The h Bar

12:16 AM

Guys, someone explained my way of thinking about quantum mechanics for me!
http://en.wikipedia.org/wiki/Relational_quantum_mechanics

@ACuriousMind ping, since I know you respect this sort of thing.

ACuriousMind

@DanielSank "zero world interpretation". I like it.

0celo7

@ACuriousMind Can it be experimentally verified?

ACuriousMind

@0celo7 No, but that's fine, because it seems to make no statements about the world at all. It just makes explicit the fact that all physical theories essentially are descriptions of information available to us rather than descriptions of "reality", I think.

0celo7

12:31 AM

This is scarily accurate I think.

Although "scientist" should include engineer.

Although my dad (engineer) made me memorize pi to five digits when I was too young to know what pi is.

Alfred Centauri

@ACuriousMind is it the case then that quantum interpretations amount to a choice of 'gauge'?

0celo7

@ACuriousMind I'm retarded...pls halp smbc-comics.com/index.php?id=393!!

ACuriousMind

@AlfredCentauri Hm...it would be the most hotly contested gauge choice of all time, then.

They indeed always seem to boil down to a choice of what is "real", though.

@0celo7 Not all SMBCs make sense to me, either.

NeuroFuzzy

@DanielSank "someone explained my way of thinking about ____ for me! " hehehe

0celo7

@ACuriousMind Is SMBC a troll?

I feel like some of these webcomics are either a reference to something or are just nonsense trolls.

NeuroFuzzy

12:38 AM

@0celo7 the earlier ones can be pretty dumb. I think "insulin shots" could be replaced by "food and water" or any other thing. The joke is taking "all we need is each other" too literally.

They're hit or miss but... doesn't he write one basically EVERY day? They can't all be good haha

ACuriousMind

@0celo7 ...sometimes, I guess

@NeuroFuzzy Yes, one comic every day. The quality is surprisingly high for that rate

0celo7

@ACuriousMind Does parallelizable imply zero curvature?

(I think Nakahara is saying this, but he's being cryptic.)

ACuriousMind

@0celo7 Yes, parallelizability implies the tangent bundle is trivial, and trivial bundles cannot have non-zero curvature

0celo7

@ACuriousMind Hmm, are Lie groups parallelizable?

ACuriousMind

@0celo7 Yes

why?

0celo7

12:50 AM

How does Yang-Mills work then?

Isn't the field strength trivially zero?

(I don't actually know what I'm talking about, have not studied bundles yet.)

ACuriousMind

Yep, you don't know what you are talking about ;) The Yang-Mills curvature is not the curvature of the tangent bundle of spacetime (or the Lie group), but of a principal bundle over spacetime with the gauge group as its structure group

0celo7

Ok, 150 pages to go for the first reference of "principal bundle"

Gimme a week.

@ACuriousMind This whole business with the contorsion tensor is new to me. It seems that we can almost "gauge transform" it away since $\Gamma+t$ with $t\in\mathcal{T}^1{}_2(M)$ is another connection.

Is that an appropriate view?

ACuriousMind

@0celo7 Why would that be a gauge transform?

0celo7

@ACuriousMind Quotes.

We have a degree of freedom, so we use it to eliminate a term we don't like, i.e. the contorsion.

ACuriousMind

@0celo7 I don't follow why $\Gamma \mapsto \Gamma + t$ would be a degree of freedom.

You aren't free to choose the connection.

0celo7

1:02 AM

@ACuriousMind I thought there were many different connections.

ACuriousMind

Yes. But they aren't equivalent

0celo7

I know they aren't equivalent.

I'm saying if you have a valid connection $\Gamma$, then you can construct $\Gamma+t$ which is also valid.

ACuriousMind

That's true

Given a connection with torsion, you can always construct a canonical torsion-free variant of it

But I would not call that a gauge freedom in any sense, since things related by a "gauge transform" should be equivalent in some sense.

0celo7

Ok.

@ACuriousMind Has Sofia held up her promise never to return?

Stan Shunpike

Did she? I hadn't heard that lol

ACuriousMind

1:08 AM

@0celo7 I've not tracked that, but I don't think I've seen anything from her, so probably: Yes.

0celo7

@ACuriousMind I just poured the last bit of a sampler of this. Have you ever tried it? Wonderful vanilla finish and aroma.

ACuriousMind

1:25 AM

@0celo7 Nope, I don't know that one.

0celo7

@ACuriousMind Do Germans like bourbon or is it seen as a heathen drink?

50%+ corn isn't for everyone.

ACuriousMind

@0celo7 I personally don't like bourbon, but the German as such isn't really a whisky drinker, so no cultural preference here, I think

0celo7

@ACuriousMind Do you similarly dislike rye whiskey?

There's something about it that I dislike, but can't put my finger on it.

ACuriousMind

I don't think I've ever tried rye whisky

0celo7

@ACuriousMind Pedantic note: American whiskeys are spelt with "ey".

@ACuriousMind Holy crap this exercise: Calculate the Riemann tensor of $\mathbb{R}^3$ using the metric in spherical coordinates, the Robertson-Walker metric and the Schwarzschild Metric.

Riemannian geometry exercises are ridiculous.

Physics Meta

2:15 AM

0

Q: Age - Score Relation

HT to Danu on this one. So there was this recent post inquiring about answering 0-answer questions in which a comment read, It is not evident that votes on answers to old questions are fewer than on new ones and, elsewhere on the site, it was mentioned that late answers are typically eithe...

Stan Shunpike

3:26 AM

Nice post @KyleKanos ^

:: hat tip :: lol

Kyle Kanos

Thanks

Stan Shunpike

Is spacetime curved whether or not other objects are present? In other words, the sun curves spacetime irrespective of whether other objects are there, right?

Alfred Centauri

@StanShunpike correct. In fact, spacetime can be curved without the presence of any objects if the so-called cosmological constant isn't zero.

Stan Shunpike

3:46 AM

@AlfredCentauri true, I hadn't thought of that. Question: are the effects of gravity still considered to extend to infinity in GR? If so, how do we know this? Or is it just an assumption?

Alfred Centauri

@StanShunpike gravity is spacetime curvature. If the the spacetime is asymptotically flat, then, 'at infinity', the curvature is zero and there is no gravity. But, honestly, 'infinity' is not obliged by what we 'know'.

Stan Shunpike

@AlfredCentauri in other words, infinity might not be a physically meaningful concept?

Alfred Centauri

4:03 AM

@StanShunpike it's meaningful but subtle. I can't do the subject justice here (maybe someone else can). It would be great to get you and a few others here around the fire pit for some libations and BBQ here in sunny FL to discuss. Maybe some day...

Stan Shunpike

@AlfredCentauri That would epic :D

DanielSank

4:53 AM

@ACuriousMind YES!

Yes yes yes yes a thousand times YES!

0celo7

5:39 AM

The book Curvature and Homology by Goldberg, despite having lengthy sections on complex geometry, does not use $\mathrm{i}$ but instead writes $\sqrt{-1}$ everywhere. Seriously.

David Z

9:28 AM

@StanShunpike I have friends who are researching that sort of thing

Just Greg

9:43 AM

Before Einstein came up with General Relativity, was there any serious reason to doubt Newton's theory (and its various developments)? I only know about the discrepancy in Mercury's orbit, which may have been caused by an error (e.g. similar to the one that caused people to make up Planet X).

Also, is this an okay question to ask here? (e.g. history of physics)

innisfree

any empirical reason?

or can one consider theoretical arguments?

Just Greg

9:58 AM

I don't know. It's a history question, so it's about whatever reasons people had in the past.

0

Q: Before Einstein came up with General Relativity, were there serious reasons to doubt Newton's theory?

Before Einstein came up with General Relativity, was there any serious reason to doubt Newton's theory (and its various developments)? I only know about the discrepancy in Mercury's orbit, which may have been caused by an error (e.g. similar to the one that caused people to make up Planet X).

general-relativity gravity newtonian-gravity history

Right now we have tons of reasons, but it seems to me we only knew why Newton's theory was wrong after the better theory came up. We certainly didn't know the kinds of experiments to perform.

innisfree

10:22 AM

i;ve written a quick answer

" we only knew why Newton's theory was wrong after the better theory came up" -< Yes, theories are rarely/never abandoned if no better explanation is available.

Kyle Kanos

3:00 PM

@JustGreg I disagree with the perception that Newton's theory was/is wrong. It's not wrong, it actually works quite well. It just cannot be extended to "bigger" things.

That would be like saying QM is wrong because it doesn't work the same as classical mechanics

ManishEarth

+1

Kyle Kanos

They simply cover different size regimes

o/ @ManishEarth!

ManishEarth

Calling newton's theory wrong is fine, as long as you call every other modern theory wrong too, because they all have the same problems :P

o/

Kyle Kanos

How goes it?

ManishEarth

Badly. Really swamped :/

Kyle Kanos

3:06 PM

With schoolwork? Or lifework?

ManishEarth

schoolwork

Kyle Kanos

Well on that note, I hear you! I've got my dissertation due to the committee on Weds

ManishEarth

@KyleKanos Ah, good luck!

Kyle Kanos

TY, but this is the easy part. The hard part comes next week when I actually defend :\

Stan Shunpike

3:25 PM

@DavidZ friends who are researching whether gravity is infinite? How?

dmckee

3:52 PM

I'm done talking to this guy:

20

Q: If the LHC-calculated mass of the Higgs is wrong, how long will it take to determine this with confidence?

After I watched "Particle Fever"--the movie about Large Hadron Collider (LHC) and the successful identification of the Higgs boson--I became a bit concerned with that team's handling of various negative PR incidents. Further, with the amount of money spent and the pressure to produce results, al...

soft-question measurement higgs large-hadron-collider

I no longer believe he is asking in good faith or that he actually wants to know the answer.

David Z

@StanShunpike studying the asymptotic behavior of spacetime with nonzero cosmological constant

ACuriousMind

I had that suspicion from the start, tbh.

dmckee

@ACuriousMind Well, it had occurred to me to, but it is a reasonable question on the face of it and there is an answer.

David Z

@KyleKanos hm, isn't the defense kind of a formality? Not literally, but in the sense that if there are any legitimate doubts about whether you can pass, your advisor wouldn't let you defend in the first place

@StanShunpike see e.g. this

dmckee

@DavidZ I've heard of cases where students insisted. And of ones where the advisor just wasn't looking out for the student like that. But those are rare enough that you always hear of them nth hand.

Certainly that is part of the advisor's job.

ACuriousMind

3:56 PM

@dmckee I think "How much confidence can we put in this?" is either trivially answered by the Sigma confidence levels or opinion based. Putting "scientific" in front of confidence doesn't make it less so.

David Z

@dmckee Yeah, I've heard of those cases too, but I think Kyle would know if that was him :-P

dmckee

@ACuriousMind I'm more ticked off by his comments than the late edit. He's asked how can we trust this stuff if it isn't replicated and I showed him the process for replication and he's simply dismissed it.

He also implies that he can guess how collaboration work better than people who've been there.

In any case, I'm done.

Kyle Kanos

@DavidZ Well, I suppose that is kinda true. But I do have one member on the committee who is not an astrophysicist and is a bit of a stickler when it comes to certain things that I may or may not be prepared for. So the nerves are based on him alone, really

There was one girl here a number of years ago who was asked at her defense to redo some experiment (a small undertaking, from what I was told) and she said no and quit the program.

David Z

Ah, I see what you're saying. Though still, even if someone on your committee is a stickler, you really have to crash and burn to actually fail. From what I understand.

Kyle Kanos

Right. So long as I present the work in a coherent manner and explain why it's important & how it connects to the observables, I should be okay to pass.

David Z

4:02 PM

@KyleKanos that's all on her. (Though it really does say something about burnout in grad students)

Sounds about right

Honestly, I was so relieved to be done writing the actual thesis that I didn't really care about the defense.

Kyle Kanos

Then I get to spend some time (hopefully not much) adding/subtracting from the dissertation. And then off to learn C++

David Z

woohoo real fun! (C++)

(lol)

I'm starting to think of C++ rather like quantum mechanics, in that nobody understands it, and anyone who says they do is either lying or clueless

3

Stan Shunpike

4:22 PM

@DavidZ that's Ashtekar as in Ashtekar variables, right? That's a name i've seen crop up many times when I have searched QG

David Z

Yeah, he's kind of the pioneer of the theory

or, one of the pioneers, really

Stan Shunpike

@DavidZ is that of LQG? I don't know much obviously but I thought Witten was the string theory guru. I know Carlo Rovelli is another LQG guy.

David Z

4:37 PM

Yeah, Witten is big in string theory

and Carlo Rovelli is (as far as I know) one of the other LQG pioneers who got involved in it around the same time as Ashtekar

(yes, I meant Ashtekar is a pioneer of LQG)

It's probably somewhat analogous to the big names in quantum field theory in its early days - Feynman, Schwinger, Dyson, etc. Similarly LQG has Ashtekar, Rovelli, and others

Stan Shunpike

Yeah, most fields need pioneers. Knowledge doesn't just fall from the sky.

Funny debate with Carlo Rovelli m.youtube.com/watch?v=jEr038WOKFI

Kyle Kanos

5:37 PM

Well that kinda sucks:

123

Q: Do I have the legal right to demand information on plagiarism of my work from another university?

A student of a German institute has translated my Russian thesis word by word to English and submitted it as her own work in 2014. I informed the university providing them with my work in Russian and presentations of the work I made in 2013. Upon receiving my email, university examinations first...

plagiarism legal-issues germany

NikolajK

5:57 PM

@DavidZ: What does it mean to understand QM? Understanding anything, like hydrocarbon chemistry say, I would quantify by knowledge of it. I think there are people who can answer the bulk of well formed questions, so I'd say they understand it. If you extend QM to it's philsophical context, then it's also fair to say that nobody understands power, death, etc.

@ACuriousMind: In the thread about cold fusion, you speak of the merit of non-mainstream theories. What's the merit of theories in general (apart from reasearch of non-non-mainstream theories having the advantage of easier getting grant money)

ACuriousMind

@NikolajK The merit of a theory consists in it predicting the results of experiments/measurements as accurately as possible, I'd say. Among those that perform equally well, we use variants of Occam's razor to choose those that have the fewest and most elegant axioms.

NikolajK

@ACuriousMind: Mhm, k, I don't know who looks at the predictions of fringe theories to see if they are accurate. I feel the label is just assigned with reference to what's been published in the bigger pictures. New areas energy as perturbations of old research, or if a famous person decided to work on them.

Everybody "knows" that cold-fusion is fringe science. I don't know anyone who dislikes the theories and has read more than 5 papers on it seriously. I feel the arguments against those theories is "these theories we learned about in university say to opposite - so it must be false". That's of course a ridiculous perspective, exactly what doesn't work. You can't argue with the established theory against the new one, only with experiment.

"Quantum electrodynamics predicts A and B. A has been confirmed. Fringe theory predicts not B. But quantum electrodynamics is true! So Fringe theory is false!"

"Conversation of energy!" ... "No perpetuum mobile!!"... etc.

ACuriousMind

@NikolajK You're correct, but I think that many non-mainstream theories (the "crackpot" ones) actually say "not A". I've honestly no idea where cold fusion falls on the scale of "crackpot" to "reasonable theory that has not been pursued for unclear reasons".

NikolajK

6:13 PM

That being said, I don't want fringde theory content on SE, just like I don't want homework threads. You only have finite time in your life so (unless you have your own money for experiments) you focus on the things where people know about it.

user54412

6:49 PM

@DavidZ Well, certain departments have hard time limits for the PhD, so at the end you either quit or defend what you have.

user54412

Also, professors in at least one such department are known to, during the defense, pull out a list of questions the student got wrong during oral quals 3 years earlier, to make sure they improved their breadth of knowledge about the field as a whole...

user54412

um what?

3

user54412

Apparently an answer from 2.5 years ago needed more cheese

Kyle Kanos

Well it's true, you do need more cheese

user54412

Is there a good reason for allowing unregistered edit suggestions?

Kyle Kanos

6:56 PM

In case they make good suggestions?