8 avril 2017

Cristaux temporels

Les découvertes dans le domaine de la physique sont si rapides et étranges que j'en ai la tête qui tourne.

Juste l'autre jour, je parlais du fait qu'aux états connus de la matière (solide, liquide, gazeux et plasma) s'ajoutait un nouvel état: le supersolide.

Ben en v'là un autre, encore plus bizarre et déroutant: les cristaux temporels.

Extraits de la nouvelle:

Earlier this year, physicists had put together a blueprint for how to make and measure time crystals - a bizarre state of matter with an atomic structure that repeats not just in space, but in time, allowing them to maintain constant oscillation without energy.

Two separate research teams managed to create what looked an awful lot like time crystals back in January, and now both experiments have successfully passed peer-review for the first time, putting the 'impossible' phenomenon squarely in the realm of reality.

(...) Time crystals are one of the coolest things physics has dished up in recent months, because they point to a whole new world of 'non-equilibrium' phases that are entirely different from anything scientists have studied in the past. 

For decades, we've been studying matter, such as metals and insulators, that's defined as being 'in equilibrium' - a state where all the atoms in a material have the same amount of heat.

Now it looks like time crystals are the first example of the hypothesised but unstudied 'non-equilibrium' state of matter, and they could revolutionise how we store and transfer information via quantum systems.

(...) Usually when a material enters its ground state - also referred to as the zero-point energy of a system - movement should theoretically be impossible, because it would require it to expend energy.

But Wilczek envisioned an object that could achieve everlasting movement while in its ground state by periodically switching the alignment of atoms inside the crystal over and over again - out of the ground state, back again, and repeat.

(...) certain objects can break this symmetry in their ground state without violating the laws of physics. 

Consider a magnet with a north and a south end. It's unclear how a magnet 'decides' which end will be north and which will be south, but the fact that it has a north and a south end means it won't look the same on both ends - it's naturally asymmetrical.

Another example of a physical object with an asymmetrical ground state is a crystal.

Crystals are known for their repeating structural patterns, but the atoms inside them have 'preferred' positions within the lattice. So depending on where you observe a crystal in space, it will look different - the laws of physics are no longer symmetrical, because they don't apply equally to all points in space.

With this in mind, Wilczek proposed that it might be possible to create an object that achieves an asymmetrical ground state not across space, like ordinary crystals or magnets, but across time.

In other words, could atoms prefer different states at different intervals in time?

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