The h Bar

4:12 AM

@anonymous

in g-block elements, 3 mins ago, by Martin - マーチン

stimmt... dann vielleicht Thiofulminat ;)

@DHMO Thanks

@anonymous no problem

Our guess was correct

:)

@anonymous have we done $\displaystyle \int_0^\infty \frac{\ln x\ \mathrm dx}{x^2+2x+2}$?

@DHMO Yes I think. Put $x=1/y$. You will get $I=-I$ probably.

rob

5:12 AM

@AccidentalFourierTransform "Proof by rotation." Brilliant.

5:23 AM

@DHMO Any idea about the oxidation number of each of the three Nitrogen atoms in N2H5NO2 ? I don't know the structure of the compound :/

5:35 AM

Okay, I found the answer ^

@anonymous learn to recognize groups like NO2

@DHMO I knew about NO2. I was confused about N2H5

Then I realized that it is a protonated hydrazine

And oxidation number does not change on protonation

@anonymous I beg to differ

@DHMO ?

@anonymous where do you think the extra H is?

5:43 AM

@DHMO Any one of the nitrogen atom in hydrazine

@anonymous why?

What else could it be ? @DHMO

See the first structure

@anonymous interesting...

:)

@anonymous I had something different in mind... looks like you are correct.

5:47 AM

@DHMO Even I had several things in mind..but they didn't seem a good fit for the structure :D

I resorted to this at last

I overslept today so I adjusted my clock to show the current time - 3 hours :P. Gives me some mental peace :D. Lots of work!

I had something like this

@DHMO I've never encountered a structure like that. Seems like an acid (strong). But from the molecular formula N2H5NO2 that doesn't seem a good fit...

Usually when the formula is given as NxHyNO2 or NxHyNO3 it refers to a ionic compound

Your compound's formula would have been NH2NH2(+)N(OH)O(-)

@anonymous but I don't like the [NO2]- anion

@DHMO Why?

@anonymous HNO2 is a weak acid

5:59 AM

So?

so [NO2]- in water tends to protonate...

@anonymous I guess I'm being silly here. Please move on.

Hehe :)

@DHMO Want to see a magic trick?

@SirCumference go ahead

OK, pick a card.

6:09 AM

@SirCumference done

Any number 1-52, any type

OK, now tell me, what's your favorite color?

green

all right, now square your number

done

crud, i messed it up...

ignore that last step. first i have to ask, is your number a prime or composite number?

6:12 AM

prime

Ok, then cube it

done

now divide that number by 27

remainder?

you can keep it, because my next question is: is your new number between 1 and 27?

6:13 AM

yes

is your card the 3 of clubs?

of course not...

godammit!

i went wrong somewhere here...

@DHMO What was your card?

@SirCumference 7 of spades...

wow, i was way off...

user228700

6:28 AM

Hello, everyone :-)

Morning Kaumudi :-)

user228700

U seem to be in a jovial mood. Nice morning?

That laptop I bought is arriving today. A new toy to play with!

user228700

Ah, that explains it. Nice! Have fun :-)

Actually ... I have two laptops arriving today :-)

user228700

6:32 AM

No wonder x'D

user228700

Did u throw away the Hajmolas yet?

I did - sorry :-(

user228700

That's a shame :-(

I did keep trying the tamarind flavour for a week, but they just aren't for me.

Oh well

user228700

OK. Why didn't u offer to anybody else?

6:38 AM

Because I don't have any enemies :-)

user228700

:-) I'm sure somebody would've like it.

Anyhow, how are things in Chennai? Have you managed to get back up to speed?

user228700

Yes, sort of :-) It's very warm over here. There have been many protests and cases of violence against the police in the past week but all is OK now.

Wow. Is that just people getting bad tempered because of the heat or is there some deeper problem?

@Kaumudi.H jallikattu ban protests ?

user228700

6:42 AM

^

ouch XD no comments.

user228700

Many of my friends participated in the protests at their respective colleges. I am pleased to report that none were injured. Most of the action happened elsewhere.

@Kaumudi.H Protests are starting up here too. One of the profs apparently cancelled class yesterday so that people could attend a Trump rally

user228700

Ohh, wow, I see.

Jallikattu doesn't seem that different from the bull running that happens in Spain

6:45 AM

@SirCumference I doubt that it will be of any use.....

Government rarely changes its decision (if at all)

user228700

@JohnRennie AFAIK, in Jalikattu, people are supposed to catch the bull.

They must be unusually good tempered bulls!

@JohnRennie People get severely injured in it :P Bulls are bulls!

Even in bull running people do get gored by the bulls, and that's without deliberately trying to grab them

Atleast in Spain they provide immediate medical support

user228700

6:48 AM

@JohnRennie ...not really. I don't quite know tho, Jalikattu is not part of my culture so I am not very aware of its rules and how it all works.

I have to say I think immediate psychiatric support would be more appropriate :-)

In India you don't get medical facility. If you are injured someone by the bull someone will have to drag you to the hospital several kms away.

The obvious solution to that is NOT to try and hug an angry bull :-)

@anonymous That's...scary

The people participating are mostly youngsters (between 18 to 30 years)...hot tempered young fools :P

user228700

6:50 AM

@JohnRennie ...it's part of their culture but I dunno why.

user228700

This is part of my culture:

@anonymous The UK is one of the few governments I've seen that takes the feelings of the citizens seriously

user228700

Thrissur Pooram

Thrissur Pooram (Malayalam: തൃശ്ശൂര് പൂരം) is an annual Hindu temple festival held in Kerala, India. It is held at the Vadakkunnathan Temple in Thrissur every year on the Pooram (Malayalam: പൂരം, pronounced [puːɾam]) day - the day when the moon rises with the Pooram star in the Malayalam Calendar month of Medam. It is the largest and most famous of all Poorams. == History == Thrissur Pooram was the brain child of Raja Rama Varma or famously known as Sakthan Thampuran, the Maharaja of Cochin (1790–1805). Before the start of Thrissur Pooram, the largest temple festival in Kerala was the one-day...

Parliament apparently has a petition website and they'll have debates for the popular ones

user228700

cdn.everfest.com/uploads/festival_series/hosted_cover_photo/…

6:52 AM

@SirCumference That's actually very nice :)

user228700

...although I dunno why this is a part of my culture either :-P

@anonymous Here's one example (that ended up failing, but still got its own debate).

Do people need a reason to have a good time? :-)

user228700

:-) BTW, have u read the "Secret" series by Pseudonymous Bosch? I suspect that they're a bit... kiddish for u but I read the first two when I was in 9th grade and enjoyed them thoroughly. I finished the second book in 3 hours on a train at night.

@SirCumference I don't find "Block Donald J Trump from UK entry" a very intelligent proposal. If that happened UK would be at a disadvantage and not US. Anyway the petition you showed system is something I like.

6:57 AM

@Kaumudi.H no I haven't

Have you read any books by Sarah Pinborough?

user228700

The book titles are certainly intriguing: "The name of this book is secret", "If you're reading this, it's too late", etc.

user228700

@JohnRennie Nopedy nope.

I've just finished one of her books, The Language of Dying, and it occurred to me it's the sort of book you might enjoy reading.

user228700

Hmm, why?

Based on the list of favourite books you posted I think Sarah Pinborough's books would fit with your preferences.

user228700

6:59 AM

Hmm, OK, I will definitely check them out, then, thanks. Oh, also, dyou have an account on goodreads? It would be helpful for me in the summer :-)

If you're interested I would start with The Death House, though be warned it's a sad ending.

amazon.co.uk/Death-House-Sarah-Pinborough-ebook/dp/B00K5UFGRC

user228700

Sad ending? I've read TFiOS--I think I can handle a sad ending :-P

TFiOS?

The Fault In Our Stars ?

user228700

goodreads.com/book/show/11870085-the-fault-in-our-stars

7:01 AM

i saw the movie :)

Aha yes, I got as soon as I posted. I've never read it or seen the film, but I remember the trailers for it.

Yes I do have a Goodreads account, though I don't use Goodreads that much.

user228700

OK :-) Also Mockingjay--boy did that one have a sad ending.

user228700

@JohnRennie Oh, OK :-|

user228700

Have u read the Numbers series?

user228700

goodreads.com/book/show/6609758-numbers

7:03 AM

Rachel Ward?

user228700

Yep.

No I haven't.

user228700

It's excellent. I absolutely loved the first book.

user228700

The second one is not as good but still worth a read. I haven't read the third book yet.

user228700

> "Whenever she meets someone new, no matter who, as soon as she looks into their eyes, a number pops into her head. That number is a date: the date they will die."

user228700

7:05 AM

Intriguing, no?

user228700

Do u focus only on the plot or does character development and all matter to you?

Does your Goodreads page show Thirteen Days to Midnight as a related book?

I ask because I've read that and I thought it was an interesting idea as well.

user228700

Why, yes it does.

It's really a young adult book but I still enjoyed it.

user228700

OK, I will surely check it out. I am not too active on Goodreads either--I haven't updated my "Has read" list... ever.

7:08 AM

@Kaumudi.H I don't have a simple answer to that.

user228700

..?

Different books appeal for different reasons. In some I enjoy the plot and in others I enjoy the characters.

user228700

In general, does that stuff add to the appeal of a novel is what I'm asking.

What I really like ina book is when it makes me think about things that hadn't occurred to me before.

user228700

@JohnRennie ...and u get this in Sci-Fi a lot? I'm quite surprised.

7:11 AM

Well take for example:

amazon.co.uk/dp/B00BU1DG1S

which I really enjoyed.

On the face of it this is regular SciFi - spaceships, instellar wars, androids, all the usual props.

But the story is about what it's like for an AI to suddenly find themselves human, and that aspect of the book is done really well.

user228700

Hmm, it sounds very interesting! Excuse me while I add it to my list...

It isn't something I'd thought about before reading the book, and it made me really think about what it would be like.

Also:

amazon.co.uk/Mongrels-Stephen-Graham-Jones-ebook/dp/B01AFKHYOO

I mean, come on. Werewolves?

But the book is about what it would actually be like to be a werewolf, and ... life as a werewolf is rubbish! Not glamorous or fun at all.

user228700

Lol, I imagine that there is a lot of room for crappy plots in Sci-Fi.

user228700

> "What really knocks me out is a book that, when you're all done reading it, you wish the author that wrote it was a terrific friend of yours and you could call him up on the phone whenever you felt like it. That doesn't happen much though."--J.D Salinger

It's the most insightful werewolf book I've ever read - in over 40 years of reading Sf!

7:16 AM

@anonymous Oh wait, they respond to petitions with 10,000 signs, and debate ones with over 100,000 signs

Wish we had that here...

user228700

@JohnRennie ...I see.

It would largely eliminate the need to protest

Jan 30 at 3:39, by thought for food

Have you guys seen this?

You do have that in US too

and petitions.whitehouse.gov

Oh wow...

How do you know more about my country than I do? o_O

user228700

I also love those books which introduce a new idea to me. Most of all, I want to read many many (what u describe as) "touchy-feely" books because these provide insights into the worlds of other human beings.

7:18 AM

Do you see the number of petitions against DT ? @SirCumference The first page is full of that

user228700

Reading stories that are similar to reality help me to try to imagine others as complexly as I imagine myself.

@Kaumudi.H You will like Sarah Pinborough's book then.

@anonymous Yep...

Did you ask for the Kindle?

user228700

And this improves the quality of my experiences so drastically.

7:20 AM

@SirCumference But again, do they have any effect in real? I doubt.

@anonymous Well I guess it's a bit different here. In the UK you get a response for 10k signs and it gets a debate for 100k. Here, the Gov only responds to 100k signs, no guaranteed debates...

@anonymous That's the point, they don't necessarily get debated here

@SirCumference How are you so sure about UK ? Do you know of any case where public demand overruled gov's decision ?

@anonymous Well because the UK's petitions get a lot of attention on Reddit. Never seen a US one on there.

Reddit is outdated XD

@anonymous Not in particular, but still, just reading from the site...

@anonymous Heck nah

user228700

7:22 AM

@JohnRennie Yes, I did!

When do you get it?

user228700

Well, I told my mother that I'd like one for my birthday in April but I dunno if I will get one.

@SirCumference See reddit.com/search?q=trump+petition

user228700

Ooh, @JohnR: it's ur birthday a week from now, no? Dyou have any plans?

@anonymous Apparently, it still brings as many pageviews as StackOverflow

7:24 AM

@SirCumference reddit.com/r/Impeach_Trump/comments/5p6961/…

That petition was listed on Reddit too

And StackOverflow gets multiple times more pageviews than all the other SE sites combined

@anonymous Wasn't on the front page. I don't look through specific subreddits :P

UK ones often reach the front page

@SirCumference Oh!

But it had a huge activity

@Kaumudi.H so it is. I had genuinely forgotten.

and 400+ upvotes

56th birthdays aren't anything special :-)

user228700

7:26 AM

@JohnRennie Oh, u really had?

@anonymous 400 ain't that much...to be on the front page you usually need over 10k

user228700

@JohnRennie Well, sure, but what dyou usually do on ur birthday?

@Kaumudi.H Yes. Birthdays are less special after you've already had 55 of them :-)

That's an example

7:27 AM

@SirCumference Oh...is Reddit not popular in US ?

Or some other reason...

@anonymous Au contraire, it's more popular in the US than most places. r/news has become so associated with the US, we needed r/worldnews, which specifically prohibits posts about the US

@Kaumudi.H the 9th is a Thursday so I probably won't do much that day. But I might go out for a drink or two on the following Friday night :-)

I think it's just that US petitions aren't taken seriously at this point

I get it

@Kaumudi.H I could buy myself a present! A laptop would be nice :-)

user228700

7:29 AM

@JohnRennie Sounds good :-)

user228700

@JohnRennie ::facepalm:: Perhaps book an appointment to go see a psychiatrist?

@Kaumudi.H I'm not sure the psychiatric profession is ready for me :-)

user228700

:-) Are u, by any chance, interested to listen to podcasts?

I do listen to podcasts, but they are all computer or music related

user228700

Recently, I discovered an excellent podcast called Invisibilia--it is extremely well edited and so so though-provoking.

7:31 AM

ACM's profile pic just changed

It's now on the zombie-level of 0celo

@Kaumudi.H npr.org/podcasts/510307/invisibilia ?

user228700

Yep! I recommend starting with this one:

user228700

acast.com/invisibilia/entanglement

user228700

All the episodes that I have listened to have been spectacular so far but this might be a good one to start with.

It looks interesting, though my free time is mostly taken by reading these days. My stack of books I really, really must read keeps on growing.

Anyhow, I have to get back to work for a bit. Back in half an hour ...

user228700

7:35 AM

Ah, OK :-) In any case, check it out when you get the time--perhaps when going someplace in a train or bus or something.

user228700

Lunch time for me!

@SirCumference Situations seem bad for foreigners living in US presently. Three of my acquaintances are leaving their jobs/internships in US and returning due to the new visa limitations. On the other hand now more jobs will be available for US people. So it is a sort of necessary evil.

@anonymous I think the ban enacted a few days ago is just implemented so wrongly...

@SirCumference Indeed. On the brighter side, the world had become increasingly US centric. Now it is high time for all the other nations to preserve their talent pool and improve themselves. This incident might be a push.

@anonymous On the contrary, I'd say the U.S. is becoming pretty ridiculous in the eyes of other nations. In one week Trump managed to piss off Mexico, Peru, Iraq, Syria, Iran, Sudan, Libya, Somalia, Yemen, and most of the EU. And he has already pissed off China.

7:47 AM

@SirCumference Hehe :P True. Well that is exactly what I was meant in my previous message. The world will now slowly move away from US centrism and that might be a good thing!

@anonymous Oh crud, misread that as "the world is becoming increasingly US centric" XD

8:26 AM

@JohnRennie I had a question to ask you: What does rest mass of an electron or any particle imply ? The electron is at "rest" relative to what ?

@anonymous the total energy of a relativistic particle is: $$E^2 = p^2c^2 + m^2c^4$$ where the parameter $m$ is a constant.

If the momentum $p$ is zero then the equation simplifies to: $$E = mc^2$$ which should be familiar.

And $m$ is interpreted as the particle mass.

So the rest mass is the mass in a frame in which the momentum of the electron is zero.

@JohnRennie Umm, then my question would be "momentum" w.r.t which frame are you talking about ? Momentum is also a frame dependent quantity. When you say momentum becomes zero, it becomes zero in which frame ?

Energy and momentum are both frame dependent, but the equation for the total energy always applies in any frame.

So $m$ is the same constant in all frames.

If you're interested in going deeper into this it arises from the energy-momentum four-vector. The magnitude (the norm) of this four-vector is an invariant.

@JohnRennie Oh I think I am somewhat getting it. However, how do we calculate the momentum of electron in a certain frame ? Is it calculated by the formula $(m_{rest}/\sqrt{1-v^2/c^2}) * v$ (where $v$ is velocity relative to that frame) or something else ?

Yes $$p = \gamma m v$$ It is as simple as that.

When you see a physicist referring to $m$ in relativity it always means the invariant mass. No-one uses the concept of a variable relativistic mass these days.

So you don't need to write $m_{rest}$ or $m_0$. Just write $m$.

8:38 AM

@JohnRennie Okay! Thanks. By the way, how long will you be online ? I might need to ask you some more questions on wave-particle duality and radioactivity :P

I have to work for about 20 minutes now. But I'll be back about 09:00 UTC and then I'm around for several hours.

@JohnRennie Sure. I'm studying the topic and will ask you my questions after 9 UTC then :)

A: Results of two equivalent scenarios in SR

8:52 AM

Another relativity denier.

-1

Gaurav Goyal is right. The result of the experiment depends on which of the reference systems is defined as to be at rest. Therefore the two postulates of SRT are in conflict and cannot both be true. Whatch this: https://www.youtube.com/watch?v=cJOTYeJqyOY Paul E.

@anonymous I'm just making myself a coffee, then I'll be back and ready for action!

@anonymous: OK, coffee is made ...

9:07 AM

Coffee

I wonder if I should make some now

One of my daughters threw up around 3am local time and now, an hour later, I'm still wide awake

@JohnRennie A photon beam is said to have a radiation pressure due to imparting of momentum to the surface by the photons. But can this pressure exertion be explained by wave theory of light ? Or wave theory fails to explain it ?

@JohnRennie Hehe :D What type of coffee do you prefer/drink ?

@anonymous I use instant coffee when I'm working. Really good coffee would be a waste since when I'm concentrating on work (or physics) I hardly taste it.

@anonymous I'm 99% certain that a classical EM wave, as decsribed by Maxwell's equations, carries momentum.

But electrodynamics isn't my strong point so there's still that 1% doubt :-)

@JohnRennie Ah! I initially used to think that waves can't have momentum. I will have a look at maxwell's equations

See this for example

9:45 AM

@JohnRennie I read it. It was a good article :) I have another question. During de-excitation of an electron in an atom (assume Bohr model to be true), to calculate recoil speed of atom can we assume that whole of the energy released is converted into photon energy $\frac{hc}{\lambda}$ ? Will it give approximately correct result or we also have to take into account the kinetic energy gained by the atom as well ?

My method: $$m_{atom}v_{recoil}=\frac{h}{\lambda}$$ and $$\frac{1}{\lambda}=RZ^2(\frac{1}{(n_1)^2}-\frac{1}{(n_2)^2})$$. Solve to calculate recoil velocity...

Under most circumstances you can ignore the recoil of the atom because the momentum of the photon is too small to move the atom much. However this isn't always true. For example in the Pound-Rebka experiment the recoil of the atom was very important.

That's because they wre using X-rays (from a nuclear not electronic transition) so the photon momentum was a lot higher, and they wre working to very high precision.

@JohnRennie That's seems a really interesting experiment. Alright, I will take into care the recoil of the atom from now on if the momentum of photon is high. In that case we need to solve two equations and for two variables. $m_{atom}v_{recoil}=\frac{h}{\lambda'}$ and $\frac{1}{2}m_{atom}v^2_{recoil}+\frac{hc}{\lambda'}=hcRZ^2(\frac{1}{(n_1)^2}-\f‌rac{1}{(n_2)^2})$. Are my equations correct ?

Some LaTeX error...don't know why...hope you can read the equations!

It's a straightforward mechanics problem. Before emission in the COM frame $E=p=0$. After emission $m_{atom}v_{atom} + h/\lambda = 0$ and $\tfrac{1}{2}mv_{atom}^2 + h\nu= E$ where $E$ is the difference in the energy levels.

@JohnRennie Yes, I wrote the same!

$$E=RchZ^2(\frac{1}{(n_1)^2}-\frac{1}{(n_2)^2})$$

:D

linuxick

Hey, I have answered a question
http://physics.stackexchange.com/questions/308186/numerical-complexity-of-different-quantum-chemistry-approaches
and my answer had two up votes, however my "reputation" point did not increase. What could be the reason?

10:00 AM

@linuxick It is a CW answer

Oswald

@linuxick because it is Community Wiki

Who made it community wiki ? @linuxick You?

no

Ask a moderator then

thx

10:01 AM

BTW it is a resource recommendation question

Those are usually made CW

linuxick

all right

@linuxick it's a community Wiki question, so answers to it are automatically also community Wiki.

Yes, resource recs. are always community wiki

So no rep for any of those queries

@KyleKanos still awake then :-)

@linuxick BTW you will gain the bounty points if your answer is selected for bounty (even if it is CW)

10:02 AM

(that's a sympathetic smiley)

@JohnRennie Yeah, opted for the coffee

Thinking about making a second soon too

@KyleKanos Instant coffee ? :D

No. I have a Keurig and a reusable K-cup

I think I'm still on an Aldi brand. I'll be opening up Peets in a couple days though

@KyleKanos Lucky you :P I'm thinking of buying one too. Are those coffee makers good ?

They're good if you're the only one drinking coffee

If there's more than one person in the house/apartment and you, together, drink multiple cups, it's not so good

10:07 AM

Ya ya....I'm the only insomniac in the house :P

I will need the machine

It'd be better for a typical drip machine, in that case (of multiple drinkers)

10:27 AM

@JohnRennie Is there any particular reason as to why number of neutrons in any stable atom is always greater than or equal to number of protons but never lesser than number of protons ?

Helium-3 has fewer neutrons than protons and it's stable

@JohnRennie Helium-3 is a very small atom. But in all large atoms number of neutrons is always greater or equal...

Is it just a coincidence or has some reasoning ?

Do neutrons help to stick the protons together or something like that ?

There isn't a simple rule. The strong nuclear force (NB not the strong force) is a kind of left over force from the internal quark-quark interactions and it's fiendishly complicated.

Protons obviously repel each other because of their charge, and neutrons are needed to act as extra glue. However I don't know of any simple argument for why they are needed.

"fiendishly complicated" XD I'll leave it for the moment then !

10:54 AM

@JohnRennie In the radioactivity law why is always $-\frac{dN}{dt}$ proportional to $N$ (i.e. first order) and not second/third or any other order of $N$ ? I couldn't find any reasoning for it. Do you know ?

$N$ is number of undecayed particles at an instant...

Junaid Aftab

11:37 AM

I'm looking for a textbook that covers, at least for a large part, special relativity with tensors/a geometrical approach. Most textbooks I have found develop tensors for the purposes of GR; I'd like a book that goes through this exercise for the purposes of understanding SR. I'll then feel more comfortable moving on with the GR bit.

Ideally, the textbook/resource will first cover tensors, and then move on to discuss tensor analysis in SR.

Any suggestions?

11:53 AM

@JunaidAftab: I don't know of any books like that but I would be interested if you find one. I have long thought that SR would be better taught using a geometrical approach.

@JohnRennie Could you have a look at my previous question ^? You probably missed it!

1 hour ago, by anonymous

@JohnRennie In the radioactivity law why is always $-\frac{dN}{dt}$ proportional to $N$ (i.e. first order) and not second/third or any other order of $N$ ? I couldn't find any reasoning for it. Do you know ?

Q: Can we find the exponential radioactive decay formula from first principles?

@anonymous I'm sure that's been asked in the main site. Do a search of the site.

It's because it's a first order reaction. A nucleus doesn't have to interact with anything else for the decay to happen.

8

Can we find the exponential radioactive decay formula from first principles? It's always presented as an empirical result, rather than one you can get from first principles. I've looked around on the internet, but can't really find any information about how to calculate it from first principles. ...

radioactivity

12:14 PM

@JohnRennie That seems like a possible explanation. I saw the question you linked. But it doesn't have any good answer other than Emilio's (which is too difficult for me to decipher at the moment) :P.

I made this search physics.stackexchange.com/search?q=radioactivity+first+order but nothing related is there

Loong

12:38 PM

@anonymous Hm, in radiochemistry, we usually explain it indirectly via activity $A$. However, that only adds one or two steps but not so much more information regarding your question. Nevertheless, it creates the connection between radiation measurements and decay law.