Thursday, May 19, 2022

Susskind Tackles Computers Falling into Black Holes

Physicist Leonard Susskind gave a lecture:
Black Holes and the Quantum-Extended Church-Turing Thesis | Quantum Colloquium

A few years ago three computer scientists named Adam Bouland, Bill Fefferman, and Umesh Vazirani, wrote a paper that promises to radically change the way we think about the interiors of black holes. Inspired by their paper I will explain how black holes threaten the QECTT, and how the properties of horizons rescue the thesis, and eventually make predictions for the complexity of extracting information from behind the black hole horizon. I'll try my best to explain enough about black holes to keep the lecture self contained.

Susskind explains that his last great accomplishment was to convince his colleagues that if two entangled particles fall into two black holes, then they will be connected by a wormhole. See EP = EPR for more.

Now he is excited by the physics of quantum complexity theory. It had long been thought that Turing machines are good models for computation, in that computable functions can be performed by Turing machines, and polynomial time computability corresponds to polynomial time Turing machines. He says this is now believed to be false, because a quantum computer might do something in polynomial time that a Turing machine might require longer time.

Susskind's insight is that a computer falling into a black hole might achieve a higher complexity than what would otherwise be possible. The catch is that it could never communicate its result to anyone.

Update: Susskind claimed that EP=EPR has become accepted wisdom, but Peter Shor says:

One of the problems with It from Qubit is that it’s really quite hard to tell the papers that are nonsense from the ones that aren’t. For example, Maldacena and Susskind’s ER=EPR paper is a speculative idea that has no chance of being correct (but listening to his most recent talk, Susskind hasn’t given up on it). And when you actually corner other people in the area they (or at least some of them) will admit that this paper has virtually no chance of being correct, but for some reason they aren’t willing to say this publicly.

There are undoubtedly other papers in this field which are equally improbable. But it seems to me that any field where you have to be in the cogniscenti to know which papers are the ones worth paying attention to is in deep trouble.

That gets this response:
I wonder on what grounds ER=EPR is supposed to have “no chance” of being correct. There is already the curious parallel of non-traversibility of wormholes, and non-transmission of information via entanglement alone; obtaining both of these limitations from a common origin is exactly the kind of beautiful conceptual connection one expects from a deep correct insight.
So there are two theoretical examples of non-communication, and saying they are the same is a deep insight. I say both are the same as the Easter Bunny. Is that deep also?

I wonder if anyone has published a respectable paper saying that EP=EPR is nonsense. Or if everyone is too polite to say so. Or if physicists think that because the EP=EPR paper was written by two great geniuses, failing to understand it must be a deficiency of their own brain power.

Peter Woit's response:

Probably others have the same problem I have with writing anything publicly about this. The literature is huge and complicated, so it would be a full time job to master it to the point of being sure there is no there there. I’ve been through this before with string theory claims and wasted far too much time on that.
It used to be that leading physicists would explain why the theory makes sense or is good for something.


  1. Thought experiment:
    Push every damn physicist who thinks mucking about with imaginary effects inside imaginary black holes actually is physics...INTO a black hole.

    What would happen?

    Aside from the t = $ conservation of no longer having to pay said physicists, nothing would happen.

    But there is a SERIOUS paradox, because,
    If you didn't push said physicists into said black hole...then still, nothing would happen. Hmm. Ok, I'm at a loss on this one.

  2. Prof. Woit need not in retrospect conclude that his going to "the point of being sure there is no there there" has been a "waste" of time. However indirectly, his book has been one of the very few which did provide reliable kind of insights, to people outside the field, as to what kind of theoretical "physics" was being pursued in premier universities. Opinions may vary, but there is no doubt that the book was very valuable, even courageous. It takes not only effort but also courage to *studiously* point out that there is no there there.