The h Bar

Sanjana

02:33

@DIRAC1930 Two of its authors have given some form of a modern treatment also: Schwarz coauthored Becker-Becker-Schwarz and Benford has some notes based on Green's lectures

The second one is not that popular I guess. Found it recently while trying to find the answer to one of my recent questions

Sanjana

04:29

Does anybody know where can I find a similar discussion on T duality for heterotic strings on $T^6$ as in here near 20:20?

Specifically I want to know how and why should one arrange the massless scalar fields on compactifying heterotic string theory on $T^6$ into this weird looking $28 \times 28$ symmetric matrix that they call $M$ obeying a pseudo-orthogonality constraint $M^T L M=L$.

Relativisticcucumber

@SirCrackpot yes

@SillyGoose i think logic must be innate. i think we are refined machines to function in a way that maps environmental inputs onto self propagating actions. if you accept that the world obeys (at least to some resolution) logic, then logic would be heavily hardwired into the function that i mentioned. you say if we didnt have clocks would we think of time -- i mean clocks [...]

[...] didnt exist until we invented them so that would imply absolutely? i think it is beneficial to consider us (and perhaps life forms in general) merely as various solutions that satisfy the function i mentioned at the beginning of this message. i dont think theres any privilege of one stable solution as opposed to another (e.g. animals that can sense broader [...]

[...] EM spectrum are not "more correct" about the reality of the world) but of course when something is built to survive in the world, it does bear information about that world.

Relativisticcucumber

05:54

what is the importance of the continuity condition here?

naturallyInconsistent

I would suspect that the continuity condition would be used in some proofs of some theorems later in the book.

Relativisticcucumber

06:10

marp

also, exciting news

my campus has started acquiring neighborhood cats now that the temp is rising

one jumped into my lab and refused to leave

there have been 5 identified so far

this one is my favorite. it moves too fast for a good picture but as u can see it is VERY cute

5

naturallyInconsistent

06:38

awwww

Sanjana

06:59

@Relativisticcucumber I love cats ❤️❤️❤️

3

123

Hello Everyone...

To apply newton's 2nd law, it is necessary system objects should interact each other by force also external forces should act on every object of the system?

ACuriousMind

07:22

@Relativisticcucumber infinite-dimensional spaces suck, and if you don't demand continuity you can get all sorts of pathologies

In the finite-dimensional case all relevant maps are usually automatically continuous, so the condition doesn't appear there explicitly

Sir Crackpot

08:37

@Relativisticcucumber I'll dub this cat "spinor"

GOAT name for a cat

Is it ok to edit a question to add details after receiving an answer?

Slereah

sure

other people may want to answer

ACuriousMind

@SirCrackpot generally edits are fine if they don't invalidate the answer (i.e. the existing answers have to remain valid answers to the new version). If you want to "add details" in the sense of clarifying "no, that's not what I was trying to ask" in response to an answer, ask a new question instead

Slereah

09:22

> Or else there might be a drug in the laurel that could have produced such an Apollonian effect. To test this, I have crushed laurel leaves and smoked quantities of them in a pipe and felt somewhat sick but no more inspired than usual. And chewed them as well for over an hour, and very distinctly felt more and more Jaynesian, alas, than Apollonian.

A true historian

Ryder Rude

09:51

@Arjun hi. this problem has the additional assumption that the expectation value of momentum is $\langle \psi |-i\frac{d}{dx}|\psi\rangle$. From this, u can prove that the probability density of measuring momentum $p$ is $|\psi(p)|^2$ in the Fourier space by reading off the weights of the eigenvalues

note that this assumption puts the cart before the horse. in the normal approaches, we first postulate the Born rule of measuring any eigenvector to be $|\langle a|\psi\rangle|^2$ from which we derive the expression for expected values

@Sanjana thanks

lucabtz

10:57

@SirCrackpot saw your question

@RyderRude i think technically speaking in the correct Dirac's notation $\frac{d}{dx} \lvert \psi \rangle = 0$

the correct statement would be something like $\langle x \rvert p = i \hbar \frac{d}{dx} \langle x \rvert$

so that $\langle x \rvert p \lvert \psi \rangle = i\hbar \frac{d}{dx} \langle x \lvert \psi \rangle = i \hbar \frac{d \psi(x)}{dx}$

Sir Crackpot

@lucabtz So did I

lucabtz

thus you would write $$\langle \psi \rvert p \lvert \psi \rangle = \int dx \langle \psi \rvert x \rangle \langle x \rvert p \lvert \psi \rangle$$

using the resolution to the identity

then you use the expression of $p$ in the basis $\lvert x \rangle$

and get what you expect

@SirCrackpot good i was worried you might have typed it closing your eyes

Ryder Rude

@lucabtz yeah... i wrote that bad notation to avoid writing the integral :P

Sir Crackpot

11:19

@lucabtz I know that was supposed to be a witty reply but it came off as a savage blast lmao

lucabtz

@SirCrackpot nah it was funny

user 85795

11:51

haven't you heard, there are no savages on the internet :P

Relativisticcucumber

@Sanjana ME TOO

@SirCrackpot omg

@ACuriousMind ok i see

@SirCrackpot spinor is much nicer than snowball.

snowball was like canonical tortured soul type cat

user 85795

is a general relativistic cucumber a pickle

(⁠＠⁠_⁠＠⁠;⁠)

How's spring break going @Jim

Sir Crackpot

12:30

@user85795 no, just a Lorentzian vegetable

@ACuriousMind why Lorentzian and not Poincarian?

@Relativisticcucumber snowball is the hbar's cat, no jokes

Slereah

15:22

> This secularization of science, which is now a plain fact, is certainly rooted in the French Enlightenment which I have just alluded to. But it became rough and earnest in 1842 in Germany in a famous manifesto by four brilliant young physiologists. They signed it like pirates, actually in their own blood. Fed up with Hegelian idealism and its pseudoreligious interpretations of material matters, they angrily resolved that no forces other than common physicochemical ones would be considered in their scientific activity. No spiritual entities. No divine substances. No vital forces.

lucabtz

omg im graduating on 27th march

5

yay

all passed in!

Slereah

> [We pledge] to put in power this truth: no other forces than the common physical chemical ones are active within the organism. In those cases which cannot at the time be explained by these forces one has either to find a specific way or form of their action by means of physical mathematical method, or to assume new forces equal in dignity to the chemical-physical forces inherent in matter, reducible to the force of attraction and repulsion.

The Reymond-Brucke oath apparently

Not well known enough to deserve a wikipedia page

naturallyInconsistent

@lucabtz congrats

lucabtz

thanks

Silly Goose

15:44

Congrats :D @lucabtz

lucabtz

thank you

Slereah

> This credo, in turn, would greatly influence a young Sigmund Freud, Brucke’s soon-to-become medical school student; who in 1895, in his “A Project for Scientific Psychology”, would go onto posit that all mental functioning could be explained, thermodynamically, via bound energy and free energy, something far ahead of its time, even by 21st standards.

I'm lacking free energy help

Ryder Rude

16:05

@lucabtz congratulations

@Slereah this repulsion toward non-materialistic ideas has somewhat backfired these days, resulting in a closed minded attitude among physicists about qualia

physicists are largely unfamiliar with a proper philosophy of physics. physics is about revealing mathematical structures in the universe, not about conflating the universe with a mathematical structure

Arjun

16:27

@lucabtz congrats!! and All the best for your future endeavors! : )

Silly Goose

16:42

@Relativisticcucumber so cute

@Relativisticcucumber hm wait so are you of the school that thinks everything is math. or are you only saying it is a useful way to think of the world (as math)

@Relativisticcucumber wait I don't get why if the world obeys logic then organisms selected to self-propagate also would have logic ingrained into them

if the entire world was underwater, then organisms would probably be selected to be specialized for such an environment, but i don't think there is one way to specialize to this environment

i.e. if the world was really "logical" i would think there are more ways to specialize to such an environment than being "logical" oneself

Obliv

all life was under water 3+ billion yrs ago

when the ozone layer formed from an oxygenation event, life could go to the surface but it didn't have to

oh nvm apparently it was 600 mya

Sanjana

17:23

@lucabtz Congrats 🎉🎉🎉

123

In the above example of KnK the bola has two forces one pulled binding thong and gravity. But he took only gravity as external force not took pull force on each bola. Why?

Also to apply N2L what i think system must interact each other by which total internal forces zero $\sum F^{int} = 0$ by N3L. But in case of bola three balls don't interact each other. How can we apply N2L in that case?

lucabtz

18:13

thanks to everyone

Silly Goose

Has anyone read adler’s Quantum Theory as an Emergent Phenomenon

Silly Goose

18:41

what is everyone's favorite quantum mechanics textbook

123

If newton's second law is time rate change of linear momentum. How can we define this momentum change in centripetal force?

Sir Crackpot

20:35

@lucabtz Remember to mention ACM in your speech

Amit

21:00

What is happening?

lucabtz

21:37

@SirCrackpot i thought of mentioning the h bar in the acknowledgements tbh

but ive been here for too short

maybe in the PhD thesis if i get admitted

Sir Crackpot

22:15

@lucabtz "why is that guy thanking a constant? He's nuts"

2

lucabtz

@SirCrackpot hahah

Transcript for