The h Bar - 2018-03-29 (page 3 of 4)

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5:01 PM

@JohnRennie : the speed of light is always locally c because we use the local motion of light to define our second and our metre, then we use them to measure the local motion of light. Duh! It is a tautology, as Magueijo and Moffat said in arxiv.org/abs/0705.4507

though really I think the one big thing JD seems to be missing from those papers is that the variable speed of light thing isn't the source of GR, it's a consequence of it

@JohnDuffield lol just got censored by woit on his blog over anticopenhagen book by becker. whatever... no censorship on my blog. almost no commenting either. :P ps just found your blog from that. start of something grand? think hossenfelder is brilliant. one mans crank is another mans visionary. she likes Verlinde. bolbteppa was just ridiculing verlinde and hossenfelder by association. whatever

@Slereah it's a fundamental failure to understand general covariance. He isn't the first and won't be the last to manage this feat.

More importantly it's not what Saint Einstein says!

@Slereah : no, it's the other way round. Light curves because the speed of light varies. Because a concentration of energy in the guise of a massive star "conditions" the surrounding space. It alters it, and the effect diminishes with distance in a non-linear fashion.

5:05 PM

@JohnDuffield youre thinking in terms of what might be called "absolute (or euclidean) coordinates" but physicists have been trained to reject that view, even though its valid.

I’m reminded of the following anecdote re: Borel summation

“Borel, then an unknown young man, discovered that his summation method gave the 'right' answer for many classical divergent series. He decided to make a pilgrimage to Stockholm to see Mittag-Leffler, who was the recognized lord of complex analysis. Mittag-Leffler listened politely to what Borel had to say and then, placing his hand upon the complete works by Weierstrass, his teacher, he said in Latin, 'The Master forbids it'.”

@vzn : Woit will happily attack some things, and will happily censor the defence, plus other things. IMHO he portrays himself as some kind of noble white knight, but he isn't.

@JohnDuffield re optical clocks "lower" are you talking about relative to earth orbit/ center?

What I'd say is that Woit is, when it comes to theor. physics, very much a conservative

@Semiclassical my sides

5:09 PM

@Slereah there is a comment about lorentz invariance by ACM that addresses this issue. think everyone is talking past each other. its like "is the glass ½ empty or ½ full". both povs are logically equivalent yet each side thinks they are not.

That means that, on one hand, he's skeptical of efforts like string theory that have gone deep into speculation without leaving much hope for contact with experiment

@vzn : lower down in the room you're in, as per the David Wineland interview : "if one clock in one lab is 30cm higher than the clock in the other lab, we can see the difference in the rates they run at".

@vzn Hell you can do GR as a flat space theory where light goes at different speed

but on the other, he's also skeptical of efforts to reinterpret or modify quantum mechanics, since from his perspective it works perfectly well

But then that's not GR

That's the Pauli-Fierz theory

where the light interacts with a spin-2 field

Although it's no more true there that gravity happens because the speed of light changes

5:10 PM

So I don't see it as an inconsistency on the part of Woit

@Semiclassical : it doesn't. I've spent months looking into this.

@SolenodonParadoxus Note that Lorentz aether theory is not the same as the standard "luminiferous aether", and experimentally indistinguishable from special relativity in its predictions, the sole difference being in its ontology/metaphysics. — ACuriousMind ♦ Feb 14 at 22:56

@Semiclassical I think Woit started out making a good point. A decade or so ago string theory was so utterly dominant it was starving other areas of funding.

@JohnRennie The Motl forbids it

But he's got caught up in his own crusade and become a bit of a charicature of himself.

5:12 PM

The issue for me is one of interpretation vs. experiment

think the descriptions of spacetime wrt GR or wrt JD thinking are equivalent but neither "side" realizes it yet. :( am going to try to search for some ref that explains this, suspect Tenev + Horstemeyer comes close...

When it comes to experiment, it frankly is hard to argue with success

The trouble is that experimental data is hard to get in HEP.

@vzn I dunno, what would JD's idea look like from changing the coordinates

5 mins ago, by Semiclassical

What I'd say is that Woit is, when it comes to theor. physics, very much a conservative

5:13 PM

Hard to say since he doesn't actually uses math

All that money spent on the LHC and they found ... the Higgs boson. And that's it.

I like face to face conversations, because it is IMPOSSIBLE to censor a face to face conversation

@Slereah exactly have you ever seen that description? think its "not inequivalent" mathematially to GR. its just different interpretations on the same eqns!

And it's hard to overstate how successful QM and QFT have been as experimental theories within the their domains

@vzn : they aren't equivalent. When you read the Einstein digital papers and understand what Einstein was saying, and when you realize what the evidence says, everything you ever thought you knew about singularity theorems and black hole physics turns out to be not even wrong.

5:14 PM

especially when it is recorded >:D

That is, for the stuff that we can actually predict using QM and QFT, they have been exceptionally successful

Also

The question is

Are all spacetimes that have the same speed of light everywhere Minkowski space?

In the absence of experimental data I think it's reasonable to allow HEP physicists to wander off down strange paths. It's not as though it's a huge amount of money involved.

I'm not even sure

@JohnDuffield your claims about incommensurability (in the kuhnian sense) need to be rigorously backed up with math. suspect there are some small discrepancies but they wont be isolated without resorting to the (difficult/ complex) math.

5:15 PM

I think that there might be equivalent classes of spacetimes with the same "speeds of light"

@Slereah ignoring topology i.e. a toroidal flat space is still treated as Minkowski?

@Semiclassical : give me some predictions from QM and QFT. Not postdictions, predictions.

But unfortunately those are all issues JD do not consider :p

Although

IIRC there is a vague formalism

GR in the optical limit

Where you do treat spacetime as a refractive medium

Stern-Gerlach effect. It's true that QM doesn't tell you whether a given spin comes out up or down, but it gives perfectly cogent statistics

But it's used as an approximation for gravitational lensing

I don't think you can get back the full GR from it

5:17 PM

@vzn : I think they can be backed up by showing flaws in the rigourous maths used to promote the "competitor" interpretation.

But you know, while it's fun all in all to think about alternative formulations of GR and whatnot

In the end it's not worth to discuss it with JD because he has no ideas about any of the issues involved

@Slereah : see Inhomogeneous vacuum: an alternative interpretation of curved spacetime.

Or the mathematics required

So it will never go anywhere

You couldn't even persuade him to write down some actual proofs if you pretended to agree with him

@JohnDuffield there is a lot of professional controversy/ disagreement on what happens in "edge cases" in GR, black holes/ big bang, singularities etc. there is probably someone authoritative who espouses views close to yours, and it would increase your credibility substantially to align with them.

$$\huge{\text{We need maths for this discussion to even go anywhere}}$$

5:20 PM

whats the hubbub about

@BalarkaSen Rigor

in GR!

@JohnDuffield No seriously, you need to formulate your arguments in mathematical form in order for us to be able to cross check our views

@JohnDuffield the modern concept of GR is basically entirely based on einsteins(-grossmann) eqns, really dont understand the crux of some of your claims wrt that (eg about some kind of divergence). semiclassical just posted great link on the history of construction of GR eqns by einstein by a pro historian, think its highly related to your claims, try reading it carefully.

@vzn : his name was Robert Oppenheimer.

I just lost about 20 minutes of my life attempting to open a SIM tray.

5:22 PM

@ACuriousMind paperclip

There was also Irwin Shapiro:

is the trick

Shapiro time delay

The Shapiro time delay effect, or gravitational time delay effect, is one of the four classic solar system tests of general relativity. Radar signals passing near a massive object take slightly longer to travel to a target and longer to return than they would if the mass of the object were not present. The time delay is caused by spacetime dilation which increases the path length. In an article entitled Fourth Test of General Relativity, Shapiro wrote: Because, according to the general theory, the speed of a light wave depends on the strength of the gravitational potential along its path, these...

@Slereah Yes, I spent 5 of them searching for a paper clip :P

@JohnRennie So equivalently about pointless ranting

5:23 PM

They commited the mistake of trying to talk to JD

@BalarkaSen there is certainly pointless ranting going on :-)

Pointless topology

In mathematics, pointless topology (also called point-free or pointfree topology, or locale theory) is an approach to topology that avoids mentioning points. The name 'pointless topology' is due to John von Neumann. The ideas of pointless topology are closely related to mereotopologies in which regions (sets) are treated as foundational without explicit reference to underlying point sets. == General concepts == Traditionally, a topological space consists of a set of points together with a topology, a system of subsets called open sets that with the operations of intersection and union for...

Really, who has paperclips these days?

this never gets old

@ACuriousMind offices

5:25 PM

@ACuriousMind have you got 5 minutes to answer a silly question (this might be a good time to decide you have to cut your nails, wash your hair or sandpaper the cat)

@Slereah Well, I'm not at a office. I finally found a solitary paperclip hanging out in a cup on a random shelf

@JohnRennie I have to eat some burgers, actually, but I can do that while I ponder how silly your question actually is

Actually...

Thinking about it...

I won't point to anyone specific but about 30% of the chat users in hbar are loud and make this place into a chaotic bazaar. No disrespect meant, but loudness do not reflect a good impression of them and people just end up making a meme out of them. Why make a laughing stock of oneself instead of involving in rational discourse?

I remember a theory where GR is done with a variable speed of light!

@ACuriousMind OK in string theory we write the action as the area of the world sheet, then quantise it then after much headscratching the five string theories emerge. Easy really :-)

5:28 PM

it's the polarizable vacuum theory!

I agree about the headscratching.

The Puthof theory

From what I recall it's not a great theory

@Slereah Huh

@ACuriousMind Suppose you did the same with a point object. GR gives us the acton as the proper length of the world line. If you start from this and apply an equivalent process does it get to any useful theory?

Polarizable vacuum

Gravitation can be described via a scalar theory of gravitation, using a stratified conformally flat metric, in which the field equation arises from the notion that the vacuum behaves like an optical polarizable medium. It was proposed by R. H. Dicke (1957) and then H. E. Puthoff (1998). Harold Puthoff (see also Bernard Haisch and SED) In theoretical physics, polarizable vacuum (PV) and its associated theory refers to proposals by Harold Puthoff, Robert H. Dicke, and others to develop an analogue of general relativity to describe gravity and its relationship to electromagnetism. == Description... ==

I know it because crazy man Eric Davies won't shut up about it

According to him it explains UFOs

5:29 PM

@vzn : I've read Michael Jannsen's paper EINSTEIN’S QUEST FOR GENERAL RELATIVITY, 1907–1920. He thinks Einstein tried out a variable speed of light in 1912, then dropped it. He didn't. Like I said, he was still talking about it in 1913, 1914, 1915, 1916, etc.

Which JD also believes in!

Aaaah

It all makes sense now

@JohnRennie Yes

It's the worldline theory

Which is roughly equivalent to QFT

@Slereah huh?

Basically the worldline diagrams become Feynman diagrams

cObOrDisM

ncatlab.org/nlab/show/worldline+formalism

cf this

It's basically string theory in the limit of infinite tension

5:31 PM

@Slereah Aaaaah

get nlab'd

I'm afraid there's no good paper on the worldline formalism because they all assume you already know string theory

Which nobody does, being the idea? :P

Too bad!

@JohnRennie Slereah already said it - that's the action of a "0-brane", and you can backport the development of string theory to formulate QFT in a very similar way, but there's little benefit to it

5:34 PM

@ACuriousMind Well, well, you live and learn. Thanks :-)

Well I dunno

i can think of a few possible applications

But I'd need to understand it better first!

Additionally, the 10 d superstring theories come from a supersymmetric generalization of the worldvolume action

As far as I know, the analogue for a superparticle has not been quantized.

But if you're starting from the GR action isn't it a way of doing QFT on a curved background?

@JohnRennie Yes

But not an easy way?

5:36 PM

And searching for generalizations in the other direction - to higher dimensions - yields the "brane scan", i.e. this is a way to determine which dimensions allow which p-branes

lol @ brain scan

@JohnRennie The "GR action" is not the worldline action of a particle, it's the Einstein-Hilbert action

I think he means the Nambu Goto action

@ACuriousMind I meant the action as the proper length of the world line, not the EH action.

I guess you'd be taking the background as fixed

Ah, sure. But quantizing the NG action - for a particle or a string - is just the first step

5:38 PM

Well if you do worldline formalism, you don't get gravitons from it

Or if you do, you just get the Feynman theory

So the background will just have to be classical

The dynamics are in the perturbative series over all worldlines/sheets, and without standard QFT as guidance you wouldn't have any idea of how to do that

@Slereah : see the conceptual foundations and the philosophical aspects of renormalization theory by Tian Yu Cao and Silvan Schweber. They say the vacuum isn’t some state of nothingness, but is a polarizable medium.

So I view the worldline formalism as a sort of circular reasoning - kinda neat, but also kinda pointless

@JohnDuffield I don't actually see him saying anything re: the variable speed of light past 1912

:-) Thanks anyway. The thought has been bugging me for a while.

5:39 PM

(if he did, I'd like to know where---I'm actually a bit annoyed that I couldn't find it in there)

@Semiclassical : who, Einstein?

I mean Janssen in that paper

he references the 1912 stuff in there, but I didn't see any discussion in that paper of what happened after re: the light postulate

@JohnRennie Do ask again if you think of something else, I haven't answered a good QFT or string theory question in a while now ;)

So if you know where MJ said something past 1912 re: the variable speed of light, I'm interested

@Semiclassical : that's the point I was trying to make.

5:42 PM

@ACuriousMind Well, now you mention it I have this theory ... :-)

well, you seemed to be saying that MJ specifically said the Einstein dropped the variable speed of light post 1912

but I don't see a statement in that paper to that effect

@BalarkaSen Painful puns are an integral part of theoretical physics :P

I mean, there is this paragraph:

"In Einstein’s 1912 theory for static gravitational fields, a variable speed of light
plays the role of the gravitational potential. Einstein thus gave up one of the
two postulates of special relativity, the light postulate, in his effort to extend the
other, the relativity postulate (Einstein 1912h, 1062). From the point of view
of the Entwurf theory, the precursor to general relativity proposed the following
year, the variable speed of light of the 1912 theory is one of the components of
the metric field. From this point of view, gravity had thus already become part of

But that's the only discussion I see of the light postulate in that paper.

@ACuriousMind One might even say they are the action integrals in theoretical physics

@Semiclassical : As far as I know he doesn't. He takes the standard line that Einstein tried out the variable speed of light in his 1912 theory. He implies Einstein dropped it thereafter. See the Wikipedia variable speed of light article. It now says what I've been saying. I haven't amended it.

5:45 PM

I think that's too strong a reading.

I don't see any conclusion in that particular paper one way or the other.

(on that specific point, I mean)

I'd be curious what MJ would say about it; maybe I'll drop by his office

@ACuriousMind : it started with Stueckelberg. It's wrong. The positron is a "time-reversed" electron, but it isn't an electron going back in time.

That^ does not relate to what I was talking about at all.

@BalarkaSen I'm trying hard to see a pun there but I'm failing to do so :P

@ACuriousMind integral part

you may rest in peace now

I honestly start to have no idea what is happening right now

Oh well, I have to finish Philip Pullman's latest book, and who knows I may even have a glass of beer too :-)

5:54 PM

@BalarkaSen Eh.

@JohnRennie I say, beer is an excellent idea, old chap!

:-)

Four day weekend coming ...

Could be messy

I will say that I think it's pretty dubious to talk about what Einstein thought about GR at the time without referencing what Einstein wrote about GR at that time

There's a danger of missing the context in which he was writing, of course, but the secondary works seem to have a lot of holes

@Semiclassical : he wrote about it.

user image

I wasn't disputing that he wrote that---if anything, I'm agreeing with you that consulting what Einstein wrote at the time is indispensable in getting the story right

@Semiclassical : I haven't missed the context in which he was writing. Nor did Irwin Shapiro.

user image

6:01 PM

I am heading to sleep. It's almost morning...

In the meantime, don't collapse h bar into a black hole with too much nonsense

@Semiclassical : make sure you read this: Is The Speed of Light Everywhere the Same? It's by Don Koks the PhysicsFAQ editor. The answer is no.

"In special relativity, the speed of light is constant when measured in any inertial frame. In general relativity, the appropriate generalisation is that the speed of light is constant in any freely falling reference frame (in a region small enough that tidal effects can be neglected).
In this passage, Einstein is not talking about a freely falling frame, but rather about a frame at rest relative to a source of gravity. In such a frame, the not-quite-well-defined "speed" of light can differ from c, basically because of the effect of gravity (spacetime curvature) on clocks and rulers."

That seems the crucial passage from there

that's pretty cool

arxiv.org/abs/1803.10237v1

they have found a galaxy that has no dark matter

^I think @Secret may have brought that up earlier?

@Semiclassical : the moot point is that if the speed of light was really constant, the observer would not be falling.

6:11 PM

That seems a non sequitor.

Plus, as has been noted before, one has to be pretty careful in saying what precisely is meant by speed

@Sleareah : Julian Schwinger wrote a paper called quantum electrodynamics II : vacuum polarization and self-energy. It was published in April 1949.

"Given this situation, in the presence of more complicated frames and/or gravity, relativity generally relinquishes the whole concept of a distant object having a well-defined speed. As a result, it's often said in relativity that light always has speed c, because only when light is right next to an observer can he measure its speed— which will then be c. When light is far away, its speed becomes ill-defined. But it's not a great idea to say that in this situation "light everywhere has speed c", because that phrase can give the impression that we can always make measurements of distant s…

That part also seems relevant.

But what I note is that the logic flows from complicated frames and/or gravity -> speed of distant objects becoming ill-defined, not vice versa

@Semiclassical : it isn't a non-sequitur. It's like what I said to 0celo7 earlier. It's how gravity works. And it doesn't work the way some people say.

user image

@0celo7 So should I hold off on reading or not?

@ACuriousMind There's actually no bad typos.

Might as well read. I don't have a totally updated version yet.

6:17 PM

I'm getting past my realm of knowledge, though, since when it comes to GR I really don't know the story well enough.

(I suspect that, at the level of details anyways, I know the history of GR better than the physics of GR)

user image

6:31 PM

@Semiclassical : when you extend your knowledge, I think you will be shocked.

OK, I have to go now. Nice talking to you.

Nice talking history with you as well.

6:45 PM

Finally a day off on monday

Thank u Jesus

You did not die in vain

7:22 PM

@Slereah dying for your sins wasn’t enough?

Dying for my day off is even better

Although technically the day off is for coming back from the dead

HE IS RISEN

7:37 PM

@Slereah It's Monday already?

Soon!

I guess today is the Last Supper

It is

The starred "Judas Motl" message is very timely :P

More like Jesus

lol

Forgive them father for they know not string theory

8:41 PM

Oh man

nice

what topic?

the topic

strings

GR?

Boo

haha

Although I guess you can do GR with strings

8:42 PM

The piddly low energy low dimension approximation after all :p

Just need to learn string theory now :'(

Hey, you can get stable wormholes from the dilaton field!

which is nice

though I have no idea how large since I don't know the typical value of the dilaton field

My sense is AdS/CFT is very GR'ey

that it is

although I don't know much about it

Bosonic string theory, superstring theory, supersymmetry, supergravity, super-yang-mills, AdS/CFT, M Theory, that's all one needs to do right :o

"all"

You say that like it's a simple thing :p

it's like the recipe for dragon stew

8:45 PM

Honestly I feel like going over relativistic quantum mechanics is correcting my QFT knowledge, so much to do

step 1 : find a dragon

I'm sure it can be done

should be fine

you're no dummy

It's one thing to learn stuff for which there's known answers, another thing to go down the dark path of 'new' things :\

you can use the old trick

find two known things

combine them to prove an unknown thing

Dawood ibn Kareem

8:47 PM

@Slereah Your map ignores Šljivovica.

That's kind of the hope

I've been to central europe, they like their beer, too

Seems like most stuff is like that, except the huge ideas

oh even the huge ideas, to some degree

If you just want to do something from thin air, it's kind of terrifying

8:49 PM

I don't think anyone ever did, really

The hope is to find something that uses something from here, something from there, and puts them together to get something cool, and that's a paper

All weird ideas are rooted in previous works

Even Newton had his Euclid and Descartes to build on

And Hooke to steal from

Dawood ibn Kareem

Newton's ideas are weird?

I suppose calculus seemed weird once.

8:50 PM

If I have seen farther than others, it is because I was standing on the shoulders of giants.
-- Isaac Newton

In the sciences, we are now uniquely privileged to sit side by side with the giants on whose shoulders we stand.
-- Gerald Holton

If I have not seen as far as others, it is because giants were standing on my shoulders.
-- Hal Abelson

Mathematicians stand on each other's shoulders.
-- Gauss

Mathematicians stand on each other's shoulders while computer scientists stand on each other's toes.

2

and people to rat out for melting coins

@DawoodibnKareem the weird idea that Newton was very criticized for was action at a distance

That's a perfect set of quotes tbh, well done

Dawood ibn Kareem

I suppose so. If you're going to divide zero by zero, you may as well do it from far away.

you'll never get far away from the dreaded 1/0

Unless you do QFT

8:57 PM

@BernardoMeurer independent.co.uk/voices/…

Zizek strikes once again

lel

Some crazy modules I get a choice from on the side, Modular Form stuff, integrability, spectral theory, even f'ing morse theory if I want to do it

Ultimate takedown of JBP currentaffairs.org/2018/03/the-intellectual-we-deserve

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