The h Bar

Terry Bollinger

5:01 PM

@DavidZ no biggy sir, it was just getting near the end and to be honest I had to see a man about a wallaby... :)

AccidentalFourierTransform

@ACuriousMind that last one sounds really cool tbh

yuggib

@AccidentalFourierTransform On a more practical ground, they also led to the development of tools that were then applied in other contexts, such as the calculation of one-loop effective actions and other anomalies for QFTs in curved background space. (e.g. worldline formalism)

Terry Bollinger

@ACuriousMind too long to explain here, but the issue is that if you are not very careful, your math can reflect certain assumptions about how information is obtained in the physical world, and those assumptions are not always physically realizable due to factors such as SR. I mention SR because any measure of length is also a measure of time.

David Z

@TerryBollinger hehe, nice

Ramanujan

Hi nerds

Terry Bollinger

5:05 PM

@Ramanujan I am not large-sand-sized sugary confection!

ACuriousMind

@AccidentalFourierTransform It is :) Sadly, we do not yet really understand much about this process in general

Or at least, I don't :P

John Rennie

@111: the direction of the field lines for an electric field is easily defined because it's the direction of the force they exert on an electric charge. The problem is that this doesn't work for magnetic fields because (as far as we know) there are no magnetic charges. Hence the rather convoluted definition.

AccidentalFourierTransform

4

ACuriousMind

@AccidentalFourierTransform lol

Did you find that on the 'net or did you make that yourself?

AccidentalFourierTransform

dude Im an artist

I thought that you already knew that

Balarka Sen

5:10 PM

why's the r and the a switched

ACuriousMind

@AccidentalFourierTransform Yes, but I wanted to make sure that my image of you pouring sugar on your desk to make that pun is accurate :D

John Rennie

@BalarkaSen SUGRA

ACuriousMind

@BalarkaSen Because SUGRA stands for "supergravity", which we were talking about.

John Rennie

Ha. Ninjad!!

First time! I must make a note in my diary :-)

Balarka Sen

ic. that does sound like an acronym physicists would use

"8-dimensional CQFT of the time-dependent SUSY"

Terry Bollinger

5:17 PM

@BalarkaSen just curious, is the n=8 in question here octonion-ish in any way?

Bernardo Meurer

@AccidentalFourierTransform Nice finger writing

Balarka Sen

@Terry I just spelt out a string of nonsense :)

AccidentalFourierTransform

@BernardoMeurer ive been known for being great with my fingers

Terry Bollinger

@BalarkaSen so, you mean were doing standard string theory?... :)

Bernardo Meurer

@AccidentalFourierTransform Didn't know you dabbled in Proctology as well

Balarka Sen

5:18 PM

I hope not!

AccidentalFourierTransform

@BernardoMeurer meh, they never complain

i must be doing something right

Terry Bollinger

@AccidentalFourierTransform I thought the image was kind of sweet...

Bernardo Meurer

@AccidentalFourierTransform Dosing the anaesthetic maybe :P

John Rennie

Hi @BernardoMeurer. The amp was collected this morning and the tracking info now shows it as on the way.

Bernardo Meurer

@JohnRennie ::shakes with excitement::

AccidentalFourierTransform

5:20 PM

Jun 17 '15 at 7:36, by DanielSank

There are few things so sweet as a truly awful mathematical pun.

John Rennie

Steady man, steady!

AccidentalFourierTransform

John Rennie

I used a cheapo courier (Hermes) because, well the amp isn't worth anything, so the tracking probably isn't as detailed as last time.

Bernardo Meurer

@AccidentalFourierTransform lol

@JohnRennie It actually goes for about 100 quid on ebay IIRC

John Rennie

Also it wouldn't be bad idea to make sure you're in to take delivery. I know you've had problems with deliveries before.

@BernardoMeurer in perfect condition yes. Remember this one has some faulty connectors.

Bernardo Meurer

5:22 PM

@JohnRennie I'll be home the next whole month basically, won't be an issue :)

@JohnRennie I felt so british saying 'quid' just now

John Rennie

Good to see our powers of cultural colonialism are undimmed by time :-)

Terry Bollinger

@AccidentalFourierTransform that is easily the most disturbing image I've ever seen on this chat group!

Bernardo Meurer

Lol, well :P

John Rennie

I hope you like the sound after all this fuss

ACuriousMind

Do not, I repeat, do not take that as a challenge @AccidentalFourierTransform :P

John Rennie

5:24 PM

What sort of amp you like can be a very personal thing.

AccidentalFourierTransform

@TerryBollinger that cannot be right lol

@ACuriousMind let me see if I can find something in my old folders

Bernardo Meurer

@JohnRennie It'll be my first ever sound system :D

:D:D:D

@TerryBollinger That just proves you're not here often :P

Terry Bollinger

@BernardoMeurer ain't that the truth!

@BernardoMeurer would the abbreviation for "quantum ID" be quid?

Bernardo Meurer

@TerryBollinger I actually have no clue why people call the GBP 'quid'

John Rennie

@TerryBollinger Bill Cosby wouldn't the first choice of role model for most of us, but I'm not sure the picture is that disturbing.

Bernardo Meurer

5:27 PM

I just say it because it makes me sound like someone who drinks tea

@JohnRennie I like how you used "most" in that sentence, you know the people here :P

John Rennie

BTW I'm getting a new laptop!

Terry Bollinger

@JohnRennie it's actually a funny image, which is why his more recent history makes it more disturbing. Kind of like one of those LMN movies my wife watches where someone's husband turns out to be a secret but very discrete ax murderer.

Bernardo Meurer

@JohnRennie Oh god no :P

Terry Bollinger

@JohnRennie major stats? brand?

John Rennie

@BernardoMeurer I did a favour for a friend's company and he's supplying me with a laptop to show his gratitude.

Bernardo Meurer

5:30 PM

@TerryBollinger He gets new laptops every other week

@JohnRennie Nice! Whatcha getting?

John Rennie

@TerryBollinger Dell Inspiron 17R 5000. i7-7500U, 8GB memory.

Terry Bollinger

@BernardoMeurer Oxford: "quid - Origin - late 17th century: of obscure origin." Hmm!

Tony Stewart

hopefully not on win10

John Rennie

The main thing is that it has a 17" screen. I've been looking for a big screen laptop to use when I'm working away from home.

DanielSank

I think this question needs a better answer

6

Q: If all particles are fields, why does first quantization work for some particles?

After a lot of Google and asking professors about the two quantization methods, I have learned that first quantization is what you use to quantize classical particles, while second quantization is what you use to quantize classical fields or a large number of classical particles. If, according t...

John Rennie

5:32 PM

@TonyStewart all laptops come with W10 these days, but being somewhat Luddite I'll be putting Windows 7 on it.

Terry Bollinger

@JohnRennie all mine have been for years, 17" is great!

Bernardo Meurer

I like it that Windows 10 is so bad that random people come here just to say crap about it

@TonyStewart :P

John Rennie

@BernardoMeurer this is the first brand new laptop I will have since about 1993.

Bernardo Meurer

@JohnRennie Smart man

AccidentalFourierTransform

@DanielSank well thank you :-(

John Rennie

5:33 PM

@TerryBollinger there aren't that manuy laptops with such large screens. At least not with a 080p 17" screen.

Tony Stewart

everything is Relative as someone said , including perceptions and assumptions

DanielSank

@AccidentalFourierTransform I didn't say your answer were bad! I just think that particular question is so important and so common that it needs an even better one.

Terry Bollinger

I am using Windows 10 right now. After you shut down about 10 pages of options Microsoft gives itself to steal your personal info, it's not TOO bad...

Bernardo Meurer

Gnome 3 with Arch Linux with Wayland

Terry Bollinger

@JohnRennie yep! you have to look a bit. Worth it, though.

Bernardo Meurer

5:34 PM

Working great

AccidentalFourierTransform

@DanielSank I wrote it in less than a minute tbh

Tony Stewart

you can disable all the call home telemetry Scheduled Tasks to prevent random hourglasses

John Rennie

Windows 10 has a perfectly good kernel. It's just annoying that MS have loaded it down with so much fluff.

DanielSank

@AccidentalFourierTransform -_-

AccidentalFourierTransform

@DanielSank yeah lol, its not my best answer i know

John Rennie

5:35 PM

On Win7 I always use the classic theme, but that's gone in W10. You have to have wallpaper whether you want it or not.

DanielSank

@AccidentalFourierTransform It's kinda wrong, or at least incomplete.

Relativity isn't the issue.

AccidentalFourierTransform

@DanielSank hmm yes it is lol

Terry Bollinger

@JohnRennie it's the default stealing I don't like. Bummer if you work on sensitive stuff.

DanielSank

This is a very common mistake on PSE: y'all often jump to relativity as the reason for some bit of theory being a particular way when relativity really has nothing to do with it.

AccidentalFourierTransform

why do you say it is not?

DanielSank

5:36 PM

@AccidentalFourierTransform Because relativity is a red herring here.

AccidentalFourierTransform

@DanielSank wait

Terry Bollinger

@DanielSank clarify?

ACuriousMind

What answer exactly are you two talking about?

John Rennie

If anyone is still interested here's a nice article on the origin of the word quid

DanielSank

6

A: If all particles are fields, why does first quantization work for some particles?

First quantisation cannot accommodate pair-production, which is non-negligible at energies comparable to the mass of the particle. Therefore, First quantisation only works for massive particles, and only in the range of energies that make motion non-relativistic. Of course, this doesn't mea...

AccidentalFourierTransform

5:37 PM

are you talikng about the problem of localisation, or the problem of many-bodies?

DanielSank

@TerryBollinger Second quantization has nothing to do with relativity.

AccidentalFourierTransform

@DanielSank lol, I though you were referring to the problem of localisation of particles.

DanielSank

wtf is wrong with this chatroom? Every message I post gets sent twice and the second one times out...

AccidentalFourierTransform

I thought it was only me lol

Terry Bollinger

@JohnRennie what?

DanielSank

5:38 PM

Ho boy, the site's in read-only.

John Rennie

Someone asked where the word quid for pound sterling came from.

Terry Bollinger

@DanielSank ah, that helps for context, thanks. PSE is a pretty bit context!

@JohnRennie think carefully about "what"...

DanielSank

@TerryBollinger Weren't you asking for clarification on why I said that relativity were a red herring?

AccidentalFourierTransform

"We apologize for any inconvenience, but an unexpected error occurred while you were browsing our site. It’s not you, it’s us. This is our fault. Detailed information about this error has automatically been recorded and we have been notified."

John Rennie

@TerryBollinger OK. I assumed you wouldn't stoop so low :-)

Terry Bollinger

5:40 PM

@DanielSank yes. I took PSE to mean physics stack exchange.

@JohnRennie when it comes to puns... "how low can you go..." :)

David Z

We are having database or network issues on Stack Overflow - investigating now.

Tweeted by StackStatus on January 24, 2017 at 5:40 PM

DanielSank

@TerryBollinger Yeah, that's what I meant. Jumping to relativity all the time is a site-wide common mistake.

Terry Bollinger

@DanielSank I see the application to second quantization, but I've never thought one way or the other about possible overuse in general. SR is after all pretty fundamental to QFT, even if GR is not.

@DavidZ is this why my screen keeps blanking out and I have to refresh it?

David Z

@TerryBollinger Probably not

DanielSank

> SR is after all pretty fundamental to QFT

False

John Rennie

5:45 PM

It is possible to construct a non-relativistic field theory

And of course it's possible to construct relativistic quantum mechanics

Is it just me getting weird effects when trying to post here. The post appears twice, then after a few seconds the second post either disappears or reports an error.

DanielSank

It's not just "possible to construct a non-relativistic field theory", it's the bread-and-butter of condensed matter theorists everywhere.

ACuriousMind

@JohnRennie No, it happens across the network

SE seems to have some major issues :P

DanielSank

Furthermore, repeatedly telling students that QFT is relativistic confuses them and obscures the essential features of what makes a field a field.

John Rennie

Obviously related to the DB issues that have brought down the main site.

AccidentalFourierTransform

@ACuriousMind a late effect of our little mathjax games?

wouldn't it be cool?

ACuriousMind

5:50 PM

@AccidentalFourierTransform Yes, the SE developers are currently fighitng with random huge text appearing in place of their code :P

DanielSank

This site is prejudiced toward looking at everything as a relativity issue because there are so few condensed matter folks. I'd ask everyone to try to keep this in mind.

Terry Bollinger

@DanielSank ah... energy conversion according to SR is completely irrelevant to QFT?

AccidentalFourierTransform

$\partial$

the matrix is weak, let's attack now

DanielSank

@TerryBollinger I'm not exactly sure what you mean.

AccidentalFourierTransform

@BernardoMeurer we need your help

DanielSank

5:51 PM

QFT is the quantum mechanics of distributed systems.

e.g. a violin string.

There's nothing relativistic about a violin string, or phonons in an elastic solid...

Or an electromagnetic waveguide resonator.

Terry Bollinger

@DanielSank I love condensed matter physics! It's so much richer than particle physics. But you can't even describe atoms accurately without SR, can you?

DanielSank

Yet all of those things benefit by treatment using second quantization.

@TerryBollinger Of course not! However, QFT is not the physics of atoms!

QFT was discovered in that context, but it applies to many things beyond atoms/particles/relativistic stuff.

Terry Bollinger

@AccidentalFourierTransform red pill or blue?...

AccidentalFourierTransform

John Rennie

A friend of mine has just texted me: I've got a joke about UDP, but I'm not sure you will get it.

ACuriousMind

5:54 PM

@DanielSank While I agree with your basic sentiment that QFT and SR should for pedagogical purposes be seen as separate, I wonder where you get that impression from. Which questions receive answers that are "prejudiced toward relativity"? Keep in mind that many askers when they say "QFT" actually do mean "relativistic hep QFT".

DanielSank

@JohnRennie We must hear it!

2

@ACuriousMind The one I linked above, for starters.

If you want to find more examples, search the chat history for other instances of me starting this same discussion ;-)

For example, every time Green's functions come up, in particular how you get the poles off the real line, someone comes in and starts talking about relativity.

AccidentalFourierTransform

@DanielSank to be fair, the link above was asking about relativistic particle physics

DanielSank

@AccidentalFourierTransform Not really.

AccidentalFourierTransform

i guess well never know

SE is broken for bad

DanielSank

OP said nothing about relativity. Unfortunately, the comments and answers jumped to relativity immediately :-(

Terry Bollinger

5:56 PM

@DanielSank I'm going to switch oddly on you, but I think it's related: I still find it fascinating that Dirac's ocean-of-electrons explanation of positrons is blithering nonsense in a continuous vacuum, but works incredibly well for explaining holes in semiconductors. It's like he was channeling/predicting solid state without understanding why or how.

DanielSank

@TerryBollinger :-D

ACuriousMind

@DanielSank But...the problems with the localizations of "particles" are relativistic in nature.

DanielSank

@ACuriousMind Why are you talking about localization?

ACuriousMind

*" I mean, you can to an extent, but it feels forced, the whole reason being Gauss' law forbidding a position eigenstate, but why does something similar not happen for other particles' fields?

I'm interested in why the localization problem applies to the photon and not to, say, the electron: Why can you (in principle) exactly locate an electron in space, if you can't do it for the photon? They are both fields, shouldn't they follow similar rules? Obviously they don't, so what is the difference?"*

AccidentalFourierTransform

@ACuriousMind there are mild problems about localisation of particles in a crystal

and so on

ACuriousMind

5:58 PM

^that's what the second half of that question said.

DanielSank

@ACuriousMind Ah yes.

That is an annoying property of the question. It's asking two different but related questions.

vzn

@JohnRennie thx for Verlinde ref. (rats missed mtg.) have been hearing more about verlinde lately & was wondering what others think. think general concept of "emergent gravity" is important/ plausible shift in general & have long mused along those lines. quantamagazine.org/20161129-verlinde-gravity-dark-matter ... as far as "doing away with dark matter" its probably regarded as somewhat radical at moment...

ACuriousMind

@DanielSank Okay, that's true; alas I'm unwilling to say that the people answering the second part with relativity are unjustifiedly "jumping" to relativity as I understood you.

DanielSank

@JohnRennie Joke!?

@ACuriousMind Indeed.

I had sort of regarded the second half of the question as an unfortunate bystander.

Oh no. I feel so stupid right now.

Terry Bollinger

@ACuriousMind ah, we are all in agreement that the concept of exact physical location of anything is non-physical, right? You can only drastically reduce wave packet sizes up to the wavelength of the probe used, but no further. Even calculating a true exact particle is non-physical, as it would require a computer within infinite memory.

John Rennie

6:00 PM

@vzn I would love something like Verlinde's theory to start making real experimentally verified predictions. Suddenly quantum gravity would start making a lot more sense if GR was just an emergent theory. However we're still miles away from that goal. Don't get your hopes up yet.

DanielSank

@JohnRennie Tell your friend he destroyed the self-esteem of a physicist wannabe programmer.

John Rennie

@DanielSank that was the joke - do I need to explain it or does no-one care? :-)

DanielSank

@JohnRennie I get it. I'm sad now, because I didn't get it at first.

vzn

@JohnRennie ok, fair point, but the paper essentially says there are (now) "real experimentally verified predictions" (albeit a "1st step")... agreed this could be a very long process, years at minimum, presumably over a decade... anyway nice to see a measurable advance along the lines... maybe a milestone already...

ACuriousMind

@DanielSank The problem is also that the first half is somewhat ill-defined - depending on your personal preference QFT is constructed from the elementary notion of particles a la Weinberg, so it's non-sensical to ask why it should be compatible with the particle interpretation

AccidentalFourierTransform

6:03 PM

im not even sure what "two quantization methods" means

as far as quantisation is concerned, the two methods are the same method

John Rennie

@vzn see Hossenfelder's view on this (she works in QG).

Terry Bollinger

@JohnRennie I didn't see that, funny!

AccidentalFourierTransform

[Q,P]=i{Q,P}

John Rennie

I've got another joke about TCP but that's connected.

DanielSank

@JohnRennie Yes yes.

I'm now terrorizing my work group with the UDP joke. Already got one!

John Rennie

6:04 PM

:-) Good man!

Terry Bollinger

@JohnRennie I saw a license plate on an SUV once (have I told this?) that said RBG-000. Sure enough, the SUV was black.

John Rennie

@TerryBollinger Excellent :-)

Terry Bollinger

@JohnRennie it's all transactional.

DanielSank

@ACuriousMind First quantization != particles IMHO.

vzn

@JohnRennie (Hossenfelder is informative.) in general think physics is much more emergent than anyone realizes right now & will continue to go in that direction (emergence), think it still has some hangover from reductionism aka "looking under streetlight for keys because thats where the light is"... :|

John Rennie

6:06 PM

@TerryBollinger no, that's the sequel ...

Terry Bollinger

Again: Does anyone really, truly think "particles" -- infinitesimal points -- are real?

AccidentalFourierTransform

@DanielSank what's the difference between 1st and 2nd quantisation anyway?

its the exact same thing

DanielSank

@AccidentalFourierTransform No, it certainly is not.

ACuriousMind

@DanielSank The term "first quantization" rather by definition means to me that you took a classical point particle system and quantized it.

DanielSank

See my answer here:

52

Q: Which is more fundamental, Fields or Particles?

I hope that I am using appropriate terminology. My confusion about quantum theory (beyond my obvious unfamiliarity with its terminology) is basically twofold: I lack an adequate understanding of how the mathematics of quantum theory is supposed to correspond to phenomena in the physical world ...

quantum-mechanics quantum-field-theory soft-question particles

Terry Bollinger

6:07 PM

@JohnRennie I tend to avoid SQL, the recursive search syntax of Prolog does all the same stuff yet is so much more powerful and concise...

Bernardo Meurer

Who called me?

AccidentalFourierTransform

in both 1st and 2nd quantisation, you take the phase space coordinates and promote them to operators

and define the algebra of operators in terms of the poisson algebra

its the exact same thing

Bernardo Meurer

@AccidentalFourierTransform What's up?

AccidentalFourierTransform

but in 1st quantisation the PSV are trajectories

and in 2nd quantisation the PSV are fields

John Rennie

There is sanity in the UK!!! There's hope for us yet!

AccidentalFourierTransform

6:08 PM

its only a small formal difference, nothing else

@BernardoMeurer youre too late, nvm

John Rennie

Sorry for the excited outburst but I've only just caught up with this.

Bernardo Meurer

@AccidentalFourierTransform What was it though?

ACuriousMind

@AccidentalFourierTransform Ah, see, that's the terminology problem here I think. "Second quantization" is, by those who think the term is useful, not used as equivalent to "quantizing a system with infinite degrees of freedom". See the answer Daniel posted and you'll see that.

AccidentalFourierTransform

@BernardoMeurer SE was having problems and I wanted to break the chat again

DanielSank

@ACuriousMind It's a notational issue.

Bernardo Meurer

6:10 PM

@AccidentalFourierTransform Ah, dangit

Call me when it's something this important!

AccidentalFourierTransform

@DanielSank you see, I strongly disagree with "interpret "particle" as "excitation of a field""

DanielSank

...tied with a conceptual one about units of excitation being distinguishable or not.

Right?

@AccidentalFourierTransform Oh, well that would be something we should sort out!

AccidentalFourierTransform

@DanielSank to me, there is absolutely nothing fundamental about fields

the concept of particle is not a derived property of something more fundamental

to me, a particle is the single most fundamental concept

DanielSank

@AccidentalFourierTransform I'm not sure what you mean. Fields, like every other theoretical idea, is a useful metaphor that helps calculate/understand stuff.

It's as "fundamental" as anything else.

@AccidentalFourierTransform That's crazy!

Terry Bollinger

Just a thought in passing... Does anyone in the world think that wave packets are fundamental and that both particles and fields are incomplete abstractions thereof?

DanielSank

6:12 PM

::sits on hands::

ACuriousMind

@DanielSank Well, yes, that's what you call "second quantization". I was introduced to "second quantization" as "quantizing the wavefunction", i.e. promoting the solutions of the Klein-Gordon equation (the SE eq. analog in relQM) to operators, thereby "again" quantizing a theory that was already quantum. This usage is somewhat historical, but it still muddles the water when talking about "second quantization".

DanielSank

::all eight of them::

Terry Bollinger

how did I pop up a MOND paper? eh?

DanielSank

@ACuriousMind Woah. Weird.

user228700

@SirCumference: Dude:

user228700

6:13 PM

acast.com/sleepwithmepodcast

DanielSank

@ACuriousMind I forget where I learned about it.

Terry Bollinger

@DanielSank so when your wife/girlfriend accuses you of having hands like an octopus...

AccidentalFourierTransform

@DanielSank the concept of particle follows from the basic properties of the Poincare Group, that is, translations, rotations and boosts

user228700

Oh, crap, is this a chat session?

DanielSank

@TerryBollinger Yessir.

ACuriousMind

6:14 PM

@DanielSank I think a modern (and condensed matter oriented) source will do it as you do; alas hep-th QFT has a strange habit of keeping useless historical clutter around for longer than necessary :P

AccidentalFourierTransform

if you accept that the universe has those symmetries the concept of particle readily follows

John Rennie

@Kaumudi.H no, the chat session has finished.

AccidentalFourierTransform

you dont need anything else. Particles are truly fundamental

user228700

Phew. OK.

DanielSank

@ACuriousMind Yeah that's more or less what I'm complaining about.

John Rennie

6:15 PM

@Kaumudi.H We're arguing pointlessly about interpretations of quantum field theory!

Terry Bollinger

@AccidentalFourierTransform true particles, true points, don't exist though...

AccidentalFourierTransform

@TerryBollinger particle in a more abstract sense if you will

David Z

@Kaumudi.H When a chat session is in progress, at least if I'm around, there will be a starred or pinned message on the sidebar asking people to hold off on other topics of discussion

Terry Bollinger

@JohnRennie was that a subtle pun?

ACuriousMind

@AccidentalFourierTransform Well, but our universe might be deSitter, and the Wigner classification analog for the deSitter group already looks differently.

Bernardo Meurer

6:16 PM

You're all talking gibberish

Everything is just magic

John Rennie

@TerryBollinger :-) Not deliberate, but strangely appropriate :-)

Bernardo Meurer

Deal with it

AccidentalFourierTransform

@ACuriousMind okayish. But I choose to think of the universe as flat

I do what I want, ok?

ACuriousMind

@JohnRennie We're not doing that, no one has even mentioned pointless topology

Terry Bollinger

@AccidentalFourierTransform particles are always just infinitely approachable limits, in both the real world and computationally. The fact that our universe enables such rules is what is intriguring.

DanielSank

6:18 PM

@JohnRennie It's not pointless.

AccidentalFourierTransform

@TerryBollinger what's your point?

=P

Terry Bollinger

This is a sharp crowd!

AccidentalFourierTransform

@TerryBollinger you see, I dont think that the universe is mathematical

ACuriousMind

@DanielSank The problem is that we don't really disagree about the physics. We disagree on nomenclature, and I have little hope that "second quantization" will ever mean the same to everyone.

John Rennie

@ACuriousMind locales - recently someone was waxing lyrical about using locales more in modern maths, though I've now forgotten where.

DanielSank

6:19 PM

@ACuriousMind Indeed. See the first sentence of my answer ;-)

ACuriousMind

@JohnRennie I think there was a hot MO question recently that had such an answer

DanielSank

> This is a tricky question because it asks about the meaning of words. People use the word "particle" to refer to various, not always well defined, notions in physics.

John Rennie

@ACuriousMind ah yes that rings a bell

AccidentalFourierTransform

I guess that I do disagree with the physics

to me, a particle is a ket $|\boldsymbol p,s\rangle$, where $s$ is the spin

you dont derive this ket from anything else

you just take it for granted and build your theory around it

|p> is not an excitation of anything, whatever that means

ACuriousMind

Yeah, that's the Weinberg approach.

John Rennie

6:22 PM

@ACuriousMind you've several times mentioned Weinberg's approach to constructing QFT starting with particles rather than the traditional free scalar field. Is there an informed amateur description of this available anywhere?

AccidentalFourierTransform

no, that's the correct approach =P

ACuriousMind

However, "canonically quantizing" a classical field theory and defining particles as being created/destroyed by the Fourier modes of a free field works equally well.

AccidentalFourierTransform

@ACuriousMind well yes, it is an equivalent approach

Terry Bollinger

@AccidentalFourierTransform I don't either, I'm actually contra-Tegmarkian. I simply think that our real physical universe enables interesting and simplifying limits, which in turn makes the kinds of abstractions needed to enable computation (and so living organisms that compute for advantage, and what we call "real math") possible. And yes, that's both multi-verse-ish and anthropic.

AccidentalFourierTransform

@TerryBollinger it's just a fortunate coincidence that the world works that way

it is remarkable how accurate math can be

ACuriousMind

6:25 PM

@JohnRennie Not to my knowledge; the issue is that Weinberg very carefully has to develop a lot of group theory in the typical sloppy physicist's way in order to be able to classify the possible sorts of particles we can in principle have. After that, the construction of the actual free fields isn't that hard, you just build them as the transforms of the c/a operators on your Fock spaces.

@AccidentalFourierTransform In the classical vein of Wigner's "The unreasonable effectiveness of mathematics", I see

AccidentalFourierTransform

truly unreasonable indeed

John Rennie

@ACuriousMind that seems a lot less intuitive than the start with a free scalar field approach ...

AccidentalFourierTransform

@JohnRennie not at all: why do you think it is intuitive to start with a field to begin with?

why fields?

that's not intuitive

ACuriousMind

@JohnRennie The advantage is that you are not quantizing a classical theory. You start from a premise that the world is quantum and contains certain quantum objects we call particles and develop QFT purely from that and symmetry consideration + some locality.

John Rennie

@AccidentalFourierTransform It's silly to argue about what is and isn't intuitive because it's a personal thing. But we learm about (classical) fields from early days of science lessons. That makes it intuitive to me.

ACuriousMind

6:28 PM

The minimalism of the approach is seductive from a theoretical perspective (alas, Weinberg's horrible notation isn't :P)

AccidentalFourierTransform

@JohnRennie but the whole motivation for QFT is to have a theory of particles

I'd say that starting from particles themselves is as intuitive as it gets

John Rennie

@AccidentalFourierTransform well, I have to say it seems intuitive to me how we get particles for free when we quantise a field. Actually it seems quite wonderful how that works.

Terry Bollinger

@AccidentalFourierTransform that's the anthropic selection part. You sort of can't be here to talk about it unless it's true, but it also makes the not-physically-accessible limits seem "more real" than they actually are. Computation e.g. works better if you don't assume precision first, and stop wasting cycles by tossing away results that never meant anything.

AccidentalFourierTransform

@JohnRennie in that case it becomes intuitive a posteriori, once you've solved the problem. It's like magic. In the end it works, yes. But in order to build the theory from scratch, it is not intuitive at all that fields might be useful in the end

John Rennie

@AccidentalFourierTransform like I say, it's a matter of personal opinion. As long as both approaches give the right answers which you prefer is a matter of taste.

Terry Bollinger

6:32 PM

Verlinde's theory of emergent gravity is a MOND derivation?? Wow, @JohnRennie, I've definitely got to take a closer look at that. Some of MOND data fitting needs explaining, even if there are other parts that are weak.

John Rennie

@TerryBollinger Hmm, maybe.

AccidentalFourierTransform

Jan 6 at 15:50, by AccidentalFourierTransform

also, I hate creation/annihilation operators and Fock spaces

I hate them indeed :-P

DanielSank

Which thing is more "fundamental" seems like an unproductive question, IMHO.

They're both useful ideas.

Ideas aren't usually orderable.

John Rennie

But MOND is just phenomenology, or at least it has been up to now. The strength of GR has always been it's foundation on clear physical principles.

Terry Bollinger

@JohnRennie I need to dig up the reference, it was a striking curve fit with a very high correlation. Argh, decades ago...

AccidentalFourierTransform

6:34 PM

@DanielSank I guess Weinberg seduced me, I can't help it

John Rennie

Other news, I got crapped on by a bird today.

That isn't the opening for a sexist joke, I really did. While I was zooming along on the push bike as well!

A pigeon dive bombed me and got me right on the shoulder.

Terry Bollinger

@JohnRennie I'm heading off now, but you caught my attention with that one. I happen to think that space is computational in nature, very much not a given... but why would that even be odd? Why would something as complex as space with isotropic real SO(3) symmetry be a "given", and not an emergent property of much simpler math?

@JohnRennie I should tell you about what happened to the US back in early November...

John Rennie

@TerryBollinger I trust that's not the opening for a sexist joke :-)

Terry Bollinger

@JohnRennie nope! We just got crapped on a bit... Later...!

Bernardo Meurer

I know a guy in Texas whose car plate says "PHYSICS"

AccidentalFourierTransform

6:42 PM

kbye

Slereah

Isn't "second quantization" just splitting the hilbert space of QFT into a fock space

DanielSank

7:13 PM

@JohnRennie push bike?

DanielSank

7:45 PM

@ACuriousMind I'm looking at your answer here.

I would consider using a more widely known notation.

Or perhaps I should say, consider defining the notation used therein.

ACuriousMind

Oops, right, I forget an explanatory paragraph after the solution to the e.o.m

Thanks for the hint

Danu

8:06 PM

o/

I lol'ed at this:

6

A: What is the evidence for the existence of gravity

The following experiment is a simple one that can be tried at home. First pick up a ball in your hand and then release the ball above the ground. If you observe carefully you may see the ball moving closer towards the Earth. This is evidence of the mysterious gravitational force.

evidence of the mysterious gravitational force

ACuriousMind

Alas, the comment was earlier:

Hold anvil aloft over foot. Let fall said stithy. Measure the time you can bear to not get help from the local hospital casualty. — WetSavannaAnimal aka Rod Vance Nov 25 '16 at 10:24

Danu

Good point.

ACuriousMind

The question itself is very puzzling, though, I cannot fathom what OP really wanted from us

Danu

0/10

This also made me lol: theguardian.com/books/2017/jan/24/…

ACuriousMind

@Danu ::unarticulated sounds possibly best interpreted as laughter::

Danu

8:17 PM

Alternative sounds

John Rennie

@DanielSank pushbike is a possibly somewhat old fashioned word for bicycle. I got used to saying it in my youth and the habit has stayed with me.

Danu

push bike?!

ACuriousMind

@Danu The phrase "alternative laughter" has a certain ring to it, I think...

Danu

There is no pushing about it

I don't understand :P

John Rennie

Attempting to apply logic to the development of a dielect is a futile exercise. That's just the slang in Somerset in the 1970s.

The word is in the OED and I'm sure they'll have some info on the etymology.

ACuriousMind

8:26 PM

@Danu Maybe this hails from a time before they invented pedals, i.e. @JohnRennie's youth.

Danu

lel

Historically that's definitely how bikes developed so I guess it has to be the right explanation.

John Rennie

I'm surrounded by comic geniuses :-)

Maybe because you have to get off and push it up hills?

ACuriousMind

@JohnRennie "What's a hill?", replied the Dutchman

John Rennie

Of which there are many in North Somerset

@ACuriousMind :-)

ACuriousMind

> German Baron Karl Drais von Sauerbronn invented an improved two-wheel version of the celerifere, called the laufmaschine, a German word for "running machine." The steerable laufmaschine was made entirely of wood and had no pedals. Hence, a rider would need to push his or her feet against the ground to make the machine go forward. Drais' vehicle was first exhibited in Paris on April 6, 1818.

Danu

8:31 PM

@ACuriousMind Oh we've got hills!

ACuriousMind

Huh. (Found here)

Danu

We just don't need to get off and push because, ya know, they're like 20 meters high.

@ACuriousMind You didn't know that that was actually how the bike was developed?

ACuriousMind

@Danu Why the hell would I know how the bike developed? :D

John Rennie

Mendip Hills

The Mendip Hills (commonly called the Mendips) is a range of limestone hills to the south of Bristol and Bath in Somerset, England. Running east to west between Weston-super-Mare and Frome, the hills overlook the Somerset Levels to the south and the Chew Valley and other tributaries of the Avon to the north. The hills give their name to the local government district of Mendip, which administers most of the area. The higher, western part of the hills, covering 198 km2 (76 sq mi) has been designated an Area of Outstanding Natural Beauty (AONB), which gives it a level of protection comparable to a...

ACuriousMind

@Danu I've seen your "hills", those are merely speedbumps :P

John Rennie

8:33 PM

That's where I grew up. They're only 300-400m high but pretty steep

Area of outstanding natural beauty my arse. They're mostly mud and cow droppings

Danu

@ACuriousMind You're practically Dutch ;)

@JohnRennie That's our tallest mountain :D

John Rennie

Anyway bed calls. I have to be at work in eight hours ...

Danu

...I should leave the office.

ACuriousMind

@Danu And Dutch have genetic memory of the invention of the bike?

@Danu lol, don't get locked in

I know people who had to flee through the tunnels below the university after getting trapped in an institute on a Friday evening :P

Danu

hahaha

dmckee

8:48 PM

@Danu Bumper sticker seen in Colorado:

> If God had meant Texans to ski he would have given them a mountain.

Danu

By the way @JohnRennie I didn't read that paper but I did note that most of the authors are from Dutch universities (some from the same as Verlinde) and thus it's highly likely that Verlinde checked with them and possibly fine-tuned based on their data before publishing his proposal. Therefore I don't find it a super convincing "check" of his theory.

@dmckee Nice

Nick Alexeev

9:07 PM

0

Q: is graphene not inheriantly conductive?

I ordered some graphene off ebay to test on some applications and I am unable to get continuity. I applied a layer of graphene on some two sided tape, made sure the adhesive was completely covered, then removed the excess with cello tape. Is there something else you're supposed do to graphene...

power-supply voltage continuity

DanielSank

9:27 PM

@JohnRennie weird

Sir Cumference

11:36 PM

@Kaumudi.H Thanks :)

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