The h Bar

0celo7

00:31

@ACuriousMind went to a German/Turkish restaurant with my parents, had Doner

oh god it was good

Nick Alexeev

As a result of cross-posting and subsequent migration, Physics.SE has ended up with a pair of duplicates: this and this.

dmckee

02:07

@0celo7 Well, none officially condoned or admitted to, anyway.

0celo7

02:28

@dmckee of course :)

0celo7

02:48

"Radical Redemption - The One Man Army (2015)" OFFICIAL TRAILER

►

GET HYPED

John Rennie

08:15

Know anyone like this? :-)

76

Q: What to do when your student is convinced that he will be the next Einstein?

As an advisor, I found it to be a detrimental motive for a student to be merely the surpassing of Einstein in achievement, for many reasons. He has busied himself with the deconstruction of relativity and strives to break it down and replace it with a much better system and not only that, he's at...

Slereah

@JohnRennie this

Or alternatively

Secret

I sometimes act like this: Thinking that I have solved some very complicated problem and then excitedly start telling my friends and professors about it to cross check, only to realise that I have overlook this, forgot that and did those wrong, and then I am back to the drawing board

Being fully aware of the consequence to my future if I am being cranked, I tend to rely on other people to check whether any of my "potential pet theory candidate" is actually sensible or not.

I then take their advice and then either fixing the problem, or if the problem turned out to be impossible, hopped to…

Secret

08:31

In short: I have a lot of "potentially pet theory" ideas going on in my mind, but to prevent me from falling into crankery, I always check with someone more reputable to ensure I am on the right track of thinking

(Especially the physics community are extremely allergic to cranks)

Secret

This is one reason why I tend to ask a lot of questions:
With each question comes a better understanding, and with each better understanding, another pet theory inside my mind get shot down

If there's a pet theory that fit experiments, and was not being shot down after cross checking with others in the scientific community, it might suggest it is worth considering.

But we expect that to happen almost nelgicibly

My dad sometimes said I have the potential to be a very dangerous crank if I cannot handle my thought process carefully

Slereah

09:43

mth.kcl.ac.uk/~streater/lostcauses.html

:D

Secret

10:18

@slereah I'll keep an eye on that, thanks

Secret

11:15

Random:
https://twitter.com/newscientist/status/652461464691810304

Danu

12:40

@Slereah This must hurt for many people, including some that visit this chat :P

skill patrol

@Secret you should listen to him...father knows best :-)

Secret

I used to be a strong suporter of MWI, but it seems too flexible to be falsified, thus I start to shift to somewhere else

This shift is also followed by a dampening (but still strong) interest in string theory and one reason I prefer to work with back to the future style time travel models when I write scifi

Because parallel timelines is jst too handwavy to be falsifiable even in a scifi context

Slereah

12:56

@Danu Well it's not exactly "You shouldn't study these topics"

It's more "These topics are quite thorny and have been well research, approach with caution'

Danu

@Slereah It kind of is.

Physics Meta

0

Q: Answering homework questions that will be closed

Sometimes I come across a homework question, like this one Terminal velocity of a sky-diver that is of little value to our collection, as any answer is only of interest and benefit to the original poster (OP). I know the question will be closed. If I think the OP really wants to learn, howeve...

discussion homework

Danu

lost causes

Slereah

Like if you are a student looking for a PhD, maybe avoid it

Danu

I think it leaves no room for interpretation :P

Slereah

12:57

@Danu : "This page contains some remarks about research topics in physics which seem to me not to be suitable for students."

Danu

lost causes :P

Slereah

Well yes, but then

Everything that comes after the title :p

mth.kcl.ac.uk/~streater/causes.html

:D

0celo7

13:21

@JohnRennie I'd be happy with getting rid of this quantum nonsense the world seems to have accepted. Einstein was alright.

Secret

Something that often intruigue me is that why basically a euclidian norm version of probability and linearity works so well in describing quanutm phenomenon

That is, why the math works

I had a feeling that quanutm gravity will be more quanutm than general relativity, I think general relativity has to give way to quantum because of all that infromation problems with black holes

and as far we know, there isn't really anything that challenge QED

0celo7

@ACuriousMind Is the operator $L_A$ on page 208 just the directional derivative along $\vec A$?

(I mean, he pretty much calls it that, just making sure.)

Danu

@0celo7 Looks more like a Lie derivative.

Slereah

L is usually Lie yes

or £

Danu

(which, on functions, coincides with the directional one, IIRC)

@Slereah Lol wat

$\mathcal L$ maybe

not the symbol for the pound :P

Slereah

13:29

I have seen £ used

Danu

where?

Slereah

I forget

0celo7

@Danu Exactly.

@Danu Wald.

See Appendix C of Wald.

It's also in his BH thermo book.

Can't think of anything else.

Danu

That's terrible.

0celo7

no u

BLT uses the pound symbol without the bar IIRC

Danu

13:38

@0celo7 That's called $\mathcal L$

0celo7

It looks different.

Danu

(and it's pretty standard for the Lie derivative, AFAIK)

0celo7

He doesn't use straight LaTeX.

But it is pretty close.

In any case, the pound symbol exists and I'm surprised you haven't seen it before.

Danu

@0celo7 Of course I know it---just not for a Lie derivative...

0celo7

*exists as a notation for the Lie derivative

so I take it you don't like that notation

you're a notationist

Slereah

13:46

Pound symbol makes sense for people who wrote papers before LaTeX was widepread,really

Danu

Papers before LaTeX make no sense ;D

2

Slereah

Then don't read any 60's paper

Ever read a paper with equations written on a typewriter?

It is not fun

Secret

Recently I was discussing with another collaborator about the background setting of our scifi, I then drew him this picture to explain my suggestions:
I am waiting for his reply tmr

(PS please ignore the words, hyperbulk and VERSE, because they are just a fancy way of saying "Our fictional universe is not reality, but is treated more or less in the same way")

Slereah

please

If you make diagrams

Use more sophisticated tools

Use a tool text

Danu

tex them lol

Slereah

13:56

And a tool to draw Bezier curves

Or lines

I wouldn't use TeX to make diagrams

I did for my thesis it wasn't fun

Danu

It's glorious

you have to invest some time initially

but eventually it's always worth it

Secret

you have any better suggestion than adobe illlustrator for the beizer curves, because thinking about a subscription paywall is just not my thing?

Danu

plus TikZ really isn't that hard

Slereah

there's a neat library to make Feynman diagrams

it's not hard but it's tedious

Danu

@Slereah Of course, feynmp is great.

Slereah

13:57

quite so

Hm

Danu

@Secret tex

I'm not even kidding

Slereah

I wonder if there's a tool for specifically conformal diagrams

Or you can use Gimp

Or Paint really

Paint has a text tool and can make lines

it would be an improvement

Secret

which paint, probably not the windows one?

Slereah

The windows one would be better than drawing diagrams free hand

Although get Gimp

It's free and it has a lot of tools

0celo7

@Slereah stop carping on those

Slereah

14:02

BUT I HATE THEM SO MUCH

0celo7

god

just chill

wonder if I should get the GSW anniversary collection

>implying I have the time to read more books

Danu

@0celo7 I think they're pretty outdated.

0celo7

I'm convinced it is impossible to learn string theory from books

the coverage of the bosonic string is decent

but it all falls apart after the basic R-NS superstring stuff

0celo7

14:22

@Danu on second thought, mind wiping that Pulp fiction post. The thumbnail isn't good

@Slereah you should type up your thesis in English on a typewriter

Make it easier to read

Ghost

14:39

LMAO

Unexplained or unfair downvotes are obviously hostility. — peterh 4 mins ago

0celo7

14:52

what is the conformal bootstrap, anyway

I imagine a poor string theorist pulling himself out of poverty by his conformal bootstraps.

Slereah

that is how you launch the universe's OS

0celo7

what?

Danu

@0celo7 I don't think it's a problem. Do you insist on removing it?

Slereah

15:10

@0celo7 : the joke is that the bootstrap is what launches when you turn your PC on

Danu

Conformal bootstrap

The conformal bootstrap is a non-perturbative method to constrain and solve conformal field theories. Unlike more traditional techniques of quantum field theory, conformal bootstrap does not use the Lagrangian of the theory. Instead, it operates with the general axiomatic parameters, such as the scaling dimensions of the local operators and their operator product expansion coefficients. A key axiom is that the product of local operators must be expressible as a sum over local operators (thus turning the product into an algebra); the sum must have a non-zero radius of convergence. The main ideas...

Slereah

Hm

That remind mer

I wanted to edit the wiki page on Misner space

Because it is shit

Misner space

Misner space is an abstract mathematical spacetime, discovered by Charles Misner of the University of Maryland. It is also known as the Lorentzian orbifold . An intuitive analogy may be drawn with a video game screen, where a screen element exits the frame through the right side, only to re-enter the frame right away through the left side. Moving the spatial limits (e.g.: the walls of a room) enclosing an existing Misner space in the physical world, could theoretically lead to time travel. == References == M. Berkooz, B. Pioline, M. Rozali. Closed Strings in Misner Space: Cosmological Production...

Look at this bullshit

John Duffield

@ArtOfCode : "If JD wants to talk about the details of his suspension when he returns, he's free to do so". Yes I would. @David Z : please advise on a suitable location.

Meanwhile, who wants to talk physics? Or maybe cosmology?

0celo7

15:32

@Danu Please.

I've had a 30 min suspension for the f word...I'm trying not to take chances

Especially when a certain somebody is around.

Danu

@0celo7 Done. Next time, you can simply flag your own message and say that you want it deleted.

0celo7

I was on mobile when it occurred to me

@JohnDuffield You were suspended? Why and for how long?

John Duffield

@0celo7 : we don't talk about moderation unless invited to do so.

@0celo7 : as for what I was up to the other day, I was chatting in "another place".

0celo7

@JohnDuffield Wrong, you can discuss your own suspension, as long as there is no speculation.

user12262

16:34

There is a formatting problem with the comments to question PSE/q/213091:
http://physics.stackexchange.com/questions/213091/time-dilation-and-reference-frame-in-an-orbiting-context
that's due to the bad formatting of the second comment, which I submitted there (as my first comment there).

Unfortunately I'm unable to delete this comment of mine, because this formatting problem prevents me from clicking on the appropriate `delete (cross)` field.

Would someone knowledgeable and/or reputable enough please delete this one badly formatted comment of mine? Thanks.

ACuriousMind

17:53

@user12262 I think you should just flag it (the flag icon is still clickable because it is on the left side of the comment) and let a moderator clean that up.

Idle wondering: Did more users start reviewing regularly, or is there just less stuff in the review queue than e.g. a month ago when it was always at ~60 pending flags?

Danu

18:17

@user12262 I already flagged it for you.

@ACuriousMind A lot less, somehow... I've noticed it too.

I'm doing less reviewing, actually.

Hmm... Is proving that the Peano curve is surjective quite complicated, or did I make a major detour in my proof (~3 paragrahs long...)? I wonder...

user12262

18:36

@ACuriousMind @ACuriousMind: "I think you should just flag it (the flag icon is still clickable because it is on the left side of the comment) and let a moderator clean that up." -- Thanks, interesting proposal. You're right in that typically there's a flag icon is on the left side comments. But remarkably not on that one unfortunately misformatted comment. Which is still present btw., now being the first. (Did you even take a look at the problem before replying? ....&)

Danu

@user12262 I did manage to flag it.

Also, the obvious alternative, if you don't manage to flag the right message, is to flag a "nearby" message and explain the situation in the custom flag box.

user12262

@Danu @Danu: "I already flagged it for you."; "I did manage to flag it." -- I notice that there's one comment gone, and the problematic comment is still there, now in first place. ....

Danu

@user12262 I flagged the one with formatting issues, IIRC.

And yes, it is gone for me now. The remaining comments have no issues on my screen.

Also you're double-replying to people. Just clicking "reply" is enough---no need to additionally type the name.

ArtOfCode

19:13

@JohnDuffield I was referring to talking about it in here with your fellows. However, if you want to contest it, I can create a private chatroom including myself, you, and another moderator.

dmckee

@ArtOfCode David Z. Is traveling this weekend and likely won't be available for such a chat. Qmechanic is also going to be in spotty touch.

ArtOfCode

@dmckee Is that the sound of you dumping this one on your own doorstep?

dmckee

I've been trying to figure out how to duck it, but my options seem pretty sparse...

3

ArtOfCode

'Fraid so.

Danu

19:44

@dmckee You can always dump it on [the ever-present ;)] Manish

0celo7

19:55

@dmckee such is the price of tyranny :)

dmckee

@0celo7 Uneasy sleeps the crowned head.

5

0celo7

@ACuriousMind read any string theory lately?

Danu

Ben Crowell seems to have become quite active on History of Science and Mathematics lately :D

ACuriousMind

@0celo7 Nope

0celo7

@dmckee does Qmechanic sleep?

Danu

19:57

I wish more Physics users would've contributing...

@dmckee That's why you take it off in bed ;)

Too pointy for the missus anyways

ArtOfCode

well then

dmckee

@Danu You have such a strong core group over there and most physicists have such a weak grasp of the details of the history of our field (as opposed to the mythology) that most of us would embarrass ourselves.

2

Danu

@dmckee The strong core group is tiny though :(

@dmckee And who said the mythology isn't important?

Just today, I was about to ask a question about the famous "Dirac found his equation by taking the square root of the Klein-Gordon equation".

Don't forget, it's not just about answering ;)

ACuriousMind

BTW, I notice that the book recommendation meta thread is no longer featured. Should I accept the top voted answer?

Danu

@ACuriousMind Featuring is just a 2-week thing by default.

ArtOfCode

20:03

@Danu * 4-week

ACuriousMind

@Danu That's not an answer to my question ;)

Danu

@ArtOfCode Woops

@ACuriousMind It just suggests that the non-featured part isn't really on purpose

hwlau

how important is it to know the history of physics

ACuriousMind

@Danu Yeah, okay. Still, should I accept the top voted answer now that voting and answering activity has died down?

Danu

@hwlau To me, it's quite important.

It creeps into everything---even simple things such as explaining the terminology for many things often forces one to dig into the history.

But it's mostly just interesting and awesome.

dmckee

20:07

@hwlau It is not required to be able to use physics well, but it is probably helpful to being able to do physics. BEcause it gives perspective on the many routes to discovery.

A lot of times history is like that. The real lessons are ones of perspective.

hwlau

@Danu I agree. But is it really helpful for me to discover new stuffs by knowing the history

I rarely care, maybe I am wrong

Danu

@hwlau It's hard to tell. I certainly think that there have been instances where "old approaches" suddenly turned out to be relevant in a different area a long time after they'd been abandoned in their original context.

@tpg2114 Nice questions; we need more of those :D

0

Q: Was Dirac really trying to take the square root of the Klein-Gordon equation?

As a student of physics one will, on several occasions, indubitably hear professors or other physicists (here is an example, from Physics.SE's highest-rep user John Rennie) tell the famous story that Paul Dirac came upon his relativistic wave equation for the electron, now called the Dirac equati...

biographical-details theoretical-physics quantum-mechanics debunking

@ACuriousMind Depends on whether you think it's acceptable ;)

^^ Any takers?

tpg2114

20:37

@Danu Thanks! Now hopefully somebody will come along to answer them! I'll probably put up some bounties in a week or two if nothing happens before then.

user54412

@tpg2114 I've been pondering your latest question for the past hour. I'm ashamed to admit I can't come up with a good answer off the top of my head.

tpg2114

@ChrisWhite I'm worried I am totally misusing/abusing the Lorentz factor and that's why I don't understand it. My knowledge of relativity is entirely from my AP physics class 11 years ago, so I know essentially nothing other than length contraction and time dilation are a thing

user54412

They are a thing, yes ;)

user54412

I want to argue that all that really matters is the Eulerian frame though -- what the fluid thinks of itself shouldn't matter.

Danu

@tpg2114 I just rederived the Lorentz transformations for myself yesterday, too, hah.

user54412

20:41

But I'm not convinced of my own intuition.

tpg2114

@ChrisWhite But wouldn't length contraction imply that if I took a picture of the fluid, what looks like 1m to me could really be 10m?

So any spatial correlations I take from my photo wouldn't be right

user54412

what does "really" mean?

Danu

RELATIVITYYYYYY

user54412

sure, in its rest frame things might have different values, but in Newtonian physics a fluid's velocity is also different in its rest frame from the lab frame

Danu

(sorry, please continue)

tpg2114

20:43

The eddy in the fluid thinks it's 10m long but I think it's 1m long. And the eddy right next door that's going much slower also look like it's 1m to me, but it think it is 1m also

user54412

what matters is consistency, and not comparing lengths in one frame to times in another

user54412

@tpg2114 But yeah, you're getting at something important. Fundamentally, the fluid parcels interact locally with their neighbors, so things better make sense in the fluid's frame.

user54412

Here's a warmup question (for myself too): Let's take a turbulent fluid with $k^{-5/3}$ spectrum. Now let's boost to a new lab frame with Lorentz factor $\gamma$. Does the spectrum change slope?

tpg2114

If we pretended that turbulence was a finite sum of sine waves for example, we could have Asin(w_1t) + Bsin(w_2t). And if A is close to the speed of light and B is small, then the frequencies in one frame are different from another, and in one frame they may be identical (and thus change the spectrum)

@ChrisWhite But how do you take an FFT of a signal that contains velocity-dependent measures of time? Maybe it's more basic than turbulence

The amplitude of the sine wave is independent of \gamma, just by dimensional analysis because it is a length/time

But the argument of the sine wave is modified, because it's really A sin(w t') = A sin(w \gamma(t-Ax/c^2))

So the frequency is modified by \gamma, and there's also a phase-shift

Or something... I really have no idea what I'm talking about and I'm sure I am abusing these ideas

tpg2114

21:04

@ChrisWhite Another thought... we compute a structure function of turbulence, which is <du(r)^2> where du(r) = u(x+r) - u(x). In a relativistic setting, what is x and r? What frame are they based in? Are they also functions of u somehow?

Wait... and what role does relativistic mass play in all this. A fast eddy is also a heavy eddy

Oh, and back to the Eulerian frame thing -- we could compute Lagrangian statistics too (autocorrelations, shape of Lagrangian triads, etc). How the heck would those behave in relativistic turbulence.

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