The h Bar

0celoñe7

12:00 AM

Although it's unfair to any decent people in CA.

That vote would be insane.

Both sides would go nuts.

skullpatrol

Ok ok enuf poli sci

Emilio Pisanty

> Two PhD students named 'Theory' and 'Experiment' are working on a project

lolz

skullpatrol

Who graduates first?

I would bet on 'Experiment.'

0celoñe7

@skullpatrol Who would more likely increase GDP?

skullpatrol

Same answer.

In the short term.

Emilio Pisanty

12:11 AM

skullpatrol

I think that's the first time I've seen her in a bathing suit :P

0celoñe7

@EmilioPisanty Do engineers know the term "two body problem"?

Sir Cumference

1:22 AM

My prof used to say: "Star systems work like relationships. When only two bodies are involved, things work out pretty nicely. However, when you add in a third body, things get a lot more complicated and sometimes more fun."

Pretty much got everyone interested in multiple body problems

0celoñe7

How very un-Christian. Gross.

skullpatrol

1:37 AM

whatever gets them interested...

0celoñe7

1:50 AM

@Slereah Huh. If $K$ is a compact space one can recover $K$ if one knows $C(K,\Bbb C)$.

There is a homeomorphism $K\to \Gamma(C(K))=\{\gamma\in C(K)':\gamma\text{ is an algebra homomorphism}\},$ where we give $C(K)'$ the weak* topology.

@ACuriousMind What is the Gelfand-Naimark theorem physicists like to throw around?

0celoñe7

4:09 AM

@ACuriousMind eye roll

0celoñe7

4:29 AM

@ACuriousMind Are monotone classes called "Dynkin systems" in Germany?

0celoñe7

4:52 AM

@JohnRennie greetings

John Rennie

Morning :-)

0celoñe7

@JohnRennie I have discovered a GOAT book, using it to procrastinate

John Rennie

Greatest Of All Time?

0celoñe7

yeah

there are some books I denote as GOAT because they are good from a technical standpoint and also just good to read

John Rennie

Not the band then :-)

0celoñe7

4:55 AM

@JohnRennie Nor the animal...

John Rennie

Goat meat is very nice. A bit like lamb but with more flavour.

0celoñe7

Can't say I've had it.

The Raiders of Las Vegas

I prefer lamb meat over goat because of the tenderness, but yes goat meat is more flavourful.

0celoñe7

@BalarkaSen Do you know an introduction to number theory, leaning analytical?

@JohnRennie You really must play TW3

John Rennie

It does sound really good, but I'm not sure I have a computer it will play on.

0celoñe7

5:08 AM

@JohnRennie surely you can stick a 1060 or better into one of your machines

John Rennie

Yes I have various desktops lying around that I could put a midrange NVidia card in.

I might look around on eBay for a card ...

The Raiders of Las Vegas

"Goat meat" on @Wikipedia: "Despite being classified as red meat, goat is leaner and contains less cholesterol, fat, and protein than both lamb and beef, and less energy than beef or chicken; therefore, it requires low-heat, slow cooking to preserve tenderness and moisture."
https://en.wikipedia.org/wiki/Goat_meat?wprov=sfti1

0celoñe7

"roasted kid"

John Rennie

Yes, I've normally eaten goat meat as a stew, curry, or something similar that has been cooked slowly.

0celoñe7

I will probably get flagged for the meme that comes to mind

the flaggers are pretty crazy

The Raiders of Las Vegas

5:13 AM

So don't do it ;)

0celoñe7

@TheRaidersofLasVegas that's giving in to blackmail.

The Raiders of Las Vegas

5 hours ago, by skullpatrol

Yeah, Big Brother is watching us ;)

0celoñe7

@JohnRennie stop watching

The Raiders of Las Vegas

lol

we mean no harm bro

0celoñe7

I wouldn't go that far

The Raiders of Las Vegas

5:16 AM

behumbole

John Rennie

I don't think I've ever flagged a post in the chat ...

0celoñe7

@JohnRennie math raps youtube.com/…

The Raiders of Las Vegas

When the scifi chat room got shutdown by shog the users went on a drive-by flagging spree.

The English language and usage room got hit pretty hard.

The room hasn't recovered since :(

0celoñe7

what happened?

The Raiders of Las Vegas

where?

0celoñe7

5:31 AM

forget it

user228700

Hi, everyone :-)

The Raiders of Las Vegas

Hello :-)

John Rennie

Morning :-)

Sid

Good morrow!

user228700

5:49 AM

YES! I finished Portal 2 just now!

John Rennie

Was it worth all the effort?

user228700

Totally!

user228700

These are the amazing credits:

user228700

Portal 2: End Credits Song 'Want You Gone' by Jonathan Coulton [1080p HD]

►

skullpatrol

Niiice

user228700

6:00 AM

And now there is the Co-op game to play but I have nobody to play it with so I will save it for another time.

user228700

Gosh, he is so good!

John Rennie

Shopping all done?

The Raiders of Las Vegas

6:23 AM

Never all done with online shopping :-)

user228700

@JohnRennie For the most part, yes :-) [Sorry about that; the water finally came and I needed to take a shower]

John Rennie

Presumably Kochi is a big enough city that the shopping there will be pretty good.

user228700

Definitely, yes. It even has one of the biggest malls in India.

John Rennie

Hopefully the water supply will be better in Kochi given that they have more of it :-)

user228700

Haha, yes :-)

John Rennie

6:34 AM

I find the most interesting shops are rarely in malls, though I guess that depends on what you consider interesting.

user228700

@JohnRennie What do u mean by interesting?

Sid

The best and cheapest things are found in roadside markets

The Raiders of Las Vegas

~~mean~~ consider

John Rennie

@Kaumudi.H not fashion

user228700

Ah, right :-) I don't think I'll be going out of my way looking to buy fashion accessories again.

Sid

6:40 AM

You will find the best things for a certain time period in roadside markets

user228700

Yes, I know.

user228700

I don't know about roadside markets in Kochi though.

Sid

6:57 AM

(heh, we are going to have a President today, about whom we have no idea. We don't know about their views on policies, nor do we know about their political acumen. All we know is their caste. Sigh)

The Raiders of Las Vegas

7:10 AM

and the rich get richer...

Dawood ibn Kareem

8:02 AM

I still can't get my head around the fact that there exists a country in which almost half of the voting population are Trump voters.

The Raiders of Las Vegas

There's nothing to understand really.

Sid

@DawoodibnKareem There were many reasons for Trump-voting. Not just his policies

A major part had to do with how badly people didn't want Clinton rather than how much they wanted Trump.

Dawood ibn Kareem

Yeah, I get that. Doesn't mean I'm capable of wrapping my head around the existence of such a place.

The Raiders of Las Vegas

Common sense is not common.

Sid

(And there is also the fact that he was regularly mocked at by the media.)

Dawood ibn Kareem

8:12 AM

I thought that one the roles of the two large parties was to field the best possible candidate to any presidential election. Then, the voting populace get to choose between the best possible democrat and the best possible republican. I feel that the parties themselves both failed in this role, in 2016.

Sid

Because of his orange-hair or how he looks, etc. I mean, they could have criticized his polices. It's not like there is any shortage of things to criticise there.

The Raiders of Las Vegas

Having a woman as a president was too much of a leap.

Dawood ibn Kareem

I've also come to believe that people outside USA had a very different perspective on the 2016 voting process from people inside USA.

The Raiders of Las Vegas

Yup.

Dawood ibn Kareem

And I've watched far too much Samantha Bee.

The Raiders of Las Vegas

8:15 AM

:-D

Sid

If for example, you would have put an Obama against a Trump. It would have been a landslide. Clinton was nowhere near Obama. She didn't even look decisive on her policies

Dawood ibn Kareem

Sure. I believe Senator Sanders would have taken him too.

But people outside USA didn't really get to witness Clinton's indecisiveness, so it was very much less clear outside USA why she wasn't seen as a viable president.

Sid

Here's my country's conundrum.

1 hour ago, by Sid

(heh, we are going to have a President today, about whom we have no idea. We don't know about their views on policies, nor do we know about their political acumen. All we know is their caste. Sigh)

Dawood ibn Kareem

Life is like a box of chocolates.

Sid

(and we don't even elect them. They are "nominated" by the MPs(Senators))

John Rennie

8:19 AM

Even in the UK, that alleged mother of modern democracy, the democratic process is not working as well as it should.

Dawood ibn Kareem

UK is going through a difficult time at the moment. The issue of who would be the best leader for the country has got itself conflated with Brexit-related business.

Sid

@JohnRennie May took a gamble. It ended in "Mayday" for UK. :P

John Rennie

There is a more fundamental problem than that. Society is becoming dangerously divided.

The Raiders of Las Vegas

Did you @JohnRennie support Thatcher?

Dawood ibn Kareem

@JohnRennie Definitely. I keep thinking that May fancies herself as a 21st century Thatcher. But she's not half the leader Thatcher was.

John Rennie

8:22 AM

I voted for Thatcher in 1979, then again at the next election. However that was the last occasion on which I voted for her.

The Raiders of Las Vegas

I see.

John Rennie

Leaders have a tendency to start thinking they always know best.

Sid

@JohnRennie I would say that is a worldwide problem. It will solve itself in a decade or two.

Dawood ibn Kareem

@Sid How?

John Rennie

That happened to Thatcher and resulted in the poll tax, which was one of the more disastrous episodes in UK politics of the last few decades.

Sid

8:23 AM

Protectionism has increased everywhere. Once, people understand its disadvantages, Globalisation will again increase, leading to more inter-cultural mixing among people

John Rennie

I voted for Tony Blair every time he stood, but then he decided he knew best and led us into the Iraq war.

ACuriousMind

@Sid We don't directly elect our president or chancellor either, it's done by the parliament. I don't think that's necessarily a bad thing.

Dawood ibn Kareem

@ACuriousMind It seems to work OK for you folk though.

Sid

@DawoodibnKareem How long do you think this world can sustain itself with division? People will understand soon

Dawood ibn Kareem

@Sid I disagree. I think it's human nature to find something to be divided about.

ACuriousMind

8:26 AM

@0celoñe7 I don't know what a monotone class is (nor a Dynkin system, unless you mean the diagrams of root systems)

Dawood ibn Kareem

@ACuriousMind Since 20 January 2017, much of the world outside USA have considered Angela Merkel to have inherited the title of "leader of the free world".

The Raiders of Las Vegas

Leaving out the USA is leaving out way too much.

ACuriousMind

@DawoodibnKareem The funny thing is that she's not even our head of state - the chancellor is formally the fourth-highest position in the country (though arguably the position with the most power)

Sid

One of our former Presidents(Dr. Abdul Kalam) wrote a book called "Ignited Minds". In that, he jots 4 important stages of countries. First, the stage after independence in which she works to be better. Then, the "warrior stage" where nationalism increases amongst people. This in early era led to war. Now it leads to internet chest-thumping(>70% of the world is in this stage). Then, comes the "Statesman stage" where countries collaborate more and are far more sober.

(I forgot the 4th stage though. It was something important..)

Dawood ibn Kareem

@ACuriousMind I think people outside Europe don't understand the distinction between Chancellor of Germany and President of Germany. I'm slightly embarrassed to admit that I don't even know who the President of Germany is. The world sees Angela Merkel as your leader, regardless of what her job title is.

Sid

8:29 AM

@ACuriousMind Merkel is probably the tallest leader of the world as of now.

ACuriousMind

@DawoodibnKareem We even got a new president a few months ago! But yeah, his duties are mostly ceremonial, comparable to the monarchs in constitutive monarchies

John Rennie

Humans are generous and benevolent when they feel secure and their standard of living is rising. They are selfish and xenophobic when they feel insecure and their standard of living is falling. I think this is all you need to understand international politics.

The Raiders of Las Vegas

@JohnRennie this is the so called "poison" of power.

Sid

@ACuriousMind Same here. There is even a running joke around these parts that our president simply puts his signature on stuff and distributes prizes to kids. :P)

ACuriousMind

Though he does hold political power in that he can technically refuse to sign laws the parliament passes. That has happened eight times so far

user228700

8:32 AM

@JohnR: Hello, again! :-) Are u terribly busy atm?

John Rennie

@Kaumudi.H No, I've finished work and am vaguely contemplating having another coffee. So now is a good time.

user228700

Haha, OK. Gchat?

The Raiders of Las Vegas

Have fun guys.

::scrambles to hack into Gmail::

:P

John Rennie

we only move to gchat for stuff that's too boring to pollute the PSE chat with.

Fixing computers, etc.

Dawood ibn Kareem

@JohnRennie None of us will ever know whether that's the truth.

Sid

8:37 AM

^

The Raiders of Las Vegas

I was kidding

user228700

Or to post 10 pictures of food. (@Dawood: You'll remember :-)

Dawood ibn Kareem

But we like your food photos!

John Rennie

OK, OK, we're really plotting the overthrow of the world!

Dawood ibn Kareem

@JohnRennie Oh, well that's all right then.

Sid

8:38 AM

@JohnRennie That's a good idea. Which country to start with first? North Korea?

The Raiders of Las Vegas

Start with Stack Exchange.

Dawood ibn Kareem

I think you have to start small and work up. What's the smallest country? :-)

Sid

Vatican City.

ACuriousMind

@DawoodibnKareem I don't think you want to start with micronations ;)

2

Dawood ibn Kareem

Right. Tomorrow, John and Kaumudi are going to overthrow the Vatican.

Sid

8:40 AM

Also, Putin is another leader the Americans(read: Trump supporters) have taken a sudden liking to.

Dawood ibn Kareem

Saturday, it'll be Monaco and San Marino.

Mithrandir

@DawoodibnKareem Hmm. You may find that a large percentage of the world won't be happy with that...

Dawood ibn Kareem

@Mithrandir I think Doctor Rennie would make an excellent pope.

ACuriousMind

Who's professor Rennie? :P

Sid

Yep! JR is wise!

John Rennie

8:42 AM

Given theway popes have behaved over the last millenium I'm not sure that's a compliment :-)

Sid

Also, was there some flag raised or something?

John Rennie

I haven't seen any flag notifications

Sid

Yeah, well.. I don't exactly see Mith around these parts. :)

Mithrandir

Nah, no flags.

Sid

@Mithrandir spying? :P

Dawood ibn Kareem

8:43 AM

@JohnRennie All the more reason to overthrow one.

Mithrandir

No, you know very well that that's plum :P

The Raiders of Las Vegas

Plum pudding?

Sid

@DawoodibnKareem Then, Liechtenstein, Maldives on Sunday.

Mithrandir

@TheRaidersofLasVegas nope, Plum the spy

The Raiders of Las Vegas

I see.

Perhaps they're starting with microscopic nations :P

ACuriousMind

9:01 AM

@0celoñe7 Hm? I think you either mean the GNS construction and the statement that the sum over all GNS constructions contains all representations. or what Wikipedia actually has under Gelfand-Naimark theorem, i.e. all C*-algebras are operators on a Hilbert space.

The Raiders of Las Vegas

Thanks for stopping by @Mithrandir

Mithrandir

I'm always happy to come join another room ;)

The Raiders of Las Vegas

y'all are welcome here anytime

:-D

Speaking of which we need more people to sign up for Jim's AMA.

chat.stackexchange.com/rooms/info/71/the-h-bar?tab=schedule

14

Q: July 2017 Ask Me Anything with Jim (long may he reign)

I'm Jim and if you haven't heard of me then, whatever "it" is, you're probably doing it wrong (I'm always self-advertising). I've been asked to do an AMA several times and I'm finally getting around to it. We'll get to the timing further down the page. About Jim Academic I have a masters degre...

discussion

Dawood ibn Kareem

He's very humble then?

Slereah

Someone deleted my comment :(

A question asked for the origin of the C asymmetry, so I commented itisamystery.com

The Raiders of Las Vegas

9:17 AM

peeps don't like mystery, i guess

Dawood ibn Kareem

Sites that start making loud noises without user agreement should be removed en masse from the Internet.

ACuriousMind

@Slereah Uh, it's still there, no one deleted it.

Dawood ibn Kareem

What does this mean? "My interest is in understanding how they came to be the way they are. Knowing why they are the way they are is not really my concern."

ACuriousMind

It means "how" and "why" are terrible words :P

The Raiders of Las Vegas

More context please.

Mithrandir

9:23 AM

There's a difference between why I'm a mod and how I became a mod. Why I became a mod is because I wanted to help my site; how I became a mod is that an employee changed my status.

Slereah

I only want to become a mod to ban JD

The Raiders of Las Vegas

Why?

ACuriousMind

@Mithrandir That distinction can apply to intentional agents, but it's more difficult to make a meaningful distinction for unliving processes

@Slereah tut-tut (I don't think you want to continue that line of conversation)

Dawood ibn Kareem

OK, fair enough. I'll go and practise my English.

The Raiders of Las Vegas

Basically, "why" is a much deeper question.

You can ask it infinitely many times...

Dawood ibn Kareem

9:29 AM

@TheRaidersofLasVegas Let me guess. Young children?

The Raiders of Las Vegas

Exactly.

ACuriousMind

:38893445 I think in physics, there is really not much distinction between "why" and "how", unless you want to make "why" into a question physics can't answer.

Slereah

@ACuriousMind You'll never stop meeee

Dawood ibn Kareem

But why Daddy?

The Raiders of Las Vegas

But also it leads you down the "rabbit hole."

Dawood ibn Kareem

9:31 AM

Sometimes, asking "why" lots of times shows you that you don't understand something as well as you thought you did.

John Rennie

So what is the reason for the failure of C symmetry?

And if you answer with a link to that web site I'll use my new status as Pope to excommunicate you!!

Dawood ibn Kareem

@JohnRennie You're not pope until tomorrow.

The Raiders of Las Vegas

@DawoodibnKareem Yup, that's a part of the Feynman method of studying.

ACuriousMind

@JohnRennie You realize you can only excommunicate Catholics?

Dawood ibn Kareem

@ACuriousMind That would be the first thing for him to change.

John Rennie

9:39 AM

I think the Pope could excommunicate anyone. For non-Catholics it would just mean they could never become Catholic.

Dawood ibn Kareem

@TheRaidersofLasVegas Why does Feynman get the credit for something 3-year-olds have known for millenia?

John Rennie

Henry VIII of England got excommunicated for setting up his own church.

The Raiders of Las Vegas

@JohnRennie is excommunication the same as putting someone on "ignore?"

Dawood ibn Kareem

@TheRaidersofLasVegas It means talking to the woman who used to be your wife.

John Rennie

@TheRaidersofLasVegas I think it forbids all Catholics from communicating with the offender

So it would be like telling all the chat room users to put the offender on ignore.

The Raiders of Las Vegas

9:41 AM

I see.

Dawood ibn Kareem

You'd have to wear a sign round your neck, saying "I've been excommunicated" in case a Catholic talks to you by mistake.

The Raiders of Las Vegas

@DawoodibnKareem That's communicating with your ex.

ACuriousMind

(In case someone is actually confused about this: The "communication" refers to the religious notion of communion, not to your usual communication.)

The Raiders of Las Vegas

Excommunication

Excommunication is an institutional act of religious censure used to deprive, suspend, or limit membership in a religious community or to restrict certain rights within it, in particular receiving of the sacraments. The term is often historically used to refer specifically to Catholic excommunications from the Catholic Church, but it is also used more generally to refer to similar types of institutional religious exclusionary practices and shunning among other religious groups. For instance, many Protestant denominations have similar practices of excusing congregants from church communities, while...

Dawood ibn Kareem

@JohnRennie I think you'll find that Henry VIII was excommunicated for desecrating the grave of Thomas à Becket.

John Rennie

9:46 AM

This question is not a duplicate

The alleged duplicate (which has a splendid answer if I may say do :-) is about the oldest date carbon-14 dating can measure. This question is about the most recent date it can measure - exactly the opposite!

ACuriousMind

@JohnRennie I think @Qmechanic misread what "earliest date" is supposed to mean

Alas, reopening it now seems a bit pointless since OP has posted a better explained folow-up

John Rennie

I thought the follow up was rather poorly written. I'd reopen the original and close the follow up.

I've edited the original question to clarify what it is asking.

Ooh, my new wireless keyboard has just arrived. Time to play!
Sadly my new 512GB SSD has not arrived. Oh well, there's always tomorrow.

Emilio Pisanty

@ACuriousMind if anything, old should be closed as dupe of the new, but frankly, the old one is better

alas, I cannot re-vote to reopen

ACuriousMind

I've closed the new as a dupe of the old, and reopened the old one since I'm pretty sure Qmechanic simply misinterpreted the meaning of "earliest"

Emilio Pisanty

@ACuriousMind excellent

John Rennie

9:58 AM

@ACuriousMind Thanks :-)

Yashas

10:36 AM

If I take a gun which shoots 1kg balls and watch the experiment from few light years away, will I see an interference pattern due to the wave nature of the balls?

John Rennie

No, because macroscopic objects decohere too fast.

Yashas

went above my head

John Rennie

16

A: Validity of naively computing the de Broglie wavelength of a macroscopic object

If you've read about optical diffraction experiments like the Young's slits, you may have noticed they all refer to coherent light. This is the requirement that all the light in the experiment is in phase. If you aren't using coherent light you won't observe any diffraction because different bits...

Yashas

aw too complicated for my brain :D

idk what coherence means for the particles of the bullet

The Dark Side

11:07 AM

Hello bar mates.

Quick question: Any non-mathematical, anecdotal reference for the development of Quantum Mechanics?

i.e. transition from classical physics to primitive quantum theory, and subsequently to the 1925-26 version of QM ?

Other than Inward Bound by Pais?

John Rennie

22

Q: Good book on the history of Quantum Mechanics?

Can anyone recommend a good book on the history of Quantum Mechanics, preferably one that is technical and not afraid to explain the maths (I did a degree in Physics many years ago) and also that explains the developments using the technical language of the time rather than using treatments as we...

quantum-mechanics resource-recommendations history

Mostafa

@JohnRennie I guess @Yashas is talking about a thought experiment using hypothetical (single) quantum particles with that mass.

ACuriousMind

@Mostafa The use of "gun", "balls" and "bullets" seems to indicate he isn't

The Dark Side

So, is it that there is no significant authoritative alternative to Pais?

John Rennie

@TheDarkSide The Age of Entanglement possibly.

The Dark Side

11:19 AM

@JohnRennie Thanks, but the description seems to indicate it is a rebirth story and not a birth story.

By Birth, I mean:

10 mins ago, by The Dark Side

i.e. transition from classical physics to primitive quantum theory, and subsequently to the 1925-26 version of QM ?

Ron gave a list in that answer, but that's a Ronesque list.

John Rennie

Well, the review says: Gilder, remarkably well-informed, delivers a comprehensive history that begins with early 20th-century giants Planck, Bohr, Heisenberg, Schrödinger and Pauli.

The Dark Side

@JohnRennie Ah yes. Missed that sentence.

Worth peeping into.

Perhaps also worth adding as an answer into that book reference question.

Mostafa

@ACuriousMind but in that case the question wouldn't involve much interesting physics, as JR stated above.

and such "extreme" thought experiments are usually designed to shed light on an interesting physical phenomenon in a stark way.

John Rennie

@TheDarkSide I would want to read the book before I'd be prepared to post it as an answer. Since I'm largely uninterested in the early history of quantum mechanics that isn't going to happen :-)

ACuriousMind

@Mostafa It doesn't involve any interesting physics for the case of a very massive particle either :P The only role mass plays in the double slit is determining the deBroglie wavelength.

The Dark Side

11:27 AM

@JohnRennie It may be a useful pointer for someone who might want to read it. Anyways it is your choice.

Thanks @JohnRennie.

user685252

for me, what makes physics interesting is how the uninteresting parts relate to each other to make it interesting

that could be purely a matter of presentation though

Mostafa

There are some interesting physics (but depends on your definition of interesting too).
For example, see the last line of the page 181, and the two following pages (182-183) of Shankar's QM (2nd ed.), where he talks about the results from applying quantum mechanics to a 1g macroscopic particle, and how it is connected to classical mechanics.

ACuriousMind

@Mostafa Ah, but then we're in the macroscopic regime again - the interesting things appear because of that and not because of the mass

Dawood ibn Kareem

11:52 AM

@user685252 Uninteresting parts?

Anonymous

Anyone here used Chegg ? Are the textbook solutions and the Q&A solutions legit/worth buying?

user685252

@DawoodibnKareem yeah, the definitions and stuff

Dawood ibn Kareem

Oh, I'm always fascinated by definitions.

user685252

memorizing them can be a pain though

verbatim

Dawood ibn Kareem

No, that's where all the fun lies.

user685252

12:06 PM

but is it interesting fun?

as compared to the "big picture"

hi @rob

rob

@user685252 Greetings

user685252

are you planning on coming to Jim's AMA?

or perhaps, you could do one? @rob

Dawood ibn Kareem

@user685252 Oh, heck yes.

rob

@user685252 I hadn't thought hard about attending because usually the group chats are at a bad time for me.

But that one is Tuesday afternoon in the US. Maybe I'll make it.

user685252

cool

rob

12:18 PM

@user685252 I have a little ambivalence about doing an AMA myself. I'm a slow typist and so live chat isn't a thing that I'm great at. But I could possibly have my arm twisted if there were a lot of interest.

2

user685252

ok, see how you like Jim's @vzn^

and speaking of @Jim :-)

Jim

my first question is why aren't you all speaking of @Jim more often?

user685252

:-D

Jim

@rob also, it's at 8am EST. That's not the afternoon in any part of the US

2

rob

@Jim Meta still says 1200z?

@Jim Aha: I'm an idiot.

2

Emilio Pisanty

12:50 PM

22

Q: A Jim for all seasons

Note: This contest is currently inactive. It may be resumed again in the future. So there has been a recent influx of new Jims (meaning maybe 2 in a while). Now, we all know that I am the one true Jim, lord of all other Jims, but nonetheless it gets confusing when someone pings Jim and Jim gets ...

discussion

(relevant background)

physics.stackexchange.com/election/3#post-282705

0celoñe7

1:03 PM

@Jim lack of intelligence

0celoñe7

1:15 PM

@Blue They are legit, but I haven't bought them myself

If you have friends who have it, just ask them for specific solutions.

Whether they are worth buying depends on how badly you need them, of course.

Anonymous

@0celoñe7 I'm working through Liboff and Shankar myself (it's not in my uni course). So sometimes I might need solutions to the problems if I'm stuck. I might ask on stack exchange but again hw type questions are not really suitable here. Also, I don't know if any of my friends has Chegg subscription. 15$ per month isn't much but I wanted to know if the solutions they give are thorough and not just random noobs answering them. BTW have you seen any of the Q&A solution yourself? Did it help you?

Slereah

"A theorem of Geroch shows that a manifold with a $C^2$ metric is necessarily paracompact"

I wonder if there are non-paracompact manifolds with $C^0$ metrics

I don't think so though

They don't even have continuous nowhere vanishing vector fields

0celoñe7

@Slereah why are you reading HE again?

Slereah

It's not HE

0celoñe7

@Blue They are thorough.

Anonymous

1:28 PM

@0celoñe7 Ah, thanks!

0celoñe7

@ACuriousMind re Gelfand-Naimark: drugs were extra strong and I was mixing things up. I "learned" that any commutative C* algebra is isomorphic to the space of continuous functions on a compact space. About halfway through the proof of that I realized I already knew that.

@ACuriousMind monotone class in the sense of measure theory.

Slereah

uridimma.hopto.org/misc/Regge/index.html

Collisions don't seem to work that great

not sure why

0celoñe7

@Blue They are not used submitted, as far as I know.

skullpatrol

Did you catch up on your sleep?

ACuriousMind

@0celoñe7 I don't know measure theory

0celoñe7

1:44 PM

@skullpatrol yeah

skullpatrol

cool

0celoñe7

90 today with 70% humidity

bruh

skullpatrol

Yeah, that kind of humidity is nasty when it's hot.

AccidentalFourierTransform

out of curiosity: is $f\in L^1\cap L^\infty$ a sufficient condition for $\hat f\in L^1$?

I guess we may also need to require continuity?

Yashas

@Blue when does ur college start?

Constantine Black

2:17 PM

Good afternoon to all- at least from my behalf. Could I ask a question here on chat on how to calculate an invariant Feynman amplitude-in fact I need some help on clarifying a certain detail. Any quick help would be appreciated. Thanks.

ACuriousMind

@ConstantineBlack Just ask your question - if someone can and wants to help you, they will. It's been a while since I had to compute a diagram though, so no promises from my side

Constantine Black

2:33 PM

Ok, thanks. The interaction lagrangian is a Yukawa isospin symmetric term, that is $\bar \psi \phi \cdot \phi \psi $, where $\psi $ stands for the nucleon( it has two components, the proton and the neutron which are Dirac spinors) and is represented in the fundamental representation of SU(2) and $\phi$ stands for the pion, a scalar triplet in the adjoint SU(2) representation.

We have to calculate on tree level a nucleon-nucleon scattering, let' s say two protons: so we have some space integrals that contain something of $(\bar \psi \phi \cdot \phi \psi)^2 $.

One standard way I see for performing the calculation is to make first all the calculations between the matrices and the vectors, then we get to square four terms for the interaction of protons neutrons and pions. The question is if there is a more straightforward way on performing the calculations without analyzing explicitly all the terms to their components: calculate the amplitude for a general nucleon-nucleon state.

I have the bad habit of writing too much:), sorry. The last paragraph is the main problem, if there is a straightforward way on calculating a tree level invariant amplitude for the isospin symmetric yukawa nucleon-nucleon interaction.

AccidentalFourierTransform

the most straightforward way to calculate anything is to draw Feynman diagrams

but I cannot be any more specific than that

Constantine Black

@AccidentalFourierTransform Yes, I know. But I have to show the Wick contractions and all that, so before using a Feynman diagramm( which happens for the pseudo-scalar interaction) I have to show how the integrals are calculated. Thanks anyway:).

AccidentalFourierTransform

oh so its an exercise

exercises tend to be stupid anyway

I dont think you will be able to compute that efficiently

just write down the terms, and calculate all the contractions, one by one

there is no "trick" I can think of

0celoñe7

@AccidentalFourierTransform Btw...

math.stackexchange.com/questions/206362/… is true if "integrable" means $L^1$, not $L^2$

Constantine Black

Its for my bachelor thesis. The first part consists of constructing the isospin symmetric yukawa interaction based on isospin symmetry and then calculate the amplitude and the second part is to construct the chiral lagrangian of the Chiral Perturbation theory and use it again at tree level to calculate the amplitude.
Anyway, I can do it as you say, without tricks( I have already done it in fact) but I thought that maybe a more elegant way exists.
Thanks.

J. Doe

2:49 PM

Hello. I have a quick question most of you probably know but I can't get my head around. Say you have a mold material with a low thermal diffusivity (plastic) vs a mold material with high thermal diffusivity (silver). You freeze the same material in the same freezer in both of these molds. Which will be frozen faster? Will it be the one with the high or low thermal diffusivity that freezes faster? I'm having trouble understanding this concept. Thanks for any help

0celoñe7

@J.Doe the silver will get colder faster

J. Doe

@0celoñe7 ok thanks!

Emilio Pisanty

@Slereah is initialize-as-random constrained to have zero center-of-mass momentum?

if not, it'd be pretty helpful

Anonymous

@0celoñe7 What does that mean: "they are not used submitted"?

Anonymous

@Yashas I don't really know. Probably first week of August. They'll update on their website.

Emilio Pisanty