The h Bar

3:00 PM

After understanding that energy is the integral of (I don't understand what it is) under time translation, it becomes easier to understand why $T^{00}$ is the total energy

ACuriousMind

@JohnRennie I have a suspicion we might have killed for that before taming fire ;P

John Rennie

@Secret total energy density ...

Secret

oops sorry

@slereah , why is a conformally not flat, ricci flat, static spacetime filled with radiation cannot be described by a rubber band model (assuming when you said that "if spacetime is a rubber band" back up there can be interpreted in the layman sense of something elastic like rubber)?

Slereah

Well for a start

What do you call "described by a rubber band model"

0celo7

@ACuriousMind Aha, the integral is finite

Secret

3:05 PM

2 hours ago, by Slereah

But if spacetime is a rubber band

0celo7

There's conformal transformation shenanigans going on

Secret

I actually don't really know if you are meaning a rubber band in the laymen sense

but when interpreted that way, I then have this question

0celo7

@Secret Yes, spacetime is literally an elastic hydrocarbon.

peterh

@JohnRennie The models have a goal. The math serves physics, physics serves engineering. On the end of the chain, there is the Human, making wonderful things with his hands, and with his mind. Now wonderful nuclear reactors, maybe once wonderful spaceships. Isn't it the goal of the whole thing?

Slereah

The simplest argument I have is that the equations of GR are non-linear

mahsa.e.1378

3:06 PM

hi

@Slereah Proof

@0celo7 : $R$

@mahsa.e.1378 Hi!

Oh my coffee tastes like ass today

Nasty

mahsa.e.1378

don't you think physic progress was better in 20 centery ?

ACuriousMind

3:09 PM

@mahsa.e.1378 Define "better"

Also, note this century has just begun.

mahsa.e.1378

ok

Secret

@slereah But aren't rubber bands can display nonlinear properties when stetched too far just before it breaks?

0celo7

@ACuriousMind Whoa

John Rennie

@peterh I think that's an optimistic view. Most humans I know blunder around like a drunken penguin and achieve progress only by virtue of something akin to a diffusion process :-)

0celo7

that's deep

@Secre I don't think spacetime can break

ACuriousMind

3:10 PM

@JohnRennie ...and you call me a cynic. :)

0celo7

Well...maybe @Slereah

Slereah

The real thing you have to decide is "what does a rubber band model means"

ACuriousMind

Also, drunken penguins are adorable. Most humans aren't!

Slereah

I can't really answer it before then

John Rennie

@mahsa.e.1378 We did all the easy stuff in the 20th century (for a small subset of meanings of the word easy). Now that only the hard stuff is left the apparent pace of progress has slowed.

0celo7

3:11 PM

@Slereah

heather

@peterh, we've always wanted to understand the world for its own sake.

vzn

@Danu think physics PR/ outreach is worth something, he has very high profile and in some ways is a major "face" for the field

0celo7

Looks a lot like a Dirac belt, tbh

Secret

Maybe you can elaborate what exactly you mean when you say if spacetime is a rubber band?
Because from what we have discussed so far, you seemed to use the meaning of rubber band in a sense that I don't know about?

0celo7

maybe there's some connection to spinors

Slereah

3:12 PM

Is that the $S^1 \times \Bbb R$ spacetime

mahsa.e.1378

but I think we have to increase it ( the progress ) cause we are smarter and we have more tools and fessilities

0celo7

@Slereah No, $S^1\times[a,b]$.

vzn

@JohnRennie that is close to a quote by churchill have you heard it? re "the truth" :|

Slereah

Well those are diffeomorphic

ACuriousMind

@0celo7 ::twitches::

mahsa.e.1378

3:12 PM

no

It is easy that we are working on but we don't observe

0celo7

@Slereah Wrong

lucas

@JohnRennie I don't want to discuss about physics as I promised before, but I just want to say easy or difficult are relative.

John Rennie

> Men occasionally stumble over the truth, but most of them pick themselves up and hurry off as if nothing ever happened.

0celo7

$[a,b]$ is compact, $\Bbb R$ is not.

Slereah

DEPENDS ON THE TOPOLOGY OF $\Bbb R$

0celo7

3:14 PM

@ACuriousMind Silly topology question: homeomorphisms are open, but are they also closed?

Slereah

nah just kidding

lucas

Past is easy for present and present is easy for future.

ACuriousMind

@0celo7 I agree that's a silly question.

0celo7

@ACuriousMind I need an answer :<

Secret

@slereah So a rubber band model will be whatever that give the notion when you say "if spacetime is a rubber band"?

ACuriousMind

3:15 PM

@0celo7 What do you think, and why?

John Rennie

@lucas though in a thousand years students will still be complaining that quantum field theory is absurdly hard :-)

0celo7

I'd have to say no, because $\Bbb R$ and $(a,b)$ are homeomorphic, but one is closed and the other is not.

ACuriousMind

@0celo7 oO

mahsa.e.1378

so lucas it means every thing is easy but we sont observe truly

Slereah

Well when I hear "spacetime as a rubber band", I'm thinking of an elastic surface

ACuriousMind

3:15 PM

How is $(a,b)$ not closed in its own topology?

Slereah

Of which spacetime is not

0celo7

@ACuriousMind Ohhh

vzn

geez can you guys type any faster? o_O

0celo7

no

This is about as fast as it gets

@ACuriousMind :)

vzn

@0celo7 always trying to pull a fast one :P

0celo7

3:16 PM

Been wondering about that for a few weeks

peterh

@JohnRennie Next to that, the society is from people knowing nothing from the physics and have much fewer interest in it as to pay a lot for accelerators. If it would be their decision, the physics had a very bad time.

John Rennie

It's a lively discussion - it must be a Friday :-)

0celo7

Yeah, and my class got canceled

That means I should get work done

mahsa.e.1378

bye dears

John Rennie

@0celo7 I've done 8 hours work today already - what's your excuse? :-)

vzn

3:17 PM

@peterh "big science" = staggering $$$

peterh

@JohnRennie The - said or unsaid - reason, why it gets billions of dollar for accelerators, telescopes, sensors, fusion reactors, despite the always very fanatic green and anti-science lines, is the hope, that once it can produce some very, very new and wonderful, objective result. The last time as it happened, it was the nuclear energy in the 30s.

0celo7

@JohnRennie I'm lazy

lucas

@mahsa.e.1378 Have a nice time! :-)

0celo7

Not an excuse, just the truth

peterh

@JohnRennie Since then, the main significant steps are coming mainly from the engineering side. But there is the said or unsaid wish, that once maybe a similar significant step will happen again.

Slereah

3:18 PM

Big science isn't big money for scientists

vzn

was just reading about some null result for neutrinos or something that cost billions $$$ ... seems like maybe a record

peterh

@JohnRennie Only to produce the GUT or TOE, without any practical usability, simply doesn't worth to pay the next accelerator below the Equator. If there is a significant hope, that we could maybe once make antigravity by the things which were found in it, it worths.

Secret

So that means the metric you mention does not have any terms that can be equated to an elastic surface?

Or perhaps is it that "if spacetime is a rubber band" does not necessary lead to the deduction that "Ozsváth–Schücking metric is impossible"?

(maybe that's how I get that wrong question)

vzn

@peterh what "next accelerator"?

ACuriousMind

@Slereah Don't bother, they can't hear you through their aluminium ear warmers :P

vzn

3:20 PM

@peterh fusion

peterh

@JohnRennie Somewhere I've read from a physicist, here on the PSE, that the only goal of the Physics to understand things better and he doesn't think it will have, or should have, any practical usability. As I read it, it made me scared.

0celo7

@ACuriousMind what

@Slereah what?

vzn

@Slereah agreed

peterh

@vzn Ok, the next size will be around 80km, but the tunnel diameters seem to grow roughly exponentially.

vzn

@ACuriousMind stave off the hordes

John Rennie

3:25 PM

@peterh there are two separate issues here. Firstly we need our blue sky thinkers, but they need to be the ones out at the $3\sigma$ end of the distribution with most scientists sat near the mean working away on things relevant to everyday life. If you hear scientists saying that practical usabilty doesn't matter that's good provided not all scientists say that.

Secondly physics splits neatly into a series of energy scales, and the new stuff we're discovering is all at extreme energy scales that are unlikely ever to be relevant to everyday life. And the everyday life energy cale we already understand pretty well.

Slereah

people tend to not know about indirect benefits of theoretical physics, either

vzn

@peterh try feynman "the pleasure of finding things out" anyway think youre kinda setting up scarecrow there

Slereah

The mathematical machinery developped for it tends to be very useful in other practical fields

John Rennie

All progress in the last 100 years has basically been technological and not down to advances in our understanding of fundamental physics.

vzn

@JohnRennie there are some big new discoveries that will play out in big ways eg superconductors, nanotubes/ nanotech etc, but we seem to be in a plateau at the moment

arent superconductors being used on japanese (maglev) trains? or have heard its close

0celo7

3:29 PM

@ACuriousMind If I have a map $f:M\to N$, and $f$ has the coordinate representation $(f^1,\dotsc, f^n)$ on $N$, what could $\partial/\partial f^i$ mean?

heather

@peterh, you are taking a very pessimistic view...not to be poetic, but think of all we've learned about the universe, from the strangeness of quarks (pun intended) to the awesome scale of the universe...even if there weren't tech benefits, isn't that worth something?

John Rennie

@vzn That's a good example. Superconductors were discovered accidentally by physicists messing around with low temperatures. Eventually the theorists came up with an explanation, but no advance in practical applications of superconductors has been driven by theory. It's all been physicists messing around to see what happened.

Slereah

Atomism took quite a while to be useful at anything, really

vzn

@JohnRennie its still basically physics innovation. but yeah agree the theory is getting more removed from daily life eg high energy, black holes etc

Slereah

High energy physics is used nowadays for medical applications

As well as industrial

lucas

3:31 PM

But I think we don't need to improve physics while a lot of people all over the world are hungry. I cannot accept that one sits in his room and think about improving the physics and has best life while another one works all day long and sleeps with empty stomach.

Slereah

As it stands, physics, especially theoretical physics, is a negligible part of national budgets

If you want to worry about improving life quality maybe look for other places to cut budgets

ACuriousMind

Regardless of whether science has pratical usage or not, it's simply not done for that practical benefit. The artist doesn't create art because he wants to sell it, the musician doesn't play because people will give him money, the philosopher doesn't write books because they will be sold and the scientist doesn't investigate nature because it will be useful. No one stands at the LHC and thinks "I can't wait till we make that accidental discovery that will have practical applications"

6

Slereah

(HINT : DEFENSE IN THE US)

0celo7

@Slereah Don't be silly

We don't spend enough

Slereah

Money spent on string theory or whatever else is peanuts

You might cut the funding for art and you'd probably get more money

0celo7

3:34 PM

@Slereah One issue is that the smartest people in the world are locked up in laboratories and universities instead of improving the world.

Secret

@slereah
Ok guys, let me try again. The full story of my question is like this:

Back in that post when Slereah mentioned that "if spacetime is a rubber band----(1)", how do you explain this?-----(2) *give the link to Ozsváth–Schücking metric*"

First I thought by rubber band, I thought he means something elastic.

Using this assumption, I then assume that if (1) then (2) and nothing else, thus using negation, if not (2) then not (1). This caused me to read about the metric and try to find anything that suggest it is not elastic, but I cannot find any. (thus the questions related to pp wave…

John Duffield

@JohnRennie : the night sky is not a manifold equipped with a metric. The map is not the territory.

Slereah

@0celo7 They might also not want to work in those fields

I certainly don't

John Rennie

@JohnDuffield that's what I said. Oh no, I'm agreeing with JD :-)

ACuriousMind

@0celo7 The world doesn't need more smart people to improve it. It needs a majority actually wanting to improve it.

0celo7

3:35 PM

@JohnDuffield How do you know it's not a manifold?

Slereah

that too

vzn

@lucas physics has something to say about wealth inequality, see econophysics... new/ small but promising

lucas

@Slereah Do you want to work in a mine?

Slereah

It's not like we lack solutions

John Duffield

@Secret : spacetime models space at all times and therefore is static. Space is dynamic. Space is elastic.

John Rennie

3:35 PM

Well, no, I said neither I nor anyone else know what the night sky is.

Slereah

@lucas Is that the only alternative

As it stands I don't work in research anymore and I certainly don't work to improve humanity

0celo7

You're a misanthrope, an anomaly.

lucas

@Slereah No, do you want to work as a building worker?

Slereah

No

John Duffield

@JohnRennie : I know what space is.

0celo7

3:36 PM

You just eat your tendies

vzn

@0celo7 lol calls someone a misanthrope

Slereah

I just looked for jobs that would actually take me

Including some jobs that would benefit mankind

0celo7

@vzn What?

Slereah

Those types of jobs are not hiring theoretical physicists

John Rennie

@Slereah that's not true, lots of physics postdocs now work as janitors ...

vzn

3:37 PM

what are "tendies"?

Slereah

Heyoooo

Chicken tenders

lucas

@Slereah Do you want to be a baker? You can learn it very soon.

John Duffield

@peterh : don't you worry peter. I got this.

0celo7

@JohnRennie Maybe they should have done something useful in their education...

John Rennie

@0celo7 become bankers?

Slereah

3:38 PM

I am already working

In software development

0celo7

@JohnRennie For instance.

vzn

@Slereah web dev? back to work?

Slereah

Data mining

Kinda

0celo7

Can I have Steam codes pls @Slereah

lucas

@Slereah You don't work. You sit on your comfort chair. Am I wrong?

Slereah

3:39 PM

Well I don't want to code in an uncomfortable chair

ACuriousMind

@lucas If you want to say that many people have it worse then I think no one is debating that. What's your point?

John Rennie

@lucas whoever flagged that please get a life.

Slereah

Apparently only manual labor is real work in his universe, I think

vzn

@Slereah hey congrats man ~½ good news, thats not entirely unscientific. what kinda of data? languages?

John Rennie

@lucas: sorry i didn't mean you, Lucas. Someone else flagged your post.

Slereah

3:40 PM

C++

Secret

I am still trying to work out how to ask slereah why the fact that spacetime is not an elastic surface will imply the Ozsváth–Schücking metric can exist (and hence if the Ozsváth–Schücking metric does not exist, then spacetime will be an elastic surface

OR, why that spacetime is not an elastic surface does not necessary imply that Ozsváth–Schücking metric must be the only thing that can exist which otherwise cannot if spacetime is an elastic surface

Slereah

And soccer match results

(It is very much not for the betterment of mankind)

peterh

@vzn Yes, I am personally very curious, but the politicians not. They are fighting for the R&D budgets, and they are also fighting, how it will be parted between the different projects. As I can see, the technochratic elite, wishing for a better world - by physics results -, seems to me currently highly overrepresented in the circles of the decision-makers, at least compared to the popularity of the physics in the common people. But this strength seems to me fragile.

vzn

@Slereah lol so you are not a sports fan? what do they do with results?

Slereah

@Secret : Because it's a spacetime with no "tension" and that has static solutions that aren't flat space

Which seems a bit odd for an elastic sheet

@vzn It's for one of those prognostication websites

Secret

3:42 PM

@ Slereah I see, makes sense

Slereah

for sports betting

vzn

@Slereah "static"? gravitational waves...

Slereah

Actually I think that might be the opposite of benefiting mankind

But hey I gotta get paid

vzn

@Slereah have read some on that field (eg horse racing), its actually conceptually quite similar to "trading"

it would be interesting to hear what ML algorithms you use

Slereah

Well it's your basic data analysis shit

I'm trying to apply neural networks on it

Because statistical methods are kind of a pain

peterh

3:43 PM

@ACuriousMind But, I think, most of them hopes that.

Slereah

The distributions get very painful to look at the more you go on

If you want to look at the statistical methods, the basic method is from Maher's paper

0celo7

@ACuriousMind Can I view the tangent map of a function $M\to N$ as the section of some bundle?

Secret

interestingly, when asking that rubber band question earlier, I have accidentally gave a concrete example on what I am saying in that big wall of text in http://chat.stackexchange.com/transcript/message/31368064#31368064

@vzn Acuriousmind, 0celo7 this is why my questions are often confusing, because the question can only become a complete question with your knowledge bases

Slereah

90minut.pl/misc/maher.pdf

John Duffield

@JohnRennie : LOL, you'll be agreeing with JD a whole lot more in future.

0celo7

3:45 PM

@JohnDuffield Omg you're going to learn physics??

vzn

@Slereah thx/ interesting, but 1982? bet theres some big stuff since then!

Slereah

Oh yeah, there's a lot of improvements on it

lucas

@ACuriousMind I mean we can produce food for all people if all (or most) of us work. But most of us don't work and eat more. We have no problem called energy problem if all of us work. But we want to sit and the others work for us.

peterh

@JohnRennie the night sky is that black thing, where we will maybe fly with spaceships. To the stars. It is my definition to the night sky.

Slereah

I think the latest big paper is like... Rue and the other guy

Salvesen

wilson.engr.wisc.edu/rsfc/oth_sites/rate/papers/…

0celo7

3:46 PM

@JohnRennie not nice

John Duffield

@0celo7 : no, I'm going to teach physics!!!

John Rennie

@0celo7 hmm, yes unworthy of me.

Slereah

God help this generation

vzn

@Slereah just saw an excellent datamining overview want me to dig it up? it was on general techniques... by a kaggle expert... rare to divulge so much

Slereah

Sure

0celo7

3:47 PM

@Slereah Says the Frenchman

peterh

@JohnRennie If the energy levels are too high, it means only, that the engineering didn't follow the physics enough well until now.

Slereah

I tend to go with neural networks because it's what I've worked on the most and I can let the computer work instead of me :p

lucas

We don't need nuclear energy if all of us work. We can easily life with windmills.

Slereah

On the other hand

Plasma acceleration

Plasma acceleration is a technique for accelerating charged particles, such as electrons, positrons and ions, using an electric field associated with electron plasma wave or other high-gradient plasma structures (like shock and sheath fields). The plasma acceleration structures are created either using ultra-short laser pulses or energetic particle beams that are matched to the plasma parameters. These techniques offer a way to build high performance particle accelerators of much smaller size than conventional devices. The basic concepts of plasma acceleration and its possibilities were originally...

John Rennie

@lucas and die of preventable diseases

0celo7

3:48 PM

You have to be German if you like windmills

Slereah

^very promising for easy high energy

vzn

@Slereah theyre very solid esp nowadays with deep learning but also just part of the "spectrum" of algorithms

Slereah

yeah

ACuriousMind

@lucas I simply disagree that that's the problem. Returning to an agrarian society doesn't solve anything. It's inequal distribution of goods, not a shortage of goods, that is the problem.

Secret

@vzn is there any term in neuroscience that can describe the way I think as what you have knew about me so far?

Slereah

3:48 PM

I mean neural networks can do anything, but they don't do anything well

John Duffield

@John Rennie : trust me, when you do move it forward, you'll find yourself reading one of my answers saying uh oh. :)

Slereah

It's kind of a lazy solution

lucas

@JohnRennie What?

ACuriousMind

@lucas What has "if all of us work" to do with what kind of energy we use?

Slereah

"Returning to an agrarian society" is the kind of solution people who have never lived in an agrarian society would give

vzn

3:49 PM

@Secret huh? memory? personality?

Slereah

We've had agrarian societies for about 40.000 years and they've never been good

0celo7

@ACuriousMind I think that's a Germanism, but I'm not sure.

vzn

@Slereah lol they had no problem with overpopulation/ environment degradation/ global warming/ mass extinction etc

peterh

@ACuriousMind The mean tax rate was around 20% in the medieval Europe. Now, if you calculate personal tax + VAT + profit tax of your employer, it can be over 80%.

Slereah

Are you kidding?

Mass extinctions happened several times

Secret

3:50 PM

@vzn
the fact that when I ask question, I need the knowledge base of both the one who answer my question and me as an answer in order for the question to make sense and understandable (despite I know little about the details of the question itself)?

Any example of neuro network that behave like this decentralised fashion?

John Rennie

@lucas we can only afford the investment necessary to develop new drugs because our society is so productive. If go back to an agrarian society that will be the end of pharmaceutical research.

ACuriousMind

@0celo7 Hmm..it would be more idiomatic if the "what" was a "the", right?

Slereah

With HUNTER AND GATHERER SOCIETIES

lucas

@ACuriousMind Windmills don't need to have plenty physicists for thinking about.

ACuriousMind

@lucas So?

John Duffield

3:50 PM

@Secret : no, but there's such a thing as "the wisdom of crowds".

0celo7

@ACuriousMind No, I meant the construction "what has X to do" is German, but I think many native speakers say that too.

ACuriousMind

Do you want to implement some sort of anti-intellectual communism? That's been tried before!

Slereah

Oh yes

The Khmer

John Rennie

The standard of living is directly linked to productivity. Lower productivity and you lower the standard of living.

Slereah

That didn't turn out so well

vzn

3:51 PM

@Secret "intelligent assistants" eg siri are close to that

Secret

ouch, so I am basically an AI

lucas

@JohnRennie We can prevent diseases by healthy food. We make most diseases ourselves.

ACuriousMind

@lucas That's just demonstrably untrue.

0celo7

I'm thinking $\mathrm df\in\Gamma(T^*M\otimes f^*TN)$.

John Duffield

@lucas : I'm afraid that isn't true Lucas.

John Rennie

3:52 PM

@lucas The biggest cause of death in agrarian societies is associated with childbirth. How is that to do with a bad diet?

Slereah

Also agrarian societies don't really have healthy food

vzn

@Secret your question also reminds me of "empathy" which is an increasingly big deal in psychology. but anyway, the "big theory" for AI is still mostly open, and intelligent dialogue is a big part of that gap (re "turing test")

ACuriousMind

No "healthy food" can save you from bacterial and viral infections. On the other hand, science (medicine) can!

Slereah

Historically agrarian societies have had pretty poor food due to a lack of diversity in crop

lucas

@ACuriousMind So if we can live without employing plenty physicists for thinking about quantum mechanics, why do we not do?

John Rennie

3:53 PM

@Slereah and rubbish crop yields

Slereah

We have healthy food these days because we can afford to import whatever food we need

that too

ACuriousMind

@lucas Because people are interested in thinking about quantum mechanics, or more generally finding out how the world works?

Life is different from survival. I wouldn't want to live in a society that lacked either art or science.

lucas

@ACuriousMind No, I think they abuse from ignorance of other people to eat without working.

ACuriousMind

@lucas ???

lucas

@ACuriousMind But you don't work in the current society.

ACuriousMind

3:56 PM

You think everyone who doesn't hunt their own food should be left to starve?

lucas

@ACuriousMind Who must work in the world?

ACuriousMind

Current society, by making funding available, has shown that it is willing to call what I (will) do "work", or at least give me money for it.

John Duffield

I must go. Bye all.

peterh

Somewhere I've read, Germany can have only around 3-5million people on the hunting-fishing society model

lucas

@JohnDuffield Bye :-)

I think for producing food, some work is necessary. Am I right?

Secret

3:58 PM

4 mins ago, by ACuriousMind

@lucas Because people are interested in thinking about quantum mechanics, or more generally finding out how the world works?

lucas

So who must work?

Secret

I will DIE for quantum mechanics. I love this subject so much almost on par with chemistry
(Post this way to avoid the reply command form pinigng acuriousmind, I pinged her too much today)

ACuriousMind

@lucas Obviously. Again, what's your point?

Obliv

@lucas just gonna chime in here. I hope that we aren't so primitive that we require the entire population to be doing physical labor in order for us to survive. In fact, I'm certain we aren't this primitive. Why do you insist that everyone work when this is not required?

The reason our knowledge about how things work (physics&math -> engineering -> better lifestyles) is because we have time to think about these things without having to tend to a farm or hunt for food.

0celo7

@Secret Her?

vzn

3:59 PM

@lucas suggest you recast your objections as questioning/ challenging the nature of capitalism in theory/ practice which is a very mainstream topic these days. it is in fact a complex system for (im-!) balancing work

lucas

@ACuriousMind Why you are not that person who works for producing food for the others?

0celo7

@ACuriousMind I think @Secret just called you a gril

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