The h Bar

Slereah

08:10

@Huy No that's engineering :p

Huy

aren't the two the same?

Slereah

prepares the stake to burn @Huy at

skill patrol

::gets gasoline::

Slereah

Going to a physics university is a good place to hear a lot of engineer hate

Secret

physics and engineer's hate is not very different then physics and biology

Slereah

08:16

Not quite

engineers is "they use all our things without understanding them"

biology is "It's not as rigorous as us!"

Secret

I guess chemistry is, "they don't produce anything as useful as us" ?

Slereah

cf also

chemistry is

smbc-comics.com/?id=2272

Secret

I am glad I have passion on all 4, thus I have no grudge against any of them

yuggib

@Slereah I do not like the addition...but classic

Slereah

I do :p

Secret

08:22

The issue of tension intrigues me,
Just today, I discovered even within a discipline, atmospheric experimental chemist and atmospheric quantum chemist also think the other is giving useless things

I wonder if a similar phenomenon happen in physics...?

Slereah

there's plenty of turf wars in academia

Slereah

08:56

sciencedirect.com.sci-hub.club/science/article/pii/…

Heyyy

There's the thing I wanted

Secret

09:44

Briefly walk me through of the significance of the positive definiteness of the integrals for interacting fermions?

Slereah

10:02

Convergence of the path integram

Secret

10:15

ok

Secret

that classic joke

Pies

11:42

@Secret Oh my God, dude. We found out that neutronos have mass

Or wait...no, I think I might be the only one who didn't know that...

Secret

it's pretty tiny though

0celo7

That's what she said

Slereah

12:13

heheh

I have made 69 answers

0celo7

What is the culminating post?

Slereah

currently

6

Q: What happens when you apply the path integral to the Einstein-Hilbert action?

The Einstein Field Equations emerge when applying the principle of least action to the Einstein-Hilbert action, and from what I understand the path integral formulation generalizes the principle of least action. What happens when you apply the path integral instead of the action principle to the ...

0celo7

You're getting challenged

He's gonna rek your ass

Slereah

He might

I'm not that knowledgable on euclidian gravity

though I am not saying his point is wrong

0celo7

12:28

I think your point is correct, if the action is not positive it obviously won't converge

Renormalization is more subtle and is a second test to pass

But it doesn't pass the first test

Slereah

though I'm not quite sure of the math

Like the paper says it is p. bad, but does it have to be positive for ALL CONFIGURATIONS?

I don't know

They don't really reference anything for that unfortunately

0celo7

I have this dream

Where all string theory contributions cancel

And Gravity is classical

Slereah

IIRC the problem is refered to as the conformal mode problem

Because you can kinda sweep it under the rug if you only do metrics of different conformal classes

In which case that action is positive

But then you have a shameful term of conformal modes that diverges

0celo7

Or

The string contributions cancel the Einstein terms

And Gravity is Newtonian

Slereah

in a shocking twist all terms cancel

Gravity is an illusion

John Duffield

12:37

@Secret : I'm in Poole. What's this garbage about you and me being the same guy? Is somebody trying to get you banned? And me too?

@dmckee : see above. Sounds dodgy. Moderation please.

@0celo7 : you're a troublemaker, kid. Maybe you need a little break from this chatroom to concentrate on your studies.

Secret

@JohnDuffield I have no idea, the earliest account that 0celo7 got that idea is when he saw my first ever handdrawn picture on the chatroom

and that's weird, because you rarely use handdrawn pictures when you are interpreting something

your most common action is referring to links

0celo7 then said to Acuriousmind that I somehow remind of you

and then the conspiracy grows

The conspiracy then lead to me discovered that there is really no way for anyone to prove they are associated to their online identities, even if we met up face to face, thus I just stopping caring about the conspiracy and focus on asking physics questions when I got one

Secret

I don't think they have any motivation to ban me, unless they think my questions are too much and annoying.
I have made interpretations, but I always ask them to check whether they make sense. This means I never have made any claims, just asking questions and clarifications

so whatever is causing the conspiracy cannot have anything to do with banning me (or possibly anyone)

ACuriousMind

@Secret I never took it for anything else that a silly joke, and it was never meant as anything else. You're taking this far too seriously, nobody is trying to get you or JohnDuffield banned because of sockpuppetry.

Secret

@ACuriousMind I know, as explained above, but 0celo7 is really serious, and this worries me because I don't know how to convince him

ACuriousMind

@Secret He isn't serious.

Slereah

12:50

You must denounce Einstein and the Evidence!

ACuriousMind

He said:

12 hours ago, by 0celo7

as serious as I was about AK

which is cryptic to you, but refers to his conspiracy theory that I am Alicia Keys

which also wasn't ever an actual option anyone believed in

Secret

...

I see...

It seems I am really bad at detecting jokes...

ACuriousMind

Yeah, I can't disagree with that :P

Secret

and maybe I am also too paranoid of losing this chat, because in the past I have made a mistake in physics forums that got me permabanned there, and thus losing a channel to self study physics

ACuriousMind

@Secret To get permanently banned here you must repeatedly cause substantial offense. I don't think you have to worry about that.

Slereah

12:54

but must JD worry

ACuriousMind

I think there are no permabans, even, the longest is one year

And that's only given as a fourth strike or something.

John Duffield

@Secret : see the Wikipedia neutrino oscillation article and look at this picture. Think of it as a splayed-out travelling breather. When the breather is at each extreme of its rotation, or int the middle, it has a "flavour".

Slereah

Hey @ACuriousMind

ACuriousMind

@Slereah Hey

Slereah

What theorem says that a path integral (euclidian) must always have positive action to converge

If any

Hawking and Gibbons seem to hint at it but offer no references

I can see the point sort of but I can't really figure out why it must be for ALL CONFIGURATION SPACE

John Duffield

12:58

@Secret : it's only a "joke" now that I've rumbled the malice.

ACuriousMind

@Slereah I know of no such theorem, and I don't think it is true that the action has to be always positive.

Slereah

Hm

They make a big deal about the conformal modes being negative action

Secret

One thing that interested me throughout the chat history is the issue related to interpretation:

Take neutrino oscillation as an example:

ACuriousMind

@Slereah Take, for instance, a gauge field coupled to some current $J^\mu$ with Lagrangian $F^{\mu\nu} + A^\mu J_\mu$. The first term is always positive, but I'm pretty certain you can make the second term arbitrarily negative for certain $A^\mu$ configurations.

Secret

I, JD, and other particle physicists each has an interpretation on it:

If we can formulate our interpretation such that it agrees with all known experimental outcomes, and the complexity of our interpretations are quite similar (thus cannot use ocams razor), how do we know which interpretation is the least misleading one?

I have this question in mind because of tring to increase my understanding of the subject and also thinking about an educational perspective

ACuriousMind

13:02

@Secret No such thing as "least misleading". Interpretations by definition agree with all experimental results (else they would be different physical theories, not interpretations) and therefore are empirically indistinguishable. How could one be more misleading than the other if they agree on all predictions?

Slereah

@ACuriousMind From Euclidian Gravity : "For Yang Mills Field, $\hat I$ is positive semi-definite, so one can expect the action to converge"

Although the problem could be that the conformal mode action is always positive

It is basically $\Omega '^2$

ACuriousMind

@Slereah Wat.

Do they show that?

Slereah

Well no, that is my problem

Lack of references

Secret

@ACuriousMind because I often came across conversations like how some professors said this is not an accurate interpretation, it shuld actually be interpreted as (blahblah)

That is, often times, it seems one interpretation is more popular than others

Take the wavefunction as an example, the most popular (and in most case, termed the mainstream one) is the copenhagen interpretation

Each interpretation has its way to describe and reproduce the expeirmental results, so what other things (besides politics in academia) that can influence which interpretation is considered more maintstream th…

ACuriousMind

@Slereah Oh, I think they are talking about the free Yang-Mills theory

Slereah

13:06

could be

ACuriousMind

But that statement doesn't hold for one coupled to a current.

Slereah

Either that or maybe the interaction term is compensated by the other terms

Hm

Maybe

After all they're configurations

They don't have to be on shell

ACuriousMind

Additionally, one has to do something about the gauge redundancy, just saying the action is positive is completely worthless for the path integral approach here.

Slereah

I guess their point is that even for free GR, it does not converge

@ACuriousMind : Man don't be like that other guy :p

Secret

That is, perhaps my question is:
What is the criteria for a physical interpretation to be considered mainstream, and more accepted?

Slereah

13:07

It's a requirement not a guarantee!

@Secret : That a lot of people accept it

ACuriousMind

@Secret I don't think it is fair to say that Copenhagen is the most accepted.

Slereah

Well it is

Copenhagen and MW are the two big ones

Along with "shut up and calculate"

ACuriousMind

Many people I know just give an exasperated sigh when someone mentions "quantum interpretations"

@Slereah But, in this case, it is really important. Maybe the action isn't positive on the space of all configurations, but it is positive on the reduced space after the redundancy has been eliminated?

skill patrol

Interpretations open to interpretation :P

Slereah

@ACuriousMind Could be, who knows!

But why is it such a big deal tho, is my question

Is there a theorem about it

That something that is always positive (or sometimes positive) will not converge

Always positive I can understand

Since you're basically integrating a positive thing all over space

ACuriousMind

13:14

Ah!

I may have an idea

Secret

@JohnDuffield While you are well known for controversial interpretations, I think the Einstein elastic your linked earlier might be workable into a full model. I think if you can step in and flesh out the descriptions a bit more using the maths and make "elastic general relativity" that can reproduce every experimental outcomes, then we might be able to start using it to guide for searches of new things in cosmology

I unforunately, due to being in chemsitry, will need to take a long time before I can catch up on general relativity before I can start trying to build my own model

Slereah

Make a chemical interpretation of GR :p

Secret

Manwhile, a transition state calculation is working as expected

I wonder if relativistic chemistry is similar to particle physics?

Slereah

Relativistic chemistry is just chemistry with some correction terms

Secret

I am talking about the future where it is a routine to react superheavy chemical elements together and then measure them

Slereah

13:19

@ACuriousMind : After some investigation the Yang Mills thing seems to be for free fields indeed

Relativistic chemistry is already a thing

there's a book about it and all

Riggs

Say we have a basic spring system that involves harmonic oscillation. In the wave equation for the spring what does the amplitdue represent? It seems the wavelength represents how far the spring will move before being pulled back...so what does the amplitude of the wave represent?

Slereah

It's just chemistry with relativistic energy levels included

Secret

I suspect there will be something interesting and more complex than correction terms when we are finally able to react multiple superheavy elements together

Currently, most of the reactions done so far are in the gas phase and involve things like fluorine, and the product has to be probed in like microseconds before they decay away

skill patrol

objection over ruled

NOOooo...

...let's try and be civilized about this guys :-)

ACuriousMind

@Slereah: I think the crux is not so much positivity as boundedness

Slereah

13:31

could be

ACuriousMind

Glimm/Jaffe prove that in two dimensions, a polynomial (inter)action defines a well-defined measure on function space if it is bounded from below.

Slereah

Though IIRC while actions have a minumum they do not have a maximum?

So if positive that goes to 0 but else it will be bad

ACuriousMind

@Slereah It need only to be bounded from below. The action can become positive all it wants, since that makes $\exp(-S)$ only smaller

Slereah

yes

skill patrol

Too late DavidZ has created a private room :'(

ACuriousMind

13:33

So their point isn't really that the action isn't positive, but that it isn't bounded from below

I think

Slereah

but since actions are unbounded, I guess that's why they don't bother saying it?

skill patrol

Now the messages disappear :O

bye pal

ACuriousMind

@Slereah Well...that's why I'm not sure, they might know something about positivity of the action I don't ;)

But AFAICS, it's really the failure of that conformal mode to be bounded from below that destroys the usual way of at least hoping the measure exists on function space.

David Z

@skillpatrol and whoever else might be wondering: Yeah, we prefer not to have moderation actions picked apart and speculated on. If someone thinks the mods are acting inappropriately, you can contact the SE team.

skill patrol

Yes Sir.

yuggib

13:43

@Slereah I think that positivity of the Euclidean action could be related to the reflection positivity property in the OS axioms. The latter is necessary in order to ensure the existence of the "rotation back" to Minkowski time.

Slereah

OS?

yuggib

Osterwalder-Schrader

@ACuriousMind With an unbounded from below classical action is almost impossible to have a bounded from below quantum Hamiltonian (even after renormalization); and so very very difficult to define it as a self-adjoint operator

So I also would be incline to avoid unbounded from below actions

ACuriousMind

@yuggib How would you do that? One can relate the reflection positivity of the measure to the reflection positivity of the two-point function, but I can't see how one gets a requirement for the action out of that?

Slereah

What a NERD

skill patrol

This account is temporarily suspended to cool down. The suspension period ends in 2 days.

0celo7, USA

1 6 26

general-relativity homework-and-exercises quantum-mechanics differential-geometry lagrangian-formalism quantum-field-theory electromagnetism

Slereah

13:54

what did he do

that rapscallion

skill patrol

If I say I'll be joining him.

Slereah

u can tell me in secret

skill patrol

27 mins ago, by skill patrol

objection over ruled

it all starts here^

yuggib

@ACuriousMind The measure should be defined using the action if I am correct (not really an expert).

@skillpatrol he returned to life

2 very fast days ;-)

skill patrol

@yuggib he can not speak

yuggib

14:00

only watch

skill patrol

yes

yuggib

that's sad

skill patrol

I've been there many times

yuggib

who is gonna defend the american way now :-D

I am fair, so I will not say anything...

skill patrol

A Day in the Penalty Box

Jeff Atwood on April 6, 2009

Are you familiar with the Penalty Box?

Two days is serious.

Slereah

14:03

did he murder JD

skill patrol

He questioned The Evidence.

But yes, it was about JD.

yuggib

What else could it be? :P

ACuriousMind

@yuggib Ah, yes, right, the measure is $\exp(-V(\phi))\mathrm{d}\mu_C$ with $\mathrm{d}\mu_C$ the Gaussian measure associated to the two-point function.

That looks like one could indeed get positivity of $V$ out of the reflection positivity.

yuggib

@ACuriousMind Maybe it has to do with that, but as I said it is really just a guess from someone that is not so expert on those stochastic things.

ACuriousMind

@Slereah: Go do some functional analysis on that measure. ;)

yuggib

14:10

Apply some Hahn-Banach and Banach-Steinhaus

use that goddamn' axiom of choice :P

ACuriousMind

It's really irritating that people denote the inverse fourier transform of that measure by $S$. I had to read the few pages in Glimm/Jaffe several times because my brain kept substituting "action" for $S$.

yuggib

@ACuriousMind :-D indeed. AFAIK it is not standard notation in mathematics either

Slereah

@ACuriousMind Nooo ;w;

yuggib

@Slereah or maybe you prefer the proof by intimidation

3

Slereah

I should maybe reread that book on path integrals

By like

Demichev

It got into measures

ACuriousMind

14:14

SMBC has a different take on proof by intimidation

2

NeuroFuzzy

@Slereah I really want to study that stuff!

Slereah

No you fool

This way madness lies

Secret

cannot upload pictue for some reason, doing a workaround now

imgur.com/Z9Zt8Yh

Currently playing a flash game which is basically a planar graph solving exercise

NeuroFuzzy

@Slereah but... Well i can't throw around buzz words because i don't know anything.

Secret

and then I noticed I have been solving it using something that I don't have words to describe

NeuroFuzzy

14:22

But functional analysis [which seems in this direction?] doesn't strike me as the worst thing in the world!

Slereah

Hitler invented functional analysis

Secret

The closest words I can get to describe that is that if "the edges connected to a vertex does not move much when you drag a vertex, it means you have made a wrong move"

NeuroFuzzy

To defeat your enemy you must know it

i guess

Secret

in light of this I then ask MSE about it
http://math.stackexchange.com/q/1468598/

Slereah

Functional analysis is done a lot in like

Hidden ways

Like Lagrangian mechanics on fields is functional analysis

but they hide it

They write the functional derivatives as derivatives

For they are ashamed

Secret

14:26

The above "feeling" described in physics is like imagine each edge of the graph is a rubber band, then a wrong move is one that makes it more taut

I have no idea how to describe this, and this is one example of what I called a non chunk,it's as if I am unconsciously solving it but I don't knwo how

skill patrol

@Danu Here is your answer pal, from a real expert :-)

Slereah

I guess I could send an email to hawking to ask him about that positive action business :p

And berate him for being generally terrible at bibliography

NeuroFuzzy

@Slereah So how is this different than regular Lagrangian mechanics? one is a functional derivative on $(L^2(\mathbb{R}))^n$ I guess, and the other is on $L^2(\mathbb{R}^k)$? Never actually done any of that.

Slereah

It's not, actually :p

since x(t) is also a function

ACuriousMind

@Secret I think that what you are doing is implementing an algorithm for the graph isomorphism problem, in particular the part where you construct the isomorphism to a planar graph.

skill patrol

14:32

@Slereah I don't think he would reply...it's nearing the end for him :(

NeuroFuzzy

@Slereah Hmm? "It"=...?

Secret

@ACuriousMind IT seems so, but I don't really know how to describe it, it seems as if deep down I know how to solve it by implementing an algorithm but I don't know what actually I am doing

Slereah

@NeuroFuzzy wot

David Z

@skillpatrol please don't speculate on the reasons for suspensions - and it is speculation, even if you think you know what happened.

Slereah

take it easy

skill patrol

14:39

@Slereah nvm, I can fight my own fights pal :-)

we've been suspended together before, remember?

and it involved JD

dmckee

Oh. My. God.

I should have expected it, but I was living on a happy pink cloud or something.

We can now expect no fewer than two dozen startlingly ignorant questions with "neutrino" in the title.

Aaaarrrrgggghhhh!!!!!

3

skill patrol

Thanks to?

Slereah

the nobel prize in physics

It's about neutrino oscillation

skill patrol

hmmm

Slereah

Can we use the oscillation of FTL neutrinos to power an EM warp drive with cold fusion

ACuriousMind

14:48

@Slereah After having seen a lot of questions, that's not the worst I've seen, but it's close

Slereah

what would be the worst

Is it about electrons being photons along a dirac belt

NeuroFuzzy

@Slereah linked the wrong message. "It's not, actually" means what?

Slereah

Oh

Lagrangian mechanics for fields and point particles

With respect to functionals

both use functionals

NeuroFuzzy

oh, I thought you were implying that regular Lagrangian mechanics isn't and that field lagrangian classical mechanics is.

Slereah

nah, both are

$\delta S / \delta \phi(x) = 0$

it is the Truth

Rigor

15:00

What happened to my pal 0celo7?

Slereah

He was struck down by THE MAN

Rigor

:(

Secret

Embarassingly, I screwed up and then accidentally clicked restart. Now I have to do this all over again

NeuroFuzzy

@Slereah oh seriously?

Slereah

apparently

Rigor

15:04

Nothing to be embarrassed about @Secret

yuggib

15:35

However, talking about neutrinos

I am quite dissatisfied by the official press release that reads “for the discovery of neutrino oscillations, which shows that neutrinos have mass” as the principal quote

dmckee

I find that the Nobel committee often choose strange ways to word the official citations. They focuses on side issues, they give at once more and less credit than is due.

yuggib

I have yet to be convinced that the implication $\text{neutrino oscillations }\Rightarrow m_{\nu}\neq 0$

dmckee

I went through all the neutrino Nobels to date the other day. They are all weird.

yuggib

is really a mathematical (or almost mathematical) implication

dmckee

@yuggib That follows from relativity. Oscillations rise from the application of the Hamiltonian over time, which requires that they be non-luminal. Or at least that all but one flavor be non-luminal.

yuggib

15:39

are we sure that there is not possible model that yields neutrino's flavor oscillations and only zero mass eigenstates?

dmckee

BUt I don't know anyone who really like the "all but one" idea. It's just a footnote.

@yuggib Well, I'm no theorists, but I think so. And the theorists I've talked to about it think so, too.

yuggib

@dmckee I would like to be convinced...for example, I am not so convinced about the reasoning above

you apply the Hamiltonian (in its exponentiated form) to get time evolution

skill patrol

@dmckee how many did you have to go through?

yuggib

but also other massless particles (photons) have an Hamiltonian time evolution

dmckee

Five or six. There aren't many.

yuggib

15:44

In principle, to prove the assertion you should have to find a contradiction yielded by $\text{neutrino oscillations } \wedge m_\nu=0$

I do not want to diminish the importance of neutrino oscillations, and their importance in suggesting that we need to find something beyond the standard model (since the latter does not allow them); simply I do not see this as a definitive proof that the neutrinos have mass.

skill patrol

disiplined indeed

yuggib

And so I would not put that assertion as the main sentence summing up the choice of this year's Nobel laureates

skill patrol

Are you happy now @JohnDuffield?

John Duffield

@Secret : that "Einstein elastic" has been worked into a full model. It's called General Relativity! It has a shear stress term in the stress-energy-momentum tensor because space is an "elastic continuum". Hence we have curved spacetime and geometry. Some people might disagree with this, but they can't disagree with that shear stress term, so the disagreement concerns nuance or interpretation. You should ask questions about GR. And try not to be a "my theory" guy.

skill patrol

What's wrong with being a "my theory" guy? @JohnDuffield

Are you racist against theorists?

Just let the kids be kids.

You want to talk physics?

How can you do Physics without a theory?

Define: Physics. Then come back.

Physics

Physics (from Ancient Greek: φυσική (ἐπιστήμη) phusikḗ (epistḗmē) "knowledge of nature", from φύσις phúsis "nature") is the natural science that involves the study of matter and its motion through space and time, along with related concepts such as energy and force. More broadly, it is one of the main analysis of nature, conducted in order to understand how the universe behaves. Physics is one of the oldest academic disciplines, perhaps the oldest through its inclusion of astronomy. Over the last two millennia, physics was a part of natural philosophy along with chemistry, certain branches ...

You see two can play the useless links game pal.

Physics

Physics, a branch of science, is the study of all forces and their impacts on the environment. Modern physics connects ideas together about the four laws of symmetry and conservation (energy, momentum, charge, and parity). The word physics comes from the Greek word ἡ φύσις "nature". == Definition == Physics is the study of energy and matter in space and time and how they are related to each other. Physicists assume the existence of mass, length, time and electric current and then define (give the meaning of) all other physical quantities in terms of these basic units. Mass, length, time, ...

Here^ something in simple English for you.

John Duffield

16:07

@skillpatrol : there's nothing wrong with being a my-theory guy if you're Einstein. But you get these young guys who don't know much physics, who come up with "my theory" about gravity or wormholes or time travel etc, and they're just peddling woo, and they ain't listening. You don't want to be like that.

skill patrol

@JohnDuffield : So we're all supposed to be like you?

John Duffield

@skillpatrol : no, be yourself. But be open and sincere too, and remember the goals of this site. As per your link, physics is the natural science that involves the study of matter and its motion through space and time, along with related concepts such as energy and force. We do it because we want to know how the universe works.

By the by, I recommend that you always use your real name when posting on a site like like this. It helps you to remember to be yourself, and to be open and sincere. I appreciate that some don't like to to this, but I do. It works for me.

DanielSank

17:31

Appeal to the masses: Please consider carefully before voting to close questions asking about the physical reasons behind technology standards. These questions admit interesting physics-based answers which you will not get from typical engineering audiences.

Furthermore, rejecting such questions suggests that physics is constrained to theory and particles. Far from it, physics is an essential element in our daily practical lives. Understanding how a toaster, vacuum cleaner, or electrical outlet works is what started many of us on the paths we now walk in physics. I hope everyone will keep this in mind when they choose how to use their daily close votes.

Slereah

17:56

Why are number states refered to as "particle states", anyway

It does not fit at all

NeuroFuzzy

@Slereah Why would you post that? i was having a perfectly good day before this

@DanielSank A grad student here is going to lecture on superconductivity for the ucsd physics club :D

Slereah

Is it because you don't like thinking about fluid mechanics

I don't either

Bloody non linear equations

NeuroFuzzy

also this: "Our department is now accepting applications for travel funds to attend/present at Physics conferences taking place between November 2015 & February 2016. The deadline to apply is Friday October 30th." wooo! Ideas?

Slereah

Newtonian flow is okay I guess

NeuroFuzzy

@Slereah :D speaking of which did you see whosits whatsisface on colbert about the navier stokes equations? That was pretty fun.

Slereah

18:00

no

NeuroFuzzy

okay.. i'm not being very specific...

@Slereah cc.com/video-clips/6wtwlg/the-colbert-report-terence-tao

Slereah

Well I doubt a lot of people on Colbert talk about Navier Stokes

NeuroFuzzy

true.

DanielSank