Friday, March 9, 2012

Goldreich is also a QC skeptic

I explained how I can believe that quantum mechanics (QM) is true while quantum computing (QC) is false, while Scott Aaronson argues that the burden of proof is on me to show that QC is false. Computer science professor Oded Goldreich explained in 2005 what is wrong with Aaronson's position:
Some (but I'm told that not all of the) believers of Quantum Computing (QC) assert that its possibility is ensured (or even required) by the Laws of Quantum Mechanics (QM). In my opinion, such an assertion is based on two fundamental confusions.

Firstly, the Laws of QM are merely a refutable model (or assumption) about the real world, they are not the reality itself nor can they ever be proved to provide a full description of reality. (This is indeed a generic remark that applies to any model of reality, but it is good to bear it in mind when one wants to talk about ``lack of assumptions'': The assumption that QM provides a ``correct'' description of reality is no less an assumption than the conjecture that one-way functions exist. On the contrary, it seems that the latter assumption may be proved correct whereas the former can only be refuted (and can never be proved correct).) [See further discussion (Nov. 2011).]

Secondly, as far as I know (and here I may be wrong), QM says that certain things are not impossible, but it does not say that every thing that is not impossible is indeed possible. For example, it says that you cannot make non-Unitary transformations, but this by itself does not mean that you can effect any Unitary transformation that you want. ... [I have held the aforementioned opinions since I first heard of QC in the early 1990's.]
Goldreich argues that QC is based on an idealized model that has been extrapolated far beyond what has ever been established in QM, and any such model has to be considered speculative, especially when it makes surprising or counter-intuitive predictions. So he says that "Being skeptic of this [QC] speculation seems to be the default and natural position."

I agee with Goldreich. Experiments have confirmed aspects of QM to fantastic accuracy, but QC may still be completely false. Aaronson wants to dismiss because I wrote a book on How Einstein Ruined Physics, but Oded Goldreich even more of a big-shot computer science professor than Aaronson, and he is also a QC skeptic.

Goldreich has written papers on one-way functions, even tho no one has proved that they exist. So his situation is somewhat analogous to Aaronson, who has written most of his papers assuming QC, even tho QC may not exist. The difference is that Goldreich admits that his position is speculative.

Goldreich also says that he sees no point in arguing, so I guess that is why he does not argue in the comments on Aaronson's blog. My guess is that there are a lot of professors who are skeptical about QC, but consider it rude to badmouth a huge source of research grant money.

Update: Aaronson just got to be more of a big-shot with today's announcement:
Today the National Science Foundation (NSF) named two young scientists, Robert Wood of Harvard University and Scott Aaronson of the Massachusetts Institute of Technology (MIT), to receive this year's Alan T. Waterman Award.

The annual award recognizes an outstanding researcher under the age of 35 in any field of science or engineering NSF supports.

In addition to a medal, each of this year's awardees will receive a $1 million grant--twice the amount of last year's award--over a five year period for further advanced study in his field.

"Robert and Scott embody the best in young, bold and talented researchers," said NSF Director Subra Suresh noting that computing is central to both of their research pursuits. "I have no doubt that these two researchers will continue to have an extraordinary impact on our nation and the world in the years to come." ...

Scott Aaronson is an associate professor of Electrical Engineering and Computer Science at MIT, affiliated with MIT's Computer Science and Artificial Intelligence Laboratory, the largest Interdepartmental lab at MIT. Aaronson, a theoretical computational scientist, pursues research interests that focus on the limitations of quantum computers and computational complexity theory more generally. ...

"By illuminating the fundamental limits on what can be computed in the physical world, and the potential implications of those limits, Scott Aaronson has staked out important new ground in computational theory," said MIT President Susan Hockfield, "I am delighted that the National Science Foundation has recognized his dual abilities, both to articulate key research questions and to offer new methods and ideas for addressing them, with the Alan T. Waterman Award."
Wow, he offers a $0.1M prize in an attempt to prove me wrong, and then a couple of weeks later the feds give him a $1.0M prize for being such a visionary. He could be proved wrong and have to pay that $0.1M, and still make a $0.9M profit on the deal!

No wonder no one wants to admit that quantum computers can only do what regular computers can do. Another physicist has already remarked:
Not only is this great news for Scott, but a rising tide lifts all boats: the entire field of quantum computing benefits when our talented researchers get recognition for their achievements.


  1. You should watch the movie (or read the book) 'The Hitchhikers Guide to the Galaxy'. In the story the protagonists fly around in a starship that uses 'The Improbability' drive (which was meant as an absurdest joke), that not so surprisingly uses the exact same idea to operate as Quantum Computing. This idea of quantum entanglement is based soley the Copenhagen interpretation, which is basically as scientific as 'because I said so'. Bad way to do science or physics.

  2. I don't think the problem has to do with the interpretation of Quantum Mechanics. As long as the Copenhagen interpretation gets the right answers, it's fine. You could interpret quantum mechanics as requiring little creatures called Gremlins collapse the wavefunction and it would still be OK if it gets the right answers.

    Everything that quantum computer theorists say is OK in theory, but in practice it just isn't feasible.

  3. It's this phase shift business that throws me off. Just now I searched on "phase observables" and Google threw me into a book, OPERATIONAL QUANTUM PHYSICS by Paul Busch et al. It looked pretty good on page 96 where Google put me, but some of the material just reinforces my notion that these "quantum gates" that perform ( to me ) miraculous state transformations are confabulations. E.g. there is the comment about "macroscopic coherent states" ( i.e. a laser beam ) that realize a fixed phase with N^-1/2 error, where N is the occupancy. In my mind, this explodes QC completely right there. But what do I know! btw, I agreed with Roger on the "Perpetual Motion" blog, and I'm posting as anonymous here just out of expediency - LM