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Azmuth
Azmuth
5:01 AM
Hans Zimmer is the best Composer that ever existed on the face of earth
Master Oogway is the best Philosopher of the time who ever existed in Universe
Change my mind!
 
Azmuth
Azmuth
5:22 AM
 
123
123
6:21 AM
GooD MoRniNG.. :-)
 
psa
psa
6:44 AM
Anyone care to give me some help on deriving the spherical harmonics?
 
 
2 hours later…
Kenzo Tenma
Kenzo Tenma
8:23 AM
This video was uploaded on 26th October and gives deja vu kind of feeling when I look at it now:
 
Nihar Karve
Nihar Karve
@psa what do you mean deriving? Their formula, why they arise in the context of the Laplace equation, etc...
 
psa
psa
more precisely, producing the first nine terms from acting on a complex number $(x+iy)^j$ ($j=0,1,2$) with the angular momentum operator
 
 
2 hours later…
Slereah
Slereah
10:03 AM
put some decoration on the GR shelf
 
 
1 hour later…
Nihar Karve
Nihar Karve
11:06 AM
I can't tell whether the decoration is the brass figure or "Quantum Fields and Strings: A Course for Mathematicians" :D
 
Ratman
Ratman
ahhahahahha I was thinking the same
 
Ratman
Ratman
11:23 AM
does anyone know a good resource to keep studyng concepts from standard model following an approach similar to the one used by Baez and Huerta in arxiv.org/abs/0904.1556 ? I am mostrly interested in see how unification of $SU(2)$ and $U(1)$ is carried out using group theory and representation theory, but even a generic resource discussing SM using group theory would be nice.
looking from the resource recomendations of the site I think group theory from Pierre Raimond could be it, but I am not sure
 
Slereah
Slereah
11:46 AM
Do you mean just gauge theory?
 
Ratman
Ratman
I think what I am looking for is particle physics using representation theory. something that goes a bit deeper respect the paper of Baez.
if there is even some gauge theory that's ok, but what i would like to see is an approach using methods of group thoery
 
Azmuth
Azmuth
12:36 PM
@Slereah You have more books than I've noodles in my packet
 
bolbteppa
bolbteppa
@Ratman section 1.1 mentions further reading, e.g. Zee's book has stuff on this
What's Witten (and Dirac, well it does have 1 chapter...) doing on the GR shelf :p
 
Azmuth
Azmuth
Well, there's odd one out too :P
 
Ratman
Ratman
Yes I have seen the further Reading part, in fact i was trying to look at the Anthony sudbery ref
I'll try to see zee as well, thank you
 
Azmuth
Azmuth
@bolbteppa Hello sir!
Do you've any idea on how many courses are there in a regular B Tech college and how much do students take?
 
Slereah
Slereah
12:57 PM
@bolbteppa some are misplaced
 
bolbteppa
bolbteppa
@Azmuth no idea sorry
 
Azmuth
Azmuth
oh okay...
 
Slereah
Slereah
Also Dirac's book has a section on GR
 
bolbteppa
bolbteppa
@Slereah I found the ultimate paper on GR spinor stuff
 
Slereah
Slereah
For spinors in GR I mostly use Springer's GR handbook
It has a nice section on GR spinors
 
JingleBells
JingleBells
12:59 PM
@Slereah have u read all of these?
 
Slereah
Slereah
They're textbooks
I have not read them cover to cover
 
Azmuth
Azmuth
@Slereah have you completed all?
 
Slereah
Slereah
There's only so many times I can take someone defining what a vector field is
 
Azmuth
Azmuth
all books?
 
JingleBells
JingleBells
@Slereah what do u do with all this knowledge?
 
Azmuth
Azmuth
1:02 PM
^Don't ask
 
Slereah
Slereah
I develop mind powers
 
Balarka Sen
Balarka Sen
Yo @Slereah
 
Slereah
Slereah
hey @BalarkaSen
 
Balarka Sen
Balarka Sen
That's a good bookrack
 
JingleBells
JingleBells
The "Dirac - Lectures on Quantum Mechanics" is for me
 
Slereah
Slereah
1:03 PM
Don't look at the shelf below
 
JingleBells
JingleBells
(the little red book at the top)
 
Slereah
Slereah
It's the Humanities shelf
 
Balarka Sen
Balarka Sen
Lol
 
Slereah
Slereah
Mostly archeology
and philosophy
 
JingleBells
JingleBells
@Slereah i'm asking seriously :P
 
Slereah
Slereah
1:04 PM
Do I need a reason to learn science
6
 
JingleBells
JingleBells
no, it can be to satisfy your curiousity
i'm just asking if you're working for nasa or something
 
Slereah
Slereah
I am not
NASA doesn't do a lot of GR
Since they do aerospatial engineering mostly
 
Azmuth
Azmuth
@Slereah I'm NASA, ask me
 
Slereah
Slereah
@Azmuth How's them rockets
 
Azmuth
Azmuth
@Slereah satellite theory stuff.... :P
 
Slereah
Slereah
1:06 PM
Plenty of people work at NASA, I assume
Cooks, drivers, mechanics, puppeteers
 
JingleBells
JingleBells
great, so there's a place for me
I'm gonna clean them rockets
 
Azmuth
Azmuth
I'm gonna fix computers
 
Balarka Sen
Balarka Sen
Imagine the guy managing the google doodles
"I work for Google"
 
JingleBells
JingleBells
@Slereah so you learn science to satisfy your curiosity but you don't apply/use the knowledge and you haven't applied/used the knowledge? Just wondering, not judging.
 
Slereah
Slereah
I mean it's GR
What would I apply it to
 
JingleBells
JingleBells
1:09 PM
gps :D
make ur own gps
oh nvm
that was SR
 
Slereah
Slereah
GPS is 1 GR thing and a million signal theory and radio waves things
 
JingleBells
JingleBells
calculate how spacetime curves around ur body :P by knowing your size, mass, earth's size and mass..
actually, what is GR used for lol?
 
Slereah
Slereah
See this bit of ancient wisdom :
 
Azmuth
Azmuth
@Slereah hehehehehe DO you have that poem GR Book?
Funny one!?
Buy that!
 
Slereah
Slereah
I do not
 
JingleBells
JingleBells
1:14 PM
@Slereah soo, what is GR used for?
 
Slereah
Slereah
Hard to find a copy that will ship to France
 
Azmuth
Azmuth
@Slereah Buy that and read those to your kids, there must be one in Amazon
 
Slereah
Slereah
I don't think that book has been printed since the 60's
 
Azmuth
Azmuth
@Slereah lemme check it
 
Slereah
Slereah
there are some, but they are used copies
that are 1) expensive 2) not necessarily shipping here
 
JingleBells
JingleBells
1:18 PM
I guess GR will become a big thing in the future after we start colonizing space. But no one knows if someone won't come and disprove GR by then lol
 
Nihar Karve
Nihar Karve
1:45 PM
@JingleBells what does 'disprove' GR mean? It makes many, many testable predictions that have been verified
Of course, it is not a complete theory at all length scales
 
JingleBells
JingleBells
@NiharKarve I don't know, but for many years people thought that the Earth was flat, then that Earth was the center of the universe/solar system and whatnot. Recently, physicists thought they had figured it all out until the blackbody radiation thing which led to QM... I'm not saying that GR is wrong, but in history, we've got enough evidence to know that things are not always what we think they are.
 
Physics Meta
Physics Meta
2:01 PM
0
Q: Does SE allow me to publish my own material (Qs/As) in a peer-reviewed journal?

Mohammad JavanshiryDoes SE return the copyright to its contributors in order for them to partially/completely republish their own material in some peer-reviewed journals, or any written permissions from SE are required?

discussion
 
Nihar Karve
Nihar Karve
@JingleBells Absolutely, it was just a quibble on your usage of "disproven". Physical theories can't really be proven or disproven from axioms the same way mathematical theorems can
 
ACuriousMind
ACuriousMind
@JingleBells The wrongness of e.g. Newtonian mechanics compared to QM is different than the wrongness of the belief in a flat Earth, and conflating the two is dangerous. GR - like Newtonian mechanics - is well-tested in many, many predictions. If it is wrong, then it is wrong in the sense that it is not the whole truth, but it must arise as a limit of the underlying truth, since we know it makes correct predictions.
The belief in flat earth makes no correct predictions at all - it can indeed be disproven by basic observation (some Greeks already knew how to do that), and nothing about it is even approximately correct.
The whole purpose of the scientific method is that we can be certain our current beliefs cannot be disproven like that - since observation and experiment conform to our predictions, we know they are at least somewhat correct.
 
Nihar Karve
Nihar Karve
@ACuriousMind you should do a Peter Shor and try out ELL
 
Azmuth
Azmuth
Twitter, SE, TG, WP, Pinterest, Chrome was down in India
what all has happened?
Linux Debian server too
 
ACuriousMind
ACuriousMind
@NiharKarve I'm not sure whether you're saying I should start answering questions there or if I would benefit from learning how to speak English :D
 
Nihar Karve
Nihar Karve
2:07 PM
XD
@ACuriousMind I've never asked, what is your profile picture? It seems eerily familiar.
 
ACuriousMind
ACuriousMind
it's Kim Kitsuragi from Disco Elysium
 
Captain Bohemian
Captain Bohemian
When it comes to learn to speak English, I had the first English language course online yesterday.
 
user 6232128
user 6232128
how did it go?
 
Captain Bohemian
Captain Bohemian
the instructor asked each person in class to answer questions throughout the class, rather than the usual lecture, in which only the lecturer talks.
 
ACuriousMind
ACuriousMind
well you can't learn to speak a language if you just listen to it :P
 
Azmuth
Azmuth
2:11 PM
I once had an English class with Dr. Sashi Throor, I only later realized that they spoke english
 
Nihar Karve
Nihar Karve
Shashi Tharoor*
 
Azmuth
Azmuth
whatever
 
Nihar Karve
Nihar Karve
Has anybody used cohomology in physics outside of a GR context?
 
Captain Bohemian
Captain Bohemian
the lecturer said the connection is poor when I was asked to make self-presentation and said I need to make self-presentation again some time when the connection is better. It's like the poor connection is a common problem. I have encountered it several times when I interacted with instructor in the online course last semester.
 
Nihar Karve
Nihar Karve
@CaptainBohemian Your English already seems quite good to me!
 
ACuriousMind
ACuriousMind
2:17 PM
@NiharKarve yes, comes up a lot in beyond-the-standard-model and string theory contexts, in particular when compactifying
 
Captain Bohemian
Captain Bohemian
@NiharKarve that English language course is a compulsory course in this physics program. I am not sure if it is only for students from non-native English speaking countries.
 
Nihar Karve
Nihar Karve
@CaptainBohemian ah, ok
 
ACuriousMind
ACuriousMind
often the (co)homology of the compact manifold is more or less directly related to the particle content of the effective theory on the non-compact part
 
Nihar Karve
Nihar Karve
that makes sense intuitively
but, ya know, anything simpler? I was inspired by Baez's piece on cohomology in circuits
 
Captain Bohemian
Captain Bohemian
the English language course is designed for PhD students and we are required to make presentation about scientific papers.
 
ACuriousMind
ACuriousMind
2:23 PM
@NiharKarve you can think about a lot of stuff related to potentials in terms of cohomology
the existence of a potential for some field $F$ with $\mathrm{d}F= 0$ is the Poincaré lemma - contractible spaces have vanishing cohomology,. essentially
 
Balarka Sen
Balarka Sen
I used de Rham cohomology in my last physics assignment
Lol
 
Nihar Karve
Nihar Karve
nice, what for?
 
Balarka Sen
Balarka Sen
To argue that some field is conservative
 
Azmuth
Azmuth
(co)homology
 
Nihar Karve
Nihar Karve
@ACuriousMind Mass “has a cohomological significance, it parametrizes the extensions of the Galileo group.” (Santiago Garcıa, hep-th/9306040) - from nLab (the other two items are regarding electrodynamics and string theory)
 
ACuriousMind
ACuriousMind
2:25 PM
so e.g. you can think about the Aharanov-Bohm effect as the solenoid in the middle being effectively removed from spacetime, making the cohomology non-trivial, so that the 4-potential $A$ is not globally defined (and also so that Stokes' theorem does not apply and you can turn the integral along the path $\int_\gamma A$ into a $\int_S F$ where $\partial S = \gamma$.
 
Azmuth
Azmuth
Gamma
 
ACuriousMind
ACuriousMind
@NiharKarve ah, that's Lie algebra cohomology, which I guess is technically cohomology but I've never seen it as as geometric as "normal" cohomology :P
The $H^2(G)$ I explain in this popular answer as the origin of central extensions is technically a second cohomology group but I've never gotten any great insight from thinking about it like that
 
Nihar Karve
Nihar Karve
That was one of the first answers I ever read on physics SE :)
obviously everything flew over my head
 
Balarka Sen
Balarka Sen
Fun fact, I learnt Lie algebra cohomology from some BRST cohomology notes ACM shared with me
I think its great
 
ACuriousMind
ACuriousMind
ah, the O'Farrill ones?
 
Balarka Sen
Balarka Sen
2:28 PM
yeah
 
Azmuth
Azmuth
Share further
I want to see his handwriting
 
Nihar Karve
Nihar Karve
@BalarkaSen Well, by all means, continue the chain
 
Balarka Sen
Balarka Sen
 
ACuriousMind
ACuriousMind
(it's not notes I took, it's just notes I recommended :P)
 
Azmuth
Azmuth
PHUN FACT:

*The planet Venus has a rotation period of 243 Earth days and it orbits the Sun every 225 Earth days. Venus takes longer to rotate about its axis than any other planet in the Solar System.*

One day on planet Venus is longer than one year.
 
Nihar Karve
Nihar Karve
2:30 PM
@Azmuth and you'd be hard-pressed to find handwritten physics notes online
 
Azmuth
Azmuth
@NiharKarve Ok
keep mine, If I became legend one day, these notes will help you get some $
 
ACuriousMind
ACuriousMind
@NiharKarve Don't say that
thsoe are the official lecture notes for a bsm course in 2010: thphys.uni-heidelberg.de/~hebecker/BSM/bsm.html
 
Nihar Karve
Nihar Karve
I mean, ironically I have the EPFL lecture notes on GR as an EFT open, most of which are handwritten
 
ACuriousMind
ACuriousMind
the theoretical mechanics lecture series I took with him in 2011 was also handwritten but it seems to have been taken down and replaced by LaTeX in the newer versions of that lecture series :P
 
Azmuth
Azmuth
@ACuriousMind Your handwriting is good or black ink makes it look good?
 
Nihar Karve
Nihar Karve
2:33 PM
On the second link you've shared, all the links are purple for me
very mysterious
 
ACuriousMind
ACuriousMind
@Azmuth it's not my handwriting, it's Hebecker's
 
Azmuth
Azmuth
okie dookie
 
ACuriousMind
ACuriousMind
my handwriting looks like this (notes from a QFT lecture I attended in 2014)
 
Nihar Karve
Nihar Karve
Excellent deltas :D
 
ACuriousMind
ACuriousMind
that's how I learnt to write it when I took Ancient Greek in school
 
Nihar Karve
Nihar Karve
2:36 PM
you took what now
 
Azmuth
Azmuth
@ACuriousMind I'd suggest to keep proper spacing and intedation, it'd look cooler in your handwriting
 
ACuriousMind
ACuriousMind
I attended a "humanistic school" where you could take Latin and Ancient Greek as foreign languages instead of modern languages
Could've also taken Hebrew but it didn't fit into my schedule :/
 
Nihar Karve
Nihar Karve
also???
 
Azmuth
Azmuth
I also write delta like that
@ACuriousMind here's my cool handwriting
Oct 23 at 15:59, by Azmuth
I'm just adding it here, If anyone requires my Entrepreneurship notes (Part -1) Notes here
 
Nihar Karve
Nihar Karve
I suppose the bare minimum of learning Ancient Greek is that you can finally write a xi without butchering it into some forlorn-looking backwards 3
 
Ratman
Ratman
2:39 PM
it is quite common even here to study ancient lenguages and literature , I studied Latin in a scientific school
 
Azmuth
Azmuth
seems adobe removed the links
 
ACuriousMind
ACuriousMind
@NiharKarve part of me dies every time some physicist or mathematician just draws a random squiggle and calls it xi :P
5
 
Azmuth
Azmuth
lemme post again
 
Nihar Karve
Nihar Karve
I got to learn French and Spanish
idk, might come in handy if Slereah shares some French stuff at some point
 
ACuriousMind
ACuriousMind
that's the downside of having learned the ancient languages - the only language I speak that's still alive and not my native language is English
 
Azmuth
Azmuth
2:42 PM
I already know french
My sister worked in French Embassy as translator
 
Ratman
Ratman
same here, just english
 
ACuriousMind
ACuriousMind
but I figured there's plenty of opportunities later in life to learn e.g. French if I want to but not quite as many for Ancient Greek
 
Nihar Karve
Nihar Karve
@Azmuth but you must speak at least 3 languages right?
 
Azmuth
Azmuth
@NiharKarve Hindi, Bhojpuri, Odia, English, French and a bit of Sambalpuri
Well, honestly, I'm expert in none of them
 
Ratman
Ratman
for us it wasn't actually a choiche, in "scientific school" you have English and Latin
 
Nihar Karve
Nihar Karve
2:45 PM
@Ratman which country was that in?
 
Ratman
Ratman
italy
I probably didn't appreciate it enough as I would now
 
Azmuth
Azmuth
 
JingleBells
JingleBells
3:39 PM
@ACuriousMind I somewhat agree with what you're saying. If GR was to be "disproved", it would most likely mean that it's not the whole truth. But I believe that our brains are very limited and there are many unknown unknowns that are unreachable to our current cognitive capacity. Just because our current brains are convinced that they are measuring reality, it may not necessarily be so.
If you realize that you're a bunch of connected neurons, just like a mouse or an ant, a whole bunch of possibilities opens up as to what happens if you add more neurons and more connections.
 
ACuriousMind
ACuriousMind
@JingleBells I don't think the idea that there is a reality wholly distinct from what we are perceiving is a consistent notion of reality. What does it mean for something to be "real" if not that we can agree on perceiving it?
@JingleBells why do you not apply the same doubt you apply to physics to biology? Maybe we aren't bunches of connected neurons and we'll find out we're something different in the future?
 
JingleBells
JingleBells
@ACuriousMind I do apply it. I can be wrong.
 
ACuriousMind
ACuriousMind
But then your objection is pointless. Everything can be wrong, all of reality might be a mirage caused by Descartes' demon so why point it out for GR specifically?
 
JingleBells
JingleBells
@ACuriousMind Because we were talking about GR and not about biology :P
I'm just a bunch of firing neurons, so who am I to be certain that anything is certain. Who am I to be certain that I'm just a bunch of firing neurons?
 
ACuriousMind
ACuriousMind
@JingleBells and if I had said that the sun shone today instead of talking about GR, would you have pointed out that I cannot be certain that the sun shone and I might have hallucinated it?
 
JingleBells
JingleBells
3:49 PM
No, but it's true that the sun MIGHT not be there. I trust my senses as much as I can, but I also trust that my senses are limited. I have an idea of why I said it about GR.
But who knows if the explanation is not just a fabrication of my left brain.
ahh how I missed our talks :D
The point I'm making is, I believe in the limited brain. But as you pointed out - I might be wrong, it's a belief after all.
 
ACuriousMind
ACuriousMind
Radical doubt should be a starting point for an epistemology, it cannot be its end. Yes, the sun might not be there (again, see Descartes' demon), but why does that matter in the contexts of the degree of knowledge (possibly incomplete vs. utterly wrong when compared with observation) I was talking about?
You don't jump out the window just because there might be solid ground directly outside it. That we can radically doubt everything does not mean that we don't trust in knowledge to different degrees.
 
JingleBells
JingleBells
You can trust in knowledge. Just like I trust in the knowledge that knowledge cannot be trusted.
lol
I don't know what we're debating at this point. :P
I don't understand your point of view. What's the point you're trying to get across?
 
ACuriousMind
ACuriousMind
@JingleBells You seem to believe that "reality" could be completely different from what we perceive. I believe that a notion of reality that has nothing to do with what we perceive is rather useless.
 
Azmuth
Azmuth
Program on design of assembler using C/C++
question^
Absurd na?
But, it can be done for
CISC x86 based 8086 processor
You dunno how the hell, I'm excited to go to college
Comtupar Engynar
 
ACuriousMind
ACuriousMind
4:04 PM
even if there "really" is a world different from what we perceive, there is no point in believing that, since what useful predictions does that make? What would you do with that "knowledge"? How does the "reality" of that world differ from all the other things that are simply untrue?
 
JingleBells
JingleBells
@ACuriousMind I think it's useless too. I'm just saying that it's possible. I also think that it's useless to doubt everything.
so let's stop :P
Nothing interesting will come out of me doubting the essence of everything
 
Azmuth
Azmuth
Y'all should listen to Comtupar Engynar and believe that GR isn't good thats why String Theory exists!
dinner time, brb :)
 
JingleBells
JingleBells
I believe in the scientific method. If observations confirm it, then I trust it. And it's possible that a "different reality from what we perceive" can exist, but as you said, nothing useful or interesting comes out of believing in it.
do we agree here? :P
 
ACuriousMind
ACuriousMind
yeah, alright
 
JingleBells
JingleBells
@ACuriousMind I guess the confusion arose from the assumption that I believe that GR can be completely disproved, but no, it's just a possibility and a useless one to think about :)
 
Azmuth
Azmuth
4:20 PM
I'm back!
Yoooo people! I know y'all missed me here :)
 
ACuriousMind
ACuriousMind
→ 9 messages moved to ­Trash
 
JingleBells
JingleBells
@Azmuth what did u eat?
 
Azmuth
Azmuth
Paneer Butter masala and Naan!
After a long time tho :)
 
Prateek Mourya
Prateek Mourya
azmuth are you ben 10 one azmuth?
 
Azmuth
Azmuth
@PrateekMourya Yes
 
Prateek Mourya
Prateek Mourya
4:27 PM
unfortunately ben 10 series now turned to shit
 
Azmuth
Azmuth
Just In: Joe Biden became 46th President of USA with +14 seats!
 
JingleBells
JingleBells
Biden wins lol
 
Azmuth
Azmuth
Biden looks older than Trump, infact trump looks 50(s) or so, BIden looks 90(s)
 
JingleBells
JingleBells
the internet is exploding right now
 
bolbteppa
bolbteppa
Finally...
 
123
123
5:00 PM
Hi
Why example of rocket motion can not be explain by newton's law???
 
Azmuth
Azmuth
5:12 PM
The Twitter exploded, Norbert Elekes is trending!
 
Jack Rod
Jack Rod
Poltics in science and science in poltics +
Does any body have the image of sun which clicked on 1916
I am searching it for last 3 hour?
 
danielunderwood
danielunderwood
5:49 PM
@123 Newton should be sufficient for explaining rocket motion, you just have to realize that you can't use $F = ma = m \ddot{x}$ because rockets depend on changing mass. The more correct form of Newton's second law is $F = \dot{p} = \dot{m} \dot{x} + m \ddot{x} $ (ignoring the vector bits), which is what's needed for rockets (at least for the case I've seen, I imagine real rockets are a bit more complicated).
 
Nihar Karve
Nihar Karve
@danielunderwood until of course we're all intrepid space explorers and we start launching our rockets between a binary black hole system
Hello @knzhou, I just wanted to say that I really enjoyed the lecture notes on your website
 
danielunderwood
danielunderwood
What's the Icarus equivalent for a black hole?
 
Nihar Karve
Nihar Karve
Trying to skim the event horizon?
 
knzhou
knzhou
6:15 PM
@NiharKarve Thanks! Glad to see people are reading them.
 
 
2 hours later…
MathCubes
MathCubes
7:53 PM
Is anyone on?
Hello @urb
I guess no one wants to have a chat
 
JingleBells
JingleBells
sup
 
MathCubes
MathCubes
Nothing much than I have a few questions
I am a layperson and I just am interested
 
JingleBells
JingleBells
just ask the questions and if anyone wants to answer, he/she will
 
MathCubes
MathCubes
Do we know what gives speed of light/casualty it's speed limit?
 
JingleBells
JingleBells
As far as I know light just travels at that speed. That's the way the universe is.
 
MathCubes
MathCubes
8:00 PM
So we don't know why it can't travel faster or slower?
in a vacuum.
 
JingleBells
JingleBells
I'm not sure. I usually ask questions here than answer, but as far as I know, that's the way the universe is. According to Wikipedia: "There are many physical constants in science, some of the most widely recognized being the speed of light in vacuum c". So it's just a constant of the universe.
 
MathCubes
MathCubes
Okay so we don't know why it's a constant than?
 
JingleBells
JingleBells
^ take a look
 
MathCubes
MathCubes
Thanks
INteresting
" voidpotentialenergy 16 July 2020 11:42
This is just my opinion but i think L speed is it's speed because the particle part of it is the fastest it can interact with the quanta distance in quantum fluctuation.
Light is particle and wave so the wave happens in the void between quanta.
Gravity probably travels in that void and why gravity seems instant. "
 
JingleBells
JingleBells
8:31 PM
Units are a weird thing. When you think about the speed of light, it is defined in meters/second, but what is a meter, and what a second? A meter is "the length of the path traveled by light in a vacuum in 1299 792 458 of a second." and a second is defined in terms of the radiation frequency at which atoms of the element cesium change from one state to another. So it all breaks down to fundamental measurements of universal properties. (as far as I know, don't take my word too seriously)
 
JingleBells
JingleBells
8:44 PM
Regarding units, I have a question. The SI base units are supposed to be defined independently of anything else, aren't they? So why is a second defined as 9 192 631 770 Hz where a Hz is defined as a cycle per second? It's like, a second is defined by itself. Am I getting this wrong?
According to Wikipedia: "Caesium atomic clocks are the most accurate time and frequency standards, and serve as the primary standard for the definition of the second." So a second is defined by this measuring device? Like, the amount of time this device takes to do something or make something happen is 1 second, something like this?
Does this mean that every unit in existence is defined from this device? (cuz a meter is the length light travels in x seconds...etc...)
 
 
2 hours later…
ACuriousMind
ACuriousMind
10:49 PM
@JingleBells You shouldn't say "Hz" in that definition because a Hertz is literally just the unit of "per second". You can count the oscillations, and when you've counted 9 192 631 770 oscillations, we say that's the time span we call a second
it's not dependent on itself, it just relies on counting (and the assumption/knowledge that the oscillation is regular)
 
ACuriousMind
ACuriousMind
11:08 PM
@SirCumference tired again? ;)
 
Sir Cumference
Sir Cumference
11:19 PM
@ACuriousMind My keyboard's command key has sometimes just not worked lately. Tried to do command+l to get to the search bar and go to facebook, but realized it didn't go through
 
ACuriousMind
ACuriousMind
ah, fair enough :P
 
MathCubes
MathCubes
THe question is why is it the speed it is
Not why it's exist but why it's it that speed
?
 
Sir Cumference
Sir Cumference
@MathCubes if you're looking for a satisfying answer explained by some theory, afaik we don't have one yet
 
MathCubes
MathCubes
Okay
 
Sir Cumference
Sir Cumference
they all just take it as a postulate that the speed of light is finite and equal to $c$, because that's what observations show
 
ACuriousMind
ACuriousMind
11:26 PM
if it was any other speed, how could we tell :P
 
MathCubes
MathCubes
Are there hypothesis on it?
 
ACuriousMind
ACuriousMind
it is not meaningful to ask about the numerical value of dimensionful constants
 
Sir Cumference
Sir Cumference
I guess it ultimately comes down to a question of why there's a finite speed limit in the universe
Because if there's a finite speed limit, it's gonna take some number
 
ACuriousMind
ACuriousMind
it's fair to say we don't know "why" the fine structure constant has the value it has, but it's not fair to ask why the speed of light has the "value" it has, because ultimately all units are defined in terms of "constants"
 
Sir Cumference
Sir Cumference
Maybe some esoteric theory gives a good fundamental explanation of it, but not anything standard I know of
 
MathCubes
MathCubes
11:29 PM
Well yeah
It probably has to take some value
 
Sir Cumference
Sir Cumference
I guess physics just isn't like math where everything has a fundamental explanation. We kinda just accept that these constants have certain values and work with them
Or maybe I'm totally wrong
 
MathCubes
MathCubes
I was just was wondering why it's that speed. I know we define the units but the speed I thought must been define by something in the universe.
 
Sir Cumference
Sir Cumference
Probably the same reason the gravitational constant and planck's constant have their value, rather than being something greater or smaller
Which isn't something anyone really knows
 
MathCubes
MathCubes
Okay gotcha
 
ACuriousMind
ACuriousMind
the last Q&A I linked explains in depth why the "value" of dimensionful constants is not as meaningful as one might naively think
 
MathCubes
MathCubes
11:32 PM
I read that
 
ACuriousMind
ACuriousMind
we can't meaningfully talk about changes in these constants any more than we can meaningfully talk about what their "precise" value means
the real constants you can ask this question about are the dimensionless constants like the fine structure constant
 
Sir Cumference
Sir Cumference
well, you could talk about changes in these constants relative to other constants of the same units
like ask why the speed of light and the planck length differ by the exact factor they do
 
ACuriousMind
ACuriousMind
@SirCumference ...and such a ratio would be a dimensionles constant, no?
 
Sir Cumference
Sir Cumference
...yes
good point lol
 
MathCubes
MathCubes
Anyways thought on this video
 
ACuriousMind
ACuriousMind
11:36 PM
I don't watch videos about physics :P
4
 
Sir Cumference
Sir Cumference
i do have to wonder if someday there'll be a model that theoretically derives the value of all these constants
like one that could tell us $c$ even if we had never measured it in history
 
MathCubes
MathCubes
Interesting
 
ACuriousMind
ACuriousMind
@SirCumference if we could discover a model that "forces" all the constants to be a particular value, we'd just shift the question to "why" that model actually models reality
 
Sir Cumference
Sir Cumference
it seems we can never be satisfied
 
ACuriousMind
ACuriousMind
I feel that a lot of the unease people have with free parameters and universal constants is just a symptom of a deeper dissatisfaction that we cannot - ever, in principle - discover by mere science the way the world was "meant" to be
Many gravitate initially towards science because it seems to explain "why" things are the way they are, and then disappointment sets in because at the end it's just a description of how the world is
 
Sir Cumference
Sir Cumference
11:41 PM
i mean it does satisfy some of that curiosity as to why things are the way they are
just not all of it
some of the unease about the double slit experiment is satisfied when you know about the wavelike distribution of particles
 
ACuriousMind
ACuriousMind
personally I think of it more as dissolving the "why" rather than answering it, but I'm not gonna claim everyone has to see it like that
 
Sir Cumference
Sir Cumference
wait shoot, which experiment was it that motivated us to model particles with wavefunctions
was it the double slit?
 
ACuriousMind
ACuriousMind
partly? the foundational experiments for QM mentioned are usually the photoelectric effect and the double slit
the photoelectric effect suggest there's something "like a particle" in waves (=light), the double slit with electrons or other particles suggests there's something "like a wave" in particles
 
MathCubes
MathCubes
So the speed of C doesn't come form it interacting with a field that we know of?
 
ACuriousMind
ACuriousMind
I'm not sure what that would mean, but no, you can't derive the value of the speed of light from QFT
it's an ingredient in (relativistic) QFT, not a result
 
MathCubes
MathCubes
11:54 PM
ok
 

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