The h Bar

Danu

08:00

You can see the poisonous color in the video from the answer

DanielSank

@Danu indeed

Danu

It comes from "pandan extract"

DanielSank

@Danu I went to Japan.

The video reminded me of it.

Food is all dependent on seasons in Japan, so when the young lady said "Spring is finally here" at the beginning of the video, it sparked the mental link.

Good food in Japan, you should go.

Danu

Too expensive to go there for me

DanielSank

@Danu Gotta find a conference.

@JohnRennie I sort of understand.

Secret

08:04

@JohnRennie I wonder if they will find the same thing for tritium

DanielSank

Summary for non-particle people?

Danu

@DanielSank Yeah, maybe next year

David Z

@DanielSank for the proton radius thing?

DanielSank

\(^^)/

@DavidZ Si.

Secret

@DanielSank You cannot really summarise the method they use to find that result in layman terms (unless the layman database knew more terms), but the main result is: deuterium nucleus was measured to have smaller radius than previously found, this and the unexpctedly small proton radius remains a puzzle to be solved

John Rennie

08:07

Because the proton has a finite size there is a region where the electron and proton overlap.

This slightly changes the 1s orbital so it isn't precisely (ironically) hydrogenic.

By measuring the 1s to 2p transition with very high resolution you can see this shift in the 1s energy, and with a bit of modelling you can calculate the charge distribution of the proton.

You can repeat the exercise with muonic hydrogen i.e. a bound state of a proton and muon.

DanielSank

@JohnRennie Well wait just a gosh durn minute there, mister.

Danu

@ACuriousMind See ^^^ the notion of size :D

John Rennie

The muon has a more compact wavefunction due to its higher mass, so the overlap with the nucleus is much bigger and the effects easier to measure.

DanielSank

You can only measure transitions energy differences, yes?

John Rennie

And when you do the muon expt you get a slightly different charge distribution for the proton.

@DanielSank yes. That's what I said isn't it?

DanielSank

08:11

Is the 2p orbital less sensitive to the deformation?

Or do we have to consider the affect of the proton size on both orbitals?

John Rennie

Yes, the 2p has a node at the proton so the effect is reduced

DanielSank

@JohnRennie Oh right.

k

John Rennie

But you're quite correct, there will be some effect on the 2p and that is taken into account.

DanielSank

@JohnRennie Ok, groovy.

So wait a minute...

The muon and electron results differ by enough to be puzzling?

::reads article again, more slowly::

John Rennie

7 sigma!

7.5 sigma for the deuteron!

DanielSank

08:13

> what they found and offer a few possible ideas to help dispel the notion that the puzzle indicates that there may be some problems with the Standard Model.

Ha, defend the standard model!

I kid.

Secret

Is the discrepancy more pronounced than the proton result compared to the deuteron result? Do we expect other hydrogen isotopes to have similar behaviour?

John Rennie

@Secret about the same

DanielSank

I remember being a grad student, and in particular being constantly terrified that my calculations missed factors of 2 etc.

When results like this come out, it's frustrating that our publication culture/system/whatever doesn't generally allow 3rd parties (i.e. not the authors or referees) to take a look at the data and analysis software.

So, when I see a result like this, I'm always wondering how certain anyone is about the numbers.

Are the experiments simple?

I guess not, or more folks would do them, no?

Secret

For starters, you need a very bright muon source, and there's pretty much only one on the planet atm

DanielSank

So the deuteron and muon results both give values of proton radius less than the so-called accepted value.

At least they both fall on the same side.

@Secret Oh.

David Z

08:19

@DanielSank Well, the data and analysis methods. If someone can replicate and verify the analysis, it shouldn't really matter what software was originally used IMO.

DanielSank

@DavidZ Well, sharing code means less mistakes --> less wasted time and less unidentified errors.

I get your point though.

I have to say that I find it unlikely that anyone can convey a complex data analysis method in a way that is even close to as precise as just sharing the code.

Secret

https://www.quantamagazine.org/20160811-new-measurement-deepens-proton-radius-puzzle/

and it seems doing the measurement itself is very difficult and very error prone

David Z

@DanielSank True, although the mistakes that are there will propagate.

@DanielSank That's a good point.

DanielSank

@DavidZ On the other hand, I'm being a tad idealistic. Sharing code is mostly useful if the code is not-horribly organized, which is.... not always the case in academic labs.

Or anywhere, to be honest.

Secret

http://phys.org/news/2016-08-physicists-discovery-nature.html
The proton puzzle also remind me to google about the hungarian neutron fith force follow up, and it seems some UCI researchers have did so

David Z

08:24

@DanielSank Haha, yeah, though I bet there's a correlation with places that use source control.

DanielSank

@DavidZ Indeed. That correlation probably exists if for no other reason than caring about the existence of version control correlates with caring about computer stuff at all.

David Z

Exactly

DanielSank

An established code submission and review workflow revolutionized our lab.

A few people went in kicking and screaming but now I have the enormous satisfaction of seeing some of those same people really care about code quality.

I'm designing a board game

David Z

Nicely done

DanielSank

In doing this, I took this evening to try to parameteize the win conditions of games I know about.

It's rather interesting.

I have three essential boolean variables:

1. Group or individual win
2. Limited or unlimited score
3. Elimination or everyone plays until the end.

John Duffield

08:33

@DavidZ : all points noted. Please do review the exchange to assess how civil I've been.

DanielSank

Most board games are individual win, unlimited score, non-elimination.

David Z

@JohnDuffield cool. For the record, we always review these things before making statements like the above (and also before taking actions like issuing suspensions).

DanielSank

@JohnDuffield Indeed. It's interesting in fact, that I don't recall you ever being uncivil, but for some reason uncivil actions tend to come out of others when you're around. This gives me pause.

I am embarrassed by my reaction a few pages up the chat log.

Secret

http://arxiv.org/abs/1608.03591

I wonder if tritium, being a radioisotope of hydrogen, will demonstrate the effect of both the proton puzzle and the protophobic fifth force result...?

DanielSank

@Secret An amazing time to be alive, eh?

Secret

08:39

Ya, I have been watching a lot of popsci, semi technical website and a few journals recently and they keep coming up with possible hints of BSM physics

John Duffield

@DanielSank : no problem. These things happen.

DanielSank

@JohnDuffield Oh, I dunno if I'd put it like that.

Things do happen for reasons after all.

I need to remember not to blow up.

Danu

Wouldn't it be hilarious if the "breaking of the SM" came from low energy physics

DanielSank

@Danu If by "hilarious" you mean "totally awesome and a reason for me to strut around Physics.SE naked for a month", then yes.

Secret

That's might be not very suprising. There have been long records of scientific discoveries came up in the most unexpected and least inquire of the places

sometimes the place we people least look at is where discoveries will lurk

and don't forget a a lot of scientific discoveries are aided by accidents

Danu

08:42

@DanielSank Perfect time for me to switch away from HEP ^^

DanielSank

@Secret Have any example in mind?

@Danu :(

Danu

@DanielSank It's a done deal ;)

Secret

Well take the discovery of plastic. Who knows a beaker of stuff accidentally mixed with some other chemicals will give us things like plastic bags

more examples here
https://en.wikipedia.org/wiki/List_of_discoveries_influenced_by_chance_circumstances

DanielSank

...continuing my observation about civility: This leads me to conclude that we are allergic to discussion where we perceive lack of good faith.

And now I wonder if that's an objective enough, or "grave" enough offence to warrant an actual rule.

It's a bit funny that such a rule could be written "No trolling".

Danu

@DanielSank Hah, I have a counterexample to all three criteria

DanielSank

08:46

And folks like me who explode at such things could be warded off by "Don't feed the trolls".

@Danu Excellent.

Danu

Though I guess it's not really a board game...

DanielSank

I was just considering whether this parametrizing is total crap or not.

Danu

There are some cards but it's mostly story*** driven :P

DanielSank

@Danu That's ok. I have video games, and sports on my list too.

@Danu ***?

Danu

@DanielSank Correction to "score"

The Werewolves of Millers Hollow

The Werewolves of Millers Hollow is a game of the French board games authors : Philippe des Pallières and Hervé Marly. The objectives are : - for the werewolves, kill all the villagers - for the villagers, kill all the werewolves This game can be played among 8 and 48 players. Each player receives a card that is either a villager or a werewolf. == Basic Game == This game contains the following cards : - 4 werewolves - 13 simple villagers - 1 seen - 1 little girl - 1 witch - 1 huntsman - 1 Cupid - 1 Thief - 1 Captain === The werewolves === Each night, they eat a villager. This eaten player doesn't...

DanielSank

08:47

I'm trying to get a good understanding of what works.

Dude, we call that Mafia.

Danu

Coolest game I've ever played (of course it's essential you have good players)

DanielSank

And it's as old as time.

WTF is this, French people claiming it as a product.

Danu

Sure it exists in many incarnations.

DanielSank

Is this a joke?

Danu

This particular incarnation is pretty good though.

DanielSank

08:48

Mafia is on my list.

It's a team win / finite score / elimination game.

Danu

Mafia (party game)

Mafia, also known as Werewolf, is a party game created in the USSR by Dmitry Davidoff in 1986 modelling a conflict between an informed minority, the mafia, and an uninformed majority, the innocents. At the start of the game, each player is secretly assigned a role affiliated with one of these teams. The game has two alternating phases: night, during which the mafia may covertly "murder" an innocent, and day, in which surviving players debate the identities of the mafia and vote to eliminate a suspect. Play continues until all of the mafia have been eliminated or until the mafia outnumbers t...

It's from '86

DanielSank

"score" doesn't mean just "points" in the usual sense.

Danu

Note the "werewolf" alternative name

:D

DanielSank

Yes yes.

Yikes that sounded snarky.

Sorry.

Danu

"Andrew Plotkin gave the rules a werewolf theme in 1997,[6] arguing that the mafia were not that big a cultural reference, and that the werewolf concept fit the idea of a hidden enemy who looked normal during the daytime"

DanielSank

08:49

Anyway, finite versus infinite score just tries to capture whether or no the game ends after a finite number of accomplishments.

@Danu Makes sense.

Danu

Check Quantum Werewolf under the variations.

DanielSank

Why didn't he call it "KGB"?

@Danu o_O

oh jeez

Yeah so, @DavidZ is "discussion not in good faith" a crime around here?

@Danu I like Mafia. Only problem is the eliminated players get bored. Only works if there's beer or whatever.

David Z

@DanielSank I dunno, I wouldn't quite call that a rule. But it's something we'd look into, for sure.

Danu

@DanielSank Yup.

DanielSank

At some point a friend of mine programmed "quantum othello". It was unplayable but fun anyway. Each piece was a spin 1/2 and its precession depended on the "fields" from the neighboring pieces.

Danu

08:53

The largest problem for me is how bad most people are at this stuff.

DanielSank

@Danu lmfao. So you're a Mafia expert, are you?

:)

Danu

If a significant fraction of people remains mostly silent it's not nearly as fun.

DanielSank

@Danu ah

Danu

@DanielSank I talk a lot, at least.

DanielSank

@Danu I'd vote you out asap.

The talkative guy has to go.

Danu

08:54

Yeah, that happens a lot :\

But I've pulled some awesome wins this way, too

DanielSank

It ruins my strategy if someone talks too much.

@Danu ;)

I survive on being a fantastic liar.

If someone's flooding the field with words I lose signal to noise ratio for my lies.

Danu

In the werewolves version I know, there is sort of "Romeo & Juliet" duo (randomly chosen) who die if the other does and can therefore only win together, just the two of them.

DanielSank

@Danu Just the two?

Can't they win with the rest of the townsfolk?

Danu

yeah

No

But the twist is

the couple doesn't have to be on the same side of the game

So my best win story is this:

DanielSank

oh my

That's an excellent mechanic.

I'm writing that down.

Danu

08:57

I once was assigned the role of werewolf, coupled with an innocent, and we managed to kill everyone and win the game.

For writing down: The rule is that if one of the two gets killed, the other dies too. They can't survive without one another :P

The look on the face of my last remaining fellow werewolf when I betrayed him in the last round (just 3 of us left) was amazing

DanielSank

@Danu You know who each other are?

@Danu That's excellent.

Danu

@DanielSank Yes, you get to open your eyes and look at each other at the start

just like the bad guys do

DanielSank

@Danu Fantastic.

Danu

It's the best

Of course a win is very rare for the couple

DanielSank

I was playing a Mafia-like game.

Danu

08:59

But when it happens it's 10/10

DanielSank

I was a "bad guy".

My wife was a good guy with the ability to check one player's status once during the game.

She checked mine.

So she knew I was a bad guy.

I convinced everyone else that she was lying and that she must be the evil one.

They all turned on her.

She was so mad, but also impressed at my ability to just lie through my teeth.

Danu

Yeah, that's great ^^

John Rennie

I've just seen this and find myself strongly tempted. Any thoughts from the panel:

facebook.com/buzzfeedpropertasty/videos/1813797818832890

DanielSank

The look on her face as everyone turned on her, knowing that I was the bad guy.

Danu

In a situation like hers, it's best to put all cards on the table

DanielSank

09:01

@JohnRennie I don't understand the question.

Vote to close as unclear.

Danu

You can guarantee that you are a good guy

What you do is:

John Rennie

@DanielSank Check the link!

Danu

You say, okay, just don't lynch me right now. I guarantee you that either I get killed this night, or I reveal another player next round.

Most parties will listen to that

DanielSank

@JohnRennie Did. If the question is "should I or should I not eat delicious things" then I question your sanity.

John Rennie

So we're agreed then. It would be a criminal offence not to cook it for my Sunday breakfast :-)

Danu

09:03

Of course the reveal can be easily checked, so you gain absolute trust. The only drawback is that you usually get killed that same night.

DanielSank

@JohnRennie Correct!

Danu

Still, giving up the information like that will usually amount to a big step in the right direction, especially if you've already spotted 2+ bad guys.

DanielSank

@Danu No no, she got one reveal the whole game.

Danu

So it almost guarantees a win in most cases

John Rennie

Although I'm not keen on the fussy little cupcake size. I wonder how it would work if I did it like a quiche in a decent sized pie tray.

DanielSank

09:04

@JohnRennie I was thinking the same thing.

Danu

@DanielSank Oh... that's a rule I haven't heard of before.

DanielSank

Forget the pansy-sized cupcake nonsense.

This is a grown person's breakfast we're talking about here.

Danu

I was just about to tell you that I consider this role a bit OP

DanielSank

@Danu We weren't playing Mafia ;)

Different, similar game.

John Rennie

@DanielSank Last Sunday I made something vaguely similar. I fried up then shredded some bacon and mixed it with a tomato/herb sauce, then put it in a baking disk and poured a quiche/egg mix on top.

Sadly I got it slightly wrong and the egg/milk didn't set completely and was a bit soft. I thought it had promise though.

Danu

09:07

@DanielSank I'm trying to think about how the single reveal tactic works best...

DanielSank

@JohnRennie Excellent.

Danu

In any case, I assume you got lynched the next day, right?

DanielSank

@JohnRennie Keep trying.

My best-in-the-world chili took a couple years to perfect.

Danu

So it's still a favorable trade in most cases (for the good guys)

DanielSank

@Danu Nope.

Danu

09:07

lolwat.

DanielSank

We weren't playing Mafia.

Different game with similarities to Mafia/Werewolf/whatever.

John Rennie

I eat healthy stuff during the week, so it will have to wait until the weekend. I'm strongly tempted to give it another go ...

Danu

@DanielSank OK, I give up on trying to find optimal tactics without knowing the rules :P

DanielSank

While we're talking about food, here's a cocktail a friend and I accidentally invented last weekend:

9 parts soda water, 1 part lemon juice, a tad of simple syrup, a shot of gin, garnish with sliced strawberry.

Hot DAMN that was good on a summer day.

@Danu A good choice to be sure.

@DavidZ It's possible that such a thing would help smooth out some roughness in the chat room by providing written guidelines. On the other hand, it could be easily abused and misunderstood.

David Z

@DanielSank I think giving useful written guidelines will be tough, but it's certainly something worth talking about.

DanielSank

09:13

@DavidZ Right, I don't know how to explain "good faith".

Danu

09:30

Thanks for lightening up my views on this chat room guys

I think I've had enough positive experiences to tank through a few more weeks of bad stuff without too much complaining, if need be ;)

David Z

09:50

@DanielSank Me neither. And it's hard to tell. I prefer to define rules in terms of observable behavior where possible - though recognizing that it's not always possible.

John Rennie

Currently listening to, and enjoying, the latest album from The Pineapple Thief. They seem to be getting a bit Radioheady, though in a good way.

CuriousOne

10:05

Hello, again. Oh, come on, I can be reasoned with. You all know that. :-)

ACuriousMind

@JohnRennie I'm not certain, but is that really unexpected? I mean, the usual models treat the proton as stationary and compute the orbitals of the electron/muon in its field. But if you're going to be so sensitive as to measure the overlap with the proton, shouldn't one need to also compute the protonic states?

CuriousOne

@ACuriousMind: With greetings from spin-orbit coupling and molecular spectroscopy... ugh..

ACuriousMind

Unfortunately, I can't seem to access the actual paper so I can't check compared to what model the proton is "too big". If the "problem" is really just that the proton "radius" doesn't appear to be the same in different systems I'm not convinced that's a problem in and of itself

Secret

@CuriousOne Out of curiosity, what is your work and education background. Are you mainly in the physics field or you also in other science fields as well?

CuriousOne

10:21

@Secret: I am a simple experimental physicist. Or, better, I was, quite some time ago. Today I am selling out by charging capitalists an arm and a leg so that they can make even more money with optimized business processes. :-)

Secret

10:32

I see

John Rennie

10:47

@ACuriousMind the details of the calculation are way over my head, but I think we can assume the people doing them haven't missed anything obvious. The results for hydrogen have been around for over a year now and they've been fairly thoroughly chewed over. No-one has identified any mistakes so far.

But I have a lot of sympathy for the view that maybe it just means we haven't understood the underlying physics as well as we think ...

David Z

Presumably the baseline model would be the standard model.

Again, I haven't checked the calculations to verify that's what they did, but I can't imagine this would be such a big deal if this prediction didn't come from well-established SM physics.

John Rennie

@ACuriousMind arxiv.org/abs/1502.05314

CuriousOne

Can they calculate the proton with precision from first principles now? I though that was still at the outer limits of numerical QCD?

John Rennie

That's a review of the original measurements on hydrogen and muonic hydrogen.

@CuriousOne they aren't calculating the proton structure. They take the observed shifts in the spectrum and calculate a charge distribution. It's a purely experimental measurement.

ACuriousMind

@DavidZ It's horribly difficult to extract any hadronic predictions from QCD with certainty, and it highly depends on the initial conditions you feed into the calculation. I don't think it's a QFT prediction that's being tested here

John Rennie

10:52

They compare the measured proton charge distribution and it's different for hydrogen and muonic hydrogen.

David Z

@CuriousOne Yeah, it is. They can calculate the proton mass, I believe, to a decent level of precision, but I don't know about radius. AFAIK that still needs to be measured.

ACuriousMind

@JohnRennie Reading that, it seems the problem really is that the "radius" of the proton is different in the electronic and muonic systems

But I'm not convinced we should expect that radius to be the same in the first place

CuriousOne

Oh, I see.

John Rennie

Well the radius is somewhat poorly defined of course. I take your point that the muon may well cause a change in the proton structure.

David Z

@ACuriousMind I know, that's what my research is on ;-) Of course we can't calculate the proton structure from scratch, but we can calculate how it changes with certain changes in external conditions. It's plausible that that calculation has been done with QCD.

John Rennie

10:53

And I don't think we understand QCD well enough to rule that out.

ACuriousMind

All the possible explanations given seem to consider QCD effects on the muon

Ah, and the QCD calculation for the radius is apparently not yet useful, at least according to the paper JohnRennie linked

CuriousOne

Does it follow from the standard model that the interaction is mostly electromagnetic? Strong electroweak interactions would change the lifetime of the muon, I suppose, or that's not even in the cards because of the effective energy scale?

John Rennie

My impression is that lattice calculations for hadrons are still ridiculously hard to do wih any great degree of accuracy.

CuriousOne

I have no intuition at this level...

John Rennie

The chance of calculating with enough precision to account for a 4% change in radius is effectively zero.

ACuriousMind

10:57

@CuriousOne they're not measuring anything regarding the lifetime, the measurement seems to rely on the Lamb shift of the muon levels.

But as I said at the beginning, I'm a bit puzzled that we should expect the proton radius to be constant, after all the protonic states in a muonic atom should also differ from the electronic atom, but everyone seems to think it's obvious that the proton "radius" should be constant across all systems.

CuriousOne

I am just trying to get (guess -:)) an idea what forces might play a role.

What's the binding energy? keV?

ACuriousMind

Yeah, I think so. The (naive) ground state energy should be the 13.6 eV of the electron times 206 from the muon being heavier

CuriousOne

Are they seriously measuring a Lamb shift in the meV range on top of that? Wow...

That's what I would expect naively, too. But how the frell can they get the necessary experimental energy resolution? That requires some serious x-ray spectroscopy.

Ah, silly me... of course, it's an optical resonance measurement. :-)

David Z

11:25

@ACuriousMind Off the top of my head, one might argue that interactions with the muon field are subleading in a QCD calculation.

0celo7

12:27

Hello?

CuriousOne

Hello!

Slereah

Hell o

CuriousOne

e4 d6

Secret

slereah i am still waiting for you so we can analyse that time travel setting together

0celo7

13:35

@Slereah still waiting on Shouten and Steenrod

Jossie Calderon

14:00

CV PLS physics.stackexchange.com/questions/274647/…

@CuriousOne d4 Nf6

ACuriousMind

@JossieCalderon What? Also, you need to calm down with your comments there.

@JossieCalderon It's not a duplicate of the question you linked (the alleged duplicate says "I know what voltage is" while this question is exactly about that), and I'd prefer that you refrain from any further insults.

0celo7

@ACuriousMind Am I disallowed from asking questions

ACuriousMind

@0celo7 what?

0celo7

@ACuriousMind I don't want to beg, so how do I ask questions

This is a legitimate question.

ACuriousMind

14:15

I think the "begging" aspect is less the act of asking itself but the frequency of it and the way you react when people don't answer.

2

0celo7

Frequency?

I've way cut down on how many questions I ask

I was proud of it

ACuriousMind

You'll have to allow for two things: a) I can't read people's mind either and b) It takes time to change people's impression of you, especially if it was negative

0celo7

It may come as a surprise to you but it's a surprise to me that anyone could have a negative impression of me

ACuriousMind

@0celo7 You knew that e.g. DS ignored you because he found you annoying and you're surprised that anyone has a negative impression of you?

0celo7

@ACuriousMind Yes. I thought he was just an ass.

ACuriousMind

14:24

That's...one way to deal with negative feedback, I guess :P

0celo7

Isolated negative feedback, sure.

John Rennie

@0celo7 nothing more to say really :-)

0celo7

@ACuriousMind I don't find anyone annoying, so it comes as a surprise that I could be annoying to anyone.

ACuriousMind

@0celo7 You...don't find anyone annoying?

0celo7

No.

I don't have anyone blocked here.

John Rennie

14:26

Not even if I sneak into your lab and set fire to your cerium?

0celo7

@JohnRennie That's not annoying in the sense we're talking about.

@ACuriousMind I've blocked people here but it never lasts long because I still want to see what they have to say.

John Rennie

For the record I don't find your questions annoying, and the chat was a lot less fun during your enforced absence.

0celo7

I cannot imagine blocking someone for a prolonged period of time is all.

John Rennie

Though since I rarely undrstand your questions maybe I'm not the best judge.

0celo7

I do have a cohomology question for @ACuriousMind but I don't know how to not beg, apparently.

If someone could provide a format, that would be helpful.

ACuriousMind

14:29

@0celo7 See, this is actually annoying me right now: I'm not the one who said you were annoying, yet now I'm the one who gets all your passive-aggressive comments about it.

Also, no one said that all your questions were begging.

That's something you inferred because you don't see any differences in the way you ask questions. I'm not saying there are or there aren't because again, I'm not the one who characterized it as begging in the first place, but you need to recognize these jumps you make between what people say and what you infer

0celo7

Your starred quote 16 minutes ago makes me think you (and someone else here) agree on the begging.

And I don't know what "passive-aggressive" means.

"of or denoting a type of behavior or personality characterized by indirect resistance to the demands of others and an avoidance of direct confrontation, as in procrastinating, pouting, or misplacing important materials."

I am pouting, but it's directed at everyone who thinks I'm annoying.

ACuriousMind

@0celo7 "but I don't know how to beg, apparently" is not a direct address to anyone (it's "passive"), yet it's clear that it's meant to say that you don't agree with that assessment of your behaviour (that's the "aggressive" part). It's the verbal equivalent of pouting.

CuriousOne

@JossieCalderon Nc3 g6

John Rennie

14:48

Does this make sense?

0

Q: How can I tell whether a normal mode is excited or not?

I came across a question in which there were 3 ions of charge $q$ and $m$ bound by a harmonic well potential $\frac{1}{2}m\omega^2$. The natural frequency suddenly changes to $\omega+\delta\omega$, and I am supposed to find the normal mode which is excited. I understand that I should be substitu...

Jim

@ACuriousMind pouting is passive aggressive?

0celo7

@ACuriousMind My question is: $f:M\to M$ is smooth, and let $\Gamma$ be the graph of $f$. Let $\eta_\Gamma$ be the Poincare dual of $\Gamma$. Is $\int_\Delta\eta_\Gamma$ an abuse of notation, where $\Delta$ is the diagonal? Shouldn't we pull back $\eta_\Gamma$ to $\Gamma$ using the embedding $\iota:\Gamma\hookrightarrow M\times M$, then follow with a diffeomorphism $g:\Delta\to \Gamma$, so that integral is really $\int_\Delta g^*\iota^*\eta_\Gamma$?

I also have the same problem with the integral $\int_\Delta\eta_\Delta$. I think it should be $\int_\Delta \iota^*\eta_\Delta$, where $\iota:\Delta\hookrightarrow M\times M$.

Note that $\Gamma\to \Delta$ can be a diff because both are diff to $M$ itself.

ACuriousMind

@0celo7 Uh, the integration over a chain $\gamma : \Delta^n\to M$ is always defined as $\int_\gamma\omega = \int_{\Delta^n} \gamma^\ast \omega$.

0celo7

A chain?

ACuriousMind

...oh dear

3

0celo7

14:57

$\Delta$ is the diagonal in $M\times M$, not a chain.

@ACuriousMind I know what a chain is.

ACuriousMind

Well, you integrate forms over chains, so the symbol $\int_\Delta$ only makes sense when you have interpreted it as a chain, no?

0celo7

Hmm? $\Delta$ is a submanifold of $M\times M$.

ACuriousMind

Let's say it like this: you are probably correct by what is meant by $\int_\Delta\eta_\Gamma$, but I wouldn't call that an abuse of notation because I would argue that $\int_\Delta \eta_\Gamma$ is defined to be that.

0celo7

@ACuriousMind I guess it's as much an abuse of notation as $\int_{\partial U}\omega=\int_U\mathrm d\omega$ is

it should be $\int_{\partial U}\iota^*\omega=\int_U\mathrm d\omega$

ACuriousMind

No, not if you have defined integration over a submanifold/chain to be always pulled back by the inclusion

"Abuse of notation" is difficult to talk about with integrals because there are many slightly different variants to define how to write such integrals

There's certainly not one "right" or "wrong" notation in this case

0celo7

15:13

@ACuriousMind Oh, I don't like that definition

I should write my senior thesis on cohomology so I can unconfusify myself

@ACuriousMind I'm confused because they write $\iota^*$ sometimes.

It's apparent when one coauthor wrote a section because the notation changes slightly.

ACuriousMind

Well, I can't debug the notation of a book I've never read for you :P

0celo7

@ACuriousMind I agree.

Do you care to revisit exact sequences of vector bundles/quotient bundles at all?

ACuriousMind

what?

0celo7

I'm still not sure about the uniqueness of quotient bundles

specifically

if I have $0\to A\to B\to C\to 0$ and $0\to A\to B\to C'\to 0$

Willo said I can get a map $C\to C'$, and then I can apply the five lemma fiberwise

He said you "lift onto $B$ and then compose with the map $B\to C'$"

How do we know this map is (a) well-defined and (b) smooth?

I guess for (a) I'm asking what the map is...I'm really not sure.

We have a map $f:B\to C$ from the first exact sequence and $f':B\to C'$ from the second

So do we need $f'\circ f^{-1}$?

ACuriousMind

@0celo7 You know that the kernel of both f and f' is A. So every ambiguity in choosing the preimage of a point in C' doesn't matter, they all get mapped to the same point in C.

That the map is smooth should follow from all other maps involved being smooth, but it might be ugly to explicitly verify

0celo7

15:28

"it might be ugly to explicitly verify" The story of my life :/

ACuriousMind

Honestly, no one verifies this shit for every map they define. Does it matter whether it is smooth, anyway?

0celo7

@ACuriousMind Yes, because vector bundle homomorphisms are smooth.

ACuriousMind

@0celo7 Are there vector bundles that are isomorphic as topological vector bundles but not as smooth vector bundles?

0celo7

Hmm.

There might be a Whitney approximation theorem that takes care of that.

@ACuriousMind Does isomorphic in the vector bundle category imply isomorphic in the manifold category?

i.e. are isomorphic vector bundles diffeomorphic

ACuriousMind

Ugh

Probably yes

0celo7

15:42

@ACuriousMind ugh?

vzn

16:31

@JohnDuffield not sure why virtual particles are such a big deal/ theme lately in chat; it seems to be at your own insistence at apparently incorrect theory. & feel some of it is verging on mere semantics. am wondering, do you know of any published povs that mesh with yours? do you have a different model? does it have math, or is it a mostly verbal construction? are there any testable predictions of your model? etc... agree with others Hossenfelder seems to be highly qualified, like her writing...

John Rennie

@vzn: have you considered that the world, or at least this chat room, might be a better place if you didn't reignite pointless arguments?

0celo7

@JohnRennie you're becoming a real savage

DanielSank

Everyone: let's not answer questions in the comments like this

1

Q: Wave superposition proof?

I've just learned the superposition of waves. It got me thinking.... For example, if we're talking about waves in a string, can't we express all the things that happens on the rope using just $F=ma$ and some other mechanic equations? Then shouldn't we be able to prove the superposition of a wave ...

newtonian-mechanics waves superposition linear-systems

John Rennie

@0celo7 if we want this chat room to be an pleasant and interesting place to be then we have to work for that end.

vzn

16:49

@JohnRennie agree with JD on some )( aspects of his questioning. virtual particles seem to be a mysterious part of modern physics that points to something deeper and/ or "BSM" physics etc., its quite interesting/ significant that even experts/ authorities have some disagreement on their significance/ interpretation etc, youve inquired about them at length yourself in chat, etc; so yes there are some pointless arguments going on but there are some other major pointed arguments going on...

DanielSank

@0celo7 good advice here: catb.org/esr/faqs/smart-questions.html

Emilio Pisanty

@JohnRennie makes plenty sense to me - and well answered already.

vzn

(and wow! how many pages is this anyway?) o_O en.wikipedia.org/wiki/Physics_beyond_the_Standard_Model

0celo7

@DanielSank So now I'm not blocked?

Emilio Pisanty

0

Q: Does incidence of appearance of quantum fluctuation particles being lowered due to space expansion?

If I understood correctly, due to space expansion density of energy decreases (L. Susskind in his online courses). Does incidence of appearance of quantum fluctuation particles being lowered due to space expansion? If answer is "no", I would like to know why not. My question may be lame but I a...

space-expansion virtual-particles

... wait, what?

Balarka Sen

16:56

@0celo7 Did you finish your lunch? :P

0celo7

@BalarkaSen Yeah, doing administrative stuff for work now

Gotta keep the grad students in check

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