« first day (2414 days earlier)      last day (2508 days later) » 
00:00 - 17:0017:00 - 00:00

12:31 AM
Guys, how would you describe the following term: Earth mass monopole and multipoles.... Is the monopole related to the non-spherical geometry of the Earth?
 
 
5 hours later…
5:55 AM
[Random] High school level question asked at graduate level: What is energy in the context of a quantum field, describe with as much or as little mathematics as you like
 
6:30 AM
Anyone know how to search chat for punctuation characters?
 
7:04 AM
I don't think the search engine is good enough for that
 
 
2 hours later…
8:52 AM
@ACuriousMind : For a moment I thought you were asking about an emoticon :P
 
user228700
@JohnR: Hi :-) Yes, I did see that link (and found it before). I am so sorry, I was too busy trying to finish some stuff.
 
@Kaumudi.H I noticed there's a course specifically targeted at bioengineering, though I'd worry that course is a bit specialised.
 
user228700
No, no, Bioengineering would not be particularly useful for CN!
 
user228700
Although... ugh, I'm finding it extremely difficult to figure out which one would be best.
 
user228700
9:09 AM
And I have no idea whom to ask either.
 
The "B.TECH DEGREE COURSE IN COMPUTER SCIENCE & ENGINEERING" course seems the obvious one. Which other courses are you considering?
 
user228700
Why does that seem to be the obvious one..?
 
user228700
I'm also considering the Electronics & Communication and the Electrical and Electronics course.
 
I get the impression those two courses are intended for people wanting to work as electronic engineers.
The CS & Eng course seems more broadly based so more useful if you aren't sure exactly what type of work you want to do.
 
user228700
...but a basic course in circuitry will greatly help with CN. I'm not sure how learning programming and how the computer works will help with it at all. The brain does not resemble a computer in the slightest...
 
user228700
9:23 AM
Oh, wow, so many more people!
 
but programmers use how the brain works to build AI
 
I am pretty sure coding is more useful for cognitive neuroscience than electrical engineering.
 
they are called neural networks
 
Look up "machine learning" and so
 
user228700
@BalarkaSen Spoke to a computational neuroscientist at IITM and he disagreed completely...
 
9:25 AM
Huh
 
user228700
@Yashas Right, but I'm not sure I care so much about the cause of developing AIs.
 
user228700
Literally the only branch comprising of both cognitive science and C.S that I've seen so far is A.I.
 
user228700
@BalarkaSen What he had to say is that the brain is almost completely different from how a computer works.
 
@Kaumudi.H: my view would be that you may not end up working in CN - four years is a long time. And even if you do CS is an excellent background skill. CS isn't just coding. It covers a wide range of analytical skills.
 
You can do anything with CS. You can do computational neuroscience :P
 
user228700
9:27 AM
@BalarkaSen ...and that training your brain to think it terms of the mechanisms of how a computer works wouldn't be as useful as learning how electronic systems function at a more basic level.
 
It's far from obvious that an electronic engineering course would be much use for working in CN. Yes the CN researchers will need equipment designing and constructing, but they'll just pay someone to do that.
 
user228700
@JohnRennie And how about if you've done C.S?
 
@Kaumudi.H I know, but there has been some excellent abstract approaches to understanding how the brain works in the past century. I recently heard (from the math room) that someone used topological approaches to the understanding neural networks (the conclusion is that brain is 11-dimensional, whatever that means)
 
I read that 11 dimension thing somewhere
the brain is capable of understanding 11 dimensions or something like that
 
@Kaumudi.H CS + Eng covers a wide range of skills so it equips you for lots of jobs.
 
user228700
9:29 AM
@BalarkaSen Oh, wow, I see. That would explain why most institutions accept people who've done even Math into their CN Masters program.
 
I dunno about that. They constructed a mystical "flag complex" out of the neural structure, which I don't grok yet.
 
Out of the three courses the CS + Eng seems to me to give you the greatest flexibility.
 
user228700
@JohnRennie But how so?! I don't understand that at all...
 
Yeah, I advocate CS + Eng
 
user228700
9:30 AM
All I've been told by others is how doing CS would narrow ur options the most.
 
@Kaumudi.H for what it's worth, I completely agree with @JohnRennie - 1. CS covers a huge range of stuff, at least when taught well. 2. Don't do something because of where you think it'll lead, but do whatever excites you and in four years, you'll be doing what you want to do, not what you thought you wanted to do four years ago
 
Every field of study needs CS in some way or the other
In fact, basic CS is taught in every branch.
You'll have a course on some CS topics even if you take up EE or Mechanical or ...
 
@Kaumudi.H I haven't been through the syllabus in detail, but it covers a lot of maths as well as basic science. Admittedly the later years specialise in the IT side, but you'll end up with a lot of knowledge about maths and science too.
 
user228700
@Mithrandir24601 ...dang it, why do I keep hearing such conflicting opinions about this?
 
In fact the CS syllabus includes several courses on electronic engineering as well.
 
9:33 AM
@Kaumudi.H because if it was clear cut, you wouldn't even need to think about it :P
 
user228700
I've been told, over and over again, that learning C.S would narrow my options down by a lot.
 
user228700
Can someone please explain to this noob why that would not be the case?
 
CS probably doesn't have the job perspective of EE, but, I don't see why that's true.
But I'll let someone who knows things say it.
 
user228700
@BalarkaSen ...actually, around these parts, C.S gets the most placements (and not in like, the IT sector. Doing core stuff, I mean)
 
@Kaumudi.H All I can go on is the syllabus, and that has lots of courses that aren't specificially about the IT side.
 
9:37 AM
@Kaumudi.H I would say that, in the UK at least, electrical engineering would narrow your choices more than CS, but maybe that's because I'm working in an area more closely related to CS than EE... Similarly, what's the background of the person who told you that?
@Kaumudi.H again, where I was, there were more jobs for CS at any careers fair alone than CS grads
(But things are probably different in India)
 
I see Countto10 again.
 
user228700
Ah, hmm, I see...
 
user228700
My dad was the one who told me (pretty convincingly at that) that C.S wouldn't be as flexible as the others but when I asked him just now, it turns out that he's heard this from only one other person.
 
user228700
...who did Mechanical Engineering.
 
user228700
I've gotta consider two things now: First, OK, considering that C.S may be a lot more flexible, I gotta understand if I would like it...
 
user228700
9:46 AM
Second: That one guy told me about how learning C.S wouldn't be so great for pursuing CN later on because the brain and any computer we've got now aren't at all similar.
 
user228700
...so learning how a computer works would spin me in the wrong direction.
 
user228700
And lastly, so, OK, what does this flexibility mean? Is it possible to do C.S and then go on to specialise in, say, some branch of electronics?
 
If you are interested in electronics, then take electronics. You'll learn some CS even if you take electronics. You'll have bits of electronics in CS too.
You'll be taught C & assembly because you need it to program microcontrollers. You also need C for IoT/Arduino/etc.
 
user228700
I don't know if I am yet. Other than that it will be useful to do CN, I am not properly interested to do any type of engineering without the context of something I really actually do love, like CN.
 
@Kaumudi.H one point of a good CS course is that it's what I'm going to call 'current technology independent', so is designed to be completely general
 
SBM
9:52 AM
oh hello
 
user228700
@Mithrandir24601 Huh. Can you elaborate..?
 
SBM
computer science discussion; interesting
 
IIITH has a lab for Cognitive Science
IIITH has a program which gives your a B.Tech degree in CS & MS in Computational Natural Science (you can choose your topic if there are profs working in your area)
 
user228700
...Oh, I see. I'm not really looking to do my Masters in India.
 
So you learn some fundamental concepts about how computers work, a bit of electrical stuff, the concepts about programming, and not 'this bit of tech. does x using y'. The focus is much more on the principles, concepts and even maths etc. and current technology is ignored
 
user228700
10:00 AM
Ah, hmm, I see...
 
But, again, it might be different in India...
 
user228700
Thing is though, these principles, they govern the technology we have used thus far and look to improve and implement in the future, yeah?
 
@Kaumudi.H sounds about right... neural stuff is also relevant in CS. The problem is that CS is so big, I'm having trouble explaining what it is... :/
 
user228700
Ah, hmm :-/ Literally the only thing I'm really concerned with is how learning C.S will affect doing CN later on.
 
Why? What makes you want to do CN?
 
10:06 AM
It probably won't affect learning CN. I can't really imagine EE being more useful to CN than CS
 
user228700
@Mithrandir24601 I am more intensely passionate about cognitive science than I am about literally anything else.
 
I have met a computer scientist who researches about how people learn languages, with a couple of aims to the research
 
user228700
@BalarkaSen Ugh, but the thing is that this guy told me otherwise, told me that learning about the basic principles that govern a system like the kind of computers we have right now is not going to be useful (and might actually be a deterrent) to learning CN because the brain operates on completely different principles.
 
Ok. Has he told you EE is useful to learning CN?
 
user228700
He has, yeah :-/
 
user228700
10:11 AM
In fact, he did EE from IITM back in the day.
 
Weird. Well, he's the one person who really has studied cognitive neuroscience, unlike any of us, so probably do that.
I had a completely different impression of things. Maybe I'm thinking more about machine learning than CN
 
SBM
machine learning ...
 
user228700
@BalarkaSen Maybe you are...
 
@Kaumudi.H that was my point from earlier, it's not about what we have now, but it's even more fundamental than that, although I wouldn't be surprised if it's different in India
 
user228700
What do u mean by "it's even more fundamental than that"? Can you please explain..?
 
10:13 AM
@Kaumudi.H even Ramamurti Shankar got EE from IITM
now everybody is using his textbook for learning physics :P
but don't follow him
he must have taken EE becaz of this unfortunate JEE system where JEE rank decides what you become in life
 
user228700
^ Even the other prof. did the same, he told me. But that he is now grateful that he took EE.
 
no wonder why India does not have a Microsoft or Google
even if you get an international informatics olympiad medal soon after brith, you won't get admission at IITs for CS unless you are an expert in JEE physics, maths & chemistry
 
Well, Dirac also did electrical engineering...
@Kaumudi.H we studied it with the explicit intent of being relevant in the future and not now. E.g. What makes a programming language good, not how do you program well.
 
user228700
Huh, I see...
 
My city was ranked best in India for quality of life :O
 
10:21 AM
thumbs up
 
SBM
oh
 
Or, how do you design a programming language, how do you build the compiler. Is a compiler even the best way to do things? How will people program in the future - will the form of interaction between humans and computers be different and if so, how? (This is a massive area in itself)
 
user228700
Oh, wow, I see...
 
SBM
yes
 
user228700
10:25 AM
Oh, thanks! :-)
 
user228700
Man, there is so much more to know...
 
user228700
Thanks for all this information!
 
I have to do chemistry but I don't want to
 
user228700
@BalarkaSen Man, I am so sorry :-( This too shall pass.
 
SBM
@BalarkaSen almost similar except for QM
 
10:29 AM
I have to decide what I would be doing in the next couple hours. More importantly, I have to decide if I will spend my time in the next couple minutes deciding what to do or not. Crucially, I have to decide if I will spend time in the next couple seconds deciding on decision-making or deciding to not, or not deciding to decide, or...
 
@Kaumudi.H the guy in the video is Peter Robinson, who is the closest person I've met to a computational neuroscientist. He did maths because he predates CS degrees, but is now a professor of CS and simply brilliant and then a lot more
 
SBM
oh :|
Mathematics is really fun.
 
user228700
@Mithrandir24601 Ah, hmm, wow, I see...
 
user228700
I'll watch it soon and get back to you, thank you so much! :-)
 
Once when Littlewood attended an international conference in France, a French mathematician greeted him: “So there really is a Littlewood, and it is not just a pseudonym which G.H. Hardy uses to publish his poorer papers!”
...
 
10:35 AM
That reminds me of Ramanujan.
 
The advisor-student trio is indeed impressive: Littlewood, Hardy, Ramanujan
 
@Kaumudi.H No-one is claiming that doing CS will help you understand the brain because the brain works like a computer. Doing CS will give you the skills in data analysis and computer modelling that will be useful for studying how the brain works.
 
(I am not a big supported of Ramanujan as a public figure. He was a good mathematician.)
 
learning programming may also help to distinguish "prediction" from "encoding" in science.
 
 
2 hours later…
12:53 PM
The secret to understanding consciousness lies with deep learning techniques
Not in understanding circuitry or understanding biology
Deep learning is a relatively new field and whether it is owned by computer scientists, mathematicians or statisticians is hard tosay
But a sold foundation in mathematics and statistical learning is what you would need to tackle the problems of human consciousness
 
1:06 PM
@Kenshin "Indeed, if there really is some day discovered a formula for all our desires and caprices—that is, an explanation of what they depend upon, by what laws they arise, how they develop, what they are aiming at in one case and in another and so on, that is a real mathematical formula—then, most likely, man will at once cease to feel desire, indeed, he will be certain to..."
"...For who would want to choose by rule? Besides, he will at once be transformed from a human being into an organ-stop or something of the sort; for what is a man without desires, without free will and without choice, if not a stop in an organ? What do you think?"
might be of interest
 
who said that?
 
The Underground Man
But clearly reflecting Dostoyevsky's own views on existentialism, fictionalized.
I think it's an interesting point. When the existential human is given a complete, mathematical formula, for determining all his actions through his life-span, the ones he has taken as well as the ones he hasn't, he will stop desiring. He is, after all, fated, and the notion of free will - to him - is shambles. Hence he stops wiling.
 
ugghh
does someone have a couple of minutes to help me?
I'm losing my mind with a souble slit exercise
HAHA NEVER MIND
I SOLVED IT
I DID IT
LOOK AT MY WORKS YE MIGHTY AND DESPAIR
 
1:24 PM
@Golokopitenko on not at :-)
 
don't kill my buzz buddy!
 
1:36 PM
[Philosophy bomb] What is the most abstract possible thing?
 
@Secret There is no such thing
Abstraction is simply a mental tool that we use
The choice of what things we make abstract and to what degree is always subjective
 
Is it really a tool though?
 
Two different abstractions therefore can't really be compared to how abstract each one is
@BalarkaSen well depends on how broad your definition of tool is of course
 
0
Q: I want to print an answer and it should still look good

ja72I want to make a nice printout of an awesome answer with lots of pictures and pretty equations. If I select the answer and use the print feature in the browser then the formatting is lost (paragraphs are too wide) and the equations don't show properly. I want to turn this into this ...

 
@JohnRennie did you hear about the tower of london? Hope all your close ones are alright
 
1:43 PM
@Kenshin vOv
 
what's that mean
 
a man shrugging
I think we study abstract objects without caring about if any of it applies or not just fine
 
@BalarkaSen well usually people make things abstract so they can deal with them better
for example
a word is an abstraction of a concept, to aid in communication and thinking
or if I have 3 apples and give some away and left with 1
 
But when we think about a word, or write down a word, do we always think about aiding communication and thinking?
 
I can abstract this to give 3 - x = 1 to make life easier
 
1:45 PM
I don't think we always abstractize to make life easier. This is a simplistic statement.
 
@BalarkaSen if I use a hammer, I don't necessarily think about aiding building. I just use the hammer
but the hammer is a tool none the less
whether I think about the hammer being a tool or not doesn't make it less of a tool
 
@Kenshin Tower of London?
 
So whether I think about abstraction as being a tool or not, that doesnt' make abstraction less of a tool
@JohnRennie yeah a tower in london caught fire
 
@Kenshin What does that even mean? Nothing is real beyond what we percieve.
 
@BalarkaSen what do you mean "nothing is real beyond what we perceive"?
 
1:47 PM
If I think it's not a tool, and it doesn't act like a tool in any way to me, it is not a tool.
 
lol
 
Ah, a tower in London, not the Tower of London :-)
 
Everything is subjective. I don't understand how are you making a universal statement like that.
 
@BalarkaSen I don't agree that everything is subjective
I think abstraction is a tool
 
Come at me bro
Why do you not think this?
That seems like a bad assumption to me
 
1:48 PM
I believe the world is objective
and exists independently of observation
 
What justifies you bro
 
so I don't believe "everything is subjective"
 
, hello @Kenshin
 
Hi @GerWyn how r u
 
@kenshin, I am good.. wbu?
 
1:49 PM
@BalarkaSen my personal experiences justify me. From what I observe I refine my hypothesis. This to me indicates the world exists beyond my perception (otherwise I likely wouldn't have to keep modifying my hypothesis)
@BalarkaSen but of course my belief in an objective world is ultimately a postulate, rather than a conclusion
@GerWyn good mate
 
One does not simply justify himself by saying "I am right", which is approximately what you said lol
 
@Kenshin, Can we be friends on FB?
 
@GerWyn yeah sure what is your name?
 
@Kenshin, Swastab Acharya
 
@BalarkaSen ultimately all logical conclusions have to be based on some fundementla assumptions
@GerWyn why do you want to be friends with me?
 
1:52 PM
@kenshin, jst for.chatting nthg mucj
h
 
@BalarkaSen if I took your view that everything is subjective, then I have no reason to blieve your not just a figment of my imagination. If you are a figment of my imagination, then I don't really have to justify anything to you do I? So therefore if you doubt that objective reality is real, then I don't need to justify to you why it is so
 
@Kenshin I agree. But that immediately implies any logical conclusion you come up with is going to vary person-to-person, consciousness-to-consciousness, because assumptions vary person-to-person, consciousness-to-consciousness. Once you accept that, that seems to break your assumption that everything is objective.
Why does that not break your whole deductive logic?
 
@BalarkaSen wrong. Just because logic requires postulates doesn't mean those postulates are ultimately subjective.
There could be objective rules out there
But they are just difficult/impossible to deduce
this doesn't mean the rules are subjective
 
what does objective/subjective even mean
 
@JoshuaLin that's subjective
 
1:55 PM
is the definition subjective? :p
lol
 
For me, I define objective vs subjective this way:
 
@Kenshin Some Hegelian shit you believe in, then.
@JoshuaLin yeah man it's all deranged
 
@BalarkaSen the whole concept of science is baesd on the assumption that there is an underlying objective reality
 
@kenshin? ?
 
Given an ensemble of worldviews, if a philosophical entity is objective, then its properties and relations to other concepts are agreed under all worldviews, if there exists at least one worldview that disagreees with it, then the entity is not fully objective
 
1:57 PM
you can hardly be surprised that people in the physics room would subscribe to this philosophy
 
nothing is objective; nothing is subjective; because definitions don't exist; logic doesn't exist; nothing really exists; so just stick to having fun and life will be good wallah
 
@GerWyn what is your asl?
 
"Nothing is real; everything is permitted" - Hassan I-Sabbah
 
science doesn't need an objective reality to exist
science exists because its fun
 
@Kenshin I don't think that's a valid assumption, but I won't speak for science because I am not a scientist. I do math.
 
1:58 PM
@kenshin 17,M, Nepal
 
I don't think the 20 different theories for the same thing are a dialectical search for an underlying "real" reality
I just think it's a search for consistency, not completeness
 
@JoshuaLin without an objective reality, the laws of physics could differ between me and you. So I could argue Einstein was wrong from my point of view. Clearly this non-sense isn't in line with the views of science as we know it today
 
Well, there's a 3rd possibility:
 
this a physics chat or a phylosophy chat
 
Reality just happened to be objective enough to reproduce the scientific findings we have so far
 
2:00 PM
@Kenshin If you are blind, there is no moon.
If the wall in your room doesn't stop you, there is no wall.
 
@BalarkaSen bs
 
how can there be a moon when there are no ice
 
@Kenshin You can't contradict me. You can say it's shit, but you can't. :P
Without an inherent assumption which contradicts mine.
 
@Golokopitenko Welcome to the weirdness of The h bar, where every topics are in perfect superposition
 
oh my
 
2:01 PM
@kenshin ??
 
@BalarkaSen yes it is ultimately a belief, but it's more practical to believe the world exists when you don't look at it (Because there are implications of being wrong, and experiment will show you time and again that you will be wrong often if you blieve the wordl stops existing when u close your eyes)
 
pracitcal?
 
Practicality is an entirely different thing I have no interest in arguing about.
 
practical
 
I don't believe in practicality
 
2:02 PM
 
@BalarkaSen there are also cases where there are consistent falsehoods, thus it is even more complicated
 
what is practicality anyway
 
shouldn't there be a comma between the 7 and the 10?
 
in order to believe something you must first survive
 
@Joshua shit that makes you survive
 
2:03 PM
wow
 
"I do not exist, but I think"
problem, descartes?
 
> I exists, therefore I am
 
@Golokopitenko what is your question?
 
@Golokopitenko I assume that is seven times ten to the eight: $7 \times 10^8$
 
2:05 PM
Lemaitre coordinates users-phys.au.dk/fedorov/GTR/09/note11.pdf should be obvious to see the $d\tau$ etc by factoring right?
 
Why does it even matter if the world still exists when I close my eyes or not
 
@JoshuaLin because survival
 
It doesn't exist if you close your eyes. If you have complete sensory detachment from the world (so not just close your eyes), then the world does not exist.
 
If you believe the world stops existing when you close your eyes, there's no need to worry about being attacked by an intruder is there?
 
If you are blind and nobody tells you there is moon, there is no moon
 
2:08 PM
IF someone holds a gun to you, simply close your eyes right?
 
@BalarkaSen though you'd still be wise not to go walking on the beach at low tide :-)
 
@JohnRennie Not if you do not know of tides.
This is exactly what I am saying. Not just a simplistic aspect of closing eyes. Complete sensory detatchment from the existence of the thing.
 
@BalarkaSen you'll soon learn about them
 
This is garbage response.
 
@Kenshin ... the hard way :-)
 
2:23 PM
@JohnRennie why aren't giant nets used to allow people to jump from burning buildings?
 
@Kenshin they are used if the height isn't too great.
 
how high would too great bew?
10 stories?
 
You could probably work it out. Estimate the maximum deceleration a person can survive and the distance the net takes to stop the person, and you can estimate the upper speed limit.
 
Do you think net's could be developed to save people from arbitrarily tall buildings
 
I would guess for someone leaping from a 27 story block (like the one on fire in London) the net would need to be impractically large.
 
2:27 PM
i see
 
After all, it would need to be large enough that a jumper couldn't miss it, and that's from 27 stories up ...
 
@MetaEd I can imagine the chat room spam you are facing...
 
Fun fact:
Is actually some master art thing made by people
but it does look SOOOOOO realistic
Pretty sure if you crop that pics and show it to random astronomers, they will start to ask where's this galaxy merger event and what have we learnt from it so far
 
The colour looks wrong for galaxies. It looks more like two nebulae merging.
 
let me ask dr. google about something...
 
2:33 PM
@Yashas Not much. And I'm wearing my fireproof suit.
 
@MetaEd why would you be facing spam?
 
@Kenshin No idea.
 
F*** this look so similar, except for colors
 
@Kenshin he/she is currently in several chat rooms
 
physics.stackexchange.com/questions/339338/… more often when in solving ODEs the zeroth case often becomes the trivial 0=0
 
2:37 PM
@Secret Suspiciously similar really ...
 
3:21 PM
0
Q: How does the wavelength of incident light and de-Broglie wavelength of molecules in a medium affect macroscopic properties of the medium?

SchrodingersCatSay I have a mixture of gases, or a liquid mixture. Now I am supposed to send photons through the mixture to study some macroscopic property of the mixture, e.g. refractive index, bulk modulus, density etc. by some procedure. The question is: How do the macroscopic properties of the mixt...

what happens if a photon's (which hits a particle) wavelength is in the order of the de Broglie wavelength of a particle?
 
all s#$% breaks loose
 
Can anyone round here help me understand what the Millennium Prize mass gap problem is?
@ACuriousMind: are you around?
 
yes but if you solve it you have to share
In mathematical physics, the Yang–Mills existence and mass gap problem is an unsolved problem and one of the seven Millennium Prize Problems defined by the Clay Mathematics Institute, which has offered a prize of US$1,000,000 to the one who solves it. The problem is phrased as follows: Yang–Mills Existence and Mass Gap. Prove that for any compact simple gauge group G, a non-trivial quantum Yang–Mills theory exists on R 4 {\displaystyle \mathbb {R} ^{4}} and has a mass gap Δ >...
that should help
 
3:37 PM
:-) I wasn't planning on solving it, but there are aspects of the discussion in Wikipedia that I don't understand and would like help with.
 
the mass gap is the mass of lightest particl
 
@JohnRennie In around 15 mins
 
@ACuriousMind Thanks :-) I shall wait!
Not patiently ... :-)
 
who writes these wikipedia articles?
people from here? or foreigners
there wouldn't be too many people who understand this stuff would there be and of those even less who have the time to edit an article
 
@JohnRennie Sooo...what I would have begun with would have been something similar to the intro of the Wiki article, so maybe just ask about what you don't understand
 
3:48 PM
The Wiki article uses the example of QCD, as an SU(3) YM theory, and talks about the mass of glueballs.
But aren't gluons elementary particles in QCD, and they are massless. So there isn't a mass gap.
When we talk about the mass gap do we mean the mass of bound states?
That would explain why the article refers to glueballs, since they are a bound state.
In fact quarks are massless too unless you invoke a Higgs mechanism ...
:: A silence falls on the chat room ::
 
@JohnRennie No, we mean relativistic mass ;) The "mass gap" is actually an energy gap, meaning that there is a finite separation between the vacuum state and the lowest lying non-vacuum state.
 
Aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaah :-)
Doh!
 
In other words, gluons would not be forbidden by this, but they can't have arbitrarily low wavelength.
Additionally, you might note that gluons are usually confined
So they wouldn't count as states in the sense of the problem - this is really a claim about the interacting spectrum of the theory, not the free theory.
 
the interacting spectrum of the theory - which we don't really understand anyway?
 
Yeah, that's why it's a millenium problem ;)
I mean, we can simulate it (or at least get the masses of the bound states from the numerical simulations of the propagators).
 
3:56 PM
Is there a mass gap in a free theory? Actually I suppose a free theory wouldn't be Yang-Mills so that's a meaningless question ...
 
The challenge is to show that's actually a property of the theory and not an artifact of the simulation
 
Thanks. You've answered in as much depth as I think I can understand. :-)
As it happens I've been asked about it by a friend who writes SF and who wants to use the idea in a story. I already knew he had completely the wrong end of the stick, but realised I didn't really understand it either.
 
Actually, I think I should retract the statement about relativistic mass. Reading up on it we really do mean the invariant mass $p^2$ and the "mass gap" challenge for gluons really is to show they are confined and therefore don't actually show up in the spectrum.
 
SBM
oh
 
But, anyway, I would probably claim that the "mass gap" part is the lesser of the two parts, establishing a mathematically rigorous definition of a 4d Yang-Mills theory is what you've got to do first.
 
4:01 PM
Hmm. But isn't the electroweak force a 4d Yang Mills theory?
And that isn't confined.
 
@JohnRennie The problem statement specifies that the gauge group be compact simple, $\mathrm{U}(1)$ is not a simple group, so it is not a "Yang-Mills theory" in the sense of the problem.
 
Aha, OK. Would all YM theories with a compact simple gauge group exhibit confinement?
 
That is the general consensus in theoretical physics, and what the problem implicitly asks to prove along the way, yes
 
Thanks, I think I have the rough idea now :-)
 
4:20 PM
Guys, I passed my tests. And I'll be doing maths for the rest of the year. I do have a retake in electromagnetism (I passed, but I'm gonna upgrade my grade). But yea, I'm kind of curious whether I'll be doing physics "on my own" this summer, which will say a lot about whether it's truly my passion or not:P I did enjoy it a lot the past couple of months tho.
 
The JEE prep room doesn't seem to die even after JEE :D
 
It was maybe even more exciting than the mathematics courses I've had. Though I must say that I've gotten a bit wary of all the assumptions and approximations made in physics, so I'm also kind of glad I can go back to the safe haven of mathematics, and just do stuff from definitions and axioms:P And prove everything.
 
SBM
@ShaVuklia Congrats
Why should a room die?
if it can't live
 
it wasn't supposed to be taken literally -,-
 
SBM
@Yashas oh; quite literally
 
4:27 PM
wow, this one is still open?
 
@ShaVuklia Congratulations :-). I suspect the thing that motivates us is trying to understand things that really exist. I can see the appeal of maths but, well, (pace Plato) it doesn't really exist.
I suspect the main factor in whether you prefer physics or maths is going to be how badly you want to understand the real world.
 
oops wrong room
 
4:43 PM
Mar 2 at 19:57, by Sir Cumference
@TungNguyen Oh crap, sorry. Wrong room, wrong person
hmm but doesnt confinement depend on the number of fermions?
or is the problem about pure YM?
 
0
Q: Has negative energy a negative temperature?

descheleschilderIf we consider a vacuum stripped from all particles except the virtual particle-antiparticle pairs, the vacuum has temperature zero, assuming that this vacuum energy is zero (despite the fact that no particles are present to support the temperature the vacuum still has a temperature; a black body...

Amazingly descheleschilder has managed to come up with a genuinely interesting problem.
 
Planting bugs for getting rep? ;-)egreg 7 hours ago
 
I could never finish listening to that song
I hope to succeed one day
 
4:52 PM
Hey Mithrandir
 
@Avantgarde hello again
 
@Mithrandir24601 That group's great
 
00:00 - 17:0017:00 - 00:00

« first day (2414 days earlier)      last day (2508 days later) »