Tuesday, July 09, 2013

Papers on the ER-EPR correspondence

This new, standardized, elegant enough name of the Maldacena-Susskind proposal that I used in the title already exceeds the price of this blog entry that you had to pay. ;-)

Yesterday, there was a one-page critical paper by Hrvoje Nikolić of Zagreb, Croatia, EU trying to criticize the ER-EPR correspondence. When I am looking at similar articles, I am often ashamed to be a European: Nikolić attacking MS reminds me of an angry and hungry dog attacking Wolfgang Amadeus Mozart and Ludwig van Beethoven except that in those good old times, the composers were European and the dogs were American. This shame largely evaporates as soon as I see similarly dumb, low-quality articles inkspilled inside other continents.

Like a five-year-old spoiled boy, Nikolić screams that he has to be given some quantitative comparisons of ER and EPR correlators to trust such a thing. But it's simply not true that this is the only possible or allowed kind of evidence that the correspondence is valid. Moreover, it's obvious that once we allow the spaces with the ER bridges at all, the observables on the opposite sides of the throat will be entangled just like the rules of entanglement require; after all, despite the apparent huge distance through the normal space, they're close to each other due to the throat. In the absence of very high energy quanta, field operators at nearby points are almost equal to each other.

Also, none of the two sides of the ER-EPR correspondence is a particular dynamical theory – at least until we add some more data – so it's nonsensical to talk about particular correlators. The correspondence is a conceptual one. We may turn the ER side into something specific but just like in the AdS/CFT correspondence, the description based on the other side, the EPR entanglement built upon a space of ordinary topology, will be the only way to truly accurately describe the quantum physics of the ER bridges. With this definition of the quantum physics on an ER bridge, the ER-EPR correspondence is tautologically true.

Similarly, he screams that the ER bridges can't be equivalent to EPR because EPR produces all the shocking correlations that have stunned Einstein. This opinion held by Nikolić reflects the fact that he is spending his career by writing misguided papers on Bohmian mechanics. If he insists on a classical description of Nature, no wonder that all quantum phenomena have to look shocking to him forever.

However Maldacena and Susskind, like any contemporary physicist who doesn't completely suck, respect the postulates of quantum mechanics at every step so none of the generic correlations predicted by quantum mechanics are shocking for them. They're just giving a new (spacetime) geometric interpretation to some particular entangled states and/or projection operators upon them; they're linking an entangled state (a superposition of non-entangled states) to a geometric configuration that used to be associated with a linearly independent state (orthogonal to the visualizations of the non-entangled states) because of its different topology but it is actually not independent.

But even with this wormhole-like spacetime, one has to do quantum mechanics on top of it and it predicts the same entanglement-like correlations like any other example of a quantum mechanical theory! Nikolić's opposition is a great example of the wisdom that whatever (correct) progress would materialize in the foundations of quantum mechanics would make the picture of the world even more quantum, not less. That's just happening because we're abandoning some incorrect assumptions about the spacetime topology that were rooted in our experience with classical physics (namely the wrong assumption that the spacetime topology is a well-defined observable on the Hilbert space). No wonder that people like Nikolić who are obsessed with the dream to undo the quantum revolution feel threatened by another step in the opposite direction.

Mark's paper

To dramatically improve the average quality (and length) of papers that refer to the ER-EPR correspondence, Mark Van Raamsdonk – the forefather of the "entanglement as a glue" paradigm – released a new, 18-page-long note:
Evaporating Firewalls
His picture is that one can bring a black hole – in his case a large AdS black hole – to a firewall state by carefully measuring its internal microstate from the outside (one could say that one of the fuzzball basis vectors is the result of this complete measurement if fuzzballs are right). However, the evolution of the black hole, while it is entangled with an auxiliary system – in his case a second identical CFT – may restore the initial thermofield configuration.

This process therefore looks like a gradual disappearance (evaporation) of the firewall. Such a result is ironic because AMPS employed entanglement as a tool to erect the firewall and to make it impenetrable. On the contrary, Van Raamsdonk shows that the entanglement has the effect of tearing down this firewall. Mark wouldn't dare to choose this Reaganite terminology in the title of his paper because the left-wing apparatchiks filling most of the Western universities would send him to Gulag for his anti-socialist jokes.

Mark also dedicates several pages to his comments on the nice Papadodimas-Raju paper that appeared in November 2012. I think that what Mark is saying is particularly compatible with the Papadodimas-Raju paper. For example, the precise measurement of the internal microstate performed from the outside is what Papadodimas and Raju would classify as "too many measurements" and that's what terminates the validity of a local effective QFT on the opposite side (inside the black hole, in this case) in their framework.

The figures in Mark's paper (e.g. Figure 8) largely reflect a lore or an understanding of "tracing over other degrees of freedom" and "coarse/fine grained observables" that has already been adopted by several others. As the Wheeler-DeWitt equation suggests, a whole causal diamond worth of operators should be assigned to a slice and we may trace over other degrees of freedom geometrically associated with horizontally separated diamonds.

I won't offer my new results on these issues because I would be giving them away at a price that is far below the fair one and I have some very bad experience with similar (or any) violations of the rules of the free markets.


  1. So when and where will your results go on the market?

  2. When the market conditions are favorable which means, I am afraid, not in my lifetime.

  3. Hi, if and when the market conditions get acceptable which will rather likely not be the case in my lifetime, given the trend in recent years. This is not just a negative statement. I just enjoy the setup of doing research for myself, for my own pleasure, ignoring the mankind and I am grateful to Nature's fate that I was kind enough that it has become possible.

  4. kashyap vasavadaJul 9, 2013, 3:24:00 PM

    Hi Lubos:

    I am a retired physics professor. I know very little
    if anything about string theory. So I do not have any problem with some people thinking that ST will be the final solution to the problems of particle
    physics. In any case, the opposing group does not have any alternative. I have a question if it can be answered without the need to go to original papers. I know Maldacena uses anti de Sitter space in his arguments. Can you explain what is so special about ADS? I understand only thing which is verified experimentally is that observable universe may have positive Lambda at this time. How can you trust any argument based on negative Lambda about entanglement or in other areas? Is there any reason to believe that the interior of a black hole may be ADS? I will appreciate if you or someone on this blog can answer or give reference to
    some simple articles or blogs. On the whole I like your blog. This is the best blog for theoretical and mathematical physics. Thanks.

  5. Thanks for your interest. Concerning the AdS space, I was answering the very same question 2 days ago:


  6. Is there any chance of these results going on the arXiv?

  7. kashyap vasavadaJul 9, 2013, 3:56:00 PM

    Thanks. I see your point.

  8. Dear Clayton, it doesn't contradict any conservation law or absolute laws of Nature so there's a nonzero chance. ;-) I am surely not among those who are spreading big words and promises they don't keep. When I say something, it's meant to be serious, and that's why I can't answer your question in either way. It's at the level of chances, indeed. Many of my results aren't even TeXed and I don't have the lust to expose anything now so it's very unlikely in near future.

  9. Thanks for the PSE link, Lubos. This kind of explanation is very helpful to obsolete physicists like me who want to understand the significance of recent work. I really do appreciate your efforts.

  10. hi lubos,

    thanks for keeping up the summaries on this. it's an exciting time.

    I of course respect your decision to not publicly share your results, but you've said enough that I'm curious about their context. are you willing to say whether you're working in Matrix theory or via holography?


  11. Both.

    BTW well, Matrix theory is sort of holographic as well.

  12. thanks for your reply. great. I won't push further.

    (and yes you're absolutely right that Matrix theory is sort of holographic, so I misspoke; the origin of this is sort of funny. it seems that young people like me are raised on thinking of "holography" as essentially "dualities like AdS/CFT", with field theory data specified on a timelike boundary. which, alas, is an overly limited perspective.)


  13. And we only require the space to be asymptotically AdS. This means that we don’t fix the actual background but only the boundary conditions. If we leave cosmological questions aside then it doesn’t really matter if the space is asymptotically AdS or asymptotically flat and we can use AdS/CFT to answer many important QG questions.

    I think this is also implied in Lubos’s answer…

  14. I understand and respect your decision not to publish given the circumstances. Still, it's kind of a waste. You deserve the original academic credit and other serious researchers could benefit from your work.
    In my opinion, you should write a paper with Maldacena. You two would make an awesome team of non-confused quantum scientists. :-)
    Perhaps such a collaboration would be rewarding enough for you that it would be reasonably close to the fair market price?

  15. Yeah, and maybe a collaboration between Lumo and some serious physicists could approach the I think fair enough market value of 3 Million ... ;-)

  16. Lubos - I had actually taken your remarks literally and now feel a bit foolish for not realizing that you had 'gone Galt' (at least from academia). Your reply brought so much to mind that I had to take some time to compose a response - covering the decline of universities, the rise of bureaucratic administrators, credentialled cliques enforcing and rewarding the correct political sentiments, etc. - which quickly became too long to post here. Perhaps I'll include it in one of the many books I keep promising myself to write.
    (I can't resist one excerpt - overheard:
    Q -Why must everyone go to university these days?
    A - How else will they learn to read and write?)
    I am pleased that you are able to be, in a sense, your own patron. I also expect that you you are not alone in this and that many more people will do the same in the coming years.
    All the best.

  17. LOL, the joke is also supplemented by one I just read in Bob Carter's new book. What's the opposite of diversity? University. ;-)

    There were many other things that sucked over there.

  18. Yes I have read it, but the phrase 'going Galt' is not my invention. The joke now is that it was written as a novel, not an instruction manual. I do not view it as literature, but as a relentless polemic. Nevertheless it is worth reading, if not in it's entirety then at least various passages in which her characters give speeches espousing her philosophy. Perhaps Tolik could give you the gist of the plot so that you would understand these. I would recommend one on the meaning of money along with John Galts speech, and of course there are others.
    What I find extraordinary about it is that when it first appeared (1957) and when I first read it (1968) her depiction of the 'bad guys' seemed completely over the top - so much so that they seemed cartoonish - and yet now actual people in high places are acting and speaking (sometimes almost verbatim) in exactly the same way.
    It's a pity that you could not have experienced the U.S. as it was before the progressive ascendency.

  19. I of course couldn't resist to become familiar with the sketch of the plot.

    Too bad to hear that her over-the-top descriptions were visionary. Even as a younger man, I do remember some things that were substantially more promising and balanced than today.

  20. "Q -Why must everyone go to university these days?"

    It is the writing on the wall for the future. Technology has made obsolete millions of jobs that could occupy the working day of a person, and the value of his/her work be enough for living and raising the next generation. Lowering the standards of universities absorbs hundreds of thousands of young people who in another case would be working in menial jobs now obsolete. Instead of being on the dole they are sent to universities. Then positions are created to absorb a number of them and mediocrity is perpetuated.

    It will get worse and worse, and nobody reads the writing. Robotics advances and nanotechnology too. Unless we manage to get into a war that will send us back to the stone age and start from the beginning.

  21. I imagine that good manners will soon be obsolete as well, but you can rest assured that I will never appropriate someone elses' joke in order to belabor them with a plethora of misconceptions about economics.

  22. "when I first read it (1968) her depiction of the 'bad guys' seemed completely over the top - so much so that they seemed cartoonish - and yet now actual people in high places are acting and speaking (sometimes almost verbatim) in exactly the same way."

    Sir, you are not wrong. Here you have the cloying, sickening "talking points" that a White House press secretary must whip up on a moment's measure,.. or else it's back to the unemployment line.

    Let them eat cake!