I didn't really get the impression of anger. Perhaps more frustration and confusion. Regardless, I still don't see the problem with rationally pointing out issues when someone else is frustrated. Ignoring the issues doesn't necessarily help them either; and I'd rather people have the information than not have it.

Knight

@JMac I agree.

user434058

@JMac I hope you saw the original post which has a really weird font for typing out variables and equations. The main motive of my edit was to remove that font (and add a homework tag which I eventually forgot).

user434058

@Knight Thanks for the sympathy! :)

Knight

05:07

@FakeMod Your welcome. Good Knight

user434058

@JMac Not a single edit by me till now has been done with the motive to earn that tiny +2. I wouldn't be worried even a bit if you take away all my +2's of all my edits.

Knight

@FakeMod Please don’t be angry on @JMac He is just trying to resolve the issue

JMac

@FakeMod I can understand that, though the symbols did look pretty close. Honestly, my issue is more that I see a lot of suggested edits that seem to mostly just recenter equations, and I'm not sure why you do it so much. For small equations I find it often makes it more awkward to read when the equation doesn't start on the left.

And you also need to be careful when suggesting edits to make sure you don't change equations when you do edits. Because reviewers can also miss that, and it can really cause confusion.

Abhas Kumar Sinha

uhh

user434058

@Knight Not at all!!! I respect JMac and this is just a discussion. Just to be clear, I have no hate for anyone here on Physics StackExchange. The question, I admit, was an impulsive reaction. I had never thought that t would blow up like this.

user434058

05:16

@JMac That was just a slip of fingers. Also, I would be more careful while suggesting "centering" edits.

Abhas Kumar Sinha

yo yo yo yo yo

yo yo yo

yo yo yo yo yo

user434058

oy oy oy oy

user434058

oy oy

user434058

oy oy oy oy

Abhas Kumar Sinha

oei

Aaron Stevens

06:06

@Knight I feel like you typically think people are angrier/ruder then they actually are. Any reason why?

Knight

06:20

@AaronStevens Because people with high reputation are so much powerful on this site that they seem to be rude even when they aren’t.

Aaron Stevens

@Knight Perhaps in the future it might help to explicitly point to what someone said that was rude/angry. Then it might help remove that bias.

Knight

06:47

@AaronStevens According to your doctor, which month will be so fortunate to have your child born in it?

Kyubey

07:11

@FakeMod I gave this answer to the question of yours.

PM 2Ring

08:52

@FakeMod No, I don't think I've ever heard them. I don't listen to much electronic music. I'm mostly into blues, jazz, and rock, but I also listen to various types of folk music & world music.

PM 2Ring

09:02

@MohamedObeidallah I see that Loong has answered your question about calcium. As he said, Ca-40 is not likely to be affected, apart from a very tiny percentage getting converted to Ca-41. It's actually quite difficult to detect that Ca-41 is radioactive:

It decays by electron capture, so it can emit a gamma ray, with the fairly low energy of 421 keV.

Ok, 412 keV isn't that low, but it's less than the pair of 511 keV photons that are usually produced when a positron & electron annihilate.

Yuvraj Singh...

09:41

@PM2Ring hello sir.

Loong

The energy would be okay. The problem for the detection would be the low activity. A Ca sample from the hypocentre would have a Ca-41 activity of only about 0.02 Bq/g.

John Rennie

10:09

3

Works for me :-)

Yuvraj Singh...

10:22

@JohnRennie same for me too!

John Rennie

@YuvrajSingh... :-)

Novalium Company

11:30

Is it just me or everyone is obsessed with Elon Musk now?

user434058

@PM2Ring Hmmm... I am only into electronic music(I am into it more than anything else).

user434058

@JohnRennie When I saw this the first time, it was in a meme.

John Rennie

@FakeMod :-) It appeared in my Facebook feed so I thought I'd share it.

user434058

@JohnRennie Are you into memes?

John Rennie

@FakeMod no.

As humour goes they usually aren't funny.

user434058

11:48

@JohnRennie I occasionally glance through a few of them. Sometimes it makes my day, sometimes I just feel like wasting my time.

Aaron Stevens

12:13

@Knight My wife isn't pregnant yet.

Yuvraj Singh...

@AaronStevens what?

user434058

@AaronStevens Hi!! I find it unusual that you took a biology oriented research topic after graduating in maths and physics. I know only a few people who love both, maths and biology.

Knight

12:33

@AaronStevens You said that you gonna have a family of your own, so I thought delivery is quite near.

Aaron Stevens

2 days ago, by Aaron Stevens

@Knight I will probably eventually have a family of my own and I will most likely care more about them than my scientific impact

I said eventually :)

@FakeMod Yeah, I found it unusual at first too :) I didn't have any idea of what subfield of physics I wanted to go into in graduate school. I decided to try a biophysics lab and really loved it.

user400188

12:50

I must say @FakeMod, that hat almost looks like it was designed to fit there.

user434058

13:13

@AaronStevens That is the final and necessary condition. You should love what you do. :) I am happy to hear that you do love what you do.

Knight

@AaronStevens Make that eventually thing as soon as possible. I would really want to see a cutie child of yours.

user434058

@user400188 Yeah.... Tried to adjust it by zooming in. I had no face so I tried to compensate it with positioning :).

M. Guru Vishnu

13:45

Could anyone clarify this doubt: I was reading about Mirascopes from this website. It says "The mirascope is made of two convex parabolic mirrors that face each other."; Shouldn't that be concave instead of convex, or is the terminology flipped for parabolic mirrors compared to ordinary spherical mirrors?

PM 2Ring

15:03

@M.GuruVishnu That website is mixed up. The Mirascope uses a pair of concave mirrors. See en.wikipedia.org/wiki/Curved_mirror (of course, Wikipedia's not always correct).

Mohamed Obeidallah

oh you're back. Thanks! So we already understand that only a very little amount of 40Ca turned into 41Ca after an atomic explosion and even that 41Ca will only be destroyed (or decayed) after 9.94×104 y which is a long time.

Do you know what process that will change (or destroy) any isotopes of calcium regardless if it is stable or not to different states in a very short time other than by the extreme temperature during silicon burning? Maybe by exposing them to intense radiation, etc.?

M. Guru Vishnu

@PM2Ring Thank you for your reply :) | I see, from the Wiki article, parabolic mirrors are a subset of curved mirrors. But, I think mirascope must use parabolic mirrors instead of concave mirrors to avoid spherical aberration.

May I know your opinion on this?

ayc

@JohnRennie I'm really sorry...something came up and I had to go offline for few days...I'm sorry it's not gonna happen again....so...few days back I asked for ur help on what to study if I'm interested in physics.....could you please just help me........I have Griffith's intro to qmech,electrodynamics and special relativity from Einstein to strings books with me....shall I work on these books?

PM 2Ring

@M.GuruVishnu Yes, a Mirascope uses a pair of identical parabolic mirrors. As this article explains, "The key to the design is that the focal point of each parabolic mirror sits at the vertex of the other, and a hole is made in the top mirror's vertex where the image is produced".

M. Guru Vishnu

15:21

@PM2Ring Thanks for sharing the article and for clarifying. Did you see - the device was discovered by accident? It's fascinating to know things like that. So it seems the earlier website is correct on this part. But I think regarding the convex part, it's wrong.

PM 2Ring

@MohamedObeidallah Generally, if you hit a nucleus with a photon or a subatomic particle with enough energy, some kind of nuclear reaction can happen. As I said earlier, with high energy gammas you can cause photodisintegration, which usually knocks alpha particles or protons out of a nucleus.

@M.GuruVishnu I only had a brief look at that article before I posted that link, but I've read it all now. I'm surprised that it was only discovered fairly recently, by accident.

BTW, Wikipedia has a nice diagram of spherical aberration in a concave mirror:

Abhas Kumar Sinha

@PM2Ring Good Evening Sir :)

PM 2Ring

Good evening, @Abhas.

Abhas Kumar Sinha

15:36

@PM2Ring a question with eign values of spin quantum number, why $S^2 = s(s+1)$?

Aaron Stevens

2

Q: A doubt in the concept of potential energy

The concept of potential energy is best understood with examples, so let me give an example: There lies a mass of $1~kg$ on ground, I lift the mass to a height of $1~m$. Since, I have done a work (force times displacement) against the gravity, therefore, I have given potential energy to the ma...

energy-conservation potential-energy

If the question I linked to isn't a duplicate, there must at least be a duplicate somewhere.

Abhas Kumar Sinha

Is that a bug? Appears perfect in official latex..

PM 2Ring

@AbhasKumarSinha I'll let someone with formal training in QM answer those questions.

Abhas Kumar Sinha

@PM2Ring oh okay :)

@PM2Ring Also, I'm a bit confused with Derivation of Schrodinger's equation. To prove : $$-\hbar^2/2m\, \nabla_x^2 \psi + v(x) \psi = E \psi$$, we define, $\psi$ as solution of differential equation $(*)$, then prove $|\psi|^2$ corresponds to probability, (I know that it's an axiom and can't be proved) by showing that two region $\delta x_0$ and $\delta x_1$ of equal magnitudes but electron spends more time in $\delta x_1$ than $\delta x_0$ hence probability in $\delta x_1 > \delta x_0$

Uh okay, \tag is not working in chat

@AaronStevens ^

M. Guru Vishnu

15:56

@PM2Ring: I think the mirrors could also be concave. This paper has reopened the confusion! BTW the paper is highly useful, that person has done everything I could imagine to do with mirascopes!

Abhas Kumar Sinha

Challange-1: Anyone who thinks having some decent knowledge with QM Can post hints to my question, I'll try to answer.

Aaron Stevens

@AbhasKumarSinha I'm confused on how you are talking about a "derivation" of Schrodinger's equation. Also, the wavefunction isn't a measure of "how much time" a particle spends somewhere.

Abhas Kumar Sinha

@AaronStevens I'm not talking about derivation. As we know $||\psi||^2$ corresponds to probability, I'm just there to find the intuition (theoritically physical) behind it.

@AaronStevens Born's postulate about wave function.

Aaron Stevens

@AbhasKumarSinha Intuition behind Schrodinger's equation, or intuition behind how the wavefunction relates to the probability of measuring a particle to be at some location?

Abhas Kumar Sinha

@AaronStevens intuition behind how the wavefunction relates to the probability of measuring a particle to be at some location

ACuriousMind

16:05

@AbhasKumarSinha Born's postulate crucially is only a statement about measurement - you are more likely to find the particle in some regions than others when you make a position measurement. There is no claim about the particle "spending its time" in these regions - what mechanism you think underlies the probability is a matter of interpretation and has no place in the formalism itself.

@AbhasKumarSinha There is no "intuition" to that. Quantum mechanics does not work like your classical intuition expects.

Abhas Kumar Sinha

@ACuriousMind Born's postulate crucially is only a statement about measurement - you are more likely to find the particle in some regions than others when you make a position measurement. doesn't makes sense to me? Why it causes, interference or some other property?

ACuriousMind

It is an axiom chosen because it reflects our observations, a brute fact about the way quantum mechanics works. It doesn't have a "reason".

Abhas Kumar Sinha

32 mins ago, by Abhas Kumar Sinha

@PM2Ring a question with eign values of spin quantum number, why $S^2 = s(s+1)$?

^ one too

@ACuriousMind I think if I assume interference to happen in form of waves over paths, then I can prove born's postulate.

ACuriousMind

A Bohmian will tell you the probability comes from unknown initial conditions, an adherent of Many Worlds interpretation will say it is a reflection of how many worlds there are with the particle in one region vs. the other, and many interpretations simply take this probabilism as a fundamental property of nature, but none of them can "derive" it.

Abhas Kumar Sinha

@ACuriousMind Okay :)

@ACuriousMind Let's talk of spin, why it has such eigenvalues?

Aaron Stevens

16:11

@AbhasKumarSinha I agree with ACM's comments; they are correct

ACuriousMind

If we knew the "mechanism" behind how the probabilities for measurements arise, then that would be a solution of the measurement problem. It has been unsolved for a century now, do not expect to solve it now.

Abhas Kumar Sinha

@ACuriousMind That's why I was asking everyone about it. measurement problem

@ACuriousMind I've seen L&L it doesn't has any proof/arugments for spin eigenvalues. I know it's different from Classical spin and has spin because of historical reason (magnetic deflection from paths)

ACuriousMind

@AbhasKumarSinha Because these are the only values that can occur in a representation of the (universal cover of the) rotation group, see en.wikipedia.org/wiki/Representation_theory_of_SU(2). Alas, unless you know the fundamentals of group and representation theory, that won't make much sense to you, either.

Abhas Kumar Sinha

@ACuriousMind I saw some arguments for spin 1/2 for electrons using Diarc's approach to relit. QM Eqns. But that didn't proved the general form...:)

@ACuriousMind Uh thanks :)

@Semiclassical Hey :) Father of Mathematics

Mohamed Obeidallah

16:31

@PM2Ring with high energy gammas, the nuclei of any elements will get destroyed in a very short time? Sorry now it is a bit confusing, because I'm not sure which factors that caused the disintegration of nuclei of elements. Is it the extreme temperature or just simply the radiation?

Knight

@AbhasKumarSinha Are you free now?

Abhas Kumar Sinha

@Knight yrs

Knight

@AbhasKumarSinha So, I’m buying you (lol)

Come to me

Abhas Kumar Sinha

@Knight Are you a girl?

That sounds very strange to me.

erie!

Semiclassical

@ACuriousMind Might be worth emphasizing: There's nothing particularly "quantum" about the thought that, if I follow a procedure to prepare a particle in a certain way, then it's more likely to be found in some places than others. You can get that just fine with Newtonian mech. The difference is that, in Newtonian mech, that uncertainty is due to you not being able to really prepare the particle in the same way each time.

In quantum, there's a real sense in which you can prepare the particle in the same initial state each time and nevertheless have dispersion in the outcomes.

Abhas Kumar Sinha

16:37

@Semiclassical exactly! That's what I was unable to say..

Semiclassical

(What one exactly means by that, of course, will depend on the interpretation. A Bohmian would insist that what you prepare 'identically' is the wavefunction; the particle itself cannot be prepared identically. In orthodox QM, by contrast, one insists that the latter concept has no operational meaning.)

Abhas Kumar Sinha

@Semiclassical Yes sir :)

Semiclassical

(That is, if the nature of QM is such that preparing the particle in the same position each time is impossible, then one shouldn't insist on those positions being meaningful in the first place. The individual position measurements have empirical content, but not what the particle is doing between such measurements.)

Abhas Kumar Sinha

@Semiclassical :53071303 We both have put our profile pic to fire

That's a rockstar style

Semiclassical

@AbhasKumarSinha eh, don't trust me too much on this. It is very easy to say stuff that looks reasonable but is actually not

Abhas Kumar Sinha

16:43

@Semiclassical who cares, reasonable stuff is always right :)

Semiclassical

riiiiight

Abhas Kumar Sinha

@Semiclassical yo sir :)

@Semiclassical My aim is to apply semiclassical theory as generalised theory to both QM and Classical stuff and ditch QM out of the box XD :)

Semiclassical

...yeah, good luck with that

Abhas Kumar Sinha

@Semiclassical Thanks sir, your blessings and fire on that profile pic, ignites me to work :)

bolbteppa

@AbhasKumarSinha your theory is wrong :p

Abhas Kumar Sinha

16:49

@bolbteppa heheheh... :) Oh sir, glad to see you back :)

bolbteppa

Thank you, what's wrong with L&L's description of spin

Abhas Kumar Sinha

@bolbteppa What are you doing holidays? Research or rest for some time?

bolbteppa

All of the above

Are you in uni or high school

Abhas Kumar Sinha

@bolbteppa high school

bolbteppa

That's not how L&L introduce Schrodinger's equation either

Abhas Kumar Sinha

16:51

@bolbteppa I'm not limited to L&L :P

Knight

@AbhasKumarSinha How can you conjecture that I’m a girl?

Abhas Kumar Sinha

@Knight Bro, that was a very strange question :P JK

Knight

@AbhasKumarSinha Your question was stranger

Abhas Kumar Sinha

@Knight sarcasm

@bolbteppa Sir, the spin quantum number $S^2 = s(s+1)$ can it be proved with Diarc's formulation of QM?

Knight

@AbhasKumarSinha Let’s make a deal

Abhas Kumar Sinha

16:55

@Knight awkey! :)

bolbteppa

Yes it can be proved

Have you studied the representation theory of angular momentum

Abhas Kumar Sinha

@bolbteppa Proof sir, please...

@bolbteppa just a bit

bolbteppa

Chapter 4 of Landau

Semiclassical

it's not that hard to understand once you grok the commutation relations for angular momentum

Abhas Kumar Sinha

@bolbteppa seriously!!? Which part? (I skipped ch - 4)

Knight

16:57

@AbhasKumarSinha I will ping you after your conversation with semiclassical and bolbteppa

Abhas Kumar Sinha

@Knight awkey :)

Semiclassical

maybe read the chapter you skipped, then

Abhas Kumar Sinha

@Semiclassical I think, I should now :P :)

bolbteppa

All you have to do is write the Casimir $L^2 = L_x^2 + L_y^2 + L_z^2$ in terms of raising and lowering operators and then apply it to the highest weight state and you get $L^2 = l(l+1)$, once you understand this we can argue why this also works for the spin operator $S$

Abhas Kumar Sinha

@bolbteppa Why it works for spin? How's it's related. That's the main question, rest I'll study...

Semiclassical

17:00

there's nothing forbidding half-integer spin, therefore it's allowed

Abhas Kumar Sinha

@Semiclassical that's a convention, joke, proved rule, axom, postulate or what?

Semiclassical

i mean, at a certain level, this comes down to "electrons have spin-1/2 because that's how the universe works"

it's a property electrons have, not one we invented for them

Abhas Kumar Sinha

@Semiclassical wow, beautiful proof.

@Semiclassical how it's related to coordinates?

experiment or theoritical?

Semiclassical

Stern-Gerlach experiment is the usual go-to example.

Abhas Kumar Sinha

@Semiclassical no, Ik, but that's unrelated because that doesn't tells 1/2 or -1/2

Semiclassical

17:03

And I'm more-or-less being serious with that earlier line: integer or half-integer spin are both allowed as possibilities for the story bolbteppa was telling

Stern-Gerlach tells you there are two outcomes. the rest is just convention

you could just as easily have taken the outcomes to be +-1

Abhas Kumar Sinha

@Semiclassical ah, that's what I wanted to know and you were not telling before.

Semiclassical

main thing is that it's up or down but not zero

Abhas Kumar Sinha

@Semiclassical gimme some time, I'll be reading CH-4. :)

Semiclassical

by contrast, spin-1 would give outcomes 1,0,-1

so spin-1 != spin-1/2

this does create headaches when talking to mathematicians, mind. in representation theory of su(2), math people typically talk about the quantity $2S$ rather than $S$. so odd vs. even integer rather than half-integer vs integer

there's other conventional differences

Abhas Kumar Sinha

@Semiclassical awkey

@Semiclassical Do you know existance of any other approximation methods after Pertubation, Variation, WKB?

@bolbteppa sir ^

@Knight You had some deal?

Knight

17:18

Yes

Abhas Kumar Sinha

@Knight Now it's your time.

Knight

@AbhasKumarSinha You upvote each of my question and answer

Abhas Kumar Sinha

@Knight No.

Knight

And I will give you $ln(1)$ dollar for each upvote

@AbhasKumarSinha Are you agree? It’s a hell lot of money

Abhas Kumar Sinha

@Knight That's too much, I can't have that much cash in my pocket!

Knight

17:20

@AbhasKumarSinha You are my friend and I will transfer it your account

Abhas Kumar Sinha

@Knight Rather make it You upvote mine, I'll yours Deal?

Knight

@AbhasKumarSinha I don’t give that much money to everyone, you are very lucky

Abhas Kumar Sinha

@Knight Awkey for each $\ln (1)$ upvote, $\ln(1)$ $? Deal!?

@Knight I don't give my upvotes to everyone, you are too!

ABC

Hi guys, I have a simple question for you. If I have a 1.5 V battery, does this one on the (+) side have an excess of electrons right? If so, why if I take a veil of aluminium spent on a wire, is it not moved in the least by my battery when I get very close to them?

Knight

@AbhasKumarSinha You can upvote only in integers

Abhas Kumar Sinha

17:22

@Knight Yes, $\ln(1) \in \mathbb{I}$

Knight

@AbhasKumarSinha I will vote all your posts by $e^{i\pi}$

Abhas Kumar Sinha

@Knight It's downvote rather

Knight

@AbhasKumarSinha But it’s a vote and there is no negative sign

I’m coming in 20 minutes

Abhas Kumar Sinha

@Knight $e^{i \pi} = -1$

@Knight -ve upvote = downvote.

Reign

Any ideas about neutrino cosmology projects

Abhas Kumar Sinha

17:30

@Reign make a new neutrino observatory at your home.

PM 2Ring

@Knight Please try to avoid making "jokes" that are almost guaranteed to annoy the moderators. Dealing with voting rings & sock puppets is one of the more unpleasant aspects of moderation, so mods are unlikely to find jokes about such topics very amusing.

Reign

@AbhasKumarSinha how can I do that .. ?

ı mean thats not possible

Abhas Kumar Sinha

@Reign Bring a laptop, get a simulation software.

Reign

@AbhasKumarSinha okay I did not understand the purpose of it..

Abhas Kumar Sinha

@Reign You can do a lot of simulation in your software and you don't need actual neutrino laboratory for it.

PM 2Ring

17:36

@MohamedObeidallah A photon is a "packet" of energy. If you throw a lot of energy into a nucleus, the nucleus has to deal with it somehow. It might just emit the energy back out again as a photon. Or it might throw out a particle or two, releasing the energy as kinetic energy.

Reign

@AbhasKumarSinha any software name ?

Abhas Kumar Sinha

@Reign Google it, then

bolbteppa

In QM the angular momentum algebra is introduced by considering differential operators acting on wave functions, leading to the angular momentum operators $L_x = i (y \partial_z - z \partial_y)$ etc... which satisfy the algebra $[L_x,L_y] = i L_z$ etc... , referred to as the $so(3)$ Lie algebra, and we want eigenvalues and eigenfunctions for these operators - another way to say this is that one is looking for complex irreducible representations of this algebra.

The $so(3)$ commutation relations imply that only one of the $L_x, L_y, L_z$ operators can have an eigenvalue at any one time, and from the angular momentum operators in spherical coordinates we know $L_x = - i \frac{\partial}{\partial \phi}$ which tells us that $L_z$ has integer eigenvalues, $L_z \psi = m \psi$, note this forces us to fix the axes.

Semiclassical

note, though, that while the angular momentum operators in position space are used to -motivate- the operator algebra, they don't define it

bolbteppa

Since $L^2$ commutes with $L_x,L_y,L_z$ it can also be diagonalized i.e. it also has eigenvalues on these eigenfunctions of $L_z$, and one can show $L^2 = l(l+1)$ for finite-dimensional representations. Note we showed that $m$ must be an integer by exploiting the $L_z$ differential operator, i.e. $-i \partial_{\phi} e^{im \phi} = m e^{im\phi}$, and one can easily show that $m$ can only take the $2l+1$ values $-l,..,0,..,l$ giving $2l+1$ possible wave functions.

Reign

17:40

@AbhasKumarSinha theres not much thing

bolbteppa

However there is no reason why we can't rotate the coordinate system, wrecking the fact that our wave function is an eigenfunction of the $L_z$ operator. If we rotated the coordinate system the wave function with $m$ known has to become a linear combination of the $2l+1$ possible wave functions, each with different $m$'s.

This is just another $so(3)$ algebra rotating the coordinate system, however now we're not talking about differential operators acting on wave functions, we're talking about abstract rotations of a coordinate system, and the $2l+1$ wave functions rotated into one another have to live in an irreducible representation of the rotation algebra analyzed from the commutation relations alone.

In other words, we can no longer assume the $L_z$ eigenvalue has to be an integer, and it turns out analyzing the $so(3)$ commutation relations abstractly one can show that half-integer eigenvalues are possible, which we call spin representations.

Semiclassical

the commutation relations are what matter, at the end of the day, not how they work in the specific case of position space (where only integer spin makes sense)

bolbteppa

Right, even if you stubbornly just worked with angular momentum operators in position space, you would still unavoidably be led to considering abstract representations of the same algebra

Abhas Kumar Sinha

@bolbteppa You are typing faster than I can read..

@bolbteppa Got some rough idea about that.

Semiclassical

well, you could insist that you should only worry about those which work in position space. it's just that, if you did, then you wouldn't describe nature :P

it's an empirical problem as much as a mathematical one.

Abhas Kumar Sinha

17:42

@bolbteppa @Semiclassical Thanks, that's a lot of good explanation :)

Semiclassical

please don't spam the starboard like that. if you want to hold on to a block of conversation, use the 'create new bookmark' feature under the room dropdown (right between the room description and the list of icons)

PM 2Ring

@MohamedObeidallah Photodisintegration in stars happens when the temperature is high because at such high temperatures there are many photons with sufficient energy to disrupt nuclei. But there are other ways to get high energy particles. If the particles are charged, like alpha particles, protons, or electrons, we can accelerate them electromagnetically. The particle energies involved in particle collisions in the LHC are far greater than what happens in a supernova.

Abhas Kumar Sinha

@Semiclassical okay.

bolbteppa

Basically, rotations of the coordinate system force us to view wave functions as living in an irreducible representation of the (rotation) $so(3)$ Lie algebra, and the irreducible representations admit both integer and half-integer eigenvalues. The reason why this happens is that the $SO(3)$ Lie group is not simply connected, which means a wave function would not be the same wave function after a rotation, it would be sent to a different wave function,

but quantum theory doesn't care about wave functions so really we want to work with wave functions defined on the 'simply connected universal cover' of $SO(3)$ rather than $SO(3)$. This perspective is introduced here

Abhas Kumar Sinha

@bolbteppa okay.

bolbteppa

17:51

'after a [360 degree] rotation'^

Abhas Kumar Sinha

@bolbteppa Got that.

@Semiclassical How do you access bookmarks? I think, I closed the tab.. :|

PM 2Ring

Greg Egan has a cute way of illustrating SO(3): gregegan.net/APPLETS/01/01.html

Abhas Kumar Sinha

@PM2Ring woooooooooooooow!

Physics + Mathematics = Beauty!

@PM2Ring It seems like it is following my cursor.

PM 2Ring

@AbhasKumarSinha Click on your avatar, which takes you to your chat profile page. There's a Conversations tab there.

Abhas Kumar Sinha

@PM2Ring very odd way of Designing UX. I think it should be placed below Create Bookmark Option.

Here's it: chat.stackexchange.com/rooms/71/conversation/…

QM and Cool Rotation and Spin thing of Small things.

18 mins ago, 9 minutes total – 20 messages, 5 users, 11 stars

Bookmarked 7 mins ago by Abhas Kumar Sinha

Don't go with name ;) 8)

PM 2Ring

17:58

@AbhasKumarSinha He also has one for SO(4), using hypercubes, but that one's pretty hard to get an intuitive grasp of, unless you're good at thinking in 4 dimensions. :D

ACuriousMind

Please don't star all messages in a particular conversation, it crowds the star wall needlessly.

PM 2Ring

There may be some gratuitous starring happening shortly, by hat-collectors...

Knight

@PM2Ring Was my joke a bad one for moderators?

Abhas Kumar Sinha

@PM2Ring oh okay, I'm learning a bit GR, I only understand basic Tensor Calculus and Basic introductory calculus stuff on different Tensors, Ricci, Matrix Tensor and stuff..

@ACuriousMind My mistake, I didn't knew about existance of bookmark feature, so I starred all messages :P

ACuriousMind

It's fine, I removed most of the stars.

Abhas Kumar Sinha

18:02

@ACuriousMind :-)

@bolbteppa @Semiclassical What's your new year plans? Resolutions?

@PM2Ring @ACuriousMind ^

PM 2Ring

It's easy for mods & room owners to unstar a message. Unfortunately, there's no easy way to unstar a bunch of them (I suppose a userscript could do it), so unstarring a bunch of posts is a bit tedious.

Knight

@AbhasKumarSinha You can’t ping everyone just for you to know what’s their new year plan, why do you want to steal their plans?

Abhas Kumar Sinha

@PM2Ring Use JS, create loop in Console tab of Chrome inspect element, create a loop for it, if that works, then similar way for plugin for it.

PM 2Ring

I don't do new year's resolutions. I might go to a party, I haven't decided yet.

Abhas Kumar Sinha

@PM2Ring Great :)

bolbteppa

18:07

Become the Thanos of science

Abhas Kumar Sinha

@bolbteppa woooooooooooooow!! That's cooooooooooooooooooool! :) XD :P :DDD

bolbteppa

Brolin compared Thanos to Perfume

Knight

Does anyone want to know what resolution I shall take? Anyone?

PM 2Ring

@AbhasKumarSinha Fortunately, it's rarely a problem in the Python room. ;)

user8718165

@Knight Yeah... Tell me.

Abhas Kumar Sinha

18:08

@Knight Team up with me to rob a bank :P That'd be fun bro at new year night :) XD

@PM2Ring why?

Knight

@AbhasKumarSinha just tell me the location and I will be there with my men.

Abhas Kumar Sinha

@Knight left side of that corner of the park :P

user8718165

@Knight You guys should visit Swiss bank for good fortune :P

Knight

@user8718165 I cannot rob that bank as my own account is there

user8718165

@Knight Ah. I can feel it :(

Abhas Kumar Sinha

18:11

@Knight That's good, new year party at Swiss Bank :)

user8718165

@AbhasKumarSinha I brought up the idea... So you better invite me okay? Otherwise I'll inform the officials XD :P

Knight

@user8718165 @AbhasKumarSinha So tickets will be from Abhas and @user8718165 will arrange for shelters, okay?

PM 2Ring

@AbhasKumarSinha Because in the Python room, our rules ask people to only star stuff that they think will be of great interest (or funny) to the majority of other people who visit the room.

Abhas Kumar Sinha

@user8718165 Inform them to US, meanwhile, we'll be there looting Swiss

@Knight No problem, Ima great fan of bear Grylls, we won't need that :) XD

@PM2Ring That's good :)

user8718165

@AbhasKumarSinha Security and surveillance services there be like: "Are we a joke to you?"

Knight

18:13

@user8718165 @AbhasKumarSinha Grylis is not your fan, you are his fan. At least please be a little logical

Abhas Kumar Sinha

@user8718165 Don't worry, we'll reply them yes XD

@Knight k

user8718165

@PM2Ring Hello sir :-) How are you?

Knight

@AbhasKumarSinha So what is timing? At what time should I tell to my men?

PM 2Ring

@AbhasKumarSinha Make sure you use a better disguise than these guys: weirduniverse.net/blog/comments/lemon_juice_bandits

Abhas Kumar Sinha

@Knight Tell them whenever sun rises XD

@PM2Ring lol, okay XD :) :D

PM 2Ring

18:16

@user8718165 Hi. I'm getting sleepy. It's 5:15 AM.

user8718165

@AbhasKumarSinha @Knight And how are we going there? Swimming right?

@PM2Ring Hello sir. You didn't sleep last night?

Abhas Kumar Sinha

@PM2Ring However, they had a plan to avoid detection: they rubbed lemon juice on their faces. LAMO!

@PM2Ring When you get up? 4?

That's too early, do you go to bed after lunch?

@user8718165 we'll hire sharks

Aaron Stevens

19:12

@Knight kind of

user434058

@AaronStevens Like Schrodinger's cat??

user434058

@user8718165 Yeah That seems OK

user8718165

@ACuriousMind that's the room all our nonsense is contained in.

ACuriousMind

→ 261 messages moved to Physics Parliament

user434058

@ACuriousMind Thank you!!

ACuriousMind

19:14

I think that's the most messages I've ever moved in one block...

user8718165

I'm sorry we disrupted the room's usual conversation. May be some people who wanted to chat about physics didn't do it because of us.

user434058

@ACuriousMind Never noticed that we talk so much. :)

user434058

@user8718165 Yeah.. I am also sorry!! :(

Aaron Stevens

@FakeMod sure? Why

ACuriousMind

For the record, it's fine to talk about things other than physics in here. Just be mindful that this is a shared space for many different users and when you're asked to take it elsewhere, just do so.

user434058

19:17

@AaronStevens No I was just confirming what I understood.... Or maybe suggesting you about a possible interpretation of your reply....

user434058

@ACuriousMind *responsible smile*(don't know whether that exists, but you get the point)

user8718165

@ACuriousMind yeah. Hope moving didn't cause you much trouble. Thank you very much :-)

ACuriousMind

19:36

@DanielSank Seen the new Star Wars already? I note the lack of a plea not to spoil it in here ;)

Novalium Company

20:49

Time remaining until 2020: 1 day

Yeiiaaahhh

Ahh I really wanna start an AI company but I don't know what it'll do :P

I'm sure the opportunities with ML and AI are endless so there is no better time than now

What do u guys think?

I feel like general AI is coming, and after it's creation...... oh baby.....

the end point of life as we know it (or maybe the end point of life)

ACuriousMind

21:11

They've been promising us "true AI" for decades now, I'm not holding my breath.

Novalium Company

@ACuriousMind Well, you never know. There is not a defined path for creating such entity and that's why the answer could hide anywhere.

Semiclassical

the standard joke applies: "X is the technology of the future, and it always will be."

Novalium Company

@Semiclassical that would imply that only the technologies that havent been mentioned in such sentence become the ones of today

Semiclassical

it's a joke, not a philosophical commitment

Novalium Company

@Semiclassical watcha think bout general AI?

Semiclassical

21:16

i don't think about it much, if I'm honest.

to the extent that I do think about it, it's in terms of how much AI/algorithms already shape human society without us necessarily paying attention to it

Novalium Company

I believe that general AI will not be like a product or something you release... it basically the turning point of reality itself. I have no idea what will happen but I expect it to be big and most importantly unimaginable for us right now.

I'm ready to devote my life to general AI.

Let me correct myself

I'm ready to devote my life to superintelligence and working towards achieving it. (either by AI or else)

And the thing is, I have no idea where to start cuz no one has achieved it yet

Semiclassical

maybe start by finding something you can achieve, then

DanielSank

@ACuriousMind I have indeed seen it.

Shall we make a separate room for its discussion?

Heck, I'll just make the room...

How do you invite people to rooms?

Semiclassical

click on their icon

it'll show up as an action

DanielSank

Thanks

Rise of Skywalker discussion room

7

^ Someone star that

HDE 226868

21:34

Want it pinned? :-)

rob

21:47

I'll pin it. I can't see the film until Thursday and if you lot spoil it for me I'll come to your house and leave a flaming bag of poo on your porch. (That's a little-known moderator superpower.)

vzn

21:58

← lol notes rare occasion of mod mentioning bohmian theory... ofc in an offhand way... btw also speaking offhandedly, there now exist "derivation(s)" of sch. eqn. based on fluid mechanics in the literature... mostly widely disregarded...

QM and Cool Rotation and Spin thing of Small things.

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