@DavidZ how do you figure out that model?

@heather However you need to

uh...

how do you begin?

i literally know nothing about this =)

I mean, it's not like there is a "standard model" of information exchange. It's a wide-open question.

are there some papers, websites, or books you'd recommend for getting started?

A lot of times people start with a uniform distribution as a default guess and work from there.

@heather No, honestly; I can't remember any of the sources I may have used in learning about this.

guess i'll ask a question on the main site.

Ask on, like Computer Science or something, not on Physics

This isn't a topic of physics

One thing it's probably worth reading about is Shannon's experiment to determine the entropy of English text. He did something clever by cutting off sentences at random points between characters and asking people to predict the next character.

The information density is related to the probability you can guess the next character in a random text string.

Actually, come to think of it, you might want to read about Markov chains. It's a slightly different topic but it's related to this idea of predicting the next character (or, next element in any sequence) based on the previous one(s).

okay, will do, thank you.

@DavidZ emergency

I've asked the question on computer science, so.

I need a letter for a bump function that's not $\phi$

it needs to be latin

@0celo7 B?

Who names a function $B$?

$h$ it is

lol

Argh!

The floating box strikes again

@0celo7 Planck

@KyleKanos he looks like someone who would do that

I'd do it too, if I ran out of letters

@JaimeGallego I could always afford it, I just didn't want to spend that much. Alas, the deal I had lined up on the 1070 fell through, and the 1080 SC wasn't that much more.

See if this proposal is required or not: <a href="https://area51.stackexchange.com/proposals/110820/experience?referrer=3A5G‌​Y1wbRGadpLMUCUdm1g2"><img src="https://area51.stackexchange.com/ads/proposal/110820.png" width="300" height="250" alt="Stack Exchange Q&A site proposal: Experience" /></a>

Error...

Link: area51.stackexchange.com/proposals/110820/…

@JohnRennie uh-oh

when you get up it's time for me to go

:-)

@JohnRennie I should be getting all of my computer parts tomorrow

will build Friday evening

quite excited

is there anything I need to do that I could have forgotten?

Building your own PC is really good fun :-)

that doesn't answer the question

but I've got to go

cheers

wish I had a high performance PC. Mac games are terrible

so much for exponential growth

Morning :-)

Sorry for the slow response. For some reason my PC didn't play the notification sound.

@Kaumudi.H lifesavingly good as always :-)

To be fair it's just instant coffee. But when you've stumbled out of bed at 5 a.m. even instant coffee tastes like the nectar of the gods :-)

How did the driving go BTW. You must be nearing the end of the course by now.

@Kaumudi.H where are you joining? (if you don't mind answering)

Aha, yes, I had forgotten about that. Weddings are always fun :-)

@Kaumudi.H idk

@Kaumudi.H You still haven't heard from MEC?

I am overwhelmed by too many options

and the deadlines to report are very bad

Tomorrow! You have a tense 24 hours ahead of you :-(

I'm a bit surprised you found lots of films you wanted weren't on NetFlix.

Admittedly I know nothing about NetFlix, but I thought it was the streaming service for films.

I've seen the first three of those ...

I thought The Godfather was a really good film.

2001 was fun.

Clockwork Orange is pretty nasty

I'm a bit of an SF snob, and I wasn't terribly impressed by 2001.

It has some great cinematography, but the story isn't great.

It was originally a short story, The Sentinel, that was pretty good. Then Clarke expanded it into a novel and it wasn't so good.

I am such an SF nerd :-)

@JohnRennie That's how they market themselves, yes, and it's true to some extent, but it is a media company and like any other media company its business is constrained by licensing deals, content fees, and who knows what else. They can't afford to host every movie and TV show in existence so they have to pick the ones that will give them the most revenue for the cost (and only among those whose studios are willing to let them be streamed on Netflix).

To an outsider the streaming video world looks like a great way to pay out lots of money. You pay for NetFlix, but they don't have everything so you pay for Amazon video as well. But they don't have anything so ... and on it goes.

Hi.

can you provide me a book or such about the language used in writing physics?

like a mini-dictionary.

does there exist such a thing?

@0celo7 like that expression "pointwise" in that image.

@AHB What language?

@Kaumudi.H 2001: A Space Odyssey is a brilliant one

@Avantgarde English.

@AHB Not that :P I mean, what do you mean by 'language used in writing physics' ?

hmmm.

You mean a list of physics terms?

The word choices that make a text seem like a scientific paper. and not a poem, for example

with a short explanation besides each of them?

@Avantgarde That would be a dictionary of technical terms of physical

I'm not sure what you mean.

aaahhh. It's hard to say that.

Papers use basic English

with, of course, lots of physics.

There's no given set of words to use when writing papers. At least, I haven't come across any

maybe there is no need to be concerned about word choice at all. and I am being so much caring.

yeah. If you're new to this, ask your professor(s) to read the draft

@AHB The specific words vary a lot from one subdiscipline to another, but every area of study does have its own particular vocabulary that you tend not to find in other texts

@Felix.C I guess if it's cyclic?

Like angles around a circle - if you add enough you get back to where you started

although I'm not totally sure if that qualifies as a vector space. A vector space should have a unique zero element IIRC.

@DavidZ Very nice example, well the null vector would just not change the angle in your example

@Kaumudi.H sorry, was distracted by work ...

Lunch and NetFlix - the ideal combination :-)

Well I always preferred dinner and Netflix myself, but to each their own

Any form of food and NetFlix :-)

I'll eat to that

Well, not really because I already ate tonight, but in spirit

@DavidZ oh. so I guess I had better just read book than to seek some prepared vocabulary list.

@AHB Yeah. There is no vocabulary list that will enable you to understand the full range of scientific papers, or even physics papers.

If you have a specific research topic in mind, I guess an expert in that field might be able to prepare a list of terms to be familiar with, but I don't think it'd do you that much good without reading books and picking up the relevant background knowledge.

Johnrennie, is there a reason why my thought process above dies not work?

@Secret what thought process above?

that (classical) portal argument by treating the portals as identified sphere surfaces

I am not sure about the GR case, but from what you said that it does not work in GR, it has to fail somehow, but other than extremely warped space at the intersection, I cannot think of any other reasons

The only principle I have used is that we knew any portal like objects must behave as follows: That no matter what enters one mouth, it must emerge at a corresponding place of the other mouth, so I don't see why the object cannot be part of one of the mouths

You cannot change the topology of the spacetime, so I can't see how you can put one mouth inside the other

O I see, I thought when wormhole mouths are moved around, it's only the spatial components that are changed. (that's what happen in some wormhole time machine proposals where they said grab one mouth near a massive object and let it sit there for some time, and then move the mouth to some convenient place

Like for example this wikipedia entry on the depiction of the construction of wormhole time machine, where a mouth seemed to be physically moved around...:

> For example, consider two clocks at both mouths both showing the date as 2000. After being taken on a trip at relativistic velocities, the accelerated mouth is brought back to the same region as the stationary mouth with the accelerated mouth's clock reading 2004 while the stationary mouth's clock read 2012. A traveler who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2004, in the same region but now eight years in the past. Such a

> configuration of wormholes would allow for a particle's world line to form a closed loop in spacetime, known as a closed timelike curve. An object traveling through a wormhole could carry energy or charge from one time to another, but this would not violate conservation of energy or charge in each time, because the energy/charge of the wormhole mouth itself would change to compensate for the object that fell into it or emerged from it.

Unless, you mean as long I move the mouths around without putting one into another is fine, but the moment when I tried to put one mouth into the other, the spacetime topology has to be changed hence forbidden by GR

@Kaumudi.H just finished work for the morning

@Kaumudi.H no it's fine. What's the problem?

@Kaumudi.H: BTW it's 16C right now. British summer eh? :-)

Btw I just realised something, I think the wormhole construction I had above might be homeomorphic to the following trouser spacetime:

So yes, there's a change in the spatial topology (which is also a spacetime topology when viewed in other inertial and accelerated frames) because we are basically going from 1 hole to 2 holes

So that means, I think... we cannot have colliding wormhole mouths unless the spacetime is already something like this, similar to the argument of the trouser spacetime

whereas for the wormhole time machine case, we always have two mouths just positioning at different positions in spacetime, thus the topology is still a spacetime with 1 hole

@Kaumudi.H my feelings too :-)

The temperature varies dramatically depending on which way the wind is blowing.

Right now we have a wind from the north west so it's blowing down from the Arctic Ocean, which is why it's flipping cold.

Last week we had a southerly wind i.e. blowing up from mainland Europe, and that made it very warm.

So the temperature has fallen by 10 degrees in a few days!

And people wonder why we talk about the weather so much :-)

So while the starting point and end point there are only one pair of wormholes, midway through, there are effectively 2 pairs of wormholes, thus it is a topology change

@Kaumudi.H S'OK. We're used to it :-)

@Kaumudi.H Remind me what phone you have. A Motorola?

@Secret why do they call it zemlja? Unless I'm much mistaken, zemlja or similar words mean "earth" or "ground" or "land" in the Slavic languages.

uh, I don't understand you question, possibly because I don't know slavic nor heard of that word before. Are you meant to tag someone else but mistagged me?

@Secret Oh, it says that already. I just didn't read far enough. I shouldn't bother posting

It was just a comment on the article you posted about the Cyrillic Z-grapheme.

Meanwhile, I need I ask slereah when he gets on, whether they exists trouser spacetimes like the one I drew above

If trouser spacetimes were possible, then other space times with even more complex arrangements of the cylindrical bits would be too.

@Kaumudi.H I've been Googling that device. If it's using the standard Lenovo software (which it will be unless you've changed it) the phone doesn't have an app tray.

The icons on your screen aren't actually the apps - they are just links to the apps. It sounds as if when the app installed it failed to create the link on your screen.

Obvious question, but have you swiped sideways through all the screens to make sure the icon isn't hiding on one of the other screens?

The easiest solution is probably to install the Google Now launcher and use that in place of the Lenovo launcher.

This is perfectly safe. The Google Now launcher is genuine Google software.

This is the link

Alternatively if you go into the app settings there may be an option somewhere in there to recreate the icon. I don't have a Lenovo phone to hand so I can't check.

Some Googling suggests lots of other people have run into the problem you describe.

:-)

Family eh?

@Kaumudi.H if you install the Google Now launcher then the next time you tap the home button the phone will ask you which launcher to use. Choose the Google Now launcher and tick the "use always" box.

If you want to go back to the Lenovo launcher you can re-enable it from the app settings.

@Kaumudi.H you've installed the Google Now launcher?

With the Google Now launcher you don't need to keep all the icons on your screen.

All the apps are always available from the app drawer, so you can have just the icons you want.

Or you can just leave it as it is i.e. with all icons present.

\o @yuggib

@0celo7 How to define curves

Should I define them as a map from a connected 1-manifold to the manifold

(and non-empty I suppose)

Doing connected subsets of $\Bbb R$ leaves out loops

@Kaumudi.H Organising the icons on your phone is an important task that can take several days to complete. Particularly if there is something else that you should be doing but don't want to.

...obviously it was an easier task than J.R. eluded to :P

btw, which movie?

@Slereah Does there exists trousers spacetime solutions where one pair of wormholes becomes two pairs due to their mouths colliding together?

You can have whatever manifold if it's not compact

So sure

Ah, in that case I need to check the compactness of this one

It's not really an issue

If your spacetime is compact, you have $\chi(M \# T^n) = \chi(M) + \chi(T^n)$

minus something I forget what

btw it seems the illustration in the wikipedia article on spacetime are getting better for example:

here this diagram depicts the gravitational time dilation near the massive object, as well the distortions in space, without assuming it is being embedded in some higher dimension like the rubber sheet analogy

that's just the simplicial manifold

The horror

I have to read experimental physics for the book

Mossbauer effects and interferometry

Are there any famous experiment of free fall?

Most gravitational experiments seem to be with torsion balances

Maybe I should just do one myself really

60 fps camera and a ball

Wouldn't you just be measuring the gravitational acceleration of the earth?

Yes

That is the experiment I want to do

More importantly how does one check the inertial mass of an object

Do you mean arxiv

No

You need approval from two existing members

or an institutional email address

@Blue Worry about publication when you get there.

For now, focus on the research.

Apparently you need a spring to determine inertial mass

@Blue You should get involved in research as early as you can, but there's no expectation that you do it alone.

@Blue: realistically you aren't going to publish anything without some mentoring from someone established in the field.

Are you starting a university degree in the fall?

@Blue At IIITH, your research topic is decided by your prof -.-

Apart from anything else you need someone who knows the field well enough to know what has and hasn't already been done.

@Blue then look at your university's research groups and choose one whose research sounds interesting

then just turn up and say "hello, I'm here, I want to do research with you guys, whaddaya got?"

@Blue u shud ensure that the college u applied for has a physics dept which does research work

many NITs don't have a physics dept

if you're ready to put in work, they're likely to take you in, or give helpful advise if not

At Cambridge undergrads could attend research seminars. I'd guess that's a reasonably common attitude. That's a good way to get to know what is being done in an area.

@Blue I would say email first then just turn up

this is you, basically

:-)

you'd be surprised how many research groups take in penguins to help out

Oh! I forgot that you were joining JU.

I am mostly going to end up at IIIT Hyderabad.

@Blue regarding your technical question on the arXiv, the help page is fairly complete

though it underplays the role that this plays in practice

> arXiv may give some people automatic endorsements based on subject area, topic, previous submissions, and academic affiliation. In most cases, automatic endorsement is given to authors from known academic institutions and research facilities.

@Blue no harm in emailing

@Blue if you were interested in research, u shud have applied for KVPY :/

u wud have got a scholarship + access to national labs/libraries/etc + NSC + ....

@Blue the research seminars I mentioned were informal affairs. One of the group would talk about their research and everyone else would listen and drink coffee. The conferences you describe sound rather more formal. Do they charge a fee to attend?

my fellowship is going to be cancelled becaz I am going for a dual degree

A duel degree :-)

uh again

You have to fight for your degree :-)

Mind you, some PhD vivas are like that!

I keep using the wrong spelling even though I know the correct spelling

@Blue u can write KVPY in ur first year (SB stream)

@JohnRennie turn and start shouting at 20 paces?

@Blue: the arxiv isn't meant as a primary publication. Originally it was only for copies of articles accepted by a journal. People do publish just on the Arxiv but it's mostly things like lecture notes rather than original research. If/when you get a paper published that's a good time to ask for Arxiv membership.

@Blue wut

what branch did u apply for?

:|

Reminds me of Prof. Ramamurti Shankar

yea

@Blue I suspect the seminars are meant for members of the institute. You could ask, but I suspect they would just point to their public outreach events.

@Blue ye!

yea

I applied for "B.Tech in Computer Science and MS by Research in Computational Natural Science"

ccnsb.iiit.ac.in/CCNSB/Research.html

I still have BITS Pilani option

MSc in Physics + B.E. in CS

@Slereah $-\chi(S^{n-1})$

@Blue and they are not as serious as IIITH people

The advantage of IIITH is that even the CNS students make it to GoSC and other computer related competitions.

gsoc

I don't know the numbers but IIITH is the best college in India for CS.

summerofcode.withgoogle.com/organizations/?sp-page=3

there are some science organizations too!