Category Archives: Physics

Physics, quants, and the crash

I am pretty much required to blog about this piece in the New York Times entitled “They Tried to Outsmart Wall Street”: “they” being physicists who left science for Wall Street. And the not-so-subtle implication of the title is that we failed to outsmart Wall Street (and possibly wrecked the economy in the process). To that I say, in the words of Bart Simpson: it was like that when I got here.
More seriously, while I have no doubt that there were crappy quant models out there that contributed to the current crisis by maximizing short-term gain over long-term risk, this was true all the way up and down the chain and the quants don’t deserve any more of the blame than anyone else. Quants respond to incentives the same way everyone else does, and the compensation structure on Wall Street can incentivize immediate profit and deferred risk. (My employer is trying to curb this effect by instituting a clawback provision on bonuses; I don’t know how widespread this is, but it seems like a good idea to me.)
The Times article is curiously focused on ex-physicists, as if quants don’t come from any other fields. In my ten months on the Street I’ve met quants from a broad range of science and engineering fields, and physicists aren’t a majority. That might be a peculiarity of my department’s hiring practices, with physicists being much more common elsewhere, but I’d be surprised. Anyway, Kevin Drum noticed this too and wonders why physicists are so suited to quant roles. He has a theory that it’s the culture:

Even among the number crunching set, physics has a reputation as the most aggressive, male dominated branch of geekdom: only 14% of physics PhDs are women, the lowest of any of the sciences. (Math is pretty male dominated too, but pales compared to physics: 29% of math PhDs are women.) If the first thing that “aggressive and male dominated” reminds you of is the big swinging dick world of high finance, give yourself a gold star. Call this the testosterone theory: physicists are attracted to Wall Street because they like the atmosphere.

I don’t think this is right: the atmosphere in a typical physics department is nothing like the stereotypical Liar’s Poker trading floor that Drum is alluding to. To the extent that the environment I work in is like academia, it’s because I’m lucky enough to work with a group run by ex-academics rather than people with a typical trader’s background. Instead, what Drum calls the “affinity theory” really is the right one. The work I do now is a lot like the problems I worked on as a physicist. It’s not just (as Drum suggests) about math; it’s about the ability to work with huge data sets and make sense of them, and to find signals in a noisy system. This is a much bigger factor than testosterone levels.

Still alive

Today at work we were discussing the self-styled “simplest weather report ever”, umbrellatoday.com. Also useful is the similarly-designed hasthelargehadroncolliderdestroyedtheworldyet.com (via a GChat status message). Personally, I keep meaning to quote Buffy the Vampire Slayer‘s Oz on the subject: “But we know the world didn’t end, ’cause… check it out.”
In my new career the big question to ask is not whether the world will end, but whether one can make money off people’s belief that it will. Intrade doesn’t seem to have a futures contract on whether the LHC will destroy the Earth, but you can buy or sell the discovery of the Higgs boson.
Of course, if you are trying to destroy the Earth, and you’ve lost confidence in the LHC, you might find your Plan B at this page.

Quantum Construction



quantum construction, originally uploaded by arcanegazebo.

I spotted this sign while running in Berkeley this morning, and had to go back for a photo. From the slogan it looks like they’re promoting energy-efficient home design, which is commendable; thus they probably want “quantum” to indicate “technologically advanced”. But of course, “quantum” also brings to mind uncertainty, which maybe isn’t what a contractor wants to associate themselves with. At the very least, I would expect Quantum Construction to be able to give a precise time estimate, or a precise cost estimate, but not both.

However, I assume their creation operators are top-notch.

Done!

I filed my dissertation this morning; I am now Dr. Arcane Gazebo. (Well, technically the degree isn’t conferred until Thursday when the semester ends, but whatever.)
The main result of the entire thesis comes down to a single plot, shown below. This isn’t the “explain my thesis” post so I’ll just say that the plot shows our ability to control the coupling energy between two qubits by applying a bias current to our readout device, hence the thesis title Solid-State Qubits with Current-Controlled Coupling. The solid curves are calculations based on device parameters and the dashed curves are one-parameter fits.

Now these points of data make a beautiful line…
If anyone needs me this evening, I’ll be at Triple Rock.

Frank Tipler {TECH}s up the Bible

When I was in high school, a physicist named Frank Tipler published a book called The Physics of Immortality. The book purported to show that modern cosmology was not only compatible with Christianity, but predicted something like Christian theology including the concept of an afterlife. At the time I was still a believer, and was becoming interested in physics, so I was curious to see what the book had to say.
It was bad—really bad. So much so that even with only a high school knowledge of physics, and a predisposition to accept its conclusions, I found it ridiculously implausible. It wouldn’t even have made it as bad science fiction (although Charlie Stross borrowed the concept in a more interesting way in Iron Sunrise). Years later, taking Caltech’s intro astronomy course, I had the pleasure of hearing the professor deliver a very unflattering digression on Frank Tipler.
I was reminded of all this when I found out (via Sean Carroll) that Tipler has a new book out: The Physics of Christianity. And it sounds even sillier, if possible. It seems that Tipler is now interested in explaining various Biblical miracles though physics, for example: (from Victor Stenger’s review)

In the case of Jesus walking on water, protons and electrons in the normal matter in a layer of water under his feet are annihilated. The neutrinos produced go off invisibly downward with high momentum, the upward recoil enabling Jesus to keep from sinking.

This is actually similar to what you see in other The Physics of… books, such as in The Physics of Harry Potter‘s explanation of how the Sorting Hat could be implemented with SQUID sensors. But those books are, as Sean Carroll points out, just fun exercises in comparing fictional worlds to the real world. On the other hand, Frank Tipler is trying to explain supposed actual historical events, and it’s hard to see what the point is of making up some story about a hypothetical decay process underpinning various miracles. Does it really change anyone’s understanding, believer or not, to go from “Jesus could walk on water because he’s omnipotent” to “Jesus could walk on water because he could annihilate protons with electrons on demand, because he’s omnipotent”? It doesn’t do any explanatory work.
And so what all this suggests to me is that Frank Tipler thinks the Bible should be more like Star Trek. A while back I found this post on an RPG-related blog, which explains how technical language gets inserted into Star Trek scripts:

I am told that the writers of Star Trek scripts do not usually come up with all of the jargon that the characters use. Instead, they just make the notation {TECH} wherever the characters should say something technical, and someone else will come along to fill in each such instance with some chunk of technobabble. This has an important story consequence: since the science is completely arbitrary, it’s necessarily the case that the plot can’t really hinge, in a compelling way, on the technical and scientific choices the characters face. It’s all just {TECH}, and at best technobabble can provides sci-fi color, and at worst it’s an excuse for a deus ex machina resolution.

So I imagine that Frank Tipler reads the Bible and sees a bunch of {TECH} notations that he feels compelled to fill in himself. And the last sentence of that quote describes the effect pretty well, which is why even as a believer I found Tipler’s book unsatisfying.

Bad quantum press releases: this time, it’s personal

Scott Aaronson points out an overly-excited press release from NEC, which claims: “NEC, JST and RIKEN successfully demonstrate world’s first controllably coupled qubits”. This was indeed an exciting development when we published it five months ago. At best NEC has the world’s fourth controllably coupled qubits.
That said, the stupidity seems to be limited to the press release, and the paper actually looks pretty interesting, apparently with time domain results that no one else has shown. (I haven’t been on the campus network today so I haven’t had a chance to read more than the abstract.)

No new neutrinos

The Standard Model wins another round: the MiniBooNE experiment, searching for neutrino oscillations to confirm or disconfirm the anomalous LSND result, found no new physics. Heather Ray explains in a guest post at Cosmic Variance.
Given the author’s last name, her use of “awesome-o” in a section heading is suspicious.

Colloquium blogging: Lawrence Krauss on the future of the universe

Today’s colloquium speaker was Lawrence M. Krauss, who is somewhat well-known for doing a lot of public outreach and having written several books aimed at the general public. (One of these books was The Physics of Star Trek, which I received from three or four separate people as birthday gifts when it came out in 1995.) He’s also done political advocacy, perhaps most notably fighting “intelligent design” creationism in Ohio. Today’s colloquium was about neither Star Trek nor politics, however, but about the “dismal future” of the universe.
The talk was basically a series of extrapolations from the fact that cosmological observations show a universe that is not only expanding, but expanding at an exponentially increasing rate. The most direct consequence is that eventually everything that isn’t gravitationally bound to our galaxy cluster will be receding away at faster than the speed of light, not only inaccessible but invisible. This won’t happen for many billions of years, so it’s not of any particular concern to us personally, but will be an issue for the future of life itself. As a result of being isolated to a single cluster, the amount of energy available becomes limited: I think the estimated number was 3×1067 Joules, for what it’s worth. Consequently, the amount of information that can be processed also is limited, to on the order of 10120 bits. One of the more interesting numbers quoted was that, if one assumes that Moore’s Law will continue to hold on the rate of information processing, civilization would run through this capacity in just 400 years. (Since at the moment we are limited to the amount of energy here on Earth, I expect Moore’s Law will fail rather sooner than this, which is why I’m skeptical about Singularity talk.)
Another section of Krauss’ talk was devoted to what cosmology would look like to a far-future civilization in one of these “island universes” created by expansion. Since these future scientists would be unable to observe the universe outside the cluster, they would be unable to infer the expanding universe or the Big Bang, and would conclude that the universe was static. (They could, however, estimate the age of the universe from abundance of various elements.)
Finally, on long timescales everything disappears, as dark matter halos evaporate and galaxies dissipate.
Krauss, being a more public figure than most physicists, was a very good speaker who gave an entertaining talk. He was deliberately provocative, declaring at the beginning that he would alienate most of the audience, and particularly targeted advocates of the anthropic principle. I was hoping for more fireworks in the question session, but it was somewhat tame. A video of this talk will appear at some point here on the department website.

March Meeting, Days 2 and 3

I thought about posting last night but this was pre-empted by the fact that the slides for my talk were unfinished (and also the Clarke group dinner). First I want to register a complaint:
hund's rules for conference seating
This is how physicists (or maybe everybody) fill seating at conferences. The first people to arrive take the seats on the outside of the rows, and then fill in to the middle. This is really annoying when arriving in the middle of the session and having to climb over a bunch of people to get into the one empty seat. I am aware that this is a really lame complaint, but please, fill from the middle!
Now that I’ve got that out of my system: the last couple days were a blur of superconducting qubit talks. There’s a lot going on in this field, and most groups had three or four (10-minute) talks in a row to have enough time to explain all their results. One experiment I thought was very neat was this one from Terry Orlando’s group at MIT. In flux qubits like the ones we study, one can measure the temperature by sweeping the flux bias across the degeneracy point and measuring the population of the qubit states. Higher temperatures will give wider curves, as energies further away from the degeneracy point are more likely to be populated by thermal activation. When we measure this on our qubits we usually get something like 150 mK, mysteriously somewhat higher than the fridge temperature (roughly 50 mK).
What the Orlando group did was to apply an analog of laser cooling (as in atomic physics) to their qubit, using a microwave pulse to induce transitions that ultimately cool the system. As a result they were able to see these temperatures (as measured from the widfh of the qubit step) reduced by a factor of 100, from 300 mK to 3 mK. It was pretty impressive; I’m not sure how important it is for quantum computing or whether it’s something we should be doing with our qubits, but it’s a nice application of techniques from another field.
This morning I gave my talk, which was helpfully introduced by Frank Wilhelm’s talk immediately prior, in which he said something like “the really important development for scalability is what Travis Hime will talk about next”. So the pressure was on, but I think I did ok. After this was… more qubit talks, but I was mostly decompressing after finishing mine and didn’t pay as much attention as usual.
Tomorrow I go to see talks by other Clarke group members, including John himself. And then, an evening flight back to Berkeley.