The h Bar

heather

00:03

i hereby curse LaTeX

i will repent as soon as this works.

...and problem fixed.

hideously, perhaps, but fixed.

0celóñe7

00:32

@ACuriousMind Make chicken schnitzel

I prefer it to pork

dmckee

01:10

The temptation to respond to

0

Q: Do couples act in current/ampere balances

I understand that the basic principle of a current balance is that mg=BIl when equilibrium is reached and thus B can be found. This means that torques must act when the mass is placed on the balance and again when the current is adjusted. However, does this mean that two couples act?

torque

with some snarky comment about couples mostly acting in the bedroom is almost overwhelming.

2

lzy

03:36

Hey, was wondering if anyone could help me with a quick question?

If E=hc/λ, which means as the energy increases, the wavelength decreases, then isn't that essentially the same as the Rayleigh-Jean Law?

John Rennie

04:15

@lzy No, the two are completely different. The Rayleigh Jeans law attempts to predict the intensity of radiation emitted by a black body based on statistical mechanics.

lzy

But are the results similar?

E=hc/λ doesn't account for the UV dip as well does it?

Anonymous

Anonymous

How do we find $-\nabla V$ in the equation for $J$ ?

Anonymous

What does $V$ represent anyway?

Anonymous

John Rennie

04:26

If we use the analogy of electrons in a metal as a (nearly) free Fermi gas, then increasing the temperature of the metal increases the pressure of the gas.

So electrons moves from the hot region to the cold region.

Anonymous

@JohnRennie I got that part. I was asking what $V$ stands for? Is it an external voltage applied to the circuit?

John Rennie

Potential energy

Anonymous

@JohnRennie Potential energy of what?

John Rennie

Thermocouples are more complicated than you think. They measure the difference in the Seebeck effects of two different metals. You can't directly measure the Seebeck effect in a single piece of metal.

I answered a question on exactly this point a few years back ...

Anonymous

I saw that answer of yours :)

Anonymous

04:30

1

Q: Thermo-Emf variation with temperature

In the following experiment for seebeck effect After a certain temperature, the thermo-emf begins to fall. Why does this happen? What is happening microscopically at this level to cause such an effect ?

thermodynamics electricity thermoelectricity

Anonymous

1

A: Thermo-Emf variation with temperature

The calibration curve you show isn't typical. In fact there is no typical calibration curve because different types of thermocouples can have very different voltage:temperature dependences. There are lots and lots of articles giving different calibration curves - I selected this PDF as being fair...

Anonymous

Actually I read that part. I couldn't understand what they meant by $V$ (i.e. local voltage) in the Wikipedia page

Anonymous

I understood that due to the temperature difference an emf is generated. So we can write $J=\sigma E$

Anonymous

"When you heat a metal you produce a population of electrons with energies above the Fermi energy, and that population is temperature dependant. The Seebeck effect arises because if two ends of a metal wire are at different temperatures the electrons at hot end will have higher energies than the ones at the bottom end and they can lower their energy by moving from the hot end to the cold end. This movement of charge creates a potential difference between the ends of the wire."

Anonymous

Yes, but that potential difference is what causes the emf, isn't it?

John Rennie

04:37

I'm busy fixing servers, I'll have to get back to you later ...

Anonymous

@JohnRennie Sure. No problem

user228700

06:32

@JohnR: HI! :-)

user228700

Fixed all those servers yet?

John Rennie

Yes. There were three servers down but in all cases they just needed an (electronic) kick up the bum and they're all fine now.

user228700

Also, spot me if you can:

John Rennie

The race!

user228700

GAH.

Bernardo Meurer

06:34

@JohnRennie Hey!

Your laptop has made it to CA

Amplifier will soon be on it's way

Guess they never thought they'd end up this far :P

John Rennie

@BernardoMeurer Hi stranger! Long time no see! How's life in Santa Barbara? :-)

@Kaumudi.H wrong picture

Bernardo Meurer

Yeah, sorry for disappearing there for a while, busy days in Rio

Pretty good, got to see Dan's fancy Google lab

Dope af

user228700

Never mind, it's taking too long too long to re-upload with the faces of all my friends blurred.

Bernardo Meurer

Made some Swedish friends, we're getting a house

user228700

Also @Bernardo: Hey! :-)

Bernardo Meurer

06:37

Registered for classes, now with a more human schedule

John Rennie

@BernardoMeurer I have just completed an awesome laptop repair. I had the thing almost completely dismantled. My goodness there are a lot of parts in a Dell laptop!

Bernardo Meurer

Missing Lisbon a bit though, guess I just have to get used to it

@JohnRennie Awesome! What model?

user228700

@JohnR: I MADE IT! I completed the marathon, even though it took me 1.5 hours to do it.

John Rennie

@BernardoMeurer A Latitude E6330

@Kaumudi.H Cool! So how are the endorphins? :-)

Bernardo Meurer

@JohnRennie I had to replace the battery on mine

it just died entirely

I got some super cheap 97Whr battery off of ebay and it's SHIT

user228700

06:38

@JohnRennie :-P Better, I s'pose.

Bernardo Meurer

lol

John Rennie

@BernardoMeurer The batteries generally only have a life of three to four years, so to be fair yours didn't owe you anything.

Bernardo Meurer

it doesn't report correctly to udev so Linux is super confused and doesn't give me correct estimates

Windows also doesn't deal well with it

I'm trying to write an acpi driver for it, but acpi is shitty Windows technology and I can't deal with it

John Rennie

@BernardoMeurer It's always best to get genuine Dell batteries. If you look on ebay.com you should be able to get a 97WHr battery fairly cheap.

user228700

On the downside, I haven't eaten in literally 24 hours so I'll be back in a while...

Bernardo Meurer

06:39

Well by trying I mean reading on it and trying to figure out what to do

John Rennie

@Kaumudi.H You ran miles on an empty stomach? Good grief!

user228700

@JohnRennie Literally, yep.

John Rennie

@Kaumudi.H GET SOME FOOD!!!

Preferably pizza! :-)

Bernardo Meurer

ebay.com/itm/…

user228700

I bought two sandwiches but they don't smell very good :-/

Bernardo Meurer

06:41

This one claims to be OEM

user228700

I'll be back in a few, after having devoured them.

John Rennie

@BernardoMeurer that looks pretty good. $42 is a bit of a blow, but to be fair that's about what you'd pay in the UK.

@Kaumudi.H See you later!

@BernardoMeurer one advantage of being in the US is that there is shedloads of stuff on ebay.com.

But if I buy from the US the UK customs intercept the delivery and add 20% import duties onto it!

@BernardoMeurer this one?

Bernardo Meurer

$42 is cheap comparatively!

Oh nice!

$24!

That must be a ripoff

John Rennie

Buying that one would be a risk because it's some random firm in China.

But I have to say when I've bought from Chinese companies I've always had a good experience.

Bernardo Meurer

I want something already in the US, don't want to wait for CN shipping

I need battery on my laptop :P

John Rennie

06:48

Yeah the one you've found is probably the best option then. $42 is not bad.

Bernardo Meurer

I'm fine with paying $42, it's a big battery and it'll last me a long time

The only thing annoying me with this laptop is the rubber feet keep coming out

and I lost a couple so now it wobbles

John Rennie

I think you get 5-6 hours from the 97 WHr battery (as long as you're not doing continuous kernel recompiles :-). I'd get that battery and use the cheap one as an emergency backup.

@BernardoMeurer just pull off the remaining feet then buy a few of those stick on rubber pads from your local hardware shop.

Bernardo Meurer

I'm currently fighting Amazon customer service to refund me for the one I got

user228700

I'm back!

Bernardo Meurer

But "Joan" isn't being helpful

Cause I filed for refund

and in the refund instructions it says not to return damaged batteries

"damaged or defective"

which this one clearly is

@JohnRennie I'll get the battery pack that goes in the DVD drive bay (30Whr) and the one that plugs under it (97Whr) for infinite battery!

Woohoo got the refund without having to return

John Rennie

06:57

@BernardoMeurer Result! :-)

Bernardo Meurer

Gonna keep this one in an anti-explosive box

John Rennie

@BernardoMeurer hmm, yes, cheap lithium batteries ...

I won't store it with a charge on it - well, not unless you like a real fire :-)

user228700

@JohnRennie Unfortunately, I only ate two sandwiches and they weren't very good; stale and also didn't taste good at all.

Bernardo Meurer

@JohnRennie Bah, don't worry! It doesn't hold charge! lol

John Rennie

@Kaumudi.H Oh well, food is food. In emergencies (e.g. if you haven't eaten anything for 5 minutes) anything with calories will do.

user228700

07:00

Hahaha :-)

John Rennie

Did you run past any food shops?

user228700

...I'm finding that my legs have died.

John Rennie

I must admit I've never really got this running thing.

user228700

@JohnRennie Of course! It was 10 Kms so yes, absolutely; they were several hotels, cafes and roadside treats on the way. I didn't stop for anything though; I knew from the start that I wouldn't be able to run all the way so I promised myself that I wouldn't stop, at the very least.

user228700

@JohnRennie Neither have I, really. Cycling FTW(for the win)!

John Rennie

07:03

Yes I like cycling

It seems more civilised and less sweaty

Plus you don't end up with destroyed knee joints :-)

user228700

Yes! And I don't mind cycling even for ~20 Kms but running all the way...no, no, dear Lord, no.

Bernardo Meurer

@JohnRennie I'm saving up to get a nice road bike

John Rennie

@BernardoMeurer one of my old friends is in the US at the moment and a keen cyclist. That's on the East coast though.

I don't know what cycling is like in California.

Bernardo Meurer

@JohnRennie Ask him if he knows any online shops or stores, etc; would you?

I want to go back to my 100km three times a week schedule

John Rennie

She's on Facebook if you want to ask?

Bernardo Meurer

07:06

@JohnRennie That'd be nice :)

John Rennie

facebook.com/eilidh.bedford

Bernardo Meurer

ebay.com/itm/2016-Specialized-CruX-Elite-X1-56cm-Carbon-Frame-/…

Most beautiful bike I've ever seen

damn

John Rennie

Two ... thousand ...dollars!!!

Bernardo Meurer

@JohnRennie I'll just message her that I'm your friend, lel

John Rennie

What's it made from? Gold?

Bernardo Meurer

07:08

@JohnRennie Yeah, not buying that one lol

@JohnRennie Carbon fiber

tbh 2k is not even that much in the high-end

there's 10k bikes

John Rennie

I use a cheap mountain bike that's about 15 years old and it's great!

user228700

@JohnRennie Bedford...bedford...AH! It's A Wonderful Life! :-)

Balarka Sen

it's not though

John Rennie

It's a bit old and tatty, but that's OK - so am I :-)

@Kaumudi.H ???

user228700

@BalarkaSen Huh?

user228700

07:09

Bedford Falls (It's a Wonderful Life)

Bedford Falls (or Pottersville) is the fictional town in which the American Christmas drama It's a Wonderful Life (1946) and Philip Van Doren Stern's 1943 short story "The Greatest Gift" (on which the film is based) are set. == Inspiration == In 1945, Frank Capra visited Seneca Falls in the state of New York to look for inspiration for the town of Bedford Falls. The two towns are very similar as they are both mill towns, they both had a grassy median down the main street (Seneca Falls does not anymore), both communities boast Victorian architecture and a large Italian population, and they both...

John Rennie

Ah. I doubt there's any relation :-)

Balarka Sen

it's a bad joke on the lines of: it's not a wonderful life

user228700

@BalarkaSen Do explain.

user228700

@JohnRennie Hehe, OK :-)

John Rennie

Bedford is a town in the UK, though again I doubt having the surname Bedford has any significance.

user228700

07:12

BTW, @JohnR: My cycle didn't arrive today so now I gotta wait till Wednesday :'-(

John Rennie

That's a pain. Oh well.

Is the delivery tracked at all?

user228700

@JohnRennie Nope, not at all!

user228700

AH. There! It worked! :-)

Bernardo Meurer

ebay.com/itm/…

Woah

user228700

07:14

(I look quite high due to aforementioned endorphins :-P)

Bernardo Meurer

Pretty

John Rennie

@BernardoMeurer it's always a bit of a risk buying a second hand bike because you don't know what condition the cassette, chain, brakes, crank, bearings, etc, etc, are in.

Bernardo Meurer

@JohnRennie True, but I like fixing bikes :p

John Rennie

You can end up paying a lot of money to replace all the bits that wear out.

@Kaumudi.H it's always a great feeling when you complete a race :-)

user228700

Absolutely! :-)

John Rennie

07:18

@BernardoMeurer in your place I'd probably buy a new entry level Trek bike, at least while I'm getting to know the area. Then you can ride over cobbles, up and down pavements, etc without worrying about the damage you're doing to it.

@Kaumudi.H so what's the agenda for the rest of the day? Shower, meal and chill for the rest of the day? :-)

Bernardo Meurer

@JohnRennie I had a Trek 3500 Disc back at home, it's an awesome bike

John Rennie

I'd have to Google that to find out what spec it is.

Bernardo Meurer

Like this one

user228700

Haha, well, I've already got two down; showered, ate, and even sweeped my room ffs!

John Rennie

My bike is a Trek.

Bernardo Meurer

07:20

I liked it, but I didn't use it as an MTB, I used it as a road bike, which it isn't suited for

(clearly)

So now I just want a road bike

but I need it to double as a commuter

user228700

I only got 4 hours of sleep last night though and I'm absolutely exhausted! :-(

Bernardo Meurer

i.e. I need a drop-down road bike with a rack mount

John Rennie

The thing is road bikes have those skinny little tyres and fragile wheels.

user228700

I might take a nap now and then visit my friend who is leaving tomorrow.

user228700

And you @JohnR?

John Rennie

07:22

@Kaumudi.H the usual. Do some work, mess around for a bit, get lunch, slump into my armchair with a SF book and some beer.

It's a hard life but well sometimes you have to step up to the plate.

Bernardo Meurer

@JohnRennie You just gotta be careful

Not go around jumping curbs

user228700

@JohnRennie :-)

John Rennie

@BernardoMeurer I used to use a pretty good quality road bike, but it felt like I was contually getting the wheels retrued.

user228700

What's fun lunch? And what did you get yesterday?

John Rennie

Now I use a Trek hybrid and it's perfect for racing round Chester.

user228700

07:23

> racing around

user228700

It's a funny picture I imagine in my mind :-)

John Rennie

@Kaumudi.H I just snacked yesterday. To be honest after eating eight ham and cheese muffins on Friday I wasn't that hungry :-)

user228700

You're weird :-o

John Rennie

@Kaumudi.H cycling is my exercise so I generally cycle faster than is necessary, and sometimes faster than is sane :-)

user228700

I envy you for the sort of stomach you've got!

John Rennie

07:25

When I die I'll leave my stomach to science

user228700

@JohnRennie :-) Once I get mine, I'm sure to become super thin; Kochi is a hilly area.

user228700

@JohnRennie THANKS!

user228700

Did I tell you, BTW, that the marathon was organised by our college?

Bernardo Meurer

@JohnRennie If the trek hybrids weren't so expensive I'd get one :P

John Rennie

@Kaumudi.H Ah I didn't realise. Who were the other people in the picture? People on your course?

user228700

07:27

Our techfest is called Excel and it is in October. This marathon was a pre-event of sorts to spread awareness about Organ Donation Day, which is today but mostly, it was really only done to promote the fest.

user228700

@JohnRennie Yep! They're all in my class :-) FRIENDS, lol.

John Rennie

@BernardoMeurer I just nipped out to the garage to check which bike i've got, and it's a Trek 7100FX.

It wasn't very expensive but it's a brilliant bike for general road work. I used to ride it to work (15 miles each way).

It has covered more miles than a lot of my friends' cars :-)

Bernardo Meurer

If I had unlimited money I'd get one of the Trek Crossrip bikes

Ah, that's a nice bike!

I hate that geometry though :P

user228700

They even gave us a T-shirt! Cost me Rs. 100 :-P

John Rennie

@Kaumudi.H You mean: They even sold us a T-shirt! There's marketing for you :-)

user228700

07:31

Haha, yes, that is exactly what I meant :-)

John Rennie

It's nice to have a souvenir of the race though.

user228700

^ YES. And it's the first item of clothing I've gotten from the college!

John Rennie

It's like buying a tee-shirt at a gig. They're always over priced but you buy it for the memories.

user228700

@JohnRennie It's not a race, really, as long as you try and complete it :-P

John Rennie

I bet the guys at the front were racing :-)

user228700

07:33

Oh, sheesh, yep! The person who finished first did it in 40 minutes!

user228700

We even had one 70 year old man complete before us! :-(

John Rennie

I'm not even sure I could run 10km

I haven't done any running for ... decades!

user228700

Could you run+(mostly)fast-walk for that distance?

user228700

That is what I did.

John Rennie

I used to be a keen walker, but my ankles are getting a touch of arthritis these days so I stick to cycling now. It's easier on old joints :-)

user228700

07:35

:-)

Bernardo Meurer

I used to be a walker, until I got hit with a car to the knee

John Rennie

I've just noticed the time. I need to get back to work!

user228700

@BernardoMeurer Wtf? Were you OK after?

user228700

@JohnRennie See you later!

Bernardo Meurer

@Kaumudi.H I tore all the ligaments in my right ankle

6 months without walking

hurts every day

user228700

07:36

OMG.

Bernardo Meurer

and I can't do impact sports anymore

user228700

That sucks, man, I'm so sorry! :-(

Bernardo Meurer

But it's mostly alright, I adapted

so now I bike and swim

user228700

Ah, right, I see.

user228700

I also like biking and swimming.

Bernardo Meurer

07:36

It's mostly alright, sometimes it goes crazy and hurts like death and then I gotta stay home and chill

user228700

Dang.

user228700

@Balarka: I was looking forward to your explanation but now I gotta nap.

Balarka Sen

it was a dumb joke about life being horrid

nothing #deep

:p

user228700

AHH. Now I understand what you really meant. ::Facepalm::

user228700

How's ur Sunday going, BTW?

Balarka Sen

07:41

David Bowie - Sunday

►

on the serious note, preparing for exams

user228700

Unfortunately, I am unable to watch videos atm.

user228700

@BalarkaSen Ah, which ones?

Balarka Sen

physics/chemistry

user228700

Ah. How are you liking Organic Chemistry?

user228700

I WISH I COULD GOOO! (Also: AH, my internet is operating better now!)

Balarka Sen

07:44

bleh. i have to remember a batshit amount of reactions which i don't like

fortunately pretest syllabus has 80% physical chem

user228700

@BalarkaSen Gah, exactly!

user228700

@BalarkaSen Ah, that's nice. And Physics? Are you liking what you're learning in Physics?

Balarka Sen

Oh very much, electromagnetism is fantastic

user228700

Nice! :-) Which bits?

Balarka Sen

pretty much everything. I think I know the 3/4 Maxwell's equations now? still haven't learnt Faraday's law of induction

harmonic functions and solutions to Laplacian equations pop up everywhere, which i like

user228700

07:48

Oh, wtf, wow. Nice! :-) I also loved some bits of Electromagnetism. F* electrostatics though.

Balarka Sen

naw that's my jam

why did you not like electrostatics

user228700

Oh, my primary reason for disliking electrostatics might actually have nothing to do with the subject itself...well, sort of; I needed to learn in twice and both times, it was extremely frustrating to understand everything and there was so much to learn as well!

Balarka Sen

i see

user228700

...I should add that the first time around (12th), I needed to learn literally everything by myself, which was nice and convinient but also quite frustrating at times.

Balarka Sen

mhm

user228700

07:52

Wokay, nap time! See you later :-)

Balarka Sen

enjoy

Bernardo Meurer

@JohnRennie do you have an 8-core server you can lend me for a couple hours?

I need to compute something

:P

John Rennie

@BernardoMeurer 'Fraid not. Actually your laptop is as powerful as any of my kit.

Bernardo Meurer

Guess I'll run it on ULisbon's computer, lol

They didn't revoke my ssh credentials

Secret

08:25

[In a few seconds, prepare for timey wimpy ball weirdness]

[Philosophy]

Secret

08:59

secretlabsultraviolet.blogspot.com.au/2017/08/…

In a nutshell: IMO Social relationships are discontinuous in time. The chemistry between you and some person some time before and after are so different that you might as well said that the person (or you or both) are different individuals

ACuriousMind

@BernardoMeurer Not revoking your credentials for a computer after you leave seems like inviting potatocalypse.

user400188

11:10

Bit of a random question; but Ive been wondering for a while how theories of physics actually infer things.

By infer, I mean logical inference ($\vDash, \vdash,\rightarrow,\implies$ , whatever floats your boat) .

It can't be a simple implication, because then every theory would at best affirm the consequent.
($[B\land(A\implies B)]\implies A$ is falacious)

My thinking is that in physics, it would need to be an "iff" situation. That is, one can't be true without the other also been true. However this is only my naive assumption.

ACuriousMind

I'm not sure I understand your question. What are $A$ and $B$ in your statement? Physical theories make statements like "If physical situation $X$ is the case, then you will observe $Y$", which seems like a straightforward implication to me. Are you worried that physics generally implicitly uses induction to conclude that the theory $T$ is "true", i.e. we have that $T\implies (X\implies Y)$, and then we inductively conclude that $T$ is true from observing $X\implies Y$ sufficiently many times?

user400188

in the notation, $A$ is meant to be a theory, and $B$ an observation.

what I'm worried about, is that if we just have a straitforward implication; then we arrive at a situation like this:

[B∧(A⟹B)]

from this we can only infer B. We cannot confirm that the thoery is correct.

ACuriousMind

Indeed, that is the problem of induction.

user400188

that seems similar, but not exactly what I was talking about.
It seems more focused upon repeated observations confirming something is true for all cases, than it is upon use of "Affirming the antecedant".

John Rennie

We can never prove a theory is correct ...

CooperCape

11:22

I'm a little confused as to why you're worried about it?

ACuriousMind

Which is why many scientists - if they bother with the philosophical/logical aspects of "knowledge" at all - adhere to a variant of Popper's falsificationism (see en.wikipedia.org/wiki/Falsifiability): We never conclude a theory is true, we conclude it is not wrong and consistent with the evidence. If pressed, you will find that "true" in science is generally understood as a shorthand for "not wrong and consistent with the evidence".

@user400188 Well, induction is essentially *affirming the antecedant" after you have observed $B$ sufficiently many times. That's how it works.

John Rennie

In physics a theory is a mathematical model. Within the model we need only not make any mistakes to calculate the phenomena predicted by the model. But we can never prove the model describes reality.

ACuriousMind

In the end, scientific truth in my sense above and logical truth are simply two different things

Induction is a logical fallacy, but it works pretty well as a method of scientific inference.

user400188

@JohnRennie are you sure about that? If I had a theory was was of the form $A\iff B$, then when we observed $B$, we would prove $A$ true as well.

John Rennie

@user400188 am I sure about what? That a physical theory is a mathematical model?

ACuriousMind

11:26

@user400188 No theory can be of that form. Or rather, the implication $B\implies A$ would itself rely on some meta-theory $A'$, and you have the same problem just one level higher.

user400188

This part: "But we can never prove the model describes reality."

@ACuriousMind Ah, that seems to be the anser to my question

John Rennie

@user400188 you test your theory by doing an experiment. If the experiment confirms the predictions of the theory all you have proved is that the theory worked this time. You can never know if some future experiment might contradict the theory.

user400188

sometimes this chat moves faster than I can abosrb.

@ACuriousMind To my knowlage, induction is generaly of the form $[A\land(A\implies B)]\implies B$

so its not always "affirming the antecedant" , in fact such a case is not even induction.

ACuriousMind

Maybe we need to be a bit more careful: 1. Induction is the belief/reasoning that because you have observed a proportion of events/things of type $X$ to have property $A$, then all these events/things have property $A$. As a special case it includes the belief that because an event went a certain way in the past, it will go that way in the future. I concede that this perhaps has nothing to do with what you are asking.

user400188

seems to be a different definition of induction to be honest.

ACuriousMind

11:37

Yes, it's not what you wrote, but that is the meaning of induction as in "problem of induction" and "indutive reasoning" as understood in philosophy of science.

2. A physical theory $T$ is a collection of statements about reality, i.e. you can get predictions $P$ about single events $e$ from it as $T\implies \forall e \in E: P(e)$

2b. If $E$ is the set of all events covered by the theory, you might even write $T\iff \forall e\in E: P(e)$.

3. By necessity, the set of events is always infinite since every experiment can in principle be repeated infinitely many times.

4. This means we can never ascertain the truth of $\forall e: P(e)$ in practice.

So in practice, what we know is that for some finite subset of events $E'\subset E$, $e\in E' : P(e)$ holds. Inductive reasoning now means that we conclude from that that $\forall e\in E: P(e)$ holds, or equivalently that the theory is true.

Caveats: The equivalence in 2b is a very narrow view of a theory. Typically a "theory" contains statements that are not directly related to any observable event/prediction, some axioms or interpretations you cannot test by observing. Different "theories" can have the same predictions.

user400188

@ACuriousMind seems to be a case of universaly generalising when we shouldn't , but i can see why its a nessecity.

Secret

Actually the following point is an interesting one, though I suspect the answer on why consistency is the norm in natural phenomenon will just bring us back to the philosophical question of the unreasonable effectiveness of mathematics, but I digress...

19 mins ago, by ACuriousMind

Induction is a logical fallacy, but it works pretty well as a method of scientific inference.

user400188

@ACuriousMind I'm not entirely sure why 2b works

oh wait never mind.

I see it now

ACuriousMind

Well, I'm essentially defining a theory to be the set of all its predictions there. It's usually not true in practice since, as I said, most theories contain some bits that don't correspond to observations.

user400188

11:56

It seems to me that we should do an experiment first. Then figure out what it implies, write it down, see what else it implies, then test the new implication.

If the new implication is observed then we have confirmed our theory. (Becuase the 'new' implication would have to be implied by the original experiment too, it just wasn't obvious without the help of a model).

ACuriousMind

@user400188 The problem is that experiments don't imply anything on their own.

Say you observe the trajectory of a stone thrown. It flies in a parabola. What does this imply?

Secret

51

Q: Why does the universe obey scientific laws?

As far as anyone is aware, the universe consistently acts according to predictable laws (and scientific inquiry exists to determine those laws). Is there any metaphysical reason for this? Is such a question even answerable? EDIT: I think my question was misunderstood, so I'll try to clarify. I ...

philosophy-of-science metaphysics

hmmm.... information requires some consistency....

0celóñe7

12:32

@BernardoMeurer I have a 6 core server

AccidentalFourierTransform

13:41

Thanks but can u show me roughly. Just a rough sketch is required — Owen 57 mins ago

apparently, countto10 left again (again)

0celóñe7

14:05

@AccidentalFourierTransform what?

AccidentalFourierTransform

14:16

user163104

731 2

0celóñe7

::googles paper::

fug

AccidentalFourierTransform

RIP in peace

Secret

cannot read russian

Secret

14:42

0

Q: Justification for differentiating a Function under the integral

In a physics book I'm reading the authors take this expression, $$\phi(t)=\displaystyle\int_0^a aB(x,t)\mathrm{d}x$$ Then they differentiate with respect to time, $$\dfrac{\mathrm{d}\phi}{\mathrm{d}t}=\displaystyle\int_0^a a\dfrac{\mathrm{d}B(x,t)}{\mathrm{d}t}\mathrm{d}x$$ I assumed that they ...

electromagnetism calculus

This concept question is a classic. I recall being stumped by it back in my electromagnetism courses

0celóñe7

15:03

@Slereah good cover art?

heather

15:19

anyone willing to help with an SE data query?

Danu

15:31

@0celóñe7 3/10

Balarka Sen

x/10 (standard is x = 2) usually follows with "would not bang", which uh does not look super relevant here

Danu

Eh.. No? Go through my history of saying x/10 in this room. Not even once did I say "would not bang" :P

Balarka Sen

lol i was joking

Danu

I knew that, but I also thought the joke was so bad that it deserved a humorless response :-)

Balarka Sen

oh well

Danu

15:40

So how about these hyperplane sections

Balarka Sen

no clue man

wait for Ted, I guess

Danu

It has to be something easy, I think

CooperCape

Guys what's the point in using the Einstein summation thing in vectors? That is $\Sigma_{i=1}^3a_i\hat e_i$ which is in a roundabout way equal to $a_x\hat i + a_y\hat j + a_z\hat k$

Balarka Sen

because for high enough dimension you run out of english alphabets lol

CooperCape

oh wowww

crazy

any reason why its an 'e'?

or is that just what I'm using to learn...

Balarka Sen

15:57

I guess it stands for "elementary basis vectors"? Dunno.

CooperCape

so I'll see that elsewhere it's not just a one-teim thing

Balarka Sen

Yeah it's pretty universally denoted by $e_i$.

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