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?
CEPI
In the golden ages, when people were just beginning to think hard about quantum information, there was a workshop held in 1988 at the Santa Fe Institute on “Complexity, Entropy, and the Physics of Information.” This produced a proceedings which is well worth reading, even after all these years. Now, thanks to the support of the Santa Fe Institute, The Quantum Institute at Los Alamos, the Center for Advanced Studies at the University of New Mexico, and the Physics Information group at the University of New Mexico, a lecture series on Complexity, Entropy and Physics of Information has been set up. Already, we’ve heard lectures about econophysics and the limits of algorithmic cooling. The schedule of speakers will be posted here.
Wick Rotation
In quantum theory, we are interested in calculating the amplitude for starting in some initial state |i> and ending in some final state |f>. For a Hamiltonian H evolving for a time t, this amplitude is given by <f |exp(-iHt)|i>. In the path integral formulation of quantum theory, we rewrite this as the path integral \int dq exp(i S(q)) where this integration is performed over all paths q and S(q) is the action (\int_0^t L(q,dot{q}) dt ). Often what we’re really interested in is the long time propogators, so our action is really integrated from minus infinity to plus infinity. What has always astounded me is that often times we can calculate this path integral by performing a Wick rotation: we substitute -it for t in the path integral and thus we obtain a path integral with terms which don’t oscillate wildly. This often results in a situation where we can then either explicitly calculate the integral, or where we can numerically integrate the path integral by standard Monte Carlo methods. In fact, you will recall, what we’ve done is transformed the path integral into a partition function from classical statistical mechanics.
So here is my question. Is this anything more than a trick or is there something profound going on here? In particular I’m thinking about hidden variables. Since we have taken a quantum system and transformed it into a classical system, we’ve effectively made the transition to a hidden variable theory. Sampling from the classical statistical mechanical system described after the Wick rotation is now sampling from some hidden variable theory. Why doesn’t this immediately work? Well the first problem is that we have transformed the amplitude into a partition function. The probability of going from the state |i> to the state |f> is the magnitude squared. But does this really mess us up? We now have something which looks like int dq exp( S[q] ) int dq’ exp (S'[q’]) for the probability. The S’ comes about because the action is now the action going from plus infinite to minus infinity. But this still looks like a partition function: however now we aren’t sampling over all paths q but instead all paths which start with |i> go to |f> and then return back to |i>. So our hidden variables are not paths from minus infinity to plus infinity, but instead are now spacetime “loops” which go from minus infinity to plus infinity and then back to minus infinity. What does this mean? Now that is an interesting question!
A Philosophical Argument
Bell’s theorem tells us that there is no local hidden variable theory which reproduces the statistics of quantum theory. Fine. One way to think about moving onward given Bell’s theorem is to given to look for nonlocal hidden variable theories which reproduce quantum theory. But now there is something strange that happens. If you have nonlocal hidden variables, i.e. quantities describing the state of the universe but which are jointly accessible by two spacelike seperated observers, what is the difference between this and assuming that your notion of spacelike separation is not correct. Suppose you come up with a nonlocal theory. What prevents anyone from reinterpreting your nonlocal theory as a totally local theory in which spacelike separation is defined different? Well there is, as far as I can tell, exactly one difference: in quantum theory we cannot use entangled particles to communicate between spacelike separated observors. But this difference doesn’t disallow interpretting a nonlocal hidden variable theory as simply spacelike separation being defined differently, it just tells us the spacelike sepearation of entangled particles must force a nonsignaling constraint (and reproduce quantum theory!) So why don’t we spend more time thinking about where the structure of our spacetime manifold comes from?
QIP 2005
Isaac Chuang sends out an email concerning QIP 2005:
This is a preliminary announcement for QIP 2005, the Eighth Workshop on Quantum Information Processing, to be held at MIT in Cambridge, Massachusetts (USA), from Thursday January 13th until mid-day Monday January 17th, 2005.
The QIP series has become the premiere conference on computer-science aspects of quantum information. This year, it will be hosted by the MIT Department of Physics (web.mit.edu/physics) and the MIT Center for Bits and Atoms (cba.mit.edu).
The conference will consist of a full schedule of invited talks on recent results in quantum information processing, plus an open session with short talks, one or more poster sessions, a banquet, and additional social activities. This year there will be a nominal conference fee.
Please mark the dates in your calendar. We hope you’ll be able to attend. Please feel free to forward this message to anyone you think would be interested. Instructions for being added or removed from this mailing list are provided below.
There will be a 2nd announcement inviting people to register for the workshop and submit proposals for posters and short talks. Limited travel support will also be available.
More information is available at http://web.mit.edu/qip2005 This will be updated further in the upcoming weeks and months.
I have never been to a QIP which has not been accompanied by some nice extreme winter weather. Last year was Waterloo, Ontario, where we froze our rear ends off. Before that it was in Berkeley, California. Which should have been nice and calm, except that there was a huge rain and wind storm during the conference. Prior to that it was held in upstate New York and prior to that Amsterdam and prior to that Monteral and prior to that Chicago. All in winter. BRRRRRR!
I hope M.I.T. (that other Tech school) can provide suitable freezing temperatures. And maybe some good talks as well?
What the Bleep Do We Know?
Yesterday I saw a showing of the movie “What the #$*! Do We Know?”–a film that advertises itself as “a spiritual film that combines quantum physics, multi-dimensional visual effects and animation, a dramatic story and interviews with leading scientists and mystics?” Sounds like some good fodder for the Quantum Pontiff, eh?
The film is basically three films in one. One film talks about quantum physics, and in particular the interpretations of quantum physics which lead people to utter sentences like “quantum consciousness” and “parallel universes exist.” The second film is about our brain, conditioning, and consciousness. Both of these first two films are narrated by a series of “leading scientists and mystics?” (How can mystics become leading if they can’t get tenure?) The third film is the story of a northwest based photographer whose life serves as a way to talk in concrete (or not so concrete) ways about the points of the first two films.
My reaction to this film was a lot like my reaction to Michael Moore’s Fahrenheit 9/11: I love the subject but can’t stand the arguments put forth in the movie. I mean, I love quantum theory, in all its strangeness and usefulness and all that good stuff, but the interpretation presented in “What the Bleep” is just way over the top. Similarly, I agree with Moore on the problems of the family Bush, but his arguments were about as shallow as the arguments I hear in middle America (whoops, I didn’t really mean to say that, did I? Damn elitist liberal.)
The quantum consciousness interpretation presented in this movie is an off shoot of the many-minds interpretation of quantum theory, which is in turn an offshoot of the many-worlds interpretation of quantum theory. Personally I don’t understand any of these interpretations. Many-worlds is the world’s largest cop-out. Many-minds is nearly humankind’s most anthropocentric theory, except that the quantum consciousness interpretations take this anthropocentric point of view to an amazingly mind-numbing height. Roughly, as needed for commenting on this film, many-worlds says something like the different states in a superposition are all real states. Many-mind’s say that the choice of which state corresponds to reality happens in the human brain: the measurement problem is resolved inside our heads. The quantum consciousness interpretations take the many-minds interpretation-that the collapse to what is real happens in our head-and makes claims that our brain, or our consciousness, or our soul, can influence this collapse.
Loosely, the film uses this argument. Many-world’s says anything is possible (why do we choose a particular basis for resolving what is real?), even if that possibility is nearly impossible. Thus (1) anything is possible in quantum theory. Many-minds says that the resolution of what actually happens occurs in our brain. Thus (2) what is possible is chosen by our brain. Finally, in the quantum consciousness interpretations, a thing called free-will or the soul or some other useless word comes into play and allows you to consciously decide which of the possibilities will occur. Thus (3) you are your own god and can choose to influence the collapse of the quantum wave function.
Now, I’m not saying that this isn’t a possible way in which quantum theory might work, but there just isn’t any evidence for any of these speculations (by the way, here in Santa Fe at the local Borders bookstore they have a whole section called “Speculations.” Awesome.) In fact I’m not even sure if the way in which these interpretations are phrased whether they are even valid scientific theories (falsifiable, making novel predictions, etc.) That withstanding, this line of reasoning, is at best, eager speculation. But the movie doesn’t portray it that way: it argues that this is what quantum theory must be telling us.
The arguments in the film lead to lots of funniness. For example, if (3) is true, then clearly we should be able to walk on water. One narrator indeed claims that it is quantum theory which explains how Jesus could walk on water. Well, at least this is an attempt at an explanation.
Another example of the silliness is dialog of another narrator who totally misinterprets a current quantum experiment. There are today experiments where one puts a system into a quantum superposition over different position states which are macroscopically distinguishable. Roughly this means that we can put a system into a superposition over two states which when we look at this system with a powerful microscope, those two states are really two distinct positions under the microscopes resolution. The narrator for this particular part of the film claims that one can indeed look and see this superposition state. But this is silly. One never sees the superposition: for a single shot one sees only the the system being in one of the two states. The narrator elevates this seeing of a superposition to some religious experience: but it’s not. You just see one of two outcomes. What has probably happened is that the narrator has misinterpreted the photos one sees in journals about such experiments: here one usually shows the result of thousands or millions of experiments and one sees the resulting probability distribution. But surely not the superposition!
Another amusement follows from the quantum consciousness crowd. If you want to support this version of quantum theory, where do you look for evidence? Well to the studies of the effect of meditation on crime in Washington D.C. (the rate of crime “adjusted for temperature” (I shit you not), using from what I can tell 8 data points, not necessarily done in a double-blind fashion) Of course the meditation in the study is shown to decrease the rate of (temperature adjusted) crime. Now, of course, this could be true. But one study a result does not make. Especially when this study comes from the “Maharishi University of Management.” Voodoo science? I judge yes.
O.K., so you are skeptical of the meditation influence the world evidence: what about the water evidence? This part of the film focuses on the work of Masaru Emote who took bottles of water, put labels on them, then froze them, and took pictures of them and got different crystallizations. Amazingly the pictures he took seem to be correlated to the words he wrote on the bottle. Now I’m not saying that this was not a scientific study, I’m just staying that this wasn’t a scientific study. But to hear this film, this is clear evidence that these words (does the universe read Japanese, English, Yiddish? I’ve always wondered) influenced the crystals formed. I vote Voodoo.
O.K. enough knit picking about the quantum part of the film (I could continue, but shall refrain.) What did I think of the rest of the film. Well I have to tell you that the sections of the film discussing the biology of the brain are very funny. I mean, laugh out loud funny. This is because this part of the film has animations of cells. Not cells of animation, no! Animations of living cells! And these animations are quite humorous in there interaction with the main storyline (remember that northwest photographer.) The main storyline is not what I would call a blockbuster storyline. But it does serve its purpose, although I gained no particular empathy for the main character.
Well what’s the bottom line then about “What the Bleep…”? Well I would recommend this to a scientist in a second. Mostly because I know a good scientist will separate the speculation from the scientifically sound in exactly 2.2 seconds. And then, what one is left with, is a movie which tries to ask big questions: questions about free will, questions about what god could be (the size of the box to which god has been reduced), etc. And in this respect this movie is like a lot of popular science. I gain a lot from reading popular science, but not from the actual content of the books–which is mostly atrocious–but from the fact that reading good popular science puts my brain into a speculative mode. Similarly watching this movie gave me a bunch of the speculating endorphins.
What if you’re not a scientist? Well if you’re a deeply religious Christian I would recommend this film. Why? Well because it basically puts some deep nails in the traditional western god. Now I’m not saying the arguments put forth are the best arguments, but a few of them are pretty good. Especially notable is of of the mystics’ arguments that human sin must be insignificant in a universe as large as our own. Basically this is the same reason I would tell a Republican to go see Fahrenheit 9/11.
What about others? Well, don’t go to this movie to learn quantum theory. Take classes, read textbooks (and also read the popular science to see how they do and do not accurately reflect the textbooks!) and, well, goddammit learn what we know about quantum theory for yourself. This movie gives a highly distorted view of quantum theory, so take what it says with a grain of salt.
So what the bleep do we know? We know that this film is distorting. But this doesn’t make it not fun. So go, be distorted, love it, hate it, but please don’t troll my comment section.
P.S. One of the most interesting narators in the film, and by far my favorite, is Ramtha which is the name of the entity channeled by an American woman, JZ Knight. Ramtha, or should I say, Knight, delivers a stunning amount of charisma on the big screen…she is exactly the reason why I am skeptical of spiritual leaders! At least scientists come across as bumbling fools (and at one point in the film you can actually see that one of the scientists is lying, or at least his body language is highly indicative of deceit.) But Ramtha’s charisma reminds me of why religions with severe cults of personality can exist. Scary.
Things Not Understood
One way people try to get out of the measurement problem in quantum theory is by continuiously bumping the problem up to larger and larger systems until at some point they get rid of the problem by invoking something new. Asher Peres’ book “Quantum Theory: Concepts and Methods” has the following to say about this:
This mental prcoess can be repeated indefinitely. Some authors state that the last stage in this chain of measurements involves “consciousness,” or the “intellectual inner life” of the observer, by virtue of the “principle of psychophysical parallelism.”[3,4] Other authors introduce a wave function for the whole Universe[5]. In this book, I shall refrain from using concepts that I do not understand.
[3] J. von Neumann, Mathematische Grundlagen der Quantenmechanik, Springer, Berlin (1932) p. 223; transl. by E.T. Beyer: Mathematical Foundations of Quantum Mechanics, Princeton Univ. Press (1955) p. 418
[4] E.P. Wigner, Symmetries and Reflections, Indiana Univ. Press, Bloomington (1967) p. 177
[5] J.B. Hartle and S.W. Hawking, Phys. Rev. D 28 (1983) 2960
Fate
One of the reasons I got interested in physics was because I have always been interested in the “question of free will.” Physicists don’t like to talk about free will much, especially since learning what quantum theory has to say about free will seems to put you smack dab in the middle of the measurement problem in quantum theory. In many ways, what I’m most interested in is not the question of free will, which I find too often to be an overly anthropocentric enterprise, but more the question of the determinism / indeterminism of physics. But the “free will question” has played a major role in shaping why I choose to do physics.
As so the question becomes: why was I interested in free will? Most of it is surely due to my older sister Cathy. You see Cathy is a little person. No one knows exactly what syndrome she has, but it causes her to be lopsided (one arm and leg shorter than the other), she has very poor vision and hearing, and has some mental difficulties. This makes it all sound really bad: which it is definitely not because Cathy is an amazing light in our family. She works at the local library in Yreka, loves to listen to her John Denver tapes, she loves to watch Jeopardy, and is, in general, a very happy person who brightens the lives of her many many friends.
But if you grow up with a sister like Cathy you can not avoid thinking about why you ended up the way you are and why she ended up the way she is? Was it fate and totally out of the hands of human choice? Science, and physics in particular, is the path one is reduced to in order to possibly find any answer to such a question. While we can argue forever whether reductionism to fundamental physics is central to answering this question, there can be no doubt that understanding the role of determinism and indeterminism in physics will have a profound impact on our view of this question.
On the other hand, Richard Feynman said: “Do not ask yourself… ‘how can it be like that?’ because you will lead yourself down a blind alley in which no one has ever escaped.” I don’t think Feynman was talking about science here: scientists spend much of their time answering how it can be like that. I think Feynman was talking about asking for reasons which somehow satisfy us as humans: answers that will give us short sentences explaining why. There are simple important questions which might have simple concise explanations, but finding these explanations seems impossibly difficult. And this is how I find myself coming full circle. Because this point of view, that there are simple questions for which there aren’t answers which can be found in a short time (and once we find them, we’ll know we’ve answered the question) is basically the complexity class NP. Which is computer science. The field, besides physics, which I most deeply admire.
So fate not only made me a physicist, but it also made me a computer scientist.
And the only question left remaining is whether or not it was destiny that I was born at a time when I could participate in the unfolding of the field of quantum computing, which merges physics and computer science like never before?
Notice the Dates
On arXiv today we find quant-ph/9804008:
from : Andrew Gray [view email]
Date (v1): Thu, 2 Apr 1998 18:51:30 GMT (27kb)
Date (revised v2): Sun, 8 Aug 2004 18:25:20 GMT (0kb,I)
A Design for a Quantum Time Machine
Authors: Andrew Gray
Comments: This paper has been withdrawn
This paper has been retracted, for obvious reasons.
Northern New Mexico
From George Johnson’s New York Times July 3, 2004 article “Los Alamos’s Super-Secret Heritage Shows Some Cracks:”
When science is conducted in secrecy it takes on the air of magic.
From its beginnings as an outpost of the Manhattan Project, Los Alamos has operated in a state where the ideal of science as the free exchange of information has been indefinitely suspended, replaced by a conviction that there is safety in ignorance, that life is more secure when certain powerful ideas are kept among a few.
Peace through the nonproliferation of knowledge, another of the ingrained absurdities of the nuclear age.
Which reminds me of why cryptography (and quantum cryptography in particular) is so disturbing to me: does the universe really allow for the hording of information? Our unsharing universe? Of course, the type of knowledge Johnson is talking about, “scientific knowledge”, does appear to be open to everyone: you don’t get exclusive rights to the science when you discover it. But what if the universe didn’t even work that way? What if the mere discovery of some new bit of science closed the door for all others investigating the same phenomenon?