The h Bar

2:25 AM

example of cutting edge scientific research via simulation/ computational physics, found on reddit compsci / High-Accuracy Mass, Spin, and Recoil Predictions of Generic Black-Hole Merger Remnants / Phys Rev Letters journals.aps.org/prl/abstract/10.1103/PhysRevLett.122.011101

Avnish Kabaj

2:45 AM

in The Periodic Table, 9 hours ago, by M.A.R. ಠ_ಠ

And I have this cricket bat with trap wires for times of zombie apocalypse. Remind me when @Avnish is on

user351417

3:55 AM

@AvnishKabaj I've met one guy who wants to be a chemist but he's still planning to do med school ¯_(ツ)_/¯

John Rennie

5:29 AM

@Loong polytraumatic :-)

2

That's such a great description :-)

user351417

6:46 AM

0

Q: Requesting features in chat

When I try to ask some questions in chat in general,the members in the room sometimes they don’t respond me (I can understand it may be they are discussing on some other topic).so then after some lots of chat the page jumps to new ,again if I want get feed from the same question I need to type wh...

PM 2Ring

7:02 AM

And of course another hazard facing the hovering observer is the tendency to turn into a thin red paste on the deck of your ship due to the outrageously high acceleration. Eg, for Sag A* it's roughly 380,000g near the event horizon. — PM 2Ring 1 min ago

And if that don't get you, the fuel bill surely will. :D

John Rennie

7:13 AM

@PM2Ring for all black holes the acceleration required to hover goes to infinity as you approach the horizon, so all black holes will have some hovering distance where the acceleration would be 380,000g. The only difference between large and small black holes is the distance where this happens.

PM 2Ring

@JohnRennie Oh, ok. In that case, what's the "surface gravity" that xaonon.dyndns.org/hawking calculates?

John Rennie

@PM2Ring surface gravity is a somewhat complicated quantity. It's kind of the acceleration at the event horizon corrected for the red shift at the horizon.

The acceleration at the horizon is infinite, but the red shift is also infinite. You kind of use these two infinities to cancel each other out to get the finite quantity called the surface gravity.

But this quantity is not something any observer would experience in their explorations of the black hole. Hawking uses it as a way to characterise the curvature at the horizon and from that get the Hawking radiation temperature.

@PM2Ring if you want the gory details (and they are pretty gory) then Wikipedia describes the calculation here.

PM 2Ring

7:30 AM

@JohnRennie That makes sense. Before I discovered the xaonon calculator, I always assumed the acceleration is infinite at the horizon, since the escape velocity is c. But I figured that the calculator's author knew what he was talking about...

@JohnRennie Thanks, John. I'll take a peek. I might understand some of it. :) And I'll delete that comment.

Ok. That wasn't too gory. And I think I understood bits of it. :) I'd like to learn more GR, but tensors make my brain melt. Which is strange, because I have no problems working with multidimensional arrays when I'm programming.

PM 2Ring

7:51 AM

"the acceleration, as exerted at infinity, needed to keep an object at the horizon". So if we have a payload hovering at the horizon because it's attached by an inextensible rope to a spaceship hovering at infinity, if we cut the rope, then the ship will go hurtling off at that acceleration.

Slereah

morning

Loong

8:49 AM

huomenta

@JohnRennie :-)

Avnish Kabaj

10:05 AM

@Chair Heh heh he

user351417

@AvnishKabaj It's still 12th grade though, so nothing particularly certain. He's applying for a molecular bio major.

Avnish Kabaj

I see

2

John Rennie

10:49 AM

@AvnishKabaj sounds fine to me :-)

Avnish Kabaj

11:07 AM

:P

ACuriousMind

11:18 AM

That is genius and I would immediately start doing it if I liked hard-boiled eggs :P

user351417

12:02 PM

Does anyone have any good Catch-22 jokes to spew right now, while we're still talking about hard-boiled eggs?

ACuriousMind

12:15 PM

Stop egging this on

user351417

I'm sure we'll all crack up though.

Anonymous

Stars and eggs. Today's a fine day.

PM 2Ring

I've had an oeuf of these egg jokes.

user351417

Can't beat that one.

Anonymous

12:36 PM

But you can poach it.

PM 2Ring

"My Uncle Marvin thinks he's a chicken."
"You should take him to a psychiatrist."
"Oh no, we can't do that!"
"Why not?"
"We need the eggs."

PM 2Ring

12:53 PM

Today I answered an Astronomy question that reminded me how small Earth is compared to the galaxy. astronomy.stackexchange.com/questions/29341/…

PM 2Ring

1:03 PM

Thanks for the edit, @Loong

Loong

no problem

Secret

1:16 PM

buzzfeed.com/stacygoldberg488/…

Kiss your memes goodbye, 4chan is shutting down

3

bolbteppa

3:48 PM

@Secret The 8 one is worse apparently

@vzn listened to half of it, boring but she was actually defending string theory against his comments in the part I heard haha

John Rennie

4:06 PM

This might prove a bit too ambitious:

vzn

@bolbteppa lol maybe shes not as much as an unmitigated villain or crazywoman as some would ~~project~~ believe :P

Anonymous

4:43 PM

@JohnRennie What are those white and round things? :D

Anonymous

Today my parents are not home and I'm ordering a big pack of chocolate ice-cream all for myself. 'Tis gonna be fun. :P

Emilio Pisanty

@ACuriousMind courtesy ping on an unilateral de-dupe-hammer. :-).

@JohnRennie are you planning on eating all of that?

goodness.

Anonymous

@EmilioPisanty I'm sure it's already in his stomach by now. ;)

Anonymous

Jan 20 at 16:47, by John Rennie

@Blue too late anyway. It has spontaneously collapsed into ... erm ... my gut. Not exactly a black hole though it's probably pretty dark in there.

ACuriousMind

@EmilioPisanty I'm less worried about you reopening the question than I am about you thinking $\delta(x)$ is an admissible state!

Sid

4:51 PM

@Blue Ice cream at night?!

Emilio Pisanty

@ACuriousMind what do you mean by "admissible"?

Sid

Your parents will be livid at you. :P

Anonymous

@Sid Is appropriateness of having ice-cream a function of daylight intensity?

Anonymous

@Sid I'll leave no traces. ;)

Anonymous

They won't be back for another 4-5 hours at least.

Sid

4:54 PM

Ice cream contains high amounts of fat which is digested at a slow rate. It also contains a lot of sugar which can keep you up at night.

So, it's not particularly healthy to eat that at night.

ACuriousMind

@EmilioPisanty That it is an object of which we may claim that it has "expectation values" and "uncertainties" for observables.

Anonymous

I'm nocturnal anyway...

John Rennie

@Blue meat pies. The crust didn't brown in the oven for some reason, so the pastry was a bit soft though the flavour was nice.

Sid

Ah. If you are nocturnal, it doesn't matter then. Screw health and eat whatever you like. :P

Yashas

Electric and magnetic ﬁeld are respectively given by $\vec{E}(~r,t)$ and $\vec{B}(~r,t)$.

(a) What is the net charge on a moving particle if it carries a charge q?

John Rennie

4:55 PM

@EmilioPisanty I have eaten the lot, and am now starting in on the dessert - custard tarts.

Yashas

What trickery is going on in that question?

Emilio Pisanty

@ACuriousMind then you're conflating "admissible" with "physical"

"Blue meat pies"? What are those?

oh, wait.

Anonymous

Lolol

ACuriousMind

@EmilioPisanty In my world, a state is by definition an element of a Hilbert space upon which the observables act. If we use wavefunctions, then this space is that of the square-integrable functions. $\delta(x)$ is not inside this space and hence not a "state". That it is a function-like object that you can plug into the same formulae as those applying to wavefunctions should not be seen as accepting it as being a "state".

Novalium Company

I was just wondering about morality (cuz I'm reading a book on philosophy) and if you think about it, morality is actually relative and it all depends on how you perceive the world. For example, for me, killing is immoral and wrong, but for a member of the ISIS, who interpretes the world another way, for him, killing is making good, for him killing is freeing another being from this jail cell called 'life'. Do you think the ISIS member felt immoral? Why haven't the ancient philosophers thought

of this?

Emilio Pisanty

4:59 PM

@ACuriousMind so you're of the opinion that rigged Hilbert spaces are heresy?

(or something?)

Sid

@NovaliumCompany Yeah. And the morality that all religions teach is to respect life. Not destroy it.

Anonymous

2

Anonymous

@Sid Just got the delivery. :P

ACuriousMind

@EmilioPisanty Yes

Emilio Pisanty

@ACuriousMind well, that's just you and your limited ways, then.

Anonymous

5:00 PM

It's a pity that I don't have four hands...

John Rennie

@Blue A worthy attempt to persuade us that you're sharing the ice cream with three other people :-)

Sid

@Blue Why are there 4 spoons on it?

Yashas

@Blue is that tape on your screen?

Anonymous

@Sid It's family pack...so they gave 4 spoons. Little did they know I'll eat it alone.

Anonymous

@Yashas Yeah, the top part was a bit broken.

Anonymous

5:02 PM

@JohnRennie Absolutely not! ;)

Sid

I got a personalized T-Shirt yesterday. Cost me just a hundred.

ACuriousMind

@NovaliumCompany 1. Some people believe in an absolute morality, i.e. that there exists something that objectively makes acts (im)moral, and that people who think differently are simply wrong. You have made no argument against this position. 2. Even the people who do not believe in an absolute morality can still be of the opinion that there is a certain morality that people should adhere to (perhaps in order to achieve certain outcomes).

@EmilioPisanty Yes

Novalium Company

@ACuriousMind How would a person know whether he is moral or immoral in a situation. If he feels the 'bad feeling' in the stomach then he is wrong? :D

@ACuriousMind There aren't any proof nor arguments that such universal absolute morality exists?

Sid

@NovaliumCompany Well, one absolute morality that I know of, is don't kill people indiscriminately.

Novalium Company

If you think about it, if such absolute morality existed, then it would apply to animals too. Animals kill each other for their own needs and I suppose they don't 'feel' immoral, therefore moral means to kill people if you have a good reason to do so xDD

bolbteppa

5:09 PM

$\mathrm{spin}(2n)$ having four elements in it's center corresponds to the whole CPT transformations on $\mathrm{SO}^{\uparrow}(1,3)$ right?

ACuriousMind

@NovaliumCompany Of course there are! For instance, Kant wrote many words about why the categorical imperative is a moral principle that every creature endowed with "reason" should follow, for his particular conception of "reason".

But much more widespread than believers in absolute morality are those that still think you can grade different moral systems according to a meta-ethic measure (e.g. utilitarists might admit there's no universal morality, but still say that those moral systems that more efficiently minimize suffering or maximize utility/happiness are better than others).

Novalium Company

@ACuriousMind How would a person know whether he is moral or immoral in a situation. If he feels the 'bad feeling' in the stomach then he is wrong?

ACuriousMind

I'm afraid I don't understand the question

Novalium Company

How do you know whether you are morally wrong in a situation or not?

ACuriousMind

@NovaliumCompany That is precisely the question the philosophical field of morality/ethics seeks to answer.

As you may have noticed, there's a plethora of competing answers.

John Rennie

5:18 PM

@NovaliumCompany humans are rather prone to kill other humans, and the motives generally have little to do with moral arguments (though moral arguments are frequently used as post rationalisations).

It's one of the triumph of modern societies that on the whole we have managed to stop people killing other people.

Novalium Company

@ACuriousMind If there is no way to understand whether you are morally wrong or right, why do you even care then? For example I can kill a person without a reason, then I should feel morally wrong?

John Rennie

@NovaliumCompany on the whole, modern societies have made life comfortable enough that there is little to be gained from killing your fellow humans, and of course should you decide to do it society imposes sanctions on you. This seems an excellent example of how a pragmatic approach has made life better without waiting for the philosophers to come to any useful conclusion.

Novalium Company

Alright then but how did humanity even come up with the concept of morality if there is no way to 'detect it' or even understand what it is?

ACuriousMind

@NovaliumCompany Where did you get "there's no way to understand whether you are morally wrong or right" from? Again, e.g. a utilitarian would say you're wrong if there would have been a different action that would have increased total utility more.

John Rennie

@NovaliumCompany post rationalisation. Morality tends to mean disapproving of things that you don't want done to you or those you love.

ACuriousMind

5:25 PM

If we had an inborn "detector" for what's right or wrong that was obvious to everyone, then we wouldn't have had to come up with moral debates because everyone would just agree

Of course, you could also imagine humans having different inborn moralities and then argue that moral debates are humans trying to argue about qualia, like a color-seeing and a colorblind person trying to debate whether something is "red". I'm sure someone somewhere holds that view.

Novalium Company

@JohnRennie If that's the case, then I'm sure my teacher wouldn't want to be told to sit and stay silent on a chair all day, being told what to learn, being judged based on grades and so on, but she still does it to us in school. Is she morally wrong? Or if I perceive school in another way, then she does good to us. Again, it all breaks down to how you interpret, therefore morality is flexible to the individual?

John Rennie

@NovaliumCompany your teacher has a job because they did precisely that some decades ago. They are doing exactly what experience has told them was good for them in the past.

Emilio Pisanty

surely this is spam, right?

Sid

@EmilioPisanty Why is it Spam?

Novalium Company

@JohnRennie I'm not making the connections. What has that have to do with anything? You said that you shouldn't do what you don't want to be done to you (and your loved ones). If she suddenly becomes a student, she may start to interpret educations as torturing, therefore, she wouldn't want to be tortured and she was doing morally wrong things as a teacher?

Anonymous

5:32 PM

@Sid Look at the email id. :P

Emilio Pisanty

@Sid well, the domain it was sent from does not resolve to anything at all, let alone an institution that would hire professors

but for the life of me I can't figure out why a spammer group would send such an email

John Rennie

@NovaliumCompany your teacher was a student once, and probably didn't like being told what do either. But as a result of being told what to do your teacher learned enough to get a job as a teacher, thereby earning money to provide for themselves and their family. This is good.

So your teacher knows that by torturing you they can ensure that you you too will get the chance to live rewarding lives when you're grown up.

Novalium Company

@JohnRennie So again, it all depends on how you perceive and intepret. Her (my teacher's) perceptions and view on the topic of educations were changed, therefore changing her morality???

Loong

@EmilioPisanty security.arizona.edu/phishing-alert/…

John Rennie

Your teacher may also have children, or be planning to have children, and will want them to live happy and rewarding lives as adults. So your teacher has a vested interest in fostering a society where education of children is important.

Emilio Pisanty

5:36 PM

@Loong interesting

John Rennie

@NovaliumCompany I'm not saying that your teacher consciously thinks this every time they tell you to sit down and shut up. However I think it very likely that their world view has been coloured by their background.

Or maybe they really hated school and are now inflicting a psychopathic campaign of terror on you lot to make themselves feel better :-)

Emilio Pisanty

@Loong so, they're just hoping for responses to get active email accounts, filtered by "is likely to respond to phishing"?

or they actually do want the HR email, so they can go on to do some more focused spear-phishing on them?

Novalium Company

@JohnRennie If she had children when she was in school and interpreted school as torturing, then she would feel morally wrong to send her children to school at that time, but when her views on education changed (she grew up...) she would feel moral and right to send her children in school, therefore "Morality is flexible and depends on how you intepret the world and you paradigms." ( - Novalium)

Abcd

@JohnRennie Why am I getting this error in MS Word 2007 ^?

John Rennie

@NovaliumCompany and how is that different from:

17 mins ago, by John Rennie

@NovaliumCompany post rationalisation. Morality tends to mean disapproving of things that you don't want done to you or those you love.

@Abcd probably a bug related to video drivers. If you print it you'd probably find it prints ok.

It would be worth checking the paragraph formatting for that line just to make sure that the line depth hasn't been set to a value too small to allow the text to be displayed.

Novalium Company

5:45 PM

@JohnRennie Your sentence doesn't mention anything about how you intepret and perceive. Whatever, I was just reading about those philosophers arguing about what morality is, and I came to the conclusion that it all breaks don't to how you intepret. Therefore there is not right answer?

John Rennie

@Abcd aha, if I set the line spacing to a silly value (0.5 lines) I get:

Novalium Company

@JohnRennie So why are philosphers still wasting their time, trying to figure out what is morally wrong or right, when it all breaks down to your paradigms...?

Abcd

@JohnRennie how to change that? It is only happening on the top line, not on the other lines

John Rennie

@Abcd right click the line and choose Paragraph. What is the line spacing set to?

Abcd

@JohnRennie "7 pt"

John Rennie

5:48 PM

Abcd

@JohnRennie "Exactly, 7 pt"

John Rennie

@Abcd that's the problem. 7 points is half a line so the line depth is too small to show the text.

Abcd

@JohnRennie Oh if I change exactly to Multiple then it shows full

@JohnRennie I dint change 7 pt

John Rennie

@Abcd BOOM! :-)

@Abcd that's what end users always say

Flushed with success at solving not only physics problems but also the issues of morality and Word formatting I am now going to repair to my armchair, drink some beer and read this weeks New Scientist. See you all tomorrow.

Novalium Company

@JohnRennie xDDDD see you <3

Unknown MathMan

6:02 PM

I was wondering, what will be change in the Schr"odinger equation when we will work on momentum.. I searched for it and got the first answer of [this question](https://physics.stackexchange.com/questions/249400/schr%C3%B6dinger-equation-in-momentum-space) .. but not getting how he is getting the first equation -
$$\Psi(x,t) = \int dp \frac{e^{i\frac{p}{\hbar}x}}{\sqrt{2\pi\hbar}}\Phi(p,t)$$
Can anyone explain me :)

ZeroTheHero

6:22 PM

@EmilioPisanty ah! you got that one too...

Emilio Pisanty

@ZeroTheHero did you get it recently?

ZeroTheHero

'bout 7-10 days ago I think.

Emilio Pisanty

@ZeroTheHero huh

ah, well

flag as phishing and move on, I guess

2

Q: What happens to the $3d$ and $4s$ levels during the ionisation of a transition metal?

I'm just wondering about the transition state of a transitional metal before (ex: $[\mathrm{Ar}]\, 3d^3 \,4s^2$) and after ionisation (which means $[\mathrm{Ar}]\, 3d^3 \,4s^1$) because before ionisation the $4s$ level is closer to the radius (the $4s$ orbital is filled before the $3d$ orbital). ...

photons electrons atomic-physics orbitals ionization-energy

huh

surprisingly nontrivial

ZeroTheHero

6:39 PM

@EmilioPisanty How many professors you don't know at all are gonna contact you to get info on how to apply for a position where you work? Unless you name is at the top of some webpage or something...

Emilio Pisanty

@ZeroTheHero yeah, it figures

I'm still curious as to what the underlying business model is for the folks sending the email

but not curious enough to go looking

ZeroTheHero

@EmilioPisanty Admittedly I asked myself the same question.

Emilio Pisanty

heck, probably the only way to tell for sure would be to convince IT to set up a honeypot HR address, reply to the spammers with that address, and see what lands there

but ultimately you're just opening yourself up for more spam.

ZeroTheHero

indeed. The blanket policy for such is to play dead.

Emilio Pisanty

indeed

Novalium Company

7:21 PM

I was thinking about the material (such as a rock) and the immaterial (such as the 'soul') and how non-contact forces (such as the magnetic force) manipulate objects without physical contact? Is there something beyond the physical?

Gravity is also a non-contact force. Maybe gravity exists in another dimension? If gravity exists beyong the physical, how about the soul? Maybe part of us exist beyond the physical?

Anonymous

Man, what has happened to you. :P

Novalium Company

I don't believe in the soul, but gravity and magnetic forces are examples that not everything is in the materialistic realm?

@Blue xDDD

@Blue It's still me, I'm just... evolving.

@Blue How are you doing anyways? I'm watching Thor 2 currently. How is university?

Sir Cumference

@NovaliumCompany These "contact forces" are all just approximations for the electromagnetic repulsion between atoms, which can act from arbitrary distances (but get stronger as objects are closer) :P

The majority of your "non-contact" forces are mediated by particles, so I guess there's the contact

Anonymous

@NovaliumCompany The point here is non-contact forces are within the frameworks of physics (and more or less explainable with our current models), whereas discussions about "soul" is simply metaphysics (and you're unlikely to find any satisfactory answer about it). If you're looking for answers to how exactly non-contact forces work it's better to start reading actual physics rather than delving into metaphysics.

Anonymous

"Materialistic realm" and "soul" are very vague terms. In physics we talk in terms of precise mathematical models.

Novalium Company

7:37 PM

Alright, I totally agree. So if those non-contact forces are just a product of electromagnetic waves then do electromagnetic waves exist in the physical 'realm' :D?

Anonymous

Again, the term "physical realm" means nothing per se, to a physicist. You need to precisely define (in mathematical terms) what you mean by that. And to be able to do that, you need to learn actual physics first.

Anonymous

As it stands, your question is simply a word-salad.

Sir Cumference

Also I said your examples of "contact" forces were all a product of EM forces. There are other forces that are not, e.g. strong force

Novalium Company

Pff, alright then.

@Blue How do you describe the 'physical realm' with mathematical equations?

Anonymous

@NovaliumCompany I don't know what you mean by "physical realm".

Novalium Company

7:47 PM

@Blue Me neither :D

Sir Cumference

Well I think I figured out the problem :P

Novalium Company

xDD

Sir Cumference

Curiosity is good, just if you want it to match reality it needs to be supported by math

Novalium Company

@SirCumference I agree. I'm just watching Thor 2 and I can't focus. I guess I'll be back tommorow. :)

See you.

Novalium Company

9:00 PM

How do we write $\frac{d}{dx}$ when $f(x, y)$ for example, maybe $\frac{d}{dx,y}$ :D?

Maybe just $f(x, y)'$?

ACuriousMind

@NovaliumCompany What do you mean by that?

You can't just write down $f(x,y)'$ and act as if it means something. You need to define what you mean first.

Novalium Company

When we want to find the derivative of a function we write $f(x)'$ or $\frac{d}{dx}$, right? But what about if the function has 2 independed variables?

Oh wait

ACuriousMind

Well, what do you mean by "the derivative" for a function with more than one variable?

Novalium Company

I have no idea.

ACuriousMind

For functions with more than one dependent variable, the notion of "derivative" is not unambiguous. There are partial derivatives and total derivatives

Novalium Company

9:05 PM

mathsisfun.com/calculus/derivatives-partial.html yep

got it

Sorry for wasting your time with retarded questions.

@ACuriousMind You seem to be quite advanced in a lot of fields such as Physics, Math, Philosophy, Biology, Chemistry... how do you know so much?

@ACuriousMind How old are you or you value your privacy?

ACuriousMind

@NovaliumCompany I have a good memory and I've had a few more years to learn stuff than you have - though I wouldn't call myself "advanced" in biology or chemistry :P

@NovaliumCompany I'll turn 26 in about two months.

Novalium Company

@ACuriousMind You must be learning things all the time? What do you mean by "I've had a few more years to learn stuff than you have"?

ACuriousMind

@NovaliumCompany iirc you're about a decade younger than me, no? :P

Novalium Company

I am exactly a decade younger :)

ACuriousMind

I didn't know many things when I was 16, though like many teenagers I sure thought I did :P

Novalium Company

9:16 PM

How did you proceed with your life? Any education, jobs...?

ACuriousMind

Well, I studied physics and now I'm a software engineer. Somewhere along the way I learned how to fake being a responsible adult, too, I guess.

Novalium Company

Judging by the fact you spend quite some time on this chat forum, you don't have many friends in real life?

ACuriousMind

I wouldn't say that - I'm happy with the number of friends I have and the amount of time I spend with them.

Novalium Company

Okay :)

Разбираш ли какво ти говоря?

ACuriousMind

No, I don't speak Bulgarian :P

Novalium Company

9:24 PM

:D

What do you plan to do with your life? Why don't you start a company? Are you satisfied with your current position as a software engineer, do you wish to proceed with it?

Btw I'm pretty advanced with all soft of programming, test me :D

ACuriousMind

@NovaliumCompany Why would I start a company? Life's good as it is.

Novalium Company

Alright then. I'll go to sleep, so cya.

pZombie

hello friends

Jake Rose

@JohnRennie you around?

ive started my quantum mechanics course so I’m probably gonna be bothering you for the next 24 lectures or so

Anonymous

He's sleeping now. :)

pZombie

9:37 PM

Can infrared radiation be bundled using lenses or dishes just like visible light can?

Jake Rose

@Blue mind if I bother you?

@pZombie yep, it’s just an em wave like light is. Not sure just typical glass would work though.

Anonymous

Nah, I need to leave too. If you have questions, just ask. Someone else might answer.

Jake Rose

the refractive index (the number which essentially determines how lenses work) often depends on wavelength

@Blue fair does

not quite sure what I’m asking so wanted to work through it in a donversation

pZombie

Jake - yes, that is what i thought too. But then what would prevent us from bundling the infrared radiation a large object emits and point it towards another object, heating it up?

@JakeRose Since any object in a non closed system subject to the atmosphere is emitting as well as absorbing infrared radiation at all times, what would happen if we bundled its emitted radiation, using aluminum or gold dishes or some lenses onto a point to heat up some other object? If that would work, then we could extract energy from the atmosphere and point it to a given object to heat it up and later do work

but i guess such a thing would be impossible as it would already be done

Jake Rose

The problem isn’t that you can’t do this, it’s just that it’s incredibly inefficient

pZombie

9:46 PM

@JakeRose So it would actually work?

Jake Rose

I mean theoretically yes, but practically no

pZombie

@JakeRose To get 100w of infrared emissions from an object, about how large would the object have to be (rough estimate) and which known material and shape would be most suited ?

Jake Rose

@pZombie I have no idea, but I’m guessing a parabolic mirror

solar farms use this principle to turn sunlight into energy

pZombie

@JakeRose at about 20° celcius i might add

Jake Rose

the temperature wouldn’t really matter

pZombie

9:49 PM

@JakeRose temperature should matter. I don't think an object would emit any radiation at absolute zero

Jake Rose

oh I was considering the solar radiation still

the question is too vague

the properties of the object decide what energy it emits

the perfect case being a black body

The dimensions of the mirror also depend on the dimensions of the object

pZombie

@JakeRose No, consider we go inside an underground cave with a temperate of about 20 degrees C. Wouldn't any object emit and absorb infrared radiation still, even if there is no light source at all?

i might ask this question on SE but first i have to know if it makes sense at all. I am trying to figure if one could come up with an energy source underground, given a large enough object and mirrors/lenses/dishes. Even if not practical i would like to hear some numbers about how large the object would have to be to get about 100w or 1kw out of it

I am not sure if this goes against the 2nd law of tm. In a closed system it should, but here i am considering an open system

Jake Rose

@pZombie things do emit infrared radiation. But the boundary conditions aren’t well set out to give any meaningful approximations

people do use the geothermal radiation, but not using mirrors because it’s just unpractical and adds unessecary ineffiencies

what you are talking about certainly doesn’t violate the 2nd law

The thing is you need to know the dimensions of an object to use lots of optic apparatus as they matter for its design

pZombie

@JakeRose I am not concerned about efficiency. Only about if one can extract useful energy from an object deep underground, just by bundling its emitted infrared radiation. Even if it just 1 picowatt

@JakeRose I mean, one could use a whole mountain's emitted radiation if there was a way to bundle it

or the ground of earth itself

Jake Rose

10:06 PM

If it’s only 1 picowatt I argue that it’s not useful

what I’m saying is we already do this

geothermal energy stations use exactly this principle just not using mirrors

bevause they aren’t needed

tk get the thermal energy from a mountain would be impossible. You’d need to completely surround the mountain, and eventually it would reach thermal equilibrium with the mirrors, which would probably radiate more energy than generated.

assuming the mountains generate heat via some mechanism, such as radioactive decay

pZombie

why would i have to surround the mountain? One dish on one side having the mountain at the focal point and another dish focusing the radiation from the first dish onto another point

the mirrors wouldn't reach equilibrium because this is an open system

the atmosphere would keep the mirrors cool enough and i am not talking about radioactive decay but simply the radiation any body absorbs and emits at a given temperature

i guess i ll just ask the question and see if it gets deleted

probably will

Jake Rose

@pZombie because the mountain would radiate energy into the areas you haven’t covered

pZombie

yes it would, as it always does, but that is radiation going into all directions. I am only concerned about the radiation of the mountain i bundle onto another point

Jake Rose

@pZombie you’d need LARGE mirrors, too big to be created.

And you’d need the atmosphere to be non existent to avoid stuff getting in the way

pZombie

as i said, i am not concerned about if it is practical or not, just if it would be possible theoretically to get useful energy this way, even if it would be just a tiny amount

Jake Rose

10:14 PM

the reason you need radioactive emissions in the mountain is that that is one of the ways the mountain generates heat.

if you overall have a loss of energy i declare that is not useful energy

pZombie

where would i lose energy?

oh, you mean like manufacturing the mirrors

lifetime of mirrors etc

i am not concerned with that either. I am not looking for some practical application. Just wondering if it is theoretically possible

also, ignore the radioactive decay. Assume there is none because i am only concerned of the usual infrared radiation any object emits and absorbs depending on its temperature

your objections might help me define my question more precise such that those won't come up in the anwers

Jake Rose

You’d lose energy in just operating the mirrors and all the other stuff you’d have to use

pZombie

why would i have to operate the mirrors? They would be fixed to reflect the radiation towards one point

Jake Rose

’theoretically possible’ in my opinion includes this. You’re asking would you theoretically be able to get energy out of this that’s usable. I’m saying no, because you’d require more energy to run the thing than it makes.

if there’s no radioactive decay then eventually the mountain would cool until it’s in thermal equilibrium with open space

ignoring the few other heat mechanisms

this is a pretty ill defined question, and in general not a useful one in my opinion

pZombie

there is no open space. There is an atmosphere still. When you pick up an item, it has a temperature and is usually not at absolute zero. Certainly not because there is radioactive decay involved, at least usually there is not

a mountain without any radioactive decay would not drop down to absolute zero, just like a rock you pick up from the ground does not

Jake Rose

10:22 PM

The rock you pick up from the ground gets energy from other sources

if you want to make a theoretical approximation you have to approximate things, such as the mountain not taking in energy from other places, the sun isn’t incident on it etc

pZombie

@JakeRose Yes it does and it emits energy towards other sources. As i said, i am not talking a closed system, but an open one

@JakeRose again, i am not talking a closed system. The sun heating up the mountain as well as the atmosphere doing so is part of the system. The radioactive decay is not though because i used the mountain just as an example. We could use the pyramids or a large metal sphere or whatever else

Jake Rose

Then there’s simply too many variables to make any meaningful calculations

why you’d even do this when you could point the mirrors at the sun is beyond me

pZombie

i am not sure about that. There should be a formula to calculate how much infrared radiation an object at a given temperature emits for a given time interval

and some formula on how much of that radiation you could possibly capture and focus onto a point

Jake Rose

10:38 PM

Which rely he sully on approximations about the source etc

your source is a mountain

thst is not an approximation

the formulas we use are based on well defined approximations

pZombie

no, my source is not a mountain. It can be any suitable source but it is alright. I asked my question now. Hopefully it won't get deleted :D

Jake Rose

11:02 PM

Probably gonna get deleted, is only too hndefined

bolbteppa

11:24 PM

My god, a spinor in 10D has 32 components, the Majorana makes them real, the Weyl condition reduces the number to 16, and the lightcone gauge again the number down to 8 transverse components, these 8 components have an $SO(8)$ symmetry and so are elements of a spinor representation of $SO(8) = SO(2 \cdot 4)$ related to the $D_4$ Dynkin diagram which satisfies triality. Madness

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