@0celo7 Googling "Bohr stripping criterion" strongly suggests to me that it is not "inertia" that strips off electron, but shooting the to-be-ionized particle into some kind of matter, where the outer electrons then are stripped off by interactions with the matter because they are weakly bound.

@ACuriousMind Yes, just asked a grad student overlord

Can you link what you're looking at?

This, this, this

All hits from the first two Google pages :P

Huh, didn't find any of those.

@0celo7 you need a googling class

maybe

@ACuriousMind Can you please link the springer site for the first link

If it's a book, I might want a copy for the lab

No, because I found that pdf link directly.

Wonder if I can charge the prof

rd.springer.com/chapter/10.1007%2F978-3-319-05564-0_1

@ACuriousMind That wasn't so hard...

Dammit Springer. It won't download.

> According to Bohr´s classical atomic model we assume now that the electrons move on periodic orbits.

@dmckee I found a powerpoint written by two ORNL physicists in comic sans.

I don't think condensed matter people give a shit about proper formatting :P

Ah, I see you have made good on your promise to prepare that meta post before the next chat session, @DavidZ!

@Danu Damn, QM prof wants me to call him by his first name

Strange...

@ACuriousMind yeah, just made it :-P

I figure it's about time we had a plan

@0celo7 at least in the US, first-name address is very common in academia, whenever the relationship is closer than that of a typical undergrad student and their instructor.

for whatever that's worth :-/

Hmm, although the post has the "featured" tag, I don't see it in that box on the main site. Caching or bug?

My guess is caching

@DavidZ I'm a freshman

The box probably doesn't update more than once every 6 hours or so

@0celo7 yeah, still, I suppose you're not the typical freshman who is nothing more than a face in class

and in any case, some people just prefer first-name address

@DavidZ I guess, I'm trying to take grad QM with him next semester

I summon @JohnRennie to this place.

@0celo7 that qualifies

@DavidZ otoh my math advisor, with whom I meet weekly, likes being called "Dr.", I guess

Yeah, sounds like just personal preference. It varies from one person to the next.

BTW folks who are here early for the chat session, I'm going to try setting an agenda this time. Anything in particular you want to be on it?

@DavidZ Are we authorized to issue fatwas?

I dunno

SE rules do not recognize fatwas though

@barrycarter Why would you want us to issue muslimic legal advice?

I propose we ban using relations to define functions

@ACuriousMind wow so intolerant

@0celo7 How else are you going to define them?

@0celo7 ?

@ACuriousMind arrows

Something must be done about @WillO

thin wa's?

medium size wa's?

@0celo7 That's not an answer. What is your definition of a function? (The arrows in category theory are explicitly not functions, you can't feed arguments to them)

BBW wa's?

OK, what do people normally discuss at these events?

Sometimes it's just like what people discuss any other time, we just have a bigger audience

Other times we discuss site policies

Sometimes we discuss recent physics news of interest

@ACuriousMind take two sets $X$ and $Y$

@DavidZ Well, there also was this meta post, but the lack of comments indicates there isn't much need for discussion

a function assigns ONE $y\in Y$ to $x\in X$

@DavidZ I'd really like to discuss if we can get some canonical relativity answers.

@0celo7 Define "assign".

@ACuriousMind Yeah, that one seemed pretty straightforward

@barrycarter OK, noted

@ACuriousMind Self-evident.

@DavidZ And I think we should make it easier to find an FAQ... it might help the poor students who come here thinking they can get homework help.

@0celo7 No, the reason we need the "relation definition" of a function is that there are subtleties to the existence of function even if we can write down the "assignment rule", cf. e.g. existence of choice functions.

@0celo7 That's a reasonable definition, but why not give it as a limiting case of a relation?

@0celo7 A relation pairs up some members of X with some members of Y.

Functions are like monogamy.

@barrycarter Boring, you mean?

@barrycarter sure. We'd need some specific ideas, of course.

@ACuriousMind I was going to say "relations are like orgies", but thought better of it.

That might be one to bring up as a meta post at some point in the future.

@barrycarter I don't think we can do that on this site, that's something for Meta Stack Exchange

@DavidZ Go through the list of closed homework questions and see what they ask. Things like "I'm launching a projectile and..." or basic Ideal Gas Law stuff. I want to say "look at the FAQ first, come back if you still don't understand"

@ACuriousMind what

is ACM a polyamorist?

@0celo7 That's a joke. Mostly.

@ACuriousMind Why meta? The one thing I dislike about SE is the lack of an easy-to-find FAQ.

I've tried to create one for astronomy, but I think the concept needs to expand.

@barrycarter Yeah, but it is something that affects all of SE, no? I.e. it's not specific to our site

And such things go to Meta Stack Exchange

Though I see your point.

We'd need a "FAQ" link or something.

@ACuriousMind mostly?

polyamorist confirmed

I have to say, that's a major no-no for me

even worse than long hair

But this is the way many sites handle the problem of newbies: put up an FAQ and direct newbies to it. Say "read this, take two asprin [sic] and come back if you still have issues"

Polyamory is becoming quite popular.

I'm a theoretical polyamorist.

Looking to do a physics PhD btw peeps

If you have anything to recommend I'm all ears

@Slereah not GR

@DavidZ OK, I'll also propose the general topic that seems to have come up in meta: best way to handle people who want homework help. Pointing them to that list of resources would be a good "canonical" thing to do.

no one cares about GR in the physics world

If you are a kindly old professor and can take me for it and give me free money even better

Yeah not a lot of GR offers

@barrycarter Are you aware we have the help center? It's right behind that help link in the top right corner

I should go back to doing some QFT

@Slereah How do you feel about astronomy?

I don't know all that much astronomy

I know the sky is up, mostly

@barrycarter that's really broad, but sure. BTW you'll have to help lead these discussions too :-P

@Slereah Well, almost up, it turns out.

@Slereah But do you love astronomy? Or do you also not like it.

Kinda eh

@DavidZ Well, yes, it's a big question but I think it can be handled as a "what to do" thing

I am kind of a theory fellow

@barrycarter We have such a list on meta already. When we rephrase the close reasons at the end of reforming the policy, we could put a link to it in the close reason.

I don't want to look at datasets

@ACuriousMind I was actually not aware of that link, thanks. That's more "meta" information about the site, I meant an actual list of questions. When people "ask question", maybe a link to frequently asked physics questions?

@DavidZ Well, I'm a little shy in chat, but OK ;)

It's an experiment, we'll figure it out somehow

@Slereah There's theory in astronomy, and datasets can lead to theories, but you're looking for something else, I take it?

Depends on what you mean but probably yeah

@ACuriousMind I realize most SE sites have a "FAQ" in the sense that you can look at the most frequently closed questions for duplicates, but you can hardly expect newbies to find that.

@barrycarter Oh, you already get a bunch of "similar questions" when you type in a question. They're actually quite useful if you take the time to read through them. Many people asking obvious duplicates just don't seem to do that

@ACuriousMind True. Perhaps we can do things that motivate people to do more site poking before asking.

Hello, is anyone working in some company, as in any non teaching jobs? I wanted to ask some questions. Can someone please help?

@Slereah How about creating your entire fictitious universe with its own consistent set of laws?

As with many other issues, user motivation is key, but also hard to influence :)

@ACuriousMind Yes, and the perfect newbie wouldn't need it, but sites usually do try to push imperfect newbies into doing the right thing.

A code word in the FAQ that confirms you've read it might be a bit much, but something on that order.

Would be neat

Tho I should probably say that ideally I kinda need the thesis to be somewhat paid

@Slereah Then, create a portal to that universe, and get a PhD there :P

Is there any value in problem solving skills that we learn by solving textbook problems while learning physics? Do those skills alone carry any value to a person who hires you?

Not sure I can live 3 years on my moneys :p

I wanted to develop some sort of AI that could solve physics problems on its own

@Iota I would say problem solving in general is a valuable skill.

There is some GR recently tho but it's mostly G wave stuff

I think I need to study up on my QFT if I want some decent thesises

Thesii

@barrycarter I would have been very annoyed if I had had to read through some physics FAQs before asking my first question here because I was pretty sure it's not a frequently asked question :P

And now I'll be off for some time, I have to cook some food

ahh where did the last 5 minutes go :-P

and bye @ACuriousMind

I did find a nice looking thesis proposition but it is 3 years old and in Corsica

I am worried about the paying part there :p

I'm trying something different today: we're going to set an agenda for the discussion, with estimated time caps on each topic of discussion.

(for when our chat session starts) Please keep the room clear of other topics while the session is in progress.

Do we actually have newcomers

@DavidZ Uh, I think it starts in an hour.

I don't know. (That's why it's a time cap)

There are 15 people here.

It does?

At least, that's what the schedule tells me

It's currently 1504 UTC

huh, that's weird.

Never mind then.

Did you remember to spring forward? :P

I could have sworn I got a notification saying that it started at this time.

@barrycarter as if by magic John appears

@JohnRennie Mr Rennie!

Never mind then. Chat session time in 1 hour.

Did SE remember to spring forward? We might be in that weird period of time where some countries are on daylight time and others aren't.

Now I'm really off :D

There's no DST transition in China

@JohnRennie I edited my question. It seems like no choice of t=0 yields the transformation I seek. I realize that wasn't exactly what your comment answered, but it's sort of related.

@DavidZ You're in China?

Yep

@DavidZ Taiwan or Red China?

"Red China"? I thought they stopped saying that in the 50's :-P

But yes, mainland China

@DavidZ Oh, BTW, I probably shouldn't lead any chat topics, since I tend to be intermittent.

@DavidZ A little later than that, but, yes, it's a bit dated.

Maybe not so much "lead" as "prompt the discussion" - the idea being that since the topic is your idea, you're likely to be more prepared with ideas and questions than anyone else

@DavidZ OK, but I tend to wander aimlessly (in real life), and I think focused chat should be real-time. I'm just saying: don't rely on me.

Duly noted

@barrycarter there's nothing sacred about the Lorentz transformations. They are a special case where the transformation is between two inertial frames. They won't tell you anything useful if one or both frames is accelerated.

OK, now a personal question not limited to physics.SE. I tend to comment-answer a lot of questions, because I feel unworthy of actually answering. However, this means I don't get notifications when people update/comment on the question. I can star the question but that doesn't really help. Aside from answering more and commenting less, is there a solution?

@JohnRennie OK, but we agree that before I accelerate and after I'm done accelerating, I'm in an inertial frame, right?

I think the correct term is "best China"

@Slereah You're there too?

No

I actually thought (seriously) that mainland China's connection to the Internet was fairly limited, and that they didn't interact much with other countries (except for Hong Kong, which is special).

@barrycarter correct. But to expect the Lorentz transformation of (-10,-10) to do anything useful is futile. If the twin had been moving at -0.8c forever, i.e. had never accelerated, then they would have been at the transformed point (-30,-30).

However they did change frames so the transform leads to a frame they weren't in at the time.

@JohnRennie OK, that almost makes sense. Let's make it easier. One guy remains stationary, the other guy's been moving at 0.8 c the whole time. When they pass, they synchronize to t=0. Can that be done?

Yes, that's the point of my third diagram in my recent answer.

You start at the meeting point and work back to the moment the acceleration ceased.

@Slereah that's North Korea :-P

@JohnRennie Sorry, I'm creating a third "twin". This one remains 10 light years away from Earth always and forever. I want to synch times when the traveling triplet passes HIM.

@barrycarter that's true, but foreigners and skilled workers in particular tend to have access to better-than-average facilities

@JohnRennie In other words, I want to pretend that one triplet has always been moving at 0.8c

OK. I assume you want a way for the travelling twin to synchronise clocks with Earth even when they are 10 lyrs away. Yes, having a third observer is a way to do this.

@JohnRennie Well, no, I just want him to synch clock with the twin who is 10 ly away.

Yes, but the twin 10 lyrs away is in the same inertial frame as Earth, so their clock can be synched with the Earth clock and will remain synched.

So by synching with the 10lyr observer you are effectively synching with Earth.

@JohnRennie True, good point. But I'm hoping I don't need that for the problem. What I'm saying is: when the never moving twin sees Earth at year 2000, he assigns it coordinates (-10, -10), right?

When the forever traveling twin passes him, what coordinates does he assign Earth at the year 2000?

Let's be cautious with that sees word. The 10lyr observer working in his coodinate system assigns Earth the spacetime position (-10,-10) when his position is (-10,0).

Good, right. What they're seeing is light delayed. OK, now how about the traveling twin? What coords does he assign Earth at the year 2000?

But the coordinate system of the 10lyr observer is the same as Earth apart from adding 10 to all the x values. Why introduce a third coordinate system?

@JohnRennie Oh, I think of never moving twin as my primary observer, but we don't have to. You want to make Earth the observer and have the never moving twin at (10, 0)?

Sorry, (10,0) obviously.

I don't see what you're trying to achieve by introducing the never moving twin ...

@JohnRennie I'm trying to show that when always moving twin passes him, they assign coordinates of (-10,-10) and (-6,-6) to the same event.

Even if there is no acceleration involved.

As you pointed out, acceleration breaks Lorentz transform (ie, it's no longer necessarily valid)

Yes, so what?

OK, so somewhere in this problem, we need a Lorentz transform that converts (-10,-10) to (-6,-6), yes?

No. The LT from Earth to travelling twin of (-10,-10) is (-30,-30) - actually I haven't checked that but you claim it's true - so the LT from the travelling twin to Earth of (-30,-30) will be (-10,-10).

@JohnRennie OK, so you're saying that there is no event in this problem that one observer sees at (-10,-10) and another sees at (-6,-6)?

And the LT from the travelling twin to Earth of (-10,-10) will be (-6,-6). Likewise the point (-6,-6) in the earth fraem transforms to (-10,-10) in the twin frame.

@JohnRennie OK, hold that first thought. You're saying (-10,-10) translates to (-6,-6) for the traveling twin?

For 64k rep points and the title of "Relativity Champion", @JohnRennie ... name that transform.

Question for all: can rep points be traded like currency?

No

I think I might've broken @JohnRennie

@ACuriousMind What are bounties?

@0celo7 That's what I was sort of thinking, but this would be more of a direct trade of points, not open bounties.

@0celo7 @ACuriousMind you could cheat and use bounties for currency transfers, but I'm guessing that's a no-no

@barrycarter There are some meta posts where that is discussed and forbidden, I think

@ACuriousMind It is FORBIDDEN. Now I sort of want to do it.

And I mean give away points, not get them.

@barrycarter Discussing it in public chat might not be the best start for that ;)

Yes, I need to work on stealth.

The mods never come here.

Only to ban me

There are signs up here that say "Buy a gun for someone who can't, spend 10 years in jail". Until then, I'd never wanted to buy a gun for anyone.

Why wouldn't you want to buy a gun o.O

@ramsay It's conventional to define the potential energy as zero at infinity. So when you see the equation for the Newtonian potential energy $U = -GMm/r$ this implicitly assumes the energy is zero at infinity.

@0celo7 For someone else?

@barrycarter I've realised I have no idea what you're trying to do.

You said anyone

@0celo7 That generally excludes self.

That includes yourself

@ACuriousMind there are ways to detect that stuff that don't rely on people talking about it

@JohnRennie OK, so you withdraw your earlier statements?

@DavidZ I'm going to start an entire underground market for SE points. 10% commission is all I ask.

@DavidZ I know, super secret algorithms and stuff ;)

@JohnRennie but what happens to kinetic energy?(because you have written total energy is zero), thanks for replying

Describe things to me in the Earth frame. Are you saying you have the traveling twin (TT) moving towards Earth at v = -0.8c$ and the TT passes through the point (-10,-10)? So they meet at (2.5,0) i.e. 12 years later?

lol

@JohnRennie Let me back up one step. Do you agree that, at some point in this problem, we need a transform from (-10,-10) to (-6,-6). I believe you said that yourself above earlier. And I'll even allow you to flip signs on either 10 and either 6.

I'm not agreeing on anything until i see a spacetime diagram, or have one satisfactorily described to me.

I know people have exchanges for virtual currencies, but never seen one for something that is completely worthless.

@JohnRennie Revisionist! So, just to confirm (and not in a bad way), you retract your earlier comment?

The sheer pointlessness of creating a non-monetary underground exchange for worthless currency... excites me.

@JohnRennie OK, never moving twin is 10 ly from Earth at the year 2010. He asks "at what coords did light leave Earth in the year 2000?". Do we agree the answer to this is (-10,-10)?

@barrycarter if I may offer an outsider's perspective, I don't think "retract" is a very useful word to be using in a discussion like this. When you talk about retracting, whatever your intentions, it basically limits the other person to two options: either they retract their earlier statement, thereby implicitly marking it as wrong, or they don't, which implicitly limits their ability to clarify and refine it.

Screw the never moving twin. Just explain your spacetime diagram and what you're trying to achieve with it.

@DavidZ OK. In this case, it was fairly mathematical statement, and I think @JohnRennie wasn't offended (hopefully), but I'll keep it in mind.

Are you still trying to mess around with the travel time of the light and what impinges on the travelling twin's retina?

@JohnRennie I'm claiming that 1) a Lorentz transform from (-10,-10) to (-6,-6) must appear somewhere in this problem, and, 2) in contradiction, no such transform can appear.

@JohnRennie Sort of, but we can ignore that for now. Just focus on assigned times, not eyeball times.

@barrycarter Yeah, I'm not saying it was offensive or inappropriate or anything. Just saying it seems to push discussions in a direction that makes it less likely to end with everyone agreeing on something.

@DavidZ Fair enough. I thought I had @JohnRennie on the ropes there, though :)

Draw me the spacetime diagram showing the spacetime point (-10,-10) and what frame you're transforming it into.

Or describe it to me precisely enough for me to draw it.

@JohnRennie I do all this relativity stuff with matrixes (or linear transforms), I don't know how to draw a spacetime diagram.

OK. That I can do

OK, never moving twin is 10 ly away from Earth forever. It is 2010. He says Earth at 2000 is (-10,-10). Are we good on that point?

A spacetime diagram is just an x:t graph

You don't know how to draw a spacetime diagram?

So it's the inverse of a t:x graph (which seems more normal to me)?

Time is vertical

@0celo7 I do not know how to draw a spacetime diagram. Dammit, Jim, I'm a mathematician, not a physicist.

@barrycarter It's conventional to draw t on the y axis for reasons that have never been clear to me.

@barrycarter I'm an engineer/mathematician and even I know how to draw a spacetime diagram

@JohnRennie So the event I'm describing is: a light beam leaves the Earth when the Earth thinks it's 2000.

OK, sorry to interrupt folks but I think now it's time for a chat session?

@JohnRennie So spacelike hypersurfaces are horizontal.