Wednesday, November 29, 2017

Witten interviewed about M-theory

Quanta mag has an interview with the world's smartest physicist:
Among the brilliant theorists cloistered in the quiet woodside campus of the Institute for Advanced Study in Princeton, New Jersey, Edward Witten stands out as a kind of high priest. The sole physicist ever to win the Fields Medal, mathematics’ premier prize, Witten is also known for discovering M-theory, the only candidate for a unified physical “theory of everything.” A genius’s genius, Witten is tall and rectangular, with hazy eyes and an air of being only one-quarter tuned in to reality until someone draws him back from more abstract thoughts.You proposed M-theory 22 years ago. What are its prospects today?

Personally, I thought it was extremely clear it existed 22 years ago, but the level of confidence has got to be much higher today because AdS/CFT has given us precise definitions, at least in AdS space-time geometries. I think our understanding of what it is, though, is still very hazy. AdS/CFT and whatever’s come from it is the main new perspective compared to 22 years ago, but I think it’s perfectly possible that AdS/CFT is only one side of a multifaceted story. There might be other equally important facets.

What’s an example of something else we might need?

Maybe a bulk description of the quantum properties of space-time itself, rather than a holographic boundary description. There hasn’t been much progress in a long time in getting a better bulk description. And I think that might be because the answer is of a different kind than anything we’re used to. That would be my guess.

Are you willing to speculate about how it would be different?

I really doubt I can say anything useful.
This guy is obviously a BS artist.

M-theory and AdS/CFT were over-hyped dead-ends. They were only interesting to the extent that they had conjectural relationships with other dead-end theories.

Witten can't say anything specific and positive about these theories.

A lot of people have idolized him for decades. It is time to face the facts. All those grand ideas of his have amounted to nothing.

Peter Woit comments. And string theory advocate Lubos Motl, of course.


  1. I'm assuming you're pre-ordering Lost in Math: How Beauty Leads Physics Astray by Sabine Hossenfelder:

  2. I do read her blog often, and occasionally comment on it.

    1. I posted something against quantum computers on her recent blog post but we'll see if she can understand it. Something I haven't heard you talk about is error correction. I think the QM people are just rediscovering analog computing but they think they are going to do magic with error correction. The fact that a classical computer can do graph-based Turbo Code or parity checks is critical but the imposition of a false digitalization metaphysics clouds the issue. A digital state is an implicit error bound that costs time and space to keep correct (bounded). The QC people somehow think that error correction solves a propagation of error but it only does this classically by a continual interruption and recalibration of computation. If an error occurs with some bits, the forward computation is immediately ruined and must be recalculated from the point of correction. That is why analog systems are an initial value chaos situation. If I have a chain of 1,000 billiard balls that are suppose to hit each other in some pattern, then the smallest error at the start ruins the whole outcome. To draw lines demarking error margins and call them “bit states” is the so-called magic of classical computing. It still requires me to stop the balls and correct them when they exceed those margins and restart the movement or computation. There is nothing mysterious or amazing about error correction because it ruins the infinite horizon of calculation and isn't free.

    2. MD Cory,
      Check this You Tube video out at the 32:30 mark. Dr Essex makes a pretty good point about the problem of digital computing, sometimes what you get in computation isn't what is mathematically true, but is an artifact of the processor of the digital computer itself, which is what I often suspect physicists are confusing with actual patterns of evidence. The pattern of granularity they may be finding could very well be computational artifacts.

    3. The gnosticism of quantum computing! There is a difference between measurement error and model leakage. Such leakage should rarely occur but computer science and engineering haven't utilized finite field libraries to do fast rational arithmetic. Actually, infinite precision is the unreal idealization (infinitely discrete) but there is certainly an issue of proper coarse graining. The point about the measuring device being part of the world was not original with 20th century physics but was mention by many others, including Kant.

      What QC people must do is explain why error correction can be performed with enough redundancy and inline with the computation as to not disturb the infinite horizon. But this is all just smoke and mirrors because this already presupposes that we are dealing with analog error propagation, otherwise it would require nothing new. There are forms of analog error correction but what they seem unable to appreciate is that they are only building analog simulatorsfor quantum mechanics and not general computers:

      "In two papers published today in the journal Nature, a team at MIT and Harvard in Cambridge, Massachusetts, and another from the University of Maryland and the National Institute of Standards in Washington D.C., reveal that they have built specialized types of quantum calculator, each of which uses more than 50 qubits—well beyond what had been demonstrated previously. In both cases, the researchers created quantum simulators, machines capable of using analog calculations to model how quantum particles interact."

  3. Lubos Motl brags about being smarter than mathematicians: "But Witten makes a general important point (which I have made many times on this blog, too): It's not only mathematics that is central in theoretical physics. It's mathematics that is hard for mathematicians. For mathematicians, it's even hard to rigorously define a quantum field theory and/or prove its existence. It's even harder with the concepts that string theory forces you to add. Why is it so? Well, I would say that the need for 'mathematics that is hard for mathematicians' simply means that the Universe is even more mathematical than the contemporary mathematicians. Contemporary mathematician still discuss objects that are too close to the everyday life while the concepts needed to discuss the laws of physics at the fundamental level are even more abstract, more mathematical."

    He has it precisely backwards and that's why everything has gone to the number crunching machines. There is no such thing as abstraction in the context of physical reality. Abstraction is an approximation of humans. Motl just engages in a reification fallacy of Plato here.

    Math As Myth by Samuel Arbesman