The h Bar

9:00 AM

@JohnRennie Hello sir, do you have some insight on this ?

0

Q: Why don't we feel accelerated when the Sun flings the Earth, when it is too close to it?

I was pondering throughout the whole night thinking why don't we feel the push of the Sun when the Earth comes too close to it. The Newtons Law says that when we are moving with the uniform velocity, we seldom experience its motion, however when the velocity changes, we accelerate hence we feel...

ACuriousMind

@Rumplestillskin no, because I don't have any particular interest in that approximation myself ;)

John Rennie

@DhirajDhakal that has already been answered. Hang on - I'll do a quick search ...

Secret

post newtonian approximation is MOND stuff, right?

user84215

@JohnRennie You mean chat physics session events?

ACuriousMind

There are many topics where interest is low, but that is not necessarily a bad thing but simply a reflection of reality

John Rennie

9:01 AM

@MathematicsAminPhysics no, I mean we help people with physics all the time as a routine part of what the chat room does.

@DhirajDhakal Here:

34

Q: Why don't we feel the subtle speed change of Earth's elliptical orbit?

Earth's orbit is a slight ellipse, so to conserve momentum its speed increases when it is closest to the Sun. If the speed changes there is an acceleration. If there is an acceleration there is a force. Even if the change is small and gradual, wouldn't we experience a force because the Earth is s...

newtonian-mechanics newtonian-gravity angular-momentum orbital-motion earth

Rumplestillskin

Modified Newtonian? No it's approximate solutions to the field equations of GR. first order approximation can look after most of the relativistic correction needs of the geodesy communities and higher order approximations can be used to study coalescing black holes. @Secret

Secret

Ah I see

It seemed as if perturbation theory is applied to the metric tensor

user84215

@ACuriousMind @JohnRennie Devoting a specific room only for doing workshops in physics is a bad idea?

Rumplestillskin

It's actually quite involved and the reason I asked is because I have been trying to get in to it as of late and doing a terrible job @Secret

John Rennie

@MathematicsAminPhysics It's a good idea for this room to be the first place to look for help with physics. If people want to take a prolonged discussion off to separate rooms then we usually create a room specifically for that purpose. This already happens all the time.

Dhiraj Dhakal

9:06 AM

@JohnRennie : Thank you sir :)

John Rennie

@MathematicsAminPhysics: to be clear, I'm not saying there's anything wrong with your idea. It's just that we already do it.

user84215

@JohnRennie I think a workshop is different from only a discussion, isn't it?

Rumplestillskin

@ACuriousMind it is interesting that interest in the subject is low. I feel it is currently the only way researchers can truly model astrophysical situations in a relativistic framework that are not necessarily heavily endowed with symmetry properties BUT it seems to be laden with a clique of experts with little room to manoeuvre for petty commoners like myself.

ACuriousMind

@MathematicsAminPhysics I have already said that I do not understand what such a "workshop", lacking the real-world component of being close to the other participants all day, would do differently than what just talking about physics in here already does. Until you clarify that I refuse to even make the judgement of it being a good or bad idea and am not interested in discussing this further.

@Rumplestillskin To my eyes, pretty much every research field in physics is filled with experts with little room for commoners! That's how specialisation works.

Emilio Pisanty

sigh

John Rennie

9:10 AM

@MathematicsAminPhysics if a group of students want to have a workshop with one of the more experienced members of the site they just have to ask here. But it's up to those students to get together and ask.

Secret

I wonder if post newtonian approximation play well with QFT, but again I don't have enough QFT to comment, thus I am going to leave it here

Emilio Pisanty

@JohnRennie thanks for your help with that one

Rumplestillskin

@ACuriousMind Well this is true and a good point.

I know absolutely nothing about QFT so I can't even begin to comment @Secret

Emilio Pisanty

@MathematicsAminPhysics Out of curiosity, have you ever attended an in-person physics workshop?

John Rennie

@EmilioPisanty: I have to say I find this sort of thing more dispiriting. It's the complete unwillingness to listen to anything that doesn't already fit their own views.

user84215

9:13 AM

@EmilioPisanty No.

Emilio Pisanty

@JohnRennie I guess it's just that I'm tired of non-answers to that question.

That one makes six.

I'd protect it, but only one of the six would've been stopped by protection.

John Rennie

@EmilioPisanty Oh yes :-)

Emilio Pisanty

@MathematicsAminPhysics That partly explains why you think an online chat event is any sort of substitute for an in-the-flesh meeting.

ACuriousMind

@Secret for that to be a well-defined question, you need to say what you mean by "playing well", given that the problem is renormalizability, and not some sort of obvious inconsistency

Emilio Pisanty

May I suggest that you actually go to a real-world workshop before pursuing this line further?

I mean, just as a suggestion.

It may help clarify in what ways workshops help people learn, and what aspects of that can be replicated in an online setting.

Secret

9:17 AM

@ACuriousMind Yeah, if I very vaguely remember, the issue of naively trying to combine GR with QFT is that something mass term something blow up to infinity in the perturbative expansion something, which is why gravity cannot be renormalised under this naive combination of the two. The number of "somethings" in the sentence is why I cannot comment further

Emilio Pisanty

As others have already told you, a majority of real-world workshop attendees is likely to tell you that the answer to that last question is "cripplingly few"

but it may be better if you see that for yourself.

Secret

However, I am not sure if approximating the metric tensor by something akin to a power series will keep those mass terms from diverging

John Rennie

@EmilioPisanty: to be fair I suspect the two of you may have different definitions of workshop

skullpatrol

::makes popcorn::

Emilio Pisanty

@JohnRennie I rather suspect MathematicsAminPhysics is operating under two concurrent but divergent definitions of the term. One which other people say is really good, and the other which they want to implement.

user84215

9:19 AM

@EmilioPisanty Thanks for your suggestion. Yes, I also think our definitions are not the same.

John Rennie

If I understand MAP correctly what he has in mind is more like a tutorial than a workshop.

(I assume we all agree what tutorial means :-)

Emilio Pisanty

@JohnRennie If that's the case, I would suggest changing the term from "workshop" to "tutorial".

but then maybe that's just me.

user84215

I think we should define workshop.

Secret

It obviously does not sound like workshop to me, as for us aussies, workshop often means a whole day event with a lot of interactivity

skullpatrol

I second that idea. Btw anybody want some popcorn?

:-)

Secret

9:22 AM

Without sophisticated VR stuff, I doubt one can organise a workshop online

user84215

According to Google, workshop is a a meeting at which a group of people engage in intensive discussion and activity on a particular subject or project.

Secret

but tutorials, it is possible and has been done before in some form (not sure for SE)

Anyway, I am heading for the train, will come back later

skullpatrol

Cya pal.

(You can take some popcorn to go :)

Emilio Pisanty

@MathematicsAminPhysics If that's what you want it to mean, go ahead. However, if you want to draw support from anybody that says that IRL workshops are really good, then you can't use the term to mean online workshops.

skullpatrol

Did you read about Chavez's brother? @EmilioPisanty

user84215

9:28 AM

We can convert impossibilities to possibilities, if we want.

John Rennie

@EmilioPisanty: this paper says: Thus, complete analytical solutions of the eigenstates of H2+, in areas of molecular interest, such as e.g. the region near the equilibrium internuclear distance (bond length) of the ground state remain elusive.

That looks like a no to me.

Emilio Pisanty

> If the answer to this is negative, then that's probably a very tall order to prove, since statements of the kind "there is no result of that type in the literature" are inherently hard to tie down. In that case, though, I will settle for a thorough exploration of the literature pointed at by the Wikipedia claim, and an explanation of what it does and does not provide.

Balarka Sen

@ACuriousMind @JohnRennie If I want to learn gauge theory in physics, what's the best way to go about that? I suspect I should learn Maxwell's theory of electromagnetism. I appreciate gauge theory (at least what I know about it, which is embarrassingly little) from a mathematical point of view, so I'd like a mathematically motivated excursion if possible

John Rennie

@BalarkaSen I suspect that when most physicists say gauge theory they mean a local gauge theory, which is a very different beast to classical electrodynamics.

skullpatrol

Finish high school first.

Balarka Sen

9:42 AM

@skullpatrol Stop trolling first.

John Rennie

Weren't you going to look into classical electrodynamics anyway? Or am I thinking of someone else.

ACuriousMind

@BalarkaSen I think Jose Figueroa-O'Farrill (hope I spelt that right) has some excellent papers on that at different levels. Maybe look at his gauge theory notes and/or electromagnetic duality for children

Balarka Sen

@JohnRennie Yeah I want to read classical electrodynamics at some point soon.

John Rennie

@BalarkaSen you'll breeze through classical EM. It really isn't hard.

ACuriousMind

@skullpatrol Please don't be so patronising, ocelot is a prime example that high school is not a prerequisite to learn advanced physics.

John Rennie

9:45 AM

@BalarkaSen: even if you want to learn it in its covariant formulation that still isn't hard by your standards (though it is by mine :-)

Balarka Sen

@ACuriousMind Thanks, I'll have a look!

ACuriousMind

@JohnRennie Hm? EM is the archetypal example of a free gauge theory of Yang-Mills type, albeit one that lacks the features of the non-American ones, obviously. Adding "local" to gauge is superfluous, there's no such thing as a purely global gauge theory.

skullpatrol

Note: I did not @ tag him and he can ignore my advice if he wants.

Mithrandir24601

@ACuriousMind Imagine how much better it would have been if they actually taught us actual physics...

skullpatrol

We are pals and I said nothing offensive.

ACuriousMind

9:52 AM

@Mithrandir24601 I liked school, and think I was taught actual physics, mostly (except for the few nonsense bits about QM)

Emilio Pisanty

@ACuriousMind what's an "American" gauge theory?

Mithrandir24601

@ACuriousMind Really? Wow, I wish we had that - the only actual physics we were taught (except, I suppose, classical gravity and that electromagnetism is a thing) was taught outside the curriculum :/ Although we did have good teachers :)

I enjoyed school once I got into the later (A level) years, but before that, it mostly felt like a bit of a waste of time :/

skullpatrol

Did you go to a public school?

Balarka Sen

@ACuriousMind lol. "Electromagnetic Duality for Children" doesn't seem to have anything remotely childish about it.

Mithrandir24601

@skullpatrol Here (in the UK) a 'public school' is a (usually extremely expensive) fee-paying school, so I'm not sure if that's what you mean or not - I went to what's called a grammar school

Balarka Sen

10:07 AM

I like the gauge theory notes at first glance though. Looks really good.

Mithrandir24601

I suppose part of the problem was that one of my friends in primary school was absurdly bright for his age, so there was always that "look at [friend] - he's doing so much better - could you do that?" (it wasn't competitive, just something to aim towards and try for) happening there, which suddenly went away at secondary school, so I had no real goals until A-level (though I didn't realise this was happening at the time)

ACuriousMind

@EmilioPisanty Autocorrect, I am on my tablet. If I had to guess I'd say that an American gauge theory values its asymptotic freedom above all else :P

Emilio Pisanty

@ACuriousMind what's an Autocorrect gauge theory, then?

ACuriousMind

@BalarkaSen Heh, yes - Figueroa has certainly met strange children. I really like his writing style, though

skullpatrol

Sounds like you went to school with Hawking @Mithrandir24601 :-)

I really like the scene from A Brief History of Time where they are working on the physics problem set...

ACuriousMind

10:16 AM

@Mithrandir24601 I was always top of the class with little effort, but I don't enjoy competitiveness or the idea that I should worry about wasting my time - I liked school for being a place where one could socialise and occasionally learn stuff ;)

@EmilioPisanty An elusive type of theory that autocorrects all constants to be exactly right, thus solving the fine tuning problem :P

Emilio Pisanty

@ACuriousMind yeah, that's what it sounds like.

there's probably a Nobel lurking in there for some brave phone to go and get

ACuriousMind

More like a brave phony

Emilio Pisanty

=P

seriously, though

you meant asymptotic, I guess?

I'm in the dark there

ACuriousMind

I meant non-American

Geezer

I meant non-Abelian

Now I remember why I don't like typing physics on this thing :P

Mithrandir24601

@skullpatrol Haha! Nope (although, something I didn't mention for my AMA is that I've met Hawking several times, have a photo with him and Wolpertinger and have had tea in his College office more times than I could count. Another one of my friends is now doing a PhD in his group). Said friend is now studying for a Masters (in law, I think)

skullpatrol

10:20 AM

Can't you shut auto-correct off?

ACuriousMind

@skullpatrol sure, but it's useful in more cases than it is harmful

skullpatrol

@Mithrandir24601 :O

Mithrandir24601

@ACuriousMind I'm not really competitive either, but it took me a few years to find the people that I did get on really well with

Gabriele Citossi

Can the pressure of water on coasts be an add-on on the theory for the movement of continents?

ACuriousMind

I still count some of my school friends among my best friends, we go on vacations together and get together whenever a few of us are back

...in our hometown

skullpatrol

10:25 AM

did you go to the heavy metal concert with them?

Gabriele Citossi

continental drift

skullpatrol

I've never heard of that? @GabrieleCitossi

ACuriousMind

@GabrieleCitossi that might be more of a question for Earth Science

Gabriele Citossi

thanks,i'll go there

skullpatrol

I think that's sorta like asking "does the wind affect the movement of glaciers?"

Emilio Pisanty

10:32 AM

@ACuriousMind =P

thanks

@skullpatrol it does

to a nonzero extent

(no claims about nonnegligibility, though)

Gabriele Citossi

Difference of 1km of deep over 1000m is a lot of pressure

mile

miles

500.000.000.000 Kg vs 2.000.000.000.000Kg

here on 1000meters

so for 1000km you have to multiply both values for 1000

LegionMammal978

10:51 AM

Finally, by digging through some papers from 2011 I was able to find that IUPAC defines 1 a as 3.1556925445·10⁷ s

John Rennie

11:09 AM

@GabrieleCitossi but aren't the continents surrounded by water on all sides?

skullpatrol

Re: Australia

ACuriousMind

@JohnRennie not in the traditional idea of continents, see Europe and Asia, but I get what you're trying to say

skullpatrol

Antarctica is surrounded by ice, right?

Sid

Nah, water.

Antarctica is ice. :P

John Rennie

@skullpatrol A thin layer of ice plus a much deeper layer of water

@Sid that's the Arctic not Antarctica!

skullpatrol

11:20 AM

Anti-artic? :P

and Uncle-tropic

0ßelö7

11:34 AM

Full suit or just a shirt?

skullpatrol

Full suit.

Sid

@0ßelö7 hm?

skullpatrol

...and pick a business tie.

(You're there to sell your idea)

Sid

@0ßelö7 an interview?

12:02 PM

@0ßelö7 Hawaii shirt, shorts and sandals

skullpatrol

and sun glasses, because your future is so bright...

0ßelö7

@ACuriousMind that sounds like something you'd do

ACuriousMind

Nah, I don't wear sandals, and shorts only very rarely

0ßelö7

@ACuriousMind you don't wear short?

You don't wear shorts in 90 degree heat?

ACuriousMind

12:11 PM

At 90 degrees, I'd be dead either way, no? :P

0ßelö7

@ACuriousMind what?

Its 90 here all the time

ACuriousMind

Oh, you're using wrong units

Sid

Eh, Fahrenheit...

skullpatrol

lol

Secret

in Mathematics, 25 mins ago, by Leaky Nun

how did you all find out SE?

skullpatrol

12:28 PM

Too long ago, can't remember.

How about you? @Secret

Secret

(Ongoing in MSE)

skullpatrol

right

It has changed a lot in the last 5 years.

The first couple years were the best, imo.

I remember stumbling upon a secret math overflow society called "Tea."

tea.mathoverflow.net/categories

0ßelö7

12:43 PM

@ACuriousMind I am using Fahrenheit

it's objectively the best unit for human use

ACuriousMind

@skullpatrol That's not a secret society, it was their meta equivalent before the migration to SE 2.0, irrc

0ßelö7

@ACuriousMind why don't you wear shorts

skullpatrol

At the time, I thought it was a secret society.

0ßelö7

@ACuriousMind epistemological crisis: how is spacetime not the aether

ACuriousMind

@0ßelö7 I don't like my legs exposed to the elements :P

@0ßelö7 Depending on your definition of "aether", it may or may not be

I mean, Lorentz aether theory basically does exactly that: Redefine "aether" such that it is consistent with SR

0ßelö7

12:47 PM

@ACuriousMind wat

ACuriousMind

@0ßelö7 I dunno, I just don't like my legs not being fully clothed

On the flip side, I wear almost only T-shirts that leave my forearms uncovered. It's weird

0ßelö7

@ACuriousMind Did you see my question about the complete field?

ACuriousMind

No, I didn't

0ßelö7

Closed field

20 hours ago, by 0ßelö7

@BalarkaSen @ACuriousMind I have a finite-dimensional $k$-algebra $A$, where $k$ is a closed field. Now $S$ is a simple $A$-module. Is $S$ a finite-dimensional vec sp.?

Emilio Pisanty

@rob thanks.

rob

1:00 PM

@EmilioPisanty No worries

skullpatrol

That option should pop-up faster.

Which would make better use of the chat rooms.

ACuriousMind

@0ßelö7 Is the algebra unital?

If so, the answer is yes, otherwise I'm not sure, but in any case I don't see what closedness of the field has got to do with it

rob

@skullpatrol The automatic "many comments" flag is raised if there are more than 20 comments posted in three days. However if you're involved in a comment discussion that's going to a place you don't like, feel free to raise a custom flag to bring it to our attention.

skullpatrol

Do I have to contact the stack team to suggest it be lowered to say 10 comments? @rob

rob

@skullpatrol You could propose that on the mother meta. There may be previous discussions.

ACuriousMind

1:08 PM

@skullpatrol Sounds like a feature-request for Meta Stack Exchange to me.

@rob Jinx

rob

jinx

double-jinx

pinch, poke, owe me a coke

skullpatrol

Thanks guys @rob @ACuriousMind :-)

0ßelö7

@ACuriousMind No clue about the algebra. Proof?

ACuriousMind

@0ßelö7 If the algebra is unital, then every ideal is a vector space over $k$. Since $S$ is simple and therefore cyclic with generator $s$, it is $A/N$ for $N$ the annihilator of $s$ in $A$, and since $N$ is an ideal, it is a vector space. The quotient of two vector spaces is a vector space, therefore $S= A/N$ is a finite-dimensional vector space.

!a?

0ßelö7

@ACuriousMind It's unital as a ring

@ACuriousMind idk man

ACuriousMind

1:12 PM

@0ßelö7 Yes, then my proof works

0ßelö7

somehow tab sends messages sometimes

ACuriousMind

No idea where "closed" is supposed to come in

0ßelö7

@ACuriousMind every ideal of what is a vector space?

of the algebra?

ACuriousMind

@0ßelö7 Every ideal of $A$

0ßelö7

"since $S$ is simple and therefore cyclic"

how am I supposed to know that

what is the annihilator of $s$

and where does the unit come in?

ACuriousMind

1:14 PM

@0ßelö7 By definition of simplicity, every non-zero submodule of $S$ is all of $S$, therefore pick any non-zero element $s$ - the module it generates must be $S$

@0ßelö7 The set of all $a\in A$ such that $as = 0$.

@0ßelö7 In the claim that $N$ is a vector space. If $A$ were not unital, $N$ being an ideal would not imply it is a vector space

0ßelö7

@ACuriousMind ah, of course

@ACuriousMind hm

@ACuriousMind Ok, I guess I don't know why being an ideal implies it's a vector space

otherwise the proof makes sense

skullpatrol

0

Q: Lowering the number of comments to 10 on questions

Currently, the system suggests a chatroom after 20 comments over 3 days. If this was lowered to 10 comments over 2 days it would make better overall use of the chatrooms, and raise awareness that this option exists.

feature-request

0ßelö7

@ACuriousMind is it because one needs a $-1$?

@ACuriousMind the definition of ideal in an algebra seems to indicate that it's a vector space

nothing about unity

ACuriousMind

1:47 PM

@0ßelö7 Ah, well, but $N$ is only an ideal in the sense of $A$ as a ring, not a vector space, i.e. it fulfills only (1) and (3) there

And as the article says, you need unitality (is that a word?) to get (2) from that

CooperCape

2:00 PM

What's the difference between say $T_{ij}$ and $T^{ij}$? I know that for a vector you have $$v^i = \begin{bmatrix}v_1\\v_2\\v_3 \end{bmatrix}$$ and that $$v_i = \begin{bmatrix}v_1 & v_2 & v_3\end{bmatrix}$$ but what happens with more than one index?

0ßelö7

@ACuriousMind because if it has a unit then the field embeds in the algebra so the ideal is closed under multiplication by the field?

ACuriousMind

@0ßelö7 Precisely

John Rennie

@CooperCape Upper indices are contravariant and lower indicies are covariant

CooperCape

Okay, thanks :)

Is there any relation between $T_{ij}$ and $T^{ij}$? Like matrix transpose etc.? or is it that $T_{ij}e^i\otimes e^j = T^{ij}e_i\otimes e_j$?

ACuriousMind

@CooperCape The latter (which of course only makes sense if you know the relationship between $e^i$ and $e_i$.)

John Rennie

2:11 PM

@CooperCape you use the metric $g_{ij}$ or its inverse $g^{ij}$ to raise and lower indicies.

CooperCape

ahh okay... so we can say that $T_{ab} = g^{ab}T^{ab}$?

ACuriousMind

@CooperCape That can't be simply because the indices are mismatched on both sides of the equation.

CooperCape

have I done a booboo?

ahh I see

so there's a sort of cancelling out thing going on here...

like $T_a = g_{ab}T^b$?

John Rennie

$T_a^b = g_{ak}T^{kb}$
Then use the metric a second time to lower the other index.

CooperCape

oh wow okay...

John Rennie

2:20 PM

Raising and lowering indices

In mathematics and mathematical physics, raising and lowering indices are operations on tensors which change their type. Raising and lowering indices are a form of index manipulation in tensor expressions. == Tensor type == Given a tensor field on a manifold M, in the presence of a nonsingular form on M (such as a Riemannian metric or Minkowski metric), one can raise or lower indices to change a type (a, b) tensor to a (a + 1, b − 1) tensor (raise index) or to a (a − 1, b + 1) tensor (lower index), where the notation (a, b) has been used to denote the tensor order a + b with a upper indices and...

CooperCape

Ahhh thanks a bunch :p

0ßelö7

@ACuriousMind i'm literally melting

it's so fucking hot

89% humidity

Sid

What is the temperature?

0ßelö7

79

I'm in a suit

have to walk uphill both ways

Sid

Only 79?

0ßelö7

2:30 PM

yes

Sid

That's not hot. That's slightly cooler than warm

Hippalectryon

2:46 PM

@JohnRennie Hi, can I ask you a question regarding your comment yesterday on flamed glass ?

John Rennie

@Hippalectryon Yes, of course.

Hippalectryon

@JohnRennie You said that flaming glass made it lower energy. I came across flamed glass in an article that used corona treated glass (which, they say, is a very high energy surface) for their experiments, and then said it could also be performed on (among other surfaces) flamed glass. How does using flamed glass help in this case ? (the end goal was to have a surface with a spreading parameter greater than 0 for water)

John Rennie

Corona treated glass won't be annealed so it will have lots of dangling Si-O- bonds on its surface. In air these will immediately adsorb water and you get a surface covered in Si-OH groups. These hydrogen bond with water so water will spread on this surface i.e. have a low contact angle.

If you heat the surface the silicon atoms will rearrange to eliminate those dangling bonds and form mainly (strained) Si-O-Si bonds. The only polarity comes from the polarity of the Si-O-Si bond, and that isn't very polar.

So an annealed surface won't interact strongly with water and water won't spread on it i.e. the water will have a high contact angle.

Hippalectryon

Wouldn't that imply that the experiments won't work on flamed glass ?

John Rennie

Maybe I have misunderstood what they mean by flamed glass ...

Hippalectryon

2:58 PM

@JohnRennie I don't think so, all the "DIY" videos about the experiments simply heat up glass over a flame then let it cool. (let me find a video)

John Rennie

@Hippalectryon as in flame polishing?

Flame polishing

Flame polishing is a method of polishing a material, usually thermoplastics or glass, by exposing it to a flame or heat. By melting the surface of the material, surface tension smooths the surface out. Operator skill is critical with this method. When done properly, flame plastic polishing produces the clearest finish, especially when polishing acrylic. This method is most applicable to flat external surfaces. Flame polishing is frequently used in acrylic plastic fabrication because of its high speed when compared to abrasive methods. In this application, a torch burning hydrogen and oxygen is...

Hippalectryon

@JohnRennie I'm not sure of technical terms, the paper just says "flaming glass", and the videos (like this one near 0:25) just say to heat glass over a flame. But that description does seem to match the process.

John Rennie

@Hippalectryon Hmm, that's a very light heat treatment. I was imagining something more like flame polishing which actually melts the surface of the glass. I'd have to say I'm not sure exactly what's going on there.

Hippalectryon

@JohnRennie Alright, thanks for your time anyway :-)

John Rennie

@Hippalectryon you could easily try it if you have some microscope slides to hand (I don't)

Hippalectryon

3:09 PM

@JohnRennie Oh, I've already dome some experiments some days ago, but I didn't heat the glass a lot (it wasn't microscope slides and I feared it might break under intense heat), thus the water didn't really spread and the droplets barely moved

I just noticed that at the really end of the video I linked above (near 4:33), the speaker says that heating the glass creates a high energy surface... not sure why though

John Rennie

@Hippalectryon that's pretty much what I'd expect i.e. it doesn't make the water spread

@Hippalectryon I've just listened to that bit of the video and the presenter says "the flame is breaking open bonds on the surface of the slide". If that's true you'd get a surface rich in Si-OH groups and water would spread well on it. I'm just not convinced it's true.

Hippalectryon

@JohnRennie Do you know by any chance a relatively simple experiment that could determine that ? For instance, a chemical that I could put on glass to reveal Si-OH bonds ? (doesn't need to be really precise, I'm just interested in knowing roughly what's going on)

John Rennie

Measuring the contact angle is the usual way of studying the surface. The only trouble is that glass surfaces usually have a layer of organics adsorbed from the environment and you need to clean it very carefully to remove this layer.

I don't know of any simple method to measure the concentration of Si-OH groups.

Hippalectryon

Alright, I'll ask around in my uni's labs :-) thanks a lot

John Rennie

Sorry I can't be of more help ...

Hippalectryon

3:20 PM

I'll tell you if I find anything!

John Rennie

Yes, do ping me here. I'd be interested to know what you discover.

Emilio Pisanty

4:36 PM

@ACuriousMind lolz

I'm not sure what I was expecting

but bloody hell

ACuriousMind

@EmilioPisanty Is that Jon Skeet's graph?

Emilio Pisanty

yes

ACuriousMind

And are you tracking your legendary progress already? :P

Emilio Pisanty

@ACuriousMind I.... maybe?

naive extrapolation puts it at between one and three years from now

ACuriousMind

@EmilioPisanty Good to see gamification has you well in its grip :)

Emilio Pisanty

4:39 PM

@ACuriousMind oh, has had for some time

May 27 at 18:08, by Emilio Pisanty

ACuriousMind

I've never asked - what are the other lines on that graph?

John Rennie

To be fair the daily max is much easier to hit on Stack Overflow because the audience is so much larger. On the PSE you are only likely to hit the limit if a question you've answered gets on the HNQ list.

Speaking of which: really Mr SE? Really?

Emilio Pisanty

@ACuriousMind MMA, Academia, plus some others

stackexchange.com/users/1370104/e-p?tab=reputation

mother meta, then MO

@JohnRennie hey

that wasn't HNQ when I answered

and frankly, there's a steep price to rep-cap days in the sheer number of people up for giving you grief over minor details on answers that ended up as HNQs for whatever reason

ACuriousMind

Yeah, HNQ comments are the flip side of HNQ rep points :P

John Rennie

People can throw sticks and stones if they want. As long as I can run off with the rep points I don't care :-)

Secret

4:55 PM

[Meme video and associated meme inspired thoughts warning]

Why Black Holes Could Delete The Universe – The Information Paradox

►

So..

Under the holographic principle, information is encoded on the event horizon, but is it completely scrambled such that even if we somehow scan the structure of the event horizon, we cannot use that to recover exactly the properties of the original matter that fell into the black hole?

Mithrandir24601

@Secret I disagree with (at least) a couple of things this says and I think there's still debate about how much info is lost in a black hole

John Rennie

Anyone would think there's a lot of us ageing Pink Floyd fans around

Secret

@Mithrandir24601 I am actually ok with the information is lost point of view, but I don't really understand what that really means

ACuriousMind

@Mithrandir24601 My honest interpretation of the state of the art in black hole information is that no one has a goddamn clue :P

Mithrandir24601

@ACuriousMind Sounds about right to my knowledge :P

John Rennie

5:09 PM

Though Hawking conceded the bet with Susskind ...

ACuriousMind

A bunch of very smart people are waving their hands about it but I haven't seen a really foolproof argument for anything

Mithrandir24601

@Secret So the above image destroys all information of the initial state of the q[2] register (note: this was a simulation on IBM)

Secret

Measuring the z component of spin gives you the value 2?

ACuriousMind

@Mithrandir24601 It's not destroyed, just forever inaccessible because it's now encoded in a hopelessly messy environment :P

Mithrandir24601

@Secret If you're looking at the arrows pointing to the bottom (classical) register, those numbers are just the number of the classical bit of the information being stored - so it's storing the result in the 3rd classical bit (it starts at 0)

@ACuriousMind It's not the measurement that's destroying the information, but point taken

ACuriousMind

5:17 PM

The information paradox is about a qualitatively different kind of "destruction" of information

I've never really understood why people seem to think we can actually meaningfully debate it without solving quantum gravity first.

Secret

what does destruction mean exactly, I can imagine it is a nonunitary process, but how...

0ßelö7

@JohnRennie just talked to a math student

I don't think he knew what was going on

Mithrandir24601

Yeah, I'm thinking about it from a computational perspective...

Alex K Chen

How can I do physics simulations like this in python or C ? I guess tkinter isn't sufficient, right ?

Secret

The closet idea I had in mind is its as if there's some process that maps any state to the vacuum state, if that makes sense

Alex K Chen

5:24 PM

(Also, anybody uses vpython for simulation ?)

Secret

Since this map is clearly not invertible, there is no hope of recovering the original state

Alex K Chen

Nobody ?

Mithrandir24601

@Secret Yeah, but as ACM mentioned, you're loosing information to the environment (same as entropy)

rob

@AlexKChen I've used vpython for teaching, but it's more useful as a visualization tool than for serious simulations.

Mithrandir24601

@Secret Anyway, yeah if you want to model it using Hamiltonians, I'll be surprised if they're hermitian :P

rob

5:26 PM

But if you're interested in animating a ball bouncing at the end of a spring, that's basically why vpython was written.

Alex K Chen

@rob Then (check (myphysicslab.com/index-en.html) how do I do serious simulations (like in the link) ? VPython, for some reasons, is way toooo slow in my pc

Secret

So whatever the notion of "destruction of information" is seemed to be something more extreme than mapping everything to one outcome

and for that I have no idea

rob

@AlexKChen Sorry, I wasn't being clear. If you want to make simulations like the ones in the link, vpython is a great tool.

There are plenty of new-programmer mistakes you can make that will make it run glacially --- but you can do that in any language.

Alex K Chen

Are you on a pc with vpython installed now ?

rob

@AlexKChen No, but I will be later today.

@AlexKChen If you have something you'd like me to look at, post a pastebin link or suchlike and I may be able to look at it

Alex K Chen