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...evidence that the fabric of space-time is not silky smooth as Einstein and many others have presumed, but rough, turbulent and fundamentally grainy stuff.... "All approaches to quantum gravity, in their own very different ways, agree that empty space is not so empty after all," says theorist Giovanni Amelino-Camelia of Sapienza University of Rome in Italy. Many models based on string theory suggest that space-time is a foamy froth of particles, and even microscopic black holes, that spark up out of nothing and disappear again with equal abandon. The alternative approach favoured by Amelino-Camelia, loop quantum gravity, posits that space-time comes in indivisible chunks of about 10^-35 metres, a size known as the Planck length.

This is truly a fascinating development, dear Kevmo! I'm attracted to Amelino-Camelia's ideas. He seems to be "quantizing" space-time, which would give it a description that is not only "grainy," but also "jumpy." If one is looking for a "graviton," this would appear to be an interesting way to go about doing it. The "foaming froth" of string theory looks a tad squishy in comparison: I don't know how it would be possible to design an experiment to observe a "foaming froth." But then I'm no scientific genius, and that's for sure.

On the other hand, it seems to me an "epistemological problem" gets dragged into this game with the concept of Planck length. All the Planck length is, when you really boil it all down, is the smallest increment of space (and time, now space-time) that the human mind can conceive or measure. But this does not necessarily mean that there are not smaller objects in Nature that escape our notice because they are on a scale less than Planck length can measure. This means such objects (if they exist) are ineluctibly unobservable in principle. In short, the Planck length seems to bespeak a limit on human cognition that cannot be overcome.

Just wondering out loud about this. And also about this: In quantum theory, we have matrix mechanics and wave mechanics, each respectively describing the same system in different ways. One focuses on particle behavior, the other on wave behavior. (Even though it was he who first put the photon — particulate light — on the map, Einstein was arguably deep-down a "wave" kind of guy. His smoothly curving space-time is perhaps a reflection of this.) Thus enters Niels Bohr's complementarity principle, which deals with physical situations in which two seemingly mutually exclusive quantum phenomena (i.e., particle or waveform) are found to be necessary to the complete description of the system they comprise. Both are measurable quantities; the problem is you can't measure them both at the same time. This is where quantum uncertainty comes into the picture. These insights pertain to material behavior at the deepest level of physics.

This is just to suggest that maybe Amelino-Camelia's quantized space-time and Einstein's smoothly curving model may be in some sense "complementarities."

Thank you again for the ping, Kevmo! Please keep me posted if you see anything more on this subject — I'll be looking, too.