The h Bar

4:00 AM

twitter.com/Maverick_bharat/status/1315129625647837186?s=20

@SirCumference IDE (Integrated Debugging Environment), most of the IDEs have that features.

twitter.com/Maverick_bharat/status/1315129625647837186?s=20

4:15 AM

Morning

Azmuth can you please answer my question on problem solving strategies

By the thanks alot for suggesting that book last night

S moultons is awesome

Is the math college level math used in it?

Can a 11 th grade study that

Because i haven't started it yet

So would be better if you tell

4:35 AM

@sheltonBenjamin I completed S Moulton in 9th grade... You only need calculus and vector calculus, rest you can easily pick up from it.

You don't need to completely study S Moulton, most of the techniques aren't required, we have got AI and couple of tech that does the job now-a-days...

5:19 AM

Vector calculus means simply vector chapter?

John Rennie

@sheltonBenjamin vector calculus is grad, div and curl.

5:38 AM

@sheltonBenjamin If you know basic vector, then too it should be enough... (Just you need a bit of effort with drad, div.... I guess curl isn't used much there)

Superfast Jellyfish

6:17 AM

@ACuriousMind getyarn.io/yarn-clip/…

Just finished a rewatch of The IT Crowd haha

6:29 AM

Hi

does the equation $TdS = C_p dT - dP/\rho$ sounds familiar to you?

have you ever dream this man?

I was thinking on dS = dU / T + PdV /T

Thermodyanamics?

No idea then..

Yes, thermodynamics

6:47 AM

I have a question - when we apply two successive linear transformations to the basis vectors, does the second one describe where the original basis vectors should go or does it describe where the now transformed (from the first transformation) basis vectors go?

I mean, does the second transformation matrix transform the basis vectors relative to some "global coordinates" (in which they started) or relative to the newly transformed basis vectors?

I'd say the 2nd transformation applies onto the result of the 1st (after operating on the basis vectors)

but I'm no expert, just a student

Yeah, I thought the same but I'm still wrapping my mind around it

Maybe it depends wether the operators commute or not

I mean, going to the second transformation directly is not the same as going to the first, then to the second, that means the second is applied to the first.

but, for example, if you think about rotation matrices

shouldn't it be the same ?

7:00 AM

Meh, I don't think so. For example, if you apply a transformation, then you apply the same transformation again, it wouldn't be the same as applying the transformation just once.

[0 -1
1 0] <--- if you do this two times, it would not be the same as doing it once, as far as I know.

yep

i'm convinced

Yup, the numbers work out

yay us

7:23 AM

but applying, let's say, 2 transformation matrices T1 T2 to A
T1 T2 A
you could apply T1 to T2 and then to A.

what about that?

you could either be switching from the original basis to the resulting one with (T1 T2) applied to A

or by "two steps"

7:54 AM

can anyone explain this to me, why I can demand G(x,x') to be zero?

Classical Electrodynamics by Jackson

8:13 AM

@holahola A(BC) = (AB)C

Do linear transformations always deal with transforming the basis vectors?

Hmm, if I have a composition of two transformations $M_2 M_1$ then the inverse of $M_2$ would get me to $M_1$, not the standard i, j basis vectors?

8:56 AM

@Shing I'm not sure what you mean by "why" there - the text explicitly refers to some freedom on (1.40) (not pictured in what you posted) as allowing this. Can you be more specific?

(1st part)

@ACuriousMind I am confused that G(x,x') can be thought as a point source, but why G(x,x') = 0 for any surface (as long as I demand)?

physically it doesn't seem to be true to me

am I missing anything?

@Shing The $S$ is not some arbitrary surface. It's the same surface as the surface for which you have specified (physically motivated) boundary conditions for the Poisson equation.

@ACuriousMind so I kind of need to pick some $S$ such that $G(x,x')=0$ ?

no

What problem do you think you're trying to solve in this section?

@ACuriousMind not yet, I am just reading this section.

9:08 AM

yes, but it says in the first sentence what the goal of the section is :P

you're trying to solve a boundary problem $\Delta \phi = \rho$ where you have Dirichlet or Neumann boundary conditions for $\phi$ on some surface $S$.

Slereah

morning

The author notes that there is not a unique Green's function $G$ such that $\Delta' G = -4\pi\delta$, and that there is a freedom of adding some $F$ with $\Delta F = 0$. So the author chooses boundary conditions for $F$ on $S$ such that $G=0$ on $S$. Nothing about that is physics, he's just using the mathematical freedom to do so (and it will turn out that this is physically useful).

@ACuriousMind okay, I kind of get it now. in that case, he chooses F(x,x') = - 1/|x-x'| , s.t. G(x,x') = 0 ?

yes

thanks, man!

@Slereah morning!

12:47 PM

mornin

uh, actually afternoonin

1:07 PM

Morning

Actually evening

1:34 PM

Does anyone here have a dog?

@sheltonBenjamin why?

A stray dog came to my home

He had swollen rashes all over bofyt

Nobody knows what he ate

That caused rashes

I wonder if there was a way to heal him

skullpatrol

1:53 PM

The Litter Box

General discussion for pets.stackexchange.com. Pet pictures an...

1

Guys, do any of you know if there’s a way I could find a sort of “personal teacher” of Physics that could clarify some questions I have about a few topics? I’d be willing to pay a modest amount of money for the trouble.

I thought about making more questions on this chat or on the main site, but I don’t think they would be relevant to the general public besides myself, which is why I thought a private message would be better. Hope I am not breaking any rules asking this. Good afternoon!

Q: Another thread about deleted comments

Either a personal tutor or a website that deals specifically with homework questions if that's the kind of question you're asking

if it's general conceptual questions they're probably on-topic on pse @RobertoValente

Physics Meta

2:10 PM

0

This question is entitled If there is an infinite number of universes doesn't that mean there is a universe where there is not an infinite number of parallel universes?. I downvoted this question and voted to close. I also left a comment that said: If there are an infinite number of triangles ...

discussion questions comments

Hmm, if I have a composition of two transformations $M_2 M_1$ then the inverse of $M2$ would get me to $M1$, not the standard i, j basis vectors?

Wow never no that stack exchange has so much variety

!

@JingleBells Yes: $$M_2^{-1}(M_2M_1)\vec v=(M_2^{-1}M_2)M_1=M_1\vec v.$$

@Charlie gotchya

sorry for the repeated pings

UGH i still missed the $\vec v$ in the second equality

2:18 PM

Yo!

The () are unnecessary, aren't they? I mean A(BC) = (AB)C and the order of execution C -> B -> A is the same in both cases so

hey

Yes matrix multiplication is associative

FWIW, I was finally able to do what I wanted to do yeaterday in python.

damn I'm getting better at linear algebra. Thanks to the one and only 3Blue1Brown

I was trying to plot the way how a simple pendulum oscillates, without using the $\sin x \approx x$ approximation.

If anybody's interested, here's how it looks like.

A sort of squarish sine.

However, the time period is significantly bigger than what is expected from the approximation.

2:27 PM

@Charlie I have tried on physics se though, and got close to no answers. These topics are bothering me quite a lot which is why I am desperate for someone to clarify them for me. If anyone could be so kind as to do this, let me know please

What are the topics?

You might receive answers if you try asking in here

(disclaimer, not necessarily from me :P)

I know, I just didn’t want to spam the chatroom with it :/

But if that’s the only way I might try later

It's worth a try, the chat is usually fairly quiet, I don't imagine anyone would object to you asking a few questions

even if you have a lot of them

Ok, that’s nice to hear! Thanks!

lord knows I've spammed the chat with questions over the last few months :P

2:37 PM

YouKnowMe

@FakeMod This looks fascinating. What's this?

@FakeMod For how wide a range of angles did you set it?

The above two figures show how a simple pendulum oscillates at different amplitudes.

@JMac 0 to $\pi$, endpoint=False

50 curves in the first, 5 in the second

There is no considerable (apparent or visible) deviation from a sinusoid until the amplitude reaches near 2.5 to 3 radians. However the time period does visibly start changing around 1.5 radians

It's wonderful to see this.

Well of course the period would be way off compared to the $\sin x = x$ approximation of a simple pendulum. The $\sin x = x$ assumption requires the angle is small, so you'd be going way outside it's domain. If you do the same pendulum but restrict the angles so it only oscillates 10 degrees to each side, you'll find the periods are actually pretty close.

@JMac Yeah. Deducing the time period in the unapproximated case is, in fact, quite a common question asked to JEE aspirants, however the shape change, although deducible, is (or was) never talked about during my HS.

2:47 PM

They glossed right over the reason simple pendulums worked like that in my high school IIRC. I only learned the details in 1st year university physics.

Another interesting one would be modeling a non-simple pendulum, with actual weight to the arm that you need to account for.

@JMac Wouldn't that just change the center of mass and the radius of gyration, however the charateristic shape and behaviour of the curve would still be the same?

I suppose you are not talking about point masses here, are you?

If not, then the model might be different, otherwise I don't see any reason for it to be different.

Yeah not point masses. Instead you would consider the rope/rod attaching the mass to the pivot as having mass, so it would be distributed along it's length too.

In other news, I have been trying really hard to somehow install the minted package in LaTeX. To do that, I ended up installing the necessary Pygments python package, but it's still not working. The error is most probably due to PATH alocation which I can't seem to figure out as of now.

Then if you want to get really spicy you can start adding damping effects.

@JMac Still, if you are going to keep the bob of the pendulum a point mass, I don't see why the rope/rod, no matter whatever kind of mass density distribution it posseses, should change the nature of the curve...

@JMac That opens a whole new set of possibilities/conditions, i.e. overdamping, underdamping and critical damping.

Interesting stuff, really.

Now if you still want to make it spicier, you can add driving forces to arrive at a forced oscillator.

2:57 PM

It's applicable to way more than just pendulums too. Basically the same model can be made for some electrical systems, fluid systems, heat transfer, vibrations. And yeah adding forcing would be the next step.

danielunderwood

If you want to look at a pendulum without the small angle approximation, phase space plots are helpful as well! demonstrations.wolfram.com/PhaseSpaceOfASimplePendulum

Jack Rod

3:41 PM

hey!

hey there! :)

Can someone help me make sense of [these two comments](https://physics.stackexchange.com/questions/129324/why-is-huygens-principle-only-valid-in-an-odd-number-of-spatial-dimensions/331257#comment845175_331257)?

I don’t really understand the relation between the Green’s function and the delta-function. What is the relation between them? Which one actually describes the propagation of the wave? Is there some way to explain this without much math?

2

@RobertoValente Assume $\hat L$ be some differential operator, then the relation between the Green function and Diarc Delta function is $ \hat L G(x, s) = \delta (s-x )$

$\hat L$ should be Linear Differential Operator.

is death well more dangerous during beginning of its climbiing sorry for interruption

becuase there is only component of friction acting

?

Please rephrase your question?

3:56 PM

also while making fbd of person in a deathwell

is friction UN or component of UN?

beacause friction also helping in person move?

Totally didn;t get your question, but I understand it's related to friction... So, can you rephase it?

You need to give more details @sheltonBenjamin

ok mr president

@MakeStackexchangeGreatAgain Good Evening Mr. President.

@RobertoValente There is no way of explaining Green's functions without math :P

3:59 PM

Hope you doing well during COVID-19 Pandemic..

Getting the best treatment money can buy.

@RobertoValente A very rough institution would be that Green Function is integration of Delta function multiplied by some other function (which depends on Differential Operator)

^not same, but that's the most rough intuition.

@Azmuth thanks for the answer, but could you maybe explain in more conceptual terms? The comment seems to imply that the Green’s function describes the wave propagation. What does it mean that it has a delta-function of the opposite sign on the light cone?

Let me check the question.

Thanks again for the answer, sorry I don’t grasp complex math :(

4:03 PM

1.32. Why is it more difficult to turn the
steering wheel of a stationary motorcar
than of a moving car?

this problem from ss krotov illustrates it better

here when at rest

there is only componnet of riction acting

@RobertoValente Sorry, I don't have any idea about Multi dimensional Light Cones and wave propagation... That's out of my area... I guess, you can wait a bit here (I'll bookmark your question here) or you can ask for clarification in comments.

@ACuriousMind check it^

sorry at motion

@sheltonBenjamin yep, that's correct. What's the problem here? It seems fine.

there is only a component of friction acting

now when climbing up a death well

which way does friction act?

4:05 PM

there is only component of friction acting

@RobertoValente The Green's function itself is not the wave, but it describes the propagation of the wave in the sense that you can use the Green's function to compute the evolution of the wave from a snapshot of the wave at an instant, see e.g., physics.stackexchange.com/a/323984/50583

so it makes it more dangerous

@MakeStackexchangeGreatAgain Hope you winning the elections on PSE Mr. President, we've to build a wall, a great wall here!

aM I CORRECT

azmuth you are like one of my mate

sarcastic + intelligent

his name was aasim

@ACuriousMind Green function describes the propagation of the wave through evolution...!?

4:08 PM

please tell if i am corect at my logic at death well

ask @JingleBells

he's an expert here

Post a picture

@RobertoValente So if the Green's function is positive-definite in some area this means that the values of the wave in that region cannot destructively interfere (since destructive interference would require subtracting stuff from each other). tparker is saying this destructive interference is made possible by the negatively-signed part of the Green's function (the $\delta$-function) on the light cone.

@Azmuth Stop being annoying.

@RobertoValente Huygen's principle and it's weird dependence on the dimension is notoriously unintuitive though and you shouldn't be too worried if you don't understand it without going through the math

okay...

Who is your avatar @Azmuth

4:13 PM

Thanks for these clarifications! It is still quite complex though, without understanding the math. Tho I think I have a better grasp at the concept now

@MakeStackexchangeGreatAgain It's my own selfie, I used an Anime converting AI Software to generate my Anime Avatar! :-)

Wow

:-)

It's not perfect tho.... X'D

nothing ever is

haha :-) But, I guess with using StyleGAN or some other Hybrid Generative Adversarial Neural Network, a better version can be made....

4:19 PM

Wow! How you got the bigger version!?

Yep, that's me! :)

4:39 PM

@danielunderwood Whoa! That was insightful. Thanks a lot!

@ACuriousMind Regarding the Huygens Principle on even dimensions, is it correct to say that waves “double back” on themselves? As in go backwards? (Sorry to be so annoying)

I ask because this post (askamathematician.com/2012/05/…) characterizes it as such

@RobertoValente I don't think asking genuine questions about physics is annoying :) It depends on what you mean by "double back" (it's not a technical term), the term I hear people use more often is that the waves leave a "wake" behind the wavefront. In any case what people are trying to describe with these phrases is that the entire region behind the wavefront remains disturbed for some time, in contrast to odd dimensions where wavefronts can pass "cleanly" though a medium

I think it's important to realize that you already know how this looks - the picture of the ripples in water in that post isn't just an analogy, waves on a water surface are to a good approximation 2d waves

5:05 PM

@ACuriousMind I can’t thank you enough for these thoughtful answers. I absolutely agree with you of course.

My confusion with it is because quite a few sources characterize it as waves “reflecting back” on even dimensions, which doesn’t seem totally correct, am I right? One post that left me thoroughly confused, for example, was this one from a while back (answer and comments): https://physics.stackexchange.com/a/365491/137288

It doesn’t seem totally correct IMO. What do you think? Thanks again for being so helpful and nice.

@RobertoValente Ah, the "reflecting back" phrasing comes from the wake moving on the opposite direction of the wavefront - think about how in the case of the circular wave of the pebble in the pond, the water inside the wavefront moves back towards the center. If you do this not for a spherical wave but a planar one, you get that the wave that moves backwards doesn't cancel out in the center (because there is no center for a planar wave), but moves indefinitely

Now I got a little more confused lol. In this article (mathpages.com/home/kmath242/kmath242.htm) the author claims that even dimensional waves propagate with “infinitely many velocities”, that is, after the first wavefront passes, there would be infinitely more “slower branches” following it. Which would “fill” the area behind the wavefront, but I don’t think it says anything about waves “reflecting back”

5:25 PM

Why does this happen? (including in the double-slit experiment)

Why the weird bending?

Anyone got an intuition example?

Are you asking why the waves are curved?

Yup

What causes them to curve?

@JingleBells It's called diffraction

@ACuriousMind I know :D

Once they pass through the opening they diffract outwards as if they were emerging from a source

5:28 PM

@Charlie Yeah, why?

@JingleBells and what about the explanation in the Wiki article don't you understand?

This might be an instance of "why" being a slippery slope, I'm not sure what the "intuitive" reason for this is

Huygens–Fresnel principle

The Huygens–Fresnel principle (named after Dutch physicist Christiaan Huygens and French physicist Augustin-Jean Fresnel) is a method of analysis applied to problems of wave propagation both in the far-field limit and in near-field diffraction and also reflection. It states that every point on a wavefront is itself the source of spherical wavelets, and the secondary wavelets emanating from different points mutually interfere. The sum of these spherical wavelets forms the wavefront. == History == In 1678, Huygens proposed that every point to which a luminous disturbance reaches becomes a source...

the waves spread out once they're on the other side of the opening

@RobertoValente All these sources aren't trying to write the definitive account of how waves propagate, they're just making more or less carefully considered remarks about how waves behave. Don't afford so much weight to the non-technical terms physicists use when waving their hands, what matters is that they got the math right

5:31 PM

I've looked into this Huygens-Fresnel principle before where: "every point on a wavefront is itself the source of spherical wavelets, and the secondary wavelets emanating from different points mutually interfere. The sum of these spherical wavelets forms the wavefront." but I'm wondering why. Is there some type of mechanical causation of it?

@JingleBells the mechanism depends on what sort of wave you're looking at - the Huygens' principle holds for everything that obeys the free wave equation, but the mechanism of propagation is of course different for a mechanical wave on a string and an electromagnetic wave in a medium or vacuum.

If every point on the wavefront can be thought of as the source of another spherical wavelet, then why aren't there any spherical wavelets of the wavefronts before the wave goes thru the slit?

but in the end the principle is just a consequence of the wave equation. There's no ingredient in there that says "this is why Huygens principle works", it's just that when you work out that the wave equation should hold for e.g. a wave on a string, the principle is a consequence of that equation.

@JingleBells There are. (look e.g. a the picture for refraction on the Wiki page - the spherical wavelets just unite into a planar front when there's no slit blocking them off)

I think I came up with an intuition - no wave is actually perfectly straight because it has originated from a spherical wave source, it's just that we're so zoomed in that we don't see the curve. When the wave goes through the small slit, it blocks most of the wave and leaves only a small bit, that can grow in a circular manner, so we've zoomed out in a way.

@ACuriousMind I always understood by “wake” that it is a portion of the wave that kind of “lags behind” but goes in the same direction as the main wave. I don’t think it means that it goes in the opposite direction - like that answer I mentioned above. Am I wrong to assume that? Do you mind having a closer look at the aforementioned answer to see what you think of it?

5:41 PM

I don't think it's impossible (in principle at least) to create perfectly straight waves

You just need a source that is wide enough that fringe effects are negligible

Hi all, it is said that if you are in an eigenstate of the Hamiltonian then the wavefunction always can be expressed as a purely real function. Now I don't understand what happens if you are in a eigenstate with non-zero angular momentum. In the cases for example the probability current is non-zero.

And it seems it is then intrisically complex.

Of course one can form linear combinations of such stated with counterwise angular momentum which can be real. But anyway.

Is this helpful at all?

Hmm, I think I have some sort of an intuition now that's satisfying enough. Thanks guyz

@Charlie Yes! Thank you!

By the way, the reason we need the slit to be small is that we see the effect. If the slit was large, there will still be diffraction but we won't see the curvature that much. If we were to zoom in as tiny humans on the small slit and check it out, we wouldn't see the effect that much. So diffraction happens on all slit sizes.

5:46 PM

So it means if its only about "eigenstates" I can choose a real representation of the space, but I cannot obviously chose one that also is eigenfunction of l_z!

(and it is connected with degeneracy)

I don't want to feed you wrong information, but if that's what the link says then yes :)

@Charlie OK ;-)

Johan Liebert

@ACuriousMind I have sent you the email.

If we put observers on the double-slit experiment but we deliberately don't hit record so we have no way to see what's going on, will the particles shot behave like waves?

@RobertoValente Yeah, sorry, it's not the wavefront that moves in the opposite direction, it's the retarded waves from the principle, but it doesn't apply in these dimensions anyway. Again, if you want to know how the wave moves you have to solve the wave equation, I'm not sure why we keep going on about different imprecise ways to talk about the wave when there's a perfectly fine quantitative description of how waves propagate in all dimensions.

@JingleBells Youi're probably trying to describe a quantum eraser, the answer is yes.

5:57 PM

@JingleBells This is a nice PBS spacetime video on the quantum eraser

@ACuriousMind Doesn't this imply that the universe tells us that it's impossible to ever figure out what has happened?

@JingleBells It means that the idea that there is a definite thing "that has happened" is inconsistent.

Quantum mechanics means the world is at least either non-local or non-realist, if not both.

@ACuriousMind Particles are shy and only exhibit their wave-like properties when we're not observing. If we were to press record, how do the electrons "know" that we're recording :p

@Charlie thx

@JingleBells How does nature ever "know" to obey the laws of physics?

@JingleBells No one knows, it's pretty spooky

6:01 PM

@ACuriousMind God programmed it.

It's easy to take things for granted in the sense that before Newton discovered gravity, people were like "yeh, that's just the way the universe works". But it turns out there's an explanation (as far as human explanations go)

bold of you to assume god is a programmer

Bold of you to type god and not God

or even GOD

Johan Liebert

I use dog instead!

God programs in the language of Universe++ or maybe Uni#

while True:
if no_humans == True:
create_humans(2)
else:
reproduce()

Faded Giant

We lost the documentation on quantum mechanics. You'll have to decode the regexes yourself.

6:07 PM

@ACuriousMind thanks again. Just to be clear, do you agree that saying that the wake “reflects back” is an imprecise interpretation? Also, I think you mean the “advanced waves” move in the opposite direction, no? That’s what I got from your answer here: physics.stackexchange.com/a/219854/137288

Sorry for my OCD regarding these topics, I hope you reply to my last one but hopefully I won’t bother you any further. Thanks :)

Yes, I think "reflecting back" is not a very useful way to phrase it

How do we know an object is in a superposition until we observe it and it has not been in that state the whole time? The double-slit experiment tells us that? Since if the electron wasn't in many places it wouldn't have been able to interfere with itself to form the pattern?

Try reading here

Also here

ahh sh*t, long Wikipedia pages of unnecessarily twisted linguistics. Still, thanks.

Pff, QM is weird

Hmm, another question - if I ask my friend to observe the result and tell me what it is, does the universe consider me as "having observed"? (u get the idea...)

^ probably doesn't make sense sorry

6:30 PM

@JingleBells you could try Simple English wikipedia, e.g.

Bell's theorem

Bell's theorem, also called "Bell's inequality," is a thought experiment. When joined with real experiments, it shows there are no hidden variables which can explain some of the consequences of quantum mechanics. This study, closely related to quantum mechanics, was done by John Stewart Bell. == Brian Greene's analogy == The following analogy has been provided by Brian Greene: Pairs of boxes have been prepared and sent to Earth and on Vulcan. There is something inside that shows a light when a door is opened. If the same doors are opened on both members of the pair, then both lights will be blue...

@SirCumference YAAA, I didn't know that existed

yeah it's not too well known but it's a lifesaver

just check the language section of a page and see if it has a simple english "translation"

@Charlie I tried reading that but I don't understand how it relates to my question

6:51 PM

Good evening to everyone

Down The Rabbit Hole Of The Delayed Choice Quantum Eraser | Answers With Joe

@Ratman Good evening

I just learned about the quantum eraser experiment and I'm lost for words. Like, despite the fact that the shot particles reach the projection board first and then it's determined whether we get to observe them or not makes me wonder if the particles went back in time or... don't know the other interpretations.

►

^ This guy explains everything so clearly!

I think you might just be a visual/auditory learner :P

7:13 PM

@ACuriousMind I've figured out I am :-)

But honestly, that delayed choice quantum eraser just blew my mind (as it does to most people)

@JingleBells if you are interested in this kind of topics on QM there is a beautiful book by Ghirardi, "Sneaking a Look at God's Cards". It can be considered at a midpoint between a divulgative book and a university text, the author doesn't use a lot of math (just some bra ket notation, without saying what a Hilbert space is), but I think is very rigouros in terms of concepts.

@Ratman Oh, thanks but I'm not looking to get into quantum mechanics seriously. I just like the concepts and ideas. I learn it for fun

actually I have the italian version, so I can't guarantee for the translated version

@ACuriousMind Regarding that comment by tparker I mentioned — “The Green's function for the (4+1)𝐷 wave equation is indeed sign-definite strictly inside the light cone, but it has a delta-function of the opposite sign exactly on the light cone” — could you paint me a picture of what that wave would look like in real life? The wave on the light cone (the fastest) would be upside down in relation to the other secondary waves (the slower branches inside the light cone)? How would that be possible?

@ACuriousMind I think the case is that books and texts require me to focus for longer and work harder to absorb the info. I still learn from books and I read, but when I quickly want to learn the intuition of something without diving deep, I watch vids :)

7:20 PM

@JingleBells started this way too, reading this book for curiosity while I was at the end of high school ahahaha, anyway no problem, just thought it could interest you

@RobertoValente nonono, as I said, the Green's function is not the wave - it determines which parts of the wave can contribute to its future evolution

* I started...

@JingleBells well, I have the opposite problem - my mind tends to wander when I just watch or listen to things but when I read something I can usually absorb it much better and often quicker than listening to the same text being spoken.

@ACuriousMind same, this is why lectures never worked for me

@SirCumference that's why I always forced myself to copy down what the lecturer was writing on the board even if there was a script

7:25 PM

yeah but even then, the textbook will be better organized than my notes

the writing suffiently focuses me so I can actually also listen to what they're saying

it's not about having the notes, really

huh, in my experience i'd never been able to focus on what they were saying bc i was too busy trying to get it down

not enough time to parse it before they're on to the next thing

Lectures don't work for me either, at least when I can't rewind backward with the left key.

i'm TAing a class right now and it kills me to see mandatory attendance on the syllabus, even for problem set sections

Not that I'm in college, or I'll ever be.

7:28 PM

lots of people go at their own speeds and won't benefit from being rushed to know the material each week, or work at 10am

My guy Abraham Lincoln understands.

And Richard Branson

I am actually quite slow, during lecture I just try to get the logic or what I can get

@ACuriousMind I guess you were raised with books, and I was raised with youtube videos and khan academy :D

but for the way it works my university is it ok, there are no assignments, you can manage on your own

i miss khan academy

but they have nothing on higher level math

7:32 PM

I don't know why different people learn in different ways

Is it nature or nurture

i mean i have adhd so that might be my reason

@JingleBells I was. Both my parents are avid readers, I spent a large part of my teenage years reading through our bookshelves (mostly fantasy and sci-fi novels) and when I expressed interest in something we'd go to the library and get a book on it.

@ACuriousMind Yeah, I guess it leans more towards nurture

Now of course I get most of my information from the internet, but I still heavily lean towards long-form articles and sometimes books rather than videos.

@ACuriousMind Yeah, I'm exactly the opposite. If I see a long text, I copy the title and paste it in youtube :P every time.

I kinda regret not reading too much in my childhood :\ It could've developed my brain more. I now try to read as much as I can, and I enjoy it, but when I learn something new, I always refer to videos or easy articles.

@ACuriousMind What's ur IQ?

7:44 PM

no idea

U should measure it

I sometimes feel like I'm not smart enough, but I don't know what smartness actually is :P

@ACuriousMind I see what you mean. I can’t exactly visualize the 4-dimensional wave as tparker explained though. Could you maybe elaborate a little? I understand there would be terms inside the light cone, that’s fine, but how would it look like exactly on the light cone (the fastest wave)? As you have said, it wouldn’t be an upside down wave, so how would it look like?

The comment is here (physics.stackexchange.com/questions/129324/…) in case it helps

Sorry, I wouldn’t be questioning so much if this wasn’t bothering me

@JingleBells I wouldn't attach too much value to people's "IQ"

"people who boast about their IQ are losers"

8:00 PM

@Charlie I agree

If you google "what's it like to have a high iq" and click any link to quora you'll find out why :P

I guess all I can do is work with what I've got. I do my best to expand my knowledge across different fields and I'm lucky to have my curiosity drive me.

I don't think you'll hear many serious academics promote the idea that "intelligence" is something you're born with or your not. Or that there are some things that are "too complicated" for an average person to understand

Sure, I don't want to become an academic or a professor, but I generally strive to learn about the world, learn about how things work, figure out diverse fields, etc... And I agree that IQ is BS.

It's late, so I'm getting emotional and dramatic again

It's not that it's necessarily bs, I'm sure it's predictive in some ways, but people who label a person as "smart" or "not smart" based on their "IQ" are not people who should be taken seriously :P

8:10 PM

Well, I don't know what smartness is so I can't say anything

@ACuriousMind do you have a professional e-mail I could contact you with? I’d be willing to pay you to clarify this topic for me, not joking

It’d be better than further disrupting the chatroom :/

lol

If that was the case I would be broke

I am serious tho, my OCD wil kill me for real

Don’t like physics and have ocd, not cool

@RobertoValente I am far from an expert on waves in arbitrary dimensions, I think I've said most of what I could say, really. I'm not sure what exactly you want to know there - on the light cone there's just a wavefront. The negative term from the Green's function on the light cone means that this wavefront can negatively interfere with the rest of the stuff inside the cone, it doesn't say anything about how the wave looks there.

@ACuriousMind what are your areas of expertise? if I can ask

just because a lot of times I end up in reading some of your answers

8:24 PM

quantum stuff, mostly, and phrasing things in a bit more mathematical fashion than average :P

@ACuriousMind So, for the wave on the light cone not to be upside down in respect to the waves inside the light cone, there must be other positive terms on it to balance it out? I don’t think tparker mentioned these terms, but is that how you understand it?

Again, the Green's function is not the wave. I don't know why you keep talking about the wave being upside down.

If you really want to understand tparker's comment you need to learn how Green's functions work - not in vague words, but in the math.

Ok I see. But I mean it because he said the green’s function is positive inside, and negative exactly on the light cone, you see? What would balance it out?

I believe I have to, indeed.

Don't mean to add to the pile of questions being asked to you, but before you decided you weren't interested in going into research, did you have a specific field in mind? @ACM

I agree on the interest of the mathematical formulation, I find always amazing how some concepts in mathematics finds their apllication in physics

8:40 PM

@Charlie I'd have liked something in QFT with gauge theories, but nothing specific.

Ah ok fair enough

0xFFF1

9:05 PM

Suppose in the far future, we decided that, instead of colonizing the galaxy by going star-to-star, we built stellar engines on each of the stars we went to and took it all with us? Imagine a literal star fleet. A fleet made of stars.
What's the logistics look on this? Do stars output enough power to keep a static relative position within an entire galaxy of stars? Or would we be forced to create fancy orbits to keep them from crashing into each other? How much could we squeeze the interstellar medium together before it started juking planetary orbits?

Would it be close enough that we could maintain a proper administrative system even if superluminal communication never became possible?

9:57 PM

ever find it weird that both "theorem" and "proposition" sound like they'd refer to statements that aren't necessarily true, but in math it's the opposite?

it's a trick to be able to make fun of non-mathematicians when they ask stuff like "but isn't that just a proposition"? :P

@ACuriousMind well i guess it's better than in physics. a "law" sounds like it should be something more reliable than a "theory", but it's usually the complete opposite

i guarantee you we wouldn't see so many "personal theories" on this site if we swapped the terms :P

Stupid question inc

11:14 PM

any idea about wth is this?