@Slereah sure, I get what you're saying. I just wouldn't have thought to phrase it that way myself, due to how unorthodox quantum theory is to begin with

I'm talking to induce collapse at the point of the two slits @Slereah

@GPhys Best excuse for talking to yourself ever!

Have a little man in each slit

it's easy to imagine a bright enough lightbulb interacts with most all of the electron wavefunctions

"No, I'm not talking to myself, I'm just trying to induce the collapse of a wavefunction"

@GPhys Localization of photons is a tricky issue, I'd say - absorbing them is the only way I can think of to "localize" them. Which is fitting, since as relativistic objects the notion of a position operator for them is rather murky

@ACuriousMind No need to absorb them

Make the photon interact gravitationally

also two photons can interact

for second order processes

@ACuriousMind maybe it is easier to just talk of electrons then (I'm just thinking about what to say in my next general physics 2 lab)

I think, the lightbulb is nice because also you can imagine a dim lightbulb that only interacts with some electrons

I have a question

In flat spacetime, c will always be observed to be the same

Yes

But what if you measure c, but the geometry of spacetime there is different to where you are

Depends how you define "measuring c"

what process do you use

I haven't really thought about that, the first thing that comes to mind is "lasers" in which case it would affect it

The speed of light can be constant or different in GR, depending on what you mean by the measurement of the speed of light

So there are measurements you can do involving a region with a different spacetime shape to yours, and still get a constant c?

you have to take into account the change of the time flow and distances along the trajectory of light

but of course, you may not know them

in fact usually it's the other way around

you assume $c$ constant and measure the geometry using this

@Slereah read my lips

Thanks for the answer, I'm wondering, atm I'm reading Munkres Topology, after that what should I read to get into the differential geometry needed for GR?

Einstein said the speed of light is variable

:O

The classic example is

Go outside

take a twirl around

The sun just travelled $2 \pi r_\odot$ around you

Do you consider it went faster than light

But relativity isn't fully Machian is it?

It's not, no

@Phase if you manage to work through topology, you're good to go right into a GR textbook. I suggest sean carroll's "Spacetime and Geometry". It's my favourite introductory GR text and leads you through the math you'll need (assuming you have a basic start)

@Jim thanks!

@Slereah is this an argument about information?

what is

About the sun going around faster than light, to answer it correctly I'd need more information than I could observe

you can see the sun

^when I say argument I dont mean the discussion kind, but like "argument for _____"

going around u

Well my answer would be no

about the "do you consider"

but then u must define what you mean by "speed"

@Phase Munkres is long and you don't need all of it.

that is the problem of defining speed in GR

But regardless of speed, for it to go around like that it would have to be subject to a huge force

there's no good notion of speed for distant objects

@0celouvsky Would it not be useful?

@Phase I don't know what your goals are.

just learning more about physics and maths

A mathematician should be aware of everything in it.

@0celouvsky Did he? You mean like in the second postulate of relativity, where he explicitly said it's constant in all inertial reference frames? Or like his vague implicit mention of the speed of light in one of his books, where you have to realize that the variable he uses in a denominator must be a scalar speed of light and is not a constant? It's a shame he never explicitly made mention of his thoughts on the matter

@Jim I was quoting JD :P

if you want to compare speeds in GR, you have to do parallel propagation of the momentum

But there ARE quotes where he says it's variable, that much is true.

But there is more than one way to do it

I'm not sure exactly how he defined it.

@0celouvsky I looked into that before making the comment. It's implied from an equation in a book

but of course, with that definition, the speed of light is still constant everywhere

but that is an assumption of the theory

@Jim It's like the "effective speed of light" is $<c$ if there's a strong g. potential.

Similar to the effect of a medium I guess.

It's been too long since I've dealt with the actual physics of GR, my GR these days is more Sobolev spaces.

Ok, well I'm getting the impression it's a fair bit more nuanced than I can appreciate

I'll drop it and try again when I've learnt more

@0celouvsky indeed. At least he was smart enough to stay out of that debate. That way lies madness

@Slereah Avez, A.: Ann. Inst. Henri Poincaré 1, 291-300 (1964). please?

@0celouvsky I thought the explanation for stuff like that, like a photon emitted radially outwards from inside an event horizon is that spacetime deformation changes the solid angle that allows escape as you get closer to the event horizon, and then past that, the deformation means all paths lead you to the centre

It might be wrong but just asking because I haven't had a chance to ask if it's right or not until now

math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/…

this was one of JD's favorite links

@Phase that's close enough

I think he was purposefully misunderstanding it, but there you go

Who is JD?

Voldemort

whoa spook

if you say his real name the mods get mad

so basically voldemort

By the way

If you define GR with spin-2 fields, in the Pauli Fierz formalism

The speed of light varies

@Phase A user of the site who likes to remind us of the origins of theories and tries to keep us pointed in the same direction that he believes they were meant to be taken

@Slereah can you help me find this paper

I can't navigate the site

If everyone takes to theories with the exact same approach then science would be forced down one strict path and likely just be wrong

it seems like a shitty site

I'll try

Imagine if the aether was still accepted

Why do the Mods get mad?

numdam.org/article/AIHPA_1964__1_3_291_0.pdf

I found it at the same time

thanks

@Phase true, he has no issue with some people doing research into alternative methods and interpretations; however, he pushes us to keep in mind what he is led to believe the original intentions are whenever we explain mainstream physics. The thought is that anything not keeping with original intentions but still mainstream is sufficiently different that it would be something new

@Jim Former user. He's banned on the main site for a year.

@Jim He has no issue?

Whoa

I'm confused though

@0celouvsky explains why I haven't been corrected in a while

He sounds like a tool but can you get banned for being a tool?

He had huge issues with people doing anything differently than what Einstein or Maxwell said.

it doesn't seem in and of itself offensive

@0celouvsky not with researchers, just with those attempting to explain accepted theory

@Phase You can get banned for talking back to the mods.

@Phase We don't get "mad" per se but we prefer that you don't discuss banned users since they can't talk back.

@Jim He had a problem with current researchers for sure.

Talking back?

Even if it's not aggressive?

@ACuriousMind stop me when I'm close to going too far

@Phase You don't get banned for being a "tool" (and please don't insult people implicitly like that). We also don't generally discuss specific suspension, but in general, no, you cannot get banned simply for saying wrong things or merely for arguing with moderators.

Sorry if the "tool" comment seemed brash, it was only describing what I was hearing of the person though. In reality I have little clue who the full person is

@Phase it sometimes could get aggressive when his view of accepted theory disagreed with that of others. He had, what I can only describe as, an "unhealthy" amount of reverence for the words and perceived beliefs of famous figures like Einstein, Maxwell, etc

Thanks for clarifying, that seems to border on Religion rather than science

perhaps. I didn't myself see the actions that led to a suspension. So I can't comment on the extent. My dealings with him were always grating, but not aggressive. That said, my dealings with anyone aren't very aggressive

Likely because people know that death awaits those who disagree with The One True Jim

Maybe Jim shouldn't denote a state, but an annihilation operator

The Jim operator

$\widehat{\text{Jim}}$

ehhhhhhhhhh

$\hat \mathcal{Jim}$

h

why doesn't that work?

Lack of curly brackets

I know it's not proper notation, but shouldn't an annihilation operator be "Jim dagger"

also hat is for single characters

you need widehat

@ACuriousMind What is a "normal" geodesic?

\widehat ?

$\widehat{\mathcal{Jim}}$

Ayyyyyyyy

$\mathfrak{Jim}$

$\widehat{Jim}\widehat{Jim^{\dagger}}$ - The Jim giveth and The Jim taketh away

$\jmath \imath m$

@ACuriousMind Unit speed. Thanks!

is that polite or rude?

Let's write the worst paper for Motl ever made

Let's make a Bohm version of LQG

@Yashas I thought it was fine.

The answerer found it rude :/

@Slereah a globalist Bohmian LQG

How would you make a Bohm LQG

It's like a non-local local theory

@Yashas if anyone finds it rude, here's the appropriate response: "I apologize. I didn't intend for it to be rude. I'll delete the comment. For the record, what I meant was [x]"

@Slereah that's GR

arxiv.org/abs/gr-qc/0005092

help

@BernardoMeurer ^

Oh god

It's in portugese again

what's up with brazil

?

Brazil physicists seem to write in portugese an awful lot

rather than english

Why would they write in English?

International readability

Completely random question but can't find a solution so maybe one of you culinary aware people know:

Is 'crispy' seaweed bad for you in terms of iodine?

There aren't many actual reliable sources, but a family member is doing a fad diet and might end up, if it is, damaging their health or whatever

just tell him to not do a meme diet, you idiot

and stop eating so much

@Slereah Be nice, please.

that is the solution, I'm afraid

@0celouvsky I wouldn't have known that anyway :P

100% efficient

@EmilioPisanty nope, I didnt review that one in the LQ queue

I reviewed it in the LA queue

Well yeah, fad diets are dumb

but this person is a bit too far gone to be convinced with that

Tie him up and control his food intake

@AccidentalFourierTransform You reviewed it in the La queue, though - what did you do? (You didn't flag it)

and @blue thanks but I'm not sure about the actual iodine content of the seaweed. Is there actually a test I can do for iodine?

A quantitative

@blue that doesn't work for cigarettes or masturbation

@blue Bored of eating?! I'm not trying to make anyone anorexic : P

the same goes for eating

it was already flagged by EP

I guess I should have flagged it as well

Ah, I forgot that voting counts as "reviewed", too

even voting a comment counts

in my case, DV'd and UV'd E's comment

you can go blind

[upside down question mark]

@AccidentalFourierTransform Moar flags never hurt, and you should have 100 of them, so you needn't be thrifty with them

maybe an extra flag could have been fine

@ACuriousMind yeah, I guess so

No big deal in this case, though, wouldn't have really changed anything about the chain of eventd

@blue Have you solved it already or do you want me to walkthrough you along a proof?

if E hadnt commented, I would have flagged it

but yeah, an extra flag never hurts

Well, I could find a way to liquify it I guess but it's more about if there's stuff that's available domestically to test quantitatively for iodine

Do they not have iodinized salt in India or does the diet prescribe no salt?

Then I don't get what the problem with iodine is supposed to be

It's bad for the thyroid too

too much anything is bad

high levels correspond to greater risk of thyroid cancer

and no iodine is just as bad as too much iodine

@blue OK. Here's a definition of limit I find very useful, other than just handwaving and mumbling about "get closer and closer". Say $f$ is a function $\Bbb R \to \Bbb R$; $\lim_{x \to a} f(x) = b$ if for every sequence $x_n$ of reals converging to $a$, $f(x_n)$ converges to $b$.

yeah but a serving of unprocessed seaweed is like 1000% your RDI

Im trying to ascertain whether the seaweed they'd use is prepared in a way so to lower the Iodine content

Can you use that definition to conclude anything about the problem?

@BalarkaSen Does he know what $x_n\to a$ means without handwaving and mumbling?

@0celouvsky I don't expect him to. This "definition" is a compromise between total handwaving and total rigor. If he wants I can explain what it means to him.

I don't see any mathematical logic when people say something more than 100 percent. Like I am 101 percent sure tomorrow is no school ....

It means $$\forall \varepsilon > 0, \exists N, \forall n > N, |x_n - a| < \varepsilon$$

Symbol salad is unhelpful.

It's delicious, though

It is best

@Fawad What? You can easily have 1000% of something, it just depends on what the "something" is as to whether it's valid

Symbol salad with quantor dressing, excellent choice

I didn't even define real numbers as Dedekind cuts here!

For instance, 1000% greater than A

@blue Let's do it with something easier. Say $f(x) = 1$ for $x = 0$ and $f(x) = 0$ otherwise.

10 is 200% of 5

just to clarify, the graph is a "peak" at $0$ and zero everywhere.

peak of height 1

consider $\infty f(x)$, the delta function

the best function

@blue So I am going to prove that $f$ is not continuous at $0$. To do this, we have to prove $\lim_{x \to 0} f(x) \neq f(0)$, agree?

Pick $x_n=1/n$.

@Phase you read my example? If you are 100 percent sure, then why can't you be 101 percent sure to show confidence? ;)

Then $f(x_n)=0$, but $\lim_{n\to\infty}f(x_n)=0\ne 1$. Done.

It's always $1/n$

@Fawad your example is an example of something that doesn't make sense, but your statement on it's own suggests that you can't have any percent > 100

@blue 0celo gave a proof of $\lim_{x \to 0} f(x) \neq f(0)$, do you understand that?

So you need to check if $\lim_{x\to 0} x+1 \neq \lim_{x\to 0} x+2$ ?

A sequence, rather.

0celo picked the sequence $1, 1/2, 1/3, ...$

Which converges to $0$

but $f(1), f(1/2), f(1/3), \cdots$

which is the same as $0, 0, 0, \cdots, 0$

converges to $0$

So as $x_n \to 0$, $f(x_n) \to 0$

But $f(0) = 1$ (by definition), so $f(x_n) \not \to f(0)$

Let's try a little harder. $f(x) = 0$ for $x < 0$ and $f(x) = 1$ for $x \geq 0$. The graph is a cliff of height 1 to the right of $0$. Can you prove $f$ is not continuous at $0$? Does $\lim_{x \to 0} f(x)$ even exist?

Using the sequence definition of limit I gave you, that is.