Category: Science

Hey, nobody told me that having a blog would involve homework. But here’s Jerry Coyne, nudging me into talking about a story in this morning’s New York Times. Fortunately it’s interesting enough to be worth taking a swipe at.

The news is an interesting result from RHIC, the Relativistic Heavy Ion Collider at Brookhaven Lab on Long Island. RHIC has been quite the source of surprising new results since it turned on in 2000. It’s not the highest-energy collider in the world, nor did it ever aim to be; instead, it creates novel conditions by smashing together the nuclei of gold atoms. Gold nuclei have lots of particles — 79 protons and 118 neutrons — so the collisions make a soup known as the quark-gluon plasma. (We ordinarily think of a proton or neutron as consisting of three quarks, but those are just the “valence” quarks that are always there. There are also large numbers of quark-antiquark pairs popping in and out of existence, not to mention scads of force-carrying gluons that hold the quarks together. So you are actually create a huge number of quarks and gluons in each collision.)

We think we understand the basic rules of quarks and gluons very well — they’re described by the theory of quantum chromodynamics (QCD), and Nobel prizes have already been handed out. But knowing the basic rules is one thing, and knowing how they play out in reality is something very different. We understand the basic rules of electrons and electromagnetism very well, but chemistry and biology (not to mention atomic physics) are still surprising us. Likewise with quarks and gluons: the results at RHIC have yielded quite a few surprises. Most interestingly, in the aftermath of the collisions the hot plasma of quarks and gluons seems to behave more like a dense fluid than a bunch of freely-moving individual particles. Still much to be learned.

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This is an idea that has been bouncing around for a while, but is now apparently seen in experiments: real-world photosynthesis taking advantage of quantum mechanics. (Story in Wired, via @symmetrymag. Here’s the Nature paper on which it’s all based.)

The idea is both simple and awesome: you want to transport energy through an “antenna protein” in a plant cell to the “reaction-center proteins” where it is chemically converted into something useful for the rest of the plant. Obviously you’d like to transport that energy in the most efficient way possible, but you’re in a warm and wet environment where losses are to be expected. But the plants somehow manage the nearly impossible, of sending the energy with nearly perfect efficiency through the judicious use of quantum mechanics.

We can think about this in terms of Feynman’s way of talking about quantum mechanics: rather than a particle taking a unique path between two points, as in classical mechanics, a quantum particle takes every possible path, with simple paths getting a bit more weight than complicated ones. In the case of the protein, different paths for the energy might be more or less efficient at any particular moment, but this bit of quantum trickery allows the energy to find the best possible route at any one time. Imagine at rush hour, if your car could take every possible route from your home to the office, and the time it officially took would be whatever turned out to be the shortest path. How awesome would that be?

The reason you can’t do that is that your car is a giant macroscopic object that can’t really be in two places at once, even though the world is governed by quantum mechanics at a deep level. And the reason for that is decoherence — even if you tried to put your car into a superposition of “take the freeway” and “take the local roads,” it is constantly interacting with the outside world, which “collapses the wave function” and keeps your car looking extremely classical.

Proteins in plants aren’t as big as cars, but they’re still made of a very large number of atoms, and they’re constantly bumping into other molecules around them. That’s why it’s amazing that they can actually maintain quantum coherence long enough to pull off this energy-transport trick. Previous studies had hinted at the possibility, but only by cooling the proteins down and shielding them from external jiggling. This new work happens at room temperature in the context of marine algae, so it seems to indicate that it can happen in real environments.

One step closer to building my teleportation machine. Get to work, quantum engineers!

This weekend at Caltech we had a small but very fun conference: the “Physics of the Universe Summit,” or POTUS for short. (The acronym is just an accident, I’m assured.) The subject matter was pretty conventional — particle physics, the LHC, dark matter — but the organization was a little more free-flowing and responsive than the usual parade of dusty talks.

One of the motivating ideas that was mentioned more than once was the famous list of important problems proposed by David Hilbert in 1900. These were Hilbert’s personal idea of what math problems were important but solvable over the next 100 years, and his ideas turned out to be relatively influential within twentieth-century mathematics. Our conference, 110 years later and in physics rather than math, was encouraged to think along similarly grandiose lines.

And indeed people had done exactly that, especially ten years ago when the century turned: see representative lists here and here. I asked the organizers if anyone was taking a swing at it this time, and was answered in the negative. I was scheduled to give one of the closing summaries, and this sounded more interesting than what I actually had planned, so naturally I had to step up.

Here are the slides from my presentation, where you can find some elaboration on my choices.

And here’s the actual list:
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… not yet released, but we’ll find out in just a bit. 2:00 p.m. Pacific time, to be exact.

Last week we mongered the rumor that the CDMS experiment was going to announce an exciting new result soon — and that time is now. (My guess remains: some interesting data that falls well short of “we’ve discovered dark matter!”) If you’d like to watch the talks online, here you go:

• Kavli Institute for Particle Astrophysics and Cosmology
• Fermilab

Further bulletins as events warrant.

All the physics blogosphere is abuzz about rumors that the CDMS experiment might have collected evidence for the direct detection of dark matter, and is going to announce their results on December 18. The original source was Resonaances, where you can read the basic story; see also New Scientist. It’s to the point where it’s more suspicious if we don’t mention it than if we do, so here you are.

Not too much point in speculating — we’ll find out next week! There was some misplaced excitement about a Nature paper, but it is true that CDMS has scheduled simultaneous talks at CERN, Fermilab, SLAC, and elsewhere. Steinn did the citizen-journalist detective work and dug up the abstract for Priscilla Cushman’s talk at CERN:

I will present new results from the recent blind analysis of 612-kg days (before cuts) of data using the CDMS germanium detectors at Soudan. CDMS uses ionization and athermal phonon signals to discriminate between candidate (nuclear recoil) and background (electron recoil) events in Ge crystals cooled to ~ 50 mK. Timing, yield and position information allows us to tune our expected background leakage into the signal region to 0.5 events. I will report on what we saw when we “opened the box”, whether we have seen WIMPs or not, and implications for future dark matter direct experiments.

It would seem unlikely to me that CDMS would be able to announce a cut-and-dried discovery of dark matter; that would require collecting an awful lot of data. (But what do I know?) It’s more plausible that they would see some kind of provocative signal, but without quite enough significance to be definitive. With many different competing experiments, several of which have been working for quite some time now, it seems like the kind of result that you would gradually sneak up on, rather than dramatically capture in one fell swoop. Or maybe they’re just updating us on their best limits, and some rumor-mongering has spiraled a bit out of control. We’ll see.

The Hubble Space Telescope has come out with a new ultra deep field image — this one in the near-infrared, taken with the Wide Field Camera 3 (WFC3) that was installed on the latest servicing mission. Colors are fake (obviously, unless you have infrared vision), but the spirit of the colors has been preserved — red regions are redder in real life, etc. Click on the image for a higher-resolution version (about 1.6 MB). Even higher resolutions available at HubbleSite.

Not too different, to the naked eye, from previous incarnations of the ultra deep field. That’s okay. I can sit and stare at these images for hours. Every one of those blobs is a galaxy! Holy crap.