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Blobs that swarm spark ‘it’s alive’ hypegasm

The mathematics of flocking

A group of scientists led by New York University’s Jérémie Palacci has demonstrated the swarming behaviour of clickbait headline-writers by showing off inanimate objects that swarm a little like living cells.

It’s not even close to life – as Palacci himself tells New Scientist, “even though the particles have no social interaction or intelligence, you can exhibit collective behaviour with no biology involved”.

What Palacci thought he was demonstrating was that the inanimate objects – microscopic plastic spheres containing hematite, which makes them both magnetic and, in the right conditions (suspended in hydrogen peroxide which, exposed to light, catalyses the solution and is shoved around by osmotic forces) clump together to form swarms. What he actually demonstrated, however, was the swarming behaviour of the media, with world+dog seizing on this quote: “[we] show that with a simple, synthetic active system, we can reproduce some features of living systems.”

The NYU media release, here, is much more prosaic, as can be seen from the opening paragraphs of the announcement:

"New York University physicists have developed a method for moving microscopic particles with the flick of a light switch. Their work, reported in the journal Science, relies on a blue light to prompt colloids to move and then assemble—much like birds flock and move together in flight.

“The method offers the potential to enhance the design of a range of industrial products, including the architecture of electronics.”

What’s going on here? The blue light causes the colloids to react with, and break down, the hydrogen peroxide near them. The lower concentration sucks in more hydrogen peroxide, buffeting the spheres – and the new hydrogen peroxide is catalysed, so the process repeats. And because the blobs contain iron, the swarms can be steered with magnetic fields.

“If there are enough spheres in the same place they will cluster together to form shapes of symmetrically arranged particles, which the team call crystals,” New Scientist notes.

The important bit – at least from the physicist’s point of view – is not the “frankenparticle” (thanks for that, New Scientist) video (below), but that they can boil the swarming behaviour down to mathematics.

“Our experiments are quantitatively described by simple numerical simulations,” as is noted in the abstract in their paper in Science.

The material science implications are interesting: “By better understanding driven colloidal self-organization, scientists have the potential to harness these particles and create new and enhanced materials”, the university’s announcement notes - and that could include contributing towards the development of self-healing materials.

And, looking at other swarming behaviours – the ones that occur in living systems, such as birds or fish – Palacci wonders if these could also be reduced to simple maths. “From a physicist's point of view, if many different systems behave in the same way there must be an underlying physical rule”. ®

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