The h Bar

GiantCowFilms

00:46

Hi!
I'm trying to implement the last equation in this answer: https://physics.stackexchange.com/a/268812/119174, however, I'm not entirely sure what to do with the first bit, where the transposed vector n is raised to the *T* power. I'm not sure what *T* is - best guess after researching is seconds, and I have no clue how to go about doing the exponentiation. I researched Matrix/Vector exponentiation, and it seems like there are multiple definitions. I'm not sure which one is the correct one for that application.

bolbteppa

01:11

@GiantCowFilms no exponentiation there

GiantCowFilms

01:28

@bolbteppa Oh?

Shows how much I know :/

David Z

02:26

@GiantCowFilms It means "transpose"

Dawood ibn Kareem

02:49

@JohnRennie No, you said you were better at physics than at nookie. It's far from the same thing.

@Yashas I may be in a minority here, but I've always considered Newton's second law to be a definition of mass. I'd like to know if there's a better definition of mass than the ratio of the force applied to an object to the resulting acceleration of the object.

And as such, this gives no scope for proving or disproving the law. It simply is what it is.

GiantCowFilms

@DavidZ As in?

Dawood ibn Kareem

@GiantCowFilms As in swap the rows of a matrix for the columns and vice versa.

GiantCowFilms

@DawoodibnKareem That is all that T means?

Dawood ibn Kareem

Yes.

Or if a vector is written as a column, it means write it as a row, or vice versa.

GiantCowFilms

Oh. Okay, so that is just a simple multiplication

Kenshin

03:02

@BernardoMeurer I have bitcoin, why would I sell?

Dawood ibn Kareem

@GiantCowFilms Yes. In that answer that you linked to, it looks like the respondent is just using T to save space.

GiantCowFilms

@DawoodibnKareem Okay. Whew. Well, that makes it easier

Avantgarde

03:22

dead chat

Yashas

@EmilioPisanty Thank You :-)

Avantgarde

03:35

@Yashas Are you less confused now?

Yashas

far less confused

Avantgarde

So what's your conclusion?

Yashas

I am reading the answer again and again. There are bits which I am hearing for the first time.

Avantgarde

keep learning

:)

Yashas

I understood what's happening but I need to study a bit to understand the mathematical details.

Avantgarde

03:37

yeah you need the math

Avantgarde

04:23

still dead chat

Yashas

Donald Trump proposes constructing a wall along the Mexican border with solar panels.

Donald: "How do we get the hippies on board with this?"
Don Jr: "Say it comes with free college?"
Jared: "Make it out of recycled stuff?"
Ivanka: "just slap solar panels on it."
Donald: "sweetheart you're a genius. Don Jr, Jared, you're fired."

lol

user228700

Someone give me a virtual high-five!

user228700

(Also, hi, everyone :-)

John Rennie

04:42

o/

user228700

\o Thanks!

John Rennie

At least, my limited knowledge of emoticons leads me to believe that's a high five :-)

user228700

I think that is often interpreted as a wave as well but it works as a high five! :-)

John Rennie

Power supply turned up yet?

Family fled the house screaming yet? :-)

user228700

I asked for one because I have been working to clean my room, sort my books, post them on sale (on two different websites using two different phones), clean my desk and at last, pack for a swimming trip since 5 AM this morning.

user228700

04:45

And I DID IT ALL!!!

John Rennie

\o/

user228700

:-D

user228700

@JohnRennie Yep, it came in yesterday and works nicely! :-)

Yashas

0

Q: Why does hard-boiling eggs work?

If eggs are so air-tight, how is moisture able to escape them? But if it's able to escape them, why doesn't the liquid the constantly seep out of the egg right from the start?

classical-mechanics

off-topic?

John Rennie

@Kaumudi.H Excellent! One less thing to worry about. I guess keep the old one around as an emergency backup.

user228700

04:47

@JohnRennie And no :-P My family is still around and suffering.

John Rennie

@Yashas Also complete lack of effort!

@Kaumudi.H :-) How is the harmonica? Is it proving to be fun learning to play it?

user228700

Yes yes! :-) It makes me quite happy!

user228700

How's life at Wookey Hole?

John Rennie

@Kaumudi.H Quiet :-)

But anyway I'm off home tomorrow. Mum is fine so there's no need for me to hang around any longer.

user228700

Ah, right, right :-) OK...

user228700

04:51

I'm going swimming today, as u may have inferred from "packing for a swimming trip".

John Rennie

Yes, I gathered. In a lake? A river?

user228700

:-( A swimming effing pool.

John Rennie

As a youngster I used to swim in the river Nile in Khartoum, though you had to be a bit careful there.

user228700

Wow.

user228700

It's miles away in an apartment complex in which we own an apartment. My family is visiting to...do what I don't know but I'm tagging along so I can use the swimming pool there.

John Rennie

04:54

Aha, good call. Might as well take advantage of the situation.

user228700

Yep yep! We're leaving soon.

John Rennie

Long drive?

user228700

45 minutes to 1.5 hours.

user228700

The new season of Invisibilia is out so I'll be listening to that on my way there!

John Rennie

Ah, yes, I think you've mentioned that podcast before.

user228700

04:57

Yes, I have! It's my favorite.

user228700

In fact, it is because of Invisibilia that I even came to realise this intense passion of mine for Cognitive Neuroscience.

John Rennie

I hadn't realised that. Presumably they did a cast on the subject/

user228700

No, their whole podcast has to do with the mind.

user228700

Every episode has various elements of CN!

Kenshin

sup peeps

user228700

05:01

Hey, C :-)

Kenshin

@JohnRennie how do you feel about the election results

Hi @Kaumudi.H

I can't believe Theresa called an election so early only to lose so poorly

John Rennie

@Kenshin I don't feel very strongly about them. Sorry if you were hoping for something more interesting :-)

Kenshin

@JohnRennie no I was just wondering what you honestly thought tho

John Rennie

The outcome doesn't have any great impact on me personally.

Kenshin

@Kaumudi.H do you like the brain or AI better?

@JohnRennie yeah but it's just entertainment

like a sports match to me

where you analyse the plays of the different teams

user228700

05:04

...I strongly suspect that my answer to that question will change but at this point, definitely the brain.

Kenshin

oh

the brain is just biology tho

user228700

Anyway, I gots to go. I'll catch you guys later! Toodles :-)

John Rennie

I suspect the result shows that people disapprove of the Brexit process more strongly that May thought. Remember that the Brexit vote was 52:48 so why May thought it was a good idea to focus on Brexit in her campaign escapes me.

@Kaumudi.H have a good swim.

Kenshin

yes my other idea is that May actually didn't mind a hung parliament or a loss, so that she wouldn't forever be known as the PM who solely negotiated brexit

if the people didnt' want it that is

so if she won in a landslide yesturday, of course it would be ok because she'd have a mandate

John Rennie

One of the good outcomes is that it appears to have ignited interest amongst the younger segment. It isn't healthy for democracy if a significant segment of the populace isn't interested enough to vote.

Kenshin

05:07

but she'd rather a loss than negotiate brexit without a mandate

John Rennie

I don't think that's true.

May only had a narrow majority, and she has to deal with a sizeable minority of rabid Europhobes.

If she had a large majority that would give her room to negotiate a less extreme agreement because she wouldn't be needing the votes of the nut jobs.

Kenshin

Yes she probably either wanted to (A) win the election by a large majority or (b) lose the election

and both (a) and (b) were probably preferrable than attempting to negotiate without the early election

John Rennie

Now, not only does she still need the votes of the lunatic fringe but she also needs votes from the DUP, who are a remarkably poisonous bunch. So for her this is a terrible outcome.

Kenshin

yeah I agree lol

John Rennie

However it will probably mean we get a better deal because there is also a sizeable subset of Tory MPs who strongly disapprove of Brexit.

I suppose it's even possible that the whole Brexit process will stutter to a halt.

Perhaps we can tell the EU we pressed the wrong key by accident and we didn't actually mean to invoke article 50 :-)

Avantgarde

06:31

What are the effects of brexit going to be on physics?

John Rennie

The UK contributes to European projects, the most obvious example being the LHC. However there's no reason to fear this participation will stop. Of more concern is that European scientists will be less willing to work at UK universities, and vice versa.

Mithrandir24601

One of the (admittedly few) 'good' things about the DUP is that they don't want a 'hard' Brexit, although they do really, really want a Brexit, so there's a chance they'll soften the process a bit. I hope

John Rennie

> admittedly few

Avantgarde

I see

John Rennie

My father was from a protestant family in Northern Ireland, and he took the first opportunity to leave even though that meant joining the army at the start of WWII. That's how bad it was.

Mithrandir24601

06:38

It has improved a lot since then, but there are still many, many issues. At least we're no longer trying to blow each other up as much as we once were

@JohnRennie The only other thing that I can think of is that their economic policies aren't that bad (I'm told). It's a struggle to think of anything else...

John Rennie

Ah, I gather from the use of we that you're in NI. Sorry, I didn't mean to diss your homeland. It's just that there is an element of the Scots-Irish community that I struggle to find much common ground with.

Mithrandir24601

@JohnRennie You're not wrong, so you don't have to apologise for it :P Having said that, if it was possible to ignore all the political stuff, NI would actually be a really nice country to live in - cost of living is cheap, it's a small, very green country etc.

(green as in the countryside is physically green and pretty much everywhere)

Kenshin

07:02

I don't get it, why are so many people blowing people up over religion

Mithrandir24601

07:12

religion is often the excuse, but not the reason :P

2

Kenshin

07:29

well what's the real reason for the North and South Ireland conflict

John Rennie

@Kenshin King James 1st

Kenshin

1566-1625

is this when the bombings were taking place?

I thought it was more recent

John Rennie

The first organised resistance to British rule started around the end of the first world war. Then things when quiet and it got nasty again in the 70s.

The point is that the underlying conflict goes back to the plantation.

Avantgarde

08:26

inspire hep crashed?

can't open links to papers

Shing

hey guys, I am not sure, in analytical mechanics, holonomic constraint means constraints that vary with time? or the time term in holonomic constraint stands for the particles?

or both ways are correct? For a same motion of a same particle: I can imagine the particle stands still, and all the constraint varying. Meanwhile, I can also imagine the particle moving in holonomic constraints that doesn't change with time.

Avantgarde

What do you mean that the constraint varies with time?

The constraint is an expression, expressed in the form of an equation f=0, where f is, in general, a function of all positions and time

Shing

08:41

@Avantgarde I am confused that if constraint is kind of a infinite potential wall keeping particle out of same directions, then what does holonomic constraint mean when it is a function of time ?

Avantgarde

Well it then means that the function f that expresses the constraint, explicitly depends on the time t

Shing

@Avantgarde how about its physics meaning? It is quite confusing to me when it comes to its physical meaning.

Avantgarde

@Shing The answer to that will depend on the specific situation in hand.

Hm, say, you have a simple situation where a particle is moving in x direction. A constraint that depends explicitly on time is x+t=0. This is of the form f=0. This constrains the particle to move along the straight line x+t=0

Now we don't know what imposes this constraint physically. It could be anything. Maybe the particle is made to move on a rail that is along the direction of x+t=0

that will depend on the specific situation

Time enters explicitly here, so as t increases, x has to decrease in order to keep the f=0 condition satisfied every time, everywhere

Shing

@Avantgarde so basely we can see holonomic constraint as infinite potential walls that will move around?

(in same cases, it sits still there)

Avantgarde

09:00

@Shing I think you're thinking of the wall as a constraint. In the sense of the English language, yeah it is a constraint. But in classical mechanics, you have to express your constraint in some mathematical form. A wall will constrain the motion of the particles inside such that you get an equation relating the different coordinates and time

If it is possible to relate the coordinates and time in that manner, then you will get a holonomic constraint

Shing

@Avantgarde so basely the infinite potential walls analog isn't quite good? Thanks for answering, I guess I will have to work out more problem set to get used to analytical mechanics.

Avantgarde

@Shing good for constructing a holonomic constraint? maybe/maybe not. I don't know. Working out exercises is good

Kenshin

11:04

wow ISIS has a city in the phillipines now, how?

The Dark Side

11:45

One of the suspended users is actually a good physicist, and we (the moderators) tried many ways and many times to get him to conform to the (quite modest) guidelines for civilized conflict on the site (because physics often engenders some conflict). I personally once spent more than an hour painstakingly editing a 30 post comment-string to strip out the personal attacks and leave the interesting and valuable physics argument therein. The user then returned and re-posted the insults and added a few directed at me. — dmckee Oct 31 '13 at 2:26

^ HAHAHAHAHAA ...

Old gem @dmckee I could not stop laughing for some 10 minutes or so.

ACuriousMind

@bolbteppa That looks promising, I'll give it a look. Thanks!

@Slereah I have not heard of him before

Slereah

12:08

I guess he is more of a french famous fellow

You know what theory I never see in books?

Fred Hoyle's version of GR

I have never seen it outside of its original paper

I know it wasn't terribly popular, but still

It's a fine historical tidbit

I'm not even quite sure what the Lagrangian would be

I think maybe $C_{\mu\nu} g^{\mu\nu}$ or somesuch

Physics Meta

12:23

1

Q: Comments deleted under my question

In the context of the post: Dimensional reduction of Rozansky-Witten theory I had commented on this question of mine, and there were some responses in the comments section as well, with some useful information I wanted to refer to later. Now all the comments are gone, and I cannot even remembe...

discussion comments policy

Sha Vuklia

Guys, I understand that $E_x$ has to be constant. However, I don’t see why $E_x=C\neq 0$ somehow doesn’t fit in the idea of a traveling wave advancing in the positive $x$-direction. Isn’t this just a wave whose profile has the same value at each plane?

Avantgarde

CMBR came like a wrecking ball. No mercy

Sha Vuklia

Is it maybe that the disturbance is equal everywhere, so it's not really physically plausible anymore? Or, at least, it's not really considered a wave anymore

Like, it doesn't really make sense that $E_x=C$ throughout the entirety of space, so we're not talking about a disturbance traveling forward? I'm guessing it's just a trivial solution we just throw away then

ACuriousMind

12:42

@ShaVuklia The point is that a field that does not vary with position at all is not a "wave" in any meaningful sense.

Avantgarde

@ShaVuklia For the EM wave to have a dynamic electric field component in the x direction, E_x should be of the form f(x-vt). You won't get this if (3.25) holds

Balarka Sen

my internet is super terrible today

my internet is the worst today

Sha Vuklia

13:00

@ACurious @Avant ah okay, thanks. kind of what I thought then

Avantgarde

:(

Balarka Sen

13:31

Great so there's proof right there how it's terrible

Avantgarde

14:10

:(

ACuriousMind

:)

Balarka Sen

..)

Picasso style

John Rennie

$\ddot{(}$

Balarka Sen

$\blacksquare$

Cubo-minimalist smiley

John Rennie

$\Huge \bullet$

Remember we are physicists. Approximate it with a circle.

SBM

14:21

hello

John Rennie

Hi

SBM

$\Huge \color{green} {\ddot \smile}$

Had a test on electrostatics today

John Rennie

On a Saturday? That's a bit harsh.

Balarka Sen

electrostatics is neat stuff

SBM

thankfully it had only about four numericals; relatively easy ones

@BalarkaSen agreed

Sha Vuklia

14:24

oh shit yea

that's it

never mind, I just deleted it

SBM

hmm :|

Avantgarde

I can't see all the math you guys write

No mathjax here

SBM

@Avantgarde tinyurl.com/cfqcvpc

check that

for the MathJax bookmarklet or the JS

Avantgarde

Thank you

Mostafa

15:46

@Mithrandir24601 About terrorism, my impression is that those who actually blow themselves (and others) up are socially, psychologically and economically vulnerable and damaged individuals that are thought to believe they're really doing it for the sake of God; by those masterminds that use religion as an excuse.

Big Ass Solutions

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Greatest brand ever ^

Balarka Sen

@Mostafa needless to say, that only applies to religious terrorism.

Avantgarde

16:36

oh man what a name hahaha

dmckee

@Mostafa Reportedly the Soviet intelligence community used a phrase that translates as 'useful idiots' to describe most of their non-professional assets, and treated such people as wholly expendable.

And yeah, unsophisticated and emotionally vulnerable misfits seem to be their recruiting demographic.

Balarka Sen

yeah, at least the Soviet community has inflicted well-organized terror against anyone opposing their totalitarian authority

that' much more of a worthy cause than isolated, religious terrorism

Bernardo Meurer

17:24

@dmckee How do I show that a function has an inverse at a point for $\Bbb R^n$

@ACuriousMind ^

@Mithrandir24601 ^

Someone save me

Ah!

It gotta be $C^1$ and $Df(x,y) \neq 0$

Coolio

Sanya

18:59

@Memor-X I'd never wait for localisation ... if you do that outside the US, you'd never see anything (and honestly said, I don't like localisations ...)

dmckee

20:01

@BernardoMeurer Sounds reasonable to me, but I'm no mathematician.

Bernardo Meurer

@dmckee Shame on you

@0celouvskyopoulo7 Please come back

When I fail this exam it will be @Shog9's fault for banning the only person who knows multivariable analysis

Sanya

Inverse function theorem

In mathematics, specifically differential calculus, the inverse function theorem gives sufficient conditions for a function to be invertible in a neighborhood of a point in its domain. The theorem also gives a formula for the derivative of the inverse function. In multivariable calculus, this theorem can be generalized to any continuously differentiable, vector-valued function whose Jacobian determinant is nonzero at a point in its domain. In this case, the theorem gives a formula for the Jacobian matrix of the inverse. There are also versions of the inverse function theorem for complex holomorphic...

Bernardo Meurer

@Sanya Yeah, I just found it on my notes

Sanya

I'm unsure what you mean by Df(x,y) for R^n

:x

Bernardo Meurer

@Sanya $n=2$ :P

Sanya

20:04

:D

@BernardoMeurer 0celo is banned again ?!?

Bernardo Meurer

@Sanya Yes, just in time for my exams ::rolls eyes::

Sanya

@BernardoMeurer that guy just can't control his keyboard ... ^^"

Bernardo Meurer

@Sanya Maybe, but he's a damn good analyst and I need him

Sanya

@BernardoMeurer I always thought he was doing topology

Bernardo Meurer

That's his focus I believe, but things aren't mutually exclusive

He's also a talented analyst

Sanya

20:10

well, if physics people have a math knowledge, it's usually analysis, so you have a decent chance to find someone here I'd expect

Jaime Gallego

And you can't contact him through another channel?

bolbteppa

@ACuriousMind Sec 3.1 of imperial.ac.uk/media/imperial-college/… gives the most direct derivation of the 11d sugra action, referencing the original paper you linked me, fleshing it out, and sec 10.2 of Freedman fleshes out the dimension counting motivating the fields, doubt anybody can do better than this

Bernardo Meurer

@JaimeGallego That's beyond the point

Anonymous

@BernardoMeurer Ask your question in the Maths SE chat. I'm sure many people would be able to help you with multivariable analysis.

Bernardo Meurer

@blue None of them will have the patience and love @0celouvskyopoulo7 did

3

Anonymous

20:23

Well, yeah :P

Jaime Gallego

That true

Bernardo Meurer

He literally sat with me for at least two hours every day for a month teaching me Analysis last semester

On Skype

Anonymous

So why not chat on Skype? :P

Bernardo Meurer

@blue Because the hbar is a loving atmosphere

bolbteppa

What was he banned for this time

Last time was calling me names :p

Anonymous

20:27

@bolbteppa <https://chat.stackexchange.com/transcript/71?m=37495214#37495214>

bolbteppa

@Slereah I se a lot of lqg comments of yours, do motls.blogspot.co.uk/2011/09/… and motls.blogspot.ie/2004/10/… not dissuade you from what apparently seems like craziness

One claims to generalize GR at the expense of the most fundamental thing in physics, the other in a sense literally just adds scalar fields to the EH action then invokes SUSY etc

wilx

Stop flag spamming.

bolbteppa

He only said that about jee because it's a tough exam :p

Anonymous

@bolbteppa Yeah, that's a touchy topic :/

Anonymous

Anyhow...let's not talk about it

Anonymous

20:32

@wilx Are you a mod? :O How did you see the flags?

wilx

@blue 10k+, that's how I saw it.

Anonymous

@wilx I see. Hmm.

bolbteppa

wikimedia.org/api/rest_v1/media/math/render/svg/…

Isn't it terrifying

Mostafa

@ACuriousMind Damn you look just as wise as you are with your new avatar...daaaaamn.

Bernardo Meurer

@bolbteppa dat notation

bolbteppa

20:35

Obviously you can just see OSp(1|32) is a symmetry amirite :\

Bernardo Meurer

Peter Sunde (The Pirate Bay) | TNW Conference | Technology is neither good nor bad: you are

►

@bolbteppa yes, that is trivial

Mostafa

@BernardoMeurer Do you use The Pirate Bay?

I don't. That's illegal.

Bernardo Meurer

21:03

@Mostafa I'm more of a fan

Slereah

@bolbteppa which is which? :p

I've reviewed a lot of QG, I don't think any QG theory is really conservative, outside of the oldest ones

The ones nobody uses anymore

Pauli Fierz, path integral, semiclassical and canonical QG are roughly conservative theory

I don't think either LQG or string theory resemble GR or QFT that'much

At least in the sense of the standard model + GR

NeuroFuzzy

@BernardoMeurer I'm definitely jealous of ocelot's analysis skillz

Slereah

" In the early June 2011, three authors found this result inconvenient because this point (discussed many times on this blog) is a simple way to see that all loop quantum gravities, spin foams, causal dynamical triangulations, octopi, all other discrete models of Planck-scale quantum gravity,

deformed special relativities, but also Hořava-Lifshitz theories etc. are just stinky piles of feces and these three authors - among dozens of others – have spent decades with a mindless "research" of these piles."

Motl's insane

NeuroFuzzy

Jealous in a hollow, "wait but why would I care about convergence and well-definedness" way.

NeuroFuzzy

21:29

@Mithrandir24601 I wish I could have your optimism!

Mithrandir24601

@Slereah I've got to ask - reading Wiki's article on Lee Smolin's 'the Trouble with Physics', why is Motl listed alongside the likes of Sean Carroll as a 'prominent physicist'? Is he considered one of the 'greats' of string theory, or is it just because of his big online presence? I mean, I've tried reading his blog (once) and just got infuriated with some of the stuff he was saying about non-stringy stuff (I'm not interested in stringy-stuff, so don't read and never tried learning any of it)

bolbteppa

@Slereah you can begin bosonic string theory from $S(g,\phi) = \int d^M x \sqrt{-g}(R - \frac{1}{2} g^{\mu \nu} \partial_{\mu} \phi \partial_{\nu} \phi - \Lambda),$ which is just the Einstein-Hilbert action, with cosmological constant, in the presence of a free scalar field $\phi$, or rather $D$ fields $S(g,\phi_i) = \int d^M x \sqrt{-g}(R - \frac{1}{2} g^{\mu \nu} \partial_{\mu} \phi^i \partial_{\nu} \phi^j M_{ij} - \tilde{\Lambda})$, but with $M \in SO(1,D-1)$ instead of say $SO(D)$.

That is basically just GR with some frills is it not

Slereah

" I believe that many of the discrete "alternative physicists" must have understood this totally robust reason why their whole research program is based on an incurable incompatibility with the observations but they're afraid to admit the truth because they're afraid

that they wouldn't be too skillful janitors in McDonald's which is what they clearly should be if the Academia were primarily something else than a huge welfare program for ordinary people who write crackpot papers and who pretend to be scientists."

Jesus

bolbteppa

haha

NeuroFuzzy

@Mithrandir24601 Totally anecdotal - I'm a baby theoretical physicist - but I've met several people who knew Lumo personally and seem to be influenced by his ideas (and take them "seriously" but with a grain of salt)

bolbteppa

21:32

He's very right wing alright

NeuroFuzzy

Plus the insults! Gotta love the insults.

bolbteppa

But on physics it's hard to question much of what he says

Slereah

Well you can

@bolbteppa Some of those motl arguments seem very hypocritical, too

"The spacetime dimensionality (four) is another assumption that cannot be questioned, much like the field content. Each of these assumptions is challenged in a general enough theory of quantum gravity, for example all the models that emerge from string theory."

One might think that assuming exactly 11 dimensions is also somewhat arbitrary!

Mithrandir24601

@Slereah Isn't there some argument in string theory that says 26(?) is as general as it gets and then this can be narrowed down to 11 or something???? How wrong am I saying that?

bolbteppa

My understanding is that 10 is predicted by superstring theory, but you can simply derive lots of things by starting from 11 and then using a math trick, offering a consistency of derivaton that hints at something deeper, not arbitrary at all

Slereah

21:43

String theory requires exactly 11 (or 10 or 26) dimensions

You can't have a 15 dimensional string theory

Otherwise the conformal anomaly fucks it up

Mithrandir24601

@Slereah Wonderful! That's just hilarious!

Slereah

"While string theory smells by God, loop quantum gravity smells by Man."

This sounds like some Czech saying that does not translate well

bolbteppa

In other words, if you just add to the EH action some scalar fields which transform amongst themselves in such a way so as to preserve lorentz invariance, you end up with bosonic string theory, 26 dimensions, but you don't have fermions, so you use supersymmetry giving 10 dimensions, and this can be merged with the 26 dimensions consistently, no flaws, no games, just the rules of qft, and you can get many disparate results by starting from 11-d in a way that hints at something deeper

But with lqg you have to throw lorentz invariance in the bin which is basically the death of physics

Slereah

I don't mind throwing out Lorentz invariance

Although apparently it doesn't agree with experiments

bolbteppa

That is crazy

Slereah

21:48

Why?

Lorentz invariance itself was crazy

bolbteppa

You get all of classical physics from it

It is preserved in QFT

In a sense it's like the only thing that matters

Slereah

A bit bold

Mithrandir24601

@bolbteppa So long as you get Lorentz invariance back on the right scales, what's the problem? The question is whether or not you get it back on said scales

Slereah

We still check experiments for Lorentz invariance breaks

For the simple reason that it can be broken and that can be checked experimentally

So far it seems to hold

bolbteppa

If you throw out SR, then what he says is true:
"loop quantum gravity does not respect even the special 1905 rules of Einstein; it is a non-relativistic theory. It conceptually belongs to the pre-1905 era and even if we imagine that loop quantum gravity has a realistic long-distance limit, loop quantum gravity has even less symmetries and nice properties than Newton's gravitational laws (which have an extra Galilean symmetry, and can also be written in a "background independent" way - and moreover, they allow us to calculate most of the observed gravitational effects well, unlike loop quant…

Slereah

21:50

Don't hold onto physical principles too dearly, the universe usually doesn't care

bolbteppa

Honestly, if you don't assume lorentz invariance, I don't know how you do physics past classical mechanics and basic QM

Slereah

Same way as usual

At typical scale Lorentz invariance holds within some limit

bolbteppa

and GR preserves it locally, QFT preserves lorentz invariance, it's the only thing constant

Slereah

Physics has to fit experiments, not the other way around

Mithrandir24601

@bolbteppa Or perhaps we end up with a pilot-wave-like theory of QM

bolbteppa

21:52

Pilot wave theory is another bunch of nonsense though

Slereah

@bolbteppa are you secretly Motl

bolbteppa

haha

Motl can derive the sugra action I'm having trouble with :\

motls.blogspot.co.uk/2012/04/…

Slereah

Overall I say don't get too hot about physical principles

Just look at theories based on the three big criterias

self consistency, completeness and agreement with experiment

Mithrandir24601

@bolbteppa Maybe. Maybe not. It hasn't yet had any verifiable results (that I know of) that are different to that of any other valid interpretation, so it's exactly as valid as all the other equally-valid theories of QM that also make the same results (i.e. essentially all of them)

Slereah

Pilot wave theory doesn't work that well with relativity

So it's kind of poor in that area

From what I've seen they struggle to find a pilot wave QFT

Mithrandir24601

21:56

@Slereah And reproducing the second law of thermodynamics in the classical limit :P

Slereah

Second law is rubbish

It's barely even a law

It can be violated by pollen

bolbteppa

lolwut

Slereah

a flower is stronger than the second law

Entropy can decrease naturally

It's not that amazing

It's just statistically unlikely

bolbteppa

I have to study it in a non-equil context properly so am not sure

Mithrandir24601

@Slereah That's the point of the second law - it's statistics. Do you mean entropy can locally decrease naturally?

Slereah

22:00

Well i mean I guess it could also globally decrease naturally, but that's even less likely

But as I said

Don't hold too dearly to any physical principle

That's not the important part of physics

Mithrandir24601

Also, I was trying to refer to this:

"The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations — then so much the worse for Maxwell's equations. If it is found to be contradicted by observation

— well, these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation."

Slereah

Not a terribly well argued point.

Entropy seems to hold fine but I wouldn't use it as a test of physical theories, especially in extreme conditions

Mithrandir24601

@Slereah The point is that it's a famous saying (and therefore joke) :P

Mithrandir24601

22:16

More seriously, you can't violate it classically because it's saying that the most likely outcome doesn't decrease entropy (or that's what I remember getting from learning about the confusing thing that was thermal and statistical physics) and the state with most entropy essentially boils down to being the most likely configuration of the system, so it's a weird circular thing and I get very confused and start waiting for someone who actually knows what they're talking about to tell me I'm wrong

(in the quantum world, I'm aware that things are very different...)

Slereah

Oh you can find things that violate the second law of thermodynamics

it's not terribly hard

Mithrandir24601

@Slereah Show me one then :P

Slereah

Usually they involve negative energy

(Not saying they're realistic examples :p)

Mithrandir24601

@Slereah Are negative energies (in the sense that you're talking about them) classical?

Slereah

You can make classical negative energies

It's not too hard

though it has plenty of problems

Mithrandir24601

22:32

OK. If I can rephrase that - are they classical and physical? :P

Slereah

Well obviously, there are currently no observed average violations of the second law

just saying it's not too hard to construct a model where it is violated

Mithrandir24601

@Slereah That's my point :P (and yes, I'm perfectly happy to accept that models that violate it exist)

Slereah

Just be mindful that all laws hold until they do not

So don't hold onto them too much

You never know what's around the corner

LegionMammal978

23:58

Question: Could one say that 1 mol = 6.022141... × 10^23, where the RHS is dimensionless?

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