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Cows
Cows
12:14 AM
Ok so as it were I'm home now
Tried the body wash and lotion. Quite good. I now smell like a god. Deal with it :P
Going to be studying tonight.. . . . Live studying and calculations on whiteboard in case anyone wants to drop by and watch. It's going to be fun
 
vzn
vzn
@heather hey heather think homegrown entanglement is not an unachievable or unrealistic goal, but alas very few )( ppl are working on these types of experiments. have long had some ideas for other experiments that would be quite significant if carried out and are less difficult... any interest? btw measuring quantum nature of light at home is not very hard, there are some basic photodetectors/ chips that do it, played with one yrs ago. dont give up! hope to see you go far with hands on stuff :)
@BernardoMeurer the so-called "mgt" seems to be slightly )( irony impaired. am thinking of quoting old near-spam msgs in this chat posted by repeated complainer(s) until others stop hassling me about obviously acceptable content esp wrt other content posted here. guess some other ppls s*** smells like perfume? :P
 
Cows
Cows
@vzn hey dude, have things to say? lol
 
vzn
vzn
12:29 AM
@Cows sometimes! like everyone else in here eh? hows your qm study going? saw your chat room for that, too bad it didnt continue :| think its great idea :)
 
Cows
Cows
@vzn the QM chat shall proceed soon. I took a break to read on time dependent peturbation theory, fermi (Dirac) Golden rule and some basic differential equation theorems about peturbation theory and eigen vectors. Once I feel comfortable with this I will resume
 
vzn
vzn
@Cows so what refs are you using for qm anyway? there sure are a zillion these days...
 
Cows
Cows
@vzn That's a great question. I use Quantum mechanics by Shankar for physical intuition but then try to learn the tools and techniques from more mathematical texts. I also have some notes from a spectroscopy prof.
 
vzn
vzn
@Cows are you a student? saw your interesting Philosophy / metaphysics question, you have some interest?
0
Q: Why are we not just a computer program?

CowsThe problem of how the Universe came about is probably too hard. So let us consider the following instead. Over years from now some huge collection of code run on a powerful computer achieves what can be considered as consciousness. The computer becomes self aware, and has enough logic to decide ...

metaphysics ontology universe faith
 
Cows
Cows
@vzn yes, some years back I wrote a program called MUZAME that can talk to you and learns from everyone else when people talk to it. It was quite cool. I made this may be 4 or 5 years ago
@vzn It was almost like talking to someone , and so i figured if I could do it, imagine what a genius with resources and power can do
 
vzn
vzn
12:41 AM
cool so are you in school?
 
Cows
Cows
Not right now but I recently got admitted to a University nearby as a transfer student in Physics
I am planning on adding CS, and Math, because I already have almost all the classes anyways
 
vzn
vzn
sounds great :) which university? nice combination
 
Cows
Cows
A very low level uni
hehe CSUDH
 
vzn
vzn
looks not bad to me. maybe even better than what BM is going to? :P csudh.edu
 
Cows
Cows
but I have spoken to some of the profs in CS, and Math there, and will be doing research on a CS topic and some math topic
 
vzn
vzn
12:44 AM
interesting, any ideas what topics in particular?
 
Cows
Cows
yes
fault tolerant networks and communication
and
Hopf algebras
 
vzn
vzn
cool fault tolerance is a great topic in CS, very deep theoretical-applied links
 
Cows
Cows
I hope to work with this guy csc.csudh.edu/lzuo
He said he is going to send me a few papers to read during the winter
I am hoping to work with math.csudh.edu/~sraianu on Hopf algebras
I have been thinking of Hopf algebras for a few years now (in secret hehe)
I first learned about them while I was hanging out in France :P
 
vzn
vzn
@Cows impressive resume, howd you meet him? yeah he seems very open/ connected to student research.
 
Cows
Cows
@vzn I called him up and said I was a student and spoke for a bit. Mentioned one or two things about cs courses I had taken and some professional experience in web dev, devops etc
Then sent him an email per his request , so he can send me some papers
 
vzn
vzn
12:51 AM
yeah think it is somewhat atypical that researchers ask for student volunteers on their web pages, dont see it that often myself. anyway lots of others around this room have worked in research, so youre in excellent company. have you heard of our speaker series? lots of talent/ similar experiences. physics.meta.stackexchange.com/questions/7783/…
 
Cows
Cows
wow! It looks pretty cool.
 
vzn
vzn
@Cows :) thx, its a "labor of luv", dont get a lot of help sometimes :| ... have been trying to nail down the next guest but it hasnt clicked yet. lots of talented ppl hang out in here but few draftees volunteers. it seems to work out better in the summer maybe.
 
Cows
Cows
nice
 
vzn
vzn
re "living in a computer program" ever seen the matrix?
 
Cows
Cows
Yes it's an awesome movie
 
vzn
vzn
12:58 AM
:D
if you liked matrix, you might like new blade runner movie... thought it was great
 
Cows
Cows
I've heard great things about it . I think I will check it out for sure.
 
vzn
vzn
esp liked the virtual gf, thought she was the most empathetic character in the whole movie, more likeable than the humans... but then read blade runner review that said the 1st movie was like that too!imdb.com/name/nm1869101
> I didn't get to play many video games when I was growing up. I think I had 'Super Mario' and 'Tetris' around, and that's it. o_O <3 <3 <3 crushcrushcrush
 
Cows
Cows
hehe, she is very attractive. :D
 
Balarka Sen
Balarka Sen
My favorite love story about a sapient and a virtual being is Videodrome, a story about how a person gets sexually involved with a TV set
Absolute banger
 
vzn
vzn
1:15 AM
@BalarkaSen havent seen it but heard its a classic. btw reminds me of this... you are in the same demographic, so whats your take on it? :P dailymail.co.uk/sciencetech/article-5156943/…
 
Balarka Sen
Balarka Sen
I don't care about humanoid robots. I'd bang a TV set tho. (don't quote me on that)
 
Prathyush Poduval
Prathyush Poduval
@BalarkaSen which ones that? I'm interested in it
 
Balarka Sen
Balarka Sen
It's directed by the same guy as Scanners (unsurprisingly), which you wanted to watch a few days ago
I recommend it to everyone
 
Prathyush Poduval
Prathyush Poduval
Well well..... Exploding heads, guy fucking tvs.... What more is there from the guy?
 
Balarka Sen
Balarka Sen
Tons and tons of pure gold, my man
Cronenberg is the king of weirdness
 
heather
heather
1:25 AM
 
vzn
vzn
cronenberg eh? ah a friend tipped me off to this yrs ago, Existenz, liked it... same yr as matrix & some similarities... imdb.com/title/tt0120907
 
 
2 hours later…
Sir Cumference
Sir Cumference
3:53 AM
@CooperCape "Invoke"? :P
 
vzn
vzn
4:44 AM
oh wow just realized cronenberg directed the excellent "dangerous method" ... with kiera knightley :) imdb.com/title/tt1571222 just perfect for all the physicists who revile soft science and/ or metaphysical mumbojumbo! o_O
 
The Dark Side
The Dark Side
5:00 AM
@rob: Minor thing: Should the textbook-erratum tag apply if there is not actually an error in the textbook here? — Qmechanic ♦ Mar 15 '16 at 14:59
@Qmechanic - I think persisting with the tag here seems to give a misleading impression, as you also indicate. The "error" was only a calculation mistake by the OP, as he/she admitted in a comment.
So, why not override that tag?
(For this and similar contexts.)
 
peterh
peterh
I am a 20th marshal badge owner of the site.
@EmilioPisanty It seems to me like a joke.
@ooolb Mods are very paranoid in this sense, particularly the ones with public indentity. This is why are they taking it so seriously. I think best to let this to them (and never threat anybody, even as joke).
 
David Z
David Z
6:17 AM
@TheDarkSide I can say the reason not to override the tag at first was that, when an experienced member decides to do something a certain way, other experienced members tend to assume they had a reason for doing so and try to find out what it is before reversing the action. But if you're asking why the tag was never removed from the question until just now, I couldn't say. Maybe everyone just forgot. That happens a lot.
 
DanielSank
DanielSank
6:33 AM
Hi, everybody.
Hats!
 
The Dark Side
The Dark Side
Hello Daniel.
@DavidZ Yes. Thanks.
 
DanielSank
DanielSank
HATS
>.>
 
The Dark Side
The Dark Side
One needs to have a head to wear it.
 
DanielSank
DanielSank
False.
I am an octopus. I don't wear hats, I play with them.
 
The Dark Side
The Dark Side
I was talking about my gravatar image !!
I am wearing a hat, just not visible in the darkness!
 
DanielSank
DanielSank
6:41 AM
An entirely black hat?
::makes skeptical face::
 
The Dark Side
The Dark Side
Black hat? YESS.
Anyways, Daniel you know a lot of quantum stuff, right?
 
DanielSank
DanielSank
@TheDarkSide You could say that.
My job title is "Quantum Electronics Engineer", so someone thinks I know something about quantum mechanics (and electronics, but they are fooled).
 
The Dark Side
The Dark Side
@DanielSank Do you know some documentation regarding instances where perturbation theory gives the correct energy corrections to (let's say) second order, but completely messes up the wavefunction corrections?
I'll provide a context for this.
 
DanielSank
DanielSank
@TheDarkSide Correct eigenvalues but wrong eigenvectors...
That's more of a math question, but lemme think.
No, not really.
I can cook up cases where regular perturbation theory completely fails, but I can't think of a case where the energies are right and the vectors are wrong.
 
The Dark Side
The Dark Side
The context is QM Griffiths' statement - " I should warn you that whereas perturbation theory often yields surprisingly accurate energies, the wavefunctions are notoriously poor "
 
DanielSank
DanielSank
6:47 AM
@TheDarkSide ah
 
The Dark Side
The Dark Side
He said "notorious".
 
DanielSank
DanielSank
Since he doesn't say how he's measuring goodness and poorness, I can't tell what he means.
 
The Dark Side
The Dark Side
@DanielSank Cook up, how?
 
DanielSank
DanielSank
It might just mean that with some usual sense of closeness, the wavefurnction sequence you get from perturbation theory converges slower than the energy sequence.
He's probably talking about infinite dimensional Hilbert spaces though. I'm not sure.
That book is terrible.
 
The Dark Side
The Dark Side
It could be that. But there seems to be a deeper problem.
There's a question on the site.
 
DanielSank
DanielSank
6:50 AM
@TheDarkSide One way is to pick a case where the unperturbed Hammy is degenerate, and the degeneracy is not lifted by the perturbation at first order.
That's a "fun" problem to work out.
("fun" = it's a royal @*^%!)
 
The Dark Side
The Dark Side
@DanielSank Hmm... Yes.
 
DanielSank
DanielSank
(But you learn a lot and I'd actually recommend doing it)
 
The Dark Side
The Dark Side
I'll give it a shot, IDK how far I'll go.
But look at this:
14
Q: Non-integrable Wavefunctions

JessicaSuppose first-order perturbation yields a credible correction to the energy, but a correction to the wave function that's not square-integrable. That can happen, I see no reason why it couldn't. Unless there is some proof that it can't happen (I haven't found any). And if it does happen, then wo...

quantum-mechanics wavefunction hilbert-space perturbation-theory
In particular, Prof. Moretti's comment:
 
DanielSank
DanielSank
That question is pretty bad though. OP says "I think this pathological thing can happen because nobody ever told me otherwise".
 
The Dark Side
The Dark Side
No, see her comment:
Yes, thanks.... The point is that, in perturbation theory, the 1st-order correction to the eigenfunction is expressed as a linear combination of all the unperturbed eigenfunctions. Each of the unperturbed eigenfunctions is square-integrable, granted, but the series may yield a non-integrable function. — Jessica Oct 11 at 6:47
 
DanielSank
DanielSank
6:52 AM
That said, I bet we can come up with a wacky case by intentionally picking a perturbation that does something horrible...
@TheDarkSide Yes but saying "may" without giving an example is pretty uninteresting.
 
The Dark Side
The Dark Side
@DanielSank Yes. But are we really this careless with the maths?
 
DanielSank
DanielSank
Huh?
 
The Dark Side
The Dark Side
(We = physicists)
 
DanielSank
DanielSank
~sigh~
What are you asking?
 
The Dark Side
The Dark Side
I mean that comment point is legit according to me.
 
DanielSank
DanielSank
6:54 AM
What's careless about using Taylor series?
If it works it works.
@TheDarkSide No, it's not.
 
The Dark Side
The Dark Side
Taylor or asymptotic?
End result?
 
DanielSank
DanielSank
That's like me saying "zomg what if adding two integers yields a pizza? Then what? Nobody ever proved to me that adding two integers can't give a pizza!".
 
The Dark Side
The Dark Side
Yes.
 
DanielSank
DanielSank
@TheDarkSide You only get asymptotic series in horrible cases such as field theory.
I think.
 
The Dark Side
The Dark Side
The reasonable objection I can think of, to the OP's point in the comment is, the coefficients occurring in the expansion are constrained in some sense.
Something like $\sum \vert c_n \vert^2 = 1$.
 
DanielSank
DanielSank
6:57 AM
Why don't you try to prove it?
It's probably not very hard.
 
The Dark Side
The Dark Side
You are right. I will take a shot at it. But just thought if Grif used the word "notorious", there might already be well documented instances, that more experienced blokes may be aware of.
I am not requesting you to do the calculation for me.
I'll take it further from the pointers.
 
DanielSank
DanielSank
Griffiths's book is really kind of awful, in my opinion.
Just look at this case: he said "notoriously bad", and neither of us has any idea what he's talking about (and I have a #*#%$& PhD in quantum physics!).
 
The Dark Side
The Dark Side
Haha ... Prof. Moretti pointed at Kato, but that's legitimately too much above my level currently.
 
DanielSank
DanielSank
That book is too sensationalistic without just giving the information.
I really, really really dislike it.
 
The Dark Side
The Dark Side
You learnt basic QM from? Sakurai?
 
DanielSank
DanielSank
7:02 AM
Griffiths -> Shankar -> Sakurai
I didn't like the subject until I got Shankar.
 
The Dark Side
The Dark Side
Ahh.
 
DanielSank
DanielSank
I still think Griffiths's quantum book has negatively impacted physics.
The Schrodinger equation is on the first page!
 
The Dark Side
The Dark Side
As a postulate.
 
DanielSank
DanielSank
This is terrible.
@TheDarkSide Right. Zero motivation.
It's horrible.
First of all, that equation should be motivated.
Second of all, starting in the Schrodinger picture wave equation is already dumb.
 
The Dark Side
The Dark Side
By "motivation", are you referring to that hand-waving "proof" of taking derivatives of a plane wave and obtaining $E$ and $p$ as operators?
 
DanielSank
DanielSank
7:04 AM
First, you should show that quantizing the E&M mode occupations fixes blackbody radiation so you have some reason to believe quantization in the first place. Then when you get to dynamics, you should do Heisenberg picture first because it's more similar to classical physics.
@TheDarkSide Well, if you want, but you can do much better.
 
The Dark Side
The Dark Side
@DanielSank For instance?
 
DanielSank
DanielSank
@TheDarkSide Start with Heisenberg picture. Learn about p and x as operators.
 
The Dark Side
The Dark Side
Yes. Your Heisenberg argument is fine.
 
DanielSank
DanielSank
Then later let the wavefunction vary in time and show that $H = p^2/2m + V(x)$ gives you the Schrodinger equation if you work in the position basis.
I hate that Griffiths shows the Schrodinger equation so early because it makes students think that quantum mechanics is all about the positions of particles being waves, which is total crap.
 
The Dark Side
The Dark Side
Yes to 1 and no to 2. Where did that belief come from?
 
DanielSank
DanielSank
7:07 AM
Did you know that you can make electrical circuits where the current and voltage are noncommuting operators? Did you know that you can write wave equations in the $p$ basis? Lots of students don't, and it's a disaster and it's Griffiths's fault.
@TheDarkSide 1 and 2 are?
 
The Dark Side
The Dark Side
@DanielSank Your two sentences above, below my last comment.
@DanielSank I didn't know about the first one !! Any references?
 
DanielSank
DanielSank
@TheDarkSide Yes, that is the basis of my entire field of research.
 
Anonymous
Anybody here has any good book suggestions for Statistics? I need some references for non-linear curve fitting techniques...
 
DanielSank
DanielSank
Any degree of freedom behaves quantum mechanically if you isolate it well enough. Current and voltage are no exception.
 
The Dark Side
The Dark Side
@DanielSank Oh. I see.
 
DanielSank
DanielSank
7:10 AM
@Blue Actually, the Numerical Recipes series is pretty darn good.
 
The Dark Side
The Dark Side
@DanielSank Any introductory level reference to that?
 
Anonymous
@DanielSank Isn't that a programming book? I'm looking for a rigorous math book which has proofs for all theory
 
DanielSank
DanielSank
@TheDarkSide Yes, I have two suggested references.
@Blue It is a programming book, but they give pretty good theoretical introductions,
 
Anonymous
I'll check. Thanks!
 
DanielSank
DanielSank
@TheDarkSide This paper is a rewrite of a famous Les Houches summer school course by Michel Devoret.
(I actually posted errata from the original, and got a callout in the "thanks" section of the rewrite!)
 
The Dark Side
The Dark Side
7:19 AM
Wow. That looks like a very useful reference. Hopefully I will read it up shortly.
 
DanielSank
DanielSank
@TheDarkSide It's a very interesting paper and I highly recommend it.
It is written well and easy to understand.
I can also recommend the appendices of my dissertation. I have been told that it is well written.
 
The Dark Side
The Dark Side
Oh wow.
Thanks for the links.
 
DanielSank
DanielSank
Take a look at appendix D.
To be honest, it's not amazingly well written, but it is complete and shows from first principles how you can get quantum logic gates from coupled circuits.
(It's not badly written, it just needs work)
In fact, I've updated it quite a lot. The source lives here.
All* of my theory calculations live on Github.
 
The Dark Side
The Dark Side
That's really nice. Like open sourcing everything?
 
DanielSank
DanielSank
Yes.
 
Anonymous
7:26 AM
Hmm, the Numerical Recipes book doesn't seem to have what I want: www2.units.it/ipl/students_area/imm2/files/…
 
DanielSank
DanielSank
My theory repository needs a slight change to make it easier for others to use, but at least it's all there.
@Blue Dang.
I also like that I can work on my calculations and writeups from anywhere, since it's all online.
 
Anonymous
It doesn't deal with theory of non-linear regression for implicit functions (level curves of $f(x,y)=c$ form) :/
 
The Dark Side
The Dark Side
@DanielSank A lot of people will thank you for that. (However, it will take me some time to get to that level.)
@DanielSank - In fact, I just realized (in my terms) what you meant by the original statement (waaay up). Please tell me if I am getting this right or not.
In the absence of degeneracy, there is a one to one correspondence between eigenvectors and eigenvalues, for well behaved solutions of Schrod Eqn. (Problem 2.54 of Grif)
The moment you add degeneracy to the problem, the uniqueness goes.
So, you may have the right energies, but if you expect the correct eigenvector to correspond to this, there's no guarantee (anymore).
 
DanielSank
DanielSank
right
If the perturbation lifts the degeneracy to first order, there's still a pretty easy way forward.
If not, you have to think :-)
 
The Dark Side
The Dark Side
Could that be what Grif meant? But he mentions it even before we have proceeded to degenerate perturbation theory!
You are right. It is difficult to see what he meant.
 
DanielSank
DanielSank
7:34 AM
I doubt that's what he meant.
He might be talking about something like this:
Consider a helium atom.
It has a rather simple-looking hamiltonian: each electron has kinetic energy and potential energy from the nucleus's electric field.
But there's also the interaction between the electrons!
 
The Dark Side
The Dark Side
Yes.
 
DanielSank
DanielSank
This is very hard to deal with.
 
The Dark Side
The Dark Side
Without approximations.
 
DanielSank
DanielSank
So maybe we try perturbation theory: we solve the problem in the absence of the electron-electron interaction, and then add the interaction as a perturbation.
If I remember correctly, you can get pretty close to the experimentally measured energy with 2nd order perturbation theory, but the wavefunctions you get are not good approximations at all.
I think that's the case.
 
The Dark Side
The Dark Side
THAT'S what I was asking.
!!!
Q1 what do you compare the eigenfunctions against?
(Because there's no analytic solution)
Q2 Where did you read this? Any references for this? (:: kneels and begs ::)
 
DanielSank
DanielSank
7:38 AM
@TheDarkSide Probably numerical solutions.
@TheDarkSide Vague memory from more than ten years ago in college.
@BernardoMeurer. Hi.
Post pics of Santa costume.
 
The Dark Side
The Dark Side
@DanielSank On a grid? There may be issues with that too, no?
 
DanielSank
DanielSank
@TheDarkSide I really don't know.
 
The Dark Side
The Dark Side
@DanielSank Dang! Has Google built any time machine, via which you can go back 10 years. (Semi-joke.)
Anyways I'll try to, uhm , Google this.
 
DanielSank
DanielSank
@TheDarkSide Not as far as you know >.>
 
The Dark Side
The Dark Side
Hmm...
Thanks a lot for this very helpful discussion and pointers, @DanielSank. I'll try to take this further from here on.
 
DanielSank
DanielSank
7:46 AM
ok
 
The Dark Side
The Dark Side
Thanks. 'cya. :)
 
DanielSank
DanielSank
bye
 
The Dark Side
The Dark Side
And will leave you with this as a kind word of thanks. Keep imagining this to be @BernardoMeurer:
(until he responds to your comment)
 
DanielSank
DanielSank
That is awesome.
 
 
1 hour later…
CooperCape
CooperCape
9:12 AM
@SirCumference Tad late now but it was in response to Bernado saying something like "Hats invoke work".
 
Loong
Loong
9:23 AM
0
Q: How does Nuclear Bomb work?

Sachin_HansakaI know nuclear bombs are really very powerful. But i need to know how does it work and what's the element of its? Why they are very powerful? And I think they are made using atoms, but how the creators create the atoms inside of the bomb? Please explain me these things one by one, if you know? Pl...

atoms nuclear
> And I think they are made using atoms, but how the creators create the atoms inside of the bomb?
sigh
 
Slereah
Slereah
9:57 AM
obviously a terrorist
 
Loong
Loong
10:13 AM
I have now more than 60 tons of slightly enriched uranium at work. Maybe he is interested.
Or I could call the fuel factory and ask "how the creators create the atoms".
Hm, sounds more like a religious question
 
Slereah
Slereah
@Loong You need to go to church for that one
 
Loong
Loong
 
Forsete
Forsete
10:37 AM
@JohnRennie are you there?
 
John Rennie
John Rennie
@Forsete morning :-)
 
Forsete
Forsete
Hi, I found yesterday an interesting question and I would like you to write your opinion. Since it a big bang could occur after a big crunch, could the new universe be governed by string theory (if this universe is not this way)? physics.stackexchange.com/questions/374744/…
 
Slereah
Slereah
What
 
John Rennie
John Rennie
@Forsete the problem is that we have no physical theory to describe what happens at a big crunch. The only experimentally tested theory we have is general relativity, and that is unable to describe what happens at a crunch because the geometry there is singular.
 
Slereah
Slereah
General relativity is perfectly capable of doing it
 
John Rennie
John Rennie
10:45 AM
So the question cannot be answered. We simply have no way of knowing what would happen at or after a big crunch.
 
Slereah
Slereah
It's just not thought to be the actual behaviour
 
Forsete
Forsete
So despite a big bounce could occur we don't know if string theory for example could be established in the "new" universe?
Due to our lacking of knowledge of what happens at these conditions
 
Slereah
Slereah
what do you mean by "could be established"
String theory is either true or not
it won't become true magically
 
John Rennie
John Rennie
@Forsete Note that a big crunch can't occur in our universe, or at least not unless dark energy turns out to be a lot stranger than we thought.
 
Forsete
Forsete
I know, but it has not been ruled out completely yet
 
John Rennie
John Rennie
10:55 AM
It is impossible to rule anything out completely, but that doesn't mean we have to believe anything is possible.
 
Forsete
Forsete
True
 
John Rennie
John Rennie
No cosmologist I know thinks a big crunch is possible.
 
Forsete
Forsete
But if somehow happened
 
Slereah
Slereah
what about a small crunch
or a captain crunch
 
Forsete
Forsete
Then a new big bang could occur but we cannot know right now with our current knowledge of physics if the new universe could be described by string theory for example
That's what i understood
 
John Rennie
John Rennie
10:57 AM
@Forsete that's kind of a meaningless statement.
We don't even know if string theory describes our universe, let alone some hypothetical collapsing universe.
 
Forsete
Forsete
Let's see
 
John Rennie
John Rennie
If string theory turns out to be a fundamental theory then it should describe all possible universes including collapsing ones.
 
Forsete
Forsete
Well, in simple words
Despite a big bonce could hapoen if somehow the big crunch occurs, we cannot know how the new universe would be
Or what would happen
Isn't it?
@JohnRennie and what do you mean by all possible universes exactly??
 
John Rennie
John Rennie
Basically yes, at our current state of understanding we would not know what happens after a big crunch.
@Forsete if we assume the universe is isotropic and homogeneous, which seems physically reasonable, then the principle variables are the density of matter and the density and equation of state of dark energy.
In our universe these densities have certain values that we've measured experimentally.
But the theory can describe universes with any values of the densities and any equation of state for the dark energy. When I say all possible universes I mean the set of universes that have different values for the densities and dark energy.
 
Forsete
Forsete
Oh I understand
Well thank you very much for your answers sir!!
 
 
1 hour later…
user228700
12:21 PM
Hi, everyone! :-)
 
John Rennie
John Rennie
@Kaumudi.H Morning :-)
 
user228700
It can't possibly still be morning there! Is it?
 
John Rennie
John Rennie
Ah, good point :-) It's 12:24
 
user228700
:-) Aha!
 
John Rennie
John Rennie
I was only 24 minutes out!
 
user228700
12:24 PM
Electrical Engineering tomorrow! ::Whimpers::
 
John Rennie
John Rennie
:-(
When are you going back to the hostel?
 
user228700
On the flipside, I successfully managed to book a train ticket back home for tomorrow, which is great!
 
user228700
@JohnRennie I just got back :-)
 
John Rennie
John Rennie
@Kaumudi.H what's the agenda for tonight? Are you going to chill or is it more cramming?
 
user228700
I'm a little tired for cramming, but I did buy a caffeinated drink, so I'm set!
 
user228700
12:27 PM
Oh, John, if I continue to chill-as I have been doing all day-I will most certainly fail! x'P
 
John Rennie
John Rennie
as I have been doing all day - oh well, at least the cramming hasn't been relentless, and this is the home stretch!
 
user228700
It is far too boring to finish in advance, you see-only the panic caused by the fear of impending doom allows me the motivation to study for the exam, haha! This fear, of course, does not descend upon me until the very last minute, which is also great, for as you have pointed out, the cramming is not relentless, then!
 
John Rennie
John Rennie
Anything nice for dinner tonight?
 
user228700
@JohnRennie YES! 4 chapatis and a curry of tomato and onion :-)
 
user228700
My grandma packed it for me :-) She has packed me enough chapatis to last all of tomorrow as well!
 
John Rennie
John Rennie
12:31 PM
Wow! Did you bring those back with you from gran's, or has the hostel canteen takena turn for the better?
 
user228700
You might want to read the last sentence of my message :-)
 
John Rennie
John Rennie
Ah, a protocol timing error :-)
 
user228700
:-) The trouble with this subject is that I don't have a reliable textbook from which I can study.
 
John Rennie
John Rennie
Does the course recommend any books?
 
user228700
Yes, but none of them are available online :-/
 
user228700
12:33 PM
And the library has run out of copies!
 
John Rennie
John Rennie
Ah. I would offer to search but I'd guess you're more experienced than me at finding books online.
 
user228700
Haha, I s'pose :-)
 
user228700
Oh, well, I must make do with what I've got.
 
user228700
Ah, I almost forgot to ask! How was the SF meeting last night?
 
John Rennie
John Rennie
Good :-)
The book generated a good discussion, and it was the meeting where we chose the next four books so that was a lively discussion.
The only negative aspect was that yesterday was the peak Christmas shopping day in Chester and that meant the pubs were all very busy.
 
user228700
12:38 PM
Ah, I see!
 
John Rennie
John Rennie
We managed to find a table in a pub but it was very cramped and near the door.
 
user228700
Yes, one more week to go until Christmas!
 
user228700
@JohnRennie Ah, dang :-/
 
John Rennie
John Rennie
So every time someone entered or left we got blasted by cold air!
 
user228700
:-( That's less than desirable.
 
user228700
12:39 PM
Also, how is the new bicycle?!
 
John Rennie
John Rennie
But ... well .. that's Christmas for you. Ho, ho f**king ho! :-)
 
user228700
Hahaha, right! x'D
 
John Rennie
John Rennie
The new pushbike is great.
You don't realise how rickety an old bike has got until you get a new one!
 
user228700
:-) Ah.
 
John Rennie
John Rennie
Though I have to say that it hasn't been great cycling weather. Since we had the snow it has been raining continuously!
My lawn now has puddles of water on it. It has been raining so much that the water is falling faster than it can soak away.
But, to be fair, it appears to have stopped raining now so I shall cycle off in search of lunch in a bit.
Friday's lunch ...
 
user228700
12:44 PM
@JohnRennie Oh, dang! :-(
 
user228700
@JohnRennie Ooh, nice! :-D
 
John Rennie
John Rennie
Pierogi. I think you've seen my pictures of them before. They are one of my favourite meals.
 
user228700
Yes, I have :-) I remember.
 
John Rennie
John Rennie
In fact they were spinach and cheese pierogi so it was a wholly vegetarian meal.
 
user228700
Aha!
 
John Rennie
John Rennie
12:46 PM
Well, apart from the butter, though no cows were killed to provide the butter :-)
And the cheese ...
Actually, having glanced at the time, I should probably be off now.
I shall have to leave you to the sinister clutches of electrical engineering revision :-(
 
user228700
:-( OK. Speak to you later!
 
Secret
Secret
@JohnRennie wow, finally something that is not deep fried or oily
 
ACuriousMind
ACuriousMind
1:07 PM
@0celo7 d'awwww
 
user228700
1:46 PM
@0celo7: Wow, is that your cat?
 
0celo7
0celo7
@Kaumudi.H yes
 
user228700
It's very cute!
 
0celo7
0celo7
Dumpster cat turned out surprisingly well
 
user228700
Dumpster cat? Really? Wow.
 
0celo7
0celo7
Yeah, literally
 
 
1 hour later…
Slereah
Slereah
3:02 PM
and if he doesn't work out
back in the dumpster
 
user228700
3:26 PM
Lol.
 
CooperCape
CooperCape
4:25 PM
142
Q: What exactly is Mining?

Phonics The HedgehogI have heard that mining is for people with ready hardware and blah blah blah... But what exactly is it? Does it operate like real mining? I mean, people talk about it like you are physically mining.

mining-reward proof-of-work mining-theory
This question was written so long ago that an answer says "...gives you 50 bitcoin..."
Damn...
 
John Rennie
John Rennie
@Kaumudi.H today's lunch was most definitely not vegetarian :-)
 
Sid
Sid
@CooperCape if only I had invested in Bitcoin 4 years ago...
 
CooperCape
CooperCape
My brother started investing 2 years ago think he's turned \$3000 --> ~\$75000 just doing nothing
He says he's gonna sit on it to $1 mill but I dunno...
 
Sid
Sid
@CooperCape it's worth the risk IMO. I mean, even if the value falls, they can always withdraw the money and still earn a huge profit.
 
CooperCape
CooperCape
I mean theoretically it should keep increasing until the 21000000 btc limit is reached but yeah... I doubt it will go drastically lower than what it is now...
 
Sid
Sid
4:32 PM
@JohnRennie That looks like Pizza.
 
John Rennie
John Rennie
@Sid Could be :-)
 
Sid
Sid
I had a hotdog today! Well, by "I had", I mean, my friends practically forced me to have it.
 
ACuriousMind
ACuriousMind
I think he just dropped a bunch of meatballs on a pizza and called that cooking ;)
 
John Rennie
John Rennie
Pieces of sausage not meatballs, but otherwise you are spot on :-)
 
CooperCape
CooperCape
I take the toppings of my pizza off before I eat it so John's basically reversed my process.
 
John Rennie
John Rennie
4:36 PM
The church of pizza is a broad one. Any way you choose to eat pizza is a good way.
 
0celo7
0celo7
Except pineapple
@CooperCape are you 5?
 
CooperCape
CooperCape
Add 11...
I dissasemble all my food
 
John Rennie
John Rennie
I don't personally put pineapple on pizza, but I will not nail any pineapple loving pizza eaters to pieces of wood.
 
0celo7
0celo7
@CooperCape that’s something children do.
 
CooperCape
CooperCape
technically I am a child...
well that wasn't a secret anyway..
 
John Rennie
John Rennie
4:44 PM
Well, I have just finished my second pizza, and now I am going to attempt to stand up. Wish me luck.
 
CooperCape
CooperCape
Enjoy...
 
00:00 - 17:0017:00 - 00:00

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