12:31 AM
@ACuriousMind Which is why the first step to take on encountering couple oscillators is to diagonalize the matrix.
Then you can get on with having too much success so more.

12:44 AM
@EmilioPisanty Actually it's the least contrived one inasmuch as it's the only one out there AFAIK. Presumably one can concoct a truly bizarre one but there seems to be no universal way of doing this.

5 hours later…
5:23 AM
There aren't separate parts to the time dilation: a gravitational part and a motion part. The time dilation cannot be divided up like that that. There is just the proper time along some curve. In this case that curve is a circukar orbit.

6:14 AM
@JohnRennie That certainly makes sense, but it seems to disagree with that text from Wikipedia, and the graph, which claims that at a certain altitude the gravitational time dilation exactly cancels the velocity time dilation, so that the time rate is in sync with time at the Earth's surface. I don't see how we can get that cancellation effect from your formula.

There is no orbit where the time dilations cancel. I think this has been asked as a question on the main site.

OTOH, the time dilation on Earth's surface uses the formula for non-orbital gravitational time dilation, and ignores the Earth's rotation.

@PM2Ring the earths rotational speed is low enough not to make much difference so it's usually neglected.
Hmm, according to:
9

We know that for a GPS we need to make a correction for both general and special relativity: general relativity predicts that clocks go slower in a higher gravitational field (the clock aboard a GPS satellite moves faster than a clock down on Earth), while special Relativity predicts that a movin...

there is an orbit where the time dilations cancel.

Understood. FWIW, I'm happy to accept that the Wikipedia article is wrong, but I'm not yet totally convinced that it's wrong. ;)

1

Consider a Mass on earth. The time dilation on the surface of Earth is $$T' = T \sqrt{1 - \frac{2GM}{rc^2}}$$ Now if the mass is moving around the earth at velocity of v w.r.t Earth, what will be the time dilation within the mass as seen from the Earth? The object could be in free fall, orbit o...

Oh wait. That first question asks for an orbit where the time dilation of the orbiting observer matches the time dilation of the observer stationary on the Earth's surface.
And yes, there is such an orbit. What I'm saying is that there is no orbit where the time dilation is zero relative to an observer far from the black hole.

6:44 AM
@JohnRennie I agree with that. I've just been skimming through the PDF by Neil Ashby, linked in this answer physics.stackexchange.com/a/390402/123208 It looks quite good, and even though it's fairly short it has derivations for most of the stuff it uses.

Anyone familiar with the $\mu-\tau$ symmetry of neutrino physics?

2 hours later…
8:37 AM
morgen

2 hours later…
10:10 AM
0

I gave a partial answer to a homework questions here and was firmly told in comments that even partial answers to homework questions are not allowed. Is that correct ? As far as I can see, the guidelines on homework questions only prohibits complete answers. Follow up question: if any answer at ...

1 hour later…
11:39 AM
I literally used the book I hate for toilet paper
but it even failed to do a good job .......
I am starting learning QFT.
and really want to get this to begin with
but the price is just too high ....

12:01 PM
you fool
QFT is the gateway to madness

@Shing I just wish they'd print bad books on softer paper.

12:14 PM
Why is $\varepsilon_{ab} \, ^{d}S_{cde} = \frac{1}{2} \eta_{bc} \varepsilon_a \, ^{pq} S_{pq e}$ for $S$ anti-symmetric in all indices in 3D Minkowski space $(t,x,y)$

you could just say in 3 dimensions :V

Hm
Did you try to rewrite $\varepsilon$ in terms of deltas
It's usually simpler to just do theorems for levi-civita like that

Hmm, using $\varepsilon_{ab} \, ^d = \delta_{ab3}^{12d}$?
I want to just say $\varepsilon_{ab} \, ^d S_{cde} = \eta_{bc} \varepsilon_a \, ^{cd}S_{cde}$ but then adding the $1/2$ because you sum over things twice but it's clearly breaking math

12:30 PM
Einstein summation is a ruse anyway, seems legit

1:19 PM
@ZeroTheHero I'm with @Slereah on this. It's doable, but that doesn't mean it's doable without using some pretty stupid stuff.
@JohnRennie you know, something that translates into itself in this correspondence

2 hours later…
3:03 PM
Trying to learn about Regge calculus
but I'm afraid first
I must learn of
THE POLYGONS ON RIEMANNIAN MANIFOLDS
GR doesn't deal with that much

3:24 PM
@DanielSank can I ask you to make a decisive statement on your answer on meta, so that this ridiculous conversation can stop?
Are you saying any arbitrarily high number of trivial edits is OK? Or do you think there should be a bar? If so, what's the bar?

what if the sequence of edits converge to a finite edit

It will always do so if the editor is descended from a Bolzano or a Weierstrass

Two months until @0celo7 can come back

But will he¿?
Banned peeps rarely return

he'd better
I'm gonna beat his ass otherwise

3:43 PM
@EmilioPisanty :-)
It's just so great being English. It's a shame everyone can't be English :-)

@JohnRennie Ghandi never learned that

4:03 PM
@JohnRennie being English sounds like a pretty terrible deal right now
or rather, it sounds like a No Deal deal

@EmilioPisanty ah, erm, yes, I'm trying not to think about the Brexit fiasco at the moment.

@JohnRennie maybe brexit fatigue can be alleviated with some suitable rebranding
The National Meltdown, maybe?
the UK Disassembly Process, perhaps?
every time I think the thing has reached peak shambles, it triples down on it

@JohnRennie interesting
3 < 17, still, but that's definitely interesting

Three million votes in two days. Obviously the rate of voting will tail off, but that's some serious pressure on the government.

4:36 PM
@JohnRennie in two days?
goodness
the petition data looks a bit strange
there's a few places listed which don't look like they're in the UK

Hmm, looking at the daTa I find: "created_at":"2019-02-14T12:14:59.326Z"
I suspect it only hit Facebook in the last two days.

I highlighted a few, then got bored

But when I first saw links to it on Facebook two days ago there were under a million votes.

I must admit I don't understand what the JSON data is showing

4:41 PM
I can't be bothered to analyze whether they're just a minority that's being loudly reported by the system or a sizable majority
@JohnRennie I don't much, either
it separates "signatures_by_country" from "signatures_by_constituency"
presumably the former goes in the bin, and the latter gets tallied up
I suspect it's just loudly-reported cruft
it shows some 10k signatures from Germany and some 10k signatures from Edinburgh East
(and also, the signature page explicitly asks whether you're a British citizen or a British resident, so the presence of foreign countries probably doesn't matter much.)
oh, IOP, I love how you spell

5:32 PM
@Slereah Ick. Even dealing with spherical polygons (a subject that just keeps coming up in my current project) is nasty compared to the equivalent planar problems.

@JohnRennie I signed it.

@AvnishKabaj Thanks :-)
(not that I condone electoral fraud of course :-)

Heh heh

5:50 PM
Single photon interferometric experiments are a things (indeed, people had to learn how to do those before they could do all the spiffy delayed choice experiments and Bell's inequality experiments that drive discussions of entanglement). Townsend's QM book has a bunch of references in the first few chapters but my copy is in another state. — dmckee ♦ 46 mins ago
@dmckee gaseous, I imagine?
I can't quite see how you liquefy a book, but then again, you never know

6:04 PM
@EmilioPisanty I'm not going to respond to that. If the readers want to argue over unrealistic interpretations of what I wrote, then they're welcome to do that. I'm not getting involved :-)

@EmilioPisanty I think that Missouri may, just possibly, qualify as a bozo condensate.
That's a thing, right?

6:45 PM
@DanielSank no, seriously. You're saying there's no upper limit?
anyways
dear native English speakers
halp
> whose dynamics have to be taken into account
vs
> whose dynamics has to be taken into account
it's the former, right?

@EmilioPisanty this non-native speaker agrees :P
this non-native speaker also spent the day crafting XML schemas, though, so his grasp of natural language may be weaker than usual :P

@ACuriousMind well, at least XML schemas don't have all the verbs at the end.
I'm going to write a paper where all the periods are replaced with commas, and then all the verbs are included in order, separated with spaces, at the end
with the aim of being as intelligible as possible to German readers

@EmilioPisanty I prefer the former as well.

@dmckee thx =).

Though on the matter of asking for native speakers, I have observed several times that really fluent non-native speakers usually have a more precise grasp of the formal grammar.

6:53 PM
@dmckee I guess you could put me in that bucket
but the concept of "formal grammar" for English is.... dubious, I should think =P

Many native speakers, including this one, basically blew off a lot of their formal instruction in grammar because (a) that stuff requires thinking and (b) feeling that they already know how to talk.

lolz

@EmilioPisanty That's a transformation that's rather easy to reverse algorithmically, so you're really only making it unintellegible to everyone not willing to write something to transform it back!

@ACuriousMind exactly
like everything ever written in German
see?
sorry if I sound bitter, btw. I'm staying at an institute guesthouse at the Garching Forschungszentrum, and I'm having to deal with the one true nightmare of living in Germany
Ersatzverkehr

@EmilioPisanty It's not our fault other people don't have enough memory to deal with our language :P

6:57 PM
It was only when studying different ways of talking that I started to grasp the real value of classifying words and structures that way.
But a large number of folks in my dear United States don't see any real value in learning how to talk foreign.
If English was good enough for Jesus Christ, it's good enough for them.

@dmckee amen

7:32 PM
@EmilioPisanty Give the full sentence.
@EmilioPisanty I am not talking about that issue. Apologies.

7:50 PM
weez
@Rick yeah, I think the GTC was pretty great. Learned a lot. :D

ahoi, colleague

8:07 PM
Ahoi :D
I'm writing documentation about my learnings from GTC mmmhm

8:54 PM
This question makes me chuckle a bit
1

I am not familiar with any notation used in physics. The paper "Non-hermitian random matrix theory: Method of hermitian reduction" by Joshua Feinberg and A. Zee (Nuclear Physics B, 1997) states: A basic tool in studying hermitian random matrices $\phi$ (henceforth all matrices will be take...

“But why is it not written that way?” because it’s a physics paper. (Also, you were able to deduce what was intended from context soooo)

"A. Zee" if one wasn't dividing by a matrix or something it would be concerning :p

I mean, there’s contexts where I’d regard it as legitimately confising
But their very question indicates that they could infer what was intended without any real issue
So...if it’s an abuse of notation, it’s a comprehensible abuse