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rob
1:02 PM
@Danu I had a look and dismissed without deleting the comments. There seems to still be some discussion going on (one of the comments was only 45 minutes old) and I had trouble telling which were suggestions that had been incorporated into the posts and which were appropriately transient.
If the commenting rate had been faster, I would have moved to chat, but I didn't see back-and-forth conversations developing.
 
@rob That was the case for one answer, but I don't believe that you think all the comments I flagged were useful*
So I hope you didn't dismiss all of them.
What, you did?!
Sorry, but that's a bit ridiculous, given e.g. this:
+1 for making it simple :) . — KDeogharkar 2 days ago
 
rob
I didn't see a mess that needed cleaning up.
 
That's literally what the comment box tells you not to post.
Are you honestly making a case for this being something to keep around?
 
user116211
I really don't understand such behaviour and attitude.
 
hey are you the same Hurkyl from the physicsforums site? — robert bristow-johnson yesterday
Really?
 
user116211
1:06 PM
They really don't know what SE is.
 
I don't mean to come off as aggressive but I don't think you can decline flags on those comments for a good reason :P
@RobJeffries Fascinating, I didn't realize. I stand completely corrected, so please disregard my previous critique, I'll be deleting those comments shortly — Kevin Wells yesterday
Note that those three comments are on three different answers, precisely the ones that I flagged comments of to attract your attention.
 
rob
Hmmm.
 
I re-flagged, now specifically those comments (but when I flag with a custom message like that I intend it to be about the comments under the posts as a whole, not just the single one I flagged).
 
user116211
I flagged them too.
 
rob
Fair enough.
 
1:09 PM
@rob Aight :)
 
rob
If you flag the noise comments as noise or not constructive, it's easier for me to get your point.
 
@rob I generally flag a lot of comments with a message like "bunch of useless comments here" or something like that when I see 1-2 that I'm 100% should be deleted, and then leave sorting the rest of the mess out to you guys :)
 
@DanielSank, no, I'm not sure yet. I'm asking my parents again soon as they get up and have coffee =)
 
It's a kind of established practice (I don't know who usually handles my flags), I've been doing it for a year or so.
 
rob
I see the custom flag reasons as an encouragement to try to puzzle out more what's going on.
 
1:11 PM
@DHMO Some super basic Calculus and you are done.
 
Okay, question:
 
@SwapnilDas I know calculus but I am not familiar with vector calculus, so could you teach me?
 
I was reading around on the internet, and came across this paper by David Deutsch. The name sounds familiar, but I'm just wondering if this is a legitimate paper, as the site I was reading that referenced it said it hadn't yet passed peer review.
 
@DHMO No vector Calculus required ,to be honest.
 
1:14 PM
@SwapnilDas but it is two-dimensional...
 
@DHMO Still not.
 
@SwapnilDas still not what?
 
No vector Calc required.
@heather Emotions understood :P
 
@SwapnilDas, emotions understood...about what?
 
@heather my emotions lol.
 
1:15 PM
David Elieser Deutsch, FRS (born 18 May 1953), is an Israeli-born British physicist at the University of Oxford. He is a non-stipendiary Visiting Professor in the Department of Atomic and Laser Physics at the Centre for Quantum Computation (CQC) in the Clarendon Laboratory of the University of Oxford. He pioneered the field of quantum computation by formulating a description for a quantum Turing machine, as well as specifying an algorithm designed to run on a quantum computer. He is a proponent of the many-worlds interpretation of quantum mechanics. == Early life and education == Deutsch was born...
 
user116211
@heather I think I heard his name somewhere. And well, this is not Vixra.
 
Sounds like he's mostly interested in hurr durr quantum interpretations
 
How do I find Radius of Curvature?
 
@SwapnilDas could you teach me?
 
@Danu, yeah, but the paper is about generalizing quantum computation, which is to some extent what the paper is about. And it sounds like he's pretty well known in the field of quantum theory.
 
1:17 PM
@DHMO Nothing to teach. Just use integration and definitions
 
@Danu I once read a essay he wrote, he is strongly against "wave function collapse", and call that nonsense.
 
In differential geometry, the radius of curvature, R, is the reciprocal of the curvature. For a curve, it equals the radius of the circular arc which best approximates the curve at that point. For surfaces, the radius of curvature is the radius of a circle that best fits a normal section or combinations thereof. == Definition == In the case of a space curve, the radius of curvature is the length of the curvature vector. In the case of a plane curve, then R is the absolute value of R ≡ | d ...
@SwapnilDas could I have a look at your equation??
 
Yes
 
Because there is no gravity. If there was, you could not even walk or been sucked in like quicksand does. — Manoj Kumar 22 hours ago
They keep getting better. I'm only half sure that's sarcastic.
 
user116211
I'm sure it's a troll.
 
1:20 PM
@HDE226868 you know, there are real flat-earthers
 
@DHMO I've encountered my fair share.
 
@DHMO Could you help me in a Chemistry problem, if you won't mind?
 
@SwapnilDas yes. do you prefer to talk about it here or in the chemistry chatroom?
 
Here. Is it fine?
 
1:22 PM
yes
 
Thanks. It is about the relative comparison of Strength of Acids
 
go ahead
@SwapnilDas wow, that is nice
 
Thanks a lot. Please wait.
 
rob
@Danu This is a reasonable attitude, and it was a mistake for me to dismiss the flags. I get so accustomed to seeing the comment threads that I forget that the point is their transience. Thanks for holding me accountable.
 
Damn sorry
@DHMO first this one please
 
1:27 PM
@rob Thanks for being super reasonable about it!! :)
 
user228700
@MAFIA36790: Oh, shit, Diwali has started in my neighborhood aah! >.< I am waiting for the day these wretched crackers are finally banned by our government.
 
rob
@Danu I'm having business cards printed. "rob: mostly-reasonable person"
 
@Kaumudi Today is Diwali?
 
@SwapnilDas hydrogen peroxide is an oxidizing agent; ferric ion (Fe3+) is in its maximum oxidation state, so it is not oxidized; manganese(II) ion in alkaline medium is oxidized to manganese(IV) oxide; therefore, the answer is A
 
user228700
@SwapnilDas No, I think it's the next weekend. But yeah, they've started gah! :'-(
 
user116211
1:30 PM
@Kaumudi We have all time patrolling. There are strict rules by the Corporation.
 
Why is everyone from India :o
 
user116211
Use noise cancelling earphones.
 
user116211
I had Bose.
 
user228700
All time patrolling? So u guys aren't allowed to burst any crackers? That's awesome! (Not for the little kids, I suppose :-P)
 
@DHMO and this one too
 
1:31 PM
@SwapnilDas hydrocarbons don't like water
so the one with the shortest hydrocarbon tail is the strongest
 
user228700
@DHMO Population of India: 1.252 billion. Bound to run into us all the time.
 
user228700
Plus, we have a lot of nerds :-P
 
@Kaumudi Population of China: 14 billion. Don't see many Chinese here
China has more nerds
 
@DHMO where does the tail start from?
 
@SwapnilDas In RCOOH, R is the tail
the COOH is not the tail
 
user228700
1:33 PM
@DHMO How are u so sure? Not many people reveal where they're from, like u...
 
and others?
 
HCOOH: R = H
CH3COOH: R = CH3
C6H5COOH: R = C6H5
but it is not so simple
for example, C6H5 is bigger than CH3, but C6H5COOH > CH3COOH
 
@DHMO How do you recognise those tails?
 
@SwapnilDas what is not COOH is the tail
 
Ohk.
Thanks.
 
1:36 PM
I've been researching this for 3 hours - it took me 3 minutes to find the duplicate!
 
@SwapnilDas it is quite complicated
for simple acids where R=CnH(2n+1), you only need to compare the size
e.g. HCOOH > CH3COOH
but why C6H5COOH is between them is very complicated
so you should just memorize it
here for more information
maybe you shouldn't just compare the size afterall
 
@JohnRennie Time to downvote! :P
 
I don't normally downvote just because something is a duplicate. It would be good to get it closed off though.
 
Obvious duplicate, right?
0
Q: Can you provide any examples of non-conservation of energy in any GR or other scenario?

John DuffieldSome people say that dark-energy density remains constant in an expanding universe. However this is something that's still rather hypothetical. It's rather atypical too, in that we have no examples of non-conservation of energy. If you move towards the E=hf photon it appears blue-shifted, but it ...

 
Caption: No question shalt stay alive. They will be killed. No matter what they are
Felt so good after killing a small question of mine a year ago
I hate plot holes,
I hate unanswered, incomplete, imperfect questions and answers
I hate anything that is similar to the concept of a gap
If any one of these were seen, they will be CLOSED, no exceptions
A question is like game, waiting to be hunted. There is no escape
To be discussed with quantum guys or to be checked later: Construct an entangled state such that the state space $A \otimes B - B \otimes A$ is nonempty. I.e. noncommutative correlations
 
2:19 PM
This answer is handwaving hypothetical waffle. There are no examples of non-conservation of energy that we know about. — John Duffield 16 mins ago
 
(NB to AB-BA, does not seemed to make sense)
 
Not asking to learn, clearly.
 
Someone claimed that the total energy of the universe is 0. Is this worthy of any attention?
 
rob
2:46 PM
@DHMO On physics.SE, or in a publication elsewhere, or do you have a visitor to your house who's telling you about the total energy of the universe?
 
A Universe from Nothing: Why There Is Something Rather than Nothing is a non-fiction book by the physicist Lawrence M. Krauss, initially published on January 10, 2012 by Free Press. It discusses modern cosmogony and its implications for the debate about the existence of God. The main theme of the book is how "we have discovered that all signs suggest a universe that could and plausibly did arise from a deeper nothing - involving the absence of space itself - and which may one day return to nothing via processes that may not only be comprehensible but also processes that do not require any external...
if I didn't understand it wrongly
 
rob
@DHMO Krauss is a good guy, and that's a good book.
 
@rob so the universe really does have 0 total energy?
 
rob
@DHMO That's plausible way to interpret the observed flatness: that, absent dark energy, the universe is at the critical density to neither expand forever nor collapse into a Big Crunch.
 
@rob what does flatness mean? I've heard that term but I have no idea what it means.
 
rob
2:50 PM
Think about how you compute a planetary escape velocity
 
@rob set its kinetic energy to be opposite to its potential energy?
 
rob
Potential energy is $U = -Gmm/r^2$, kinetic energy is $K=\frac12 mv^2$
Exactly.
The escape velocity is the zero-total-energy condition of the system.
In general relativity, the gravitational potential energy and the kinetic energies of the moving particles both contribute to the curvature of spacetime.
 
how do we measure flatness?
 
rob
If there's not enough kinetic energy, so that the eventual fate of the universe is collapse, that's negative curvature.
 
@rob I have time now.
About to type up a study guide for analysis.
 
rob
2:55 PM
And vice-versa for "expand away forever" and positive curvature.
We seem to live on the cusp between the two.
 
@rob how do we know that the universe has zero curvature?
 
rob
@DHMO The independent measurements of density and curvature were the major result of the WMAP observations.
The Wilkinson Microwave Anisotropy Probe (WMAP), originally known as the Microwave Anisotropy Probe (MAP) was a spacecraft operating from 2001 to 2010 which measured temperature differences across the sky in the cosmic microwave background (CMB) – the radiant heat remaining from the Big Bang. Headed by Professor Charles L. Bennett of Johns Hopkins University, the mission was developed in a joint partnership between the NASA Goddard Space Flight Center and Princeton University. The WMAP spacecraft was launched on June 30, 2001 from Florida. The WMAP mission succeeded the COBE space mission and was...
 
@rob but how do you ignore the dark energy?
 
rob
@DHMO The dark energy component of the density seems to have "turned on" relatively recently in the evolution of the Universe, perhaps 3-5 Gyr ago
 
@rob and how do we know that?
 
vzn
2:58 PM
in theory salon, Oct 19 at 13:56, by YOUSEFY
read this article in Scientific American with David Deutsch. It is good to give you a reasoning why 'computation' and 'information' needs to be refreshed. https://www.scientificamerican.com/article/a-meta-law-to-rule-them-all-physicist‌​s-devise-a-theory-of-everything/
 
rob
So in the early universe, the dominant contribution to the energy density was radiation. Then, for a while, it was matter. Currently, we don't know what it is, so we call it dark energy.
 
@rob I see, thanks
 
user228700
@DHMO Has ep. 2 come out yet?
 
@Kaumudi yes, even to ep. 4
 
user228700
Wtf? OK...
 
3:00 PM
Ep. 1: https://www.youtube.com/watch?v=yKbJ9leUNDE
Ep. 2: https://www.youtube.com/watch?v=3AMCcYnAsdQ
Ep. 3: https://www.youtube.com/watch?v=MTFY0H4EZx4
Ep. 4: https://www.youtube.com/watch?v=sAMlGyaUz4M
@Kaumudi ^
 
user228700
Thank you :-) (Wow, that was so quick!)
 
rob
@DHMO Krauss addresses all of your questions in the book you linked to. You'd enjoy it.
 
@rob alright thanks
 
vzn
@Kaumudi my co is having a sponsored diwali celebration maybe for 1st time. (we have many indians.) what is a "cracker"?
 
rob
@0celo7 thanks for making time to talk. I appreciate it.
 
3:06 PM
@Danu That's from me?
 
@rob So what do you want to talk about?
 
rob
@0celo7 So my question for you was: when you flag a message in a chat room, what's the outcome you are hoping to acheive?
 
the person begin suspended, clearly
 
rob
Suspended = gone for a minute, or gone for a year, or burnt at the stake, or ... ?
 
gone for 30 minutes
burning at the stake would be too much
although there are exceptions.
 
rob
3:13 PM
@0celo7 Phew
@0celo7 Oh.
@0celo7 But: a flagged chatter generally should be welcome to resume after a break, when the discussion has moved on?
 
Yes, but there are exceptions.
 
rob
Sure, that's fine.
@0celo7 So, one thing that I've noticed in hbar is that, apart from flagging troublesome messages, there are also comments within the chat about which messages may or may not have been flagged.
Some examples (poster-agnostic):
4 hours ago, by Bernard Meurer
@JohnRennie Flagged
19 hours ago, by 0celo7
I flagged all of SC'a messages.
2 days ago, by Sir Cumference
@0celo7 Flagged you for flagging
 
Yes, I'm aware.
 
rob
Oct 11 at 0:07, by 0celo7
Flagged
@0celo7 Okay.
 
I'll flag you if you keep this up :P
 
rob
3:25 PM
I think that this sort of meta-discussion defeats the purpose of the flag system.
One of the clever things about the Stack Exchange model (which they got from Metafilter) is the idea of a separate space for discussions about content and for meta-discussions about the discussion itself.
This is why we have one space for questions about physics, and a different space for "why was my question closed" and "should we allow questions about warp drives"
If you're involved in a discussion that goes in a direction that you don't like, part of the process is to disengage from the troublesome behavior.
... which is why the flags, which bring in outside help, aren't visible to the people who are just trying to use the room.
The acronym (which I've seen elsewhere, but perhaps not here) is "fiamo", for "flag it and move on". The second half is just as important as the first.
3
 
@ACuriousMind google it? :P
 
@Danu Now there's something my hungover mind didn't think of!
 
#rekt
Talk to ya later
 
3:44 PM
@rob I don't see what point you're trying to make.
If you want me to stop flagging, I can do that.
But you're not going to convince me to stop it on my own.
 
user228700
@vzn I see. These wretched creations that do nobody any good aah, why are we so dumb?!
 
@0celo7 Uh, what does that mean? You're going to stop flagging things but only if expressly told to?
 
user228700
This times a thousand is what the environment sounds like for like, 4 days a year.
 
@ACuriousMind Yes.
@ACuriousMind I am too simply-minded to see what's wrong with flagging, so if you tell me to stop I will trust you.
 
rob
3:51 PM
@0celo7 So, this could be a good outcome. But you said earlier that you have a purpose in mind when you flag a comment. How would you accomplish that purpose?
 
@0celo7 Stop flagging.
I'll say it.
 
Don't know what took you so long.
 
rob
@0celo7 My question stands: what about the outcome you were hoping to achieve by flagging chat messages?
 
I echo what rob said - I'd also be interested to know the answer to that.
 
I've already said it.
 
rob
4:01 PM
@0celo7 You said what your goal was. But if flagging isn't available to you, what about that goal?
 
Huh?
 
rob
@0celo7 Suppose you agree to quit flagging messages. Later you are talking with someone and they're rude to you. You think, "I wish I didn't have to read any more messages from this rude person for a while." You reach for the flag menu, and pause. What next?
 
@rob Sorry for butting in as an outsider, but I find it hard to parse that message any way other than condescendingly.
 
I won't do anything.
 
user218912
why is this even a conversation?
 
rob
4:09 PM
@MikeMiller You know, that's a fair point. My apologies, @0celo7.
 
I didn't notice.
@ACuriousMind Hey do you have the link to that picture you drew?
of the Lebesgue covering?
 
Many thanks.
@ACuriousMind I'll credit it as by Bajoran.
 
fine with me
 
4:49 PM
@JohnRennie Yep, thanks :)
 
@ACuriousMind You're an artists
 
 
2 hours later…
7:00 PM
How can I prepare a hydrogen atom be in a state of superposition of energy eigenstates?
 
7:25 PM
@Shing In real life?
 
7:57 PM
2
Q: What does a "real" quantum computer need for cryptanalysis and/or cryptographic attack purposes?

e-sushiThe cryptographic world has been buzzing the word "quantum" for a while now (even the NSA is currently preparing itself for a post-quantum crypto world) and quantum-related hardware engineering is evolving constantly. For example: the 5-qubit quantum computer created at MIT by using the technique...

(Someone suggested to ping you about this question.)
 
@e-sushi I strongly believe that physicists have a much better chance at answering that question cryptographers, even though it is of high cryptographical relevance
 
@e-sushi I am a quantum computation experimentalist.
 
8:28 PM
@ACuriousMind my advisor: "you seem to know a lot of graduate students"
He's gonna show up one day D:
 
@0celo7 what? show up where?
 
Stack exchange
 
8:46 PM
@SEJPM I posted an answer to the question.
 
@DanielSank Thank you very much! :)
 
 
2 hours later…
10:53 PM
@ACuriousMind Suppose I have an interval I and a cont function f:I-->R. Suppose that f(I) contains [a,b]. Certainly there's an interval J contained in I such that f(J)=[a,b]?
It's a little harder than just intermediate value theorem
Because it could vary wildly in I and leave and enter [a,b] many times.
 
@0celo7 Obviously not a strict subset (think about identity).
 
11:23 PM
@Danu Sure.
So I could be J, but the idea is clear?
 
@0celo7 Then you always find $J$, namely $I$.
Your question as currently posed it useless :P
You're going to need more conditions on $f$.
 
@0celo7 Just look at $f^{-1}(a)$ and $f^{-1}(b)$, and choose one point from each such that between them no other points from these preimages lie, and there's your interval.
@Danu what
 
11:39 PM
@ACuriousMind For something nontrivial to happen.
If you allow $I$ you're always going to find it. If you don't, you're not.
 
I think one of us is misunderstanding his question, because I have no idea what you're trying to say
 
I'm saying you cannot find a properly contained $J$.
cf. identity map
So unless you have something more interesting that $f$ obeys, this question is not interesting.
 
Huh?
 
So take the identity map $[a,b]\to [a,b]$.
The only $J$ that works is $[a,b]$ itself.
 
The question is basically whether the preimage of an interval under a continuous function always contains an interval that already maps to the interval we took the preimage of
 
11:42 PM
@ACuriousMind That's not how I interpreted it, but okay.
I guess then my answer is not useful.
 
@Danu What do you mean, "the only $J$ that works"? The image contains $= [c,d]$ for $a \leq c < b \leq d$ and the $J$ we're seeking is then also $[c,d]$.
 
@ACuriousMind Right. I'm taking a general interpretation, with a very special case, choosing the interval it has to contain to be again $[a,b]$
This is just to point out that you won't, without postulating any more conditions, get anything interesting for $J$.
 
Uh, still not following you, but whatever
 
Sigh.
So if 0celo7 is really asking this for any continuous function, for any interval that the image may contain, I was just pointing out that you cannot always find a $J$ that is a proper subset of $I$ that still contains the interval.
I assumed the main point of the question was to have some kind of nice subset $J$ (since it's *stupid to just get $I$ back again), and was just pointing out that you don't get something nontrivial in a general case.
My example to demonstrate that is: $[a,b]\to [a,b]$ identity map, considering the interval $[a,b]$. Clearly $f(J)\supset [a,b]\Leftrightarrow J=I$.
That is all.
So unless you put some restrictions on the interval or on $f$, this question has no interesting answer.
In that interpretation of the question.
Your interpretation is different and probably more useful!
(but not obvious to me, apparently)
 

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