The h Bar

If $(f_n)$ is a sequence in $L^p$ that converges pointwise a.e. to $f$, and if furthermore $||f_n||\le C$ for all $n$, then $$\lim_n \int||f_n|^p-|f_n-f|^p-|f|^p|\, dx=0.$$

OBE

nvm it will take too long to type

0celouvsky

1:12 AM

@OBE I put Lee back, moved something else to a different shelf

springer sale has been good for the yellow on my shelf :)

@OBE what?

just type it or you won't get help

@OBE learn measure theory from Halmos

OBE

it's not different than before so whatever.

0celouvsky

that's all I can say

OBE

same books you recommended

0celouvsky

1:29 AM

@OBE do you know the book by halmos?

OBE

seen it

how can you tell if a measure theory book is good?

0celouvsky

I've read it?

OBE

indicators?

0celouvsky

it's very abstract yet very concrete

not a single picture in the book

lots of examples but all optional if you want to get the heart of the matter

He basically proves everything you'd want from basic measure theory

OBE

okay I'll look at it when I want to learn measure theory

0celouvsky

1:32 AM

You should learn measure theory as soon as possible

OBE

I am doing everything right now and I feel overwhelmed

0celouvsky

it opens many doors

@OBE what are you learning rn?

OBE

everything

I don't even know

I just have like 30 tabs of books open in my reader

0celouvsky

like what?

let's talk about something

I'm bored, don't want to study

OBE

oh

what do you want to talk about

0celouvsky

1:39 AM

whatever you're learning

analysis, geometry, GR preferably

will tolerate algebra I guess

OBE

okay

I don't have any questions right now because I didn't do many exercises yet

which is bad

0celouvsky

tsk

what books have you been reading, I can think of a good exercise.

OBE

no exercise right now plz

I'm not ready for one

0celouvsky

oh come on

OBE

lol I just don't want to risk not being able to do it

it's public embarrassment

0celouvsky

1:46 AM

skype then

OBE

can we do it in a few days from now I don't feel so well today and I got a new laptop so I forgot my skype acc

I also don't want to disappoint you since that's all I've been doing recently

0celouvsky

ok

hope you feel better

OBE

thanks

0celouvsky

books.google.com/…

oooo

so many interesting books in the world

OBE

what's that about

0celouvsky

1:53 AM

geometric measure theory

OBE

oh sounds cool

what have you been studying recently btw

still analysis?

0celouvsky

@OBE Fourier transforms

Currently working on the Malgrange-Ehrenpreis theorem

It says that any constant coefficient linear PDE has a Green's function, and gives an estimate for the solutions it produces

after I do that, then I want to learn about pseudodifferential operators

but I also want to learn some geometry/topology

and some cosmology

too much stuff to learn

OBE

cosmology?

you're doing physics again?

0celouvsky

I just want to know what's going on in the sky is all

OBE

true

you still have solid state listed in your interests

how much do you know about it?

0celouvsky

2:04 AM

Not much, more practical stuff

OBE

oh okay

what music have you been listening too lately?

0celouvsky

I am trying to understand impedance spectrometry from a theoretical perspective but it's hard

Handler's EM class was awful and did not prepare me for it

I don't understand what e.g. complex resistivity is supposed to be

rob

@0celouvsky Complex resistivity or complex impedance?

Or is there a difference?

0celouvsky

Complex resistivity

@rob Apparently, which is what's screwing me up

I know that our impedance spectrometer can plot complex resistivity and complex impedance and apparently these are different things

I'm scared to ask what it's supposed to be

rob

Is this where a capacitor has an impedance $1/jωC$, and an inductor an impedance $jωL$, so that the magnitude of the impedance depends on the frequency?

OBE

2:08 AM

@0celouvsky wow this is not how science works

0celouvsky

@rob yes, that's the basic idea of the machine

it can also change temperatures and atmospheres

it's super fancy

rob

I don't know that I've heard of an "impedance spectrometer." Can you describe what it is/does?

0celouvsky

@rob Broadband dielectric spectrometer. It can measure complex impedance/ionic conductivity to a very high degree of precision. It gives real time data with variable temperature/frequency

It's a hot topic in the nuclear community because ionic conductivity is a major player in nuclear materials and fuel cells

rob

So, you put samples in it? Solid samples? liquid samples? circuit parts?

0celouvsky

powders and pellets

there's a setup for liquid samples but we don't have it

rob

2:12 AM

Is the geometry of the sample constrained somehow? I'd expect that to affect the complex part of the impedance.

0celouvsky

@rob As long as the sample completely covers both electrodes, it doesn't matter.

The thickness is the only variable then, and the software accounts for that.

rob

@0celouvsky Ah, okay. I'm wiki-ing. I'll be an expert in a minute.

0celouvsky

@rob I saw someone in an eno slung across the columns on the side of South College today

I didn't know such a thing was possible

rob

2:28 AM

So I guess you fill the gap between your electrodes with the material you're interested it, drive the electrodes with some AC voltage (possibly atop some polarizing DC bias), and measure the amplitude and phase shift of the current that's transmitted through the material. If you're clever, you could interpret details in the way the impedance changes with frequency in terms of some model of the material.

@0celouvsky Is that the basic idea? What sorts of materials are you testing? What sorts of driving frequencies?

0celouvsky

@rob that's it

@rob Everything from pyrochlores to spinel to copper

We hope to get another one to be able to use it on radioactive samples

Frequencies go from E-3 Hz to E7

rob

@0celouvsky Conducting metallic copper, or some insulating oxide? Your other exmaples seem to be minerals.

0celouvsky

@rob Metallic, but we're interested in an oxide on the surface

so...both

rob

@0celouvsky Okay. The JLab presentation I linked a couple of comments up is about characterizing surface chemistry.

0celouvsky

you have to do a trick with copper because the conductivity is literally "off the charts"

rob

2:35 AM

@0celouvsky So suppose you put your favorite stuff in this spectrometer, at your favorite temperature and pressure, and you get an interesting-looking report about its impedance over some frequency range. What does that interesting spectrum look like?

Give me an example to work with, something you've tried so far.

0celouvsky

I haven't done anything with it yet! I've only measured things, not interpreted data

Actually measuring things is a PITA, I'm just getting the hang of it

rob

@0celouvsky When you "measured things," did you get data and not understand what you were looking at? or did the machine just beep at you and email the results to your supervisor?

0celouvsky

I hope to run ceria-gallia pellets through it shortly. Then I can tell you more. Supposedly the gallia doped ceria will explode the ionic conductivity

@rob Yeah I got data, then gave it to the postdoc

TBH I don't think any of the profs in my department do research. They're always at conferences and whatnot

rob

@0celouvsky The grad student is dying to explain it to somebody.

Ask her.

0celouvsky

Him

rob

2:39 AM

Whichever.

0celouvsky

@rob I'm going to be making samples for the machine tomorrow

So we'll see

I need to perfect my pellet pressing technique. We have a German collaborator who makes these pellets that look too good to be true

@OBE Ransom 2 by Mike Will

0celouvsky

3:03 AM

> Last update: December 13, 1999

wonderful

0celouvsky

3:31 AM

@yuggib Are the Hormanders self-contained? i.e. if I know something about FT/distributions, can I read Volume III, or do I need to know specific estimates from previous volumes? It seems exactly aligned with my interests.

vzn

4:11 AM

@Secret interesting! theres actually a large body of research now on econophysics, intend to write a blog on that sometime... esp like articles that attempt to discern dynamics of inequality and its possible deleterious effects... taking a political question and turning it into a scientific one... an occasional triumph of other areas of math... eg somewhat like arrows thm! etc

Yashas Samaga

4:23 AM

Today I am fighting with a bunch of people who believe the earth is flat.

skill patrol

4:48 AM

are you winning?

Physics Meta

0

Q: How to use Young diagrams to express the product of an SU(2) doublet and an SU(2) singlet?

How to use Young diagrams to express the product of an SU(2) doublet and an SU(2) singlet, i.e. $2 \otimes 1 = 2$? I can only think of it as follows: \begin{equation} \Box \otimes \Box = \Box\Box \oplus \begin{array}{|r|r|} \hline \\ \hline \\ \hline \end{array} \end{equation} But this seems not...

feature-request

Yashas Samaga

@skillpatrol nope... they talk shit and if I tell that "they are talking shit" then they tell I don't know science

ignorants have to be ignored

John Rennie

5:11 AM

@dmckee Silverberg's output is mixed, but then I guess you could say that of most writers. I remember loving The Book of Skulls as a teenager, but then I recently reread The Gate of Worlds and it was pretty average.

I don't think Amanda and the Alien is a great story and I'm a bit mystified as to why that question has attracted so much attention. I suspect the hand of the HNQ is at work again.

skill patrol

6:11 AM

@YashasSamaga you got it pal. Don't let them drag you down to their level.

They will beat you with experience :-)

yuggib

6:29 AM

@0celouvsky not conpletely self-contained; some theorem from the other books is used.

user228700

7:03 AM

@JohnR: Hello! :-)

user228700

@YashasSamaga Not to be pedantic but is "ignorants" a legit word?

John Rennie

@Kaumudi.H ignoramuses ?

user228700

Heh. I suppose there is no way around this one; "ignorants" doesn't sound legit and "ignoramuses" sounds overly pretentious.

user228700

@JohnR: BTW, do u happen to have any thoughts (interesting or otherwise) about the distinction between inherent "us-ness" and the "us" that is constituted by the thoughts/opinions of the people around us, the content that we consume, etc?

user228700

(If so, I'd like to hear said thoughts after my exams :-P)

John Rennie

7:13 AM

I must admit I'm not sure what you are getting at

You're presumably wondering about the different ways groups of people can bond?

user228700

Huh? No, I'm wondering about possibly the broadest branch of Philosophy, the inquiry of "What does being human even mean?" :-P

user228700

Wokay, it might take me some more time to express what I really mean. Never mind, I'll ask again later.

skill patrol

7:25 AM

ignorants

Noun: ignorants

plural of ignorant

Adjective: ignorants m pl

masculine plural of ignorant...

user228700

Eh, nice!

skill patrol

yeah, it must be built in

TrY iS CheM

8:14 AM

Hii

@JohnRennie

John Rennie

Morning

TrY iS CheM

I have statement , which I am unable to understand

A parallel beam of fast moving electrons is incident normally on a narrow slit . A screen is placed at a large distance from the slit . If the speed of the electrons is increased ,then why the angular width of the central maximum of the diffraction pattern will decrease .

@JohnRennie can you please explain me this statement

John Rennie

@skillpatrol @Kaumudi.H I'm unconvinced about this

skill patrol

+1 @JohnRennie

John Rennie

@TrYiSCheM the electrons are being diffracted by the slit in the same way that light is diffracted by a slit. The diffraction pattern will be a sinc function. OK so far?

TrY iS CheM

8:24 AM

it will not excat sine function

John Rennie

I'm just going to nip off and make a copy while you're thinking about that ...

@TrYiSCheM why not?

TrY iS CheM

because it is single slit

in ydse there is sine function

skill patrol

@Kaumudi.H

TrY iS CheM

encrypted-tbn3.gstatic.com/…

@JohnRennie

John Rennie

@TrYiSCheM sinc not sine. The sinc function is $\sin\theta/\theta$.

Sinc function

In mathematics, physics and engineering, the cardinal sine function or sinc function, denoted by sinc(x), has two slightly different definitions. In mathematics, the historical unnormalized sinc function is defined for x ≠ 0 by sinc ⁡ ( x ) = sin ⁡ ( x ) x . {\displaystyle \operatorname {sinc} (x)={\frac {\sin(x)}{x}}~.} In digital signal processing...

TrY iS CheM

8:29 AM

oh sorry

ok it is sinc function

John Rennie

OK. When you change the speed of the electrons you change their de Broglie wavelength because the wavelength is given by $$ \lambda = \frac{h}{p}$$. And when you change the wavelength you change the diffraction pattern.

TrY iS CheM

oh great

that's why angular width decreases

Thanks for helping

John Rennie

@TrYiSCheM you're welcome - hope it helped!

@BernardoMeurer: take note :-)

TrY iS CheM

@JohnRennie yeah it helped

user228700

9:11 AM

@JohnRennie Thank you! :-) I'm reading the question now and

user228700

> My local library has just closed

user228700

Has it really? x'D

John Rennie

@Kaumudi.H The library hasn't gone for good. It is moving to a new building and it's closed for a month while they do the move.

The new building looks really nice so the downtime will be well worth it.

user228700

Oh, I see. I thought u meant it as "It's evening and my local library has just closed"

John Rennie

I should have said recently closed. I always feel a bit nervous asking questions on the English SE in case my question is criticised for poor grammar :-)

user228700

9:16 AM

Ah, I was just about to edit "Hindu" to "Hindi" but I doubt if Yashas is a native Hindi speaker. Besides, I don't believe that this is a case in which it is OK to accept this usage if being used in "Indian English".

user228700

...sure, we may be allowed to include slang of our own and yes, it's quite difficult to rectify deep-rooted mistakes (such as using "doubt" as a synonym to "question") but it is English, after all.

John Rennie

Not everyone will agree, but I consider Indian English, Caribbean English, etc, to be perfectly valid forms of the language. There is nothing sacred about English as defined by the OED and Fowler.

And American English as well of course, though it's traditional to disparage American English just to annoy Americans :-)

user228700

:-) Heh. I suppose this leads me to think about the origin of language itself etc. :-|

user228700

...better think about revision first. I'll revisit this in a while :-P Oh, hang on, can you please help with something else English-related?

John Rennie

@Kaumudi.H yes, if I can

user228700

9:24 AM

OK. When to use "a while" and "awhile"? I Googled this but I'm afraid I don't understand it :-|

John Rennie

awhile in an adverb.

So you say I walked awhile.

user228700

Ohhh. Right.

John Rennie

In the form a while the word while is a noun.

user228700

I have been making this mistake for a horribly long while :-|

John Rennie

I don't hear the word awhile used much these days. I suspect it is going out of fashion in modern English.

user228700

9:28 AM

All this is scary for a person who hopes to write something someday that at least a little people will like :-|

John Rennie

Writing doesn't have to be grammatically perfect to be entertaining. Rather the reverse I think. All the best authors take liberties with the language. Shakespeare just invented words when he ran out :-)

user228700

x'D Right.

user228700

...although, u have to admit that writing in Indian English sounds terrible. It also constricts the reach of the article or book or whatever.

user228700

Then again, there are exceptions.

John Rennie

As an English speaking Englishman, when authors write in other dialects it adds an exoticism that can make books more interesting.

user228700

9:42 AM

I understand that but you haven't read what I've read (or rather, tried to read :-P) I suppose it boils down to how one uses the words more than the dialect, etc. I mean-and please don't hang me for this-I genuinely like some of Chetan Bhagat's books.

user228700

This is all too subjective though.

Bernardo Meurer

Good morning folks

user228700

Hi :-)

John Rennie

Morning

Bernardo Meurer

@Kaumudi.H Surprised I get attention when the cuter nerd, JR, is around

user228700

9:44 AM

Oye, @SirCumference: What about the book?!

Bernardo Meurer

:P

user228700

@BernardoMeurer :'-(

John Rennie

@Kaumudi.H try reading this:

Glasgow Fairytale by Alastair D. McIver

user228700

I'll check it out, thanks :-)

John Rennie

It's written in Glasgow dialect and even for a native English speaker it's almost incomprehensible. But it's strangely fascinating.

user228700

9:46 AM

Jeez, @SirCumference, I didn't mean to wake u up or whatever.

Kenshin

yo

do you want to be a poet or author @Kaumudi.H

user228700

@Kenshin Yeah, kind of.

user228700

I mean, I dunno. I already write loads. I just don't share it with people.

Kenshin

what do you write about?

user228700

...that's a difficult question to answer. I write about many many things.

Kenshin

9:50 AM

like stories and stuff?

like magic?

user228700

Nope. I'm no good at plot development and all yet. Not stories.

Kenshin

or crime?

user228700

No man, I don't write stories.

Kenshin

oh k

what stuff then

adfaklsdjf

u no.. science stuff

Kenshin

9:51 AM

oh like philosophy

user228700

No...

Kenshin

oh umm like non-ficiton?

like text books?

user228700

Dude -_-

Kenshin

cool

I could never write a textbook

user228700

Dood -_-

Kenshin

9:52 AM

:D

adfaklsdjf

like totally non-fiction.

Kenshin

^ who is dis guy

user228700

x'D

adfaklsdjf

idek.. imma dismiss myself

user228700

I don't think it's possible for me to accurately describe exactly what I write about. Just...stuff will have to do for now.

user228700

9:54 AM

I mean, I also write letters and poems and crap from time to time but not as frequently as the other "stuff".

Kenshin

cool

i hope one day I may get the pleasure to read some

user228700

:-P They're terrible...which is why I don't share it any other human beings. I mean, except the letters. That I write for other people and heh, it's so true how u write so much better when you write as a gift for people. The other stuff I write just for myself so wow, that stuff is not nearly as good.

user228700

Anyhoo...

Kenshin

it's ok bro good or bad i don't judge it

user228700

I am marvelling at how "hipster-y" I sound x'D

Secret

9:59 AM

@JohnRennie I actually prefer flashlight, because I often need to refer to both torches (the fire on a stick type) and torches (the electronic device that illuminate places directionally)

5minuteenglish.com/mar25.htm

My preferences:

Truck > lorry (I tend to use the latter for trucks that have lots of pipes or log like goods strapped on it)

This is the first time I learnt of the word Bonnet

Trunk > Boot

Petrol > Gas (Petrol is more descriptive)

No preference between diapers and nappies

I should say there exists something called tin can

I tend to use biscuits when it is not round in shape, and cookies usually for the chocochips ones

I have a slight preference of football to soccer

Flashlight for the electronic thing, torch for either. Useful when I need to refer to both types of torches at the same time

I have slight preference to lift. elevator I tend to use for larger ones

No preference between rubber and eraser

In short, I prefer more descriptive sounding words

Bernardo Meurer

@JohnRennie Burned myself making Tea :(

John Rennie

Ouch :-(

The sacrifices we make to feed our addictions :-)

Bernardo Meurer

Pretty bad burn on my left index finger

But it was because I'm a dumbass

I was washing the pan I used to heat the water

And a little meta thing near the end of the handle hadn't cooled down yet because it hadn't touched the water

John Rennie

Years ago at the works canteen I picked up a bowl of sponge pudding with (hot) custard and started walking towards the till to pay for it. Halfway there I realised the tip of my thumb was in the (hot) custard. It was so badly scalded I had to go to the health centre!

Bernardo Meurer

How can it take you halfway there to realize that? :P

John Rennie

10:15 AM

I think the skin of your thumb is quite thick because it gets calloused. Plus it was only a couple of seconds before I realised - you can walk a fair distance in two seconds.

I didn't want to just drop the bowl so I rushed to the till where I could put the bowl down, and got burned some more during the time that took.

Bernardo Meurer

Holy crap

John Rennie

And did I get any sympathy from my friends? What do you think? :-)

Bernardo Meurer

Nope

That means they're good friends

Good friends poke your burned finger

John Rennie

And say Does this hurt? :-)

Bernardo Meurer

Yep

@ACuriousMind Can I burn your finger?

Secret

10:34 AM

[Philosophy] Good luck finding a way to test this : plato.stanford.edu/entries/qualia-inverted

ACuriousMind

@BernardoMeurer No.

innisfree

10:50 AM

@JohnRennie that made me laugh, how English - getting scolded by hot custard and prolonging the pain by trying to gracefully put it down without creating a scene

John Rennie

Shrug :-)

innisfree

Any good science book recommendations? This historical fiction about the invention of the light bulb may interest physicists, a.co/7vtslZp

Bernardo Meurer

@innisfree This one is pretty good

ACuriousMind

::waits for @JohnRennie to recommend that book about breasts again::

innisfree

@BernardoMeurer can you recommend something more introductory? ;)

John Rennie

10:59 AM

@innisfree I really enjoyed Bill Schutt's book Cannibalism. I suppose biology counts as a science :-)

Bernardo Meurer

@innisfree Absolutely

John Rennie

@ACuriousMind ah, yes :-)

It's also biology, but I recommend Raymond Coppinger's book What Is a Dog. It gives some fascinating accounts of evolution in action.

I tend not to read popular science physics books these days - I've learned too much physics for them to be interesting. Sad in a way.

innisfree

Haha, that's perfect @BernardoMeurer. That looks great, I learnt something right away from the blurb. It never crossed my mind that most dogs were wild

John Rennie

Coppinger's studies of the dog communities at third world rubbish dumps are absolutely fascinating. Any evolution denier should be forced to read them!

innisfree

Aren't there lots of mysteries about the evolutionary history of dogs?

John Rennie

11:09 AM

Ah, yes, and for more on that read Coyote America by Dan Flores. It's (obviously) about coyotes not dometic dogs but it does go into canine evolution.

Yashas Samaga

I am watching atheists who don't understand physics fighting with religious people who also don't understand physics. This world is a ridiculous place.

Religious people trying to explain gravity of a flat earth using Gauss law! It's funny.

Apparently, the atheists who are arguing there have no clue about Gauss law.

Koolman

11:25 AM

@YashasSamaga have you read that question on jee prepation room

Bernardo Meurer

Casually Explained: Absolute Hot

►

Koolman

in JEE Preparation, 3 hours ago, by Koolman

Bernardo Meurer

Very interesting, I hadn't thought there could be maximum temperature!

Koolman

physics.qandaexchange.com/?qa=1787/work-in-toppling

Sir Cumference

@Secret Oh my god

Now I'm starving

@Kaumudi.H Sorry, it came last night, forgot to tell you XD

Secret

11:38 AM

That's not even a chocolate chip cookie. It is not even the original, but a duplicate from google search

Sir Cumference

I'll have to start reading when I'm done with my next few tests

Secret

Previous night dream:

forgot except in h bar, someone talked about

"There are infinite number of words of ..."

which converges to some number according to mathematicians. Sir Cumference then expressed that this is the reason he dislike mathematicians defining stuff. His comment is then being starred once

Reality check: Nope I never have any records of Sir Cumference ranting about mathematicians

user228700

12:18 PM

@SirCumference -_- OK. Have u started reading it?

user228700

@SirCumference Oh, I didn't read this message :-P OK.

Sir Cumference

12:32 PM

They told me I would have more free time in college ;-;

Or at least more than high school

user228700

@SirCumference :-P Who is "they"? No one ever tells me that.

heather

^

0celouvsky

@Kaumudi.H they tried to play us

Sir Cumference

@Kaumudi.H Some family and friends

0celouvsky

They tried to hold us down

Down with they

ACuriousMind

12:41 PM

They always told me university would be hard.

0celouvsky

Bless up

They told me I would have to study

Sir Cumference

@ACuriousMind You have a good they, I didn't

0celouvsky

::memorizes proof of Egorov's theorem::

I have an exam in 20 mins pls give energy

heather

::gives energy::

user228700

"They" told me that University will be much easier than high school but again, not much time to be proactive about what to do.

user228700

12:43 PM

@0celouvsky ::Sends "energy vibes" in your direction:: (To the general West :-P)

Sir Cumference

@0celouvsky You have the potential to give yourself energy

heather

"They" told me that it's what you make it, but if you are doing it right, it should be hard, but fun.

ACuriousMind

::devours energy:: (I'm a vampire, what can I do?)

heather

@SirCumference lol

puns are great

Sir Cumference

The best puns are the worst puns :)

0celouvsky

12:44 PM

@ACuriousMind wtf you don't even like measure theory

Sir Cumference

@ACuriousMind Vampire robots. The world is doomed.

ACuriousMind

Nov 25 '16 at 16:38, by John Rennie

What do you get if cross a vampire with a robot?

Nov 25 '16 at 16:39, by John Rennie

NosfeR2-D2

Sir Cumference

Darn it that's good...

Yashas Samaga

Where does the energy of redshifted light go? One article says conservation of energy does not work and another article says it goes into the space.

The point is pretty simple: back when you thought energy was conserved, there was a reason why you thought that, namely time-translation invariance. A fancy way of saying “the background on which particles and forces evolve, as well as the dynamical rules governing their motions, are fixed, not changing with time.”

But in general relativity that’s simply no longer true. Einstein tells us that space and time are dynamical, and in particular that they can evolve with time. When the space through which particles move is changing, the total energy of those particles is not conserved.

First, unlike with ordinary matter fields, there is no such thing as the density of gravitational energy. The thing you would like to define as the energy associated with the curvature of spacetime is not uniquely defined at every point in space.

So the best you can rigorously do is define the energy of the whole universe all at once, rather than talking about the energy of each separate piece. (You can sometimes talk approximately about the energy of different pieces, by imagining that they are isolated from the rest of the universe.) Even if you can define such a quantity, it’s much less useful than the notion of energy we have for matter fields.

The second reason is that the entire point of this exercise is to explain what’s going on in GR to people who aren’t familiar with the mathematical details of the theory. All of the experts agree on what’s happening; this is an issue of translation, not of physics.

And in my experience, saying “there’s energy in the gravitational field, but it’s negative, so it exactly cancels the energy you think is being gained in the matter fields” does not actually increase anyone’s understanding — it just quiets them down. Whereas if you say “in general relativity spacetime can give energy to matter, or absorb it from matter, so that the total energy simply isn’t conserved,” they might be surprised but I think most people do actually gain some understanding thereby.

0celouvsky

@ACuriousMind that only makes sense with a British accent.

ACuriousMind

12:54 PM

@0celouvsky To my knowledge, John is British

@YashasSamaga see physics.stackexchange.com/q/7060/50583 and its many linked duplicates. It's a matter of some dispute, but the "mainstream" view, as far as I know, is simply that you don't have global conservation of energy because the expanding universe plainly doesn't have time-translation invariance.

0celouvsky

I thought he was welsh

ACuriousMind

@0celouvsky Aren't the Welsh British, but not English? :P

0celouvsky

Then I meant an English accent

ACuriousMind

Also, "British" is a weird-looking word.