Thursday, February 05, 2015 ... /////

String theory cleverly escapes acausality traps

String theory's forefather Gabriele Veneziano and three equally Italian co-authors submitted an interesting preprint,

Regge behavior saves String Theory from causality violations
They were intrigued by a Maldacena and 3 pals paper from July 2014 (I encourage all serious readers to get familiar with the names of the co-authors in both papers). All these folks studied the violations of causality in quantum gravity.

Causality is the obviously necessary principle saying that the cause must precede its effect. In special relativity, this principle is strengthened. Because it has to be valid in all reference frames – which are mutually related by Lorentz transformations – the cause must actually belong to the past light cone of the effect: the influence cannot spread faster than at the speed of light in the vacuum.

Maldacena et al. have designed a scattering (thought) experiment that allows the delay between the cause and effect to be negative. That's a problem, isn't it? If you can order the events so that one may say that "the past affects the future", things are OK. But once you may affect both the past and the future, it becomes unlikely that the collection of all these events can make any sense. Due to the lethal causal loops, it's unlikely that any laws of physics may be obeyed.

Maldacena et al. have already shown that the delay may be positive as well as negative for various choices of the parameters describing the thought experiment.

They noticed that there existed one loophole – the existence of additional particle species whose spin $J$ must be unlimited, just like in string theory. Veneziano et al. are showing that the Hagedorn tower of excited vibrating string modes indeed seems to be sufficient to cure these problems.

If you consider a non-gravitational quantum field theory and it's described by some Lagrangian or other form of laws of physics that are "manifestly" Lorentz-invariant, then it's guaranteed that all of physics will obey causality in some relevant variables. If the information can't exceed the speed of light microscopically, e.g. on the lattice (and the UV, very short behavior, of the field theory is often "free field theory" where everything manifestly propagates by the speed of light and not a higher speed), then it's guaranteed that the information can't really be sent superluminally in appropriate effective field theories or in long-distance experiments, either. (Stability of the vacuum needs to hold, too.)

However, quantum gravity cannot be put on the lattice. And many important coefficients in the effective Lagrangian may appear to have wrong signs. You may imagine some effective Lagrangian of the schematic type$S = \frac{1}{16\pi G} \int d^D x\,\sqrt{-g}\,\zav{ R + a R^2 + b R^3+\dots }$ In non-gravitational quantum field theory, stability and similar conditions would imply lots of natural inequalities for the coefficients $a,b,\dots$. However, in quantum gravity, many of these signs may be "wrong". For example, the kinetic term for the "overall scaling of the metric tensor" that you may derive from the Einstein-Hilbert Lagrangian has the wrong sign – this degree of freedom looks like a bad ghost (a particle that exists with a negative probability).

There are probably many other inequalities that are obeyed. For example, the higher-derivative corrections seem to be constrained by the apparently valid conjecture that gravity is the weakest force. At any rate, it seems possible to produce delays of both signs – if the corrections are there at all, one can always get some acausal behavior (effects precede their cause) if the parameters of the experiments are adjusted in the correspondingly dangerous way.

If I simplify, Veneziano et al. write the delay as$\Delta t = \Delta t_0 \zav{ 1- a\frac{b^4}{\ell_s^4} + \dots }$ where $\Delta t_0$ is positive and $b$ is some parameter describing the experiment. $\ell_s$ is the string length and $a$ is a higher-derivative coefficient from the Lagrangian. For a high enough $b$, the delay may get negative which would mean that causality is violated. However, they also show that if one includes the contribution of the asymptotic, highly excited string modes (the Hagedorn tower), the whole sum gets completed to something that is non-negative, imagine something like$\Delta t = \Delta t_0 \exp\zav{ - a\frac{b^4}{\ell_s^4} + \dots }.$ It's not quite exact but I think it's an OK caricature for what's going on. You have to read the papers to learn more.

To summarize, I think it's fair to point out that in any consistent theory of quantum gravity, the vague potential to produce the negative delays has to be there. If it's not there, e.g. because the loops are absent etc., the theory violates unitarity (which require the loop processes to be represented), decoupling of the unphysical modes of the graviton, or something else.

At the same moment, this potential threat has to be mitigated in a consistent theory of quantum gravity, too. This really means that the effective field theory's "fields" in the spacetime must have an unlimited spin which means that the elementary particles have some internal structure that generates these modes as energy eigenstates of some "internal motion". The stringy internal architecture is the only known way to achieve these "curing" spacetime fields for arbitrarily high values of $J$ that is compatible with the weak coupling even at very short distances.

String/M-theory in the more general sense offers "other" ways to obtain all the additional fields, too. But even if we consider these "more general descriptions of quantum gravity" that are not defined by perturbative expansions, it seems that all the consistent solutions to the problem seem to be "a form of string theory". They are the strongly coupled limits of known perturbative string "theories" or they are related to them through other dualities.

When it comes to quantum gravity, string/M-theory is the only game in town and its highly nontrivial ability to escape the threat of acausality in similar quantum gravitational (thought) experiments is one of the ways to understand why its consistency is so precious and why all other conceivable theories (especially those based on completely different principles) are almost guaranteed to fail.

snail feedback (56) :

Dear Johannes, LOL. Acropolis is fine but when I compare it to other styles, perhaps older ones and more Eastern ones, I am at most ambiguous.

You are probably not, as a German, you have been building these renaissance-like buildings everywhere. Look e.g. at some of the architecture planned under Nazis in Prague:

http://www.metro.cz/foto.aspx?r=co-se-deje&c=A140107_183523_metro-extra_row&foto=&thumbs=1#JBS506917_9_bmp.jpg

Click a picture to zoom in. Of course, the best neighborhoods would host Germans - and later all of them.

It's ordered, organized, "German" (and was partly realized, anyway LOL) - although this German architecture is indeed originally ancient Greek know-how! ;-) But is this architecture better than baroque or gothic things, or mosques, or the Babylonian Tower? My view is ambiguous. Acropolis is more "ours" but I don't really feel that if something makes our civilization "better" than others, it's the ancient Greek tradition of architecture.

You know, I feel that when the Greeks - and now you ;-) - were/are promoting their taste about architecture etc., they are also (or primarily) doing service for themselves. If they succeed, good for them. But if the people who bought these ideas didn't agree with payments for copyrights etc. and the Greek/German ancestors couldn't prevent them from building those things, you must view it simply as open source know-how which was for free. ;-)

Hi Lubos: I have to still understand the main result of these papers. But I have some naive questions.
(1) does gravity remain weakest force in multi dimensional string theory?
(2) does it remain weakest force very close to a black hole or inside the black hole?

Thanks, Giorgios, you are surely a rare example of someone in Greece who agrees with me.

You said it nicely: it's up to each of us to promote the name of our ancestors and old civilizations of "ours" - and it's optional for everyone else.

Of course, you probably have an easier job with ancient Greece than I have with Czechs. Most of us weren't quite thrilled by these - although touching - stories of the famous achievements of the Czech kingdom in 14th century or other centuries so I can fully understand if most foreigners just don't give a damn!

I also agree with you that the problem was (almost) only at the government-management level. Even the Greek commercial banks, however despised or hated, have been a rather great example of how banks *should* behave.

Right, I don't have problems with Greeks individually or for their biological substance because I indeed believe the papers that say that they're the same species as the ancient Greeks we admire.

Of course that I am worried what e.g. Kyriakos Papadodimas or Savas Dimopoulos think about my rants - but I am not worried too much. Savas have always thought that the Greek politics was mess, while he was a Democrat in the U.S. So I guess he understands that my feelings are much stronger. And I don't want to discuss politics with Kyriakos at all. It seems better to be ignorant. Chances are that almost all Greeks would disagree with me/us on these fundamental matters.

Your comment that the Greeks are preprogrammed not to cooperate (even from the city states that were at war, Athens Sparta, I suppose that's what you mean) is interesting. But we are saying the same things about Czechs. By itself, it has lots of advantages, too. If I looked beyond stereotypes, I am not sure whether some nations are really "more cooperative".

For example, what about Germany? Do they like to team up with other Germans? The Third Reich could suggest so. But if that's intrinsically the case, why they spent all those centuries in hundreds of minikingdoms while the non-cooperative Czechs maintained a compact, never divided land for the whole time? I feel that this particular label could be a myth.

Or take Russia. They're also said not to cooperate with other Russians - well, except for the wartime. Is that really true? Has it been measured and compared with the French cooperativeness or someone else? I don't see a clear difference.

Sorry, I don't believe your comments that "no sensible (?) Greek in the discussions wants to avoid repaying the debt". Of course, if one defines sensible as "understanding that debts should be repaid" (plus other things) then it's true by definition. But the people who participate in the discussion probably use a different definition. I believe that there are almost no Greeks who want to repay the full debt now, in the conventional counting of what it means.

Why "causality trap"? A little bit of acausality in the gravitational sector at Planckian scale would be an unusual feature absent in the low-energy limit. But I don't see how it would conflict with data or with other aspects of the theory.

Hi, the delay you may get in these experiments is in no way "Planckian". It may be as large as you want, like 5 minutes.

Maldacena et al. consider objects at spacing L, with a mass M around, and the time delay is G*M / L^(D-4). For D=4, it's just the radius of the black hole of mass M, for example.

This delay is a sharp inconsistency unless you believe that you may change the "sell" order on Forex that you did 5 minutes ago. ;-)

Dear Luboš,

"If you want the EU to decay..."

"If"? You're pulling my leg, aren't you? Haha! Very good! :)

For the avoidance doubt, and just in case, there is no 'IF' about it. And I don't so much want it to decay as to DIE, to be dead and buried as soon as possible, which judging by the number of dumbfuck supporters it still has will be a while yet.

"...it's bizarre that you support this Greek propaganda about the evil euro bankers. What they want to achieve with these silly excuses is more redistribution across Europe, and therefore tighter Europe than ever before."

Christ! WTF?! Again, I don't know whatever gave you that idea.

Look, I DO NOT SUPPORT GREEK ANYTHING, let alone any of its dumbfuck propaganda. I have no fucking interest in Greece whatsoever, nor any in what it thinks and does. Nothing. Zero. Fuck all. I just don't fucking care about Greece. End of. All right? Conversely, I certainly don't wish it any harm either—which I'm sure the Hellenes will all be absolutely delighted to hear—because I just don't fucking care about it one way or the other! That's why.

Moving on, as they say....

As it happens I do have an opinion on banks generally (both central and private) and what they—or rather some of them at least—get up to, but I have deliberately stayed out of that discussion. Funnily enough my reasons for doing so are exemplified here. What I mean by that is it seems all too easy for people to read all sorts of unexpressed views or positions into others' remarks, but especially where they're are so many potential 'threads to the rotten fabric'—not the least being hideously leftard external political interference—as there certainly are in the case of banks. I know if I start on that one I'd end up having to clarify every single word. Fuck it. I'm not going do it.

Before I say any more let me say this about Greece. They have no one to blame for the position they're in now but themselves. They voted for their politicians, so now they've got what's coming to them as a result. Again, end of. But exactly the same can be said of Germany. In short, fuck the whole damned lot of them. They've made their bed; now they can fucking lie in it.

I'm interested in the bed-making though. That's where the real problem lies. Plumb your bed into the lavatory and you'll end up with shit all over the sheets. Which is where they are now.

They've all been suckered by cowboy plumbers. I suggest they wise up.

"What [the Greeks] want to achieve ... is more redistribution across Europe, and therefore tighter Europe than ever before."

Luboš, I have to be blunt here. If you and others here cannot see that this is also PRECISELY what the EU wants, ALWAYS HAS DONE—from its very beginning with Salter and Monnet more than eight decades ago—and WILL NOT STOP UNTIL IT ACHIEVES IT then I say you have NO IDEA of the nature of the beast you are dealing with. It is NOT REFORMABLE. The only way to deal with it is to KILL IT. Stone dead.

But then I would say that, wouldn't I, because I'm an extreme fucking right-wing lunatic. Yeah.

Take comfort in that, suckers! Because in the end that's all you'll have.

The euro is a big part of the problem here. Sure, nations can borrow too much and default without a common currency, but its much less likely to happen when they have both the full control over and full exposure to the risks of mismanaging their currency.

This also creates indirect political problems. The reason this circus has gotten this far, is because EU fetishists would rather prop up a zombie nation with taxpayer money, than confront the fundamentally poor design choices of their own political union, which has to be saved regardless of the costs.

Hi Lubos,

Off-topic: The latest news is that Ettore Majorana may not have committed suicide:

Nice article :-)

But now it picks me that I dont see why including Hagedorn towers exponentiates the potentially negative delay away (?) ...

I agree.

However,

"... EU fetishists would rather prop up a zombie nation with taxpayer money, than confront the fundamentally poor design choices of their own political union, which has to be saved regardless of the costs."

You're missing a trick here. You and others might (very naively, I say) attribute the problem to "fundamentally poor design choices" but that's not how the EU sees those choices. They were DELIBERATE, PRECISELY because such choices would INEVITABLY end up causing 'beneficial crises' which the EU would then use to grab further powers. So they were most emphatically not due to "poor design". Anyway, they would then sell these power grabs as being necessary "in light of these new unforeseen circumstances". This, of course, is a lie. They knew all along that these "new unforeseen circumstances" were coming one way or another given their set-up and planned to use them to further their scheming for "more Europe". That's just the way these bastards work.

Of course, eventually their meta-plan here (or plan within a plan), like all plans, is subject to unforeseen events. In that regard, my guess is that the EU hadn't figured on anything like the the disruption of the global financial crisis of 2008. That really was an "external unforeseen event" even in their terms and frankly they could probably have done without it because all told with its repercussions it seems the EU really has now bitten off more than it can chew. We'll see though. Don't underestimate the determination of these fuckers. You'd see hell freeze over before they give up. They're going to have to be actively stopped. I for one do not care how that is done. Frankly, if it turned out they were all torn to pieces by the mob that would be a bonus in my book.

Hi John,

"As it happens I do have an opinion on banks generally (both central and private) and what they—or rather some of them at least—get up to, but I have deliberately stayed out of that discussion"

Well I - for one - would be interested to hear your views on banking should you change your mind. It might be enlightening.

Thank you, Michael.

I'll try not to let your kind words go to my head. :)

I will say this though: I doubt very much that anything I'd have to say hasn't already been said by people far more knowledgeable than I am.

Sure you are going to be happy, as he always mentions you in his articles, i.e.:
http://arxiv.org/pdf/hep-th/0606100v2.pdf

Ok, I will try to locate them ;-)

http://physics.stackexchange.com/questions/12899/charged-particle-close-to-a-charged-black-hole-what-happens

Lubos and Tony: Thanks.In addition to what you (Tony) pointed out, there could be many general situations. If my memory serves right (!), several years back there was this conjecture that gravity in our 4 dim world is weak because it is leaking out of higher dimensions. I do not know if people still believe in it or not, but from Lubos' reply , I understand that string theorists must have figured out that in all vacua gravity will be the weakest. The answer to second question follows because they use the same ST to study interior. Eventually at some extremely high energy,gravity will be unified with other interactions. But we are talking about the current universe and not the big bang! Right?

It is very depressing that warp drive is impossible.

God loves humankind so much that he put an untraversable distance between us and the other intelligent species.

Dear Eelco, I know that it's often being said that the shared currency dramatically increases countries' borrowing - said by people whom I often agree with - but I simply think that there's no evidence and the claim is probably wrong.

Why wouldn't Greece in the absence of any European Uinons behave just like Argentina or others?

Or look at countries by their debt/GDP ratio.

https://en.wikipedia.org/wiki/List_of_countries_by_public_debt#List

Sort the table by the ratio.

Japan, Zimbabwe, Greece, Saint Kitts, Antiqua Barbuda, Portugal, Lebanon, Jamaica, Italy, Iceland, Eritrea, Ireland, Singapore, Grenada...

The percentage of the eurozone countries isn't extreme. Even in Europe, see that Iceland was there and had these big debt issues. They have the Icelandic crown and are outside the EU.

I am convinced that it's exactly this kind of meme of yours - and many other Euroskeptics - that is the main propaganda weapon to deepen the integration of Europe. "Because the countries were in touch, they hurt itself in some way, and it has to be fixed, and therefore we need a deeper EU", and so on.

It's rubbish. Countries interact but it's legitimate and virtually everything they do with their finances is always up to them as long as they physically have the power to decide whether they make deficit budgets and print the bonds or not!

Dear Kashyap, this - old large dimensions and warped dimensions - have always been a long shot. My guesses were it was 1-2 percent range that those models may be right and people generally agreed.

They haven't been discovered and they haven't been "completely disproved" because they have parameters that can be pushed away from the observations. But that's exactly what happened, so we know from the LHC now that the dimensions can't be too large and the lightest new particles predicted by these models can't be lighter than several TeV.

So just by the quoted masses, these models are "more excluded" than most currently studied models of supersymmetry, for example.

It is of course true that the charged black holes will repel charges whenever there is a threat that the resulting new object would be a superextremal - forbidden - black hole.

Just a comment about a point that is marginal in Ben's answer. It is not true that the cosmic censorship hypothesis is alive and kicking. For general multidimensional black holes etc., it has been pretty much proven incorrect.

There is no reason why this Penrose's conjecture should be correct according to the modern understanding of quantum gravity. His heuristic argument was that the naked singularity is always bad because classical GR can't predict things because there are infinity. But quantum gravity tames all harmful effects of infinities and even if the classical GR is unpredictive, the quantum counterpart may be predictive.

Dear Dilaton, do you know that exp(x) may be written as Taylor series? So the individual terms are roughly speaking coming from ever higher floors of the Hagedorn tower. But you have to read the actual Veneziano et al. article to get a more accurate answer.

Dear John

I will reply to your anti EU rants as they are not virulently concentrated on trashing anything Greek, as our honorable host enjoys doing.

You speak somewhere in your voluminous replies of countries that are completely disparate forced by insidious powers into uniting in an EU.

If these countries are so disparate the US should not exist, since most of it is composed of immigrants from Europe. Instead it is a great melting pot and it thinks itself as a nation.

Bear with me. When I was young I used to have a pair of quails in a cage in the garden . When the male ( or female died) and I brought a replacement the survivor would not accept it, chased it all over the cage and pinched it. Then I thought: take both to a new environment. I put them both in a box for a day, and then back in the cage. They were in love after this. It is the same with hens, a new hen will be picked, but if the coop is changed for all for a day, then peace reigns . Humans are not different. IMO the US exists peaceably with the fragments from the EU nations because they all found themselves in a new cage.

Thus, the problem is not as intrinsic as you think, and not insurmountable. It would need some mass psychology experts but we have not reach that big brother state yet.

Now Greece and the EU. Greece wanted to enter the EU because of Turkey and the continuous causus beli threats and threats to Cyprus. NATO with the US in which plays a double game with Turkey was not considered enough of a safety ( as obviously happened with the occupation of half of Cyprus in 1974, but that is another story).

Had we not been enticed into the euro, we would probably coast along with our tourism and maritime the biggest industries, something like a Florida of the EU.

IMO again, what happened in Greece with the euro started the downfall into unsupportable debt. Suddenly every-day prices trippled. Something that used to cost 100 drachmas was priced at 1 euro instead of 0 .25. Even beggars on streets and car window cleaners at lights who would have been happy with 50 drachmas would not accept a 0.20 of the euro. This put a big public pressure on the government to increase pensions and civil service salaries. They had no restraint in borrowing, and also increasing the civil sector again from voter pressures. A down slide on debt that brought us here, bad politicians and bad decisions. Had we abstained from entering the eurozone we would not be in this big a mess.

BTW if you read the economic history of Greecein greek, http://el.wikipedia.org/wiki/%CE%99%CF%83%CF%84%CE%BF%CF%81%CE%AF%CE%B1_%CF%84%CE%B7%CF%82_%CE%BF%CE%B9%CE%BA%CE%BF%CE%BD%CE%BF%CE%BC%CE%AF%CE%B1%CF%82_%CF%84%CE%B7%CF%82_%CE%95%CE%BB%CE%BB%CE%AC%CE%B4%CE%B1%CF%82 you will see that Greece has defaulted several times in its modern history for a few years at a time, and then the debts were again acknowledged and and payed back . I have heard that we just finished with the debt of 1821 :) for the greek revolution, which was a big fraud orchestrated between British money lenders and dishonorable Greeks, From the 2,000,000 gold pounds only 10% came to the revolutionary coffers, the rest was mediators!

Hi Lubos,

I guess you will find mistakes in this faster-than-light paper in QED: http://xxx.lanl.gov/pdf/0706.1661v3.pdf , but what I find intriguing is the experimental result! Reference 15 is here (subscription) http://scitation.aip.org/content/aip/journal/jap/101/2/10.1063/1.2409771, and a related non-subscription experimental paper by the same team is here: http://iopscience.iop.org/0295-5075/93/6/64004/fulltext/epl_93_6_64004.html

Apologies for all the links, but I also came across two less formal experiments, but intriguing anyway: http://www.cumberlandastronomicalsociety.org/memberspotlight/Allens_Paper_part_2.pdf and http://www.gsjournal.net/old/physics/erdmann.pdf , and you may be familiar with http://arxiv.org/pdf/1211.2913.pdf

So we have some peer-reviewed experimental papers, plus some less formal results showing FTL components for near-field 'electrostatic' or 'magnetostatic' interactions. They all agree that radiation interactions occur at c, but claim that near-field interactions don't. I've been trying to pick flaws in the experiments, but would appreciate your help :)

Warpdrive is not only possible, it is also a prediction of Heterotic String theory ;-) http://journals.aps.org/prd/pdf/10.1103/PhysRevD.85.044007

Why do you think that this paper, freely at

http://arxiv.org/abs/1111.4049

has anything to do with warp drive?

Dear lubbos,
I cannot claim to be up to speed with the empirics of the matter; but as you describe in this post, there is plenty of manipulation of the markets going on at the political level. Not just the stopgap measures, but also the structural rot, like forcing all government bonds to be treated on an equal footing. All else being equal, we should expect that to influence behavior. Maybe Greece would have actually lived up to its historical glory, if it wasn't handed over heroin as if it was candy? Not trying to excuse their behavior, but just saying...

I am not sure where you get the idea that someone who talks of EU fetishists fancies deeper European integration. These kind of issues are unavoidable in a political union. Just look across the ocean; the US had federalism deeply ingrained in its DNA; but massive transfer payments across states' boundaries have been the norm there since any of us can remember; and you better get ready for van rompuycare here in Europe too.

The only solution to avoid that kind of fate is a radial rollback of the transfer of sovereignty to Brussels; and the euro should be the first project to be killed off. As long as there exists a common currency, all the political consequences necessary to prop it up will come flooding right after it. And the only people who stand to gain are the loonies for whom van rompuycare is actually a part of their vision of a brave new world. They are still a tiny minority though, and they can still be stopped.

But hey, at least we don't have to swap any currency when we cross the border, right? God bless the EU!

Because it is a sound realization of Sagan/Thorne (FTL) traversable wormhole hypothesis.

Is this meant to be a joke? ;-)

What Sagan with Thorne's help did with wormholes was arts - science-fiction (Sagan's story "Contact"), not science!

It's like Interstellar or Romeo and Juliet.

Yes, Greece is junk. So was Germany after the WWII when 50 % of their debt was cancelled. Now, this is not allowed for Greece, apparently they have to start a war first...

Right, shockingly enough, they have to start the war first.

Germany's debt was largely forgiven because others have flattened Germany so that it looked like the Netherlands.

What nutcases like you and the Greeks are saying to be analogous is that Greece has lived beyond their means and ate too much for 40 years. Do you really think that overeating is the same kind of damage as bombardment of all cities?

LM

Dear Eelco, maybe without the EU, Greece would now be an epicenter of civilization of 2015 like in the ancient Greek era. Much more likely, it would remain the same kind of third-world periphery of Europe that it was in the 19th century. Huge amounts of money have been donated to Greece so it's common sense that without them, Greece would probably be doing worse now.

At any rate, using assumptions about these complete speculations about a hypothetical parallel world to determine the actual political decisions in 2015 would be insane.

The ECB may help each bond from each member state "to the same extent" (which is fair) but it has surely never tried to make the actual yields the same for everyone.

These kind of issues are unavoidable in a political union.

Right, exactly, and unlike you, I oppose this superstate, a political union of Europe.

I appreciate the fact that you are a busy man; but if you are not going to read my posts, its probably better not to reply to them either.

Luboš, well.

I agree they live(d) beyond their means, so to most people of most developed world. And China's total debt quadrupled in the last 14 years. Is that sustainable? We in a way are all Greeks, they are just ahead of us :)

And I also agree there *has to* be some sort of austerity etc., but hey, I am not the one denying limits to (consumption) growth. Also I am not the one claiming there can be 50 billion happy people enjoying the living standards of... say average Swiss banker :-)

You see, geo-political tension are at the level of cold war already, if not much worse. So why should I be optimistic about the future (as most readers here probably is)?

Alex

So could you please point me the mistake in 1111.4049 ?

Of course that China's public debt is sustainable. Not only it's sustainable. If they wanted, they may repay it tonight.

The sovereign debt of China is about $1.5 trillion but they have over$4 trillion in reserves. If they wanted, they could repay not only the sovereign debt but also all the local public debt around $3 trillion, too. reader John Archer said... Dear Eelco, Just a hat tip. I note that you see the problem very clearly too. I can't understand why others are so blind to it. "The only solution to avoid that kind of fate is a radial rollback of the transfer of sovereignty to Brussels; and the euro should be the first project to be killed off. As long as there exists a common currency, all the POLITICAL consequences necessary to prop it up will come flooding right after it. And the only people who stand to gain are the loonies for whom van rompuycare is actually a part of their vision of a brave new world. They are still a tiny minority though, and they can still be stopped." [My emphasis] That's it in a nutshell. You've got the criminals pegged. "Structural rot" indeed! Where I'd differ with you is on the achievability of the rollback. That many might think such a thing possible is perfectly understandable, but in this case their thinking is fundamentally mistaken. The EU is very different from all other political constructs. In particular, it has no reverse-gear mechanism — a deliberate non-feature built in at design time. The EU can move in only one direction, and that is towards further 'integration', snd all on subterfuge tyres. Incidentally, it's this that gives the lie to Camermoron's egregious fakery of "renegotiating a better deal for Britain" in the EU which he's trying to sell to the mostly moronic electorate here. It can't be done. The man is just another in a long line of two-faced liars we've had to suffer as Prime Ministers and, of course, an arch europhiliac. The "only solution" to the problem of the EU is to end it completely. Meanwhile I want to see Britain out of it. I don't know whether you are interested but the authors of the 2005 book The Great Deception: Can the European Union Survive? have now made it freely available as a PDF downloadable from here. By the way, in connection with the euro, although I've never been able to verify it I recall reading over twenty years ago that something like 40% of the US Federal budget was given over to those interstate transfer payments you mentioned, a practical necessity in a single-currency zone if one wants to keep the country together. I imagine the figure in Britain is not dissimilar and quite likely much bigger given our very unfortunate post-war entanglement with socialism. reader Alexander Ač said... Luboš, you got me here, I have no words ... :) Alex reader Eelco Hoogendoorn said... Don't get me wrong; when I say that only a tiny minority wants van rompuycare, I don't mean to say that this matters, in a democratic sense of the word. Im not an idiot. Its precisely the give or take 751 wrong people who strive for this. The train will keep moving and picking up steam until a forceful and deliberate attempt is made to stop it. Indeed, the typical 'eurosceptic' politician, who considers it an act of grave defiance to renegotiate a few fraction of a percent of the budget, are not going to make a difference. But if 99% of people understand the direction they are headed in, and that it isn't in their interest, this is going to make a difference, one way or the other. But just talking about the end the EU is not very realistic. In one way or the other, the EU has existed since the time of the roman empire. And in one way or another, there will always be a political structure overlaying the nations of Europe, whatever you want to call it. I think its better to focus on a positive vision of what this ought to look like in practice, rather than only talk about the monstrosity which is the EU. reader Alexander Ač said... Ok, I try some numers on China's debt: *Chinese total debt rose$20.8 trillion in 7 years, or 281%.

*China's total debt is now 28 trillion dollars

*China's debt reached 282% of GDP (higher than some developed countries)

*China passed the point of no return five years ago. etc ...
Sources: http://www.bloomberg.com/news/articles/2015-02-05/a-world-overflowing-with-debt

and: http://www.telegraph.co.uk/finance/comment/ambroseevans_pritchard/11391211/Devaluation-by-China-is-the-next-great-risk-for-a-deflationary-world.html

Alex

You're mixing apples with oranges. "The total debt" is something completely different than the government's debt, and when this "total debt" is at 282% of GDP, it's no problem whatsoever. Germany, US, Australia, South Korea are above 250%, too.

In China's case, as the Bloomberg page shows very clearly, the largest portion of the "total debt" is the non-finantial corporate debt (125% of GDP). This simply means that China has built lots of companies who net equity is small. But it's very clear what happens if this bet goes bust: the companies that were built are simply used to partly satisfy the lenders. It's business-as-usual. There is nothing unsustainable about it whatsoever.

If I got you, Alex, then I haven't gotten too much because you have no words and no knowledge and no intelligence, either.

Sorry, NumCracker, maybe you should see a doctor to check your ears, or eyes, or whatever.

I didn't write that this 1111.4049 paper has "mistakes", although it probably has. I said that the paper says nothing about "warp drive" - so your suggestion that this paper is supposed to support your fantasies about warp drive boils down to a simple mistake or a cheap trick.

Then, you that the say the following paragraph (below) is blatantly wrong and thus GB term does not "follows naturally from the compactification of the 10-dimensional heterotic superstring theory" ?

"It was noted recently in [23], too, that the presence of the GB term in the context of a scalar-tensor theory has the property to evade the various no-go theorems of General Relativity. Indeed, various wormhole solutions were found in the context of gravitational theories with higher curvature terms [24–27]. In the presence of t
he Gauss-Bonnet term in particular, wormhole solutions were found in the context of higher-dimensional gravitational theories [28–36]. In this work, we will investigate the properties of wormhole solutions that arise in the context of the four-
dimensional dilatonic Einstein-Gauss-Bonnet theory, first reported in [37]. The presence of the higher-curvature GB term, that follows naturally from the compactification of the 10-dimensional heterotic superstring theory down to four dimensions, suffices to support these types of solutions without the need for phantom scalar fields or other forms of exotic matter."

I am do sorry Lubos, but the author could not be more explict:

"The existence of traversable wormholes in the context of General
Relativity relies on the presence of some form of exotic matter. However, in the framework of a string-inspired g
eneralized theory of gravity, the situation may be completely different. Here we have investigated wormhole solution
s in EGBd theory, which corresponds to asimplified action that is motivated by the low-energy heterotic string
theory. Indeed, as we have demonstrated,
EGBd theory allows for stable,traversable wormhole solutions, with out the need of introducing any form of exotic matter. The violation of the energy conditions, that is essential for the existence of the wormhole solutions
[43], is realized via the presence of an effective energy-momentum tensor generated by the quadratic-in-curvature
Gauss-Bonnet term."

"Next, we have studied and classified the geodesics of massive and massless test particles in these wormhole spacetimes. Depending on the respective effective potential, there are two general kinds of trajectories for these particles. The particles may remain on bound or escape orbits within a single asymptotically flat part of the spacetime, or they may travel from one asymptotically flat part tothe other on escape orbits, and travel back and forth on bound orbits."

Dear NumCracker, the words "warp drive" don't appear anywhere in the quote - and heterotic string theory doesn't allow warp drive or FTL transfer in general. I am telling you this trivial fact for the 5th time but it still seems too be too little.

Dear Anna

I intended to respond to you earlier but didn't get round to it. Now I can't for a while.

Please regard this as a placeholder. I enjoyed your post but don't agree with some of it.

At least demanding that Greece start a war before having their debt forgiven sets a standard that is high enough so that lending can resume. If all a country has to do is to say they can't and won't pay with their hand out for more, why should anybody give them one further Euro?

While waiting for Lubos' reply, here is my non-expert 2 cents worth comment! As far as I can recall, these experiments did not make any news like FTL neutrino Italian experiment which proved to be wrong. So my guess is that the experts may have seen holes in these papers right away! I understand near field is a very complicated subject.Virtual photons (coulomb effects) are not particles in the usual sense. They are just disturbances in the field. Approximations one makes for far field are certainly not applicable. Just the fact that it went through some referee does not really mean all that much. I am not saying that your curiosity is not justified. I would also like to understand this little better.

Lubos,

if Greece used it's own currency it's prolific borrowing would have led to compensating exchange rate changes. Imports would have become more expensive and exports cheaper. Austerity would have happened automatically with Greece importing less and exporting more.

Analogous to a person being forced to work harder and consume less.

Using the Euro has enabled Greece to continue importing more than it can afford.

Am I missing something?

Dear br, they are not real papers by competent physicists, they are texts on an archive dedicated to armchair physicists, and they completely failed to learn the basics of electromagnetism. When someone writes an abstract saying the "two electrons while scattering surely act on themselves immediately", what can I say? It's just wrong, wrong, wrong. He didn't read even elementary classical electrodynamics, like in the Feynman lectures on physics. Maxwell's equations guarantee that the action is retarded. One may subtract the Coulomb's field from the particles and this may be done at equal time but this is just a form to decompose the field into pieces - which doesn't change the fact that any change of the state of the charged particle is only propagating at the speed of light.

It is not possible or useful to look for "mistakes" in such papers. It's like a lousy schoolkid who offers you a one-page alternative calculation proving that 5 x 7 = 24, or something like that. Of course that the calculation won't make much sense. People who know what they are doing know that this is a simple multiplication and there's really "nothing extra that has to be said" to prove that it's 35. So something or everything leading to 24 is going to be wrong in some way but it's more sensible to describe the right solution from scratch than to try to "fix" a wrong solution of someone who really has no idea about the relevant problems.

No, sorry, Congniscentrum, but again, the reason why the German debt was largely forgiven was because Germany was decimated by the war, not because it started the war.

So if Greece wants to get the same treatment as Germany in the past, it must start the war *and* to be flattened as Germany was. Greece has 10 days (the time up to the ultimatum on February 16th) if it wants to avoid both bankruptcy *and* obeying all the rules that have been agreed upon 2-4 years ago.

Charles, what you are missing is that your "things would be different out of the EU" implicitly assumes that the Greek government would behave more sensibly "in real terms" if they had their own currency. This is in no way logical, justifiable, or guaranteed, and I think it is unlikely.

In the eurozone on a given year, the Greek government was e.g. hiring N employees per this year, and their real income was increased by P percent.

The most sensible "mean value" prediction what would happen outside the eurozone would be that on the same year, the Greek government would have hired N employees per this year, and their real income was increased by P percent.

What would happen with the nominal income would be different but none of these things matters.

Of course that if the Greeks got "used to" some increase of their income each year and if there were some extra J percent inflation, the politicians would have to promise a higher increase of the wages, including these extra J percent - either inflation or the annual drop of the drachma exchange rate - so the things in the real term would end up the same.

The idea that the Greek politicians would only be promising the same *nominal*, and lower real, increase of salaries outside the eurozone is a skewed speculation.

One more simple obvious argument why "the euro is to blame for the big debt" isn't right. Just look at the graph of the debt-to-GDP ratio of Greece as a function of time:

Greece entered in January 2001. Nothing special happened around that point in the graph. It was a nearly stabilized era. The new skyrocketing growth began around 2007.

The existing debt-to-GDP wouldn't jump in 2007 so much if there were drachma at that moment. But Greece would still have to repay it and the interest rates would jump more than in the euro because they would incorporate the weakening rate of the drachma, too. So instead of 10% for 10-year bonds like in the euros today, Greece could have 30%-yield bonds.

The difference is that the jump that is abrupt on the actual graph - that was using euros in 2007 - would be smoothened over the period of the during of the debt. But after that time scale, there would be no difference. The Greek debt would be equally out of control. And in fact, the absence of the sudden growth would encourage the governments to continue or escalate their borrowing policies even relatively to what we saw recently.

I don't think it works like that. China's debt is in RMB and is held by Chinese households. China's assets are in USD and is held by China. Chinese households are not allowed to own USD assets and foreigners are generally not allowed to own RMB assets (China has capital controls). So how will China sell the USD and buy the RMB?

No one has trillions of RMB outside China that they can sell for China's stock of USD assets.

Now in principle, it could find a small amount -- perhaps billions -- of RMB assets outside of China, and agree to exchange all of its USD assets for the smaller RMB assets. That means 1) the dollar falls agains the RMB and China becomes a net importer of U.S. goods which would undermine China's employment policy and 2) the amount of RMB China gets is only billions -- much less than than what it needs to extinguish the debt.

There is a real issue with adding different units here, particular in a world with floating exchange rates. And yes, China's RMB debt is a real problem, although that does not mean that China is insolvent. What it does mean, is that *someone* has to pay that debt, whether it be socialized (e.g. levied on the Chinese consumer) or paid for by the Chinese government (e.g. government asset sales to the household sector that holds the RMB bonds).