The h Bar

John Rennie

05:56

Wikipedia seems to be down. It's just timing out. Is it just me or is it down for everyone?

naturallyInconsistent

it is working here

John Rennie

06:57

@naturallyInconsistent Thanks. That's weird as I've tried on two different PCs in different parts of the UK. I wonder if it's some proxy that's used from the UK that's to blame. I could try using Tor I guess.

naturallyInconsistent

why not use one of the 3rd party mirrors? You know, those trying to circumvent the great firewall

John Rennie

Aha, it works if I go via Tor.

But on the same PC it times out if I use Edge or Chrome.

naturallyInconsistent

try typing the ip address directly. it might be the DNS

John Rennie

Huh? It has literally just this minute started working again!

naturallyInconsistent

lol

John Rennie

07:02

Ah, no, if I refresh the page it's down again.

Ryder Rude

What The Prisoner's Dilemma Reveals About Life, The Universe, and Everything

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John Rennie

Shrug. I'll use Tor or as you suggest one of the mirrors for now.

@RyderRude No spoilers! I haven't watched that yet!

Ryder Rude

this is one of the most informativw videos ever made

@JohnRennie plsss see. it's his best

John Rennie

Most of Veritasium's videos are excellent.
Not all ... but most!

2

Ryder Rude

Derek has mastered storytelling like few people

Giorgi Lagidze

09:57

@RyderRude thanks. will watch it at the end of the day

@RyderRude have you seen this ? youtube.com/watch?v=6GDv4f2zUus (unfortunatelly, my knowledge of chemistry is horrible, so didn't really grasp everything)

Ryder Rude

10:49

@GiorgiLagidze i will see it. thanks

Ryder Rude

11:14

@GiorgiLagidze i also dont know any chemistry jargon. i think the second guy put out a substantial theory. the assembly theory

the first guy was just attacking the lack of progress and calling it all a scam

the second was just defending the attacks. but he also puts forward his assembly theory where he can take a substance and measure if it's a life substance

Giorgi Lagidze

@RyderRude problem is 2nd guy is not a chemist in that sense, he is a computer scientiest

so i believe the 1st guy is more knowledgable :P

it's pretty annoying though that some say that we can create life and some say we never did

Ryder Rude

maybe. the first guy says that the public has been misled. but everyone has their own bias. i just hope the first guy isnt religious :P @GiorgiLagidze

Giorgi Lagidze

haha same ! completely agreed

Ryder Rude

it is ok to attack a lack of progress if it's genuine. but pushing for creationism as an alternative wud b ridiculous

the second guy explains that this is just how science works

Giorgi Lagidze

so basically you can't just trust anything lightly until you also possess the knowledge and in that case, you need to know biology, chemistry, physics at a very high level

Ryder Rude

11:26

but maye the public has been misled. scientists do spread their agenda misleadingly

Giorgi Lagidze

yes, I also start to believe that it's been misled or not at all, but what someone calls "life creation" might not be the same for other people

Ryder Rude

@GiorgiLagidze yeah, in principle, we shud learn those subjects. but it's hard to learm everything in practice

Giorgi Lagidze

yes, lifetime wouldn't be enough

i also watched a very good explanation why free will is an illusion

Ryder Rude

the assembly theory is good for detection of life but i dont see an immediate connection with the origin of life

Giorgi Lagidze

yes, i don't think that theory can really explain origin at all

Ryder Rude

11:28

@GiorgiLagidze oh. free will just seems incoherent imo. u either hav determinism or random chance or a mixture?

@GiorgiLagidze yes

Giorgi Lagidze

some people don't like sam harris, but watch his interview about free will with lex fredman

Ryder Rude

i will check it out

i havent watched the dinner part yet. it seemed super awkward lol

Giorgi Lagidze

he explains it very well, i always had doubts that free will never existed but once I hear Sam also say the same, now I believe 99.99% in it

nah, i also skipped that

Ryder Rude

thwy were trying so hard to make high level jokes

looked like a parody :P

i will see it. they also seem to be discussing religion there

Giorgi Lagidze

yeah, hate such discussions. I love debates with no agenda, just pure explanation

youtube.com/watch?v=SYq724zHUTw this is the part

btw, @RyderRude i also got interested in what spinoza's god is and from first glance, it's something that could be the best explanation :P

spinoza is really hard to understand though and one also needs lifetime to conclude what the hell he was saying lol

Ryder Rude

11:38

@GiorgiLagidze he sounds like Dennett when he says he has convinced himself tht he doesnt hav qualia :P

but i agree. free will is incoherent. so it's not even wrong in Pauli's words

@GiorgiLagidze i havent tried to read his work yet but i love panpsychism

i have read some from wiki. r u reading his books @GiorgiLagidze

Giorgi Lagidze

no, i wish. learning physics takes all my time

Ryder Rude

oh

Giorgi Lagidze

i only watch videos before sleep

Ryder Rude

i too only read wiki and videos

for philosophy

ive been recommended a book

Giorgi Lagidze

yep. you also continue to learn physics ?

Ryder Rude

11:42

no

Giorgi Lagidze

i think you are at good level

if i were you, i would also focus on other areas

which book ?

Ryder Rude

it's this book rads.stackoverflow.com/amzn/click/com/3030500829 i read a few pages but havent continued yet

but i plan to. it's about the role of consciousness in physics

it's from a physicist i think

@GiorgiLagidze i plan to learn some more physics like Standard Model and General Relativity

Giorgi Lagidze

i thought you knew general relativity

Ryder Rude

@GiorgiLagidze do you also intend to study bio and chem after physics

@GiorgiLagidze no, only surface level

Giorgi Lagidze

definitely. I think physics is gonna take me 4 years at least to get at normal level.

Ryder Rude

11:46

i dont like chemistry at all. maybe ill read some biology

Giorgi Lagidze

i hate chemistry as well

to me, chemistry is the physics as well

but biology is definitely good

you also learned quantum or not yet ?

Ryder Rude

i have

but not standard model

Giorgi Lagidze

self taught ?

Ryder Rude

yes

Giorgi Lagidze

nice. trying to do the same as well

Ryder Rude

11:47

i know upto qft rn

@GiorgiLagidze a lot of people here like this

Giorgi Lagidze

how long have you been learning physics ?

Ryder Rude

i think i started 3 yeara ago

sorry 2 years

but i already knew Newton then

so i started lagrangian and qm

Giorgi Lagidze

from my learning processes, what I realized is that physics is not as much as hard as mathematics lol

Ryder Rude

yes

mathematics requires rigor, so it's not my thing

Giorgi Lagidze

same, but at the other hand, i like proofs. if you don't look into proofs, there's no point to learn physics or math at all

that's the problem of school education

Ryder Rude

11:50

yeah

what do u like about panpsychism

Giorgi Lagidze

unfortunately, i am not educated in it. but long story short, i am not a true panpsychist.

maybe at some level, but not fully

Ryder Rude

same

i will learn it at some point maybe. it just sounds like the truth

Giorgi Lagidze

same here.

Ryder Rude

i see no way else to explain qualia

Giorgi Lagidze

there're lots of things i am interested

but each one of them is complex as hell

Ryder Rude

11:54

spinoza was called an atheist

Giorgi Lagidze

that depends on how one defines atheism

Ryder Rude

@GiorgiLagidze it's satisfying when u learn these

Giorgi Lagidze

in true sense, he was not an atheist

i think he believed in a god, but not in religious gods

Ryder Rude

im not sure in what sense he cud call the entire world a god

Giorgi Lagidze

i do the same lol

Ryder Rude

11:55

as in, i dont know what that means

Giorgi Lagidze

here is how i interpret it

imagine that universe always existed.(always)

if so, god always existed :P

god = nature

it's hard to imagine how universe could always exist, but that's my best guess and most probable one for me

Ryder Rude

ummm.. this is still meaningless to me lol. why not just call it nature then

what does renaming it to god do

is it just a name

Giorgi Lagidze

well, physics laws had to come from somewhere

god is someone with infinite attributes

Ryder Rude

godel made a similar argument

Giorgi Lagidze

and god = nature is just a connecting term between those too

yeah. exactly

Ryder Rude

11:59

godel defined god as having all the good attributes. hav u seen his ontological argumwnt

@GiorgiLagidze godel excludes the bad attributes of nature lol

Giorgi Lagidze

that's what I don't like. it can't have all the good attributes

Ryder Rude

to me, the set of all good attributes is meaningless

Giorgi Lagidze

if something has infinite attributes, it most likely contains bad ones as well(note that we don't know what good or bad is in terms of all powerful being lol)

same here

Ryder Rude

so Godel's argument is just word play to me

Giorgi Lagidze

spinoza doesn't say the same

Ryder Rude

12:00

yeah

Giorgi Lagidze

i think what he says is it has infinite attributes and doesn't have the possibility to feel pain

Ryder Rude

oh

Giorgi Lagidze

you might say why infinite attributes doesn't mean that it can feel pain, but in my opinion, that could be the case

Ryder Rude

i dont know what pain even means in that context

Giorgi Lagidze

you're suffering right ?

Ryder Rude

12:02

so it's not even wrong lol

Giorgi Lagidze

we all suffer in this life

do you think god can feel compassionate about you or me ?

Ryder Rude

oh

this is like Buddhism

Giorgi Lagidze

spinoza says that it can't feel that

Ryder Rude

so spinoza's god doesnt care

Giorgi Lagidze

yes. I think that's the best explanation to be honest, otherwise, if it can feel pain and be compassionate, how does that god watch the humanity suffer

Ryder Rude

12:03

this is a deism position

Giorgi Lagidze

yes

something like that

but again, spinoza is hard to understand and i am just saying what the internet says about him which could be not fully correct

Ryder Rude

yeah. thw details would be more sophisticates. spinoza was hunted for his entire life for speaking this

Giorgi Lagidze

but day by day, i understand why einstein believed exactly in spinoza's god :p

Ryder Rude

lol

einstein had a balanced view on things. criticising both creationism and atheism

Giorgi Lagidze

yes exactly.

Ryder Rude

12:05

he called the former naive and criticised the latter

Giorgi Lagidze

if you think more and more, that's why spinoza's explanation seems best lol

in some sense, spinoza's god is not fully creationism and also not fully atheism

Ryder Rude

it's pretty nice

do u watch veritasium

the video i gave is about nuclear war too

Giorgi Lagidze

rarely, but have to watch that video definitely.

Ryder Rude

ya. it's really good.

gtg

Giorgi Lagidze

ok. see you later ^_^

ACuriousMind

12:15

@Relativisticcucumber @naturallyInconsistent See this answer for a lengthier statement of the "all Hilbert spaces are the same" argument

@Mr.Feynman If you didn't keep the mixed terms, how would a commutator ever appear anywhere? If you never kept mixed terms, all infinitesimal transformations would commute!

Mr. Feynman

12:50

@ACuriousMind Oh sure, I agree about that. Parallel transport wouldn't change anything at first order only. The problem is that you can't just neglect quadratic second order and keep mixed second order terms, it's kind of contradictory

In a comment Qmechanic suggests that they should instead cancel, so there must be something I lost in my computations

Sanjana

15:22

What is the justification behind taking both the internal and external fields in some dimensional reductions in supersymmetric field theories/string theory to be independent of internal coordinates?

E.g. While obtaining $\mathcal{N}=4$ SYM in $D=4$ from $\mathcal{N}=1$ in $D=10$ all the references assume both $A_{\mu}$ (external space vector) and $A_i$ (external space scalar) which are obtained from the 10 dimensional $A_M$, are independent of internal coordinates. Is that done just for simplicity or are there additional justifications?

ACuriousMind

@Sanjana it has nothing to do with supersymmetry or string theory; when you do dimensional reduction, you're looking by assumption for the theory you get when you ignore some (usually compact) degrees of freedom

if you kept the dependence on the additional coordinates, whatever you're doing would not be dimensional reduction :P

Sanjana

I am reducing the dimension...why won't it be dimensional reduction :p I mean...isn't it a bit unnatural to consider all the fields to be independent of the internal coordinates? I would keep internal coordinate dependence for the internal fields and external coordinate dependence for the external ones...but the assumptions are weaker than this---why?

I have seen this previously too...Even in the original Kaluza Klein reduction. I thought they were doing this for simplicity

ACuriousMind

how would a theory in which the "internal" fields still depend on the 6 additional dimensions be a theory reduced to 4d?

if any of your fields depend on more than 4d, your result is not a 4d field theory :P

the idea of dimensional reduction is precisely that you want to know what theory you get if you ignore the (compact) d.o.f.

Claudio Menchinelli

guys, I have a question: my professor's notes contain the following computations: in the case of the free particle Hamiltonian $\hat{H} = \hat{p}^2 / 2m$ we have that $$\langle p |e^{-i\hat{H}t/\hbar }|\psi \rangle = e^{-\frac{ip^2t}{2m\hbar}}\langle p | \psi \rangle $$

now my question is: is it possible that the time evolution operator, although not hermitian, acts on bras and kets identically?

Sanjana

@ACuriousMind Oh yes...I had another question---Is it trivially true that if the original higher dimensional theory is unitary then the compactified theory also is or is it to be checked separately?

ACuriousMind

15:33

"unitary" is one of these words that doesn't really mean anything unless you are more specific :P

@ClaudioMenchinelli This is where Dirac notation sucks, usually there shouldn't be a minus on the r.h.s. anymore

Claudio Menchinelli

I'm quite sure my professor completely ignored the fact that the t-e. operator is not hermitian and just wrote this superquickly

@ACuriousMind could you look at this things I wrote

ACuriousMind

@ClaudioMenchinelli what do you mean?

Claudio Menchinelli

I'd like to upload a file of my notes lol

but I can't lmaooo

well I've computed the adjoint of the time-evol operator

ACuriousMind

what is there to compute? $U^\dagger = (\mathrm{e}^{-\mathrm{i}Ht})^\dagger = \mathrm{e}^{\mathrm{i}Ht}$

Claudio Menchinelli

no no wait it's a bit more complicated than that I think

no it's correct

ACuriousMind

15:38

no it isn't more complicated :P

Claudio Menchinelli

You're right

but I made so mani calculations

I had to show that $(A^{\dagger})^n =(A^n)^{\dagger}$

but the minus sign is again introduced when I take the of adjoint $(\langle \psi |U^{\dagger}(t)|p\rangle )^{\ast}$

wait a second

you considered the power series expansion of $U^{\dagger}$ right @ACuriousMind

to get to that equality

or is there a quicker way of seeing that

I hate bracket notation when dealing with operators

ACuriousMind

@ClaudioMenchinelli no :P

naturallyInconsistent

@ACuriousMind I'm confused as to what you mean. $\left<p\right|\hat p=\left<p\right|p$ should imply that the formula is correct.

Claudio Menchinelli

@naturallyInconsistent I thought so too, but I think you need to consider $(\hat{p}^{\dagger}|p\rangle)^{\ast}$

ACuriousMind

@ClaudioMenchinelli If you want the proof that this is the adjoint, just consider it in the basis where the operators are diagonal, that's the simplest way to see it

@naturallyInconsistent caution: $p$ is self-adjoint, $U$ is not!

naturallyInconsistent

15:48

@ClaudioMenchinelli $\hat p{}^\dagger=\hat p$

Claudio Menchinelli

12

Q: How does a linear operator act on a bra?

I'm studying QM from Shankar. He introduces linear operators and says that an operator is an instruction for transforming one ket into another. But then a few lines below he says operators can also act on bras. So does the complete specification of an operator include its action on bras? Or does...

ACuriousMind

for self-adjoint operators, you don't need to pay attention in which direction they act, but for non-self-adjoint ones you need to

Claudio Menchinelli

yeah but the time evolution is not hermitian

exactly

naturallyInconsistent

@ACuriousMind I'm not disagreeing, but I do not see where that is appearing in that computation.

Claudio Menchinelli

my professor, during that lecture just wrote the single line of computations

saying that it was hermitian

assuming

ACuriousMind

15:50

@naturallyInconsistent The $\mathrm{e}^{-\mathrm{i}Ht}$ is $U(t)$. When we write something like $\langle p \vert U(t)\vert \psi\rangle$, then by default we mean $\langle p, U(t)\psi\rangle$ (in careful inner product notation). If you want to apply the $U$ "to the left", you first need to take the adjoint, $\langle U^\dagger p, \psi\rangle$

naturallyInconsistent

ahhh

ewww

Claudio Menchinelli

that's what I was trying to say too hahaha

there are like thousands of questions on this topic hahaha

ACuriousMind

Dirac notation just sucks for operators that aren't self-adjoint :P

Claudio Menchinelli

bracket notation leads to being superficial

@ACuriousMind I completely agree

Ryder Rude

i also have a post about this

this math.stackexchange.com/questions/4493307/…

this is my answer math.stackexchange.com/a/4493320/445404

@ClaudioMenchinelli however, i dont think there is anything wrong with this equation. the operator is $e^{-ip^2/2m} \delta (p-p')$, so it doesn't matter whether you contract with p or p'

naturallyInconsistent

16:08

sigh, why cant you read the chat before saying stuff?

Ryder Rude

lemme see

so yall r agreeing or disagreeing with me?

im getting $\langle p' | e^{-iHt} |\psi\rangle= \int dp \delta (p-p') e^{-i \frac{p^2t}{2m}} \psi (p) = e^{-i\frac{p'^2t}{2m}} \psi (p')$

Ryder Rude

16:31

this may be easier to understand with a finite dimensional anti hermitian matrix. let's say diag(i,i,i) now whether u right multiply with the column vector [1,0,0], or left multiply with the row vector [1,0,0], u wud get $i$ as ur eigenvalue

Sanjana

Santa is approaching China right now.

user587860

17:03

@ACuriousMind We know that Casimir element of a Lie algebra $\mathfrak{g}$ classifies irreducible reps of the Lie algebra. But is it the case that this fails in infinite-dimensional irreps, in the sense that it might not be acting as a scalar multiple of identity, or that it fails to be invariant under Lie algebra isomorphisms? Former looks true, but I am not sure about the latter.

user587860

17:16

(Assuming that \mathfrak{g} is semi-simple so Casimir element always exists)

Loong

18:26

Nightwish (Walking in the Air Live Performance) [HQ]

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ACuriousMind

22:06

@Supersymmetry Why would any of this fail for infinite dimensional representations? We usually classify the irreps of the Poincaré group by its Casimirs mass and spin, don't we?

user587860

23:38

@ACuriousMind Haha, yes. Sorry for asking a trivially false question :)

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