Sunday, December 20, 2009

Spiral Control

Researchers at the University of Japan have found that they can change sea snails from lefties to righties by nudging early embryonic cells with a glass rod. The shells of Lymnaea stagnalis curve either to the left or the right, a trait determined by genetics and which begins to show in very early development. It appears that by simply nudging the snails in the right way, we can change this.

Photo: The snail shells can curve to the left or right. Glass rods prod the embryos. Large photo: Kuroda lab. Inset: B. Endo.

Whether a snail is a lefty or a righty is often described as handedness, or more accurately, chirality. The mirror image of a chiral event is not the same as the original. So, while handedness sounds like an odd word, it is used because one of the most common examples of chirality is our hands. The mirror image of your right hand is actually your left. You can use your right hand to shake someone elses right hand, but not the mirror image of a right hand (the left). The trip through the mirror changes things.

So with the snail shells, the results are up for debate. Have the researchers really done anything incredible? Maybe not. But they did chose to use baby animals in their work and that almost guarantees a news story (even when its baby snails). But ultimately, the researchers haven't quite determined anything concrete about biological chirality. They did go out exploring and found something interesting; hopefully it will lead to some more definite conclusions. What people really want to find is the gene causes handedness, and that remains a mystery.

But the notion of messing with chirality is interesting. In the particle realm the definition of chirality is a bit more complicated, but a particle's spin can be used to define it's chirality. Spin up or down - right handed or left handed. For most particles, physicists seem to have chirality mapped. Did you know there are right handed and left handed photons? They are interchangeable, so even though they have different chirality, they can perform the same functions and appear in equal amounts. Electrons are also ambidextrous - you can find right and left handed electrons. It's the neutrinos that cause the trouble.

Ah, neutrinos. Those odd little particles that took us so long to discover and yet rain down on us all the time. They pass right through matter, through the layers of the Earth, through our bodies, and through massive particle detectors with almost no interaction. Thankfully for particle physicists, neutrinos do, very rarely, collide with regular matter, and with large enough, sensitive enough machines that we put underground to block out false alarms, we can detect them. In the 1950's scientists studying beta decay found that neutrinos are left handed. This sent quite a shock wave through the physics community because it was the first time that such one-sided chirality had been observed in the fundamental particles. Did this mean there was a law governing chirality? What made neutrinos behave this way? It was later discovered that the neutrino's antiparticle, the antineutrino, is right handed.

The antineutrino is still a bit of an enigma of its own. Even though these particles have been observed, scientists aren't sure how they fit into the standard model of the universe. The positron is the antiparticle of the electron, with the same mass but opposite charge. The antiproton has the same mass as a proton but different charge. The antineutron has no charge, just like the neutron, but has other opposite properties: it's made up of antiquarks, while a regular neutron is made up of regular quarks. The neutrino isn't made up of quarks and has no charge. So there lurks the possibility that the neutrino and the antineutrino are the same particle, and that the neutrino is both right handed and left handed, but that each chirality arises in different circumstances. There are experiments going on right now to determine whether or not the neutrino is it's own antiparticle. There is also the possibility that there are right-handed neutrinos and left-handed anti-neutrinos lurking somewhere in the universe. Confusing, but important to point out. The neutrino remains not fully understood, and chirality is one big piece of the puzzle.

So coming back to the snails - is there a connection between particle chirality and biological chirality? Could these experiments with snails help us understand particle chirality? Well, it's hard to say. Mostly I think the consensus is no. Particle chirality is a whole different beast. You've got quantum mechanics making things's a bit of a mess. But what is interesting is that right now biologists are trying to find a gene that causes chirality while neutrino physicists want to know if the neutrino and antineutrino are the same particle. It might be possible - might - that a discovery in one field could aid understanding in another.

I find chirality rather spooky, actually. In the same way that I find all fundamental rules of the physical world a little eerie, but more than a little exciting. Down at the very smallest level, where we begin to see the fundamental workings of the universe exposed, I always feel as though we are approaching the veil. We are tearing away the layers and getting closer to...what? Is the universe an onion with nothing beneath the layers? Of course, that's the wrong metaphor. Even if we don't figure out what's behind the veil, watching those rules play out from the subatomic level upwards, just watching our universe act itself out, is much more interesting than an onion.

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