The h Bar

cows

12:22 AM

Back home, mood is a little different. Not feeling like coding. In pajamas . . .

Won't be heading out tonight either. . . . . .

Seems nobody is on here too.

what to do. . . what to do . .

don't feel like watching tv alone either.

I don't want to bother my &*#^ fr*(@^ (girl friend. . . yeah got one of those) . She is doing some work

So yeah anyone beyond bored interested in talking about anything but physics and not ashamed of it ;) ping me

. . . . might still begin coding tonight but not sure when. The mood is not one for coding at this time

Let me may be use this time to plot the immediate future.

So on Monday, I get to see a Dentist. Second visit in two weeks.

We will still not (yet) address the gap. It takes some significant financial commitment to do this. But we shall take care of the other stuff

I have an appointment with a doctor on Tuesday.

Ah screw this. . .

Just going to sleep

I meant lay in bed and watch tv and drink water

. . . . alright

cows

2:03 AM

ok gf available now . . . talking to her now.

ZeroTheHero

@dmckee Thanks mon.

dmckee

@ZeroTheHero I'd been rather hope that it would get marked abusive by a gang of roving users, but it seems to be going slowly, so I rubbed the rust off of my modhammer...

BTW, do we have a question that covers the way the work-energy theorem works for a single situation observed at multiple relative velocities?

I'd have sworn we did, but I can't find it.

And we really need to point that user in it's direction (though it may or may not actually do any good).

dm__

3:25 AM

Is anyone familiar with degenerate pert theory?

If so, how would I go about finding the energy eigenvalues of the following setup:

$\begin{bmatrix}
a & 0 & b \\
0 & 2a & 2b \\
b^* & 2b^* & a+b+b^*
\end{bmatrix}
=
\begin{bmatrix}
a & 0 & 0 \\
0 & 2a & 0 \\
0 & 0 & a
\end{bmatrix}
+
\begin{bmatrix}
0 & 0 & b \\
0 & 0 & 2b \\
b^* & 2b^* & b+b^*
\end{bmatrix}
= H_0+H'
$

I see that (1,0,0) and (0,0,1) are degen, so I am thinking I need to look at $H'$ in this subspace: $\begin{bmatrix}
0 & b \\
b^* & b+b^*
\end{bmatrix} $

here we assume that $|b| << a$

need to find them to second order in $|b|/a$

ZeroTheHero

@dm__ Yeah you need to first diagonalise in the degenerate subspace.

dm__

ok great, understand that part for the moment. now am I correct in saying the following?

the evecs of that reduced $H'$ are the coefs on (1,0,0) and (0,0,1) for the states that distinctly split in energy when perturbed, and the first order energy shifts are the eigenvals?

cows

4:42 AM

Watching "Lincoln" . . . Powerful scene on equality

It's hard to believe that there were even debates about whether to add amendments , proclamations etc.

Lincoln turned out to be a decent Kat

Miss Lincoln was threatened with the mad 🏠. Good ol days

Hmm was going to make some commentary on the slave situation as narrated through the movie but let me not trigger anyone lol(not so funny)

Should enroll in an (American) History course at some point

Hmm Lincoln was Republican whaaaaaa

Hmm I wonder if there were other motivations

Jan 31

Votes day

Ah yes there was a war too

Avnish Kabaj

5:10 AM

Do we know how to make a space sunshield?

Heck ever since I joined Reddit I realized that 9gag simply copies their memes

Literal repost the entire popular section of Reddit is the same as that of 9gag's hot page

cows

What I gather here is that a self declared superior group democratically decided whether another group have full human whatever. Sexy sad stuff

It was even a tough decision to make for some people

At the end of the day we are all animals, must eat,poop and try to reproduce. Beyond the organization we all poop

At any rate according to the movie even the speaker voted

dm__

please stop.

cows

talking to me?

Just exploring how the movie shows the events leading up to the 13th amendment

It's more important than physics(to me)

dm__

5:27 AM

great, go here: movies.stackexchange.com

cows

I'm not going there

No.

It's a Steven Spielberg movie come on

user8718165

5:40 AM

hello sir @JohnRennie

good morning

cows

@dm__ certainly the link you provided makes sense. However I guess I am doing this to sort of throw serendipity into the pool. Who knows some people might even Google the 13th amendment or watch the movie

John Rennie

5:57 AM

@user8718165 morning :-)

user8718165

had some problems @JohnRennie

John Rennie

@user8718165 you mean like homework problems? If so you should probably ask in the Problem Solving chat room.

user8718165

not that sir just some conceptual ones involving magnets

1

Q: Interacting magnetic fields

Is there a reason why two magnetic fields perpendicular to each other do not interact? If they are parallel or at a non-90 degree angle they interact. Is it because magnetic field lines can be viwed as forces (perpendicular forces have no effect on each other). Edit: Sorry I didn't mention that ...

here floris says that the field lines around the wire will change from closed circles to spiral...but how ? Please explain it to me sir

sir please help

John Rennie

You'll have to give me a moment. I'm just answering a question in another chat room.

user8718165

Ok sir no problem that's fine :-)))

user8718165

6:24 AM

are you free now sir @JohnRennie

John Rennie

@user8718165 just dealing with a problem at work. Sorry, I'll be a few minutes yet.

user8718165

ok sir :-)))

user8718165

6:50 AM

Sir is your prob solved? :-))

John Rennie

7:01 AM

@user8718165 I've tried to draw the field lines to show what is happening:

user8718165

😊😊😊😊😊😊

sir thank you so much...I have some other questions...can I ask?

John Rennie

Yes, go ahead

user8718165

sir could you please tell me how will the field lines from the uniform mag field interact with that wire carrying current parallel to that mag field?

to create the resultant field which you have drawn?

Secret

Haragei

Haragei (腹芸 or はらげい) is a Japanese concept of interpersonal communication. It also appears in martial arts circles, with a somewhat different meaning; see below. Literally translated, the term means "stomach art", and it refers to an exchange of thoughts and feelings that is implied in conversation, rather than explicitly stated. It is a form of rhetoric intended to express real intention and true meaning through implication. In some societies, it can also denote charisma or strength of personality. Haragei is considered difficult for non-Japanese, particularly Westerners, to fully understand.Takie...

I will probably have great trouble adapting to this, because my logical thinking is intensely anti-law of implication

Most of my thinking don't really have A => B in mind

What I have is an unpredictable, artistic like A->B->C-> where from one idea to the next, they are linked by some kind of feeling that is in common in between

Specifically, if you don't say it I will neither assume it is a yes nor a no, I will just treat it as "no information". Only for contexts I have experienced enough time, will I be comfortable to interpret it as e.g. yes or no

This is partly arised from my science trainning, which is not to assume that no evidence of yes means there is evidence of no

user8718165

7:16 AM

hi sir @JohnRennie

imgur.com/a/U5cTgjy

John Rennie

@user8718165 sorry, busy again. I'll be a few minutes.

user8718165

😊just need your attention...anytime

Secret

33

Q: A language made of silence

Currently, most, if not, all human languages use sound to communicate. What if, language A, a language much like English in terms of its global dominance and widespread use, on a planet much like ours, used silence instead of sound to communicate. If you don't understand, speak the following sent...

language

The language of silence is a very poorly understood one

> To speak of ineffables, one must forgone all sound

user8718165

7:44 AM

still working sir? @JohnRennie :-)))

dm__

Anyone have a reference they like for degenerative perturbation theory? I find Sakurai 5.2 to be pretty awful.

user8718165

hello sir @john rennie

user8718165

8:06 AM

hello sir @JohnRennie

dm__

8:26 AM

@user8718165 think about adding the components along the loop. what would your resultant look like?

user8718165

$B_net$ down and right the screen?

dm__

yep, for the 'top view' of any point along your loop. so what does a downward right slanting field (for a top view) at every point along your loop create?

useful to draw this for a few points

dm__

8:47 AM

@user8718165 have to go now, so I'll say this. introducing a parallel magnetic field has no effect on the charge carriers, so we can just superimpose the two known fields. without an external field, we have closed loops. introduce the parallel field, now each location on the loops obtains some B component along the current, slanting the loops. note that it also breaks them being closed --> helix

user8718165

that's what I thought thank you.But what will happen to the remaining field lines?will ther pass through? imgur.com/a/xqws4Kc

hello @dm__

hi @dm__

Avnish Kabaj

Please don't ping a user more than once

Is that in the guidlines

user8718165

I got the helix part but why wont that affect the charge moving parallel to the field or the wire carrying current( whatever is there)?

@AvnishKabaj I'll take care...sorry

Avnish Kabaj

Lorentz force acts perpendicular to the magnetic field

And velocity

user8718165

9:14 AM

could you please tell why that charge won't feel any force.I know it doesn't (from lorentz equation) but could you please tell me with examples of the field lines i.stack.imgur.com/l5VNZ.png imgur.com/a/xqws4Kc

@dm__

Aaron Stevens

Anyone going to the APS meeting in Boston?

user8718165

could you please tell why that charge won't feel any force.I know it doesn't (from lorentz equation) but could you please tell me with examples of the field lines i.stack.imgur.com/l5VNZ.png

imgur.com/a/xqws4Kc

user8718165

9:30 AM

hello sir@JohnRennie

John Rennie

@user8718165 hi

user8718165

are you free now sir?

John Rennie

@user8718165 Yes, I'm around fir a couple of hours now.

user8718165

could you please tell why that charge won't feel any force.I know it doesn't (from Lorentz equation) but could you please tell me with examples of the field lines why it won't feel any force? thats the last thing i anty eo know

last thing i want to know

@JohnRennie

John Rennie

The charges in the wire feel no force because the circular field lines are only created outside the wire.

The only field lines inside the wire will be the ones for the external field.

user8718165

9:36 AM

but the fields around the moving charge is slanted and made helical right?

@JohnRennie

John Rennie

@user8718165 only outside the wire

And of course all the charges are inside the wire.

user8718165

Sir I'm not getting it....could you please explain it?please

Mauro Giliberti

Hello everyone! It's my first time in this chat thing. How does this work? How is it different than "normal" stack exchange?

John Rennie

@user8718165 The magnetic field around a current carrying wire consists of circles centred on the wire. Yes?

user8718165

yes sir

John Rennie

9:40 AM

@MauroGiliberti hi Mauro. The chat rooms are for discussing anything you want. At the moment we're discussing magnetic field lines, but you can chat about anything - it doesn't even have to be physics.

@user8718165 but those are the field lines outside the wire.

Mauro Giliberti

That's cool! Thanks.

John Rennie

@user8718165 Inside the wire there is no magnetic field, or at least the field is negligibly small.

user8718165

won't the wire as a whole be affected...like pulled up, pushed down ,left/right or something else?

John Rennie

No, why should it? The only field inside the wire is the external field, and that is parallel to the wire so the charges inside the wire are moving parallel to the field lines.

user8718165

will a charge experience force if it moves parallel to the mag field? because as it moves the circular fields around it will be slanted by the external mag field and the resulting field will be helical. wont that helical path change the motion of the charge?

@JohnRennie

John Rennie

9:46 AM

@user8718165 the charge is right at the centre of the circles. There is no field at the charge except the external field.

user8718165

but the circular field lines around it are no longer circular... @john rennie

John Rennie

@user8718165 the total field is the sum of the circular field due to the current, and the external field parallel to the wire.

Inside the wire the circular field due to the current is zero, so the total field is zero plus the external field parallel to the wire.

i.e. inside the wire the only field is the external field.

user8718165

Sir thank you so much sir. Finally it makes sense. I had to think hard since yesterday. Thank you so much sir...once again😊😊

PM 2Ring

10:01 AM

I mentioned Alan Gee & his anti-GR propaganda the other day. In the mean time, he's posted a question, now closed. I get the feeling that he won't be easily discouraged...

John Rennie

@AlanGee no it is not. This is a fundamental misunderstanding of GR. GR is a theory based on the proper distance being a scalar invariant. The local constancy of the speed of light is a side effect of this. — John Rennie 18 hours ago

@JohnRennie - It amounts to the same thing. Since there is no (significant) difference in the peculiar velocities of Jane and Jim, the only way the speed of light can change is if the properties of the metric are different at the two altitudes. This is contrary to the principles of GR. Anyway, forget GR and just look at the measurement of GTD, which is all the image depicts. — Alan Gee 18 hours ago

He just does not get it. There are none so blind ...

PM 2Ring

10:15 AM

His mind is locked onto his pet theory, which makes it hard for him to see its flaws, or to understand alternatives.

In case it's not obvious, I'm not implying that Alan is stupid. He seems eloquent and intelligent to me. It's just that preconceived notions can be really powerful. Lorentz and Poincaré were smart guys, but their thoughts about the æther stopped them from inventing SR. I've read a little of Poincaré's work, and I got the impression he never really grokked SR.

bolbteppa

10:52 AM

@vzn inference-review.com/article/long-lost-love

John Rennie

@bolbteppa thanks, it's an interesting read.

bolbteppa

"String theory demands the existence of supersymmetry" at least for the RNS string it is shocking that susy is really needed, if you ignore it you get stuck when trying to implement constraints when trying to eliminate ghosts, pretty cool

user351417

11:22 AM

Has anyone read L. Pauling's Introduction to Quantum Mechanics? I found a copy lying around in a bookshelf. I've been using Shankar's book for a while, and I have a copy of Griffith's which I think I've never opened, but I'm wondering if this one will give me something new since it looks like it's primarily for chemists.

bolbteppa

@Chair I've looked in it a good bit, it's a standard QM book really, uses wave functions the whole way through, no state vector kind of stuff in Shankar

John Rennie

Storm Freya is currently blowing in from the Atlantic. It is just about to reach Chester, though right now there is no wind. This is presumably the calm before the storm.

user351417

@bolbteppa Cool, thanks! Does that lack of state vectors ever become particularly troublesome though?

bolbteppa

I would see it as like an advanced version of Griffiths, the reason it's chemistry-ey is because the second half is on approximating multi-particle systems i.e. atoms, but this is in many QM books anyway (Shankar leaves it out), so it's mainly just a good QM book, it's all equivalent to working the way Shankar does so not really troublesome no

So it will solve e.g. the Harmonic oscillator using ODE's, no raising/lowering operators, Griffiths and Shankar do both, think Shankar does it a bit better, but there's a real directness/quality in Pauling you wont get in the others

user351417

12:22 PM

Thanks! Maybe I'll look at it once I've gone through the other two books then.

pZombie

12:39 PM

@PM2Ring there is an equivalent theory to SR, as in arriving at exactly the same predictions locally but with a special reference frame and an aether involved. Unfortunately, you cannot tell which is the special reference frame by observation. You can declare any frame to be the special one.

@PM2Ring The aether in such a theory has quite some weird features which i guess makes SR more elegant. For once, the reason why someone moving at a given relativistic velocity observes light to be moving away of him at c always is because the aether causes his clock to run slower and also shrinks everything including himself.

@PM2Ring This shrinkage and slow down of clocks by the aether is why the Michelson Morley experiment would give the same results even within this theory involving an aether. Which is why the Michelson Morley experiment did not really prove there is no aether

John Rennie

12:55 PM

Right I'm off. Today's lunch will be coronation chicken with kitchuri rice - when I get around to making it. Watch this space.

pZombie

@PM2Ring . By this point, most vestiges of a substantial ether had been eliminated from Lorentz's "ether" theory, and it became both empirically and deductively equivalent to special relativity. The main difference was the metaphysical postulate of a unique absolute rest frame, which was empirically undetectable and played no role in the physical predictions of the theory, as Lorentz wrote in 1909 -wikipedia

PM 2Ring

@pZombie Sure. One of the quirky things is that the æther has to be tenuous enough for it to not interfere with mundane mechanical motion at non-relativistic speed, but OTOH, it has to have insanely high rigidity to support the high speed of EM.

pZombie

One could say that the first postulate of Special relativity, as in all inertial frames being equal is also metaphysical, as it cannot be empirically determined if it is true.

SR is way more elegant than Lorentz's ether theory but Lorentz's ether theory is way more rational as you have absolute simultaneity with it and two observers meeting at different velocities at one point in absolute spacetime can now agree on if their cats are dead or alive "at this moment"

PM 2Ring

1:10 PM

I guess so, although we usually express it in a negative form. If you're in a lab floating in intergalactic space there's no experiment you can perform that will tell you your velocity wrt some external inertial frame, unless you cheat & look outside the lab.

If there were a real physical absolute rest frame, then there ought to be some measurement that can be performed anywhere that will tell you your absolute velocity.

pZombie

@PM2Ring Your last statement is not true, because there can be an absolute rest frame that cannot be detected by any measurement as shown by the Lorentz ether theory

bolbteppa

ETHER PHYSICS 101 - THE MAN WHO DISPROVED EINSTEIN

►

Apparently Einstein was not as good as people say he is :o

This ether stuff is hilarious

PM 2Ring

1:26 PM

"ether theory is way more rational as you have absolute simultaneity" For certain values of rational... ;) Local simultaneity makes more sense to me. Extending my space of simultaneity through the entire universe (not just the observable part) may be simple geometrically in flat spacetime, but it doesn't make a lot of physical sense.

pZombie

@PM2Ring Then you have to accept that if we were to meet at some point in spacetime, yet traveling at different velocities relative to each other, the question on if your cat is alive or dead on a far away planet would be nonsensical in the frame of SR. We simply could not tell.

Your cat would be a smear rather than a point in spacetime

PM 2Ring

@pZombie Sorry, I'm not a fan of supposed physical entities that aren't detectable, even in principle. Like invisible pink unicorns, they don't belong in physics. IMHO.

pZombie

@PM2Ring and i am not a fan of theories which create an image of "the world out there" that's irrational. Basically shut up and calculate and only care about if the theory gives you accurate local predictions

neither SR nor Lorentz's ether theory is really satisfying. One is irrational, the other requires a way too specific ether to make it un-observable. Maybe there is a third theory...

bolbteppa

What's irrational about SR

PM 2Ring

@pZombie Yes, that's sometimes called Penrose's Andromeda paradox. I'm sure it was mentioned here a few days ago. To me, talking about "right now, but a million ly away" is a silly thing to talk about. It's similar to wondering what's happening 0.1 metre east and 10000 km north of me. Things that are 0.1 m away are nearby, things that are 10000 km away are distant, and it seems strange to try & combine them into some kind of hybrid.

GodotMisogi

1:46 PM

@PM2Ring By hybrid, do you mean a theory that accounts for events in all of space measured at a given slice of time?

PM 2Ring

@GodotMisogi Pretty much. "Near me" in spacetime means events that are near in time and near in space. Events that are near me in space but distant in time, or conversely near me in time but distant in space, don't seem to be natural or useful categories.

GodotMisogi

@PM2Ring "Near me in space but distant in time", so you disagree with the usual notion of causality?

PM 2Ring

@GodotMisogi No. I can say that an event is in my past lightcone without needing to pin down its exact location in spacetime.

GodotMisogi

@PM2Ring I see; that does seem like a nice frame-invariant perspective

pZombie

@GodotMisogi We are talking about events which are neither in your past nor future cone. What is defined as the present by Einstein. Imagine your cat's worldline being in the present on a far away planet and you meet with me in spacetime at a given location, but we travel at different velocities. We cannot agree if your cat is alive or dead, given that your cat dies somewhere along the worldline in the present, depending on how we chose our velocities

In fact, you could do an acceleration dance by yourself, back and forth, and the instance of your cat on the simultaneity axis could switch from dead to alive. Which means that even asking the question if your cat is dead or alive is nonsensical in the frame of SR when the death occurs somewhere on the worldline in the present

Which to me means that SR cannot create a sensible image of the world out there. One that would make sense to most humans. It does deliver accurate local predictions though

ACuriousMind

2:03 PM

@pZombie The world out there is not required to conform to our notions of "sense" that were formed down here.

pZombie

@ACuriousMind I disagree. Maybe it is not required by physicists

ACuriousMind

And some people have an entirely different notion of how the world should make sense. Take Aristotle's "physics", where things have telos - inherent purpose, goals. He would rightly complain that not even classical mechanics "makes sense" in his framework.

PM 2Ring

What ACM said. Our physical intuitions are adequate for the conditions they evolved in. That doesn't mean that they therefore should also be applicable to extreme conditions that we and our ancestors have never experienced.

ACuriousMind

It's easy to forget that we're just monkeys in shoes.

GodotMisogi

@pZombie I don't see how this is nonsensical. I believe your requirement of simultaneity is axiomatic based on intuition (correct me if I'm wrong), but plenty of results/theorems are unintuitive and rational under their axiomatic (based on intuition) constructions, especially in algebra and analysis

user351417

2:13 PM

2

A: Update on the Manish situation

Oh, wow, I hadn't realized this was going on :) I first just wish to apologise to the community, both Chem.SE and Physics.SE, for my lack of activity. I'll shortly explain what happened, but I also just feel bad for causing this conflict, and think I could have handled this better. Sorry about t...

GodotMisogi

@ACuriousMind I wish there was "see monkey observe 4 dimensions" c:

pZombie

@GodotMisogi there is no simultaneity in Special Relativity. The so called simultaneity axis or plane or cube are not at all what the world simultaneity implies. One should never have called it the simultaneity axis. When someone asks you, what is your mother doing while you are here in this chat, if you were to answer this correctly in the frame of SR, you would have to answer that this question is nonsensical.

There is no "what is your mother doing at this very moment" in the frame of SR when your mother is not local to you

your mother is a smear in the present

GodotMisogi

This sounds like a very elaborate yo mama joke

pZombie

i agree, that did not come out well

GodotMisogi

Yo mama so not local that she a smear in the present?

2

ACuriousMind

2:18 PM

lol

GodotMisogi

I think I'm losing my innocence in investigating a "proper" definition of an event in spacetime

ACuriousMind

Hm? "event" is just synonymous with "point in spacetime", isn't it?

I mean, that doesn't always neatly map to the colloquial use of the word, but that's how one uses it in relativity

GodotMisogi

Oh, in SR/GR terminology, yes. I'm trying to incorporate a "state change" phenomenon into the definition (because it's more like the colloquial use then)

pZombie's claim is that 'state changes' at points in spacetime are nonsensical investigations in the framework of SR, from what I can see

ACuriousMind

@GodotMisogi I think their problem is more that there is no universal notion of "present", so different observers will disagree on what is happening "right now". You can point to the point on the worldline where the cat dies, but the observers will disagree on how that point relates temporally to other such points.

I.e. "there is an event where the cat dies" is uncontroversial, but the temporal relation to any spacelike separated event is not

GodotMisogi

2:34 PM

@ACuriousMind Aren't spacelike-separated events considered as causally disconnected?

Sorry, I'm having trouble parsing the sentence. There's a controversy with agreement on measurements of spacelike-separated events between different reference frames?

ACuriousMind

@GodotMisogi Sure. But if you take any "present"(=spatial slice), all the events in it are spacelike separated, meaning that there is no stable definition of "present" different observers could agree on. Of course, this is just relativity of simultaneity, but as far as I can tell pZombie is simply saying that this is not conforming to how humans intuitively expect a notion of simultaneity to work.

Which...is true.

GodotMisogi

Oh, then my first thought jumps to 'lack of experience' (similarly with the inability to perceive higher dimensions, but still being able to write it down). I'm sure (in the present? lol) our descendants will mock us for not seeing such a triviality once they're travelling at near-light speeds

Surprisingly, I found this easier to consider in QFT, particularly in which the commutators are basically forced to vanish for space-like separated intervals

ACuriousMind

@GodotMisogi The mental makeup of beings that actually travel at ultra-relativistic speeds will anyway be utterly foreign to us. Imagine routinely travelling thousands of years into the future while for you only a week passes.

@GodotMisogi Well, that's just the quantum manifestation of "spacelike separated events are causally disconnected"

GodotMisogi

2:52 PM

@ACuriousMind I'm not sure about the directness of this statement. The way I've studied it is by investigating the quantisation of a relativistic particle, and that leads to weird paths considered in the path integral in some frame that's not the MCRF (like the particle crossing a spatial slice some k number of times), leading to infinite DOF/fields

ACuriousMind

The paths in the path integral are always weird :P Even in the bog-standard non-relativistic case, the nice(=differentiable) paths have measure zero.

GodotMisogi

Even zero particle processes (closed loop computations of the propagator) are just freaky, and I don't know how those can be interpreted as spacelike separated events

ZeroTheHero

4:07 PM

@EmilioPisanty If only my grant could be increased to cover the cost of OA...

vzn

4:17 PM

> Sabine Hossenfelder shows even less understanding of her forsaken discipline in a recent essay for The New York Times. ... Hossenfelder’s humor, honesty, and discontent should be appreciated both by students of physics and the foundational sciences.

Keep these mind

What is the best way to maintain an external battery (Li-on?)? Almost deplete it before recharging, or recharging as often as possible? Or something else?

John Rennie

@Keepthesemind try to keep it between 50-80% charged

Keep these mind

@JohnRennie OK. What's the theory here?

John Rennie

Lithium batteries degrade due to cumulative changes in their structure. Keeping the charge level within the 50-80% band minimises these changes.

Keep these mind

@JohnRennie I will take your word for it, but any reference or anything else that makes sense to a layman?

pZombie

4:24 PM

i think the temperature you keep your lithium-ion batteries in is also a very important factor

John Rennie

@Keepthesemind there will be loads of info a quick Google away ...

Keep these mind

@pZombie 19 degrees Celsius

@JohnRennie Yes, but not very informed.

@JohnRennie Loads of people repeating something they saw somewhere else...

ACuriousMind

Repeating what you saw somewhere else is the cornerstone of civilization

John Rennie

Well I'm repeating what I have read. I have never personally done any research into degradation of lithium batteries.

pZombie

@Keepthesemind 19°C is pretty good for the lifespan. According to wikipedia, the perfect temperature would be around 25°C

Keep these mind

4:28 PM

@pZombie I'll keep it closer to my body then.

vzn

@pZombie that is a very crucial factoid that seems rarely taught. related, what is not widely appreciated is that lorentzian ether theory actually has very strong parallels to phenomena measured in gases... ie sound waves... if you ask me the nearly identical math is more than eerie and pointing to something deeper... btw there is some theory that builds on this by Tenev + Horstemeyer.

pZombie

A good battery should have mechanism to not allow itself to discharge below a certain threshold or above a threshold as in to prevent degradation. In such a case it would be pretty difficult to kill a lithium ion battery if kept at proper temperatures, given that li-ion batteries lose their charge very slowly. But most batteries do not have such elaborate protective measures built in which is why a lot of people manage to kill their li ion batteries

John Rennie

It's not a matter of killing batteries. All rechargeable batteries have a finite lifspan and the aim is to maximise that lifespan.

pZombie

One could imagine a battery that does not allow itself to discharge below 50% capacity but have an emergency button or a setting to allow itself to go lower if you are stuck in some kind of emergency where your life depends on it

John Rennie

I agree that it's hard to kill a modern battery in the sense of a short term assassination. But you can prolong or reduce the life depending on how you treat it.

Keep these mind

4:39 PM

@pZombie I like that. But that's not what my battery has.

@pZombie Also I would be more concerned with the upper limit of 80%. That is the more practical (avoidable) side. In my case.

John Rennie

@Keepthesemind the battery in e.g. your phone has been designed to be fully charged and fully discharged every day and still have a life of two to three years or so. But it will be showing significant reductions in capacity after a year.

The 50-80% guideline is not an essential part of battery care, it's a way you can extend the life to longer than the manufacturer's spec.

cows

ok so a few things happened that I've been thinking about. Let me just commit them to this chat rather than talk about other things. I have confronted the individual involved about it so it's not slander or gossip

ok so here goes

. . . .

So during a physics conversation a term or topic was brought up

Keep these mind

@JohnRennie OK. My phone is 3 years old (and I love it). But I have an external battery. That's the thing I am asking about.

cows

I said oh I know a professor at such and such school I used to attend he worked on that topic

person I'm talking to dismisses,

ok

I continue, I lived in the same building as said professors daughter

. .

Person says nonchalantly . .

"what kind of building would it be if they let me live in it"

he was not joking

then leaves conversation and walks away

Well first off, It was a pretty epic building, in a super awesome town

ACuriousMind

@cows Please don't fill the chat with many individual messages, especially not if you are not engaging in the currently ongoing conversation.

cows

4:51 PM

Secondly why does this matter?

Keep these mind

@cows Yes, please get to the point. A summary/conclusion first at least.

cows

@ACuriousMind I think the person in question is on this platform too, but this help me deal with the situation. I am not trying to personally message the person. I am using this as a wall to commit this here just so I feel better

Please let me continue

John Rennie

@Keepthesemind the external battery is likely to be very similar to the phone battery in design, an will be designed to have the same lifespan.

ACuriousMind

@cows I'm afraid this room is not a wall for you to "commit" messages to, no matter how therapeutic it may feel.

Keep these mind

@JohnRennie Thanks!

ACuriousMind

4:54 PM

If you have something you want to get off your chest but that doesn't really relate to this chat or its conversations, consider writing a blog post instead

cows

@ACuriousMind it's not therapy , it's physics.

ACuriousMind

Or make your own chat room and post it there, everyone can do that

John Rennie

@Keepthesemind I guess my point is not to worry too much. You'll struggle to reduce the life to less than the design spec no matter what you do, and any extra life over and above that spec is a bonus.

cows

@ACuriousMind no, I'm not trying to permanently commit atrocities to the internet

Keep these mind

@cows Everything is physics. Ultimately. Some people will say. Other people will say mathematics, and they would be right, too.

cows

4:56 PM

@ACuriousMind I don't do this everyday, there is a point to this if you'd let me finish

John Rennie

John Baez relates this quote:

A student of physics once asked a famous expert how much mathematics a physicist needs to know. The expert replied: “More.”

cows

This has caused me to have to pause what I was working on

I won't be able to work for at least two weeks

I'm not even calling this guy bad.

It's just something he is doing without knowing the effects

ACuriousMind

@cows Again, you're interrupting an ongoing conversation here with something completely unrelated, filling the screen with many messages in a short time, and refusing to desist when asked to do so. This is not acceptable.

Avnish Kabaj

Well we do have a guideline

In written form

Don't interrupt ongoing conversations. One of the great things about Stack Exchange chat is that the reply system allows multiple conversations to take place simultaneously. But that only works if you're discreet, and you don't post walls of text which occupy space on the screens of people who're talking about something else. If there's a discussion taking place, scroll up to figure out what it's about, and don't force a change in topic (unless what's going on is actually harmful, of course).

Will physics have an election now?

cows

test

Jesus, I got kicked off the chat for a minute lol

ACuriousMind

5:01 PM

@cows Yes, that was me, since you seemed to not get the point otherwise.

@AvnishKabaj Because of Manish officially stepping down? Most likely not, we've been doing fine "without him" for quite a while already

John Rennie

@cows if you get kicked twice more that's a 30 minute ban and a permanent black mark on your record. Bear that in mind.

ACuriousMind

Elections happen when there's a need for more moderators, not to fill slots.

cows

@JohnRennie ok ok

Avnish Kabaj

I see

Thanks

My money would have been on emilio pisanty

John Rennie

@cows But for what it's worth, as a non-mod, I think the battery conversation has discharged now so you wouldn't be interrupting anything were you to continue.

cows

5:04 PM

@JohnRennie ok thank you

well to continue

Keep these mind

@cows I've noticed that Academia SE may be interested in/helpful with workplace issues. And Workplace SE of course.

Avnish Kabaj

@JohnRennie I see what you did there

;)

John Rennie

@AvnishKabaj I've toyed with the idea of standing as a mod twice and have decided against it twice.

cows

I do feel a bit weird having to talk about this stuff but damn, it psychologically hit me a strange way

John Rennie

It's a lot of responsibility and I have to admit I find the prospect a bit daunting.

ACuriousMind

5:05 PM

@AvnishKabaj I think he said in the last election already that he doesn't want to be a mod.

(he didn't nominate there either)

John Rennie

I'm faaaaar too untrustworthy to be a mod! :-)

ACuriousMind

Maybe he's changed his mind, but I wouldn't bet on it

@JohnRennie Most of the time it's just cleaning up comments :P

John Rennie

Born's rule cannot be valid universally, and must be considered as a scientific law with a restricted domain of validity - that seems surprising ...

cows

@Keepthesemind may be if I was trying to do something about it, but I'm just discussing what happened plus I sent him a text telling him I was not happy so he should probably think it through and change

Although I will still take that 2 weeks vacay from physics just to recuperate

Anyways that's all about the story. I don't think I wan't to start a blog over this.

ACuriousMind

@JohnRennie A cursory reading suggests it is not surprising - we already have the notions of "weak measurements" that are not measurements in the sense of the Born rule, and it seems he's just pointing out more "measurement-like" situations in which the Born rule is not appropriate to apply

But of course it's nice to open with such an iconoclastic claim ;)

John Rennie

5:12 PM

I find it hard to summon up much enthusiasm for this type of foundational stuff, which is a shame really as it's probably good someone is thinking about it.

It seems awfully dry though.

Keep these mind

5/12 - 6/12 = ?

John Rennie

$$ \sum n $$

Keep these mind

@JohnRennie Good boy!

John Rennie

:-)

If there's an obvious joke I can usually be relied on to make it :-)

cows

I don't get it

danielunderwood

5:17 PM

Looks close enough to 0 to me

Therefore $\sum n = 0$

cows

oh

ZeroTheHero

nature.com/articles/s42254-018-0005-3

John Rennie

@cows see here

Avnish Kabaj

@JohnRennie I was referring to the pun

But i think you would make a fantastic mod

John Rennie

@AvnishKabaj ah yes

Keep these mind

5:19 PM

1 + 2 + 3 + 4 + ⋯

The infinite series whose terms are the natural numbers 1 + 2 + 3 + 4 + ⋯ is a divergent series. The nth partial sum of the series is the triangular number ∑ k = 1 n k = n ( n + 1 ) 2 , {\displaystyle \sum _{k=1}^{n}k={\frac {n(n+1)}{2}},} which increases without...

Avnish Kabaj

it is a lot of work i agree

danielunderwood

@JohnRennie are you already a chat mod as a room owner?

ACuriousMind

@danielunderwood Room owners only have powers in their own room

John Rennie

@AvnishKabaj I like to throw in these little jokes. Amazingly no-one has called me out on this one yet

ACuriousMind

There aren't really dedicated "chat mods" - all site moderators are chat moderators by default

John Rennie

5:20 PM

@danielunderwood I'm only a second rate super hero

Avnish Kabaj

@JohnRennie Can't seem to catch it

First sentence ...

you humans?

That's the one :-)

John Rennie an alien catch the latest scoop at VOX

ACuriousMind

5:23 PM

@ZeroTheHero "Publication rates have exploded in recent years in HEP, Nuclear and Astro" Hmmmmm

Keep these mind

@JohnRennie Seems a non-answer.

John Rennie

@Keepthesemind it does?

Keep these mind

@JohnRennie You seem to explain the difference between a tone and noise. But you neglect the difference between a frequency and a tone. Right? Maybe not.

46

Q: What are the differences between tone, note, and pitch?

I was wondering what the differences are between "tone", "note", and "pitch"?

theory terminology

PM 2Ring

JR's answer about the plucked guitar string looks fine to me. The core part being that the harmonic series has the same frequency as its fundamental.

Keep these mind

@JohnRennie In any case, I know nothing about this.

John Rennie

5:33 PM

@Keepthesemind I didn't want to get into the theory of music because I don't think that's physics. It's more about the signal processing that goes on it what we laughingly refer to as our brains.

PM 2Ring

Of course, a real string isn't an ideal 1D string. It's a cylinder, and it's response isn't perfectly linear. OTOH, even crude string models can be used to synthesize quite realistic sounds.

John Rennie

The only point I wanted to make is that as PM2Ring says the function describing the sound is periodic with the same frequency as the fundamental.

Keep these mind

Music theory

Music theory is the study of the practices and possibilities of music. The Oxford Companion to Music describes three interrelated uses of the term "music theory": The first is what is otherwise called 'rudiments', currently taught as the elements of notation, of key signatures, of time signatures, of rhythmic notation, and so on. [...] The second is the study of writings about music from ancient times onwards. [...] The third is an area of current musicological study that seeks to define processes and general principles in music — a sphere of research that can be distinguished from analysis in...

PM 2Ring

@EricDuminil No it doesn't, since the high harmonics get filtered out rather quickly. You may enjoy playing with Karplus–Strong string synthesis. It's very easy to implement (eg, in Python), and gives a surprisingly realistic plucked string sound for such a simple algorithm. — PM 2Ring Sep 19 '18 at 17:34

John Rennie

Anyway, I'm off to digest lunch, read this week's New Scientist and eat a bag of mints (in no particular order)

Keep these mind

5:39 PM

Enjoy

PM 2Ring

The Python code I linked in that comment is rather short, but the waves it makes sound pretty good. And it should be pretty easy to adapt to other languages if you don't like Python.

cows

@PM2Ring going to run the code and see what happens

hmm

cool

PM 2Ring

6:02 PM

Glad you like it. I think it's pretty cool that you can make realistic sound waves without using the sine function. That's not such a big deal these days, but it was a couple of decades ago. And it's still nice to avoid trig functions when you can.

cows

The last thing I tried to pin down before my 2 week hiatus was this idea of " downfolding technique"

@JohnRennie can you perhaps point me somewhere on this ^^

or @ACuriousMind

Let me search the site a bit for it

I get nothing physics.stackexchange.com/search?q=+downfolding+technique

Anyways I should really take that break now

bolbteppa

6:29 PM

@JohnRennie there are some serious issues with that Born paper, especially 3.3

Lots of quoting of Landau in there, to quote my most-posted article motls.blogspot.com/2007/11/exceptionally-simple-theory-of.html , "you bet that I have opened the paper" :p

Discussion of it here physicsforums.com/threads/…

bolbteppa

6:47 PM

Point 2 in 3.3 is kind of unbelievable, the continuous spectrum issue makes unavoidable the very necessity of density matrices in the first place for such systems, with 'stat mech' being the replacement of density matrices with simpler distributions, the idea this doesn't come from the Born rule is simply wrong

Without Born we have nothing, with Born we can't have everything - it's like he's saying because density matrices are also needed, this means Born is incomplete,... density matrices arise because "there is no complete set of measuring processes whose result can be uniquely predicted", it's like saying Born is bad because nature doesn't conform to it, it's not Born's fault nature is that way

Sir Cumference

Morning

dm__

8:18 PM

Anyone have a reference they like for degenerate perturbation theory? I've found (1) Shankar to be lacking in rigor, but qualitative explanations are clear; (2) Cohen-Bernard-Frank to be relatively more quantitative, and the explanations are easy to follow -- however, I do think his notation is a bit annoying; (3) Sakurai, which attempted to be mathematically rigorous, but did this with almost no explanation and is a headache to follow; e.g. going from 5.2.5 to 5.2.6 is a grand mystery to me.

What I'd like to find is a source that is clear in exposition and detailed in rigor.

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