The h Bar

Fawad

03:24

@dmckee rudely correct

dmckee

03:43

@Fawad Hmmm ... "stupid [descriptor]" is sometimes used as a very casual way of saying that the description applies intensely, which is what I had in mind.

Shing

05:19

I have seen second hand book shop selling Steven Weinberg's Quantum Field Theory, Vol I, II, for $70 USD.

not sure if I should get it

Secret

05:42

@dmckee Ah interesting, that's even more well thought of than that passing idea of mine. Sometimes in both worldbuilding and research, I often found it hard to check whether some ideas had already been taken since if you don't know the exact terminologies they use, you will never find it by googling or other database searching unless you happened to stumble upon it yourself

Secret

I am not sure why (but I do have said that many times), you guys seemed to be pretty good at comprehending my semi sensical babbles, and often return highly relevant resources or answers to me, as if somehow you guys know how to read my mind

peterh

06:45

@BernardoMeurer The internet tries to overload our mind.

Kenshin

08:51

Breaking News: Governor of Jakarta (capital of indonesia) has been found guilty of a crime and sentenced to 2 years in prison.

user228700

09:16

@JohnR: Morning! :-)

John Rennie

Hi

You're late today - pressure of revision?

user228700

@JohnRennie Yep :-/ I write one test (3 hours) in the morning everyday, you see. Today, I woke up later than usual because I was up for 2 hours in the middle of the night last night; wasn't well.

John Rennie

Wow, how are you doing on the practice tests?

wasn't well - ouch. Nothing serious I hope.

user228700

Doing OK! :-) Much to do but hopefully, I can get there.

user228700

@JohnRennie Nah, just cramps :-)

John Rennie

09:21

@Kaumudi.H Good :-) I guess doing masses of practice tests is the best preparation for passing the exam, even though I don't think it's a great way to learn. But then it's all about passing the exam.

Sir Cumference

Morning :)

John Rennie

Hi

user228700

I too agree that it's not a great way to learn but yes, it's about passing the exam :-)

user228700

@SirCumference No howdy? :-)

Kenshin

lol just like JG says

user228700

09:23

:-P

Sir Cumference

@Kaumudi.H Funny enough, that's a southern-state saying. I'm from the northernmost states but kind of just picked it up, so people look at me funny when I say it :P

user228700

Ah, I see :-) DID U GET AROUND TO READING THE BOOK?

Sir Cumference

I am XD

user228700

Wow, OK...

user228700

OK, I gots to have lunch!

loltospoon

09:29

Hello all

Sir Cumference

Howdy @loltospoon

loltospoon

Question: If I have a space probe that is being propelled by bouncing a laser off its reflective sail, how do I find the speed of the probe as a function of time?

Assume that the momentum transferred by the light beam will diminish due to red-shift and that the effect mass increases

Any ideas?

John Rennie

In the ground frame the rate of change of energy of the probe is the same as the power emitted by the laser, and the energy of the probe is $$E^2 = p^2c^2 + m^2c^4$$

It's going to turn into a messy expression though ...

loltospoon

09:58

@JohnRennie messy equation here makes sense

So what you're saying is

$P_{laser}=\frac{dE_{probe}}{dt}=\gamma ^3mav$

Oh wait, I used $E=\gamma m c^2 - m_0 c^2$

Is there a difference?

@JohnRennie you're my only hope. If you help me with this I will metaphorically buy you a metaphorical lunch :)

0celouvskyopoulo7

11:26

@Slereah Trying to move all of my books is a pita

Maybe it's not such a good idea after all

Balarka Sen

had to look up pita

kids these days

Bernardo Meurer

11:42

@BalarkaSen Pita bread

0celouvskyopoulo7

@ACuriousMind How do I recycle a spiral notebook?

Bernardo Meurer

@0celouvskyopoulo7 Burn it

Recycle it to the gods

0celouvskyopoulo7

that's not very eco friendly of me

loltospoon

Anyone have any ideas for my question?

Bernardo Meurer

11:58

@loltospoon You want ideas of a question to ask?

loltospoon

@BernardoMeurer no, please see above

I need help with a question about a light sail

GPhys

12:14

a question I found while studying for finals

I hope this one is on the exam, haha! (this problem is cuter than it looks)

Bernardo Meurer

@GPhys It's a trick question, the answer is Nepal

GPhys

@BernardoMeurer (it is actually a trick question)

ACuriousMind

@loltospoon Assume the rate of photons $n$ hitting the sail is constant, then express the (redshifted) momentum of a single photon $p_\text{ph}$ in terms of the current velocity, then solve the equation $p_\text{ph} n = \dot{p}$ for velocity.

@0celouvskyopoulo7 What?

0celouvskyopoulo7

@ACuriousMind Why do you like making people feel stupid?

My question is perfectly reasonable.

ACuriousMind

Reasonable as it may be, why would you ask me that?

0celouvskyopoulo7

12:22

@ACuriousMind Because you're German?

ACuriousMind

I throw things I want to recycle into the corresponding recycling bins :P

0celouvskyopoulo7

I don't have a bin for metal.

ACuriousMind

Well, I can't help with that.

GPhys

If you naively solve the above question with the usual methods and simplify, you get the energy of the proton is of the form m_p-c for c>0

0celouvskyopoulo7

well I sure would hope the speed of light is positive!

GPhys

12:25

@0celouvskyopoulo7 🤔

pfft nobody writes in speed of light c

loltospoon

@ACuriousMind can I substitute $\dot{p}=\frac{d}{dt}(\frac{hf_0}{c}(1+\frac{\Delta v}{c}))=\frac{hf_0 \Delta a}{c^2}$ ?

ACuriousMind

@loltospoon What's the $\Delta$, what's $f_o$?

More generally, how did you arrive at that expression?

loltospoon

@ACuriousMind $f$ is the redshifted frequency

$f=(1+\frac{\Delta v}{c})f_0$

Sorry, forgot to throw the $n$ in here: $\dot{p}=\frac{d}{dt}(\frac{hf_0}{c}(1+\frac{\Delta v}{c}))n=\frac{hf_0\Delta an}{c^2}$

@ACuriousMind I used the equation you gave me

ACuriousMind

So, what you mean is that your expression there is $p_\text{ph}n$ and you're setting it equal to $\dot{p}$, right?

loltospoon

@ACuriousMind correct

ACuriousMind

12:30

Then yes, that's correct

loltospoon

@ACuriousMind ok, so then where does the change in mass come into play?

ACuriousMind

Well, you can't solve that equation for velocity yet, can you? Express $p$ in terms of $v$.

loltospoon

@ACuriousMind wait, forgot to mention that I need to express the speed of the probe in terms of the power, $P$, and the mass of the probe, $m$

ACuriousMind

@loltospoon So?

loltospoon

@ACuriousMind So I'd use $P=\frac{dE}{dt}$

Also, I took $p_{ph}n=\dot{p}$ and solved for $v_f=\frac{\Delta a}{n}-c+v_i$

Oh wait, for $\dot{p}$ can I use the momentum of the photon?

Or was it suppoed to be the momentum of the probe?

ACuriousMind

12:41

It's the momentum of the probe

loltospoon

Woops

ACuriousMind

But I might be realizing now that the DE you obtain from that isn't actually solvable for $v$...

loltospoon

@ACuriousMind Even with Mathematica at my disposal?

ACuriousMind

Oh, that might work, I did not try that.

loltospoon

Ok so using $p=Ev/c^2$, I found that $\dot{p}=\frac{Ea}{c^2} + \frac{dE}{dt}\frac{v}{c^2}$

I'd like to say that $\Delta v = v_f - v_i = v_f - 0 = v_f$, but I'm not sure if that would change the problem

ACuriousMind

12:46

I'm still not sure what your $\Delta$s are.

If you want to find $v$ as a function of time, you can't act as if there's an initial or final speed.

loltospoon

Doppler effect

The Doppler effect (or the Doppler shift) is the change in frequency or wavelength of a wave (or other periodic event) for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler, who proposed it in 1842 in Prague. A common example of Doppler shift is the change of pitch heard when a vehicle sounding a siren or horn approaches, passes, and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession. When the source of the waves...

ACuriousMind

...and do you not assume that the sail started at rest relative to the source?

loltospoon

@ACuriousMind I think I can. I did at first, but then my whiteboard started to look funny so I thought maybe I can't assume that.

Then how do I account for the redshift without that definition for shifted frequency?

ACuriousMind

You account for it, but I'd just have written $v$ instead of $\Delta v$ in there. What I intended to do was to write $p_\text{ph}n = \dot{p} = \partial_t(m\gamma v)$, express $p_\text{ph}$ as a function of $v$ as you did, and solve this differential equation for $v$.

ACuriousMind

13:01

Ah, after some simplification I can get Wolfram to spit out a solution, so yeah, this works, and my solution looks sensible (it grows asymptotically toward $c$)

Rajath Krishna R

physics.stackexchange.com/questions/331782/… Could someone please help me with this question.

loltospoon

@ACuriousMind Mathematica tells me that "This system cannot be solved with the methods available to Solve"

ACuriousMind

You need to do some tricks with the $\gamma$. What have you got currently?

loltospoon

Yea I just noticed the trick, one sec

@ACuriousMind didn't work. I simplified to $hf_0/c + hf_0 v/c^2 = \dot{v}(\frac{m}{(1-v^2/c^2)^{3/2}})$

But Mathematica still can't solve this

DanielSank

@ACuriousMind in English, when you want to form the possessive of a proper noun that ends in an "s", simply append 's.

Appending ' is done only for regular nouns ending in s, usually plurals

For example, "The apples' cores were small".

"I learned Bayes's theorem".

loltospoon

13:13

@ACuriousMind What equation did you start with before the trick?

ACuriousMind

@loltospoon You made some mistakes - most notably one earlier that I only now see: You used the classical doppler formula, but you need to use the relativistic one here.

loltospoon

Ohhhhhhhh

ACuriousMind

@DanielSank A quick search leads me to believe that that is not a universally accepted rule, for differing viewpoints, see english.stackexchange.com/a/79083. dailywritingtips.com/possessive-of-proper-names-ending-in-s seems to indicate it is purely a question of style, not of correctness.

(Also, how come you just now decided to tell me that? :D)

loltospoon

@ACuriousMind so then before the simplification, I have $hf_0 n \sqrt{\frac{1+v/c}{1-v/c}}=\frac{v^2\dot{v}m}{c(1-v^2/c^2)^{3/2}}$

0celouvskyopoulo7

@BernardoMeurer

Migos Goes Sneaker Shopping with Complex

►

ACuriousMind

13:25

@loltospoon Your r.h.s. looks funky. You sure you did all the chain rules for $\partial_t(m\gamma v)$ correctly?

The $\gamma^3$ is correct, one of it cancels against a $\gamma$ "hidden" in the root on the l.h.s., but the r.h.s. should have two summands and the $v^2$ is also odd.

0celouvskyopoulo7

@BernardoMeurer lmao, Quavo is Takeoff's uncle

offset and Quavo are cousins

loltospoon

@ACuriousMind $\frac{d}{dt}(\gamma mv) = \gamma m \dot{v} + \frac{v^2m\dot{v}}{c^2(1-v^2/c^2)^{3/2}}$

user228700

@Balarka: What did u decide to read, then?

loltospoon

@ACuriousMind How would that derivative not have a $v^2$?

ACuriousMind

@loltospoon It's $v$, not $v^2$: $\dot{\gamma} = -\frac{1}{2}\gamma^3\partial_t(-v^2/c^2) = \frac{1}{2}\gamma^3 (-2\frac{v}{c^2})\dot{v} = \frac{1}{c^2}\gamma^3 v \dot{v}$

loltospoon

13:39

@ACuriousMind Right, but then you have to use that $\dot{\gamma}$ in $\frac{d}{dt}(\gamma mv)=\gamma m\dot{v} + \dot{\gamma}mv$

ACuriousMind

Oops, you're right. Carry on, then

loltospoon

@ACuriousMind but then Mathematica poops out on me :(

It can't solve for $v$

Do you know any other ways to simplify this?

ACuriousMind

Hm, yeah, I end up with $\dot{\beta} = k(1 + \beta - \beta^2 - \beta^3)$ for $\beta = v/c$ and $k$ a bunch of constants, which seems unsolvable.

Hm, maybe the idea of $\dot{p} = p_\text{ph} n$ was nonsense

loltospoon

@ACuriousMind oh gosh........

ACuriousMind

I mean, $p_\text{ph}(\beta)n$ is the force the beam exerts on something in the frame moving with $\beta$ with respect to the source, but in the frame moving with $\beta$, the velocity of the sail is zero...

loltospoon

13:50

Another idea I had was to start with $P=\frac{dE}{dt}$ and say that the doppler shift reduces the power like $P-\sqrt{\frac{1+\beta}{1-\beta}}P$ or something

ACuriousMind

On the other hand, do you have a reason to believe this has to be analytically solvable?

loltospoon

Nope

I'm encouraged to use mathematica

ACuriousMind

I mean, outside of very special situations physics can just yield such ugly equations. It's possible that my equation for $\beta$ there is actually correct - that we can't solve it doesn't mean it's wrong

loltospoon

I know I definitely need to find a differential equation for $\beta$ but one of my friends told me that I needed to doppler shift twice because the probe is both a receiver and transmitter of power

I wasn't sure what that meant

ACuriousMind

I don't know what that's supposed to mean either

DanielSank

13:55

@ACuriousMind I choose to believe that my seventh grade teacher is the universally accepted authority.

loltospoon

@ACuriousMind can we drop one of the $\beta$ terms somehow?

ACuriousMind

@loltospoon Eh, you could neglect the $\beta^3$ "at low velocities", I don't have any other idea

The solution to that looks "reasonable" for $\beta < 1$, and since we assumed $\beta < 1$ it's not too worrisome that it shoots over $\beta = 1$ eventually.

loltospoon

@ACuriousMind I get this really gross answer though

wolframalpha.com/input/…

ACuriousMind

Why is it gross?

user228700

14:17

@JohnR: How's the car situation?

John Rennie

Not too bad.

A proper repair would cost more than the car is worth. torepair it with new Ford parts would cost £1,500!

AccidentalFourierTransform

so, half a laptop

John Rennie

But I 've found a mechanic who can hammer the bent bits back into shape for about £200.

user228700

@JohnRennie Ah, that's great! :-)

RogUE

@AccidentalFourierTransform half a laptop is of no use ;p

John Rennie

14:19

It won't look immaculate, but it's an old car anyway so I'm not fussed if it looks a bit scruffy.

AccidentalFourierTransform

touche

user228700

@JohnR: EEEK, a nerdfighter I met online wants to meet in person!

John Rennie

Half a lap-
top is crap
It'd leave young Ryan
sad and cryin'

@Kaumudi.H as long as they aren't a crazed axe wielding psychopath I'd say go for it. Have you asked them if they're a crazed axe wielding psychopath?

user228700

I have, I have x'D

user228700

John Rennie

14:25

@Kaumudi.H :-)

OMG there are loads of really amazing cheap laptops on eBay right now!

user228700

Anyhoo, I don't know how my parents would take it.

user228700

:-P

John Rennie

Why would I want to control my emotions?

user228700

Resist buying them all is what I meant :-)

AccidentalFourierTransform

14:28

resistance is futile

John Rennie

I might wait and see how much the car repairs are before buying any more laptops. But then I've got a large cheque coming soon for some programming work I did ...

Actually I was seriously considering this.

AccidentalFourierTransform

wut

they sell cars on ebay?!

man, the future is now

user228700

@JohnRennie But I thought you were having ur old one repaired? :-|

John Rennie

@Kaumudi.H Initially I thought the repair was going to be about £500, and that car will probably sell for less than £1,000. If so it would make sense to buy the replacement car and sell my old one for scrap.

user228700

Ah, OK...

user228700

14:33

@JohnRennie Haha x'D As long as u don't kill...

John Rennie

Now I know the repair is only about £200 that makes less sense, but then the repair will leave the car looking tatty.

It's possible that the car on eBay will sell for not much more than the £500 starting price, and if so it still might make sense to buy it and scrap the old one.

@Kaumudi.H I don't think I've killed any macroscopic organisms for ages.

Actually that's not true as I do kill flies.

user228700

Ah, flies. Well, my grandpa is all for non violence. He reprimands me even when I swat at annoying (af) mosquitoes :-/

John Rennie

That's very much a Brahmin viewpoint. You're not even supposed to accidentally breathe in and swallow flies.

My view is that there are lots of flies. The few that I swat won't be missed :-)

AccidentalFourierTransform

A for Asthma

►

user228700

@JohnRennie I guess. Enough about flies! I don't know what to do about this nerdfighter meetup thing :-/

ACuriousMind

14:38

@JohnRennie As long as you don't make that argument about humans...

John Rennie

@Kaumudi.H if he/she/it wants to meet somewhere public like a CCD I can't see any great harm in it.

@ACuriousMind hmm, there are times when I'm tempted :-)

Slereah

Hey hey

user228700

I'm not sure any human would want to be referenced using it even if they are gender fluid hmm. Anyhoo, right, I guess. I've never done that sort of thing before.

Slereah

For a physically realistic scenario, since the EFE doesn't determine the metric, is it a good idea to pick the Weyl tensor as $0$?

I'm fairly sure that it would translate as no gravitational waves coming from all over the place but i'm not sure

John Rennie

@Kaumudi.H If it's a lady then there's no issue. If it's a boy then there is the potential problem that the less well adjusted end of the spectrum think that if a girl even speaks to them it means she finds them attractive, and that can get messy.

But it may very well be that whoever it is just genuinely wants to be friendly.

Secret

14:44

I am lazy, I do use "it" a lot

0celouvskyopoulo7

I have too much stuff to move

this is terrible

I don't even use 75% of it

Jaime Gallego

Howdy

user228700

@JohnRennie Right, but I don't think that is a concern; although he is male, he says he's gender fluid and heh, I don't know, he seems genuinely excited just to meet another nerdfighter irl.

John Rennie

he says he's gender fluid - WHAT!!!

He's telling strangers about his sexuality. That's a red flag that is!

0celouvskyopoulo7

@JohnRennie is a horrible bigot it appears

wot

what does gender have to do with sexuality

AccidentalFourierTransform

14:46

genders are sexy

user228700

@JohnRennie No, it's not like that. There was this info. page to fill out and on that, gender was asked and he wrote gender fluid.

John Rennie

@0celouvskyopoulo7 absolutely not. I have no views on anyone's sexual preferences. However I do think anyone keen on discussing their sexual preferences with strangers is a bit odd.

ACuriousMind

@JohnRennie Gender and sexual orientation are generally considered distinct. If you have no problem telling others you're a man, you shouldn't have a problem with someone telling others they are gender fluid.

Jaime Gallego

@Kenshin That's the first time I've been adressed by initials, unless you meant John Galt or something :P

John Rennie

@ACuriousMind I don't think I have ever told a stranger I'm heterosexual. I restrict myself to statemnts like isn't the weather nice/awful today.

ACuriousMind

14:48

@JohnRennie I'd agree that sexual preference would be a bit odd to discuss upfront, but "gender fluid" is a characterization of gender, not of sexual preference.

0celouvskyopoulo7

We're not talking about sexuality

John Rennie

sexual preference would be a bit odd to discuss upfront - that was my point.

My concern begins and ends with starting conversations with strangers on that topic.

Though as K says I had misunderstood anyway.

Slereah

@0celouvskyopoulo7

Do u know

7 mins ago, by Slereah

For a physically realistic scenario, since the EFE doesn't determine the metric, is it a good idea to pick the Weyl tensor as $0$?

AccidentalFourierTransform

so you dont want to hear about my sexual preferences? just like my dad sigh

Slereah

wait, I don't think that makes sense

nevermind

how does one pick initial conditions in GR, anyway

John Rennie

14:51

@Kaumudi.H oops, that got lively :-)

Slereah

If you consider like a star

user228700

Sheesh, it did.

0celouvskyopoulo7

I was about to say that the initial/boundary conditions should help you out

Slereah

How do you define the initial conditions?

0celouvskyopoulo7

@Slereah I am trying to understand that for my research

Slereah

14:52

Do you just pick the Kerr metric and hope that's correct?

0celouvskyopoulo7

It's not straightforward at all

Slereah

Are there more possible initial conditions for GR than the "obvious" one + sourceless gravitational radiations?

John Rennie

@Kaumudi.H I'm not sure how good my advice is in these areas, but if the guy is proposing miles and hours of travel to meet up that would seem a little over eager to me. If you and he happen to be in the same area then meeting up for a coffee seems fine.

user228700

Although, @JohnR: ACM does have a point. Sexual preferences have little do with one's gender, you know. Not on the broad spectrum anyway.

0celouvskyopoulo7

I don't know. I desperately need to read stuff on this but skyrim is too damn good

Slereah

14:53

I mean I guess technically, we can pick a totally arbitrary initial condition

Skyrim's alright

John Rennie

@Kaumudi.H I agree, but I wasn't saying otherwise.

user228700

@JohnRennie Nah, he's coming to Chennai for an interview in June. In any case, I doubt if my parents would approve of this sort of thing.

Mostafa

[Stephen Hawking Says Humans Have 100 Years to Move to Another Planet](http://time.com/4767595/stephen-hawking-100-years-new-planet/)

(categorized under *Entertainment* section by Time.)

user228700

@JohnRennie What was the "That's a red flag, that is" about, then..?

Slereah

@Mostafa is that a threat

Are you threatening me mister Hawking

ACuriousMind

14:55

lol

Slereah

What is he going to do if we don't

AccidentalFourierTransform

stare

user228700

Ouch.

Slereah

Will he unleash the black hole

ACuriousMind

@Mostafa It's entertainment for most humans alive now - maybe not so much for our progeny ;)

John Rennie

14:56

@Kaumudi.H I thought from what you posted that he had been discussing his orientation with someone he'd never met before i.e. you. If a stranger did that to me I would (a) find it excruciatingly embarrassing and (b) think they were a creep.

ACuriousMind

Wait a moment, @JohnRennie, what do you think "gender fluid" means?

Slereah

Is gender a newtonian fluid

user228700

@JohnRennie Right, but he wasn't telling me about his sexual orientation, was he? His username is not his real name so I was unsure what pronoun to use. When I asked, he told me that he's gender fluid but leans in toward the female side of the spectrum.

Mostafa

@Slereah He must have got the idea from Interstellar.

user228700

Even so, he could be straight, you know. I don't know if he is and that goes to show that he hasn't been discussing his sexual preferences with me.

John Rennie

14:58

@Kaumudi.H Yes, I now realise I'd made unjustified assumptions.

Slereah

if genderfluid obviously he can't be straight, unless his sexual orientation perfectly matches his change in gender identity

user228700

@Slereah I was wondering about this and it seems that sometimes, this is the case.

Slereah

Consider his gender expression as a time series $f : \Bbb R \to I$

AccidentalFourierTransform

and assume some initial conditions

user228700

@JohnRennie Ah, hmm, OK :-)

Slereah

15:00

Where $0 \equiv ♂ $ and $1 \equiv ♀$

ACuriousMind

@AccidentalFourierTransform ...worst setup for a "did you just assume their gender" line I've ever seen.

AccidentalFourierTransform

did you just assume I'm differentiable?

Slereah

Then his gender orientation would have to be towards $1 - f(t)$ to perfectly match and be "straight"

This works on a broad class of functions even if non-continuous

AccidentalFourierTransform

is the manifold of genders orientable?

Slereah

I'm not sure, it depends if, after rotating from male back to male, your sexual orientation is still the same

For all paths

John Rennie

15:02

@Kaumudi.H: Anyway, where we came in was that if he's in Chennai anyway, and you know him through the nerdfighter stuff, to meet up for a coffee seems fine to me. It would not concern me if my 18 year old daughter did that.

But I guess your parents may have different views.

→ 1 message moved to Trash

Slereah

There isn't any default gender symbols in latex

Very inconvenient

You need a specific package

John Rennie

@AccidentalFourierTransform A step too far! Remember I am young and innocent.

user228700

@JohnRennie I suspect they will, yes :-/ He's older too; 25, I think. I agree that it would be a nice experience and all! I've never done that sort of thing. Anyhoo, I'll ask my parents and let you know what happens!

ACuriousMind

@Slereah Hm? The mars/venus ones seem to work in MathJax, no?

Slereah

Not that I know

$\mars$

0celouvskyopoulo7

15:04

@Kaumudi.H your future husband is gender fluid?

Slereah

nope

ACuriousMind

Ohhhh, you used unicode up there

user228700

@0celouvskyopoulo7 -_-

Slereah

yeah

ACuriousMind

damn unicode

Secret

15:05

I am a quantum gender fluid, I consists of equal parts of female and male eigenstates that flucturates in time

and depend on who I interact with, I show my boy side or girl side more

The hamiltonian that governs this fluctuation cannot be solved analytically

Mostafa

@ACuriousMind As you probably know, Lubos is also interested in climate change discussions...and he once said a wise word about it:

If they're hypothetical worries about the future generations, then please leave the problem to future generations who will know 10 times more about these issues than myself and 500 times more than you. But it is silly to extrapolate. The climate is a chaotic system and most of the changes are short-term noise that cancels over longer periods of time. If the temperature changes by less than 1 K in 100 years, it doesn't mean that it will jump by 10 K in 1,000 years. And the changes due to CO2 are slowing down due to the log character of the greenhouse effect, they'll be more and more negligible. — Luboš Motl Jan 25 '14 at 15:10

If they're hypothetical worries about the future generations, then please leave the problem to future generations who will know 10 times more about these issues than myself and 500 times more than you. (Lubos Motl)

Secret

The world have changed so rapidly it is meaningless to answer that typical "where do you see yourself in 10 years"

For one, it is equally likely for the world to spontaneously implode as to remain stable and growing rapidly

Mostafa

@Secret Yeah, the world will either implode or not implode, so it's 50-50.

Secret

Art is what you think art is

Jaime Gallego

Why do we keep coming back to pineapples

Secret

15:15

We seemed to know well what is art (despite we are unable to express that fact verbally), but we have no idea what a non-art is in general

Balarka Sen

@Kaumudi.H I looked for Doubtfire by Robert Nye but I couldn't find it so I ended up working math.

Here is some good stuff, however. It's probably on my list of top 5 (postmodern) short stories.

John Rennie

@BalarkaSen Wow, Kirkus reviews says: Even though it may seem impulsively premature, it would be hard not to think that this might be the most irritatingly unintelligible book of the year. A triumph of logorrhetic matter over mind which no amount of application can combat.

They aren't fans of the book then :-)

Balarka Sen

yeah, i saw that. exactly my kind of stuff, seems like

(You might like the sci-fi short I linked above, BTW, JR)

John Rennie

@BalarkaSen Reading now ...

AccidentalFourierTransform

why does $\mathfrak r$ look so bad

Slereah

15:35

Haag defines properly the derivatives of field operators, which is nice

$$\lim_{\lambda \to 0}\lambda^{-1} \| \alpha_\lambda \Phi - \Phi \|$$

AccidentalFourierTransform

with $\alpha_\lambda\Phi(f)=\Phi(T_\lambda f)$, with $T_\lambda f(x)=f(x+\lambda)$, I guess

Slereah

Yeah

It is the famed Poincaré automorphism

That generates a Poincaré transformation

AccidentalFourierTransform

and what about those $||$?

Slereah

And $\| \|$ is the uniform topology on operators

although he defines a bunch of topologies for the operators

0celouvskyopoulo7

Are ywe doing functional analysis now?

Slereah

15:44

in the end isn't everything functional analysis

AccidentalFourierTransform

in the end it doesn't even matter

Secret

what last night dream told me the end of all existence might look like: A white void of countable number of $\infty$ symbols

Slereah

This is not interesting in the slightest

AccidentalFourierTransform

$\prod_{j=1}^\infty\infty$

Slereah

that is most certainly true

Apparently Noel Hicks has been dead since 1979

I guess I can't send him an email

AccidentalFourierTransform

15:56

why not

Slereah

No internet in hell

apt45

Hi guys. A question about the strong CP problem. How can I prove that under a chiral transformation $\psi_R \rightarrow R \psi_R$ and $\psi_L \rightarrow L \psi_L$, the theta angle shifts by Arg Det ( R^\dagger L ) ??s

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