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12:12 AM
@ACuriousMind what's a linear op in German?
@loltospoon No, there are infinitely many excited states - look at the formula for the energy levels, it goes like $\propto 1/n^2$, so they get closer and closer the higher they are.
@0celo7 Care to take a guess?
@ACuriousMind Say the English word with a German accent?
@ACuriousMind what do you mean by "they get closer"?
@0celo7 Yep
Physically closer?
12:16 AM
@loltospoon The difference in energy between two successive levels gets smaller
"physically closer" would need a careful interpretation before I'd apply it quantum mechanically.
Ah ok.
So what do you picture in your mind when you think of an excited electron? And what changes in your visualization when you think of increasing its energy state?
Honestly, my only "visualization" of an electron in an atom is a term diagram and for the lower levels those fancy pictures of orbitals.
12:32 AM
Ah I see. What is your opinion on this - I'm having issues keeping up with the math and science in my undergrad physics career. I've noticed that it seems to be because I try to visualize everything, i.e. I try to associate a physical representation to everything I learn. Did you ever do this and notice that it was slowing you down? Or have you never had this problem?
Can't help you there I'm afraid, I've never had that problem. Maybe someone else here knows what you're describing
12:49 AM
Yea hopefully. It seems to be common to not visualize things. I was talking to my friend who is double majoring in physics and math and he said that he doesn't even try to visualize things. That drives me crazy - how, then, does he think?!
1:05 AM
@loltospoon Lots of people have this problem.
@DanielSank hooray!! It's very relieving to hear that!
Do you have any advice? What are your thoughts on this topic??
Can somebody explain wtf happened to this bounty?
I was really looking forward to making the rep cap 'yesterday'
@EmilioPisanty I suspect it's caching. There's a discrepancy of about half an hour sometimes between the notice and the bounty actually being removed. The revision history does not indicate that the bounty has ended.
@HDE226868 'caching' is some pretty cold comfort ¬¬
Unless SuperCiocia awards it sooner, I think you'll be awarded it within an hour.
1:17 AM
Naw, grace period was set to expire before midnight UTC, by rights the bounty award should be timestamped then
rep-caps don't come often, y'know
1:29 AM
@loltospoon Yeah: practice going between math and physics a lot.
Get comfortable with both and with going between them.
Practice practice practice.
As a student, I regularly would go through mathematical descriptions of various things to become more familiar.
@EmilioPisanty You know that bounties, like accepts, don't count towards the rep cap, right?
@ACuriousMind bounties don't count towards limiting your rep (like accepts), but they do count towards the badge
hitting the rep cap in the sense of the badge does not mean...hitting the rep cap?
> Epic - Earn 200 daily reputation 50 times.
Hm, right. Have you tested that it actually means exceeding 200 and not hitting the rep cap?
1:33 AM
@ACuriousMind I can confirm that it does.
pretty sure
nnyways, whaddayer complainin 'bout, you're at 43/50
though still well behind in rep if you factor in offered bounties =P
@EmilioPisanty My most recent >200 rep gain is in October '16, I guess I should aim for more HNQs :P
@ACuriousMind huh
I had a ridiculous streak at start of term
100+ rep coming in from ten different votes in year+ old answers
1:54 AM
Every once in a while I suspect that a user is following the path that Douglas Adams made so plain in his line concerning Slartibartfast's plans for his retirement
> He had also been planning to write an eccentric and relentlessly inaccurate monograph on the subject of equatorial fjords in order to set the record wrong about one or two matters he saw as important.
2 hours later…
3:58 AM
@skillpatrol what's good
@KyleKanos Hi! I don't know much about the likings of Physics.SE for community promotion ads. I posted one. Also consider to see revision. I want to discuss in order to get the idea and understand how should it looks like etc...
@KyleKanos can you give me suggestions?
2 hours later…
5:45 AM
6:01 AM
The most viewed question on the site is closed as off-topic :)
( query )
and only its views account for %0.56 of the all-time views of the whole Phys.SE .
6:42 AM
@Pandya I think the reason your ad is not getting a good reception is that the thing it's advertising - Hinduism SE - is just not relevant to the Physics SE community, or at least no more relevant than it would be to a random group of internet users. Going beyond that, the reason it's getting a bad reception is that it tries to make a connection between Hinduism SE and Physics SE out of nothing, in a sense.
6:55 AM
Is there anyone who uses VASP and Transition state search in particular here ?
@DavidZ First of all Thanks for replying. ok. In brief, it looks unsuitable here right?
@DavidZ so, Is there any scope of promoting Hinduism.SE through Community Promotion Ads here?
7:19 AM
what paper is this, it seemed to be formulating some kind of SUSY type TOE?
7:44 AM
@Pandya Honestly, I think no, i.e. there is no suitable way to promote Hinduism SE in our community ads.
The topics are just too different.
Of course, if you wanted to hang out here in chat, if you happen to run into anyone who might be interested, you can point them to Hinduism SE.
Hello, everyone :-)
Morning :-)
I've managed to fix my old bicycle!
8:00 AM
@JohnRennie how does gamma radiation work? I don't see any electrons in the nucleus...
@DHMO the protons and neutrons in the nucleus occupy energy states just like the electrons in an atom.
Transition in nuclear energy levels
Gamma ray emission from a radionucleus occurs when the nucleons transition between energy levels.
but photons have spin 1...
So what?
8:02 AM
Transition from a level 1/2 spin to -1/2 spin will produce the correct spin
by which particle?
A proton or neutron
Hmm, that isn't really a good way to describe what is happening
Well yeah but it's basically impossible to describe correctly nuclear processes
too complex
The central field approximation doesn't work in nuclei so you can't talk about the states of individual nucleons.
What you can say is that the total spin of the nucleus will change by one when a gamma ray is emitted.
8:04 AM
ok thanks
I mean even the sigma effective model is awful and it's still far from accurate
what is the total spin of a typical nucleus?
There isn't a typical nucleus. Nuclear spins vary wildly.
what can their spin range from?
1/2 to a lot
8:06 AM
how lot?
although when total spin is high it's pretty unstable
@Slereah Isn't 3/2 the actual upper limit as far as we know?
@DanielSank depends on what you consider
Oh oh oh we're talking nucleons. Never mind.
8:07 AM
@DanielSank no, see the document I linked. There are nuclei with spin 3.
You can have very high spin nuclei but those are unstable
also depends what you mean by "spin"
the proton has "spin" 1/2 but that's a lie
Proton spin isn't actual spin
it's a combination of spin and angular momentum of its components
${}_{11}^{24}$Na has spin 4!
The lesson to learn is that nuclear physics is awful and don't try to learn it
@JohnRennie Ooh, really? What are u going to do with it now that u've ordered another one?
8:09 AM
^ Got it
or if you do learn it, don't get too bothered by approximations
@Kaumudi.H I've cancelled the order for the new bicycle.
there are no exact QCD models for nuclei
@JohnRennie Oh. Did u fix it up on ur own? All of it?
The bike shop told me the bicycle was beyond economic repair, and they were quite right that it's uneconomic to repair it properly.
8:11 AM
@JohnRennie will die of bicycles this month
But I managed to find some used parts, and bought some new parts, and managed to fix it up enough to make it work for another year or so.
@JohnRennie in your table, do those nuclides having a positive level undergo gamma decay?
@JohnRennie Very nice! :-) What kind is it?
@Slereah -__- "Bicycles" is not a disease.
@Kaumudi.H Do you mean what make/model is my old bicycle?
8:12 AM
No but you can die from your bicycle falling apart
@Kaumudi.H this is the model though the picture shows a ladies' bike while mine is a gents bike.
Are we supposed to flag or VTC stuff like this?
@DHMO there are no simple rules for whether a nucleus decays by gamma radiation.
@JohnRennie ok thanks
8:16 AM
Ohh, cool. Mine doesn't have gears and all so it barely even qualifies as a "proper" bicycle in this day and age (:-P)
Hmm, although mine has 21 gears they are largely cosmetic since I only ever use one gear. Cycling into town isn't that arduous :-)
21?! Wow, OK...
I suspect the fitting of multiple gears to town bikes like mine is just a marketing strategy and not actually useful.
Actually 14 of those 21 gears don't work because the front shifter is broken :-)
Another thing that isn't worth repairing ...
Lol, OK. My cycle is old and looks nothing like it used to before, when I first bought it, which is why I doubt if I really will take it to college with me, even if possible.
Another Ship of Theseus bicycle? :-)
8:20 AM
And of course, it looks so different because it doesn't work as well and has lost many parts along the way. It used to have a wire-basket at the front, which came loose many years ago.
@JohnRennie Sort of, but I haven't replaced those many parts-they're not there anymore but it works fine even without them so :-P
In a funny sort of way I quite like my bicycle being a bit old and rickety. Being a bit old and rickety myself it feels comfortable to have my bicycle in the same state :-)
Haha :-) It's true, I really do feel a somewhat intimate connection with my cycle--riding other bicycles, (even the same model!) doesn't quite feel the same.
Anyway, I shall take it for the first (post-repair) long ride today. I did about five miles on it yesterday so it's working reasonably well.
@JohnR: I have a quick random question for you (since you are much, much older than me) -how dyou feel about getting a tattoo?
That's an odd question ...
I don't have any tattoos, and it's never occurred to me that getting one would be an improvement.
8:27 AM
Um, you see, I was wondering if u've ever wanted to get a tattoo and then when u became older and all, felt that it was good/bad that u didn't/did get a tattoo.
I've never regretted being tattooless.
OK :-)
I could get this side up tattooed on my forehead. That might be useful for when I've drunk too much.
Were you thinking of getting a tattoo?
8:32 AM
Well, yes, I have something in mind. I've decided that if I still feel the same way about it in 15 years, I'll get it.
Perhaps I should make that 20...
Oh, I don't understand how people are able to get tattoos of something that they're into at the moment. I mean, they've got to have that on their bodies for the rest of they're lives!
What if they grow out of it?!
("It" being whatever they used to be into-books, T.V shows, artists, etc.)
Yes, tattoos are a lot easier to create than to have removed. You'd need to be pretty sure you weren't going to regret it later.
> A poll conducted in January 2012 by Harris Interactive reported that 1 in 7 (14%) of the 21% of American adults who have a tattoo regret getting one.
1 in 7 actually seems quite low.
Oh my God, did I really just spell "their" as "they're"?! ::Facepalm:: Now I can't even edit it.
8:37 AM
Ha, quick star that :-)
@JohnRennie Not that low, but for tattoos and all, certainly! Hmm...
If there's a friendly mod around they can correct it for you.
Anyway, I have to get back to work for half an hour or so.
Alright then, bye :-)
9:12 AM
I'm back - work is done for the day! Now for some more coffee.
9:36 AM
hm, 4D GR only has $R$ and $\Lambda$ as terms for the Lagrangian if we want conservation of energy
but semiclassical gravity requires at least two extra terms in products of the Riemann tensor
Does it mean that semiclassical gravity has some violation of (local) conservation of energy or is it not a problem there
@DavidZ ok. Btw, I think there are few questions/topics on Hinduism.SE in which this community may be interested. Ok, I'll update my ad answer with summarizing it.
@DavidZ btw, I'm out side and will be able to update it after couple of days. Meanwhile should I keep the current answer or should delete it?
10:00 AM
This poor question is being tortured with the same answers.
Q: Why a body always rotate about its center of mass?

ShashaankI found after searching that This question has been asked before . But all the answers were not convincing. Suppose I have a body which is free, not constrained always rotate about its center of mass. Why is that so? A convincing answer that I found was that in most cases moment of inertial ab...

2 hours later…
12:29 PM
Like danielsank have said, there are *LOTS* of people having this issue. Take myself as an example, I am such an extreme visualisation freak that I try to visualise everything from algebra to infinite sets, overinterpreting physics formulae by trying to give a physical meaning to every single maths symbol in the formulae and end up up basically verbalising the formulae instead of getting the correct physics context, and I also heavily relied on drawings

My way out of this problem is luckily that I can also learn things abstractly without any pictures (because once I know what is happening
Above wall of text is one reason I found category theory attractive even before fully learning abstract algebra. It is so abstract that it helps emphasising only the most essential detail of the mathematical object in question, making it easier to understand as it simplify the thought process on trying to make sense of it and not get distracted by details
My current learning strategy is a mix of pictures and abstractions. The picture reflect my visual learning nature and allow me to manipulate concepts visually on paper, while the abstraction help me to stay focus and general
1:18 PM
@Slereah what?
is energy conserved in a $\Lambda$-vac?
I tried pal.
you wouldn't listen
1:31 PM
(not forgotten)
@skillpatrol so sad,I stand with you
United we stand.
Feb 10 at 0:28, by rob
Please don't use the chat message edit/delete functions to "temporarily" say things.
Why not?
1:34 PM
Divided we fall.
The delete function exists for a reason.
Feb 10 at 0:28, by rob
And deleting is for removing messages that shouldn't have been posted at all --- for instance if you accidentally send a message while you're still in the middle of typing a sentence.
You're telling me I can't use the delete function as it's intended?
Lots of things I say shouldn't have been said at all.
Hence why I delete them.
0celo totally got a point
He just accidentally sent them
He can tell you whatever he wants to tell you, he is a mod @0celo7
1:35 PM
@BalarkaSen Are all 3-manifolds orientable or do you need compact?
@skillpatrol meh
If you wish to further discuss the appropriate use of the delete feature, please take it to the meta room.
@0celo7 Lots of closed 3-manifolds are there which are not orientable.
There's that word again
s h o g defined it for me
It means: "shut up and listen"
1:43 PM
@BalarkaSen Sorry, I meant parallelizable.
Orientable 3-manifolds are always ever parallelizable. If it's not compact then easily so: just take three independent vector fields and push the singularities off to infinity
Push off to infinity?
@BalarkaSen Why do there exist three independent vector fields?
Sorry, that was wrong. There exists one nowhere zero vector field but no reason that I can get another independent one (and a further one).
But I think it should still be true for noncompact fellows, although not obviously so.
@BalarkaSen even noncompact nonorientable?
Parallelizable implies orientable...
1:49 PM
I didn't know that
It's a trivialization of the tangent bundle. A smooth choice of basis at each tangent space; much stronger than a choice of orientation at each tangent space.
Oh, you just take a global frame and declare it to be positively oriented.
of course
@BalarkaSen So every compact 3-manifold is indeed orientable?
Total garbage. When did I say that?
Idk. Too much to remember
Compact orientable 3-manifolds are parallelizable. There's an easy example of a compact nonorientable 3-manifold: the nonorientable S^2-bundle over S^1.
1:58 PM
How would I know that such a thing exists?
S^2 x I mod identifying the ends by the antipodal map S^2 --> S^2. Then project down to I/{0, 1} = S^1.
Or even just RP^2 x S^1
2:38 PM
@0celo7 energy conserved locally, not globally
3:13 PM
Can someone explain to me how this was not closed as a duplicate of this?
OP literally asked the same question again without any indication what's wrong with the earlier answers.
@ACuriousMind halp, I don't understand perturbation theory
@ACuriousMind how does second order degenerate perturbation theory work?
Exactly as it is described in the standard references :P
I'm looking at a standard reference and it assumes I understand what is going on
not a very good prerequisite tbh
@ACuriousMind In the nondegenerate case, I have to sum over all states except for the one I'm perturbing, right?
But here it says in the degenerate case to only sum over the degeneracy subspace
3:28 PM
@JohnR: Anything interesting for lunch today?
@0celo7 Well, the assumption of degenerate perturbation theory is essentially that the effects from within the degenerate subspace will be much stronger than from outside.
Faggots are a traditional dish in the UK, especially South and Mid Wales and the Midlands of England. It is made from meat off-cuts and offal, especially pork. A faggot is traditionally made from pig's heart, liver and fatty belly meat or bacon minced together, with herbs added for flavouring and sometimes bread crumbs. Faggots originated as a traditional cheap food of ordinary country people in Western England, particularly west Wiltshire and the West Midlands. Their popularity spread from there, especially to South Wales in the mid-nineteenth century, when many agricultural workers left the land...
that's an actual food?? I thought it is some swear word
The food called faggots existed several centuries before the insult :-)
At first glance, I was afraid you'd turned into a homophobic cannibal, then Googled "Faggots food" :-P
3:31 PM
@ACuriousMind and in my lecture notes it says to sum over everything NOT in the degenerate subspace
this is terrible
They are a surprisingly healthy meal. Rich in protein and low in fat.
@JohnRennie that's offensive
I eat them quite often during the week when I'm tryiong to eat healthily.
@JohnRennie Wow, I see...
> A faggot is traditionally made from pig's heart, liver and fatty belly meat or bacon minced together, with herbs added for flavouring and sometimes bread crumbs.
I have to say, that does not sound appetising to me :-)
By decree of @ACuriousMind , if a reasonable person finds it offensive, regardless of context, it should be punished. @JohnRennie I respectfully ask you remove that hateful word from the chat.
@0celo7 prove you're a reasonable person :-)
@JohnRennie I didn't vote for Trump
@Kaumudi.H a lot of traditional UK recipes sound dreadful but taste nice. For example the traditional Scottish dish, haggis, is made from sheeps lungs.
@0celo7 Well - you also have a contribution from the non-degenerate part that you compute in the usual manner. I get that it's a bit confusing, which contribution you want to look at depends on the exact context. Applying perturbation theory correctly is a bit of an art.
I see...
3:36 PM
In that street food video you linked, the first one not the one in Chennai, one of the meals was sheeps brain curry.
What I meant with the assumption up there is that degenerate perturbation theory assumes you can diagonalize the Hamiltonian within the degenerate subspace separately. In general, the perturbation may well shift the eigenspaces such that this is not possible.
Lots of westerners would find that revolting.
I don't remember it well but sure, yes, lots of people eat...brains of animals over here, I suppose.
I have eaten lambs brain in a posh French restaurant, but wasn't very keen on it.
@ACuriousMind Right, I did diagonalize it already in the subspace
I'm supposed to show that the second order shift vanishes, but I don't know what I'm supposed to compute
@JohnRennie I told you.
3:39 PM
@JohnRennie Will it be OK if I asked about ur food preferences?
Told me what?
@Kaumudi.H Yes of course.
Ah, can you unban yourself?
And there we see a shining example of why chat flags should be shown in context.
@0celo7 I keep my super powers a secret.
@JohnRennie Are u non-vegetarian because u were brought up in that way?
3:40 PM
@Randal'Thor ninja'd me
@Kaumudi.H He's a meat eater because he hates life and animals
@0celo7 No, @Randal'Thor unbanned him because the flag was clearly invalid.
@BernardoMeurer Lol, and what about urself?
@Kaumudi.H Guilty as charged
@ACuriousMind Not any less valid than the BS I constantly get locked up for.
3:41 PM
^ True
@Kaumudi.H I was brought up to eat whatever was put on my plate. Sometimes that was meat and sometimes vegetarian.
Another clearly invalid flag.
ok, I thought we were done with flags after a couple days ago
Jesus christ
So many mods
i'm not a mod!
also omg I remembered why I don't enter this room ;-; why do you guys keep this ticker on
3:43 PM
Who got flagged this time?
Wasn't me who did it.
@Riker For what?
@JohnRennie I changed the speakers :P
nah it was a garbage flag
just one of the messages you sent iirc
@0celo7 Someone flagged ACM's last message.
3:44 PM
absolutely invalid
@BernardoMeurer aha! Did you go for the more expensive B&Ws or a different make?
@Randal'Thor that's only 1 though I think, thought I saw another
...I'm going to wait till this dies down to ask some more, @JohnR.
@JohnRennie I got a pair of new ELAC speakers, engineered by Andrew Jones
of former KEF fame
3:45 PM
is bernardo a bot that insults people or is he just insulting me a lot
They're awesome
@Riker he doesn't like mods
@BernardoMeurer B5? B6?
I'm Brazilian, we're born to destroy structure and order
@JohnRennie The Uni-Fi UB5
It's a three-way which is pretty cool
concentric mid-driver and tweeter
That's an interesting design. The tweeter is integrated into one of the two woofers?
3:47 PM
Yep, into the midrange one
How do they sound?
Whoever banned me, I was giving a medical diagnosis.
I don't see how that's a bannable offense.
KEF does this a lot, e.g. their world-renowned LS-50 speakers
@JohnRennie Amazing, really
@0celo7 Don't diagnose people over the internet. Period.
@BernardoMeurer Cool :-)
3:48 PM
The bass is great, and the soundstage is really nice and wide
It's exactly what I was looking for
Now I'm in peace :P
@ACuriousMind You've diagnosed him before
as being stupid
When the hi-fi is just right it's amazing. To be able to just relax back and lose yourself in the music is fantastic.
@ACuriousMind What do I do when the Hamiltonian is already diagonal in the degenerate subspace?
It's job interview time!
See you guys later!
good luck
3:49 PM
@JohnRennie I see. Why have u continued to stay a non-vegetarian? Do u just happen to like the taste..?
5 messages deleted
@ACuriousMind I have a two level system and the whole space is degenerate
@0celo7 Good for you.
@Kaumudi.H aha, I was just about to say I think things have quietened down if you want to talk about food again.
3:50 PM
@ACuriousMind So what do I do since the degeneracy is not removed at first order?
@Bernardo I know this isn't my room, but calling people scum and losers isn't Nice. Please don't.
@Kaumudi.H I don't recognise vegetarian/non-vegetarian as a useful way of categorising people.
Most vegetarians I know will occasionally eat meat, and even the rabid non-vegetarians do eat vegetables.
@JohnRennie What dyou mean "useful"? It's a very real category!
You're making it too binary.
For example you've said you eat eggs i.e. baby chicks :-)
3:52 PM
Well, of course, there will be small changes. I, for one, eat eggs but only when in pastries. Some others don't do even that.
I'm talking mainly about meat, I suppose.
Well I almost never eat steaks. I can't remember the last time I ate a steak.
Don't mind me.
@JohnRennie If you eat unfertilised eggs, you aren't killing animals in order to do so.
And I rarely eat roast meats - usually only at my brother or mother's house if they've cooked a roast.
3:54 PM
@JohnRennie I...don't know what "steak" is, I'm afraid.
A steak is a meat generally sliced perpendicular to the muscle fibers, potentially including a bone. Exceptions, in which the meat is sliced parallel to the fibers, include the skirt steak that is cut from the plate, the flank steak that is cut from the abdominal muscles, and the Silverfinger steak that is cut from the loin and includes three rib bones. When the word "steak" is used without qualification, it generally refers to a beefsteak. In a larger sense, there are also fish steaks, ground meat steaks, pork steak and many more varieties of steaks. Steaks are usually grilled, but they can be...
Is this for real?
Or is it just fantasy?
Caught in a ...
Or am I hallucinating from these cough drops?
3:56 PM
I don't know the differences b/w different kind of meat. I'm only trying to understand why the idea that what u are eating used to be alive sits well with you...
There's my earworm for the day, I guess :)
@0celo7 What is "this"?
@ACuriousMind Are you salty and don't want to help me?
@Kaumudi.H I don't see anything wrong with killing animals in order that I can eat them.
@JohnRennie It't not a necessity =).
3:58 PM
Well, it goes further back than "killing", I suppose. Breeding would be the term that I am looking for...
As a boy the local farmers used to pay my brother and I to kill vermin. That was mostly rats, which aren't good eating, but also pigeons and we used to bring those home to eat.
So killing things then eating them was part of my life from early on.
00:00 - 16:0016:00 - 00:00

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