Author: dabacon

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Twirling, Twirling, Twirling Towards Freedom

From blackboxvoting comes this funny:

P.S. Not that this has anything to do with what we’re discussing (or maybe it does), but there were two separate “I voted” stickers that voters were given after they voted. If you voted electronic, you were given a big gorgeous flag-waving colorful sticker that said something akin to “I Voted Electronically!” If you voted paper, you were given a crappy little sticker that looked like it was made by a low bidder from China with faulty equipment that said “I voted”. I’ll be forever haunted by the interaction I witnessed between one lady and a poll worker. The lady said “I want to vote on a paper ballot. I’ve read that I should use a paper ballot.” The poll worker reached for a paper ballot and started to hand it to the lady, but that’s when the lady saw the two bowls of stickers. She said “Oh, you mean I can’t have one of those stickers unless I vote with the machine?” The poll worker said “Yes, that’s right. Those stickers are for the people who vote with the machines.” The lady looked wistfully downwards, pondering, and then grinned giddily and said “I want to vote electronically!”

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Bashing Our Heads Against the Planck Length

If we take Planck’s constant, h, Newton’s constant, G, and the speed of light, c, we can form a constant which has as its unit the unit of length. This is the Planck length: sqrt(Gh/c^3) or approximately 4 times 10^(-33) cm (I’ve not used hbar here for some silly reason.) It is often argued that the Planck length is the natural length at which an as yet undiscovered theory of quantum gravity will take over.
There is a nice argument where the Planck length emerges naturally from considering gravitational collapse. Consider a system of energy E. If this energy confined to a ball of radius c^4R/G<E , then the system will eventually collapse to a black hole (this is called the Hoop conjecture.) On the other hand, if the system has energy E, then it cannot be localized more than it’s Compton wavelength R=hc/E. What then is the minimum radius achievable? Well it’s just the Planck length!
So the Planck length arises naturally when we ask what is the minimal size object we can make which doesn’t collapse into a black hole and which obeys the uncertainty principle. But does this mean that the Planck length is the smallest length we can measure? I mean, just because the Planck length follows from the above argument doesn’t imply that we cannot make measurements which localize a particle to a distance less than the Planck length. However, a recent Physical Review Letter (vol 93, p.21101, 2004), “Minimum Length from Quantum Mechanics and Classical General Relativity” by Xavier Calmet, Michael Graesser, Stephen D.H. Hsu attacks exactly this issue (for the arXiv version click here.) And what do the authors discover? They discover that if they try to use an interferometer, or simple time of flight measurements to determine locality, they get the answer that the minimal distance measureable is the Planck length! So there really is a sense in which distance shorter than the Planck length has no meaning.

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Day Two

It snowed here in Santa Fe on Saturday. My brain reacted in the only way it knows how to react to snow: it ordered me to go skiing. So Sunday, I made the journey again to Wolf Creek with UNM grad students, Steve and Devan. At this rate, I might hit more than 20 days of skiing this season!

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Strings Versus Loops

A favorite pastime of scientists of all ilks is to discuss the pros and cons of string theory. Of course, very few scientsts are equiped to properly critique string theory (myself included), yet a large number of scientists are very sceptical. You might just say that “they smell a rat.” Why might this be? Take a look at this wikipedia article which is an attack on a different proto-theory of quantum gravity, loop quantum gravity. In the link, the authors are clearly string theory biased. And they put forth such great arguments as….loop quantum gravity is bad because it only talks about four dimensional spacetime…loop quantum gravity is bad because it does not allow an infinite variety of new fields and objects….loop quantum gravity is bad because it, oh my god, only purports to be a theory of gravity….loop quantum gravity is bad because it doesn’t predict any new particles…loop quantum gravity does not produce any new mathematics…etc., etc. It’s arguments like these which give string theory a bad name. There are good reasons to be skeptical of loop quantum gravity, but the arguments put forth from this stringy perspective are simply absurd.

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CEPI Seminar 10/10/04 Wim van Dam

Complexity, Entropy, and the Physics of Information Lecture Series
Wednesday, November 10, 2004, 5:00 PM. Refreshments 4:15 PM.
Robert N. Noyce Conference Room, Santa Fe Insitute
Wim van Dam
Computer Science Dept., University of California, Santa Barbara
Quantum Computing, Zeroes of Zeta Functions & Approximate Counting
Abstract:
In this talk I describe a possible connection between quantum computing and Zeta functions of finite field equations that is inspired by the ‘spectral approach’ to the Riemann conjecture. The assumption is that the zeroes of such Zeta functions correspond to the eigenvalues of finite dimensional unitary operators of natural quantum mechanical systems. To model the desired quantum systems I use the notion of universal, efficient quantum computation.
Using eigenvalue estimation, such quantum systems are able to approximately count the number of solutions of the specific finite field equations with an accuracy that does not appear to be feasible classically. For certain equations (Fermat hypersurfaces) I show that one can indeed model their Zeta functions with efficient quantum algorithms, which gives some evidence in favour of the proposal.

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Alice, Bob, and …

In cryptography there has been a long tradition of calling two parties involved in a protocol Alice and Bob. This tradition has been proudly maintained in quantum information science, no doubt in large part because quantum cryptography was one of the first ideas in quantum information science. One of the nicest things about the Alice/Bob labeling scheme is that it allows one to use gender to distinguish parties. I suspect that since gender is dear to our animal hearts, this concise way of refering to parties has significant syntactic advantage. David Mermin once said something along the lines of “if quantum information contributes nothing else to physics it least it will have given us Alice and Bob.” Actually, where I’ve found the Alice/Bob labeling scheme most efficient is in special relativity where it allows one to give gender to different reference frames (note also that since all frames are equal…) It is much clearer to most students when you refer to “his reference frame” or “her reference frame.”
Along these lines, when you have to introduce a new party, it is traditional to call this party Eve. This is usually done because in cryptography, Eve is the eavesdroping malicious third party. But this screws up the whole gender roles efficient labeling. I therefore propose that instead of calling the third party Eve, we should call the third party E.T., or Elephant, or Eagle such that we can use “it” to refer to this party. Now what do we do for four parties?

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Day One

Yesterday I drove the 3+ hours to Wolf Creek in Colorado to go skiing. And boy was it worth it! While Wolf Creek doesn’t yet have great coverage, most of the mountain was open, and, if you worked for it, you could still large stashes of untracked powder. If they get about another 18 inches they will be in great condition.
My most notable episode was an epic crash I had in the powder. I had climbed up this ridgeline to get to some nice steep tree lined runes with about a foot and a half of powder. It was a super nice day, very hot, and so I wasn’t wearing any gloves. I took off down the run and after about 5 turns I may a spectacular nosedive into the pow. Standing up, I was covered in powder and my hands were freezing cold. I mean really really freezing cold. It was at this moment that I realized that I was dehydrated from both the high altitude and the long climb I had made to reach the stash. Doh. Taking off my glasses was my next smart move. The next few seconds I could feel myself get light headed and thought “Headline: Santa Fe postdoc proves that even with a Ph.D. you can still be a moron.” After a few moments chilling in the sun, however, I recovered and promptly went to buy a Gatorade. Earlier in the morning I had noticed how many people were wearing packs for carrying water. I thought that was kind of funny, but now I think I’m going to go buy one.

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An Amazing Histogram

For all political junkies this study of the 2004 presidential election by Michael Gastner, Cosma Shalizi, and Mark Newman is extremely interesting.
Update: It seems that the authors have gotten rid of the final histogram which claimed that 302 counties voted nearly fully for Kerry (IIRC >90% of the vote for Kerry.) This was the most interesting part of the article, unfortunately. Still an interesting article, but not nearly as shocking.

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Welcome to Theocracy

Let’s give a warm welcome to the world’s latest theocracy, the United Christian States of America! All hail our new Commander and Pope, George Bush. Shall we kiss his ring?
On November Second, we learned that over fifty percent of America is totally and completely irrational. Don’t believe me? Go ask that epitome of rationality, a scientist. I know only two scientists who voted for George Bush, out of a sample of a few hundred. This election wasn’t a referendum on George Bush’s first term, as many a pundit would claim, because there is no rational way to argue that his term has been anything but a disaster. Don’t believe me? Ask a scientist. So the reason over fifty percent of America voted for the George Bush must be something a scientist cannot comprehend, and indeed it was: that bastion of irrationaly, religion. Ever tried to argue about the theory of evolution with a member of the religious right? Feel strangely familiar to arguing with a Bush supporter? Indeed.
Hearing the election results on November 2nd, the first thought which crossed my mind was that I wished that those who have not educated themselves enough to be able to put a rational thought together were banned from enjoying the benefits of the brilliant scientists who have advanced society. But that thought is too harsh. Instead, we must think about how to turn that irrational fifty percent into rational coherent human beings. It’s surely one of the reasons I want to end up as a teaching professor. And you, my dear audience, you a bastion of rationality, you should not shrink in expressing your disdain for the irrational. Let us drive out the idiot out of America, not by physically revolting, but by teaching America how to think coherently.