I don't know PDE theory m8

Of course you do

You were talking about it a few months ago

Was I

Take a look at this wacky question I just found. I don't even know how to react, it's so off-topic: physics.stackexchange.com/questions/273148/…

Good lord

Sorry to just barge in and say that, but it's pretty funny

hahahahahaha

Never seen the "ghosts" tag before.

Nicole fine as hell doe

can't disagree

it s OK guys

found her

she has a kid and no husband

so she s available

Yikes

I ain't about that life

u aint about women>

?

Ha-ha

Single mom is never good

everybody makes mistakes

u d never date a single mom?

once u get older

Unless she was one by choice (and had a good reason), no

Widows don't count

What's the logical alternative? Date married women, only? :-)

Would someone with the right background write at least a summary for the ghosts tag?

To try too minimize the recurrance of questions like

@CuriousOne Huh?

@dmckee haha

why not get Shog to delete it

yhea we need someone who went to hogwart university and has a Phd in ghostology

to write a summary for that tag

@0celo7: I didn't get the logical alternative to single moms. What's that? Married women without children?

he likes to have husbands hunting him I guess

@CuriousOne How about not dating mothers

you don t like experience?

you can be experienced without being a mom though...

@dmckee who upvoted that question?

this is getting really weird

the person who upvoted this is the person who feels lonely at night

@Slereah How the heck does $$\limsup_{t\to T}\sup_M|R_{g(t)}|=\infty$$ make sense when $M$ is compact?

@0celo7: Depends on neediness. If you can't stand being eternal number three+, then you shouldn't.

I'm number one, bro

Hmm

I guess $[0,T)\times M$ isn't compact

@ChrisWhite Hey, you work with PDEs. Do you know anything about parabolic equations / the maximum principle?

@ChrisWhite ok, well

you guys are mean

Let $F:\Omega\times [0,\tau]\to\Bbb R$ be smooth, where $\Omega\subset\Bbb R^n$ is open and $F(x,0)=0$ $\forall x\in\Omega$. Suppose $\partial_t F\le\Delta F+C\tau^{-2}$ on $(0,\tau]$, where $C>0$ is a constant. Why does the maximum principle imply $\sup_\Omega F(\cdot, t)\le C\tau^{-2}t$?

@0celo7: I am not even a "bro". :-)

@CuriousOne it s OK bro , we all appreciate u for what u do

@DaveCoffman We seem to have a small but persistent cadre of users who vote for anything that interests them no matter how off-topic or cast pity votes (no idea which is more prevalent).

@privetDruzia: So do I. I especially appreciate myself for all the stuff that I don't (have to) do, anymore. :-)

@dmckee: I like to hope that my occasional pity vote will prevent me from going to hell. Call me an eternal optimist. ;-)

@CuriousOne do you want to be a sistah instead

@0celo7: Are we talking reincarnation? Can I choose? In that case I want to be a bird, first.

I'm confused

Or are you confused

don t worry guys I ll figure it all out if u r too confused to do so

let s just build a wall

and make the mexicans pay for it

I agree with this plan.

OK @CuriousOne start building the wall, I ll join u guys later

everybody will participate in the construction of this wall: we are all equal in here.

But some are more equal than others

@privetDruzia: Nothing to worry about, birds can fly over walls. :-)

Some

some birds

sometimes I use so much oil when grilling birds, I am affraid the US army invades my kitchen

*some birds

Not funny

because u r American, hahaha

@0celo7: You didn't think I wanted to be an emu, did you?

just to be clear: I am laughing because the joke was so good, not because u r American

I'm German

I'm Belgian

you disgust me

Don't make me invade you

@privetDruzia: Real Americans can still laugh about themselves. Sadly, it's a dying breed. Too many Americans are channeling their inner German, these days, and are not funny.

@Shrodinger2016 c'mooon there are worse things than being German

Belgian, Spanish

Belgian, Spanish, Chinese

Indian

Russian

Canadian

Somalian

These ICHEP slides are getting out of hand

(courtesy Christos Leonidopoulos's slides)

does any of you like the big bang theory?

Sheldon Cooper must be your hero, right?

no

Being german is cool.

k

@PhysicsGuy So is being Werner von Braun

or Elon Musk

I know.

@GPhys Strangely enough in that one frame Jack Nicholson looks a lot like one of my former bosses who works on CMS.

@privetDruzia One of my experiment got on the white board. Does that count?

We made fun of the way they butchered our typographical conventions for spelling it, however.

@dmckee There are a few details sometime that indeed are quite funny. Things that the producers are not aware of I think

the simplest example is how Howard, the engineer, holds a soldering iron

Hehe, Howard from "The Big Bang theory".

the way he holds it (like a knife), he won t ever be able to solder anything properly

@dmckee one of your own invented experiments or an experiment invented by someone else that you are studying?

@dmckee Nice

@privetDruzia One that I worked on. DoubleChooz. The first experiment to get published with evidence for $\theta_{13}$ non-zero. Alas, Daya Bay got to 5 sigma about 2 months before we did, so they score the big prize.

What is $\theta_{13}$

@0celo7 On of the neutrino mixing angles.

@dmckee nice. Did they ask your permission or anything to use it?

@privetDruzia Not that I heard. But why would they?

@dmckee What's that

@dmckee idk. when using someone elses song they have to ask permission to the singer or songwriter or someone else, in order to not infringe laws and all that stuff

@0celo7 It has nothing to do with differential geometry or category theory.

@dmckee I can never remember off the top of my head if it's PMNS or PNMS

You'd think I would, since it's alphabetical

@dmckee That's fine, I know nothing about the second

Although if it were the first, that would be helpful

I'm interested in topology and geometry btw, not cat theory :)

are there today really students as intelligent as Sheldon Cooper was when he was a student?

@dmckee ELI5 neutrino mixing angle pls

@privetDruzia found her where? if a few ppl give her more upvotes shell have enough rep to chat =D

@vzn hahahaah. facebook

@privetDruzia lol ok right ofc didnt occur to me (maybe too old) :(

@0celo7 What? Should I know what "ELIS" means?

@dmckee explain like I am 5

@dmckee Yeah, I did expect that...

It's a number about neutrino mixing.

But then a 5 year old wouldn't know a neutrino from a numerator, so what's the point?

@dmckee What's that?

@dmckee ELI18 then

Hmmm ... looks like I've never written out the mixing matrix on the site.

Look on page 7 of ...

The limits on page 8 are now very much out of date, of course. Indeed there were a few of important announcements in the last month.

lol what

what are these things

@dmckee I know nothing about particle physics, what is happening

@0celo7 Experiments have been running. The evidence is increasingly holding that the mass hierarchy of the neutrinos is "normal", and that $\delta_{CP}$ is likely non-zero.

...$\delta_{CP}$?

Maury Goodman's "long baseline neutrino newsletter is a great way to follow that without having to read tons of papers.

@0celo7 Another number about neutrino mixing. The CP-violating phase; and a possible explanation for the matter/antimatter asymmetry in the universe.

For that to work we needed relatively large $\theta_{13}$ (check) and large $\delta_{CP}$.

The evidence for tha latter is starting to look pretty good.

@dmckee What's the latest experiments? Was it.... JUNO or something (?)

going to sleep it s 4am here

bye folks

There was one using the Super-Kamiokande I thought too

let your day be as nice as you were to me

I don't know so much about neutrino experiments

$\text{NO}\nu\text{A}$, T2K. Super-k is still running as are Daya Bay and Double Chooz. KamLAND is doing yet another re-configuration. microBooNE is starting.

crazy names.

It is easy, when reading the popular press to get the feeling that the LHC is particle physics, but on the ground that simply isn't true.

ICECUBE is still the most exciting particle physics experiment to visit

DUNE planning is ramping up fast, too.

or is it IceCube?

@GPhys ICECUBE is way cool. ::get it? get it?:: But in some ways it is an astrophysics experiment that just happens to be a neutrino telescope.

@GPhys Don't recall.

@dmckee hahaha

@dmckee When I visited Stony Brook's open house while deciding on a graduate program, I spoke with one of the grad students that had just got back from IceCube

He was only there for the "summer" though

He said he enjoyed it, though

@GPhys Very few members of the experiment over-winter, the guys who are there know how to do what little actually needs hands on-site to fix.

makes sense

I enjoyed talking with the nucl-exp guys at Stony Brook a lot

I was impressed

@Dave are you new to chat? are you affiliated with IYPT? looks interesting can you say something about it?

@GPhys we are always looking for chat speakers, any interest?

@vzn I do not believe I am qualified to answer anything interesting (I only have a BS in physics, and I'm only just starting graduate school)

@vzn I was affiliated with the 2015 USA team that attended the IYPT in Thailand, though I didn't actually go. I just worked on some of the problems in school. I have no current affiliation with any teams, though I believe that there is an effort to begin recruiting for the 2017 USA team. I can look into that, if you are interested. Bear in mind I won't be able to get any information about that for a few weeks.

@vzn If you're interested in the International Young Physicist's Tournament, their main website is here: iypt.org

They can explain it far better than I could.

But in short, it's a physics research competition between high school students.

So, possibly stupid question

Say we know the mass of an elementary particle

I have a stupid question

Then, according to the uncertainty principle, shouldn't the particle have no specific velocity, rather than momentum?

you're right

that is a stupid question

Cool?

Oh

Dammit

velocity is not an observable

But if we know the mass of an object, and p=mv, shouldn't the only thing undefined be velocity?

hmm

I'm trying to compute something stupid

this should be trivial

Er?

@GPhys ok. (reading your profile) did you do a sr honors thesis? how many pgs? did you do a presentation?

@vzn yes/yes, and other research with ATLAS and solid state neutron detectors (as an undergraduate)

@SirCumference that all depends on its position localization

but (I guess?) that's probably typical of most people going into ~top 20-30 physics programs

Let $f:S^2\to \Bbb R$ be the function associated with a gradient Ricci soliton $g$ on $S^2$. Let $\xi=\mathrm{grad}(f)$, and let $J$ be an almost complex structure on $S^2$ compatible with $g$. Then $J\xi$'s flow is a group of isometries $\varphi_t$. Let $p$ be a critical point of $f$, then $a:=\rho -\frac{1}{2}\mathrm{scal}_p$, where $\rho $ is the soliton constant. Then $(\mathrm d\varphi_t)_p(v)=\cos(at)v+\sin(at)Jv$.

But the basic idea is right: in nonrelativistic quantum mechanics, if the mass is fixed, then the uncertainty in momentum is related to the uncertainty in velocity. Under these circumstances the velocity operator is defined as $\vec{v} = \vec{p}/m$.

This last equation is giving me trouble.

All right, next question

Degenerate gases

You know about them?

Me? No

D:

@vzn only ~30 pages, nothing significant

I wish I knew about Ricci solitons

@0celo7 Er...do you know about degenerate gases, by chance?

my math thesis ended up being horrendously long, ~50 pg even after I switched it to two column. It was inflated a lot because it needed a lot more background information than is probably typical

@SirCumference no

D:

@GPhys It wasn't on Ricci flow, by chance?

@GPhys its nearly as long as some masters theses. think 30pg thesis as an undergraduate is significant. & another 50 in math? think you would be interesting speaker, plz consider it. plz note theres a substantial undergrad contingent on the site

@0celo7 Internal Set Theory

Close enough I guess

@GPhys huh, I was going to say that does not seem very long

@0celo7: Did you ever get out of a speeding ticket with "Velocity is not an observable!"? ;-)

@DavidZ Maybe I'm just deluded from the experience of writing two theses at the same time :P

@0celo7: Or... in relativity with "It's all observer dependent... "

there were only 3 of us dumb enough to try simultaneous honors degrees at my university that year

@GPhys oh, well if you write two your page count is the total of both

That just goes without saying :-P

@GPhys "dumb," lol

Hmm, maybe I have to differentiate that equation

@0celo7 (uttered the magic word!) why? what are they good for?

@vzn I wish I knew

Ricci flow, apparently

No offense, but does page count matter for those of us who are gifted? I know that I wrote a lot to deflect from the fact that I didn't have much intelligent to contribute (I had basically figured out why everybody was designing the wrong DAQ architecture for an experiment, which made me correct but looking stupid...).

@0celo7 havent heard of em, where did you hear of em

In a Ricci flow book

@CuriousOne Page count doesn't matter for anyone except those who impose page count restrictions (and those who have to meet them), I'd say. But still, it's one of those numbers people compare because that's what we do, we compare numbers.

Or something like that.

@CuriousOne pages alone are not significant but apparently a lot of undergrads write nearly nothing

@vzn: Interesting... I wasn't aware of that problem. Having said that... US undergrads? I think the expectations are a bit different between the US and the European system.

@vzn: In the US I would expect the grad students to do the heavy lifting, while in Europe one can occasionally get useful work out of an undergrad (not always, of course).

I thought it was exactly the other way around.

Undergrad research is very common in America, and completely unheard of in Europe.

From what I've heard, the prevailing attitude in the US is that if you have done research as an undergrad, it gives you a big boost in getting into grad school in that field. Which implies that a lot of people don't.

@0celo7: We got pretty good results from our undergrads, on average. That's in Germany, maybe it's different in other countries. Personally I was working in a research group after my first exams... for a living, I needed to money from the RA position. OK, I was lucky getting that job.

at least at my undergrad university and physics department (larger "R2", but luckily nice physics department), I had to rely on charisma/class performance and seeking out professors to secure research opportunities

I was one of the only ones in the department, but I had convinced a good portion of friends to do as well

undergrad research was available, but you had to seek it out and it wasn't the "norm", I guess is what I'm saying

In my department at an R1, you're weird if you're not working for someone.

it seems like it would be a very departmental thing

Freshman research is a little unusual

But I know 5 who are

That's 10% of the class

@CuriousOne it depends who you talk to whether its a "problem", its not regarded as one in the US

There are probably more

@GPhys: Anybody who says that one can just stumble trough university without personal contacts to and help from faculty doesn't understand how science works... who you know (and who trusts you) is an enormous deal.

If there is nobody around who can help you... run!

So what that means is that 90% of the undergrads who don't move on to grad school never learn the real deal? Ouch.

[scifi] Yet another day to wrestle with those wiki markup...

@CuriousOne I mean 10% of first year students are, at least

@0celo7: Ah... OK. Yeah, nobody cared about first year students in my university, either. They were waiting for us to wash out in the first exams. Not that many did in my year, but still. After that I got the job and a lot more exposure to what science really involves (like writing grant applications...).

Either? I think 10% is pretty good

One guy went to the same physics professor week after week until the guy said to him "I can't get rid of you, so I might as well give you something to do... ".

That's weird

In hindsight... not a bad strategy.

I'd call security on him

He was actually good at math.

@GPhys exactly, understood, thats how it was in my time. btw are you in US or europe? can you say state? yes undergrad initiative/ effort/ results similar to yours seems notable/ uncommon all over the world, in a word "honors"

How on earth does one take the differential of a flow

@vzn US

this is nutso

what's the ODE that's solved by $\cos at+\mathrm i\sin at$?

@GPhys what do you want to work on now? your enthusiasm for particle physics is duly noted

HEP-exp, but Stony Brook almost convinced me to jump ship to nuclear-exp

they were this close

$x''=-a^2x$?

There is a large ATLAS collaboration at the university I'm going to, but there are also some neutrino guys

I'm eying particular advisor (who isn't?), but keeping open, mostly

already had lunch/met with people I was interested in some months ago before deciding

@GPhys this stuff is increasingly moving online/ open science/ open source, rewarding those with initiative/ selfmotivation, have some links on that, posted one recently

@GPhys just wondering are there aspects of HEP that are not particle oriented?

@CuriousOne yeah its kind of wild sometimes what actually constitutes a bachelors of science... it means more learned science not nec practiced it much different scenarios

@vzn Sure, there's plenty of long meetings with ATLAS management

(sarcasm, kind of)

@GPhys so (your take, recent fiery topic in here) what are the directions post Higgs?

@vzn What do you mean in particular? The next big discovery, big experiment, big theoretical idea?

@GPhys any/ all of the above, or whatever else... buzz, rumors, gossip etc

aka as the (silicon valley) media sometimes says, Next Big Thing™

Whereas theoretical physics is evolving (somewhat, jab) in meeting the latest data, I can focus on effectively providing the data to shape discussion regardless of origin. Even those of us not on the diphoton analysis always have something to excite people with

regarding the next big experiments, I think everybody (or at least me) is looking forward to DUNE getting off the ground

and keeping an eye on what China is going to be doing wrt colliders

but the LHC will live on for some years

@GPhys what do you mean "focus on effectively providing the data to shape discussion regardless of origin"? are you talking about the IT infrastructure etc? "origin" in different experiments?

@vzn in different experiments or analyses

@GPhys yeah they are a big deal and DZ is there & up to his elbows as you may have noticed (see his blog for more gory detail)

at, e.g. ATLAS, analysis is broken up into, say, a team doing a search for vector-like bosons all by themselves, and another team doing a dark matter search, etc etc

@origin

even if I'm on, say, the vector-like boson search and I don't think vector-like bosons exist, it's still an important analysis

Theoretical physicists better come up with a good reason why there will be more to see below 10TeV than there was just below 1TeV... otherwise the taxpayer will cut us off. Sigh...

@DanielSank Chris White and I are room owners so we can pin messages and deal with any fracas. I will be present at the chat.

@SirCumference momentum is a useful quantity to work with for several reasons. For example it is conserved, and in Langrangian/Hamiltonian mechanics it is the conjugate variable to position. So we generally use momentum rather than velocity even though for a specific particle they are proportional to each other.

@JohnRennie I do hope the level of fracas is reasonably civilized.

I'd hate to be remembered as the guy who's AMA had too much fracas.

In fact, @JohnRennie I hereby appoint you moderator of the fracas level of my AMA.

Should the fracas level be too high or too low, you will be held accountable.

Should the level of fracas be pleasing, you will be rewarded.

OMG the resposibility :-)

::looks up "fracas"::

Yet another English word that isn't English. We must have the most promiscuous language ever!

Indeed.

While you're here, a while back you mentioned that vacuum fluctuations could be detected as noise in electronic circuits.

Yes! Indeed they can.

Would you like a reference paper?

I'd be interested to know more about that. What's the best way to pursue it?

Well, there's a reasonably accessible paper by Roger Koch.

I'm looking for it.

journals.aps.org/prl/abstract/10.1103/PhysRevLett.47.1216 ?

Alternatively, if you post a question on the main site I might be able to answer it.

@JohnRennie That might be it.

I don't have journal access at the moment so I can't check.

Yeah, that abstract looks right.

How do you read papers... you're retired, yes?

Thanks, that gives me a starting point. I'll do an author search on the Arxiv and see what he's written that's publically available.

@DanielSank I only have access to the publically available stuff.

Though you'd be surprised what can be downloaded if you search.

I suspect a lot of academics don't like the way journals behave and are quite happy to quietly leak stuff :-)

@JohnRennie Yes, paying to have your paper published and then paying access it is rather irksome.

Let me know if you need anything.

Thanks :-)

It will help in your reading to know the following simple facts:

1. An infinitely long transmission line is like a one-dimensional electromagnetic vacuum: if you send a pulse into the line, it never comes back.

2. From a circuit theory point of view, a resistor is equivalent to an infinitely long transmission line. For example, if I have a finite length transmission line with characteristic impedance of 50 Ohm, and I terminate it with a 50 Ohm resistor, then a pulse traveling in the line will go into the resistor without any reflected part (i.e. we have matched impedances).

The same thing would happen if we had "terminated" our finite transmission line with an infinite transmission line. Therefore, the infinite line is equivalent to the resistor.

3. Resistors produce voltage noise, called Johnson-Nyquist noise. Therefore, the transmission line must also produce voltage noise.

This noise is required to exist because of statistical mechanics, so a classical theory predicts it. It's actually exactly equivalent to black body radiation!

However, because of quantum mechanics, the voltage noise is still there at zero temperature.

How's that sound?

Feel like an expert now?

Allow me to advertise a question about a paradox that arises if you forget about Johnson-Nyquist noise.

:-) Thanks. It sounds as if what we're seeing are effectively zero point fluctuations in a free electron gas.

@JohnRennie Mmmmm, I dunno about that.

> Johnson–Nyquist noise (thermal noise, Johnson noise, or Nyquist noise) is the electronic noise generated by the thermal agitation of the charge carriers (usually the electrons) inside an electrical conductor at equilibrium, which happens regardless of any applied voltage.

@JohnRennie Indeed.

Note, however, that the quantum noise is there even in a superconductor at near zero temperature.

In the superconductor, the electrons are all in their ground state.

Thanks, I'll have a read around and attempt to get to grips with the subject.

Great.

It's one of my favorite topics.

I still haven't given up hope of understanding what vacuum fluctuations are without actually having to learn QFT.

This is hopefully one more step on that path.

Ahhhh, warning, warning!

You absolutely 100% do not need QFT to understand vacuum fluctuations.