Category: General

I’m going to take another hiatus from blogging, until at least August 1, 2006. I was hoping to come back to my blog properly, but realize that I have too many other things going on. I do hope to blog again one day, and have some ideas for large project into which the blog would be integrated. (I rather like the way Kevin Kelley is using a blog to test out ideas for a book, and could potentially see myself doing the same thing.)

For now, I’ll leave you to ponder a provocative recent comment posted by John Sidles. I haven’t yet read the paper in question, but the authors, Conway and Kochen, are top-notch mathematicians, and I’m looking forward to reading it at some point.

Boy, is it quiet, both here and on Bacon’s Quantum Pontiff. Just to stir things up, what do people think of the preprint on the arxiv server this morning:

The Free Will Theorem” http://www.arxiv.org/abs/quant-ph/0604079

Such titles are often associated with fringe physics — except that these particular nutjobs are the mathematicians John Conway and Simon Kochen!

These guys may be nutjobs, but they are high-power nutjobs, and I enjoyed their preprint very much.

In engineering, we tend to think of every quantum problem as an exercise in model order reduction (MOR). But our MOR colleagues (and there are a lot of them — there are more academic articles by far on MOR than on open quantum systems!) always complain that simulation algorithms for open quantum systems are stochastic. “Can’t you eliminate the stochasticity, and make your open quantum system model deterministic?” they complain.

The Conway/Kochen Free Will Theorem answers that question pretty crisply, by showing that open quantum systems have properties that *no* (locallyrealistic) deterministic simulation can exhibit. And, they prove it in a fun way.

Also, it’s just not right to ignore an article that begins “Do we really have free will, or, as a few determined folk maintain, is it all an illusion? We dont know, but will prove in this paper that if indeed there exist any experimenters with a modicum of free will, then elementary
particles must have their own share of this valuable commodity.”

All the above is just to stimulate some comment!

This seems a little redundant, given my recent 6 month break from blogging, but I’m gone on holidays for three weeks starting in about 36 hours, first for two weeks in New Zealand, and then for one more week’s back in Brisbane, which will mostly be spent attending the Ideas Festival. Should be fun, but I won’t be blogging during that time.

This is a plug for a free public lecture (with free drinks and nibblies after) about junk DNA and the role it plays in biology, by Professor John Mattick of the University of Queensland. It’s to be held 6:30 pm, Monday March 13 in the Judith Wright Center, Fortitude Valley, Brisbane.

(The lecture is the first of a monthly series to be known as BrisScience. My partner, Jen Dodd, is running the series.)

The topic of the talk is really interesting. One of the biggest problem in modern biology is how we go from DNA to fully fledged living beings. It’s pretty well understood how we go from DNA to the proteins which form the building blocks for living beings. But that’s a far cry from a full understanding: knowing how to put together a steel girder doesn’t imply that you can build the Eiffel tower or the Empire State building. Figuring out the link between DNA and the large-scale structure (the architectural design, if you like) seems to be very poorly understood.

The speaker, John Mattick, has some really interesting (and controversial) ideas about how this happens. He thinks the so-called junk DNA in the human genome (pieces of the DNA which don’t code for proteins) carries the information about the design. As an outsider it’s hard for me to judge how successful the ideas are, but they’re certainly getting some attention: his work was named by Science magazine in its list of the ten most significant breakthroughs of 2004, and he had an article about it in Scientific American a couple of years back.

It’s probably surprising if you don’t already know it, but in the standard “quantum circuit” model quantum computers are actually quite similar to ordinary computers. A quantum computation is built up out of quantum gates that perform quantum logic operations on quantum bits. All of this proceeds pretty much by analogy with classical computers, where gates perform logical operations on bits. There are some technical differences, but the broad picture is pretty similar.

Mark Dowling, Mile Gu, Andrew Doherty and I have recently developed a rather different geometric approach to quantum computation. (Here’s the link to the abstract, and here’s the link to the full text at Science. Jonathan Oppenheim has also written a nice perspective piece (sorry, I don’t have the full text).)

Our result is pretty simple: we show that finding the best (read smallest) quantum circuit to solve a particular problem is equivalent to finding the shortest paths between two points in a particular curved geometry. Intuitively, this problem is like an orienteer or hiker trying to find the shortest path between two points in a hilly landscape, although the space we are working in is harder to visualize. There’s some technical caveats to the result, but that’s the general gist.

What use is this? At the moment it’s difficult to say – unfortunately, we don’t yet have any killer applications of the result. But our result does mean that problems in quantum computation can be viewed in terms of equivalent problems in the field known as Riemannian geometry. This opens up the possibility of using some of the deep ideas of Riemannian geometry to solve problems in quantum computing. And who knows: maybe ideas from quantum computing will have a useful stimulating effect, injecting new ideas into the study of geometry!

Scott Aaronson is apparently Shtetl-Optimized.

What’s the difference between neon and ammonia?

In its most common isotope, a single neon molecule (one atom, in fact) contains 10 neutrons, 10 electrons, and 10 protons. A single ammonia molecule also contains 10 neutrons, 10 electrons, and 10 protons. It’s the same stuff! I think this is very cool.

Update: Well, I can’t count. Ammonia only has 7 neutrons. I know this kind of phenomenon is possible, because I set it as a problem once in a mini-course I gave on metals and superconductors, and people came back with several solutions. Unfortunately, I don’t remember what they were.

Update II: Potassium Bromide (K Br) and Calcium Selenide (Ca Se) appear to do the trick, assuming no more silly mistakes. Can anyone find a simpler example?

Update III: Helium and Deuterium both have 2 protons, 2 neutrons, and 2 electrons. It’d still be nice to have examples involving two more familiar substances.

Update IV: Commenter Kurt points out a better example: Nitrous Oxide (laughing gas) and Carbon Dioxide, both with 22 electrons, protons, and neutrons. Any better? I think salt and nickel 58 (the most common isotope) also provide an example.

Another quantum wiki – Qwiki. (Who comes up with these names?)

Go forth and contribute!

Quantiki, a wiki based around quantum information. Could be very useful, with enough content. Maybe the quantum bloggers should look to see if any of their old content is useful, and perhaps look into a Creative Commons license.

If you haven’t seen it yet, I strongly suggest taking a look at Cosmic Variance, which is a really terrific new group blog on things physical and cosmological.