Archive for February 2007

Tao on Many-Worlds and Tomb Raider

27th February 2007

Terence Tao has an interesting post on why many-worlds quantum theory is like Tomb Raider.  I think it’s de Broglie-Bohm theory that is more like Tomb Raider though, as you can see from the comments.


Dates for your diary

20th February 2007

Update: I am informed that the Oxford Everett meeting will be in the summer rather than in September and is invitation only.  Also, there will be a Symposium on the Foundations of Modern Physics in Vienna 7th-10th June.  Registration for that is open until the end of March.

I haven’t been contemplating too many quantum quandaries recently because I was away at a workshop on Operator Structures in Quantum Information in Banff (a very interesting meeting and a highly recommended location) and am currently visiting Caltech. My brain is mostly full of mathematics and non-foundations oriented physics. In the meantime, here are some interesting foundations events coming up this summer.

Firstly, Perimeter Institute is organising its first Summer School on Quantum Foundations August 27th-31st. There have been several summer schools in other locations in the past, which have mostly been philosophy/interpretations oriented. The PI School will have a distinctly “physics” flavor, e.g. it will include lectures on experiments amongst other things. I’ve seen the list of speakers and it looks like it’s going to be really interesting. For grad students and postdocs interested in foundations, summer schools are highly recommended because of the sparsity of experts in the subject at most institutions. It’s how I became reasonably competent in the subject at any rate. Please don’t write to me requesting further details because I can’t help you. All the information is going to be posted on your favorite quantum websites/mailing lists very soon. Alternatively, you’ll be able to get to the school website via this link once it is up and running.

Secondly, the Institute for Quantum Computing and Perimeter are jointly running a series of quantum oriented workshops this summer under the banner Taming the Quantum World. There’s lots of interesting events for quantum information folks, so check out the website, but the workshop on Operational Quantum Physics and the Quantum-Classical Contrast, June 4th-7th, organized by Paul Busch and Lucien Hardy will be of special interest to readers of this blog.

Since I’m plugging foundations meetings at my own institutions, I should also mention Many Worlds at 50, organized by Jonathan Barrett, Adrian Kent and David Wallace, taking place September 21st-24th.

Given the number of meetings in Waterloo this year, it is somewhat surprising that the foundations community has also found time to organise some events at other locations. Here’s the rundown of the rest:

– March 5th-9th: APS March Meeting, Denver – Two focus sessions on quantum foundations have been organised.

– March 29th-31st: 15th UK and European Meeting on the Foundations of Physics, Leeds.

– April 13th-15th: New Directions in the Foundations of Physics, Maryland. It’s invitation only (and full) I’m afraid.

– June 11th-16th: Quantum Theory: Reconsideration of Foundations 4, Vaxjo.

– July 2nd-13th: Operational probabilistic theories as foils to quantum theory, Cambridge. It’s invitation only (and full).

– Sometime in September: Everett at 50, Oxford.

If I’ve missed any meetings or you have any new info on any of these then please leave a comment.

Quantum Brains

7th February 2007

OK, I should be preparing a talk, but it is late and my mind is wandering, so it’s not going to happen tonight.  Instead, I’ll pose this puzzler:  If quantum computers are more efficient than classical ones then why didn’t our brains evolve to take advantage of quantum information processing?

I have a vague recollection of seeing this question on a physics blog somewhere before, and it does have a family resemblance to Scott’s infamous post, albeit a more politically correct version.

There are a number of assumptions behind this question:

  • Evolution usually does a very efficient job of coming up with information processing devices.  As evidence for this note that the best algorithms we have for some tasks simply imitiate nature, e.g. neural networks, simulated annealing, etc.
  • Some functions of the brain, such as the ability to solve math problems, are best understood by regarding the brain as a kind of computer.  Note that we don’t need to say that the brain is merely a computer, only that it can be regarded as such for understanding some of its functions, i.e. we don’t need to get into a big philosophical debate about conciousness and artificial intelligence.
  • Further, in these respects the brain is a classical computer and not a quantum one.  It certainly seems that the information processing function of neurons can be understood in classical terms, i.e. neural networks again.  There is a small minority of experts who believe that quantum mechanics plays an essential role in the information processing functions of the brain for whom my question is nonsense.

Here are all the possible explanations I can think of.

  • The set of problems in BQP, but not in P does not include anything that would have conferred a significant survival advantage for our ancestors.  Admittedly, efficient factoring could be useful for surviving high-school math class, as well as for cracking codes, but this wouldn’t have mattered so much to cave-people.  This would be disappointing, although not devastating, news for people trying to come up with new quantum algorithms.
  • There is some big problem with building a stable quantum computer of any appreciable size, and so present day experimentalists will eventually run into the same problems that nature did.
  • Dumb luck.  Evolution tends to find local minima in the landscape of all possible species.  Having a quantum brain is indeed a lower minimum than our current classical brain, but we never got a big enough hit to get over the mountain separating that solution from ourselves.

The first two explanations seem like the most interesting ones.  If the third explanation wasn’t a possibility then there would have to be a tradeoff between the amount of progress possible in developing quantum algorithms and the amount possible in actually building a quantum computer.  Given that much quantum computing funding is predicated on the idea that massive progress is possible in both areas, I’d say we should thank Darwin for dumb luck!