New Caelifera

New Caelifera

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Tips for a Resigned Pontiff

On February 11, 2013, Benedictus PP. XVI, a.k.a. Pope Benedictus XVI, also once known as Joseph Aloisius Ratzinger, announced that effective February 28, 2013,  he was stepping down as Roman Pontiff (not abdication, resignation or renuntiatio).  Pope Benedictus XVI was the 265th (or maybe 266th? or maybe 267th?) Bishop of Rome, perhaps the nineth pope to resign, not counting conditional resignation (important if you think you might get caught by Nazis.)  Now normally, the comings and goings of the College of Cardinals would not stir me to write a blog post, especially not a blog post written in advice column style (so often used to convey certitude in the face of overwhelming selection bias.)  But, you see, I was once a pontiff.  Indeed according to Google for one brief period in 2004, I was once the top search result for this word.  (Take that Beattles!)

Which is all to say, I thought it might be a good time to offer some advice to Pope Benedictus XVI for his life after leaving the papacy.

Tip 1  It’s time to get serious about how your identity shapes your ego.  You were once the leader of one billion souls, God’s main man on the ground, infallible and all that,  but now you’re going to be living a humble monk’s life in a Vatican monastery.  No longer infallible.  No longer the leader of a billion souls (tweeter to 1.5 million.)  You may think that your ego is separated from your job, but in my own transition from pseudo professor blogger to software developer it was quite a shock to no longer be able to rely on the accumulated status symbols that my job title carried along with it.  In my case this meant no longer being introduced at parties as a “theoretical physicist doing quantum stuff.”  In your case, people aren’t going to be kissing your ring any more (oh yeah, and you’ll have to give the ring up too!)  My advice?  I’d go for some Zen koans: Joshu’s dog and Zuigan Calls His Own Master would be a good  place to start.

Tip 2 You’re not going to get to travel all around the world anymore.  Tip: volunteer to pick up people from the airport!  Or visit an air museum where they will let you sit in airplane seats.  Bonus tip: I find the air museum seats a really good way to fall asleep as well (If you can’t empathize with this, I would suggest you try getting up for way too many 6am flights, and you too will learn to fall asleep on contact with the too tight armrests of airline seats.)

Tip 3 It’s going to be tough to keep up with your past life’s passion.  When you got into the flow during your papal years, I’m sure there was no one able to compete with you for your knowledge and understanding of how to guide your flock forward.  But now you are going to have to dedicate your time to your own solitary monastic life.  You may think that this transition will not be abrupt, that you can slowly ween yourself from the papacy, but in my experience you’re not going to have the time to, say, give advice to the next Pope.  Which is not to say that you have to give up you mission: you will just to choose what battles you’d like to carry forward.  For me, it was self study of shortest vector in a lattice problems.  For you, well I’m sure there is a suitable equivalent.

Tip 4 You’re going to miss all of the friends around the world.  Hopefully, if you’re lucky, some of them will start blogs.  For you I’d suggest adding Whispers in Loggia to your RSS feed.

Tip 5 People are still going to look to you for expertise in your past life, but the slow creeping pace of entropy will gradually strip you of your knowledge of the secrets to the universe, and you’ll have to tell them that you don’t know.  You’re just going to have to live with the accumulated slippage of your brain from the most up to date theology of our day.  You can try to keep up, of course, though I’m not sure of what the equivalent of the arXiv is, but you’re just going to have to live with a new world where you say “I don’t know.”  I recommend testing those words out every morning: “I don’t know.”  “Nescio.”  “Nescio.” “Nescio.”

The end of an era, pope.  There is life afterwards, beyond an event horizon.  Enjoy the transition, just hope that the black hole firewall ideas are wrong.


dabacon February 24, 2013 Leave A Comment Permalink

The Viewpoint Skeptics of Quantum Computers Don’t Want You To Hear

Quantum computers are fascinating devices.  Our current understanding of these devices is that they can do something that classical computers cannot: they can factor numbers in polynomial time (thank you Peter Shor!)  Interestingly, however, we can’t prove that these devices outperform classical computers on any class of problems.  What this means is something very particularly: we can’t show that the model of a quantum Turing machine can solve problems more efficiently than the classical model of a Turing machine.  Complexity theorists say that we can’t show that BPP does not equal BQP.  Complexity theorists remind me of my son learning new letters.  Sorry I can’t help it.  S. T. O. P. spells….stop!

A dark secret (okay it’s not really secret, but this is a blog) of classical computing is that we (or rather, they, since I’m as much a complexity theorist as I am handsomely good looking) also can’t say a lot along the same lines about classical computers.  The most famous example of this, currently (2012), is that classically we don’t know whether there are computations which take polynomial (in the size of the problem) space and unlimited time, but can’t be done with just a polynomial (in the size of the problem) limit in time.  In jargon this is the fact that we don’t know whether P (or BPP) equals PSPACE.  That’s a huge gap, because PSPACE includes nearly everything in the sun, including computers which use time machines.  That’s right.  Classical complexity theory has yet to show that computers that use frickin’ time machines aren’t more powerful than the laptop I’m typing this on.

A reasonable person, I would think, given this state of affairs, would admit that we just don’t know and try to figure out more about the model of quantum computation.  Interesting, however, academia attracts an interesting class of hyper smart person who try to get places in life by being contrarian.  That’s great when it leads to results, and often it does.  Being skeptical is an important part of the scientific process.  But when it doesn’t lead to results, which I think is the current state of arguments about quantum computers, it leads to senior professors acting very unprofessionally, and stifling a field.  Quantum computing is in exactly this state of existence.  I can count the number of jobs given to theorists in quantum computing over the last decade on my hands.  It’s far greater than the number of senior folks I’ve talked to who are credulously skeptical of quantum computers and show know better (i.e. they’ve at least read the relevant papers.)  The number who are skeptical but who haven’t actually read the papers?  My registers don’t count that high.

For an example of this phenomenon, hop on over at to the awesome and widely read blog Godel’s Lost Letter and P=NP where one of the coauthors of the blog Ken Regan has a post describing some work on trying to understanding the limits of quantum computers.  That’s great!  But in this post, Ken, who is an associate professor, can’t help but in a dig at quantum computers along the lines of “we can’t prove that it can’t do anything”:

But there is no proof today—let me repeat, no proof—that quantum circuits in BQP are not easy to simulate classically

Because I like poking tigers, and am no longer beholden to the whims of an academic community that strongly rejects quantum computing, I posted a comment (okay I’d post this even when I was a psuedo-professor) which included the last line

Oh, and, p.s. there is also no proof that classical circuits can’t solve NP-complete problems efficiently, but for some reason I don’t see that in all of your posts on classical computers ;)

to which Ken responded

As for “no proof”, Dick provided some thoughts which I merged into my intro; I pondered upgrading that line to add “…, nor even a convincing hardness argument”—but thought that better left-alone in the post

So you can see the kind of thoughts that go through many theoretical computer scientists which confronted with quantum computing.  Instead of “lets figure this out” the response is “I want to remind you that we haven’t proved anything, even though we also haven’t proved the same thing about likely even more powerful models of computation.”  If you don’t think this isn’t a case of bias in academia, then you’re reading a different novel than I am.  And if you don’t think this has an impact on junior academics, please see the correlation evidence of past hiring in academia (Or if you don’t like that: do an experiment.  Give the damn people the jobs to hang themselves by.  Or at least don’t give them advice to avoid quantum computing because of your own biases, I’m looking at you, you know who you are.  Pffst!)

Like I said, however, I think focusing on making actual progress in understanding quantum computers is the important path to take (and to the credit of Ken, who I’m picking on simply because he’s at the top of the temporal queue of a long line of guys who like to pontificate about the power of quantum computers without having any arguments that go beyond “I think…”, he has tried to answer this question.  But not without throwing in a backhand that he seems to find utterly professionally appropriate.)  And of course the previous two paragraphs are enough of the same ad slander’n reasoning, but exactly from my own completely biased perspective.  But toward being *ahem* productive, I’m completely convinced that quantum computers offer significant, proven, reasons to be built.  This is a controversial statement, because I know all complexity theorists will disagree with this point of view.  So this is aimed at the group of people with minds open enough to think not about complexity classes, but about real world experiments (we might call them, physicists.). 😉

The argument is almost as old as quantum computing itself.  These are the so called “black-box” query complexity results in quantum computing, albeit as seen through a physicist’s measuring device.  What these models do is as follows.  They consider a set of black box functions (say functions from n bits to 1 bit, so-called binary functions) and ask one to identify something about this set of black box functions.  For example, the set of functions could be all binary functions that are either constant (on all inputs they output 0 or on all inputs they output 1) or balanced (on half of inputs they output 0 and on the other half they output 1). Then the problem would be to distinguish whether, if I give you a machine that implements one of these functions, whether the function is constant or whether it is balanced.  Then one “measures” the effectiveness of an algorithm for solving this by the number of times that you have to use the black box in order to figure out which set the function belongs to.

So what is the state of query complexity differences between classical and quantum computers?  It can be proven that there are black box problems that can be solved by quantum computers using a polynomial number of queries in the size of the problem, but that require an exponential number of queries classical.  That’s right.  There is a proven exponential separation.  (For those who would like to argue that the comparison is not fair because a quantum device that computes a function implements a different physics than that which gives you a classical computation, I would only note that our world is quantum mechanical, and we can compare a quantum querying of the quantum device to a classical one.  A classical query of this quantum device is exponentially less efficient.)

At this point you may then wonder why all of the fuss about quantum computers not being proven to be more powerful than classical computers.  The answer is interesting and starts with the way we set up the problem.  We were given a black box that computes a classical function.  We can think about this literally as a machine that we can’t probe any deeper into how it actually works.  In this respect it is a sort of a-physical device, one that isn’t connected to the normal context of what a computation is (as modeled by, say a parallel Turing machine.)  Suppose that this were a real physical device, then you could take it apart and look at how it worked.  This means that you could get more information about the computation being performed.  And when you allow this, well, it is then not clear that you couldn’t solve the problems for which quantum computers offer speedups just as fast on a classical computer.  Thus while we know that with respect to these black box problems, quantum computers are exponentially faster than their classical brethren, we can’t carry this over to statements about models of computation.

But take a step back.  Suppose you are an experimental physicist and I give you a black box and ask you to figure out whether the box implements one or another sets of functions.  Well then, if you use this experimental device without peering into its innards, then you really really want to use a quantum computer for your experiment.  The difference between exponential graduate students and polynomial graduate students is most certainly something that will get your grant funded by the NSF.  Because the universe is quantum mechanical, damnit, and if you want to perform experiments that more quickly reveal how that universe operates, you’ve got to query it quantum mechanically to be most efficient.

Okay, you may not be convinced.  You may argue that at its heart you can’t ever have a box that one can’t take apart and probe its innards (can you?)  Fine.  So I’ll modify the game a bit.  I’ll give you a quantum system that is the output of the standard way this device if queried in these computeres $sum_x |x> |f(x)>$.  Now you either get to query this using only classical measurements on this device in the computational basis, or you get to use the full power of quantum computers, querying with a measurement you can build in your quantum laboratory.  In that case, you can show that a quantum experimentalist will exponentially outperform characterizing this state, i.e. solving the given promise problem.  Think about this as a game, a game in which you can win by being quantum mechanical exponentially faster than you could being classical.

Of course this won’t convince anyone, especially not classical theoretical computer scientists (who once were at the vanguard of a totally new field, but now find themselves defending their own legacy code.) Does it at least pass the test of trying to present evidence in either direction for the power of quantum computers?  Not really, for those who refuse to believe that quantum theory isn’t actually the right theory of nature.  But it does seem to tell us something is fundamentally very very different about the ability to use quantum theory in a setting where you’re trying to extract information about an unknown quantum system.  And it’s proven.  And it’s not a way of thinking that the old guys would like you to think 🙂

dabacon July 16, 2012 9 Comments Permalink

dabacon July 13, 2012 3 Comments Permalink

To Catch Terrorists, Think Quantum Mechanically?

An interesting paper in PNAS from a few years back that I missed, “Strong profiling is not mathematically optimal for discovering rare malfeasors” by William H. Press.

Suppose you have a large population of people and a single bad guy who you want to catch.  You could look through the entire population to  find the bad guy, or you could set up checkpoints (err I mean airline security screening areas) to look for people, sampling only some small fraction of the population that goes through the checkpoint.   Now, if you don’t know anything about the population you’re sampling, you might as well just sample them randomly until you find your baddie, since you don’t have any other information that could help you.

But suppose that you are able to come up with some prior probabilities for different people to be the bad guy.  I.e. you’ve developed a model for what makes someone more likely to be a bad guy, and further assume that this model is really pretty accurate.  To each person you can assign a probability p_i that the person is indeed the bad guy.  Now you could continue to sample uniformly, but you have this great model that you want to use to help catch the bad guy.  What do you do?

It turns out that the wrong thing to do is to sample in proportion to the probability p_i.  To figure out the correct strategy, suppose that you sample from the population with probability q_i.  Then if k is your man, the probability that you get him in one sample is q_k.  Or, another way to say it is that the mean number of screenings you’ll need to find the baddie is 1/q_k.  Assuming your model is correct, the mean number of people you will have to sample is sum_i p_i/q_i.  So now to calculate the optimum we need to minimize this expression for q_i subject to the constraint that sum_i q_i =1.

To calculate this optimum, you use a Lagrange multiplier

    \[{partial over partial q_j} left[ sum_i {p_i over q_i} + lambda (sum_i q_i -1)right]=0\]


    \[- {p_j over q_j^2} + lambda = 0\]

Which, in order to satisfy our contraints (and also positive probabilities) gives us the answer for the optimum of

    \[q_j = { sqrt{p_j}  over sum_i sqrt{p_i}}\]

Or, in other words, you should sample proportional to the square root of the probabilities.  Pretty cool, a nice easy, yet surprising answer.

Even more awesome is that we got some square roots of probabilities in there.  Quantum probability amplitudes are, of course, like square roots of probabilities.  Now if only we could massage this into insight into quantum theory.  Do it.  Or the terrorist win.

Higgs rumors

Some good links:


Exciting to see what they’ve found, but also what hints about compatibility with the standard model, Whoever named that model was a prophet 🙂

Update 1:14am PST July 4: CERN press release  Discovery!

My Voice

What is my voice?  Lacking one, I choose pseudo-plagiary (the original, far more illuminating, can be found here):

The other one, the one called Dave Bacon, is the one things happen to.  I walk through the halls of Google Seattle and stop for a moment, perhaps mechanically now, to look at the green glow of code from flat screens, and the blocks and arrows on the whiteboard; I know of Dave Bacon from his email and see his name on a list of (former) professors or in another person’s blog.  I like Borges, mountains, omphaloskepsis, the taste of chiles and the prose of Pynchon; he shares these preferences, but in a vain way that turns them histrionic.  It would be an exaggeration to say that ours is a hostile relationship;  I live, let myself go on living, so that Dave Bacon may have contrived his theories, and these theories justifies me.  It is no effort for me to confess that he has achieved some valid pages (or more accurately he had great co-authors), but those pages cannot save me, perhaps because what is good belongs to no one, not even to him, but rather to the science and to experiment. Besides, I am destined to perish, definitively, and only some bits of information about myself can survive in him.  Little by little, I am giving over everything to him, though I am quite aware of his perverse custom of flipping certain important bits about himself.

Feynman knew that all things change; the electron exchanges a photon with another electron, scattering to a new state.  I shall remain in Dave Bacon, not scattered to another person (if it is true that my evolution is unitary), but I recognize myself less in his papers than in many others or in the laborious strumming of a guitar.  Years ago I tried to free myself from him and went from the foundations of quantum theory to games correcting quantum computing machines, but those games belong to Dave Bacon now, and I shall have to imagine other things.  Thus my life is a flight and I lose everything and everything belongs to oblivion, or to him.

I do not know which of us has written this webpage.


One year since I left the tower and joined Google. I think it may be time to start blogging again.

dabacon June 21, 2012 3 Comments Permalink

IDE Tools for Reading Research Papers?

It’s been over six months I made the jump from quantum computing theory professor at the University of Washington to software engineer at Google. When I hear from my friends back in quantum computing, the second question they ask is, “what’s it like?” (the first question is whether Google wants to build a quantum computer.)  There are lots of answers to this question, but what I think is really interesting is not how I feel about the ins and outs of this new career, but what I found the most surprising about the similarities between my new jobs and my old job.  And, for me, hands down, the most surprising similarity is between reading papers and reading other peoples code.

Reading a a paper in a new subject area was definitely one of the favorite parts of my old job (and a central skill to being a good researcher.)  You’d start out, often, with only a small clue about the subject of the paper.  Often you were led to the paper by a search that hit a few keywords, and an abstract that seemed interesting.  But after a few pages it often becomes clear that there are all sorts of terms and ideas that you just haven’t seen before.  And so you often have to spend some time doing some reading of other papers that contain the terms you don’t understand and see if they help.  Mostly they don’t, but sometimes they do and then you can backtrack and figure out some of what the first paper said.  This sort of jumping around, at least for me, occurred quite a bit as I’d try to parse a paper, interspread with periods of logical thought and pen and paper verification of calculations.

Reading other peoples code is very similar.  At first you start looking at some class, say, and you have some vague idea what it does.  Documentation and implicit documentation through naming gives  you some idea of what is going on, but quickly you often see the code start calling code that you don’t know how it works or what it exactly does, and so you have to go track down that other class, and then figure it out, and then backtrack.  Of course this is often interspread with bits of following the logic of the code.  Today, with modern IDE tools, this sort of jumping back and forth becomes a quick habit and makes the process of figuring out someone else’s code significantly easier.

Which got me thinking.  Why aren’t there modern tools for reading research documents that provide some of the functionality that is found in IDEs such as Eclipse?  Certainly some authors are gracious enough to compile their LaTeX such that their citation data is a link, but this is a long way from having PDFs where you can click on citations in the text and then you get immediately transported to the other paper, maybe even to the particular location in the paper that is relevant.  I think the technical challenge here is providing hooks between the documents: how do I make a citation that is more than just citing the full paper (wouldn’t it be nice if you specified the set of ranges of relevant lines in the paper?)  There are certainly very cool tools out there now for storing and parsing your scientific papers, but while the implicit linking between these papers is complex, most of this complexity is buried in the [12] citation pater.  But maybe solutions for this are already out there?  Thoughts?

dabacon January 15, 2012 7 Comments Permalink

The Wolf That Cried Education Bubble

Foster, You’re Dead!” is a Philip K. Dick short story published in 1955 describing the struggle of a young boy, Mike Foster, whose father refuses to purchase his family a bomb shelter.  The story describes a classically Dickian society: paranoia over nuclear war so consumes everyone that the purchase of a bomb shelter and participation in a financial plan to provide protection from nuclear war are basic actions that every member of the society is assumed to have to participate in.  Mike’s father, who refuses to participate in this hyper-consumeristic cross with the military industrial complex is labeled an “anti-P” and, without giving away too much, the story provides a strikingly empathetic description of Mike and his father’s struggles around their ostracized state.  The story is in Second Variety (The Collected Stories of Philip K. Dick, Vol. 3) which also contains a few other Dick gems (“The Golden Man” is particularly interesting in its stark view of evolution and it’s rebellion against the sympathetic mutant theme prevalent in the science fiction literature at the time.) In the footnotes of “Second Variety”, Dick describes where the inspiration for this story came from:

One day I saw a newspaper headline reporting that the President suggested that if Americans had to buy their bomb shelters, rather than being provided with them by the government, they’d take better care of them, an idea which made me furious. Logically, each of us should own a submarine, a jet fighter, and so forth.

Which is what got me thinking about tuition.

You see, in a former, quantized life, the rhythms of my life were centered squarely on the academic world.  And if you’re in the world of academia in the United States, you most certainly know that college tuition prices have risen over the last few decades at a rate greatly exceeding that of inflation.  These rising tuition costs have led to an increasing indebtedness are the part of students, causing some not very famous people and some very famous people to speculate that there is a higher education bubble.  Since I made those impetuous comments about there being a higher education bubble, however, I’ve had time to dig around and see what actual data I could find on the subject.

Enter the treasure trove of reports from the delta cost project (for those who want to investigate the bias of this report note it is in part sponsored by the Lumina foundation who has a mission to increase higher education in the United States, along with an interesting enough story behind its founding to set off all you tin hat conspiracy theorists.  That’s right you Sn-hatters…set off for somewhere else to post your canned responses!)  First off the full reports are a data lovers delight: there’s some good stuff here!

But what I found most interesting, highlighted particularly in the 2009 report, was a question I’ve often wondered about: cost shifting.  While it is true that tuition costs are rising, this does not, of course, mean that universities themselves have spending increasing at the same rates.  For example at the in the sate of Washington, tuition hikes have been directly tied not to spending costs, per se, but to a declining state revenue.  So are spending costs increasing?  Page 34 of the report has a great graphic of spending per degree across different kinds of higher education institution:

This shows pretty strikingly that spending has actually remained fairly constant….except at private research institutions.  And even more remarkably is the question of how much tuition costs are the result of increased spending:

The primary cause of tuition increases in public institutions is not increased spending, but rather cost shifting to replace losses in state appropriations and other revenues.  In public research institutions, 92 percent of revenues from tuition increases since 2002 have resulted from shifts in costs. In other public institutions, costs are declining even as prices are increasing.  Private institutions are both raising tuition and increasing spending.  Only about 30 percent of revenues from tuition increases in the private research universities can be attributed to cost shifts, though in private master’s and bachelor’s institutions, about 85 percent of tuition are from cost shifts rather than spending increases

Which brings me back to good old Philip K. Dick.  Let me get this straight: spending per degree has been basically flat…except among the private institutions.  Tuition costs, which everyone is yelling about, have been entirely due to shifting funding at public institutions, while private institutions have increased tuition and spending.  So yeah, I do believe Dick had every right to pissed off at his president asking him to shoulder the costs of bomb shelters because people would “take better care of them” if they owned them themselves.  As do we have a right to be pissed off at the reckless abandonment of higher education by our state governments, which has led to the regressive burden of tuition increases.  Except by the private institutions.  Who, if anyone, will once again be responsible for riding the boom that is the bubble of expanded public leverage (and yes I know the private institutions here are mostly “nonprofits”, but having gone to both public and private research universities of some caliber, you can bet your horse I’ve seen which can lay claim to being more egalitarian.)

Now if only I could figure out how to turn this into a short story….

dabacon September 21, 2011 1 Comment Permalink

A New Start

“Nothing endures but change” – Heraclitus

dabacon June 17, 2011 2 Comments Permalink