The h Bar

Emilio Pisanty

00:23

@DanielSank lol

DanielSank

@EmilioPisanty Glad you thought that was funny. I was a little worried you'd think I were trying to insult you.

Emilio Pisanty

no, I just loved the "show your thinking" bit

DanielSank

@EmilioPisanty It's hilarious.

Emilio Pisanty

glad there's at least one taker, then =)

my brain is pretty close to meltdown, that's about the most sophisticated humour I can muster at the moment

I have to turn that ↑ into a literature review

buckets of fun, it's gonna be

DanielSank

Wait, what?

Emilio Pisanty

00:26

and I'm not even done gathering papers

DanielSank

It takes me a week to read a paper.

So you've got what, six months of work there?

Emilio Pisanty

Yeah, I spent a lot of time digesting about maybe 50% of that literature

Some of it is mostly incidental so I don't need to scrutinize it as closely ("these guys also tried to do X but they used approaches Y and Z")

some of it still needs a bit of going through

some of it will get dropped

0celo7

Sequences of sequences, yay

Emilio Pisanty

At the moment I'm just gathering the papers that are relevant from a bunch of different sources

Physics Meta

01:54

-1

Q: Why is it not indicated anywhere how many comments got removed?

Sometimes when reading the comments under a question/answer I get very confused. Then I realise that there are random @someones without that person making a comment before. I mean I get the point why people can delete comments and that is a very useful tool. But why is there not at least an indi...

DanielSank

03:09

PSA: The original paper by Nyquist on thermal noise from resistors (aka black body radiation) is awesome and you should read it.

journals.aps.org/pr/abstract/10.1103/PhysRev.32.110

Secret

04:22

@0celo7 I would have taken the UNSW topology and differential geometry course back in my undergrad had it not clashed with one of my physics major core courses. As I am currently on my way to PhD, perhaps taking any formal course outside my major is going to be impossible thus the only option I have is self study (which I have not started for topology because I am revising my quantum (got a couple more quantum books to read to bring me up to the level of quantum))

John Rennie

05:02

@EmilioPisanty: I strongly recommend Coyote America as it's a highly entertaining read. The Coppinger book is interesting but it isn't well written - it wanders out about and tends to repeat itself.

Q. How does a coyote mate with a wolf?
A. Very carefully!

Slereah

Coyotes are the crazy ones :p

John Rennie

Bonus cool points for anyone who can identify the comic that comes from :-)

Bernard Meurer

05:20

Lol

John Rennie

Volume 4 is definitely my favourite Sabbath album. It hit that sweet spot where they had learned their business but before the drugs destroyed them.

Slereah

@JohnRennie Garfield?

John Rennie

@Slereah No - you have scored zero on the cool scale.

Slereah

Aw

Remember that time Garfield died?

Hilarious!

Bernard Meurer

@JohnRennie I like Paranoid a lot right now

My tastes are very volatile though

Secret

07:02

[scifi idea memo] Consider the vector space $\mathbb{R}^n$ and suppose extra nonzero elements $q$ which has an arbitrary direction, and $c$ which has an arbitrary magnitude being added to this vector space. Check if this new set is still a vector space

Regardless, determine interesting properties of the absorbers $c$ and $q$, if any

David Z

07:17

@Slereah That was weird

John Rennie

That's from the arc Garfield on acid

Secret

[to be asked on mse] Is there exists a mathematical object where the sentence that describe it (sentence as defined in ocw.mit.edu/courses/mathematics/…) has a length of zero

Slereah

07:34

@JohnRennie It was a spooky halloween episode, actually

John Rennie

@Slereah If you're a Garfield fan somewhere in my archive I have scans of all the Garfield strips up to a few years ago. But I guess if you're a arfield fan you already have them :-)

Slereah

Eh

Not really

Garfield is similar to the Simpsons

Ran too long

John Duffield

10:22

@JohnRennie : it's The Adventures of Fat Freddy's Cat #2. See the second sample page.

ACuriousMind

10:59

@JohnRennie @Numrok In the interest of gathering data for the renewal of the homework policy, I'm curious why you thought this question was not homework-like.

svavil

11:15

What do I do if a stack.imgur image in my answer is not loading? Should I reupload it?

ACuriousMind

@svavil What exactly do you mean by "not loading"? Do you have a link to the answer (or the image)?

Numrok

@ACuriousMind 2 reasons: 1. I thought the attempt at the question was done quite carefully. 2. As a result of that I thought it was quite clear what the problem was. While the person was asking "what went wrong" which is probably homework I therefore voted to leave it open since even though the person could not identify it, the underlying problem was conceptual (even though rather easy to resolve).

ACuriousMind

11:44

Oh, hell, one of the plagiarists I once uncovered has just been doing it again.

svavil

@ACuriousMind Yes, the second image in this answer: physics.stackexchange.com/questions/274676/…

ACuriousMind

Or, well, I guess they tried to cite their sources but it seems the concept of clearly marking a "quotation" is too complicated for them...

@svavil Looks perfectly fine to me

svavil

@ACuriousMind OK, then it must be me, 'cause it's not loading for me.

ACuriousMind

Yeah, the problem must be on your end, both pictures load without issues for me

John Rennie

@ACuriousMind I'm afraid this the sort of thing I've babbled on about before. If an OP just wants the answer to a question then that's homework and I'll vote to kill it with fire. But if the OP wants to understand the question, i.e. understand the physics behind the question, then I'll often (not always) vote to leave open.

In my personal experience I've found worked examples to be a very useful way to learn. But sometimes I've found myself stuck and I need someone to show me how it's done. It's not that I just want the answer, I want to learn how to approach problems like this in the future.

ACuriousMind

12:19

@dmckee We do escalate the duration of plagiarism suspensions, right? I'm not going to edit in all those attributions again if I have to do it every week for the repeat offenders.

ACuriousMind

12:32

This user has gotten a bit more crafty too, swapping single words to synonyms, and swapping around the order of sentences, making it harder to find the source

0celo7

I like this guy.

Dedicated to his craft

He's been suspended once?

ACuriousMind

@0celo7 Well, if one actually reads the posts it's somewhat obvious because they a) don't specifically address the question at hand but just present general information and b) don't really fit well together as a text. Copying four sentences from four different paragraphs in the Wiki article has that effect.

Alas, it's not obvious enough because it still gets upvoted, although not much (presumably exactly because it doesn't exactly address the question)

Secret

@JohnRennie Worked examples also show the logical flow and the physical thinking needed to move from one step of the problem to another, and this logical reasoning can really help on solving similar problems and physical intuition in general

0celo7

13:00

@ACuriousMind First analysis problem set is making me hurt inside.

I don't even know what an integral is and L1 is on it.

Emilio Pisanty

Folks, does anyone know if there's a playable demo for this game?

How to walk through walls using the 4th Dimension [Miegakure: a 4D game]

►

I found this themarysue.com/miegakure-4d-game-info-no-demo-download but it's from ages ago

Sebgr

Hello everybody

Do you have any recommendations for a book on Quantum Entanglement? For someone who has already studied QM at the level of Cohen-Tannoudji's two volumes.

Maybe even a review article

Emilio Pisanty

@Sebgr Maybe try Nielsen and Chuang then

It sort of depends on what you want to get from "quantum entanglement"

that's a really broad concept

Sebgr

I was reading Susskind's ideas about ER=EPR and now i'd like to have a solid understanding of entanglement

Secret

Sebgr

13:15

@EmilioPisanty Thanks, I'll check it out

Secret

Caption: I suspect that once we encounter phenomenon that is discontinuous in time, and then get used to it, then this cutaneous rabbit illusion should start to fade

@Sebgr whcih susskind book, is it The Theoretical Minimum?

Sebgr

@Secret arxiv.org/abs/1604.02589

Sebgr

13:28

Nielsen and Chuang seems excellent, thanks a lot!

Bass

Why does Maggiore get a minus sign on the r.h.s. of $(3.180)$? Here my calculation (with $A=0$ and without the $e^{imt}$ term): $(i\gamma^\mu\partial_\mu - m)\Psi = (i\gamma^0 \partial_0-i\vec\gamma \cdot \vec\nabla -m)\Psi = 0$, so for $\Psi=(\phi,\chi)$ in the Dirac representation the first vector component is $(i\partial_0 - m)\phi - (i\vec\sigma \cdot \vec\nabla)\chi = 0$, so we get $(i\partial_0 - m)\phi = (i\vec\sigma \cdot \vec\nabla)\chi$ without the minus sign.

Secret

I'll get back to you on that article later, it seems very recent thus what I learn in the theoretical minimum does not seemed quite applicable

John Rennie

@ACuriousMind Spill, spill, who is it?

ACuriousMind

@JohnRennie That's not hard to deduce from my recent activity ;)

Secret

14:14

@ACuriousMind
http://physics.stackexchange.com/questions/275168/doubt-in-lecture-1-of-allan-adams-course-on-qm#comment617094_275168

It does seemed to me that white/black, hard/soft can be represented by the spin states up down left right. Then it is easy to see that because left and right can be resolved in terms of up and down, and vise versa. Therefore a color box is measuring spin in one axis, and the hardness box is measuring spin in an othogonal axis. However teaching the resolution of identity and stern gerlac like this is very misleading, as students will be mistaken that the spin s…

ACuriousMind

@0celo7 You mean, the course did not yet formally introduce integrals and the problem set is on it? Because I don't believe that you don't know what an integral is :P

@Secret And your point is? I'm not sure what you're trying to tell me, I already understood that this is supposed to be some analogy to spin as evidenced by the comment you link.

Secret

Basically, I suspect he might be talking about two different type of observables for an electron, which one of them can be reasonably deduced to be spin. However I don't know of any observable whose hilbert space is also two dimensional such that adding its basis elements will result in an element in the hilbert space for spin, therefore it is weird

> In the lecture adams describes two properties of electrons, which he names color and hardness, both being binary in nature, i.e. white/black, and soft/hard. He claims these are alternate names for two conventionally well known properties of electrons, and shall be referred to via these names at the moment.

the psot does mentioned two conventionally well known properties of electrons, but I knew of no such property such that a linear combination of basis elements corresponds to one property will lead to an element belong to another property

ACuriousMind

The properties are "spin in x-direction" and "spin in z-direction".

Secret

O I see, I thought when "two different property" is mentioned, it means the two properties not necessary share the same hilbert space

ACuriousMind

@Secret What?

What does "share the same Hilbert space" mean?

You really need to pay attention to how you use technical terms. Precise technical language is only useful when you take care to use it correctly.

Secret

14:26

both "spin in the x direction" and "spin in the z direction" are related to the spin state, which lives in a hilbert space of 2 dimensions. Therefore, due to some naive reasons, I thought they are not two very different properties (e.g. momentum vs spin, charge vs mass etc.)

0celo7

@ACuriousMind Yes, but we're doing $L^p$ over $C^0[0,1]$

So Lebesgue is not really important

Secret

I really should stop assuming that when people say "two different properties", they mean something that has nothing in common

ACuriousMind

@Secret The "two properties" obviously do not commute, since measurement of one affects the measurement of the other as described in that question. If you have operators that live on disjoint subspaces of the space of states, then they necessarily commute, hence cannot belong to the properties in question.

0celo7

and we did the basics of Riemann integration in my previous analysis course

ACuriousMind

@0celo7 Lebesgue is not important for $L^p$ spaces?!?!?!

0celo7

14:28

@ACuriousMind Not for what we're doing

John Rennie

Barry Carter is back!

Secret

I see, seems I don't understood commutators and the uncertainty principle enough...

ACuriousMind

Also, what does $L^p$ "over $C^0[0,1]$" mean? Are you saying "we're integrating continuous functions on an interval"?

0celo7

@ACuriousMind Yes.

One of my homeworks is to show that $C^0[0,1]$ is not complete in the $L^1$ norm

ACuriousMind

@0celo7 How is "$L^p$ over $C^0[0,1]$" an improvement over just saying that? :P

0celo7

14:29

@ACuriousMind Vast improvement.

What you said has no mention of $L^p$.

ACuriousMind

And what you're saying strictly speaking is false because the $L^p$ norm is not even a norm on $C^0[0,1]$ :P

0celo7

for $p\ge1$ it is.

ACuriousMind

No, it isn't

0celo7

Why not, pray tell

ACuriousMind

You have to quotient out the functions of zero "norm"

Hmmm

0celo7

14:31

@ACuriousMind Are any of those continuous?

ACuriousMind

It might be that only looking at continuous ones gets rid of all of them

0celo7

We've had this discussion before, btw.

@ACuriousMind I'm sure that two continuous functions cannot differ only a countable set

ACuriousMind

Yeah, all the null functions appear to be discontinuous.

0celo7

And since we're using Riemann integration, the sets of measure zero are the countable ones.

On the other hand, he didn't give us the Minkowski inequality in $\ell^p$. I wonder if I'm supposed to assume it/derive it/give up

ACuriousMind

@0celo7 What does that mean? Riemann integration has nothing to do with measures

0celo7

14:34

@ACuriousMind Primitives are defined only up to countable sets

i.e. two functions have the same primitive iff they disagree on a countable set (possibly empty)

so any continuous function that has zero Riemann integral must be nonzero on a countable set

I believe this is absurd

(take a sequence in the complement or something and use continuity)

ACuriousMind

Wait, I'm a bit puzzled now. What kind of analysis lecture is this that starts with $L^p$-norms on continuous functions with Riemann integration?

0celo7

@ACuriousMind WHO KNOWS

ACuriousMind

@0celo7 What about the function $f=0$?

0celo7

@ACuriousMind ...except for 0 itself, smartass.

That's the point, we're arguing that the kernel of the Riemann integral is precisely $0$ itself.

ACuriousMind

Aha

@0celo7 Is this a continuation of another lecture?

Because this does not make much sense to me as the start of a "new" lecture course

0celo7

14:38

@ACuriousMind Supposedly a continuation of "analysis in $\Bbb R$", i.e. he's not repeating stuff that simply carries over

@ACuriousMind At the beginning he said "this course is an excuse for me to teach you things you need for grad school"

I've mentioned this is my advisor, right?

ACuriousMind

Hmmmmm.

0celo7

@ACuriousMind The first homework has Banach spaces, basic function spaces, $L^p$, $\ell^p$, and some limits stuff.

This is supposed to be accessible without any analysis background.

ACuriousMind

lol

0celo7

One cool thing I proved is that if a function $f:E\to F$ of Banach spaces is continuous along every continuous curve through $x\in E$, then it is continuous at $x$.

@ACuriousMind I take it you disagree?

ACuriousMind

@0celo7 Well, I certainly would not call that "accessible without any analysis background", and it sounds more like the start of a functional analysis than a "normal" analysis course to me

0celo7

14:44

@ACuriousMind The prof is a geometric analyst, so he's basically a functional analyst.

@ACuriousMind Currently proving continuous functions from an interval into a Banach space are bounded...

vzn

15:05

Quantum mechanics trumps nonlocal causality / physicsworld

0celo7

@ACuriousMind uh, what's the arrow for uniform convergence

$\rightrightarrows$?

ACuriousMind

I don't think there's a universally recognized "arrow" for that

Emilio Pisanty

15:28

@DanielSank Looks interesting enough. Maybe bring it in a few weeks along with the travelling wave parametric amplifiers?

Secret

15:56

I interpret it this way. The wavefunction of the entangled state contains all possible outcomes of the system (which must be correlated because they are elements in the tensor product hilbert space of the subsystems). Measurement then decohere the state and we see one of the many outcomes at random

Therefore, sort of like a computer (that does not really exists) having everything stored, but once the switch is flicked, it only choose one out of the many governed by some probability

in other news, I wonder how will they test the backward in time causation model...?

Secret

16:26

> is filled with subsystems, any one of which can play the role of observer. There is no place
in the laws of quantum mechanics for wave function collapse; the only thing that happens
is that the overall wave function evolves unitarily and becomes more and more entangled.
The universe is an immensely complicated network of entangled subsystems, and only in
some approximation can we single out a particular subsystem as THE OBSERVER.
Until recently my view about these things was pretty similar to Feynman’s with maybe

Is Susskind thinking about the wormhole entanglement model?

and is a maximally entangled state one with the highest entropy?

> If Alice’s system interacts with a nearby environment, the entanglement with Bob’s
system can be transferred to the environment, but as long as the environment stays on
Alice’s side and does not interact with Bob’s system the entanglement will be conserved.

Wait, aren't monogamy prevent 3 subsystems to be maximally entangled to each other. If I have the environment interacting with Alice's half of the Alice Bob system, then the environemnt will be entangled to alice's half and thus by monogamy, the entanglement of Alice and bob will become weaker?

> That’s the modest meaning of ER=EPR. The more adventurous meaning is that even
the simple Bell pair has a highly quantum version of an ERB connecting it, and when
brought together with a great many other quantum ERBs, they merge to form a large
ERB

If that's the case, then why don't we get black holes when some research groups have entangled so many photons together?

> According to Everett’s Relative-State Formulation there is only one system, the universe;
all observers are part of it, and are subject to the unitary laws of quantum mechanics.
The system can be divided into subsystems any of which can be regarded as an observer.
Collapse of the wave function never takes place; instead interactions cause subsystems to
become entangled. The entire tree, i.e., the entire wave function, must be retained and
the universe is the complicated network of entanglements that I referred to earlier.

Wait, so my conception of how an entangle state behave is many worlds except denying the wavefunction as a real object?

vzn

@Secret susskinds opinion on QM as "provisional" is actually pretty radical (hadnt heard that before, interesting, whats the ref?) but basically in line with the einstein/ EPR intuition that its "incomplete". physicists have been trained to regard this as a radical pov, but its actually quite reasonable... its roughly/ essentially similar to a "wait and see attitude"... and in line with scientific skepticism that (known) science is never the "ultimate truth" etc

Secret

> In fact the tree is not a tree [7]. In principle everything is reversible. For example if
the system is closed it will execute quantum recurrences, eventually growing together and
reforming the initial root. As we will see there are other faster ways to reverse observations.
Accordingly the relative phases in the wave function are always important and may not
be thrown away.
The thing that in practice allows us to get away with the irreversible collapse postulate
is the enormous technical complexity of ordinary observations which usually makes it

vzn

@Secret re "monogamy" where did you get that term?

Secret

16:42

comment for text block above: Ok, so you can disentangle something...

@vzn Monogamy is mentioned in the context of quantum computing and quantum information theory. It described how more than 2 subsystems cannot be all 100% entangled at the same time, as otherwise it will violate no cloning theorem

2

Q: What is the "monogamy principle" in enganglement?

What does the "monogamy" principle imply? At a superficial level, it seems to say that a particle can be entangled with at most one other particle. However, I keep reading that several particles are entangled. For example: Weird! Quantum Entanglement Can Reach into the Past. Here they descri...

quantum-mechanics entanglement

vzn

did you say you went to QM + art mtg lately? cant find it again in transcript

ah here it is, how was it?

2 days ago, by Secret

Today I joined this talk
https://sydneyscience.com.au/event/quantum-physics-and-art/

and

Secret

pretty good, it told me about how some surreal art is inspired by the discovery of quantum mechanics

vzn

reminds me a little )( of "google deep dream"... which made a lot of headlines lately... have you seen it?

Secret

17:15

https://en.wikipedia.org/wiki/Wigner%27s_friend

Huh, so you are saying that what wigner's friend see for the cat's state does not necesssary agree with with wigner's sees?
(To be elaborated)

Danu

@EmilioPisanty Seems cool!

Secret

Let's suppose we make this thought experiment on a more realisable level by replacing Wigner and Wigner's friend into two measuring devices W and WF, and the cat by an electron with some initial prepared spin state. These devices are like stern galac devices in that they measure the z component of the electron's spin, therefore they either get 0 or 1 as outcomes.

Now suppose we brought WF to interact with the electron. Then WF will either show readings 0 or 1. After the measurement, we transfer the result of this reading into a computer to store it

There's also a complication, obviously transferring the result of WF to the computer will cause the computer's memory to be entangled with WF. Therefore when W measure it it s result must agree with that of the computer

I wonder, whether after transferring the result to the computer, we can break this entanglement before letting W to do the measurement. That way we can get a result where W measures 1 but WF measures 0?

I have to discuss this with acuriousmind later, after figuring out how to simplify it so that it will not be too confusing for him to read

Secret

17:37

The gist of the above is that we knew that measurements disturbs the system and hence introduce noncommutativity in some observables. Therefore there should be no reason to expect what W measures to agree with what WF measures. However the maths showed that to be that the result of WF will always be the same as W regardless on whether the measurement is carried out in the sequence W followed by WF or the reverse. I need to figure out how this is ensured

vzn

17:48

Fake human sacrifice filmed at Cern, with pranking scientists suspected / guardian

Danu

@vzn Physicists' attempt at "humor"...

Emilio Pisanty

@Danu Yeah, I know. I saw it today and I'm really itching to play it

vzn

@Danu liked the hindu deity at least... oppenheimer would be proud

Secret

@vzn Not really, although I previous stumble upon it, but found no need to use it for the moment being

DanielSank

18:04

@EmilioPisanty Bring in a few weeks?

dmckee

@ACuriousMind Well, that's an indication that the offense is intentional rather than negligent. Plus, it's as much or more work than simply admitting to the source(s) up front, so what's the point?

0celo7

18:19

@ACuriousMind ...ok, the homework asks for a precise definition of continuity but that's not been actually defined in class

He just started talking about continuous functions.

Emilio Pisanty

@DanielSank Nothing much. Just remind me that there's cool physics there in a few weeks.

0celo7

18:59

@BernardMeurer Got three compliments about my shoes

Bernard Meurer

@0celo7 Your mom, your aunt and Kathy who was probably mocking you?

0celo7

@BernardMeurer No.

I don't even have an aunt

Bernard Meurer

That's what they want you to think

0celo7

And Michelle has bought me a pair of Jordans

Bernard Meurer

Which ones?

0celo7

19:12

I'll take a pic when I get home.

I don't remember the name.

Bernard Meurer

Alrighty

0celo7

No it was Rebecca, her best friend and a grad student

Bernard Meurer

Rebecca is biased

Her best friend is most likely biased too

0celo7

Biased?

Bernard Meurer

Yes

0celo7

19:17

What do you mean

Bernard Meurer

I mean your tongue is too far in her mouth so she can't say the truth

0celo7

...

*your

Bernard Meurer

Thanks

0celo7

In any case, she's not biased about my shoes.

0celo7

19:35

@BernardMeurer Should I ask my Brazilian prof what he thinks about them

Emilio Pisanty

20:13

@peterh Good catch with this edit physics.stackexchange.com/posts/218085/revisions . The answer also could have used a going over once you were in an editing mood, though.

0celo7

There's a dude using his thigh as a mousepad

How does that even work

dmckee

20:35

@0celo7 If it is an optical mouse then pores and hairs provide the needed fine-grained optical structure.

user507974

20:52

@dmckee This. Many a times I've done this too

dmckee

Or the fabric of ones pants. But for some reason I was envisioning a guy in shorts. Ugh.

0celo7

@dmckee If I had seen a guy doing it on his pants, I would have said pants.

user507974

@JohnRennie depends on the method you use. One thing I've never seen done with most of these physics texts is a rapid revision system. Could be a tough to implement but let's say you had a nephew in high school and wrote for his comprehension, then had other peers read it to make sure you didn't botch anything in rewriting, then gave it to his friends, then sent it off to some first year students, each time really rewriting sections in realish time. Basically you evolve to a better book fasteri

anybody here in the mood to help me get my head around this diffusion problem thats bugging me

its probably really trivial but i havent been thinking physics for like 2 months so im kind of feeling brain dead

Emilio Pisanty

21:27

@dmckee This was mighty well handled.

dmckee

@EmilioPisanty Glad you liked it. That's the version I wrote after deleting the version I wrote after I tried and failed to be diplomatic.

peterh

22:07

@EmilioPisanty Thanks :-) I don't know, how could I have made the answer yet better after you :-)

Emilio Pisanty

22:23

@dmckee Yeah, I can see that not being easy at all. I'm sort of idly wishing I could defuse / shut down way-off-topic rants that effectively, but then you have formal mod powers that really do help there. But I'll keep up the idle wishing though.

@peterh Point is, if you're editing, do everything that you see needs doing in the whole thread, even if it's minor - the question has already been bumped up.

peterh

@EmilioPisanty It should have been done also in the case of an answer? I.e. if I had edited an answer, I should have edited also the question (if it requires any improvement)?

Emilio Pisanty

@peterh If you see improvements to be made, yes.

If it's a bad edit, then you shouldn't make it.

peterh

@EmilioPisanty Ok. But, you know, you edited the answer, just before I edited the question. :-)

Emilio Pisanty

If it's a good edit, you should make it.

@peterh No, not really - check the time stamps. I edited the answer about an hour after your question edit.

The only problem with edits is if they're too frequent, because that clogs up the front page (and other active views) with inactive threads. But once it's bumped, be as thorough as you can, is all.

peterh

@EmilioPisanty I know the problem (ref and I am sad that the SE doesn't even try to solve it.

Shing

22:41

just wondering, how many good physicists are good at picking up girls too? (I know Feynman is)

peterh

@Shing As I know them, they tend to follow more conservative behavior in the girls/wife line, but the geek stereotyp mainly doesn't stay.

1

Q: Calculating the size of an effervescent tablet

An effervescent tablet is dropped into water. Find it's size as a function of time. It's a question from the Rudolph Ortvay Competition '97. How do I proceed?

flow

Question from Ortvay Competition '97, citated literally, has currently 4 close votes...

Probably "too broad", "unclear" and "opinion-based", but at least 2 of this 3

privetDruzia

23:05

Hello

If there is no convection can water still go from liquid state to gas state?

peterh

@privetDruzia Still? Put in vacuum, it will boil. And it will be still.

privetDruzia

@peterh boil but there will be no transition to gas state?

peterh

@privetDruzia Boiling means the liquid goes to gas state

privetDruzia

oh ok. I initially thought the following:

imagine someone sneezes ( without putting his hand in front of his mouth) on the ISS in space. The water particles that that person expelled could travel accross the ISS without ever evaporating due to the fact there is no convection

@peterh

peterh

@privetDruzia They will still evaporate.

privetDruzia

23:13

@peterh so the fact there is no convection has no influence. correct?

peterh

@privetDruzia There is convection. If somebody farts, everybody feel it.

@privetDruzia There is also diffusion

privetDruzia

@peterh ca.answers.yahoo.com/question/index?qid=20080528183002AA6Hy4b

oooh yes ok, there may be convection inside the ISS but not in space. Is that what you mean?

peterh

@privetDruzia Yes, on the ISS there is air, in this air there is diffusion. If there is no air, then the water boils up.

@privetDruzia There are also many convective effects on the ISS, the astronauts are moving, there is a ventillating system and many other

@privetDruzia Actually, liquids are quite unstable things. The overwhelming majority of the non-plasma baryonic matter in the Universe is either gas or solid.

privetDruzia

hmm

the main reason I am thinking about this is because:
Americans developed a special pen to write in space in stead of pencils. Because pencils could have little pieces of it to break off when writing. And those little pieces/particles can get into electronics and conduct electricity, which is undesired

But such a pen imo may be overkill, because there can be so many other things

@peterh

I initially thought saliva would never evaporate and could conduct electricity as well. But that seems to be wrong

peterh

@privetDruzia Ok, but the little pieces are from graphite. B

privetDruzia

23:22

yes

peterh

@privetDruzia Graphite doesn't evaporate and as I know, penciles are used.

@privetDruzia Saliva will evaporate. The astronauts doesn't talk about it a lot, but I suspect not the odor makes the ISS a very good workplace.

privetDruzia

@peterh indeed graphite doesn t evaporate. But the little parts that breakoff when one writes could potentially get into electronic devices and conduct electricity, which is an undesired effect. That s why that special pen was designed, appareantly

peterh

@privetDruzia Aha, possible

privetDruzia

now question is:

Emilio Pisanty

@peterh No, it's not a problem. It's by design and it's a good thing it works like this. It just requires some minor amount of due diligence to work with, that's all.

privetDruzia

23:25

@peterh how big of a percentage of the graphite breaks off when writing and "travels" accross the space station?

I suspect that percentage to be extremely small

peterh

@privetDruzia Yes. I don't have any data but I don't think it would be a serious problem.

privetDruzia

I think it s something political and was maybe done only to show off

to show how much money they invest and about how many little details thay care etc...

peterh

@privetDruzia Yes, and ionsidering the cost of the ISS, maybe it wasn't so bad decision.

@privetDruzia I've heard an urban legend, as the USA has also developed a pen, what is capable to write upwardly, below water and even in vacuum, everywhere, but it costed a lot of money. While the Russian used simply pencils.

@EmilioPisanty But it results that old posts can't be fixed.

@EmilioPisanty I find it surreal, hardening voluntary fixes. There are a lot of very good questions and answers on the site, from around 2012-2014. If something could exist to organize them in topics in a network-like structure grouped by skill level, it would be very useful.

I collapse, good by until morning

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