The h Bar

Sir Cumference

1:00 PM

@Jim How do you go about doing that? As in, what would a day of researching look like?

Jim

@0celoñe7 I have hundreds of games. Is there a specific genre you'd like to know?

0celoñe7

@Jim First I'd like to know how you have hundreds of games but not Skyrim?

Second, have you played The Witcher 3?

skullpatrol

Time's up :(

0celoñe7

@skullpatrol Shame. Guillotine time.

ACuriousMind

@skullpatrol We can continue as long as @Jim has time

Jim

1:01 PM

@SirCumference that depends on where you are in a research cycle. early on, you'd sit down and read papers, obsess over their details, and talk to colleagues. After that, you'd obsess over equations; trying to work them out on paper and rearrange them into interesting forms. Next, a day might involve writing code all day or running computer simulations and modifying initial conditions

There's a variety of "normal days"

0celoñe7

@Jim I am currently at the "code" stage, but it's taking weeks instead of a day!

Jim

@0celoñe7 I have the fallout series, but I strangely could never get into the elder scrolls series

Sir Cumference

@Jim Hmm...and how do you go about "looking for" a discovery, or something to write a paper on?

0celoñe7

@SirCumference Someone smarter than you gives a tip.

Jim

@0celoñe7 well yeah, it always takes weeks or months. That's just part of the cycle. the part when coding is an average day

0celoñe7

1:03 PM

@Jim My grant wants me to have result in a few weeks. Not sure how they expect me to do that in three months. Lit review took two months.

Anonymous

@Jim I'd like to know what advice you have for undergraduate electronics engineering student (i.e. me) who wishes to pursue a career in physics and is more inclined towards application but enjoys theoretical physics too. What are some of the undergraduate projects that I should take part in? And what courses apart from my engineering courses should I take to enable me for higher studies in physics?

Anonymous

Also, would it be helpful to take in initiative in writing a research paper on a topic that interests me? Or would it be better to just take part in summer physics workshops/projects in nearby universities?

Jim

@SirCumference That's an interesting question. It means a lot of reading recently publishings, going to conferences and colloquia, talking to peers. Basically you try to learn as much about new research as you can until you go "I wonder about this. What happens if we extend that or if this is the case? Can we do this?"

0celoñe7

@Blue Why are you doing EE if you know you want to do physics later?

Jim

Then you research

Anonymous

1:05 PM

@0celoñe7 I wasn't allowed to take up physics in my undergraduate (due to my family)

0celoñe7

@Blue Oh lord. My condolences.

user400188

same problem here

0celoñe7

@Jim If you have not played The Witcher 3, play it. @ACuriousMind forced me and it was amazing.

One of the best games, ever. It's amazing they made it.

Jim

@Blue as for the courses, talk to the undergrad physics advisor. Every school is different. I talked to mine in advance and she old me what courses would make it more likely to get me into grad school in physics. I can tell you to take quantum mechanics, EM, math, SR, math, statistical physics, and math

If you like application more, do some experimental physcis

skullpatrol

and don't forget math ;)

Jim

1:08 PM

@Blue don't just write your own paper; at your stage, it's best to do a project for a prof and try to get attached to their paper. Someone with a reputation is the best for working you into the field

Anonymous

@Jim Who is an "undergrad physics advisor" ? Any physics prof from my university who is willing to help me out?

Jim

@skullpatrol Yes, exactly. Thanks for reminding me on that one. Math

Sir Cumference

@Jim Interesting. Though considering how many cosmologists there are in the world, isn't it likely that someone has inevitably answered your question already?

Jim

@Blue usually, there is a prof designated as the advisor for students. I can speak for all schools, but when in doubt, ask the head of the department/faculty.

@0celoñe7 I was looking at Witcher 2. Could jump ahead a bit I guess

Anonymous

@Jim Makes sense. I'll try talking to someone from the physics department. Thanks for your advice. :)

Mostafa

1:11 PM

@Blue Are you sure it was due to your family who forced you not to study physics, or rather because you, yourself, also found their concerns (about your possible future career if you study physics) reasonable?

skullpatrol

Great advice from a great guest!

Sir Cumference

@Mostafa That's a little assumptive

Mostafa

@SirCumference I'm asking this because it happens to a lot of people in countries like India or Iran. And I think the society should be blamed here, not one's parents.

Jim

@SirCumference no, this is why you look at recent publications. They are answering a question for the first time. If you have a question from that, then it is likely unanswered. However, it is always best to research your question to ensure it's unanswered. And it is definitely a thing where you'll spend time researching it only to have someone else publish first. That's why make scientists race to put out a first publication on a topic they start.

It lets them establish it as theirs and keep working at their own pace

Sir Cumference

@Jim Ah. And do you ever regret not mentioning something, or wishing you had explained something better, after you had written your paper?

Jim

1:14 PM

@Mostafa really? because I see a lot of physics students coming from Iran. And, honestly, they're usually high quality physicists.

Secret

> I wonder about this. What happens if we extend that or if this is the case? Can we do this?"

My issue is that I already have loads of questions like these before I even crawl through 1/1000 of the literature, which means I bump into the wall alot when I realised they are already answered

0celoñe7

@Jim Sunny side up, scrambled and creamy, soft boiled, or heresy?

Jim

@SirCumference it's the opposite more often. As an engineer, I was trained to write ideas in a way that they'd be most easily understood by even a novice to the field. Unfortunately, that tends to make my work seem less significant than it is. Especially when other scientists have a practice of obfuscating their work. The harder to understand, the more likely reviewers think it's good and push it through.

Anonymous

I did have an option of Physics + Computer Science dual major at a good university called BITs Pilani but since it was a 5 years course instead rather than the conventional 4 year BTech my parents didn't allow me. They unfortunately want me to become "employable" as soon as possible. If given a choice I would have happily gone for the Physics+Computer Science dual major at BITs Pilani.

Anonymous

@Mostafa Both actually. First of all an undergraduate physics degree is not valued at all in India. You need to have atleast a PhD in Physics to be taken for a job or a professor at any university. While an undergraduate degree in Electronics gives you much greater job security and also a chance to change field to physics. I intend not to pursue my higher studies in India anymore as physics research is not encouraged here as such.

Jim

1:16 PM

@SirCumference So I sometimes wish I had explained it less clearly

@0celoñe7 heresy

@Secret gotta read things that were published within the last month

Sir Cumference

@Jim That's kind of incredible and backwards

ACuriousMind

What's the recipe for "heresy egg"?

Do I have to draw pentagrams in the yolk or something?

Jim

@SirCumference I agree. I hate it. But when they want something published that isn't worth it, they make it seem more important by complicating it. My supervisor and I once both wrote separately about our joint work. Both papers described the same thing, but mine was simplistic and straightforward. His was complex and messy. His seemed way more important even to me, and I understood it

Sir Cumference

@Jim I've also kind of worried about the low paying period of being a postdoc. Any advice to make a big impact and get a job as soon as possible?

Jim

It works to publish papers, not to help science

Mostafa

1:19 PM

@Jim That's because every single decent student here tries his best to go to North America for his/her graduate studies.

Jim

@SirCumference None, I've never been post-doc. I'm still pre-doc

Mostafa

But this a reality that many of the students who really love to study physics or math are forced (the question is by who?) to study engineering (or even medicine).

Sir Cumference

@Jim Huh. Does it offer any advantage then?

0celoñe7

@ACuriousMind over cooking

Jim

@SirCumference absolutely. It is a time to do research, make a name for yourself, and show what you're capable of. It sets you apart from the rest for when you apply to be a professor

Anonymous

1:21 PM

@Mostafa Same here. And I guess it is same for all developing countries which need more engineers than physicists. :P

0celoñe7

@Jim favorite cut of steak?

Jim

@Mostafa sure, but I mean specifically Iran. It's to a point where I see Arabic characters and think "That's Farsi". Arabic doesn't even enter my mind

Sir Cumference

@Jim That's good to know. Also, have you ever disagreed with someone as to who should be the lead author of a paper? How would you go about solving that?

Jim

@0celoñe7 prime rib, obviously

ACuriousMind

Are there "lead authors" in cosmology?

In hep-th, all I see is alphabetical order.

Jim

1:23 PM

@SirCumference not for the lead. Usually it's fairly obvious. And if there's a person deserving of the lead authorship, they can usually have enough power to wield to make sure they get it. I did disagree once about who should get second author.

Slereah

@Jim Favorite Ghostbusters?

Sir Cumference

@Jim Alright. One more question before I have to go: As a professor, how do you make your teaching as intuitive as possible, if you have to cram a lot of information into a single semester?

Jim

I had done half of the work and writing for a paper. My supervisor did the harder half. Obviously he got first. I felt I should get second, but he gave it to a colleague of his from England that I'd never heard of before. I asked about it and he said the guy gave novel ideas for the direction. I was unhappy, but couldn't do much to change it. I was a masters student

ACuriousMind

@SirCumference Uh...he just said he's "pre-doc", not a professor.

Jim

@Slereah the original

Sir Cumference

1:26 PM

@ACuriousMind Oh wow, I'm blind...again

ACuriousMind

Nothing new there ;P

Jim

@SirCumference yeah, I have a masters. I run a lab. I'm not a prof

Mostafa

@Jim Are you working at the University of Toronto? one of my undergraduate friends (actually one of the very close friends!) started his PhD in EE, information theory, last year (2016) in Frank Kschischang's group :)

0celoñe7

@Jim I resent the implication

djsmiley2k

well I got distracted away by work :( /me starts reading ze backlog

Jim

1:28 PM

@Mostafa Strictly speaking, I work at the Mississauga campus. It's not the downtown campus, it's like 20km west of the main campus

0celoñe7

@Jim I'm not even sure how to describe TW3...but anyone who plays it must preach about it

Jim

@0celoñe7 is that in the EULA?

0celoñe7

Just set aside 100 hours of your life and play it

@Jim No, in the soul contract.

For full immersion you must sell your soul to Master Mirror...

Anonymous

@Jim Which country would you choose between USA and Canada to pursue a physics grad degree ? And why? (Just a random question :P)

ACuriousMind

@0celoñe7 Then take another 100 and do it again :)

0celoñe7

1:31 PM

@ACuriousMind I seriously considered doing a second run right again :D

I can't imagine it being as good the second time around though

Maybe if one waits a year

Jim

@Blue Canada for a few reasons. First, it's more familiar to me and closer to family. Second, I'm not a fan of the current politics or social structure of the US (no offense, but it's different than what I'm used to). And third (most important), they require to to complete the GRE exams to do grad school there. With my disability, time-based tests like that are extremely difficult to complete. It's an unfair disadvantage when I have to constantly reread questions in the same amount of time

ACuriousMind

@0celoñe7 The Dandelion sequence drags on even longer the second time ;P It's interesting to see which things certain actions change and which they don't, though.

Jim

also, I currently get free education at the university of toronto. That's a sweet deal

0celoñe7

@ACuriousMind Sadly there is no "evil" option, just an "asshole" option.

Anonymous

@Jim Oh. But doesn't Canada take any test like GRE to admit overseas students for MS ?

0celoñe7

1:35 PM

Like, Ciri dies if you do reasonable things that might be a little "not nice."

Jim

@Blue possibly, but I'm not an overseas student here

0celoñe7

@ACuriousMind I don't like how the Baron story was "resolved" in my playthrough.

Anonymous

@Jim From here it seems they accept TOEFL and GRE scores in Canada also. So that makes US and Canada similar for me. :P I'd probably apply to both the countries

Anonymous

graduateshotline.com/enggcan.html

Jim

anyway, this will have to be the end of the AMA with Jim (long may He reign). I have to get to my job. But I'm still around if you don't mind being answered a bit late

Anonymous

1:38 PM

But, yeah. One good thing is that the cost of education is lower in Canada. :)

Slereah

@Jim I meant character

ACuriousMind

@0celoñe7 I think Ciri's fate is less about being "nice" to her and more about trusting her to do the right thing vs. trying to tell her what's best like everyone else does. It's also not really about taking the reasonable course of action (cf. trashing Avallach's lab).

@0celoñe7 I'm not sure I really like any of the resolutions

Probably that's kinda the point - the situation is beyond getting truly fixed.

ACuriousMind

Everytime I answer a question that's not about QM or string theory, it goes hot :/

djsmiley2k

@Jim Well thanks for showing people with disabiltiies can succeed.

I consider myself a success in that way, and it grinds me down to see both people thinking it can't be done, and people with disabilties helping to enforce that view by either being lazy and claiming it can't, or using it as an excuse.

2

Secret

> It cannot be made precise in the context of QFT because the quantum field is operator-valued and has no definite values, so it is wholly unclear what rigorous sense could be given to it being "excited".

Hmm...

HDE 226868

1:53 PM

@Jim Thanks. I think I just missed then end of the AMA.

0celoñe7

@ACuriousMind Yes, that's what it ends up being about for her. But the choices Geralt is presented end up being about "nice" and "not nice."

Secret

A field is invariant under lorentz transformation, thus it is something physical like a tensor

Jim

@HDE226868 Yeah, but I'm around every day anyway. So you can always ask me any question. It's only the response time that varies

HDE 226868

Sure, thanks.

Mostafa

OK; I bookmarked this AMA

0celoñe7

1:54 PM

And you should not be penalized for taking Emhrys's coin. Ciri knows Geralt needs it.

Secret

so, what prevents a tensor from being some excited state (question probably does not make sense)?

0celoñe7

@ACuriousMind I got the "good" ending but we never find out what happens to Anna after she goes to the Blue Mountains.

Secret

(I think I need to revise what "excitation" mean in classical field also...)

ACuriousMind

@0celoñe7 Not so sure - choices like whether to trash the lab or to accompany Ciri to the meeting with the sorceresses don't strike me as nice vs. not nice

@Mostafa Nice, I always forget that's a feature

0celoñe7

@ACuriousMind I never even saw the option to trash the lab. And I don't remember the sorceress meeting. Can't imagine I didn't go though.

ACuriousMind

1:59 PM

@0celoñe7 When you are in Avallach's lab Ciri get's angry and starts smashing something and Geralt can either calm her down or join in, iirc. And the meeting is in Dandelion's tavern where you either go in with her or listen at the door with Yen

0celoñe7

@ACuriousMind I think I calmed her down and gave her an amulet.

@ACuriousMind Snowball fight vs. drinking was strange

ACuriousMind

@0celoñe7 Well, I'll grant that she's not entirely rational about that - but I don't think that's a flaw in the game, only a flaw in her character (though I find it hard to fault her for it)

0celoñe7

Especially because the dialogue options didn't explain what either choice actually was

ACuriousMind

@0celoñe7 Heh, yes, but once again not "nice vs. not nice".

@0celoñe7 That irked me, too

0celoñe7

@ACuriousMind Maybe not nice vs. not nice then...

There are just some decisions that are either betrayed by the dialogue options or are simply things that could be resolved by a short talk afterwards.

@ACuriousMind I think that Geralt should have handled the situation better.

ACuriousMind

2:04 PM

@0celoñe7 Well, Geralt is terrible at handling situations!

0celoñe7

I didn't pick the money, but I saw a video where someone did take it

ACuriousMind

It's easy to forget that this isn't a blank slate character - Geralt comes already with a lot of baggage and a certain...inability for diplomacy before the player starts projecting on him

0celoñe7

@ACuriousMind Yeah, that's why it's not a true RPG. The dev's guiding hand is felt quite strongly in certain situations.

ACuriousMind

Also, his emotions are subdued and/or altered due to being a witcher, so he lacks the kind of empathy the fully human player would have used to choose a better response than the choices given.

0celoñe7

I'm not sure that I've played any true RPG, save for maybe Mass Effect 1 and New Vegas.

Mass Effect 2 can go pretty horribly towards the end though, I've heard.

ACuriousMind

2:07 PM

Well, "true" RPGs are very difficult to make, you'll always omit some possible choices some player think they should have been able to make

0celoñe7

@ACuriousMind Is Morrowind good about that?

ACuriousMind

(which is why computer RPGs will never be a full substitute for playing RPGs at a table with other people)

@0celoñe7 Morrowind...doesn't have a lot of choices in that sense. You decide which factions to join (some are exclusive), but most of the quest lines are fairly linear

@0celoñe7 Mass Effect had a far bigger problem with "Renegade" often just equating to being pointlessly rude or cruel to people, imo

0celoñe7

@ACuriousMind I haven't done my Renegade playthrough yet.

ACuriousMind

And then it wasn't even consistent about that and sometimes it was a genuine moral choice

0celoñe7

I downloaded them so it's just a matter of me finding 150 hours

@ACuriousMind Right. My Paragon character had a few Renegade choices.

ACuriousMind

2:11 PM

It made discerning what exactly the Paragon/Renegade dichotomy was supposed to mean very difficult; I'm still not sure

Slereah

Morrowind is mostly a linear narrative but it is done well

ACuriousMind

The whole art style clearly casts paragon as good and renegade as evil, but the way the choices are coded doesn't really reflect that

0celoñe7

@EmilioPisanty Is "are you familiarized with the Laplacian" something a Spanish-speaking person would say in English?

ACuriousMind

@Slereah Well...I'd rather say it's bunch of linear narratives that you can also completely ignore and just go explore random places :D

That's the thing that really hasn't changed in the later iterations. What Oblivion and Skyrim lack is the delightful strangeness of Morrowind's setting.

Secret

ok, google and PSE are not helping, what does a local excitation of a classical field even mean?

0celoñe7

2:14 PM

@ACuriousMind I gave in to Skyrim modding again...I'm an addict.

@ACuriousMind so wonderfully gloomy

John Rennie

@Secret a light pulse is a local excitation of the EM field.

0celoñe7

That image has an amazing amount of JPEG

Secret

Ah I see

ACuriousMind

@0celoñe7 "amount of JPEG"?

Do you mean JPEG artifacts?

0celoñe7

@ACuriousMind Can you not see the compression artifacts?

ACuriousMind

2:16 PM

See my message right before yours ;)

0celoñe7

@ACuriousMind We posted it at the same time.

So you know what I'm talking about.

@ACuriousMind So, amazingly, I now have more mods than ever and it runs stably.

Secret

Right in that case, I don't see the problem of having a tensor field to have a localised excitation by being somehow bounded, compact, or have finite support

Unless, being lorentz invariant is not a sufficient condition for operator valued fields to be tensors...

0celoñe7

I think there were core engine issues that got fixed in the Special Edition.

@JohnRennie Any idea why my GPU is sometimes at 2050MHz, and sometimes at 2038?

ACuriousMind

@Secret Why do you think there's a "problem" with that? Also, why do you call tensors "Lorentz invariant", when every one else calls them covariant?

0celoñe7

$\leftarrow$ still has no clue what covariant means

ACuriousMind

2:20 PM

@0celoñe7 I think "transforms in a linear representation of the gauge group" (as opposed to transforming like a gauge field) captures it well

0celoñe7

@ACuriousMind I mean for e.g. a field theory

ACuriousMind

For geometry, the gauge transformations are the Jacobians of the diffeomorphisms

0celoñe7

"GR is covariant"

whatever the hell that means

John Rennie

@0celoñe7 it's doing it deliberately to creep you out

Secret

@ACuriousMind I am thinking about this part of your answer to user400188. Sure, the observables don't have definite values until they are measured, but the underlying mathematical construct (wavefunctions in QM and operator valued fields in QFT) should be as a whole a well defined object. Since it is covariant, do operator valued fields form a tensor field and hence we can define its local exictation by considering that the operator to obey something like compact, bound or finite support notions?

29 mins ago, by Secret

> It cannot be made precise in the context of QFT because the quantum field is operator-valued and has no definite values, so it is wholly unclear what rigorous sense could be given to it being "excited".

0celoñe7

2:22 PM

@JohnRennie ...Should I be worried?

ACuriousMind

@0celoñe7 Ah, a "covariant theory" is one whose action is invariant under coordinate changes. It's kind of a silly thing to say about a field theory because almost all field theories are like that, but then again many people don't seem to understand that coordinate invariance is not really what makes GR special, so I wouldn't worry to much about that phrase

John Rennie

@0celoñe7 No

0celoñe7

@JohnRennie I have a sentient GPU!

Is that not a big deal??

John Rennie

@0celoñe7 See, I warned you not to overclock too far

ACuriousMind

@0celoñe7 And you have enslaved it to render god-knows-what. Good job.

0celoñe7

2:24 PM

@ACuriousMind The Witcher 3 sex scenes

...which are really not necessary

The graphics in the game are not good enough

It's like strippers in GTA 4 or even San Andreas

Or 5

FreeMind

Hi,
Is it physics chatroom guys? :)

0celoñe7

@FreeMind No, math and video games.

And computer building.

Occasionally cooking.

FreeMind

Play CS GO then :D

John Rennie

@FreeMind it is yes. Don't be put off by the chatter about gaming :-)

FreeMind

Lots of cheaters out there !

0celoñe7

2:25 PM

@FreeMind Too many Koreans

Slereah

@ACuriousMind Almost all good RPGs have a weird setting imo

FreeMind

@0celoñe7 You've got to download matchmaking game server program and block korea ip so you won't face them anymore whenever matchmaking of Steam tries to join you to the game.

Slereah

Planescape, Morrowind, Arcanum, Vampire

ACuriousMind

@Secret Your point being? Yes, you can say that the field has compact support. But the field is operator-valued and this operator-valued distribution does not encode the quantum state.

0celoñe7

@ACuriousMind I must say, I don't know what you're referring to with "special" here.

We've been over the confusion of what a diffeomorphism is to physicists before.

ACuriousMind

2:27 PM

@0celoñe7 Yeah, it's related to that, I think.

Emilio Pisanty

@0celoñe7 I don't think there's anything particularly Spanish about that.

ACuriousMind

Ding! Repcap!

4 days left to go for that sweet silver badge :P

0celoñe7

@EmilioPisanty Specifically, "familiarized" over "familiar"

Secret

@ACuriousMind Just as a localised excitation of a classical field can be defined as the field having nonzero values in some finite "small enough" region, since operator valued fields are tensors, we can perhaps make sense of a localised excitation of the operator valued field by requiring all operators to have finite support (or other notions such that the operators don't do unbounded things)?

ACuriousMind

@Secret You can do that. Then you have defined a notion of "excitation of a quantum field" that exactly no-one else uses. What are you gonna do with it?

Slereah

2:31 PM

Operator valued fields aren't tensors

They're operator valued fields

Emilio Pisanty

@0celoñe7 yes. It looks like a mis-speaking among a million others.

0celoñe7

@AccidentalFourierTransform Apparently the physicist method for solving variational problems is called the "indirect method."

John Rennie

@Secret the quantum field is a mathematical object not a physical one. The quantum field presumably describes some physical object, and you can presumably have excitations of whatever the quantum field is describing ...

ACuriousMind

(also, what Slereah says, your constant mentioning of "tensors" is not really relevant to anything you say)

Emilio Pisanty

@ACuriousMind dammit

I was catching up

ACuriousMind

2:33 PM

@EmilioPisanty I sinned and answered a question that's not about QFT or string theory. Hitting the repcap through the powers of HNQ is my penance :P

Secret

@Slereah but it is lorentz invariant, won't that make it covariant as long we are not doing QFT in curved spacetime, and hence a tensor?

Emilio Pisanty

@ACuriousMind no, feeding the HNQ beast is the sin, not the penance

John Rennie

I would have a lot more rep if @Emilio hadn't PUBLICLY CRITICISED MY ANSWER ABOUT ANTIMATTER!!!

0celoñe7

What?

Emilio Pisanty

we've yet to see you pay your penance

@JohnRennie "you would have a lot of rep"?

I'm confused

Slereah

2:34 PM

@Secret The field is a tensor field

John Rennie

Oops, typo

Slereah

You have a map of test tensor fields to the Hilbert space

Or wait

No

ACuriousMind

@Secret You can have operator-valued tensor fields. What's your point? Why are we even talking about covariance? Once again, I have no actual idea what you are talking about, or why.

Emilio Pisanty

you've got 1.5x more rep than the runner-up

and the runner-up is Lubos

0celoñe7

Lumo for mod

Slereah

2:35 PM

It's a map from compact support functions but they are mapped to the Hilbert space which transforms under the appropriate Lorentz rep

ACuriousMind

@EmilioPisanty The penance is the shame and guilt I feel over feeding it ;P

Emilio Pisanty

@JohnRennie for what it's worth, I am actually paying penance over it, in the form of having to defend the spirit of that comment over and over and over again

John Rennie

... from all the JUSTIFIED CRITICISM!!! :-)

Emilio Pisanty

@JohnRennie no, I don't think so, no

John Rennie

Can you add a pseudovector and a vector?

ACuriousMind

2:38 PM

Yes, but it's not a good idea :P

John Rennie

In any physically meaningful way that is

Secret

I suspect Johnrennie has said something important here. I think I might have a misconception that the quantum field encodes all possible information of all possible ways a given quantum state will be transformed, analogous to how wavefunction encodes all information about a quantum state

6 mins ago, by John Rennie

@Secret the quantum field is a mathematical object not a physical one. The quantum field presumably describes some physical object, and you can presumably have excitations of whatever the quantum field is describing ...

0celoñe7

@JohnRennie How is vector addition physically meaningful?

ACuriousMind

@JohnRennie Well, people sometimes write $\vec F = \vec E + \mathrm{i}\vec B$ and do some shenangians with it...

0celoñe7

lol

John Rennie

2:39 PM

Hmm ...

ACuriousMind

@Secret No it doesn't. The field is not the analogue to the wavefunction, it's the analogue to operators like $x$ and $p$

Just like the momentum operator doesn't encode anything about a specific quantum state on its own, the quantum field doesn't, either.

John Rennie

@0celoñe7 If I fire two rocket motors in different directions the vector sum of their thrusts give the total thrust I experience. Isn't that physically meaningful?

Secret

and thus me thinking (perhaps wrongly) that an excitation of the quantum field in terms of imposing some condition on all its operators will thus describe all the possible excitations that any arbitrary quantum state will experience under said field.

0celoñe7

@JohnRennie Oh, you're looking for a specific instance in which vector + pseudovector = something in the night sky?

Secret

so for the example of the momentum operator, although it does not encodes any specific quanutm state, any quantum state, when fed to it, will produce the momentum eigenvalue

John Rennie

2:41 PM

@0celoñe7 I was just thinking aloud. There was a question (now deleted) about what you'd get if you added a vector and pseudovector, and I was wondering if the question even made sense.

Emilio Pisanty

@JohnRennie No, but you can get something meaningful from the dot product of a vector and a pseudovector

0celoñe7

A global no seems pretty strong.

Emilio Pisanty

One interesting case being the dot product between the spin of an electron and its electric dipole moment

ACuriousMind

@JohnRennie Well, it won't be meaningful in that way since the result of adding a vector and a pseudovector doesn't transform in a good way under reflection. Geometrically, what you've done is adding a representation of a direction and a representation of a (hyper)plane, which yields a representation of...nothing in particular.

0celoñe7

I just spent 5 minutes wondering why $f\equiv 0$ meant $\nabla f\equiv 0$

I need to play fewer video games

John Rennie

2:45 PM

@ACuriousMind I suspected something like that might be the case

Secret

typo: the momentum eigenvalue -> the spectrum of momentum eigenvalues

John Rennie

To be fair one of the options for the answer was undefined

ACuriousMind

@Secret What do you mean by "fed"? Please use standard terminology.

0celoñe7

@ACuriousMind fed $=\mapsto$

Secret

@ACuriousMind Sorry, I mean the quantum field acting onto the quanutm state

ACuriousMind

2:47 PM

@Secret And do you really mean to say that acting with the momentum operator on a state produces "the spectrum of momentum eigenvalues"?

Secret

and what 0celo said

ACuriousMind

If so, stop thinking about QFT this instant and go back to QM.

Emilio Pisanty

@JohnRennie Well, when people are taking huge open problems and decreeing them to be unimportant edge cases, they deserve to have that made explicitly clear to them

0celoñe7

Haven't we been discussing QM for years?

Literally?

Secret

@ACuriousMind I know if it is the momentum eigenstate, it will give you the momentum of the state as its eigenvalue, but if the state is not an eigenstate of the momentum operator, you get some other state, but isn't the momentum operator always tell you something about the distribution of momenta of the quanutm state?

ACuriousMind

2:49 PM

@JohnRennie the question that user had is horribly posed: What is the difference between "neither (a) or (b)" and "undefined" supposed to be?

Emilio Pisanty

@Secret No.

John Rennie

@EmilioPisanty no-one is dismissing the problem of baryogenesis. The point of my answer is that the physics responsible acted at energies far above any lab experiment on a beaker of anti-water.

Emilio Pisanty

$\hat p|\psi\rangle$ has no physical meaning.

0celoñe7

@ACuriousMind Are you assuming the law of the excluded middle?

Emilio Pisanty

@JohnRennie you're not, Luaan is.

ACuriousMind

2:49 PM

@Secret No. The application of the operator to a non-eigenstate doesn't tell you anything.

0celoñe7

@EmilioPisanty Please don't put pretentious hats on operators.

ACuriousMind

And frankly, I feel as if I've told you this dozen of times in varying disguises.

John Rennie

@EmilioPisanty Luaan says: John does address your mysterious asymmetries in his answer, he just doesn't consider them important for human-scale stuff.

Emilio Pisanty

@JohnRennie Well, I tend to consider baryogenesis to be relevant for human-scale stuff.

Particularly, with the "me not dying of an antimatter meteorite falling into the solar system" kinda human-sized stuff

John Rennie

Sigh
Though I will concede that without baryogenesis we wouldn't be here discussing this :-)

Emilio Pisanty

2:51 PM

> almost all of normal matter in the universe ("by weight") has mass derived from the binding energy of quarks and anti-quarks

0celoñe7

@ACuriousMind Now that I have solved the mysteries of elliptic PDE, I can move to parabolic PDE :D

Emilio Pisanty

a.k.a. I have made up a metric that conveniently lets me ignore the fact that by baryon number matter dominates over antimatter by 100 to 0

John Rennie

This is a classic case of people arguing past each other.

The OP is not a QFT expert. They just want to know what a glass of anti-water would be like.

And my answer is just like water

ACuriousMind

@0celoñe7 Yay?

Emilio Pisanty

@JohnRennie you and me, or me and the bunch of hardheads that decided to take up an issue with an obviously-off-the-cuff comment of mine?

0celoñe7

2:54 PM

@ACuriousMind That :D needs to look horrified, actually

John Rennie

My point being that whatever caused the CP violation that produced a matter excess isn't going to make a glass of anti-water look different to a glass of water.

Emilio Pisanty

@JohnRennie Seriously, I'm not arguing with your answer.

ACuriousMind

@0celoñe7 D:, then.

Mostafa

Jun 13 at 17:04, by ACuriousMind

@DanielSank I always forget that's a feature that exists!

:)

0celoñe7

@ACuriousMind Hmm. Do you think "bounded in $C^\infty$" means "all partial derivatives are uniformly bounded by the same constant" or perhaps varying constants?

ACuriousMind

2:56 PM

@0celoñe7 I think it means whatever the author found convenient :D

Secret

> No. The application of the operator to a non-eigenstate doesn't tell you anything

I am suspecting, the cases for the varying disguise might be related to how in the long past, I think acting some operator on a quanutm state is the same as measuring it, but I think this is the first time I realise that not only acting some operator on a non eigenstate is not the same as measuring it (you need the hamiltonian of the system-device to do so), but that any operator correspond to some observable does not tell you anything when acted on a non eigenstate

Emilio Pisanty

> I think acting some operator on a quanutm state is the same as measuring it

no

7 mins ago, by Emilio Pisanty

$\hat p|\psi\rangle$ has no physical meaning.

Secret

@EmilioPisanty No that was a long time ago misconception of mine, I just quote it here as contrast

ACuriousMind

@Secret You should be more careful with your tenses - I think means you still believe that, if it is in the past, it's I thought.

Emilio Pisanty

@Secret oh. carry on, then. post confusing comments, people get confused, but other than that, sure.

Secret

2:58 PM

Yeah sorry for the confusion (chinese language is tenseless and I am not fully native yet) I will be more careful

John Rennie

You have a language with no tensors?????

Secret

Tenseless language

In linguistics, a tenseless language is a language that does not have a grammatical category of tense. Tenseless languages can and do refer to time but they do so using lexical items such as adverbs or verbs, or by using combinations of aspect, and mood, and words that establish time reference. Examples of tenseless languages are Burmese, Dyirbal, Chinese, Malay (including Indonesian), and in some analyses Greenlandic and Guaraní. == References == == Bibliography == Bittner, Maria (2005). "Future discourse in a tenseless language". Journal of Semantics. 12 (4): 339–388. doi:10.1093/jos/ffh029....

ACuriousMind

@JohnRennie Yes, it's called Scala.

Emilio Pisanty

@JohnRennie yes, there are languages where only flat lists are possible

0celoñe7

@ACuriousMind Some German guy wrote a PhD thesis on quasilinear parabolic PDE on compact manifolds!

John Rennie

2:59 PM

I suppose I'll have to go away and Google Scala now ...

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