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1:18 AM
> Undergraduates who live on [MIT] campus must begin packing and moving out of their residences by this Saturday, March 14. This also applies to students in our FSILGs. You will be required to leave by noon on Tuesday, March 17. For first-years, sophomores and juniors: Please pack your belongings and make plans to travel home or to another location off-campus as if you do not expect to return here until the fall semester.
 
1:41 AM
@skullpatrol dang, MIT is closing for the entire semester?
 
 
4 hours later…
5:43 AM
Does anyone know how I can make an image that when folded in some specific way or cut and recombined or reconfigured... produces some type of message? You know, like in the movie Contact.
 
@SirCumference the UK Minister of Health has just tested positive for COVID!
 
@JohnRennie OMG!
 
There still only 400 cases in the UK so it isn't an epidemic yet
 
@JohnRennie might be. But I think that most of the cases go undetected and hence leading to community transmission. Which is what happened in USA and might be happening in India.
 
6:00 AM
@JohnRennie seems no one is protected
It is more likely for me to get run over by a bus on my way to the mall than to catch COVID in the mall. I think there's too much unnecessary panic. The virus will come and will go but the bus can still run me over, why is no one panicking about that..
 
6:19 AM
@SirCumference i wouldn't expect anything else from the rich, ie go and hide in your mansions
 
6:31 AM
@tpg2114 I'm sure, I'll ask so many questions that :P
 
Well done, China!
 
@skullpatrol as opposed...to staying somewhere where a bunch of people gather while a virus is spreading?
not sure if that has to do with being rich or not
@JohnRennie yikes
 
> During today's White House press briefing, US Surgeon General Jerome Adams said:
β€œPeople over the age of 60 are much more likely to develop complications from the coronavirus and to be hospitalized. The average age of death is age 80 [...] If you are a child or young adult you are more likely to die from the flu - if you get it - than you are to die from coronavirus. So there is something about being young that is protective" Source: US Coronavirus Task Force Press Briefing
 
We're making coronavirus the biggest celebrity ever. Everyone is talking about it.
 
i personally am not worried about my health if i contract it
i'm much more worried about spreading it to my parents, or my sister who's pregnant
 
6:40 AM
@skullpatrol cripes, I'm 59. It's a good job the epidemic happened this year not next year :-)
7
 
Anyone who wants to protect himself/herself from Covid-19 should take a protective cow dung bath and drink cows' urine!!!!!! πŸ˜‚ πŸ˜‚ πŸ˜‚
I am not joking. This is what those illiterates are spreading on the social media.
 
-_-
what's next? ceremonial sacrifices...
 
wanna have a look?
 
nah, I believe you pal
thnx for sharing :P
 
7:01 AM
Hi. Is anyone other than me facing this issue? :
After posting a question and opening the "Ask question" to ask the next one, I can still see my already submitted question saved as a draft and hence need to discard it first before I type my next one.
 
@GuruVishnu I haven't asked any questions after this feature was released but I think that it is intentional.
 
Ok Johan. In the older version, I faced this but that was before submitting the question. I agree if that was the case then it's intentional. But this seems to be a little different behaviour. Thanks for the reply.
 
7:41 AM
@JohanLiebert however that would probably be very effective at making other people avoid you, so at least you wouldn't be passing COVID on :-)
 
Or may be that virus would be afraid to get close to you and hence people say that it's a good preventive measure.
 
@JohnRennie :-)
 
8:48 AM
@JohanLiebert thanks for sharing the link
the population section is interesting, also
 
@skullpatrol you are welcome! That website was keeping track of this since Feb 2020 and I visit it everyday to see the statistics.
It is interesting to see how china was able to curb the spread of disease and now the active cases are steadily declining.
 
yeah, that is what their goverment is saying
their are cases in North America where hospital employees are under a gag order, where their jobs are being threatened if they speak to the press (according to tweeter)
 
9:05 AM
It's seems like no one is interested in giving suggestions for the new ask question page customization. What happened to the community spirit?
@skullpatrol yeah, the governments are very much interested in maintaining their economic growth than to say the truth.
 
some things will never change
 
9:45 AM
Hello. Resonance occurs at the same frequency of the body being aggitated. However what is a simple start of the mathematical explination for this? i dont want the full proof i just want a headsup in which direction this has been proven. I know the examples of the swing and such on. But i want the mathematical guide. I ve seen that when resonating the phase difference have 90 degree difference between them. i thought that they would have a 0 degree diference so they add up to a double.
It is also to be noticed that when the amplitude is strongly countered then the ratio of the frequencies is no longer 1 but slightly smaller.
 
@JohanLiebert Dun worry, Indians are naturally immune to most of the diseases, (That's the reason most of the Cases in India are actually european tourists), refer Dr. Khandelwal's show on DD News National.
This natural immunity isn't genetic tho^
 
I correct my question: i just saw the mathematical equation and i see why it is when close to each equal to null thus resulting in an infinite amplitude
I guess what i want now is more of intution why this is true, other than the swing intution.
 
10:26 AM
@JohanLiebert Have you seen @KnightadmiresChappo there? I've not seen him for a while.
 
@AbhasKumarSinha he deleted his account recently.
 
@JohanLiebert Ik, that's sad :'(
@JohanLiebert Messaged him on facebook, lets see if he replies.
@JohanLiebert ah, he replied :)
<3
 
@AbhasKumarSinha I forgot my FB password! Now I think I would have to generate a new one.
 
#118 on PSE
I'm coming for you, J. Murray
 
11:30 AM
@Slereah You know how to write Stress Energy Tensor with Lagrangian?
 
Yes.
 
@Slereah tell mah
 
Apply the Euler-Lagrange formula to the Lagrangian
the stress energy tensor is the part that doesn't stem from the Einstein-Hilbert action
 
@Slereah Ok, next
@Slereah didn't get it fully
@Slereah tell mah the book for that, I'll see it karephully
@Slereah Urgent Help!
@Slereah Is it Modern Physics or Mathematical Biology: ncbi.nlm.nih.gov/pubmed/15889967
Quantum Mechanics + General Relativity + Biology = That Paper!
 
11:52 AM
@Slereah So, is that Hilbert action? $I = \int_{\mathcal M} dv \, \mathcal L$?
 
12:08 PM
That's just a generic action
 
12:19 PM
1
Q: How to handle questions that could belong to physics.SE and other, more specialized, SE websites?

Sylvain LerouxFirst of all, I joined physics.SE only for the purpose of asking this question on Meta. I asked a couple of questions regarding acoustic in sound.SE. For example What are combs, nodes and how to calculate the nodes and comb frequencies at a given position? or to a lesser extent How works perfora...

 
@Slereah Book or reference for beginners to perform such stunts?
 
Carroll's book on GR
is fine
 
@Slereah Lewis Carrol?
 
Yes, Alice in Wonderland
 
@Slereah Okay.
 
 
2 hours later…
2:01 PM
study regularly in uni kidz
not possible to consume one month of study material in a day
memes are mems
How to fake a covid-19 epidemic in your college to shut it down in 4 days
pls help
 
2:15 PM
@AvyanshKatiyar Wear a chinese costume and cough a lot
 
Is the homework and exercises tag appropriate for this question?
 
@Korra Dark matter causes expansion of universe.
 
Yeah, but the news. Is it true?
 
@Korra not sure, I wasn't the member of research team
 
Haha funny
 
@Korra I can realize the enormous amount of energy put to generate a line to whom people react by the act of laughter.
@Slereah Is 5000 citations on a paper bad?
 
2:46 PM
Hi everyone!
 
@YuvrajSingh... Hi
 
@AbhasKumarSinha use these notes
 
@bolbteppa Good evening sir, you are again back to help :) :DDDD
@bolbteppa Thanks sir :)
@bolbteppa Sir, I was trying to understand how to write Stress Energy Tensor using Lagrangian..?
 
Maybe those notes are too advanced, they seem to define out of thin air the stress-energy tensor
 
@bolbteppa As far I understand, Stress Energy Tensor is defined by Variation of $g_{\mu u}$ tensor of an Action Integral, $I = \int_{M} L dv$
 
2:54 PM
Have you studied lagrangian's for classical mechanics
Do you know Noether's theorem
 
@bolbteppa Yep, yep, I know
 
The stress-energy tensor is found via Noether's theorem
 
@bolbteppa But, it's related to General Relativity, and Noether's Theorem is Classical
 
@Slereah hmmmmmmmmmmmmm
 
interesting, Field Theory version
Noether's theorem or Noether's first theorem states that every differentiable symmetry of the action of a physical system has a corresponding conservation law. The theorem was proven by mathematician Emmy Noether in 1915 and published in 1918, after a special case was proven by E. Cosserat and F. Cosserat in 1909. The action of a physical system is the integral over time of a Lagrangian function (which may be an integral over space of a Lagrangian density function), from which the system's behavior can be determined by the principle of least action. This theorem only applies to continuous and smooth...
@bolbteppa sir, page 67 (last part), example 1: How he is writing stress energy tensor?
of that^
@bolbteppa This one uses similar method: phys.ufl.edu/~det/6607/public_html/grNotesVarPrin.pdf
Eqn (8)
 
3:05 PM
GR is classical too, Noether's theorem gives the stress-energy tensor by considering actions which are invariant under translations in space-time. This applies in GR too, but the resulting SE tensor is usually not symmetric, but you can use total derivatives to re-write the result in a symmetric way. An alternative way to get the symmetric stress-energy tensor is to consider only how the metric changes under space-time translations, and this leads to the definition (4.46) in the notes I sent.
 
@bolbteppa One situation can have multiple Stress Energy Tensor? (One symmetric and other non symmetric)?
 
The last set of notes you just sent, above equation 5, use this idea to directly motivate deriving the symmetric stress-energy tensor by varying with respect to the metric itself
The Lagrangian is not unique, it is only defined up to total derivatives. Same with the stress-energy tensor
 
@bolbteppa hmmm.... Okay....
 
The usual example is the electromagnetism stress-energy tensor, compute it both ways and compare
 
@bolbteppa Okay,,,
 
3:09 PM
Between pages 66 and 67 of Hawking he makes this point fyi
 
@bolbteppa Hmmm....
makes sense...
Gimme some time to try myself.
 
Important questions of our time!
27
Q: Why are most cranks old men?

AllureWhat To Do When The Trisector Comes claims that most cranks (for lack of a better word) are old men (trisector refers to a specific type of crank): One obvious characteristic of trisectors is that they are old. The typical trisector heard of the trisection in his geometry class, but did not s...

 
@bolbteppa Seems it'd take me 1-2 days to understand, the formal derivation and Stress Energy Tensor, Thanks for the notes, the gap in hawking's book can now be explained :)
Okay, it's easier than what I thought...
 
@JohnRennie even I struggled.
 
@bolbteppa How the lagrangian in General Relativity, 4D action is defined?
 
3:18 PM
Read the notes above
 
@bolbteppa He directly starts with equation (4.42)
 
3:31 PM
Try (4.1)
 
@bolbteppa These notes are very detailed, usually even reference books like R Wald don't have such detailed mathematical manipulation.
 
Hi everyone. This is my first time on a SE chat.

I'm here as a result of a discussion on Meta: https://physics.meta.stackexchange.com/q/12763/256325
I posted a question on sound.SE:
https://sound.stackexchange.com/questions/47023/what-are-combs-nodes-and-how-to-calculate-the-nodes-and-comb-frequencies-at-a-g

But it didn't get much attention there, and the only answer I got is not entirely satisfying. So if some of you had a look there, that would be very helpful.
(BTW, I hope this is the right chatroom for asking that)
 
3:51 PM
@JohnRennie looks like the whole question is a satire!
 
4:08 PM
@bolbteppa Thanks sir :)
@bolbteppa @JohanLiebert Good Night :)
Bye ...
 
4:26 PM
JUST IN: Angela Merkel says that experts claim that between 60-70% of Germany's population could become infected by coronavirus.
or everyone here, please don't take these warnings lightly.
 
 
1 hour later…
5:29 PM
 
3 messages moved from General chat
 
The answer is "Mark" because ? is read "question mark" :-)
 
@AbhasKumarSinha Please don't give unsolicited medical advice.
 
Adjective: unsolicited (comparative more unsolicited, superlative most unsolicited)
  1. Not requested, welcome or invited.
 
5:46 PM
Just get it from the DARK WEB
 
is there a "grey web"?
 
@Slereah You can download placebo forte for free.
 
Is there a physical interpretation of the convolution of lines of constant time and space in a two dimensional pseudo-euclidean manifold?
 
6:16 PM
@skullpatrol That just makes me realize how I read the symbol "?" in my head. I don't read it like "question mark"; it almost feels like I'm reading an upward inflection but without any specific letter being inflected.
 
Indeed, that is how I was taught to "read" it also.
 
@JMac the problem with me is that I don't read it as "question mark" . I just get the feeling and hence took 2min in solving the riddle.
 
Then how would you figure out it was "Mark" @JohanLiebert?
"Mark" is a proper name.
 
@skullpatrol I just looked at the riddle and the names back and forth and found the connection.
 
I see, you found the logical link :-)
 
6:38 PM
I'm changing my legal name to Enturb Pertanglement
Are dichromatic polynomials applied in high energy physics?
 
@ACuriousMind looping back to this, what was on my mind a few days ago was the comparison of his involvement in the (successful) US nuclear program vs. Heisenberg's involvement in the (unsuccessful) German nuclear program
on the one hand, it's not hard to see the moral problem of working as a scientist for a Nazi program.
on the other, said program never got even as far as success on nuclear energy let alone nuclear weapons
So it's an interesting question IMO about how to judge von Neumann's involvement in a successful American nuclear program vs. Heisenberg's complicity in an unsuccessful Nazi nuclear program
 
6:56 PM
let's not forget that the history books are written by the successors :-)
 
(even my use of the words "involvement" vs. "complicity" points to the thorniness of that)
@skullpatrol right. in particular, the US nuclear program is often judged on the grounds of them wanting to bring resistance in Japan to a swift conclusion
when the real explanation is probably more in terms of sending a message to the Soviets and looking ahead towards (what would become) the Cold War
 
yup, don't forget Cuba's proximity to the US and if they got nukes :-/
 
ah, cuban missile crisis
 
exactly
 
of course, one shouldn't forget one point of context: the Americans put together a deal to have nukes in Turkey
so the idea that the Soviets were the only ones looking to place nukes in proximity of their enemies is a bit unbalanced
 
7:01 PM
true
 
in conclusion, history is complicated :P
 

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